JP2004262281A - Lift axle device of front two-axle car - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase starting performance by increasing ground-contact loads of drive wheels. <P>SOLUTION: A hydraulic cylinder 11 is installed between front and rear axles and a frame on the upper side of the axles of a front biaxial vehicle. Hydraulic oil flowing from an oil pump 13 to a steering gear box 14 is switched by energizing a solenoid-operated first switching valve 16 to be extracted and led to the hydraulic cylinder 11 through a hydraulic oil supply line 17, and contracted to lift up the front and rear axles. To lower the front and rear axles, hydraulic pressure is merely released by energizing to open a solenoid-operated second switching valve 22 in a communication line 20. In normal traveling, the second switching valve 22 is closed again by deenergization, a pilot-operated shutoff valve 21 is returned to an open state by the dissipation of hydraulic pressure on the hydraulic oil supply line 17 side, and the hydraulic cylinder 11 is brought into a hydraulic pressure free state to absorb a suspension stroke. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lift axle device for a front two-axle vehicle.
[0002]
[Prior art]
2. Description of the Related Art In general, a front two-axle three-axle vehicle having a front front shaft, a front-rear shaft, and a rear shaft to which a driving force is transmitted is applied to a large vehicle such as a truck.
[0003]
FIG. 4 illustrates an example of a front two-axle three-axle suspension device including a front front axle, a front-rear axle, and a rear axle, and reference numeral 1 in FIG. Reference numeral 2 denotes a frame of the front two-axle three-axle wheel 1. The front end of the trailing leaf spring 4a is connected to a bracket 3a fixed to the front end of the frame 2 by being wound around a pin 5a. A front front shaft 6a is attached to the middle of the frame 2. An air spring 7a is interposed between the upper surface of the trailing end of the trailing leaf spring 4a and the lower surface of the frame 2. Has become.
[0004]
A front end of a trailing leaf spring 4b is wound around a pin 5b and connected to a bracket 3b fixed to a position behind the bracket 3a at a front end of the frame 2, and is connected to a middle portion of the trailing leaf spring 4b. The front and rear shaft 6b is attached, and an air spring 7b is interposed between the upper surface of the rear end of the trailing leaf spring 4b and the lower surface of the frame 2.
[0005]
Further, the front end of the trailing leaf spring 4c is connected to the bracket 3c fixed to the rear end of the frame 2 by winding the front end of the trailing leaf spring 4c around the pin 5c. An air spring 7c is interposed between the upper surface of the rear end of the trailing leaf spring 4c and the lower surface of the frame 2.
[0006]
The trailing leaf springs 4a, 4b, and 4c described above support the front-rear shaft 6a, the front-rear shaft 6b, and the rear shaft 6c in the front-rear, left-right, and torsion directions. 7a, 7b and 7c support the vertical load applied to the front front shaft 6a, the front and rear shaft 6b and the rear shaft 6c.
[0007]
In FIG. 4, reference numerals 8a, 8b and 8c denote sub-leaf springs which are superposed on the lower surface of the trailing leaf springs 4a, 4b and 4c to form a double structure, 9a denotes a front front wheel, and 9b denotes front and rear. The reference numeral 9c denotes a rear wheel, and 10a, 10b and 10c denote shock absorbers.
[0008]
This type of front two-axle three-axle vehicle is also described in the following unpublished prior applications: prior application 1, prior application 2, and prior application 3.
[0009]
[Prior application 1]
Japanese Patent Application No. 2001-374563 [Prior application 2]
Japanese Patent Application No. 2002-190413 [Prior application 3]
Japanese Patent Application No. 2002-190414 specification
[Problems to be solved by the invention]
However, in the front two-axle three-axle wheel 1 as described above, the vehicle always travels using all of the front front wheels 9a, the front and rear wheels 9b, and the rear wheels 9c irrespective of the load condition. In this case, the load applied to the rear shaft 6c to which the driving force is transmitted is reduced, and the ground contact load of the rear wheel 9c as a driving wheel is reduced. There was a possibility that it might be.
[0011]
In addition, since the vehicle always runs using all of the front front wheels 9a, front and rear wheels 9b, and rear wheels 9c, there is a drawback that the rolling resistance of the wheels with respect to the road surface increases and the running fuel efficiency deteriorates.
