Patent GB-538746-A (GB)
Title: Improvements in power transmission systems
IPC: F01B3/00
Filed: 1940-08-05
Abstract: 538,746. Hydraulic pumps and motors. VICKERS, Inc., HERMAN, K. R., and VICKERS, H. F. Aug. 5, 1940, No. 12580. [Class 102 (i)] [Also in Group XXIX] In a hydraulic gear comprising a pump and motor of the piston and rotary-valve type, the valve-members are subject to a separating force which increases with the pressure, and means responsive to the separation is provided for forcing them together, the arrangement preventing slip of the pump and motor under abnormal pressure. The pump shown in Fig. 1 is of the type comprising a barrel 44 coupled to a driving-shaft 16 and provided with pistons 24 in connection with a swash-plate 18, the barrel running on valve-plate 34 formed with seats 40 and ports 48. The barrel is now connected to a rod 58 having a flange 68 abutting on a spring 70. A piston 66 on the rod works in a bore 64 communicating through a passage 88 with a chamber 74 containing a valve 76 which is urged to the right by a spring 86 but is restrained by a lever 82 abutting on the rod 58. Normally, the valve connects the passage 88 to a passage 90. When the critical pressure is exceeded, the barrel overcomes the spring 70 and tends to separate from the valve 34, the piston is displaced slightly, and the spring 86 is permitted to displace the valve 76. Thereupon the bore 64 is connected through the passage 88 and a passage 92 to the upper or high-pressure port 48, and the piston 66 prevents the barrel from separating further from the valve-plate 24. If the pump is so arranged that either the upper or lower port 48 may be the high-pressure port, the passage 92 leads to both ports, and an auxiliary valve is provided for connecting the valve 74 to the port that is under high pressure. In the construction shown in Fig. 3, the additional force for urging the barrel 44 into contact with the valve 34 is determined by the amount of leakage. For this purpose, the bore 100 for the spring-urged piston 112 in connection with the barrel 44 is connected by passages 108, 134 to a recess 106 in the valve-plate 34, and a groove 136 in a cap 124 respectively. The groove 136 opens into a bore 138 containing a spring-urged pilotvalve 148 having large and small apertures 160, 162 for communication with the groove, and a chamber 140 having a restricted orifice 146 respectively. Normally the spring 122 holds the barrel in contact with the valve-plate, and leakage passes through the orifice 146. When the critical pressure is reached, pressure in the chamber 140 increases, and the valve 148 is depressed to restrict flow into the chamber 140. When leakage increases beyond the amount for which the valve and orifice are set, excess leakage is trapped in the bore 110, and the piston 112 prevents the barrel from separating further from the valve-plate. In a modification, Fig. 4 (not shown), a spring-urged pilot-valve 164 is arranged to connect a passage 134 leading to the bore 110 either with a passage 166 leading to the upper port 48, or to an outlet 168. The pilot-valve bore communicates through passages 176, 178 with the recess 106 in the valve-plate 34, and the outlet 168 respectively. When leakage increases, the pilot-valve lifts, pressure is admitted to the bore 110, and the piston 112 prevents the barrel from separating further from the valve-plate. In another modification, Fig. 2 (not shown), the pilot valve is omitted, and the bore 110, in addition to communicating through a passage 108 with the recess 106, communicates with a restricted outlet-passage 132. When leakage increases, resistance in the passage 132 increases, and the piston 112 presses the barrel on to the valve-plate.