Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1996-04-15
1998-03-03
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 841, 3031161, B60T 834, B60T 848, B60K 2816
Patent
active
057227381
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Appl Ser. No. PCT/EP94/02350.
TECHNICAL FIELD
The present invention generally relates to a hydraulic brake system and more particularly relates to brake slip control and tranction slip control for use in vehicle brake systems.
BACKGROUND
A brake system of this type is disclosed in German patent No. 34 39 408. The known brake system operates by the feedback principle during brake slip control operations. The return pump is of the self-priming type and aspirates pressure fluid from the low-pressure reservoir through a first suction valve and a first suction line for brake slip control. For traction slip control, the return pump aspirates pressure fluid from the pressure fluid reservoir through a second suction valve and a second suction line including a change-over valve, through the brake line and the master cylinder. Compared to other brake systems, in which the two suction lines are connected to conduct fluid through a common suction valve to the suction side of the pump and in which an additional suction valve is arranged in the first suction line preventing the development of a vacuum in the low-pressure accumulator, the parallel arrangement of the suction valves has the advantage that only one suction valve must be overcome during brake slip control and traction slip control operations. This reduces throttling effects, so that the delivery rate of the pump is improved.
A pump of this type is disclosed in German patent application, No. 40 27 794, for example. The pump described in the application is a radial piston pump with a delivery piston on which the valve seat for the suction valve is provided. The closure member of the suction valve is acted upon by a valve spring supported on the housing. The preload of the valve spring increases when the pressure chamber is decreased by a movement of the piston. The preload of the valve spring is at its maximum at the upper dead center of the piston, i.e. when the pressure chamber has its smallest volume. Thus, the opening pressure of the suction valve to be overcome is greatly increased compared to the lower dead center of the piston.
To provide a constant opening pressure of the suction valve, attempts have been made to captivate the valve spring of the suction valve. However, even this arrangement does not achieve the optimal flow characteristic curve of a pump of this type that is intended for use in a traction-slip controlled brake system, for example.
An object of the present invention is to provide a favorable structure of a generic brake system.
Another object of the present invention is to provide a hydraulic pump wherein the pilot pressure of the suction valve proximate the upper dead center of the delivery piston is lower than the pilot pressure proximate the lower dead center.
This object is achieved by the provisions indicated in the main claim and the subclaims.
The integration of both suction valves in the pump housing permits an easy assembly because there is no need for additional valves in the suction lines.
In an arrangement which is especially favorable in terms of mounting space, one of the suction valves is provided on the movable pump piston and the other one is arranged on the housing.
It is an advantage that the suction valves are axially opposed because, as a result, the axial dimensioning of a cylindrical pressure chamber is regardless of the position of the suction valves.
The difference of the pilot pressures during a brake slip control operation and a traction slip control operation can be produced by differently dimensioning the opening cross-sections of the suction valves.
Thus, an application of both closure members of the suction valves by a common compression spring in the direction so as to close is possible, because the opening pressures are determined by the different opening cross-sections.
Even when using a common compression spring for both closure members, the load of the closure member of the second valve can be reduced by a second compr
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Beck Erhard
Otto Albrecht
Reinartz Hans-Dieter
Butler Douglas C.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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