Patent GB-661652-A (GB)
Title: Improvements in or relating to hydraulic pumps or motors
IPC: F01B13/06
Filed: 1947-07-16
Abstract: 661,652. Hydraulic motors; fluid pressure servomotor control systems. OILGEAR CO. July 16, 1947 [Jan. 14, 1942] No. 18957/47. Classes 69 (ii) and 135. Also in Group XXVIII. In a revolving cylinder hydraulic motor having a valve seat arranged upon the cylinder barrel and provided with a number of cylinder parts which communicate with the cylinders, a valve engaging the seat being provided with high and low pressure valve ports with which each cylinder port communicates alternately as the barrel rotates, a number of hold-up motors are arranged behind the valve to urge it against the seat, at least one balancing motor being provided for assisting the hold-up motors in urging the valve against the seat and the balancing motor being intermittently energized and de-energized in accordance with the number and angular positions of cylinder ports communicating with the high pressure port. Figs. 1 and 2 show a revolving cylinder type hydraulic pump. Fig. 2 being a section on the line 2-2 of Fig. I. Rotation of a shaft 5 rotates a cylinder barrel 7 which may be integral with the shaft 5 or the shaft may be firmly pressed into the cylinder barrel. The barrel contains 14 cylinders 10, alternate cylinders being oppositely inclined to enable the maximum number of cylinders to be used in a given size of barrel. Each cylinder contains a piston 9 and the outer end of each piston engages the internal surface of a ring 16 which to save space forms the inner race of a roller bearing 17, the pump shown being very small. The outer race of the bearing is constituted by the annular inner surface of a slide block 18. The slide block may be supported on side plates but as shown is mounted in the pump casing 1 on four rollers 19 so that it can be moved transversely to the cylinder barrel axis to vary the pump displacement. The shaft 5 has seven passages 11 formed in it and each passage communicates with two adjacent cylinders 10. The passages 11 co-operate with ports 14, 15 in a flat faced valve 13. Each piston engages the ring 16 at a single point which is offset from the piston axis so that the piston is caused to rotate in its cylinder as it reciprocates therein. When the pump is operating liquid under pressure will be discharged from the cylinders 10 through one of the ports 14, 15 and liquid under low zero or negative pressure will be drawn into the cylinders through the other port. In the case of a motor, liquid under pressure will be delivered to the cylinders through one port and discharged through the other. Since liquid in one port is under high pressure and liquid in the other is at low, zero or negative pressure minute quantities of liquid will escape from the high pressure port and spread over the valve seat. The pressure in the high pressure port will extend into the lubricating film and the pressure in one or both ports and the film will tend to move the valve away from its seat. In order to limit the area of the film into which pressure may extend a recess 20 is formed in the face of the valve 13 at the centre thereof and a limit groove 21 is formed in the face of the valve near its periphery and drain ducts 20' and 21' extend respectively from the recess 20 and groove 21 so that liquid may drain from the recess and groove into the casing 1. To prevent the valve 13 being moved away from its seat it is urged towards its seat by the pressure in spaces 40 (Fig. 6) and by piston 27 (Fig. 1) and pistons 33 (Fig. 7) acted on by liquid pressure and respectively by springs 28, 34. The valve port 14 communicates with a passage 23 leading through a thimble 26 and the bore of piston 27 to a connection 25 and the port 15 communicates with two passages 29 each of which extends (Fig. 5 and 7) through the valve 13 and leads through a thimble 32 and piston 33 to a connection 31. The pistons 33, 27 are termed hold-up pistons and regardless of which of ports 14, 15 is the high pressure port apply to the valve 13 a force. tending to hold the valve against its seat. The pistons are also so arranged that the force exerted thereby or by a group of hold-up pistons on one side of the cylinder barrel axis is applied to the valve at a point which is approximately opposite to the pressure centre of a pressure area surrounding the valve port on the same side of the cylinder barrel axis. The arrangement of one hold-up piston on one side of the cylinder barrel axis and two on the other is designed to reduce overall dimensions to a minimum. A greater number of hold-up pistons than that shown could be provided. The