United States Department of TransportationInterpretation ID: aiam0003
Esq. Legal Staff General Motors Corporation New Center One Building 3031 West Grand Boulevard P.O. Box 33122 Detroit
MI 48232;
"Dear Mr. Selander: This responds to your February 17, 1992 request fo interpretations of Federal Motor Vehicle Safety Standards No. 101, Controls and Displays and No. 105, Hydraulic Brake Systems, as those standards would apply to an electric vehicle (GMEV) that General Motors (GM) is preparing to sell in the future. You requested the agency's concurrence with, or guidance regarding, nine proposed interpretations. Your questions are addressed below. Before discussing the substantive issues that you raised, I note that you requested confidential treatment for portions of certain materials that you provided relating to the brake system planned for the electric vehicle. These materials were previously submitted to NHTSA, and the agency granted confidentiality for portions of the materials in letters dated July 18, 1991 and August 12, 1991. In a letter accompanying your request for interpretation, GM released from its request for confidential treatment portions of the materials for which confidentiality had previously been granted. NHTSA's earlier grants of confidentiality remain in effect for the remaining portions for which GM continues to seek confidential treatment. Accordingly, this letter does not cite any of the confidential information. I also note that, in one of the attachments to your letter, you suggested several amendments to Standard No. 105 that you believe would facilitate the introduction of electric vehicles. As you know, NHTSA recently issued an advance notice of proposed rulemaking (ANPRM) to solicit comments to help the agency determine what existing standards may need modification to meet the needs associated with the introduction of electric vehicles and what new standards may have to be written specifically for electric vehicles. See 56 FR 67038, December 27, 1991. We will consider your recommendations concerning Standard No. 105 as we evaluate the comments on the ANPRM. The scope of this letter is limited to addressing how the current requirements of Standards No. 101 and No. 105 would apply to your planned vehicle. By way of background information, NHTSA does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, it is the responsibility of the manufacturer to ensure that its vehicles and equipment comply with applicable requirements. The following represents our opinion based on the facts provided in your letter. Standard No. 101, Controls and Displays GM Proposed Interpretation 1: Permit electrically powered vehicles to use symbols that are appropriate for indicating electric power reserve. You asked two questions regarding how Standard No. 101 would apply to the GM electric vehicle. The first question concerned the identification for a gauge that would monitor battery charge as a percent of full charge. This gauge would serve as the functional equivalent of a fuel gauge in traditional internal combustion engine (ICE) vehicles. You stated, however that it would be inappropriate and potentially misleading to use Standard No. 101's fuel symbol (a picture of a gasoline pump) for a gauge indicating electric power reserve. You stated that you planned to identify the gauge with the ISO battery symbol (a picture of a battery), which you indicated is substantially similar to that found in Standard No. 101 for electrical charge. You requested NHTSA's concurrence that electric vehicles are permitted to use symbols that are appropriate for identifying electric power reserve and not the Standard No. 101 fuel symbol. Standard No. 101 requires that new vehicles with any display listed in the standard must meet specified requirements for the location, identification and illumination of such display. See S5(a). Thus, the primary issue raised by your question is whether a gauge indicating electric power reserve is among the displays listed in the standard, and if so, what identification requirements apply. As you noted in your letter, one of the displays listed in Standard No. 101 is a fuel gauge. See S5.1 and Table 2. The dictionary defines 'fuel' as combustible matter used to maintain fire, as coal, wood, oil, etc. See Random House Dictionary of the English Language (unabridged edition). Electrical power provided by a battery does not come within the meaning of 'fuel.' Therefore, a gauge indicating electric power reserve for an electric vehicle is not a fuel gauge. Another display listed in Standard No. 101 is an electrical charge gauge. This term refers to gauges that indicate whether, and the extent to which, a vehicle's battery is charging. Therefore, a gauge indicating electric power reserve for an electric vehicle is not an electric charge gauge within the meaning of Standard No. 101. Since a gauge indicating electric power reserve is not otherwise covered by Standard No. 101 or any other standard, its identification is at the option of the manufacturer. GM