JP5321107B2 - Turning behavior control device and turning behavior control method - Google Patents

Description

  The present invention relates to a turning behavior control device and a turning behavior control method.

In general, in four-wheel steering, if the front and rear wheels are steered in the opposite phase at low speed and the front and rear wheels are steered in the same phase at high speed, the vehicle body direction (turning direction) can be matched to the traveling direction. It is said that it is easy.
By the way, turning the front and rear wheels in opposite phases at low speed improves the vehicle's turning performance, but the rear end side of the vehicle body (especially the corner between the back and side surfaces) protrudes to the outside of the turn. Become. Therefore, the average trajectory of the front end point of the vehicle body is calculated, the steering speed of the rear wheel is limited so that the trajectory of the rear end point of the vehicle body passes inside the average trajectory of the front end point of the vehicle body, and the rear wheel steering angle Have gradually increased (see Patent Document 1).

JP 2003-54435 A

However, in the conventional example described in Patent Document 1, in order to gradually increase the rear wheel steering angle, the steering operation of the driver has already stopped at a certain steering angle, but the rear wheel steering angle Will gradually increase. That is, although the driver keeps the wheel at a constant steering angle, the turning trajectory changes every moment, which may give the driver a sense of incongruity.
An object of the present invention is to improve response characteristics of turning behavior with respect to a steering operation of a driver while preventing a rear portion of a vehicle body from projecting to the outside of the turning.

In order to solve the above-described problems, a turning behavior control device according to the present invention includes a turning mechanism capable of individually turning front and rear wheels, and sets a target yaw rate of a vehicle according to a vehicle speed and a steering angle. Then, a target side slip angle of the vehicle whose turning inward is restricted is set according to the set target yaw rate and vehicle speed, and the drive mechanism is driven and controlled so that the set target yaw rate and target side slip angle are achieved. Further, when setting the target side slip angle, an upper limit value is set for the rate of change of the yaw rate or the change rate of the steering angle. The smaller the set upper limit value, the more the target side slip that limits the turning to the inside of the turn. Set the corner.

  According to the turning behavior control device according to the present invention, the target yaw rate and the target side slip angle that restricts the turning to the inside of the turn are realized, so that the steering of the driver is prevented while preventing the rear part of the vehicle body from protruding to the outside of the turn. It is to improve the response characteristics of the turning behavior to the operation.

It is explanatory drawing of a term. It is a schematic configuration. It is a flowchart which shows a drive control process. It is a block diagram. It is a simulation result of a first embodiment. The difference of the turning operation | movement of a prior art and 1st embodiment is represented. It is a turning locus of the vehicle body outline according to the prior art. It is a turning locus of the vehicle body outline according to the first embodiment. It is another embodiment. It is a block diagram of a second embodiment. It is a simulation result of a second embodiment. The difference of the turning operation | movement of a prior art and 2nd embodiment is represented. It is the turning locus | trajectory of the vehicle body external shape by 2nd embodiment. It is a block diagram of a third embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<< first embodiment >>
First, terms used in the present embodiment will be described.
FIG. 1 is a reference diagram of terms.
[Reference point]
This is the coordinate origin fixed on the vehicle. Although it is possible to set the reference point at an arbitrary position on the vehicle, in this embodiment, the reference point is set to the center of gravity of the vehicle. Further, in order to facilitate the calculation, it may be set to the midpoint of the line segment connecting the bisector of the front axle and the bisector of the rear axle.

[Vehicle coordinates]
This is a coordinate system in which the reference point is the origin, the longitudinal direction of the vehicle body is the X axis, the lateral direction of the vehicle body is the Y axis, and the front side and the left side of the vehicle body are forward (+) directions from the vehicle reference point. As for turning, the counterclockwise direction is represented by a positive direction.
[Vehicle speed]
The speed of the reference point.
[Slip angle]
This is the angle formed by the vehicle speed with respect to the X axis. Counterclockwise is represented in the positive direction.
[Yaw rate]
The rotation speed of the vehicle coordinates. Counterclockwise is represented in the positive direction.
[Swivel center]
This is the point where the ground speed becomes zero when viewed from the reference point.
[Turning radius]
This is the distance from the reference point to the turning center.

"Constitution"
FIG. 2 is a schematic configuration of the present embodiment. The vehicle 1 is equipped with a steering mechanism 3i that can individually steer each wheel 2i (i = FL, FR, RL, RR), and each of them is driven and controlled by the controller 4 so that the steering operation of the driver is performed. In response to this, so-called steering-by-wire control (hereinafter simply referred to as steering-by-wire) is performed to steer each wheel mechanically separated from the steering.
The steered mechanism 3i includes an electric motor that applies a steering torque to the wheel 2i, and steers the wheel by driving the wheel 2i to be steered by the electric motor.

