Towed Vehicle System

Abstract

To provide a towed vehicle system with high practicality.SOLUTION: For a towed vehicle 10 including front wheels 24f and rear wheels 24r which are freely turnable, at least two of a front wheel orientation unchangeable condition where the orientation of the front wheels is made unchangeable, a rear wheel orientation unchangeable condition where the orientation of the rear wheels are made unchangeable, and a front and rear wheels orientations unchangeable condition where both the orientation of the front wheels and the orientation of the rear wheels are made unchangeable are selectively made feasible. The conditions are changed according to a travel road or travel mode, whereby the towed vehicle can be properly traveled.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a towed vehicle system including a towed vehicle towed by a towing vehicle. [Background technology]

[0002] Considering that a towed vehicle will turn while being towed by a towing vehicle, the towed vehicle is generally configured so that the direction of the wheels located at the front can be freely changed and the direction of the wheels located at the rear is fixed in the front-to-rear direction. The towed vehicle described in the following patent document is configured to be towed from either the front or rear side, and the direction of the wheels located at the rear can be fixed depending on the side being towed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-196384 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, as described in the above patent document, it is desirable for the front wheels to be freely steerable and the rear wheels to be unable to steer, but depending on the road on which the towed vehicle is traveling, that is, the road, this may not be desirable, and a towed vehicle that is maintained only in this state cannot necessarily be said to be highly practical. The present invention was made in consideration of this situation, and an object of the present invention is to provide a towed vehicle system that is highly practical. [Means for solving the problem]

[0005] In order to solve the above problems, the towed vehicle system of the present invention comprises: a towed vehicle having front and rear wheels that can be turned freely and a wheel direction fixing device that can fix the directions of the front and rear wheels in the front-to-rear direction independently of each other, the towed vehicle being connected to the towing vehicle so as to be rotatable relative to the towing vehicle; and a controller that selectively realizes at least two of a front wheel direction fixed state in which only the direction of the front wheels is fixed, a rear wheel direction fixed state in which only the direction of the rear wheels is fixed, and a front / rear wheel direction fixed state in which the directions of both the front wheels and the rear wheels are fixed, using the wheel direction fixing device. It is assumed that the first towed vehicle system is configured such that the controller achieves the front wheel lock state when turning on a narrow roadway; The second towed vehicle system is configured such that the controller realizes the front and rear wheel direction fixed state when the towed vehicle travels straight on an inclined roadway; The third towed vehicle system is characterized in that the towed vehicle is towed by the towing vehicle, which does not have steering wheels and can turn by driving the left and right wheels independently of each other. [Effects of the Invention]

[0006] According to the towed vehicle system of the present invention, at least two of the three states mentioned above, i.e., front wheel direction fixed state, rear wheel direction fixed state, and front and rear wheel direction fixed state, can be selectively realized as a state for fixing the direction of the wheels of the towed vehicle (sometimes called "wheel direction fixed state"), and therefore, by switching between these states depending on the road and driving conditions, for example, it becomes possible to drive the towed vehicle more appropriately.

[0007] The "wheels" of a towed vehicle include front and rear wheels. The front wheels are the wheels closest to the towing vehicle, and the rear wheels are the wheels furthest from the towing vehicle. There may be a pair of front and rear wheels, one on each side, or only one front or one rear wheel. The structure that allows each wheel to turn freely is not particularly limited, and may be, for example, a structure similar to a so-called swivel caster. Specifically, the wheels may be supported on forks so as to be rotatable about a horizontal axis, and the forks may be supported on the towed vehicle body so as to be rotatable about a vertical axis.

[0008] A "wheel direction locking device" locks the direction of the wheels in the forward / backward direction; in other words, it maintains the wheel position when the towed vehicle moves forward or backward. The wheel direction locking device (hereinafter sometimes simply referred to as a "locking device") may be configured by providing a single wheel locking device for prohibiting the turning of one wheel, the number of which is equal to the number of wheels. Alternatively, if there are multiple front and / or rear wheels, a multiple wheel locking device for prohibiting the turning of all of the wheels may be provided for at least one of the front and / or rear wheels. It is also possible for the locking device to prohibit the turning of only one of the multiple wheels. The specific structure of the locking device is not particularly limited. Specifically, for example, if a structure similar to the swivel caster described above is used for the wheels, the locking member for permitting / prohibiting the rotation of the fork may be configured to be operated by an actuator.

