GB1356845A - Pneumatic anti-skid devices - Google Patents

Abstract

1356845 Anti-skid device KNORR-BREMSE GmbH 1 June 1971 [1 June 1970] 18463/71 Addition to 1335916 Heading F2F A pneumatic anti-skid device for use in a vehicle braking system which has a skid sensing means connected to the device is, in use, connected in the braking line and allows braking pressure build up for normal applications until a skid is sensed whereby the device brings about a throttled reduction of braking pressure and then permits a subsequent increase in. braking pressure at a rate less than the build up of braking pressure during normal braking applications. The pressure builds up to a steady state pressure which is less than that at which skidding was sensed, the lower the "skid" pressure the higher the pressure difference between the "skid" pressure and the steady state pressure. The device is shown in its rest position whence fluid pressure can pass through chambers 58, and 39 to the brake cylinder 7 for normal application of the brakes . On a skid being sensed a solenoid operated valve 29 is actuated to close off a vent 32 to atmosphere and pressurize a chamber 20 from a reservoir 5 to depress a piston 14 hence closing a valve 46, 47 in the brake fluid supply circuit and opening a venting valve 18, 47, braking fluid passing to the atmosphere through a throttle 19. Reservoir pressure also flows into a chamber 11 which has a throttled outlet 12 to atmosphere through grooves 38 in the rod 17 of piston 14. With the depression of the piston a throttling piston 51 is spring urged into a passage in the brake fluid supply circuit. After the skid has ceased the solenoid operated valve is de-actuated so that chamber 20 is vented which allows piston 14 to rise under its spring loading until it engages a floating piston 21 which has been depressed by the residual pressure in chamber 11. Valve 18, 47 is closed and valve 46, 47 opened but since the rise of piston 14 is limited the throttling piston 51 still throttles the flow of braking fluid to the brakes, hence the build up of braking pressure is at a rate less than normal build up. The valve seat 46 of valve 46, 47 is provided on a spring loaded piston 41 an annular chamber 42 surrounding the piston 41 being in communication with the braking circuit through a one way valve constituted by the peripheral seal of the piston 41. Thus chamber 42 is substantially at the initial braking pressure. When pressures on both sides of the piston 41 are equalized the piston 41 moves upwardly so that the valve 46, 47 is closed and the steady state pressure is achieved in the brake cylinder until such time that the pressure in chamber 11 decays sufficiently to allow the pistons 14 and 21 to rise and thus open valve 46, 47 and remove the throttling piston from the passage. The time spent by the device in its "steady state pressure" state becomes less as the initial braking pressure increases.