Dynamic Braking on Dynamic Braking on AC Haul TrucksAC Haul Trucks

Surface Haulage Safety WorkshopNational Mine Health and Safety AcademyBeckley, West VirginiaMay 2005

The electrically driven Liebherr Rear Axle (T 282)

Axle BoxTorque Tube

Final DriveElectric Motor (one per drive) with

Roller BearingsHub

motor speed dry disc brakes

T 282

Double discs per each rear wheel, armature speed brakes and excellent accessibility

T 282

Access from inside the axle box. Fully protected from road dirt and weather.Controlled brake cooling with forced air flow.

T 282

inside

Double dry disc, armature speed brakesfor each rear wheel

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’smechanical brakes but instead the

Electrical System

•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

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 theelectric 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 repeatedlyand met/exceeded the ISO 3450 requirements.

25%

•Electric toggle or rocker switch: Hand brake

•Handbrake = Service brakeswill hold the fully loaded truck on a slope of up to 25%

B6&7 - Hand Brake & Emergency Brake

•As a safety feature in an emergencythe handbrake can be applied while driving

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

Twelve full brake applications

Min. three 90° steering actions

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.

If the sensors on the rear wheels detect motion in the opposite direction, the service brakes are applied automatically and instantly.

controlled via sensors on both rear wheels

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.

Dumping

Loading

up hilllevel

x : set C/C to high speed or over-ride the y-setting with the accelerator pedal

x

Loading

down hill

level

y : set C/C to maximum allowed down hill speed

y

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.

Servicebrake

Electricretarding

Retarding start outside the retarding envelopenecessitates application of service brake (DC & AC)

Servicebrake

Electricretarding

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:

2. Applies full brake pressure from the two brake accumulators to all service brakes on front and rear wheels

4. Used when operator is inside cab with engine running and truck stopped, i.e. during loading, dumping and while being stopped and waiting

6. Designed to HOLD the fully loaded truck on inclines of up to 25%

3. Will only function with accumulators pressurized. If one of the two brake circuits has a line failure, the second one will still function

1. Applied by operator via toggle (or rocker-)switch, located on center console

5. In an emergency the Hand Brake could be used to stop the truck

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 driveor 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* Rear, armature speedO

T 252 & T 262: 6 calipers/2 discs* 4 calipers/4 discsO

TI 272: 8 calipers/2 discs* 8 calipers/4 discs*T 282: 10 calipers/2 discs* 4 calipers/4 discsO

Front wheel brakes:T 252 (inside) T 262 (outside) TI 272 (in) T 282 (outside)

1 2

34

1

2

34

5

1

23

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 repeatedlyand 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?

The Park Brake (rear wheels only) will hold the fully loaded truck on a slope of at least 15%

- the Hand Brake = service brakes will hold the fully loaded truck on a slope of at least 25%

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

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)

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 brakesb. 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 hold and accelerate the truck. This is Part 1 of the automatic “anti roll back” feature which is controlled by the computerBut 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

This is Part 1 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 propeland retard. It will bring the truck up to or down to the set speedand 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 thetruck 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 existing 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)

“Retarding Window”

Operating conditions:• 12% down hill,• 2% rolling resistance• GVW 820 000 lbs(Required rim pull for retarding: 81 000 lbs )

Retarding limit:• Any retarding speedbetween 6.5 and 16 mph

Speed too high or too low:above 16 mph or below 6.5

Service brakes must be applied

Retarding Power

Grid box with fan

Amount of retarding iscontrolled by the computer within the wheel drives via the retarding pedal

2x3 inverters

3-phaseAC

LR

2x3 rectifiers2x3 inverters

DC

Choppers

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 RetardingElectronic.Tells the computer (CPU)when and how much the operator wants to slow down. Keeps truck at safe down hill speed.

Service BrakeFull 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

Wheel Motor

Diesel

Service brakes locatedinside of axle box(armature speed)

and cooled by forced air

•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.

Performance Chart AC-Drive Truck

Diesel engine performance curve

Trolley performance curve

Electric retarding curve

Continuous extendedrange retarding

Performance Chart AC-driveSample: T 282 Propelling US units

Rim

pull

x 10

00

300280260240220200180160140120100806040200

Speed0 5 10 15 20 25 30 35 40 45 mph

0 200 400 600 800 1000 1200 lbsGross Vehicle Weight x 1000

Perc

enta

ge G

rade

24

22

20

18

16

14

12

10

8

6

4

2

0

Performance ChartCurves based on

0% rolling resistance

Required rim pull:116,000 lbs

Max. possible speed: 9.3 mph

T 282 (3500 hp):•GVW: 1,160,000 lbs•Actual grade: + 8%•(Roll resistancegrade equivalent = 1% for each 20 lbsper ton of rolling resistance)@ 40 lbs/ton: + 2%

•Effective Grade:10%

RetardingPerformance Chart AC-driveSample: T 282

•Required rim pull for safe retarding:

69,000 lbs•Safe retarding:

from 32.7 mph down to ~zero mph

T 282 (3500 hp):GVW: 1,160,000 lbs,•Actual grade: + 8%,•(Roll resistancegrade equivalent = 1% for each 20 lbsper ton of rolling resistance)@ 40 lbs/ton: - 2%

•effective grade: 6%

Rim

pull

x 10

00

300280260240220200180160140120100806040200

Speed0 5 10 15 20 25 30 35 40 45 mph

0 200 400 600 800 1000 1200 lbsGross Vehicle Weight x 1000

Perc

enta

ge G

rade

24

22

20

18

16

14

12

10

8

6

4

2

0

Performance ChartCurves based on

0% rolling resistance

Torque Verification Calculations

1. The Performance Curve shows a total truck Retarding Rimpull of 700,000 Newtons, or 350,000 Newtons per wheelmotor.2. SIBAS shows a maximum toque of –16573 Nm from each wheelmotor during Retard at 14 MPH and less.

Rimpull = Wheelmotor Torque x Gear Ratio / Rolling Radius

Tire Diameter = 3.693Tire 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 Newtons per wheelmotor

Performance Curve - Nominal Load

Warning Decal in Operator’s Cab

Service Brake Application Report

date / time ................... : 11.05.2005 16:19:21vehicle number ................ : 239Data valid since .............. : 15.04.2005 16:11:37

Service Brake Applications:

Seconds on brake during this hour (hh:00 - hh:59);5 - 10 mph ................: 0 s10 - 15 mph ...............: 0 s15 - 25 mph ...............: 0 s25 - 30 mph ...............: 0 s30+ mph ...................: 0 s

Seconds on brake during this day (0:00 - 24:00);5 - 10 mph ................: 0 s10 - 15 mph ...............: 0 s15 - 25 mph ...............: 0 s25 - 30 mph ...............: 0 s30+ mph ...................: 0 s

Seconds on brake during this week (SUN - SAT);5 - 10 mph ................: 0 s10 - 15 mph ...............: 0 s15 - 25 mph ...............: 0 s25 - 30 mph ...............: 0 s30+ mph ...................: 0 s

Seconds on brake since last clear (see Date valid since);5 - 10 mph ................: 9 s10 - 15 mph ...............: 1 s15 - 25 mph ...............: 3 s25 - 30 mph ...............: 4 s30+ mph ...................: 0 s

SAFE HAUL TRUCK OPERATION REQUIREMENTS:

1. A properly designed haul truck

2. A properly trained operator

3. Properly maintained equipment

Thank youLiebherr Mining EquipmentNewport News, Virginia

www.liebherr.com