Patent GB-1490167-A (GB)
Title: Anti-skid braking system for a motor vehicle
IPC: B60T8/58
Filed: 1975-06-03
Abstract: 1490167 Antiskid braking systems SOC ANON DBA 3 June 1975 [25 June 1974] 23957/75 Heading F2F An antiskid braking system for a motor vehicle comprises a tandem master cylinder 10 connected by respective circuits 16, 22 to rear wheel brake actuators 18 and front wheel brake actuators 24; the circuit 16 incorporates a modulating device 28 for modulating the pressure in actuators 18 when the risk of wheel lock is detected by electronic control means 30 and the circuit 22 incorporates a modulating assembly 34 which has a solenoid isolation valve 38 whose coil 42 is energizable by an electrical control circuit 44 to disconnect the master cylinder 10 from actuators 24 and to connect them to a normally closed relief device 40; the relief device 40 is responsive to the ratio between the pressures prevailing in the actuators 24 and 18 during energization of valve 38 so as to relieve the pressure in the front wheel actuators 24 when the ratio exceeds a predetermined value. As seen in Fig. 1, the relief device 40 comprises a ball 76, normally urged into engagement with a valve seat 73 by a piston 78 slidable in a bore connected to the rear brake actuators 18 by a line 72. The valve seat 73 is formed in a passage 74 and when, after energization of valve 38, the aforesaid ratio is exceeded the ball 76 moves away from seat 73 to connect the front wheel actuators 24 to the reservoir 12 of the master cylinder 10. The circuit 44 which controls the energization of the coil 42 of the valve 38 may be responsive to a number of signals. As seen in Fig. 1 the circuit 44 is responsive to the operation of the vehicle brakes as detected by a pressure operated switch 46 in the rear circuit 16, to a signal representing the angular position of front wheels 26 detected by a steering switch 48, and to the presence of an output signal from the electronic control means 30 which itself receives signals representing the angular speed of the rear wheels 20 from sensors 32. Fig. 2 illustrates one embodiment of the control circuit 44 and shows the positions of the various components when idle. In use, signals from the control means 30, the switch 46 and the switch 48 operate respective switching means in the form of a transistor 83, an on-off switch 84 and a change-over switch 86 to cause energization of the coil 42, until the end of the pulse from the steering switch 48. The circuit 44 is designed to limit to two the number of plates energizing the coil 42 during an antiskid operation to prevent excess loss of pressure from actuators 24, and only the first two steering pulses are operable to cause energization of the coil 42. To achieve this effect the circuit 44 incorporates an arrangement of relay coils 96, 112 controlling switches 98, 100, 114. In the embodiment of Fig. 3 (not shown) this effect is achieved by providing the circuit with normally blocked thyristors (198, 216, 218) instead of relays. The circuits of Figs. 2, 3 may be modified to restrict energization of the coil to any number of pulses. Fig. 4 (not shown) illustrates a modification whereby energization of the solenoid valve coil (342) is controlled as a function of vehicle speed. To this end a capacitor (300) and a resistance (302) are connected in parallel with the solenoid (342) and the voltage from the electronic control means (330) is delivered to a common terminal between the capacitor (300) and the resistance (302). This arrangement ensures a delay in the energization of the coil (342) following delivery of a signal from circuit (344) which delay is a function of vehicle speed. Alternatively the position of the steering switch (48) may be modified directly as a function of vehicle speed measured in control means (30).