JP2016097897A - Rear-wheel steering control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear-wheel steering control apparatus capable of suppressing discomfort in a vehicular behavior associated with steering while securing vehicular maneuverability.SOLUTION: A rear-wheel steering control apparatus includes: a rear-wheel steering device 30 for steering a rear wheel WR by driving a rear-wheel steering motor 31; and a rear-wheel steering controller 40 for operating the rear-wheel steering device 30 so as to steer the rear wheel WR with a first-order delay relative to a steering angle θ. Further, the rear-wheel steering controller 40 performs: calculating a rear-wheel steering angle target value δ(S) on the basis of a product of a steady-state gain α(θ) that is set so that a rear-wheel steering angle is changed with a pre-set characteristic in response to a front-wheel steering angle and a first-order delay-derived component {1/(1+τ*S)}θ that is set so than the rear-wheel steering angle is changed with a first-order delay relative to the front-wheel steering angle, and, in the case of an absolute value of steering angular velocity θexceeding an angular velocity determination value θ, decreasing the first-order delay-derived component proportionately as an absolute value of the steering angular velocity θincreases.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a rear wheel steering control device for steering a rear wheel with a predetermined characteristic with respect to a steering angle of a front wheel.

2. Description of the Related Art Conventionally, a rear wheel steering control device that steers a rear wheel with a predetermined characteristic with respect to a steering angle of a front wheel is known (for example, see Patent Document 1).
This prior art performs rear wheel steering based on the vehicle speed and the front wheel turning angle. When the steering angle is in the increasing direction, the rear wheel turning angle is controlled with a first-order lag with respect to the front wheel turning angle, and the steering angle is in the decreasing direction or the steering angle decreasing direction and the steering speed is a predetermined value or more. If so, the rear wheel turning angle is controlled in proportion to the front wheel turning angle.
Therefore, when turning in the reverse phase of the front and rear wheels, the rear wheel turning angle is steered with a primary delay relative to the front wheel turning angle, thereby preventing the rear end of the vehicle body from projecting to the outside of the turn and being high. A handling property can be obtained.

JP 7-172336 A

However, in the prior art, when the steering wheel is suddenly turned back in the reverse direction after a large steering, the rear wheel turning angle is controlled by the first-order lag, the proportional control by returning the steering wheel, the reverse direction The first-order delay due to the increase, and the control mode is switched in a short time.
For this reason, the rear wheel turning angle changes unnaturally, and accordingly, the yaw rate behavior of the vehicle also changes unnaturally, which may give a strong sense of discomfort to the driver.

  The present invention has been made paying attention to the above-described conventional problems, and an object thereof is to provide a rear wheel steering control device capable of suppressing the uncomfortable feeling of the vehicle behavior with respect to the steering while ensuring the maneuverability of the vehicle. To do.

In order to achieve the above object, the present invention provides:
In the rear wheel steering control device provided with control means for operating the rear wheel steering device to steer the rear wheel with a first order delay with respect to the front wheel steering angle,
The control means includes a steady-state gain that is set so that the rear wheel turning angle changes with a preset characteristic in accordance with the front wheel turning angle, and a first order delay of the rear wheel turning angle with respect to the front wheel turning angle. The rear wheel turning angle is determined based on the product of the first-order lag-derived component set to be changed at
And, when the absolute value of the front wheel turning angular velocity exceeds a preset threshold value, the rear wheel turning control device reduces the first-order lag-derived component as the absolute value of the front wheel turning angular velocity increases. did.

In the rear wheel steering control device of the present invention, when the rear wheel is steered with a first order lag with respect to the front wheel steering angle, the rear wheel steering angular velocity is lower than the threshold, such as at the start of steering. Steering delay due to primary delay is secured. Therefore, as compared with the front-rear simple reverse phase, the overhang of the rear end of the vehicle body is suppressed, and handling properties can be secured.
On the other hand, in a scene where the absolute value of the front wheel turning angle is higher than the threshold value, the primary delay-derived component is reduced as the absolute value of the front wheel turning angular velocity is larger. Therefore, at the time of steering switching with a high front wheel turning angular velocity, it is possible to suppress an unnatural change in the rear wheel turning angle due to a delay in turning the rear wheel, thereby suppressing an unnatural change in the yaw rate behavior of the vehicle. Can reduce the sense of incongruity.
As described above, in the present invention, when the front wheel turning angular velocity is high, that is, when the absolute value of the front wheel turning angle is higher than the threshold value, the vehicle behavior is uncomfortable due to the rear wheel turning delay without impairing the maneuverability. The effect that it can reduce can be acquired.

