-1-

WP #2005-2

Heavy Truck Brake Designer Validation Testing

Thomas H. Vadnais, P.E.Vadnais, Wood & Rivers, Atlanta, GA

Wesley D. Grimes, P.E.Collision Engineering Associates, Mesa, AZ

ABSTRACT

In late August 2004, a week-long series ofwell-documented heavy truck braking tests wasconducted at Transportation Research Center(TRC) in East Liberty, OH. Using the sametractor and flatbed semi-trailer, tests wereperformed with and without ABS, on wet anddry surfaces, loaded and unloaded, and at both30 and 60 mph. Additional tests were donewith the semi-trailer’s ABS disabled, with onlythe tractor’s ABS system cross-wired, withsome of the tractor and trailer brakes out ofadjustment, and with the bobtail tractor alone.Both the tractor and semi-trailer weredocumented to allow creation of an accurateHVE vehicle model, including all brakecomponents.

For this initial paper, SIMON runs, using theBrake Designer, were made of several actualtest runs to validate the software against theactual test data. These were compared tosimilar simulations using generic vehicles. Forthis paper, only loaded, non-ABS, 60 mphtests were modeled, with all brakes inadjustment, and some out of adjustment.

INTRODUCTION

Reams of data from almost 100 tests weregenerated during a series of heavy truckbraking tests performed at TRC in late August

2004. Several data acquisition systemsrecorded speeds and distances, or returneddeceleration rates over time. Brake systempressures and dynamic pushrod strokes weremonitored, as were brake temperatures. Anytire marks were documented with a totalstation.

TEST VEHICLE DETAILS

For all tests, the same tractor and semi-trailerwere used. Brake adjustments were madebefore almost every series of runs, and theywere checked again afterward. Weights of thetractor steer axle, tractor drive axles, andtrailer axles were obtained for each vehicleconfiguration.

TRACTOR

The tractor was a 2003 Freightliner Columbiawith a walk-in sleeper. It has a GVWR of52,000 pounds, with a front GAWR of 12,000pounds, and two rear axles with a GAWR of20,000 pounds each. The front Spicer axle hada two-leaf steel spring suspension. Both rearMeritor axles were suspended by a FreightlinerAirLiner with Firestone air bags. A DetroitDiesel Series 60 engine with a DDEC IV wasmated to an Eaton Fuller 10-speedtransmission.

-2-

All tires were 295/75R22.5 radials mounted onwhite steel hub-piloted wheels. For the tests, apair of new Dayton Radial Metro All Positiontires was used on the steer axle. New BandagDrive Axle retreaded tires were used on bothrear axles.

All wheel positions had S-cam drum brakeswith a 4S-4M Wabco ABS system. (For thetests modeled for this paper, the ABS systemwas disconnected.) On the front axle, it had15" x 4"drums, Type FF linings, Type 20L(long stroke) MGM air chambers, and 5.5"Rockwell automatic slack adjusters. On bothrear axles, it had 16.5" x 8 5/8" drums, Type30/30L MGM spring brakes, and 5.5"Rockwell automatic slack adjusters. All liningswere thicker than 0.5 inches. Figure 1 showsa screen shot of those S-Cam details in theBrake Designer for the rear brakes of thetractor model.

For the tests discussed in this paper, the clevispins were removed from the automatic slackadjusters to disable the automatic adjustmentfeature. This allowed them to behave and to beadjusted as manual slack adjusters.

The rolling radius for each front tire was 18.5inches. At the rear, the rolling radius at eachposition was 19.5 inches.

SEMI-TRAILER

The semi-trailer was a 2001 Wabash flatbed,with an 80,000 pound GVWR. Although it hadthree 20,000 pound GAWR axles, the tires andwheels were removed from the forwardmostaxle, which was then chained to the frame soit would be out of the way. It had a Wabash airsuspension.

All tires were new 295/75R22.5 Bandagretreads with a trailer tread pattern. All weremounted on white steel hub-piloted wheels. At

each wheel, the rolling radius was 19.5 inches.

