JP2003343505A - Dynamic damper for working vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively control vibration of vehicle body 1 even when a mass of working apparatus 2 is changed. <P>SOLUTION: The working apparatus 2 is provided in the vehicle body 1, and comprises a working portion 13, and an elevating cylinder 12 provided between the working portion 13 and vehicle body 2 which moves up and down the working portion 13. A selector valve 38 and variable relief valve 33 are arranged between the elevating cylinder 12 and an oil tank 16. The selector valve 38 is switchable between a connecting position for connecting a load retaining side oil chamber 28 of the elevating cylinder 12 with the oil tank 16 via the variable relief valve 33, and for connecting a load side oil chamber 26 of the elevating cylinder 12 with the oil tank 16, and a blocking position blocking aforementioned connection. Accumulators 41 and 42 for high pressure and low pressure are connected with a passage between the selector valve 38 and variable relief valve 33. A changing device 43 changing set pressure of the variable relief valve 33 and a change switch 52 operating the changing device are provided. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work vehicle dynamic damper.

[0002]

2. Description of the Related Art In a wheel loader, a working device is provided in a vehicle body. The working device is, for example, a boom that is vertically movable in a vehicle body, a boom cylinder that raises and lowers the boom, and a rotating portion at a tip portion of the boom. It has a working unit (sometimes referred to as a mounting attachment) such as a snow removal blade and a bucket that are movably provided, and a working unit cylinder that rotates the working unit.

In such a wheel loader, in order to suppress vibration such as pitching and bouncing of the vehicle body during traveling, a vibration suppressing accumulator is connected to the load holding side oil chamber of the boom cylinder to serve as a mass member. A dynamic damper has already been proposed by using an accumulator that acts as a spring. In such a dynamic damper, in order to effectively suppress the vibration of the vehicle body, it is necessary that the natural frequencies of the vehicle body and the working device be substantially the same.

By the way, the natural frequency of the working device is determined by the mass of the entire working device and the spring constant of the accumulator. However, in the working device, the working unit is changed (the working unit (attachment attachment is changed by a one-touch carrier or the like (for example, a snowplow blade is changed to a bucket)), and the earth and sand loaded on the working unit such as the bucket are changed.
The mass changes due to the change in the mass of the load such as gravel,
Not constant.

Therefore, if the spring constant of the accumulator is made constant, the natural frequency of the working device changes. However, since the natural frequency of the vehicle main body is substantially constant, the vibration of the vehicle main body will change. Cannot be effectively suppressed.
Therefore, in the case where the mass of the entire work device changes, a dynamic damper as shown in FIG. 4 has already been proposed so that the vibration of the vehicle body can be suppressed well by changing the spring constant of the dynamic damper. There is.

In the above dynamic damper, a switching valve 72 and a variable relief valve 73 are interposed between the lifting cylinder 70 and the oil tank 71. The switching valve 72 connects the load holding oil chamber 74 of the lifting cylinder 70 to the oil tank 71 via the variable relief valve 73, and connects the load oil chamber 75 of the lifting cylinder 70 to the oil tank 71; The switching valve 72 is freely switchable to a disconnecting position for disconnecting the connection.
A high pressure accumulator 76 and a low pressure accumulator 77 are connected to an oil passage between the variable relief valve 73 and the variable relief valve 73.

In the above dynamic damper, when the vibration of the vehicle body is suppressed, the working part has a small mass,
When the mass of the entire working device is small, such as when the loading amount in the working unit is small, the low pressure accumulator 77 is exclusively operated by manually lowering the set pressure of the variable relief valve 73. Further, when the mass of the entire working device is large, such as the mass of the working unit is large or the loading amount in the working unit is large, the set pressure of the variable relief valve 73 is manually increased to Not only the low pressure accumulator 77,
The high pressure accumulator 76 is also activated.

