Patent GB-1051343-A (GB)
Abstract: 1,051,343. Hydrostatic transmissions. GENERAL MOTORS CORPORATION. April 23, 1964 [May 10, 1963], No. 16832/64. Headings F2C and F2D. [Also in Division F1] An hydrostatic transmission comprising delivery and return passages between positive displacement pump and motor units, and with a displacement control device for at least one of the units is provided with a pressure relief by-pass valve under the control of a signal pressure responsive to the speed of the pump such that the valve is caused to establish a fluid connection between the delivery and return passages whenever the speed of the pump exceeds a predetermined value. Hydraulic system.-As shown this comprises a pair of pumps 257, 262 driving motors 278, 297, liquid being supplied by a pump 308 through a pressure regulating valve 316, filter 312 and cooler 322. A restriction 313 in the supply line furnishes pressure differentials operating a governor valve 328. The system is also provided with a low pressure relief valve 371 and cooling supply valves 351, 352 which ensure the continuous flow of a predetermined volume of liquid through the heat exchanger. Pump and motor units Y.-The pumps and motors are of similar construction and of the swashplate type controlled by tiltable crank arms 135, Figs. 3 and 4. The double-acting pistons 127, 128 are connected by axial bolts 141 passing through ball joints 132 on the swashplate 136 which bears through a universal joint 171 against an abutment 172. The end of the crank arm has a ball joint connection 52 with an axially adjustable transverse piston unit 47 in a housing 36 rotated by a ring gear 33 meshing with a pinion 32 on a drive shaft 16. The piston unit 47 is connected by a lever 76 with an annular balance weight 71. The inclination of the crank arm 135 is adjustable by an extension a of an axially movable valve 102 bearing against an inclined surface 107 of the piston body 48, the valve being controlled by a lever 93 whose ends are respectively connected to a manual control rod 91 and a fluid pressure piston 83 connected to the governor valve 328. Reversing valves 267, 293 are provided between the pump and motor units. Valves 396, 397 connected to the pressure regulating valve 316 and governor valve 328 by lines 359, 309 control the displacement of the motors. A plug 407 at the left-hand side of valve 396 is subjected to the pressure in line 359 to bias the valve for increased displacement, while an axially movable member 411 at the right-hand side houses a spring 409 biasing the valve for decreased displacement. The member 411 is connected by a reversing link 414 to a rod 412 connected to the pump manual control rod 91, for conjoint control of pump and motor displacement in accordance with the setting of member 91. Pressure regulating valve.-The valve 316 has large and small lands a, b subjected respectively through lines 309, 319 to the motor displacement control pressure and the power circuit pressure, to maintain a constant proportion between these pressures, e.g. one-tenth. Excess liquid is exhausted by a cooling and make-up line 321, and exhaust connection 323 ensures free movement of the valve element. Pressure relief by-pass valves.-To prevent excessive pressure in the event of pump overspeeding the supply lines 279, 296 and exhaust lines 286, 304 are interconnected by relief cutoff valves 341, 342 of which the valve elements have lands a, b, c located, in the case of valve34]. in a three-step bore 344, the effective areas of lands b, c being equal. The lower surface of land a communicates with an overspeed signal line 337 connected to governor valve 328, its upper surface being vented to an exhaust 346. In the event of excessive pressure in line 277 during forward drive, this pressure communicated by a line 277to the unbalanced area of land b overcomes the pressure on land a to open a port 348 to the motor exhaust line 286. Similarly, on overrun, excessive pressure in the motor exhaust line 286 acting on land c also opens port 348 to the supply line 277. Opening of valve 341 uncovers a port 348 to allow heated liquid to escape through a by-pass port 345 to the sump 306 from which it passes through filter 312 and cooler 322 to the port 361 of cooling supply valve 351 located downstream of port 348. Modifications (Figs. 9 and 10, not shown).- These include the provision of differential control of right- and left-hand pump or motor units for vehicle steering purposes. The control rod 412 for conjoint control of the pump and motor displacement, acting in association with the plug members 407 of the motor displacement control valves 396, 397 forms the subject of Specification 1,051,344, while the displacement control valves 396, 397 and associated regulator valve 316 for maintaining constant proportionality between the motor displacement control and power circuit pressures forms the subject of Specification 1,051,345.