Self-Study Programme 475 For internal use
ESC Audi
Audi Training Service
Introduction
Traction control and support systems based driver automatic braking make an important
To Service personnel, knowledge of functional relationships is an important challenge.
contribution to active safety in road traffic. Most of the time we do not even notice these
Knowledge in this area are essential to be able to explain to the client commands and
auxiliaries during everyday driving.
functions for controlling functions for fault detection, to diagnosis and ultimately for troubleshooting.
Recent years have seen a rapid development in the field of driver assistance systems. Technological advances, especially in the development and production of electronic
This self-study program is to teach you the fundamentals of these systems.
components, are provided. Common use of sub-functions of several systems, the exchange of information between different systems and v arious outbuildings are the logical consequence of this development.
Illustration of development using the example of the size and weight of the unit ABS / ESC (computer and hydraulic unit)
475_001
from Bosch.
Due to the change of the ESP designation ESC in 2012 at the Group level, the ESC
These designations containing the abbreviation "ESP" will continue initially be used
designation is used for the first time in this self-study program. The designations of
in the service of documents and systems.
components, such that "unit G419 ESP sensors" are an exception here.
2
Summary basic knowledge of driving dynamics The pneumatic connection - floor _______________________________________________________________________________________________________________________ 5
System overview Classification systems _______________________________________________________________________________________________________________________________11
Control systems based on ABS / ESC The anti-lock system (ABS) ____________________________________________________________________________________________________________________________12 electronic distributor of braking force (EBV) ________________________________________________________________________________________________21 Electronic differential lock (EDS) _______________________ ________________________ _________________________ ________________________ ______________23 Traction control (ASR). _______________________ ________________________ _________________________ ________________________ _________________________ ____26 Torque control of
external systems Electromechanical parking brake - emergency brake function (EPB) ________________________________________________________________58 Cruise Control (GRA +) __________________________________________________ ______________________________________________________ _____________________59 Adaptive Cruise Control (ACC) __________________________________________________ ______________________________________________________ ____________________60
Systems mandated by the ESC dynamic leadership _______________________________________________________________________________________________________________________________________64 Driver Steering Recommendation (DSR) _________________________________________________________________________________________________________________66
control strategy __________________________________________________________________________________________________________ 67
Control and information of conducteur_______________________________________________________________ 68 Operations Control
•
Service_____________________________________________________________________________________________________________ 71
connaissances________________________________________________________________________________________________ 76
The self-study program provides basic notions of design and function of new vehicle models, new vehicle components or new
technologies. The Self-Study Programme is not a repair manual! The values shown are for information only and refer to the software version valid in the drafting of the self-study program.
For maintenance and repair, please refer to the current technical documentation.
!!
Note
return
3
Designations systems and abbreviations used in brochure
The designations provided by Audi AG on the German market are used. In some cases, it is possible that different designations, generally used during the development process, are used. The right column shows the pages featuring detailed information on systems / functions considered.
Designation
antilock Braking system
12
ABS
electronic distributor of braking force
EBV
21
electronic differential lock
EDS
23
traction control
ASR
26
Regulation of engine drag torque
MSR
28
electronic stabilization control
ESC
29
hydraulic assistance for emergency braking
HBA
39
electronic differential lock
-
wheel torque control selection
43
-
Startup Wizard
44
-
descent assistant
Drying the brake discs
41
-
Hill Start Assistant
47
-
49
-
51
Stabilization of the coupling
-
53
Fading Brake Support
FBS
54
Optimized Hydraulic Brake Assistance
OHBV / HBV
55
Indicator monitoring tire pressure (more)
RKA (+)
56
Detection ofa luggage carrier
-
57
Electromechanical parking brake - emergency brake
EPB
58
Cruise Control more
GRA +
59
ACC
60
Adaptive Cruise Control
dynamic leadership
Driver Steering Recommendation
4
Page
Abbreviation
-
64
DSR
66
basic knowledge of driving dynamics To begin, we will briefly explain the essential basics of vehicle dynamics necessary for the understanding of the functions of the systems treated in this brochure.
The pneumatic connection - floor The tire's contact surface of a vehicle wheel with the floor is called wheel plane. This
It is at this level that takes place the transmission of the force r equired for different driving
surface is in practice a form virtually oval.
maneuvers such as propulsion (acceleration), braking or cornering.
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Forces acting in the wheel plane There are various types of forces acting as reaction forces in the wheel plane between the tire and the roadway. gravity forces resulting loads on the axle / wheel are always in action. Next traffic conditions, driving forces, braking and lateral guiding forces are added. Forces differ in their direction of action. gravity forces acting in the vertical direction of the vehicle. The driving forces acting in the direction, the braking forces are opposed to the direction of travel.
lateral guide forces occurring in the bends. Their effect a circular trajectory of the rolling wheel and therefore act essentially perpendicularly with respect to the driving and braking forces (in the transverse direction). For the following observations, it is mainly the forces acting in the longitudinal direction of the vehicle (driving and braking forces) and the lateral guiding forces are important.
force of gravity lateral guiding force braking force Driving force 475_003
5
mutual relation of forces - the "circle of Kamm" The forces described can not be increased at will. This is what is proposed to demonstrate the following example braking.
A vehicle without ABS function is straight, braked so hard that the front wheels lock almost.
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The maximum value of the effective forces can be defined in a modeled representation.
to drive straight. Lateral forces thus come by in action.
This representation is called the " Kamm circle" after the name of its inventor, Professor Kamm.
additional turning of the steering wheel. Despite the steered wheels, the vehicle continues
continues to drive straight. To avoid an obstacle, the driver shall immediately after an
force is established. Despite turning, the lateral guide forces can not act. The vehicle 475_005
475_006
Total Force lateral guiding force longitudinal force (braking force)
The radius of the circle characterizes the maximum total power that can be transmitted by the tire (wheel) to the floor. Based on this, the maximum transmissible transverse force (lateral guiding force) depends on the longitudinal force (driving force or braking) performed.
6
Representation effective forces of the above example: The maximum possible braking
The size (radius or diameter) of the "circle of Kamm" depends on the adhesion relationship between the wheels and the road. The more "grip" is, the higher the circle is large. Greater forces can then be transmitted.
minimum braking forces transmitted wet floor
dry pavement
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If, for example, for a given condition, the nature of the road surface suddenly changes (eg sec. To wet), the forces that were still transmitted may become too high. Here come into play "electronic aids" to be described below.
In the chart, a traffic situation of this type is represented via the "Kamm circle". The
In our example, the braking force controlled by the driver is too high to achieve more
vehicle rides on dry pavement, the driver brakes in a bend. The available potential is then
stable lateral guidance of the vehicle. Without use of stabilization systems, the vehicle
not used. During braking, the vehicle arrives on a wet portion. Due to the variation of the
would be in a state of unstable operation in terms of driving dynamics. The radius of
surface condition and therefore of the adhesion relationship between the road surface and
curvature necessary would not be feasible due to the loss of the lateral guide and the
the tires, the maximum forces transmitted are now much smaller.
vehicle leave the road.
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Working condition: dry roads
Working condition: wet 475_008a
7
In the second example shown herein, the vehicle is negotiating a bend. maximum
In extreme cases, it follows a critical dynamic behavior of the vehicle, the wheels can lock
possible lateral guiding forces are then achieved. If the driver has to brake for example
due to braking forces induced. The immediate consequence is the involuntary exit the
due to a vehicle traveling more slowly before him, the transmission sufficiently large
vehicle their lane, with imminent risk of acc ident.
braking forces to the road is no longer possible.
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The "circle of Kamm" is an idealized representation perfectly describes the basic
The criteria determining the grip conditions are:
situation. The absolute magnitude of the maximum forces transmitted (and thus the corresponding radius of the "circle of Kamm") essentially depends on the adhesion
•
Material road surfa ce (asp halt, concrete, etc.)
relationship between the tires and the road surface. In motorsport, it is called "grip" (grip
•
Properties of the tr ead material (rubber blend)
surface, one can see a kind of "nesting" between the tire rubber and the road surface.
•
State of the road surface (dry, wet, icy, etc.)
Over the nesting effect is "marked" more traction between the tires and the road is
•
vehicle speed
important and transmitted forces are high.
•
thermal behavior of the tire (eg. the differences between summer and winter tires)
•
thermal behavior of the pavement
of the tire). If the image magnification is observ ed in the tire contact area with the road
"Nesting" between the tire and the road
8
475_010
The coefficient of adhesion μ
No adhesion between the tire and the road, no force transmission is possible. The drive wheel spins without any moving forward. The braked rotating wheel blocks without reducing the speed. The grip coefficient μ is defined to describe the adhesion relationship between the two body surfaces. It is defined as the ratio between the force compressing a body on the surface of another body and the force required to move the body on that surface. tensile force and maximum deceleration then occ ur at the transition between the body of the rest position and the start of displacement. The friction coefficient corresponding to this state is called coefficient of static adhesion. when
FV FG
In the case of the friction torque "tire rubber - road surface, "this distinction is however not possible. In practice, static friction and dynamic friction occur simultaneously, in the cas e of a rotating wheel between the tire
G μ = FF V
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and the roadway. In the case of the friction torque "tire - road surface", the adhesion coefficient essentially depends on:
•
State of the road surface
•
State of the tires
•
vehicle speed
Approximate values of coefficients of adhesion to different states of the road surface to a vehicle speed of 60 km / h:
•
dry asphalt:
0.9
•
wet asphalt:
0.4
•
Dry concrete:
0.9
•
wet concrete:
0.5
Thanks to the specific characteristics of the tire material, adhesion factors> 1 are possible in special cases of application (motor racing, this coefficient can go up
2).
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9
Ice skating For a power transmission tire to the road to be possible, the rubber particles in the tire
Next there is induction of traction or braking power, a distinction is made between
profiles of the blocks must be deformed (preloaded). This results in a continuous relative
skating acceleration and braking to skating. The optimal transmission of tensile force
movement of the tire relative to the c arriageway. This speed difference is c alled slip.
necessary for maximum slip values of the order of 10%. It is in this range that the maximum driving forces can be transmitted.
The graph shows a rubber tire deformation model of a rotating wheel. In this model, the rubber consists of a large number of small individual blocks. When "Enter" rubber blocks in the plane of the wheel, they are compressed. Because of the elastic behavior of rubber, it is then a deformation of the blocks. In the rear area of the wheel plane, blocks deformed relax again before "leaving" the contact surface of the tire.
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Blocks profiles "tablets"
When accelerating, skating takes negative values. During braking, the ratios are reversed. = Vehicle speed = Speed of the wheel 475_014
Other factors affecting the value of maximum forces transmitted:
Moreover the coefficient of adhesion, the gravitational force (load on the wheel) and the size of the contact surface of the tire bearing on the value of transmitted forces.
When the load on the wheel increases, transmitted forces increase; they also increase in case of enlargement of the contact surface of the tire. Therefore generously dimensioned tires are used for vehicles with powerful engines.
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10
System overview Classification systems The starting point of the dynamic development of control systems Traction was ABS is.
For clarity, the systems have been grouped according to the following criteria:
The developments that followed such ASR (traction control) and EDS (Electronic Differential Lock) are, like ABS, control systems skating "classic". Their mission is to
•
Systems influencing the braking, start / acceleration or operating state itself.
•
Some of the systems developed in recent years have also ex ploited the opportunity to
influence traction and braking defined by performing wheel slip values or to have a direct positive influence on the dynamic behavior (ESC). In recent years, many other systems not explicitly included in the category of "traditional" systems have been dev eloped. Thus,
perform on "demand" ESC active generation (automatic) brake pressure
the brake disc drying function assists the braking function in the rain and with the wiper
independently of driver behavior (eg ACC.). We speak here of "external systems".
activated, but is not of
•
The third main group of systems is characterized by the fact that the ESC itself uses in the "mandating" another system to increase directional stability.
