Patent GB-936491-A (GB)
Title: Improvements in or relating to liquid pressure braking systems for vehicles
IPC: B60T8/18
Filed: 1960-06-01
Abstract: 936,491. Fluid-pressure brakes. FOSTER NORTH & KERR Ltd., and H. J. KERR. Aug. 31, 1961 [June 1, 1960; June 27, 1960], Nos. 19414/60 and 22452/60. Class 103 (1). In an hydraulic braking system for a motor vehicle including a master cylinder 10 and wheel cylinder 12, maximum pressure in the wheel cylinders is determined independently of pressure in the master cylinder by a device 15 comprising a casing 17, a first piston 24 acted on by the fluid supplied by the master cylinder to an inlet chamber 25 via an inlet plug 21, a valve member 27 having a tubular stem 26 which is screwed into the piston 24, a second, annular, piston 22 having a valve seat 30 adapted to be closed by the valve member 27 when the master cylinder pressure exceeds a predetermined value, and a third piston 28 coupled to a resilient member which is connected with the suspension such that the pressure in the outlet 19 leading to the wheel cylinder is modified according to either the load on or the deceleration of the vehicle. The inner end of the plug 21 acts as a stop for the pistons 22, 24 in the released condition of the brake, piston 22 being urged downwardly by a compression-spring 20 and piston 24 upwardly by the link 29. A light compression spring 31 acts between pistons 22, 24. An overall maximum pressure in the outlet 19 is determined by a spring ring 32 acting as a relief valve closing a radial passage 33 interconnecting the interior of the stem 26 and the inlet chamber 25. Pressure is exerted upwardly on piston 28 in accordance with load or deceleration control forces whereby, when master cylinder pressure has risen above that necessary to close the valve member 27 on the seat 30, pressure in the outlet 19 is determined by movement of piston 28 in accordance with variations in this pressure, an increase in upward pressure on piston 28 causing upward movement of all three pistons to increase wheel cylinder pressure, subject to the overall maximum determined by spring ring 32, and a reduction of upward pressure allowing fluid to pass down the interior of stem 26 into a cavity in the top of piston 28, so reducing wheel cylinder pressure. In one arrangement for controlling the maximum pressure in the wheel cylinder, a link 29 is connected between piston 28 and a piston 35, Fig. 5, acted on by a spring 34 in a cylinder pivoted to the rear axle 37 of the vehicle which is suspended by leaf-springs 39, the arrangement then responding to the vehicle load. In another arrangement, Fig. 6, a tappet 42 acts on piston 28 through a spring 41 or, when the latter is fully compressed, directly, the tappet being acted on by a ball 49 which during braking is forced upwardly out of a socket in a sleeve 43 mounted on the vehicle chassis by movement of a tie rod 44 which is connected with a wishbone of the front suspension such as to respond to deceleration forces but not to the load. Should the wheel skid the tension in rod 44 will be relaxed and rubber buffers 45 ,46 return the tie-rod to a neutral position in which the ball 49 rests in the bottom of a recess 48 in an enlargement 47 of the tie-rod, whereby maximum wheel cylinder pressure is reduced. In a further arrangement, Figs. 8, 9, the rear axle 52 of the vehicle is located in the fore-and-aft direction by pivoted links 53, 54 incorporating resilient bushes to allow longitudinal movement of the axle under deceleration forces. A control rod 55 has an enlargement within a sleeve 56, a recess in the enlargement accommodating a ball 59 when deceleration is reduced by skidding to reduce maximum wheel cylinder pressure, normal braking causing the ball to be forced upwardly to press a tappet 61 against the force of spring 62 towards the piston 28. The tappet 61 may be arranged to contact piston 28 when deceleration is normal, spring 62 exerting an initial pressure low enough to prevent skidding of the wheels in the most adverse conditions likely to be encountered by the vehicle.