| 摘要 |
<p>1,158,618. Masted lift trucks. PARKERHANNIFIN CORP. 13 April, 1967 [14 April, 1966], No. 17061/67. Heading B8H. [Also in Divisions F1 and F2] A spool valve 21, 11 for controlling a fluid pressure lifting motor 8 of a fork lift truck has a central neutral position (as shown), in which motor passages 29 connected to the ends of the motor are isolated; second and third positions in which one motor passage 29 is connected to its respective inlet passage 25 pressurized by a pump 16 while the other motor passage is connected to its respective outlet passage 30; and a fourth position in which fluid returning from the small area side of the motor is blocked and has to pass through a check valve 39 to its large area side of the motor to supplement the flow thereto and increase the motor speed. During normal operation of the motor for lifting a load the return from the upper cylinder chamber flows to an upper motor passage 29, through ports 35, 36 in the spool 21 and is discharged to an upper return passage 30 connected by a port 15 to the tank 17. If the spool 21 is upwardly displaced to its fourth position ports 36 are closed by a sleeve 38 and the return flow to the passage 30 is blocked. A second spool valve 20 controls the operation of a motor 5 for varying the lift of the truck mast and when both valves 20, 21 are in their neutral positions the pump output is returned to the tank through a by-pass passage 23.</p> |
