FMVSS 121 Brake Performance and StabilityTesting

FINAL REPORT - Revision A

SwRI Project No. 03-05190

Prepared for

Mr. Bill WashingtonAir Brake Systems

4356 E. Valley RoadMount Pleasant, MI 48804-0293

April 22, 2002

FMVSS 121 Brake Performance and StabilityTesting

FINAL REPORT - Revision A

SwRI Project No. 03-05190

Prepared for:

Mr. Bill WashingtonAir Brake Systems

4356 E. Valley RoadMount Pleasant, MI 48804-02983

Prepared by:

John Bishop, Group LeaderSouthwest Research Institute

6220 Culebra RoadSan Antonio, TX 78238

Reviewed by:

Scott T. McBroom, ManagAdvanced Vehicle Techno

fu

January 31, 2002This report must be reproduced in

ll, unless SwRI approves a summaryor abridgement.

Approved:

er Gary L. Stecklein, Directorlogy Vehicle Systems Research Department

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EXECUTIVE SUMMARY

Southwest Research Institute (SwRI) contracted with Air Brake Systems to provide aperformance comparison test of a truck equipped with the Air Brake Systems MSQR-5000 brakesystem device to a baseline vehicle without the MSQR-5000. The comparison was made usingthe dynamic stopping procedures taken from FMVSS 121 to determine stopping distance from60 mph on a dry surface and stopping stability in a curve from 30 mph on a wetted surface.These tests were run with the vehicle loaded to GVWR and with the vehicle empty. Twodifferent stopping techniques were used during the testing. The FMVSS 121 requirements statethat the driver use full treadle brake application. This procedure was used and in addition, thewet stops were repeated using the manufacturer’s recommended procedure consisting ofmodulated or “best effort” stopping procedures.

For the straight-line test, results indicate that the vehicle is able to stop from 60 mph on drypavement within FMVSS 121 required stopping distances with the OEM brake system and withthe MSQR-5000 system installed. The stopping distances are generally very similar. The onesignificant exception is that the empty vehicle with the MSQR-5000 installed stopped from 60mph on a dry surface in an average of 13% shorter distance than the OEM equipped vehicle.There was no such difference at GVWR.

For the wetted curve test, the vehicle is required by FMVSS 121 to stop from 30 mph on awetted surface while negotiating a 500-foot radius curve and maintaining itself within in a 12-foot wide lane. When using full treadle brake application per FMVSS 121, the vehicle did notstay in the 12-foot lane. This occurred for the vehicle with and without the MSQR-5000 brakevalve at both vehicle weights.

Based on the test results and discussions with the manufacturer, SwRI found that theMSQR-5000 system does not function in the same manner as an electronic anti-lock brakesystem (ABS). With full treadle application, it is possible to cause wheel lockup that results inthe vehicle not staying within the 12-foot lane.

When using the Air Brake System’s MSQR-5000 recommended braking procedure for thewetted surface stops, the vehicle is able to stay in the 12-foot lane. During the stopping testing,the MSQR-5000 system did not significantly increase or decrease vehicle stopping performance.

A more detailed discussion of the test procedure and the test results is contained in thebody of this report.

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TABLE OF CONTENTS

Page

1.0 INTRODUCTION................................................................................................................. 11.1 Vehicle Procurement and Break-in..................................................................................... 11.2 Vehicle Description ............................................................................................................ 11.3 Test Plan Development ....................................................................................................... 51.4 Vehicle Preparation and Instrumentation Installation......................................................... 51.5 Brake Burnishing ................................................................................................................ 51.6 Stopping Test Results Summary......................................................................................... 61.7 Stopping Distance Testing Loaded to GVWR.................................................................... 71.8 Stopping Stability Testing Loaded to GVWR .................................................................... 81.9 Stopping Distance Testing at Empty Vehicle Weight ........................................................ 91.10 Stopping Stability Testing at Empty Vehicle Weight......................................................... 91.11 Conclusion .......................................................................................................................... 9

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LIST OF ILLUSTRATIONS

Figure Page

1 Air Brake Systems Test Vehicle, Left View...........................................................................22 Air Brake Systems Test Vehicle, Right View ........................................................................33 MSQR-5000 Diagram and Installation Schematic .................................................................44 Vehicle Entering 500-foot radius............................................................................................85 Vehicle After Stop ..................................................................................................................8

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LIST OF TABLES

Table Page

1 Test Configuration and Test Matrix........................................................................................12 Vehicle Description ................................................................................................................23 Air Brake Systems Truck Instrumentation .............................................................................54 Stopping Results Summary.....................................................................................................7

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1.0 INTRODUCTION

Southwest Research Institute (SwRI) was contracted by Air Brake Systems to dobrake performance testing of its tractor-trailer vehicle. The vehicle was supplied by AirBrake Systems for the testing. SwRI did not perform any modifications to the vehicleother than repairs that were absolutely necessary in order to complete the testing.

