Patent GB-1447362-A (GB)
Title: Anti-lock vehicle brake systems
IPC: B60T8/1761
Filed: 1972-09-18
Abstract: 1447362 Anti-skid systems MULLARD Ltd 29 Aug 1973 [18 Sept 1972] 43228/72 Heading F2F In a fluid-pressure-operated anti-lock vehicle brake system of the character comprising a fluid pressure source, e.g. master cylinder 2 which in response to a braking action 4 provides fluid under pressure via a fluid pressure connection 11, 12 to the brake 10, an anti-lock control valve 5, wheel-movement sensing means 6 for producing an output function for causing actuation (via electronic circuit 7) of the antilock control valve 5 when, e.g. wheel slip exceeds a chosen value, and a relief connection 18, 17 interconnected with the fluid pressure connection 11, 12, or, as shown, with the brake 10 and opened when appropriate by the valve 5, the relief connection includes at the outlet side of the anti-lock control valve 5 a fail-safe arrangement 1 for comparing the fluid pressure at the outlet side of the anti-lock control valve with the fluid pressure at the brake 10. This arrangement must satisfy both of the following conditions:- (a) if there is fluid flow at the outlet side of the anti-lock control valve 5, due to its being at least partially unsealed, at the onset of brake pressure application when the anti-lock control valve is unactuated, this results in a pressure build-up at the outlet side which causes the fail-safe arrangement 1 to seal the connection thereby preventing displacement of fluid through it; (b) if there is no fluidpressure build-up at the outlet side because the anti-lock control valve is sealing correctly, at the onset of brake pressure application, the fail-safe arrangement 1 is responsive to the fluid pressure at the brake 10 to unseal the relief connection 18, 17 and thereafter maintain it unsealed in spite of subsequent build-up of fluid pressure at the outlet side of valve 5 due to any bona fide actuation of it. In operation, before brake-pressure is applied, and assuming valve 5 is not faulty, plunger 29 is biased by a spring 35 to a normal position cooperating with seat 32, Fig. 1. On brake application, fluid pressure at 12 is communicated via connection 18 and armature 14 to region 33 and thence to the underside of plunger 29, and quickly exceeds the force of spring 35 while chamber 26 is devoid of pressure, so plunger 29 is raised, thereby unsealing port 28. If the antilock control valve is now energised, relief flow is from connection 18 via armature 14, port 27, chamber 26, port 28, connection 17 and reservoir 19, where piston 20 is displaced to the right so that its stem 21 restricts fluid flow into line 12. Because of the fluid pressure drop between the inlet and outlet sides of the valve seal 16 when valve 5 is energised, fluid pressure at the lower end of plunger 29 remains sufficiently high to keep the plunger off seat 32 (until a low value of braking pressure exists). (When valve 5 is de-energised on wheel-recovery, pump 25, 22, 23 moves sufficient fluid from reservoir 19 to pressure line 11 to permit piston 20 to return to the left). Pail-safe operation.-If valve 5 is fully open, due to malfunction, before brake pressure is applied, when brake pressure applied the force due to the pressure are a product and the spring at the upper end of plunger 29 is greater than that due to the pressure-area product at the lower end, so the plunger remains seated, so outlet 28 remains sealed and braking pressure can build up, braking being intended. If valve 5 is only partially open (due to grit, &c.) but sufficiently so to permit an adequate build-up of pressure in chamber 26 as just described, the plunger again remains seated. The fail-safe operation in both cases is made possible by the absence of significant pressure drop across the already-open valve 5 due to relatively-slowlyincreasing braking pressure at the start of a brake application. Anomalous operation due to prolonged energisation of valve 5 when the vehicle is on a slippery road surface may be prevented by the modification depicted in either Fig. 2 or Fig. 3 (not shown).