[0009] The "towing vehicle" is not particularly limited in its structure, configuration, or manner, as long as it is connected to a towed vehicle so as to be rotatable relative to the towed vehicle in a generally horizontal direction and tows the towed vehicle so as to allow it to turn. For example, it may be an automatic vehicle or one driven by a driver. For example, it may be a vehicle having three or more wheels, including steerable and non-steerable wheels, with at least one of the three or more wheels functioning as a drive wheel. Specifically, it may be a vehicle having four wheels, front, rear, left, and right, with two rear wheels being non-steerable and two front wheels being steerable, and at least one of the two front wheels and the two rear wheels being a drive wheel. It may also be a vehicle that does not have steerable wheels but can turn by independently driving the left and right wheels, a so-called two-wheel differential vehicle. Incidentally, the steerable wheels referred to here refer to wheels that can be actively steered to change the direction of the towing vehicle.

[0010] The "controller" controls the securing device and may be configured to include, for example, a control computer and a driver (drive circuit) for the securing device. The controller may be disposed in the towing vehicle or the towed vehicle. Alternatively, the computer may be disposed in the towing vehicle and the driver may be disposed in the towed vehicle.

[0011] The "rear-wheel direction fixed state," which is one of the wheel direction fixed states, is a basic wheel direction fixed state, and the controller may be configured to realize the rear-wheel direction fixed state as this basic state. For example, when the towed vehicle and the towing vehicle are coupled together and backing up and turning, in the front-wheel direction fixed state, the turning center changes significantly, making it difficult to properly maintain the orientation of the towed vehicle itself. In contrast, in the rear-wheel direction fixed state, it is possible to properly control the attitude of the towed vehicle even when the towed vehicle and the towing vehicle are coupled together and backing up and turning.

[0012] On the other hand, the controller may be configured to realize the "front wheel direction fixed state" when the towed vehicle turns on a narrow roadway (hereinafter sometimes referred to as a "narrow road"), or, simply put, when turning left or right. When the towed vehicle turns while being towed by a towing vehicle, if the rear wheel direction fixed state is used, the difference between the inside wheels will be relatively large. In contrast, if the front wheel direction fixed state is used, the difference between the outside wheels will be somewhat large, but the difference between the inside wheels will be significantly smaller. In other words, the front wheel direction fixed state is a state suitable for turning on narrow roads. This is particularly suitable when turning left while driving on a narrow road with left-hand traffic, or when turning right while driving on a narrow road with right-hand traffic, etc.

[0013] Furthermore, the controller may be configured to achieve the "fixed front and rear wheel orientation" when the towed vehicle travels straight on an inclined road. For example, when the towed vehicle is towed by a towing vehicle and traveling on a road that slopes to the left or right, a so-called canted road, if the rear wheels are in the fixed orientation, the front wheels will tend to drop toward the lower side of the slope, causing moments in opposite directions to act on the towed vehicle and the towing vehicle, which could result in the so-called jackknife phenomenon between the towed vehicle and the towing vehicle. The fixed front and rear wheel orientation is effective in preventing this jackknife phenomenon. Also, when the towed vehicle and the towing vehicle are coupled together and traveling straight downhill, if the center of gravity of the towed vehicle shifts to the left or right, the jackknife phenomenon could occur in the fixed rear wheel orientation. This is particularly likely when the towing vehicle applies the brakes. The fixed front and rear wheel orientation is also effective in preventing the jackknife phenomenon in this case. Preventing the jackknife phenomenon is particularly meaningful when the towing vehicle is a two-wheel differential vehicle as described above.

