JPH0214976A - Rear wheel steering gear - Google Patents

Abstract

PURPOSE:To enable requirement for steering rear wheels to be set according to various travelling requirements by enabling the steering of the rear wheels to be controlled by controllably rotating a cam body. CONSTITUTION:A rear wheel steering gear 1 is provided in a case 11 fixedly supported on an axle beam 39 with a cam body 13 connected to the rear end of an input shaft 12 extending longitudinally of a car body to be rotated by the rotation of the input shaft 12 and rotary rollers 14 as cam followers opposed to each other widthwise of the car body to sandwich the cam body 13 and abutting against the outer peripheral surface of the cam body 13. The rear wheel steering gear 1 is provided with a movable lever 15 supported slidably widthwise of a car body by a case 11 for supporting a pair of cam follower 14 on the intermediate portion as a body interlocked with the cam. Said movable lever 15 is supported on a slide support to slide a slide shaft section 17 widthwise of the car through a slide bearing 21 and a rubber bushing 22.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a rear wheel steering mechanism applied to a four-wheel steering vehicle.

[Conventional technology]

Various ideas have been proposed in the past in which the rear wheels are steered in addition to the front wheels in order to obtain optimal driving performance depending on various situations. Typical examples include those in which the rotation of the steering wheel is mechanically transmitted to the rear wheel steering mechanism to steer the rear wheels, and those in which the rear wheels are steered and rotated by a hydraulic actuator and the hydraulic By controlling the drive of the actuator, the steering ratio (the steering angle of the rear wheels relative to the steering angle of the front wheels)
There are some that are designed to change depending on the vehicle speed, etc. In the former case, when the steering angle of rotation is small, the rear wheels are steered in the same phase, and when the steering angle is large, the rear wheels are steered in the opposite phase.On the other hand, in the latter case, At low speeds, the rear wheels are steered in opposite phases, and at high speeds, the rear wheels are steered in the same phase. This is because when the front wheels are steered significantly, it is usually when making a U-turn or other turn at low speed, and by steering the rear wheels in the opposite phase at this time, the turning radius of the vehicle is reduced. This makes it possible to improve the ease of handling. Also, when changing lanes at high speeds, the steering angle of the front wheels is small, and at this time the rear wheels are steered in the same phase, actively giving a sideslip angle to the rear wheels to generate cornering force. This makes it possible to quickly change direction while suppressing vehicle skidding caused by centrifugal force.

[Problem to be solved by the invention]

However, in the case of a four-wheel steering system that mechanically transmits the steering rotation to the rear wheel steering mechanism as described above to steer the t & wheels, the amount of rear wheel turning is determined by the steering rotation angle (front wheel steering mechanism). The degree of freedom in setting the steering ratio is small, and the problem is that it cannot easily accommodate various rear wheel steering patterns. Wheel steering patterns vary depending on the vehicle's load distribution, suspension characteristics, etc., and in order to achieve optimal driving performance, it is desirable to have a large degree of freedom in setting the rear wheel steering pattern. In the case of a four-wheel steering system that steers the rear wheels, the drive of the actuator is controlled by the control device to steer the rear wheels, so there is a large degree of freedom in setting the steering ratio and rear wheel steering pattern. In addition, there is the advantage that the rear wheel steering conditions can be set to suit various driving conditions. However, in such a four-wheel steering system, when the actuator loses hydraulic pressure, the rear wheels are held in a neutral position. In addition, since rear wheel steering is performed by an actuator, there is also the problem that the fail-safe mechanism provided to ensure safety in the above-mentioned cases becomes complicated. The invention was devised under the above circumstances, and has a large degree of freedom in setting the rear wheel steering pattern.
In addition, a rear wheel steering mechanism applied to a four-wheel steering vehicle is configured to be able to determine rear wheel steering conditions according to various driving conditions and achieve high fail-safe performance. Its purpose is to provide.

