JPH08337106A - Wheel steering device - Google Patents

Abstract

PURPOSE: To avoid occurrence of troubles such as to drop in suspension rigidity and to limit a steering angle at a small value, and independently control steering operation of each wheel, with a wheel steering device constituted by use of components of a suspension device. CONSTITUTION: Rear wheel steering actuators 50 and 51 are laid at positions off a rotational center line of right and left rear wheels 128 and 129 in a longitudinal direction. Furthermore, a moving shaft and a casing of each of the actuators 50 and 51 are jointed to wheel support members 125 and 126, and a sub-frame 127 via rubber bushes respectively at joint sections 120 and 122. Also, the actuators 50 and 51 respectively have a built-in screw mechanism as well as a built-in electric motor, and are controlled for expansion and contraction via rotational control of a motor. The members 125 and 126 turn around the connection points thereof with lower arms 40 as a center, thereby controlling the directions of the right and left rear wheels 128 and 129 independently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wheel steering device.

[0002]

2. Description of the Prior Art As a type of wheel steering system, the actual fair 2-22
As described in Japanese Patent No. 389, some steering is performed by moving an arm constituting a suspension. Both ends of the lower arm extending substantially parallel to the center line of rotation of the wheel are connected to the wheel support member and the vehicle body via rubber bushes for absorbing vibration, and the end on the side connected to the vehicle body is rubberized by an actuator. By moving the bush while elastically deforming it, the directions of the wheel support member and the wheel can be changed. As the lower arm in this case, one or two of the two lower arms of the strut suspension are planned. When only one is moved by the actuator, steering is performed by rotating the wheel support member around the connection point between the lower arm and the wheel support member on the side that is not moved, and the two are moved. When moved by the actuator, the two are moved in opposite directions to perform steering.

The actuator includes a main body, a movable shaft movably supported by the main body in the axial direction, and a drive mechanism for moving the movable shaft with respect to the main body. The main body is fixed to the vehicle body in a posture extending in the width direction, and both ends of the movable shaft are engaged with the left and right lower arms. In this way, by steering the wheels by moving the lower arm, the components of the suspension device can also be used as the components of the steering device.
The structure of the entire vehicle can be simplified.

[0004]

However, in this wheel steering system, the maximum steering angle cannot be made too large. In order to increase the maximum steering angle, it is necessary to make the rubber bush soft and large, but with such a rubber bush, the mounting rigidity of the wheel to the vehicle body becomes low, and it becomes difficult to secure running stability. is there. Therefore, the present invention makes it possible to easily increase the maximum steering angle while using the constituent elements of the suspension device as the constituent elements of the wheel steering device, and it is not necessary to deform the rubber bush for steering. It was made as a subject to obtain.

[0005]

The object of the present invention is to provide a telescopic actuator having a first connecting portion and a second connecting portion, and capable of controlling extension and contraction between the both connecting portions, from the rotation center line of the wheel to the vehicle front-rear direction. At a position spaced apart from each other in a direction at an inclination angle of 45 degrees or less with respect to the rotation center line of the wheel, and the first connecting portion to a wheel supporting member that rotatably supports the wheel,
This is solved by connecting the second connecting portion to each of the vehicle body side members. For steering the wheels, it is desirable to dispose the telescopic actuator parallel to the center line of rotation of the wheels, but it is also possible to tilt it to some extent depending on the situation.
However, the steering angle per unit expansion / contraction amount of the expansion / contraction actuator decreases as the inclination angle of the wheel with respect to the rotation center line increases. In addition,
The vehicle body-side member means a member on the vehicle body side with respect to the wheel support member, and includes not only a member fixed to the vehicle body but also a member movable relative to the vehicle body.

[0006]

In the wheel steering system according to the present invention, the actuator can be arranged between the wheel supporting member and the vehicle body-side member in the same manner as a lateral member such as a normal lateral rod or tie rod, and a rubber member can be used. Since it is not necessary for the bush to have a particularly large deformability, even if the maximum steering angle is increased, the mounting rigidity of the wheels does not decrease, and traveling stability can be secured.

