Interpretation ID: nht91-3.41

DATE: May 8, 1991

FROM: Paul Jackson Rice -- Chief Counsel, NHTSA

TO: John E. Calow -- Senior Safety Engineer, Oshkosh Truck Corporation, Chassis Division

TITLE: None

ATTACHMT: Attached to letter dated 3-4-91 from John E. Calow to Chief Council, NHTSA (OCC 5805)

TEXT:

This responds to your letter of March 4, 1991, which requested an interpretation of Standard No. 105, Hydraulic Brake Systems. You asked whether the standard specifies parking brake actuation times for hydraulic brake systems. In a telephone conversation with Mark A. Holmstrup of my staff, you also asked whether the standard specifies a certain percentage of braking torque or brake pedal force to actuate the brake stop lamp switch. You stated that you have designed a braking system where the brake pedal must be depressed 1/8" before the brake stop lamp switch is actuated. I will answer your questions in that order.

By way of background information, the National Highway Traffic Safety Administration 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 or equipment comply with applicable standards. The following represents our opinion based on the facts provided in your letter and in the aforementioned telephone conversation.

Standard No. 105 does not expressly provide that the parking brake must be actuated within some specified period of time. However, S5.2 of Standard No. 105 provides that the standard's parking brake holding requirements (set forth in S5.2.1, S5.2.2, and S5.2.3) must be met when a vehicle is tested according to the procedures specified in S7. S7.7.1.3 provides that a vehicle's parking brake is applied by a single application of the force specified by the standard, except that a series of applications to achieve the specified force may be made in the case of a parking brake system design that does not allow the application of the specified force in a single application. The parking brake test procedure is continued in S7.7.1.4, as follows:

Following the application of the parking brake in accordance with S7.7.1.3, release all force on the service brake control and commence the measurement of time if the vehicle remains stationary. If the vehicle does not remain stationary, reapplication of the service brake to hold the vehicle stationary, with reapplication of a force to the parking brake control at the level specified in S7.7.1.3(a) or (b) . . .may be used twice to attain a stationary position.

The parking brake test procedure specified in S7 does not provide for any waiting period between the time a vehicle's parking brake is applied in accordance with S7.7.1.3 (by means of applying a specified force to the parking brake control) and the time all force on the service brake control

is released to see if the vehicle remains stationary. Thus, during compliance testing by the agency, all force on the service brake control would be released as soon as the specified force had been applied to the parking brake. After the release of force on the service brake control, the agency would determine if the vehicle remains stationary.

If the vehicle did not remain stationary, S7.7.1.4 specifies that forces may be reapplied and released twice more if necessary. After each reapplication and release of the specified forces, the agency would determine if the vehicle remains stationary. If the vehicle does not remain stationary after the two additional reapplications and releases of the specified forces, the parking brake would not comply with Standard No. 105.

Regarding your second question, Standard No. 105 does not specify actuation forces for brake stop lamp switches. However, Standard No. 108, Lamps, Reflective Devices, and Associated Equipment, is relevant to your question. Section S5.5.4 of the standard requires that "(t)he stop lamps on each vehicle shall be activated upon application of the service brakes."

In interpreting S5.5.4, a distinction must be made between depression of the brake pedal by a driver and application of the service brakes. When a brake pedal is depressed by a driver, there may be a small amount of "free-play" before the service brakes begin to apply. Since section S5.5.4 requires the stop lamps to be activated "upon application of the service brakes," the stop lamps must be activated as soon as the service brakes begin to apply. Thus, the stop lamps would not need to be activated during any initial free-play of the brake pedal which does not result in application of the service brakes. The stop lamps must, however, be activated as soon as any measurable brake torque occurs.

I hope that this information has been helpful. Please feel free to contact us if you have any further questions.