Patent GB-902185-A (GB)
Title: Improvements in and relating to hydrostatic transmission for self-propelled vehicles
IPC: F16H61/472
Filed: 1960-03-24
Abstract: 902,185. Hydraulic transmission of power. PEARSON, R. C. Feb. 24, 1961 [March 24, 1960], No. 10534/60. Class 69 (2). [Also in Group XXXI] Each track of an endless track vehicle is driven by a servo-controlled hydraulic motor or set of motors working together in parallel or series, the motor or motors of both tracks being driven by a servo-controlled pump or set of pumps working in parallel and driven by the vehicle prime mover, a single driving control element controlling the servo of the pump or pumps, there being also means responsive to the pressure in the supply line to the motors to increase the displacement of the motors with increase of pressure and vice versa and means for operating the motor servos concurrently in opposite directions whereby relative changes of speeds of the tracks are produced for steering purposes. As shown in Fig. 1, the engine 1 drives a variable displacement swashplate pump 3 which has output and input lines 5 and 6 having branched connections 51, 52 and 61, 62 leading to motors 7 and 8, each of which is of the variable displacement over-centre type, e.g. swash-plate motors, and which are connected by bevel gears 25 and 26 to the driving-wheels of the endless tracks 27 and 28. The angle of the swash-plate of the pump 3. may be varied, whereby variations of pressure in either line 5 or 6 according to the desired direction, may be produced by a lever 4 operated by an hydraulic servo 11 with a follow-up valve 12 which are connected by a link 13 rocked through an operating rod 14 from a lever 15, the link-13 being centralized by springs 313 and 314 which also give "feel" to the driver's control. The motors 7 and 8 have swash-plate operating levers 9 and 10 moved by servos 17, 18, each having its follow-up valve, 19, 20, there being interconnecting links 21, 22 respectively. The various servos are supplied by a pump 29 driven through gears 30 from the motor 1, the pump being supplied from a reservoir 34 and also making up the motor conduits 5 and 6 through non-return valves 35 and 36. Relief valves 33, 37 and 38 avoid excess pressure in the various circuits. A shuttle valve 39 having a piston 40 is connected between the lines 5 and 6 and is connected to a pressure-sensitive device 42 having a piston 43 acted upon by a spring 44. The rod 45 of piston 43 rotatably carries a toothed wheel or disc 46 which carries a pair of diametrically-opposite pins 47 and 48, normally at right-angles to the piston-rod and which engage within slots 49 and 50 in the links 21..and 22. A worm 57 is rotatably carried by an arm 58 attached to the piston-rod 45 and may be rotated by shaft 56 and gears 55 from a steering- wheel 54 so that by rotation of the steering- wheel 54, the disc 46 is rotated so moving of the links 21, 22 in opposite directions to increase the speed of one motor relative to the other. The steering action may be sufficient to reverse the direction of one motor. If resistance to motion is encountered the pressure in the line 5 or 6 is increased so moving the piston 42 and thus bodily moving the disc 49 whereby both links 21 and 22 are moved an equal amount to simultaneously increase the output of both motors 7 and 8. As the excess pressure drops, the spring 44 will restore the piston 43 to its original position. Adjustable limit stops 63 and 64 are provided for the piston 42. In a modification, Fig. 2, the operating links 21 and 22 are connected to piston-rods 122, 123 in a telemotor system which comprises transmitters 117 and 118 and the receivers 119, 120 connected by fluid lines 151, 152, 153 and 154, the pistons,of the receivers following the pistons of the transmitters which are operated by a lever 115. The receivers 119 and 120 are carried by the piston-rod 125 of a pressure-sensitive device connected to a shuttle valve 39 in a manner corresponding to the first embodiment. The opposite sides of the piston 125 are connected by conduits 190 and 129 to a spring-loaded ballvalve 130 which communicates through lines 133 and 134 with the reservoir. A flow restrictor 128 normally maintains a pressure differential across the device 124 when there is pressure in the line 127 whereby the piston 125 is moved when through a cam 136 and plunger 132, the pressure on spring 131 is increased to the point at which the leak is decreased and the piston is balanced. In a further embodiment, Fig. 3, the track-actuating motors 201, 202 are of the type comprising a fixed swash-plate and movable body. The motor bodies are rotatable by servos 19 and 20 having follow-up valves 17 and 18, the actuating arms 21 and 22 being connected to spring-loaded plungers 203 and 204 which bear upon cam surfaces 205, 206 of a member 207 carried upon a rod 208 attached to the pistonrod 45. The cam member 207 is movable up and down upon the rod 208 through steering links 210, 211, and this through the plungers 203, 204 produces the differential steering effect. Simultaneous movement of both motor bodies is produced by the member 207 according to movements of valve 42 in a similar manner to the first embodiment. In another modification, Fig. 4, the operating levers 21 and 22 are connected to toggle levers 213 and 214 which are connected to a member 215 of the piston 45 of valve 42. Movement of the piston causes simultaneous movement of the operating levers and differential movement for steering is produced by a member 216 from the steering link 211. The drawing accompanying the Provisional Specification shows an alternative hydraulic circuit in which a prime mover 1 drives a pair of pumps 5, 6 through gears 2, 3 and 4 and a pump 48. Pumps 5 and 6, which supply the track driving-motors 16 and 17 are controlled by a servo 10 through links 7 and 8, the servo being operated by a pair of pedals 11 and 12, one for forward motion and one for reverse. The motors 16 and 17 are operated from a steering- wheel 29 and valve 18 in a manner corresponding to that in Fig. 1 above. The pump 48, which draws fluid from a reservoir 49, supplies the servos and makes up the fluid in the track motors and pumps circuit through non-return valves 51 and 52. The pressure and return lines of the pumps 5 and 6 are connected by lines 61 and 64 and pressure-relief valves 50, 55 and 56 are provided. The lever 13 operating servo 10 is also connected to the speed control 15 of the prime mover, which may be an internal-combustion piston engine or shaft driving combustion turbine engine.