Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1995-12-14
1997-07-15
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031131, B60T 836, B60T 850
Patent
active
056476442
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Application No. PCT/EP94/03622.
FIELD OF THE INVENTION
The present invention pertains to a solenoid valve, especially for hydraulic brake systems with slip control, having an opening formed in an annular piston in the valve and through which pressurizing medium passes to control brake operation.
BACKGROUND OF THE INVENTION
The intermittent control of pressurized medium in slip-controlled brake systems by digitally switchable inlet and outlet valves leads to undesired sound emission as a consequence of the pulsed changes in pressure.
It was found in the brake systems described in German Patent Application No. P 43 19 227.0 that the solutions suggested for arranging the annular piston provided with a switchable diaphragm in the inlet valve do not always make it possible to avoid an unintended switching of the annular piston into the diaphragm position during manual, slip-free brake actuation. The annular piston having a "switchable diaphragm" moves between a first position and a second position (i.e., "diaphragm position"). At the first position, a pressurized medium flow path across a face of the annular piston extends unhindered from the valve seat to a pressure line, in parallel to the diaphragm. At the second position, this pressurized medium flow path is closed and pressurized medium flows from the valve seat to the pressure line exclusively through the diaphragm. An undesired premature activation of the switchable diaphragm associated with the inlet valve cannot be ruled out with sufficient certainty, especially in the case of rapid actuation of the brake (e.g., panic braking). In the event of such premature activation of the switchable diaphragm, the feel of the pedal and the vehicle-specific pressure build-up gradient will change. A reduction in the pressure build-up gradient brought about by the diaphragm action inherently leads to a reduction in braking power.
It was therefore proposed in German Patent Application No. P 43 32 819.9 that fixed diaphragms be additionally arranged upstream or downstream of the solenoid valve (inlet valve), but the result is that the switchover pressure or the switching pressure difference of the switchable diaphragm remains relatively high, which may lead to undesired fluctuations in the volume flow during the brake pressure control.
SUMMARY OF THE INVENTION
A task of the present invention is therefore to prevent a premature, undesired activation of the switchable diaphragm during the slip-free normal braking phase, while possibly maintaining unchanged the simple design of the brake system disclosed in German Patent Application No. P 43 19 227.0.
According to the present invention, a pressurized agent channel arranged upstream of the valve seat has a portion having a reduced cross section (i.e., a channel constriction). Opening into this channel is a channel branch of small nominal diameter, extending in the direction of a front surface of the annular piston. Consequently, the pressure energy of the pressurized medium column flowing into the solenoid valve is converted in the portion having a reduced cross section into kinetic energy, which initiates a pressure gradient in the channel branch.
Due to the design according to the present invention, the pressure gradient generated directly at the narrowest flow cross section is used to hold the annular piston in the deactivated switching position in order to prevent premature switching of the annular piston into the diaphragm position during slip-free normal braking.
Additional features, advantages and possible applications of the present invention will become apparent from the following description of a number of exemplary embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 shows a partial view of a solenoid inlet valve on an enlarged scale, with the channel arrangement according to the present invention under the valve-closing member,
FIG. 2 shows an alternative embodiment of the present invention, and
FIG. 3 show
REFERENCES:
patent: 5076538 (1991-12-01), Mohr et al.
patent: 5290096 (1994-03-01), Beck et al.
patent: 5333946 (1994-08-01), Goossens et al.
patent: 5370450 (1994-12-01), Volz et al.
patent: 5388899 (1995-02-01), Volz et al.
patent: 5401087 (1995-03-01), Goossens
patent: 5443309 (1995-08-01), Beck
English translation corresponding to WO 9 429 150, entitled Hydraulic Brake System with Slip Control and labeled PC 7511.
English translation corresponding to DE 4 332 819, entitled Hydraulic Brake System with Slip Control and labeled PC 7564.
Volz Peter
Zaviska Dalibor
Butler Douglas C.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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