A test plan was developed to evaluate the stopping capability of the vehiclecompared to the dynamic stopping requirements specified by FMVSS 121. The stoppingtests and evaluations performed are shown in Table 1.

Table 1. Test Configuration and Test Matrix

1.1 Vehicle Procurement and Break-in

SwRI obtained the 1990 Kenworth T600 tractor/trailer from Air Brake Systems.This vehicle had approximately 552,000 miles on the odometer at the start of the project.The test plan for the vehicle was to leave the tires and brakes in the as received conditionto best simulate a typical in-service vehicle with used tires and brakes. Since the vehicleis a used vehicle, no vehicle break-in was required. However, burnishing of the brakeswas performed prior to brake performance testing to insure that there was no glazing orother pre-existing conditions of the brake components.

1.2 Vehicle Description

The test vehicle is a 1990 Kenworth T600 tractor with a 1984 Trailmobile dry vantrailer as shown in Figures 1 and 2 and a description is shown in Table 2. The vehicle isequipped with Air Brake Systems MSQR-5000 brake valve. A diagram and schematic ofthe MSQR-5000 brake valve is shown in Figure 3.1 The was converted to the OEMconfiguration by replacing the MSQR-5000 brake valve shown in Figure 3 with a pipetee.

1 Information taken from Air Brake Systems’ web site: www.airbrakes.com

Testing Procedure for Air Brake Systems Test Vehicle

Number Procedure Test SpeedBraking Effort Result

Number of Stops

Brake System Configuration

Vehicle Weight

Burnish 40-20 mph .31 g Stop Monitor Brake Temp Dry Stay below 500 F 500 With MSQR 5000 GVWR1 Stability 30 mph Full 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 4 With MSQR 5000 GVWR2 Stability 30 mph Best Effort 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 2 With MSQR 5000 GVWR3 Stability 30 mph Full 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 4 With MSQR 5000 Empty4 Stability 30 mph Best Effort 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 2 With MSQR 5000 Empty5 Stability 30 mph Full 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 4 Without MSQR 5000 GVWR6 Stability 30 mph Best Effort 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 2 Without MSQR 5000 GVWR7 Stability 30 mph Full 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 4 Without MSQR 5000 Empty8 Stability 30 mph Best Effort 500 ft radius turn Wet 12 ft lane Stay in Lane (3 times) 2 Without MSQR 5000 Empty9 Stopping Distance 60 mph Full Dry Stop in 355 ft 6 With MSQR 5000 GVWR10 Stopping Distance 60 mph Best Effort Dry Stop in 355 ft 6 With MSQR 5000 Empty11 Stopping Distance 60 mph Full Dry Stop in 355 ft 6 Without MSQR 5000 GVWR12 Stopping Distance 60 mph Best Effort Dry Stop in 355 ft 6 Without MSQR 5000 Empty

Operating Conditions

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Figure 1. Air Brake Systems Test Vehicle, Left View

Table 2. Vehicle Description

Make 1990 KenworthModel T600 Tandem conventional with sleeperS/N 1XLADE9X7LS545471Trailer Dry van/ tandem axleMileage 551,896 (as received)Engine Caterpiller 3176 ATAAC 350 hpTransmission Eaton/Fuller 9 speed – RT014613Rear Axle 3.70 ratio – F23105CBrakes Drum, not equipped with electronic anti-lock brakesWeight 80,000 lbs GVWRTires 11R 24.5 Tractor – various brands

11R 22.5 Trailer – various brands

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Figure 2. Air Brake Systems Test Vehicle, Right View

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Figure 3. MSQR-5000 Diagram and Installation Schematic

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1.3 Test Plan Development

The test plan is based on the dynamic stopping requirements set in FMVSS 121for vehicles with air system brakes. The dynamic portion of the tests done was done asclosely as possible to FMVSS requirements. The stopping tests done are shown in Table1.