The pressure monitoring indicator tire, which uses treated ESC measurement values for a driving assistance function, represents an exception. It therefore acts as an external system, despite the fact that the RKA software is integrated into the ABS / ESC calculator. That is why in our list, the tire pressure monitoring indicator is in the category of external systems.
Control systems based on ABS / ESC
•
ABS (antilock braking system)
•
EBD (Electronic Brake-force)
•
HBA (brakingdevice)
•
FBS (Fading Brake Support)
•
Drying the brake discs
•
OHBV (hydraulic brake assist. Optimized)
•
MSR (control of engine braking torque)
external systems
Systems mandated by the ESC
•
•
Dynamic steering (for ESC and DSR)
•
Electromechanical power steering (DSR)
•
propulsion engine (for ASR and MSR)
ACC (Active Cruise Control)
•
GRA + (speed controller "more")
•
EPB (electromechanical parking brake)
•
RKA + (pressure monitoring indicator tire "more")
•
ASR (traction control)
•
EDS (electronic differential lock)
•
Hill Start Assistant
•
Startup Wizard
•
ESC (Electronic Stability Control)
•
electronic limited slip differential (locking differential inter-wheelers)
•
wheel torque control selection
•
descent assistant
•
Stabilization of the coupling
•
Detection of a luggage carrier
Influence on the brake
Influence on the start / acceleration
Influence on driving dynamics
11
Control systems based on ABS / ESC The order in which the traction control systems "classic" corresponds approximately to the
This order was chosen for a clear presentation of the system extensions.
history of their development.
The anti-lock system (ABS) History, basic function In explaining the "Kamm circle", it was already given the example of a brake for which the braking force is so high that it is no longer possible to establish lateral guide forces. The vehicle is more airship in this situation. from
1920, a hydraulic system for the aerospace implementation, which aimed to limit the maximum braking force and the locking of the braked wheels was developed.
Following this, a patent describing this type of control applied to the automobile was awarded to Bosch. It was in 1969 that the first ABS system with electronic control of the company ITT was presented to the public. Audi AG, the Audi 200 was in 1980 the first vehicle model to be equipped with ABS Bosch.
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The principle of operation of the ABS is to limit the brake pressure to a value still
As road conditions can vary during braking, the system must be able to maintain brake
enabling the transmission of lateral guide forces.
pressure or authorize, for fast regulation process, the establishment of a brake pressure by the driver or although the reduction in brake pressure (see example below).
brake pressure
Time
μ = 0.3
μ = 0.8
μ = 0.5
475_018
The driver starts braking in wet conditions (section 1). brake pressure induced by the
After the increase, there is again a new control value (section 4). When the wheels come
driver would, for these road conditions, a wheel lock. The ABS must c ontrol the braking
on the coating of wet pavement, reduce the brake pressure to prevent blocking (section
force to an appropriate value, as the condition of the road does not change (section 2).
5). The objective of this control strategy is to reduce the braking stroke to a minimum
Thereafter, the road conditions change, as the coating is dry now, the brake pressure can
while maintaining the steerability of the vehicle.
be increased slightly (section 3).
12
technical implementation
Overview We will present briefly, taking as an example Audi Q5, all system components necessary
Achieving the required braking pressure is generally provided by the following three
to achieve control systems explained below. The components marked in blue are
control functions:
essential to achieving the ABS function. •
constant maintenance of the momentary braking pressure
•
Decrease the momentary braking pressure
•
Increasing the instantaneous brake pressure
In the following text, the three control functions will be designated by "maintaining brake pressure", "brake pressure reduction" and "generation of braking pressure".
Calculator ABS / ESC (1)
Witnesses and displays for driver information
transverse acceleration transmitters / longitudinal and
- Calculates the required braking pressure - controls the
(2)
yaw rate (3)
actuators
- Measure the dynamic behavior
the hydraulic unit
vehicle in the longitudinal and transverse directions as well as rotation about the vertical vehicle axis
(2) steering angle transmitter (4) - Measures the position / movement of the steering wheel
(5)
Control ASR / ESC (5) - Influence on the driver ESC / ASR functions
(4)
(8)
(1)
(3)
(6)
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(7)
Hydraulic unit ABS / ESC (6)
Brake light switch (7)
Speed Sensors (8)
- Contains actuators for carrying
- Delivers a signal upon actuation of
- Measure the wheel speeds - a separate
braking pressure necessary
the brake pedal
sensor is assigned to each wheel
- Closes a / sensor (s) for the recorded tration of the brake pressure
13
hydraulic unit The hydraulic unit contains all hydraulic components needed to achieve the generation
The unit is completed by pressure accumulators, various internal piping and check valves.
functions, maintaining and brake pressure reduction. It is essentially solenoid valves and
Following execution, at least one internal brake pressure sensor is mounted for recording
the return pump and its electric motor drive.
controlled braking pressures.
electric motor of the
Housing with internal piping and
pressure pump
pressure accumulators
coils
calculating
pump element
brake pressure sensor 047_020a
Piston pressure accumulators solenoid
275_020
14
HBZ = brake master cylinder with brake booster and brake pedal HR = rear right wheel brake VL = Left front wheel brake VR = front right wheel brake HL = Left rear wheel brake M = An electric drive motor of the return pump RFP = Pressure Pump EV
= AV = suction valves Valves exhaust S = Battery D = Shock
1 switching
In order to better understand the hydraulic diagram, we will briefly explain solenoid
position (neutral
Switching position 2 (with pilot
position)
valve)
switch positions. It uses 2/2 switching valves. Designation indicates that it is switching valves to two connections and two possible switching positions. The valves can be traversed in both directions depending on the pressure conditions considered.
Electro magnet
On the hydraulic diagram, all the valves are represented in the non-activated switching state (unmanned). suction valves are open in the neutral position, the closed exhaust valves. 475_021
When electrical control valve, the latter pass into second respective switch position, the suction valve closes, the exhaust valve opens.
275_022
suction valve in a neutral position (open)
controlled suction valve (closed)
exhaust valve in neutral (closed)
exhaust valve controlled (open)
275_023
15
For clarity, only the steering wheel of the brake of the wheel is observed. The ABS computer allows individual drive all four wheels.
Generating a brake pressure by the driver (without active control)
When the driver actuates the brake pedal, there is also establishing brake pressure with non-piloted valves (valves in the neutral position). Because of the open intake valves, the direct connection of the brake master cylinder to the wheel brakes is ensured in all circumstances. If the driver releases the pedal, the brake pressure is reduced in the same manner.
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regulatory function "maintaining brake pressure" If the brake pressure generated by the driver is too high (the brake pressure does not allow additional lateral guiding force - see "Kamm circle"), the exhaust valves are considered selectively driven wheel and closed. Although the driver continues to exert pressure on the brake pedal, the braking force does not increase further.
If the brake pressure can be increased again because of changed conditions, the suction valve is open again.
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control function "reduction in braking pressure" If the brake pressure is too high at wheel level considered, the brake pressure reduction function is activated. The corresponding suction valve is closed, the exhaust valve is open. For rapid reduction of pressure, internal batteries are met first. If that is not enough, we must discharge the brake fluid against the brake pressure controlled by the driver. The required pressure is achieved by control of the electric motor which drives the discharge pump. The driver notices this process sensitive to slight pulsing of the brake pedal.
475_026
16
pressure braking
Time Generating a brake pressure by the driver, without controlling the braking pressure control
Generating a brake pressure by the driver, without regulation "brake pressure holding" control function control function "brake pressure reduction" control function "generation of braking pressure" 475_027
ABS regulation consists of a rapid sequence of the described features, namely
The functions are performed by short pulses of the order of several milliseconds. The
generation, maintaining and brake pressure reduction.
graph shows for example that type of pulse sequence.
calculating The computer detects that a regulation is necessary by ongoing evaluation of the input signals. The computer then executes the control through targeted control of solenoid valves and the return pump. In the case of the first generation of ABS, the computer and the hydraulic unit were located in different places of the vehicle. Since Bosch 5.3 generation, the ABS computer and the hydraulic unit are combined into a single unit.
Since the generation 5.7, the ABS / ESC calculator and the hydraulic unit are also a unit.
475_028
1 7
2
1
wheel speed sensor: right back
G44
2
wheel speed sensor: front right
G45
3
wheel speed sensor: rear left G46 4 wheel speed sensor: Left Front
3
8
5
G47
Brake light switch F + test contactor brakes 6 brake pressure transmitter 7 feed pump with electric motor 8
4 9 solenoid valves
ABS witness 10 brake system warning light
5
9
K47 K118
11 Diagnostic connector 12 Edition, eg. : - Vehicle speed - Signal bad roads
6
11
10
12
475_029
17
Input signals essential for ABS
Signal output
wheel rotation speeds:
Pilot solenoid valves:
The computer calculates the vehicle speed from the wheel speeds. It compares the
The calculator delivers the solenoid control signals.
speeds of the individual wheels with the vehicle speed and calculates the brake slip values.
Steering the pressure pump: The drive of the electric motor of the pressure pump performs the brake pressure
brake pressure:
reducing function.
The brake pressure sensor measuring the brake pressure in the primary circuit. This braking pressure is taken into account when determining the necessary control
Editing the speed of the vehicle:
algorithm. In addition, this signal plausibilise the function of the stop lamp switch / test
The speed of the vehicle is calculated current issued and made available to other users
brakes.
/ vehicle systems. As the speed determined by the ABS is very precise, it is also the basis for the speedometer in the instrument cluster.
Signal brake light switch: The signal is used to detect when the driver starts braking.
Editions for driver information: If necessary, important system information is signaled to the driver as text and by
Signal brake test switch:
witnesses. You can find detailed information about the chapter Control and driver
The reverse signal brake light switch is used as a redundant signal.
information.
Edition of the bad roads signal: The signal is sent bad roads if required by the ABS computer to the engine controller.
The engine control unit evaluates the signals of the detectors for detecting the knock misfires and unstable operation of the engine resulting therefrom.
On bad roads, excitations (forces) transmitted from the floor to the drive wheels can also cause an engine operating instability. The ABS computer recognizes the bad roads by use of wheel speed signals. This is communicated to the engine control unit. The engine control unit thus knows the reason for the engine operating instability and does not react with interventions in engine management.
475_030
18
sensors
Speed sensors G44-G47: wheel rotational speeds are measured separately on the four wheels. On all current Audi models, it uses active sensors. "Active" means that the sensors have their own power supply and convert physical quantities into electrical quantities or deliver them in digital form.
The sensors used on Audi vehicles operate on two different physical principles. They use either the magnetoresistive effect, or the Hall effect.
475_031
Magnetoresistive:
Semiconductor
The resistance of a semiconductor varies if it is in a magnetic field which intensity and direction vary. This resistance variation is the subject of evaluation.
Magnetic tape where the north and south poles are arranged alternately is used as pulse crown.
magnetic field lines (North Pole)
magnetic field lines (South Pole)
Magnetic tape
475_032
Hall: When a conductive path through which the current is in a magnetic field, the electrons are repelled to one side of the conductive path due to the magnetic field. On this side, there is an excess of electrons. On the other hand, there is a lack of electrons. An electric voltage can be measured via contacts on both sides of the magnetic track. The polarity (position + and -) depends on the direction of the magnetic field (blue arrows). Magnetic tape where the north and south poles are arranged alternately is used as pulse crown. Each pole of change, there is a change of direction of the measured voltage.
The change number of poles (pulses) per unit time is directly proportional to the speed of the wheel and is read by the ABS computer. The computer then calculates the speed (rotational) present for each wheel. 475_033
On the basis of these wheel speeds, the calculator calculates the vehicle speed, which is delivered as a message on the bus to the attention of other users.
