JPH1111125A - Hydraulic circuit of industrial vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage to a damper by an excessive load without enlarging the damper. SOLUTION: A damper 12 is arranged between a body frame 1a and a rear accelerator 11 to supply and discharge a hydraulic fluid according to the rocking of the rear accelerator 11. A controller C controls the damper 12 so as to lock it as occasion demands and fix the rear accelerator 11 to the body frame 1a. A shut-off valve 13 switches each piping P1-P3 for carrying the hydraulic fluid supplied and discharged from the damper 12 to interrupted state and communicating state according to the control of the controller C. When the hydraulic pressure within the damper 12 reaches a relief pressure in the state where the pipings P1-P3 are laid in the interrupted state by the shut-off valve 13, first and second valves 19, 20 reduce the pressure so that this hydraulic pressure does not exceed the maximum resistant hydraulic pressure of the damper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit for an industrial vehicle having an axle swingably provided.

[0002]

2. Description of the Related Art Conventionally, forklifts have been proposed in which an axle can be swung with respect to a body frame in consideration of the traveling performance and riding comfort of the vehicle. In this forklift,
When the forklift turns, it swings according to, for example, lateral acceleration (centrifugal force). For this reason, the running stability at the time of turning was reduced, and the running speed could not be increased.

Japanese Patent Application Laid-Open No. 58-211903 has provided a turning detecting means for detecting a centrifugal force generated at the time of turning of a forklift. When the detected value of the centrifugal force exceeds a predetermined value, the swinging operation is performed. A technique has been proposed in which an axle that is supported is fixed by an axle fixing mechanism.

[0004] In this forklift, when the centrifugal force acting on the lift during turning of the forklift becomes a predetermined value or more, the turning can be performed in a stable state with the axle fixed.

The axle is fixed by locking a damper which is a double-acting hydraulic cylinder disposed between the vehicle body frame and the axle. That is, by blocking the passage for supplying and discharging the hydraulic oil to the damper so that the damper cannot supply and discharge the hydraulic oil, the damper is locked and the axle is fixed. Further, by making the passage communicated, the locked state of the damper is released, and the axle can swing.

[0006]

The forklift is transported on a truck or the like. Then, there is a case where one of the rear wheels lands first, such as when being hung by a crane and lowered on the ground. Further, when a heavy load is loaded on the fork, the center of gravity of the forklift may be shifted forward and the rear wheel may float, and then one of the rear wheels may land first. At this time, the supply and discharge of the hydraulic oil from the damper is prevented, and in a state where the damper is locked, the weights of the axles and wheels rapidly act on the damper, and the pressure in the hydraulic chamber changes instantaneously and greatly. At this time, the hydraulic pressure in the hydraulic chamber to which a large pressure is applied in the double-acting hydraulic cylinder is five times the pressure applied to one of the hydraulic chambers when turning and traveling on a flat place with the axle fixed. That is all. The pressure applied to one hydraulic chamber when turning while climbing over a protrusion or the like with the axle fixed is one hydraulic pressure when turning on a flat place with the axle fixed. It is about 2-3 times the pressure applied to the chamber.

Therefore, the above-described damper of a forklift has a large hydraulic chamber in one of the hydraulic chambers when one of the wheels provided on the axle interlocking with the damper comes in first when the forklift is lowered from the truck. A damper having a withstand pressure standard that does not damage the cylinder of the damper even when pressure is applied is used.

However, in consideration of the damage of the damper due to the landing of one wheel, which is a special state, when the above-mentioned pressure-resistant standard is large, that is, when the damper having a thick cylinder is used, its outer diameter becomes large. Become. Therefore, there is a problem that the degree of freedom in design is reduced in order to secure a mounting space for the damper. In addition, there is a problem that the cost of the damper increases as the thickness of the cylinder increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an industrial vehicle which can prevent damage to a damper due to an excessive load without increasing the size of the damper. It is to provide a hydraulic circuit.