Further, if necessary, the left and right wheels can be steered independently. For example, as described above, when an abnormality occurs in one of the actuators and steering becomes improper, the other actuator is controlled to prevent or reduce its instability so that the occurrence of the abnormality occurs. The effect can be positively reduced, which is effective as a fail-safe measure. In addition, steering can be performed in consideration of toe changes due to braking force, lateral force, bumps, rebounds, and the like. For example, an acquisition unit that acquires the braking force applied to the tire, the lateral force, the tire bump amount, the rebound amount, and the like is provided, and the target steering angle is corrected based on these acquisition results. The bump is a stroke on the compression side of the suspension, and the rebound is a stroke on the tension side. In the past, passive measures were taken by optimizing the suspension geometry and compliance, but this can be controlled actively and continuously, improving vehicle running stability and reducing suspension Design is simple. The relationship between the bump / rebound size and the toe-in / toe-out is as shown in FIG. 1, for example. This relationship depends on the geometry of the suspension and the compliance, and is different for each vehicle type. Normally, the performance on the weak understeer side is preferred, so the front wheels are set to bump toe-out and the rear wheels are set to bump toe-in. According to the figure, in the rear wheel strut type suspension, if the bump stroke is 40 mm, the suspension leans toward the toe-in side by about 0.2 degree.
Although this amount of change appears small, it is directly connected to the lateral force generated by the tire and the self-aligning torque, so a minute value of this magnitude has a large effect. In the usual suspension design, efforts are made to optimize the shape itself of the graph shown in FIG. 1, but any shape may be used as long as each wheel is provided with an actuator, and the shape may be known.
The same applies to the braking force and the lateral force.

Further, according to the present invention, wheel steering can be performed by configuring at least one of the lateral control arms, which is a component of the suspension device, by an extendable actuator. Therefore,
Most of the configurations can be shared between the 2WS and 4WS, and it becomes easy to manufacture vehicles of both the 2WS and 4WS modes.

[0009]