[0008]

As described above, in the related art, when the vibration of the vehicle body is suppressed, the mass of the working device is manually changed by manually changing the set pressure of the variable relief valve 73. Therefore, it takes a lot of time and labor, and the work mode is changed due to the change of the working part (for example, the change from the snow removal blade to the bucket etc.) or the mass change of the load such as earth and sand and gravel loaded on the working part such as the bucket. There was a problem that it was not possible to easily respond to changes in.

An object of the present invention is to provide a dynamic damper for a work vehicle that solves the above problems.

[0010]

In order to achieve the above object, the present invention is characterized in that a working device is provided in a vehicle body, and the working device is provided between the working portion and the working portion and the vehicle body. It has an elevating cylinder that is interposed and moves up and down the working part, and a switching valve and a variable relief valve are interposed between the elevating cylinder and the oil tank.The switching valve is a variable relief valve for the load holding side oil chamber of the elevating cylinder. Is connected to an oil tank and the load-side oil chamber of the lifting cylinder is connected to the oil tank, and a disconnection position that disconnects the connection. , In the case where the high pressure accumulator and the low pressure accumulator are connected,
It has a change device for changing the set pressure of the variable relief valve and a change switch for operating the change device. still,
The changing device is a. An accumulator that is separate from the high-pressure and low-pressure accumulators and that applies back pressure to the pressure setting spring of the variable relief valve; It is installed between the variable relief valve and the accumulator and connects them intermittently,
It may have a control valve for change operated by a change switch. Further, the variable relief valve has a high pressure relief valve and a low pressure relief valve, and the changing device selectively connects both the high pressure and low pressure accumulators to the high pressure relief valve and the low pressure relief valve. In some cases, the control valve for change is operated by the change switch. Further, there may be a pressure switch for operating the changing device which is opened and closed when the hydraulic pressure of the load holding side oil chamber of the lifting cylinder exceeds or falls below the set pressure.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A first example of an embodiment in which the present invention is applied to a wheel loader will be described below with reference to the drawings of FIGS. 1 and 2. FIG. 1 shows the wheel loader, and the wheel loader is a vehicle. It is composed of a main body 1 and a working device 2 provided in the front portion of the vehicle main body 1.

The vehicle body 1 has a vehicle body 6 composed of front and rear frames 4, 5 and the like, front and rear wheels 7, 8 which are paired left and right, and a cabin 9 and the like.

The working device 2 has a front frame 4 on which a pivot shaft 10 is attached.
A pair of left and right booms 11 pivotally supported by
A pair of left and right lifting cylinders 12 exemplified as a boom cylinder interposed between the front frame 4 and each boom 11, and a working unit exemplified as a bucket rotatably supported at the front end of the boom 11 (attachment attachment). 13 and a working unit cylinder 14 exemplified as a bucket cylinder interposed between the front frame 4 and the working unit 13.

FIG. 2 shows a hydraulic circuit of the working apparatus 2. In FIG. 2, 16 is an oil tank, 17 is a main hydraulic pump, 18 is a first control valve for a bucket cylinder, and 19 is a second control cylinder for a lifting cylinder. With the control valve, both control valves 18 and 19 are
It is provided in the main valve device 20.

The first control valve 18 is connected via a load side oil passage 22 to a head side oil chamber 21 which is a load side oil chamber of the working part cylinder 14, and at the same time, a load holding side oil chamber of the working part cylinder 14. Bottom side oil chamber 23 and load holding side oil passage 24
Connected through. The first control valve 18 is a 6-port 3-position switching solenoid valve, and is in a neutral position (middle solid position) for stopping the working unit cylinder 14, a rising position (raising position) for extending the working unit cylinder 14, and a working unit. Cylinder 1
It is possible to switch to a lower position (lowering position) for reducing the position 4. The first control valve 18 is set to the neutral position when not energized.