[0010]

According to the first aspect of the present invention, in an industrial vehicle having an axle supported to be vertically swingable with respect to a body frame, the industrial vehicle is disposed between the body frame and the axle. A damper for supplying and discharging hydraulic oil in accordance with swinging of the axle, locking control means for locking the damper as necessary and fixing the axle to the body frame, and control of the fixing control means On the basis of,
A control valve for switching the pipeline through which the hydraulic oil supplied / discharged from the damper flows when fixed, and for switching the pipeline to a communication state when the pipeline is not fixed, and when the control valve is in a blocked state. In the case where the hydraulic pressure in the damper in which supply and discharge of the hydraulic oil cannot be performed reaches a preset suppression pressure that is smaller than the maximum hydraulic pressure that the damper can withstand,
The gist of the invention is to provide a suppression means for suppressing the oil pressure from exceeding the maximum oil pressure that the damper can withstand.

In the invention according to claim 2, the gist is that the suppressing means is a pressure reducing means for reducing the pressure. In the invention according to claim 3, the gist is that the suppression means is a pressure control valve connected in parallel to the control valve.

[0012] In the invention described in claim 4, the damper is a double-acting type having two hydraulic chambers, a first chamber and a second chamber partitioned by a piston. A first valve that passes hydraulic oil to the second chamber when the hydraulic pressure in the chamber reaches the suppression pressure; and a first valve that passes hydraulic oil to the first chamber when the hydraulic pressure in the second chamber reaches the suppression pressure. The gist is that two valves are connected in parallel.

According to the fifth aspect of the present invention, the suppression pressure is the maximum hydraulic pressure applied to the first chamber or the second chamber when the vehicle normally travels with the axle fixed to the vehicle body frame by locking the damper. The gist is to make the value larger than the value.

According to the first aspect of the present invention, the damper is disposed between the vehicle body frame and the axle, and supplies and discharges the hydraulic oil according to the swing of the axle. The fixing control means controls the damper to be locked as necessary to fix the axle to the vehicle body frame. Based on the control of the fixed control means, the control valve switches the pipeline through which the hydraulic oil supplied / discharged from the damper flows to the shut-off state when fixed, and switches the pipeline to the communication state when not fixed. The suppression means, when the control valve is in the shut-off state, when the hydraulic pressure in the damper, which is incapable of supplying and discharging hydraulic oil, reaches a preset suppression pressure smaller than the maximum oil pressure that the damper can withstand,
The oil pressure is suppressed so as not to exceed the maximum oil pressure that the damper can withstand. Therefore, even if an excessive load is applied to the damper, the oil pressure does not exceed the maximum oil pressure that the damper can withstand, so that the damper is not broken.

According to the second aspect of the present invention, since the suppressing means is a pressure reducing means for reducing the pressure, supply and discharge of the hydraulic oil cannot be performed when the control valve is in the cutoff state. When the oil pressure in the damper reaches a preset suppression pressure smaller than the maximum oil pressure that the damper can withstand, the pressure is reduced so that the oil pressure does not exceed the maximum oil pressure that the damper can withstand. Therefore, even if an excessive load is applied to the damper, the oil pressure does not exceed the maximum oil pressure that the damper can withstand, so that the damper is not broken.

According to the third aspect of the present invention, the hydraulic pressure in the damper, in which supply and discharge of the hydraulic oil cannot be performed, reaches the suppression pressure only by connecting the pressure control valve in parallel with the control valve. At this time, the oil pressure is controlled so as not to exceed the maximum oil pressure that the damper can withstand. Further, since the hydraulic oil is supplied and discharged similarly to the control valve, it can be processed in the circulating hydraulic circuit.

According to the fourth aspect of the present invention, the pressure control valve includes: a first valve that passes hydraulic oil to the second chamber when the hydraulic pressure in the first chamber reaches a suppression pressure; When the hydraulic pressure in the second chamber reaches the suppression pressure, the first and second valves are constituted by the second valve that allows the hydraulic oil to flow through the first chamber, so that the first and second valves include a relief valve, a spring-loaded check valve, and the like. The simple valve can be used.