All wheel positions had S-cam drum brakes,with 16.5" x 7" drums, 420FF linings, 5.5"manual slack adjusters, and Type 30/30 springbrakes. All brake linings were more than 0.5inches thick. There was a 2S-2M Wabco ABSsystem, but it was disconnected for this seriesof tests.

TEST FACILITY

All testing was performed on the VehicleDynamics Area (VDA) of the TransportationResearch Center (TRC) in East Liberty, OH.The TRC scale was used to weigh the tractorand semi-trailer with and without the load. Allinstrumentation installation, brake adjustments,and loading or unloading were done at Link-Radlinski, also in East Liberty, OH.

For these simulations, a 3-D surface wascreated from a survey of the VDA. A few carskid tests were performed to establish abaseline, but the data from them hasn’t beenused.

INSTRUMENTATION

While extensive instrumentation was used,only that significant to this paper will bediscussed.

Pressure transducers were installed in thecontrol line and in the brake lines for both theleft and right sides of the steer axle, theforward drive axle, and the front trailer axle.Speeds and distances were obtained with theDatron Optical “fifth wheel” sensor.

TESTING OVERVIEW

Overall, the testing was segmented into elevenSeries. There were several test configurationsin each Series, and two or three tests with each

-3-

configuration. In each test, after attaining thetarget speed, the driver fully applied thebrakes, and held them firmly until the vehiclecame to rest.

In this paper, only a few of the configurationsactually tested will be discussed. Common toall the tests under consideration are thefollowing: 60 mph initial speed, dry road, noABS. The other specifics, listed by testnumbers, are as follows (test details are inparentheses):

UD6-1 & UD6-2 (Unloaded, Dry,configuration 6, Runs 1 & 2)

UW6-1 & UW6-2 (Unloaded, Wet,configuration 6, Runs 1 & 2)

LD6-1 & LD6-2 (Loaded, Dry, configuration6, Runs 1 & 2)

LAD2-1 & LAD2-2 (Loaded, some brakes out-of-Adjustment, Dry, configuration 6, Runs 1& 2)

The unloaded tests (those beginning with “U”)used the tractor and with unloaded semi-trailer.In the tractor, there was the driver, plus twopassengers to attend to the data acquisitionsystems. For the loaded tests (beginning with“L”), concrete blocks, weighing a total ofapproximately 46,000 pounds, were distributedalong the flatbed trailer body.

BRAKE ADJUSTMENTS

The following is the nomenclature that will beused for this paper:

Axle 1 (A1) - Steer AxleAxle 2 (A2) - Forward Drive AxleAxle 3 (A3) - Rear Drive AxleAxle 4 (A4) - Front Trailer AxleAxle 5 (A5) - Rear Trailer Axle.

For the UD, LD, and UW tests, all the brakeswere manually adjusted for optimum brakingperformance. All adjustments were performedwith the engine off, and 100 psi in thereservoir. On Axle 1, both Type 20L frontbrakes had their pushrod stokes set to 1 3/8".All drive and trailer brakes (Type 30/30L)were adjusted to 1 5/8". All adjustments weremade to +/- 1/16".

For the two tests with “A” as the second letter,the brakes on Axles 1, 2, and 4 were backedoff to 1/8" beyond the CVSA out-of-servicecriteria. Brakes on Axles 1 and 4 wereadjusted to 2 1/8"; on Axle 2 to 2 5/8" (all +/-1/16").

SIMULATIONS

SIMON was used for all simulations. Bothtractor and trailer vehicle models weremodified using the actual dimensions and axleloads from the test vehicles. Finally, the BrakeDesigner was used, incorporating all thephysical component measurements from thevehicles. For nomenclature, these simulationsall kept the original test numbers, but addedSim to their names, e.g. UD6-1Sim.

In addition to the brake system, other vehiclemodel modifications included adjustingconnection heights and CG locations to achieveproper axle loads, both with and without thepayload. From the EDC database, 11R22.5Michelin ZXA tires were fitted to all positionson the tractor and semi-trailer.

