Motor vehicle safety standards: Light vehicle brake systems; performance levels establishment,
[Federal Register: February 24, 1999 (Volume 64, Number 36)]
[Proposed Rules]
[Page 9115-9118]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr24fe99-15]
DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
[Docket No. NHTSA-99-5114]
RIN 2127-AH31
Federal Motor Vehicle Safety Standards: Light Vehicle Brake Systems
AGENCY: National Highway Traffic Safety Administration (NHTSA), Department of Transportation (DOT).
ACTION: Termination of rulemaking.
SUMMARY: This action terminates rulemaking initiated by the agency's granting of a petition for rulemaking submitted by the American Automobile Manufacturers Association (AAMA) concerning the Federal motor vehicle safety standard on light vehicle brake systems. The standard currently uses data from the cold effectiveness tests to establish performance levels for the ``hot performance'' and ``recovery performance'' test requirements. AAMA requested use of a different procedure for establishing these performance levels, which would be based on three new constant deceleration stops.
The agency has decided to terminate this action because the procedures AAMA requested would not assess the effect of heat on light vehicle braking systems any more accurately or repeatably than the procedures currently specified in the standard. In addition, the procedures currently specified in the standard are presently harmonized with the procedures in the counterpart standard established by the United Nation's Economic Commission for Europe (ECE) for light vehicle brake systems. Absent sufficient safety reason to change the existing procedure, and considering that such a change would move NHTSA's standards away from harmony with the ECE standards, the agency has decided to terminate its consideration of the requested change.
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FOR FURTHER INFORMATION CONTACT:
For technical issues: Mr. Samuel Daniel, Jr., Safety Standards Engineer, Office of Crash Avoidance Standards, Vehicle Dynamics Division, 400 Seventh Street, SW, room 5307, Washington, DC 20590; telephone (202) 366-2720; fax (202) 493-2739.
For legal issues: Mr. Walter Myers, Attorney-Advisor, Office of the Chief Counsel, National Highway Traffic Safety Administration, 400 Seventh Street, SW, room 5219, Washington, DC 20590; telephone (202) 366-2992; fax (202) 366-3820.
SUPPLEMENTARY INFORMATION:
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Background
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Regulatory History
On February 2, 1995, NHTSA published in the Federal Register (60 FR 6411) a final rule establishing Federal Motor Vehicle Safety Standard No. 135, Passenger car brake systems. This new standard replaced Standard No. 105, Hydraulic and electric brake systems, insofar as it applied to passenger cars.
On September 30, 1997, the agency published in the Federal Register (62 FR 51064) a final rule extending the new standard to trucks, buses and multipurpose passenger vehicles with a gross vehicle weight rating (GVWR) of 3,500 kilograms (7,719 pounds) or less. The name of the standard is now Standard No. 135, Light vehicle brake systems.
Standard No. 135 resulted from the agency's efforts to harmonize its hydraulic brake standard with ECE standards. The agency believed that the new standard would promote the goal of international harmonization while remaining consistent with the statutory mandate to ensure motor vehicle safety.
Among other requirements, the new standard specifies a ``cold effectiveness'' test which is intended to test the vehicle's ability to come to a quick, controlled stop with all braking systems functional, simulating emergency stopping in real-world driving. In this test, the vehicle is required to stop within 70 meters from a speed of 100 km/h with a brake pedal force that does not exceed 500 Newtons. Six ``best- effort'' stops are performed for this test; in at least one of the six stops, the vehicle must meet the 70-meter stopping distance requirement.
The standard also requires a ``hot performance'' and a ``recovery performance'' test sequence. The purpose of these tests is to ensure adequate braking capability during and after exposure to the high brake temperatures caused by prolonged or severe use. Examples of such severe use include mountain descents and severe stop-and-go driving. Heat affects the performance of the foundation brake system components, often resulting in longer stopping distances.
The hot performance test specifies a percentage limit on degradation from the performance achieved in the cold effectiveness test. This controls the amount of reduction in performance that a vehicle experiences when the brakes are heated.
The recovery performance test places both lower and upper limits on the difference between the stopping distance achieved after several normal brake applications immediately following the hot performance test and the distance achieved in the cold effectiveness test. The lower limit controls the amount of degradation, while the upper limit ensures that brakes do not become too sensitive when heated and ``over- recover.''
