Patent GB-895497-A (GB)
Title: Improvements in or relating to hydraulic servo-devices
IPC: F15B9/10
Filed: 1960-07-27
Abstract: 895,497. Fluid-pressure servomotor-control systems; valves. LEDUC, R. July 27, 1960 [July 27, 1959], No. 26081/60. Class 135. [Also in Group XXXIV] A valve assembly for controlling a spring- loaded servopiston 13, Fig. 2, comprises an input member 4 movable relatively to a valve member 23 whereby to interrupt communication between a chamber 2a and an exhaust passage 10, 9 and to open communication between an inlet 11 for pressure liquid and the chamber 2a. The pressure in the chamber 2a reacts on the member 4 so that the force exerted by the servopiston 13, which is connected through an annular restriction 5 with the chamber 2a, is proportional to the effort applied to the member 4. Due to the restriction 5 the rate of flow of liquid to the servopiston is dependent upon the " error " between the instantaneous value and the required or final value of the pressure acting on the servopiston whereby the final pressure is attained in a damped and stable manner. The restriction 5 may alternatively be situated in the delivery connection 2. Fig. 3 illustrates an arrangement in which the servopiston 13 provides a seating for a piston valve 12a, 14 and may operate the master cylinder of a vehicle hydraulic braking system, the member 4 being then connected with the brake pedal. The left-hand side of the servopiston is permanently connected to the pressure supply at 11 and the right-hand side may be connected through the restriction 5 either with the pressure supply or, through passages 10, 9, with exhaust depending upon the direction of movement of the member 4. The hydraulic pressure reaction on the member 4 is taken by a surface 6. The restriction 5 may alternatively be an annular one surrounding an extension of the piston valve 12a, 14. Instead of a piston valve a valve arrangement as in Fig. 2 may be mounted in the servopiston or the latter may carry a pair of loose-ball valves actuated by tapered portions of the member 4. An arrangement for controlling front and rear brakes of a vehicle in dependence upon the loads carried by the front and rear wheels is shown in Fig. 9. A member 82 connected to the brake pedal has rollers 52, 53 which provide movable fulcra for levers 54, 55 whereby the output pressures of valve assemblies 12x, 23a &c. and 12y, 23a &c. controlling the front and rear brakes, which assemblies are similar to that shown in Fig. 2, are proportional to hydraulic pressures dependent upon the front and rear wheel loadings, applied to pistons 56, 57 acting on the levers 54, 55. These hydraulic pressures are derived from valve assemblies similar to that shown in Fig. 2 and in each of which the member 4 is loaded by a spring the degree of compression of which is dependent upon the displacement of a sprung part of the vehicle relative to an unsprung part. The connections 68, 69 to the two sets of brakes are through annular restrictions 72, 73 and "feel" is transmitted through plungers 74, 75. An additional valve assembly 76, 81 connected at 89 to the front and rear brakes is operated by the member 82 in the event of failure of the other elements.