A total station survey provided the dimensionaldata to build the environment. Numeroussimulations were run to determine theappropriate Friction Factor for both the wetand dry tests. The asphalt surface of the VDAwas quite aggressive. These Friction Factorswere 0.84 for wet and 0.94 for dry.

-4-

The starting point of each simulation was madeto correspond to the initial speed from theappropriate test. To ensure that the simulationsettled down before the brakes were applied,the truck was run for one second before thebrake application. Rather than adding a pre-braking throttle table to the Driver Table, thespeed at time zero was adjusted until the speedat one second equaled the speed from theactual test. Then, to make it easier to obtainthe braking distance, that distance reached attime one second was reset to zero.

When the target speed was reached, at 1.0seconds in the simulation, the brakes wereapplied according to a Driver Table created tomimic the air pressure variations measuredduring the actual tests. Figure 2 shows theDriver Table for UD6-1.

For comparison, both 60 mph, dry, unloadedtests were repeated with two different setups.The first, referred to as UD6-1Gen & UD6-2Gen, used a generic Class 4 tractor andgeneric Class 4 semi-trailer. The second usedthe actual vehicle models, but used genericbrakes. These were referred to as UD6-1ActGen (for Actual Generic) and UD6-2ActGen. With generic brakes, the InitialStroke setting in the Wheels section of the Set-Up menu is disabled.

The Actual Generic (Act Gen) tests were alsorepeated with the loaded trailer with somebrakes out of adjustment. These were calledLAD2-1ActGen and LAD2-2ActGen. AllGeneric and Actual Generic simulations usedthe Driver Table shown in Figure 3.

DISCUSSION

Many problems were encountered, a lot waslearned, and much remains to be done to fullyunderstand both the dynamic behavior of thebrake system of a heavy truck, and the most

effective way to simulate that behavior withBrake Designer in SIMON. The followingsummarizes some of the problemsencountered, and the solutions tried.

Developing the proper Driver Tables, BrakeRise Times, and Brake Lag Times for thesimulations was quite challenging, since theyall interacted. During each actual test, theapplication pressure was measured, as were thepressures at both brake chambers on Axles 1,2, and 4. But since these chamber pressuresnever reached the application pressure, usingthe application pressure in the Driver Table inthe Event Editor led to excessive decelerationrates and short braking distances. By studyingplots of the brake pressures versus time, aDriver Table was created for each event thatmimicked the actual brake pressure variation.Likewise, Brake Rise Times and Brake LagTimes in the Brake Designer were modified tomatch the rate of air pressure buildup in theactual truck’s brake system.

Looking at an overall air pressure versus timegraph did not yield enough detail about theinitial phase of the air pressure rise. Therefore,a second graph was made for each run thatdisplayed the air pressure rise over the firstsecond only. This allowed for a betterunderstanding of how the brakes reached theirfull application pressure. Figures 4 and 5 showair pressure versus time graphs for the UD6-1test, for the full stop and for the first second,respectively.

The tires used during the tests were not in theHVE database, so an 11R22.5 Michelin XZAwas chosen. While the differences in treadcompound and other specific properties wereunknown, it was the closest in size and loadcapacity. Any effects from the tire model areunknown, but are suspected to be slight.

-5-

Both the tractor and semi-trailer had airsuspensions, which are not modeled by HVE.Consequently, any interaxle load transfer oroverall load transfer effects on the brakingperformance of the model are not known.

A number of runs were made to determine theFriction Factor on the high-grip VDA surface.In lieu of a specific baseline, a number ofsimulations were run with various testconfigurations until one value producedconsistent, meaningful results. As expected,the wet surface tests yielded a lower FrictionFactor than the dry surface.

When trying to establish the appropriatedeceleration rates to use, it was deemed best tosplit the actual measured values into twosegments; from time 0 to 0.5 seconds, andfrom time 0.5 seconds until the end of thebraking. Since neither the test instrumentationnor the simulation respond predictably nearzero mph, the tests were considered stopped at2 mph. The deceleration segment from 0.5seconds to the end of the test at 2 mph wasused to create the Driver Table for each test.

