Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1991-05-28
1993-02-23
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 962, 303 975, 3031131, 3031161, 3031191, 303900, 303901, B60T 832, B60T 1316
Patent
active
051884330
DESCRIPTION:
BRIEF SUMMARY
INTRODUCTION
The present invention relates to an anti-lock hydraulic brake system comprising at least one wheel brake and an auxiliary-pressure source, an inlet valve being inserted into the pressure conduit between the auxiliary-pressure source and the wheel brake, and the wheel brake being connected to a return conduit via an outlet valve, with a differential pressure limiter being inserted into the conduit between the auxiliary-pressure source and the inlet valve, the control piston of which limiter is acted upon by both the force of a spring and the pressure in the wheel brake in a manner opening the conduit.
BACKGROUND OF THE INVENTION
A brake system of the type described above German Patent application is known from the P 38 42 699.4 filed Dec. 19, 1988. The differential pressure limiter ensures that a defined pressure prevails a cross the inlet valve. It has been proven that employment of this arrangement reduces the switching noises made by the inlet valve considerably. Yet there is also created a disadvantage: the inlet valve exhibits a throttling characteristic when in its opened position. On the one hand, this is due to design reasons, since the valve passage cannot be opened as wide as desired. On the other hand, however, there are considerations in respect of control technology: the velocity of pressure increase is to be limited in the pressure-build-up phase of a braking operation with anti-lock control in order to prevent the pressure from rising beyond a specific amount.
Once the master brake cylinder is actuated quickly and abruptly during braking without anti-lock control, a large quantity of pressure fluid is pressed through the throttle of the inlet valve in a short time. This causes a pressure difference across the inlet valve, the consequence thereof being in turn that the differential pressure limiter will close. Pressure build-up is decelerated. This phenomenon occurs in particular when the brake fluid is cold and has a high viscosity, at which time a slow pressure fluid speed will suffice to generate the critical pressure difference across the inlet valve.
BRIEF DESCRIPTION OF THE INVENTION
It is, therefore, the object of the invention to preserve the advantages of a differential pressure limiter, on the one hand, and to accomplish a rapid unhindered pressure build-up over the entire temperature range of the brake fluid in the event of braking without anti-lock control, on the other hand.
This object is achieved in that a temperature-responsive force-generating element acts upon the control piston.
Most simply, such an element can be a bimetal spring.
Principally, two ways of solution can be followed. On the one hand, the bimetal spring can be arranged in parallel with the control spring of the pressure limiter. When constructing the spring so as to expand when exposed to cold temperatures, an additional force generated by the bimetal spring will be provided at low temperatures besides the force of the control spring. Thereby, the switch point of the differential pressure limiter is raised, in consequence whereof the differential pressure limiter will not close, not even in the presence of high pressure difference across the inlet valve. In the presence of high temperatures, the bimetal spring will compress so much that its length becomes smaller than the coil-bound length of the control spring. Subsequently, the bimetal spring has no influence on the control behavior of the differential pressure limiter so that the switch point is determined by the control spring alone.
Another possibility resides in arranging the bimetal spring between the control piston and a tappet which abuts on the closure member of the differential pressure limiter. When the bimetal spring expands at cold temperatures, the closure member will be forced to lift from the valve seat so that the valve passage will remain open in any case irrespective of the movement of the control slide due to a pressure differences across the inlet valve.
The bimetal spring can be realized in various shapes. Individual b
REFERENCES:
patent: 3819235 (1974-06-01), Bowler et al.
patent: 4762300 (1988-08-01), Inagaki et al.
patent: 5098173 (1972-03-01), Beck et al.
Patent Abstracts of Japan vol. 13 No. 318 Jul. 19, 1989.
Patent Abstracts of Japan vol. 5, No. 108 Jul. 14, 1981.
Patent Abstracts of Japan vol. 11 No. 146 May 13, 1987.
Beck Erhard
Reinartz Hans
Steffes Helmut
Volz Peter
Alfred Teves GmbH
Butler Douglas C.
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