Patent ID: 9631613
Date: 2017-04-25
CPC Classifications: B60L,B66F,F04B,F15B

Claim:
1. A hydraulic drive device for a cargo handling vehicle provided with a plurality of hydraulic cylinders including an up-and-down hydraulic cylinder for moving an object up and down with supply and discharge of hydraulic oil, and a plurality of manual control members including an up-and-down control lever configured so as to actuate the up-and-down hydraulic cylinder, the hydraulic drive device comprising: a tank reserving the hydraulic oil; a hydraulic pump having an inlet port for drawing in the hydraulic oil and an outlet port for discharging the hydraulic oil; an electric motor for driving the hydraulic pump; a first oil passage connecting the tank and the inlet port; a second oil passage connecting the outlet port and the plurality of hydraulic cylinders; a third oil passage branching off from the first oil passage and connecting the first oil passage and a bottom chamber of the up-and-down hydraulic cylinder; a solenoid-controlled proportional valve disposed on the third oil passage and configured to open with a valve travel depending upon a control input of a descent control of the up-and-down control lever; a pressure compensation valve disposed between a branch portion of the third oil passage and the tank on the first oil passage and configured to open with a valve travel depending upon a pressure difference between pressures upstream and downstream of the solenoid-controlled proportional valve on the third oil passage; a directional control valve disposed between the pressure compensation valve and the tank on the first oil passage and configured to be switched between an open position and a close position, wherein, while the descent control of the up-and-down control lever is performed, the directional control valve is configured to be placed in the open position, unless the descent control of the up-and-down control lever is performed singly and a difference between a command rotation rate and an actual rotation rate of the electric motor is less than a predetermined value; and a controller configured to control the solenoid-controlled proportional valve and the directional control valve.