Patent GB-1513805-A (GB)
Title: Anti-lock brake control system
IPC: B60T8/48
Filed: 1975-10-08
Abstract: 1513805 Anti-skid brake systems TELDIX GmbH 8 Oct 1975 [25 Oct 1974 18 Dec 1974 28 June 1975] 41311/75 Heading F2F A brake control system comprises a first closed-loop circuit 12 with a first brake pressure producing means 8 (booster 8, master-cylinder or displacer 52), brakes 5, wheel sensor 6 and closed loop control device 11, 13, 14 responsive to signals from the sensor to vary the braking pressure, and a second open-loop circuit 20 with a master cylinder 17 actuated by the pressure in the first circuit as modified by the control device. In normal braking of the arrangement in Fig. 1 the booster 8 moves the piston 9 to displace fluid to the rear brakes 5 through the valve 11 and through a shunt valve 14 to a chamber 15 of the master cylinder 17 to displace its piston 16 and actuate the front brakes 1, 2. Signals from the sensor 3, 4, 6 are supplied in turn to an evaluation circuit an output signal from which charges over the electro-valve 11. Fluid from the circuit 12 and the rear brakes then enters the storage chamber 13 displacing the piston 23 to the right together with the ball element of the shunt valve 14 to close it. Fluid from the chamber 15 also passes via a by-pass valve 19 to the storage chamber 13 relieving the front brakes. When the valve 11 is returned to its first condition and with the valve 22 opened by the conical surface secured to the piston 23 a pump 24 returns fluid from the chamber 13 to the rear brake circuit and through a restriction 18 to the chamber 15 to reapply the front brakes but at a slower rate than the rear brakes. (Fig. 4a, not shown.) In a modification (Fig. 3, not shown) two valves (11a), (11b) are provided to control the rear brake circuit 12 and the line to the chamber 15 and hence front brakes independently. The valves 11 and 14 and the restriction 18 may be replaced by an electro-valve (Fig. 2, not shown) with 3 positions in which respectively the booster output is connected to the circuit 12 and the master cylinder 17, the inflow from the booster is cut off by valve (28) and the pump 24 drains the master cylinder chamber 15 (through valve (27)), the circuit 12 is drained (through valve (29)) in addition the circuit 20 although, if a further value (31) which closes the line to the master cylinder 17 in the third position is provided the circuits 12 and 20 are controlled independently in response to the sensor signals. Separate similar master cylinders 17 may be provided for independent control of the front brakes using a 4-position electro-valve. In Fig. 5 the pedal 51 operates a displacer from which fluid passes to a non-suction pressure pump 56 through a changeover valve 55, which is changed over when one of the sensors causes actuation of an electro-valve 59. This connects either the front or rear circuit 64 or 60 to a storage chamber 67 the piston of which is coupled to the valve 55, the pump 56 then draining the circuit 64 or 60. A four-position valve and two front wheel master cylinders may be provided (Fig. 7, not shown). To alter the transmission ratio on failure of the power pump 56<SP>1</SP> (Fig. 6) the pedaloperated piston 74 has an annular surrounding part 75, which parts move together while pressurised fluid from the pump acts on a coaxial piston 80 to close a valve 81 thus trapping the fluid surrounding the piston 74. On pump failure pedal rod 73 displaces the piston 80, in the absence of the opposing pump pressure, and opens the valve 81 permitting the annular piston 75 to remain stationary to reduce the effective piston diameter, fluid from around the piston escaping to a reservoir 84. A valve 85 is provided to limit loss of fluid should the circuit 64<SP>1</SP> leak and to reduce pedal movement. Normally just before the valve 85 seats as the piston 63<SP>1</SP> is displaced the piston chamber 88 is connected to an adjacent reservoir when the pressure in the master cylinder chamber 58<SP>1</SP> acting on the piston 87 opens the valve 85 with the plunger 86. In the absence of such pressure in the chamber 58<SP>1</SP> because of a leak the valve remains closed preventing fluid from entering the control chamber 62<SP>1</SP>.