Patent GB-1186788-A (GB)
Title: Brake Actuator Improvements
IPC: B60T17/08
Filed: 1967-07-10
Abstract: 1,186,788. Fluid-pressure brakes; internal shoe-drum brakes. NORTH AMERICAN ROCKWELL CORP. 10 July, 1967 [8 July, 1966], No. 31604/67. Headings F2E and F2F. In a combination service and auxiliary brake actuator assembly, a fluid pressure responsive service motor 12 is operably connected by means of a wedge (29) and roller (31) device for actuating the vehicle service brakes, a fluid pressure responsive auxiliary motor 13 is arranged in tandem with the service actuator motor 12 and is provided with a spring chamber 51, passage means 66, 67, 68 being provided for passing fluid from the service motor through a movable piston 43 into the spring chamber 51 during actuation of the service brakes by the auxiliary motor, a unidirectional check valve 72 being provided for the spring chamber to permit exhaust of fluid from the spring chamber but preventing direct introduction of the ambient air into the spring chamber during all operating conditions. Fig. 1 shows the actuator in the disengaged position wherein fluid from a reservoir P is introduced into the auxiliary actuator motor 13 into chamber 49 to move the fluid pressure responsive element 43 against the spring 54 to compress the latter. A stem portion 46 of the fluid pressure responsive element 43 is flush with the surface 37 of the actuator casing 16 and the flexible diaphragm 19 in the service chamber 22 is pressed against both surfaces 37 and 48. At this time the port 66 in the stem 46 is closed and the check valve 72 in the end member 41 is also closed. During the normal service application of the brakes, air under pressure is introduced into the service line 39 and into chamber 22 of the actuator to displace the diaphragm 19 to the right and apply the brakes via the wedge and roller mechanism 29, 31. During the normal service brake operation there is no change in the position of the parts in the auxiliary motor 13. Should the air pressure in the reservoir P drop below a predetermined level the holding pressure in the control chamber 49 drops and the spring 54 expands to drive the piston 43 to the right and allow air pressure in the service line to escape via the ports 66 and 68 into the spring chamber 51 and escape to atmosphere via the check valve 72 (Fig. 2). This allows the emergency spring 54 to expand to move the fluid responsive element 43 to the right and apply the brakes in the emergency condition. Fig. 4 shows an alternative embodiment wherein the end wall 103 of the piston stem is formed with an annular face 104 and bears a resilient seal 105 adapted to seat on the surface 106 surrounding the opening in the actuator wall 107. An annular rib 113 may be formed on the face 106 to increase the sealing action by embedding into the resilient ring. In a further embodiment (Fig. 5, not shown), an alternative form of relief valve is disclosed which takes the form of a spring- loaded poppet valve. The service brakes may be disengaged by removing a nut 93, rotating the head 84 and thus the rod 82 to cause movement of the non-rotatable nut 87 to the left (Fig. 1) to displace the piston 43 to the left to compress the spring 54 to disengage the service brakes.