GB1345654A - Hydraulic antiskid braking system and a hydraulic fluid distributor for use therein - Google Patents

Abstract

1345654 Anti-skid hydraulic braking system FIAT SpA 5 June 1972 [14 June 1971] 26078/72 Heading F2F An hydraulic anti-skid braking system has a source of hydraulic pressure 10 (e.g. a master cylinder), operable to draw hydraulic fluid from a reservoir 11 and direct it via an electrically operated valve 18 and a distributer 28 to a brake actuator 52 operating on a brake disc 54 mounted for rotation with a wheel; a tachometric generator 104 is associated with the disc 54 and acts to supply wheel velocity signals to an anti-skid control circuit 108 which energizes solenoid 20 of electrovalve 18 when an incipient skid occurs and cause reduction of braking pressure via the distributor 28, the construction of the distributer 28 allowing of two modes of anti-skid braking in dependence on whether the road surface has a low or high coefficient of friction. In the normal position of the valve 18 an input port 16 is connected to a first output port 22 which is connected to a conduit 26 of distributer 28 which leads via a chamber 30 and passageways 34, 46 to a delivery conduit 50 leading to the brake actuator 52. A valve shutter 38 having a throttled orifice 42 is located in chamber 30 and is normally held away from a valve seat 36 by an axial projection 78 of a piston 74. The piston 74 which is biased upwards by a compression spring 12 has a lower axial projection 80 which extends into a guideway 66 of a plug 58 and terminates adjacent a ball valve 64 in the guideway 66. Below the plug 58 is a perforated diaphragm 84 and below this is a chamber 82 containing a cushion 96 of synthetic elastic material which is filled with a fluid of high compressibility. The chamber 82 communicates at one side through the diaphragm 84 with a conduit 98 leading to an output port 24 of the distributer 18 and at the other side with a conduit 100 incorporating a constriction 102; the conduit 100 leads to an outlet 59 connected to the reservoir 11. When braking on a road surface of low coefficient of friction, and providing the braking pressure does not rise above a discrimination pressure y 0 determined by the strength of spring 72 the piston 74 will stay in its position as illustrated. If a skid is sensed ports 22 and 24 of valve 18 are interconnected and port 16 is closed to isolate source 10 so that braking pressure is released into chamber 82 which has a variable capacity owing to the presence of cushion 96. The fluid can drain freely from the chamber 72 via the ball valve 64, through a passage 67 in the plug 58 and back to reservoir 11. This represents a virtual instantaneous discharge of pressure When braking on a surface of high coefficient of friction braking pressure can exceed y 0 before skidding could occur, and this pressure will move piston 74 downwardly to allow shutter 38 to close on seat 36 whereby fluid flow to the actuator 52 is via the orifice 42. The ball valve 64 is now held closed by the projection 80 so that if a skid is now sensed flow of fluid from chamber 82 can only take place via constriction 102 and this slows down the discharge to allow of a quick increase in pressure should the incipient skid condition disappear. The system can be arranged to control the brakes on all wheels of the vehicle.