Forklift and fork control method

Patent metadata

Field	Value
Publication number	US-10752480-B2
Application number	US-201616465182-A
Country	US
Kind code	B2
Filing date	Dec 19, 2016
Priority date	Dec 19, 2016
Publication date	Aug 25, 2020
Grant date	Aug 25, 2020

Abstract

A forklift includes forks, cylinders for causing the forks to perform an ascending/descending operation in accordance with the flow rate of hydraulic oil, a first valve for controlling the flow rate of the hydraulic oil in accordance with an energizing current, a second valve 6 for regulating the flow rate of the hydraulic oil in accordance with cylinder pressure, and a control portion that calculates the flow rate to be regulated by the second valve, on the basis of cylinder pressure detected by a pressure sensor, calculates a current command value for the energizing current, with the flow rate to be controlled by the first valve being set equal to the regulated flow rate, and changes the energizing current in two stages, with the current command value as the upper limit of the energizing current, thereby decelerating the forks in two stages when stopping the ascending/descending operation.

First claim

The invention claimed is:

1. A forklift comprising:
forks for holding a load;
cylinders for causing the forks to perform an ascending/descending operation at an ascending/descending speed in accordance with a flow rate of hydraulic oil;
a first valve for controlling the flow rate of hydraulic oil in accordance with an energizing current;
a second valve for regulating the flow rate of hydraulic oil between the cylinders and the first valve in accordance with cylinder pressure on the cylinders;
a control portion for supplying the energizing current to the first valve;
an operating portion for stopping the ascending/descending operation; and
a pressure sensor for detecting the cylinder pressure, wherein,
the control portion calculates a regulated flow rate, being the flow rate to be regulated by the second valve based on the cylinder pressure,
the control portion calculates a current command value for the energizing current, with the flowrate to be controlled by the first valve being set equal to the regulated flow rate, and
the control portion changes the energizing current in two stages, with the current command value being set as an upper limit of the energizing current, thereby decelerating the forks in two stages when stopping the ascending/descending operation.

2. The forklift according to claim 1 , wherein,
the operating portion causes the ascending/descending operation to start,
the control portion calculates the regulated flow rate based on the cylinder pressure,
the control portion calculates the current command value, with the controlled flow rate being set equal to the regulated flow rate, and
the control portion changes the energizing current in two stages, with the current command value being set as the upper limit of the energizing current, thereby accelerating the forks in two stages when starting the ascending/descending operation.

3. The forklift according to claim 1 or 2 , wherein,
the control portion calculates a first command value for the energizing current in accordance with an amount of manipulation of the operating portion,
when the first command value is greater than a second command value being the current command value, the control portion changes the energizing current in two stages, with the second command value being set as the upper limit of the energizing current, and
when the first command value is less than the second command value, the control portion changes the energizing current in two stages, with the first command value being set as the upper limit of the energizing current.

4. The forklift according to claim 3 , comprising:
a memory portion having first data and second data stored therein, the first data indicating the relationship between the cylinder pressure and the regulated flow rate, the second data indicating the relationship between the energizing current and the controlled flow rate, wherein,
the control portion includes:
a first command calculation portion for calculating the first command value in accordance with the amount of manipulation;
a second command calculation portion for calculating the regulated flow rate based on the cylinder pressure and the first data and the second command value based on the regulated flow rate and the second data; and

a current supply portion for changing the energizing current in two stages, with the second command value being set as the upper limit of the energizing current when the first command value is greater than the second command value and the first command value being set as the upper limit of the energizing current when the first command value is less than the second command value.

5. The forklift according to claim 1 or 2 , wherein the first command calculation portion includes;
a speed calculation portion for calculating a speed command value for the ascending/descending speed in accordance with the amount of manipulation; and
a current calculation portion for calculating the first command value based on the speed command value.

6. A method for controlling forks of a forklift including forks for holding a load, cylinders for causing the forks to perform an ascending/descending operation at an ascending/descending speed in accordance with a flow rate of hydraulic oil, a first valve for controlling the flow rate of hydraulic oil in accordance with an energizing current, a second valve for regulating the flow rate of hydraulic oil between the cylinders and the first valve in accordance with cylinder pressure on the cylinders, a control portion for supplying the energizing current to the first valve, and an operating portion for starting and stopping the ascending/descending operation, the method comprising:
a first step for the control portion to calculate a first command value for the energizing current in accordance with an amount of manipulation of the operating portion;
a second step for the control portion to calculate a regulated flow rate, being the flow rate to be regulated by the second valve based on the cylinder pressure, calculate a second command value for the energizing current, with the flow rate to be controlled by the first valve being set equal to the regulated flow rate, and compare the first command value and the second command value; and
a third step for the control portion to change the energizing current in two stages, with the second command value being set as an upper limit of the energizing current when the first command value is greater than the second command value and the first command value being set as the upper limit of the energizing current when the first command value is less than the second command value, wherein,
the forks are accelerated in two stages when starting the ascending/descending operation and decelerated in two stages when stopping the ascending/descending operation.

7. The method according to claim 6 , wherein in the second step, the control portion calculates the regulated flow rate based on first data and the second command value based on second data, the first data indicating the relationship between the cylinder pressure and the regulated flow rate, the second data indicating the relationship between the energizing current and the control flow rate.

Assignees

• Mitsubishi Logisnext Co Ltd

Inventors

• Kimura Harukazu

Classifications

• F15B13/042

  operated by fluid pressure {(F15B13/0401, F15B13/0416 take precedence)} · CPC title

• B66F9/22 Primary

  Hydraulic devices or systems · CPC title

• B66F9/07559

  Stabilizing means · CPC title

• F15B13/0401

  Valve members; Fluid interconnections therefor · CPC title

• F15B2211/205

  Systems with pumps · CPC title