| 摘要 |
1,148,455. Hydraulic control systems for lifts. COAST ELEVATOR CO. 23 May, 1966 [17 Sept., 1965], No. 22879/66. Heading B8L. [Also in Divisions F1 and G3] An hydraulically operated lift is decelerated as it approaches its required stopping position and completes its travel at a slower uniform speed so as to allow almost instantaneous stopping. As shown, a pump 12 supplies fluid via line 14 to a cylinder containing a liftraising piston 10. A by-pass valve 18 in bypass line 20, 22 is biased to an open position by spring 28 and by line pressure acting on piston 26A, and is closed by line pressure acting via restriction 34 on piston 26, the latter pressure being modulated by valves 38, 48 which control the leakage from chamber 27. During starting, valve 18 is open but a small backpressure is generated and this acts in chamber 27 (valve 38 being closed) to close valve 18 to a small extent, this action increasing the backpressure and causing further closure of valve 18. This action is self perpetuating and valve 18 closes to allow all of the fluid to pass to cause movement of piston 10. During this starting process, the piston accelerates to a relatively high uniform speed. As the lift approaches its destination solenoid-operated valve 38 is opened to vent chamber 27 to allow the by-pass valve to move towards its fully open position. The flow to piston 10 therefore decreases but, at a predetermined flow rate, a check valve 44 causes valve 48 to restrict the vent line 36. Valves 44, 48 then function to maintain movement of the lift at a relatively low uniform speed by preventing complete opening of the by-pass valve. When the lift reaches its destination it is stopped virtually instantaneously by causing pump 12 to stop or by causing a dump valve to open to by-pass all the output of the pump. |
