Patent GB-980635-A (GB)
Title: Hydraulic apparatus
Inventor: BOWERS ERIC HIDER
IPC: F16H39/08
Filed: 1960-09-12
Abstract: 980,635. Reciprocating pumps. DOWTY HYDRAULIC UNITS Ltd., and UNIPAT A.G. Sept. 5,1961 [Sept. 12,1960; Nov. 25,1960], Nos. 31387/60 and 40610/60. Heading F1A. [Also in Division F2] An hydraulic transmission comprises a pump and motor each having a rotatable cylinder block 23, 42, Fig. 1, with cylinders parallel or nearly parallel to the axis of rotation, and a rotary thrust plate 16 having a shaft 14, 41 fixedly secured thereto and arranged to rotate about an axis variably inclined to the axis of rotation of the cylinder block, the cylinder blocks of the pump and motor being rotatably carried in a carrier 18, 19, 21, which is controllably movable for the simultaneous adjustment of the inclinations between the thrust plates and their respective cylinder blocks. The transmission may be used between an engine and the ground-engaging wheels of a vehicle, the engine being connected by a shaft 2 and bevel gearing or a universal joint 10, such as is described in Specification 932,724, to the input shaft 14 of the pump, and the wheels being driven by the output shaft 41 of the motor. The shaft 14 of the pump is integral with the thrust plate 16 which is connected by rods 25 to pistons reciprocable in the cylinder block 23 and to the cylinder block by a universal coupling 28. The cylinders in the block co-operate with kidney-shaped ports in a surface 24 of the carrier part 21, the ports communicating by way of passages 32, 33, Fig. 4, with similar ports in a surface 36 engaging the cylinder block 42 of the motor to reciprocate pistons therein connected to the thrust plate and output shaft 41 driving the wheels. The cylinder blocks are urged by springs 93, Fig. 5, and high pressure fluid in a passage 27 connected to whichever of the passages 32, 33 in the carrier is at the higher pressure supplied to a cylinder 88, a seal 92 preventing the high pressure fluid escaping from the cylinder. The parts 18, 19, Fig. 1, of the carrier are bolted to the part 21 and are pivotally mounted on trunnions 17, 37, Fig. 3, trunnion 17 being supported on a casing 15 providing a support for the bearings of the shaft 14, and trunnion 37 being supported in a casing 38 which is fixedly secured to a reservoir 1 housing the transmission and provides a support for the bearings of the shaft 41. The carrier 18, 19, 21 is connected by a linkage 49, Fig. 1 to a servo motor 47 having a manual control member 51 which when operated pivots the carrier about the trunnion 32 to vary the inclination between thrust plate and cylinder block of the motor, the movement of the carrier also varying the inclination of the thrust plate 16 and cylinder block 23 of the pump by angular movement about the trunnion 17; the universal joint 10 permits the shaft 14 to vary its inclination with the shaft 2. The arrangement is such that the transmission can be varied from the position shown, in which the pump displacement is zero, to either a position 45 which increases the pump displacement and decreases the motor displacement to provide maximum speed ratio in the forward direction, or to a position 46 in which the motor displacement is increased and the displacement of the pump reversed for driving the shaft in the reverse direction at a lower speed than the maximum in the forward direction. A make-up pump 52, Fig. 4, driven by a chain from the shaft 2, supplies fluid through a filter 81, flexible pipe 54 and one or other of one-way valves 56, 57, depending on which of the passages 32, 33 is at the lower pressure, to passage 32 or 33. In order to ensure a continuous circulation of liquid, a shuttle valve 58 is provided to connect the passage 32 or 33 at the lower pressure to a passage 59 and relief valve 61 leading to the reservoir. The fluid in the passage 32, 33 at the higher pressure passes a one-way valve 63 or 64 to a space 65 which, in addition to being connected to the passages 27, 44 leading to the cylinders 88 for pressing the cylinder blocks against the surfaces 24, 36, also passes to a valve 69 having a bleed passage 71. Where a valve 75 is moved to disconnect the pressure supplied by the make-up pump 52 from a pipe 74, the decrease in pressure acting on a piston 73 permits the pressure at the back of the valve 69 to lift a ball valve 72 to reduce the pressure in the passages 32, 33 and render the transmission inoperative. When the pump 52 is connected to the piston 73, the valves 72, 69 close to permit actuation of the transmission and the valve 69 then acts as a high pressure relief valve to pass fluid at excess pressure through passage 55 and one or other of valves 56, 57 to the passage 32 or 33. A constant-pressure reducing valve 78 is provided to supply fluid to the servo-motor 47 for controlling the ratio of the transmission.