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Fork-lift system

  • US 4,761,954 A
  • Filed: 03/16/1987
  • Issued: 08/09/1988
  • Est. Priority Date: 03/16/1987
  • Status: Expired due to Fees
First Claim
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1. In a fork-lift vehicle, wherein a battery-operated electric motor is relied upon for selective up/down positioning drive of a fork-lift slide having a predetermined span of operational displacement along upstanding guides, the improvement in which a single-acting hydraulic-hoist actuator is connected for direct up/down positioning of the slide and in which said actuator and a hydraulic accumulator and a power integrator are interconnected as a fluid-conserving hydraulic system, said power integrator being a liquid-displacement device and having first and second ports respectively connected to said actuator and to said accumulator, a volume of hydraulic fluid self-contained within the included volume of said actuator and integrator and accumulator to the extent at least sufficient to enable operation of said actuator for more than said span, said accumulator having a volume substantially in excess of said hydraulic-fluid volume and said actuator being under gas pressure at a level at least more than sufficient to balance a load in excess of a deadweight-load condition on said actuator;

  • a first pilot-operated check valve in the port connection to said actuator and a second pilot-operated check valve in the port connection to said accumulator, each of said check valves being oriented to check flow in the direction toward said integrator, and said integrator further including rotatable means having a torsionally responsive relation to port-to-port flow through the integrator and said rotatable means having a shaft connection to said electric motor; and

    control means including a motor-driven connection and fluid-pressure operated means responsive to liquid displacement by said rotary device and connected to both of the respective pilots of said check valves, whereby regardless of the direction of liquid displacement by said device, both pilot-operated check valves will be opened by pilot action and will remain open, and fluid pressure will be applied to both of the respective pilots of said pilotoperated check valves, during all up or down operations of said fork-lift slide.

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