JP4622452B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a steering apparatus for a vehicle that changes the direction of a vehicle.

To change the direction of the vehicle, it is generally possible to control the steering angle of the rear wheel. A rear wheel steering angle control device for a vehicle is known and disclosed in, for example, Patent Document 1, Patent Document 2, and Patent Document 3.
For example, in Patent Document 3, the direction of the vehicle body is changed without changing the traveling direction of the traveling vehicle, or the direction of movement of the vehicle is changed without changing the direction of the vehicle body. There has been proposed a steering device capable of directing the vehicle body in an arbitrary direction. Specifically, a method has been proposed in which the traveling direction of the vehicle is operated with a steering wheel and the direction of the vehicle body is operated with a direction indicator operator.
JP 2004-34792 A JP 2001-334951 A JP 2000-43748 A

In the apparatus disclosed in Patent Document 3, when it is desired to change the direction of the vehicle body while changing the traveling direction of the vehicle, it is necessary to operate the steering wheel and the direction indicator operator simultaneously. However, it is generally difficult to perform two operations simultaneously. If it is a battle vehicle, a driver with sufficient training will be able to operate the vehicle. However, in the case of a normal vehicle, an ordinary driver will drive, so these two operations must be performed simultaneously. It is difficult to reproduce the same vehicle movement every time.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a vehicle steering apparatus that can individually control the traveling direction of the vehicle and the direction of the vehicle body without complicated operation by the driver.

  In the vehicle steering apparatus according to the present invention, a target point through which the host vehicle passes in the future on a traveling track at the time of turning is set by a target point setting unit, and the vehicle is directed to the target point set by the target point setting unit. Further, the vehicle body angle with respect to the current traveling direction is determined by the vehicle body angle determining means, and the wheels are steered by the steering control means so as to be the vehicle body angle determined by the vehicle body angle determining means.

  According to the present invention, the vehicle is directed to the target point where the host vehicle will pass in the future on the running track during turning without the driver performing complicated operations only by steering control of the wheels. It is possible to individually control the traveling direction and the direction of the vehicle body.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described in detail with reference to the drawings.
In the present embodiment, the present invention is applied to a vehicle that can steer front wheels and rear wheels. In the vehicle according to the present embodiment, it is possible to travel on a traveling track that the vehicle normally draws while turning while keeping the vehicle body in a predetermined direction.

(1) Operation of vehicle First, the operation of the vehicle of this embodiment will be described.
For example, a vehicle that can steer front wheels and rear wheels includes a front active steering system and a rear wheel steering system that can change the steering wheel angle operated by the driver and the steering angle of the front wheel. And vehicles equipped with a so-called steer-by-wire system.
In such a vehicle, the front wheel and the rear wheel are steered, and in the region where the vehicle turns around the position of the turning center determined geometrically by the turning angle of the wheel, the position of the turning center is arbitrarily set. Set the direction of the car body, or if the wheel generates a lateral force according to the slip angle, add it to the vehicle by arbitrarily operating the front / rear distribution of the lateral force generated by the wheel The vehicle body orientation is set by adjusting the lateral force and yaw moment independently.

FIG. 1 shows the relationship between the direction of the vehicle body and the direction of the wheels when turning.
FIG. 1A shows the vehicle 1 in which only the front wheels 2FL and 2FR can be steered. In the figure, V indicates the speed of the vehicle 1. FIG. 2B shows the vehicle 1 that can steer the front wheels 2FL and 2FR and the rear wheels 2RL and 2RR, and maintains the speed V while changing the direction of the vehicle body from the vehicle direction shown in FIG. The state where only the angle α is changed is shown. Thus, the front wheels 2FL, 2FR and the rear wheels 2RL, 2RR can be steered, so that the direction of the vehicle body can be changed while maintaining the turning motion.

For example, if the turning motion is a steady motion, in order to change the direction of the vehicle body by the angle α, the rear wheels 2RL and 2RR are steered by substantially the angle α and the front wheels 2FL and 2FR are also based on weight distribution. Is a state in which the vehicle 1 is turned back by substantially the angle α, even if the motion of the vehicle 1 (the motion about the center of gravity of the vehicle) is the same, the angle (direction) of the vehicle body is different.
Even if the turning motion is transitional, the lateral force and the yaw moment can be adjusted independently by turning the front wheels 2FL, 2FR and the rear wheels 2RL, 2RR. The movement of the vehicle body can be changed even if the movement is the same.