As described above, according to the present invention, a wheel steering system can be constructed by replacing at least one of the arms constituting the suspension with an actuator capable of controlling expansion and contraction, and the device can be mounted on the vehicle body. Since this is the same as mounting an arm of a normal suspension, it is not necessary to deform the rubber bush for steering, a large steering angle can be secured without lowering mounting rigidity, and the degree of freedom in vehicle design can be increased. Further, if necessary, each wheel can be independently controlled for steering, so that fine steering control can be performed. For example, it is possible to cancel or reduce the influence when an abnormality occurs in the wheel steering device, and to adjust the steering angles of the left and right wheels according to the braking force, the lateral force, the bump and the amount of rebound. It can be changed and the running stability can be improved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, some of the preferred embodiments of the invention will be enumerated and related explanations will be given as necessary. (1) The wheel steering device according to claim 1, wherein the actuator is expanded and contracted by a screw mechanism having zero reverse efficiency. The screw mechanism having zero reverse efficiency includes a female screw member and a male screw member that are screwed with each other, and if a rotational force is applied to one of the two screw members, the both screw members can be relatively moved in the axial direction. Is a screw mechanism that cannot be relatively rotated even when an axial force is applied to both screw members, and can be obtained by setting the lead angle of the screws of both screw members to be less than or equal to the friction angle. If the actuator includes such a screw mechanism, the actuator will not expand or contract even if it receives an external force in the axial direction, so it is necessary to continue to give a large amount of energy to the drive source in order to hold the wheel in a fixed direction. In addition, even if the drive source is damaged, the actuator does not expand or contract unintentionally, and the same function as a lateral member such as a normal lateral rod or tie rod is achieved. (2) The actuator includes a casing including one of the first connecting portion and the second connecting portion, a movable shaft including the other of the first connecting portion and the second connecting portion, and the actuator and the movable shaft. A screw mechanism including a combined male screw member and female screw member, one of both screw members being immovable relative to the casing, and the other of both screw members being immovable relative to the movable shaft; and a screw mechanism thereof. 2. The wheel steering device according to aspect 1, further comprising: a rotation driving device that relatively rotates the male screw member and the female screw member. (3) The wheel steering device according to aspect 2, wherein the rotation drive device includes an electric motor capable of controlling a rotation angle. (4) The wheel steering device according to any one of claims 1 to 1 including a controller including a right control unit and a left control unit that respectively control the steering angles of the left and right wheels. (5) Travel speed, rudder angle, bump, rebound, braking force,
A controller comprising an active control unit for controlling the toe-in of the wheel by controlling the actuator based on at least one of lateral forces.
The wheel steering system according to any one of the first to fourth embodiments. (6) A wheel steering system in which the steering tie rod is replaced by the actuator according to any one of claims 1 to 5. The tie rod coupling type steering device in which the movable member of the main actuator that assists the steering force of the driver is coupled to the wheel support member by the tie rod is used in the active 4W.
This is a useful configuration when a fine adjustment actuator is required in addition to the main actuator when the S function is added. (7) A 4WS vehicle in which the wheel steering device according to any one of claims 1 and 5 is provided for the rear wheels. (8) A 4WS vehicle in which the wheel steering device according to any one of claims 1 and 5 is provided for both the rear wheels and the front wheels.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, steering of the left and right rear wheels of a 4WS vehicle is
This is done independently by actuators attached to the left and right rear wheels. As shown in FIG. 2, one of two lower arms 40 of the left and right rear wheels 128 and 129 of a vehicle equipped with a strut-type rear wheel suspension device is capable of extending and controlling rear wheel steering. In place of the actuators 50 and 51, the wheel supporting members 125 and 126 that rotatably support the rear wheels 128 and 129 are connected to the lower arm 40 by controlling the expansion and contraction of the rear wheel steering actuators 50 and 51. The steering is performed by rotating the point.

The left and right rear wheel steering actuators 50 and 51 will be described. The actuator 5
Since 0 and 51 are the same, only the left rear wheel steering actuator 50 will be described below.
FIG. 3 is a detailed view of the left rear wheel steering actuator 50. The left rear wheel steering actuator 50 includes a hollow cylindrical casing 52. The casing 52 is configured by closing both ends of a thin-walled cylindrical main body portion 54 having a constant diameter and extending straight, by a pair of closing members 56, 58. A movable shaft 60 is attached to the casing 52.
Is coaxially penetrated. The movable shaft 60 is positioned by the closing members 56 and 58 so as to be coaxial with the casing 52 and supported slidably in the axial direction. Further, the movable shaft 60 is spline-fitted with the closing member 56 to prevent rotation with respect to the casing 52.

A brushless motor 64 is arranged in the casing 52. The brushless motor 64 is configured such that a rotor 66 and a stator 68, both of which have a cylindrical shape, are arranged coaxially and the rotor 66 penetrates the stator 68. The rotor 66 is of a four-phase type in which four permanent magnets are mounted in a state in which the polarity is alternately changed between the N pole and the S pole in the circumferential direction. The stator 68 corresponds to the rotor 66, and is of a four-phase type in which the amateur coil 70 is mounted in a state where the polarity alternates between the N pole and the S pole in the circumferential direction. The stator 68 is arranged outside the rotor 66 with a suitable magnetic gap. On the other hand, the movable shaft 60 is coaxially inserted through the center hole of the rotor 66. The rotor 66 is arranged on the outer peripheral surface of the movable shaft 60 at appropriate intervals, and its both ends are rotatably and immovably supported by a pair of bearings 74 mounted on the casing 52. Therefore, if the amateur coil 70 of the stator 68 is excited and a rotating magnetic field is formed, the rotor 66 is rotated as the rotating magnetic field rotates.