SIMULATION RESULTS

Table 1 shows the simulation results comparedto the actual test results.

Using a Driver Table in the models thattracked the air pressure variations in the actualtests, the SIMON simulations using the BrakeDesigner calculated the braking distances to anerror of 4.8%, and the 0.5 seconds-to-2 mphdecelerations to within 0.037 g.

In the unloaded, dry, 60 mph tests, using pureGeneric vehicles in the simulation produced anerror of up to 25.5% in the stopping distance,and up to 0.078g in deceleration error.

Using actual vehicle models, but with genericbrakes, greatly reduced the error toapproximately 8% of the braking distances,and up to 0.045g in deceleration error. Thisshowed the value of modeling the dimensionsand wheel loads accurately.

Finally, with the actual vehicle models and theBrake Designer, the stopping distance errorswere less than 1%. The errors in the 0.5second to 2 mph deceleration rates werenegligible at less than 0.01g.

With some of the brakes out of adjustment,(tests LAD2-1 and LAD2-2), the ActualGeneric simulations resulted in brakingdistance errors of 15 to 19.3%, anddeceleration errors of approximately 0.10 g.By comparison, both LAD simulation runswhere the Brake Designer was used yieldedbraking distance errors of 4.8%, anddeceleration errors of less than 0.037 g.

CONCLUSIONS

For all of the conditions of unloaded dry,unloaded wet, loaded dry, and loaded dry withsome brakes out of adjustment, the bestcorrelations between the actual tests and theSIMON simulations were when the actualvehicle models and the Brake Designer wereused with the appropriate Driver Tables.

Then, when the actual vehicles were used withgeneric brakes (ActGen), they generatedgreater errors in both deceleration rates andbraking distances. The errors when the brakeswere out of adjustment were approximatelytwice what they were when all brakes were inadjustment.

Finally, when pure Generic (Gen) vehicleswith generic tires and brakes were used tosimulate the unloaded dry tests, the errorswere up to 25.5% in braking distance and up

-6-

to 0.078 g in decelerations. Users should becautioned from blindly using pure Genericvehicles because the accuracy is unknown andthe error could possibly be quite large.

But since no vehicle-specific inertial ordimensional data was used, there was no wayto either qualify or quantify why the errorsmight have occurred.

Further validation work will continue usingmany of the other actual test configurations.

ACKNOWLEDGMENTS

The authors are indebted to all the participantsin the 2004 tests. All brought their uniqueknowledge, skills, and perspectives to thetesting. In alphabetical order, they were: ErikAnderson, Ken Baker, Randy Bicknese, ChrisBloomberg, Terry Day, Ron Heusser, TimReust, George Rivers, Don Rudny, DaveSallman, Tom Schaefer, Jim Sneddon,Sebastian van Nooten, Blake Wood, and theauthors. Thanks to Dick Radlinski, JerryLawruk, and David Domine of Link-Radlinski,who provided essential equipment, services,and expertise. Finally, none of this would havebeen possible without our illustrious testdriver, Woody Woodruff, whose consistencyin driving and tolerance for capriciousengineers is the stuff of legend.

-7-

Fig

ure

1 -

S-c

am d

ata

scre

en i

n B

rake

Des

igner

.

-8-

Fig

ure

2 -

Dri

ver

Tab

le f

or

UD

6-1

Sim

.

-9-

Fig

ure

3 -

Dri

ver

Tab

le f

or

Gen

eric

and A

ctual

Gen

eric

sim

ula

tions.

-10-

Fig

ure

4 -

UD

6-1

Air

pre

ssure

v.

Tim

e fo

r en

tire

bra

kin

g e

ven

t.

-11-

Fig

ure

5 -

UD

6-1

Air

pre

ssure

v.

Tim

e fo

r fi

rst

seco

nd o

f bra

ke

appli

cati

on.

-12-