Patent GB-1435536-A (GB)
Title: Hydraulic braking systems
IPC: B60T/
Filed: 1973-06-16
Abstract: 1435536 Hydraulic brake systems GIRLING Ltd 4 June 1974 [16 June 1973] 28722/73 Heading F2F In an hydraulic braking system for vehicles and of the kind incorporating a power valve assembly and means for relieving the braking pressure in the event of a skid, a piston 21 working in a cylinder of the power valve assembly is adapted upon axial movement in response to actuation of a brake pedal to open a normally closed valve 20 and to close a normally open valve 22, the valve 20 controlling a connection to a fluid pressure source and the valve 22 controlling a connection to a reservoir 6; a pressure space 43 is defined between the piston and cylinder. In the event of a skid, the pressure space is supplied with pressure fluid to retract the piston to close the valve 20 and open the valve 22 to relieve the braking pressure. As shown, in a duel braking system, one circuit includes a pair of front wheel actuators 1 and a rear wheel actuator 2 and the other circuit includes a second pair of front wheel brake actuators 3 and a rear wheel actuator 4. A pump 5, supplied from a reservoir 6, pressurizes an hydraulic accumulator 7 through an unloader valve 8, the accumulator being connected to a power valve 9 controlling each brake circuit, and also to a control valve 10; the valves 9 are each operated by pressure fluid from separate pressure spaces in a pedal-operated tandem master cylinder and each valve 10 is operated by a signal from skid sensing means 12 associated with each rear wheel. The valve 9 comprises a stepped piston 21 working in the stepped bore 14, 15 of a housing 13 which is connected via port 17 to the master cylinder 11 and has a recess 18 connected to an inlet port 19 and housing a ball valve 20; a cone valve 22, spring- loaded away from a passage 23 in the piston communicates with radial passages 24 in the piston, the valve being adapted to lift the ball valve 20 from its seat. A piston 31 carries a valve 32 which co-operates with the step in the bore 28, 29 and a cone valve 33 spring loaded away from passage 34 in a plug 30 and connected to a pressure space 40. In the normal state of the valve 9, the valve 20 is closed and pressure fluid from accumulator 7 in recess 18 acts upon piston 31 via passage 35 to hold the valve 32 open and valve 33 closed. The valve 22 is open and connects the brakes via port 37, passages 36, 23 and 24 and port 41 to reservoir 6. Fluid from master cylinder 11 to pressure space 40 via port 17 advances the piston 21 to close valve 22 and open valve 20 to allow pressure fluid to pass from recess 18 to port 37 via bore portion 14, passage 36 and valve 32. Failure of the supply of fluid pressure results in the valve 20 being held open by the piston 21 and closing of the valve 32 to isolate the brakes from the pressure supply, the valve 33 opening whereby fluid from the pressure space 40 passes to port 37 via passages 39, 38 and 34. In the event of a skid, signals from the sensing means 12 operate the solenoid control valve 10 to allow pressure fluid to pass into chamber 43 to retract the piston 21 whereby the valve 22 is opened to connect port 37 to port 41 to relieve the braking pressure to the reservoir. The valve 10 has ports 48, 49 respectively connected to the reservoir 6 and the valve 8 and a port 50 connected to the accumulator 7, and incorporates a solenoid coil 54 on a sleeve 55 surrounded by a permanent magnet 56, and which, when energized moves a valve 52 into engagement with its seating and allows the valve 53 to open. In modifications, (a) the pump 5 pressurizes separate accumulators for each circuit, the valves 32, 33 being omitted, (b) the valves 9, Fig. 6, are linked together and applied directly by a pedal through push rods 60, the plug 17 being omitted; the two parts of the piston 21 are separated by a spring 58.