Dynamic Braking on AC Haul Trucks Surf ace Ha Surface Haul ulage age Sa Safety fety Works Wor ksho hop p Nati Na tion onal al Mine Hea Healt lth h and Safety Ac ademy Beckley, West West Virginia Virgin ia May 2005
The elect electri ricall cally y dri d riven ven Li ebhe bh err Rea Rear Axl A xle e (T 282 282) Ax A x l e Bo Box Torque or que Tube Roller ol ler Beari Bearings ngs Hub Hu b
T 282
Fina in al Drive Driv e Electric Motor (one per per drive) dri ve) with wit h motor moto r spe sp eed dry disc dis c brakes brakes
The elect electri ricall cally y dri d riven ven Li ebhe bh err Rea Rear Axl A xle e (T 282 282) Ax A x l e Bo Box Torque or que Tube Roller ol ler Beari Bearings ngs Hub Hu b
T 282
Fina in al Drive Driv e Electric Motor (one per per drive) dri ve) with wit h motor moto r spe sp eed dry disc dis c brakes brakes
Double oub le dis cs per each each rear rear whee w heel, l, arma rm ature tur e speed speed bra br akes and and excellent accessi bili bi lity ty
T 282 T 282
inside
Ac A c c ess es s f r o m i n s i d e th t h e axl ax l e bo b o x . Ful Fu l l y prote prot ected from fro m roa r oad d dirt d irt and we w eather. Controll ontr olle ed brake cooling cool ing wi th forced for ced air flow. fl ow.
Double oub le dry disc di sc,, arma rm ature tu re speed speed bra br akes for fo r each each rear rear whee w heell
On a Liebherr truck most of the deceleration by far is done electrically – not mechanically
NOTE: •The main system used to slow down a Liebherr truck is NOT it’s mechanical brakes but instead the
Electrical System = Electric Retarding •The mechanical brake system (dry disc brakes on front and rear wheels) are to be used only: A. To bring the truck to a complete stop after it has been slowed electrically to a near stand still B. To stop the truck in an emergency (Test per SAE J 1040)
Electric retarding is virtually wear free •The mechanical or service brakes on a Liebherr truck are normally used very little and virtually NEVER during retarding on a down hill run to keep the truck at a constant safe speed.
NOTE: • When retarding, the energy to slow down the truck is transformed into electric energy. This electric energy is dispersed via the electric resistor grids into the air in form of heat. • During retarding there is no friction of any components. So, when slowing down the truck electrically –
• there is no component wear and • there is practically no required maintenance.
B1 - Retarding Horse Power •Retarding horse power: The electric drive system will retard the loaded truck with up to 2½ times the engine hp to a near stop of: • AC ~ 0.8 kmh / .5 mph or DC ~ 5 kmh / 3 mph.
B2 - Full Retarding with Dead Engine (AC drive) •Liebherr AC drive trucks have full retarding hp even with a dead diesel engine. •During retarding the drive motors produce their own exciting current (self excitation) which means that there is no current required from the engine driven alternator. •This current will also power the grid cooling fan. •If grid cooling is still required once the truck has stopped, the current will be automatically supplied by the diesel engine/alternator.
B3 - Automatic Brake Application (AC drive) • Automatic Brake Application : - The truck is brought to a final stop and held in place with it’s mechanical disc brakes. -The brakes are applied automatically . The computer gradually blends in the brakes while blending out retarding between .8 kmh / .5 mph and stop. -The operator still has a third separate pedal to apply the brakes at will. Full 30° pedal arc for both - electric retarding pedal and - service brake pedal provides safer control for the operator • Accelerator pedal • Retarder pedal • Service brake pedal (for emergencies and uphill acceleration)
B4 - Service Brake System – ISO requirements
ISO 3450: The service brakes are required to bring the fully loaded truck to a safe and complete stop five times consecutively on an actual down hill grade of 9 ±1 %.
All four Liebherr truck models have been tested repeatedly and met/exceeded the ISO 3450 requirements.
B6&7 - Hand Brake & Emergency Brake •Handbrake = Service brakes will hold the fully loaded truck on a slope of up to 25% • As a safety feature in an emergency the handbrake can be applied while driving •Electric toggle or rocker switch: Hand brake
25%
B9 - Accumulators for Steering and Braking • Accumulators for steering and braking: Independent nitrogen pressurized accumulators supply enough energy after the diesel engine has stopped running to complete at least - three 90° steering actions plus - twelve complete brake applications
Min. three 90° steering actions
Twelve full brake applications
B10 - Anti-Roll-Back: AC Drive Truck • Anti-Roll-Back: The truck will not roll back on a grade when starting to drive. This works in forward and reverse. The control system will allow the rear wheels to only turn in the direction the operator has selected with the selector switch.
controlled via sensors on both rear wheels
If the sensors on the rear wheels detect motion in the opposite direction, the service brakes are applied automatically and instantly.