19
brake pressure sensor On all current Audi models, at least one brake pressure sensor is integrated in the hydraulic unit; it is not accessible from outside. The sensor measures the pressure in the primary circuit of the braking system.
electric motor of the pressure
Housing with internal piping and
pump
pressure accumulators
coils
calculating
pump element
as during active braking by the driver.
estimated braking pressure in the wheel brakes. ABS regulation is activated if necessary
evaluated by the ABS computer. The measurement values output the basis of the
initiates a braking operation, the braking pressure increases. This is recorded and
information to the computer responsible steering of the brake lights. When the driver brake pressure 475_034
sensor
Piston pressure accumulators
solenoid
computer or the engine control unit. The corresponding computer transmits the
Brake light switch F / brake pedal switches F47 / F63
The brake light / brake pedal is on the current Audi models, with the exception of the Audi
The switch signals are, depending on the vehicle model, read quietly by the ABS
A1, the TT and Q3, mounted on the brake pedal. Of the above models, it operates on the brake master cylinder. The Audi A3, the two versions are used. The ABS computer needs the information that the driver starts braking for the plausibility of the brake pressure sensor signal. ABS regulation is activated if necessary as during active braking by the driver.
Mounting on the brake pedal
20
475_035
Mounting on the brake master cylinder
475_035a
Electronic distributor of the braking force (EBV)
During braking of a vehicle, there is an increase of the load on axle at the front axle, while
To avoid an unstable working condition due to a "recovery" of the rear axle, it should not
the rear axle is relieved (dynamic charge transfer). This is due to the inertia of the mass
be applied to the rear axle brake pressure generating transmissible maximum braking
of the vehicle body. There is generation of a torque about the transverse axis of the
forces. If the vehicle is braked by braking pressures identical on all four wheels, it
vehicle, to cause a higher load on the front axle. In practice, this effect is observed by a
'wasting' of the braking distance. This is because braking forces much lower than the
deflection of the front body at the axle during braking (brake dive).
maximum forces that can be transmitted are carried out at the wheels.
Due to the increased load on axle at the front axle, the transmitted maximum braking forces also increase it. The shedding of the rear axle causes the opposite effect, communicable maximum braking forces decrease.
475_036
Braking force gravitational force Centrifugal force
braking force braking force
braking skating
EBV ABS 475_037
lateral guiding force
The regulation prevents EBV-braking the rear axle. Depending on the brake slip values
This allows for the physical performance of braking as high as possible. The braking
of the wheels of the rear axle brake pressure required at this point is calculated and set
distance is reduced to a minimum.
by the ABS computer. At the front axle brake pressure adjusted by the driver continues to act without reduction.
EBV control begins before the ABS control, or to significantly lower brake slip values.
21
Operation In the past it was uses hydraulic pressure limiters for limiting the brake pressure at the rear axle. With the advent of ABS, this function may be provided by the EBV function. Upon detection of a locking tendency of the rear wheels, the brake pressure is limited at the corresponding wheel brake. It is primarily for this called the function "maintaining brake pressure" by closing of suction valves.
If necessary, there is also reduction of the braking pressure: this is achieved by opening of the exhaust valves and closing of suction valves. To reduce the level of pressure, the brake fluid is forced into the internal batteries. It is only from a certain level is batteries that brake fluid is pumped back towards the brake master cylinder, overcoming the opposing force of the brake pedal. 475_026
Reduction of the brake pressure at Maintenance of the brake pressure at the rear axle
level of the right rear wheel
475_039
Note: Legend, cf. Figure 475_020 page 15
In reverse, there is a possibility of over-braking of the front axle by the EBV function. And reverse is the front axle that gives the direction of travel, a front axle-braking can cause skidding of the vehicle. The vehicle is then no longer airship. The consequence is, in terms of driving dynamics, a state of unstable walking accompanying is a high risk of accident.
This is especially critical when driving backwards downhill on an unstable ground. Audi also provided the models for all-terrain use (Audi Q7, Q5), the EBV function is inverted in reverse: the front axle is then dampened with a reduced brake pressure. The condition is, on the Audi Q7, activating the "Offroad Mode" by pressing the ESC key.
On the Audi Q5, regulation EBV "reverse" is activated when activating the function of downhill driving assistant. The reverse is detected by the speed sensor. In the case of speed sensors without detection of the direction of travel (eg. Audi A1, TT), the detection of the reverse gear is ensured by a corresponding evaluation of the wheel speeds, 475_040
steering angle and the yaw rate.
return Detailed information on the ESC key functions on page 68.
22
Electronic Differential Lock (EDL) The following example describes the behavior of the wheels of a driven axle with conventional center differential: a wheel of a drive axle is on a slippery (low coefficient of friction between the tire and the road), the other wheel of the axle based on the asphalt, which has a high coefficient of adhesion. The wheel resting on the slippery ground running at high speed because the low adhesion between the tire and the road opposes little resistance to the spinning wheel. In extreme cases (eg. When a wheel based on a very slippery ground such as ice), the wheel while skating the other is stationary. The entire power output is then converted to power dissipated by friction instead of being in propulsion. This behavior is due to the differential action. The latter transmits the same torque to both wheels. If a wheel has a slip at high acceleration, driving torque transmitted 475_041
fall. The couple, in adverse conditions (such as a wheel lying on the ice) so low that it is not enough to drive the wheel. The vehicle is then left there with a spinning wheel and a stationary wheel.
The EDS function remedied. The most high-speed rotating wheel (and of greatest skating) is braked in a targeted manner. This braking torque (M
B)
increases the resistance to the
spinning wheel. Or to put it another way: in order to turn the wheel, it requires a higher drive torque. As, due to the function of the differential described above, the same torque is transmitted to both wheels, the drive torque increases at the other wheel. This increase in torque by braking the wheel having the largest skating takes place until both drive wheels rotate at a substantially identical speed.
475_042
23
Generation In order to perform the DHS function, actively generating the brake pressure is necessary.
In return, it is necessary during a control EDS that the line from the feed pump to the
For this, we use the return pump already implemented for the ABS. The ABS hydraulic
brake fluid reservoir is closed in order to establish a braking pressure at the wheel brake
unit must be completed by four switching valves in total. The discharge pump can suck
in question. This function is also ensured by an additional solenoid valve for each brake
the brake fluid in the reservoir to achieve the EDS function. For the ABS function of
circuit. The determination of the need of software c ontrol, calculation process control and
"generation of the brake pressure" to continue to be performed with the corresponding
drive signals to the corresponding solenoid valves and the return pump is implemented in
discharge of brake fluid by opposing the brake pressure controlled by the driver, this
the ABS computer. Other components of the ABS system changes are necessary to
suction line must be closed . This is accomplished by the suction valves (ASV) Extra.
make the EDS function.
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Hydraulic unit ABS / EDS for front wheel drive vehicles
ASV 1:
suction valve Circuit floating piston brake master cylinder
ASV 2
Suction valve of the circuit of brake master cylinder pushrod
AV:
exhaust valve
D: DBV:
Damper pressure relief valve
EV:
suction valve
RFP:
feed pump
S:
Accumulator
USV 1:
Reversing valve circuit of the floating piston brake master cylinder
USV 2:
Diverter valve of the circuit of the brake master cylinder push rod
24
Electronic differential lock EDS operation Thereafter, the embodiment of the DHS function is explained using the example of a front wheel drive vehicle.
Generating brake pressure For the realization of the establishment of the brake pressure, the corresponding suction valve is controlled by the computer. The suction pipe is then opened and the feed pump can suck the brake fluid in the brake fluid reservoir via the brake master cylinder.
By closing the corresponding switching valve, the connection between pressure side of the return pump and brake fluid reservoir is closed. The discharge pump is driven by control of the electric motor and the brake pressure is generated.
475_044
Maintenance of the brake pressure For the realization of the function "maintaining brake pressure", the pressure pump is switched off. The switching of the valve remains unchanged compared to the "generation of the braking pressure."
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Reduction of the brake pressure When the control valve is disabled, the direct connection between the wheel brake and brake fluid reservoir is restored. The brake pressure is reduced.
active braking interventions cause global components of the wheel brakes. To avoid overheating and damage it would cause, a temperature model is integrated in the software. The temperatures of the brake discs are calculated on the basis of the duration of the braking force, the vehicle speed, the braking pressure considered material and component values. When temperature thresholds are reac hed, the regulation is progressively disabled.
Depending on the vehicle model, the EDS is active up to a speed defined.
475_046
25
traction control (ASR) ABS control assists the driver during start and acceleration. In the case of vehicles including powerful engine, it can occur in adverse road conditions, an acceleration slippage increased due to the low coefficient of friction between the tires and the roadway and high drive torques . In an extreme case, the drive wheels can even skate time. This not only leads to restriction of the propulsion, but also a deterioration in the steerability of the vehicle. This can result in critical situations in terms of movement dynamics, during acceleration during cornering in particular.
The ASR effectively prevents the acceleration slippage reaches a critical level.
475_047
Representation in the "Kamm circle": The effective driving force (yellow arr ow) is greater than the maximum transmissible force. Skating acceleration reaches a critical value, the RAS begins to regulate. The driving power (driving force) is reduced to a realizable value in propulsion (orange arrow).
475_048
Architecture and operation of the ASR system For the realization of the ASR, no additional software is required in addition to ABS with EDS. The control software is, as in the case of the EDS, integrated in the ABS computer. Communication between the ASR and engine management has on all current Audi models place on the data bus.
ASR gives when skating at too high acceleration around the engine control unit to reduce the torque. The driving forces in the wheel plane is reduced. The acceleration slippage is reduced and additional lateral guide forces can be transmitted if necessary. The vehicle remains steerable by and therefore the case of critical condition described above is avoided.
On some vehicle models, the control can be disabled using the ASR button (see page 68). Traction control is however always enabled when you put the ignition.
475_049
26
Key input information for the ASR control software are the wheel speeds and the
Simultaneously, the box computer receives, on vehicles with automatic transmission or
momentary torque of the vehicle engine ( "engine torque real"). The wheel speed
an automated manual gearbox, the demand not to make gear changes during the active
information is the basis for determining the acc eleration slippage of the drive wheels. If
control.
this value is, at a wheel, the prescribed threshold, the TCS is activated. The ASR determines the engine torque reduction required to reduce slippage to a non-critical value.
The engine control unit can realize a reduction in power by corresponding engine
It is "asked" to the calculator engine to reduce the engine torque accordingly. The engine
measures level:
torque to realize is transmitted by the engine control unit as a concrete torque setpoint ( "rated motor torque").
•
Changing the throttle angle variation
•
Reduction of injection rate and / or removal of injection pulses
•
Change the ignition angle (ignition delay) or deleting ignition pulses
The measures put into practice depends on the application (the type of vehicle, the engine, etc.).
Control via the throttle (gas engines)
speed sensor, front left
Rated torque motor
Regulating the injection rate Speed sensor front right
(petrol and diesel) actual engine torque
Regulation via the ignition rear left speed sensor
system (gasoline engines) Calculator ABS
engine control
/ ASR
unit
Management of the box (petrol rear right speed sensor
and diesel) 475_050
Implementation of ASR and EDS The ASR and EDS are complementary. Both systems have the task of improving the
In given situations, the drive wheels, however, are on a roadway having a "hooking
traction of the vehicle.
capacity" different. In these cases, the wheel with the least grip coefficient introduce
ASR affects the regulation, because of the torque reduction, the same on both wheels of
skating to the highest acceleration. In this case, the preference is for activation of EDS
a drive axle. When both wheels have a slip in too high acceleration, the ASR regulation is
control.
the appropriate measure to limit wheelspin.