The rotation of the motor 64 is converted into a linear motion by a screw mechanism 78 as a motion converting function, and the movable shaft 60 is moved.
Is transmitted to A male screw is formed on a part of the outer peripheral surface of the movable shaft 60 to form a male screw member 80, and a nut 82, which is a female screw member screwed to the male screw member 80, is supported by the casing 52 rotatably and axially immovably. Has been done. The screw mechanism 78 is configured by screwing the male screw member 80 and the nut 82 together. In this embodiment, the male screw member 80 and the nut 82 are trapezoidal screws.

In the present embodiment, the rotation of the motor 64 is not directly transmitted to the screw mechanism 78, but is transmitted via the speed reducer 90 in order to boost the rotational force of the motor 64. The speed reducer 90 is configured such that two planetary speed reducers 92, 94 are connected in series with each other. As is well known, the planetary type speed reducers 92, 94 are arranged between (a) one sun gear 100, (b) one ring gear 102, and (c) those sun gear 100 and ring gear 102. A plurality of planetary gears 104, and (d) a carrier 104 that rotatably supports each planetary gear 104 while keeping their relative positional relationship constant.

The two ring gears 102 are the casing 5
It is fixed to 2. The two sun gears 100 are both hollow, and the movable shaft 60 coaxially penetrates the two sun gears.
The planetary type speed reducers 92 and 94 are arranged in the axial direction of the movable shaft 60. These planetary type speed reducers 92, 9
Among the four, those closer to the rotor 66 are referred to as the input side speed reducer 92, and those closer to the screw mechanism 78 are referred to as the output side speed reducer 94. In the input side speed reducer 92, the sun gear 100
Is rotatably connected to the rotor 66 integrally therewith, while in the output reduction gear 94, the sun gear 100 is
The carrier 106 of the input speed reducer 92 is rotatably coupled to the carrier 106, and the carrier 106 of the output speed reducer 94 is rotatably fixed to the nut 82 integrally therewith.

Therefore, when the rotor 66 is rotated, the sun gear 10 in the input-side speed reducer 92 is accordingly accompanied.
0 and the planetary gear 104 are rotated, the rotation speed of the sun gear 100 is reduced, and the sun gear 100 is transmitted to the carrier 106. As the carrier 106 rotates, the output-side speed reducer 9
4, the sun gear 100 and the planetary gear 104
Is rotated, the rotation speed of the sun gear 100 is reduced, and the sun gear 100 is transmitted to the carrier 106. That carrier 10
As the nut 6 rotates, the nut 82 is rotated, and its rotation is converted into a linear motion by the screw mechanism 78 to move the movable shaft 60 in a direction parallel to its axis.

The left rear wheel steering actuator 50 includes
Rotational position sensor 110 for detecting the rotational position of the rotor 66
And an axial position sensor 112 for detecting the axial position of the movable shaft 60. In addition, similarly to the right rear wheel steering actuator 51, the rotational position sensor 11
1 and an axial position sensor 113 are provided respectively. The left and right rear wheel rotational position sensors 110 and 111 are of a magnetic type (an example of a non-contact type) in the present embodiment.
It is configured by a combination of a permanent magnet 116 that rotates together with the rotor 66 and three position-fixed magnetic detection elements 118. The magnetic detection element 118 is arranged close to the permanent magnet 116 and outputs a pulse signal that changes according to the passage of the permanent magnet 116, whereby the rotational position (relative position) of the rotor 66 is detected. An example of the magnetic detection element 118 is a Hall element. The rotational position sensor 110 is used so that the rotational angle change amount of the brushless motor 64 becomes equal to a specified value during the rear wheel steering angle control.

On the other hand, the left and right rear wheel axial position sensors 112, 113 are of the potentiometer type (contact type) in this embodiment. Axial position sensor 11
2 is constituted by a combination of a slider that linearly moves together with the movable shaft 60 and a fixed electric resistor. The electric resistor is provided so as to always contact the slider,
The electric resistance value changes according to the position of the slider, and an electric signal corresponding to the change is output, whereby the axial position (absolute position) of the movable shaft 60 is detected. The axial position sensor 112 is used to initialize the rotational position of the brushless motor 64 (return to the origin) prior to the rear wheel steering control.

