Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1992-07-16
1994-05-10
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031161, 303900, 303901, 3031191, 3031171, B60K 2816, B60T 832, B60T 840
Patent
active
053102533
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a braking pressure control device, in particular for automotive vehicles equipped with an anti-lock control system (ABS) and/or a traction slip control system (TSC).
The braking pressure control device of this type tends to form a residual pressure in the wheel brake when operating in the low-temperature range during the slip-controlled pressure reduction phase due to the viscosity of the brake fluid. Because of the unsatisfactory pressure relief of the wheel brake, in particular when disc brakes are used, the wheel acceleration ability may be impaired undesirably after opening of the outlet valve, since the pressure accumulated in front of the opened outlet valve may react on the piston in the wheel brake cylinder under the action of the auxiliary pressure pump during slip control. Also, the long control spring required due to the relatively high pressure to be reduced causes a related delayed response behavior during braking pressure control.
Therefore, it is an object of the present invention to improve upon a braking pressure control device of the type referred to in order to overcome the disadvantages described and to realize in a cost-saving fashion a slip-controlled pressure reduction phase with reduced formation of residual pressure in the wheel brake.
SUMMARY OF THE INVENTION
This object is achieved according to the present invention by a brake pressure control device including a stepped diameter outer piston with an inner piston slidable within the outer piston. An inlet valve is mounted in the outer piston which is held opon by the inner piston until the outlet valve is opened, the inlet valve then closing. Thereafter the outer piston acts as a modulator of outflow from the brake cylinder, acted on by a control spring and wheel cylinder pressure.
Hence a braking pressure control device is provided by a surprisingly simple arrangement which permits favorable pressure reduction gradients by way of a slidable piston furnished with a piston step subjected to the prevailing wheel cylinder pressure, while a corresponding design of the control spring safeguards a considerably improved control of the pressure fluid flow even in low-temperature operation.
In a preferred embodiment of the invention , the inlet valve has a closure member in direct contact with a first spring of low stiffness, while a second spring of greater stiffness acts on the inner piston in opposition to the first spring.
It is provided according to another aspect of the invention that the piston step on the larger front-face outer piston surface is acted upon by a control spring, movable into abutment on the valve housing. This accomplishes pressure reduction gradients which are favorable in terms of control technology, and an almost complete pressure relief of the wheel brake during the pressure decrease phase is permitted without regard to the temperature of the pressure fluid.
In order to enable modulation of the pressure fluid in correspondence with the wheel cylinder pressure, the channel connecting to the wheel brake is suitably arranged in the area of transition from the large diameter of the piston step to the smaller diameter.
To safeguard a functional control of the pressure fluid variation between the wheel brake and the outlet valve, the connecting channel emanating from the master cylinder is disposed in the area of the large diameter of the piston step.
DESCRIPTION OF THE DRAWINGS
The present invention will be explained hereinbelow by way of an embodiment according to the Figure, which is a fragmentary sectional view of a brake pressure control device according to the invention together with a diagrammatic representation of associated brake system components.
DETAILED DESCRIPTION
Referring to the Figure, the brake pressure control device 24 according to the present invention is utilized as part of a hydraulically operated automotive wheel brake system including at least one wheel brake cylinder 22, a brake pedal operated master cylinder 27, and a mot
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Alfred Teves GmbH
Butler Douglas C.
Lewis J. Gordon
Seitter Robert P.
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