If, following the acceleration slippage is too high for both wheels and v irtually identical, ASR is enabled.
27
Regulation of engine drag torque ( MSR)
The mission of the MSR control is to limit wheelspin braking at the drive wheels due to
By evaluating the wheel speeds, the control software determines the slip values of the
the use of the engine brake. The control software is integrated into the ABS computer.
driving wheels. If the brake slippage exceeds, at a wheel, a defined threshold, the control is enabled. Based on the value of the actual engine torque received by the engine control unit, the control unit calculates the MSR engine torque necessary to reduce the braking skid. This calculated value is transmitted by the engine control unit as rated motor torque
If, during the march, the driver removes his foot from the accelerator, the propulsion
demand. The engine control unit performs this couple assigned by corresponding action
engine speed is brutally greatly reduced. The drive wheels are then braked accordingly. A brake slip is generated depending on the conditions of adhesion between the roadway and tires. In an extreme case, there may be a wheel lock, combined with the loss of
at the motor (change in throttle position). The speed of the driving wheels is increased again and the slippage is reduced. The slip values produced are in a range allowing an optimum braking torque of the engine. Simultaneously,
controllability of the vehicle.
The same condition can occur if the driver engages too low in the current operating condition report.
Throttle position speed sensor, front left
Rated torque motor
Speed sensor front right actual engine torque
rear left speed sensor
Calculator ABS / ASR
engine control unit
diesel) injection rate (petrol and engines) Regulation of Operation via the throttle (gas
rear right speed sensor 475_051
The MSR control is activated in case of need when the following conditions are met:
•
Accelerator pedal not pressed
•
non-actuated clutch pedal
•
Gear engaged
MSR regulation is also, in the mentioned conditions, activated in the case of a braked vehicle.
Bosch ABS / ESC systems have, on vehicles with automatic transmissions, an additional
It is then "asked" to the calculator engine to reduce the engine torque accordingly. The
function that is activated in case of simultaneous operation of the accelerator and the
value of the reduction considered here depends on the value of the braking torque
brake pedal. This function is specially designed for startup and is active up to a vehicle
controlled by the driver. If the value of the actuation of the pedal exceeds the actuating
speed of about 15 km / h. If we first actuates the brake pedal, and then immediately, the
travel of the brake pedal of a préparamétré threshold (about 30%), the action is
accelerator pedal, the ABS computer bus J104 sends a message to the engine controller.
interrupted. There are also drop when running a "kickdown".
28
Electronic stability control (ESC) Basic principle The basic principle of the ESC system is quickly described: it is possible to influence the
This can be demonstrated very clearly using the example of a tracked vehicle. In this
direction of a vehicle by braking individual wheels.
case, this behavior is targeted used to drive the vehicle.
475_052
Th e b r ak i ng tr a ck s l e ft le a ds to ne go ti a te a l e ft tu r n
Th e b r ak i ng tr a ck s s tr ai gh t e nt a il s n eg ot ia ti ng a right turn
Represented on the vehicle, the front right wheel is braked in forward. The braking
Torque = force x lever arm Md = F xs
force F acting on the wheel at a distance s with respect to the vehicle vertical axis. Accordingly, the braking force generates a torque Md around the vehicle's vertical axis.
If there is no correction at the direction the driver, torque causes a change in direction of travel (right turn).
Md
S
F
475_053
29
Design - Overview Compared with ABS with EDS, it uses a hydraulic unit of modified design. The control
In addition to ABS with EDS, it also requires a steering angle sensor to the angle
software of the ESC and other control systems are grouped in a central computer. In
before driving. Witnesses and displays inform the driver on system status. The driver
addition to the wheel speed sensors, it requires for the ESC other sensors function,
can proceed with a command (key) to various cuts and switching system.
which record the movements of the vehicle. On current Audi models, these movements of the vehicle input sensors are housed in a central component or in the ABS / ESC calculator (Audi A1, A3) or else in the computer of the electromechanical parking brake (Audi Q3) .
Control ASR / ESC
steering angle transmitter
transverse acceleration transmitters / longitudinal and yaw rate
Calculator ABS / ESC with hydraulic group
Components of the system modified / additional for realization of the ESC
thirty
475_054
Operation As the name suggests, ESC serves to stabilize the vehicle in the case of critical operating
An ESC control with braking intervention is illustrated below using the example of an
states in terms of driving dynamics. To do this, the system typically uses three sources of
avoidance maneuver:
influence: The driver noticed a car stopped in front of him on their lane. He quickly makes a turning to steer the vehicle on the adjacent left lane. Due to adverse road conditions, the vehicle •
Establishment active brake pressure with brake intervention targeted wheels
•
Intervention in engine management to a power reduction
•
Intervention in the management of the gearbox in view of inhibition of the shift
tends to oversteer, the rear of the vehicle tends to s kid. Without regulatory intervention, the vehicle "would be through." A steering-initiated against the driver does not suffice to stabilize the vehicle. ESC reacts by generating a braking pressure actively at the front left wheel. The torque thus generated acts against the slippage of the rear of the vehicle and therefore stabilizes the vehicle.
transition
On vehicles with dynamic steering, stabilizing corrections of the steering angle are also initiated by the ESC as needed. (For detailed information see pages 64/65) braking interventions constitute the bulk of regulation.
The ESC regulations take only a few milliseconds. They use sub-functions "generation of brake pressure," "maintaining brake pressure" and "brake pressure reduction" that we have already described.
Power reduction is achieved by the same measures as those applied to ASR. (See pages 26/27)
Without ESC regulation: the vehicle oversteer and does not follow the desired path
475_055
475_056
With regulation ESC: a stabilizing torque is generated around the vertical axis of the vehicle target braking the left front wheel. Oversteer is avoided and the vehicle follows the desired trajectory.
31
System components
hydraulic unit Compared to the hydraulic unit ABS / EDS, no extension is required for the ESC
In this case, the brake pressure at the wheel in question is also increased beyond the
regulation. EDS is able to automatically establish a braking pressure at the wheel drive.
value controlled by the driver. Suction valves used in the hydraulic unit are therefore
The ESC, however, must be able, on vehicles with front wheel drive, individually control
special high pressure switching valves. The hydraulic achievement of sub-functions
the brake pressure at all four wheels. In addition, the suction valves of the return pump
"generation of brake pressure," "maintaining brake pressure" and "reduction of the brake
must, unlike the DHS able to switch even in case of total brake pressure controlled by
pressure" is identical to that of the EDS (see page 25). On current Audi models, the
the driver. This is necessary because, unlike the DHS, the ESC control must if
hydraulic unit is grouped into one component with the computer.
necessary be performed also during braking.
475_057
HSV 1:
High suction valve system pressure piston floating brake master cylinder
HSV 2:
suction valve high pressure circuit of the brake master cylinder push rod
AV:
exhaust valve
D: DBV:
Damper pressure relief valve
EV:
suction valve
RFP:
feed pump
S:
Accumulator
USV 1:
Reversing valve circuit of the floating piston brake master cylinder
USV 2:
Diverter valve of the circuit of the brake master cylinder push rod
32
calculating The software of the ESC control is integrated with that of ABS regulations, EBV, EDS and ASR in a computer. The computer continuously determines and compares the actual behavior and the theoretical behavior of the vehicle. If the gap between actual behavior and s etpoint exceeds predefined thresholds, regulation is activated.
Determining the actual behavior of the vehicle: The evaluation focuses on the measurement v alues of the yaw rate ( yaw moment around the vertical axis of the vehicle), the longitudinal and transverse acceleration. The wheel slip values, and the vehicle speed, acceleration and deceleration are calculated from the measured values of the speed sensors. (The) transmitter (s) brake pressure deliver information on the momentary pressure in the primary circuit of the braking system. On vehicles with automatic transmission, the currently selected report also said the ABS / ESC calculator by a message on the data bus. 475_029a
Determination of vehicle theoretical behavior: To determine the theoretical behavior of the v ehicle, the following driver activities should be recorded: steering, accelerator operation (acceleration / deceleration) and braking.
The measured value of the s teering angle transmitter transmits the desire direction of the driver. Pressing the accelerator pedal by the driver is transmitted to the ABS / ESC calculator with a message on the bus of the engine control unit. By the signal stop lamp, the calculator takes into account a braking initiated by the driver. The measured value of brake pressure transmitter provides a redundant signal, which is also the basis of calculation of stabilizing braking interventions ESC.
Driver's wish
steering angle transmitter Engine control unit
Direction of desired speed
Brake light switch and brake pedal switch brake
desired deceleration
pressure transmitter
behavior
ESP intervention if the behavior of the vehicle does not match the driver's wish vehicle behavior
braking pressure generator speed sensors
yaw rate (yaw torque) longitudinal and
longitudinal and transverse acceleration
transverse acceleration
transmitters gearbox calculator yaw sensor
actual vehicle behavior theoretical vehicle
475_058
33
Synoptic ESC system
1 11
2
12
AT
3
4
13
5
17 14 6
7 15
8
16
475_059
9
10
1 wheel speed sensor: right back
G44
2 wheel speed sensor: front right
G45
3 wheel speed sensor: left back
G46
4 wheel speed sensor: Left Front
G47
5 steering angle transmitter
G85
6 Brake light switch / brake pedal switch 7 brake pressure transmitter 8 sensors ESP unit, with: - transverse acceleration sensor - Yaw sensor - longitudinal acceleration sensor 9 electronic calculator sensors
F / F47
G201 G419 G200 G202 G251 J849
(Replacing G419) 10 Operation of ASR / ESC
E256
11 hydraulic unit with pressure pump and switching valves 12 Solenoid 13 LED ABS K47 14 brake system warning light
K155
Witness 16 2 ESC / ASR
K216
17 Diagnostic Connector A calculator ABS / ESC
34
K118
15 Indicator ESC / ASR
sensors To achieve these extremely complex regulations, wheel speed signals alone are not
All movements of the vehicle are recorded by special sensors - lateral acceleration,
enough. It is important to know the movements of the vehicle (vehicle dynamics) and
longitudinal acceleration and yaw torque (rotational movement around the vertical axis of
those of the steering angle.
the vehicle).
steering wheel angle (or steering angle) indicates the driver's (direction desired).
yaw moment
Steering angle
wheel speed
longitudinal acceleration
transverse acceleration
475_060
steering angle transmitter Three different sensors are used on current Audi models. All used sensors transmit the steering wheel angle on the data bus.
The sensor implemented in the Audi Q7 features a optical operating principle.
When the light diodes (3) arrives via the incremental shadow mask (1) and the absolute outperformed mask (2) on the optical sensors (4 + 5), there is generation of a signal voltage varying due to the not variable of the toothing.
This "coding" is evaluated by the electronics and delivers an angle information in the measurement range of 0 to 360 °.
475_061
35
On current models Audi A3, TT, Q5, A8, R8, a call is made to a sensor system which determines the steering angle on the basis of a camera system.
mounted photodiodes (fixedly) in the sensor housing act as "cameras". A coded disc is connected to the steering shaft. This disc contains several tracks encoded, analog and digital (similar to a bar code). Unprinted areas of these tracks are coded as transparent. LEDs are used as light source.