At the protruding end of the movable shaft 60, a cylindrical connecting portion 1 is provided.
20 is provided, the bottom of the casing 52, that is, the closing member 58 is provided with a cylindrical connecting portion 122. As shown in FIG. 2, the connecting members 120 and 122 are connected to the wheel supporting members 125 and 126 and the sub-frame 127 which is one of the vehicle body side members via rubber bushes 124, respectively. Wheel support member 125
Is the right rear wheel 128, and the wheel support member 126 is the left rear wheel 129.
Are rotatably supported, and the rear wheel steering actuators 50 and 51 extend parallel to the center lines of rotation of the left and right rear wheels 128 and 129.

In addition, it is possible to use permanent magnets of a number other than four as the rotor 64, or to use a brush motor instead of the brushless motor 64. Also, another type of actuator such as a hydraulic actuator may be used. However, for example,
In the case of a hydraulic actuator, it is necessary to be careful that the oil in and out of the cylinder must be prohibited when it is not driven.

Next, the electrical configuration of the apparatus of this embodiment will be described. The rear wheel steering control device includes a rear wheel steering controller 200, as shown in FIG. The rear wheel steering controller 200 has a computer 208, and the computer 208 has a CPU 202, a ROM 204, and a RAM 206.
Is included. A vehicle speed sensor 210, a steering angle sensor 212, a yaw rate sensor 214, left and right rear wheel rotational position sensors 110 and 111, and left and right rear wheel axial position sensors 112 and 113 are provided in the input section of the rear wheel steering controller 200. Each is connected. Vehicle speed sensor 21
0 measures the traveling speed of the vehicle. Steering angle sensor 212
Detects the steering angle θ which is the rotation angle of the steering wheel operated by the operator. Yaw rate sensor 21
4 measures the actual yaw rate γ of the vehicle. On the other hand, the brushless motors 64 of the left and right rear wheel steering actuators 50 and 51 are connected to the output section of the rear wheel steering controller 200. The brushless motor 64 is configured such that the CPU 202 is RAM 206 based on input signals from various sensors.
Is controlled by executing the control program stored in the ROM 204. Therefore, the ROM 204 stores the rear wheel steering control routine shown in FIG. 5 and the abnormality processing routine shown in FIG.

In this embodiment, as the vehicle speed sensor 210, a Doppler type ground vehicle speed sensor is used which detects the relative moving speed of the vehicle body with respect to the road surface based on the Doppler effect of the transmitted wave and the received wave reflected on the road surface. , A wheel provided with, for example, a sensor for detecting the rotational speed of the wheel and a vehicle speed estimating means for estimating the vehicle speed based on the rotational speed of the wheel detected by the wheel speed sensor Other vehicle speed detectors such as a speed-dependent vehicle speed sensor may be used. The steering angle sensor 212 includes, for example, a slit plate attached to the steering shaft and a photo interrupter attached to the column tube. The steering angle is detected based on the number of times the photo interrupter is turned ON / OFF in accordance with the size of the rotation angle of the steering wheel. However, other steering angle detectors such as rotary potentiometers are used. Good. The yaw rate sensor 214, when an angular velocity in a direction perpendicular to the vibration direction is given to an object vibrating in one axis direction,
Although the Coriolis force generated in the direction perpendicular to the vibration direction and the angular velocity vector direction is applied, other yaw rate detectors such as a fiber gyro may be used.