According to the fifth aspect of the present invention, the suppression pressure is applied to the first chamber or the second chamber when the vehicle normally travels with the damper locked and the axle fixed to the body frame. Since the oil pressure is set to a value larger than the maximum value of the oil pressure, the same effect as the effect of claim 1 is obtained, and at the time of normal running, the oil pressure applied to the first chamber or the second chamber is suppressed by the suppression means, and the hydraulic oil is passed. Never. Therefore, when the vehicle travels normally, it is possible to perform stable traveling without releasing the blocking state of the damper. Therefore,
When the vehicle travels with the damper locked, the suppression pressure is set to a value close to the maximum value of the hydraulic pressure applied to the first chamber or the second chamber, and the maximum hydraulic pressure that the damper can withstand the suppression pressure Is set to a close value, the above effect can be obtained, and the damper can have a small withstand pressure standard, that is, the thickness of the cylinder can be reduced.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 3 is a side view showing the forklift 1 as an industrial vehicle. The forklift 1 includes a pair of left and right outer masts 2 at the front thereof.
An inner mast 3 is arranged between the lifts so as to be able to move up and down. A fork 4 is provided on the inner mast 3 so as to be able to move up and down. That is, the fork 4 moves up and down along the outer mast 2.

A tilt cylinder 5 is connected between the outer mast 2 and the body frame 1a of the forklift 1. The body 5a of the tilt cylinder 5 is connected to the vehicle body frame 1a, and the piston rod 5b of the tilt cylinder 5 is connected to the outer mast 2. That is,
The outer mast 2 is tilted in accordance with the expansion and contraction of the piston rod 5b of the tilt cylinder 5, and the fork 4 is tilted.

The inner mast 3 has a lift cylinder 6
, And the body 6a of the lift cylinder 6 is fixed to the outer mast 2. That is,
The inner mast 3 moves up and down based on the expansion and contraction of the piston rod 6 b of the lift cylinder 6, and the fork 4 moves up and down as the inner mast 3 moves up and down.

A pair of left and right front wheels 7 are provided at the front of the body frame 1a of the forklift 1. Each front wheel 7
Is connected to the engine via a differential ring gear (not shown) and a transmission (not shown), and each front wheel 7 is driven by the engine. That is, the front wheels 7 are driving wheels.
Also, at the rear of the body frame 1a of the forklift 1,
Left and right rear wheels 8a and 8b are provided.

FIG. 1 shows a connecting structure for connecting the rear wheels 8a and 8b. A rear axle 11 extending in the vehicle width direction is provided at a lower rear portion of the body frame 1a of the forklift 1.
Are provided so as to be able to swing (rotate) about the center pin 11a. The rear wheels 8a and 8b are connected to the left and right sides of the rear axle 11, respectively. Rear wheels 8a, 8b
Are steered wheels that are steered based on the operation of the steering wheel 10 in the cab 9. The rear axle 11 forms an axle connecting the rear wheels 8a and 8b.

A hydraulic damper (hereinafter simply referred to as "damper") 12 is connected between the body frame 1a and the rear axle 11. The damper 12 is a double-acting hydraulic cylinder. That is, the damper 12 is connected to the rear wheel 8
a, 8b are absorbed.

The damper 12 has a substantially cylindrical body 12a.
And a piston 12b disposed in the body 12a. The piston rod 12 includes a piston rod 12
c are connected. The rear axle 11 is connected to the tip of the piston rod 12c.

The interior of the damper 12 is partitioned by a piston 12b into a first chamber R1 and a second chamber R2, which are hydraulic chambers. The first and second chambers R1 and R2 have first and second chambers, respectively.
The pipelines P1 and P2 are connected in a communicating state. The first pipeline P1 is connected via a shutoff valve 13 as a control valve to a third pipeline P3 having a fixed throttle valve 14 for limiting the flow rate of hydraulic oil. Shut-off valve 13 is 2
Port 2 position switching valve, and its spool has a flow valve section 1
3a and a stop valve portion 13b with a check valve are formed.
The shut-off valve 13 includes an electromagnetic solenoid 13c, and the switching between the excited state and the non-excited state of the electromagnetic solenoid 13c is performed by a controller C as fixed control means connected to the solenoid 13c as shown in FIG. .

The second and third pipes P2 and P3 are connected to the fourth pipe P
The fourth pipeline P4 is branched to a fifth pipeline P5 having a fixed throttle valve 15 for restricting the flow rate of hydraulic oil.