B11 - Cruise Control • All Liebherr trucks have TWO semi-automatic retarding features: a. Cruise Control - functions in both propel and retard. - as a down hill safety feature it will keep the truck at the set speed. level
x
l l i h p u
level Dumping
y d o w n
Loading
x:
set C/C to high speed or over-ride the y-setting with the accelerator pedal
y:
set C/C to maximum allowed down hill speed
h i l l
Loading
B12 - Two Speed Over Speed Retarding • All Liebherr trucks have TWO semi-automatic retarding features: b. Two Speed Over Speed – - automatically starts the retarding process on a down grade and prevents the truck from going faster than the set limit. - there are two different automatic speeds, one for loaded and one for empty. - as a safety feature “ Two speed over speed” will override cruise control. Note: If the truck in a given situation starts retarding outside the retarding envelope, it HAS to be slowed down by the operator with the service brakes until it is inside the envelope.
Service brake Electric retarding
Retarding start outside the retarding envelope necessitates application of service brake (DC & AC)
Service brake
Electric retarding
B13 - Slip/Slide Control: AC Drive Truck •Slip/Slide Control: Sensors on either rear wheel constantly report the exact rpm of each wheel to the central computer. If there is a discrepancy to the average travel speed of the two wheels, the computer automatically will supply • propelling:
- less drive power to the faster turning wheel or
• retarding:
- less retarding power to the slower wheel
• Curve travel: The computer automatically considers the mandatory rpm difference by constantly monitoring the front wheel steering angle.
1- Difference between Hand Brake, Park Brake and Emergency Brake A- HAND BRAKE, all Liebherr truck models: 1. Applied by operator via toggle (or rocker-) switch, located on center console 2. Applies full brake pressure from the two brake accumulators to all service brakes on front and rear wheels 3. Will only function with accumulators pressurized. If one of the two brake circuits has a line failure, the second one will still function 4. Used when operator is inside cab with engine running and truck stopped, i.e. during loading, dumping and whi le being stopped and waiting 5. In an emergency the Hand Brake could be used to stop the truck 6. Designed to HOLD the fully loaded truck on inclines of up to 25%
1- Difference between Hand Brake, Park Brake and Emergency Brake C- EMERGENCY BRAKE, all Liebherr truck models: 1. In an emergency, i.e. electric retarding failure, the Service Brake System is used 2. Operator controlled via the left foot pedal in the cab 3. Two independent Brake Circuits:
4. The service brakes are tested to fully comply with ISO 3450, requiring to bring the fully loaded truck to a safe and complete stop five times consecutively on an actual down hill grade of 9 ±1 %
2- What’s so great about Liebherr’s “ Service Brake System” ? a- Uncomplicated dry disc brake system b- Service checks of discs and calipers/pads possible at any time, anywhere, without tools c- No separate, extensive liquid cooling system required with it’s many “ must” components: pump(s), valve(s), cooling radiator and hydraulic pipe and hose circuitry leading to & from all four wheels d- Exchange of brake pads, calipers and discs possible - with relatively simple tools, - in relatively short time - in the field, if required AND - without having to take the rear wheels off and - without having to disassemble the rear wheel drive or the front wheel bearing assembly respectively
2- What’s so great about Liebherr’s “ Service Brake System” ? e- Complies with ISO 3450, requiring to bring the fully loaded truck to a safe and complete stop five times consecutively on an actual down hill grade of 9 ±1 %. f-
Front, wheel speed* T 252 & T 262: 6 calipers/2 discs* TI 272: 8 calipers/2 discs* T 282: 10 calipers/2 discs* Front wheel brakes: T 252 (inside) T 262 (outside)
Rear, armature speed O 4 calipers/4 discs O 8 calipers/4 discs* 4 calipers/4 discs O
TI 272 (in)
1 1
T 282 (outside) 1
2
2
5 3
2
4 3
4
3
4- What are the mandatory service brake features in case of an electric retarding failure?
ISO 3450: The service brakes are required to bring the fully loaded truck to a safe and complete stop five times consecutively on an actual down hill grade of 9 ±1 %.
All four Liebherr truck models have been tested repeatedly and met/exceeded the ISO 3450 requirements.