The software configuration of this embodiment will be described.
FIG. 5 is a flowchart showing a rear wheel steering control routine.
is there. In this routine, the vehicle traveling speed V, the actual
Wheel steering angle δ_f, Real yaw rate γ, real left rear wheel steering angle δ _rland
Real right rear wheel steering angle δ_rrBased on the target left rear wheel steering angle δ_rl´
And target right rear wheel steering angle δ_rrCalculate ´ and steer left and right rear wheels
The yaw rate feedback that drives the actuator for
4WS of the standard method is performed. First, step S101
(Hereinafter, simply referred to as S101. For other steps as well,
Same), the actual left rear wheel steering angle δ_rlAnd the real right rear wheel rudder
Angle δ_rrAre the left rear wheel rotational position sensor 110 and
And the signal from the right rear wheel rotational position sensor 111
To be detected. Next, in S102, the vehicle traveling speed
V indicates from the vehicle speed sensor 210 that the actual front wheel steering angle δ_fIs the steering angle
From the sensor 212, the actual yaw rate γ is detected by the yaw rate sensor 2
It is detected based on each signal from 14. What
For the sake of convenience in the following explanation, the value of the steering angle should be in the straight traveling state.
B) When steering to the right is positive, when steering to the left
Is negative.

Next, in S103, the target yaw rate γ ^{* is} calculated based on the vehicle traveling speed V and the actual front wheel steering angle δ _f ^.
Is determined. In this embodiment, the vehicle traveling speed V,
The relationship between the actual front wheel steering angle δ _f and the target yaw rate γ ^* is RO
It is stored in M204, and the target yaw rate is determined according to the relationship. Then, S104
Then, the difference between the target yaw rate γ ^* and the actual yaw rate γ is calculated as the yaw rate deviation Δγ, and then the left and right rear wheel steering angle change command values Δδ _rl and Δδ _rr are determined based on the yaw rate deviation Δγ. . In this embodiment,
Yaw rate deviation Δγ and left and right rear wheel steering angle change command value Δ
The relationship between δ _rl and Δδ _rr is stored in the ROM 204, and the left and right rear wheel steering angle change command values Δ are stored according to the relationship.
δ _rl and Δδ _rr are determined. At this time,
The bump / rebound amount of each rear wheel suspension may be detected, and correction such as changing the left and right rear wheel steering angle change command values Δδ _rl and Δδ _rr may be performed using the relationship shown in FIG. .

Further, in S106, the actual left rear wheel steering angle δ_rl,
Real right rear wheel steering angle δ_rr, Left rear wheel steering angle change command value Δδ_rl， Rear right
Wheel steering angle change command value Δδ_rrBased on the target left rear wheel steering angle δ
_rl´, Target right rear wheel steering angle δ_rr'Is calculated, and then S10
7, drive the left and right rear wheel steering actuators 50, 51
Is started. Next, in S108, the rear wheel steering actuation is performed.
Waiting for the time required for the operation of the data 50, 51, S10
9 shows the actual left rear wheel steering angle δ after the actuator is operated._rl， Actual right
Rear wheel steering angle δ_rrIs obtained. Then, in S110, S1
Real left rear wheel steering angle δ acquired in 09_rl, Real right rear wheel steering angle δ_rr
Based on, it is determined whether the system is abnormal,
If there is no abnormality, the processing from S102 is restarted.
If it is in an abnormal state, an abnormal process described later is performed in S111.
Will be In S110, the actual left rear wheel steering angle δ_rlAnd goals
Left rear wheel steering angle δ _rlThe size of the deviation from ´ and the real right rear wheel
Rudder angle δ_rrAnd target rear right wheel steering angle δ_rrLarge deviation from ´
If either or both are greater than the tolerance ε, then
It is determined to be in an abnormal state. That is, left and right rear wheel operation
Target values for the operation of the rudder actuators 50, 51 and the actual rudder
If the angle and the angle do not match even after considering the error factor ε,
It is in a normal state.