The photodiodes receive light passing through the transparent areas of the code tracks photodiodes
and thus sweep the each turning movement coded tracks of the steering wheel. Detecting the position of the steering wheel in the steering angle range of 0 ° -360 ° (in the region of one rotation) or in the range of 361 ° -720 °, is ensured by a further mechanical engagement. As a microgroove disk, a small lever is guided in a volute track on the
encoder disc
underside of the encoded disk. Evaluation of coded signals and the position of the mechanical lever deliver the steering wheel angle signal. 475_062
LED
encoder disc
sensing lever
Track volute
475_063
encoder disc
On models Audi A6 and A7 present, it is used a sensor whose operation combines optical and magnetic principles. The optical sensor operates similarly to the sensor described above. The code disk is connected to the rotor to which is attached the steering shaft. The rotor has the form of a pinion. This pinion is in permanent engagement with a second pinion, smaller, mounted in the housing. This second pinion is connected to a permanent bipolar magnet. Each movement direction imparts a rotation to the magnet. Two Hall sensors fixed in the housing record the position (steering angle) of the magnet. For evaluation of the optical signal and the Hall signal, the electronics can record the entire adjustment range of the steering wheel angle. 475_064
optical system
36
magnetic system
transverse and longitudinal acceleration sensors and yaw rate
Two types of sensor units, which are integrated in the actual sensors are used.
The Audi A1, A3 and Q3 current are exceptions. On the Audi A1 and A3, the sensors are part of the ABS computer J104. The Audi Q3, the sensors are integrated into the parking brake J540 calculator.
475_065
The ESP sensor unit G419 'classic' team vehicles without FlexRay data bus. electronic calculator
475_065a
ESP sensor unit G419
the J849 sensors
The transverse and longitudinal acceleration sensors operate on the principle of "seismic mass." In our simplified representation, an oscillating weight is between two capacitor plates. The mass has bilateral contacts, so that two capacitors are formed with the two outer capacitor plates. Plates of capacitor
Capacitor C1 seismic mass capacitor C2
silicon spring 475_066
Acceleration
During acceleration of the vehicle, the position of the mass varies due to the inertia of the latter, between the capacitor plates. The distance plates of the two capacitors while also varies. When the distance increases, the capacitance decreases. In the example, capacitor C1 of the capacity is decreasing, C2 increases. These capacitance variations are evaluated by the electronics and a direct measure of the acceleration considered.
Capacitor C1 seismic mass
capacitor C2
475_067
The longitudinal acceleration sender is required on the Audi A3 and TT equipped with
floor. The longitudinal acceleration sender also functions on the principle of "seismic
quattro drive and / or a startup wizard Hill / s tartup wizard. On these models, the quattro
mass." According to the importance of the angle of inclination of the road, the gravitational
transmission is performed by a Haldex coupling. Due to its operating principle, there is,
acceleration effect (gravitation) on the seismic mass also varies, and with it the measured
when the coupler is closed, a fixed coupling of the front and rear wheels.
value of the sensor. Models of older vehicles with electromechanical parking brake are also equipped with a longitudinal acceleration transmitter. These measured values are evaluated for the parking brake function as startup assistant and hill start assistant.
If low-adhesion, ESC can not, in certain c ircumstances, to determine with sufficient
Following the model of the vehicle, the longitudinal acceleration sender is either part of the ABS computer J104, is part of the sensor unit of
precision the actual vehicle speed from the measured values of the speed sensors. The longitudinal acceleration transmitter signal can then be used as reference signal. For the startup wizard functions coast and startup wizard, it is important to know the angle of inclination of the
37
On current vehicles with FlexRay data bus (Audi A6, A7 and A8), determining the movements of the vehicle is provided by the electronic calculator J849 sensors. Several versions of this computer are implemented depending on the vehicle equipment. In the maximum equipment version detection sensors for longitudinal acceleration, v ertical, lateral and torques around the three vehicle axes x, y and z are integrated. The transverse and longitudinal acceleration signals as well as the yaw rate about the vertical axis of the vehicle (y aw moment) are important for the ESC.
475_068
z
x there
475_069
return You will find detailed information on the design and operation of electronic computer sensors in the self-study program 458.
38
hydraulic assistance for emergency braking (HBA)
Analysis on braking behavior in emergency situations show that the majority of drivers
The objective of the HBA is increased, in case of emergency braking, the brake
do not operates the accelerator with enough force. physically achievable braking forces
pressure so as to perform a short braking distance as possible while maintaining the
are not achieved, there is "waste" of the braking distance.
steerability of the vehicle.
The HBA is a functional extension of the ESC and is integrated in all current Audi models. For safety reasons, it can not be deactivated by the driver.
How a braking control with HBA The following conditions must be met for the activation of the HBA:
•
The brake pressure controlled by the driver must match a minimum value (approx. 30 bar).
•
The establishment of the speed brake pressure must be a minimum.
•
The stop lamp switch from the brake pedal must be pressed (the driver brakes).
475_070
In the case of an emergency brake, the driver actuates the brake pedal at a significantly higher speed and with a greater force than in the case of a preventive braking (braking comfort). It follows a very rapid increase in brake pressure. Whereas in the case of a braking comfort, the settling speed of the braking pressure is approximately in a range of 30 to 60 bar / s, it is the multiple of this value in the case of a braking emergency. The control unit recognizes the emergency braking situation by evaluation of the rate of increase of the brake pressure. This information is provided by the pressure sensors in the hydraulic ESC control unit.
brake pressure
t [s]
475_071
braking comfort Emergency braking
Phase 1 A speed threshold for generating the brake pressure induced by the driver is exceeded, the emergency braking situation is detected. The active establishment of the brake pressure is initiated. There is why control of high pressure switching valves and switching valves. The pressure pump is driven and sucks the brake fluid from the high pressure switching valves. brake pressure controlled by the driver is subject to an additional increase in active generation of pressure in the four wheel brakes. The objective is to trigger as soon as possible the ABS control.
475_072
39
Phase 2 Because of the braking into the ABS control range, the vehicle is decelerated by the best
ABS control is ensured by the functions "generation of the braking pressure,"
braking deceleration physically possible while fully retaining its steerability.
"maintaining brake pressure" and "brake pressure reduction".
Enabling the HBA
Shedding the brake pedal
Cutting off the HBA
ABS control range
brake pressure
475_073
t [s]
Pedal pressure the driver brake pressure regulated by the HBA
In each brake circuit, then there is regulation with the suction valve assigned to the wheel with the lower brake pressure and the wheel with the higher brake pressure with the reporting reversing valve.
In the example shown, the brake pressure in the wheel brake front right is greater than the left rear. front right brake pressure must, "maintaining brake pressure" not be increased more, the left rear pressure may continue to rise. The corresponding suction valve to the right front wheel is controlled. The link wheel brak e pump is interrupted. A new generation of pressure can take place at the left rear wheel due to open intake valve.
If we maintain here too the pressure constant braking, the corresponding suction valve is also closed.
475_074
Phase 3 The driver releases the brake pedal. It is detected by evaluation of the braking pressure sensor pressure signal and the HBA control is interrupted.
HBA on vehicles with Adaptive Cruise Control (ACC) On vehicles with ACC, the traffic situation ahead of the vehicle ACC is "observed" continuously by the radar sensors. This also occurs with the ACC is not activated by the driver. If a situation represents a high potential accident risk is detected, the HBA system activation conditions are altered. The function is already activated earlier, during a school speed brake pressure so low. This allows sensitive trigger a new braking distance reduction in the event of emergency braking.
475_075
40
electronic limited slip differential (locking differential
The differential "distributed" always the total torque of the drive for 50% on each drive
inter-wheelers)
wheel (see also in this connection the explanations on the functioning of electronic differential lock EDS).
The electronic differential lock serves to improve traction when cornering and to reduce / neutralize the tendency to understeer and increase dynamic. This system is used on the
As at the inner wheel in the turn, only small driving forces (and therefore lower pairs) are
traction Audi models before. The transverse electronic lock is a software extension in
transmitted due to the lower load exerted on the wheel, only the same driving force (the
the ABS / ESC control unit. The control is always activated when needed and can not be
same torque) than the inner wheel in the curve can be transmitted in spite of the higher
deactivated by the driver.
potential.
In each turn, the centrifugal force into action. It occurs at the center of gravity and is
Unlike the regulation EDS, the electronic differential lock acts preventively, when there is
radially outwardly of the bend. The result is shedding the inner wheels in the corner and a
no critical skating at the wheels. The control software considers this purpose the load
greater stress on the outside wheels in a turn. As has already been explained in the
variations on the wheels based on the vehicle behavior. Vehicle behavior is here
chapter "Basic knowledge of driving dynamics," larger forces to the wheel contact point is
essentially determined on the basis of measured values of steering angle sensors and
usually transmitted when the load on the wheel increases. This means that higher drive
lateral acceleration.
forces can be transmitted at the outer wheels in the turn at one of the inside wheels to turn. This is however not possible in the case of the implementation of a conventional differential for compensation regime. The control is similar to the active braking interventions of regulation EDS.
However, as there is already control before it happens critical slip values, braking interventions may take place with much lower brake pressures than in the case of regulation EDS. The material is then formed and the control comfort increased. EDS control remains active but only operates as defined slip values. Centrifugal force
475_076
force of gravity to the outside of the turn
gravitational force within the torque curve
Due to the centrifugal force acting on the center of gravity of the vehicle body, it results a couple more strongly urging the outer wheels in the turn. Force of gravity to the outside of the bend> force of gravity to the inside of the turn
475_077
A conventional differential still divides the total torque propulsion equally (50%) between the two drive wheels.
41
M AT
M A max outside in Turn
M A max inside in Turn
at t here
475_078
drive torque to the inside of the turn driving torque outside the braking torque curve
The graph shows the transmission of the wheel drive torques M AT depending on the
2.) + 3.) Toned with open differential and limited slip intervention:
transverse acceleration at there. can generally be seen that the maximum transmittable torques at the outer wheel in the curve increases as the lateral acceleration increases. At
Due to the active generation of braking pressure, an additional braking torque is applied
the inner wheel, they diminish in proportion about.
at the inner wheel in the curve relieved. This additional braking torque increases the total torque at the wheel, since an additional drive torque is required to overcome the braking torque. The result is the action of a higher drive torque (a value equivalent to the total torque to the inside of the turn) at the outside wheel.
1.) Turn with open differential without intervention of the transverse locking:
The transmittable torques are, at the outer dr iven wheel in turn biased, equally high at the level of the inner driving wheel in the relieved corner. Higher driving torques could however be transmitted to the outer driven wheel in the turn. This is not possible without additional braking interventions with a conventional differential.
yaw moment
The higher driving force from the outer side of the turn causes a torque (steering torque) about the vehicle vertical axis. This yaw torque assists the driver when steering and then results in agility (dynamic) significantly higher vehicle.
The electronic differential lock is not active at very low values of friction between the tire and the road. The function can not be deactivated by the driver.
475_079
42
wheel torque control selection The wheel-selective torque control appeared on vehicles with quattro drive. The system is
steering and acceleration is virtually neutralized. ESC control interventions take place
a further development of the electronic limited slip differential. individual automatic
much later, provided they are still needed. As the electronic limited slip differential, control
braking interventions are possible on all four wheels. The operation corresponds broadly
of wheel-selective torque is not active when the coefficient of friction between tires and
to that of the electronic limited slip differential. The wheel-selective torque control is
road is very low.
already active by braking interventions before a skating at high speed can be established. Road behavior is significantly longer neutral. Understeer when The wheel-selective torque control is also a software extension in the ABS / ESC control unit. The control is always activated when needed and can not be deactivated by the driver.
Walk in a straight line: The load on the wheel and the driving torque is uniformly distributed.
Bend under load: Due to the centrifugal force, there is offset of the load on the wheel toward the outer side in the bend.
By braking interventions at the inside wheels in the turn, the drive torque is diverted to the outside wheels in a turn.
The resulting yaw torque helps the car turn into the turn.
475_080
43
Start Assist Systems On Audi models it uses three different systems to assist the driver when starting. The
The other two systems, the "Hill Start Assistant" and "Start Wizard" using the hydraulic
"Start Assistant EPB" is exclusively carried out on the parking brake electro vehicles
ABS / ESC for start-up assistance.
