JPH075266B2 - Hydraulic circuit in forklift - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydraulic circuit in a forklift,
In particular, it relates to prevention of temperature rise of hydraulic oil.

[Prior Art] There are various types of hydraulic circuits for forklift trucks, and a typical one is as shown in FIG.

That is, in FIG. 3, the hydraulic oil sucked up from the oil tank 1 is pressurized by the hydraulic pump 2 and sent to the control valve 3, and the first hydraulic fluid in the control valve 3
The hydraulic oil is supplied to and discharged from the lift cylinder 8 or the tilt cylinder 9 by moving the second spools 4 and 5 by the respective operating levers 6 and 7.
Further, as shown in the drawing, when the spools 4 and 5 are in the neutral position, the working oil is directly returned to the oil tank 1 via the pipe line 10.

[Problems to be Solved by the Invention] However, since the hydraulic circuit is housed in the machine frame together with the engine, when the temperature in the machine frame rises due to the operation of the engine, the hydraulic oil in the conventional hydraulic circuit increases. Could not sufficiently dissipate heat and the oil temperature could exceed the appropriate temperature, which could adversely affect hydraulic equipment and seals.

An object of the present invention is to solve such a problem.

[Means for Solving the Problems] Therefore, the hydraulic pump for a forklift according to the present invention forms an exhaust port communicating with an oil tank at the upper end of a cylinder tube of a lift cylinder, and introduces an operating oil. Is formed below the discharge port, and a first conduit for guiding the working oil that has passed through the control valve in a neutral state into the cylinder tube through the introduction port and a second conduit for directly returning to the oil tank. A pipe line is provided, and when the piston of the lift cylinder is located below the introduction port, the first pipe line is opened,
If it is on the upper side, open the second conduit,
It is characterized in that a switching valve for selectively opening and closing the first pipeline and the second pipeline is provided.

[Operation] In the hydraulic circuit for a forklift according to the present invention having the above-described structure, when the piston of the lift cylinder is lower than the introduction port and the control valve is in the neutral state, the hydraulic oil flows in the lift cylinder. Therefore, the lift cylinder functions as a radiator and the working oil is cooled.

[Embodiment] A preferred embodiment of a hydraulic circuit for a forklift according to the present invention will be described in detail below with reference to the drawings.

It should be noted that the same or corresponding portions as those of the conventional configuration will be described using the same reference numerals.

As shown in FIG. 1, the hydraulic circuit is
It is provided with an oil tank 1, a hydraulic pump 2 that pumps hydraulic oil from the oil tank 1 and supplies it to the lift cylinder 8 and the tilt cylinder 9, and a control valve 3 that controls the flow of hydraulic oil. The control valve 3 has a first spool 4 and a second spool 5, and the former selectively supplies / discharges hydraulic oil to / from the lift cylinder 8 by operating the operation lever 6, and the latter has the operation lever 7. Operation oil is selectively supplied to and discharged from the tilt cylinder 9. The hydraulic oil discharged from the lift cylinder 8 and the tilt cylinder 9 is returned to the oil tank 1 through the pipe line 10.

When both the first and second spools 4 and 5 are in the neutral position, the hydraulic oil passing through the control valve 3 passes through the pipe line 12 in which the check valve 11 is provided, and then the cylinder tube 8a of the lift cylinder 8. It is adapted to be guided into the interior through the introduction port 13. The introduction port 13 is formed at a position where the working oil can be supplied into the cylinder tube 8a above the piston 8b when the piston 8b is lowered to the lowest position. A discharge port 14 is provided at the upper end of the cylinder tube 8a, and the working oil in the upper portion inside the cylinder tube 8a is discharged from the discharge port 14 and returned to the oil tank 1 through the pipe line 15.

Further, a bypass pipe 16 is provided between the pipe line 12 and the pipe line 15, and a normally open type two-port two-position switching valve 17 is provided in the bypass pipe 16. The switching valve 17 is fixed to the outer mast 18, as clearly shown in FIG. Further, a roller 20 is attached to the spool 19 so as to engage with a cam plate 22 fixed to the inner mast 21, and the piston 8b of the lift cylinder 8 is
When is located below the introduction port 13, the cam plate 22 pushes the roller 20 to close the switching valve 17.