[0014] The controller may be configured to realize a "front / rear wheel orientation unfixed state" in which the orientation of neither the front nor rear wheels is fixed, as a state other than the above three states. For example, if this front / rear wheel orientation unfixed state is realized when the towed vehicle is not coupled to the towing vehicle, it will be possible to change the orientation of the towed vehicle even in a relatively narrow space by, for example, performing a pivot turn. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view showing a towed vehicle that constitutes a towed vehicle system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing wheels (casters) and wheel direction fixing devices of a towed vehicle. [Figure 3] 10A and 10B are schematic diagrams showing differences in behavior during backward turning depending on the state in which the wheels are fixed in direction. [Figure 4] 10A and 10B are schematic diagrams showing differences in trajectories during turning depending on the state in which the wheels are fixed in direction. [Figure 5] FIG. 10 is a schematic diagram for explaining the advantage of fixing the orientation of both the front and rear wheels. [Figure 6] 10 is a flowchart of a wheel direction fixed state switching program executed by the controller. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes in detail a towed vehicle system according to an embodiment of the present invention, with reference to the drawings. In addition to the following embodiment, the present invention can be embodied in various forms, including those described in the above section "Modes of the Invention," with various modifications and improvements made based on the knowledge of those skilled in the art. [Example]

[0017] [A] Configuration of towed vehicle As shown in FIG. 1, the towed vehicle 10 constituting the towed vehicle system of this embodiment is towed by a towing vehicle 12. The towed vehicle 10 includes a bedplate 20 and four swivel casters 22 attached to the bottom of the bedplate 20. The side towed by the towing vehicle 12 is the front side, and the opposite side is the rear side. The four casters 22 are arranged in a pair of left and right on the front side, and a pair of left and right on the rear side. The four casters 22 have the same structure, and each has a wheel 24. Of the four wheels 24, the wheel 24 on the front caster 22 functions as a front wheel, and the wheel 24 on the rear caster 22 functions as a rear wheel. In consideration of this, hereinafter, each wheel 24 will be referred to collectively as wheel 24, and, as necessary, the wheel 24 on the front caster 22 may be referred to as a front wheel 24f and the wheel 24 on the rear caster 22 may be referred to as a rear wheel 24r, as shown in the figure.

[0018] As shown in Fig. 2(a) as viewed from the side and in Fig. 2(b) as viewed from below, the caster 22, like a typical caster, is configured to include a top plate 26 fixed to the base plate 20, a fork 28 held on the top plate 26 so as to be rotatable about a vertical axis, and a wheel 24 held at the lower end of the fork 28 via an axle 30 so as to be rotatable about a horizontal axis. Like a typical swivel caster, when a force with a horizontal component acts on the base plate 20, the present caster 22 rotates so that the wheel 24 faces in the direction of that component.

[0019] In the towed vehicle 10, each caster 22 is provided with a device that prohibits the rotation of the fork 28, in other words, a wheel direction fixing device 32 (hereinafter sometimes simply referred to as a "fixing device 32") that fixes the direction of the wheel 24. The fixing device 32 is configured to include an actuator 34 and a stopper 36 that is a locking member that is moved forward and backward by the actuator 34. The figure shows the rear caster 22, and the fixing device 32 is disposed in front of that caster 22. Although not shown, a fixing device 32 is disposed behind the front caster 22.

[0020] The actuator 34 is a cylinder device including an electromagnetic solenoid, and when the solenoid is not energized, the piston 38 is positioned in a retracted position, and when the solenoid is energized, the piston 38 is positioned in an advanced position. As the piston 38 advances and retreats, the stopper 36 also advances and retreats. The solid lines in the figure indicate the state in which the piston 38 and stopper 36 are in the advanced positions, and the two-dot chain lines in the figure indicate the state in which the piston 38 and stopper 36 are in the retracted positions.

