Interpretation ID: nht88-2.34

TYPE: INTERPRETATION-NHTSA

DATE: 05/27/88

FROM: TEVES, ALFRED -- TEVES TECHNICAL SERVICE

TO: ERIKA Z. JONES -- NHTSA CHIEF COUNSEL

TITLE: BRAKE FLUID RESERVOIR DESIGN ACCORDING TO FMVSS 105 REQUEST FOR INTERPRETATION

ATTACHMT: OCTOBER 9, 1981 LETTER FROM BERNDT TO KAWANO, OCTOBER 3, 1988 LETTER FROM JONES TO BURKARD, EBNER, AND TEVES, FEBRUARY 3, 1981 LETTER FROM KAWANO TO BERNDT, JULY 10, 1974 LETTER FROM DYSON TO NAKAJIMA, AND MAY 24, 1988 LETTER FROM TEVES TO GREG ORY

TEXT: during his visit at NHTSA on May 17th, 1988 Mr. Ebner presented our new brake system to your experts.

We request an interpretation of S 5.4.2 (reservoir capacity) and S 5.3.1/b (Fluid level indicator) of FMVSS 105, with respect to the proposed brake fluid reservoir shown in the attachment.

Essential is the existence of an ancillary brake unit in this new brake system. This ancillary brake unit serves the brake circuits 1 and 2 directly.

Compared with a conventional reservoir the proposed brake fluid reservoir's distinctive feature is the exit for the ancillary unit.

This ancillary unit serves the brake circuits 1 and 2. When the brake pedal is released, the used brake fluid will flow back to the reservoir. This unit does not cause any additional fluid volume.

Teves interprets standard 105 S 5.4.2 and S 5.3.1/b) as follows:

1. The total minimum capacity of a reservoir shall be equivalent to the fluid displacement resulting when all the wheel cylinder or caliper pistons serviced by the reservoir move from a new lining, fully retracted position to a fully worn, fully applied position.

2. Reservoir systems utilizing a portion of the reservoir for a common supply to two or more subsystems, individual partial compartments shall each have a minimum volume of fluid equal to at least the volume displaced by the master cylinder piston servi cing the subsystem, during a full stroke of the piston.

3. The total amount of the fluid shall be solely available for the brakes.

4. The ancillary unit shall not use brake fluid for other purposes than for the brake circuits.

5. A drop in the level of brake fluid in any master cylinder reservoir compartment to less then the recommended safe level specified by the manufacturer ot to one-fourth of the fluid capacity of that reservoir compartment, which ever is greater.

The ancillary unit does not diminish the built in safety features of the reservoir. In case of a circuit failure, volume 1 resp. volume 2 remains still available for the brakes and the fluid level indicator lamp gives a warning to the driver.

In case of a fluid leakage in the ancillary unit, the unit is switched off. The fluid level indicator lamp and additional a separate warning lamp gives a warning to the driver. The fluid volumes 1 and 2 remain in the reservoir and are fully usable fo r applying the brakes with the master cylinder.

Accordingly, we believe that the proposed brake fluid reservoir described in this letter and presented to your experts fulfils the requirements S 5.4.2 and S 5.3.1 (b) of FMVSS 105.

We ask that you confirm our interpretation at your earliest convenience.

FMVSS 105, S 5.4.2: V = V[1] + V[2] + V[3] + V[4] V: GREATER OR EQUIVALENT TO FLUID DISPLACEMENT RESULTING WHEN ALL W/C MOVE FROM A NEW LINING POSITION TO A FULLY WORN LINING POSITION. MAX V[4] FLI V[3] V[1] V[2] BRAKE BRAKE ANCILLARY UNIT CIRCUIT 1 CIRCUIT 2 SERVICING BRAKE CIRCUIT 1+2

FMVSS 105, S 5.3.lb V[1] + V[3] >/- 0.25 (V[1] + V[3] + V[4]) V[2] + V[3] >/- 0.25 (V[2] + V[3] + V[4])

V[1] VOL. DISPLACEMENT EQUIVALENT TO A V[2] >/- FULL STROKE OF THE RELATED M/C-PISTON. TEVES MASTER CYLINDER RESERVOIR DESIGN ACCORDING TO FMVSS 105 3-34513-07