1.4 Vehicle Preparation and Instrumentation Installation

Prior to the performance of any testing, SwRI inspected the vehicle for anyapparent mechanical problems. During inspection of the brake systems, SwRI found thattwo of the air hoses connecting the MSQR-5000 system to the rest of the brake systemwere in need of repair. DOT approved hoses and fittings were used to repair thesecomponents. A fifth wheel was installed on the vehicle to measure vehicle speed. A g-meter was installed to assist the driver during the process of burnishing the vehiclebrakes. The brake temperatures were evaluated during the brake burnishing using anoptical pyrometer rather than using a relatively time consuming and expensive method ofinstalling thermocouples that requires removal of the brake shoes. This procedure wassubstituted based on SwRI’s experience in brake burnishing of heavy vehicles that hashistorically found that a properly working heavy truck brake system generally maintainan adequate operating temperature throughout the burnishing procedure. SwRI installed50,000 lbs ballast to the vehicle to bring the weight of the vehicle up to GVWR or 80,000lbs. Table 3 shows a list of the instrumentation installed on the tractor-trailer.

Table 3. Air Brake Systems Truck Instrumentation

Instrumentation Measurement AccuracyOptical pyrometer Brake pad temperature Reference onlyDayton microwave fifth wheel Speed/ Stopping distance +/-0.5 mph +/- 0.5 feetG-Tech Pro Stopping deceleration rate Reference only

1.5 Brake Burnishing

Proper brake system testing requires burnishing of the vehicle brake system shoes.This process is equally critical to achieving accurate and consistent results for new brakesystems as it is for brake systems that have been in service for some period of time. Inthe case of a new brake system, the burnishing procedure breaks in the new brakes andallows the components to properly “seat” themselves. In the case of vehicle with an olderbrake system, the shoes can become glazed during heavy or hard stopping which canresult in significantly reduced brake performance. The brake burnishing procedure isdesigned to heat the brake components up and maintain a moderately high temperatureduring a series of 500 snubs. This process insures that good test results are obtained.

The Air Brake Systems vehicle brakes were burnished by making 500 snubs from40-20 mph at a deceleration rate of 10 ft/sec2. After approximately 80 snubs were made,

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one of the trailer brake drums cracked and came apart from the vehicle. Fortunately,there was no additional damage done to the vehicle. The vehicle was taken to a repairfacility where SwRI explained the nature and purpose of the testing to the repair facility.SwRI asked for their recommendation as to the proper repair procedure to insure that thevehicle would finish the test. Their findings suggested that all of the drums hadconsiderable heat cracking and could also fail at some unknown time. In addition, thetrailer wheel seals were leaking which could damage the brake shoes on the trailer. SwRIcontacted Air Brake Systems and obtained permission to repair the vehicle using therepair facilities recommendations.

Once the repairs were complete, the burnishing process was restarted. Afterapproximately 1/3 of the snubs had been performed, it became apparent that two of thetrailer wheel brakes were not working as well as the rest of the wheel locations and thatthese brakes were likely out of adjustment. These brakes were readjusted which broughtthe operating temperatures of these brakes to a level more in line with the rest of thebrake locations as allowed by FMVSS 121. In addition, the front wheel seal and or ventshowed evidence of leakage. SwRI returned the vehicle to the repair facility where theleaking problem was repaired at no cost to Air Brake Systems. The burnishing procedurewas then completed with no additional complications.

1.6 Stopping Test Results Summary

The stopping tests were performed in accordance with both the FMVSS 121recommendations and using the recommended stopping procedure agreed upon with themanufacturer prior to the testing. FMVSS 121 states that the test be performed with thedriver applying maximum treadle valve pressure to the system for both the 30 mph wetsurface stops and the 60 mph dry surface stops. The manufacture recommends that thedriver operate the brake system using a modulated or “best effort” stop mode. During thewet stops, the tests were performed using both procedures. In the case of the unloadedvehicle stops from 60 mph on dry pavement, the stops were performed only using besteffort procedure.

The stopping results showed that the vehicle is able to stop from 60 mph within355 feet on dry pavement per FMVSS 121 requirements for all stops except one. Thislonger stop occurred from 60 mph with the OEM brake system and with the vehicleempty.