FIG. 6 is a flow chart showing an abnormality processing routine executed when it is determined in S110 that the state is abnormal. In this routine, the rear wheel steering actuator that is not in the abnormal state is operated to perform control so that the traveling stability of the vehicle is maintained. First, in S201, the actual left rear wheel steering angle δ _rl and the target left rear wheel steering angle δ
It is determined whether or not the magnitude of the deviation from _rl 'exceeds the allowable error ε. If the allowable error ε is not exceeded, the abnormal state is that the rear wheel steering actuator 5 of the right rear wheel 128
1, the actual right rear wheel steering angle δ _rr is acquired in S202, and subsequently, in S203, the target left rear wheel steering angle δ _rl ′ has the same size as the actual right rear wheel steering angle δ _rr. The steering angle is set in the opposite direction. After that, in S204, the left rear wheel 129 is steered to the counter side with respect to the steering angle of the right rear wheel 128 which does not perform the original steering due to the abnormality. Then, in S205, the alarm output 1 is output, and the abnormality processing ends.

If the result of S201 is YES, S20
At 6, it is determined whether the absolute value of the difference between the actual right rear wheel steering angle δ _rr and the target right rear wheel steering angle δ _rr ′ exceeds the allowable error ε. If the result is NO, it is determined that the rear wheel steering actuator 50 of the left rear wheel 129 is in an abnormal state, and S202
The same processing as the processing from S to S204 is executed in S207 to S209 by interchanging the left and right. After that, the alarm output 1 is output in S210, and the abnormality processing ends.

If the determination result of S206 is YES, it is determined that both the rear steering actuators of the left and right rear wheels 128 and 129 are in an abnormal state. In this case, in S211, the actuators 50, 51 of the left and right rear wheels 128, 129 are
To return the steering angle to zero. This process is seemingly useless, and although it seems impossible to return the steering angle to zero, this is not the case. The rotational position sensors 110 of the left and right rear wheels 128, 129 are used for the determinations in S110, S201, S206.
111 value and calculated by CPU202, RAM
The target left rear wheel steering angle δ _rl ′ and the target right rear wheel steering angle δ _rr ′ stored in 206 are used. Therefore, for example, when the left / right rear wheel rotational position sensor 110 or 111 fails or has an abnormal value due to electrical noise or the like, it is determined that the actuator is in an abnormal state although it is normal. In such a case, it is important for fail-safe to return the steering angle to zero at least without immediately abandoning the rear wheel steering control. Here, in order to return the steering angle to zero, it is necessary to recognize that the steering angle is at least zero. For this purpose, the output values of the left and right rear wheel axial position sensors 112 and 113 can be used. Since the left and right rear wheel axial position sensors 112 and 113 can output the absolute position in the axial direction of the actuator, the left and right rear wheel rotational position sensors 110 or 1
Although not as accurate as 11, it is robust against electrical noise and the like. After S211, in S212, after waiting for the time required to operate the rear wheel steering actuator 50.51, the output values of the left and right rear wheel axial position sensors 112 and 113 are acquired in S213. Here, the output value of the left rear wheel axial position sensor 112 is represented by δ _rl ^* , and the output value of the right rear wheel axial position sensor 113 is represented by δ _rr ^* . Next, by using δ _rl ^* and δ _rr ^* , it is determined whether or not the rear wheel steering actuator 50.51 is actually operated in S2.
It is judged at 14. The determination in S214 is YES if both wheels have a steering angle of zero within the allowable error range, an alarm output 1 is output in S205, and if at least one of the steering angles is not zero, an NG is output and an alarm output is output in S215. 2 is output and the abnormality processing ends. When the alarm output 1 is output, the system is abnormal, but the abnormality processing routine prevents the traveling stability of the vehicle from being deteriorated so much, so it can be determined that the vehicle should be driven carefully.
On the other hand, when the alarm output 2 is output, it can be determined that it is not desirable to drive at high speed, and it is desirable to travel at low speed to the repair shop.

However, since the probability of failure of both the left and right rear wheel steering actuators 50 and 51 which are independently controlled is smaller than the probability of failure of only one actuator, the probability that the alarm output 2 is output is relatively small. . That is, by providing the two rear wheel steering actuators 50 and 51, parallel redundancy is provided, although partially, on the fail-safe function of the system. In order to further increase the parallel redundancy of the rear wheel steering system, it is also effective to have the rear wheel steering controller independently on the left and right sides. Furthermore, when an abnormality occurs in either the left or right steering controller, the other one steering controller detects both the left and right rear wheel steering actuators 50 and 51, and both rear wheel steering actuators 50 and 51 are operated together. It can also be configured to be in a controlled state. With such a configuration, it becomes an electrically dual system, which is more robust.

