GB1177082A - An Improved Hydraulic Brake System - Google Patents

Abstract

1,177,082. Tractor/trailer brake systems. F. W. PETTIT Ltd. 7 April, 1967 [19 April, 1966; 9 May, 1966; 14 Oct., 1966], Nos. 16991/66, 20498/66 and 45925/66. Heading F2F. Hydraulic brake control means for a trailer unit comprises a motor vehicle mounted control valve device connected by pressure and return pipes in an hydraulic pump system and a remote control valve, connected mechanically to a vehicle brake operating member, providing for pressure fluid to be cut off from the return port and directed to a service port which is connected through a releasable coupling and a flexible pipe to a piston and cylinder actuator mounted on the trailer and connected to a trailer brake-operating member so that by connecting the releasable coupling the trailer brake system can be operated from the vehicle brake system. In the " OFF " position of the trailer brakes, a brake piston 16 is in position 16a, Fig. 4, and ram 9 is in position 9a whilst valve members 20, 27 are in the Fig. 3 position. Fluid flows freely from pump 6 through pressure inlet 12b, passage 12f and pressure outlet 12a, Fig. 3, to cylinder 8 and also to signal plunger 29b and via pressure outlet 12c to reservoir R. The spring-biased plunger 29b closes switch 30 to signal the presence or absence of oil pressure through a flasher unit 33 and an indicator lamp 34. Depression of pedal 4 blocks fluid passage to the return, thereby raising the pressure in cylinder 8 so that ram 9 moves piston 16 to pressurize the fluid in pipe lines 18, 19, thus applying the trailer brakes. The other tractor hydraulic devices may be operated without operation of the brakes by manual movement of the valve member 27 to the position shown in dotted lines, Fig. 3. In this position valve part 27a closes valve opening 12j to cut-off inlet pressure from chamber 12i to the pressure outlet 12a and the lower valve part 27b opens the valve opening 12k to pass inlet pressure from chamber 12i via pressure outlet 12l to the other hydraulic devices. In a modification, failure or reduction of fluid pressure from the tractor, due either to accidental detachment of the trailer or incorrect setting of control valve 12, causes automatic application of the trailer brakes by a secondary brake control, Fig. 7. In normal brake operation the hydraulic pressure in pipe line 11 is communicated to cylinders 43, 46 so that the secondary brake control remains inoperative by allowing the end of ram 16 to slide relative to socket 36. Loss or reduction of pressure causes spring 48 to return ram 47, thereby bringing valve recesses 49a into register with pipe connection 51 to release pressure fluid from cylinder 43. Thereupon, spring 40 acts through ram 39, lever 37 and socket 36 to move ram 16 to its brake-operating position. In a further modification, Fig. 8 (not shown), the valve 49a is replaced by a spring (54) connected to the lever and a releasable catch (57) has a releasable connection with the lever under the control of an hydraulic cylinder (60) and ram. In further modifications the valve 20, Fig. 3, is replaced by a slide valve or conical needle valve. The brakes may be applied mechanically from the hand brake lever through links (45, 46), Fig. 11 (not shown), acting on a lever compensator connection (47) to the ram 9.