A Seminar Report On
Adaptive Cruise Control Submitted in the partial fulfillment of the requirement for the award of degree of
Master of Technology In Electronics Engineering (Control & Instrumentation)
Submitted By
DeVvrat
MEE-197-2K10
Department of Electronics, Instrumentation & Control Engineering
Sector -6, Faridabad -121006, (Haryana)
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Sector -6, Faridabad -121006, (Haryana)
Department of Electronics, Instrumentation & Control Engineering
This is to certify that seminar work entitled “Adaptive Cruise Control” is a bonafide work carried out in the second semester by “DeVvrat (MEE-197-2K10)” in partial fulfillment for the award of Master of Technology in“Electronics Engineering (Control & Instrumentation)” from YMCA University of Science & Technology, Faridabad during the academic year 201011who carried out the seminar work under the guidance and no part of this work has been submitted earlier for the award of any degree.
Seminar Coordinators Dr. Munish Vashishth Professor Department of Electronics, Instrumentation & Control Engineering
Mr. Dushyant Singh Lecturer Department of Electronics, Instrumentation & Control Engineering
Table of Contents 2
S.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Chapter Title Introduction Why Adaptive Cruise Control Adaptive Cruise Control How It works Definitions & Physical Overview Operational Overview Control System Interfaces Initialization Engaging cruise control ACC Speed Control ACC Time gap control Cancelling Cruise control operation Adaptive cruise control features Advantages Limitations Conclusion Modeling & Simulation References
Page No. 4 4 4-5 5-6 6-8 8(i) 8(ii) 9 9 9 9-10 10 10 10-11 11 11 11-13 13
Adaptive Cruise Control Introduction 3
Mentally, driving is a highly demanding activity - a driver must maintain a high level of concentration for long periods and be ready to react within a split second to changing situations. In particular, drivers must constantly assess the distance and relative speed of vehicles in front and adjust their own speed accordingly. Those tasks can now be performed by Adaptive Cruise Control (ACC) system, which is an extension of the conventional cruise control system. Like a conventional cruise control system, ACC keeps the vehicle at a set constant speed. The significant difference, however, is that if a car with ACC is confronted with a slower moving vehicle ahead, it is automatically slowed down and then follows the slower vehicle at a set distance. Once the road ahead is clear again, the ACC accelerates the car back to the previous set cruising speed. In that way, ACC integrates a vehicle harmoniously into the traffic flow. Adaptive Cruise Control (ACC) is an automotive feature that allows a vehicle's cruise control system to adapt the vehicle's speed to the traffic environment. A radar system attached to the front of the vehicle is used to detect whether slower moving vehicles are in the ACC vehicle's path. If a slower moving vehicle is detected, the ACC system will slow the vehicle down and control the clearance, or time gap, between the ACC vehicle and the forward vehicle. If the system detects that the forward vehicle is no longer in the ACC vehicle's path, the ACC system will accelerate the vehicle back to its set cruise control speed. This operation allows the ACC vehicle to autonomously slow down and speed up with traffic without intervention from the driver. The method by which the ACC vehicle's speed is controlled is via engine throttle control and limited brake operation. Why Adaptive Cruise Control? Comfortable distance to the car ahead increases driving safety and ensures a more relaxed driving experience. Adaptive Cruise Control ensures that there is enough distance to the car ahead, even if it unexpectedly lowers the speed. With Adaptive Cruise Control we have enhanced the conventional systems for speed control to a driver assistant with an added value. The system makes it possible to adapt the distance to the car ahead without the driver’s intervention, effectively relieving the driver. Highway and rural road drives are more relaxed and traffic flows better altogether, since acceleration and braking maneuvers are automatically adjusted. Adaptive Cruise Control Two companies are developing a more advanced cruise control that can automatically adjust a car's speed to maintain a safe following distance. This new technology, called adaptive cruise control, uses forward-looking radar, installed behind the grill of a vehicle, to detect the speed and distance of the vehicle ahead of it. Adaptive cruise control is similar to conventional cruise control in that it maintains the vehicle's pre-set speed. However, unlike conventional cruise control, this new system can automatically adjust speed in order to maintain a proper distance between vehicles in the same lane. This is achieved through a radar headway sensor, digital signal processor and longitudinal controller. If the lead vehicle slows down, or if another object is detected, the system sends a signal to the 4
engine or braking system to decelerate. Then, when the road is clear, the system will reaccelerate the vehicle back to the set speed. The 77-GHz Auto cruise radar system made by TRW has a forward-looking range of up to 492 feet (150 meters), and operates at vehicle speeds ranging from 18.6 miles per hour (30 kph) to 111 mph (180 kph). Delphi's 76-GHz system can also detect objects as far away as 492 feet, and operates at speeds as low as 20 mph (32 kph). Adaptive cruise control is just a preview of the technology being developed by both companies. These systems are being enhanced to include collision warning capabilities that will warn drivers through visual and/or audio signals that a collision is imminent and that braking or evasive steering is needed. Adaptive Cruise Control (ACC) technology improves upon the function of standard cruise control by automatically adjusting the vehicle speed and distance to that of a target vehicle. ACC uses a long range radar sensor to detect a target vehicle up to 200 meters in front and automatically adjusts the ACC vehicle speed and gap accordingly. ACC automatically decelerates or accelerates the vehicle according to the desired speed and distance settings established by the driver. As per standard cruise control the driver can override the system at any time.