As noted above, the stopping performance for both the hot stop and recovery performance tests is based on the performance achieved in the cold effectiveness test. The average pedal force used during the cold effectiveness test establishes the allowable average pedal force (and thus the stringency) for the hot performance test and the recovery performance test. S7.14 of Standard No. 135, Hot Performance, requires a vehicle with heated brakes to be capable of achieving at least 60 percent of the deceleration obtained during the best cold effectiveness stop, with an average pedal force that does not exceed the average pedal force recorded during that cold effectiveness stop. S7.16, Recovery Performance, requires the vehicle to be capable of achieving between 70 percent and 150 percent of the deceleration obtained during the best cold effectiveness stop, with an average pedal force that does not exceed the average pedal force used during that cold effectiveness stop.
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AAMA Petition
The AAMA submitted a petition for rulemaking requesting that NHTSA amend Standard No. 135 to add 3 constant deceleration stops at the beginning of the thermal test sequence to establish baseline performance for the hot and recovery tests, rather than using the results of the current cold effectiveness test to establish such baseline performance.
In its petition, AAMA noted that General Motors (GM) had previously requested an interpretation from the agency concerning ``the pedal force that may or must be used during cold effectiveness testing of ABS
[antilock brake systems] equipped vehicles for purposes of establishing allowable pedal force for thermal testing.'' In its May 16, 1996 response, NHTSA stated:
We anticipate that test drivers will utilize a variety of pedal forces during the six cold effectiveness stops in an effort to achieve the shortest possible stopping distance consistent with the test procedures. The average pedal force that resulted in the shortest stopping distance of these six tests would be used to ascertain compliance with the thermal and recovery performance requirements under S7.14 and S7.16. If, as you suggest, the shortest distance can be achieved at more than one average pedal force level (e.g., if the ABS cycles at a variety of pedal forces below 500 Newtons, or the test driver is able to modulate braking forces to avoid wheel lock while matching the stopping performance of the ABS system), the vehicle must be capable of satisfying the thermal and recovery performance requirements at all such average pedal force levels.
In a subsequent meeting with the agency, GM indicated that it believed it is impractical for test drivers to determine both the minimum achievable stopping distance and the minimum pedal force that can provide that stopping distance within the six stops prescribed for cold effectiveness testing. It argued that this ``practicability'' problem is most acute for vehicles fitted with ABS. GM stated that the best resolution would be an amendment to Standard No. 135 adding constant deceleration stops at the beginning of the thermal test sequence in order to establish performance requirements for the subsequent hot and recovery tests.
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Discussion
The concerns identified by GM ultimately led AAMA to submit its petition for rulemaking. AAMA's arguments and the agency's responses can be summarized as follows:
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The requested amendments would promote international harmonization by more closely aligning Standard No. 135 with its European counterpart, ECE Regulation R13-H. The European approach is to use constant pedal force applications to determine braking performance, including cold effectiveness capability. This contrasts with the U.S. approach of using an initial pedal force spike during cold effectiveness tests in order to minimize the response time of the system, thereby minimizing stopping distance. These requested amendments would reduce that disparity.
NHTSA: The agency disagrees with the AAMA statement. A review of R13-H test procedures indicates that a constant pedal force application is not specified in European Type-O tests,
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which specify test procedures nearly identical to the cold effectiveness test procedures of Standard No. 135. Although test drivers in Europe may use different techniques than those in the U.S., those techniques are within the test parameters to achieve the best stop with a pedal force of 500 Newtons or less. Thus, they should not be considered disparate. The agency believes that all other hot and recovery test procedures and performance requirements in R13-H are sufficiently harmonized with Standard No. 135.