Next, the operation of the hydraulic circuit according to the present invention having such a configuration will be described.

When the engine 23 of the forklift is started and the hydraulic pump 2 connected to the rotary shaft of the engine 23 operates, hydraulic oil is pumped up from the oil tank 1 and supplied to the control valve 3. When the first and second spools 4, 5 of the control valve 3 are in the neutral position and the piston 8b of the lift cylinder 8 is in the lowest position, the cam plate 22 fixed to the inner mast 21 pushes the roller 20,
Since the switching valve 17 shuts off the bypass pipe 16, the hydraulic oil that has passed through the control valve 3 flows through the pipe line 12 into the cylinder tube 8a. The cylinder tube 8a of the lift cylinder 8 is exposed to the outside air, and the surface area of the cylinder tube 8a is considerably larger than that of other pipelines in the hydraulic circuit. Therefore, the cylinder tube 8a serves as a radiator. The working oil, which flows through it, effectively cools by exchanging heat with the outside air. The working oil cooled in the cylinder tube 8a is returned to the oil tank 1 through the discharge port 14 and the pipe line 15.

Next, when the first spool 4 is switched by the operation lever 6 to raise the fork, the hydraulic oil from the control valve 3 is supplied to the lower portion inside the cylinder tube 8a through the port 24 at the lower end of the lift cylinder 8. . As a result, when the piston 8b rises and reaches a position beyond the introduction port 13, the cam plate 22 on the inner mast 21 rolls over.
After switching from 20, the switching valve 17 is opened. Further piston 8b
As the hydraulic pressure rises, the hydraulic oil tries to flow backwards from the introduction port 13 through the line 12, which is prevented by the presence of the check valve 11. In this way the piston 8b
When the first spool 4 is returned to the neutral position when it is located above 13, the hydraulic oil flows to the oil tank 1 through the pipe 12, the bypass pipe 16 and the pipe 15, and the lift cylinder 8
Is maintained as is.

[Effects of the Invention] As described above, according to the present invention, in a normal operating state in which the cargo handling operation is not performed, the hydraulic oil in the hydraulic circuit flows in the lift cylinder, so that the heat of the hydraulic oil enters the outside air. It is dissipated and the oil temperature rise can be prevented. Therefore, the hydraulic equipment and seals are not adversely affected by heat, the reliability of the entire hydraulic system of the forklift truck is improved, and the service life is extended. Further, there is also an effect that rusting inside the lift cylinder can be prevented by constantly flowing oil to the upper part inside the cylinder tube.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic circuit for a forklift according to the present invention, FIG. 2 is a perspective view showing a main part of the present invention, and FIG. 3 is a hydraulic circuit diagram of a conventional device. In the figure, 1: Oil tank, 2: Hydraulic pump 3: Control valve 4,5: Spool 8: Lift cylinder, 8a: Cylinder tube 8b: Piston, 12,15: Pipe line 13: Introduction port, 14: Discharge port 16 : Bypass pipe, 17: Switching valve

Claims (1)

[Claims] 1. A hydraulic circuit for a forklift comprising an oil tank, a hydraulic pump for pumping hydraulic oil from the oil tank, and a control valve for supplying / discharging hydraulic oil pumped from the hydraulic pump to a lift cylinder or a tilt cylinder. In the above, a discharge port communicating with an oil tank is formed at the upper end of the cylinder tube of the lift cylinder, and an introduction port for introducing hydraulic oil is formed below the discharge port, and passes through the neutral control valve. A first conduit for guiding hydraulic oil into the cylinder tube through the introduction port and a second conduit for returning directly to the oil tank are provided, and the piston of the lift cylinder has the introduction port. When it is located lower than the above, the first pipeline is opened, and when it is located above In the hydraulic circuit of the forklift, a switching valve that selectively opens and closes the first pipeline and the second pipeline is provided so as to open the second pipeline when the hydraulic circuit is opened.