1 is an overall system diagram showing a steering system of a 4WS vehicle provided with a rear wheel steering control device of Embodiment 1. FIG. 6 is a flowchart showing a flow of processing of rear wheel steering control in the rear wheel steering control device of the first embodiment. 6 is a time constant gain characteristic diagram showing a time constant gain corresponding to the steering angular velocity in the rear wheel steering control device of Embodiment 1. FIG. FIG. 6 is a steady gain characteristic diagram showing a steady gain corresponding to a steering angle in the rear wheel steering control device of the first embodiment. 6 is a time chart showing an operation example by the rear wheel steering control device of the first embodiment. 6 is a time chart illustrating an operation example according to a comparative example with respect to the first embodiment. 6 is a time chart illustrating an operation example according to a comparative example with respect to the first embodiment. FIG. 6 is an operation explanatory diagram illustrating an operation at the time of starting from parallel parking by the rear wheel steering control device of the first embodiment. FIG. 6 is an operation explanatory diagram illustrating an operation at the time of starting from parallel parking by the rear wheel steering control device of the first embodiment. It is effect | action explanatory drawing which shows the operation | movement at the time of the start from parallel parking by the comparative example with Embodiment 1. FIG. 6 is a flowchart showing a flow of processing of rear wheel steering control in the rear wheel steering control device of the second embodiment. FIG. 10 is a time constant gain characteristic diagram showing a time constant gain with respect to a steering angle in the rear wheel steering control device of the second embodiment. It is a steady rear-wheel steering angle characteristic figure which shows the rear-wheel steering angle based on the time-constant gain calculated in the rear-wheel steering control apparatus of Embodiment 2. FIG. 10 is an overall system diagram showing a steering system of a 4WS vehicle including a rear wheel steering control device according to a third embodiment. 12 is a flowchart illustrating a flow of processing of rear wheel steering control in the rear wheel steering control device of the third embodiment. 10 is a time chart showing an example of turning when an upper limit cut of a provisional value of the rear wheel turning angle is performed in the rear wheel turning control device of the third embodiment. 10 is a time chart showing a turning example of a comparative example in which the upper limit cut of the provisional value of the rear wheel turning angle of the third embodiment is not performed.

  EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing the rear-wheel steering control apparatus of this invention is demonstrated based on embodiment shown to drawing.

Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings.
(Embodiment 1)
First, the configuration will be described.
The configuration of the vehicle steering control device to which the rear wheel steering control device of the first embodiment is applied will be described separately in “overall system configuration” and “rear wheel steering angle control”.

[Overall system configuration]
FIG. 1 is an overall system diagram showing a vehicle steering system to which a rear wheel steering control device of Embodiment 1 is applied.
The overall system configuration will be described below with reference to FIG.
The rear wheel steering control device A of Embodiment 1 is applied to the 4WS vehicle MV shown in FIG.
That is, this 4WS vehicle MV can steer the rear wheels WR and WR independently of the steering of the front wheels WF and WF by the rear wheel steering control device A of the first embodiment.

  The 4WS vehicle MV is an electric vehicle and includes a drive motor 10 as drive means. The drive force of the drive motor 10 is transmitted to the front wheels WF and WF via the drive shafts 11 and 11 to drive.

Further, the front wheels WF and WF are steered by the front wheel steering device 20.
The front wheel steering device 20 includes a front wheel rack and pinion 21 and a handle 22. That is, when the driver steers the handle 22, the pinion gear (not shown) inside the front wheel rack and pinion 21 rotates and the rack (not shown) moves to the left and right, thereby rotating the front wheels WF and WF. Rudder.

  The steering wheel 22 is provided with a steering angle sensor 51 that detects a steering angle. In the present embodiment, the handle 22 is mechanically coupled to a pinion gear (not shown) inside the front wheel rack and pinion 21 via a shaft 22a and a joint (not shown). Therefore, in the first embodiment, the steering angle θ is detected by the steering angle sensor 51 as the front wheel turning angle.

