JP2001294170A - Three-axle truck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand a cargo carrying volume by lowering the floor of a cargo room, and to restrain a rear part of a truck from being expanded toward a direction opposite to a turning direction in turning. SOLUTION: In this truck, one front wheel 17 is provided in each end of both ends of a front axle 11, one intermediate wheel 19 is provided in each of both ends of an intermediate axle 12, and a set of two rear wheels 22 is provided in each end of both ends of a rear axle 13. A relation of 0.4<=(L1/L0)<=0.5 is satisfied, where L0 represents an interaxle distance between the front axle 11 and the rear axle 13, and L1 represents an interaxle distance between the front axle 11 and the intermediate axle 12. A-controller 63 having a timer controls, based on a detection output from a steering angle sensor 59, a rear wheel steering means 21 to make the rear wheels 22 steered with a phase same to the front wheels 17 after a prescribed time counted from the steering of the front wheels 17 when a traveling speed detected by a vehicle speed sensor is a prescribed value or less exceeding zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a truck having three axles.

[0002]

2. Description of the Related Art Conventionally, a rear two-axle vehicle having a front frame, a rear-rear shaft and a rear front shaft on a chassis frame as a three-axis truck, and a front two-axle vehicle having a rear shaft, a front front shaft and a front-rear shaft on a chassis frame It has been known. In such a three-axle truck, as a result of the load being distributed to the wheels provided at both ends of each axle, the load on the platform provided on the chassis frame can be reduced to a truck having two axles. Can be increased in comparison. Further, the truck is provided with front wheel steering means for steering the front wheels by rotation of the steering wheel. When the driver turns the steering wheel to steer the front wheels, the vehicle turns according to the steering angle of the front wheels. By turning the steering wheel in this way, the vehicle can be turned according to the target direction. For this reason, in such a three-axis truck, the driver can transport the load to a destination in a state where a relatively large amount of load is loaded on the carrier.

[0003] On the other hand, a three-axis truck has a relatively long overall length, and in order to reduce the turning radius of the truck, a truck provided with rear wheel steering means for steering rear wheels in conjunction with steering of front wheels is provided. Are known. In such a truck, the rear wheels are steered by the rear wheel steering means in the opposite phase to the front wheels, thereby turning the rear portion of the truck in a direction opposite to the direction in which the front end of the truck turns, thereby reducing the turning radius of the truck. Thus, the so-called small turning performance can be improved.

[0004]

However, in a truck in which the rear wheels are steered in the opposite phase to the front wheels by the rear wheel steering means, the turning trajectory at the rear of the truck at the time of turning is indicated by a solid line arrow as shown in FIG. There is a problem that the swelling greatly in the direction opposite to the turning direction. For this reason, when there is a side wall or the like near the truck, if the front wheels are steered in a direction away from the side wall, the bulge may cause the rear portion of the truck to come into contact with the side wall. The rear of the truck may come into contact with an oncoming vehicle traveling straight from the front right. In recent years, there has been a growing demand for increasing the load capacity of luggage without changing the size of the entire truck. SUMMARY OF THE INVENTION An object of the present invention is to provide a three-axle truck capable of equalizing the load balance received by each wheel and increasing the load capacity of the load by lowering the luggage compartment. Another object of the present invention is to provide a three-axis track capable of suppressing bulging in the direction opposite to the turning direction of the rear portion of the track during turning.

[0005]

The invention according to claim 1 is
As shown in FIGS. 1 and 2, a front shaft 11 that supports a front portion of the chassis frame 14 and has front wheels 17 that are steered by front wheel steering means 16 at both ends and a rear portion of the chassis frame 14 and A rear shaft 13 provided with a rear wheel 22 that is steered by the rear wheel steering means 21 in a phase opposite to that of the front wheel 17, and a chassis frame 14 between the front shaft 11 and the rear shaft 13 are supported and interlocked with the front wheel steering means 16. An intermediate shaft 12 provided at both ends thereof is provided with an intermediate wheel 19 that is steered in the same phase as the front wheel 17 by the intermediate wheel steering means 18. The front wheels 17 are provided one at each end of the front shaft 11. 1 at both ends of the intermediate shaft 12
This is an improvement of a triaxial track in which two rear wheels 22 are provided at each end of the rear shaft 13. Its characteristic configuration, when before the center distance of the axis 11 and the rear shaft 13 and L _0, the center distance between the front axle 11 and the intermediate shaft 12 and L _1,
It is configured to satisfy the relationship of 0.4 ≦ (L ₁ / L ₀ ) ≦ 0.5.