[Means for Solving the Problems] In order to solve the above problems, the present invention takes the following technical measures. That is, the rear wheel steering mechanism according to claim 1 of the present invention includes: a pair of cams connected to an input shaft extending in the longitudinal direction or the vertical direction of the vehicle, and driven to rotate around its axis by rotation of the input shaft; a pair of cam followers that are opposed to each other in the vehicle width direction on both sides of the cam body, are in contact with the outer circumferential cam surface of the cam body, and are supported so as to be movable in the vehicle width direction; a cam interlocking body that is moved in the same direction in the vehicle width direction as the vehicle moves in the vehicle width direction, and an electric motor whose rotation is controlled by a control means is interlocked with the input shaft; The outer peripheral cam surface is formed to push the cam follower in a predetermined direction in the vehicle width direction when the cam body rotates from the neutral rotation position, and the cam interlocking body has a rear wheel steering It is characterized by connecting members. In addition, in the invention set forth in claim 2 of the present application, the cam body in the invention set forth in claim 1 is arranged such that the rotational axis is centered on an example of the axis connecting the contact points with each cam follower at the neutral rotation position. and a pair of left and right first cams having substantially cylindrical outer surfaces whose distance from the rotation axis gradually decreases as the rotational angular position from the contact point increases with respect to a reference circle whose radius is the length to the contact point. A pair of left and right second cams each having a substantially cylindrical outer surface shape, the face of which is disposed on the other side of the axis, with respect to the reference circle, the distance from the rotation axis increases as the rotation angle position from the contact point increases. Each has a face and passes through the axis of rotation."
In particular, a cam body is used in which the cross-sectional length between the cam face and the second cam face is set to be the same as the diameter of the reference circle at any rotation angle position. Note that this cam body will hereinafter be referred to as a cam capable of fine control. [Operation and Effect] When the cam body is rotated from the neutral rotation position and its outer cam surface pushes one of the cam followers, each cam follower is moved in a predetermined direction in the vehicle width direction, and as a result, the cam interlocking body is also moved in the same direction as the cam follower. As a result, a movement in the vehicle width direction is applied to the rear wheel steering member connected to the cam interlocking body, and the rear wheels are steered. When the cam body rotates in this way, the latter is steered, but in other words, by controlling the rotation of the cam body,
The steering of the rear wheels can be controlled, and the input shaft that rotationally drives this cam body is rotated by an electric motor whose rotation is controlled by a control means. In other words, the rotation of the cam body and the steering of the rear wheels can be controlled by the control means, and by changing the shape of the cam body, the distance that the cam body pushes the cam follower can be adjusted. The rotational angle position for pushing the cam follower can also be changed to node 1. Therefore, the degree of freedom in setting the amount of turning of the rear wheels is large, and various rear wheel turning patterns can be easily set. moreover,
Rear wheel steering conditions can also be determined to suit various conditions. Moreover, in the present invention, high fail-safe performance can also be obtained. In other words, even if the force that the wheel receives from the ground is transmitted to the cam follower as a force in the vehicle width direction via the rotary marine member and the cam interlocking body, the cam follower will not move the cam body toward the reference circle (
A state in which the state is in contact with a circle centered on the rotation center of the cam body and whose radius is the distance between the contact point with the cam follower on the outer peripheral surface of the cam body at the neutral rotation position and the rotation center, that is, the neutral state In this case, the above-mentioned force is stopped by the cam body that the cam follower contacts, and even if the cam body receives a force in the vehicle width direction from the cam follower, the cam body is not rotated thereby. That is, since the rotational position of the cam body does not change, in the above case, the movement of the cam follower and the cam interlocking body in the vehicle width direction, and furthermore, the inadvertent steering rotation of the rear wheel is prevented. Therefore, when the rear wheels are not steered, or when the cam body cannot be rotated in an emergency, the neutral position (steering angle 0 state)
It is possible to reliably hold the rear wheel in that position. As described above, in the rear wheel steering mechanism according to the present invention, the degree of freedom in setting the rear wheel steering pattern is high, and high fail-safety can be obtained. In addition, when the above-mentioned microcontrollable cam is used as the cam body, the second cam face has a distance from the rotation axis that is larger than the distance between the contact point of the cam body with the cam follower and the rotation axis at the neutral rotation position. When it comes into contact with the cam follower, the cam follower is pushed by the cam body and moved in the vehicle width direction. That is, in the case of a microcontrollable cam, the second cam face functions as the cam surface.

