GB837998A - Improvements relating to hydraulic motor systems - Google Patents

Abstract

837,998. Hydraulic transmission of power; fluid-pressure servomotor control systems. KEELAVITE CO. Ltd. Jan. 8, 1959 [Jan. 8, 1958], No. 773/58. Classes 69 (2) and 135. An hydraulic transmission system for driving a vehicle O1 the hoisting gears of a crane comprises a power-driven pump 1 of the displacement type having its inlet 2 and outlet 3 connected respectively to the outlet 4 and inlet 5 of an hydraulic motor 6 also of the displacement type, an hydraulic servomotor the operating member 20 of which actuates a mechanism 7, 8 for varying the capacity of the pump and/or motor to vary the ratio of the transmission therebetween, a control member 37 for operating a pilot valve 25 for the servomotor, and means 42 responsive to the working fluid pressure of the motor arranged to connect the outflow passage 33 from the servomotor to a source of fluid pressure automatically if and when the fluid pressure exceeds a predetermined value. The pump 1 is connected to a prime mover through a member 15 and the motor 6 to a driven member 16. The capacity of the pump and motor is varied by the movement of levers 7, 8 pivoted at one end to shafts 9, 10 and at the other end to the servomotor casing 13 by links 11, 12. The servomotor consists of a cylinder 20 in which is a piston 21 connected by a rod 22 to a fixture 23. The opposite ends of the cylinder are connected by passages 30, 31 to the pilot valve 25 which has an inlet pipe 32 communicating with a pump 40 and outlet pipe 33 connected by a restriction 39 to a tank 38 and by valves 42, 17 and a pipe 19 to the pipes 2, 4 and 3, 5, the valve 42 being normally closed by engagement of an abutment 44 spring-urged into contact with a cam 45 on the casing 13, and the valve 17 connecting whichever of the pipes 2, 4 or 3, 5 is at the higher pressure to the pipe 19 leading to the valve 42. When it is desired to vary the transmission ratio, the spool of the pilot valve 25 is axially moved by the control rod 37, which may be operated independently or simultaneously with a member controlling the speed of the prime mover, and a lever 34 to connect the inlet pipe 32 to one or other of the ends of the cylinder 20 to move the casing 13 along a slide 14 in the same direction as the movement of the rod to pivot the levers 7, 8 and adjust the pump or motor. If the rate of adjustment results in the pressure in either pipes 2, 4 or 3, 5 rising above a predetermined value, this pressure is communicated by the valves 17, 42 to the outlet 33 from the servomotor to slow, stop or reverse the movement of the casing and thus to control the adjustment of the pump and motor until the pressure drops to a value determined by the spring and the cam 45 closing the valve 42. The valve 42 may also open if, by reason of a sudden braking force on the driven member, the pressure in one or other of the pipes 2, 4 or 3, 5 falls to a predetermined level resulting in a rise in pressure in the other pipes. In an alternative embodiment, restrictions are placed in the passages 30, 31 one or both of which may be connected to the pipes 2, 4 or 3, 5.