Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1998-09-14
2000-11-21
Schwartz, Chris
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031132, B60T 832
Patent
active
061492477
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a hydraulic vehicle brake system for a vehicle with an external power service brake system and a muscle power auxiliary brake system.
A vehicle brake system of this kind has been disclosed by the S.A.E. Paper 96 0991. The known vehicle brake system has a master cylinder which is connected to wheel brake cylinders with the interposition of at least one block valve. Furthermore, the known vehicle brake system has a hydraulic pump that aspirates the brake fluid from a reservoir and feeds it into a high pressure hydraulic accumulator. The high pressure hydraulic accumulator constitutes an external energy accumulator and the hydraulic pump, together with the high pressure hydraulic accumulator, constitutes an external energy source. The wheel brake cylinders are connected to the high pressure hydraulic accumulator or to the pressure side of the hydraulic pump by way of brake pressure increase valves. The wheel brake cylinders can be connected to the reservoir by way of brake pressure reduction valves connected after each of the wheel brake cylinders.
For external power braking, the at least one block valve is closed and the brake pressure increase valves are opened so that pressurized brake fluid flows out of the high pressure hydraulic accumulator into the wheel brake cylinders. Desired wheel brake pressures in the wheel brake cylinders and brake moments thus generated can be adjusted and changed by means of the brake pressure increase valves and the brake pressure decrease valves in a manner that is known per se. The master cylinder, which is hydraulically separated from the wheel brake cylinders during external power braking by means of the at least one closed block valve, is thus used exclusively as a brake moment set point adjuster and the wheel brake pressure is adjusted as a function of the actuation of this set point adjuster.
For auxiliary braking, e.g. upon failure of the external energy source, braking can be executed in the conventional manner by means of the master cylinder, for example, by means of automatic opening of the block valve and the automatic return of the brake pressure increase valves and brake pressure decrease valves to their closed position.
ADVANTAGES OF THE INVENTION
The vehicle brake system according to the invention has a low-pressure hydraulic accumulator, from which the hydraulic pump aspirates brake fluid and into which the brake fluid flows from the wheel brake cylinders, when the brake pressure decrease valve is opened in order to reduce the wheel brake pressure. Through the use of the low pressure hydraulic accumulator, a brake fluid reservoir can be eliminated, at least for the external power brake system, the hydraulic pump is not connected to a brake fluid reservoir of the master cylinder, and during external power braking, no brake fluid flows from the wheel brake cylinders back in the direction of the master cylinder or into its reservoir. The external power brake system constitutes a closed system that assures a high degree of reliability against failure. No hydraulic connections to the reservoir of the master cylinder are required and no hydraulic lines are needed as an intake line for the hydraulic pump and as return lines from the wheel brake cylinders. First, this has the advantage that an existing master cylinder with a brake fluid reservoir placed on it can be used without connections having to be attached to the reservoir. Another advantage is that this kind of connections and hydraulic lines bring with them the risk of leaks. A leak in one of these connections of the reservoir or of the hydraulic lines mentioned would have the fatal result that it would affect both the external power brake system and the muscle power brake system and thus render the entire vehicle brake system nonfunctional. The vehicle brake system according to the invention therefore has the advantage that its external power service brake system and its muscle power auxiliary brake system are redundant and thus has the advantage of a considerably incr
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Binder Juergen
Hofmann Dirk
Pfau Martin
Schunck Eberhardt
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Schwartz Chris
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