Figure: THE CONCEPT OF ACC. How Does It work? The radar headway sensor sends information to a digital signal processor, which in turn translates the speed and distance information for a longitudinal controller. The result? If the lead vehicle slows down, or if another object is detected, the system sends a signal to the engine or braking system to decelerate. Then, when the road is clear, the system will re-accelerate the vehicle back to the set speed. The adaptive cruise control (ACC) system depends on two infrared sensors to detect cars up ahead. Each sensor has an emitter, which sends out a beam of infrared light energy, and a receiver, which captures light reflected back from the vehicle ahead. The first sensor, called the sweep long-range sensor, uses a narrow infrared beam to detect objects six to 50 yards away. At its widest point, the beam covers no more than the width of one highway lane, so this sensor detects only vehicles directly ahead and doesn't detect cars in other lanes. Even so, it has to deal with some tricky situations, like keeping track of the right target 5
when the car goes around a curve. To deal with that problem, the system has a solid-state gyro that instantaneously transmits curve-radius information to the sweep sensor, which steers its beam accordingly. Another challenge arises when a car suddenly cuts in front of an ACC-equipped car. Because the sweep sensor's beam is so narrow, it doesn't "see" the other car until it's smack in the middle of the lane. That's where the other sensor, called the cut-in sensor, comes in. It has two wide beams that "look" into adjacent lanes, up to a distance of 30 yards ahead. And because it ignores anything that isn't moving at least 30 percent as fast as the car in which it is mounted, highway signs and parked cars on the side of the road don't confuse it. Information from the sensors goes to the Vehicle Application Controller (VAC), the system's computing and communication center. The VAC reads the settings the driver has selected and figures out such things as how fast the car should go to maintain the proper distance from cars ahead and when the car should release the throttle or downshift to slow down. Then it communicates that information to devices that control the engine and the transmission. There are several inputs: System on/off: If on, denotes that the cruise-control system should maintain the car speed. Engine on/off: If on, denotes that the car engine is turned on; the cruise-control system is only active if the engine is on. Pulses from wheel: A pulse is sent for every revolution of the wheel. Accelerator: Indication of how far the accelerator has been pressed. Brake: On when the brake is pressed; the cruise-control system temporarily reverts to manual control if the brake is pressed. Increase/Decrease Speed: Increase or decrease the maintained speed; only applicable if the cruise-control system is on. Resume: Resume the last maintained speed; only applicable if the cruise-control system is on. Clock: Timing pulse every millisecond. There is one output from the system: Throttle: Digital value for the engineer throttle setting. Definitions Adaptive Cruise Control (ACC ) - An enhancement to a conventional cruise control system which allows the ACC vehicle to follow a forward vehicle at an appropriate distance. ACC vehicle - the subject vehicle equipped with the ACC system. active brake control - a function which causes application of the brakes without driver application of the brake pedal. clearance - distance from the forward vehicle's trailing surface to the ACC vehicle's leading surface.