In the three-axle truck according to the first aspect, the front shaft 11 and the intermediate shaft 1 to which a relatively small load acts.
Two front wheels 17 and one intermediate wheel 19 at each end
Are provided, and two rear wheels 22 are provided at both ends of the rear shaft 13 on which the largest load acts, respectively.
The load balance received by each of the wheels 17, 19, 22 can be equalized. As a result, each wheel 17, 19, 2
By making the size of the truck 2 uniform, the floor space of the luggage compartment can be reduced, and the load capacity of the luggage can be increased without changing the size of the entire truck. Also, if a relatively large wheelbase (the distance between the front shaft 11 and the rear shaft 13) is ensured, the steering stability during straight running can be improved.

The invention according to claim 2 is the invention according to claim 1, wherein a vehicle speed sensor 62 for detecting a traveling speed and a steering angle sensor 59 for detecting a steering angle of the front wheels 17 as shown in FIG. And a controller 63 for controlling the rear wheel steering means 21 based on the detection outputs of the vehicle speed sensor 62 and the steering angle sensor 59. The controller 63 is provided with a timer 63b. The controller 63 controls the rear wheel steering means 21 so that the rear wheel 22 is steered in the same phase as the front wheel 17 for a predetermined time after the front wheel 17 is steered when the value exceeds zero and is equal to or less than a predetermined value. And According to the third aspect of the present invention,
In the case of an axle track, when the track 10 changes its traveling direction at a relatively slow speed that exceeds zero and is equal to or less than a predetermined value, such as a turn in a factory yard or a turn at an intersection, the rear wheel 22 for a predetermined time is It rotates in the same direction as the front wheels 17 and prevents the turning trajectory at the rear end of the truck from expanding significantly in the direction opposite to the turning direction.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. As shown in FIG. 1, the truck 10 includes a front shaft 11 supporting a front portion of a chassis frame 14, a rear shaft 13 supporting a rear portion of the chassis frame 14, and a chassis frame between the front shaft 11 and the rear shaft 13. And an intermediate shaft 12 that supports the same. The truck 10 in this embodiment is a truck having a total weight of 25 tons. Front wheels 17 steered by front wheel steering means 16 (FIG. 2) are provided at both ends of a front shaft 11, and both ends of an intermediate shaft 12 are provided at both ends thereof. Intermediate wheels 19 that are steered in the same phase as the front wheels 17 by intermediate wheel steering means 18 (FIG. 5) interlocked with the front wheel steering means 16 are provided at both ends. Further, at both ends of the rear shaft 13, rear wheels 22 which are steered by rear wheel steering means 21 (FIGS. 2 to 4) are provided.

The front wheels 17 are provided one at each end of the front shaft 11, the intermediate wheels 19 are provided one at each end of the intermediate shaft 12, and the rear wheels 22 are provided two at both ends of the rear shaft 13. Provided. The rear wheel 22 is configured to be steered in the opposite phase to the front wheel 17, and the rear shaft 13 is provided with a differential 23 (FIGS. 1, 3 and 4). The driving force generated by the engine 20 is transmitted to a transmission 24 and a propeller shaft 26.
Through the drive shaft 13a of the rear shaft 13 (FIG. 3). That is, the rear wheels 22 are so-called drive wheels, and the rear wheels 22 as the drive wheels are rotated by the driving force of the engine 20 so that the truck 10 travels.

As shown in FIG. 2, the front wheel steering means 16 includes a power steering device 29 connected to a steering wheel 27 via a steering shaft 28, and a pitman arm 31 and a front drag link 32 connected to the power steering device 29. And a front knuckle 33 connected to the front knuckle 33. The front wheel 17 is rotatably attached to the front knuckle 33. In this embodiment, the power steering device 29 is an integral power steering device in which a control valve and a power cylinder are integrally formed with a steering gear, and assists the operation force of the steering wheel 27.

As shown in FIGS. 2 to 4, the rear wheel steering means 2
1 is a pair of rear king pins 3 at both ends of a rear shaft 13 (FIG. 1).
A pair of rear knuckles 36 each pivotally connected via
A rear tie rod 37 provided rearward of the rear shaft 13 in the vehicle width direction and having both ends connected to connection arms 36a (FIG. 4) of a pair of rear knuckles 36; And a knuckle arm 36b whose tip is connected to a piston rod 38a of a hydraulic cylinder 38. A pair of side members 14a, 14a of the chassis frame 14 is provided with a cylinder bracket 14b so as to be located in front of the rear shaft 13, and a link is provided between the rear shaft 13 and the cylinder bracket 14b. Bracket 14c is installed (FIGS. 3 and 4).