(EPB) EPB and uses the function. We will not discuss this system further, because it works without the intervention of active braking.
The corresponding control software is integrated into the ABS / ESC calculator.
Hill Start Assistant Force slope
The hill start assistant was pr oposed for the first time on the Audi A3 2006 vintage.
The system was developed to help the driver on hill starts, if somewhat fluid circulation particular. Over the inclination of the slope, the greater the component of the gravitational force by decreasing the non-braked on the slope is large vehicle: the gradient force.
A critical time when hill start is the period between the passage of the foot from the brake pedal to the accelerator until the establishment of the required torque of the driv e motor. If this period is too long, the vehicle recedes before a torque sufficient to drive the vehicle is available. This is where the "hill start assistant."
The hill start assistant is activated when the following conditions are met:
•
The vehicle is stopped, the detection is performed by the speed sensor.
•
The Audi A3, TT and Q3, the driver's door must be closed. The main engine
475_081
gravitational force (depending on model)
is running.
•
The gradient of the roadway (mounted) is higher than approx. 3-5%. The detection is performed by the longitudinal acceleration sensor (see page 37).
44
During braking by the driver, the switching valves are opened in the hydraulic unit ESC. brake pressure controlled by the driver is supplied to the wheel brakes.
475_082
When the driver releases the brake pedal, the switching valves of the hydraulic unit ESC are closed. Brake pressure previously controlled by the driver is well preserved, the vehicle can not roll back. This stop function is limited in time approx. 1.5 s maximum. Once the elapsed period, the control valve is cut. This is enough to change the foot place to start immediately. In general, the transposition occurs more quickly, so that the driver is already accelerating after less than 1.5 s. The control logic determines on the basis of the inclination of the slope the engine torque required to prevent the vehicle from moving backwards. Once the torque reaches,
The angle of inclination of the floor is determined by the longitudinal acceleration sensor (depending on the vehicle model, the ABS / ESC calculator, in the unity of sensors G419) or the electronic calculator J849 sensors.
The momentary engine torque is transmitted to the ABS / ESC calculator by the engine control unit via a message on the bus.
The function can not be deactivated by the driver.
475_083
Currently, this function is part of the standard equipment on all vehicles with automatic transmission. It is optional on Audi A1, A3, TT and Q3 with manual transmission. The Audi Q7, the function is performed by the active brake servo and not by the hydraulic ABS / ESC.
45
On vehicles with manual transmission, the information represented on the graph are
On vehicles with start-stop system and manual transmission, the gear position is detected
used for determining the release point of the service brake. On vehicles with automatic
by corresponding and taken into account in regulating sensors.
transmission, the inclination of the slope is also taken into account in the regulation. On vehicles without start-stop system with manual transmission, detection of the direction desired requires assessment of the contactor reversing lights. Via a message on the bus of the engine control unit, the software controller receives information about the operation of the accelerator. Here it is primarily the operating speed of the pedal is evaluated. The accelerator operation characterizes the restart time by the driver.
Tilt the floor
propulsion engine torque
Actuation of the accelerator pedal
Direction of desired
475_084
The Startup Wizard Hill is also activated when the start-up takes place in reverse. The reverse gear engagement is signaled to the ABS / ESC calculator with a message on the bus.
475_086
46
descent assistant
Force slope
The descent assistant aid the driver during raids in any field.
Under the effect of the gradient force, a vehicle traveling downhill is ac celerated even if the driver does not operate the accelerator. The descent assistant sends a selective braking of the vehicle wheel to ensure a constant vehicle speed. The steerability of the vehicle is further enhanced by a targeted distribution of the braking force.
The function is realized by additional software in the ABS / ESC calculator. It is available in standard equipment on the Audi Q7 and Q5.
The operating principle is the same on both models: when the couple propulsion motor inertia is not enough to avoid a vehicle acceleration, active braking interventions take place. The pressure pump is driven and the wheels are braked considered by generating a brake pressure. As with DHS or the ESC, it is called for lowering the brake pressure generating sub-functions assistant, keeping the braking pressure and reducing pressure braking. The ABS control remains active. 475_092
gravitational force
Applications differ on points of detail in the Audi Q5 and the Audi Q7.
The Audi Q7, the function is activated by pressing the button ASR and ESC and the engagement of the offroad mode. On the Audi Q5, the driver can activate using a separate command.
475_093
Control ASR / ESC on the Audi Q7
475_094
activation control the descent assistant on the Audi Q5
49
Drying the brake discs In the case of a wet road, it is not possible to avoid that water and impurities are
This causes the "waste" of valuable braking distance. It is not possible to completely
deposited on the brake discs and clutch facings. This has a negative effect on braking.
avoid this behavior by technical systems. The brake discs drying function, however,
At initial time of application of the brake lining on the brake disc, the film of water
allows a considerable improvement. Drying the brake discs is a software extension in the
substantially reduces friction between pad and disc. The expected braking action only
ABS / ESC computer and is carried out on all current Audi models. The function can not
takes effect once the eliminated or evaporated moisture.
be deactivated by the driver.
operation: In case of detection of water on the floor, the brake linings of the wheel brakes of the
The periodicity of application of the brak e linings is also dependent models; it may
front axle are periodically applied to the brake discs with a low brake pressure (0.5 to 1.5
be a fixed interval or may depend on the route.
bar, depending the vehicle model). The film of water / impurities between pad and disc is thus eliminated. Because of the low brake pressure, the driver does not perceive the
The detection of the wet requires assessment of the operation of the wipers . When the
regulation and it does not occur noticeable wear of the lining or brake disc. The period of
wipers are operated by the driver or automatically in the case of equipment with rain
application of the brake lining is very short and takes, depending on the model, only a
sensor (intermittent included), control is activated as soon as a defined minimum speed is
few seconds.
exceeded.
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51
Brake pressure [bar]
1.5 bar
0.5 bar
475_097
Time / distance
52
Optimized Hydraulic Brake Assistance (OHBV) The power mode depression most effective booster is operating the depression of the
The necessary depression can generally be provided by a separate generator (eg. A
combustion engine intake manifold. Depending on the engine versions and box used, the
pump electrical / mechanical depression). The lack of depression may also be offset by a
depression of the intake manifold, however, not always enough to defined load states.
brake pressure active property. The ESC computer compares the required depression
This may for example be the case on gasoline engines with automatic transmission,
(set) with the actual value in the intake manifold. When recording a defined gap, the
especially during the cold start phase. If, in this case, the throttle is wide open, the
computer initiates an active generation of pressure for driver assistance. brake pressure
depression of the intake manifold fall. Due to the lack of depression, the brake booster of
seen at the wheel brakes is then set to the value that would exist if sufficient vacuum
the activation point is reached earlier. It occurs when no other braking assistance. A new
supply. The driver barely notices this "aid" to him, the relationship between the pressure
braking pressure generating n '
of the pedal and the braking force performed remains the same. This is also the
brake pressure setpoint curve
Curve with level too low depression
475_130
Pedal pressure Brake assist by OHBV activation point of the brake booster of the reference curve activation point of the servo brake in case of vacuum level too low 1 2
The OHBV function has been implemented on the first time in 2004 on the Audi A3. A differential pressure sensor there was used for the measurement of the pressure / vacuum. The brake booster activation point was determined by measuring pressures in the two chambers of the brake booster. The activation point is reached in case of pressure equilibrium. If this happened to too low brake pressure, the OHBV feature was enabled by initiating a braking pressure generation.
Currently, there is performed a direct measurement of the vacuum in the intake manifold by a sensor in the line from the intake manifold to the brake booster.
475_131
55
Indicator monitoring tire pressure (RKA)
475_100
ESP is also on virtually all new Audi models, the head of indirect measure tire pressure
The RKA + uses the raw signals of speed sensors for analyzing rolling circumferences of
control system of the second generation, dubbed VW / AUDI pressure monitoring indicator
the wheels and evaluation of oscillations tire characteristics (spectral analysis) to
tires + (RKA +). The RKA + is a fully software module using ESP as host computer. It
conclude indirectly that there is pressure loss as possible. The signals read in addition,
would be workable in principle accommodate this software in any other computer of the
such as yaw rate or engine torque, and to detect the operating condition and plausibiliser
vehicle with a ROM, RAM and a sufficient processor speed. Accommodation in the ESP
the read wheel speed information. Full spectral analysis information of the evaluation of
has the decisive advantage that the wheel speed signals required by RKA + are already
the tread circumference and allows, in addition to the display of the position of the tire
delivered in the required quality. It is not necessary to take account of separate speed
concerned by the loss of air, the detection of a gradual loss of tire pressure by diffusion.
sensor outputs, with additional signal cables in the vehicle.
Figure 1 schematically represents a curve in case of loss of pressure signals before
To detect a gradual loss of pressure at several wheels, it is mainly used the information
left. To identify this "case of failure", the change in the rolling circumference is
from the oscillations of the analysis (see Chart 2).
evaluated.
wheel speed
wshpeeeeld
Amplitude
Time
A m pl i t ude
Time
Frequency
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475_101
Detecting a loss of pressure on a wheel (Troubleshooting)
pressure monitoring systems Tire Direct measurement as an indirect call in case of different levels of tire pressure (front / rear axle, full load / partial load), a system of order by the customer, where:
•
we made a replacement wheels / tires (summer / winter) or when replacing the vehicle (front / back, left / right).
56
Frequency
Detecting a pressure loss on all wheels (diffusion)
•
pressures vary in one or more tires, for example due to significant changes in the load, towing a trailer or after repairing a puncture.
external systems Electromechanical parking brake - emergency brake function (EPB) For mechanical basic function of the opening and closing of the parking brake, EPB does not need the ESC s ystem components.
A special feature of the EPB emergency braking function. As in the case of a conventional mechanical parking brake, the driver can also activate the EPB during operation in case of emergency (eg. In case of failure of the control of conventional brakes). Particularly in the case of high speeds, in the case of such one incurs the risk that the brake braking forces to the rear axle of level become so high that it is no longer possible to transmit lateral guidance forces (see "basic knowledge of driving dynamics" from page 5).
compared to conventional parking brake is notable.
avoid this situation, the ESC assists the emergency braking function. The advantage
re-accelerates. The vehicle is then no longer steerable and there is a major accident. To
emergency braking function is interrupted as soon as you release the button or that you 475_104
An audible warning signal sounds during the actuation of the pressure switch. The Pressure Switch for parking brake F234
than approx. 7 km / h. The brake pressure ESC is reduced when the EPB is fully closed. Operating principle: If the driver operates at higher speeds approx. 8 km / h the pressure switch F234 parking
The EPB starts to close as soon as the vehicle speed has been reduced to a value less
brake (by pulling the control), the vehicle is decelerated by the ESC. An active generation of pressure takes place at the four wheels. The pressure increases until the applied deceleration is reached (approx. 6 m / s 2) or by rain / snow season, until the ABS control.
7 km / h
0 km / h
EPB ~
ESC
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58
Regulating the distance in critical cases In some road situations, the selected distance from a preceding vehicle is no longer feasible in spite of the braking by the CSE. In practice, this is the case if a preceding vehicle brakes suddenly or if a vehicle from another line of traffic comes between the vehicle with the ACC and the vehicle ahead.
In these situations, it is necessary for the driver increases brake pressure "also inhibiting" and increases the brake to a value> 40% of the maximum deceleration. If the remote DISTANCE
control of the computer detects that the automatic braking is no longer possible to achieve the desired distance, this is indicated visually and acoustically to the driver.