[Explanation of Examples]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 schematically shows the overall configuration of a four-wheel steering vehicle equipped with the rear wheel steering mechanism 1 of this example. The front wheel steering mechanism 2 can use a boat fishing mechanism,
In this example, a rack and pinion steering mechanism is used. This means that the rotation of the steering wheel 3 transmitted via the steering shaft 4 is transmitted to the gear box 5.
This movement of the rack rod 6 is converted into a movement in the vehicle width direction, and this movement of the rack rod 6 is further converted into a rotation about the axis 9.9 of the knuckle arms 8, 8 via the tie rods 7.7 at both ends. be done. The rotation of the knuckle arms 8, 8 causes the front wheel (1) to rotate. (1) is designed to be steered. On the other hand, as shown in FIGS. 1 and 2, the rear wheel steering mechanism 1 is connected to the rear end of an input shaft 12 extending in the longitudinal direction of the vehicle in a case 11 fixedly supported by a vehicle body member such as an axle beam 39. connected to the input shaft 12
The cam body 13 is rotated around its axis by the rotation of the cam body 13.
A pair of rotating rollers 14, 14 are provided as cam followers that face each other in the vehicle width direction with the cam body 13 in between and come into contact with the outer peripheral cam surface of the cam body 13. Further, the rear wheel steering mechanism 1 is provided with a movable rod 15 as a cam interlocking body, which is slidably supported by the case 11 in the vehicle width direction and supports the pair of cam followers 14, 14 at an intermediate portion. The movable rod 15 is housed inside the case 11 so as to surround the cam body 13, and is integrated with a cam follower support section 16 made of a frame-shaped member with open upper and lower walls, and both ends of the cam follower support section 16, respectively. A pair of left and right slide shaft portions 17 that extend in the vehicle width direction and protrude from each other. It has IT. In the cam follower support part 16, bolt support shafts 18 installed between the front wall part 16a and the rear wall part 1 (ib) as shown in FIG. and this bolt support shaft 1.
The rotary roller 14 is rotatably supported via a bearing 20 on a collar 19 which is mounted on the collar 19 so as not to be relatively rotatable. Furthermore, the sliding shaft 17 of the moving rod 15 is supported by shaft supports 11a provided at both ends of the case 11 via a slide bearing 21 and a rubber bush 22 so as to be slidable in the vehicle width direction. In this example, each slide shaft portion 1 of the moving rod 15 is
Tie rods 25, which are connected to the rear wheels 23 via knuckle arms 24, are connected to the tip portions of 7.17 as rear rotary marine members. On the other hand, in the case of this example, the cam body 13 has the above-mentioned rotating rollers 14, 14 on its outer periphery, as shown in FIG.
On both sides of the roller opposite to the roller !4 at the neutral rotation position as shown in FIG. , the distance from the rotation axis 0 is the distance between the contact point of the cam body 13 with the rotating roller 14 at the neutral rotation position and the rotation axis 0 (hereinafter, this is referred to as the roller distance).
A cylindrical inner surface that is smaller than
A concave portion 26 is provided. Further, in a portion having a larger rotational angular position range than this -th concave surface portion 26, the distance from the rotational axis 0 is larger than the roller distance, and the distance J,! A second cam surface 27 is provided in which I gradually increases as the rotational angular position increases. Further, a first cam surface in the form of a cylindrical outer surface whose distance from the rotation axis 0 is larger than the roller distance is provided at a portion on the outer periphery of the cam 13 that faces the first concave surface portion 26 across the rotation axis 0. 28 faces the second cam surface 27 across the rotation axis O, F! The distance between the rollers is smaller than the roller distance (the second four-sided portions 29 are provided for allowing the rotating rollers 14 to move inward in the vehicle width direction. Therefore, the cam body 13 rotates from the neutral rotation position,
As shown in FIG. 3 (bl), when the first cam surface 28 faces the rotating roller I4 on the right side in the figure, the rotating roller ■4 on the left side faces in the vehicle width direction with the rotating roller 14 and the cam body 13 in between. The fourth surface portion 26 faces the first cam surface 28. Since the distance from the rotation axis 0 of the first cam surface 28 is 1 distance greater than that of the roller, at this time, the right rotating roller 14 is closer to the first cam. outward in the vehicle width direction (
(in the direction away from the rotational axis O), and on the other hand,
The left rotating roller 14 is inward in the vehicle width direction (the direction that corresponds to the outward direction of the one rotating roller 14 in the vehicle width direction)
The moving rod 15 supporting these rotating rollers 14, 14 is slid in the direction of arrow R in FIGS. 1 and 2. The accompanying movement of each tie rod 25, 25 in the vehicle width direction causes the rear wheels 23 to be steered. Furthermore, the rotation angle of the cam body 13 increases, and as shown in FIG.