The base end of the hydraulic cylinder 38 is pivotally connected to the cylinder bracket 14b, and the piston rod 38a of the hydraulic cylinder 38 projects rearward and is connected to the upper end of a swing link 39. A substantially middle portion of the swing link 39 is pivotally attached to the link bracket 14c. The lower end of the swing link 39 is connected to the front end of the rear drag link 41, and the rear end of the rear drag link 41 is connected to the tip of the knuckle arm 36b. Piston rod 3 of hydraulic cylinder 38
The rear wheel 22 is configured to be steered via the swing link 39, the rear drag link 41, the rear knuckle 36, and the rear tie rod 37 as the 8a expands and contracts.

On the other hand, as shown in FIG. 2, hydraulic oil 47 is supplied to the power steering device 29 from a hydraulic pump 44 driven by the engine 20 through a main supply pipe 46 and discharged from the power steering device 29. The hydraulic oil 47 is configured to be returned to the oil tank 49 through the main return pipe 48. The main supply pipe 46 is provided with a flow dividing valve 51, which is connected to the throttle 51a and the branch port 5a.
1b. The branch port 51b is connected to a first port 38b of the hydraulic cylinder 38 via a branch supply pipe 52, and the second port 38c of the hydraulic cylinder 38 is connected to a main return pipe 48 via a branch return pipe 53. Branch supply pipe 5
The second and branch return pipes 53 are provided with a proportional valve 54 and a cutoff valve 56. The hydraulic oil 47 supplied to the flow dividing valve 51 by the hydraulic pump 44 is throttled to a constant flow rate by the throttle unit 51a and supplied to the power steering device 29.
b to be supplied to the hydraulic cylinder 38.

The proportional valve 54 is a four-port three-position switching valve, and the first port 54a is connected to the branch supply pipe 5 on the side of the branch valve 51.
2 and the second port 54b is connected to the branch supply pipe 52 on the hydraulic cylinder 38 side. The third port 54c
Is connected to the branch return pipe 53 on the flow dividing valve 51 side, and the fourth port 54d is connected to the branch return pipe 53 on the hydraulic cylinder 38 side. This valve 54 has first and second control units 54e,
54f is configured to be electromagnetically and mechanically (spring) switched and controlled. The first control unit 54e is turned on and the second
When the controller 54f is turned off, the first and second ports 54
a and 54b are communicatively connected, and the third and fourth ports 5
4c and 54d are communicatively connected. Also, the first control unit 54e
Is turned off and the second control unit 54f is turned on, the first and fourth
The ports 54a and 54d are communicatively connected, and the second and third ports 54b and 54c are communicatively connected. Further, when both the first and second controllers 54e and 54f are turned off, the ports 54a to 54d are shut off.

The cutoff valve 56 is a two-port two-position switching valve. The first port 56a is connected to the branch supply pipe 52, and the second port 56b is connected to the branch return pipe 53. The valve 56 is configured to be electromagnetically and mechanically (spring) switched and controlled by the controller 56c. When the control unit 56c is turned on, the first port 56a and the second port 56b are communicatively connected. When the control unit 56c is turned off, the first port 56a is connected to the first port 56a.
The port 56a and the second port 56b are configured to be cut off. The valve 56 is configured to be turned on when the hydraulic cylinder 38 fails. Note that reference numerals 57 and 58 in FIG. 2 are relief valves.

The power steering device 29 includes a front steering angle sensor 5 for detecting the rotation angle of the pitman arm 31.
Reference numeral 62 in FIG. 2 denotes a vehicle speed sensor for detecting the vehicle speed of the truck. The detection outputs of the front steering angle sensor 59 and the vehicle speed sensor 62 are respectively connected to the control inputs of the controller 63, and the control outputs of the controller 63 are the first and second control units 54e and 54f of the proportional valve 54.
And a control unit 56c of the cutoff valve 56.

