Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Patent
1997-04-10
2000-06-06
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
303 969, B60T 1134
Patent
active
060709502
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a braking control valve for interposition between a source of hydraulic pressure and a brake circuit of an automobile vehicle and comprising: a housing provided with at least one bore; a hydraulic piston sliding in this bore and defining therein first and second pressure chambers sealed from each other by means of an elastic annular seal surrounding the piston and capable of communicating selectively with each other through a one way valve installed in a passage in the piston, the first and second chambers being connected in use respectively to the source of pressure and to the brake circuit; and a tappet acting on the one way valve in a direction such as to enable it to open when a relatively low pressure exists in the second chamber, whereas the piston slides axially in the bore under the influence of an increase in pressure in the second chamber in a direction such as to enable the one way valve to close.
BACKGROUND OF THE INVENTION
Braking control valves are well known in the prior art, as illustrated for example in the patent documents U.S. Pat. Nos. 4,615,566, 4,624,507, and EP 0 223 641, and enable a modified braking pressure to be developed at their outlet and applied to the rear brakes of a motorised vehicle which is related to the braking pressure applied both to their inlet and to the front wheels of the vehicle, but is nonetheless lower than the front wheel braking pressure at values greater than a defined threshold value.
One of the problems encountered in the design of such control valves resides in the difficulty of obtaining the desired variation of the outlet pressure relative to the inlet pressure and, more precisely, of avoiding that the relationship between the outlet pressure and the inlet pressure contains an anomaly, or "flat", corresponding to a more or less local defect in the variation of the outlet pressure.
SUMMARY OF THE INVENTION
In this context, the invention has as object to provide a control valve which is free from any anomaly of this kind and resides in the dual virtue of having identified the cause of this anomaly and having provided a remedy for it.
To this end, the braking control valve of the invention is characterised essentially in that the annular seal is fitted without axial clearance in a groove which is formed in the piston and which comprises a first bearing surface of circular ring shape on the side of the first chamber, a second bearing surface also of circular ring shape on the side of the second chamber, and a cylindrical bottom surface connecting the first and second bearing surfaces, the groove thus presenting a rectangular cross section, in that the seal presents a circumference which is at least partially cylindrical and which makes contact between the seal and the bore, in that the seal presents an annular zone which is also of circular ring shape facing the second bearing surface by means of which it lies flat on the second bearing surface, and in that the seal presents at least relative to the first bearing surface and to the cylindrical bottom surface recesses communicating with the first chamber to enable the pressure existing in the first chamber to deform the seal radially by urging it against the bore.
In accordance with the simplest embodiment envisaged, the seal is symmetrical relative to a median plane, while the first and second bearing surfaces of the groove have different external radiuses, and the annular zone presents an internal radius which is greater than the external radius of the first bearing surface and less than the external radius of the second bearing surface.
Other features and advantages of the invention will appear clearly from the following description, given by way of indication and not by way of limitation, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall sectional view of a control valve in accordance with the invention;
FIG. 2 is an enlarged view showing the piston of the control valve of FIG. 1;
FIG. 3 is an enlarged detail vie
REFERENCES:
patent: 3992063 (1976-11-01), Falk
patent: 4615566 (1986-10-01), Perrin
patent: 4624507 (1986-11-01), Carre et al.
patent: 4982999 (1991-01-01), Rossigno et al.
Bacardit Juan Simon
Cortes Guasch Esteve
Sacristan Fernando
Bosch Systemes de Freinage
Comstock Warren
Graham Matthew C.
McCormick, Jr. Lee H
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