Patent GB-1017877-A (GB)
Title: Improvements in braking systems
IPC: B60T13/10
Filed: 1962-12-19
Abstract: 1,017,877. Fluid pressure brakes. A. F. MURTY & B. P. MURTY. Dec. 19, 1962 [Dec. 19, 1961], No. 47870/62. Headings F2E and F2F. A safety brake for a vehicle having a primary braking system wherein brakes are applied by fluid under pressure, comprises spring means contained within a reservoir for the braking fluid used in the primary system and adapted to apply brakes on failure of the fluid pressure in the primary system, and a chamber associated with the reservoir and adapted when supplied with fluid from the primary braking system to expand and release the brakes applied by the spring means. The safety brake may adopt a variety of forms, so as to apply brakes associated with one or a pair of axles. In Figs. 1 and 4, compressed air motors 36, 38 are fed by a primary braking system to apply brakes 28, 30 on axles 24, 26, respectively, via levers 40, 42 secured to brake shafts 32, 34. A safety brake 20 acts additionally on the brake shaft 32 through a lost-motion connection 46, there being also a lost-motion connection 43 between the motor 36 and the lever 40 so that the two applying means are independent. Safety brake 20 comprises a reservoir 52 secured to the vehicle chassis and containing the compressed air supplying the motors 36, 38, a casing 58 secured to one end of the reservoir and containing a piston 60 on a piston-rod 44 to form a chamber 72 connectible at 74 with the primary brake system, and a prestressed compression spring 66 acting between casing wall 56 and a cup 68 on the inner end of rod 44 to apply the brake 28 in the absence of pressure in the chamber 72. Casing 56, 58, together with the piston 60, rod 44 and spring 66 are removable from the reservoir as a unit so that spring 66 can be compressed in a press to allow removal of normally shrouded clips 70 which allow the spring to be extended. Piston 60 is held in place on rod 44 by a nut 71 accessible on removal of a cover 62. In addition to having connections 80, 82 for compressed air, the reservoir also has an opening 79 normally closed by a plug 78, removal of which allows the attachment of a mechanical or hydraulic jack (Figs. 5, 6, not shown), for compressing the spring to release the brakes, e.g. if the vehicle is to be moved after a failure of the primary braking system. The mechanical jack 86 is of the kind including a rack bar 87 and reversible pawl assembly controlled by a reversing catch 90. The hydraulic jack 92 is a cylinder containing a piston 94 and fed via a pipe 96 from a manually-operated pump 132, Fig. 2, via a manually operated inlet and exhaust valve 130, a lamp 136 lighting when pressure detected by a gauge 134 corresponds to full compression of the spring 66 to release the brakes. The piston and cylinder 94, 92 may be replaced by one in which the piston extends outside the reservoir and is secured at its inner end to the rod 44 (Fig. 8, not shown), so that the safety brake can exert a push-pull action on brakes associated with both axles of the vehicle (Fig. 3, not shown). Alternatively (Fig. 7, not shown), the safety brake reservoir 150 accommodates two springs 66 and has casings 55, 58 secured to both ends each providing an expansible chamber for compressing the associated spring, the pistons in these chambers being connected by rods 44 to brakes of the two axles. A floating piston and cylinder 164, 162 is provided between the spring cups 68 for releasing the brakes by operation of a manually-operated pump. To save space the spring cups may be deeply recessed (Fig. 9, not shown), the recesses accommodating the piston and cylinder. In a tractor/trailer system (Fig. 10, not shown), safety brakes 20 provide the tractor and trailer reservoirs for an automatic system comprising compressor 100 on the tractor, and driver's valve 112 operates relay valve 116 on the tractor and, via tractor protection valve 110 relay valve 117 on the trailer to supply the respective motors 36. The system also includes manuallyoperated hydraulic pumps 132, 142 for releasing the spring applied brakes, a safety valve 124 which must be manually-operated before the primary system will operate, via relay valves 126, 128, to release the brakes, the arrangement being such that the brakes remain released only if pressure is above a predetermined value, a valve 114 for applying the trailer brakes only, and a valve 108 for exhausting the system on the trailer.