Patent GB-1402685-A (GB)
Title: Vehicle braking systems
IPC: B60T8/48
Filed: 1973-06-29
Abstract: 1402685 Dual braking systems; anti-lock systems; valves AUTOMOBILES CITROEN SA 29 July 1973 [3 July 1972] 31009/73 Heading F2F A vehicle braking system comprises first and second independent braking circuits 6, 11 connected respectively to one or more brake cylinders 5a, 5b controlling the braking at one or more wheels 1, the first circuit 6 containing an electrically operated valve 9 controlled in dependence upon wheel slip to prevent locking of the wheel 1, and the second circuit 11 incorporating a quantity regulating valve 11 controlled in dependence on the pressure in the first circuit downstream of the valve 9. In the embodiment of Fig. 1, the cylinders 5a, 5b control braking members 4a, 4b to brake a disc 3 connected to the wheel 1. The two circuits 6, 11 are connected to a pedal operated quantity regulating valve 7 which is connected to a source of pressure. When the slip of wheel 1 reaches a predetermined value, valve 9 closes to reduce the pressure in circuit 6 downstream of the valve 9, and this reduction in pressure is repeated in circuit 10 by valve 11; as a result pressure in cylinders 5a, 5b is reduced to avoid risk of wheel locking. Valve 11 takes the form of valve 19 shown in Fig. 3. In the embodiment of Figs. 2, 3, the front wheels 12 are braked by members 14a, 14b controlled by brake cylinders 15a, 15b connected respectively to braking circuits 16, 18. The circuit 16 incorporates an electricallyoperated valve 17 which is controlled in accordance with the slip of wheels 12 and the circuit 18 includes a quantity regulating valve 19 controlled by the pressure downstream of valve 17. The braking circuit 18 is also connected to cylinders 24 of rear wheels 21 via an electrically operated valve 25 controlled in accordance with the slip of the wheels 21. Thus locking of the front wheels 12 is prevented by the action of valves 17, 19 and locking of the rear wheels 21 is prevented by the action of valve 25. The valve 19 shown in greater detail in Fig. 3, comprises a body 28 having two aligned bores 28a, 28b, each slidably mounting a respective slide 29, 30. The slide 29 bounds two chambers 32, 33. The chamber 32 connects via a duct 34 with the circuit 16 downstream of valve 17. The chamber 33 is connected with bore 28b via a duct 36-the duct 36 may be placed in communication with circuit 18 downstream of valve 19 via a groove 30a in slide 30. The slide 30 bounds two chambers 38, 39. The chamber 38 is connected by a duct 40 to the circuit 16 upstream of valve 17. The chamber 39 is connected to a reservoir 42 but can be connected to duct 36 through a branch duct 43. The slide 30 has a rigid thrust member 44 which may be brought into contact with slide 29. When the valve 17 is operated the pressure in chamber 32 is decreased and slide 19 is moved rightwards to separate two ducts 18a, 18b of circuit 18 and connect duct 18a to a duct 31 to reservoir 27. If a leak occurs in circuit 18 the slides 29, 30 remain in position and the circuit 16 continues to operate. If a leak occurs in circuit 16 the pressure in chambers 32, 38 decreases and slide 30 is displaced leftwards to also displace slide 29. Thereby the front brake cylinders 15b continue to be fed with fluid and the rear brake cylinders 24 continue to be fed with fluid via valve 25.  In the embodiment of Fig. 4 (not shown), the braking circuit (16) is connected to the front brake cylinders (15a) via the valve (17) and to the braking cylinder (24a) of one of the rear wheels (21) via the valve (25). The braking circuit 18 is connected to the front braking cylinders (15b) by a quantity regulating valve (19a) controlled in dependence on the pressure downstream of the valve (17), and to the second brake cylinder (24b) through a quantityregulating valve (19b) controlled in dependence upon the pressure downstream of the valve (25)