As shown in FIG. 1, when the second concave surface portion 29 faces the rotating roller 14 on the right side in the figure, the second cam surface 27 faces the rotating roller 14 on the left side. At this time, the left rotating roller 14 is pushed outward in the vehicle width direction by the second cam surface 27, while the right rotating roller 14 is pushed inward in the vehicle width direction (outside the left rotating roller 14 in the vehicle width direction). In this case as well, the moving rod 15 is slid in the vehicle width direction, thereby steering the rear wheels 23. Moreover, in this case, a pair of rotating rollers 14, 1
4 and the moving rod 15 in the vehicle width direction are opposite to the above case in which the right rotating roller 14 is pushed by the cam surface (in the direction of the arrow in FIGS. 1 and 2). The steering direction of the wheels is also reversed. Therefore, if the steering direction of the rear wheels in the former case is the same phase direction, the steering direction of the rear wheels in the latter case is the opposite phase direction. In other words, by changing the amount of rotation of the cam body 13,
By changing the cam surface that pushes the rotating roller 14,
This allows the steering direction of the rear wheels 13 to be changed. Further, in the case of FIG. 3, the case is shown in which the cam body 13 is rotated counterclockwise in the figure, but when it is rotated clockwise, the rotating roller 14 can be moved to the first cam surface 2.
8 and the second cam surface 27 to steer the rear wheels 23. In this case, the first cam 28 pushes the rotating roller 14 on the left side in the figure. , the second cam surface 27 is connected to the right rotating roller 1
4, the steering direction of the rear wheels is opposite to that when the cam body 13 is rotated counterclockwise. That is, by changing the rotation direction of the cam body 13,
The steering direction of the rear wheels 23 can be changed. Furthermore, if the distance between the cam surface and the rotation axis O changes,
The distance that the cam surface pushes and moves the rotating roller 14 also varies. Therefore, if the cam surface of the cam body 13 is formed so that the distance between the cam surface and the rotation axis O changes depending on the rotational angular position of the cam body 13, as shown in this example, the cam By changing the amount of rotation of the body 13, the amount of rolling of the rear wheels 23 can also be changed. The cam body 13, which is thus rotated by a predetermined angle in a predetermined direction, pushes the rotating roller 14 and steers the rear wheel 23 in a predetermined direction by a predetermined angle, as shown in FIGS. 1 and 2. , is fixedly disposed within the case 11 and rotationally driven by an electric motor 30 operatively connected to the input shaft 12 . Further, this electric motor 30 is rotationally controlled by a control means 31 constituted by a micro combinator. In this example, the electric motor 30 receives an input shaft via the reduction mechanism 40. The speed reduction mechanism 4
0 is attached to the small gear 40a attached to the motor shaft 30a of the electric motor 30 and the front end of the input shaft 12,
It is composed of a large gear 40b that meshes with the small gear 40a. By using this speed reduction mechanism 40, it is possible to obtain a large rotational torque for the cam body 13. On the other hand, the control means 31 includes a vehicle speed sensor 32 and a steering angle sensor 33 that detects the steering angle (rotation angle) of the steering wheel 3, as shown in FIGS. 2, 5, and 6.
