GB562589A - Improvements relating to servo-mechanisms - Google Patents

Abstract

562,589. Hydraulic accumulators. PRATT, J. H., and GIRLING, A. H. G. Nov. 24, 1942, No. 16624. [Class 69 (ii)] [Also in Groups XXVIII and XXXIV] An hydraulic servomechanism suitable for operating the brakes of a motor vehicle comprises an accumulator supplied by a pump driven by an eccentric from the driving shaft of the vehicle and means for disengaging the pump piston from the eccentric when a predetermined volume has been delivered to the accumulator. A control valve device for controlling the supply and release of liquid to and from the brakes &c. may be attached to the pump and accumulator housing. A housing 5 supported by brackets 8 from a vehicle transverse frame member 9 contains a pump piston 11 arranged to be driven inwards by an eccentric 6a on the driving shaft 6 of the road wheels, the piston being returned by a spring 13. The liquid is drawn from a reservoir 19 through a passage 5d and past double non-return valves 24 into the pump cylinder 11a and is forced past a non-return valve 26 and through passage 5e into an accumulator chamber 16, thus forcing outwards the piston 15 against the pressure of springs 20, 21 bearing on a seat 22. The piston 15 is secured to a rod 17 upon which the piston 11 is slidable and the piston 11 has a greater area than that of the piston 15. As the pistons move to the right a rubber buffer between the piston 11 and the rod 17 is thus compressed. When the accumulator is full, the pressure in the chamber 11a falls by leakage past the piston 11 permitting the buffer to move the piston away from the eccentric 6a. Control of the brakes is effected by valves 28a, 28b contained in a casing secured to the housing 5. The chamber 27 is connected to the pipelines and is normally connected to the reservoir 19 through passages 29b in a piston 29 and a passage 5g. Operation of a lever 31 by the pedal moves the piston so as first to seat the exhaust valve 28b and then to lift the valve 28a to permit the supply of liquid from the accumulator to the chamber 27 and the pipelines through passages 5e, 25a. The brake pressure reacts through the piston 29 on to the pedal. A braking pressure in excess of that produced by the accumulator may, if desired, be applied by the pressure applied to the piston 29, this being rendered possible since outward movement of the accumulator piston 15 is limited by a stop 34.