As shown in FIGS. 3 and 4, a chassis frame 14 is mounted on the rear shaft 13 via an air spring 71. That is, an intermediate portion between a pair of supports 72, 72 extending substantially parallel to the pair of side members 14a, 14a of the chassis frame 14 is attached to the lower surface of the rear shaft 13, respectively. Four air springs 71 are interposed between the front and rear ends of the support members 72, 72 and the pair of side members 14a, 14a, respectively. The upper surfaces of the air springs 71, 71 are attached to the lower surfaces of the pair of side members 14a, 14a. The rear shaft 13 is connected to the chassis frame 14 by a torque rod 73, respectively. The torque rod 73 has a pair of upper rods 74, 74 having a rear end pivotally attached to an upper middle portion of the rear shaft 13 and a front end pivotally attached to the chassis frame 14 forward of the rear shaft 13, and a pair of support members 72 having a rear end. ,
A pair of lower rods 77 are pivotally mounted at the center of each of the rods 72, and the front ends thereof are fixed to both ends of a stabilizer bar 76 in front of the rear shaft 13. A pair of upper rods 7
The rear ends of the upper and lower rods 74, 74 are integrally formed, and the upper rods 74, 74 are disposed so as to gradually expand toward the front (FIG. 4). A pair of upper rods 74, 74
Are pivotally attached to the inner surfaces of the pair of side members 14a, 14a. Further, the stabilizer bar 76 is provided to extend in the vehicle width direction, and is rotatably held by a pair of brackets 78 suspended from the pair of side members 14a, 14a. The pair of lower rods 77, 77 are disposed substantially in parallel, and also function as a stabilizer arm. That is, the lower rods 77, 77 have a function of suppressing the rolling of the vehicle body together with the stabilizer bar 76.

Returning to FIG. 1, the three-axis track is
When the center distance between the front shaft 11 and the rear shaft 13 is L ₀ and the center distance between the front shaft 11 and the intermediate shaft 12 is L ₁ , 0.4 ≦ (L ₁ / L
₀ ) ≦ 0.5. In this relation, the intermediate shaft 12 is located closer to the front shaft 11 than the center of the front shaft 11 and the rear shaft 13, but the interval between the front shaft 11 and the intermediate shaft 12 is different from that of a so-called conventional front two-axle wheel. , The load distribution to the front shaft 11, the intermediate shaft 12, and the rear shaft 13 can be made closer to 1: 1: 2 corresponding to the number of the respective wheels 17, 19, 22 provided at both ends of the shaft, and the entire truck can be distributed. Can be evenly distributed to the wheels 17, 19, and 22. The reason for limiting L ₁ / L ₀ to the above range is that
If L ₁ / L ₀ is less than 0.4, the front shaft 11 and the intermediate shaft 12 are too close to be able to evenly distribute the load to the front wheel 17 and the intermediate wheel 19, and the rear shaft 13 is separated from the rear shaft 13 by the rear. This is because there is a problem that an excessive load acts on the wheel 22. On the other hand, if L ₁ / L ₀ exceeds 0.5, an excessive load acts on the front shaft 11.
Even if the total length of the chassis frame or the maximum load capacity changes due to a change in the type of the vehicle, (L ₁ / L ₀ ) is appropriately determined within the above range, so that the front shaft 11, the intermediate shaft 12, and the rear shaft 13 can be changed. The load distribution can approach the target of 1: 1: 2.

As shown in FIG. 5, the intermediate wheel steering means 18 is connected to a rotating shaft 82 having a front end connected to a steering shaft 28 below the steering wheel 27 via a bevel gear 81, and a rear end of the rotating shaft 82. And a middle drag link 86 composed of a plurality of links connected to a pitman arm 84 of the power steering device 83. Middle wheel 1
9 is rotatably attached to an intermediate knuckle (not shown),
An intermediate drag link 86 is connected to the intermediate knuckle. The intermediate power steering device 83 is an integral power steering device having the same structure as the power steering device 29 in the front wheel steering means 16 described above. The intermediate wheel steering means 18 is configured to steer the intermediate wheel 19 in the same phase as the front wheel 17 in conjunction with the front wheel steering means 16, the distance between the front shaft 11 and the rear shaft 13 being L ₀ , when the center distance L ₁ between the 11 and the intermediate shaft 12 is configured to steer the intermediate wheel 19 at an angle corresponding to L ₁ / L ₀ of the steering angle of the front wheels 17.

The operation of the three-axis track configured as described above will be described. A front wheel 17 and a middle wheel 19 are respectively provided at both ends of a front shaft 11 and a middle shaft 12 which support a front portion and a center portion of the chassis frame 14 of the truck 10 and apply a relatively small load, respectively. 14
Since two rear wheels 22 are provided at both ends of the rear shaft 13 on which the largest load acts by supporting the rear part,
The load balance received by each of the wheels 17, 19, 22 can be equalized. As a result, each wheel 17, 19, 2
By making the size of the truck 2 uniform, the floor space of the luggage compartment can be reduced, and the load capacity of the luggage can be increased without changing the size of the entire truck. Also, if a relatively large wheel base (the distance between the front shaft 11 and the rear shaft 13) is ensured, steering stability during straight running can be improved.