[0012]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made to improve the starting performance by increasing the contact load of the drive wheels, and to improve the running fuel efficiency by suppressing the rolling resistance of the wheels against the road surface. It is intended to provide a lift axle device for an axle.
[0013]
[Means for Solving the Problems]
The present invention is a front axle lift axle device including a front front shaft and a front-rear shaft, and at least one rear shaft,
A hydraulic cylinder provided between the front and rear shafts and a frame above the hydraulic cylinder, and hydraulic oil flowing from an engine-driven oil pump toward a steering gear box is extracted via a first electromagnetic switching valve, and a first chamber of the hydraulic cylinder is extracted. A hydraulic oil supply line for contracting the hydraulic cylinder by guiding the hydraulic oil to the hydraulic cylinder, a hydraulic oil return line for extracting hydraulic oil from the second chamber of the hydraulic cylinder and returning it to the oil tank, a hydraulic oil return line and the hydraulic oil supply A pair of communication lines connecting between the lines, a pilot-operated shut-off valve provided on one of the communication lines, and an electromagnetic type second valve provided on the other of the communication lines With a switching valve,
When the first switching valve is in the non-excited state, the hydraulic oil continues to flow to the steering gear box as it is, and in the excited state, the flow of the hydraulic oil is switched and extracted, and the shut-off valve is always open and the hydraulic pressure is applied to the hydraulic oil supply line side. The second switching valve is configured to be closed only when it occurs, and to be closed in a non-excited state and open in an excited state.
[0014]
Thus, when the vehicle is in a lightly loaded state, the first switching valve is energized to be in an excited state, thereby switching the flow path and extracting hydraulic oil from between the oil pump and the steering gear box. When the second switching valve is de-energized and closed in a de-energized state, the shut-off valve also closes due to the generation of hydraulic pressure on the hydraulic oil supply line side, thereby interrupting the flow of hydraulic oil in each communication line. As a result, the hydraulic oil from the first switching valve is introduced into the first chamber of the hydraulic cylinder, and the hydraulic oil in the second chamber is returned to the oil tank via the hydraulic oil return line, and the hydraulic cylinder contracts, By this contraction operation, the front-rear shaft is raised, and the front-rear shaft is lifted up to the frame side.
[0015]
Then, in this lift-up state, the first switching valve is de-energized and returned to the non-excited state, whereby the flow path is switched to stop the extraction of hydraulic oil from the first switching valve, and the first switching valve and the hydraulic cylinder By shutting off the flow of hydraulic oil to and from the first chamber, the hydraulic pressure between the shut valve that is already closed (closed state is maintained by holding the hydraulic pressure on the hydraulic oil supply line side) and the second switching valve The lock state is established, whereby the operation of the hydraulic cylinder is fixed, and the front-rear shaft is held in a state of being lifted up to the frame side.
[0016]
As a result, the load applied to the axle to which the driving force is transmitted is increased, and the ground load of the driving wheels is increased, so that the driving wheels are prevented from slipping at the time of starting or the like, and the starting performance is improved.
[0017]
Further, since the front and rear wheels are lifted up to the frame side together with the front and rear shafts, the rolling resistance of the wheels with respect to the road surface is reduced, so that the running fuel efficiency is improved and the wear of the front and rear wheels is also reduced.
[0018]
Then, when the second switching valve is energized to be in an excited state, the communication line on one side is opened to release the hydraulic pressure in the first chamber of the hydraulic cylinder, the hydraulic cylinder is lowered due to the weight of the front and rear shafts and front and rear wheels. When the hydraulic cylinder is extended, the hydraulic oil is appropriately replenished to the second chamber via the hydraulic oil return line, whereby the front and rear shafts are lowered and the front and rear wheels are brought into contact with the road surface. And the shut-off valve returns to the open state.
[0019]
Then, in the normal running state thereafter, the second switching valve is de-energized and returned to the non-excited state and closed again, but free flow of the hydraulic oil through one connection line by the shut valve is permitted. Therefore, the hydraulic cylinder is maintained in the hydraulic free state, and the suspension stroke during normal traveling is absorbed by the expansion and contraction operation of the hydraulic cylinder.
[0020]
Further, in practicing the present invention more specifically, for example, a bypass flow path that guides hydraulic oil from an oil pump to a steering gear box by bypassing the first switching valve is provided, and a priority valve is provided to the first switching valve. It is preferable that the flow of the working oil is narrowed down to give priority to the distribution amount of the working oil to the bypass flow passage.
