| 摘要 |
1,095,736. Hydraulic apparatus. I. SOYLAND and K. SOYLAND. Dec. 17, 1964 [Dec. 18, 1963], No.51408/64. Heading F1P. A control system for a hydraulic cylinder A having a ram B comprises an assembly of valves Va. . . Ve each having a piston member 1 controlling the flow from an inlet 4 to an outlet 5 and each being loaded by a spring 8 and by the pressure of fluid which passes through a restricted by-pass passage 6 in each valve to pilot lines 31, 32 or 43', the pressure in which is controlled by a spool valve 14 and by an adjustably loaded pilot valve 44 to thus control the operation of the valves Va... Ve. In the position of the control system shown, the spool valve 14 is in a position in which a control pressure line 25 connected to the valve Va communicates via an annular passage 21 and a conduit 23 with the tank 11. The piston member 1 of the valve Va is therefore only loaded by its spring 8 and hence opens to by-pass the output from the pump 12 back to the tank 11 through conduits 26', 27. In the position shown hydraulic fluid is trapped in both sides of the cylinder A by valves Vc, Ve which cannot open since fluid is trapped in the pilot lines 31, 32 by the spool valve 14. If however the pressure in the cylinder A reaches an excessive value the pilot valve 44 opens to allow the pressure to be relieved from the cylinder through valve Ve or Vc and a conduit 27. Movement of the spool 16 to the left opens the pilot conduit 32 to tank and closes the control pressure line 25. Closure of the line 25 causes pressure to build up therein to close the valve Va whereby the pump 12 supplies fluid to the right hand end of the cylinder A through a check valve 30, a main 26, the valve Vb which can open since the pilot conduit 32 is depressurized, and a main 28. The ram B therefore moves to the left and fluid is discharged from the left hand end of the cylinder A through a main 29, the valve Vc and the conduit 27 to the tank 11. In order to prevent fluid passing through the by-pass passage 6 of the valve Vb to the tank via pilot conduit 32 and spool valve 14, a ball 41 engages the rear end of the piston 1 when the valve Vb is open and hence closes the by-pass passage. The spool valve 14 is displaced to the right for operation of the ram in the opposite direction and in a similar manner to that described. To cushion the ram B at the ends of each stroke, normally open valves (not shown) are disposed in the pilot lines 31, 32, the valves being arranged to be closed by the movement of the ram 3, either through a direct mechanical link or via an electric circuit. The closing of these valves causes controlled closure of the associated valve Vc or Ve through which fluid is returning to the tank 11 and thus decelerates the ram 3. |