5- What keeps the fully loaded T 282 from rolling backwards on a 15% upgrade when starting to drive? a. Once stopped, the truck is held in place by the service brakes (front and rear wheels) and/or the park brakes (rear wheels only) The Service Brakes will hold the fully loaded truck on a slope of at least 25%. They are applied by the - service brake pedal, or - automatically by the retarding pedal, or - automatically by the anti roll back feature - the Hand Brake = service brakes will hold the fully loaded truck on a slope of at least 25% The Park Brake (rear wheels only) will hold the fully loaded truck on a slope of at least 15%
5- What keeps the fully loaded T 282 from rolling backwards on a 15% upgrade when starting to drive? a. Once stopped, the truck is held in place by the service brakes b. When starting to drive up hill with the drive lever in “ up hill” direction (F or R), the AC drive system automatically will apply as much up hill torque as required, to hol d and accelerate the truck. This is Part 1 of the automatic “ anti roll back” feature which is controlled by the computer But what happens during that time when the brakes are already released but the engine has not yet built up enough power to create sufficient uphill torque??? • Sensors on both rear wheels sense any motion of either wheel • The computer can determine if that motion is forward or reverse • If the control lever is in F but the computer senses R-motion, (or visa versa) the computer automatically reapplies the service brakes until the engine/drive motors have built up the power to hold and accelerate the truck uphill This is Part 2 of the automatic “ anti roll back” feature
6- True or false? – The T 282 has fully automatic retarding when loaded and going down hill. • The T 282 and the T 252, T 262 and TI 272 do have TWO automatic retarding features: a. Cruise Control Adjustable by the operator, this feature functions in both propel and retard. It will bring the truck up to or down to the set speed and keep it there. Has to be initiated by the operator. b. Two Speed Over Speed – Preset by the factory and adjustable by the mine, it automatically will start the retarding process on a down grade and prevent the truck from going faster than the set limit. There are two different speeds, one for loaded and one for empty (weigh system required). This feature can not be controlled by the operator (i.e. on/off) As a safety feature it will override the cruise control setting NOTE: • Limits have to be set to match existi ng operating conditions • Cruise Control has to be initiated by the operator while the truck is still within the retarding envelope
NOTE: In either case the limits have to be set to match existing operating conditions Definition (sample chart T 262)
Operating conditions: • 12% down hill, • 2% rolling resistance • GVW 820 000 lbs (Required rim pull for retarding: 81 000 lbs ) Retarding limit: • Any retarding speed between 6.5 and 16 mph Speed too high or too low: above 16 mph or below 6.5 Service brakes must be applied “ Retarding Window”
Retarding Power 2x3 inverters
2x3 rectifiers inverters
Choppers DC
R L 3-phase AC
Amount of retarding is controlled by the computer within the wheel drives via the retarding pedal
Grid box with fan
Retarding What are the basics of electric retarding? • The rear wheels turn their respective electric wheel motor, which now is working in alternator fashion, producing electric current • The produced electric current is turned into heat energy within the resistor grids • The produced heat is dissipated into the outside air by a large blower fan • The total amount of all dissipated heat energy equals the braking energy used to slow down the truck
Liebherr’s three pedal operation gives the operator better control of the truck’s movements Accelerator (throttle pedal) Electronic. Tells the computer (CPU) how fast the operator wants to go. Electric Retarding Electronic.Tells the computer (CPU) when and how much the operator wants to slow down. Keeps truck at safe down hill speed. Service Brake Full hydraulic power brake. Pedal resistance increases with brake power. Full 30° pedal arc for both - electric retarding pedal and - service brake pedal provides excellent control for the operator
AC Retarding System: STOP and HOLD • At .5 mph / 0.8 km/h the service brakes on all four wheels are applied automatically by the computer, without the operator having to do anything. •The service brakes will bring the loaded truck to safe stop and will hold the truck on any grade. Automatically. Service brakes located inside of axle box (armature speed) and cooled by forced air Diesel
Wheel Motor
Performance Chart AC-Drive Truck
Diesel engine performance curve Trolley performance curve Electric retarding curve
Continuous extended range retarding
Performance Chart AC-drive Sample: T 282 Propelling Gross Vehicle Weight x 1000 200 400 600 800 1000
0 300 280 260 240 0220 0 0200 1 x180 l l u160 p 140 m i R 120 100 80 60 40 20 0
US units
1200 lbs
Performance Chart
24
Curves based on 0% rolling resistance
22 20 18
e
16 d
a r 14 G e 12 g a t 10 n e c 8 r e P
6 4
T 282 (3500 hp): •GVW: 1,160,000 lbs • Actual grade: + 8% •(Roll resistance grade equivalent = 1% for each 20 lbs per ton of rolling resistance) @ 40 lbs/ton: + 2% •Effective Grade:10% Required rim pull: 116,000 lbs
2 0
0
5
10
15
20
25 30 Speed
35 40
45 mph
Max. possible speed: 9.3 mph
Performance Chart AC-drive Retarding Sample: T 282 Gross Vehicle Weight x 1000 200 400 600 800 1000
0 300 280 260 240 0220 0 0200 1 x180 l l u160 p 140 m i R 120 100 80 60 40 20 0
1200 lbs
Performance Chart
24
Curves based on 0% rolling resistance
22 20 18
e
16 d
a r 14 G e 12 g a t 10 n e c 8 r e P
6 4 2 0
0
5
10
15
20
25 30 Speed
35 40
45 mph
T 282 (3500 hp): GVW: 1,160,000 lbs, • Actual grade: + 8%, •(Roll resistance grade equivalent = 1% for each 20 lbs per ton of rolling resistance) @ 40 lbs/ton: - 2% •effective grade: 6% •Required rim pull for safe retarding: 69,000 lbs •Safe retarding: from 32.7 mph down to ~zero mph
Torque Verification Calculations
1. 2.