, and an A/D conversion signal from a rotational position detector 37 consisting of a rotational potentiometer or the like provided on the input shaft 12 or the motor shaft 30a of the electric motor 30 are input as control information. There is. Further, the control means 31 is provided with the following means as shown in FIGS. 5 and 6, which are substantially realized by a program. The first is a lateral G calculation means 35 that calculates the lateral G that theoretically occurs when turning, etc., based on information from each signal value from the vehicle speed sensor 32 and the steering angle sensor 33. The second is a rear wheel turning angle determining means 36 which receives the lateral G information from the lateral G calculation means 35 and determines the direction in which the rear wheels 23 should be steered and the amount of steering thereof. Furthermore, the third method is to determine the direction in which the cam body 13 should be rotated and its rotation angle based on the rear wheel steering information received from the rear wheel steering angle determination means 36, and to determine the rotation angle in which the cam body 13 is to be rotated based on the rear wheel steering information received from the rear wheel steering angle determination means 36, and to determine the rotation angle in which the cam body 13 should be rotated. A motor control means 38 receives the bank signal and controls the motor drive circuit 30b. In addition, lateral G means the lateral acceleration that acts on the center of gravity of the vehicle, and this is approximately calculated as a function of the steering angle (θ) from the neutral position of the front wheels and the vehicle speed (V) using the following formula: [Here, l is the size of the wheel base, and K is a constant for correction. ] As can be clearly seen from this relational expression, the lateral G increases as the vehicle speed increases when the front wheel steering angle is constant, and increases as the front wheel steering angle increases if the vehicle speed is constant. The control means 31 controls the driving of the electric motor 30 and the rotation of the cam body 13 according to the driving conditions by the above-mentioned means, so that the rear wheels 23 can be controlled so as to achieve optimal driving performance. Perform steering. In this example, rear wheel steering control is performed using the lateral G calculated by the lateral G calculation means 35 as a reference and the steering angle as auxiliary control information. An example of this is the 7th example.
This will be explained along the flowchart shown in the figure. First, vehicle speed information from the vehicle speed sensor 32 and! 2 Steering angle information from the steering angle sensor 33 is read (SIOI, 3(1)2), from which lateral G is calculated (S(1)3), and the magnitude of this lateral G, etc. In response to this, the rear wheels are steered in a predetermined direction and at a predetermined angle. The size of lateral G is 0.1 G or less (YES in 5 (1) 4)
, Steering angle (steering angle here refers to the rotation angle of the steering wheel itself, not the turning angle of the front wheels. The front wheel turning angle is the steering angle divided by the overall gear ratio. ) is greater than a predetermined value (for example, 240'), then (S(1
)5: YES), the rear wheels 23 are steered to the opposite phase (S(
1)7), On the other hand, when the magnitude of lateral G is 0.1G or less (S
(1) 4: YES), and the steering angle is smaller than the predetermined value (S (1): 5: No), the lateral G
If the size of is thicker than 0.1G and less than 0.2G, then (
S (1) 4 is N01S (1) 6 is YES), rear wheel 23
in the so-called 2WS state ((3 (1) 8
). Furthermore, if the magnitude of the lateral G is larger than the above case (NO in S l 06), the rear wheels 23 are steered to the same phase, and in this case, according to the magnitude of the lateral G (3 ( 1)9,
3111, 3113), and also controls the amount of steering of the rear wheels 23 (31(1), 5112, 5114, 3115). That is, when LAG is smaller than the predetermined value, the rear wheel 2
3 are made to have opposite phases, and when the lateral G is larger than a predetermined value, the rear wheels 23 are steered to the same phase. This is because when the lateral G is small, it generally occurs when turning at low speed, and by steering the rear wheels 23 in the opposite phase at this time, the maneuverability of the vehicle can be improved. be. On the other hand, lateral G generally increases when turning at medium or high speeds, and by steering the rear wheels 23 in the same phase at this time, the lateral shear of the vehicle is suppressed and the running is stabilized. This is because direction changes can be made quickly while improving performance. In this case, the larger the lateral G, the larger the steering ■, but this is because the larger the lateral G, the stronger the tendency of the vehicle to skid, and this is because the steering wheel is required to suppress this. This is because the wheel steering ■ also increases. Also, when the lateral G is within a certain range, the rear wheel 23