In addition, the harmonization of Standard No. 135 and ECE R13-H would be adversely affected because the ECE brake standard group, the Meeting of Experts on Brakes and Running Gear (GRRF), has shown no interest in modifying R13-H to be consistent with the AAMA proposal. A review of test data generated by the GRRF during the development and coordination of ECE R13-H and FMVSS No. 135 indicated that constant deceleration stop tests similar to the tests proposed by AAMA were difficult to execute. There was also considerable disagreement among European researchers on the appropriate deceleration rate for the tests and the number of test runs to require in the regulation.
b1. AAMA: The requested amendment would resolve a practicability problem presented by the current test provisions of Standard No. 135. The standard currently bases hot and recovery deceleration performance requirements and pedal force constraints to the best cold effectiveness stop. It is not possible for test drivers to determine with certainty that they have achieved both the shortest possible stopping distance and the minimum pedal force that will provide the specified stopping distance within the 6 cold effectiveness stops, especially for vehicles equipped with ABS.
NHTSA: The stopping distance procedure specified in S6.5.3.2 requires that the test vehicle be stopped in the shortest distance achievable on all stops. There is no requirement for the test driver to use the minimum pedal force to achieve the best stop.
The agency adheres to its previous position that if the shortest stopping distance can be achieved at more than one average pedal force, the vehicle must be capable of satisfying the hot and recovery performance test requirements at all such average pedal force levels.
The agency conducted most of the cold effectiveness tests during the development of FMVSS No. 135 using a constant 500 N pedal force. Recent compliance tests indicate that, as AAMA stated in its petition, the average pedal force can vary considerably for the six (6) cold effectiveness stopping tests with small variations in stopping distance. However, all tested vehicles complied with the hot and recovery performance requirements based on cold effectiveness test results, as follows:
Stopping Average pedal force (Newtons)
distance (Meters)
Vehicle A: 307......................................................
60 302......................................................
57 319......................................................
58 364......................................................
57 388......................................................
59 412......................................................
54 Vehicle B: 130......................................................
65 297......................................................
52 346......................................................
52 316......................................................
53 402......................................................
51 372......................................................
52 Vehicle C: 197......................................................
51 424......................................................
48 350......................................................
46 330......................................................
48 453......................................................
47 361......................................................
47 Vehicle D: 301......................................................
57 328......................................................
51 376......................................................
54 386......................................................
54 407......................................................
53 Vehicle E: 379......................................................
53 234......................................................
55 314......................................................
52 340......................................................
52 368......................................................
50 Vehicle F: 366......................................................
46 337......................................................
47 388......................................................
47 298......................................................
49 313......................................................
50 280......................................................
48
Note: The agency does not have a reading for the 6th stop on Vehicles D and E.)
b2. AAMA: The current language of the standard almost guarantees that the cold effectiveness deceleration and pedal force combination results obtained by a manufacturer will be different from the results obtained by NHTSA in an enforcement test of the same vehicle model. This disparity will be magnified in subsequent hot and recovery results since the manufacturer and NHTSA will be operating with different pedal force constraints and performance requirements.
NHTSA: The test procedures require best effort on all runs (S6.5.3.2) with only six (6) runs to achieve the shortest stopping distance in the cold effectiveness test. Thus, NHTSA believes that there will be little variation in the stopping techniques used by test drivers. The degradation of the brake system as a function of heat, as well as the allowable pedal force value, is a key factor in determining compliance with the hot and recovery performance requirements. As stated above, the agency believes that the hot and recovery performance should comply with the requirements at any pedal force that produces the shortest stopping distance in the cold effectiveness test. The cold effectiveness compliance test data provided above indicate that there can be considerable variation in the average pedal force required to produce similar stopping distances. Nevertheless, the test results indicate that all the vehicles tested complied with the hot and recovery requirements of the standard. Accordingly, NHTSA believes that the testing problems suggested by AAMA will not develop into compliance issues unless the vehicle's brake performance is substantially degraded by heating.
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AAMA: The requested amendments would not reduce the stringency of the standard's requirements and would therefore have no adverse effect on safety. If anything, the requested amendments would increase the stringency of the standard. For example, AAMA members have conducted Standard No. 135 testing using the allowable pedal force of 500 Newtons. This affords maximum flexibility for using a pedal force of up to 500 Newtons in the hot and recovery tests. Applying the full 500 Newton pedal force during cold effectiveness tests would be practical, objective, and repeatable and would provide a well-defined pedal force constraint for the thermal tests. The one shortcoming of such a force is that it fails to assure the ``apples-to-apples'' comparison intended for the hot and recovery tests since it allows artificially inflated pedal forces to be used during the hot and recovery stops. The requested amendments would resolve this problem, however. Further, the petition does not seek any change to the relevant performance requirements of the standard, namely that hot brakes be capable of achieving at least 60 percent of cold deceleration capability and that recovered brakes be capable of achieving between 70 percent and 150 percent of cold deceleration capability.
