GB1402690A - Anti-skid brake circuit for a motor vehicle - Google Patents

Abstract

1402690 Anti-skid braking systems SOC ANON DBA 30 Aug 1973 [6 Sept 1972] 40795/73 Heading F2F An anti-skid braking system for a motor vehicle comprises an hydraulic servomotor 20 with an operator-operated control valve 18 actuable to control the fluid communications amongst an accumulator 10, a reservoir 14 and an actuating chamber 22 of the servomotor 20; an actuator positon 24 of the servomotor 20 is connected to a master cylinder comprising at least one pressure chamber 32 connected by a supply duct 38 to a system of anti-skid solenoid valves 46, 50 capable of modulating the fluid pressure in a set of brake actuators 42 in response to electrical instructions from a control device 82 responsive to the deceleration of at least one vehicle wheel 54; a replenishing duct 62 connects the actuating chamber 22 to the supply duct 38 by way of a one-way valve 66 and in the supply duct 38 there is a cut-off solenoid valve 74 between the pressure chamber 32 and the junction of the supply and replenishing ducts 38, 62 which valve 74 is controlled by the control device 82, so as to isolate the pressure chamber from the brake actuators 42 during modulation of the fluid pressure in the actuators 42 by the anti-skid valves 46, 50. The embodiment illustrated is of a dual circuit braking system with the actuators 42 on the front wheels 54 and actuators 44 on rear wheels 56; the rear wheel circuit has components analogous to the front wheel circuit as illustrated but the following will refer to the front wheel circuit only. The valve 46 is an isolation valve and the valve 50 is a relaxation valve, and all the solenoid valves 46, 50, 74 are shown in their deenergized state with valves 46, 74 open and valve 50 closed. The valves 46, 50 are energized by the control device 82 which converts speed signals from wheel speed sensors 86 to deceleration signals. Energization of the cut-off valve 74 is controlled by a supplementary channel of the control device 82 comprising an AND gate whose two inputs are connected to the energizing circuit of the isolation valve 46 and to a control circuit controlled by a contactor 87, a conventional monostable device providing timing having its input connected to the output of the AND gate and its output connected to a power amplifier which controls energization of the winding of the cut-off valve 74. The control device 82 is made operative by a circuit connected to the vehicle stop lights and controlled by the contactor 87, which is responsive to motion of a pedal 28, or by a conventional pressure responsive switch. When the driver presses the pedal 28 the contactor 87 closes to energize the control device 82 and the valve 18 is operable by a lever system 26 to pressurize the actuating chamber 22 and operate the master cylinder; initially pressure from the chamber 22 also passes to the brake actuators 42. If a risk of wheel locking is detected the modulation cycle begins. In a first phase the valve 46 is closed and the valve 50 is opened to connect the actuators 42 with the reservoir 14. In the second phase the valve 50 is closed again and in the final phase the valve 46 is reopened. The cut-off valve 74 is closed from the beginning of the cycle when the valve 46 is energized and each instruction to energize valve 46 causes the monostable device to take up an unstable position corresponding to energization of the valve 74. The monostable device returns to its stable position after a period greater than the maximum possible duration of a modulation cycle and thus the valve 74 reopens only after the end of a full anti-skid modulation. To prevent any delay following release of the brakes, a non-return valve 78 mounted in parallel with valve 74 allows fluid from the actuators 42 to the master cylinder before the cut-off valve 74 reopens. In an alternative embodiment the valve 74 is kept closed from the beginning of the first modulation cycle until the driver releases the brake pedal 28. A pressure sensitive switch 88 is operable to cut-off the electricity supply to the solenoid valves in the event of failure of assisted braking, for example breakdown of a pump 12; and in this event the master cylinder is operable directly by pedal 28. The switch 88 may be replaced by a pressure imbalance switch between ducts 62, 38. The master cylinder has a reservoir 36 connected to the reservoir 14.