HYDRAULIC CONTROL DEVICE OF A FORKLIFT TRUCK

摘要

A hydraulic control device of a forklift truck includes a first hydraulic cylinder, a first instruction member, a second hydraulic cylinder, a second instruction member, a hydraulic pump, an electric motor, a first passage which has a drain passage, a lowering control valve that controls flow of hydraulic oil, a flow rate control valve, and a controller. When a lowering operation of forks and an operation of a hydraulically-operated unit are performed simultaneously, when a required rotation speed of the hydraulic pump that is required for operating the hydraulically-operated unit at an instruction speed based on an operation of the second instruction member is a specified rotation speed or lower, the controller controls an instruction rotation speed of the electric motor so as to operate the hydraulic pump at the required rotation speed to thereby restrict the operation of the hydraulic pump.

主权项

1. A hydraulic control device of a forklift truck comprising:
a first hydraulic cylinder that lifts and lowers forks of the forklift truck; a first instruction member that instructs lifting and lowering operation of the forks; a second hydraulic cylinder that operates a hydraulically-operated unit other than the forks; a second instruction member that instructs operation of the hydraulically-operated unit; a hydraulic pump that supplies hydraulic oil to the first hydraulic cylinder and the second hydraulic cylinder; an electric motor that is connected to the hydraulic pump and causes the hydraulic pump to operate; a first passage through which the first hydraulic cylinder and an intake port of the hydraulic pump are connected to each other; a lowering control valve that is disposed in the first passage and allows flow of hydraulic oil from the first hydraulic cylinder toward the hydraulic pump while the forks are being lowered and that blocks the flow of hydraulic oil from the first hydraulic cylinder toward the hydraulic pump while the forks are being lifted or at a stop; a drain passage that is branched from the first passage at a portion between the lowering control valve and the hydraulic pump; a flow rate control valve that is disposed in the drain passage and controls a flow rate of hydraulic oil; and a controller that controls the electric motor based on operation of the first instruction member and the second instruction member, wherein in a case of a simultaneous operation mode in which a lowering operation of the forks and an operation of the hydraulically-operated unit are performed simultaneously, when a required rotation speed of the hydraulic pump required for operating the hydraulically-operated unit at an instruction speed based on the operation of the second instruction member is a specified rotation speed or lower, the controller controls an instruction rotation speed of the electric motor so as to operate the hydraulic pump at the required rotation speed, and when the required rotation speed of the hydraulic pump is higher than the specified rotation speed, the controller controls the instruction rotation speed of the electric motor so as to operate the hydraulic pump at the specified rotation speed to thereby restrict the operation of the hydraulic pump.