Proposed Interpretation 2: Allow the 'Service Soon' telltale to indicate loss of powertrain oil pressure for the GMEV. Your second question concerned whether low oil pressure may be indicated by activation of a 'Service Soon' telltale instead of one identified by Standard No. 101's oil pressure symbol (a picture of an oil can) or the word 'oil.' You stated that a 'Service Soon' telltale would be more appropriate for an electric vehicle, since it (unlike ICE vehicles) can continue to be driven without oil pressure. One of the displays listed in Standard No. 101 is an oil pressure telltale. While the seriousness of low oil pressure may be different for electric vehicles than ICE vehicles, the condition for activation of an oil pressure telltale (low oil pressure) would be the same. It is our opinion that Standard No. 101's identification requirements would apply to an oil pressure telltale for an electric vehicle. If a manufacturer is concerned that the oil pressure symbol or the word 'oil' might be misleading to drivers familiar with ICE vehicles, the manufacturer is free to provide additional words or symbols for the purpose of clarity. See S5.2.3. It is not clear, however, that the telltale you plan would be considered a low oil pressure telltale within the meaning of Standard No. 101. You state that, as currently planned, the electric vehicle will be equipped with a 'Service Soon' telltale which will light in the event of a malfunction that could eventually cause damage to the vehicle powertrain, but does not require immediate attention. It thus appears that the telltale might monitor several possible vehicle conditions, one of which is low oil pressure. Standard No. 101 does not require that any of the displays listed in the standard be provided or that two or more displays, if provided, be provided separately. NHTSA has previously concluded that a multipurpose telltale which monitors two functions, oil pressure and coolant temperature, may be identified by the word 'Engine.' See December 29, 1978 letter to Ford Motor Company. The basis for this interpretation was that while Standard No. 101 specifies requirements for oil pressure and coolant temperature telltales, it does not specify any requirements for a single telltale which covers both conditions. For the same reason, if GM provided a single telltale monitoring several vehicle conditions, one of which was low oil pressure, the standard's requirements for an oil pressure telltale would not apply and the identification for that telltale would be at the discretion of the manufacturer. Standard No. 105, Hydraulic Brake Systems You asked seven questions regarding how Standard No. 105 would apply to the GM electric vehicle. You provided the following general description of the brake system planned for the vehicle: The brake system consists of front hydraulic disc (service) brakes, rear electric drum (service and parking) brakes, four-wheel ABS, and regenerative braking. Brake pedal forces and travel are comparable to conventional power assisted hydraulic brake systems, and are independent of the state-of-charge of the vehicle's battery pack. The design features a manual hydraulic 'push through' to apply the front brakes in the event of any electrical failure. Standard No. 105 applies to passenger cars and various other vehicle types with 'hydraulic service brake systems.' See S3. Since the service brakes of the GM electric vehicle would be partly hydraulic brakes and partly electric brakes, a preliminary issue is whether the standard would apply to the vehicle. As discussed below, it is our opinion that the standard would apply to the vehicle. The term 'hydraulic brake system' is defined in S4 as 'a system that uses hydraulic fluid as a medium for transmitting force from a service brake control to the service brake, and that may incorporate a brake power assist unit, or a brake power unit.' The term 'service brake' is defined at Part 571.3 as 'the primary mechanism designed to stop a motor vehicle.' The planned braking system would use hydraulic fluid as a medium for transmitting force from the service brake control to the front brake portion of the service brake. It is our interpretation that this is sufficient, under the definition of 'hydraulic brake system,' for the braking system to be considered a 'hydraulic brake system,' even though hydraulic fluid is not used for the rear brake portion of the service brake. Therefore, Standard No. 105 would apply to the vehicle. GM Proposed Interpretation 3: The GMEV parking brake is mechanically retained in accordance with the requirements of S5.2. Your first question on Standard No. 105 concerned S5.2's requirement that vehicles be manufactured 'with a parking brake system of a friction type with a solely mechanical means to retain engagement.' You stated that the parking brake on the GMEV would be applied and released by electrical means, but would be retained by a mechanical latching device. You requested NHTSA's concurrence that the planned parking brake would satisfy