The second control valve 19 is connected to the head-side oil chamber 26, which is the load-side oil chamber of the lifting cylinder 12, via the load-side oil passage 27, and is also the load-holding-side oil chamber of the lifting cylinder 12. It is connected to the bottom side oil chamber 28 via a load holding side oil passage 29. The second control valve 19 is a 6-port 4-position switching solenoid valve, and controls the neutral position (middle solid force) for stopping the lift cylinder 12 and the lift position (lift position) for extending the lift cylinder 12 and the lift cylinder 12. It is freely switchable between a lowering position (lowering position) for contraction and a float position (floating position) that allows the elevating cylinder 12 to freely expand and contract. The second control valve 19 is in the neutral position when not energized.

A load-side branch oil passage 30 and a load-holding side branch oil passage 31 are branched from the midpoints of the load-side oil passage 27 and the load-holding oil passage 29, respectively. The load holding side branch oil passage 31 is connected to the oil tank 16 via a throttle 32 and a variable relief valve 33. The pressure setting spring 34 of the variable relief valve 33 is provided in the cylinder 35, and the piston 3 for applying back pressure to the spring 34 is provided in the cylinder 35.
6 is slidably provided.

A switching valve 38 is interposed between the lifting cylinder 12 and the oil tank 16 and is a solenoid pilot switching type, 4-port 2-position switching type spring offset type switching valve 39 and 4-port 2 type. It is composed of a position switching type spring offset type single coil type solenoid valve 40. The switching valve 38 throttles the load holding side branch oil passage 31.
Connection position (position) for connecting to the variable relief valve 33 without connecting the load side branch oil passage 30 to the oil tank 16
And a disconnection position (position) for disconnecting the connection. It should be noted that the switching valve 38 is placed in a shut-off position by being biased by a spring when not energized, and in a connection position when energized.

Reference numeral 41 is a high pressure accumulator, and 42 is a low pressure accumulator. The switching valve 38 and the variable relief valve 33 are provided.
Is connected to the oil passage between the high pressure accumulator 41
Is set to be larger than the spring constant of the low pressure accumulator 42. Each accumulator 41, 42 is, for example, a piston type in which nitrogen gas is sealed.

Reference numeral 43 denotes a changing device for changing the set pressure of the variable relief valve 33, which has a brake accumulator 44, a changing control valve 45, a control circuit 46 for the changing control valve 45, and the like.

The brake accumulator 44 is exemplified as an external accumulator, and is a hydraulic pump 48.
To a control valve (not shown) and a check valve 50.

The change control valve 45 is a 2-port 2-position switching type spring offset type solenoid valve, which connects and disconnects the oil passage between the brake accumulator 44 and the check valve 50 and the rear side of the piston 36 in the cylinder 35. Connect freely. The change control valve 45 is in the shut-off position (position) when not energized.

The control circuit 46 has a change switch 52 and a pressure switch 53. The change switch 52 is an open / close type electric switch, and operates the change device 43 when turned on. The pressure switch 53 is used when the pressure in the oil passage between the high pressure / low pressure accumulators 41, 42 and the variable relief valve 33, that is, the hydraulic pressure in the bottom side oil chamber 28, which is the load holding side oil chamber, exceeds a set pressure. When the hydraulic pressure becomes equal to or higher than the set pressure, the switching device 43 is opened and closed to operate the changing device 43.

Reference numeral 55 is a controller exemplified as control means, which controls the first and second control valves 18 and 19, the switching valve 38, and the control valve 45 for change, and the controller 55 includes a change switch 52 and a pressure switch 53. , The switch 56 for operating the dynamic damper, the switch 5
A pilot lamp 57 and a vehicle speed sensor 58, which are turned on when 6 is turned on, are connected. The vehicle speed sensor 58
When the traveling speed of the wheel loader is 7 km / h, it is turned on, and when it is 5 km / h, it is turned off. Controller 5
No. 5 is the changeover valve 3 when the changeover switch 56 is in the ON state and the traveling speed of the wheel loader exceeds 7 km / h.
The solenoid of the solenoid valve 40 of No. 8 is energized to set the switching valve 38 to the connection position, and the changeover switch 56 is turned off.
Alternatively, when the traveling speed of the wheel loader becomes 5 km / h or less, the energization of the solenoid of the solenoid valve 40 of the switching valve 38 is stopped and the switching valve 38 is set to the shut-off position. Further, the controller 55 includes the change switch 52 and the pressure switch 5
When 3 is in the ON state, the solenoid of the change control valve 45 is energized to bring the change control valve 45 to the connection position.