FMVSS 121 also requires that the vehicle be able to stop from 30 mph on awetted surface while negotiating a 500-foot radius curve. FMVSS 121 requires that thisstop be made with full treadle application and requires that the vehicle be able to stopwithin a 12-foot wide lane. Using full treadle application, the vehicle is not able to stayin a 12-foot lane for any of the brake applications. Using the MSQR-5000 manufacture’srecommended stopping procedure, the vehicle is able to negotiate the 500-foot radiuscurve and stay in the 12-foot lane for all of the stops except one case with the OEM brakesystem.

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Table 4 shows the stopping results. In most cases, the average stopping distancesare within 5% for cases with the OEM brake system compared to the stops with theMSQR-5000 installed. This is within testing repeatability and does not indicate asignificant difference between the OEM system and the vehicle with the MSQR-5000system. The only case where a significant difference in stopping performance orstopping distance is noted was a dry stop from 60 mph with the vehicle empty. In thiscase, the vehicle with the MSQR-5000 installation stopped in an average distanceapproximately 13% shorter than the OEM configured vehicle.

Table 4. Stopping Results Summary

Tests Results For Air Brake Systems MSQR-5000SwRI Project 03.05190

StopWet Loaded Full

Treadle 30 MPH

Stayed In Lane

Wet Loaded Best Effort 30

MPHStayed In

Lane

Wet Loaded Full Treadle 30 MPH

Stayed In Lane

Wet Loaded Best Effort

30 MPHStayed In

Lane

Wet Loaded Full Treadle 30 MPH

Wet Loaded Best Effort 30

MPH1.0 75.0 N 80.0 N 84.0 N 80.5 Y -10.7% -0.6%2.0 68.0 N 87.5 Y 71.0 N 91.0 Y -4.2% -3.8%3.0 73.0 N 72.0 N 1.4%4.0 71.5 N 74.0 N -3.4%

Avg. 71.9 83.8 75.3 85.8 -4.5% -2.3%

Highway Loaded 60 MPH

Highway Loaded 60 MPH

1.0 288.0 284.42.0 305.6 317.53.0 339.6 304.04.0 325.7 303.05.0 331.9 343.76.0 290.2 317.2

Avg. 313.5 311.6

Wet Unloaded Full Treadle

30 MPHStayed In

Lane

Wet Unloaded Best Effort 30

MPHStayed In

Lane

Wet Unloaded Full Treadle

30 MPHStayed In

Lane

Wet Unloaded Best Effort

30MPHStayed In

Lane

Wet Unloaded Full Treadle

30 MPH

Wet Unloaded Best Effort 30

MPH1.0 152.3 N 155.8 Y 152.0 N 169.3 Y 0.2% -8.0%2.0 144.6 N 160.5 Y 159.9 N 144.1 Y -9.6% 11.4%3.0 144.2 N 147.5 N -2.2%4.0 137.7 N 153.9 N -10.5%

Avg. 144.7 158.2 153.3 156.7 -5.6% 0.9%

Highway Best Effort Unloaded

60 MPH

Highway Best Effort Unloaded

60 MPH1.0 381.6 246.72.0 318.5 264.13.0 273.8 293.34.0 264.7 275.15.0 314.8 274.76.0 252.9 249.5

Avg. 301.1 267.2

Percentage Difference (positive indicates improvement with

MSQR-5000)

YYY

MSQR-5000

MSQR-5000

Meets FMVSS 121 Stopping Distance

YYY

YYYY

Meets FMVSS 121 Stopping Distance

YYYY

Y

YY

Y

N

Meets FMVSS 121 Stopping Distance

Y

Unloaded Brake Test 1/16/02

MSQR-5000

YYYYY Y

GVWR Brake Test 1/15/02OEM

Meets FMVSS 121 Stopping Distance

YY

OEM

Highway Loaded Full Treadle 60 MPH

1.3%

MSQR-5000OEM

OEM

20.6%-6.6%-3.8%

Highway Best Effort Unloaded 60 MPH

14.6%1.4%

12.7%

-3.7%

-8.5%0.6%

-3.4%

11.7%7.5%

54.7%

1.7 Stopping Distance Testing Loaded to GVWR

The stopping distance testing was performed with the vehicle loaded to GVWRand the stop initiated from 60 mph. The test was performed with the MSQR-5000 systeminstalled and with the MSQR-5000 system removed or what is called the OEM

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configuration. The stopping distance tests were performed on Highway 90 west of SanAntonio. This stretch of road has asphalt in good condition, is very flat, and hasrelatively low traffic volumes. The results showed very little difference in the averagestopping distance with and without the MSQR-5000 system. The stopping test was donewith full treadle application and met the FMVSS stopping distance requirements for allstops.