the requirement for mechanically retained engagement. We agree that S5.2 permits the parking brake to be applied and released by electrical or other non-mechanical means, so long as engagement is held by solely mechanical means. Your next several questions concern Standard No. 105's brake failure requirements. As noted by your letter, these requirements are set forth in S5.1.2 (partial failure), S5.1.3 (inoperative brake power assist unit or brake power unit), and S5.5 (failure in antilock or variable proportioning brake system), and the test procedures for these requirements are set forth in S7.9 and S7.10. GM Proposed Interpretation 4: The subject brake system is a 'split service brake system' consisting of four subsystems--one at each wheel. Standard No. 105 specifies different partial failure requirements depending on whether a vehicle is manufactured with a split service brake system. The term 'split service brake system' is defined in S4 as 'a brake system consisting of two or more subsystems actuated by a single control designed so that a leakage- type failure of a pressure component in a single subsystem (except structural failure of a housing that is common to two or more subsystems) shall not impair the operation of any other subsystem.' We agree that your planned vehicle can be viewed as having four subsystems, one at each wheel. In only two of the subsystems, however, can leakage-type failures occur (the two hydraulic subsystems). Thus, in determining whether the vehicle has a split service brake system within the meaning of Standard No. 105, the key is whether a leakage-type failure of a pressure component in either of those two subsystems (except structural failure of a housing that is common to two or more subsystems) impairs the operation of any other subsystem (i.e., the other hydraulic subsystem or either of the two other subsystems). After reviewing the information provided with your letter, we have no reason to doubt that your planned system qualifies as a split service brake system. GM Proposed Interpretation 5: The four service brake subsystems may be certified to the requirements of S5.1.2 in accordance with the test procedure of S7.9.1 through S7.9.3 by disabling each subsystem in a way that does not affect the other three subsystems. Standard No. 105's requirements for partial failure are set forth in S5.1.2. For vehicles with a split service brake system, 5.1.2.1 provides that, in the event of a rupture or leakage type of failure in a single subsystem, other than a structural failure of a housing that is common to two or more subsystems, the remaining portion(s) of the service brake system shall continue to operate and shall be capable of stopping a vehicle from 60 mph within specified stopping distances. You suggested that certification of the requirements of S5.1.2.1, consistent with the procedure of S7.9.1 through S7.9.3, should be established by disabling each of the four subsystems in turn. You also stated that, for purposes of compliance testing, the subsystems would be disabled in such a way that the functioning of only one subsystem would be affected. It is our opinion that, in testing under S5.1.2.1, only the two hydraulic subsystems of your planned brake system would be disabled, as S5.1.2.1 only addresses rupture/leakage types of failures. It does not address any type of failure of a subsystem for which a rupture or leakage type failure cannot occur. We would not consider a break in an electrical system to be a 'rupture' within the meaning of Standard No. 105. We are uncertain as to the meaning of your statement that, for purposes of compliance testing, the subsystems would be disabled in such a way that the functioning of only one subsystem would be affected. This could be read as meaning that the agency must induce a rupture or leakage type failure in a place that doesn't affect other subsystems. However, under S7.9.1, any one rupture or leakage type of failure is introduced, other than a structural failure of a housing that is common to two or more subsystems. If any such leakage type failure impaired another subsystem, the brake system would not, of course, be considered a split service brake system within the meaning of Standard No. 105. GM Proposed Interpretation 6: The GMEV brake system may be certified to the requirements of S5.1.3 in accordance with the test procedure of S7.10 by functionally disabling the BCU. Such a procedure will completely disable the brake power assist, and since the electric motors within the hydraulic unit and the rear brake drums are separately disabled during S5.1.2 testing, there is no need to separately consider these electric motors when certifying to the requirements of S5.1.3. Standard No. 105's requirements for inoperative brake power assist unit or brake power unit are set forth in S5.1.3. You stated that your planned brake system would not utilize conventional power assist, but brake power assist would be provided by the combination of the BCU and four electric motors. You stated that