The high pressure / low pressure accumulator 4
The variable gas pressures of the change device 43 when the change device 43 is in operation and when the change device 43 is not in operation are defined as PAC (H) and PAC (L), respectively, and the maximum allowable pressure of these accumulators 41 and 42 is set to PACL (H). Set the set pressure of the valve 33 to PL (H), P
When L (L) and the set pressure of the pressure switch 53 are PS, PAC (L) <PL (L) <PS <PAC
(H) <PL (H) <PACL (H).

According to the above configuration example, the boom 11 and the bucket 13 can be operated regardless of the switching position of the switching valve 38. In particular, the operation of the boom 11 will be described. When the boom 11 is lifted, the second control valve 19 is operated to supply the working oil into the bottom-side oil chamber 28 of the lifting cylinder 12 to extend the lifting cylinder 12. Boom 1
Increase 1 In this case, the head-side oil chamber 26 of the lifting cylinder 12 communicates with the oil tank 16 via the second control valve 19 or the switching valve 38, so that the operating oil in the head-side oil chamber 26 is oil. It flows to the tank 16.

When lowering the boom 11, the second
With the control valve 19 in the lowered position, hydraulic oil is supplied to the head side oil chamber 26 of the lifting cylinder 12, and the bottom side oil chamber 28 is communicated with the oil tank 16. At this time, the switching valve 38
Is the connection position, the head side oil chamber 26 of the lifting cylinder 12 also communicates with the oil tank 16 via the switching valve 38 and the like, but the boom 11 descends by its own weight, so there is no problem. When the boom 11 is moved up and down, the bottom-side oil chamber 28 of the lift cylinder 12 is constantly connected to the high-pressure / low-pressure accumulators 41 and 42 through the throttle 32. When the vehicle body 1 vibrates due to pitching, bowing, etc., the high-pressure / low-pressure accumulators 41, 42 perform some cushioning action even when the switching valve 38 is in the shut-off position, and the vehicle body 1 vibrates. Is suppressed to some extent.

Further, during work such as dosing work by a wheel loader in which the hydraulic pressure in the bottom side oil chamber 28 of the lifting cylinder 12 is increased, the changeover switch 56 is turned off and the changeover valve 38 is set to the closed position. By doing so, work can be performed without any problems.

In order to prevent vibrations such as pitching and bouncing of the vehicle body 1 while the wheel loader is running, the second control valve 19 is set to the neutral position and the changeover switch 56 is turned on to turn on the pilot lamp. Turn on 57. And the traveling speed of the wheel loader is 7 km
When / h is exceeded, the controller 55 sets the switching valve 38 to the connection position, thereby connecting the head-side oil chamber 26 of the lifting cylinder 12 to the oil tank and connecting the bottom-side oil chamber 28 of the lifting cylinder 12 to the oil tank. , Is directly connected to the low pressure / high pressure accumulators 41 and 42 without passing through the throttle 32.
In the above case, since the bottom oil chamber 28 of the lifting cylinder 12 is connected to the high pressure / low pressure accumulators 41, 42 via the throttle 32, the switching valve 3
When 8 is set to the connection position, even if the hydraulic pressure in the head side oil chamber 26 of the lifting cylinder 12 is high, the hydraulic pressure in the oil chambers in the high pressure / low pressure accumulators 41, 42 may suddenly rise. There is no fear, and due to this sudden rise in hydraulic pressure,
For example, there is no fear that the high pressure / low pressure accumulators 41, 42 will be damaged or damaged.

