Interpretation ID: aiam1239
U.S. Resident Engineer for Citroen S.A
U.S. Technical Research Corp.
801 Second Avenue
New York
New York 10017;
Dear Mr. Belier: This is in reply to your letter of July 24, 1973, asking for a interpretation of several aspects of Standard No. 105a.; You have asked the following questions >>>'1. *Paragraph S5.1.2 'Partial failure.*' It is required that '...the remaining portion(s) of the service brak system shall continue to operate...' What is the exact meaning of 'continue to operate'? Does it mean that the remaining portion of the brake system must be permanently fed or does it mean that it is required to have *temporary* braking with the operative portion reserve capability? In this latter case, how many brake applications are required?'<<<; 'Continue to operate' means that the portion of the brake system tha has not failed continues to operate indefinitely, i.e., to the point that it wears out or until a second failure occurs in the brake system. It requires a permanent feed and does not depend upon the reserve capability of operative portion of system.; >>>'2. *Paragraph S5.1.3.3 'Brake power units':* What exactly constitutes the power source? On the Citroen D and models, the front brake circuit is fed by a brake accumulator while the rear brake circuit is fed by the pressure prevailing in the read suspension. The brake accumulator and the rear suspension are fed from the high pressure source (which includes an HP pump, A pressure regulator and a main accumulator)...What is meant by 'inoperative brake power unit'? Does that mean that the high pressure pump *only* is inoperative or also the other components of the power source (main accumulator and regulator)?...What is meant by 'when the inoperative unit is depleted of all reserve capability' (paragraph S5.1.3.3.(ii))? Are we correct in assuming that it means that *only* the main accumulator is depleted of reserve capability? (It is obvious that if one considers that not only the main accumulator, but also the brake accumulator and the rear suspension are depleted, no braking is possible).'<<<; The power source consists of pumps, accumulators and/or back up system such as a separate electric or hydraulic pump, etc. A primary power source would be the pump, while the accumulators would constitute a secondary source and would be the portions used in optional test. A high pressure source would include the pump, regulator and, in Citroen's case, the main accumulator.; 'Inoperative brake power unit' could mean that the (1) main pump i out, but the accumulators are functioning, (2) the main pump is operating but only one brake accumulator is operating, (3) the pump and brake accumulator are operating, but the suspension accumulator is out, (4) the pump or accumulator is out, and the system is operating on reserve or backup pump. This list is meant to be illustrative rather than exhaustive.; 'When then inoperative unit is depleted of all reserve capability means that one of the units (pump, accumulator, etc.) is completely nonfunctional, e.g., the pump has failed, the accumulator has failed, the check valve has failed, etc.; >>>'3. *Paragraph S7.10.2 'Optional procedures'* We believe that the subparagraph 'b' (vehicles with brake power unit applies to our vehicles.; The test procedure mentioned in paragraph S7.10.2(a) cannot be applie to our vehicle since, if the system is depleted of '*any residual* brake power reserve capability', it is obvious that no braking is possible. We believe that the power source *only* should be depleted of any residual reserve (HP pump inoperative, main accumulator depleted), but not the entire brake system. Since by definition, a 'brake power unit' is a unit where the operator action consists 'only of modulating the energy application level, ' but not of supplying energy to the system, it is obvious that no braking is possible if all internal residual energy left in the brake system is depleted (since, in this case, there would be no energy available for braking from either the HP source, the driver or the system).<<<; S7.10.2(b) does apply to Citroen. Your comments on S7.10.2(a) ar correct.; Yours truly, Richard B. Dyson, Assistant Chief Counsel