The left and right rear wheel steering actuators 5
Independent control of 0 and 51 is not an essential condition for carrying out the invention of the present application. If it is recognized that the control structure needs to be simplified, the left and right controls may be the same. In the conventional wheel steering device, since both ends of one movable shaft are engaged with the left and right lower arms, it is impossible to independently control the steering angles of the left and right wheels. When an abnormality occurs in the actuator of the movable shaft, the left and right wheels are erroneously steered in the same direction, so that the influence of the abnormality is large. However, in the wheel steering system of this embodiment, the rear wheel steering actuators 50, 5
1 is provided for each of the left and right rear wheels 128 and 129, and if the control at the time of abnormality shown in FIG. 6 is performed, in the unlikely event that an abnormality occurs in one of the rear wheel steering actuators, Even if the steering of the wheel is not proper, the other actuator operates normally and the steering of the other wheel is properly performed, so that the influence of the abnormality occurrence is small. Further, in the conventional wheel steering device, a strong actuator for greatly deforming the rubber bush for steering is necessary, whereas the wheel steering device of the present embodiment uses the rubber bush for steering. Since it is not necessary to deform the rear wheel steering actuators 128 and 129,
A relatively small actuation force is sufficient. Further, in the conventional wheel steering system, since the components of the wheel steering system need to be arranged near the vehicle center line sandwiched between the left and right wheels, the interior space of the vehicle may be narrowed and the comfortability may be deteriorated. However, the wheel steering system of the present embodiment can advantageously proceed with the design for expanding the vehicle interior space and improving the comfortability. The 4WS of the present embodiment is configured by the yaw rate feedback system, but the front wheel steering angle proportional system,
4WS of other methods such as steering force feedback method, zero center skid angle control method, model following method, etc.
It is also possible to apply the present invention to. Further, although the present embodiment applies the present invention to a strut type suspension in which two lower arms 40 are parallel to each other,
It is also applicable to those with other types of lower arms, such as trapezoidal links. Further, it may be applied to a suspension of a type other than the strut type such as a double wishbone type or a multi-link type. If necessary, two or more steering actuators may be provided for one wheel. Besides, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of drawings]

FIG. 1 is a graph showing an example of changes in toe-in / toe-out with respect to a bump / rebound size.

FIG. 2 is a plan view showing a rear wheel steering system according to an embodiment of the present invention.

FIG. 3 is a front sectional view showing a rear wheel steering actuator of the rear wheel steering device.

FIG. 4 is a block diagram showing an electric control unit of the rear wheel steering system.

FIG. 5 is a flowchart showing a rear wheel steering control routine stored in a ROM of the electric control unit.

FIG. 6 is a flowchart showing an abnormality processing routine of S111 in the flowchart of FIG. 40 Lower Arm 50.51 Rear Wheel Steering Actuator 52 Casing 60 Movable Shaft 64 Brushless Motor 78 Screw Mechanism 80 Male Thread Member 82 Nut 90 Speed Reducer 110,111 Rotation Position Sensor 112 Axial Position Sensor 120,122 Connection Part 124 Rubber Bush 125,126 Wheel support member 126 Subframe 128 Left rear wheel 129 Right rear wheel

Claims (1)

[Claims] 1. An extendable actuator having a first connecting portion and a second connecting portion and capable of extension and contraction control between the connecting portions is provided at a position spaced apart from a rotation center line of the wheel in a vehicle front-rear direction. Is arranged at an angle of inclination of 45 degrees or less with respect to the rotation center line, and the first connecting portion is connected to the wheel supporting member that rotatably supports the wheel, and the second connecting portion is connected to the vehicle body side member. Wheel steering device characterized by.