When the vehicle body 1 is prevented from vibrating, the working portion 13 is always small in mass or the working portion 1
The total working apparatus 2 has a small mass, such as a small load in 3, and the hydraulic pressure in the bottom side oil chamber 28 of the elevating cylinder 12 causes the variable relief valve 33 when the changing apparatus 43 is not operating. When it is assumed that the set pressure is not exceeded, for example, the change switch 52 is turned off and the change device 43 is deactivated. As will be described later, in this case, there is no problem even if the change switch 52 is turned on and the change device 43 is turned on.

In the above case, the bottom side oil chamber 28 of the lift cylinder 12 is connected to the high pressure / low pressure accumulator 40 via the load holding side oil passage 29, the load holding side branch oil passage 31, and the switching valve 38. Communicate with 41. Also, the lifting cylinder 12
The head-side oil chamber 26 communicates with the oil tank 16 via the load-side oil passage 27, the load-side branch oil passage 30, and the switching valve 38.

When the wheel loader is run in this state, the vehicle body 1 of the wheel loader tries to pitch or bounce according to the ups and downs of the road surface or during acceleration and deceleration. As a result, the working device 2 vibrates, the boom 11 tries to swing in the vertical direction, and the bottom side oil chamber 28 of the lifting cylinder 12 that supports the boom 11 is moved.
Fluctuations occur in the internal hydraulic pressure.

In this case, the bottom side oil chamber 28 of the lifting cylinder 12 has the high pressure / low pressure accumulator 4
The hydraulic pressure in the bottom side oil chamber 28 is smaller than the set pressure of the variable relief valve 33 when the changing device 43 is not operating, and is lower than the gas pressure filled in the high pressure accumulator 41. Since it is small, the high pressure accumulator 41
Has little or no spring action, and the low-pressure accumulator 42 exclusively acts as a spring. That is, the bottom side oil chamber 2
The hydraulic oil in 8 is exclusively used for the low pressure accumulator 42.
First, the hydraulic oil flows in against the pressure of the enclosed gas, and the hydraulic oil flows from the low pressure accumulator 42 into the bottom side oil chamber 28 due to the pressure of the enclosed gas. Further, since the head-side oil chamber 26 communicates with the oil tank 16, the working oil flows between the head-side oil chamber 26 and the oil tank 16, allowing the lift cylinder 12 to freely expand and contract.

That is, the boom 11, that is, the working device 2
Vibrates up and down against the spring action of the low pressure accumulator 41 to move (vibrate) the front portion of the vehicle body 1.
Since the vehicle body 1 moves in the direction opposite to that, vibrations such as pitching and bouncing of the vehicle body 1 are suppressed.

In the above case, the bottom side oil chamber 2
Even if the hydraulic pressure in 8 becomes larger than the set pressure of the variable relief valve 33 when the changing device 43 is not in operation, the variable relief valve 33 only operates and there is no problem.

Further, when there is a possibility that the mass of the working unit 2 as a whole is large, such as the mass of the working unit 13 is large or the loading amount in the working unit 13 is large, the change switch 52
Is turned on so that the changing device 43 can be operated.

When the vehicle body 1 is prevented from vibrating, the working device 2 as a whole has a small mass, and the hydraulic pressure in the bottom oil chamber 28 of the lifting cylinder 12 is lower than the set pressure of the pressure switch 53. When it is small, the pressure switch 53 is not turned on. Therefore, the changing device 43 does not operate, and the same operation as described above is performed.

Further, in reality, the working apparatus 2 has a large mass, and the hydraulic pressure in the bottom oil chamber 28 of the lifting cylinder 12 is
When the pressure becomes higher than the set pressure of the pressure switch 53, the pressure switch 53 is turned on, and the changing device 43 operates as described below.

That is, the solenoid of the change control valve 45 is energized to bring the change control valve 45 to the connecting position, and the gas pressure of the brake accumulator 44 is changed to the back pressure by the spring 34 of the variable relief valve 33 via the piston 36. And the set pressure of the variable relief valve 33 becomes higher than the gas pressure filled in the high pressure accumulator 41.

