Patent GB-1277807-A (GB)
Title: Improvements in or relating to hydraulic vehicle braking systems
Inventor: BLAKEY ROY
IPC: B60T13/14
Filed: 1969-10-17
Abstract: 1277807 Hydraulic systems; indicating pressure loss GIRLING Ltd 13 Oct 1970 [17 Oct 1969 10 Aug 1970] 51103/69 and 3844/70 Headings F2E and F2F An hydraulic vehicle braking system has front wheel cylinders FC, rear wheel cylinders RC and lock units RL on at least the rear wheels, hydraulically separate accumulators 3A, 3B fed by separate pump elements of an engine driven pump 1 which draws fluid from a reservoir 2, a foot-operated treadle valve 5 to supply hydraulic pressure from each accumulator 3A or 3B to at least some of the wheel cylinders FC, RC for service braking a hand operated valve 6 to supply hydraulic pressure from each accumulator to at least some of the wheel cylinders FC, RC for emergency braking the valve 6 also controlling operation of the lock units, and the system also comprising changeover valves 8 through each of which a pressure line from the valve 5 is branched into a pressure line from the valve 6 to thereby act as a check valve. As shown in Fig. 1, two single chamber wheel cylinders FC are provided on each front wheel and a double chamber wheel cylinder RC and a lock unit RL are provided on each rear wheel, which lock units RL are operated by relieving them of pressure. The valve 6 includes a gate which prevents operation of the lock units RL when the pressure transmitted to the wheel cylinders RC exceeds a predetermined value. A service override valve 7 prevents the lock units RL being relieved while the service brake pressure exceeds a predetermined value. Load apportioning valves 14 are interposed in the pressure lines to the rear wheel cylinders RC between the valve 5 and the change-over valves 8 and a dual chamber pressure gauge 15 is connected to the accumulators 3A and 3B separately. In service brake operation, the valve 5 is operated to pass pressure fluid from the accumulators 3A, 3B to the front wheel cylinders FC, the two cylinders FC on each wheel being fed by a different accumulator, and to the rear wheel cylinders RC one accumulator being connected to one chamber of each of the two wheel cylinders RC and the other accumulator to the remaining chambers. The valve 6 is connected to the rear wheel cylinders RC only and to the lock units RL, and to apply the lock units RL, the rear cylinders RC are pressurized, the lock units RL are relieved and the rear cylinders RC are then relieved. Failure of any of the four main pressure lines will not affect the others. In Fig. 2 (not shown) each wheel has two single chamber double piston wheel cylinders FC and RC and two lock units FL and RL. The two lines from valve 6 each serve one wheel cylinder on all four wheels, and two additional changeover valves 8 are required. In Fig. 3 (not shown) the rear wheels only are fitted each with two lock units RL and the pressure supply to the lock units is split. In Fig. 4 the hand control valve unit is split into separate elements 6 (controlling the supply of pressure to the wheel cylinders) and 6A (controlling the supply of pressure to the lock units). Low pressure warning switches 4, for initiating a visual and/or audible signal in the event of pressure loss in either accumulator, replace the gauge 12. In Fig. 5 (not shown) the lock units RL are applied by fluid pressure and are normally biased by resilient means to an unlocked condition.