On the other hand, as in the case of a turn in a factory yard or a turn in an intersection, the track 10 changes its traveling direction at a relatively slow speed exceeding zero and equal to or less than a predetermined value. When the driver turns the steering wheel 27 to the left (in the direction indicated by the solid arrow in FIG. 2), the pitman arm 31 rotates in the direction indicated by the dashed-dotted arrow with the assistance of the power steering device 29. The steering wheel is steered leftward (in a direction indicated by a broken arrow) by an angle corresponding to the rotation angle of the steering wheel 27. On the other hand, when the vehicle speed sensor 62 detects that the vehicle speed exceeds zero and is equal to or less than a predetermined value, and the front steering angle sensor 59 detects that the pitman arm 31 has rotated by a predetermined angle in the direction of the dashed line arrow, Controller 63
The rear wheel 22 is driven by the front wheel 1 for a predetermined time from the time when the front wheel 17 is steered based on the detection outputs of the sensors 62 and 59.
The second control unit 54f of the proportional valve 54 is turned on so that the steering is performed in the same phase as that of the control valve 7. As a result, the first and fourth ports 54a and 54d of the proportional valve 54 are connected to each other and the second and third ports 54b and 54c are connected to each other.
The hydraulic oil 47 is supplied from the second port 38c of the hydraulic cylinder 38 to the opposite rod side chamber of the hydraulic cylinder 38, and the hydraulic oil 47 of the rod side chamber of the hydraulic cylinder 38 is discharged from the first port 38b of the hydraulic cylinder 38. As a result, since the piston rod 38a projects, the rear wheel 22 rotates in the same direction as the front wheel 17, that is, the direction shown by the dashed arrow. As a result, as shown in FIG. 6, the turning trajectory at the rear end of the truck 10 does not swell greatly in the direction opposite to the turning direction, and even if there is a side wall or the like near the truck 10 when turning inside the factory yard, Also, even if an oncoming vehicle goes straight ahead from the right front when turning left at an intersection, it is avoided that the rear part of the truck 10 advances in a direction away from the side wall or the oncoming vehicle and the rear portion contacts the side wall or the oncoming vehicle. Is done.

On the other hand, when a predetermined time has elapsed from the time when the front wheel 17 was steered, the controller 63 returns to a normal control state, that is, a state in which the rear wheel steering means 21 steers the rear wheel 22 in the opposite phase to the front wheel 17. . The predetermined time in this embodiment is a time until the truck 10 travels 1 m based on the detection output of the vehicle speed sensor 62, and a time obtained by the controller 63 comparing the data stored in the memory 63a with the vehicle speed. It is. Whether or not the predetermined time has elapsed is measured by a timer 63b built in the controller 63. After the predetermined time has elapsed, the controller 63 controls the steering angle sensor 59 so that the rear wheel 22 is steered in the opposite phase to the front wheel 17. The rear wheel steering means 21 is controlled based on the detection output.

As specifically shown in FIG. 2, after a predetermined time has elapsed, the controller 63 controls the first control unit 5 of the proportional valve 54.
4e is turned on, and the first and second ports 54a and 54b of the proportional valve 54 are connected and connected. As a result, the third and fourth ports 54c and 54d are connected to each other, so that the hydraulic oil 47 is supplied from the first port 38b of the hydraulic cylinder 38 to the rod side chamber (not shown) of the hydraulic cylinder 38, Hydraulic cylinder 38 from 2 port 38c
The hydraulic oil in the non-rod side chamber (not shown) is discharged. As a result, the piston rod 38a retracts, and the swing link 3
9, the rear drag link 41 moves in the direction shown by the solid arrow, so that the rear wheel 22 rotates in the direction opposite to the front wheel 17, that is, the direction shown by the solid arrow. The rotation angle of the swing link 39 is fed back to the control input of the controller 63, and when the rear wheel 22 has reached a predetermined steering angle, the first control unit 54e of the proportional valve 54 is turned off and the hydraulic cylinder 38
The supply of the hydraulic oil 47 to is stopped. As a result, the truck 10 can turn with a relatively small turning radius.
Note that, when the steering wheel 27 is turned clockwise, the operation is the reverse of the above, and thus the repeated description is omitted.