[0021]
In this way, even when the flow path of the first switching valve is switched to extract the hydraulic oil toward the steering gear box, the priority valve gives priority to the distribution amount to the bypass flow path side, so that the hydraulic oil is insufficient on the steering side. Can be avoided beforehand.
[0022]
Also, it is preferable to provide an orifice in the middle of the communication line having the second switching valve. In this case, when the front and rear shafts are lowered and the front and rear wheels are brought into contact with the road surface, the first of the hydraulic cylinders is used. The lowering speed of the front and rear shafts can be adjusted by giving resistance to the flow of the hydraulic oil released from the chamber.
[0023]
Further, it is preferable to provide an orifice on the downstream side of the point where the pilot pressure for the shut-off valve is taken out in the hydraulic oil supply line, so that the orifice allows the hydraulic oil to flow through the hydraulic oil supply line appropriately. It is possible to reliably guide the pilot pressure to the shut-off valve by giving an appropriate resistance.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
1 to 3 show an example of an embodiment of the present invention. Portions denoted by the same reference numerals as those in FIG. 4 represent the same components, but for convenience of explanation, the trailing portions in FIGS. The illustration of the leaf spring 4b, the sub leaf spring 8b, and the air spring 7b (all shown in FIG. 4) is omitted. However, the technical content of the present invention is not limited by the form of this type of suspension device.
[0026]
As shown in FIGS. 1 and 2, the basic configuration in this embodiment is substantially the same as the conventional front two-axle three-axle wheel 1 shown in FIG. 4 described above. The point is that a hydraulic cylinder 11 is provided between the shaft 6b and the frame 2 above the shaft 6b, and the hydraulic cylinder 11 is operated with hydraulic oil diverted from a steering hydraulic source.
[0027]
More specifically, a bracket 12 extending in the vehicle width direction is provided between the left and right frames 2 located above the front-rear shaft 6b, and a pair of left and right hydraulic cylinders 11 is provided between the bracket 12 and the front-rear shaft 6b. The upper end and the lower end of each hydraulic cylinder 11 are pin-coupled to the bracket 12 and the front-rear shaft 6b so as to be tiltable.
[0028]
The hydraulic system for operating the hydraulic cylinder 11 will be described below with reference to FIG. 3. In this hydraulic system, an oil pump 13 driven by an engine operates between a steering gear box 14 and an oil tank 15. The oil is circulated, and hydraulic oil flowing from the oil tank 15 toward the steering gear box 14 is extracted via the first electromagnetic switching valve 16 and guided to the first chamber 11A of the hydraulic cylinder 11. A hydraulic oil supply line 17 is provided, and the hydraulic cylinder 11 is configured such that when hydraulic oil is introduced into the first chamber 11A, the piston 11C is pushed up and contracts as a whole.
[0029]
Here, the first switching valve 16 is configured to continuously flow the hydraulic oil from the oil tank 15 toward the steering gear box 14 and to shut off the flow path to the hydraulic oil supply line 17 side. And the second position in which the hydraulic oil is drawn out to the hydraulic oil supply line 17 side and the flow path is shut off with respect to the steering gear box 14 side can be appropriately switched. , While being energized when energized, it is switched to the second position against the spring force by the electromagnetic force.
[0030]
Further, a hydraulic oil return line 18 is provided for extracting hydraulic oil from the second chamber 11B, which is narrowed when the hydraulic cylinder 11 contracts, and returning the hydraulic oil to the oil tank 15. The hydraulic oil return line 18, the hydraulic oil supply line 17, Are connected by a pair of communication lines 19 and 20, one of the communication lines 19 is equipped with a pilot operated shut-off valve 21, and the other of the communication lines 20 is equipped with an electromagnetic second switching valve 22. Have been.
[0031]
Here, the shut-off valve 21 provided on one of the communication lines 19 can appropriately switch between a first position in an open state allowing the flow of hydraulic oil and a second position in a shut-off state preventing the flow of hydraulic oil. When the hydraulic pressure is not generated on the hydraulic oil supply line 17 side, the pilot line 17a is maintained at the first position by the spring force while the hydraulic pressure is generated on the hydraulic oil supply line 17 side. The hydraulic pressure is guided as the pilot pressure via the control unit and is switched to the second position.
