Interpretation ID: nht92-9.4

DATE: February 17, 1992

FROM: Stephen E. Selander -- Attorney, GM Legal Staff

TO: Paul Jackson Rice -- Office of the Chief Counsel, NHTSA

TITLE: Re: General Motors Corporation; FMVSS 101, 105; Request for Interpretations

ATTACHMT: Attached to letter dated 4/29/92 from Paul J. Rice to Stephen E. Selander (A39; Std. 101; Std. 105)

TEXT:

General Motors Corporation (GM) is currently preparing an electric vehicle (GMEV) which will be offered for sale in the near future. The GMEV contains basic design strategies that differ from traditional Internal Combustion Engine (ICE) vehicles. While these strategies are intended to comply with all Federal Motor Vehicle Safety Standards (FMVSS), questions have arisen about how to correctly apply the requirements of FMVSS 101 - Controls and Displays and 105 Hydraulic Brake Systems. The purpose of this letter is to seek the agency's concurrence with, or guidance regarding the proposed interpretations of these requirements.

FMVSS 101 PROPOSED INTERPRETATIONS

FUEL GAUGE REQUIREMENTS Proposed Interpretation: Permit electrically powered vehicles to use symbols that are appropriate for indicating electric power reserve.

FMVSS 101 S5.2.3 requires that information pertaining to fuel level be identified by the fuel level symbol found in Table 2 of FMVSS 101 or by the corresponding word: FUEL. This identification appears quite appropriate for traditional ICE vehicles that consume combustible fuels. However, the GMEV will not use combustible fuel; rather, it will rely on electrical energy stored in its battery packs. In this context the fuel symbol is inappropriate and potentially misleading.

As currently planned, the GMEV will be equipped with a gauge that will monitor battery charge as a percent of full charge. This gauge is to be identified by a symbol substantially similar to that found in FMVSS 101 Table 2 for Electrical Charge. We believe that this type of gauge is more appropriate for Electric Vehicles (EVs). It will allow the operator to readily monitor electric power remaining in the batteries and will serve as the functional equivalent of a fuel gauge found in traditional ICE vehicles.

It should be noted that the GMEV is being designed for domestic and international sale. In order to optimize cost effectiveness, it is imperative that we harmonize requirements whenever possible. To that end, we have reviewed our current design strategy for the "electric fuel" gauge with the appropriate European agencies. They have agreed that the ISO fuel symbol is inappropriate to indicate "electric fuel" and that a more appropriate symbol is the ISO battery symbol.

Therefore, we request the agency's concurrence that EVs are permitted to utilize symbols that are appropriate for identifying electric power reserve and not the FMVSS 101 fuel level symbol.

OIL PRESSURE REQUIREMENTS Proposed Interpretation: Allow the "Service Soon" telltale to indicate loss of powertrain oil pressure for the GMEV.

FMVSS 101 S5.2.3 requires information pertaining to oil pressure be indicated by the oil pressure symbol found in Table 2 of FMVSS 101 or by the corresponding word: OIL.

As currently planned, the GMEV 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. GM proposes to light this telltale in the event of a loss of oil pressure to the powertrain. We believe this to be a more appropriate telltale because the GMEV can continue to be driven without oil pressure.

The GMEV powertrain consists of an electric motor which drives a single speed transmission. Lubricating oil, contained in a reservoir below the powertrain, is splashed onto the gears and bearings of the powertrain by the motion of the vehicle and the turning of the transmission gears. Under normal conditions, the splashing oil sufficiently lubricates most of the powertrain pans except for the rear motor bearing. Oil is supplied to the rear bearing by an oil pump.

While a loss of oil pressure in traditional ICE vehicles causes significant damage in a very short period of time, a loss of oil pressure in the GMEV is not a catastrophic event. The normal motion of the GMEV supplies sufficient oil for it to continue to operate for some time. We estimate the GMEV would be able to operate approximately 500 miles without sustaining serious damage to the powertrain. This is a significant distance, especially for this commuter vehicle which has a maximum range between recharging of far less than 500 miles.

In the event of a loss of oil pressure, activating a traditional oil pressure telltale could send the wrong message to the operator of a GMEV. In its traditional context, an active oil pressure telltale means that severe engine damage is imminent. An explanation of low oil pressure found in a typical GM owner's manual of an ICE vehicle reads as follows:

CAUTION: An engine low on oil can catch fire. You could be seriously burned. If your oil warning light stays on, don't keep driving. Check your oil immediately and have the problem corrected.