The controller 4 detects the steering angle of the steering wheel 6 detected by the steering angle sensor 5, each wheel speed detected by the wheel speed sensor 7, and each detected by the turning angle sensor 8 that detects the turning angle of each wheel. The turning angle is input, and the drive control process in FIG. 3 is executed.
The controller 4 performs drive control of the reaction force motor 9 connected to the steering system in order to apply an appropriate steering reaction force to the driver's steering operation when performing steering-by-wire. .

Next, drive control processing executed by the controller 4 will be described with reference to the flowchart of FIG. FIG. 4 is a block diagram thereof.
In step S1, various data, such as a steering angle, each wheel speed, and each turning angle, are read.
In the subsequent step S2, the vehicle speed V is calculated based on each wheel speed.
In the subsequent step S3, the target yaw rate γ is calculated according to the steering angle θ as shown in the following equation (1). Re is a gain for the steering angle θ.
γ = Re × θ (1)

Note that, as shown in the following equation (2), the gain Re may be calculated by using a primary response model having a time constant Ts and a steady gain Gr.
Re = Gr / (1 + Ts) (2)
In the subsequent step S4, as shown in the following equation (3), the target side slip angle β is calculated according to the vehicle speed V and the target yaw rate γ. Lr is the distance from the center of gravity of the vehicle to the rear wheel axle.
β ≦ − (Lr / V) γ (3)

The target side slip angle β is a value for restricting not to go to the inside of the turn, that is, to turn to the outside of the turn, and to place the turning center P on the rear side of the rear wheel axle. According to the above equation (3), when the vehicle speed V increases with the yaw rate γ equal, the target side slip angle β decreases, and when the yaw rate γ increases with the vehicle speed V equal, the target side slip angle β increases.
In the subsequent step S5, as shown in the following equation (4), the target turning angles δf (s) and δr (s) of the front wheels and the rear wheels are calculated according to the target side slip angle β and the target yaw rate γ. Here, a calculation method using a linear two-degree-of-freedom model representing the dynamic characteristics of the host vehicle is shown. V is the detected vehicle speed, A is the vehicle stability factor, m is the vehicle mass, Iz is the vehicle yaw moment of inertia, Cf is the front wheel equivalent cornering power, Cr is the rear wheel equivalent cornering power, Lf is the center of gravity and front The distance between the axes, Lr is the distance between the center of gravity and the rear axis, and L is the wheelbase.

In the subsequent step S6, each turning mechanism 3i is driven and controlled so that the actual turning angle (the turning angle of each wheel detected by the turning angle sensor 8) coincides with each target turning angle. Return to the main program.
Based on the above, it is possible to control the vehicle behavior in a feed-forward manner without requiring a device for detecting a motion state quantity such as a yaw rate sensor, a lateral acceleration sensor, or a side slip angle sensor. Of course, for the purpose of further improving the follow-up performance to the target performance of the motion, for example, as shown in Japanese Patent Laid-Open No. 62-247919 and Japanese Patent Laid-Open No. 2-106469, an actual measured value of the motion state quantity is detected. Thus, the present invention can be applied even to a system that performs feedback compensation.

<Action>
In normal front wheel steering (2WS), the direction of the rear wheel substantially coincides with the direction of the vehicle body, so that cornering force acts on the front and rear wheels according to the vehicle speed and turning radius in steady turning, and cornering acting on the rear wheels. The side slip angle of the vehicle is changed so that the side slip angle of the force and the rear wheel is balanced. That is, in front wheel steering (2WS), the vehicle body is directed to the outside of the turn at a lower speed during cornering, and the vehicle body is directed to the inside of the turn at a higher speed.

On the other hand, in the present embodiment, the target yaw rate γ is calculated according to the vehicle speed V and the steering angle θ (step S3), and the target of the vehicle in which the turning to the inside of the turn is limited according to the vehicle speed V and the target yaw rate γ. The side slip angle β is calculated (step S4), and the target turning angles δf (s) and δr (s) of the front and rear wheels are calculated according to the target yaw rate γ and the target side slip angle β (step S5). The steering mechanism 3i is driven and controlled so that the target turning angles δf (s) and δr (s) are achieved (step S6).
As described above, in the four-wheel steering (4WS), the side slip angle that is the difference between the traveling direction of the vehicle and the direction of the vehicle body can be controlled to an arbitrary position. Can be maintained. Thereby, the overhang | projection of the vehicle body rear part can be reduced compared with front-wheel steering (2WS).