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forward vehicle - any one of the vehicles in front of and moving in the same direction and traveling on the same roadway as the ACC vehicle. set speed - the desired cruise control travel speed set by the driver and is the maximum desired speed of the vehicle while under ACC control. system states ACC off state - direct access to the 'ACC active' state is disabled. ACC standby state - system is ready for activation by the driver. ACC active state - the ACC system is in active control of the vehicle's speed. ACC speed control state - a substate of 'ACC active' state in which no forward vehicles are present such that the ACC system is controlling vehicle speed to the 'set speed' as is typical with conventional cruise control systems. ACC time gap control state - a substate of 'ACC active' state in which time gap, or headway, between the ACC vehicle and the target vehicle is being controlled. target vehicle - one of the forward vehicles in the path of the ACC vehicle that is closest to the ACC vehicle. time gap - the time interval between the ACC vehicle and the target vehicle. The 'time gap' is related to the 'clearance' and vehicle speed by: time gap = clearance / ACC vehicle speed Physical Layout As shown in Figure 3, the ACC system consists of a series of interconnecting components and systems. The method of communication between the different modules is via a serial communication network known as the Controller Area Network (CAN). ACC Module - The primary function of the ACC module is to process the radar information and determine if a forward vehicle is present. When the ACC system is in 'time gap control', it sends information to the Engine Control and Brake Control modules to control the clearance between the ACC Vehicle and the Target Vehicle. Engine Control Module - The primary function of the Engine Control Module is to receive information from the ACC module and Instrument Cluster and control the vehicle's speed based on this information. The Engine Control Module controls vehicle speed by controlling the engine's throttle. Brake Control Module - The primary function of the Brake Control Module is to determine vehicle speed via each wheel and to decelerate the vehicle by applying the brakes when requested by the ACC Module. The braking system is hydraulic with electronic enhancement, such as an ABS brake system, and is not full authority brake by wire. Instrument Cluster - The primary function of the Instrument Cluster is to process the Cruise Switches and send their information to the ACC and Engine Control Modules. The Instrument Cluster also displays text messages and telltales for the driver so that the driver has information regarding the state of the ACC system. 7
CAN - The Controller Area Network (CAN) is an automotive standard network that utilizes a 2 wire bus to transmit and receive data. Each node on the network has the capability to transmit 0 to 8 bytes of data in a message frame. A message frame consists of a message header, followed by 0 to 8 data bytes, and then a checksum. The message header is a unique identifier that determines the message priority. Any node on the network can transmit data if the bus is free. If multiple nodes attempt to transmit at the same time, an arbitration scheme is used to determine which node will control the bus. The message with the highest priority, as defined in its header, will win the arbitration and its message will be transmitted. The losing message will retry to send its message as soon as it detects a bus free state. Cruise Switches - The Cruise Switches are mounted on the steering wheel and have several buttons which allow the driver to command operation of the ACC system. The switches include: 'On': place system in the 'ACC standby' state 'Off'': cancel ACC operation and place system in the 'ACC off' state 'Set +': activate ACC and establish set speed or accelerate 'Coast': decelerate 'Resume': resume to set speed 'Time Gap +': increase gap 'Time gap -': decrease gap Brake Switches - There are two brake switches, Brake Switch 1 (BS1) and Brake Switch 2 (BS2). When either brake switch is activated, Cruise Control operation is deactivated and the system enters 'ACC standby' state. Brake Lights - When the Brake Control Module applies the brakes in response to an ACC request, it will illuminate the brake lights to warn vehicles behind the ACC vehicle that it is decelerating. Operational Overview The driver interface for the ACC system is very similar to a conventional cruise control system. The driver operates the system via a set of switches on the steering wheel. The switches are the same as for a conventional cruise control system except for the addition of two switches to control the time gap between the ACC vehicle and the target vehicle. In addition there are a series of text messages that can be displayed on the instrument cluster to inform the driver of the state of the ACC system and to provide any necessary warnings. The driver engages the ACC system by first pressing the ON switch which places the system into the 'ACC standby' state. The driver then presses the Set switch to enter the 'ACC active' state at which point the ACC system attempts to control the vehicle to the driver's set speed dependent upon the traffic environment.