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Audi braking guard Audi braking guard is an extension of the ACC function. The system warns the driver
Approximately at the time of the advance notice, there precharging of the brake system
of an imminent collision with a vehicle ahead.
with a brake pressure of approx. 2 bars by active generation of pressure by the ESC. This measure serves to reduce the dead time of the braking system and to clean / dry the
If the driver does not react when the warning, the distance control ECU primer, about 0.9
brake discs by applying the brake linings on the brake discs. Simultaneously, the criteria
s to 1.5 s before the last opportunity brake to avoid the collision, a short-term pressure
for triggering the hydraulic brake assist (HBA) are changed. Triggering the HBA then
generation by ABS / ESC control unit. This warning jolt clearly perceptible by the driver is
takes place even at low speeds of the pedal.
not used to the deceleration of the vehicle, but to warn once again that an immediate reaction on his part is essential to avoid the imminent collision.
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- Optical and acoustic warning
Emergency alert braking jolt
- Prefill the brake system
Significant deceleration of the vehicle traveling in front
- more sensitive response of the HBA
The Audi braking guard functions as described here team current Audi models A8, A7, A6, Q5, Q7, A4 and A5 / S5 with ACC.
61
Phase 4 is generally triggered only when the vehicle is also equipped with Audi side
Unlike the basic function ACC the Audi braking guard also reacts in the presence of
assist. With this equipment (ACC and Audi side assist), the pre sense function is
stationary targets. In these cases, optical and acoustic alert the driver takes place and, if
available under the name Audi pre sense plus. With the Audi side assist function,
necessary, the warning jolt is triggered. It is however not conducted an active braking.
circulating behind vehicles are included in the determination of risk potential. Phase 4 is initiated if, because of the traffic that follows, there is no additional risk to a total deceleration. Since the 2012 vintage, a new feature has been implemented as a sub-function of the Audi braking guard (first use on the Audi A4 and the A6, A7, A8). This function performs an emergency brake in a collision with a vehicle in front at speeds below 30 km / h. The ESC realizes, "on behalf" of the ACC, fast generation of brake pressure for a deceleration of about 8 m / s 2.
This function is also deactivated if the driver turns off the Audi braking guard.
return Detailed information on the Audi pre sense in the self-study program 456.
order The distance warning functions / optical / acoustic collision (notice) and the integral Audi braking guard feature can be disabled in the MMI if desired.
Raise
Doc. edge
Audi braking guard
driver assistance
System
activated
Early warning
activated
Car systems Set individual 475_113
Stop-and-go On current vehicle models Audi A6, A7 and A8, the stop-and-go function is performed on vehicles with ACC. If the vehicle in front, recorded by the ACC, just to stop the vehicle with the ACC system is braked if necessary until a complete stop without driver activity.
If the vehicle is restarted about a short downtime, the ACC vehicle reacc elerates automatically. Braking necessary for realization of this function are realized by the "generation of the braking pressure" ESC.
ACC: ready to start
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return Detailed information about the stop-and-go function in the s elf-study program 458 and in the use of the respective vehicle model notices.
63
Systems mandated by the ESC dynamic leadership 08 The Audi A4 was the first Audi vehicle to be fitted with dynamic leadership. This
Two major benefits result from:
steering system is able to change the steering angle of the front wheels independently of the driver. This has enabled a variable steering ratio.
•
The overall stability of the vehicle is improved by simultaneous interventions of braking and steering, active safety is considerably increased.
Interact with the ESC and its sensors, the system is also activated in case of threat of
•
In less critical road situations, it is possible to waive partly or entirely to ESC braking
critical operating states. In these specific driv ing situations, stabilization of the operating
interventions, making the stabilization of more harmonious and comfortable vehicle.
state can be achieved by correcting the deflection angle. Dynamic steering assists the
The vehicle is driven, due to the reduction brake interventions on roads with a low
ESC in a limit driving dynamics r ange by targeted variation of the front wheels.
coefficient of adhesion (snow eg.) With a workability significantly higher than that of a vehicle that is stabilized via interventions brak ing.
Superposition gear (actuator)
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calculating
ESC uses the dynamic management function in the case of a vehicle oversteer and understeer and when braking on roads with different coefficients of adhesion (μ-split).
return Detailed information on the design and operation of the dynamic leadership in the self-study program 402.
64
The regulatory intervention in the case of an oversteering vehicle illustrates the
Regulatory intervention in the event of understeer and braking on roads with different
interaction of the ESC and dynamic steering.
coefficients of adhesion (μ-split) are described in the self-study program 402.
vehicle oversteer During oversteer, ESC stabilizes the vehicle by bringing the dynamic leadership. There shall be targeted against-steer to avoid skidding the rear of the vehicle.
A typical situation that can easily cause oversteer of a vehicle is a rapid change in traffic queue. During the recovery of the vehicle to take the new traffic queue, the back of the vehicle may skid, in particular high speeds. The driver usually starts against the stabilizer-steering too late or does not make at all. The consequence are important braking interventions ESC. On the graph, it can be recognized by brake pressure curves.
Steering angle
wheel steering angle Steering angle stabilization corner braking pressure front left brake pressure angle brake pressure AV D
Time
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With dynamic steering, the stabilizer against-steering is done automatically without the driver noticing. This significantly reduces the steering maneuver performed by the driver. Just that adjusts the angle of deflection needed in a comparable steady traffic situation.
braking interventions ESC are also significantly reduced. Compared braking pressure curves of the graph above, we see that the maximum pressures are significantly lower. It follows, therefore, if traffic lane change, not only improved road stability but also a higher pass rate. Steering
wheel steering angle Steering angle stabilization corner braking pressure front left brake pressure AV D
Against-steering stabilizer dynamic steering
brake pressure
Time 475_117
65
Driver Steering Recommendation (DSR) This function is to assist the driver when braking on roads with different coefficients of
The DSR function is implemented as standard on the current Audi models A3, Q3, A6 and
adhesion between the wheels of the right and left sides of the vehicle and the roadway.
A7. The function is realized by a software extension in the ABS / ESC calculator. It is
The prerequisite for RSD feature is that the vehicle is equipped with an electromechanical
always activated when needed and can not be deactivated by the driver.
steering.
In the example shown, the wheels of the vehicle left side are on the icy road, those on the right side on dry pavement. braking forces (FB) higher are therefore transmitted to the
FB
FB
FB
FB
wheels straight. During braking, it follows the generation of a torque around the vertical axis of the vehicle towards higher coefficients of adhesion. In our example, the vehicle "pulls" (yaw) to the right when braking. The red dotted arrow indicates the deviation from the desired path. To maintain the path of the vehicle, the driver must c ompensate the yaw moment by a reaction against-steer (in our example turning to the left).
475_118
Deviation from the desired path
Steering angle ( "reaction")
This is where the DSR function. It incorporates the electromechanical steering in r egulating the yaw moment. Based on
FB
FB
FB
FB
the vehicle speed (determined by assessment of the speed sensor signals) and the yaw rate (determined by the yaw rate sensor), the ABS computer calculates the pulse of J104 necessary direction. The J104 computer transmits its "management action request" in J500 computer management. By activation of the electric motor, the rack is briefly moved in the specified direction with a maximum force at the wheel of approx. 2-3 Nm.
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This pulse direction signals to the driver which way the steering wheel must be turned. While the driver does not consciously generally view this impulse direction, it intuitively moves the wheel in the direction "correct" stabilization.
66
Steering angle
control strategy Besides the ESC system itself, the various " subsystems" such qu'EBV, ABS, EDS, ASR,
A unique and still valid prioritization systems is not possible. The need for regulation
working under the "generic name" ESC. To avoid conflicts between the different systems,
depends on the actual traffic situation. It is therefore possible that the currently active
their regulatory operations are harmonized. The overriding objective is always the safety
regulations are cut to other systems or the regulation of different systems takes place in
of preservation. One of the main "core systems" is the electronic distribution of braking
parallel (simultaneously). In most operating states, the ESC remains the system having
force EBV. The importance of this function is that a ds-braking wheels of the rear axle
the highest priority.
always entail loss of lateral guidance and causes instability of the vehicle. Where systems defects, EBV For this reason the last system to be disabled.
67
Control and driver information As it is, in the case of the ESC and its sub-systems and road safety systems, it is
The only ESC control element is the key ESC and ASR. By pressing the button, the
essential that the driver has no influence on the systems that affect security. The
driver can influence the function of the TCS and ESC. The resulting changes in the
control functions related to the driver and system information at the driver are shown
operation depends on the respective vehicle model. The table shows the respective logic
below.
of the key current Audi models.
vehicle model
Logic button
Logic of the ASR button and ESC
A1, A3 *, S3, TT
a position
•
The operation disables ASR and restricts the ESC interventions
Q3
a position
•
The operation disables ASR
** Q5, Q7,
a position
•
The active operation the "Offroad Mode"
two positions
•
A4 allroad quattro, A6 allroad quattro
A4, A5, S4, S5
An operating time of less than 3 seconds deactivates the ASR (with front wheel drive only possible up to 50 km / h, from 70 km / h there is automatic activation)
A6, A7
a position
•
Superior operating time 3 s off the ASR and ESC (only possible if the ACC is off)
•
Pressing switches the ESC in "sport mode"
•
The ASR remains active with restr ictions on vehicle s with front wh eel drive and is disabled on veh icles with quattro
AT 8
R8
*
a position
two positions
•
ESC interventions are restricted
•
Pressing switches the ESC in "sport mode"
•
ESC interventions are restricted
•
An operating time of less than 3 seconds switches the ASR and the ESC in "sport mode"
•
The ASR / ESC interventions are restricted
•
Superior operating time 3 s o ff the ASR and ESC
valid for the Audi A3 12
* * On the Audi Q5, automatic detection of offroad conditions is met. Technical realization is carried out by evaluation of the oscillations of the wheel, determined from the speed signals. By actuation of the control ASR / ESC, detection of offroad condition occurs faster than in the case of automatic detection.
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Control ASR / ESC on the Audi A7
68
The different control logic of the ASR button and ESC is related to the dynamic behavior
Following the model of vehicle, ESC is, when braking by the driver, or not activated again
of the specific vehicle model.
for the duration of braking. ESC deactivated by the driver is automatically reactivated when restarting.
Disabling the ASR is particularly sensible in a loose soil on start-up, driving with snow chains and a "clearance operation" of a stuck vehicle. Because skating in higher
On some vehicle models, disabling the ESC does not occur. Pressing the button activates
acceleration, traction is improved in the case of these road conditions.
a special sport mode. A considerably higher float angles are possible before the ESC intervenes to stabilize the vehicle.
475_094a
Button ASR / ESC and descent control assistant on the AUDI Q5
In the case of vehicle models also planned to roll all paths, the "ESC offroad mode" is
The Audi Q7, activating the ESC offroad mode caus es if necessary the ac tivation of the
activated when operating the control ASR / ESC. The thresholds of ESC regulations are
downhill assistant. On the Audi Q5, there is a separate command for this function.
defined so to achieve the best traction of the vehicle.
Depending on the model and the vehicle equipment, it can occur under circumstances defined forced activation of an ESC off. This is the case in the presence of other systems defects (electronic control of damping eg.) That may result in a modification of road behavior.
69
The current state of ESC system and its subsystems is indicated to the driver, when
If the system has no defects, witnesses are again extinguished. ESC is now ready for use.
their proper operation (no fault of the system) by the ESC witness K155. After turning
ASR or ESC intervention is indicated by the flashing K155 witness. After pressing the
the ignition (terminal 15), a check is performed witnesses. Witnesses are driven for
ASR control and ESC, the K216 light comes on until the ignition is off or a new actuation
about three seconds. During this period, an internal control system applicable.
of the (logic of the key, see page 68).