A sixth pipeline P6 is connected to the accumulator 16 which stores hydraulic oil at a predetermined pressure. The shuttle valve 17 closes the low-pressure pipe of the fourth and sixth pipes P4 and P6, and allows the fourth pipe P4 to communicate only with the high-pressure pipe to the fifth pipe P5. P4 and the sixth conduit P6 are connected. That is, the accumulator 16 and the shuttle valve 17 are configured such that the hydraulic pressure of the hydraulic oil interposed in the first and second chambers R1 and R2 and the first to fifth pipes P1 to P5 is higher than the hydraulic pressure of the hydraulic oil in the accumulator 16. Only when it becomes smaller, the hydraulic fluid is connected from the accumulator 16 to the hydraulic circuit via the sixth pipeline P6.

The first pipe P1 is connected to a second pipe P2 via a manual valve 18, and the manual valve 18 communicates with the first and second pipes P1 and P2 based on a manual operation from outside. State or a cut-off state, and the pipes P1, P
2 is shut off.

The first pipe P1 is a first valve 1 for relief as a suppressing means and a pressure reducing means which is a pressure control valve.
9 is connected to the second pipeline P2. More specifically, when the oil pressure on the first pipeline P1 reaches the relief pressure X as the suppression pressure, the first valve 19 for relief sends the hydraulic oil on the first pipeline P1 to the second pipeline P2. The first pipeline P1 and the second pipeline P2 are connected so as to flow.

Further, the second pipe P2 is connected to the first pipe P1 via a second valve 20 for relief as a pressure control valve and a relief means as a pressure reducing valve. More specifically, when the oil pressure on the second pipeline P2 side reaches the relief pressure X as the suppression pressure, the second valve 20 for relief sends the hydraulic oil on the second pipeline P2 side to the first pipeline P1 side. The first pipeline P1 and the second pipeline P2 are connected so as to flow. That is, the shutoff valve 13 and the first and second relief valves 19 and 20 are connected in parallel.

The first and second valves 1 for relief are
In the present embodiment, for example, as shown in FIG. 2, the valve bodies 9 and 20 include valve bodies 19a and 20a, springs 19b and 20b,
It is composed of poppets 19c and 20c. The relief pressure X is determined based on the strength of the springs 19b and 20b, the shape of the poppets 19c and 20c, and the like.

When the forklift 1 thus configured is stopped, the electromagnetic solenoid 13 of the shutoff valve 13
Since c is not excited, the first pipeline P1 and the third pipeline P3 are cut off by the valve stop 13b.

When the forklift 1 travels, the electromagnetic solenoid 13c is excited, and the first pipe P1 and the third pipe P3 are switched by the flow valve 13a so as to be in communication. That is, the damper 12 is in an unlocked state, and the rear axle 11 to which the rear wheels 8a and 8b are connected is in a state capable of swinging with respect to the vehicle body frame 1a. In this state, the force acting on the rear wheels 8a and 8b is
And the traveling of the forklift 1 becomes stable.

When an excessive centrifugal force is applied to the forklift 1, for example, at the time of a heavy load and a high lift, or a sharp turn, the lift 1
If 2 is in the unlocked state, it cannot turn in a stable state. In such a case, the damper 1
When the lock of the second axle 2 is required, the controller C controls the rear axle 11 to be fixed to the vehicle body frame 1a, the excitation solenoid 13c of the shut-off valve 13 is de-energized, and the first line P1 The third pipe line P3 is switched to the shut-off state by the stop valve portion 13b.

Here, based on the turning direction, the presence or absence of protrusions on the running surface, the load of cargo handling, etc., the first
The hydraulic pressure in one of the hydraulic chambers R1 and R2 is increased. During normal running, the set value of the relief pressure X is determined based on the maximum hydraulic pressure Y during normal running, which is the maximum value of the hydraulic pressure applied to the one hydraulic chamber. That is, the relief pressure X is equal to the maximum hydraulic pressure Y during the normal running.
It is set to a larger value.

At the same time, the relief pressure X is increased by the damper 12.
Is determined based on the withstand voltage standard. That is, the relief pressure X is set to a value smaller than the maximum hydraulic pressure Z that the damper 12 can withstand.