[0021] The stopper 36, which is a locking member, has a generally U-shape with two arms, and when it is in the forward position, the fork 28 of the caster 22 is clamped between the two arms, preventing the fork 28 from rotating, i.e., preventing the wheel 24 from changing its orientation. In other words, the orientation of the wheel 24 is fixed in the forward / rearward direction. On the other hand, when the stopper 36 is in the backward position, the clamping of the fork 28 is released, allowing the fork 28 to rotate freely, i.e., allowing the wheel 24 to change its orientation freely. In other words, the wheel 24 is free to turn.

[0022] The towed vehicle 10 is provided with four locking devices 32 corresponding to the four wheels 24. These locking devices 32 can operate independently of one another. That is, each locking device 32 can lock or release the orientation of its corresponding wheel 24, regardless of whether the orientations of the other wheels 24 are locked. The towed vehicle 10 can also be considered to have the four locking devices 32 constituting one wheel orientation locking device, that is, a wheel orientation locking device that can lock the orientations of the front wheels 24f and rear wheels 24r in the fore-and-aft direction independently of one another.

[0023] Here, we will briefly explain the towing vehicle 12 shown in Figure 1. The towing vehicle 12 has a body 40 with a generally rectangular parallelepiped external shape and a pair of left and right drive wheels 42, a left drive wheel 42L and a right drive wheel 42R. A coupler 44 is attached to the rear of the body 40, and auxiliary wheels 46 in the form of swivel casters are attached to the bottom of the coupler 44 to enable the towing vehicle 12 to stand on its own. In other words, the towing vehicle 12 does not have steerable wheels that are actively steered. A connecting bar 48 is fixed to the bedplate 20 of the towed vehicle 10 so that it protrudes forward. By connecting the front end of this connecting bar 48 to the coupler 44, the towed vehicle 10 is connected to the towing vehicle 12 via the coupler 44 so that they can move relatively to each other. More specifically, when connected, the towing vehicle 12 and towed vehicle 10 are allowed to freely rotate relative to each other in a generally horizontal direction around the connecting point JP of the coupler 44.

[0024] The left drive wheel 42L and the right drive wheel 42R of the towing vehicle 12 are driven independently of each other by electric motors 50, which are in-wheel motors. By rotating the left drive wheel 42L and the right drive wheel 42R at the same speed, the towing vehicle 12 moves forward or backward in a straight line. By creating a speed difference between the rotation of the left drive wheel 42L and the right drive wheel 42R, the towing vehicle 12 turns. Braking of the towing vehicle 12, i.e., braking of the left drive wheel 42L and the right drive wheel 42R, is also performed by the electric motor 50.

[0025] The towing vehicle 12 travels unmanned, that is, automatically, based on commands from a control device. Any common method may be used for this automatic travel, and a detailed description thereof will be omitted here. However, for automatic travel, the towing vehicle 12 incorporates a communication device, a camera, a positioning sensor, a yaw rate sensor, an acceleration sensor, a wheel speed sensor, etc. in a sensor box 52 attached to the top of the vehicle body 40. A controller, a power supply, etc. for automatic travel are also incorporated in the vehicle body 40. The controller is configured to include a computer, a driver for the electric motor 50, etc.

[0026] The controller of the towing vehicle 12 also functions as a controller for the fixing device 32 installed on the towed vehicle 10. Specifically, it also controls the operation of each actuator 34. For this reason, the controller is configured to include a driver for each actuator 34. As will be explained in detail later, when the towed vehicle 10 is coupled to the towing vehicle 12, the controller can excite only the actuator 34 corresponding to the front wheel 24f, only the actuator 34 corresponding to the rear wheel 24r, or all of the actuators 34. As a result, the controller selectively realizes a "front wheel direction fixed state" in which only the orientation of the front wheel 24f is fixed in the fore-and-aft direction, a "rear wheel direction fixed state" in which only the orientation of the rear wheel 24r is fixed in the fore-and-aft direction, and a "front and rear wheel direction fixed state" in which the orientations of both the front wheel 24f and the rear wheel 24r are fixed in the fore-and-aft direction.

[0027] [B] Conditions regarding wheel direction fixation As described above, when the towed vehicle 10 is being towed by the towing vehicle 12, the wheel direction is fixed by selecting one of the following: a front wheel direction fixed state, a rear wheel direction fixed state, and a front and rear wheel direction fixed state. The selection of these three states according to the driving state and the driving road will be explained below.

