Patent GB-1221857-A (GB)
Title: Hydrostatic transmission
IPC: F16H47/04
Filed: 1968-04-24
Abstract: 1,221,857. Hydromechanical change speed gear control. SUNDSTRAND CORP. 24 April, 1968 [8 May, 1967], No. 19506/68. Heading F2D. In a hydromechanical variable speed gear for a motor vehicle wherein planet pinions 46 on a carrier 47 connectible to an input shaft 14 mesh a sun gear 51 on an output shaft 21 and a reaction ring gear 45 controlled by one or more hydrostatic transmissions 16, 17 driven from the input shaft 14 and hydraulically operated friction clutches 53, 55 are selectively engaged to lock-up the planet train for a pure hydrostatic drive and to connect the carrier 47 to the input shaft 14 for a split torque hydromechnical drive, the pump displacement of each hydrostatic transmission is controlled by an engine speed responsive governor valve 65 which meters pressure liquid to a displacement adjusting servo 33 through a reversing valve 147 and a shift valve 145 which reverses the connections between the governor valve 65 and servo 33 when the gear changes from hydrostatic drive to a hydromechanical drive. Fluid system components.-The governor valve 65 is urged left by a centrifugal governor 263 against the bias of a spring 266 which reacts against a rod 272 positioned in accordance with accelerator pedal position. The shift valve 145 changes over automatically when the servo pressure acting through a line 202 (or 201) on the end of the shift valve overcomes main supply pressure 140 acting between differential lands 185, 186 (or 188, 189). A neutral control valve 153 normally blocks lines 303, 304 from the hydrostatic transmission supply and return lines 112, 113. When the right hand end 295 of the valve 153 is vented a spring 301 moves the valve right to connect the lines 303, 304 to opposite ends of the servo 33 whereafter unequal pressure in the lines 112, 113 adjusts the pump displacement to equalize the pressures. A governor valve 151 supplies pressure liquid to the end 295 of the neutral valve 153 when the engine speed exceeds 1000 r.p.m. and vents the neutral valve at engine idle. A manual control 69 may over-ride the governor valve 151 and vent the neutral valve 153 at any time. Pressure liquid for the neutral valve 153 is supplied from the shift valve 145 through valves 155, 157 associated with the actuating piston 164, 160 of the friction clutches 53, 55. Make-up fluid is supplied to the hydrostatic transmission through check valves 119, 120 and a high pressure relief valve 125 is provided. Operation.-To start in forward ratio the reversing valve 147 and shift valve 145 are positioned as shown, whereupon pressure liquid is supplied to the clutch actuating servo 164 to engage the clutch 53 for pure hydrostatic drive. On depression of the accelerator pedal the governor valve 65 is moved right and as the engine speed increases is returned to the left by the governor 263. This initial movement of the governor valve 65 does not change the displacement of the hydrostatic transmission pump 23 since the neutral valve 153 is still vented. When the engine speed exceeds 1000 r.p.m. the governor valve 151 supplies pressure liquid to the neutral valve 153 which blocks lines 303, 304 whereafter the displacement of the pump 23 is controlled by the governor valve 65. As the engine speed rises above the value determined by the accelerator pedal position the governor valve 65 is moved left to supply pressure liquid through line 229 to the left end of the servo 33 to increase the displacement of the pump 23 and additionally load the engine to maintain its preset speed . When the pump displacement attains its maximum value the pressure in the line 229 and line 202 is sufficient to move the shift valve 145 right whereupon the clutch servo 164 is vented to disengage the clutch 53 and the clutch servo 160 pressurized to engage the clutch 55 for hydromechanical drive. In addition the shift valve 145 reverses the connections between the governor valve 65 and servo 33 so that the line 229 is connected to the right end of the servo 33. Thereafter further increases in engine speed cause the pump displacement to be reduced and thus additionally brake the ring gear 45 to increase output speed. During hydromechanical drive the pump displacement may be reduced to zero for a purely mechanical drive and then increased to a maximum in the opposite direction. Hydromechanical operation is not available for reverse drive since, with the valve 147 changed over, increasing pressure the line 229 due to increase engine speed acts through the line 201 on the right end of the shift valve whilst the line 202 is vented.