This is because when the magnitude of lateral G is within the predetermined range as mentioned above, steering performance is better if the rear wheels 23 are not steered. be. Furthermore, if the magnitude of the lateral G is less than a predetermined value (including 0) and the steering angle is also less than a predetermined value (including 0) (YES in S I O4, NO in 3 (1) 5) ,
That is, even when the vehicle is traveling straight ahead, the rear wheels 23 are not steered. Note that the reference value of the lateral G shown in the above flowchart is a rough one, and if it is further subdivided and the rear wheel steering conditions are determined accordingly, the driving performance can be further improved. Furthermore, if the steering amount in the opposite phase increases as the steering angle increases, the maneuverability in the low speed range is further improved. Further, when the rear wheels 23 are steered in accordance with the lateral G, the steering direction and the amount of steering are determined by the rear wheel steering angle determining means 36 based on the calculated magnitude of the lateral G. be done. Then, in response to this t&rotation blue information, the motor control means 38 controls the rotation of the electric motor 30 to rotate the cam body 13 in a predetermined direction by a predetermined angle, so that the rear wheels 23 are adjusted to the rear wheel steering angle. The vehicle is steered to match the target steered angle determined by the determining means 36. Additionally, if the magnitude of lateral G acting on the vehicle changes during a turn, the motor control means 38 controls the rotation of the electric motor 30 and the cam body 13 to steer the rear wheels depending on the situation. is carried out, and when there is no longer a need to steer the rear wheels, the rear wheel steering angle determining means 36 determines the steering position (O), thereby returning the cam body 13 to the neutral rotation position. That is, the rear wheels 23 are returned to the neutral state with the steering angle O. As described above, in this example, the theoretical lateral G that occurs when turning is calculated in real time from the front wheel turning angle determined by the vehicle speed and the steering angle using the above relational expression. Rear wheel steering is controlled based on G. In other words, the lateral G that occurs when turning, etc. is predicted in advance, and the rear wheel steering is controlled based on this, and when the rear wheels are steered in the same phase, the amount of steering is determined by the magnitude of the lateral G. It is decided according to the Therefore, the amount of steering of the rear wheels, especially 1.
・Since it is possible to always set the steering angle at the same level in the high speed range to the optimum size according to the situation, turning performance in the medium and high speed ranges can be greatly improved. . The amount of lateral shear of a vehicle when turning at medium or high speeds changes from moment to moment depending on the amount of centrifugal force (lateral G), and the amount of centrifugal force also depends on the vehicle speed and steering control.・Varies from moment to moment depending on the rotation angle, that is, the turning radius of the vehicle. Therefore, as mentioned above, by calculating the lateral G in real time from the vehicle speed and the front wheel steering angle, and determining the amount of rear wheel steering accordingly, it is necessary and appropriate to always suppress the vehicle's sideslip. This is because the amount of steering of the rear wheels can be set to a certain value. Also, when determining rear wheel steering conditions based on lateral G, the cam body 13 is rotationally driven by the electric motor 30 controlled by the control means 31 as described above, so that the rear wheel 23 can be steered. The degree of freedom in setting the steering amount, in other words, the degree of freedom in setting the steering ratio, is extremely high, and the rear wheel turning pattern can also be set in a wide range of ways. Also, the rear wheel is 237! ! <Even if the force received from the ground is transmitted to the moving rod 15 as a force in the vehicle width direction via the tie rods 25, etc., the rotating roller 14 is applied to the cam body 13 in the reference circle C (centered around the rotation center of the cam body 13). , and a circle whose radius is the distance between the rollers), that is, in a neutral state, the above force is stopped by the cam body 13 via the rotating roller 14, and Even if the rotating roller 14 pushes the cam body 13 with the above force, this causes the cam body 13 to
is never rotated. That is, when the rear wheels are not steered, the rear wheels 23 can be reliably held at the neutral position (steering angle O), resulting in extremely high fail-safe performance. Moreover, if an abnormality occurs in the vehicle speed sensor 32 or the like, if this is detected and the cam body 13 is forcibly returned to the neutral rotation position, the fail-safe property is further improved. By the way, various aspects of the rear wheel steering mechanism 1 of the present invention are conceivable in addition to the above-mentioned embodiments. For example, the rear wheel steering mechanism shown in FIG.
