Patent GB-1218842-A (GB)
Title: Improvements in or relating to hydraulic brake systems
Inventor: GODDARD ARTHUR
IPC: B60T13/24
Filed: 1968-02-09
Abstract: 1,218,842. Hydraulic braking systems. GIRLING Ltd. 7, Feb., 1969 [9 Feb., 1968; 19 Feb., 19681, Nos. 6638/68 and 7917/68. Heading F2. An hydraulically operated braking system for motor vehicles includes a manually-actuated master cylinder 3 having a pressure chamber connected directly to a group of front wheel brake slave cylinders, a servo-motor 9 having a control device 11 and arranged to generate pressure in a set of rear wheel brake slave cylinders and to a further group of front wheel brake slave cylinders additional to the first group, and means associated with the master cylinder for operating the control device. As shown, each front brake 1 has at least two separate, opposed, slave cylinders, one set being connected by line 2 to one pressure generating space of the driver-operated ,tandem master cylinder 3 and the other set being connected to the line 4 for the rear brakes, the pressure for which is generated in an auxiliary cylinder 7 operated by a push rod 8 of the servomotor 9 subject to operation of the device 11 and connected by line 12 to the other pressure generating space of the master cylinder. Actuation of the latter normally pressurizes line 2 and the front wheel slave cylinders and line 12 to operate the servomotor, whereupon cylinder 7 pressurizes line 4, the rear brake slave cylinders and the remainder of the front brake slave cylinders. The push rod 8, Fig. 2, is coupled to a pressureresponsive wall 13 dividing the servomotor housing into a compartment 9A which is connected at all times to a source of vacuum, and a compartment 9B in which pressure is controlled by valve gear normally connecting the compartment to vacuum but which admits atmospheric air in response to a signal from the master cylinder to establish a pressure differential across the wall 13 to advance the push-rod 8. In a casing 16 a hollow valve 17 has a flange 18 which co-operates with a fixed seat 19, and a vacuum valve 21 seats on the valve 17, both valves being spring biased to the left as seen in the Figure and the space to the left of the valves being permanently connected to vacuum; the space between the valves is connected to atmosphere by duct 22. Valve 21 is fast with the core 24 of a solenoid 26 and has pinned thereto a spring lever 27 abutted by a lever 28 operated on by a plunger 29 hydraulically connected to the master cylinder by line 12. The solenoid is connected directly to a speeddetecting circuit and is energized by current from a control module 31, the rate of change of speed of the rear wheels being sensed by an electronic device 32 coupled to the propeller shaft 33 of the vehicle. In normal braking, pressure generated in line 12 causes plunger 29 to urge, through levers 27. 28, the core 24 rearwardly to close valve 21 and unseat valve 17 to admit air to compartment 98, whereby wall 13 and rod 8 are moved to pressurize auxiliary cylinder 7 and line 4 to operate the braking equipment and to produce a deceleration measured by a device 32 so that the control module provides deceleration feedback to the solenoid, an opening effect on the valve 21 being produced. When the loads on the valve 21 due to air pressure and solenoid force balance the loads on the plunger 24 from the lever 27, the valve 17 closes and a reduction in the load on the plunger reopens the valve 21 to allow relief of the air pressure in the compartment 98 and the reduction of rear wheel braking. In a modification, the servomotor control device 11 includes an hydraulic, pressure responsive, two stage piston assembly consisting of inner and outer pistons, both of which are initially moved in unison in response to an initial signal pressure, after which the outer piston moves relative to the inner piston to load a spring between the pistons and until the outer piston encounters a stop, further increase in signal pressure then acting on the inner piston alone to operate the air valve and to energize the servomotor. The tandem master cylinder may be replaced by a single master cylinder and non-hydraulic means may be employed to generate a signal for controlling the servomotor, e.g. a load cell associated with the master cylinder for generating an electrical signal to operate the servomotor.