  First, the vehicle motion characteristics corresponding to the vehicle speed and the driver's steering operation are determined, and the steering control is performed to realize the motion characteristics, so the convergence of the yaw rate can be accelerated. Since the vehicle is steered to achieve the target yaw rate and the target side slip angle, the same tire steering from the low speed range where the vehicle moves geometrically to the mid and high speed range where the cornering force is generated at the tire slip angle. It can be controlled by the angle concept. In a front-wheel steering (2WS) vehicle, the vehicle body has a characteristic of turning inside as the vehicle speed increases. In this embodiment, the vehicle body is centered on the rear side of the rear wheel from the low speed range to the high speed range. A turning operation is performed, and the rear wheel position does not protrude to the outside of the turn regardless of a change in vehicle dynamic characteristics due to an increase in vehicle speed.

FIG. 5 is a simulation result when the steering angle θ is increased from a state where the vehicle is traveling straight at a vehicle speed of 20 km / h.
In the present embodiment, by calculating the target side slip angle β according to the equation (3), the rear wheel steering angle is controlled in phase with the front wheel steering angle, and there is no response delay. As a result, the rear wheel steering angle responds without delay to the driver's steering operation, and when the driver steers at a constant steering angle, the yaw rate also converges to a constant value corresponding to the steering operation immediately after that. .

Next, the simulation results of the prior art and this embodiment are compared.
FIG. 6 shows the difference in the turning operation between the prior art and the present embodiment.
In the prior art, the turning center position is at the rear of the vehicle at the beginning of turning, and thereafter the turning angle of the rear wheel increases at a rudder angle opposite to that of the front wheels. Come on. Therefore, the turning center moves regardless of the steering operation, and the movement speed increases as the vehicle speed increases.
On the other hand, in this embodiment, by limiting the side slip angle to the inside of the turn, that is, maintaining the side slip angle on the outside of the turn, the turning center is always located behind the rear wheel of the vehicle, and according to the yaw rate and the vehicle speed. The overhang amount at the rear of the vehicle body is reduced.

FIG. 7 is a turning trajectory of the vehicle body outline according to the prior art.
FIG. 8 is a turning trajectory of the vehicle body outline according to the present embodiment.
In the prior art, the steering angle amount changes not according to the steering operation but according to the travel distance, and thus is greatly affected by the vehicle speed. In addition, since the rear wheel rudder angle gradually increases, if the vehicle is stopped with the rear wheel rudder angle increasing, and then restarted, a large rear wheel rudder angle just before the stop cannot be obtained. As a result, the driver feels uncomfortable.
On the other hand, in this embodiment, the influence of the vehicle speed change can be suppressed, and the overhang of the rear portion of the vehicle can be kept in a very slight and substantially constant state at any vehicle speed range.

《Application example》
In this embodiment, the steering mechanism 3i capable of individually turning all the wheels 2i is mounted. However, at least the respective turning angles of the front and rear wheels may be individually controlled. 9, in the steering device in which the steering and the front wheels are mechanically connected, the gear ratio variable mechanism 10 capable of changing the steering angle ratio of the front wheels 2FL and 2FR (the ratio of the steering angle to the steering angle); Even with a configuration in which the turning angles of the front and rear wheels can be individually controlled by providing the turning mechanism 11 capable of turning the rear wheels 2RL and 2RR, the same as in the above embodiment. The effect of this can be obtained.

"effect"
From the above, the process of step S3 corresponds to “yaw rate setting means”, the process of step S4 corresponds to “side slip angle setting means”, the process of step S5 corresponds to “calculation means”, and the process of step S6 is performed. Corresponds to “control means”.
(1) A steering mechanism capable of individually turning the front and rear wheels, a yaw rate setting means for setting the target yaw rate of the vehicle according to the vehicle speed and the steering angle, and the target yaw rate and vehicle speed set by the yaw rate setting means A side slip angle setting means for setting a target side slip angle of the vehicle that restricts turning to the inside of the turn in response, a front yaw rate according to a target yaw rate set by the yaw rate setting means and a target side slip angle set by the side slip angle setting means Calculating means for calculating the target turning angle, and control means for drivingly controlling the drive mechanism in accordance with the target turning angle calculated by the calculating means.
This realizes the target yaw rate and the target side slip angle that limits the turning to the inside of the turn, improving the response characteristics of the turning behavior to the steering operation of the driver while preventing the rear part of the vehicle body from protruding to the outside of the turn. It is to let you.

