Patent GB-1051439-A (GB)
IPC: F16D65/78
Abstract: 1,051,439. Brakes. CATERPILLAR TRACTOR CO. Sept. 7, 1964 [Oct. 4, 1963], No. 36561/64. Heading F2E. [Also in Divisions F1 and F4] A vehicle fluid braking system comprises a fluid retarder, a fluid motor driven fan for cooling the fluid of the retarder, a source of fluid for actuating the fan motor, means for pressurizing said fluid, means to direct a limited flow of fluid under pressure to the fan motor, and means automatically operable upon charging the fluid retarder for increasing the flow to the fan motor. As shown, the system comprises a receiver 17, a pump 18, a control spool valve 19, fluid motors 16 driving fans 15, fluid retarders 10, chambers 11 for supplying liquid to the retarders, heat exchangers 14 for cooling the retarder liquid, and a driver's valve 13 for controlling compressed air delivery through pipe 40 from a source (not shown) to pressurize the chambers 11 and actuate the retarders. The components on the left of the chain-line are mounted on the trailer and those on the right, on a tractor of a tractor/ trailer combination. In order to conserve power when the retarders are not in operation and only low-speed fan operation is required, a by-pass or relief valve 29 is incorporated between supply and return lines, 23 and 27 respectively. The valve comprises a piston 30 biased to the right or closed position by a weak spring 31, an orifice 32 equalizing pressures in chambers on opposite sides of the piston. Operations of the valve is controlled by a spring- loaded pilot valve 33 which is opened against the bias of its spring 34 when the pressure in conduit 23 exceeds a predetermined value to vent the spring chamber on the left of the piston through duct 36. The piston then moves to the left and permits by-passing from supply line 23 to return line 27 through orifices 38. On actuation of the retarders by opening the driver's valve 13, compressed air is also bled to cylinder 43 thereby advancing plunger 44 and automatically loading spring 34 so that the pilot valve will not open until a much higher delivery line pressure is attained. Thus, the required high speed fan-drive motor operation is attained automatically on actuation of the retarders. To conserve power when braking appears an unlikely requirement for long periods spring chamber of the relief valve may be vented continuously through a manual valve 70. However, this valve is automatically closed, as shown, on actuation of the retarders by compressed-air in line 42 urging plunger 79 to the right thereby preventing by-passing fluid through valve 29 when the retarders are in operation. The braking circuit is combined with the circuit of a fluid motor 50, such as a jack for raising or lowering the trailer. On actuation of the jack control valve spool 53 to the " raise " or " lower " positions R or L, jack pump 51 pressurizes the jack circuit and also chamber 65 of the valve spool 19. This spool is automatically depressed and the combined volumes of both pumps 51 and 18 are directed to the jack. In a modification, Fig. 2 (not shown), in order to render the fandriving motors inoperative when the retarders are not actuated, the relief valve spring 31 is made extremely weak so that on a slight pressure in the supply conduit 23 is sufficient to open the valve and by-pass to reservoir. On actuation of the retarders, compressed air is initially fed through a further valve linked mechanically to the control valve such that the by-pass valve 29 is closed and the fan motors actuated prior to the retarders.