Therefore, for example, when the left rear wheel 8a lands first and a large load is applied to the damper 12 in the direction of contraction when the forklift 1 with the damper 12 locked is lowered from the truck, etc. Although the oil pressure in the chamber R1 suddenly increases, when the pressure reaches the relief pressure X, the working oil flows from the first pipe P1 to the second pipe P2 via the first relief valve 19. Therefore, since the hydraulic pressure of the first chamber R1 does not become larger than the maximum hydraulic pressure Z, the cylinder or the like of the damper 12 is not damaged.

For example, when the right rear wheel 8b lands first when the forklift 1 with the damper 12 in the locked state is lowered from the truck, and a large load is applied to the damper 12, the second chamber R2 Hydraulic pressure increases rapidly, but when the pressure reaches the relief pressure X,
The hydraulic oil flows from the second pipeline P2 to the first pipeline P1 via the second valve 20 for relief. Therefore, since the hydraulic pressure of the second chamber R2 does not become larger than the maximum hydraulic pressure Z, the cylinder of the damper 12 is not damaged.

That is, when an excessive load is applied to the damper 12 due to a special state such as landing of one of the rear wheels 8a, 8b, the first pipes 19, 20 for relief use the first pipe. The hydraulic oil is allowed to flow between P1 and the second pipeline P2, and the damper 12 is unlocked, that is, the rear axle 11 can be swung, so that the hydraulic pressure in the damper 12 becomes excessive. To prevent.

The relief pressure X is a cracking pressure Xa which is a pressure at which oil starts flowing through the valves 19 and 20.
And a pressure Xb at the full flow rate, which is the pressure at which the oil flowing through the valves 19 and 20 reaches the maximum flow rate (allowable maximum flow rate). Therefore, in detail, the cracking pressure Xa is set to a value larger than the maximum hydraulic pressure Y during the normal running, and the pressure Xb at the full flow rate is
2 is set to a value smaller than the maximum hydraulic pressure Z that can be endured. The allowable maximum flow rate is a flow rate at which sufficient hydraulic oil flows so that when the hydraulic pressure in one of the hydraulic chambers suddenly increases, the hydraulic pressure does not become larger than the full flow pressure Xb.

As described above, according to the present embodiment,
It has the following features. (1) In the present embodiment, the relief pressure X of the first and second relief valves 19 and 20 in the hydraulic circuit is the maximum hydraulic pressure applied to one hydraulic chamber when the vehicle travels with the damper 12 locked. The value is set to a value larger than the maximum hydraulic pressure Y during normal running, and is set to a value smaller than the maximum hydraulic pressure Z that the damper 12 can withstand.

Therefore, when the rear axle 11 is fixed to the vehicle body frame 1a during a sharp turn or the like, the first and second relief valves 19 and 20 are connected to the first pipe P1 and the second pipe P1.
In order to shut off the flow of the hydraulic oil between the pipelines P2, the damper 1
2 is maintained, and stable running can be performed.

When the forklift 1 is lowered from the truck, one of the rear wheels 8a and 8b lands first.
Even if the hydraulic pressure in the damper 12 increases, when the hydraulic pressure reaches the relief pressure X, the first and second relief valves 1
Reference numerals 9 and 20 denote dampers 12 for permitting the flow of hydraulic oil from the high pressure side to the low pressure side between the first pipeline P1 and the second pipeline P2.
Is released and the hydraulic pressure is
2 is depressurized so as not to exceed the maximum hydraulic pressure Z that can be withstood.
Therefore, the forklift 1 with the damper 12 locked is in a locked state.
Even if one of the rear wheels 8a, 8b lands first when the vehicle is unloaded from the truck, the hydraulic pressure generated at that time causes the damper 1
2 does not exceed the maximum hydraulic pressure Z that can be withstood and does not break.

(2) In the present embodiment, the maximum hydraulic pressure Z that the damper 12 can withstand is the rear wheels 8a, 8
The determination may be made based on the relief pressure X without having to consider the case where the oil pressure in one of the hydraulic chambers suddenly increases due to the landing of one wheel b. Therefore, if the relief pressure X can be reliably maintained in the locked state during normal operation and the value is close to the maximum hydraulic pressure Y during normal traveling, the damper 1
2 can be set to a value close to the maximum oil pressure Y during normal running. As a result, the damper 12 can have a smaller withstand pressure standard than the conventional damper, that is, a thinner cylinder.

