GB1197114A - Improvements in or relating to Vehicle Skid Control Systems - Google Patents

Abstract

1,197,114. Anti-skid braking systems. KELSEY-HAYES CO. 27 May, 1968 [1 June, 1967]; No. 25278/68. Heading F2F. An anti-skid system comprises a brake fluid pressure modulating valve 24 which controls the pressure applied to the brake on detection of a skid to first reduce the pressure to a level at which skid no longer occurs, to then increase the pressure rapidly to an intermediate level and then gradually towards the original braking pressure. For controlling the braking of the rear wheels 10 of an automotive vehicle (or an aircraft) provided with hydraulically actuated drum brakes 12, the master cylinder 20 is connected to the brake cylinders via valve 24 energized by the output of a deceleration sensor 26, 28, 30 which produces an output when the sensed deceleration attains a preset magnitude. Valve 24 comprises a housing 40 divided into chambers 54, 50 by a diaphragm assembly 42, both sides of which are normally connected to a vacuum supply, the chamber 54 directly via vacuum inlet 52 and chamber 50 via connector 56, cavity 144, a normally open valve arrangement, passageway 176 and throttle valve 200. Mounted in the housing is a solenoid 230 connected to the sensor circuit 26 to be energized when a skid occurs to move its plunger 228 towards the left (as shown), resulting in movement of the diaphragm assembly to the left-hand side and the opening of throttle valve 200 to allow unrestricted connection between atmosphere and chamber 50. A piston 46 is biased against the centre of the diaphragm assembly to move therewith when the solenoid is energized. The piston is slidable in a cylinder 62 connected at 16 to the brake cylinders and connected via bore 92 to a second cylinder 60 housing a check valve 76 and. bleed valve 100 and connected at 18 to the master cylinder. Piston 46 is normally biased to maintain valves 76 and 100 open, and when the solenoid is energized is moved to the left to close both valves thereby disconnecting the master cylinder from the brake cylinders and increasing the volume of cylinder 62 occupied by the brake fluid. Upon de-energization of the solenoid, chamber 50 is immediately connected to vacuum, throttle valve 200 is not initially closed so that unrestricted evacuation of chamber 50 can take place with rapid increase of brake pressure caused by rapid movement of piston 46 back into cylinder 62. At the intermediate point the throttle valve 200 is closed to restrict the continued evacuation of chamber 50 and thereby reduce the rate at which braking pressure is reapplied. At the end of the return travel of piston 46 it first opens the bleed valve and subsequently the check valve so that the master cylinder pressure is gradually applied to the brake cylinders.