The appropriate action by the operator is to stop the vehicle immediately, turn the engine off and correct the underlying condition.

In the event of a loss of oil pressure in the GMEV, the preceding action is not appropriate. It is not necessary for the driver to pull over immediately to prevent damage to the powertrain. Even if the operator did pull over, the oil could not be checked because the GMEV does not require traditional routine oil maintenance and therefore, is not equipped with an oil dip stick.

Therefore, in the event of a loss of oil pressure, we believe it is appropriate to light the "Service Soon" telltale which indicates that service is needed, but immediate action by the driver is not required.

FMVSS 105 PROPOSED INTERPRETATIONS

GM has previously submitted a letter from Mr. R. A. Rogers to the agency (USG 2886, dated July 2, 1991) which describes the brake system planned for the GMEV. This brake system consists of front hydraulic disc service brakes, rear electric drum service and parking brakes, four wheel ABS, and regenerative braking. USG 2886 also describes the regulatory requirements within FMVSS 105 which must be addressed, either through interpretation or rulemaking, to facilitate introduction of the GMEV brake system. A copy of USG 2886, Part III with the cover letter and the information for which confidential treatment is requested removed, is attached to this document. (Note: The content of USG 2886 Part III is identical to that which was originally submitted as USG 2886, July 1991; however, the document has been revised to reduce the portions for which GM continues to request confidential treatment. There are a few very minor inaccuracies in this document with respect to current design intent for the GMEV brake system. These slight differences in the brake system do not affect the FMVSS 105 interpretations being requested. It is likely that additional minor changes in the brake system will occur as it is refined. GM will keep the agency advised of any changes which have new FMVSS implications.)

GM's request for interpretations, as described in USG 2886, Part III, have not changed, so we respectfully request that the agency refer to the attachment for a detailed discussion of the issues which we propose be addressed by interpretation. A summary follows:

PROPOSED INTERPRETATIONS:

1. The GMEV parking brake is mechanically retained in accordance with the requirements of S5.2

2. The GMEV brake system is a "split service brake system" consisting of four subsystems, one at each wheel.

3. 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.

4. 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 Brake Control Unit (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.

5. 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.

6. 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.

There is one additional FMVSS 105 interpretation that we would now request which was not discussed in USG 2886:

BRAKE TELLTALE ILLUMINATION

Proposed Interpretation: 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.

S5.3.1 of FMVSS 105 prescribes the conditions during which the brake telltale shall be illuminated. This section requires that the telltale illuminate when there is a gross loss of hydraulic pressure (or, alternatively, a drop in fluid level), a total functional electrical failure in the ABS or variable proportioning brake system, or when the parking brake is applied. On the GMEV, the brake telltale will illuminate whenever these prescribed conditions exist. However, a diagnostic capability will also exist to detect faults in the brake system which do not cause any of the conditions explicitly listed in S5.3.1. That is, a fault may be detected in a redundant component that does not affect brake system performance. However, such a fault would leave the brake system vulnerable to a single additional failure that could substantially diminish braking capability.

A specific example of this with respect to the GMEV's brake system could be a stuck solenoid within the hydraulic unit. Such a failure would not necessarily have an effect on brake system performance, nor would any of the explicit conditions listed in S5.3.1 be exhibited. Yet such a fault would decrease the overall reliability of the brake system and make the system more vulnerable to a significant degradation in performance should a second failure occur.

We believe that the opportunity should be afforded to alert the driver to brake system faults of the nature described above. Accordingly, we request the agency's concurrence that the language of S5.3.1 allows for illumination of the brake telltale when a fault is detected which INCREASES THE LIKELIHOOD of a substantial degradation in brake system performance, even if the fault in question does not strictly fall into any of the categories listed in that section of FMVSS 105.

SUMMARY

GM would be pleased to discuss with the agency any of the issues that we propose be handled through interpretation. Our overriding interest is to provide the agency with the information it needs to quickly resolve any and all compliance questions involving the applicability of FMVSS 101 and 105 to the GMEV so that design work can continue and plans to offer the GMEV to the public can be carried out promptly.

We appreciate the NHTSA's consideration of these proposed interpretations. If the agency has any questions or requires additional information please contact me at (313) 974-1704.

Attachment

USG 2938 - Attachment 1 -- USG 2886 Part III. (Text omitted here.)