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Hydraulic lifting mechanism

  • US 4,723,107 A
  • Filed: 01/13/1987
  • Issued: 02/02/1988
  • Est. Priority Date: 01/28/1986
  • Status: Expired due to Term
First Claim
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1. A hydraulic lifting mechanism for a battery-powered industrial truck, having a hydraulic lifting cylinder;

  • a hydraulic unit operating pump in a load lifting operational mode, in which a pressure medium is supplied to the lifting cylinder, and operating as a motor in a load lowering operational mode, in which the pressure medium exiting from the lifting cylinder powers the hydraulic unit;

    a DC generator coupled to the hydraulic unit which operates as an electromotor in the load lifting operational mode and as a generator in the load lowering operational mode;

    a regenerative brake circuit supplied by the DC generator in the load lowering operational mode;

    a control valve arrangement located in a pressure path between the hydraulic cylinder and the hydraulic unit; and

    a lifting mechanism control controlling the regenerative brake circuit and the control valve arrangement;

    characterized in that the control valve arrangement comprises a proportional valve, wherein the lifting mechanism control opens the proportional valve in accordance with a ramp-like function in the load lowering operational mode and activates the regenerative brake circuit, depending on an output current of the DC generator operating as a generator, if the generator output current exceeds a predetermined value.

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