Patent GB-1151223-A (GB)
Title: Vehicle Anti-Skid Braking Systems
Inventor: DAVIS JOHN WALTER
IPC: B60T8/40
Filed: 1965-07-15
Abstract: 1,151,223. Fluid-pressure brakes. DUNLOP CO. Ltd. 7 July, 1966 [15 July, 1965], No. 29998/65. Heading F2F. In a compressed-air or vacuum brake system for the tractor portion of a tractor/trailer vehicle, each of the rear wheel brake cylinders 9, 10 is provided with two chambers 14, 15, the former being connected with the driver's valve 6, which is supplied by a reservoir 5, and the latter being connected via an anti-skid valve unit 20 to either atmosphere or an anti-skid reservoir 18 which is isolated from the reservoir 5 by a check valve 4, the arrangement operating such that when a skid is imminent the valve unit 20 operates to cut off the connection of chambers 15 to atmosphere and to connect them instead to the reservoir 18 whereby the brake is released, pressure build-up in the chambers 14 during operation of the valve unit 20 being prevented by balanced exhaust valves 56. The embodiments described are compressed-air systems. In the embodiment of Fig. 1, the valve unit 20 also controls the supply of compressed-air to the chambers 14, cutting off the supply when a skid is imminent. When a skid-correcting pressure is supplied by the valve unit 20 to the chambers 15, the resultant pressure rise in chambers 14 overcomes the combined effect of the pressure in the lines 60, which are now isolated by the valve unit 20, and springs 59, so that pistons 57 are moved to open exhaust valves 61 which relieve the pressure. The valves 56 also act as quick-release valves during release of the brakes, A ball-valve 64 in each piston 57 prevents release of pressure from the chambers 14 except by way of the exhaust valves 61, but allows flow of air into the chambers 14. Instead of or in addition to the isolating effect of the valve unit 20 on the air supplied to chambers 14, a sensitivity control valve 70, Fig. 4, may be incorporated in the system, its inlet 74 being connected with the driver's valve 6 while its outlet 73 is connected either directly or via the valve unit 20 to the chambers 14. The valve 70 is responsive to a control pressure at 80 which is conveniently obtained from that used to control the position of the spool 23 of the valve unit 20 where, as shown in Fig. 1, valve unit 20 is a two-stage valve having a primary valve 21 which is operated mechanically by the control-rod 22 of an inertia unit (not shown), driven by the vehicle transmission and which determines the control pressure. The control pressure passes via a check valve 78 of the valve 70 to a chamber 77 where it controls the position of a spring-loaded restrictor member 75 so as to determine the throttling effect of a waisted central portion 85 of the restrictor member on the air passing between inlet 74 and outlet 73, whereby should the driver maintain a heavy pressure on the brake pedal, pressure in chambers 14 and 15 is not allowed to build up too quickly and so reduce the differential between the pressures in chambers 14 and 15 during a sustained skid correction. When valve 70 is used, the valve unit 20 may be simplified by omitting its function of isolating the air supplied to chambers 14 (Fig. 5, not shown). Alternative means for ensuring that pressure in reservoir 18 is always higher than the pressure supplied to chambers 14 comprises the provision of a pressure-balancing valve (170, Figs. 11, 12, not shown) between the driver's valve 6 and the valve unit 20 of the Fig. 1 embodiment which limits the pressure supplied to chambers 14 to a value below the pressure in reservoir 18. In another embodiment (Fig. 6, not shown) a sensitivity valve (101) similar to the valve 70 is used in conjunction with a single-stage anti-skid valve unit 100, Fig. 7, which comprises coaxial plungers 105, 109, slidable in a sleeve 107 and urged away from one another and from an adjustable top cap 108 by springs 110, 111. When plunger 22 of the anti-skid device moves upwards, an exhaust valve 117, 118 is first closed and an inlet valve 120, 121 then opens to perform the change-over of chambers 15 from atmospheric pressure to that supplied by the reservoir 18. The positions of the valve seats 118, 120 are simultaneously adjusted by adjustment of the cap 108, which includes an exhaust flap 115, movement of the cap in turn causing the sleeve 107 to be adjusted. Alternatively, individual adjustment of both inlet and exhaust valves may be provided (Figs. 8, 9, not shown). Exhausting of the chambers 15 may be accelerated by the provision of a quickrelease valve (160, Fig. 10, not shown). Where the pressure-limiting valve (170, Figs. 11, 12, not shown) referred to above is used in conjunction with a two-stage valve unit 20, a pressure-reducing valve 190, Fig. 13, may also be included between the reservoir 18 and the primary valve of the valve unit 20 to control the pressure in the chambers 15 in accordance with the pressure of air being supplied to the chambers 14. The valve 190 comprises a diaphragm 196 between two bore portions of different diameter respectively associated with inlet 191 from the reservoir 18 and a connection 191 to the line between valve unit 20 and one of the chambers 14, whereby a valve member 199 attached to the diaphragm moves to engage a valve seat 200 when the pressure at outlet 198 to the primary valve of the valve unit 20 rises to a predetermined value with respect to that being supplied to the chambers 14. The valve 190 includes a check valve 204, 205 to allow release of pressure from the primary valve of the valve unit 20 when air is released from the line feeding the chambers 14, i.e. when the brakes are released. The chambers 14, 15 may either be formed in a single brake cylinder, as shown, by using a filling member (216, Fig. 14, not shown), or may be provided in separate cylinders (Fig. 15, not shown), whose diaphragms are connected to a common brake-operating lever. The brake cylinders may act on the brakes via a master cylinder instead of directly.