[0032]
Further, the second switching valve 22 provided in the other communication line 20 appropriately switches between a first position in a shut-off state that blocks the flow of hydraulic oil and a second position in an open state that allows the flow of hydraulic oil. The first position is maintained by the spring force in a non-energized state, and is switched to the second position by being excited when energized and resisting the spring force by the electromagnetic force.
[0033]
Further, in the example shown here, there is provided a bypass flow path 23 that guides the hydraulic oil from the oil pump 13 to the steering gear box 14 by bypassing the first switching valve 16, and the priority valve 24 controls the first The flow of the hydraulic oil toward the switching valve 16 is narrowed to give priority to the distribution amount of the hydraulic oil to the bypass passage 23 side.
[0034]
An orifice 25 is provided in the middle of the communication line 20 where the second switching valve 22 is provided, so that an appropriate resistance can be given to the flow of the hydraulic oil in the communication line 20.
[0035]
On the other hand, a similar orifice 26 is also provided in the hydraulic oil supply line 17 on the downstream side of the hydraulic pressure take-out point of the pilot line 17a, and the orifice 26 provides an appropriate resistance to the flow of the hydraulic oil in the hydraulic oil supply line 17. Thus, an appropriate pilot pressure is guided to the pilot line 17a side.
[0036]
In FIG. 3, reference numeral 27 denotes a check valve for preventing backflow of hydraulic oil from the first switching valve 16 toward the steering gear box 14, and reference numeral 28 denotes a hydraulic cylinder from the first switching valve 16 via the hydraulic oil supply line 17. This is a check valve for preventing the backflow of hydraulic oil toward 11.
[0037]
Thus, when the vehicle is in a lightly loaded state, the first switching valve 16 is energized to be in an excited state, thereby switching the flow path and allowing the hydraulic oil to flow from between the oil pump 13 and the steering gear box 14. When the second switching valve 22 is de-energized and closed in a de-energized state, a hydraulic pressure is generated on the hydraulic oil supply line 17 side, so that the shut valve 21 also closes, whereby each communication line 19 As a result, the hydraulic oil from the first switching valve 16 is introduced into the first chamber 11A of the hydraulic cylinder 11 and the hydraulic oil from the second chamber 11B is passed through the hydraulic oil return line 18. The hydraulic cylinder 11 is returned to the oil tank 15, and the hydraulic cylinder 11 contracts. The contracting operation raises the front-rear shaft 6b and lifts the front-rear shaft 6b toward the frame 2.
[0038]
Then, in this lift-up state, the first switching valve 16 is de-energized and returned to the non-excited state, whereby the flow path is switched to stop the extraction of hydraulic oil from the first switching valve 16 and the first switching valve 16 By shutting off the flow of hydraulic oil between the first hydraulic chamber 11A and the first chamber 11A of the hydraulic cylinder 11, the shut valve 21 (closed state is maintained by holding the hydraulic pressure on the hydraulic oil supply line 17 side) and the second switching The hydraulic pressure is locked with the valve 22, whereby the operation of the hydraulic cylinder 11 is fixed, and the front-rear shaft 6b is held in a state of being lifted up to the frame 2 side.
[0039]
As a result, the load applied to the rear shaft 6c (see FIG. 4) to which the driving force is transmitted increases, and the ground load of the rear wheel 9c (see FIG. 4) as the driving wheel increases. Is prevented from slipping, and the starting performance is improved.
[0040]
Further, since the front and rear wheels 9b are lifted up to the frame 2 along with the front and rear shafts 6b, the rolling resistance of the front and rear wheels 9b with respect to the road surface is reduced, so that the running fuel efficiency is improved and the wear of the front and rear wheels 9b is also reduced. Will be.
[0041]
Thereafter, when the second switching valve 22 is energized to be in an excited state, the communication line 20 on one side is opened to release the hydraulic pressure of the first chamber 11A of the hydraulic cylinder 11, and the front and rear shafts 6b and the front and rear wheels 9b are released. Due to the weight, the piston 11C of the hydraulic cylinder 11 is lowered and the hydraulic cylinder 11 is extended and the hydraulic oil is appropriately replenished to the second chamber 11B via the hydraulic oil return line 18 while the hydraulic cylinder 11 is extended, whereby the longitudinal shaft 6b is lowered. Since the front and rear wheels 9b are in contact with the road surface, the hydraulic pressure on the hydraulic oil supply line 17 side disappears, and the shut valve 21 returns to the open state.
