Patent GB-957321-A (GB)
Title: Improvements in or relating to hydraulically operated power transmission systems andto vehicles incorporating such systems
IPC: F16H39/00
Filed: 1960-08-31
Abstract: 957,321. Hydraulic transmission of power. C. VAN DER LELY N.V. Aug. 31, 1960 [Sept. 15, 1959], No. 30095/60. Heading F2C. [Also in Divisions B7 and G3] An hydraulically-operated power transmission comprises a swash plate actuated, multiplepiston pump 1, Figs. 1 and 2, adapted to supply hydraulic pressure medium to a similar motor 2, the pump and motor each having a housing 3, 30, formed with a plurality of chambers 5, 32 which receive the pistons 4, 31, each housing being rotatable about an axis 65 and at least on swash plate 11, 37 being turnable about an axis 15, 41 which intersects the said axis of rotation by a coupling rod 72 connected to the swash plate at a distance from the axis of rotation and the axis about which the swash plate is turnable. The housing 3 of the pump is mounted in bearings 7, 8 and driven by a shaft 6 connected to the engine of a tractor and bears against a port plate 25 urged into contact with the housing by dish-springs 26 abutting a stationary part 27 of the casing of the transmission ; the housing 30 of the motor is similarly arranged and the part 27 has passages 63, 64 therethrough serving to connect together the high and low pressure sides of the pump and motor. The swash plates are rotatably mounted in bearings 18, 19, 44, 45 in the casing and are connected by rods 72 to pins eccentrically disposed on the ends of a shaft 75 having a gear 86 engaging a rack movable by a followup servomotor 87 actuated by a manuallyoperated control rod 91. The rod has a valve portion which when the rod is moved to the left relative to the piston 89 of the servomotor connects a passage 108, Fig. 5, which communicates with a source of fluid pressure and a chamber 110 on one side of the piston, to a chamber 111 on the other side to move the piston as a result of the differential areas also to the left. When the rod 91 is moved to the right the chamber 111 is connected to an exhaust passage 121 and a reservoir 122 so that pressure in the chamber 110 moves the piston to the right. A lost-motion connection consisting of a disc 94 secured to the rod and urged to a central position in a cavity in the piston 89 by springs 96, 97 permits the rod to move relative to the piston and also permits the rod to move the piston in the absence of fluid pressure in the passage 108. The swash plate of the pump is adjustable in either direction from a position perpendicular to the axis 65 of rotation of the housing 3 and the swash plate of the motor is adjustable from a minimum position inclined at 6 degrees from a plane perpendicular to the axis 65 to enable the tractor to be driven either forwardly or backwardly. The eccentricities of the pins on the shaft 76 are such that for a given rotation of the shaft, the swash plate of the pump moves through a greater angle than does that of the motor and in such a manner that as the swash plate of the pump is moved to increase the stroke of its pistons, the swash plate of the motor is moved to reduce the stroke of its pistons. The port plates 25, 52 of the pump and motor are provided on one side with recesses 58, 59, 60, 61, Fig. 2, having an area substantially equal to the areas on the other side of the plates exposed to the high and low pressure so that the plates are in equilibrium. The recesses 58, 59, 60, 61 are engaged by bosses on the part 27 to prevent movement of the port plates transversely to the axis 65. The surfaces 154, Fig. 11, of the port plates abutting the housings may be provided with circular or arcuate grooves 158, 159 and a groove 162 and recess 166 connected by passages 164, 167 to the reservoir; the grooves 158, 159 are connected by passages 160, 161 to the recesses 155, 156 which are at high and low pressures so that oil passes between the grooves and forms a lubricating film between the relatively moving surfaces of the plates and housings. Pins 185, Fig. 16, may be disposed in the passages between the recesses and groove and have an inclined end 188 whereby upon relative rotation between the housing and pin, the pins rotate and reciprocate to prevent blockage of the passages. The transmission 202, Fig. 19, is disposed between the engine 203 and back wheels 204, 205 of the tractor which has a single steerable front wheel 206. A control lever 209 is operable by the driver in either of two directions and is connected to the rod 91 to control the transmission for forward or backward drive, the seat 214 of the tractor being rotatable through 180 degrees. The control lever has an extension 221, Fig. 21, which, when the lever is in a neutral position towards which it is urged by springs 225, 226, depresses a piston 229 against a spring 230 to displace fluid beneath the piston so as to displace a free piston 275, Fig. 25, and the spool 267 of a valve to connect together passages 261, 262 between the pump and motor whereby the outlet of the pump is connected to the inlet of the pump and the supply to the motor by-passed. The spool 267 of the valve has a rod 271 connected to a pivoted feeler 258, Fig. 19, which in the event of the tractor tilting as a result of engaging a heavy load, pulls the spool 267 downwardly to again by-pass the supply to the motor and prevent further torque being applied to the back wheels. The spool 267 is also movable downwardly to by-pass the supply to the motor when fluid pressure is supplied to a passage 279 to move the free piston 275 and act on the spool upon a pedal 260 being actuated to apply the brakes of the tractor. The tractor is normally steered by movement of a handle 237 rocking a cylinder 239, Fig. 24, in a direction N or S about a pivot 240 so that a lever 241 extending from the cylinder actuates a link 242 of an hydraulically-operated and steering mechanism for the front wheel. If a tight-curve is to be negotiated, further movement of the cylinder 239 causes lostmotion in a connection between the lever 241 and a rod 247 to be taken up and a valve 246 is operated to apply the brake of one or other of the back wheels to assist the steering operation. Specifications 957,322, 957,323, 957,324, 957,325 and 957,326 are referred to.