[0024]

As described above, according to the present invention, according to the present invention, the center distance between the front axle and the rear axle and L _0, when the center distance between the front axle and the intermediate shaft and L _1, 0 _0.4 ≦ (L ₁ / L ₀ ) ≦ 0.
5, one front wheel and one intermediate wheel are provided at both ends of the front shaft and the intermediate shaft on which a relatively small load acts, and two front wheels and two intermediate wheels are provided on both ends of the rear shaft on which the largest load acts. Since the rear wheels are provided one by one, the load balance received by each wheel can be equalized. As a result, the floor size of the luggage compartment is reduced by making the size of each wheel uniform, and the load capacity of the load can be increased without changing the size of the entire truck. When the traveling speed detected by the vehicle speed sensor exceeds zero and is equal to or less than a predetermined value, the detection output of the steering angle sensor is set so that the rear wheel is steered in phase with the front wheel for a predetermined time from the time when the front wheel is steered. If the controller is configured to control the rear wheel steering means on the basis of the rear of the truck when changing its traveling direction at a relatively slow speed, for example, turning at a factory yard or turning at an intersection It is possible to avoid that the turning trajectory at the point swells greatly in the direction opposite to the turning direction.

[Brief description of the drawings]

FIG. 1 is a plan view of a three-axis track according to the present invention.

FIG. 2 is a configuration diagram showing front wheel steering means and rear wheel steering means and a control circuit thereof.

FIG. 3 is a sectional view taken along line AA of FIG. 4;

FIG. 4 is an enlarged view of a portion B in FIG. 1;

FIG. 5 is a configuration diagram showing a relationship between front wheel steering means and intermediate wheel steering means.

FIG. 6 is a conceptual diagram showing a turning state of a truck according to the present invention.

FIG. 7 is a conceptual diagram corresponding to FIG. 6, showing a conventional truck turning state.

[Explanation of symbols]

Reference Signs List 10 track 11 front shaft 12 intermediate shaft 13 rear shaft 14 chassis frame 16 front wheel steering means 17 front wheel 18 intermediate wheel steering means 19 intermediate wheel 21 rear wheel steering means 22 rear wheel 59 steering angle sensor 62 vehicle speed sensor 63 controller L ₀ center distance between the center distance L ₁ front shaft and the intermediate shaft and the rear shaft

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D032 CC02 DA03 DA23 DA50 EA06 EA09 EB01 EC04 GG05 3D033 CA13 CA17 EB08 EC08 ED07 GB02 JA02 KA02 KA06 3D034 CA02 CB06 CC02 CC07 CC08 CC14 CD04 CD13 CE12

Claims (2)

[Claims] 1. A front shaft (11) which supports a front portion of a chassis frame (14) and is provided at both ends with front wheels (17) steered by front wheel steering means (16); A rear shaft (13) provided with a rear wheel (22) that supports a rear portion and is steered at opposite ends by a rear wheel steering means (21) in an opposite phase to the front wheel, and the front shaft (1
An intermediate wheel steering unit (18) that supports the chassis frame (14) between the (1) and the rear shaft (13) and is interlocked with the front wheel steering unit (16).
And an intermediate shaft (12) provided at both ends with an intermediate wheel (19) steered in phase with the front wheel (17), and one front wheel (17) at each end of the front shaft (11). And three intermediate wheels (19) are provided at both ends of the intermediate shaft (12), and two rear wheels (22) are provided at both ends of the rear shaft (13). In the truck, the center distance between the front shaft (11) and the rear shaft (13) is L ₀ ,
When the center distance between said front axle (11) and said intermediate shaft (12) and _{L 1, 0.4 ≦ (L 1} / L 0) that is configured to satisfy the relation of ≦ 0.5 A three-axis truck characterized by the following. 2. A vehicle speed sensor (62) for detecting a traveling speed,
A steering angle sensor (59) for detecting a steering angle of the front wheels (17), and a controller for controlling rear wheel steering means (21) based on each detection output of the vehicle speed sensor (62) and the steering angle sensor (59). The controller (63) is provided with a timer (63b), and when the traveling speed detected by the vehicle speed sensor (62) is greater than zero and equal to or less than a predetermined value, the front wheel (17) is provided. The controller (63) controls the rear wheel steering means (21) so that the rear wheel (22) is steered in the same phase as the front wheel (17) for a predetermined time from the time when the vehicle is steered. 3 axis truck.