A pair of arm members 41 whose rear ends are supported pivotably around a vertical axis, and which face each other with the cam body 13 in between.
．． 41, and a rotating port 14 provided as a cam follower is supported at the intermediate portion of each arm member 41.4-1. Further, the pair of arm members 41, 41 are connected at their front ends via a connecting body 42 provided as a cam interlocking body, and a rear wheel steering member is attached to both ends of this connecting body 42. Tie rods 25 are connected to each other. When the rotating roller 14 is rotated by the cam body 13, the arm member 41.41 is swung in the arrow direction or the R direction by being pushed by the outer circumferential cam surface of the cam body 13. 42 in the vehicle width direction, the tie rod 25
Also in the rear wheel steering mechanism of this embodiment in which the rear wheels are steered by applying a movement in the vehicle width direction to the vehicle width direction, an electric motor is interlocked and connected to the input shaft 12 that rotates the cam body 13. Similarly, various rear wheel steering patterns can be set while achieving high fail-safety. Furthermore, a minutely controllable cam as shown in FIG. 9 may be used as the cam body 13. This finely controllable cam has an example (upper side) of the axis connecting the contact points with each cam follower 14 and 14 at the neutral rotation position as shown in FIG. The first cam face 43 has a first cam face 43 whose distance from the rotation axis O becomes smoothly smaller as the rotational angular position from the contact point increases with respect to a reference circle C whose radius is the length of (the roller distance) . On the other hand, on the other side (lower side) of the axis, a second cam face 44 whose distance from the rotational axis O with respect to the reference circle C smoothly increases as the rotational angular position from the contact point increases. has. In this example, the cam follower 1 on the outer periphery of the cam body 13
4. A non-operating surface 34 having a cylindrical outer surface shape that coincides with the reference circle in a predetermined rotation angle position range in a clockwise direction and a counterclockwise direction from the contact point is provided on both sides of the contact point 4.14 facing each other. . And each inactive surface 34
, 34 are formed with the first cam face 43 and the second cam face 44, which are constituted by a convex curved surface having a substantially semi-cylindrical outer surface. Further, the cross-sectional length between the first cam face 43 and the second cam face 44 passing through the rotational axis 0 is configured to be equal to the diameter of the reference circle C, etc. at any rotation angle position. There is. In the cam body 13 configured as described above, even if the cam body 13 rotates from the neutral rotation position, the cam follower 14. 14 is not subjected to any cam action from the cam body 13. In other words, the rear wheels are not steered at all. When the cam body 13 further rotates so that the second cam face 44 faces one cam follower 14 and the first cam face 43 faces the other cam follower 14, the second cam face 44 and the rotation axis center 0 as described above. Since the distance between them is larger than the radius of the reference circle C, the one cam follower 14 is pushed by the second cam face 44. In addition, since the cross-sectional length between the first cam face 43 and the second cam face 44 passing through the rotation axis 0 is the diameter length of the reference circle C and the distance, in the above case, the other cam follower 14 is It is allowed to move inward in the vehicle width direction (in a direction that matches the outward direction in the vehicle width direction of the negative cam follower 14), and as a result, each cam follower 14.14 is moved in the vehicle width direction. As a result, the rear wheels are steered. The second cam face 44, which functions as a cam surface, moves toward the rotation axis 0 as the rotation angle position increases.
Since the distance from the rear wheels increases gradually, as the amount of rotation of the cam body 13 increases, the amount of steering of the rear wheels also increases. Further, the steering direction of the rear wheels can be changed by controlling the rotation direction of the cam body 13. That is, by changing the rotation direction of the cam body 13,
The rear wheels can be steered in the same phase and in opposite phases. By the way, in the case of the cam body 13 of this example, since the second cam face 44 is formed in a wide range, the setting area of the cam surface can also be made large. Therefore, unlike the cam body shown in FIG. 3, the ratio of the amount of change in the distance between the cam surface and the rotation axis ○ to the rotation angle of the cam body 13 can be made small. That is, it is possible to reduce the amount of movement of the cam follower 14 when the cam body 13 is rotated by a certain angle, thereby shifting the steering of the rear wheels to the minute side ff.