[0042]
Then, in the normal running state thereafter, the second switching valve 22 is de-energized and returned to the non-excited state and closed again, but the shut-off valve 21 allows the free hydraulic oil to flow through one of the communication lines 19 on one side. Is permitted, the hydraulic cylinder 11 is maintained in a hydraulic free state, and the suspension stroke during normal running is absorbed by the expansion and contraction operation of the hydraulic cylinder 11.
[0043]
Therefore, according to the above-described embodiment, the ground load of the rear wheel 9c as the driving wheel can be increased, so that the starting performance can be greatly improved as compared with the related art, and the rolling resistance of the front and rear wheels 9b with respect to the road surface can be improved. , The traveling fuel efficiency can be improved, and the wear of the front and rear wheels 9b can be reduced.
[0044]
Further, since the hydraulic cylinder 11 is operated by using the hydraulic pressure of the hydraulic pressure source for steering, it is not necessary to separately provide a hydraulic pressure source for lifting up the longitudinal shaft 6b. , The cost required for implementing the lift axle device can be significantly reduced, and the mountability (layout) on the vehicle is improved. A significant increase in vehicle weight can also be avoided.
[0045]
Also, with regard to the hydraulic system, the shut-off valve 21 which does not require electric power in the pilot operation system, and when the front and rear shafts 6b are lifted up and lowered, it is only necessary to individually energize each of them, and during the normal traveling, both are required. Since it is only necessary to provide the first switching valve 16 and the second switching valve 22 that do not need to be energized, the durability can be made extremely excellent.
[0046]
Further, in the present embodiment, in particular, a bypass flow path 23 for guiding the hydraulic oil from the oil pump 13 to the steering gear box 14 bypassing the first switching valve 16 is provided. Since the flow of the hydraulic oil is narrowed down and the distribution amount of the hydraulic oil to the bypass flow path 23 side is prioritized, the flow path of the first switching valve 16 is switched so that the hydraulic oil flowing to the steering gear box 14 is reduced. Also in the case of extracting, by giving priority to the distribution amount to the bypass flow path 23 side by the priority valve 24, it is possible to avoid the possibility that hydraulic oil shortage occurs on the steering side.
[0047]
Further, since the orifice 25 is provided in the middle of the communication line 20 where the second switching valve 22 is provided, the first chamber 11A of the hydraulic cylinder 11 is used when the front-rear shaft 6b descends to bring the front and rear wheels 9b into contact with the road surface. The lowering speed of the front-rear shaft 6b can be adjusted by giving resistance to the flow of the hydraulic oil released from the shaft, and the safety at the time of the lowering of the front-rear shaft 6b after lift-up can be improved.
[0048]
Further, since a similar orifice 26 is provided on the hydraulic oil supply line 17 on the downstream side of the hydraulic pressure take-out point of the pilot line 17a, the orifice 26 provides an appropriate resistance to the flow of the hydraulic oil in the hydraulic oil supply line 17. Thus, the pilot pressure can be reliably guided to the pilot line 17a side, and the reliability of the hydraulic operation of the shut valve 21 can be improved.
[0049]
It should be noted that the lift axle device for a front two-axle vehicle of the present invention is not limited to the above-described embodiment, but includes a front front shaft, a front-rear shaft, and a rear shaft to which a driving force is transmitted. The present invention is not limited to the front two-axle three-axle, but can be similarly applied to the front two-axle four-axle provided with the front two-axle and the rear two-axle, and other ranges that do not depart from the gist of the present invention. It is needless to say that various changes can be made within.
[0050]
【The invention's effect】
According to the lift axle device for a front two-axle vehicle of the present invention described above, the following various excellent effects can be obtained.
[0051]
(I) Since the ground contact load of the drive wheels can be increased, the starting performance can be greatly improved as compared with the conventional art, and the running resistance of the front and rear wheels can be improved by reducing the rolling resistance of the front and rear wheels against the road surface. Wear can also be reduced.
[0052]
(II) Since the hydraulic cylinder is operated by using the hydraulic pressure of the hydraulic pressure source for steering, it is not necessary to separately provide a hydraulic pressure source for lifting up the front and rear shafts, and the hydraulic cylinder is used. The structure can be made relatively simple and compact, so that the cost required for implementing the lift axle device can be significantly reduced, and the mountability (layability) with respect to the vehicle is improved and the vehicle weight is improved. Can also be avoided.
