GB1468014A - Hydraulic braking systems - Google Patents

Abstract

1468014 Hydraulic brake systems; anti-lock brake systems CLAYTON DEWANDRE CO Ltd 16 Oct 1974 [25 Oct 1973] 49732/73 Heading F2F An hydraulic braking system has a master cylinder 1 operable to actuate the brakes 4 on one axle and also to actuate a reaction valve 5 in a full power circuit 6, 7 8 whereby pressure fluid from an accumulator 8 is supplied to the brakes 9 on a second axle and to a servo cylinder 10 for boosting the output delivery from the master cylinder 1 to the brakes 4; the system also incorporates at least one solenoid valve 14 forming part of an anti-lock system and operable under the control of the anti-lock system logic to vent one or more of the brakes 4, 9 to a low pressure reservoir 6 of the full power circuit. In the embodiment of Fig. 1, fluid pressurized by master cylinder 1 is led by a line 2 to an output cylinder 3 hydraulically connected to the brakes 4, and the output of the master cylinder 1 or the movement of its piston, actuates the valve 5 to supply fluid from the accumulator 8 to the brakes 9 and the servo cylinder 10. The piston 11 of cylinder 10 is thereby moved to displace the piston 12 of output cylinder 3 to augment the master cylinder pressure and to close a bore 13 therein which otherwise directly connects the brakes 4 with the master cylinder 1. In this embodiment a two-way solenoid valve 14 is inserted in a line 15 between valve 5 and brakes 9 and is operable to decrease or cut-off line pressure to brakes 9 and to vent line 15 to reservoir 6, for example, via a port 16 in valve 5. For anti-lock control of brakes 4 only, a solenoid valve (17) is inserted in a full pressure line (18) to the servo cylinder 10 to vary the degree of boost provided by the servo cylinder 10. However, an additional solenoid valve (19) may be inserted in the line 2 which valve is energized by the system logic to cut-off flow from the master cylinder to the output cylinder and to vent the servo side of the output cylinder piston via a line (20)-this prevents a rise in pressure in the master cylinder forcing back the servo piston 11 to open bore 13 and thereby override the anti-lock control. Fig. 2 (not shown) illustrates such a system which, however, also has anti-lock control to both first and second axles simultaneously and includes both solenoid valves (14) and (17). Any of the above systems may also include at least one inlet solenoid valve (14a, 17a) to give a pressure hold facility. In the embodiment of Fig. 3, each wheel brake 4, 9 has its own two solenoid valves 14, 14a or 17, 17a. Two servo cylinders 10, 10a and two output cylinders 3, 3a are provided for respective brakes 4. If desired anti-lock control may be provided for individual brakes on one axle with the brakes of the other axle under common control.