[0028] i) Basic situation In consideration of the proper turning of the towed vehicle 10 while coupled to the towing vehicle 12, the present towed vehicle system basically selects the rear-wheel-direction fixed state. In particular, in situations where the towed vehicle 10 is being reversed while turning (for example, during reverse positioning), specifically, as shown in Figure 3(a), when the towing vehicle 12 pushes the towed vehicle 10 with a force PF, and the towed vehicle 10 is being reversed and shifted laterally, the rear-wheel-direction fixed state is desirable. Incidentally, the diagrams showing the towed vehicle 10 and towing vehicle 12 coupled from Figure 3 onwards are schematic diagrams, and in these diagrams, the turning centers of the front wheels 24f and rear wheels 24r of the towed vehicle 10 and the auxiliary wheels 46 of the towing vehicle 12 are indicated by ● when the directions of those wheels 24, 46 are fixed, and by ○ when they are not fixed, i.e., are free to turn.

[0029] More specifically, in the front-wheel-direction fixed state, as shown in Figures 3(b-1) and 3(b-2), the turning center CP is the point where a line connecting the ground contact points of the left drive wheel 42L and the right drive wheel 42R of the towing vehicle 12 intersects with a line connecting the ground contact points of the left and right front wheels 24f of the towed vehicle 10. If, while the towed vehicle is bent at the coupling point JP, the direction of the force PF exerted by the towing vehicle 12 on the towed vehicle 10 changes from the state shown in Figure 3(b-1) to the state shown in Figure 3(b-2), the turning center CP will move significantly, which means the turning radius will change significantly, making appropriate operation difficult. In other words, the bend angle between the towing vehicle 12 and the towed vehicle 10 about the coupling point JP will increase, inducing a so-called jackknife phenomenon.

[0030] In contrast, in the rear-wheel-direction fixed state, as shown in FIGS. 3(c-1) and 3(c-2), the turning center CP is the point where a line connecting the ground contact points of the left drive wheel 42L and the right drive wheel 42R of the towing vehicle 12 intersects with a line connecting the ground contact points of the left and right rear wheels 24r of the towed vehicle 10. Because the turning center CP is relatively far from the towing vehicle 12 and the towed vehicle 10, even if the direction of the force PF exerted by the towing vehicle 12 on the towed vehicle 10 changes from the state shown in FIG. 3(c-1) to the state shown in FIG. 3(c-2), the amount of movement of the turning center CP is small, meaning the change in turning radius is small, allowing for appropriate operation. In other words, the possibility of inducing a jackknife phenomenon is low. Taking the above into consideration, it is desirable to achieve the rear-wheel-direction fixed state as the basic state.

[0031] ii) Turning on a narrow road Let us consider the case where the towed vehicle 10 is traveling on a roadway that turns at a right angle, that is, the case where the towed vehicle 10 turns at a right angle while being towed by the towing vehicle 12. In the rear wheel fixed state shown in FIG. 4(a-1), the tractive force TF required by the towing vehicle 10 when turning is relatively small, and driving stability is relatively high. However, as shown in FIG. 4(a-2), the travel path of the towed vehicle 10 shifts significantly to the inside of the turn relative to the travel path of the towing vehicle 12. In other words, the difference in the inside wheel radius becomes quite large. When the roadway has a certain width, this difference in the inside wheel radius is tolerable, but when the roadway is narrower than a certain width, turning becomes difficult.

[0032] In contrast, in the front-wheel-direction fixed state shown in FIG. 4(b-1), the tractive force TF required by the towing vehicle 12 during turning is somewhat large, but the inside wheel difference is small, as shown in FIG. 4(b-2). More specifically, the rear of the towed vehicle 10 protrudes to the outside of the turn to some extent, causing the outside wheel difference to be somewhat large, but the travel path of the towed vehicle 10 generally coincides with the travel path of the towing vehicle 12. As a result, compared to the rear-wheel-direction fixed state, turning is possible even on narrower roads. Therefore, in this towed vehicle system, when turning on a road narrower than the set width (narrow road), or simply when turning around a narrow corner, the front-wheel-direction fixed state is realized. Note that when the traveling speed is high, the outside wheel difference becomes large due to inertia, so it is desirable to reduce the traveling speed to some extent when turning on a narrow road.