(2) The side slip angle setting means sets the target side slip angle so that the side slip angle becomes zero behind the rear wheel axle.
As a result, the vehicle body turns around the rear of the rear wheel from the low speed range to the high speed range, so that it is possible to prevent the rear portion of the vehicle body from projecting to the outside of the turn regardless of the vehicle speed.
(3) equipped with a steering mechanism capable of individually turning the front and rear wheels,
The target yaw rate of the vehicle is set according to the vehicle speed and the steering angle, the target side slip angle of the vehicle that restricts turning to the inside of the turn is set according to the set target yaw rate and the vehicle speed, and the set target yaw rate and target side slip angle are The drive mechanism is controlled to be achieved.
This realizes the target yaw rate and the target side slip angle that limits the turning to the inside of the turn, improving the response characteristics of the turning behavior to the steering operation of the driver while preventing the rear part of the vehicle body from protruding to the outside of the turn. It is to let you.

<< Second Embodiment >>
"Constitution"
In the second embodiment, an upper limit value of the yaw rate that is an allowable value is set as the rate of change of the yaw rate, and the overhang of the rear part of the vehicle body is suppressed to improve the turnability.
FIG. 10 is a block diagram of the present embodiment.
In step S4, when the target side slip angle β is calculated, a limit value is set for the rate of change of the yaw rate. Here, the upper limit value (maximum yaw rate response) of the yaw rate with respect to the steering operation amount θ is set based on the target frequency fc (= 1.2 Hz).

First, as shown in the following equation (5), a limit value γd of the yaw rate change rate is calculated according to the frequency of the vehicle body. dγ / dt is the rate of change of the yaw rate.
γd ≦ (1 / 2πfc) × (dγ / dt) (5)
Then, as shown in the following formula (6), a target side slip angle β that suppresses the overhang of the rear part of the vehicle body and changes the direction of the vehicle body is calculated.
β−∫ (γd) dt ≦ − (Lr / V) γ
β ≦ {(1 / 2πfc) − (Lr / V)} γ (6)
The target side slip angle β is limited so that the rear wheel rudder angle becomes zero when the vehicle stops, and gradually moves toward the inside of the turn as the vehicle speed increases.

<Action>
In the present embodiment, since the degree of restriction on the target side slip angle is set according to the upper limit value for the rate of change of the yaw rate, the point at which the traveling direction of the vehicle coincides with the direction of the vehicle body in the low speed range is As the vehicle speed increases, the limit value of the direction of the vehicle body gradually increases and turns toward the inside of the turn.
As a result, the convergence of the yaw rate generated according to the driver's steering operation does not change regardless of the change in the vehicle speed, and the rear part of the vehicle body does not protrude at the beginning of turning, and it is possible to face the inside of the turn during steady turning. The turning ability of the vehicle can be improved.
FIG. 11 is a simulation result when the steering angle θ is increased from a state where the vehicle is traveling straight at a vehicle speed of 20 km / h.
In this embodiment, differential steering angle control is performed by adding a steering amount according to the steering angle θ and a steering amount according to the steering speed, and the convergence of the yaw rate is improved with respect to the driver's steering operation. doing.

Next, the simulation results of the prior art and this embodiment are compared.
FIG. 12 shows the difference in the turning motion between the prior art and the present embodiment.
In the prior art, the turning center position is at the rear of the vehicle at the beginning of turning, and thereafter the turning angle of the rear wheel increases at a rudder angle opposite to that of the front wheels. Come on. Therefore, the turning center moves regardless of the steering operation, and the movement speed increases as the vehicle speed increases.

On the other hand, in the present embodiment, the turning center is located behind the rear wheel at the beginning of turning, and the vehicle shifts to a steady state so that the front part of the vehicle body is caught according to the maximum value of the change rate of the yaw rate. For this reason, the side slip angle of the vehicle is limited so that the amount of overhanging of the vehicle with respect to the ground becomes small at the initial stage of steering.
FIG. 13 is a turning trajectory of the vehicle body outline according to the present embodiment.
In the present embodiment, the rear portion of the vehicle body is limited so as not to protrude at the initial stage of steering, and thereafter, a side slip angle is generated so as not to impair the convergence of the yaw rate, thereby improving the turnability of the vehicle body. Thus, the amount of overhang of the rear part of the vehicle body can be suppressed while reducing the limit value of the side slip angle.

"effect"
(1) The side slip angle setting means sets an upper limit value for the rate of change of the yaw rate, and sets the target side slip angle that restricts the turning to the inside of the turn as the set upper limit value is smaller.
Thereby, without changing the convergence of the yaw rate depending on the vehicle speed, the turning ability can be improved by facing the outside of the turn at the beginning of turning and facing the inside of the turning at the time of steady turning.

