GB998626A - Improvements in or relating to a braking system for road vehicles, chiefly tractors - Google Patents

Abstract

998,626. Hydraulic brake systems; disc brakes; valves; ATLIERS CONSTRUCTIONS MECANIQUES DE VEVEY S.A. Jan. 21, 1963 [Jan. 24, 1962], No. 2487/63. Headings F2E, F2F and F2V. A braking system for road vehicles comprises a piston and cylinder device 7, 8, kept in its inoperative position by liquid under pressure derived from a pump driven by the engine and urged into its operative position by an energy storing means 5. At least one distributer (Fig. 2) controls the feed of liquid to the servomotor, the distributer including concentric pistons 22, 23, working in a housing 21. The supply of liquid is taken to one extremity of the distributer. The outer piston 22 engages a seat 24 of the housing so that hydraulic pressure is transmitted from a line 20, through a diaphragm 27, channels 105, 25 and line 103 to the power unit. On the initial actuation of the inner piston 23 the hydraulic supply is cut off and the power unit is vented through a restricted port 28 and pipe E. On further movement of the inner piston 23, a collar 104 abuts against and unseats the outer piston to vent the hydraulic fluid directly through pipe E. The piston and cylinder device shown in Fig. 3, comprises two pistons 35, 36, the brake actuating spring 38 working between them. Hydraulic pressure from a distributer 30 of the type described acts on the lower surface of piston 35 to release the brakes. The upper surface of piston 36 is vented through a valve 31, the face 114 of a piston 112 of the valve being pressurized directly from the hydraulic pump 116. On the distributer being operated lines 103, 113, 120 are vented, piston 112 moving to the left to allow hydraulic fluid to act on piston 36 through channel 118 and pipe 117. If the fluid circuit fails the brakes are applied by the spring alone. The pump 116 may be connected directly to the pipe 117 whereby the brake is actuated by the decompression of chamber 32 of piston 35. Two distributers each constructed as described above, may be mounted in parallel in the same housing and fed from an electromagnetically-operated valve (Fig. 5, not shown). The pressure outputs of the distributers are linked when both of the latter are actuated to provide equalized outputs. If a supply of hydraulic fluid is required to retain released a further set of brakes when one or other of the distributers are actuated a shuttle valve is used to allow fluid to pass from the non- actuated distributer to the further set of brakes (Fig. 6, not shown). A tractor-trailer system in which the tractor possesses brakes as described above and the trailer hydraulically actuated, spring retracted brakes is provided with a reversing distributer comprising a stepped piston spring loaded against the tractor brake releasing pressure and sliding within a cylinder (Fig. 4, not shown). The distributer shown in Fig. 8 has incorporated therein two electromagnetically-operated slide valves. The slide valves each include a large area piston 137 attached to a small area piston 83. The brake release fluid pressure acts on the outer faces of both pistons, this holding the valve in its inoperative position. On actuation of the electromagnetic valve(s) 141 the large piston chambers are vented so that the slide valve(s) rise in its housing to cut-off the supply of hydraulic fluid to and vent the auxiliary power unit(s). The piston and cylinder devices (Figs. 1, 3) are each provided with a wearcompensating means comprising a segmented sleeve 11 having a ribbed inner surface, the ribs co-operating with grooves of a rod 6 (Fig. la). The segments are held about the rod by a spring clip 12. The brake may be applied manually by the lever 16 and link 13.