Front wheel control mechanism of four-wheel drive type vehicle, and four-wheel drive type vehicle

Abstract

To provide a front wheel control mechanism of a four-wheel drive type vehicle capable of stably controlling a travel state of front wheels included in the four-wheel drive type vehicle, with a simple device configuration applicable to a caring vehicle that carries a person requiring nursing care thereon, and provide the four-wheel drive type vehicle.SOLUTION: Front wheels and rear wheels are mounted to right and left both sides of a frame. In turn operation of a four-wheel drive type vehicle from a straight travel route, through a turn route, to the straight travel route again by steering of front wheels, by holding a state of bringing a rod-shaped member into contact with an end of a front and rear direction rear side of a long hole under a condition of Vf>Vr due to a difference between a rotation speed Vf of the front wheels and a rotation speed Vr of the rear wheels while controlling the steering state of the front wheels by a steering control part, or by holding a state of bringing the rod-shaped member into contact with an end of a front and rear direction front side of the long hole under a condition of Vf<Vr, the front wheels caused to turn according to a restoration moment acting with an axial core of the rod-shaped member as a fulcrum is restored from a steering state to a straight travel state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a front wheel control mechanism for a four-wheel drive vehicle that is used for outdoor travel, etc., primarily for passengers who require assistance and have difficulty walking, such as elderly people or physically disabled people, and who are accompanied by an attendant, and to a four-wheel drive vehicle equipped with such a front wheel control mechanism. [Background technology]

[0002] Elderly people, physically disabled people, and other people who require assistance because they have difficulty walking may go out in a wheelchair, and an attendant must walk while pushing the wheelchair with the care recipient in it from behind. In this case, the weight of the entire wheelchair, including the care recipient, can reach several tens of kilograms, sometimes exceeding 100 kg, and the effort required by the attendant is immeasurable. Therefore, Patent Document 1 discloses an example of technology that can reduce the burden on the attendant.

[0003] Patent Document 1 discloses a wheelchair drive system that includes two drive wheels, each driven by an independent motor, on both the left and right sides of the center of a carriage that carries the rear wheels of a manual wheelchair, four driven omni-wheels that can move up and down via suspensions at each of the front and rear ends of the carriage, and a control device that can independently control each of the left and right drive wheels. In the wheelchair drive system of Patent Document 1, the rear wheels of the manual wheelchair are mounted on the carriage, while the front wheels are not mounted on the carriage and can be grounded. The left and right drive wheels can be moved forward and backward and steered using a remote control such as a joystick, allowing the wheelchair to move in the desired direction. Furthermore, this wheelchair drive system is equipped with magnetic sensors and cameras, and is said to be capable of automatic driving, as well as of driving non-wheelchair users onto the carriage and transporting luggage placed on the carriage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-284944 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the wheelchair drive device of Patent Document 1, while the device is turning, the control device feeds back signals detected by rotary encoders indicating the rotational states of the left and right motors, and continues to control the rotation of the motors using the fed-back detection signals from the start to the end of steering. Furthermore, because the wheelchair drive device is equipped with magnetic sensors and cameras necessary for automatic driving, the control device also requires signal information output from the magnetic sensors and signal information captured by the cameras as essential factors in controlling the rotation of the motors. Therefore, when attempting to control the rotation of the motors in this way, the control device becomes a complicated configuration involving cumbersome electrical control, which is one of the reasons why the technology of Patent Document 1 leads to high costs.

[0006] Particularly in recent years, many sites that provide support for people requiring care are seeking cheaper mobility devices for assisting the mobility of people requiring care, such as those described in Patent Document 1, and the demand for mobility devices for care is potentially high, with great market potential. However, mobility devices for care according to conventional technology, such as those described in Patent Document 1, are generally expensive due to their highly sophisticated configurations, which has been one factor hindering the widespread adoption of mobility devices for care at sites that wish to support people requiring care and are considering introducing them.

[0007] The present invention has been made to solve the above problems, and aims to provide a front wheel control mechanism for a four-wheel drive vehicle that can stabilize and control the running state of the front wheels of a four-wheel drive vehicle, and a four-wheel drive vehicle, with a simple device configuration that can be applied to nursing care vehicles and the like that transport people in need of care. [Means for solving the problem]

[0008] In order to achieve the above object, the front-wheel control mechanism and the four-wheel drive vehicle according to the present invention have the following configurations.

[0009] (1) For a four-wheel drive vehicle in which front wheels and rear wheels, both of which are drive wheels, are mounted on both left and right sides of a frame, and which can turn during low-speed running with steering of the front wheels, the direction connecting the front wheels and the rear wheels is defined as the front-rear direction, the direction connecting both left and right sides is defined as the left-right direction, and the direction orthogonal to both the front-rear direction and the left-right direction is defined as the height direction. The frame has a first frame portion that supports the front wheels at an end of a front axle member that linearly extends in the left-right direction, includes a link member that extends in the front-rear direction, and has a second frame portion that supports the rear wheels at an end of a rear axle member that extends in the left-right direction, and a connecting portion that connects the first frame portion and the second frame portion. In the first frame portion, a front-wheel support portion that connects to the axle of the front wheels is swingably connected in a free state with respect to the end of the front axle member with a support shaft parallel to the axle as a fulcrum. The driven-side mechanism portion provided on the second frame portion side of the connecting portion is disposed to be relatively rotatable about a rotation shaft vertically provided along the height direction at a position on a virtual line passing through the center in the left-right direction of the front axle member among the operation-side mechanism portions fixed to the first frame portion side of the connecting portion, and a steering control portion for controlling the steering of the front wheels is disposed in the connecting portion. When the four-wheel drive vehicle turns from a straight-running state while controlling the steering state of the front wheels by the steering control portion based on the difference between the rotational speed Vf (0 < Vf) of the front wheels and the rotational speed Vr (0 < Vr) of the rear wheels, the front wheels are offset to the rear side in the front-rear direction by the swing of the front-wheel support portion under the condition of Vf > Vr, or the front wheels are offset to the front side in the front-rear direction by the swing of the front-wheel support portion under the condition of Vf < Vr, and the turned front wheels are restored from the steering state to the straight-running state based on the restoring moment acting on the front axle member. (2) For a four-wheel drive vehicle in which both the front wheels and the rear wheels, which are both drive wheels, are mounted on both the left and right sides of the frame and can turn during low-speed driving with steering of the front wheels, the direction connecting the front wheels and the rear wheels is defined as the front-rear direction, the direction connecting both the left and right sides is defined as the left-right direction, and the direction perpendicular to both the front-rear direction and the left-right direction is defined as the height direction. The frame includes a first frame portion that supports the front wheels at the end of a front axle member that linearly extends in the left-right direction, a link member that extends in the front-rear direction, and a second frame portion that supports the rear wheels at the end of a rear axle member that extends in the left-right direction, and a connecting portion that connects the first frame portion and the second frame portion. In the connecting portion, a long hole that extends in the front-rear direction and a rod-shaped member that is inserted through the long hole with a gap in the front-rear direction are provided. The front end portion of the link member is connected to a driven-side mechanism portion provided on the second frame portion side of the connecting portion in a manner that can relatively move in the front-rear direction with respect to the first frame portion within a range of movement amount corresponding to the gap in conjunction with the relative movement between the long hole and the rod-shaped member. On the other hand, the rear end portion of the link member is fixedly connected to the rear axle member. The driven-side mechanism portion is disposed so as to be rotatable relative to the superposed operation-side mechanism portion with a pivot axis vertically provided along the height direction at a position on a virtual line passing through the center in the left-right direction of the front axle member among the operation-side mechanism portions fixed on the first frame portion side of the connecting portion. A steering control portion for controlling the steering of the front wheels is provided in the connecting portion. When the four-wheel drive vehicle turns from a straight-ahead driving state while controlling the steering state of the front wheels by the steering control portion based on the difference between the rotational speed Vf (0 < Vf) of the front wheels and the rotational speed Vr (0 < Vr) of the rear wheels, by holding the state where the rod-shaped member abuts against the rear end in the front-rear direction of the long hole under the condition of Vf > Vr, or by holding the state where the rod-shaped member abuts against the front end in the front-rear direction of the long hole under the condition of Vf < Vr, the turned front wheels are restored from the steering state to the straight-ahead driving state based on a restoring moment acting about the member axis of the rod-shaped member.

[0010] The concept of low-speed driving in a four-wheel drive vehicle and the front wheel control mechanism of the present invention means that the maximum speed during driving is set to about 10 km / h, and the vehicle is driven at a speed slower than that.

[0011] (3) In the front wheel control mechanism for a four-wheel drive vehicle described in (2), the front wheels are characterized in that they oscillate in one direction relative to the radial direction centered on a oscillating axis along the axle of the front wheels. (4) In the front wheel control mechanism of a four-wheel drive vehicle described in (2) or (3), the outer peripheral shape of the cross section of the rod-shaped member perpendicular to the axis of the member is circular, and the end of the long hole is formed in an arc shape. (5) In the front wheel control mechanism of a four-wheel drive vehicle described in any one of (2) to (4), the swing angle θ of the swingable front wheel is -5≦θ≦5 (rad) based on the vertical direction of the ground, and the clearance is a size that satisfies the swing angle θ. (6) In the front wheel control mechanism of a four-wheel drive vehicle described in any one of (2) to (5), the steering control unit is characterized in that it regulates the turning angle of the front axle member, which rotates relative to the front end of the link member with the turning axis as a fulcrum. (7) In the front wheel control mechanism of a four-wheel drive vehicle described in (6), the steering control unit is characterized in that a guide consisting of an arc-shaped groove centered on the axis of the pivot shaft is formed on the first flat plate side having a first plane in the operating side mechanism part, and a pin is provided on the second flat plate side having a second plane in the operated side mechanism part, the operating side mechanism part and the operated side mechanism part are overlapped with the first plane and the second plane facing each other, and the pin slides relatively within the guide. (8) A four-wheel drive vehicle in which the front and rear wheels, both of which are drive wheels, are mounted on the left and right sides of the frame, respectively, and which can turn at low speeds by steering the front wheels, is characterized by being equipped with a front wheel control mechanism for a four-wheel drive vehicle described in any one of (1) to (7). (9) The four-wheel drive vehicle described in (8) is characterized by comprising an electrical control unit that performs electrical control, a motor that drives the front wheels and the rear wheels with electricity, and an operating unit that drives the front wheels and the rear wheels. (10) A four-wheel drive vehicle as described in (8) or (9) is characterized in that it is a care vehicle equipped with a seat and capable of traveling at a maximum speed of 6 km / h or less with a person requiring care seated in the seat. [Effects of the Invention]

[0012] The operation and effects of the front wheel control mechanism for a four-wheel drive vehicle and the four-wheel drive vehicle according to the present invention having the above-described configuration will be described.

[0013] (1) For a four-wheel drive vehicle in which the front wheels and the rear wheels, which are both drive wheels, are respectively mounted on both the left and right sides of the frame and can turn at low speed with steering of the front wheels, when the direction connecting the front wheels and the rear wheels is defined as the front-rear direction, the direction connecting both the left and right sides is defined as the left-right direction, and the direction orthogonal to both the front-rear direction and the left-right direction is defined as the height direction, the frame includes a first frame portion that supports the front wheels at the end of a front axle member that linearly extends in the left-right direction, a link member that extends in the front-rear direction, and a second frame portion that supports the rear wheels at the end of a rear axle member that extends in the left-right direction, and a connecting portion that connects the first frame portion and the second frame portion. In the first frame portion, a front wheel support portion that connects to the axle of the front wheels is swingably connected in a free state to the end of the front axle member with a support shaft parallel to the axle as a fulcrum. The passive side mechanism portion provided on the second frame portion side of the connecting portion is pivotally disposed relative to the superimposed active side mechanism portion with a pivot shaft vertically provided along the height direction at a position on a virtual line passing through the center in the left-right direction of the front axle member among the active side mechanism portions fixed to the first frame portion side of the connecting portion. A steering control portion for controlling the steering of the front wheels is disposed in the connecting portion. When the four-wheel drive vehicle turns from a straight running state while controlling the steering state of the front wheels with the steering control portion based on the difference between the rotational speed Vf (0 < Vf) of the front wheels and the rotational speed Vr (0 < Vr) of the rear wheels, under the condition of Vf > Vr, by maintaining the state in which the front wheels are offset rearward in the front-rear direction by the swing of the front wheel support portion, or under the condition of Vf < Vr, by maintaining the state in which the front wheels are offset forward in the front-rear direction by the swing of the front wheel support portion, the turned front wheels are restored from the steering state to the straight running state based on the restoring moment acting on the front axle member.

[0014] Due to this feature, while the four-wheel drive vehicle is traveling, a restoring moment that attempts to return the steered front wheels to their original turning state acts on the axis of the rod-shaped member due to the presence of a gap between the rod-shaped member and the elongated hole, allowing the four-wheel drive vehicle to achieve stable straight-line driving. Furthermore, because the steering control unit maintains the turning angle of the front axle member and controls the steering state of the front wheels, the four-wheel drive vehicle can achieve turning operations with the front wheels in a stable steering state. Therefore, in controlling the driving state of the front wheels, the front-wheel control mechanism for a four-wheel drive vehicle does not require a complex device configuration, as in the technology of Patent Document 1, and can achieve both stable straight-line driving and stable cornering with a simple device configuration without implementing a complex electrical control device.

[0015] (2) For a four-wheel drive vehicle in which both the front wheels and the rear wheels, which are both drive wheels, are mounted on both the left and right sides of the frame, and can turn at low speed with steering of the front wheels, when the direction connecting the front wheels and the rear wheels is defined as the front-rear direction, the direction connecting both the left and right sides is defined as the left-right direction, and the direction orthogonal to both the front-rear direction and the left-right direction is defined as the height direction, the frame includes a first frame portion that supports the front wheels at the end of a front axle member that linearly extends in the left-right direction, a link member that extends in the front-rear direction, and a second frame portion that supports the rear wheels at the end of a rear axle member that extends in the left-right direction, and a connecting portion that connects the first frame portion and the second frame portion. In the connecting portion, an elongated hole that extends in the front-rear direction and a rod-shaped member that is inserted through the elongated hole with a gap in the front-rear direction are disposed. The front end portion of the link member is connected to a driven-side mechanism portion provided on the second frame portion side of the connecting portion in a manner that is relatively movable in the front-rear direction within a range of movement amount corresponding to the gap in conjunction with the relative movement between the elongated hole and the rod-shaped member. On the other hand, the rear end portion of the link member is fixed to and connected to the rear axle member. The driven-side mechanism portion is disposed to be relatively rotatable about a rotation axis vertically provided along the height direction at a position on a virtual line passing through the center in the left-right direction of the front axle member among the operation-side mechanism portions fixed on the first frame portion side of the connecting portion, with respect to the overlapped operation-side mechanism portions. A steering control portion for controlling the steering of the front wheels is disposed in the connecting portion. When the four-wheel drive vehicle turns from a straight running state while controlling the steering state of the front wheels by the steering control portion based on the difference between the rotational speed Vf (0 < Vf) of the front wheels and the rotational speed Vr (0 < Vr) of the rear wheels, by maintaining a state where the rod-shaped member abuts against the rear end in the front-rear direction of the elongated hole under the condition of Vf > Vr, or by maintaining a state where the rod-shaped member abuts against the front end in the front-rear direction of the elongated hole under the condition of Vf < Vr, the turned front wheels are restored from the steering state to the straight running state based on the restoring moment acting about the member axis of the rod-shaped member.

[0016] This feature allows a restoring moment that attempts to return the steered front wheels to their original turning state to act on the front axle, enabling the four-wheel drive vehicle to achieve stable straight-line driving. Furthermore, the steering control unit maintains the turning angle of the front axle and controls the steering state of the front wheels, allowing the four-wheel drive vehicle to achieve turning operations with the front wheels in a stable steering state. Therefore, in controlling the driving state of the front wheels, the front-wheel control mechanism of a four-wheel drive vehicle does not require a complex device configuration, as in the technology of Patent Document 1, and can achieve both stable straight-line driving and stable cornering with a simple device configuration, without the need for a complex electrical control device.

[0017] Therefore, the front wheel control mechanism for a four-wheel drive vehicle according to the present invention has the excellent effect of being able to stabilize and control the running state of the front wheels of a four-wheel drive vehicle with a simple device configuration that can also be applied to nursing care vehicles that transport people in need of care.

[0018] The front wheel control mechanism for a four-wheel drive vehicle described in (3) is characterized in that the front wheels swing in one direction relative to the radial direction centered on a swing axis along the axle of the front wheels.

[0019] This feature allows a four-wheel drive vehicle to travel smoothly in a desired turning direction with the front wheels steered in a way that reduces excessive load on the front wheels.

[0020] In the front wheel control mechanism of a four-wheel drive vehicle described in (4), the outer peripheral shape of the cross section of the rod-shaped member perpendicular to the axis of the member is circular, and the end of the long hole is formed in an arc shape.

[0021] Due to this feature, even if the turning angle of the front axle member changes between a straight running state and a cornering state, a restoring moment is generated that returns the vehicle from the cornering state to the straight running state regardless of the turning angle, thereby making the four-wheel drive vehicle a vehicle with excellent straight running and cornering performance.

[0022] In the front wheel control mechanism of a four-wheel drive vehicle described in (5), the swing angle θ of the swingable front wheel is -5≦θ≦5 (rad) based on the vertical direction relative to the ground, and the clearance is a size that satisfies the swing angle θ.

[0023] This feature allows the four-wheel drive vehicle to ensure stable driving performance without significantly disrupting the balance of the vehicle body when turning compared to when driving straight ahead.

[0024] In the front wheel control mechanism of a four-wheel drive vehicle described in (6), the steering control unit is characterized in that it regulates the turning angle of the front axle member that rotates relative to the front end of the link member with the turning axis as a fulcrum.

[0025] Due to this feature, when the four-wheel drive vehicle is turning, the pin in the steering control unit can remain in contact with the end of the guide, allowing the four-wheel drive vehicle to turn along a non-serpentine trajectory while maintaining a constant turning angle of the front axle member relative to the front end of the link member.

[0026] In the front wheel control mechanism of a four-wheel drive vehicle described in (7), the steering control section is characterized in that a guide consisting of an arc-shaped groove centered on the axis of the pivot shaft is formed on the first flat plate side having a first plane in the operating side mechanism section, and a pin is provided on the second flat plate side having a second plane in the operated side mechanism section, and the operating side mechanism section and the operated side mechanism section are overlapped with the first plane and the second plane facing each other, and the pin slides relatively within the guide.

[0027] This feature allows the two front wheels on the left and right to turn reliably along the intended turning path based on the steering operation that follows the trajectory of the pins sliding within the guide.

[0028] (8) A four-wheel drive vehicle in which the front and rear wheels, both of which are drive wheels, are mounted on the left and right sides of the frame, respectively, and which can turn at low speeds by steering the front wheels, is characterized by being equipped with a front wheel control mechanism for a four-wheel drive vehicle described in any one of (1) to (7).

[0029] Due to this feature, the four-wheel drive vehicle according to the present invention can be used as a care vehicle for people who have difficulty walking and require assistance, such as elderly people or people with physical disabilities, to be used by an attendant to travel outdoors, etc. The four-wheel drive vehicle according to the present invention can also be used as a transport vehicle for transporting items, such as products at a factory site, returnable boxes containing parts, or parcels to be delivered, within a specified area on site.

[0030] The four-wheel drive vehicle described in (9) is characterized by having an electrical control unit that performs electrical control, a motor that drives the front and rear wheels with electricity, and an operating unit that drives the front and rear wheels.

[0031] Due to this feature, the four-wheel drive vehicle according to the present invention can be driven autonomously, and can also be driven by remote control.

[0032] (10) A four-wheel drive vehicle as described above is characterized in that it is a care vehicle equipped with a seat and capable of carrying a person requiring care in the seat at a maximum speed of 6 km / h or less.

[0033] This feature allows a person sitting in a seat to quickly take appropriate action to avoid danger even when the person suddenly senses danger due to an unexpected incident while the vehicle is in motion. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is an explanatory diagram showing a plan view from above that schematically illustrates only the main parts of a four-wheel drive vehicle equipped with a front wheel control mechanism for a four-wheel drive vehicle according to an embodiment of the present invention; [Figure 2]It is an explanatory diagram schematically showing only the main part in a plan view from above, regarding the drive system of the four-wheel drive vehicle according to Embodiment 1. [Figure 3] In FIG. 2, it is an explanatory diagram showing the details of the drive system enlarged in a front view from the front. [Figure 4] In FIG. 2, it is an explanatory diagram showing the operation side connecting member formed at the connecting part of the frame, where (a) is a plan view from above, (b) is a cross-sectional view taken along the A-A arrow in (a), and (c) is a cross-sectional view taken along the B-B arrow in (a). [Figure 5] In FIG. 2, it is an explanatory diagram showing the passive side connecting member formed at the connecting part of the frame, where (a) is a plan view from above, (b) is a cross-sectional view taken along the C-C arrow in (a), and (c) is a cross-sectional view taken along the D-D arrow in (a). [Figure 6] It is an explanatory diagram showing the movement of the connecting part in the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 1. [Figure 7] In FIG. 2, it is an explanatory diagram showing the elongated hole and the rod-shaped member formed at the connecting part of the drive system. [Figure 8] It is an explanatory diagram showing the operation part configured in the four-wheel drive vehicle shown in FIG. 1. [Figure 9] It is a diagram showing the drive control flow performed by the electric control unit for the four-wheel drive vehicle shown in FIG. 1. [Figure 10] It is a schematic diagram showing the turning operation of the four-wheel drive vehicle by the front wheel control mechanism of the four-wheel drive vehicle according to the present embodiment, where (a) shows the straight-ahead driving state and (b) shows the turning introduction driving state. [Figure 11] It is a schematic diagram showing the turning operation of the four-wheel drive vehicle by the front wheel control mechanism of the four-wheel drive vehicle according to the present embodiment, where (a) shows the state of traveling on the straight-ahead path in the first state (straight-ahead driving), (b) shows the state of traveling from the introduction driving path to the turning restoration path when Vf > Vr (turning restoration driving), and (c) shows the state of traveling from the introduction driving path to the turning restoration path when Vf < Vr (turning restoration driving). [Figure 12]It is a schematic diagram showing the state of the front wheels that swing in a four-wheel drive vehicle during turning shown in FIG. 11. (a) shows the state of traveling on a straight driving path in the first state (straight driving), (b) shows the state of traveling from an entry driving path to a turning restoration path when Vf > Vr (turning restoration driving), and (c) shows the state of traveling from an entry driving path to a turning restoration path when Vf < Vr (turning restoration driving). [Figure 13] As an explanatory diagram of the turning mechanism of a four-wheel drive vehicle by the front wheel control mechanism of the four-wheel drive vehicle according to the present embodiment, it is a schematic diagram showing the force acting on the rod-shaped member in the longitudinal direction of the long hole of the connecting portion. (a) shows the turning restoration driving state when Vf > Vr, and (b) shows the turning restoration driving state when Vf < Vr. [Figure 14] It is a schematic diagram showing the turning operation of a four-wheel drive vehicle by the front wheel control mechanism of the four-wheel drive vehicle according to the modified example of Embodiment 1. (a) shows the state of traveling on a straight driving path in the first state (straight driving), (b) shows the state of traveling from an entry driving path to a turning restoration path when Vf > Vr (turning restoration driving), and (c) shows the state of traveling from an entry driving path to a turning restoration path when Vf < Vr (turning restoration driving). [Figure 15] It is an explanatory diagram schematically showing only the main part in a plan view from above regarding the drive system of a four-wheel drive vehicle provided with the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 2. [Figure 16] In FIG. 15, it is an explanatory diagram showing an enlarged view of the details of the drive system viewed from the front. [Figure 17] It is a schematic diagram showing the state of the front wheels that swing in a four-wheel drive vehicle during turning by the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 2. (a) shows the state of traveling on a straight driving path in the first state (straight driving), (b) shows the state of traveling from an entry driving path to a turning restoration path when Vf > Vr (turning restoration driving), and (c) shows the state of traveling from an entry driving path to a turning restoration path when Vf < Vr (turning restoration driving).

Mode for Carrying Out the Invention

[0035] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First and second preferred embodiments of a front wheel control mechanism for a four-wheel drive vehicle and a four-wheel drive vehicle according to the present invention will be described in detail below with reference to the drawings.

[0036] The four-wheel drive vehicle of the present invention is intended for use as a care vehicle for people who have difficulty walking and require assistance, such as elderly people or people with physical disabilities, to be used by an attendant to move around outdoors, as well as a transport vehicle to transport items such as products at a factory site, returnable boxes containing parts, and parcels to be delivered, for movement within a specified area on site.

[0037] In addition, when driving a four-wheel drive vehicle according to the present invention, if it is necessary to comply with laws and regulations such as the Road Traffic Act, it is assumed that the four-wheel drive vehicle according to the present invention will be used in a manner that meets the requirements of those laws and regulations.

[0038] The front wheel control mechanism of the four-wheel drive vehicle of the present invention relates to a mechanism necessary for the turning operation of the four-wheel drive vehicle of the present invention, and in embodiments 1 and 2, the front wheel control mechanism of the four-wheel drive vehicle of the present invention will be mainly described below.

[0039] (Embodiment 1) Fig. 1 is an explanatory diagram showing only the main parts of a four-wheel drive vehicle equipped with a front wheel control mechanism for a four-wheel drive vehicle according to this embodiment in a plan view from above. Fig. 2 is an explanatory diagram showing only the main parts of the drive system of the four-wheel drive vehicle according to embodiment 1 in a plan view from above. Fig. 3 is an explanatory diagram showing an enlarged front view of the details of the drive system in Fig. 2.

[0040] In this embodiment, the directions of the four-wheel drive vehicle 1 are defined as follows: the up-down direction in Fig. 1 is the "front-rear direction FB," the left-right direction is the "left-right direction LR," and the up-down direction in Fig. 3 is the "height direction HW." The directions defined in Figs. 2 and 4 and subsequent drawings also conform to those defined in Figs. 1 and 3. In addition, to make the drawings easier to see, wiring such as electrical cables is omitted from the drawings.

[0041] First, an overview of a four-wheel drive vehicle 1 will be described with reference to FIG. 1. As shown in FIG. 1, the four-wheel drive vehicle 1 is a vehicle that has front wheels 3 and rear wheels 5, both of which are drive wheels, mounted on the left and right sides of a frame 2, respectively, and that can turn at low speeds by steering the front wheels 3. In this embodiment, as an example, the four-wheel drive vehicle 1 is a care vehicle that has one seat 92 on a vehicle body 91 and travels at a maximum speed of 6 km / h or less with a person requiring care seated in the seat 92. The four-wheel drive vehicle 1 includes a drive source unit 70, an electric control unit 78 that performs electrical control, an operation unit 80 that operates the drive operation of the front wheels 3 and the rear wheels 5, and a power source (not shown) (for example, a battery such as a primary battery or a secondary battery, or an AC power source). One drive source unit 70 is independently mounted on each of the four wheels, the two front wheels 3 and the two rear wheels 5.

[0042] Next, the frame 2 will be described with reference to Figure 2. As shown in Figures 2 and 3, the frame 2 is made up of a first frame portion 10, a second frame portion 20, and a connecting portion 30 that connects the first frame portion 10 and the second frame portion 20. The first frame portion 10 has a front axle member 11 that extends linearly in the left-right direction LR, and a support member 12 that is located above and along the front axle member 11. Both front wheels 3 are mounted on the front axle member 11 with the axles 4 journaled and supported at the ends of the front axle member 11.

[0043] As shown in FIG. 2 , the second frame portion 20 includes a link member 22 extending in the fore-and-aft direction FB, a connecting member 23 formed in a quarter-turn U-shape, a rear axle member 21 extending linearly in the left-right direction LR, and a support member (not shown) positioned above and along the rear axle member 21. Both rear wheels 5 are attached to the rear axle member 21 with their axles 6 journaled and supported at their ends by the rear axle member 21. The connecting member 23 is connected at its center to a rear end 22B of the link member 22 in a generally inverted Y-shape, and is fixedly connected to both ends of the rear axle member 21 in a bifurcated manner. As will be described in detail later, the front end 22A of the link member 22 is connected to a connecting portion 30.

[0044] The drive source unit 70 includes a motor 71, an output transmission unit 72, a motor control unit 73, a first sprocket 74, a second sprocket 75, and a chain 76. The motor 71 is an example of an electrically driven motor that is a DC brushless motor with a brake function and a built-in encoder, and has the characteristic of generating high torque in a low rotation speed range of several to several tens of revolutions.

[0045] The motor control unit 73 is electrically connected to the motor 71, and has a controller and a driver as part of the electrical control unit 78 to perform drive control. The controller outputs an operation command (target value) to the driver, and the driver drives the motor by outputting a power signal that follows the command of the controller to the motor 71. In addition, the driver inputs a feedback signal from the encoder of the motor 71, and the controller inputs a feedback signal from the driver.

[0046] As shown in Figure 3, the motor 71 and the output transmission unit 72 are disposed on the support member 12 on the side of the front wheel 3. In the output transmission unit 72, a first sprocket 74 is connected to the output shaft of the motor 71 via a clutch mechanism, while a second sprocket 75 is attached to the axle 4 of the front wheel 3. Similarly, on the side of the rear wheel 5, the motor 71 and the output transmission unit 72 are disposed on a support member (not shown) for the rear wheel 5. In the output transmission unit 72, the first sprocket 74 is connected to the output shaft of the motor 71 via a clutch mechanism, while a second sprocket 75 is attached to the axle 6 of the rear wheel 5.

[0047] A chain 76 is stretched between first sprocket 74 and second sprocket 75 on the front wheel 3 side and rear wheel 5 side. In this embodiment, the ratio of the number of teeth on first sprocket 74 to the number of teeth on second sprocket 75 is 1:10, giving four-wheel drive vehicle 1 power performance with high climbing ability, allowing it to travel even on steep slopes with an incline angle of, for example, 30°.

[0048] The electrical control unit 78 is an interface unit for controlling between the motor control unit 73 and the operation unit 80, and is configured to include a microcomputer of known configuration (for example, a single-board computer with the product name "Raspberry Pi"), an AC / DC converter required when the power source is an AC power source, and the like.

[0049] Next, the connecting portion 30 of the frame 2 will be described with reference to Figures 2 to 6. Figure 4 is an explanatory diagram showing the operating-side connecting member configured at the connecting portion of the frame in Figure 2, where (a) is a plan view from above, (b) is a cross-sectional view taken along the line AA in (a), and (c) is a cross-sectional view taken along the line BB in (a). Figure 5 is an explanatory diagram showing the operated-side connecting member configured at the connecting portion of the frame in Figure 2, where (a) is a plan view from above, (b) is a cross-sectional view taken along the line CC in (a), and (c) is a cross-sectional view taken along the line DD in (a).

[0050] 2 and 3, the connecting portion 30 includes an operating-side connecting member 40 (operating-side mechanical portion) fixed to the first frame portion 10, an operated-side connecting member 50 (operated-side mechanical portion) provided on the second frame portion 20, a rotating shaft 31, a fixed member 32, a rod-shaped member 33, and an elongated hole 34. As shown in FIG. 4, the operating-side connecting member 40 includes a plate-like first flat plate portion 41 having a first flat surface 41a, and a boss portion 42 formed in a substantially cylindrical shape protrudes from the first flat surface 41a, forming a step with the first flat surface 41a. A female screw is formed in the center of the boss portion 42 so as to be able to screw into a male screw formed on the tip side of the rotating shaft 31.

[0051] As shown in FIG. 5, the operated-side connecting member 50 has a plate-shaped second flat plate portion 51 having a second flat surface 51a. A boss hole portion 52 that fits with the boss portion 42 is drilled at a step with respect to the second flat surface 51a. A through hole 53 through which the rotating shaft 31 is inserted is formed in the center of the boss hole portion 52. The operating-side connecting member 40 and the operated-side connecting member 50 are arranged in a stacked configuration with the first flat surface 41a and the second flat surface 51a facing each other. The male thread of the boss portion 42 is threadedly engaged with the male thread of the rotating shaft 31 through the through hole 53 of the operated-side connecting member 50, so that the operating-side connecting member 40 and the operated-side connecting member 50 are rotatable relative to the axis of the rotating shaft 31 that extends vertically in the height direction HW. As shown in FIG. 1, the axis of the rotating shaft 31 is located on an imaginary line VL that passes through the center of the front axle member 11 in the left-right direction LR.

[0052] As shown in FIGS. 3 to 5, a steering control unit 60 that controls the steering of the front wheels 3 is disposed in the connecting portion 30. The steering control unit 60 regulates the turning angle of the front axle member that turns relative to the front end portion 22A of the link member 22 about the axis of the turning shaft 31. Specifically, the steering control unit 60 is made up of a guide 61, a pin 62, and a female screw portion 63. As shown in FIG. 4, the guide 61 is a groove formed in the first flat plate portion 41 of the operating-side connecting member 40 in an arc shape centered on the turning shaft 31, with its circumferential ends formed in a semicircular shape, with a step formed between the first flat surface 41a and the first flat plate portion 41.

[0053] 6 is an explanatory diagram showing the movement of the connecting portion in the front wheel control mechanism of the four-wheel drive vehicle according to the first embodiment. As shown in FIGS. 5 and 6, the female thread portion 63 is formed on the second flat plate portion 51 of the operated-side connecting member 50, on the path of the guide 61 of the operating-side connecting member 40 that is superimposed on the operated-side connecting member 50. The pin 62 has a male thread on its outer periphery that screws into the female thread portion 63, and is attached to the operated-side connecting member 50 with its tip side housed within the guide 61.

[0054] As shown in Figure 6, when the operating side connecting member 40 fixed to the front axle member 11 swings relative to the operated side connecting member 50 provided on the second frame portion 20 side at a rotation angle α (0 < α) with the axis of the rotating shaft 31 as a fulcrum, the pin 62 slides relatively on the guide 61 within the range of the movement path in the guide 61 as it swings.

[0055] As shown in Figures 2 and 3, the front end 22A of the link member 22 is placed on the surface of the operated side connecting member 50 opposite the second plane 51a, and is connected to the operated side connecting member 50 with the left and right sides of the front end 22A sandwiched between the fixing members 32.

[0056] 7 is an explanatory diagram showing the elongated hole and rod-shaped member formed in the connecting portion of the drive system in FIG. 2. As shown in FIG. 7, the connecting portion 30 is provided with a rod-shaped member 33 and an elongated hole 34 extending in the front-rear direction FB. The rod-shaped member 33 is inserted into the elongated hole 34 with a gap K in the front-rear direction FB. Although not shown, the rod-shaped member 33 is fixedly attached to the fixed member 32, and the elongated hole 34 is formed on the front end 22A side of the link member 22. The rod-shaped member 33 is formed in a form that forms a thin rod from the head to the end like a bolt, and as shown in FIG. 7, the outer periphery of the cross section perpendicular to the axis M (member axis) is formed in a circular shape. The elongated hole 34 is formed in an arc shape at both ends in the longitudinal direction (front-rear direction FB).

[0057] Specifically, a rod-shaped member 33 extending from the fixed member 32 is inserted through a long hole 34 on the front end 22A side of the link member 22 between the opposing sides of the fixed member 32 and the front end 22A of the link member 22. As a result, the front end 22A of the link member 22 is movable relative to the first frame portion 10 in the front-to-rear direction FB within a range of movement corresponding to the gap K, as will be described later, in conjunction with the relative movement between the rod-shaped member 33 and the long hole 34, as shown in FIG.

[0058] FIG. 8 is an explanatory diagram showing an operation unit configured in a four-wheel drive vehicle, and FIG. 9 is a diagram showing a drive control flow performed by the electrical control unit. FIG. 8 is an explanatory diagram showing an operation unit configured in a four-wheel drive vehicle, and FIG. 9 is a diagram showing a drive control flow performed by this electrical control unit. As illustrated in FIG. 8, the operation unit 80 has a first switch 81, a second switch 82, a third switch 83, a fourth switch 84, and a fifth switch 85, as well as various other switches (not shown). In the four-wheel drive vehicle 1, when remote operation is performed using the operation unit 80, the drive of the front wheels 3 and the rear wheels 5 is controlled by the electrical control unit 78 via the motor control unit 73. In this embodiment, the four-wheel drive vehicle 1 is capable of traveling at a maximum speed of 6 km / h in high-speed traveling mode and at a maximum speed of 3 km / h in low-speed traveling mode.

[0059] Specifically, the first switch 81 (labeled "A" in FIG. 8) can be turned on / off to activate the regenerative brake of the motor 71 and select whether or not to forcibly bring the four-wheel drive vehicle 1 to an emergency stop. The second switch 82 (labeled "B" in FIG. 8) can be turned on / off to stop the rotation of the motor 71 and select whether or not to release the connection of the motor 71 to the output shaft with the clutch mechanism, leaving the front wheels 3 and rear wheels 5 free to rotate. The third switch 83 (labeled "X" in FIG. 8) can be turned on / off to select whether or not to operate the motor 71 in the forward rotation direction. The fourth switch 84 (labeled "Y" in FIG. 8) can be turned on / off to select whether or not to operate the motor 71 in the reverse rotation direction.

[0060] The fifth switch 85 (indicated by an arrow in FIG. 8) can select forward or backward movement, left or right turning of the four-wheel drive vehicle 1 by an operation performed in an arbitrary direction among the front, rear, left, and right directions. Other switches can select the traveling speed of the four-wheel drive vehicle 1 to a low speed mode (denoted as "LB" in FIG. 8) or a high speed mode (denoted as "LT" in FIG. 8), and can also select whether to reset the speed command value to cancel the set traveling speed. Further, the electric control unit 78 performs rotational control separately on the motor 71 on the front wheel 3 side and the motor 71 on the rear wheel 5 side by the operation unit 80, and can perform independent rotational control for the left and right sides on the motor 71 on the front wheel 3 side when the four-wheel drive vehicle 1 is turning.

[0061] Next, the turning operation of the four-wheel drive vehicle 1 will be described using FIGS. 10 to 13. The four-wheel drive vehicle 1 turns from the straight-ahead path in the first state through the turning-introduction path while the steering state of the front wheel 3 is controlled by the steering control unit 60 based on the difference between the rotational speed Vf (0 < Vf) of the front wheel 3 and the rotational speed Vr (0 < Vr) of the rear wheel 5 until it reaches the straight-ahead path in the second state with the changed path direction.

[0062] The rotational speed Vf of the front wheel 3 and the rotational speed Vr of the rear wheel 5 are maintained in a state where the rod-shaped member 33 is in contact with the rear end of the front-rear direction FB of the long hole 34 under the condition of Vf > Vr, or in a state where the rod-shaped member 33 is in contact with the front end of the front-rear direction FB of the long hole 34 under the condition of Vf < Vr. Based on the restoring moment acting on the axis M (member axis) of the rod-shaped member 33 as a fulcrum, the turned front wheel 3 restores from the steering state to the straight-ahead traveling state.

[0063] Specifically, a case of turning during a forward movement will be described. FIG. 10 is a schematic diagram showing a turning operation of a four-wheel drive vehicle by a front-wheel control mechanism according to the present embodiment, where (a) shows a straight-ahead running state and (b) shows a turning-introduction running state. FIG. 11 is a schematic diagram showing a turning operation of a four-wheel drive vehicle by a front-wheel control mechanism according to the present embodiment, where (a) shows a state of traveling on a straight-ahead path in the first state (straight-ahead running), (b) shows a state of traveling from an introduction running path to a turning-restoring path when Vf > Vr (turning-restoring running), and (c) shows a state of traveling from an introduction running path to a turning-restoring path when Vf < Vr (turning-restoring running). FIG. 12 is a schematic diagram showing the state of the front wheels that swing in a four-wheel drive vehicle during turning shown in FIG. 11, where (a) shows a state of traveling on a straight-ahead path in the first state (straight-ahead running), (b) shows a state of traveling from an introduction running path to a turning-restoring path when Vf > Vr (turning-restoring running), and (c) shows a state of traveling from an introduction running path to a turning-restoring path when Vf < Vr (turning-restoring running).

[0064] <In the case of straight-ahead running> When the four-wheel drive vehicle 1 is in a straight-ahead running state on a straight-ahead path in the first state or a straight-ahead path in the second state, the electric control unit 78 sets the acceleration command value and the speed command value to be the same for all four motors 71, and performs rotation control with a normal rotation setting for forward movement and a reverse rotation setting for backward movement. Therefore, all four wheels, namely the front wheels 3 and the rear wheels 5, travel with equal acceleration and equal speed. For this reason, in the steering control unit 60, the pin 62 is located at the center of the movement path within the guide 61 and is not restricted by the turning angle of the first frame portion 10.

[0065] On the other hand, when the four-wheel drive vehicle 1 is in a straight-ahead running state, as shown in FIGS. 10(a) and 11(a), since the rod-shaped member 33 is located at the central portion of the long hole 34 (the portion shown by the solid line in FIG. 7), no external force acting on the rod-shaped member 33 in the front-back direction FB of the long hole 34 occurs due to the positional relationship between the rod-shaped member 33 and the long hole 34.

[0066] Also, as shown in FIGS. 7, 10(a), and 11(a), when the four-wheel drive vehicle 1 is in a straight running state, the rod-shaped member 33 is located at the central portion of the long hole 34 (the portion shown by the solid line in FIG. 7). Therefore, as shown in FIG. 12(a), the axis of the axle 4 of the front wheel 3 is on the straight running reference line AX1 passing through the swing center N (fulcrum N) located above the first frame portion 10 along the axle 4 of the front wheel 3 with respect to the vertical direction of the ground G.

[0067] <In the case of turning-introduction running> Next, when the four-wheel drive vehicle 1 travels on a turning-introduction path from the straight running path in the first state (turning-introduction running) as shown in FIG. 10(b), the electric control unit 78 makes the rotational speed Vf of the front wheel 3 on the outer wheel side larger than the rotational speed Vf of the front wheel 3 on the inner wheel side in the turning operation, and makes the rotational speed Vf of both front wheels smaller than the rotational speed Vr of the rear wheels 5, i.e., Vf<Vr, and enters from the straight running path to the turning-introduction path. As a result, in the steering control unit 60, within the angular range until the pin 62 reaches and abuts against the end on the turning direction side from the center of the movement path in the guide 61, while sliding along the movement path in the guide 61, the four-wheel drive vehicle 1 continues the turning operation at the turning angle α (see FIG. 6) of the front axle member 11 in the turning direction (in the case of FIG. 10(b), the left-turning direction). At this time, while the four-wheel drive vehicle 1 is traveling on the turning-introduction path, the rod-shaped member 33 is in a state of being located at the front end of the long hole 34 (the portion shown by the upper two-dot chain line in FIG. 7).

[0068] <In the case of turning-restoring running> Next, when the four-wheel drive vehicle 1 travels on a turning-restoring path (turning-restoring running) while returning the steering of the front wheel 3 taken in the turning direction from the introduction running path in which the vehicle travels in a steering state where the steering of the front wheel 3 is taken in the turning direction until it becomes the straight running path in the second state, either one of the first operation要领 and the second operation要领 according to the first embodiment is selectively performed.

[0069] (First embodiment) In the first operating procedure, under the premise that the rotational speed Vf of the front wheel 3, which is the outer wheel in the turning operation, is greater than the rotational speed Vf of the front wheel 3, which is the inner wheel, the electrical control unit 78 sets the rotational speed Vf of both front wheels 3 to be greater than the rotational speed Vr of both rear wheels 5, i.e., Vf>Vr. As a result, in the steering control unit 60, the pin 62 slides along the movement path within the guide 61 within an angle range from the end of the guide 61 where it abutted on the turning direction side to the return to the center of the movement path, while the four-wheel drive vehicle 1 continues turning while returning the turning angle α (see FIG. 6) of the front axle member 11 in the opposite turning direction (in the case of FIG. 11(b) , from left to right turning direction), and completes the turning recovery running. At this time, when the four-wheel drive vehicle 1 completes the turning recovery run, the rod-shaped member 33 within the long hole 34 moves from the front end (the part shown by the upper two-dot chain line in Figure 7) where it was positioned during the turning introduction run to the rear end (the part shown by the lower two-dot chain line in Figure 7) and then returns to the center (the part shown by the solid line in Figure 7), which is the position where the turning recovery run is completed.

[0070] On the other hand, in conjunction with the relative movement of the rod-shaped member 33 from the front end to the center within the elongated hole 34, the front axle member 11 of the first frame portion 10 swings counterclockwise in the radial direction CR1 at a swing angle θ (0<|θ|) from the swing center N (fulcrum N) as shown in Figures 11(b) and 12(b). As a result, between a turning tilt line AX2 passing through the swing center N (fulcrum N) and the axis of the axle 4 of the front wheel 3 and a straight-ahead reference line AX1, the distance from the axis of the axle 4 of the front wheel 3 to the straight-ahead reference line AX1 in the horizontal direction along the ground G is the amount of movement of the rod-shaped member 33 from the center to the rear end within the elongated hole 34, i.e., clearance S corresponding to the amount of movement of the rod-shaped member 33 within the gap K within the elongated hole 34.

[0071] That is, in the four-wheel drive vehicle 1, compared with the position state of the front wheels 3 during straight-ahead travel (see Fig. 12(a)), the position state of the front wheels 3 during turning restoration travel (see Fig. 12(b)) is such that both wheels are offset by substantially the clearance S by moving backward in the front-rear direction FB starting from the swing center N (fulcrum N). Therefore, through such a steering operation of the front wheels 3, the four-wheel drive vehicle 1 completes a turning operation from the turning introduction path through the turning restoration path to the straight-ahead path in the second state by forward travel.

[0072] (Embodiment 2) In the second operation procedure, the electric control unit 78 continues from the turning introduction travel state as it is, on the premise that the rotational speed Vf of the front wheel 3 on the outer wheel side is made larger than the rotational speed Vf of the front wheel 3 on the inner wheel side during the turning operation, and sets the rotational speed Vf of both front wheels to be smaller than the rotational speed Vr of the rear wheels 5, i.e., Vf < Vr. As a result, in the steering control unit 60, while the pin 62 slides along the movement path in the guide 61 within the angular range from the end in the guide 61 where it was abutting on the turning direction side to returning to the center of the movement path, the four-wheel drive vehicle 1 continues the turning operation in the counter-turning direction (in the case of Fig. 11(c), from left to right turning direction) while returning the turning angle α (see Fig. 6) of the front axle member 11 to complete the turning restoration travel. At this time, when the four-wheel drive vehicle 1 completes the turning restoration travel, in the elongated hole 34, the rod-shaped member 33 moves from the front end (the portion indicated by the upper two-dot chain line in Fig. 7) where it was located during the turning introduction travel and then returns to the center (the portion indicated by the solid line in Fig. 7) which is the turning restoration travel completion position.

[0073] On the other hand, in conjunction with the relative movement of the rod-shaped member 33 from the front end to the center within the elongated hole 34, the front axle member 11 of the first frame portion 10 swings in the clockwise radial direction CR2 at a swing angle θ (0<|θ|) from the swing center N (fulcrum N) as shown in Figures 11(c) and 12(c). As a result, between a turning tilt line AX3 passing through the swing center N (fulcrum N) and the axis of the axle 4 of the front wheel 3 and a straight-ahead running reference line AX1, the distance from the axis of the axle 4 of the front wheel 3 to the straight-ahead running reference line AX1 in the horizontal direction along the ground G is the amount of movement of the rod-shaped member 33 from the center to the rear end within the elongated hole 34, i.e., clearance S corresponding to the amount of movement of the rod-shaped member 33 within the gap K within the elongated hole 34.

[0074] That is, in the four-wheel drive vehicle 1, the position state of the front wheels 3 when traveling straight (see FIG. 12(a)) is compared with the position state of the front wheels 3 when traveling from the turning start position (see FIG. 12(c)), and both wheels move forward in the fore-and-aft direction FB from the swing center N (fulcrum N), so that the position state of the front wheels 3 is substantially offset by the clearance S. Therefore, through such steering operation of the front wheels 3, the four-wheel drive vehicle 1 travels forward, completing a turning operation from the turning introduction path to the turning start path, and then to the straight path in the second state.

[0075] The description of when the four-wheel drive vehicle 1 turns in reverse is omitted because it is substantially the same as when it turns in forward motion.

[0076] In the four-wheel drive vehicle 1, the swing angle θ of the swingable front wheels 3 is -5≦θ≦5 (rad) with respect to the vertical direction of the ground G, regardless of whether the vehicle is moving forward or backward, and the clearance S is a size that satisfies the swing angle θ. If θ exceeds 5 (rad), the running stability of the four-wheel drive vehicle 1 will be impaired.

[0077] Next, the turning mechanism of the four-wheel drive vehicle by the front wheel control mechanism of the four-wheel drive vehicle according to the present embodiment will be described with reference to FIGS. 11 and 13. FIG. 13 is a schematic diagram showing the force acting on the rod member in the longitudinal direction of the long hole of the connecting portion as an explanatory diagram of the turning mechanism of the four-wheel drive vehicle by the front wheel control mechanism of the four-wheel drive vehicle according to the present embodiment, where (a) shows the turning restoration traveling state when Vf > Vr, and (b) shows the turning restoration traveling state when Vf < Vr, respectively.

[0078] As shown in FIGS. 11(a) and 13(a), in the first embodiment, for both wheels, the rotational speed Vf of the front wheels 3 is under the condition of Vf > Vr, where the rotational speed Vf of the front wheels 3 is greater than the rotational speed Vr of the rear wheels 5 for both wheels. Therefore, in the connecting portion 30, during the turning restoration traveling of the four-wheel drive vehicle 1, the rod member 33 is in a state of being abutted and held at least at the rear end in the long hole 34 (the portion shown by the two-dot chain line on the lower side in FIG. 7). At this time, under the influence of the propulsive force F1 (see FIG. 10(b)) in the traveling direction accompanying the forward traveling of the four-wheel drive vehicle 1, an external force F2 directed toward the second frame portion 20 (around the link member 22) acts on the rod member 33 at the rear end of the long hole 34 while being in contact. As shown in FIG. 13(a), the external force F2 is the resultant force of a first component external force F2a in the longitudinal direction of the vehicle between the front and rear parallel to the virtual line VL and a second component external force F2b in the direction between the axles perpendicular to the virtual line VL along the front axle member 11.

[0079] In the connecting portion 30, the movement of the rod member 33 in the long hole 34 is interlocked with the movement of the front axle member 11 of the first frame portion 10 that swings with the rotation axis 31 as a fulcrum. Further, due to the second component external force F2b, a restoring moment acting with it as a fulcrum is generated at the axis M of the rod member 33. Therefore, when the first frame portion 10 is in a turning posture (in the case of FIG. 13, a left-turning posture) that rotates with the rotation axis 31 as a fulcrum, due to the restoring moment generated in the interlocked rod member 33, the first frame portion 10 tends to be restored in the direction opposite to the turning direction through the rod member 33 and the long hole 34.

[0080] Similarly, as shown in FIGS. 11(b) and 13(b), in the second embodiment, for both wheels, the rotational speed Vf of the front wheel 3 is under the condition of Vf < Vr, where Vf is smaller than the rotational speed Vr of the rear wheel 5 for both wheels. Therefore, in the connecting portion 30, during the turning recovery running of the four-wheel drive vehicle 1, the rod-shaped member 33 is in a state of being abutted and held at least at the front end within the elongated hole 34 (the portion indicated by the upper two-dot chain line in FIG. 7). At this time, under the influence of the propulsive force F1 (see FIG. 10(b)) in the traveling direction accompanying the forward running of the four-wheel drive vehicle 1, an external force F3 directed toward the opposite side of the second frame portion 20 (around the link member 22) acts on the rod-shaped member 33 at the front end of the elongated hole 34 which remains in the abutted state. As shown in FIG. 13(b), the external force F3 is the resultant force of a first component external force F3a in the vehicle longitudinal direction parallel to the virtual line VL and a second component external force F3b in the inter-axle direction perpendicular to the virtual line VL along the front axle member 11.

[0081] In the connecting portion 30, the movement of the rod-shaped member 33 within the elongated hole 34 is interlocked with the movement of the front axle member 11 of the first frame portion 10 that swings with the rotation axis 31 as a fulcrum. Further, due to the second component external force F3b, a restoring moment acting on the axis M of the rod-shaped member 33 with it as a fulcrum is generated. Therefore, when the first frame portion 10 is in a turning posture (in the case of FIG. 13, a left-turning posture) turning with the rotation axis 31 as a fulcrum, due to the restoring moment generated in the interlocked rod-shaped member 33, the first frame portion 10 tends to be restored in the direction opposite to the turning direction through the rod-shaped member 33 and the elongated hole 34.

[0082] Next, the front-wheel control mechanism of the four-wheel drive vehicle according to the modification of the first embodiment is shown in FIG. 14. FIG. 14 is a schematic diagram showing the turning operation of the four-wheel drive vehicle by the front-wheel control mechanism of the four-wheel drive vehicle according to the modification of the first embodiment, where (a) shows the state of traveling on the straight-ahead path in the first state (straight running), (b) shows the state of traveling from the introduction traveling path to the turning recovery path when Vf > Vr (turning recovery running), and (c) shows the state of traveling from the introduction traveling path to the turning recovery path when Vf < Vr (turning recovery running).

[0083] As shown in Fig. 14, the connecting portion 30 configured in the first embodiment has two elongated holes 34, one on each side of the pivot shaft 31 of the front axle member 11. Two rod-shaped members 33 are movably inserted into each of the elongated holes 34, and a brake unit 38 having four rod-shaped members 33 integrated therein is provided so as to be slidable in the longitudinal direction of the two elongated holes 34. The brake unit 38 is attached to the link member 22 (see Fig. 2) side of the second frame portion 20 with some play, and the play of the brake unit 38 is used to move the first frame portion 10 having the front axle member 11 forward and backward.

[0084] Next, the operation and effects of the front wheel control mechanism for a four-wheel drive vehicle and the four-wheel drive vehicle 1 according to the first embodiment will be described.

[0085] Regarding the front-wheel control mechanism of the four-wheel drive vehicle according to Embodiment 1, for a four-wheel drive vehicle 1 in which the front wheels 3 and the rear wheels 5, which are both drive wheels, are respectively mounted on both the left and right sides of the frame 2 and can turn during low-speed driving along with the steering of the front wheels 3, when the direction connecting the front wheels 3 and the rear wheels 5 is defined as the front-rear direction FB, the direction connecting both the left and right sides is defined as the left-right direction LR, and the direction orthogonal to both the front-rear direction FB and the left-right direction LR is defined as the height direction HW, the frame 2 includes a first frame portion 10 that supports the front wheels 3 at the end of the front axle member 11 that linearly extends in the left-right direction LR, a link member 22 that extends in the front-rear direction FB, and a second frame portion 20 that supports the rear wheels 5 at the end of the rear axle member 21 that extends in the left-right direction LR, and a connecting portion 30 that connects the first frame portion 10 and the second frame portion 20. In the connecting portion 30, a long hole 34 that extends in the front-rear direction FB and a rod-shaped member 33 that is inserted through the long hole 34 with a gap K in the front-rear direction FB are provided. The front end portion 22A of the link member 22 is connected to a passive-side connecting member 50 provided on the second frame portion 20 side of the connecting portion 30 in a manner that can move relative to the first frame portion 10 in the front-rear direction FB within a range of movement amount corresponding to the gap K in conjunction with the relative movement between the long hole 34 and the rod-shaped member 33. On the other hand, the rear end portion 22B of the link member 22 is fixedly connected to the rear axle member 21. The passive-side connecting member 50 is disposed on the virtual line VL passing through the center in the left-right direction LR of the front axle member 11 among the operation-side connecting members 40 fixed to the first frame portion 10 side of the connecting portion 30, and is pivotally arranged relative to the superimposed operation-side connecting members 40 so as to be pivotable about a pivot shaft 31 vertically provided along the height direction HW. A steering control unit 60 for controlling the steering of the front wheels 3 is provided in the connecting portion 30. When the four-wheel drive vehicle 开始从直进行驶状态转弯时,基于前轮3的旋转速度Vf(0<Vf)与后轮5的旋转速度Vr(0<Vr)的差,在操舵制御部60控制前轮3的操舵状态的情况下,在Vf>Vr的条件下,通过保持棒状部材33与长孔34的前后方向FB后侧的端部抵接的状态,或者在Vf<Vr的条件下,通过保持棒状部材33与长孔34的前后方向FB前侧的端部抵接的状态,基于以棒状部材33的轴心M为支点作用的复原力矩,使旋转后的前轮3从操舵状态复原到直进行驶状态(参照图13中、It is characterized by having a rotation direction CRX.

[0086] Due to this feature, while the four-wheel drive vehicle 1 is traveling, the presence of the gap K between the rod-shaped member 33 inserted in the elongated hole 34 causes a restoring moment that attempts to return the steered front wheels 3 to their original turning state to act on the axis M of the rod-shaped member 33, allowing the four-wheel drive vehicle 1 to achieve stable straight-line traveling. Furthermore, because the steering control unit 60 maintains the turning angle α of the front axle member 11 and controls the steering state of the front wheels 3, the four-wheel drive vehicle 1 can achieve turning operations with the front wheels 3 in a stable steering state. Therefore, in controlling the traveling state of the front wheels 3, the front-wheel control mechanism of the four-wheel drive vehicle does not require a complex device configuration, as in the technology of Patent Document 1, and can achieve both stable straight-line traveling and stable cornering with a simple device configuration without implementing a complex electrical control device.

[0087] Therefore, the front wheel control mechanism of the four-wheel drive vehicle according to embodiment 1 has the excellent effect of being able to stabilize and control the running state of the front wheels 3 of the four-wheel drive vehicle 1 with a simple device configuration that can also be applied to care vehicles that transport people in need of care.

[0088] Furthermore, the front wheel control mechanism for a four-wheel drive vehicle according to embodiment 1 is characterized in that the front wheels 3 oscillate in one direction relative to the radial direction CR centered on the oscillating axis N along the axle 4 of the front wheels 3.

[0089] This feature allows the four-wheel drive vehicle 1 to travel smoothly in a desired turning direction with the front wheels 3 steered in a way that reduces excessive load on the front wheels 3 .

[0090] Furthermore, the front wheel control mechanism for a four-wheel drive vehicle according to embodiment 1 is characterized in that the outer peripheral shape of the cross section of the rod-shaped member 33 perpendicular to the axis M is circular, and the end of the long hole 34 is formed in an arc shape.

[0091] Due to this feature, even if the turning angle α of the front axle member 11 changes between a straight running state and a turning running state, a restoring moment is generated that returns the vehicle from the turning running state to the straight running state regardless of the turning angle α, and ultimately the four-wheel drive vehicle 1 becomes a vehicle with excellent straight running and turning performance.

[0092] Furthermore, the front wheel control mechanism of the four-wheel drive vehicle according to the first embodiment is characterized in that the swing angle θ of the oscillating front wheel 3 is -5≦θ≦5 (rad) based on the vertical direction of the ground G, and the clearance S is of a size that satisfies the swing angle θ.

[0093] This feature allows the four-wheel drive vehicle 1 to ensure stable driving performance without significantly losing balance in the vehicle body when turning compared to when driving straight ahead.

[0094] Furthermore, in the front wheel control mechanism of the four-wheel drive vehicle according to this embodiment, the steering control unit 60 is characterized in that it regulates the turning angle of the front axle member 11, which rotates relative to the front end 22A of the link member 22 with the turning shaft 31 as a fulcrum.

[0095] Due to this feature, when the four-wheel drive vehicle 1 is turning, the steering control unit 60 can keep the pin 62 in contact with the end of the guide 61, so the four-wheel drive vehicle 1 can turn along a trajectory without meandering while maintaining a constant turning angle of the front axle member 11 relative to the front end 22A of the link member 22. In particular, since the turning angle of the front axle member 11 is based on mechanical control, which is more likely to exhibit high durability than electrical control, which is more likely to fail due to water damage or broken wires, the durability of the four-wheel drive vehicle 1 is high even if the turning operation of the four-wheel drive vehicle 1 is repeated multiple times, and the four-wheel drive vehicle 1 can be used safely even in locations with poor driving environments.

[0096] Furthermore, in the front wheel control mechanism of the four-wheel drive vehicle according to embodiment 1, the steering control unit 60 is characterized in that a guide 61 consisting of an arc-shaped groove centered on the axis of the pivot shaft 31 is formed on the side of the first flat plate portion 41 having the first plane 41a of the operating side connecting member 40, and a pin 62 is provided on the side of the second flat plate portion 51 having the second plane 51a of the operated side connecting member 50, and the operating side connecting member 40 and the operated side connecting member 50 are overlapped with the first plane 41a and the second plane 51a facing each other, and the pin 62 slides relatively within the guide 61.

[0097] This feature allows the two front wheels 3 on the left and right to turn reliably along the intended turning path based on the steering operation that follows the trajectory of the pin 62 sliding within the guide 61.

[0098] Furthermore, the front wheels 3 and rear wheels 5, both of which are drive wheels, are mounted on both the left and right sides LR of the frame 2, respectively, and the four-wheel drive vehicle 1, which can turn at low speeds by steering the front wheels 3, is characterized by being equipped with the front wheel control mechanism of the four-wheel drive vehicle of this embodiment.

[0099] Due to this feature, the four-wheel drive vehicle 1 can be used as a care vehicle for people who have difficulty walking and require assistance, such as elderly people or people with physical disabilities, to be used by an attendant to travel outdoors, etc. The four-wheel drive vehicle 1 can also be used as a transport vehicle to transport items such as products at a factory site, returnable boxes containing parts, or parcels to be delivered, within a specified area on site.

[0100] Furthermore, the four-wheel drive vehicle 1 according to this embodiment is characterized by having an electrical control unit 78 that performs electrical control, a motor 71 that drives the front wheels 3 and rear wheels 5 using electricity, and an operating unit 80 that operates the front wheels 3 and rear wheels 5.

[0101] This feature allows the four-wheel drive vehicle 1 to travel autonomously, and also allows it to travel by remote control.

[0102] In addition, the four-wheel drive vehicle 1 according to the present embodiment is a care vehicle that includes a seat 92 and travels with a person requiring care on the seat 92 at a maximum speed of 6 km / h or less.

[0103] With this feature, even when a person sitting on the seat 92 suddenly perceives danger in an unexpected situation during driving, appropriate danger avoidance actions can be taken promptly and sensitively.

[0104] (Embodiment 2) Next, the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 2 and the four-wheel drive vehicle will be described. In the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 2, the description will focus on the parts different from Embodiment 1, and the description of the parts common to Embodiment 1 will be simplified or omitted using the same reference numerals.

[0105] FIG. 15 is an explanatory diagram schematically showing only the main part of the drive system of a four-wheel drive vehicle equipped with a front wheel control mechanism of a four-wheel drive vehicle according to Embodiment 2 in a plan view from above. In FIG. 15, FIG. 16 shows an explanatory diagram enlarging the details of the drive system viewed from the front. FIG. 17 is a schematic diagram showing the state of the front wheels that swing in a four-wheel drive vehicle during turning in the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 2. (a) shows the state of traveling on a straight-ahead path in the first state (straight-ahead driving), (b) shows the state of traveling from an introduction driving path to a turning restoration path when Vf > Vr (turning restoration driving), and (c) shows the state of traveling from an introduction driving path to a turning restoration path when Vf < Vr (turning restoration driving).

[0106] 1, 15, and 16, in a four-wheel drive vehicle 101 equipped with a front wheel control mechanism for a four-wheel drive vehicle according to the second embodiment, a frame 102 includes a first frame portion 110, a second frame portion 20 that includes a link member 22 extending in the fore-aft direction FB and supports a rear wheel 5 at an end of a rear axle member 21 extending in the left-right direction LR, and a connecting portion 30 that connects the first frame portion 110 and the second frame portion 20. Similar to the front axle member 11 of the first embodiment, the first frame portion 110 includes a front axle member 111 that extends linearly in the left-right direction LR, and a support member 112 that is parallel to and disposed above the front axle member 111.

[0107] Front wheel support parts 120 are attached to the ends of the support member 112 on both the left and right sides (LR). As shown in FIG. 17 , the front wheel support parts 120 are attached to a cylindrical support shaft 131 fixed to the end of the support member 112 so as to be able to swing freely in the circumferential direction. A suspension member 121 is formed on the front wheel support part 120 so as to extend downward in the radial direction of the support shaft 131. As in the first embodiment, the front wheel 3 is attached to the axle 4 of the front wheel 3 together with the second sprocket 75 via the motor 71, the output transmission part 72, the first sprocket 74, and the chain 76. The axle 4 is suspended and supported by the suspension member 121, and the front wheel 3 is attached to the axle 4 so as to be rotatable.

[0108] In the case of the front wheel control mechanism for a four-wheel drive vehicle according to the first embodiment, the connecting portion 30 is formed with a rod-shaped member 33 and an elongated hole 34. However, in the second embodiment, the connecting portion 30 does not include such a rod-shaped member or an elongated hole.

[0109] Next, the operation and effects of the front wheel control mechanism for a four-wheel drive vehicle and the four-wheel drive vehicle 101 according to the second embodiment will be described.

[0110] In the front wheel control mechanism of the four-wheel drive vehicle according to Embodiment 2, the front wheels 3 and the rear wheels 5, which are both drive wheels, are mounted on both the left and right sides of the frame 102 respectively. For the four-wheel drive vehicle 101 (see FIG. 1) that can turn during low-speed driving with the steering of the front wheels 3, the direction connecting the front wheels 3 and the rear wheels 5 is defined as the front-rear direction FB, the direction connecting both the left and right sides is defined as the left-right direction LR, and the direction perpendicular to both the front-rear direction FB and the left-right direction LR is defined as the height direction HW. The frame 102 includes a first frame portion 110 that supports the front wheels 3 at the end of the front axle member 111 that linearly extends in the left-right direction, and a link member 22 that extends in the front-rear direction FB. At the end of the rear axle member 21 that extends in the left-right direction LR, it has a second frame portion 20 that supports the rear wheels 5, and a connecting portion 30 that connects the first frame portion 110 and the second frame portion 20. In the first frame portion 110, a front wheel support portion 120 that connects to the axle 4 of the front wheels 3 is connected to the end of the front axle member 11 with a support shaft 131 parallel to the axle 4 as a fulcrum Q in a freely swingable manner. The driven-side connecting member 50 provided on the second frame portion 20 side of the connecting portion 30 is arranged to be relatively rotatable with respect to the overlapping operation-side connecting member 40 around a rotation shaft 31 vertically provided along the height direction HW at a position on a virtual line VL passing through the center in the left-right direction LR of the front axle member 111 among the operation-side connecting members 40 fixed to the first frame portion 110 side of the connecting portion 30. A steering control portion 60 for controlling the steering of the front wheels 3 is arranged in the connecting portion 30. When the four-wheel drive vehicle 101 turns from a straight running state while controlling the steering state of the front wheels 3 by the steering control portion 60 based on the difference between the rotational speed Vf (0 < Vf) of the front wheels 3 and the rotational speed Vr (0 < Vr) of the rear wheels 5, under the condition of Vf > Vr, by maintaining the state where the front wheels 3 are offset to the rear side in the front-rear direction FB by the swing of the front wheel support portion 120, or under the condition of Vf < Vr, by maintaining the state where the front wheels are offset to the front side in the front-rear direction FB by the swing of the front wheel support portion 120, the turned front wheels 3 are restored from the steering state to the straight running state based on the restoring moment acting on the front axle member 111.

[0111] Due to this feature, a restoring moment that attempts to return the steered front wheels 3 to their original turning state acts on the front axle member 111, allowing the four-wheel drive vehicle 101 to achieve stable straight-line driving. Furthermore, because the steering control unit 60 maintains the turning angle α of the front axle member 111 and controls the steering state of the front wheels 3, the four-wheel drive vehicle 101 can achieve turning operations with the front wheels 3 in a stable steering state. Therefore, in controlling the driving state of the front wheels 3, the front wheel control mechanism of a four-wheel drive vehicle does not require a complex device configuration, as in the technology of Patent Document 1, and can achieve both stable straight-line driving and stable cornering with a simple device configuration without implementing a complex electrical control device.

[0112] Therefore, like the front wheel control mechanism of the four-wheel drive vehicle according to embodiment 1, the front wheel control mechanism of the four-wheel drive vehicle according to embodiment 2 also has the excellent effect of being able to realize the turning operation of the four-wheel drive vehicle 101 with a simple device configuration that can be applied to care vehicles and the like that transport people in need of care.

[0113] Although the present invention has been described above in accordance with the first and second embodiments, the present invention is not limited to the first and second embodiments and can be appropriately modified and applied within the scope of the gist of the present invention.

[0114] In the first and second embodiments, as shown in Figures 1, 2, and 16, the four-wheel drive vehicle 1, 101 is configured so that only the essential parts are shown. However, when commercialized, it is preferable that the four-wheel drive vehicle according to the present invention be configured in a manner that includes equipment that allows for safe use.

[0115] Furthermore, for example, in the embodiment, four-wheel drive vehicle 1 having a speed reduction mechanism in output transmission section 72 was mentioned, but an example of a four-wheel drive vehicle having a speed reduction mechanism is "a four-wheel drive vehicle in which a pair of front wheels and a pair of rear wheels, both of which are drive wheels, are mounted on both the left and right sides of a frame, and which can turn at low speeds with steering by the front wheels, is provided with a motor as a drive source on each of the front wheels and the rear wheels, and a speed reduction unit is mounted between the front wheels and the motor, and between the rear wheels and the motor, respectively, and the speed reduction ratio of the speed reduction unit is 1 / N, where the ratio of the number of rotations on the motor side is 1 and the ratio of the number of rotations on the front wheel side or the rear wheel side is N, and the ratio N of the number of rotations on the front wheel side or the rear wheel side is 10≦N." This characteristic enables a four-wheel drive vehicle to have better hill climbing performance while suppressing traveling speed. [Explanation of symbols]

[0116] 1,101 four-wheel drive vehicles (nursing care vehicles) 2,102 frames 3 Front wheels 4 Front wheel axle 5 rear wheels 10 First frame section 11 Front axle member 20 Second frame section 21 Rear axle member 22 Link member 22A Front end 22B Rear end 30 Connecting part 31 Rotating shaft 33 Rod-shaped member 34 long hole 40 Operating side connecting member (operating side mechanism part) 41 1st flat plate part (1st flat plate) 50 Operated side connecting member (operated side mechanism part) 51 2nd flat plate part (2nd flat plate) 60 Steering control unit 61 Guide 62 pins 71 Motor 73 Motor control unit (electrical control unit) 78 Electrical control unit 80 Control section 92 seats 111 Lower support member 120 Front wheel support section 131 Support shaft K Gap S Clearance M axis center, fulcrum (member axis center) Q Axis center, fulcrum θ Swing angle α Swing angle of front axle member FB front / back direction RL Left / right direction HW Height direction CR1,CR2 Radial direction VL Virtual Line

Claims

1. The vehicle is a four-wheel drive vehicle in which the front and rear wheels, both of which are drive wheels, are mounted on the left and right sides of the frame, respectively, and can turn at low speeds by steering the front wheels. If the direction connecting the front wheels and the rear wheels is defined as the front-rear direction, the direction connecting the left and right sides is defined as the left-right direction, and the direction perpendicular to the front-rear direction and the left-right direction is defined as the height direction, the frame has a first frame portion that supports the front wheel at an end of a front axle member that extends linearly in the left-right direction, a second frame portion that includes a link member that extends in the front-rear direction and that supports the rear wheel at an end of a rear axle member that extends in the left-right direction, and a connecting portion that connects the first frame portion and the second frame portion, and in the first frame portion, a front wheel support portion that connects to the axle of the front wheel is connected to the end of the front axle member so as to be able to swing freely around a support shaft that is parallel to the axle as a fulcrum; the operated-side mechanism provided on the second frame portion side of the connecting portion is disposed rotatably relative to the overlapping operating-side mechanism portion, among the operating-side mechanism portions fixed to the first frame portion side of the connecting portion, at a position on an imaginary line passing through the center in the left-right direction of the front axle member, with a rotation shaft vertically disposed along the height direction as a fulcrum, and a steering control portion for controlling the steering of the front wheels is disposed on the connecting portion; When the four-wheel drive vehicle turns from a straight traveling state while controlling the steering state of the front wheels with the steering control unit based on the difference between the rotational speed Vf (0<Vf) of the front wheels and the rotational speed Vr (0<Vr) of the rear wheels, By maintaining a state in which the front wheels are offset rearward in the front-to-rear direction by swinging the front wheel support parts under the condition of Vf>Vr, or By maintaining a state in which the front wheels are offset forward in the front-to-rear direction by the swing of the front wheel support parts under the condition of Vf<Vr, the front wheels that have been turned are restored from a steering state to a straight running state based on a restoring moment acting on the front axle member; A front wheel control mechanism for a four-wheel drive vehicle.

2. The vehicle is a four-wheel drive vehicle in which the front and rear wheels, both of which are drive wheels, are mounted on the left and right sides of the frame, respectively, and can turn at low speeds by steering the front wheels. If the direction connecting the front wheels and the rear wheels is defined as the front-rear direction, the direction connecting the left and right sides is defined as the left-right direction, and the direction perpendicular to the front-rear direction and the left-right direction is defined as the height direction, the frame has a first frame portion that supports the front wheel at an end of a front axle member that extends linearly in the left-right direction, a second frame portion that includes a link member that extends in the front-rear direction and that supports the rear wheel at an end of a rear axle member that extends in the left-right direction, and a connecting portion that connects the first frame portion and the second frame portion, and the connecting portion is provided with an elongated hole that extends in the front-rear direction and a rod-shaped member that is inserted into the elongated hole with a gap in the front-rear direction, a front end of the link member is connected to an actuated mechanism portion provided on the second frame portion side of the connecting portion in a manner that allows the front end of the link member to move relatively to the first frame portion in the front-rear direction within a range of movement corresponding to the gap in conjunction with the relative movement between the elongated hole and the rod-shaped member, while a rear end of the link member is fixedly connected to the rear axle member; the operated-side mechanism is disposed at a position on an imaginary line passing through the left-right center of the front axle member, among the operating-side mechanism parts fixed to the first frame part side of the connecting part, so as to be rotatable relative to the overlapping operating-side mechanism part, with a rotation shaft vertically disposed along the height direction as a fulcrum, and a steering control part for controlling the steering of the front wheels is disposed on the connecting part; When the four-wheel drive vehicle turns from a straight traveling state while controlling the steering state of the front wheels with the steering control unit based on the difference between the rotational speed Vf (0<Vf) of the front wheels and the rotational speed Vr (0<Vr) of the rear wheels, By maintaining the rod-shaped member in contact with the rear end of the elongated hole in the front-rear direction under the condition of Vf>Vr, or By maintaining the rod-shaped member in contact with the front end of the elongated hole in the front-rear direction under the condition of Vf<Vr, the front wheels that have been turned are restored from a steering state to a straight running state based on a restoring moment that acts with the axis of the rod-shaped member as a fulcrum; A front wheel control mechanism for a four-wheel drive vehicle.

3. 3. The front wheel control mechanism for a four-wheel drive vehicle according to claim 2, The front wheels swing in one direction relative to a radial direction centered on a swing axis along the axle of the front wheels. A front wheel control mechanism for a four-wheel drive vehicle.

4. 3. The front wheel control mechanism for a four-wheel drive vehicle according to claim 2, an outer circumferential shape of the cross section of the rod-shaped member perpendicular to the member axis is a circle, and the end of the long hole is formed in an arc shape; A front wheel control mechanism for a four-wheel drive vehicle.

5. 3. The front wheel control mechanism for a four-wheel drive vehicle according to claim 2, The swing angle θ of the swingable front wheels is −5≦θ≦5 (rad) based on the vertical direction of the ground, and the clearance is large enough to satisfy the swing angle θ. A front wheel control mechanism for a four-wheel drive vehicle.

6. 3. The front wheel control mechanism for a four-wheel drive vehicle according to claim 2, the steering control unit restricts a turning angle of the front axle member that turns relative to the front end of the link member around the turning shaft as a fulcrum; A front wheel control mechanism for a four-wheel drive vehicle.

7. 7. The front wheel control mechanism for a four-wheel drive vehicle according to claim 6, In the steering control section, a guide consisting of an arc-shaped groove centered on the axis of the rotating shaft is formed on a first flat plate side having a first plane in the operating side mechanism section, and a pin is provided on a second flat plate side having a second flat plane in the operated side mechanism section, the operating side mechanism portion and the operated side mechanism portion are superposed with the first plane and the second plane facing each other, and the pin slides relatively within the guide; A front wheel control mechanism for a four-wheel drive vehicle.

8. A four-wheel drive vehicle in which front and rear wheels, both of which are drive wheels, are mounted on the left and right sides of a frame, respectively, and which can turn at low speeds with steering of the front wheels, is provided with a front wheel control mechanism for a four-wheel drive vehicle as set forth in any one of claims 1 to 7. A four-wheel drive vehicle characterized by:

9. 9. The four-wheel drive vehicle according to claim 8, The vehicle is provided with an electric control unit that performs electrical control, a motor that drives the front wheels and the rear wheels with electricity, and an operation unit that performs drive operation of the front wheels and the rear wheels. A four-wheel drive vehicle characterized by:

10. 9. The four-wheel drive vehicle according to claim 8, A care vehicle equipped with a seat and capable of traveling at a maximum speed of 6 km / h or less with a person requiring care in the seat. A four-wheel drive vehicle characterized by:

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