GB737762A - Improvements in or relating to servo braking apparatus - Google Patents

Abstract

737,762. Fluid-pressure brakes. CLAYTON DEWANDRE CO., Ltd. July 6,1954 [July 20, 1953], No. 20085/53. Class 103 (1). In a servo-assisted brake operating mechanism of the kind wherein the output of a vacuum or compressed-air servo device employing a piston or diaphragm as the pressure responsive operating member is transmitted hydraulically to the wheel brake cylinders of the vehicle, the servo device is controlled by an actuator mounted at one end of and in alignment with an hydraulic cylinder within which a displacement device operates to transmit to the liquid in the hydraulic cylinder effort produced by the servo device and manual effort applied to the actuator such that the displacement device is movable indepedently of the operating member of the servo device. In the embodiment shown, a vacuum servo-assisted brake operating mechanism includes a hydraulic cylinder 1 provided at the forward end of the mechanism and having an outlet port 2 to the wheel brake cylinders of the vehicle. At the other end of the hydraulic cylinder 1 is arranged a vacuum servo device 3 consisting of a piston 4 mounted within a cylinder 5. Extending concentrically through the servo device into the hydraulic cylinder 1 and slidably supported thereby is a displacement device 7 comprising an outer component 8 whose forward end projects into the hydraulic cylinder 1 through a vacuum chamber 9 formed at the rear thereof. Within the outer component 8 is mounted an inner component formed of two parts 13 and 14 and in the forward end of the component 8 a plug 23 is provided to form a valve chamber 20 to seal off the interior of the displacement device from the interior of the hydraulic cylinder. In the inoperative position illustrated the inner component occupies a rearward position wherein the front end of the forward part 14 is disengaged from a disc valve 19 which only permits vacuum to be supplied via port 10 to chambers 9 and 20. In this position both sides of the servo piston 4 are subjected to atmospheric pressure. When the brake pedal is depressed effort is transmitted through rod 26 to the inner component of the displacement device which moves to the right to engage the disc valve 19 and so cut off the forward space of the servo cylinder from atmosphere and allow vacuum to be supplied to this space. This action advances the servo piston 4 in its cylinder 3 so as to advance the displacement device further into the hydraulic cylinder to apply increased liquid pressure to the wheel brake cylinders of the vehicle. The output effort of the servo piston is transmitted to the outer component 8 of the displacement device 7 through reaction beams 34 so that this effort reacts through the beams against the inner component of the displacement device and against the manual effort applied to the brake pedal thus giving the operator " feel " of the degree to which his own effort is being power assisted. Projections 40 are provided on the inner component of the displacement member so that should no vacuum be available manual effort is transmitted directly to the liquid in the hydraulic cylinder by the displacement device which slides through the servo piston 4 and is movable independently thereof. Radial ports 49 are provided in the forward end of the displacement device which when in the inoperative position shown register with an annular recess 45 to permit replenishment of the hydraulic cylinder with liquid from a reservoir via port 42 and annular space 43. Specifications 709,017 and 733,823 are referred to.