(3) Since the thickness of the cylinder of the damper 12 can be reduced, the cost of the damper 12 can be reduced. (4) Since the thickness of the cylinder of the damper 12 can be reduced, the outer diameter of the cylinder can be reduced.
Therefore, the space required for mounting the damper can be reduced, and the layout of the damper and its surrounding components becomes easy.

(5) In the present embodiment, a first relief valve 19 and a first relief valve 19 are provided between the first and second pipelines P1 and P2.
Since the relief second valve 20 in the opposite direction to the valve 19 is connected, when one of the oil pressures reaches the relief pressure X, the oil pressure flows from the larger one to the smaller one. Therefore,
Even if the locked state of the damper 12 is released due to a special state such as the landing of one of the rear wheels 8a and 8b, it can be processed in the circulating hydraulic circuit. Therefore, simply the first and second
Compared to a system in which relief valves are provided in the pipelines P1 and P2 to release the oil into the oil tank, there is no need for a means for supplying the released hydraulic oil after the treatment.

(6) In the present embodiment, the first and second relief valves 19 and 20 as the suppressing means and the pressure reducing means are used.
Are valve bodies 19a and 20a, springs 19b and 20b,
A simple valve composed of the poppets 19c and 20c is used. Therefore, the cost does not increase due to the first and second relief valves 19 and 20 as the suppressing means and the pressure reducing means.

(7) In the present embodiment, the accumulator 16 and the shuttle valve 17 are connected to the first and second chambers R1, R
When the hydraulic pressure of the hydraulic oil interposed in the second and first to fifth pipes P1 to P5 becomes smaller than the hydraulic pressure of the hydraulic oil in the accumulator 16, the hydraulic oil is supplied from the fifth pipe P5 into the hydraulic circuit. Therefore, even if hydraulic oil leaks from the damper 12 or the like, the hydraulic circuit is always filled with an appropriate amount of hydraulic oil,
The locking effect of the damper 12 does not decrease. or,
Even if the hydraulic pressure in the hydraulic circuit increases when a load is applied to the damper 12 or the like, the shuttle valve 19 shuts off the hydraulic oil to the sixth pipe line P6, so that the hydraulic oil flows back to the accumulator 22. There is no.

The embodiment is not limited to the above, but may be modified as follows. In the above embodiment, one hydraulic damper is disposed between the vehicle body frame 1a and the rear axle 11, but two dampers 30, 31 are disposed on the left and right as shown in FIG. May be.

In this case, the piston 30 in the damper 30
The third chamber R3, which is a hydraulic chamber in which the piston rod 30b defined by a does not exist, is a fifth chamber which is a hydraulic chamber in which the piston rod 31b defined by the piston 31a in the damper 31 does not exist. R5 and a seventh pipe P7. Piston rod 30 in damper 30
The fourth chamber R4, which is the hydraulic chamber in which b exists, is connected to the first pipeline P1, and the piston rod 3 in the damper 31
The sixth chamber R6, which is the hydraulic chamber in which 1b exists, is the second chamber R6.
It is connected to the pipeline P2. Even in this case, the same effect as in the above embodiment can be obtained.

The first and second valves 19 and 20 for relief
Can be any valve that can control the flow of hydraulic oil based on the oil pressure, such as a type that maintains the oil pressure at a constant pressure.For example, using a valve such as a relief valve or a spring-loaded check valve You may comprise.

In the above embodiment, the first relief
And the second valves 19 and 20 are separately connected in parallel, but the present invention is not limited to this. For example, bidirectional relief may be performed by a valve in which both are integrated.

In the above embodiment, the first and second pipes P
A first valve 19 for relief and a second valve 20 for relief in a direction opposite to the first valve 19 are connected between the first and second pipes P1 and P2. A valve may be provided to release the hydraulic oil to the oil tank when the relief pressure X is reached. In this case, the escaped hydraulic oil is supplied by the accumulator 16.

In the above embodiment, the shuttle valve 17 and the fixed throttle valve 15 are used. However, if the backflow from the damper 12 to the accumulator 16 can be prevented, another type of valve is used instead. May be. For example, you may implement using a check valve.

