Patent GB-1309199-A (GB)
Title: Valve device for dual hydraulic brake systems
IPC: B60T8/26
Filed: 1971-11-09
Abstract: 1309199 Pressure reducing valves for brake systems KELSEY HAYES CO 9 Nov 1971 [13 Nov 1970] 51968/71 Headings F2E and F2F A valve device for a hydraulic brake system having a master cylinder 12 adapted to separately supply fluid braking pressure for the front and rear brakes 14 and 16 of a vehicle comprises a housing 28 having an inlet 42 adapted to receive front fluid braking pressure, an inlet 38 adapted to receive rear braking pressure, an outlet 44 adapted to be connected to the front brakes of the vehicles for supplying braking pressure to the front brakes, and an outlet 40 adapted to be connected to the rear brakes of the vehicle for supplying fluid braking pressure to the rear brakes; a differential area member 46 located in the housing for axial movement therewithin for modulating the fluid braking pressure delivered from the rear brake pressure inlet to the rear brake pressure outlet and having a bypass valve portion interposed between said rear brake inlet and said rear brake outlet; and a second member 76 located in the housing adapted for axial movement therewithin in response to a predetermined reduction in the front braking inlet pressure relative to said rear braking inlet pressure, said second member including a bypass valve portion normally co-operable with the bypass valve portion on the differential area member but adapted to provide a bypass pressure transmission passage upon said axial movement of the second member whereby in use of the device substantially full braking pressure is transmittable to the rear brakes upon failure of braking pressure to the front. As shown, fluid braking pressure delivered at the inlet 38 causes a resultant force which acts on the differential area piston 46 against the bias of a spring 70 and when a predetermined pressure is attained the piston overcomes the spring loading and moves so that a shoulder 62 of the member engages a seat 64 to interrupt the transmission of full fluid pressure from the inlet to the outlet 40 and to the annular end surface to the right, as seen in the figure, of the shoulder; as the pressure increases the shoulder is moved into and out of engagement with the seat so as to modulate the fluid pressure to the rear brakes. A detent member 76 having an end 82 thereof slidable in the bore 55 of the piston is exposed to the fluid pressure of the front brakes and, in response to a failure of that pressure, moves to the right whereby an 0-ring 84 disengages from the periphery of the bore 55 so that fluid pressure in the chamber 56 is communicated to the housing bore 52 which in turn communicates via a clearance or recess 17, with a counterbore 109 communicable with the outlet 40, fluid pressure thereby being bypassed to the rear brakes and without being subjected to proportioning or modulating operation of the by-pass valve assembly 34. The valve plate 114  of the metering valve assembly 32 carries a sealing member 135 which in the leftward position of the valve plate engages a shoulder 132 but upon rightward movement of the valve plate fluid pressure passes from the inlet 42 through the peripheral serrations 134 of the valve plate and to the outlet 44 this latter movement being resisted by a spring 136. The member 135 is lifted from the shoulder either by a differential pressure across the valve plate and the member 135 or by abutment of a snap ring 138 on the rod 106 the rightward movement of which causes the flange of the retainer 92 to engage the non-serrated inner portion of the member 135 to interrupt fluid pressure transmission to the outlet 44. The member 76 has a detent portion 88 which, when a reduction of fluid pressure to either the front or rear brakes occurs, cams a plunger 100 upwardly by the ramp sides thereof to close contacts 104 of a brake failure warning indicator 36.