(2) Setting of target vehicle body angle FIG. 2 is a view of the traveling state of the turning vehicle as viewed from above the vehicle. For simplicity, a case will be described in which the vehicle turns around the position of the turning center that is geometrically determined by the turning angle of the wheels.
The vehicle 1 is in a state in which the rear wheels are not steered, and is turning around a point P on the extension of the rear axle. The vehicle 1 ′ is a vehicle to which the present invention is applied, and the direction of the vehicle body is changed by turning the rear wheel.
The vehicle 1 ′ travels on a travel path centered on the point P and turns while passing the target reaching point Q, but is perpendicular to the line connecting the current travel position O and the point P. The vehicle 1 is tilted by a target vehicle body angle (hereinafter referred to as a target vehicle body angle) α with respect to the vehicle 1 in a correct posture. Here, the target vehicle body angle α is calculated as follows.

  First, when turning at a vehicle speed V according to a certain steering wheel steering angle, a turning radius R (of the center of gravity) as a vehicle motion is obtained from the steering wheel steering angle. Next, the yaw rate γ as the motion (turning motion) of the center of gravity of the vehicle is calculated for the point P from the vehicle speed and the turning radius R, and the target arrival point Q is set by multiplying the yaw rate γ by a predetermined time Δt. Then, a target vehicle body angle α is calculated such that the vehicle body faces the target arrival point Q.

Here, the predetermined time Δt is a preset value and can be set as a function of the vehicle speed V. FIG. 3 shows an example of a characteristic diagram showing the relationship between the vehicle speed V and the predetermined time Δt.
In this characteristic diagram, the predetermined time Δt is set to 0 regardless of the vehicle speed V in the low speed range from 0 to the vehicle speed V1. As a result, the target arrival point Q becomes the current travel position, and the steering angle of the rear wheels becomes zero.

Further, in the medium speed range from the vehicle speed V1 to the vehicle speed V2, the predetermined time Δt is proportionally increased with the vehicle speed V, and the predetermined time Δt is kept constant after a certain vehicle speed V. As a result, since the target arrival point Q is no longer the current travel position, the steering angle of the rear wheels is not zero, and as a result, the vehicle body turns inward, that is, the vehicle body angle has a certain value.
Further, in a high speed range where the vehicle speed is equal to or higher than the vehicle speed V2, the predetermined time Δt is decreased with respect to the increase in the vehicle speed V and finally set to zero. As a result, the target arrival point Q is set closer to the vehicle as the vehicle speed V increases, and as a result, the target vehicle body angle that turns inward becomes smaller. It should be noted that, in a transient manner, the predetermined time Δt may be a negative value (the vehicle body is turned outward).

Thus, the predetermined time Δt is set according to the vehicle speed V.
Further, the target vehicle body angle α is the turning center point P ′ and the vehicle body angle when the vehicle body angle is 0 when the vehicle is in a steady turning state without turning the rear wheel. Coincides with the angle formed by the turning center point P when the angle is α.
Here, the target vehicle body angle α is determined on the assumption that the vehicle travels on a normal travel path, which will be described next.

  The movement of the vehicle where the center of gravity of the vehicle turns on the ground coordinates is now called “revolution”, and in addition to that revolution, the movement of the vehicle where the vehicle body rotates around the center of gravity of the vehicle is called “spinning”. Then, when trying to change the direction of the vehicle body in the process of moving from a straight traveling state to a steady turning state, in addition to the revolution that is a normal turning motion, there is a rotation movement to change the direction of the vehicle body. Necessary.

Here, as shown in FIG. 4, if the turning center point is gradually moved from P ′ to P, the vehicle rotates. However, if the turning center point is moved in such a manner, the revolution yaw rate is reduced. Therefore, when attention is paid to the revolution, the vehicle swells outside the turning and travels.
For this reason, it is necessary to compensate for the yaw rate in order to prevent the vehicle from running inflating outside the turn. For example, the yaw rate can be compensated by controlling the turning angle of each wheel so that the turning radius r represented by the following equation (1) is obtained.
r = 1 / (1 / R + 1 / v · dα / dt) (1)
Here, R is a desired revolution radius (turning radius), V is a vehicle speed, and dα / dt is a moving angular velocity of the turning center.
Here, FIG. 5 shows the relationship between the yaw rate and the vehicle body angle when a ramp-like angle input is applied to the steering wheel.

  The figure (a) is when only the front wheels are steered, and the figure (b) is when the present invention is applied and the direction of the vehicle body is changed (vehicle angle is given). It is. The vehicle body angle is obtained by setting the predetermined time Δt to 0.2 seconds, for example. Further, the result of FIG. 5B is a result obtained by using the above-described equation (1) so that the vehicle center of gravity passes on the revolution track so that the vehicle does not travel due to swelling outward. .

  Comparing FIG. 6A and FIG. 6B, the yaw rate during steering is larger in FIG. This is because the yaw rate necessary for rotation is added to the yaw rate for revolution. From this result, it is understood that a predetermined vehicle body angle can be generated in the vehicle while maintaining a steady turning motion. Here, the vehicle body angle is about 2.5 °, for example.

