| 摘要 |
1,237,561. Variable speed gearing. CATERPILLAR TRACTOR CO. 14 June, 1968 [14 June, 1967], No. 13583/68. Heading F2D. A hydrostatic transmission comprising a variable displacement pump 31 in a closed loop 33, 34 with a variable displacement motor 32 is driven by an engine driving a positive displacement pump 70 with an output proportional to engine speed supplying fluid through a venturi 72 and a first chamber 75 and then a speed control valve 79 in parallel with an underspeed valve 80 to a second chamber 76 at a lower pressure due to restriction in the valve 79, the difference in pressure between the chambers 75, 76 being converted by a sensor 90 to a mechanical output adjusting a servo 37 controlling the pump 31 displacement. The underspeed valve 80 may be connected to the venturi 72 so as to open as the engine speed drops to cause the pump 31 displacement to reduce. The valve 80 may be in series with an idling valve 155 which closes when the engine is idling. The control may also vary the motor 32 displacement by a sensor 100 so that as the pressure differential increases the pump 31 displacement is first increased to a maximum and the motor displacement is then reduced. Steering of a two pump-motor transmission for a track-laying tractor may be effected by sensors 161 mounted on linkwork joining the sensors 90 to the pumps 31. The linkwork may comprise a link 65 pivoted to the sensor 90 and at 164 to two plates 162 pivoted at 163 and connected by a link 170 to the pump servo 37. Each sensor 161 is mounted on its plate 162 so that when actuated it moves the pivot of the link 170 on a path across 163. The sensors 161 are selectively controlled by a valve 175. Override control.-The pressure difference between the chambers 75, 76 may be reduced by an override valve operated either if excess pressure build up in the hydrostatic loop 33, 34 signalled via a line 255 to a sensor 136, or if a pedal 134 is depressed. Overspeed control.-If the engine overspeeds the pressure differential in lines 71, 72a of the venturi will actuate a valve 140 to apply the brakes 149. Relief and replenishing of the hydrostatic loop 33, 34 may be effected by the arrangement of ball valves and orifice units of Fig. 2 or of Figs. 8 and 9 (not shown) claimed in Specification 1,237,564. The ball valves of Fig. 2 may be replaced by the variable orifier valve of Fig. 13 (not shown) claimed in Specification 1,237,562. |