You will be able to do full. In this case, −
This is particularly advantageous in steering in the same phase direction where the amount of steering is small in terms of a. In addition, in a cam body provided with a concave portion 26 as shown in FIG. The forming part (point of change in wheel steering direction) cannot be polished to a smooth finish. However, when the cam face is constructed of a convex curved surface having a substantially cylindrical outer surface, as in this example, the cam face and the inflection point forming part on the cam surface can be ground without any problem, and the cam face can be Can be finished smoothly. Due to this and the ability to reduce the rate of change of the cam curved surface as described above, it is possible to eliminate the feeling of catching when the rear wheels are steered, especially during return steering rotation. Further, as described above, if the setting area of the cam surface is made large, fine control of rear wheel steering can be achieved while downsizing the cam body. Further, such miniaturization of the cam body contributes to miniaturization of the rear wheel steering mechanism itself. Note that the scope of the present invention is not limited to the above-described embodiments (for example, it goes without saying that the rear wheel steering conditions can be determined in accordance with various conditions other than lateral G). Furthermore, the shape of the cam body can be modified in various ways. Also, various types of motors such as a DC motor and a stepping motor can be used as the electric motor.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a rear wheel steering mechanism according to an embodiment of the present invention viewed diagonally from the front, and FIG. 2 schematically shows the overall configuration of a four-wheel steering vehicle in which the rear wheel steering mechanism according to the embodiment is adopted. Figure 3 is a diagram illustrating the operation of the cam mechanism by the cam body and rotary roller according to the embodiment when viewed from the direction of the arrow mm line in Figure 1, and Figure 4 is a diagram according to the embodiment. FIG. 5 is a system block diagram, FIG. 6 is a control block diagram, FIG. 7 is a flowchart showing an example of rear wheel steering conditions, and FIG. 8 is a diagram showing how the rotating roller is supported by the moving rod. FIG. 9 is a diagram showing a rear wheel steering mechanism according to another embodiment when viewed in a plane direction, and FIG. 9 is a diagram showing a modification of the cam body. 12...Input shaft, 13...Cam body, 14...
・Cam follower (rotating roller), 15... cam interlocking body (moving rod), 25... rear rotary marine member (tie rod),
27...Cam surface (second cam surface), 2nd...cam surface (
30... Electric motor, 31... Control means, 42... Cam interlocking body (connecting body), 43... First cam face, 44... Second cam face, C...
・Reference circle.

Claims (2)

[Claims] (1) A pair of cams connected to an input shaft extending in the vehicle longitudinal direction or vertical direction, and driven to rotate around the axis by rotation of the input shaft; a pair of cam followers that are opposed to the outer peripheral cam surface of the cam pair and are supported so as to be movable in the vehicle width direction, and as the pair of cam followers move in the vehicle width direction, the vehicle width an electric motor whose rotation is controlled by a control means is interlocked with the input shaft, and an outer cam surface of the cam body is configured to move the cam body from a neutral rotation position. A rear wheel steering mechanism, characterized in that the cam follower is formed to push the cam follower in a predetermined direction in the vehicle width direction when rotated, and a rear wheel steering member is connected to the cam interlocking body. . (2) On one side of the axis connecting the contact points with each cam follower at the neutral rotation position, from the rotation axis A pair of left and right first cam faces each having a substantially cylindrical outer surface shape whose distance gradually decreases as the rotational angular position from the contact point increases is placed on the other side of the axis from the rotation axis with respect to the reference circle. The first cam face and the second cam face each have a pair of left and right second cam faces each having a substantially cylindrical outer surface shape, the distance of which gradually increases as the rotation angle position from the contact point increases, and the first cam face and the second cam face pass through the rotation axis. 2. The rear wheel steering mechanism according to claim 1, wherein a cam body is used, the cam body having a cross-sectional length substantially equal to the diameter of the reference circle at any rotation angle position.