1.8 Stopping Stability Testing Loaded to GVWR

The stopping stability was performed with the vehicle loaded to GVWR both withthe MSQR-5000 installed andwith the OEM brake system. Thetest was performed at an airportfacility using the tarmac area ofthe facility. This is a concretesurface similar in appearance androughness to an asphalt road. Inorder to achieve a thoroughlywetted surface, two fire truckswere used to soak the surfacebetween each pass of the vehicle.The vehicle was driven into the500-foot radius curve set up on thetarmac surface as shown in Figure4. Once the vehicle entered thecurve, the brakes were applied.

The first set of stops used afull treadle application perFMVSS 121. These applicationsresult in lockup of the steer axletires and consequently, the vehicleis not able to negotiate the 500-foot radius curve within a 12-footwide lane as shown in Figure 5.

The second set of stops wasmade using Air Brake Systemsrecommend stopping procedure.This procedure required best effortor modulated braking. Using thisprocedure, the vehicle is able tonegotiate the curve for all but onestop with the OEM brake system.

Figure 4. Vehicle Entering 500-foot radius

Figure 5. Vehicle After Stop

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1.9 Stopping Distance Testing at Empty Vehicle Weight

The stopping distance testing was performed with the vehicle empty and the stopinitiated from 60 mph. The test was performed with the MSQR-5000 system installedand with the MSQR-5000 system removed or what is called the OEM configuration. Thestopping distance tests performed are the same as those used during the GVWR testing.The stopping test was done with best effort treadle application and met the FMVSSstopping distance requirements for all stops except for one of the OEM brake systemstops.

These tests found the only significant difference in stopping distances with andwithout the MSQR-5000 system. In this case, the vehicle with the MSQR-5000installation is able to stop in an average distance approximately 13% shorter than theOEM configured vehicle.

1.10 Stopping Stability Testing at Empty Vehicle Weight

The stopping stability was performed with the vehicle empty both with theMSQR-5000 installed and with the OEM brake system. The test was done at the airportfacility using the same test course and the same test procedures as the GVWR testing.

The first set of stops used a full treadle application per FMVSS 121. Theseapplications result in lockup of the steer axle tires and consequently, the vehicle is notable to negotiate the 500-foot radius curve within a 12-foot wide lane as shown in Figure5.

The second set of stops was made using Air Brake Systems recommend stoppingprocedure. This procedure required best effort or modulated braking. Using thisprocedure, the vehicle is able to negotiate the curve for all cases.

1.11 Conclusion

For the straight-line test, results indicate that the vehicle is able to stop from 60 mphon dry pavement within FMVSS 121 required stopping distances with the OEM brakesystem and with the MSQR-5000 system installed. The stopping distances are generallyvery similar. The one significant exception is that the empty vehicle with the MSQR-5000 installed stopped from 60 mph on a dry surface in an average of 13% shorterdistance than the OEM equipped vehicle. There was no such difference at GVWR.

For the wetted curve test, the vehicle is required by FMVSS 121 to stop from 30mph on a wetted surface while negotiating a 500-foot radius curve and maintaining itselfwithin in a 12-foot wide lane. When using full treadle brake application per FMVSS 121,the vehicle did not stay in the 12-foot lane. This occurred for the vehicle with andwithout the MSQR-5000 brake valve at both vehicle weights.

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Based on the test results and discussions with the manufacturer, SwRI found thatthe MSQR-5000 system does not function in the same manner as an electronic anti-lockbrake system (ABS). With full treadle application, it is possible to cause wheel lockupthat results in the vehicle not staying within the 12-foot lane.

When using the Air Brake System’s MSQR-5000 recommended braking procedurefor the wetted surface stops, the vehicle is able to stay in the 12-foot lane. During thestopping testing, the MSQR-5000 system did not significantly increase or decreasevehicle stopping performance.