  The rear wheel steering control device A includes a rear wheel steering device 30 that steers the rear wheels WR and WR. The rear wheel steering device 30 includes a rear wheel steering motor 31 and a rear wheel rack and pinion 32. That is, the rear wheel steering device 30 rotates the pinion gear (not shown) in the rear wheel rack and pinion 32 by the rear wheel steering motor 31 so that the rack (not shown) moves to the left and right. Turn WR.

The rear wheel steering motor 31 controls driving by the rear wheel steering controller 40 so that the steering angle of the rear wheel WR becomes the rear wheel steering angle target value δ _r ^* (S) calculated by the rear wheel steering controller 40. Is done.
The rear wheel steering controller 40 is connected to the steering angle sensor 51, the rear wheel steering motor rotation angle sensor 52, and the rear wheel speed sensor 53.
The rear wheel turning motor rotation angle sensor 52 detects the rotation angle of the rear wheel turning motor 31, and the rear wheel turning controller 40 obtains the turning angle of the rear wheel WR from this rotation angle.
The rear wheel wheel speed sensor 53 sends a pulse signal representing the wheel speed of the rear wheel WR to the rear wheel steering controller 40 as vehicle speed information, and the rear wheel steering controller 40 calculates the vehicle body speed from this rotational speed.

[Rear wheel turning angle control]
Next, the flow of processing for determining the aforementioned rear wheel turning angle target value δ _r ^* (S) in the rear wheel steering control by the rear wheel turning controller 40 will be described based on the flowchart of FIG.
This rear wheel steering control is started by turning on an ignition switch (not shown), and is repeatedly executed at a preset control cycle until the ignition switch is turned off.

First, in step S101, after detecting the steering angle θ and calculating the steering angular velocity θ ^* based on the signal of the steering angle sensor 51, the process proceeds to the next step S102. Note that θ ^* is a one-time differential value of θ.

In subsequent steps A102 to S104, a time constant gain is determined.
That is, in step S102, the steering angular velocity theta ^* size to determine whether (the absolute value) of the angular velocity determination value theta ₀ ^* or previously set in the case of more than the angular velocity determination value theta ₀ ^* proceeds to step S103, the angular velocity If it is less than the determination value θ ₀ ^* , the process proceeds to step S104.
In step S103 the steering angular velocity theta ^* size proceeds when more than the angular velocity determination value theta ₀ ^*, time constant gain, corresponding to the steering angular velocity theta ^*, small constant gain at higher steering angular velocity theta ^* is set large Then, the process proceeds to step S105.
On the other hand, in step S104 that proceeds when the magnitude (absolute value) of the steering angular velocity θ ^* is less than the angular velocity determination value θ ₀ ^* , the time constant gain is set to 1, and then the operation proceeds to step S105.

That is, in steps S102 to S104, the relationship between the steering angular velocity θ ^* and the time constant gain is set as shown by a solid line in FIG. That is, when the absolute value of the steering angular velocity θ ^* is smaller than the angular velocity determination value θ ₀ ^* , it is fixed to 1. When the absolute value of the angular velocity determination value θ ₀ ^{* is} greater than or equal to, the time constant gain becomes 0 as the steering angular velocity θ ^* increases. The time constant gain is set to approach 1 as the steering angular velocity decreases.
In FIG. 3, the dotted line indicates the case where the angular velocity determination value θ ₀ ^* is set to a value near 0. In this case, the time constant gain is set to 1 when the steering angular velocity θ ^* is close to 0, and the time constant gain is set to approach 0 as the steering angular velocity becomes larger than 0.

In step S105, which proceeds after setting the time constant gain, the first-order lag time constant τ (θ ^* ) is calculated, and then the process proceeds to step S106.
In step S105, a value obtained by multiplying a constant value set in advance for each vehicle by the time constant gain set in either step S103 or S104 is set as a first-order lag time constant.

In subsequent steps S106 to S108, the steady gain α (θ) is determined.
First, in step S106, it is determined whether or not the magnitude (absolute value) of the steering angle θ is 0. If the steering angle θ = 0, the process proceeds to step S107. If the steering angle θ ≠ 0, the process proceeds to step S107. The process proceeds to S108. Then, in step S107 that proceeds when the magnitude (absolute value) of the steering angle θ is zero, the steady gain α (θ) is set to zero.
On the other hand, in step S108 that proceeds when the steering angle ≠ 0, the steady gain α (θ) is set by a linear characteristic corresponding to the magnitude of the steering angle θ. Here, the steady-state gain α (θ) having a linear characteristic corresponding to the magnitude of the steering angle θ is shown in FIG. As shown in FIG. 4, the steady gain α (θ) when the steering angle θ is fully steered (front steering wheel maximum steering angle) is a linear characteristic such that (maximum rear wheel steering angle / maximum steering angle). Therefore, the steady gain α (θ) is set to steer the rear wheel WR to the maximum rear wheel turning angle when the front wheel WF is at the maximum steering angle.
Note that, based on the vehicle speed V, the steady gain α (θ) decreases as the vehicle speed V increases, that is, this linear characteristic is laid down, and the turning angle of the rear wheel WR during full turning decreases. You may set as follows.