[0033] iii) When driving straight on a sloped road To get straight to the point, when traveling straight on an inclined road, this towed vehicle system achieves a fixed state of front and rear wheel orientation as shown in Figure 5(a) instead of the basic state of fixed rear wheel orientation. The reason for this is explained below.

[0034] For example, when the towed vehicle 10 and the towing vehicle 12 are coupled together and traveling forward or backward on a canted road that slopes left and right, if the rear wheels are in a fixed orientation, a lateral force SF acts from the road surface only on the rear wheels 24r, as shown schematically in FIG. 5(b), causing a moment due to the gravity component GF at the center of gravity GC of the towed vehicle 10. Opposing this moment, a moment is generated at the center of gravity GC of the towing vehicle 12 in the opposite direction to the moment acting on the towed vehicle 10. These moments cause the towed vehicle 10 and the towing vehicle 12 to bend at the coupling point JP. In other words, a jackknife effect occurs. With this towed vehicle system, the front and rear wheels are fixed when traveling straight on a canted road, preventing the jackknife effect.

[0035] Furthermore, depending on the load on the towed vehicle 10, it is expected that the center of gravity GC of the towed vehicle 10 may shift left or right. For example, if the towed vehicle 10 goes down a slope with the center of gravity GP shifted, a gravity component GF will generate a moment around the center of gravity GP of the towed vehicle 10 if the rear wheels are fixed in the direction shown in FIG. 5(c-1). This moment will cause the towed vehicle 10 to deflect, resulting in jackknife motion. This phenomenon is particularly noticeable when the towing vehicle 12 is braking. However, if the front and rear wheels are fixed in the direction shown in FIG. 5(c-2), the moment will be offset by a lateral force SF acting from the road surface on the four wheels 24, so the towed vehicle 10 will not deflect and jackknife motion will be prevented.

[0036] [C] Controller Functions The controller built into the towing vehicle 12 has a travel control function that controls the travel of the towing vehicle 12, and also has a wheel direction fixed state switching function that switches the state regarding the direction of the wheels of the towed vehicle 10 being towed. These functions will be explained below in order.

[0037] i) Driving control function The towing vehicle 12 travels automatically in accordance with instructions from an external control device. Simply put, the control device wirelessly instructs the towing vehicle 12 on which route to take and where to head. The controller of the towing vehicle 12 has map data related to the travel route, and while referring to this data, the towing vehicle travels based on information obtained from its own cameras, positioning sensors, yaw rate sensors, acceleration sensors, wheel speed sensors, and the like. The method for automatic travel is a common method, so detailed explanations thereof will be omitted.

[0038] ii) Wheel direction fixed state switching function As explained above, when the towed vehicle 10 is coupled to the towing vehicle 12, the controller switches the state related to the fixing of the wheel direction. More specifically, it selectively realizes one of a front wheel direction fixing state, a rear wheel direction fixing state, and a front and rear wheel direction fixing state. This switching is performed by the computer constituting the controller executing a wheel direction fixing state switching program, the flowchart of which is shown in Figure 6, at short intervals (e.g., 0.1 to 1 second). Below, we will explain the processing executed by the controller to switch the wheel direction fixing state in accordance with this program.

[0039] In processing according to the wheel direction fixed state switching program, first, in step 1 (hereinafter abbreviated as "S1," the same applies to the other steps), the current positions of the towing vehicle 12 and towed vehicle 10 are identified based on information from the positioning sensors, etc. Next, in S2, the condition of the road on which the towing vehicle 12 and towed vehicle 10 are currently traveling is identified based on map data, specifically, whether it is an inclined road, whether it is a narrow road, etc., and in S3, the current traveling mode of the towing vehicle 12 and towed vehicle 10, specifically, whether they are going straight or turning, moving forward or backward, etc., is identified.