NHTSA: The agency disagrees with AAMA on this point. NHTSA believes that the proposed procedure would reduce the stringency and severity of the hot and recovery performance tests. The
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constant deceleration rate proposed by AAMA for the baseline tests (5.5 m/s‹SUP›2‹/SUP›) is lower than the current deceleration rate (6.43 m/ s‹SUP›2‹/SUP›) the vehicle must achieve in order to meet the 70-meter cold effectiveness stopping distance performance requirement. The average minimum stopping distance for the cold effectiveness stopping tests shown above is about 50 meters. That results from an average deceleration rate of approximately 7.7 m/s‹SUP›2‹/SUP›, or about 30 percent higher than the average deceleration rate of AAMA's proposed baseline tests. Thus, AAMA's proposal to use a lower deceleration rate would result in the allowance of a longer stopping distance for the hot and recovery performance tests. Additionally, the agency has not used the allowable 500 N pedal force in the FMVSS No. 135 compliance tests conducted to date, so the allowable pedal forces for the hot and recovery performance tests conducted to date are not inflated.
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AAMA: The adoption of baseline stops at the beginning of the thermal sequence would avoid the effects of intervening tire and brake conditioning inherent in the current procedure. As currently written, high speed effectiveness, stops with the engine off, failed antilock, failed proportioning valve, hydraulic circuit failure, and parking brake tests, some under both gross and lightly-loaded vehicle conditions, are performed between the cold effectiveness test and the thermal tests. This sequence can confound the comparison between the hot, cold, and recovery tests. Adding the requested baseline stops at the outset of the thermal sequence would facilitate a more direct comparison of cold versus thermally affected braking capability.
NHTSA: The agency agrees that baseline stopping runs at the beginning of the thermal sequence would avoid the effects of tire and brake conditioning that occur between the cold effectiveness testing and the thermal test sequence. NHTSA believes, however, that such effects are negligible when compared to the total brake and tire usage that occurs during conduct of the entire Standard No. 135 test series. In addition, the AAMA did not demonstrate any performance or safety benefits that would result from the requested change in test sequence. Accordingly, NHTSA sees no need to amend the testing procedures of Standard No. 135 to specify AAMA's proposed baseline testing for the purpose of eliminating the effects of tire wear or brake conditioning that might occur during testing.
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Agency Determination
The agency's declination to amend Standard No. 135 as suggested by AAMA includes the fact that the test procedures in Standard No. 135 and ECE R13-H are now harmonized. The AAMA proposals would move Standard No. 135 away from harmonization with its European counterpart. Absent sufficient safety reasons to change the existing test procedures in Standard No. 135, NHTSA finds no justification for adopting the manufacturers' request to move NHTSA's standards away from harmony with the European standards.
The agency believes that the testing practicability problems asserted by AAMA in its petition for rulemaking will not result in vehicle noncompliance. As determined by NHTSA's compliance test results discussed above, the considerable range of pedal forces that result in similar stopping distances in the cold effectiveness testing has not resulted in any noncompliances with the hot and recovery requirements. Thus, NHTSA believes that it is more appropriate to compare hot and recovery brake performance to peak cold effectiveness performance than to compare non-peak cold brake performance against the hot and recovery performance. The agency also believes that the amendments to Standard No. 135 suggested by AAMA would reduce the stringency and severity of the hot and recovery performance tests specified in the standard, and thus would be inconsistent with motor vehicle safety.
Finally, the proposed amendments would add complexity to the compliance test procedures in Standard No. 135 without demonstrated safety or testing benefits.
For the reasons stated above, the agency terminates rulemaking initiated by the petition for rulemaking submitted by the AAMA.
Authority: 49 U.S.C. Secs. 322, 30111, 30115, 30117, and 30166; delegation of authority at 49 CFR 1.50.
Issued on: February 18, 1999. Ricardo Martinez, Administrator.
[FR Doc. 99-4522Filed2-23-99; 8:45 am]
BILLING CODE 4910-59-P