(3) Description of Revolution Movement of Vehicle (Turning Movement of Vehicle) Next, the revolution movement of the vehicle (turning movement of the vehicle) will be described.
The revolving motion is the same as the steering input of the driver regardless of whether or not the vehicle body angle is given.
In other words, in the speed range where the geometric movement according to the turning angle of the wheel is performed, the turning radius of the revolution movement of the vehicle is defined by the steering steering angle, and the revolution yaw rate γ is obtained from the vehicle speed and the turning radius at that time. . Then, the target vehicle body angle α and the target arrival point Q are obtained by multiplying the revolution yaw rate γ by a predetermined time Δt.

In the speed range where the vehicle moves due to the lateral force generated according to the slip angle of the wheel, the revolution yaw rate γ is determined from the steering angle and the vehicle speed, while the revolution radius is determined from the relationship with the vehicle speed. Then, the target vehicle body angle α and the target arrival point Q are obtained by multiplying the revolution yaw rate γ by a predetermined time Δt.
Thus, while obtaining the target vehicle body angle α and the target arrival point Q, the revolving motion of the vehicle is made the same regardless of whether or not the vehicle body angle is applied based on the current steering angle and vehicle speed.

Here, FIG. 6 shows a flow of a series of processes.
First, in step S1, a turning radius R for making a revolution motion of the vehicle (a turning motion of the vehicle) is determined. Subsequently, in step S2, the target vehicle body angle α is determined. In step S3, the turning angle of each wheel is controlled so that the direction of the vehicle body becomes the target vehicle body angle α while the vehicle revolves at the turning radius R.

7 and 8 show an example of the configuration of the vehicle that can realize the processing shown in FIG.
As shown in FIG. 7, the vehicle 1 includes a controller 10 that controls the turning angle of each wheel. As shown in FIG. 8, the controller 10 includes a turning radius determining unit 11 that determines a turning radius R in step S1, a target vehicle body angle determining unit 12 that determines a target vehicle body angle in step S2, and a step S3. And a turning control unit 13 for controlling the turning angle of each wheel. It goes without saying that the present invention is not limited to this configuration.

(4) Effects Next, effects in the present embodiment will be described.
As described above, the target vehicle body angle is determined, and the front wheel and the rear wheel are steered so that the vehicle body direction is the target vehicle body angle. I try to turn inward. That is, it is possible to individually control the traveling direction of the vehicle and the direction of the vehicle body without causing the driver to perform complicated operations.
As a result, the vehicle body is directed to a point where the vehicle passes by turning, so that a good field of view can be provided and the driver can feel comfortable driving. In other words, since the vehicle body is turned, the driver himself / herself also faces the inside of the turn, so that the prospect of turning ahead is improved. In addition, since the vehicle body is turned inward, the direction of the headlamp is more directed forward in the turning direction, and the visibility ahead of turning is improved at night.

Further, as described above, the direction of the vehicle body is set according to the predetermined time Δt. Here, since the predetermined time Δt is a function of the vehicle speed, the direction of the vehicle body is set according to the vehicle speed. Thereby, the direction of the set vehicle body can be made continuous from the start to the stop of the vehicle.
For example, in the technique described in Patent Document 2, when the front wheels and the rear wheels are steered in opposite phases, the overhang of the rear end of the vehicle becomes large, and therefore the turning center is moved according to the amount of movement of the vehicle. Thus, it has been proposed that the turning center of the vehicle is finally on a line passing through the center of the front shaft and the rear shaft so that there is no difference between the inner wheels while suppressing the overhang of the rear end of the vehicle.

However, in the case of this technology, when the vehicle comes to a stop with no difference in the inner wheel, the difference between the vehicle movement just before stopping (no inner wheel difference) and the movement at the time of re-starting (no rear end overhang) May occur and give the driver a sense of incongruity.
On the other hand, when the present invention is applied, the yaw rate γ decreases as the vehicle speed decreases. When the vehicle speed decreases to 0, γ also becomes 0, and the current travel position and the target arrival point Q coincide. The target vehicle body angle α is also zero. As a result, the target vehicle body angle α starts from 0 even when restarting. By doing in this way, it becomes possible to give continuity to the direction of the vehicle body before and after stopping, and it is possible to prevent the driver from feeling uncomfortable.