this design does not lend itself to an obvious way of distinguishing brake power assist from other service brake subsystem components, and suggested that the brake system be certified to the requirements of S5.1.3 by disabling the BCU (which would disable all four electric motors and completely eliminate functional brake power assist) and then satisfying the provisions of either S5.1.3.1, S5.1.3.2, or S5.1.3.4. You also sought the agency's concurrence that there is no need to otherwise take the four electric motors into account when certifying to the requirements of S5.1.3. S4 of Standard No. 105 defines the term 'brake power assist unit' as a device installed in a hydraulic brake system that reduces the operator effort to actuate the system, and that if inoperative does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control. Under the options of S5.1.3.1, S5.1.3.2, and S5.1.3.4, stopping distance requirements must be met with one brake power assist unit inoperative. We believe that each electric motor comes within the definition of 'brake power assist unit.' In addition, given the integrated nature of the BCU and the four electric motors, we believe that the combination of the BCU/four electric motors also comes within the definition of 'brake power assist unit.' It is therefore our opinion that the requirements of S5.1.3 must be met both when the BCU is disabled (which would disable all four electric motors and completely eliminate functional brake power assist) and also when each of the four electric motors is disabled individually. We note that, under our interpretation of S5.1.2 discussed above, not all of the four electric motors are separately disabled during S5.1.2 testing. GM Proposed Interpretation 7: The GMEV brake system may be certified to the requirements of S5.5 in accordance with the test procedure of S7.9.4 by functionally disabling the BCU. Since such a procedure will completely disable ABS and the variable proportioning function, no other testing is required in connection with S5.5. Standard No.105's requirements for failed antilock and variable proportioning brake systems are set forth in S5.5. You stated that the BCU is the functional power source for the GMEV's ABS, and that the BCU also regulates the proportion of front to rear braking. You sought the agency's concurrence that disabling the BCU is the appropriate means of complying with S5.5, and is consistent with the procedure of S7.9.4. S5.5 provides that a vehicle shall meet certain stopping distance requirements in the event of failure (structural or functional) in an antilock or variable proportioning brake system. S7.9.4 provides the following test procedure: With vehicle at GVWR, disconnect functional power source, or otherwise render antilock system inoperative. Disconnect variable proportioning brake system. Make four stops, each from 60 mph. If more than one antilock or variable proportioning brake subsystem is provided, disconnect or render one subsystem inoperative and run as above. Restore system to normal at completion of this test. Repeat for each subsystem provided. We concur that your planned brake system should be tested to the requirements of S5.5 in accordance with the test procedure of S7.9.4 by functionally disabling the BCU, and that no other testing is required. Under S7.9.4, the antilock system is to be rendered inoperative and the variable proportioning system is to be disconnected. Both of these procedures are accomplished by functionally disabling the BCU. Further, it is our opinion that the planned brake system would not have antilock or variable proportioning subsystems, since antilock at all four wheels and variable proportioning are all controlled by the BCU. GM Proposed Interpretation 8: Assuming the conditions established in proposed S6.2, regenerative braking is permitted to function normally when conducting the test procedures of S7. In particular, the phrase 'service brakes shall be capable of stopping' (found in S5.1.4 and S5.1.5, for example) is not to be construed as prohibiting the normal operation for regenerative braking. In addressing how the current requirements of Standard No. 105 would apply to your vehicle, we cannot assume the conditions you recommend establishing in a new S6.2. The agency would need to add those conditions to the standard in rulemaking. I will therefore address how regenerative braking would be treated under the current requirements. As discussed in your letter, regenerative braking assists in decelerating the vehicle by converting the kinetic energy of the moving vehicle into stored electrical energy within the vehicle's battery pack. Regenerative braking on the planned GM electric vehicle will supplement, under certain conditions, the friction braking provided by the service brakes. You stated that regenerative braking will only be available when the vehicle is 'in gear.' Since the large majority of Standard No. 105 tests are conducted with the vehicle in 'neutral,' regenerative braking will have no influence on the outcome