<< Third embodiment >>
"Constitution"
In the third embodiment, a steering upper limit value, which is an allowable value, is set as the rate of change in the steering operation amount, and the overturning of the rear part of the vehicle body is suppressed to improve the turnability.
FIG. 14 is a block diagram of the present embodiment.
In step S4, when the target side slip angle β is calculated, a limit value is set for the rate of change of the target turning angle. Here, the upper limit value of the change rate dθ / dt in the steering operation is set based on the frequency fc (= 3 Hz).

First, as shown in the following formula (7), the limit value γd of the yaw rate change rate is calculated according to the steering upper limit value fc of the steering angle by the above formulas (1) and (2). dθ / dt is the rate of change of the steering angle.
γd ≦ {1 / (2πfc)} Re (dθ / dt) (7)
Then, as shown in the following equation (8), the target side slip angle β that suppresses the overhang of the rear portion of the vehicle body and changes the direction of the vehicle body is calculated.
β−∫ (γd) dt ≦ − (Lr / V) γ
β ≦ {(1 / 2πfc) Reθ− (Lr / V)} γ (8)
The target side slip angle β is limited so that the rear wheel rudder angle becomes zero when the vehicle stops, and gradually moves toward the inside of the turn as the vehicle speed increases.

<Action>
Conventionally, when the rate of change in the amount of steering operation by the driver increases, the front and rear wheel steering angles operate at the maximum speed of the actuator, and the movement of the rear wheels and the movement of the front wheels operate at approximately the same speed. Had a problem of overhanging. In the present embodiment, the above problem can be prevented by providing an upper limit value for the rate of change of the steering angle and reducing the limit value of the target side slip angle as the upper limit value is smaller.

"effect"
(1) The side-slip angle setting means sets an upper limit value for the rate of change of the steering angle, and sets the target side-slip angle that limits the turning to the inside of the turn as the set upper limit value is smaller.
Thereby, it is possible to prevent the rear portion of the vehicle body from projecting to the outside of the turn due to the steering speed.

DESCRIPTION OF SYMBOLS 1 Motor vehicle 2FL-2RR Wheel 3FL-3RR Steering mechanism 4 Controller 5 Steering angle sensor 6 Steering wheel 7 Wheel speed sensor 8 Steering angle sensor 9 Reaction force motor 10 Gear ratio variable mechanism 11 Steering mechanism

Claims (4)

A turning mechanism capable of individually turning the front and rear wheels, a yaw rate setting means for setting the target yaw rate of the vehicle according to the vehicle speed and the steering angle, and turning according to the target yaw rate and the vehicle speed set by the yaw rate setting means Side slip angle setting means for setting a target side slip angle of the vehicle that is restricted to turn inward, target yaw rate set by the yaw rate setting means, and target rotation of the front and rear wheels according to the target slip angle set by the side slip angle setting means. Calculation means for calculating a steering angle; and control means for driving and controlling the drive mechanism in accordance with the target turning angle calculated by the calculation means ,
The side-slip angle setting means sets an upper limit value for the rate of change of the yaw rate, and sets the target side-slip angle that restricts turning to the inside of the turn as the set upper limit value is smaller. Control device. A turning mechanism capable of individually turning the front and rear wheels, a yaw rate setting means for setting the target yaw rate of the vehicle according to the vehicle speed and the steering angle, and turning according to the target yaw rate and the vehicle speed set by the yaw rate setting means Side slip angle setting means for setting a target side slip angle of the vehicle that is restricted to turn inward, target yaw rate set by the yaw rate setting means, and target rotation of the front and rear wheels according to the target slip angle set by the side slip angle setting means. Calculation means for calculating a steering angle; and control means for driving and controlling the drive mechanism in accordance with the target turning angle calculated by the calculation means ,
The side slip angle setting means sets an upper limit value with respect to the rate of change of the steering angle, and sets the target side slip angle that limits the turning to the inside of the turn as the set upper limit value is smaller. Behavior control device. 3. The turning behavior control device according to claim 1, wherein the side slip angle setting means sets the target side slip angle so that the side slip angle becomes zero behind the rear wheel axle. Equipped with a steering mechanism that can individually steer each of the front and rear wheels,
The target yaw rate of the vehicle is set according to the vehicle speed and the steering angle, the target side slip angle of the vehicle that restricts turning to the inside of the turn is set according to the set target yaw rate and the vehicle speed, and the set target yaw rate and target side slip angle are Drive control of the drive mechanism to be achieved ,
When setting the target side slip angle, an upper limit value is set for the rate of change of the yaw rate or the rate of change of the steering angle, and the smaller the set upper limit value, the more the target side slip angle that limits the turning to the inside of the turn. The turning behavior control method characterized by setting .

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