Hydraulic control device for forklift

Patent metadata

Field	Value
Publication number	US-9771250-B2
Application number	US-201214368410-A
Country	US
Kind code	B2
Filing date	Dec 10, 2012
Priority date	Dec 26, 2011
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

A hydraulic control device for a forklift includes a hydraulic pump, a single electric motor for driving the hydraulic pump, an outflow control mechanism provided between a lift cylinder and the hydraulic pump, a flow control valve provided between the outflow control mechanism and a draining portion, and a controller. When a lowering operation of a fork and either forward or rearward mast tilting operations of a mast are performed at the same time, the controller controls the electric motor based on a target speed of the hydraulic pump. The flow control valve controls the flow rate of hydraulic fluid from the lift cylinder to the hydraulic pump and the flow rate from the lift cylinder to the draining portion in accordance with the difference between the actual rotation speed of the hydraulic pump and the target rotation speed of the hydraulic pump.

First claim

The invention claimed is:

1. A hydraulic control device for a forklift, wherein
the hydraulic control device selectively raises and lowers a fork by supplying hydraulic fluid to a lift cylinder or discharging hydraulic fluid from the lift cylinder through manipulation of a raising/lowering instruction member,
the hydraulic control device tilts a mast to which the fork is attached selectively forward and rearward by supplying hydraulic fluid to a tilt cylinder and/or discharging hydraulic fluid from the tilt cylinder through manipulation of a tilting instruction member,
the hydraulic control device comprises:
at least one hydraulic pump;
a single electric motor for driving the hydraulic pump;
an outflow control mechanism arranged between the lift cylinder and the hydraulic pump, wherein the outflow control mechanism permits hydraulic fluid to flow from a bottom chamber of the lift cylinder to the hydraulic pump when the fork is lowered, and the outflow control mechanism prohibits hydraulic fluid from flowing from the bottom chamber of the lift cylinder to the hydraulic pump when the fork is in a stopped or raised state;
a flow control valve arranged between the outflow control mechanism and a draining portion; and
a controller that controls the electric motor, wherein, when the fork is lowered and, simultaneously, the mast is tilted forward or rearward, the controller controls the electric motor based on a target rotation speed of the hydraulic pump necessary for operation at an instructed speed corresponding to a manipulation amount of the raising/lowering instruction member or a manipulation amount of the tilting instruction member,
wherein, in order to obtain a flow rate of hydraulic fluid flowing from the lift cylinder corresponding to the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed, the flow control valve controls a flow rate of the hydraulic fluid flowing from the lift cylinder to the hydraulic pump and a flow rate of the hydraulic fluid flowing from the lift cylinder to the draining portion in correspondence with a difference between an actual rotation speed of the hydraulic pump and the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member.

2. The hydraulic control device according to claim 1 , wherein, when the actual rotation speed of the hydraulic pump is short in relation to the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member, the flow control valve delivers the flow rate of the hydraulic fluid flowing from the lift cylinder to the draining portion by a flow rate corresponding to a shortage in the rotation speed.

3. The hydraulic control device according to claim 2 , wherein
the controller controls the electric motor based on the target rotation speed of the hydraulic pump necessary to tilt the mast forward or rearward at the instructed speed corresponding to the manipulation amount of the tilting instruction member, and
when the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member is greater than the actual rotation speed of the hydraulic pump, the flow control valve delivers the flow rate of the hydraulic fluid flowing from the lift cylinder to the draining portion by a flow rate corresponding to the shortage in the rotation speed.

4. The hydraulic control device according to claim 2 , wherein
the controller controls the electric motor based on the greater one of the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member and the target rotation speed of the hydraulic pump necessary to tilt the mast forward or rearward at the instructed speed corresponding to the manipulation amount of the tilting instruction member, and
the hydraulic control device further comprises a flow rate adjustment mechanism arranged between the hydraulic pump and the tilt cylinder, wherein the flow rate adjustment mechanism adjusts the flow rate of the hydraulic fluid discharged from the hydraulic pump to a flow rate necessary to tilt the mast forward or rearward at the instructed speed corresponding to the manipulation amount of the tilting instruction member.

5. The hydraulic control device according to claim 2 , wherein
the outflow control mechanism includes an electromagnetic proportional valve having an adjustable opening degree,
when the fork is lowered, the controller adjusts an opening degree of the electromagnetic proportional valve to deliver the flow rate of the hydraulic fluid flowing from the lift cylinder to the hydraulic pump and the flow rate of the hydraulic fluid flowing from the lift cylinder to the drain portion by a flow rate necessary for the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member, and
when the fork and the mast are operated simultaneously and the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member is less than the target rotation speed of the hydraulic pump necessary to tilt the mast forward or rearward at the instructed speed corresponding to the manipulation amount of the tilting instruction member, the controller adjusts the opening degree of the electromagnetic proportional valve to restrict outflow of hydraulic fluid by a flow rate corresponding to the difference between the target rotation speed of the hydraulic pump necessary to lower the fork at the instructed speed corresponding to the manipulation amount of the raising/lowering instruction member and the target rotation speed of the hydraulic pump necessary to tilt the mast forward or rearward at the instructed speed corresponding to the manipulation amount of the tilting instruction member and the flow control valve delivers the flow rate of the hydraulic fluid flowing from the lift cylinder to the hydraulic pump.

6. The hydraulic control device according to claim 1 , wherein the flow control valve regulates the flow rate of hydraulic fluid flowing from the lift cylinder to the draining portion by adjusting an opening degree of the flow control valve in correspondence with a difference between a pressure in a portion between the lift cylinder and the outflow control mechanism and a pressure in a portion between the outflow control mechanism and the hydraulic pump.

7. A hydraulic control device for a forklift, wherein
the hydraulic control device selectively raises and lowers a fork by supplying hydraulic fluid to a lift cylinder or discharging hydraulic fluid from the lift cylinder through manipulation of a raising/lowering instruction member,
the hydraulic control device tilts a mast to which the fork is attached selectively forward and rearward by supplying hydraulic fluid to a tilt cylinder and/or discharging hydraulic fluid from the tilt cylinder through manipulation of a tilting instruction member,
the hydraulic control device comprises:
a single hydraulic pump;
a single electric motor for driving the hydraulic pump;
an outflow control mechanism arranged between the lift cylinder and the hydraulic pump, wherein the outflow control mechanism permits hydraulic fluid to flow from a bottom chamber of the lift cylinder to the hydraulic pump when the fork is lowered, the outflow control mechanism prohibits hydraulic fluid from flowing from the bottom chamber

Assignees

• Toyota Jidoshokki Kk
• Nishina Kogyo Kk

Inventors

• Ueda Yuki
• Matsuo Tsutomu
• Ishikawa Hirohiko
• Goto Tetsuya
• Morita Junichi
• Fukatsu Toshinari
• Nakajo Akira
• Yazawa Ryo

Classifications

• E02F9/2246

  Control of prime movers, e.g. depending on the hydraulic load of work tools · CPC title

• F15B2211/40515

  with variable throttles or orifices · CPC title

• F15B11/044

  by means in the return line {, i.e. "meter out"}(F15B11/046, F15B11/05 take precedence) · CPC title

• F15B11/0423

  by controlling pump output or bypass, other than to maintain constant speed · CPC title

• F15B2211/761

  Control of a negative load, i.e. of a load generating hydraulic energy · CPC title