The Performance Curve shows a total truck Retarding Rimpull of 700,000 Newtons, or 350,000 Newtons per wheelmotor . SIBAS shows a maximum toque of –16573 Nm from each wheelmotor during Retard at 14 MPH and less.
Rimpull = Wheelmot or Torqu e x Gear Ratio / Roll ing Radius Tire Diameter = 3.693 Tire Radius = 3.693/2 = 1.8465 ~ 1.8 meters for Rolling Radius Gear Ratio = 37.33:1
Rimpull = 16573 Nm x 37.33 / 1.8 m = 343,700 Newtons Assume an Electrical Efficiency of 97%: 0.03 x 343700 = 10311 Newtons
Therefore, 343700 N + 10311 N = 354,011 Newton s per w heelmot or
Performance Curve - Nominal Load
Warning Decal in Operator’s Cab
Service Brake Application Report dat e / t i me . . . . . . . . . . . . . . . . . . . : 11. 05. 2005 vehi cl e number . . . . . . . . . . . . . . . . : 239 Dat a val i d s i nce . . . . . . . . . . . . . . : 15. 04. 2005
16: 19: 21 16: 11: 37
Ser vi ce Br ake Appl i cat i ons: Seconds on br ake dur i ng t hi s hour ( hh: 00 - hh: 59) ; 5 - 10 mph . . . . . . . . . . . . . . . . : 0 s 10 - 15 mph . . . . . . . . . . . . . . . : 0 s 15 - 25 mph . . . . . . . . . . . . . . . : 0 s 25 - 30 mph . . . . . . . . . . . . . . . : 0 s 30+ mph . . . . . . . . . . . . . . . . . . . : 0 s Seconds on br ake dur i ng t hi s day ( 0: 00 - 24: 00) ; 5 - 10 mph . . . . . . . . . . . . . . . . : 0 s 10 - 15 mph . . . . . . . . . . . . . . . : 0 s 15 - 25 mph . . . . . . . . . . . . . . . : 0 s 25 - 30 mph . . . . . . . . . . . . . . . : 0 s 30+ mph . . . . . . . . . . . . . . . . . . . : 0 s Seconds on br ake dur i ng t hi s week ( SUN - SAT) ; 5 - 10 mph . . . . . . . . . . . . . . . . : 0 s 10 - 15 mph . . . . . . . . . . . . . . . : 0 s 15 - 25 mph . . . . . . . . . . . . . . . : 0 s 25 - 30 mph . . . . . . . . . . . . . . . : 0 s 30+ mph . . . . . . . . . . . . . . . . . . . : 0 s Seconds on br ake si nce l ast cl ear ( see Dat e val i d si nce) ; 5 - 10 mph . . . . . . . . . . . . . . . . : 9 s 10 - 15 mph . . . . . . . . . . . . . . . : 1 s 15 - 25 mph . . . . . . . . . . . . . . . : 3 s 25 - 30 mph . . . . . . . . . . . . . . . : 4 s 30+ mph . . . . . . . . . . . . . . . . . . . : 0 s
SAFE HAUL TRUCK OPERATION REQUIREMENTS: 1. A properly designed haul truck 2. A properly trained operator 3. Properly maintained equipment