of those tests. You indicated that since some Standard No. 105 tests, notably fade and recovery and the water test, are conducted with the the vehicle 'in gear,' regenerative braking could occur during these tests. You stated that you believe that regenerative braking should generally be allowed to function normally during Standard No. 105 testing. You argued that the regenerative braking which may occur during 'in gear' Standard No. 105 tests is little different from the engine braking which occurs in conventional ICE vehicles. We agree that regenerative braking should function normally during Standard No. 105 testing, just as engine braking occurs normally during Standard No. 105's 'in gear' tests. Another issue that you raised in connection with regenerative braking is the state of battery charge during testing, which can affect the amount of regenerative braking. You proposed (for your recommended new S6.2) that tests be initiated with a full charge of the vehicle's battery pack, so that the amount of regenerative braking that would occur during the tests would be minimized to the least amount that could occur in real world driving, i.e., the tests would be conducted under 'worst case' conditions. While Standard No. 105 specifies many test conditions, it does not specify state-of-battery charge. In an interpretation letter to Mazda dated October 2, 1990, we provided general guidance concerning how NHTSA interprets a standard where it does not specify a particular test condition. First, we stated that, in the absence of a particular test condition, we believe there is a presumption that the requirements need to be met regardless of such test condition, since the standard does not include any language which specifically limits applicability of its requirements to such test condition. We also indicated, however, that before reaching such a conclusion, we also consider the language of the standard as a whole and its purposes. It is our opinion that the braking requirements of Standard No. 105 must be met regardless of the state of battery charge. The purpose of Standard No. 105 is to ensure safe braking performance under normal and emergency conditions. Since an electric vehicle will be driven with the battery at various states of charge, safe braking performance can only be ensured if the standard's requirements can be met in all such conditions. This would generally be consistent with GM's suggestion that compliance testing be conducted under 'worst case' conditions. GM Proposed Interpretation 9: In addition to the explicit conditions for activation of the brake telltale set forth in S5.3 of the standard, permit illumination of the service brake telltale when an impending or latent brake system malfunction is detected during electrical diagnosis. As noted by your letter, S5.3.1 of Standard No. 105 requires a brake telltale to illuminate when there is a gross loss of hydraulic pressure (or, alternatively, a drop in fluid level), a total functional electrical failure in the antilock or variable proportioning brake system, and when the parking brake is applied. You stated that a brake telltale on the planned GMEV would illuminate under these prescribed conditions. You indicated, however, that a diagnostic capability will also exist to detect other faults in the brake system, and requested the agency's concurrence that S5.3.1 permits illumination of the brake telltale when other faults are detected which increase the likelihood of a substantial degradation in brake system performance. While Standard No. 105 requires that a brake telltale be provided which activates under certain specified conditions, it does not expressly state whether the required telltale may also be activated under other conditions. It is our opinion that the telltale may also activate under other conditions so long as such activation does not obscure or confuse the meaning of the required telltale or otherwise defeat its purpose. I note that this test is similar to one the agency has long used in addressing the issue of whether additional information may be provided along with information that is required to be labeled on certain products in the context of our safety standards. See, for example, NHTSA's December 20, 1991 interpretation letter to GM concerning Standard No. 209. The purpose of the brake telltale is to warn the driver of one of two conditions: (1) the parking brake is applied (and hence should be released before driving), or (2) the brake system has a significant fault which should be corrected. Since the additional conditions for activation which GM contemplates would represent significant brake system faults which should be corrected, it is our opinion that activation of the brake telltale under such conditions would not in any way defeat the purpose of the brake telltale. I hope you find this information helpful. If you have further questions, please contact Edward Glancy of my staff at this address or by telephone at (202) 366-2992. Sincerely, Paul Jackson Rice Chief Counsel";