number of high pressure passages 11 and the number of low pressure passages continuously varies. For example in the pump shown there will be four high pressure passages and three low pressure passages at one instant and three high pressure passages and four low pressure passages at the next instant. This causes the pressure area surrounding the high pressure valve port to vary between a minimum and a maximum and the centre of pressure of the area to move radially. When the pump is operating at low speed as at starting the change in the pressure area and the centre of pressure causes the valve to be lifted off its seat. In order to prevent this the hold-up pistons are so arranged that the force or resultant force exerted thereby is applied to the valve at a point approximately opposite the centre of pressure of the minimum pressure area and balancing motors (spaces 40 and co-operating pistons 41) are provided to compensate for increases in the pressure areas and shifts of the centre of pressure. Pressure is transmitted to the spaces 40 of the balancing motors by passages 42 which extend to the face 12 of the valve 13 at positions between the ends of the ports 14, 15. The regions between the ends of the ports are termed bridges. The ends of the passages may be offset from the path of the cylinder ports. In a modification the capacity of the pump may be increased by adding additional rows of pistons and cylinders and the cylinder passages are arranged in at least two concentric circular rows and the leading edges of the passages in one row are offset from the leading edges of the passages in the other row. For example the cross section of the passages in the outer row may be elongated and that of the inner passages circular. In this case six balancing motors are arranged at the rear of each bridge between the valve ports and two hold-up pistons are employed on each side of the cylinder axis. The passages communicating with the outer three balancing motors in each bridge are arranged in the path of the outer row of cylinder passages and the corresponding motors are brought into operation successively. The passages of the inner motors are similarly in the path of the inner cylinder passages and the inner motors are brought into action successively. A larger number of balancing motors may be arranged behind each bridge. A medium size machine ordinarily has ten balancing motors behind each bridge. The rear part of the pump 2 and the valve 13 are connected together as a sub-assembly by pins 43 fixed to the rear part 2 fitting in bores in the valve, dowels 44 co-operating with reduced parts of the pins to hold the valve to the rear part. Various forms of mechanism may be used for shifting the block 18 but as shown a cam 50 (Figs. 2 and 12) is used for this purpose. A projection 51 on the slide block is held in engagement with the cam by a spring 52 and when the block has moved to the right (Fig. 2) past its neutral position the pressure delivered to a conduit 31 acts on a piston 53 to assist the movement of the block. The cam track has a portion 62 parallel with the line of motion of the cam and the track portion 63 rises abruptly from one end of the portion 62 and the track portion 64 drops away abruptly from the portion 62. The drop from one section to the other in practice may amount to only a few thousandths of an inch. This enables the pump to supply liquid as soon as the section 63 or 64 engages the projection 51 the amount of displacement being sufficient to compensate for leakage losses. Exact adjustment to the neutral position is effected by turning a screw 68 (Fig. 12) which bears on the lower end of an inclined roller 65 the cam 50 being capable of being inclined slightly by virtue of the fact that a piston 59 or 56 attached to it fits loosely in a corresponding piston 60 or 57. The pump displacement is controlled by rotation of a hub member 99 by a control member (not shown). Rotation of the hub member causes an eccentric part 96 of a shaft 95 connected to it to either move or allow a spring 90 to move a lever 91. Movement of the lever operates a valve 82 which controls the position of the cam 50. When the cam moves it brings the valve 82 back to its neutral position by means of cam surface 93 and rod 92. A torsion spring 98 returns the hub member to its neutral position when it is released. A gear pump 71, 72 which supplies pressure for operating the cam 50 is located in the pump casing 1 and driven from the shaft 5. To limit the distance through which the shaft 95 may be rotated a recess (not shown) is formed in the hub member 99, a stop bolt (not shown) co-operating with the recess.