[0053]
(III) Regarding the hydraulic system of the hydraulic cylinder, a shut-off valve that does not require electric power in a pilot operation system, and a lift-up of the front and rear shafts and a lowering thereof only need to be individually energized, and both are required during normal running. Since it is only necessary to provide the first switching valve and the second switching valve that do not need to be energized, the durability can be made extremely excellent.
[0054]
And (IV) a bypass passage for guiding the hydraulic oil from the oil pump to the steering gear box by bypassing the first switching valve. If the configuration is such that the distribution amount of the hydraulic oil is prioritized, the priority valve prioritizes the distribution amount to the bypass flow path side even when switching the flow path of the first switching valve and extracting the hydraulic oil toward the steering gear box. As a result, it is possible to avoid the possibility that the operating oil is insufficient on the steering side.
[0055]
(V) If an orifice is provided in the middle of the communication line with the second switching valve, the flow of hydraulic oil released from the first chamber of the hydraulic cylinder when the front-rear shaft descends and the front and rear contact the road surface. , The descent speed of the front-rear axis can be adjusted, and the safety at the time of the descent after the lift-up of the front-rear axis can be improved.
[0056]
(VI) If an orifice is provided on the downstream side of the point where the pilot pressure for the shut-off valve is taken out in the hydraulic oil supply line, the orifice gives an appropriate resistance to the flow of the hydraulic oil in the hydraulic oil supply line, thereby ensuring the pilot oil. The pressure can be guided to the shutoff valve, and the reliability of the hydraulic operation of the shutoff valve can be improved.
[Brief description of the drawings]
FIG. 1 is a side view schematically showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a rear view of the structure of FIG.
FIG. 3 is a system diagram showing an example of a hydraulic system that operates the hydraulic cylinder of FIG. 1;
FIG. 4 is an overall side view showing an example of a conventional suspension device for a front two-axle three-axle vehicle.
[Explanation of symbols]
1 front two-axle three-axle (front two-axle)
2 Frame 6b Front and rear shaft 11 Hydraulic cylinder 11A First chamber 11B Second chamber 13 Oil pump 14 Steering gear box 15 Oil tank 16 First switching valve 17 Hydraulic oil supply line 18 Hydraulic oil return line 19 Communication line 20 Communication line 21 Shut valve 22 second switching valve 23 bypass flow path 24 priority valve 25 orifice 26 orifice

Claims (4)

A front axle lift axle device including a front front shaft, a front-rear shaft, and at least one rear shaft,
A hydraulic cylinder provided between the front and rear shafts and a frame above the hydraulic cylinder, and hydraulic oil flowing from an engine-driven oil pump toward a steering gear box is extracted via a first electromagnetic switching valve, and a first chamber of the hydraulic cylinder is extracted. A hydraulic oil supply line for contracting the hydraulic cylinder by guiding the hydraulic oil to the hydraulic cylinder, a hydraulic oil return line for extracting hydraulic oil from the second chamber of the hydraulic cylinder and returning it to the oil tank, a hydraulic oil return line and the hydraulic oil supply A pair of communication lines connecting between the lines, a pilot-operated shut-off valve provided on one of the communication lines, and an electromagnetic type second valve provided on the other of the communication lines With a switching valve,
When the first switching valve is in the non-excited state, the hydraulic oil continues to flow to the steering gear box as it is, and in the excited state, the flow of the hydraulic oil is switched and extracted, and the shut-off valve is always open and the hydraulic pressure is applied to the hydraulic oil supply line side. A lift axle device for a front two-axle vehicle, wherein the lift axle device is configured to close only when it occurs, and to close the second switching valve in a non-excited state and open in an excited state. A bypass flow path that guides hydraulic oil from the oil pump to the steering gear box bypassing the first switching valve is provided. 2. The lift axle device for a front two-axle vehicle according to claim 1, wherein the distribution amount is prioritized. The lift axle device for a front two-axle vehicle according to claim 1 or 2, wherein an orifice is provided in the middle of a communication line having the second switching valve. 4. The lift axle device for a front two-axle vehicle according to claim 1, wherein an orifice is provided downstream of a location where the pilot pressure for the shut-off valve is extracted in the hydraulic oil supply line.

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