In the above embodiment, the shut-off valve 1
Reference numeral 3 denotes a normally closed type that cuts off in a non-excited state, but is not limited thereto, and may be implemented using a normally open type.

In the above embodiment, the shut-off valve 1
Although the control valve 3 is used, any other control valve may be used as long as the control valve can be switched between the communication state and the cutoff state.

In the above embodiment, the double-acting damper 12 is used, but a single-acting damper, a multi-stage damper, or the like may be used. -If the axle can be fixed, it may be applied to any industrial vehicle such as a battery-powered forklift.

[0060]

According to the first and second aspects of the present invention, it is possible to provide a hydraulic circuit for an industrial vehicle that can prevent damage to the damper due to an excessive load without increasing the size of the damper. Can be.

According to the third aspect of the present invention, there is provided a hydraulic circuit for an industrial vehicle which can easily obtain the effects of the first or second aspect of the present invention and can perform processing in the circulating hydraulic circuit. can do.

According to the fourth aspect of the present invention, the effects of the first to third aspects of the present invention can be obtained by using a simple valve such as a relief valve or a spring-loaded check valve. A hydraulic circuit can be provided.

According to the invention set forth in claim 5, according to claim 1,
In addition to the effects of the inventions of (1) to (4), when the vehicle travels normally with the damper locked, stable traveling can be performed, and the damper has a small withstand pressure standard, that is, the cylinder has a small thickness. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a mechanism for fixing a rear axle according to an embodiment.

FIG. 2 is an explanatory diagram for explaining a relief valve.

FIG. 3 is a side view showing the forklift.

FIG. 4 is a schematic configuration diagram showing a mechanism for fixing a rear axle in another example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Forklift as an industrial vehicle, 1a ... Body frame, 11 ... Rear axle which comprises an axle, 12, 3
0, 31: Damper, 12b, 30a, 31a: Damper piston, 13: Shut-off valve as control valve,
19: a first valve as a suppressing means and a pressure reducing means, 20 ... a second valve as a suppressing means and a pressure reducing means, C ... a controller as a fixed control means, P1 to P3 ... a first as a pipe line
To the third pipeline, R1 to R6: first to sixth chambers as the first and second chambers, X: relief pressure as a preset suppression pressure, Y: maximum hydraulic pressure during normal running.

Claims (5)

[Claims] 1. An industrial vehicle having an axle vertically swingably supported with respect to a body frame, disposed between the body frame and the axle, and supplying and discharging hydraulic oil in accordance with the swing of the axle. A damper; fixed control means for controlling the damper to be locked as necessary to fix the axle to the vehicle body frame; and, based on the control of the fixed control means, supplied and discharged from the damper when fixed. A control valve that switches a pipeline through which the hydraulic oil flows to a shut-off state, and switches the pipeline to a communicating state when the hydraulic oil is not fixed, and that when the control valve is in a shut-off state, the supply and discharge of the hydraulic oil are disabled. If the set oil pressure in the damper reaches a preset suppression pressure that is smaller than the maximum oil pressure that the damper can withstand, the oil pressure should not exceed the maximum oil pressure that the damper can withstand. Hydraulic circuit of an industrial vehicle, characterized in that a restraining means for win. 2. The hydraulic circuit for an industrial vehicle according to claim 1, wherein said suppressing means is a pressure reducing means for reducing pressure. 3. The hydraulic circuit for an industrial vehicle according to claim 1, wherein said suppression means is a pressure control valve connected in parallel to said control valve. 4. The damper is a double-acting type having two hydraulic chambers, a first chamber and a second chamber partitioned by a piston, and the pressure control valve is configured to reduce the hydraulic pressure in the first chamber to a suppression pressure. A first valve through which hydraulic oil is passed to the second chamber when
4. The hydraulic pressure for an industrial vehicle according to claim 3, wherein a second valve for passing hydraulic oil to the first chamber when the hydraulic pressure in the second chamber reaches the suppression pressure is connected in parallel. circuit. 5. The restraining pressure is set to a value larger than a maximum value of a hydraulic pressure applied to the first chamber or the second chamber when the damper is locked and an axle is fixed to a body frame and the vehicle travels normally. The hydraulic circuit for an industrial vehicle according to any one of claims 1 to 4, wherein: