Vehicle with steering devices for front and rear wheels

Abstract

A vehicle is provided of which the four wheels are steerable, and which is prevented from unexpectedly moving forward or backward when switching the travel mode. The vehicle includes a steering device for front right and front left wheels of the vehicle capable of steering the front right and front left wheels, respectively, in one and the other of the right and left directions, a steering device for rear right and rear left wheels of the vehicle configured, simultaneously when the steering device for the front right and front left wheels are actuated, to be capable of steering the rear right and rear left wheels in the other and the one of the right and left directions, respectively, and in-wheel motors provided in at least one of each of the front right and front left wheels and each of the rear right and rear left wheels.

Claims

1. A vehicle comprising: a first steering device configured to steer front right and front left wheels of the vehicle, respectively, in one and the other of right and left directions which are opposite to each other; a second steering device configured to steer rear right and rear left wheels of the vehicle in the other and the one of the right and left directions, respectively, simultaneously when the first steering device is actuated; and in-wheel motors provided in at least one of each of the front right and front left wheels and each of the rear right and rear left wheels; wherein the in-wheel motors are configured to be activated to assist in the steering of the respective wheels about king pin axes by rotating the wheels under driving forces of the in-wheel motors while the first steering device steers the front right and the front left wheels, respectively, in one and the other of right and left directions opposite to each other and the second steering device simultaneously steers the rear right and rear left wheels in the other and the one of the right and left directions, respectively.

2. The vehicle of claim 1, wherein each of the first steering device and the second steering device further includes: tie rods connected, respectively, to the corresponding right and left wheels so as to move and steer the respective right and left wheels; a pair of rack bars connected to the respective tie rods; a synchronizing gear meshing with rack teeth of the pair of rack bars and configured such that a movement of a first one of the rack bars in one of the right and left directions is converted to a movement of a second one of the rack bars in the other of the right and left directions; and a rack bar moving device configured to move the pair of rack bars in one and the other of the right and left directions, respectively, wherein the rack bar moving device comprises: a first pinion gear meshing with the first one of the rack bars; a second pinion gear meshing with the second one of the rack bars; and a coupling mechanism configured to selectively couple together the first pinion gear and the second pinion gear, and selectively uncouple the first pinion gear and the second pinion gear from each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a vehicle on which are mounted steering devices embodying the present invention.

(2) FIG. 2 is a plan view of the vehicle of FIG. 1.

(3) FIG. 3 is a plan view of the vehicle of FIG. 2 during a normal travel mode (normal steering mode).

(4) FIG. 4 is a plan view of the vehicle of FIG. 2 during a small-radius turning mode.

(5) FIG. 5 is a plan view of the vehicle of FIG. 2 during a pivot turn mode.

(6) FIG. 6 is a plan view of the vehicle of FIG. 2 during a lateral travel (parallel travel) mode.

(7) FIG. 7 is a sectional view of a wheel, showing how the wheel is supported.

(8) FIGS. 8(a) and 8(b) are, respectively, a perspective view as seen from below, and a perspective view as seen from above, of either of the steering devices shown in FIG. 2.

(9) FIGS. 9(a) and 9(b) are a back view and a plan view, respectively, of either of the steering devices shown in FIG. 2, showing its interior.

(10) FIGS. 10(a) and 10(b) are back views of either of the steering devices shown in FIG. 2, showing, respectively, the state in which two rack bars are close to each other, and the state in which the two rack bars are open.

(11) FIGS. 11(a) and 11(b) are side views of either of the steering devices shown in FIG. 2, showing, respectively, the state in which a coupling mechanism is uncoupled, and the state in which the coupling mechanism is coupled.

(12) FIG. 12 is a plan view of the vehicle of FIG. 2 in which only the front wheels are moved to a pivot turn mode.

DETAILED DESCRIPTION OF THE INVENTION

(13) While the vehicle 1 according to the present invention may be provided with any steering devices provided such steering devices can steer the front wheels and the rear wheels simultaneously, it is especially preferable to use steering devices 10 and 20 shown in, and described with reference to, FIGS. 8(a) to 11(b). Description is now made of the operation of the steering devices 10 and 20 as mounted on the vehicle 1, and the behavior of the wheels w of the vehicle during respective travel modes.

(14) The vehicle 1 according to the present invention includes in-wheel motors M each mounted in the wheel body of a respective one of the wheels w of the vehicle, i.e., the front right, front left, rear right and rear left wheels. The in-wheel motors M allow various travel patterns. However, the in-wheel motors of either the front wheels or the rear wheels may be omitted.

(15) FIG. 1 shows the vehicle 1, in which the steering devices according to the present invention are used. This vehicle 1 is an ultra-small (laterally arranged) two-seater mobility vehicle. The wheels w of this vehicle 1 are steerable by operating a steering wheel 2, thus turning a steering shaft 3 about its axis. The present invention is not only applicable to such an ultra-small mobility vehicle but also to an ordinary vehicle.

(16) FIG. 2 is a schematic plan view of the vehicle, showing its drive line and control line. In this embodiment, the steering devices 10 and 20 according to the present invention are coupled, respectively, to the front right and front left wheels FR and FL, and to the rear right and rear left wheels RR and RL, through tie rods 12 and 22.

(17) The vehicle includes a four-wheel steering mechanism which, when the steering 2 is operated, allows the first steering device 10 for the front wheels to steer the front wheels in a normal manner, and allows the second steering device 20 for the rear wheels to steer the rear wheels according to the travel mode, through an actuator such as a motor. When the wheels w are steered in this manner by operating the steering wheel 2 and actuating the actuator, the in-wheel motors M of the respective wheels w are also activated to assist in the steering of the respective wheels w about king pin axes P by rotating the tires T under the driving forces of the in-wheel motors M. It is also possible to steer the wheels under the driving forces of the respective in-wheel motors M alone, without a driver operating the steering wheel 2 or without actuating the above actuator.

(18) One of the steering devices 10 and 20 may be omitted. If the steering device 10 for the front wheels is omitted, an ordinary steering device may be used instead of the steering device 10.

(19) Each of the first steering device 10 for the front wheels and the second steering device 20 for the rear wheels includes two rack bars, i.e., a first rack bar 53 connected to the left (with respect to the fore-and-aft direction of the vehicle) wheel w, and a second rack bar 54 connected to the right wheel w. In each of FIGS. 2 to 6, the arrow on its left-hand side indicates the forward direction of the vehicle. Travel modes shown in FIGS. 3 to 6 will be described later.

(20) For each of the steering devices 10 and 20, connecting members 11 and 21 of the rack bars 53 and 54 are connected to the right and left wheels w through the respective tie rods 12 and 22. Knuckle arms or other members are disposed between the tie rods 12 and 22 and the respective wheels w.

(21) FIG. 7 shows how each tie rod 12, 22 is connected to the corresponding wheel w, in which is mounted the in-wheel motor M. Any of the wheels w is steerable about a kingpin axis P connecting together the center lines of ball joints BJ provided, respectively, at the distal ends of an upper arm UA and a lower arm LA supported by the vehicle frame. The in-wheel motor M includes a motor main body 101, a speed reducer 102 and a wheel bearing 103 which are arranged in series in this order from the inboard to outboard side of the vehicle. The in-wheel motor M of each wheel w is capable of assisting in the steering of the wheel about the king pin axis P (about which the wheel is steered) by rotating the tire T under the driving force of the in-wheel motor M, if, as shown in FIG. 7, the contact point P′ between the kingpin axis P and the ground is not coincident with the center T′ of the ground contact area of the tire T (i.e., if the scrub radius is not zero).

(22) Now the steering devices 10 and 20 are described in a detailed manner. For each of the steering devices 10 and 20, as shown in FIGS. 8(a) and 8(b), the first and second rack bars 53 and 54 are mounted in a rack case (steering cylinder) 50 extending in the right-and-left direction of the vehicle relative to the direction in which the vehicle moves in a straight line (fore-and-aft direction of the vehicle). The rack case 50 comprises a front cover 52 and a rear cover 51, and is fixed directly or indirectly to the frame (chassis), not shown, of the vehicle 1 at its flange portions 50a by screws or bolts.

(23) While not shown, each steering device 10, 20 includes boots extending from the respective tie rods 12 and 22 to the rack case 50 to prevent entry of foreign substances into the moving parts of the steering device. A first rotary shaft (pinion shaft) 61 is connected to a steering shaft 3 through a steering joint, not shown.

(24) As shown in FIG. 2, when the steering 2 is operated by a driver, the first rack bar 53 and the second rack bar 54 of each steering device 10, 20 can be moved in one of the right and left directions by the same distance, together with each other, directly by the steering wheel 2, or by a normal steering actuator 31 which is actuated when the steering wheel 2 is operated. When the rack bars 53 and 54 are moved in this manner during a normal travel mode, the right and left wheels w are steered in one of the right and left directions.

(25) As shown in FIG. 9(a), each of the steering devices 10 and 20 includes a rack bar moving device 60. The rack bar moving device 60 is capable of moving the first and second rack bars 53 and 54, respectively, in one and the other of the right and left directions relative to the direction in which the vehicle moves in a straight line (i.e. the opposite directions in which the rack teeth are arranged) by the same distance.

(26) As shown in FIG. 9(a), the rack bar moving device 60 includes first synchronizing gears 55 each meshing with both a synchronizing rack gear 53a of the first rack bars 53 and a synchronizing rack gear 54a of the second rack bar 54, which faces the synchronizing rack gear 53a.

(27) The first synchronizing gears 55 comprise three gears 55a, 55b and 55c that are arranged in the direction in which the rack teeth of the rack gears of the rack bars 53 and 54 extend, and are spaced apart from each other at regular intervals. When the first rack bar 53 is moved in one of the opposite directions in which the rack teeth are arranged under a driving force applied from the rack bar moving device 60, this movement is converted to the movement of the second rack bar 54 in the other (second) of the opposite directions by the same distance as the movement of the first rack bar 53 in the one (first) of the opposite directions.

(28) As shown in FIGS. 9(a) and 9(b), the rack bar moving device 60 further includes second synchronizing gears 56 comprising gears 56a and 56b which are disposed between the adjacent first synchronizing gears 55, i.e. between the gears 55a and 55b and between the gears 55b and 55c, respectively. The second synchronizing gears 56 are in mesh with neither of the synchronizing rack gear 53a of the first rack bar 53 and the synchronizing rack gear 54a of the second rack bar 54, and are in mesh with only the first synchronizing gears 55. The second synchronizing gears 56 serve to rotate the three first synchronizing gears 55a, 55b and 55c by the same angle in one same circumferential direction. The second synchronizing gears 56 ensure smooth relative movement between the first rack bar 53 and the second rack bar 54.

(29) As shown in FIG. 10(b), the first and second rack bars 53 and 54 include, besides the synchronizing rack gears 53a and 54a, steering rack gears 53b and 54b, respectively. The synchronizing rack gears 53a and 54a may be formed integral with the respective steering rack gears 53b and 54b, or may be separate members from, and fixed to, the respective steering rack gears 53b and 54b.

(30) When the first rack bar 53 is moved from the position shown in FIG. 10(a) to the position shown in FIG. 10(b) under the driving force applied from the rack bar moving device 60, this driving force is transmitted to the second rack bar 54 through the first synchronizing gears 55, so that the second rack bar 54 is also moved from the position shown in FIG. 10(a) to the position shown in FIG. 10(b). While the rack bars are being moved in this manner, it is possible to assist in the steering of the wheels w by driving the in-wheel motors M of the respective wheels w to rotate the tires T under the driving forces of the in-wheel motors M. It is also possible to steer the wheels not under the driving force applied from the rack bar moving device 60 but under the driving forces of the in-wheels motors M alone. While the rack bars are moved as shown in FIGS. 10(a) and 10(b), the below-described coupling mechanism 63 is uncoupled.

(31) After the rack bars 53 and 54 have reached the positions shown in FIG. 10(b), the coupling mechanism 63 is coupled. Once the coupling mechanism 63 is coupled, the rack bars 53 and 54 are fixed to each other, so that the rack bars 53 and 54 can be moved in one of the right and left directions by the same distance.

(32) The operation of the rack bar moving device 60 is now described.

(33) The rack bar moving device 60 of the first steering device 10 for the front wheels includes the pinion shaft (first rotary shaft) 61 of the steering device 10 (see FIG. 10(b)). The first rotary shaft 61 is directly rotated by the steering wheel 2 when a driver turns the steering wheel 2. However, the rack bar moving device 60 may be configured such that instead of the first rotary shaft 61 being directly rotated by the steering wheel 2 when the driver turns the steering wheel 2, the first rotary shaft 61 is rotated under a driving force of the normal steering actuator 31 of the first steering device 10, which is actuated when the driver turns the steering wheel 2, or under a driving force of a mode switching actuator 32 of the first steering device 10 which is actuated when a mode switching element 42 mounted on the vehicle 1 is operated.

(34) The rack bar moving device 60 of the first steering device 20 for the rear wheels includes the first rotary shaft 61 of the second steering device 20. This rotary shaft 61 is configured to be rotated under a driving force of the normal steering actuator 31 of the second steering device 20, which is actuated when the driver turns the steering wheel 2, or under a driving force of a mode switching actuator 32 of the second steering device 20 which is actuated when a mode switching element 42 mounted on the vehicle 1 is operated. The rack bar moving device 60 further includes a first pinion gear 62 mounted to the first rotary shaft 61 so as to rotate together with the first rotary shaft 61. Rotation is transmitted from the actuating shaft of the normal steering actuator 31 or the mode switching actuator 32 to the first rotary shaft 61 through the steering joint.

(35) Each rack bar moving device 60 includes a second rotary shaft 64 aligned with the first rotary shaft 61, and a second pinion gear 65 mounted on the second rotary shaft 64 so as to be rotatable together with the second rotary shaft 64.

(36) As shown in FIG. 10(b), the first pinion gear 62 is in mesh with the steering rack gear 53b of the first rack bar 53, and the second pinion gear 65 is in mesh with the steering rack gear 54b of the second rack bar 54.

(37) The rack bar moving device 60 includes the coupling mechanism 63. The coupling mechanism 63 is disposed between the first pinion gear 62 and the second pinion gear 65, and is configured to selectively uncouple the first and second rotary shafts 61 and 64 from each other (so that they can rotate relative to each other; see FIG. 11(a)) and couple the shafts 61 and 64 together (so that they cannot rotate relative to each other; see FIG. 11(b)).

(38) As shown in FIGS. 11(a) and 11(b), the coupling mechanism 63 includes a moving part 63a provided on the first rotary shaft 61, and a fixed part 63b provided on the second rotary shaft 64. The coupling mechanism 63 is configured such that when the moving part 63a is pressed against the fixed part 63b, protrusions 63c formed on the moving part 63a are engaged in recesses 63d formed in the fixed part 63b, thereby allowing the rotary shafts 61 and 64 to rotate together. However, conversely to the above, the protrusions 63c may be formed on the fixed part 63b, and the recesses 63d may be formed in the moving part 63a.

(39) The coupling mechanism 63 is further configured such that the moving part 63a can be moved axially away from the fixed part 63b, i.e., axially upwardly in FIGS. 11(a) and 11(b), by an external driving source such as a push solenoid until the fixed part 63b and the moving part 63a are uncoupled from each other, and the first and second rotary shafts 61 and 64, and thus the first and second pinion gears 62 and 65, are uncoupled from each other and become rotatable independently of each other.

(40) In this state, the first pinion gear 62 is in mesh with the first rack bar 53, and the second pinion gear 65 is in mesh with the second rack bar 54. Further, the first synchronizing gears 55 are in mesh with both the first rack bar 53 and the second rack bar 54. Thus, when rotation is transmitted to the first pinion gear 62, and the first rack bar 53 is moved in one of the right and left directions of the vehicle, along which the rack teeth of the first rack bar 53 are arranged, the first synchronizing gears 55 are rotated, and the second rack bar 54 is moved in the direction opposite to the direction in which the first rack bar 53 is moved (the other of the right and left directions) by the same distance. As the second rack bar 54 is moved, the second pinion gear 65 is rotated.

(41) Thus, by selectively coupling together the first and second pinion gears 62 and 65 and uncoupling them from each other by the coupling mechanism 63, it is possible to easily change between the state in which the rack bars 53 and 54 are moved in one of the right and left directions together with each other, and the state in which the rack bars 53 and 54 are separately moved in the opposite directions to each other.

(42) That is, with the first pinion gear 62 and the second pinion gear 65 coupled together through the coupling mechanism 63, when a driver turns the steering wheel 2, the first rack bar 53 and the second rack bar 54 are moved together with each other in one of the right and left directions with respect to the direction in which the vehicle is moved in a straight line by the same distance, under the driving force of the normal steering actuator 31, which is actuated when the steering wheel 2 is operated. As a result, the corresponding right and left wheels w are steered about the respective kingpin axes P (see FIG. 7) in the same direction. At this time, since the first rack bar 53 and the second rack bar 54 are moved together with each other, the first synchronizing gears 55 do not rotate.

(43) On the other hand, when the first pinion gear 62 and the second pinion gear 65 are uncoupled from each other by the coupling mechanism 63, it is possible to move the first rack bar 53 and the second rack bar 54 by the same distance in one and the other of the right and left directions, with respect to the direction in which the vehicle is moved in a straight line, thereby steering the right and left wheels w in opposite directions to each other about the respective kingpin axes P (FIG. 7).

(44) With this arrangement, the rotation of the steering wheel 2 during normal operation is transmitted to the first rotary shaft 61 through the steering shaft 3. The rack bar moving device 60 also serves to move the first rack bar 53 and the second rack bar 54 together with each other during normal operation.

(45) During mode switching, the driving force of the mode switching actuator 32 is transmitted to the respective rack bars 53 and 54 due to rotation of the first pinion gear 62 and the first synchronizing gears 55. While the driving force of the mode switching actuator 32 is being applied to the respective rack bars 53 and 54 through the first pinion gear 62, the rotation of the steering wheel 2 may or may not be transmitted to the steering shaft 3.

(46) The normal steering actuator 31 may have the function of the mode switching actuator 32 too. That is, during mode switching, the rotation of the steering shaft 3 may be transmitted to the first rotary shaft 61 through the normal steering actuator 31.

(47) Now description is made of several travel modes of the vehicle 1 in which the steering devices 10 and 20 are mounted.

(48) (Normal Travel Mode)

(49) With the wheels positioned as shown in FIG. 2, in which the vehicle is supposed to travel in a straight line, the coupling mechanism 63 of the steering device 10 for the front wheels is coupled (as shown in FIG. 11(b)), whereby the first rack bar 53 and the second rack bar 54 are movable together with each other. When the steering wheel 2 is operated in this state, the pair of rack bars 53 and 54 in the rack case 50 mounted to the frame of the vehicle 1 are moved together with each other.

(50) When the first and second rack bars 53 and 54 of the steering device 10 are moved together with each other in one of the right and left directions with respect to the direction in which the vehicle is moved in a straight line, under the driving force of the normal steering actuator 31 or by operating the steering wheel 2, the front right and front left wheels w are steered by a predetermined angle. FIG. 3 shows the state of the vehicle when the front wheels are steered to the right. That is, by completely fixing the rack bars 53 and 54 to each other, the vehicle 1 can travel in the same manner as ordinary vehicles. During the normal travel mode, when a driver operates the steering wheel 2, the front wheels are steered through the steering device 10 for the front wheels such that the vehicle can travel in a straight line, turn right or left, or travel otherwise according to situations.

(51) (Small Radius Turning Mode)

(52) FIG. 4 shows a small radius turning mode, in which the first steering device 10 for the front wheels is moved as shown in FIG. 3, and further, the coupling mechanism 63 of the second steering device 20 for the rear wheels are coupled, whereby the first rack bar 53 and the second rack bar 54 of the second steering device 20 are movable together with each other (see FIG. 11(b)). Thus, when the steering wheel 2 is operated, the pair of rack bars 53 and 54 in the rack case 50 of the second steering device 20, which is fixed to the frame of the vehicle, are also moved together with each other in one of the right and left directions of the vehicle 1.

(53) When the first and second rack bars 53 and 54 of the second steering device 20 are moved in one of the right and left directions with respect to the direction in which the vehicle is moved in a straight line under the driving force of the normal steering actuator 31, the rear right and rear left wheels w are steered by a predetermined angle as shown in FIG. 4. At this time, the rear wheels are steered in the opposite direction to the direction in which the front wheels are steered. (In FIG. 4, the front wheels are steered to the right, while the rear wheels are steered to the left.) This allows the vehicle to be turned with a smaller radius than during the normal travel mode. In FIG. 4, the rear wheels are steered in the opposite direction to the direction in which the front wheels are steered by the same angle as the front wheels, but may be steered by a different angle from the angle by which the front wheels are steered.

(54) (Pivot Turn Mode)

(55) A pivot turn mode is shown in FIG. 5. In this mode, for each of the steering devices 10 and 20, the coupling mechanism 63 is uncoupled (see FIG. 11(a)), whereby the first rack bar 53 and the second rack bar 54 are movable separately from each other. Thus, when the driving force of the mode switching actuator 32 is applied to the first pinion gear 62, the first rack bar 53 and the second rack bar 54 are moved by the same distance in the opposite directions to each other by the action of the first synchronizing gears 55 disposed between the first rack bar 53 and the second rack bar 54.

(56) The first and second rack bars 53 and 54 of each of the steering devices 10 and 20 are moved in the opposite directions to each other until, as shown in FIG. 5, the center axes of all four wheels w substantially extend to the center of the vehicle, and the coupling mechanisms 63 of the respective steering devices 10 and 20 are coupled in this state. Since the center axes of all four wheels w substantially extend to the center of the vehicle, the vehicle can turn on the same spot with the center of the vehicle remaining unchanged (or substantially unchanged) under the driving forces from the in-wheel motors M mounted in the respective wheels w.

(57) During steering for switching to the pivot turn mode, the tires T are rotated under the driving forces of the in-wheel motors M mounted in the front and rear wheels w to steer the wheels w about the respective king pin axes P. At this time, by simultaneously generating driving forces from the in-wheel motors M of the front and rear wheels w, it is possible to prevent the vehicle from unexpectedly moving forward while switching to the pivot turn mode. When switching from the pivot turn mode to the normal travel mode too, by simultaneously generating driving forces from all of the in-wheel motors M, it is possible to prevent the vehicle from unexpectedly moving backward at this time.

(58) In this mode, the vehicle can be turned on the same spot not by all of the in-wheel motors M mounted in the respective wheels w but by at least one of them.

(59) (Lateral Travel Mode)

(60) A lateral travel mode is shown in FIG. 6. In this mode, as in the pivot turn mode, for each of the steering devices 10 and 20, with the coupling mechanism 63 uncoupled (see FIG. 11(a)), the first rack bar 53 and the second rack bar 54 are moved in the opposite directions to each other such that all of the front and rear wheels w are oriented in the direction perpendicular to the direction in which the vehicle travels in a straight line (right and left direction with respect to the direction in which the vehicle travels in a straight line), by applying a rotational force from the mode switching actuator 32 to the first pinion gear 62. When the wheels w are oriented in the direction perpendicular to the direction in which the vehicle travels in a straight line, the coupling mechanism 63 is coupled (see FIG. 11(b)) to fix the rack bars 53 and 54 in position.

(61) With the coupling mechanism 63 coupled in this manner, the first and second rack bars 53 and 54 can be moved in one of the right and left directions with respect to the direction in which the vehicle travels in a straight line, under the driving force of the normal steering actuator 31 or by operating the steering wheel 2, to finely adjust the directions (tire angles) of the wheels w.

(62) FIG. 6 shows the positional relationship between the steering devices 10 and 20 for the front and rear wheels w, respectively, and the directions of the wheels w, during the lateral travel mode. Compared to the pivot turn mode, the rack bars 53 and 54 protrude laterally outwardly to a larger degree. Thus, in this mode, the connecting points between the tie rods 12 and 22 and the respective wheels w are located at the outermost positions in the width direction of the vehicle. During the lateral travel mode too, it is possible to finely adjust the directions (tire angles) of the wheels w under the driving force of the normal steering actuator 31 or by operating the steering wheel 2.

(63) During steering for switching to the lateral travel mode, the tires T are rotated under the driving forces of the in-wheel motors M mounted in the front and rear wheels w to steer the wheels w about the respective king pin axes P. At this time, by simultaneously generating driving forces from the in-wheel motors M of the front and rear wheels w, it is possible to prevent the vehicle from unexpectedly moving forward while switching to the lateral travel mode. When switching from the lateral travel mode to the normal travel mode too, by simultaneously generating driving forces from all of the in-wheel motors M, it is possible to prevent the vehicle from unexpectedly moving backward at this time.

(64) (Further Travel Mode)

(65) In a further travel mode, when an electronic control unit (ECU) 40 determines that the vehicle 1 is traveling at a high speed, based on an output of the ECU 40, an actuator driver 30 drives the mode switching actuator 32 for the rear wheels such that the rear left and rear right wheels RL and RR are turned from the parallel position so as to be slightly closed at their front ends (toe-in state). This allows stable high-speed travel.

(66) Such toe adjustment may be made based on travel states of the vehicle, such as the vehicle speed and loads on the axles, as determined by the ECU 40, or based on the input from the mode switching element 42, which is provided in the driver/passenger cabin. A driver can switch the travel mode by operating the mode switching element 42. The mode switching element 42 may be a switch, a lever or a joystick operable by a driver.

(67) (Mode Switching)

(68) The mode switching element 42 is also used to switch one of the above travel modes to another. That is, by operating the mode switching element 42, it is possible to select any of the normal travel mode, pivot turn mode, lateral travel mode, small-radius turning mode, etc. Since any travel mode is selectable by operating e.g. a switch, the mode switching can be made safely.

(69) During the normal travel mode, the ECU 40 calculates the necessary moving amount of the rack bars 53 and 54 of the steering device 10 in one of the right and left directions, based on information from a sensor 41 when the steering wheel 2 is operated, and based on the results of calculation, the ECU 40 controls the normal steering actuator 31 for the front wheels, to move, together with each other, the rack bars 53 and 54 received in the rack case 50 in the one of the right and left directions, thereby steering the front right and front left wheels w by necessary angles in a necessary direction.

(70) When, for example, the pivot turn mode is selected by operating the mode switching element 42, it is possible to steer the four wheels w through the steering devices 10 and 20 for the front and rear wheels, respectively, and under the driving forces generated simultaneously from the in-wheel motors M of the front and rear wheels w such that the vehicle 1 turns substantially about the center of the vehicle. This mode is permitted only while the vehicle 1 is at a stop. During the pivot turn mode, the ECU 40 calculates the relative movements of the rack bars 53 and 54 of the respective steering devices 10 and 20, and based on the results of calculation, the ECU 40 controls, through the actuator driver 30, the mode switching actuators 32 for the front and rear wheels, thereby steering the wheels.

(71) When the lateral travel mode is selected by operating the mode switching element 42, it is possible to steer the four wheels w through the steering devices 10 and 20 for the front and rear wheels, respectively, and under the driving forces generated simultaneously from the in-wheel motors M of the front and rear wheels w such that the four wheels w form a steering angle of 90 degrees. At this time, too, the ECU 40 calculates the relative movements of the rack bars 53 and 54 of the respective steering devices 10 and 20. Based on the results of this calculation, the ECU 40 controls, through the actuator driver 30, the mode switching actuators 32 for the front and rear wheels, thereby steering the wheels. The normal steering actuators 31 may be configured, during the lateral travel mode, to be deactivated, or kept activated so that the steering angles can be finely adjusted by the normal steering actuators 31.

(72) When the small-radius turning mode is selected by operating the mode switching element 42, the front wheels and the rear wheels are steered in opposite directions to each other so that the vehicle can turn with a smaller radius. During the small-radius turning mode, the ECU 40 calculates moving amounts of the rack bars 53 and 54 of the steering device 20 for the rear wheels, which are received in the rack case 50, based on e.g. the operation of the steering wheel 2, and based on the results of calculation, the ECU 40 controls, through the actuator driver 30, the normal steering actuator 31 and the mode switching actuator 32 for the second steering device 20 to steer the rear wheels. The first steering device 10 for the front wheels is controlled in the same manner as during the normal travel mode.

(73) As described above, based on the steering angle of the steering wheel 2 when the steering wheel 2 is operated by a driver, the information from the sensor 41, which detects e.g. the steering torque, and/or the input from the mode switching element 42, or based on the travel condition of the vehicle determined by the ECU 40 itself, the ECU 40 calculates necessary moving amounts of the rack bars 53 and 54 of the respective steering devices 10 and 20, and based on the results of calculation, the ECU 40 controls, through the actuator driver 30, the normal steering actuators 31 or the mode switching actuators 32, of the respective steering devices 10 and 20, thereby steering the front and rear wheels in a predetermined direction.

(74) In the embodiment, the second steering device 20 for the rear wheels is controlled by the steer-by-wire configuration, in which the steering operation as well as the operation of the mode switching actuator 32, which are carried out by a driver, are converted to electric signals to steer the wheels.

(75) For the steering device 10 for the front wheels too, the steer-by-wire configuration using the normal steering actuator 31 and the mode switching actuator 32 may be used. In another arrangement, the normal steering actuator 31 for the steering device 10 comprises a motor coupled to a steering wheel 2, which is operated by a driver, or to the steering shaft 3, and configured to assist the manual steering operation by generating torque necessary to move the rack bars 53 and 54 in the right and left directions. In this arrangement, the mode switching actuator 32 for the front wheels is of the same structure as the actuator 32 for the rear wheels.

(76) The first steering device 10 for the front wheels, which is used for steering during the normal travel mode, may be an ordinary steering device using an ordinary mechanical rack and pinion mechanism.

(77) The above-described travel modes are mere examples, and other control modes using the above-described mechanism are feasible.

(78) According to the present invention, in a vehicle including steering devices capable of steering the front right and front left wheels, respectively, in one and the other of the right and left directions, which are opposite to each other, and steering the rear right and rear left wheels, respectively, in said other and said one of the right and left directions. The steering devices for the front wheels and the rear wheels are actuated simultaneously to switch the travel mode. With this arrangement, when switching the travel mode, it is possible to prevent the vehicle from unexpectedly moving forward or backward, thus improving safety of the vehicle 1.

DESCRIPTION OF THE NUMERALS

(79) 10, 20. Steering device 12, 22. Tie rod 53, 54. Rack bar 55. Synchronizing gear 60. Rack bar moving means 62. First pinion gear 63. Coupling mechanism 65. Second pinion gear M. In-wheel motor w. Wheel