GB992070A - Hydraulic transmission - Google Patents

Abstract

992,070. Hydro-mechanical variable speed gears; hydraulic transmission. SUNDSTRAND INTERNATIONAL CORPORATION S.A. March 12, 1962 [March 13, 1961], No. 9371/62. Headings F2C and F2D. An hydraulic transmission comprises a swashplate pump driving a swash-plate motor in which the transmission is brought up to speed by manual control of a servomotor, an override being provided responsive either to rapid movement of the manual control or to increase in load on the motor to control the servomotor by overriding the manual control. The swashplates 28, 45, Fig. 1, of a pump and motor are each connected to a cylinder 53, 75 movable on fixed pistons 55, 77. The spaces on either side of the piston are fed with fluid from a make-up pump through passage 59, the spaces 69, 90 being supplied through a restriction while the spaces 66, 86 are fed through ports 64, 85. The spaces 69, 90 are connected to drain by passages controlled by a valve plate 100 having valve to passages shaped so that rotation of the plate from the position shown first restricts the passage from space 69 to cause cylinder 53 to move outwards, cylinder 75 remaining stationary, to increase the pump output after which space 19 is opened to drain to allow cylinder 75 to move inwards, cylinder 53 remaining stationary, to decrease the motor displacement thus increasing the speed to a maximum. The valve plate 100 is rotated by a manually controlled lever 115 acting through a cylinder 120 and link 122. The lever 115 is connected to a piston member 119 which normally remains centred in a cylinder 120 by springs 121 throughout movement of the lever. Fig. 8 shows a modified control in which the pump and motor swash-plates 238, 239 are varied in the above described manner by valve cam slots 251, 252 in a valve plate 250 actuated by a piston 262. The cylinder spaces 266, 267 on either side of the pistons are fed from the make-up pump 229 through restrictions 271 and these spaces are connected to drain through passages 262, 273 under the control of a reduced portion 275 of a manually actuated valve 261 and to restricted passages 266<SP>1</SP>. Override control.-The connecting lines between the pump and motor 23, 24, Fig. 1, have passages 142, 143 leading to passages 192 such that the pressure in these lines acts on enlarged pistons 200 of control valves 181, 182. A makeup pump 33 supplies passages 140, 141 and passages 191 leading to ports in the control valve 181, 182 which on actuation of the valve 181 or 182 are connected to passages 194 leading to cylinder 120. Assuming that the lever 115 is actuated in a counter clockwise direction, the line 24 is the high-pressure line and if the lever is moved rapidly, the pressure in line 24 increases above a predetermined value which causes the spool 196 of valve 182 to move to the right allowing pressure fluid from the make-up pump to flow into the right-hand side of cylinder 120. The cylinder 120 then moves to the right relative to the piston 119 and overrides the manual signal to reduce the speed of rotation of valve plate 120 and hence the speed of swashplate adjustment. A similar action takes place when the transmission is set for maximum speed and the load on the motor increases. This subsequent movement of the cylinder 120 then rotates the valve plate to first increase the inclination of the motor swash-plate and if the pressure in line 124 is still excessive, the inclination of the pump swash-plate is reduced to cause stalling without a pumping action. The override in Fig. 8 is provided by a spring-loaded spool valve 281 subjected at either end to the pressure in the transmission lines 227, 228 such that in the event of excessive pressure in the high-pressure line, the space 266, 267 is connected to drain through passage 283 to retard or adjust movement of the piston in response to rapid manual movement of the valve or load on the motor as above. In a further modification, the cam slots are formed on a rotatable member having teeth meshing with a rack on the servomotor piston in this case, separate valves similar to the valves 181, 182 of Fig. 1 control flow from the cylinder spaces direct to drain. Cooling.-The make-up pump is also used to cool the fluid and the pump and motor. The pump 33, Fig. 1, delivers to the low-pressure line and excess of fluid required to make up losses. Non-return valves 144 loaded by springs and pressure in lines 23, 24 control the flow of make-up fluid from passage 141. The excess hot fluid in lines 23, 24 is forced through passages 130 or 131 to passages 160, 161 having branches 167, 168 leading to the ends of a shuttle valve 165 such that the high-pressure line, say 24, causes the valve 165 to move to the left and close passage 161 while opening passage 160 to a passage 172 whereby the hot fluid of lowpressure line 23 flows through passage 175, cooling tubes 176 and sprays 177 to cool the pump and motor casings. A valve 152 is provided which in the non-operative condition of the transmission connects the passages 148, 149 and hence lines 23, 24 but is moved to close this connection prior to starting the transmission. In a modification the non-return valves 144 may be extended to act as piston valves controlling the flow from the low-pressure line to the passage 175 thus replacing the shuttle valve. Variable speed gears.-An input shaft 379, Fig. 10, of an hydraulic transmission extends through the motor shaft 400 of motor 377. The shaft 379 carries a sun gear 406 and the motor shaft carries a ring gear 407. The output shaft 410 is formed with a carrier 409 for a planet set 411 meshing with both ring and sun gear. The transmission is manually adjusted to vary the speed of output shaft 410 in relation to input shaft 379. Specifications 992,071, 992,072, 992,073 and 992,074 are referred to.