| 摘要 |
<p>1,190,422. Tractor power lift mechanisms. WEATHERHEAD CO. 29 June, 1967, No. 30136/67. Heading A1P. Supply of pressure fluid from a variable displacement pump 45 to a ram 21 is controlled by a poppet valve 55 associated with a differential pressure regulator 53 and exhaust of ram fluid is controlled by another poppet valve 63 also associated with a differential pressure regulator 61. The valves are operated by a rockable cam 39 whose movement is controlled in dependence on the draft load on the lift linkage and its position, through a mechanical, electrical, or hydraulic connection. Fluid from the pump 45 passes through piston 77 which moves against a spring bias to throttle the fluid passage as pressure increases. For raising, the cam 39 moves clockwise to open valve spool 103 whence the fluid passes to the ram. A high pressure in the ram keeps non-return valve 57 closed until pump pressure is built up by fluid returning from valve 55 via conduit 75 and check valve 48 to operate the pump control 46. In an embodiment the supply circuit incorporates a pressure intensifier and the cam 39 has an additional cam to hold the valve spool 103 open and then to ensure a quick cut-off.</p> |