Further, as described above, the predetermined time Δt is changed according to the vehicle speed V (see FIG. 3).
That is, in the low speed range from 0 to the vehicle speed V1, the predetermined time Δt is set to 0 regardless of the vehicle speed V. As a result, the target arrival point Q becomes the current travel position, and the steering angle of the rear wheels becomes zero. By doing so, it is possible to suppress overhang of the rear portion of the vehicle in a low speed range where the vehicle speed is from 0 to the vehicle speed V1, or to make the vehicle posture optimal for width adjustment.

  Further, in a medium speed range from the vehicle speed V1 to the vehicle speed V2, the predetermined time Δt is proportionally increased with the vehicle speed V, and the predetermined time Δt is kept constant after a certain vehicle speed V. As a result, the target arrival point Q is no longer the current travel position, so the steering angle of the rear wheels is not zero, and as a result, the vehicle body turns inward. For example, it is often required to change the direction of the vehicle mainly by a steering operation such as turning an intersection on a general road, and such a request can be met in a medium speed range from the vehicle speed V1 to the vehicle speed V2. it can.

  In addition, when the vehicle speed is in a high speed range after the vehicle speed V2, the predetermined time Δt is decreased with respect to the increase in the vehicle speed V. As a result, as the vehicle speed V increases, the target arrival point Q is set closer to the current travel position, and as a result, the target vehicle body angle α decreases. For example, when changing lanes on a highway, it is required to move laterally without changing the direction of the car body, rather than changing the direction of the car body, or when the car body angle increases, the lateral speed increases and the driver feels uncomfortable. In order to give it, it is required to avoid the body angle. On the other hand, in the high speed region where the vehicle speed is the vehicle speed V2 or later, it is possible to meet these requirements.

The embodiments of the present invention have been described above. However, the present invention is not limited to being realized as the embodiment.
That is, in the embodiment, the target reaching point Q is determined based on the predetermined time Δt. However, it is not limited to this. For example, the target reaching point Q may be determined based on the distance based on the traveling trajectory in the turning motion, and the target vehicle body angle may be determined so as to face the target reaching point Q. Here, the determination of the target arrival point Q with reference to the distance on the traveling track in the turning motion will be described with reference to FIG. For example, the target attainment point Q at a predetermined distance (the length of the arc OQ) on the arc when turning around the point P is determined. For example, when an autonomous driving vehicle or the like is operating based on a camera image so as to follow a specified trajectory, it may be convenient to make it easy to track a target position a predetermined distance away from the image. is there. In other words, when taking an image with a camera fixed to the vehicle, if the turning radius is small, the target position beyond a predetermined distance may deviate from the angle of view of the camera. The frequency of occurrence can be reduced.

  In the description of the above-described embodiment, the target vehicle body angle determination unit 12 sets the target point set by the target point setting means and the target point setting means for setting the target point where the host vehicle will pass on the traveling track at the time of turning. The vehicle body angle determining means for determining the vehicle body angle with respect to the current traveling direction is realized so that the vehicle faces, and the steering control unit 13 steers the wheels so that the vehicle body angle determined by the vehicle body angle determining means is obtained. Steering control means to control is realized.

It is a figure which shows the direction of the vehicle body in the turning state, and the mode of a wheel. It is the figure which looked at the running state of the vehicle which is turning from the vehicle upper part. FIG. 5 is a characteristic diagram showing a relationship between a vehicle speed V and a predetermined time Δt. It is the figure used for description of calculation of a yaw rate. FIG. 6 is a characteristic diagram showing a relationship between a yaw rate and a vehicle body angle when a ramp-like input is applied to the steering wheel. It is a flowchart which shows a series of processing procedures of the vehicle of this embodiment. It is a figure which shows an example of the vehicle structure of this embodiment. It is a block diagram which shows an example of a structure of the controller of the vehicle of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Controller 11 Turning radius determination part 12 Target vehicle body angle determination part 13 Steering control part

Claims (6)

Target point setting means for setting a target point where the host vehicle will pass in the future on the traveling track at the time of turning;
Vehicle body angle determining means for determining the vehicle body angle with respect to the current traveling direction so that the vehicle faces the target point set by the target point setting means;
Steering control means for steering the wheels so that the vehicle body angle determining means determines the vehicle body angle;
A vehicle steering apparatus comprising:   2. The vehicle steering apparatus according to claim 1, wherein the target point setting means sets a passing point after a predetermined time on the traveling track as the target point.   The vehicle steering apparatus according to claim 2, wherein the predetermined time is determined based on a vehicle speed.   The vehicle steering apparatus according to claim 1, wherein the target point setting means sets a scheduled passing position at a predetermined distance from a current traveling position on the traveling track as the target point.   5. The vehicle steering apparatus according to claim 4, wherein the predetermined distance is determined based on a vehicle speed.   The vehicle steering apparatus according to any one of claims 1 to 5, wherein the traveling track is determined based on a current steering angle and a vehicle speed.

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