Initialization
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When the ignition key is in the off position, no power is applied to any of the systems. When the key is cycled to the on position, the ACC system initializes to the 'ACC off' state. Engaging Cruise Control Entering 'ACC standby' - Before active cruise control can be engaged the driver must first enter 'ACC standby'. This is performed by the driver pressing the ACC 'On' button. If no system faults are present, the ACC system will transition to the 'ACC standby' state. Entering 'ACC active' - The driver enters the 'ACC active' state by pressing the 'Set' or 'Resume' button. If a prior set speed is present in memory, the system uses this prior value as the target speed when Resume is pressed, else, the current speed of when the Set button was pressed will become the target speed. The following conditions must be true for the system to enter 'ACC active' in response to the cruise switches: Brake Switch 1 = brake not applied Brake Switch 2 = brake not applied Vehicle Speed >= 25 mph When entering active ACC control, the vehicle speed is controlled either to maintain a set speed or to maintain a time gap to a forward vehicle, whichever speed is lower. Operation During Speed Control Mode (ACC Speed Control) Operation during this mode is equivalent to that of conventional speed control. If no forward vehicle is present within the Time Gap or clearance of the system, the vehicle's speed is maintained at the target speed. The engine control system controls the engine output via throttle control to maintain the vehicle speed at the target speed. Operation During Follow Mode (ACC Time Gap Control) The ACC system enters follow mode or 'ACC time gap control' if the radar detects a forward vehicle at or within the clearance distance. During this mode of operation, the ACC system sends a target speed to the Engine Control Module and deceleration commands to the Brake Control module to maintain the set time gap between the vehicles. deceleration control - The ACC system decelerates the vehicle by lowering the target speed sent to the Engine Control Module and sending a brake deceleration command to the Brake Control Module. The maximum allowed braking effort of the system is 0.2 [g]. During brake deceleration events, the Brake Control Module activates the brake lights. acceleration control - The ACC system accelerates the vehicle by increasing the target speed sent to the Engine Control Module. The Engine Control Module tries to maintain the target speed and can accelerate the vehicle at a rate of up to 0.2 [g] of acceleration. adjusting the time gap - The driver can adjust the time gap via the 'Time Gap +' and 'Time Gap -' switches. Pressing the 'Time Gap +' switch causes the time gap value to increase and therefore the clearance between the two vehicles to increase. Pressing the 'Time Gap -' switch causes the time gap value to decrease and therefore the clearance between the two vehicles to decrease. 9
reaction to a slow moving or stopped vehicle - Situations may occur such that the ACC system is not able to maintain the time gap within the deceleration authority of the system, 0.2 . The clearance between the ACC vehicle and the forward vehicle may be rapidly decreasing or the minimum vehicle speed of 25 [mph] may be reached. Under these situations the ACC system enters 'ACC standby' and alerts the driver by displaying a "Driver Intervention Required" text message on the instrument cluster and by turning on an audible chime. If the brakes were being applied by the ACC system, they will be slowly released. At this point the driver must take control of the vehicle. Transitioning Between Speed Control and Follow Modes The ACC system automatically transitions between Speed Control and Time Gap (Follow) Modes. The mode of operation is determined by the lower of the set speed for Speed Control Mode and the target speed to maintain the gap between the ACC vehicle and a forward vehicle. Basically, if no vehicle is present within the clearance distance, the system will operate in Speed Control mode, else, it will operate in Time Gap mode. Canceling Cruise Control Operation Cruise Control operation may be canceled by the operator or automatically via the ACC system. Either of the following conditions will deactivate ACC:
Brake pedal is pressed 'Off' button is pressed Vehicle Speed < 25 mph An ACC system fault is detected
Features
Maintains a safe, comfortable distance between vehicles without driver interventions Maintains a consistent performance in poor visibility conditions. Maintains a continuous performance during road turns and elevation changes Alerts drivers by way of automatic braking.
Advantages Some of those advantages include: Its usefulness for long drives across sparsely populated roads. This usually results in better fuel efficiency. Some drivers use it to avoid unconsciously violating speed limits. A driver who otherwise tends to unconsciously increase speed over the course of a highway journey may avoid a speeding ticket. Such drivers should note, however, that a cruise control may go over its setting on a downhill which is steep enough to accelerate with an idling engine. 10
Reduction in accident rate for vehicles fitted with collision avoidance type systems Reduction in driver fatigue Interconnection to more advanced future systems. Limitations One of the biggest challenges in designing ACC systems today are the costs associated with the robust system. Though current costs are substantial, they are slowly decreasing. Auto manufacturers stress that advanced cruise control does not drive the car for you, and it's not meant to be used in heavy traffic. But, for long trips, it's a convenience that allows you to focus more on your driving. Conclusions Despite the introduction of the system to the market place, these are still early days. The current system can measure up to 150m ahead of the car and reduce the car's speed if an obstruction appears. What it can't do, at the moment, is bring the car to a halt. Whatever happens, the ACC market looks set to explode. The projected figures make startling reading. In 2002 there are no more than 100,000 vehicles fitted with ACC, but that figure is set to reach eight million in four years' time, with Europe, South-East Asia and the US accounting for about a third each. Around 17% of all European-built cars are likely to have ACC fitted as standard by then. Expansion is bound to slow down thereafter, but by 2010 the global market will be 11.5 million units, representing an industry value of around $2.4 billion - and enormously more than that saved in repair bills, hospital bills and, indeed, funeral bills. Modeling & Simulation
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References www.siliconchip.com.au/cms/A_105086/article.html www.audi.com/audi/com/en1/glossary/adaptive_cruise_control.html www.pcmag.com/encyclopedia www.ford.com/en/innovation/safety/accidentAvoidance/adaptiveCruiseControl.html Seminar Topic from :: www.edufive.com/seminartopics.html
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