Interpretation ID: nht74-1.7

DATE: 12/18/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

Dec 18 1974 N40-30 (TWH)

Mr. J. R. Farron Group Director of Engineering The Bendix Corporation 401 Bendix Drive P. 0. Box 4001 South Bend, Indiana 46634

Dear Mr. Farron:

This responds to your undated letter which requests a determination that the Bendix "Hydro-boost" qualifies as a brake power assist unit" as that term is defined in Standard No. 105-75. You describe the unit as designed with a "push through" cabability in both the "normal" and "failed power" operating conditions, and with an accumulator that permits low pedal effort for a limited number of brake applications after a power failure has occurred.

The following definitions distinguish a "Brake power assist unit" from a "Brake power unit":

"Brake power assist unit" means a device installed in a hydraulic brake system that reduces the operator effort required 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.

"Brake power unit" means a device installed in a brake system that provides the energy required to actuate the brakes, either directly or indirectly through an auxiliary device, with the operator action consisting only of modulating the energy application level.

In the preaamble to Notice 8 of Docket No. 70-27, we made the further clarification that the capabilities of the unit in the "failed power" condition determine whether it is a brake power assist unit. A copy of this discussion is enclosed. Because the Bendix "Hydro--boost" in the "failed power" condition does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control (i.e.. with "push through" capability), it qualifies as a brake power assist unit under the definitions of Standard No. 105-75.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

Enclosure SECURITY=000