System Status
State K118 braking system
State K47
State K155 ESC
State K216 ESC
ABS
and ASR
and ASR
Note
Terminal 15 on, light control
flawless system and ready to work
Intervention ASR / ESC
No display
No display
No display
No display
No display
No display
No display
No display
No display
K155 flashes
When braking, the ESC can actuated control TCS and ESC
70
No display
be activated automatically
Service operations This chapter provides an overview of ESC system service operations. Due to the use of
there are differences in detail at the Service's operations.
systems of different manufacturers as well as specific modifications to the models, Please therefore take into account the service works and use the service systems provided for this purpose.
Diagnostic System All ESC systems used on current Audi models are suitable for diagnosis.
Defects discovered within the self-diagnosis are enrolled in the vehicle event memory and can be read with a diagnostic tester suitable vehicle.
The system faults are also reported to the driver by witnesses and text messages.
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System Status
State K118 braking system
Failure ASR / ESC No display
ASR failure / ASR / EDS / ESC
State K47
State ESC
ABS
K155
No display
No display
total failure
Note
EBV, EDS and ABS remain active
An emergency EBV function is retained
All systems are off - immediately go to the studio!
Removing and installing / replacing ABS / ESC ECU and the hydraulic unit
The computer and the hydraulic unit are on the Audi A3 and A8 today, separable. On these models, a faulty computer can be replaced separately. In case of failure of the
After replacing a computer or ABS / ESC complete unit must perform consecutive operations indicated on the next page.
hydraulic unit, always replace the complete unit (ECU and hydraulic unit).
71
c ur r e n t v e h i c l e m o d e l
Se p a r a t e r e p la c e m e n t
consecutive operations after replacement
possible calculator
A1
No
A3
Yes
venting - the computer coding - Sensor Calibration * - diagnosis actuators
venting - the computer coding - Sensor Calibration * - basic setting suction and cut valves - adaptation of the electronic limited slip - Actuator diagnosis - driving test and syste m
Q3
No
TT
No
Q7
No
A4, A5, Q5
No
A6, A7
No
AT 8
Yes
R8
No
venting - the computer coding - Sensor Calibration * - ** adaptations executions - diagnosis actuators
venting - the computer coding - calibration of sensors * - diagnosis actuators - driving test and system
venting - the computer coding - calibration of sensors * - diagnosis actuators - driving test and system
Air vent - coding of the computer (online) - Actuator diagnosis - driving test and system
venting - the computer coding - calibration of the steering angle transmitter - diagnosis actuators
venting - the computer coding - calibration of the steering angle transmitter - diagnosis actuators
venting - the computer coding - calibration of sensors * - diagnosis actuators - driving test and system
* : Steering angle transmitter, brake pressure sensors, transverse and longitudinal
* * : Because this computer is also used by other Group brands, different functions (. Eg
acceleration, longitudinal acceleration sensor is mounted on vehicles with AWD or
stabilizing coupling) must be validated by corresponding adjustments after encoding.
descent assistant.
The braking system of venting is always necessary when the brake lines have been
After installation of the hydraulic unit, always make the diagnosis of actuators. This
opened. It is always necessary after removal and installation of the hydraulic unit. To
ensures that the lines from the wheel brakes are connected to the correct positions of
separate the calculator of the hydr aulic unit, it must also file the complete unit. The Audi
the hydraulic unit.
A8, it is essential to removing the computer to use a workstation with ESD protection (workshop equipment VAS 6613) to prevent damage to the computer due to electrostatic charge.
Bracelet Shop Equipment VAS 6613 ESD table mat with potential compensation
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72
The encoding of an ABS / ESC new calculator is made online on all current Audi models. An online connection is established with the SVM database (SVM = managing software versions). The encoding values are then transmitted without doing anything (and display content) in the ABS / ESC control unit.
475_029a
Depending on the vehicle model and version ESC, it is necessary, after coding of the
The computer reads the value sent and the interpreter as the immobile state of the
ABS / ESC calculator, calibrate some sensors (see table on page 72). To evaluate the
vehicle (lateral acceleration = 0). In our example, this measurement value is 0.2 V. The
measured values (digital numbers) of a sensor, the computer should at least know the
fictitious example computer knows, due to the previously stored characteristic, a change
actual physical condition for a measurement value. The characteristics of the sensors
in the measurement value of 0.1 V corresponds to a variation transverse acceleration of
are stored in the computer. If the computer is experiencing a real mesurevaleur value
0.1 m / s 2. Thereafter, the computer knows assigning each measured value of a transverse
assignment, it can calculate all other measurement values values (physical)
acceleration value. The measured value is 0.5 V for example interpreted as transverse
corresponding real.
acceleration of
0.3 m / s 2. In the example shown, this principle is shown for the hypothetical curve of a transverse acceleration sensor: The illustrated curve is stored in the computer. The computer "knows" and any variation of the measured value corresponds to any variation of the transverse acceleration. During calibration, the vehicle must be stationary.
measurement value [V]
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lateral acceleration [m /2]s
73
Removing and installing / replacing electronic calculator sensors J849
After replacing the J849 calculator, a computer calibration is required. For this, the vehicle must be stationary on a flat surface. In this position, the ABS / ESC calculator reads the measurement values of the sensors and stores the state as "vehicle stationary". Since the characteristics of the sens ors are stored in the ABS / ESC, the computer may subsequently affect all other measured values an actual movement of the vehicle and convert them to actual physical values.
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Removing and installing / replacing steering angle sender G85:
After replacing the steering angle transmitter, it must be calibrated. The condition is that the ESC computer is encoded. The calibration begins with a defined rotation of the steering wheel by the mechanic. Following the model of vehicle, it must then briefly r oll forward. It is then carried out a comparison of the sensor measured values with the speed sensors of individual wheels. The "zero position" of the sensor is then determined (the sensor signal forward). This "zero signal" is the basis for the subsequent conversion of all measurement values to the actual values of steering angle.
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The Audi Q7, the transmitter "loses" his boot when disconnected from the vehicle battery (terminal 30). Then the transmitter must also be reset as described.
Overview of ESC systems fitted current Audi models
vehicle model
ESC
A1
Bosch 8.2
A3, S3
Continental MK 60 EC
TT
Continental MK 60 E1
Q3
TRW 450
A4, S4, A5, S5, Q5
Q7
A6, A7, A8
R8
Bosch 8.1
Continental MK 25
Bosch Premium
Bosch 8.0
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Knowledge check Among answers indicated, there may be one or more correct answers.
Question 1: What forces can be transmitted between the tires and the roadway?
at)
Exclusively by gravity and lateral guiding forces.
b)
Exclusively forces in the longitudinal and transverse directions of the vehicle.
c)
gravitational forces, transverse guiding forces, driving and braking forces.
Question 2: What is the basic function of the ABS anti-lock system?
at)
The ABS provides better traction.
b)
The ABS shortens the braking distance.
c)
SBS limits the brake pressure in order to still transmit lateral guide forces.
d)
ABS ensures that the vehicle remains steerable during braking.
Question 3:
What essential control functions form the basis for regulating operations of the ESC?
at)
Reduction and increase in the torque of the drive motor.
b) Maintenance of the brake pressure, the brake pressure reduction and the generation of brake pressure. c)
Question 4:
Reduction and increase of the injection flow rate and change the ignition point.
Why the electronic distribution of braking force EBV he is one of the most important systems for the conservation of driving safety?
at)
EBV causes excessive braking forces at the front axle. The vehicle thus remains airship in all driving situations.
b)
EBV causes excessive braking forces at the rear axle.
c)
EBV prevents acceleration slippage too high for vehicles with front wheel drive.
d)
EBV prevents the rear of the vehicle skids during braking.
Question 5: What additional sensors are compared with ABS, necessary for the implementation of the ESC? at)
Sensors for recording the steering angle, lateral and longitudinal acceleration and the yaw rate.
b)
recording sensors of acceleration of the body.
c)
speed recording wheel sensors and the brake pressure.
Question 6: What are the installation of transverse and longitudinal acceleration sensors and yaw rate locations on current Audi models?
at)
The sensors are mounted only in the unity of ESP G419 sensor.
b)
The sensors are mounted only in the unity of ESP G419 sensors and the electronic calculator J849 sensors.
c) d)
The sensors are mounted exclusively in the J104 calculator. The sensors are, depending on model, built-in unit G419 sensors in the electronic calculator J849 sensors in the ABS / ESC J104 and J540 in the electric parking brake ECU.
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Question 7: Which statement is correct?
at)
Enabling the HBA hydraulic brake assistant is performed on vehicles with ACC, depending on the traffic situation considered.
b) A vehicle is equipped or not the ACC has no influence on the activation conditions of the HBA. c)
On the vehicle with ACC, the HBA is generally disabled. The HBA function is performed by the ACC.
Question 8: What benefit is the electronic limited slip he has in relation to the electronic differential lock EDS?
at)
No.
b)
The electronic differential lock is already activated even if one is not yet in the presence of a critical slippage at the wheels.
c)
The braking pressures are, in the case of the electronic differential lock, significantly lower than in the case of regulation EDS.
Question 9: A vehicle is fitted with the indicator of pressure RKA tires. The driver has increased pressure Front tires go on vacation. Should he carry on other activities regarding the system?
at)
No other activity is required.
b)
The driver must go to the nearest customer service workshop to adapt the new tire pressures are with the vehicle diagnostic tester.
c)
The driver must validate the tire pressures modified by an input via the MMI or using the planned monitoring key.
Question 10: What is the reaction triggered upon actuation of the control ASR / ESC?
at)
The ASR is disabled on all Audi models, the ESC remains active without restrictions.
b)
The TCS and ESC are disabled on all Audi models.
c)
The system response is not identical on all Audi models.
d)
The reaction of the system depends on the use of the vehicle target. Thus, the vehicles also provided to ride in all ways, the "Offroad Mode" is activated.
Question 11: Why does it always diagnose actuator after installing the hydraulic unit ABS / ESC?
at)
To calibrate the braking pressure transmitters of transverse and longitudinal acceleration.
b)
To calibrate the steering angle transmitter.
c)
To ensure that the lines from the wheel brakes are connected to the correct positions of the hydraulic unit.
Question 12: What is the test drive and the system?
at)
To verify the plausibility of the measured values of the transverse and longitudinal acceleration sensors as well as the yaw rate.
b)
To calibrate the steering angle transmitter.
c)
To check the operation of the ESC.
;t a ) 2 1 ; c ) 1 1 ; dc ) 0 1 ; c ) 9 ; c b ) 8 ;t a ) 7 ; d ) 6 ;t a ) 5 ; d b ) 4 ; b ) 3 ; d c ) 2 ; c ) 1
: tson oi t u l o S
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self-study programs (SSP) You will find more information on ESC Audi vehicles in the following self-study programs.
Progr. autodidact. 362
Audi Q7 - Links to the ground, Reference: A05.5S00.15.40
Progr. autodidact. 381
Reference: A06.5S00.26.40 Audi TT Coupe 07 - Wheels and suspension,
Progr. autodidact. 394
Audi A5 - Links to the ground, Reference: A07.5S00.36.40
P r o g r . a ut o d i d a c t . 4 3 3
Audi A udiQ5, Q 5 ,Reference: A08.5S00.49.40
Progr. autodidact. 458
Audi A8 10 - Links to the ground, Reference: A10.5S00.62.40
P r o g r . a ut o d i d a c t . 4 7 7
Audi A udiA1, A 1 ,Reference: A10.5S00.70.40
Progr. autodidact. 480
Audi A7 Sportback - Links to the ground, Reference: A10.5S00.73.40
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Subject to all rights and technical changes.
Copyright AUDI AG I / VK-35
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AUDI AG D-85045 Ingolstadt Technical definition 07/12
Printed in Germany A11.5S00.79.40