As a result, when the vibration of the vehicle body 1 is suppressed,
The hydraulic oil in the bottom oil chamber 28 of the lifting cylinder 12 flows into not only the low pressure accumulator 42 but also the high pressure accumulator 41 against the filled gas pressure,
Further, the working oil flows from the high pressure / low pressure accumulators 41, 42 into the bottom side oil chamber 28 due to the enclosed gas pressure.

In this way, the low pressure accumulator 4
In addition to 2, the high-pressure accumulator 41 also performs a spring action, so that the spring constant of both accumulators 41 and 42 as a whole becomes large, and a good vibration suppressing action is performed. Then, in the above case, when the traveling speed of the wheel loader becomes 5 km / h or less, the controller 55 sets the switching valve 38 to the shutoff position, thereby stopping the vibration suppressing action of the vehicle body 1 of the wheel loader. To be done.

FIG. 3 shows a second example of the embodiment of the present invention. Explaining only the changes from the first example, the variable relief valve 33 includes a high pressure relief valve 60 and a low pressure relief valve 6.
It is composed of 1.

Further, the change control valve 45 connects both the high pressure and low pressure accumulators 41 and 42 to the relief valve 6 respectively.
Connected to 0,61 selectively, 4 ports 2
It is a position switching type spring offset type solenoid valve, and is a low pressure position (position) in which both the high pressure and low pressure accumulators 41 and 42 are connected to the low pressure relief valve 61.
And both accumulators 41, 42 to the high pressure relief valve 6
It can be switched to a high pressure position (position) connected to 0. The change control valve 45 is in the low pressure position when not energized.

The high pressure and low pressure accumulators 4
Set the filled gas pressures of 1, 42 to PAC (H) and PAC (L), set the maximum allowable pressure of these accumulators 41 and 42 to PACL (H), and set the high pressure relief valve 60 and the low pressure relief valve 61. Pressure is PL (H), PL (L)
When the set pressure of the pressure switch 53 is PS,
PAC (L) <PL (L) <PS <PAC (H) <PL
(H) <PACL (H).

According to the above configuration example, when the vibration of the vehicle body 2 is prevented, the mass of the working unit 13 is always small, the loading amount in the working unit 13 is small, etc. When the mass is small and it is assumed that the hydraulic pressure in the bottom side oil chamber 28 of the lifting cylinder 12 does not exceed the set pressure of the low pressure relief valve 61, for example, the change switch 52 is turned off, The changing device 43 is deactivated.

As a result, the changing control valve 45 is set to the low pressure position, and both the high pressure and low pressure accumulators 41 and 42 are connected to the low pressure relief valve 61. As a result, similar to the first example, the high pressure accumulator 41
The low-pressure accumulator 42 exclusively acts as a spring, and vibrations such as pitching and bouncing of the vehicle body 1 are suppressed.

In the above case, the bottom side oil chamber 2
Even if the hydraulic pressure in 8 becomes higher than the set pressure of the low pressure relief valve 61, the low pressure relief valve 61 only operates and there is no problem.

Further, when there is a possibility that the mass of the working unit 2 as a whole is large, such as the mass of the working unit 13 is large or the loaded amount in the working unit 13 is large, the change switch 52 is used.
Is turned on so that the changing device 43 can be operated.

When the vibration of the vehicle body 2 is prevented, the working apparatus 2 as a whole has a small mass, and the hydraulic pressure in the bottom oil chamber 28 of the lifting cylinder 12 is lower than the set pressure of the pressure switch 53. When it is small, the pressure switch 53 is not turned on. Therefore, the changing device 43 does not operate, and the same operation as described above is performed.

In reality, the working device 2 has a large mass, and the hydraulic pressure in the bottom oil chamber 28 of the lifting cylinder 12 is
When the pressure becomes higher than the set pressure of the pressure switch 53, the pressure switch 53 is turned on, and the changing device 43 operates as described below.

