Patent GB-1215988-A (GB)
Title: Improvements in or relating to hydraulic braking systems
IPC: B60T8/38
Filed: 1968-12-23
Abstract: 1,215,988. Anti-skid control of hydraulic braking systems. SOC. ANON. D.B.A. 23 Dec., 1968 [27 Dec., 1967], No. 60956/68. Heading F2F. An hydraulic braking system comprises a master cylinder operative to control the pressure to a set of wheel cylinders, and an antiskid control valve operatively connected to be actuated by deceleration-responsive means for connecting the wheel cylinders either with the master cylinder or with an hydraulic reservoir according to the skidding of the wheels as sensed by the responsive means, the braking system being characterized in that it further comprises a power control device connected to be controlled by the braking pressure from the master cylinder for delivering a second hydraulic braking pressure varying as a function of the first pressure to the wheel cylinders through the anti-skid control valve, valve means responsive to the differential between the first and second braking pressures being provided upstream of the anti-skid control valve to connect the latter either with the power control device or with the master cylinder, depending on whether the second braking pressure is above or below the first braking pressure respectively. As shown in Fig. 1, a conventional primary master cylinder 10 is controlled by a brake pedal 12 to pressurize hydraulic fluid from a reservoir 14. The outlet 16 of the primary master cylinder is connected to a servo valve 20 controlling the operation of a conventional power control device 22 consisting of a secondary master cylinder 32 and, preferably, a vacuum-suspended pneumatic servomotor 34. The outlet 30 of the secondary master cylinder is connected via one side of a balancing valve 26 to a conduit 54 leading to an anti-skid control valve 56, the element of which is normally in the position shown to permit operation of the wheel cylinders 60, 60<SP>1</SP>. On skidding, a deceleration-responsive device 58 moves the valve element to the left to connect the wheel cylinders to the reservoir 14. Also as shown in Fig. 1, the outlet of the primary master cylinder 10 is also connected by conduit 19 with the left-hand side of the balancing valve 26 and from there to the conduit 54 leading to the anti-skid control valve 56. Thus in normal operation the outlet pressure from the secondary master cylinder 32, which is proportional to and greater than the outlet pressure from the primary master cylinder 10, forces piston 40 in valve 26 to the left against primary and spring pressures to close outlet orifice 50. If the secondary pressure becomes less than the primary pressure, e.g. upon failure or malfunction of the power control device, the primary pressure and spring 64 force piston 40 to the right, closing outlet 52 and permitting primary master cylinder pressure to reach conduit 54 via inlet orifice 24 and outlet orifice 50, and thus operate the brakes directly. A practical form of valve 26 is shown in Fig. 2, where outlet orifices 50, 52 are provided at the ends of the piston, and communicate via respective inner passages 70, 72 with respective annular grooves 66, 68 in the piston and thence alternatively with a common outlet groove 74 and outlet orifice 76 provided in the casing. Inlet orifices 24, 36 and fixed valve seats 46, 48 are also provided in the casing. A practical form of valve 20 is shown in Fig. 3, but its orientation is inverted in relation to Fig. 1. Thus vacuum port 112 is connected to the engine intake manifold (not illustrated) and communicates permanently through the valve with orifice 114 leading to the first variable volume chamber of the vacuumsuspended servomotor 34. In the valve position shown the second variable volume chamber communicates via orifice 116 in the valve casing and axial passage 118 in poppet valve 104 with vacuum port 112, but on actuation of valve 104 by hydraulic pressure from conduit 18 (see also Fig. 1), the valve is forced to the right against spring 124 to make contact with spring-loaded check valve element 119, closing passage 118. Thereafter valve 119 is forced to the right to connect atmospheric opening 120 with orifice 116 and thus with the second variable volume chamber.