Patent GB-1409207-A (GB)
Title: Vehicle braking system including an anti-skid device
IPC: B60T8/42
Filed: 1973-12-20
Abstract: 1409207 Hydraulic anti-skid braking systems; pressure reducing valves NISSAN MOTOR CO Ltd and ATSUGI MOTOR PARTS CO Ltd 20 Dec 1973 [23 Dec 1972] 59020/73 Heading F2F A vehicle hydraulic anti-skid brake system with a master cylinder B and a brake cylinder 10 incorporates a modulator valve C disposed between the master cylinder B and the brake cylinder 10 and communicable with a source of fluid under pressure 48 by means of a control valve 60; the control valve 60 is normally open to allow fluid communication between the source 48 and the valve C but is operative to close to thereby block such communication and to connect the modulator valve C to a fluid reservoir under substantially atmospheric pressure in response to an electrical skid signal from a sensor 8 which signal is generated when the angular deceleration of a vehicle wheel is above a predetermined value; with such communication blocked a piston 38 in valve C is movable leftwardly to close a valve 35 to shut off the connection between the master cylinder B and the brake cylinder 10 and to relieve braking pressure; the system also includes a by-pass valve D communicating with the source 48 such that if the pressure of the source 48 drops below a predetermined value, causing operation of valve C and closure of valve 35, a by-pass fluid flow path is opened around the modulator valve C and through the by-pass valve D between the master cylinder B and the wheel cylinder 10 so that braking force is still available. As shown in Fig. 1, the modulator valve C comprises first and second pressure chambers 26, 28, the chamber 26 being connected to master cylinder B and the chamber 28 to an inlet 84 of by-pass valve D. The chambers 26, 28 are separated upon closure of the valve 35 which is acted on by the plunger portion 40 of the piston 38; the piston 38 is acted on by fluid under pressure in a chamber 32 connectable to the source 48 by the valve 60, the source 48 comprising a pump 50 connected through a check valve 52 to an accumulator 54 and with a regulator valve 56. The by-pass valve D comprises a valve spool 90 controlling communication between the inlet 84, on outlet 86 connected to wheel cylinder 10 and an inlet 88 connected directly to master cylinder B. A inlet 89 connects a chamber 72 to the source 48, so that fluid under pressure normally acts on portion 94 of the spool 90. During normal operation braking pressure is supplied from master cylinder B via chambers 26, 28 through open valve 35, to inlet 84 of by-pass valve D and thence through outlet 86 to brake cylinder 10. When the angular deceleration of the wheel exceeds the predetermined value, the valve 60 is operated to drain fluid from chamber 32, and the piston 38 moves rightwardly under the action of a compression spring 37, valve 35 closes and the volume of chamber 28 increases to reduce the braking pressure in cylinder 10 to eliminate the skid condition. When the skid signal ceases the valve 60 opens again. If the pressure of fluid supplied by the source 48 drops below a predetermined level the fluid drains from chamber 32 and from chamber 72; the piston 38 moves rightwardly to close valve 35 but so also closes spool 90 under the action of a spring 100 to shut off inlet 84 and to connect inlet 88 and outlet 86-braking pressure is thereby maintained. In the embodiment of Fig. 2 (not shown) a microswitch (122) generates an electrical signal when the spool (90) moves rightwardly upon failure of the source (48), and this causes the control valve (60) to move to its closed position to prevent loss of fluid from the chamber (32) and closure of valve (35). In the embodiment of Fig. 3 (not shown) the portion (94) of the spool (90) is formed with cam lobes (126a, 126b) co-operable with a spring biased cam follower (132) to accelerate leftward and rightward movement of the spool (90). In the embodiment of Fig. 4, the by-passvalve D is formed with tilting valves 182, 184, 186 co-operable with a valve spool 146 to control communication betwixt inlets 170, 172 outlets 168, 174 and a flow passage 166. During normal operation fluid from master cylinder B passes via inlet 172 through open valve 184 to outlet 168, thence through chambers 26, 28 of valve C to inlet 170, through open valve 186 to outlet 174 and to cylinder 10. Should the pressure source 48 fail, spool 146 moves rightwardly to close valves 184, 186 and open valve 182 whereby fluid from master cylinder B flows to brake cylinder 10 via inlet 172, through a passage 150a in spool 146, through opened valve 182 and passage 166 and thence into a line 161 also connected to outlet 174.