That is, the solenoid of the change control valve 45 is energized to bring the change control valve 45 to the high pressure position, and both the high pressure and low pressure accumulators 41 and 42 are connected to the high pressure relief valve 60. . Thus, similar to the first example, not only the low-pressure accumulator 42 but also the high-pressure accumulator 41 exerts a spring action, so that the spring constants of both accumulators 41 and 42 become large, and a good vibration suppressing action is performed. Be seen.

Although the pressure switch is provided in each of the embodiments, the pressure switch may be omitted. In this case, the changing device 43 operates only by operating the change switch. Further, although each of the embodiments applies the present invention to a wheel loader, the present invention is also applicable to work vehicles other than the wheel loader.

[0053]

As described in detail above, according to the present invention,
Even if the mass of the work device changes, it can be handled with one touch, and vibrations such as pitching and bouncing of the vehicle body can be effectively suppressed. According to claim 4, when the change switch is operated, the change device is operated / stopped by the pressure switch in response to the change in the mass of the working device, and the high pressure / low pressure accumulator is good. It is possible to effectively suppress vibrations such as pitching and bouncing of the vehicle body while responding to changes in the mass of the working device.

[Brief description of drawings]

FIG. 1 is a side view of a wheel loader showing a first example of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a first example of an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second example of the embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional example.

[Explanation of symbols]

1 Vehicle Main Body 1 2 Working Device 11 Boom 12 Lifting Cylinder 13 Working Part 16 Oil Tank 26 Head Side Oil Chamber (Load Side Oil Chamber) 28 Bottom Side Oil Chamber (Load Holding Side Oil Chamber) 33 Variable Relief Valve 34 Pressure Setting Spring 38 Switching valves 41, 42 High pressure / low pressure accumulator 43 Change device 44 Brake accumulator (external accumulator) 45 Change control valve 46 Control circuit 52 Change switch 53 Pressure switch 55 Controller 60, 61 High pressure / low pressure relief valve

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2D003 AA01 AB03 AC04 BA08 BB13                       CA02 DA02 DA04 DB02                 3H089 AA21 AA61 BB05 CC01 DA02                       DB03 DB13 DB33 DB47 DB50                       DC02 EE15 EE24 EE31 FF13                       GG02 JJ01                 3J048 AA06 AC04 BE03 EA36

Claims (4)

[Claims] 1. A vehicle body is provided with a working device, and the working device has a working part, and an elevating cylinder interposed between the working part and the vehicle body for elevating the working part, and between the elevating cylinder and the oil tank. A switching valve and a variable relief valve are installed in the switching valve.The switching valve connects the load holding oil chamber of the lifting cylinder to the oil tank via the variable relief valve and connects the loading oil chamber of the lifting cylinder to the oil tank. It is possible to freely switch between the connection position for disconnecting and the disconnecting position for disconnecting the above connection, and the high pressure accumulator and the low pressure accumulator are connected to the oil passage between the switching valve and the variable relief valve. A dynamic damper for a work vehicle having a changing device for changing the vehicle and a changing switch for operating the changing device. 2. The changing device comprises: a. An accumulator that is separate from the high-pressure and low-pressure accumulators and that applies back pressure to the pressure setting spring of the variable relief valve; Interposed between the variable relief valve and the accumulator,
The dynamic damper for a work vehicle according to claim 1, further comprising a changing control valve that is intermittently connected and that is operated by a changing switch. 3. The variable relief valve has a high-pressure relief valve and a low-pressure relief valve, and the changing device is configured so that both the high-pressure and low-pressure accumulators are selectively used as the high-pressure relief valve and the low-pressure relief valve. The dynamic damper for a work vehicle according to claim 1, further comprising a change control valve connected to the switch and operated by a change switch. 4. Opening and closing when the hydraulic pressure in the load holding side oil chamber of the lifting cylinder exceeds or falls below the set pressure,
A dynamic damper for a work vehicle according to claim 2 or 3, further comprising a pressure switch for actuating the changing device.