Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1992-03-06
1994-02-01
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 10, B60T 1318
Patent
active
052826775
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an anti-lock hydraulic brake system with at least one wheel brake and an auxiliary pressure source, wherein an inlet valve is inserted into the line between the auxiliary pressure source and the wheel brake and the wheel brake is connected to a return line via an outlet valve, wherein a differential pressure limiter is disposed within the line between the auxiliary pressure source and the inlet valve, the closure member of which is acted upon by both the force of a valve spring and the pressure in the wheel brake in a manner opening the line.
A brake system of this type is known from German published patent application 38 42 699.1. The latter describes a dual-circuit brake system with a tandem master cylinder and a pump for each brake circuit. The wheel brake cylinders each communicate via a respective inlet valve with the pressure line leading to the pump and, also with the brake line leading to the master brake cylinder. Each brake cylinder communicates via a respective outlet valve with the return line to the supply reservoir. Each inlet valve is normally open, while the outlet valves are normally closed.
The rotational behavior of the wheels is constantly monitored during a braking operation. In the event of an imminent locked condition of any one of the wheels, the drive of the pump is activated, and the inlet and outlet valves of the imminently locking wheel controlled such as to develop an amount of pressure in the wheel brakes which correlates with an optimal slip value of the wheel. To decrease the pressure, the outlet valve is opened and the inlet valve closed. Both valves are closed to retain the pressure, whilst for the pressure increase the inlet valve is open and the outlet valve is closed.
The inlet and the outlet valves are electromagnetically operated valves having a closure member which is seated on a valve seat.
Starting from a brake fluid pressure which is in excess of the pressure which corresponds to the force of the valve spring, a differential pressure limiter between the auxiliary pressure source and the inlet valve causes a defined constant pressure gradient to prevail on the inlet valve which is determined by the valve spring. This pressure gradient can be adjusted to 25 bar for example, and hence is considerably less than the pressure gradient which usually occurs when an emergency stop anti-lock controlled braking operation is performed by the brake system.
However, it has been discovered that dynamic actions in the return line and in the differential pressure limiter can cause the pressure in front of the inlet valve to build up to a level higher than what is desired.
Hence the present invention has for its object to develop measures ensuring that the pressure gradient at the inlet valve remains constant under all circumstances.
SUMMARY OF THE INVENTION
This object is achieved in that a pressure relief valve opening towards the wheel brake is connected in parallel to the inlet valve.
To realise the circuitry in a compact unit which conforms to all demands made on the stability of the control operation in the differential pressure limiter, the differential pressure limiter has a housing which incorporates three chambers, a control chamber, an inlet chamber, and an outlet chamber. A valve member is included comprised of a stepped piston furnished with an annular groove. The housing is provided with at least one port terminating into the annular groove of the stepped piston, and a piston part adjacent to the annular groove is slidable in the way of a valve slide to close the port.
The differential pressure limiting valve is thus designed as a valve slide which, in addition, permits the pressure relief valve to be incorporated in the piston of the valve slide.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a hydraulic circuit diagram of the brake system including a master cylinder shown in cross-section.
FIG. 2 is a cross sectional view of a first embodiment of a differential pressure limiter included in the brake system o
REFERENCES:
patent: 4828338 (1989-05-01), Ocvirk et al.
patent: 4964681 (1990-10-01), Burgdorf et al.
patent: 5178442 (1993-01-01), Toda et al.
Alfred Teves GmbH
Lewis J. Gordon
Muratori Alfred
Oberleitner Robert J.
Seitter Robert P.
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