Patent GB-1308941-A (GB)
Title: Hydrostatic propulsion drive for motor vehicles
IPC: F04B1/04
Filed: 1970-03-06
Abstract: 1308941 Controlling vehicles; tractors DEERE & Co 6 March 1970 [6 March 1969] 10867/70 Heading B7H [Also in Division F2]  An auxiliary hydrostatic transmission for driving the front wheels of a tractor comprises a pump 10 supplying pressure liquid to wheel motors 18, 20 through a forward-reverse valve 16 which is actuated through a relay valve 14 by a control valve 12 responsive to rotation of the tractor wheels. The pump output pressure is maintained at a preselected value by a regulating valve 48. The selected pump output pressure may be adjusted by a manually controlled relief valve 22. An override valve 122 ensures maximum pump output pressure when auxiliary equipment operated by the pump is in use. A flow-divider 166 on the spool of the forward-reverse valve 16 normally prevents differential action between the motors 18, 20 but enforces differential action on the motors 18, 20 during cornering. During operation of the vehicle service brakes an auxiliary control acts on the relay valve 14 to condition the forwardreverse valve 16 for reverse operation whereby hydrostatic braking is effected in the motors 18, 20. When the pump output pressure falls below a predetermined value the drive through the motors 18, 20 to the wheels is automatically disconnected. Pump construction and control.-Pump 10 has radial pistons 34 engaging an eccentric ring 32 on a driving shaft 24. The pistons 34 draw in liquid through an inlet valve 40 and discharge the liquid through an outlet valve 36 to a pressure supply line 38. The pump regulating valve 48 comprises a spring pressed piston 52 which urges a valve element 60 into engagement with a valve seat 64. The pump output pressure is supplied through passages 44, 68, 64, 70 to chambers 46, 78 and the pump pressure is additionally supplied from the chamber 46 through a bore 62 in the valve element 60 to the interior of the piston 52. When a rapid rise in pump output pressure occurs the valve 60 moves left against the action of the spring 54 and the pressure within the cylinder 52 to connect the duct 78 with a passage 72 leading to the interior 74 of the pump casing. The ensuing build up of pressure in the pump casing lifts the pistons 34 off the eccentric 32 to reduce pump displacement to a minimum. The pump output pressure additionally acts through lines 82, 84 on a piston 118 having a rod 120 which acts on the valve 60 to maintain pump output pressure at a preselected value. The pump output pressure is selected by a manually controlled relief valve 22 which determines the pressure supplied to the piston 118. An override valve 122 is opened when auxiliary hydraulic equipment is in use to vent the line 84 to the piston 118 and thus increase pump output pressure to a maximum. Motor construction.-Each motor comprises axial pistons 304 reciprocable in cylinders 314 of a cylinder block 302 fast with an output shaft 300 driving the vehicle wheels. The pistons 304 are connected to slippers 306 which slide on a swash-plate 308. The swash-plate 308 is axially slidable on the output shaft 300 and is connected by a sleeve 322 to a valve plate 320. When the supply pressure from the pump 10 exceeds a predetermined value the pressure in the cylinders 314 acts through the pistons 304 and slippers 306 to move the swash-plate 308 into engagement with a brake lining 324 on the motor casing 299. The swash-plate 308 is thus held against rotation and the motor operates in the normal way. When the pump supply pressure is below the predetermined value a spring 326 moves the swash-plate 308 away from the friction lining 324 to permit the swash-plate to rotate with the cylinder block and thus render the motor inoperative. The motor slippers 306 are interconnected by a ring 310 which is urged towards the swash-plate 308 by springs 311. The motor supply and return lines 168, 172 are connected to the motor by connectors 338, 336 which are aligned with steering pivots for the wheels. Control circuit.-A valve spool 148 of the forward-reverse valve 16 selectively connects the pump pressure supply duct 38 to motor supply lines 168, 170 (or 172, 174) and connects the motor return lines 172, 174 (or 168, 170) to lines 176, 178 which are connected through a filter 180 to a reservoir. The spool 148 is urged by spring 150, 152 to a central, neutral, position in which it blocks the pump supply duct 38. The pump supply pressure is supplied through lines 270, 268 to chambers 266, 264 at the ends of the spool 148. The chambers 266, 264 are connected through lines 262, 260 to the relay valve 14 which has a pointer 224 that selectively throttles exhaust from the lines 262, 260 to cause a pressure build-up in one of the chambers 266, 264 to move the valve spool 148 into its forward or reverse position. The pointer 224 is pivoted about its shaft 220 by pistons 236, 238, 240, 242. The piston 240 is manually actuated by a lever 258 and holds the pointer 242 in its central, neutral, position. The piston 242 is actuated by pressure liquid supplied through a line 276 from a brake valve 278 when the vehicle brakes are applied. The piston 242 pivots the pointer 224 to its reverse position in which it throttles the line 262. The pistons 236, 238 are actuated by pressure liquid supplied through lines 214, 212 from the control valve 12 and respectively move the pointer 242 to its reverse and forward positions in which it throttles the lines 262, 260. The control valve 12 comprises spring closed ball valves 200, 202 which are selectively opened by plungers 186, 188 actuated by a rocker 184 having a friction drag connection to a shaft 182 which rotates with the vehicle wheels. When the vehicle wheels rotate the rocker 184 pivots about the shaft 182 and acts through one of the plungers 186, 188 to open one of the ball valves 200, 202 to supply pressure liquid to one of the lines 212, 214. The pointer 224 of the relay valve 14 indicates the ratio engaged and can be seen through a magnifying glass 282. The flow divice 166 on the valve spool 148 normally supplies equal quantities of liquid to the motor supply lines 168, 170 but, when one motor tends to run faster than the other, is rotated to throttle the supply to the faster running motor. The pressure in the motor supply lines 168, 170 is fed through lines 288, 290 and restrictions 298, 296 to the opposite sides of a rotary piston 284 fast with the valve spool 148. The drop in pressure in the faster running motors supply line thus acts on the piston 284 to rotate the valve spool 148 and throttle the supply to that line. The opposite sides of the piston 284 are additionally connected through lines 292, 294 to a steering control valve which causes rotation of the valve spool 148 to enforce differential action on the motors for steering purposes.