[0040] In the next step S4, it is determined whether the towing vehicle 12 and towed vehicle 10 are traveling straight. If it is determined that they are traveling straight, it is determined in S5 whether the towing vehicle 12 and towed vehicle 10 are traveling on a slope, i.e., a canted road or a hill. If it is determined that they are not traveling on a slope, in S6 the state related to fixing the wheel direction is set to the basic state, that is, the rear wheel direction fixed state. If it is determined in S5 that they are traveling on a slope, in S7 the front and rear wheel direction fixed state is set.

[0041] If it is determined in S4 that the towing vehicle 12 and towed vehicle 10 are not traveling straight, or simply that they are turning, then in S8 it is determined whether they are moving forward. If it is determined that they are not moving forward, or simply that they are moving backward, then in S6 a rear wheel direction fixed state is established.

[0042] If it is determined in S8 that the towing vehicle 12 and towed vehicle 10 are moving forward, it is determined in S9 whether the towing vehicle 12 and towed vehicle 10 are traveling on a narrow road. If it is determined that they are not traveling on a narrow road, that is, if they are turning on a relatively wide road, a rear-wheel direction fixed state is established in S6. If it is determined that they are turning on a narrow road, that is, a road narrower than a set width, a front-wheel direction fixed state is established in S10. [Explanation of symbols]

[0043] 10: Towed vehicle 12: Towing vehicle 20: Bed plate 22: Caster 24: Wheel 24f: Front wheel 24r: Rear wheel 32: Wheel direction fixing device 34: Actuator 36: Stopper 40: Body 42: Driving wheel 42L: Left driving wheel 42R: Right driving wheel 44: Coupler 46: Training wheel JP: Connection point CP: Center of rotation

Claims

1. a towed vehicle having front and rear wheels that can be turned freely and a wheel direction fixing device that can fix the directions of the front and rear wheels in the front-to-rear direction independently of each other, the towed vehicle being connected to the towing vehicle so as to be rotatable relative to the towing vehicle; a controller that selectively realizes at least two of a front wheel direction fixed state in which only the direction of the front wheels is fixed, a rear wheel direction fixed state in which only the direction of the rear wheels is fixed, and a front and rear wheel direction fixed state in which the directions of both the front wheels and the rear wheels are fixed, by the wheel direction fixing device, The towed vehicle system is configured such that the controller achieves the front wheel lock state when turning on a narrow roadway.

2. a towed vehicle having front and rear wheels that can be turned freely and a wheel direction fixing device that can fix the directions of the front and rear wheels in the front-to-rear direction independently of each other, the towed vehicle being connected to the towing vehicle so as to be rotatable relative to the towing vehicle; a controller that selectively realizes at least two of a front wheel direction fixed state in which only the direction of the front wheels is fixed, a rear wheel direction fixed state in which only the direction of the rear wheels is fixed, and a front and rear wheel direction fixed state in which the directions of both the front wheels and the rear wheels are fixed, by the wheel direction fixing device, The towed vehicle system is configured such that the controller causes the front and rear wheel orientations to be fixed when the towed vehicle travels straight on an inclined roadway.

3. a towed vehicle having front and rear wheels that can be turned freely and a wheel direction fixing device that can fix the directions of the front and rear wheels in the front-to-rear direction independently of each other, the towed vehicle being connected to the towing vehicle so as to be rotatable relative to the towing vehicle; a controller that selectively realizes at least two of a front wheel direction fixed state in which only the direction of the front wheels is fixed, a rear wheel direction fixed state in which only the direction of the rear wheels is fixed, and a front and rear wheel direction fixed state in which the directions of both the front wheels and the rear wheels are fixed, by the wheel direction fixing device, A towed vehicle system in which the towed vehicle is towed by the towing vehicle which does not have steering wheels and can turn by driving left and right wheels independently of each other.

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