Patent GB-1378368-A (GB)
Title: Hydraulic brake systems
IPC: B60T8/1763
Filed: 1973-07-31
Abstract: 1378368 Hydraulic anti-skid circuits AISIN SEIKI KK 31 July 1973 [31 July 1972] 36331/73 Heading F2F A motor vehicle hydraulic brake system has a power booster 10 between a brake pedal 18 and a master cylinder 21 and having a power pressure source, an electronic circuit 47 for generating a first signal to a first electromagnetic valve 31 for reducing the action of the booster and a second signal to a second electromagnetic valve 38 for reducing the rate of re-establishment of the action of the booster, the circuit receiving input signals from one or more wheel rotation rate sensors 71. For brake actuation, a piston 12 of the booster 10 is moved rightwardly to throttle a passage 26 from a chamber 15 to a reservoir so that pressure in the chamber 15 builds-up due to fluid from a pump 34 via the valve 31; this build-up causes rightward movemerit of a piston 13 due to the differential in pressure to that in a chamber 16 communicating with the reservoir via the valve 38. The piston 13 contacts a piston of the master cylinder 21 to apply the brakes. If wheel deceleration of one wheel at least attains an undesirably high value, Fig. 5, a voltage from the emitter of a transistor T 2  exceeds a threshold for actuation of a Schmitt trigger comprising transistors T 3 , T 4 , and resistors R 7 , R 8 , R 9 , R 11 , R 12  to render a transistor T 5  conductive to energize a coil .46 of the valve 31; a spool 44 thereof moves rightwardly to communicate the chamber 15 with the reservoir to relieve brake actuation by the booster. Furthermore, a chamber 14 which was previously communicated with the reservoir 29, is now closed off to resist rightward movement of the piston 12. In the circuit 47, a transistor T 6  is energized, a transistor T 7  is de-energized so that a capacitor C 1  receives a charge depending on the emitter voltage of the transistor T 2  this being calculated to be higher than the Zener voltage of a Zener diode D 3 . A capacitor C 2  charges to the Zener voltage of a Zener diode D 5 , a transistor T 10  conducts to close a relay 200 by a coil 300. A transistor T 8  is conductive, and a transistor T 9  is non-conductive so that a coil 63 for the valve 38 is not energized. Subsequent decrease in wheel deceleration causes the emitter voltage of transistor T 2  to decrease until it reaches the threshold of the Schmitt trigger, this being lower than the increasing signal threshold due to hysteresis thereof, so that the coil 46 is de-energized; thus full booster braking is re-established. However, discharge of the capacitor C 1  until it falls below the Zener voltage of the diode D 3  to de-energize transistor T 8 , energize transistor T 9  and energize the coil 63. A spool 62 is moved rightwardly so that flow from the chamber 16 of the booster passes through a restriction 68 to the reservoir 29 thus decreasing the booster effect. The capacitor decay is dependent on a chosen resistor R 20  and the transistor T 7  so that a fast rise in braking pressure is followed by a more gradual rise for each successive braking cycle after initial relief. Pressure failure in chamber 15 is overcome by a mechanical connection between the pistons 12 and 13 for brake actuation.