In step S109, which proceeds after setting the steady gain α (θ) in either step S107 or S108, the rear wheel turning angle target value is set, and the flow of one process is terminated.
Here, the rear wheel turning angle target value δ _r ^* (S) is calculated by the following equation (1) as the product of the steady gain α (θ) and the first-order lag-derived component.
δ _r ^* (S) = − α · {1 / (1 + τ · S)} θ (S) (1)
In the above formula (1), the minus sign indicates that the rear wheel turning angle is steered in the opposite phase with respect to the steering angle and the front wheel turning angle. That is, in the rear wheel steering control, the rear wheel WR is steered in the opposite phase with respect to the front wheel WF.
In the first-order-lag-derived component {1 / (1 + τ · S)} θ, τ is the first-order lag time constant as described above, S is a Laplace operator, and θ is a steering angle.

(Operation of Embodiment 1)
Next, the operation of the first embodiment will be described based on FIGS. 5 to 9A and 9B while comparing with the comparative example.
FIG. 5 shows a case where, in the 4WS vehicle MV equipped with the rear wheel steering control device A according to the first embodiment, the vehicle is started with full steering from the stop state and then turned back with full steering in the reverse direction. A change in the steering angle of the front wheel WF and the rear wheel WR and a change in the yaw rate are shown.
The start while performing such steering is, for example, a running example in which the 4WS vehicle MV starts from the parallel parking state (MV (st)) shown in FIG. 8 and exits on the road RW as indicated by an arrow. .

During such traveling, in the first embodiment, at the time of start (ta in FIG. 5), the steering angular velocity θ ^* is a low speed lower than the angular velocity determination value θ ₀ ^* , and based on the processing of steps S102 → S104. Set the time constant gain to 1. Therefore, the first-order lag time constant τ (θ ^* ) obtained by multiplying the constant value by the time constant gain is a preset constant value.
Therefore, the rear wheel turning angle target value δ _r ^* (S) calculated based on this first-order lag time constant τ (θ ^* ) is set to a value corresponding to the vehicle body overhang suppression, and the vehicle body rear overhang is suppressed, Excellent handling characteristics.

After that, when the steering wheel 22 is turned back (tb in FIG. 5), if high-speed steering is performed in which the steering angular velocity θ ^* is higher than the angular velocity determination value θ ₀ ^* , the time constant is determined based on the processing of steps S102 → S103. The gain is set to a lower value as the speed increases according to the steering angular velocity θ ^* . Therefore, the primary delay time constant τ (θ ^* ) is smaller than the constant value, and the rear wheel turning delay is reduced.
Further, since the magnitude (absolute value) of the steering angle θ once becomes 0 when the steering wheel 22 is turned back, the steady gain α (θ) is once set to 0 based on the processing of steps S106 → S107.
Therefore, in the scene of tb after t0 in FIG. 5 in which the steering angle θ is switched from the straight traveling state to the reverse direction by turning the steering wheel 22, the rear wheel turning angle once becomes zero and then the front with the delay reduced. Gently rises to the opposite side of the wheel turning angle.
As a result, the change in the yaw rate of the vehicle is smooth, and the effect of greatly reducing the uncomfortable feeling of the vehicle behavior with respect to steering can be obtained. Regardless of the value of the steering angular velocity θ ^*, the steering angle of the rear wheel always returns to 0 when the steering is turned back, so that the yaw rate of the vehicle body can be brought close to 0 and the feeling of unsettled rear wheel WR is eliminated. Yes.

6 and 7 show a change in the steering angle and a change in the yaw rate of the front wheel WF and the rear wheel WR of the comparative example when the same operation is performed.
FIG. 6 is an operation example when the value of constant value × 1 is always used as the first-order lag time constant τ (θ ^* ) in step S105 without performing the processing of steps S102 to S104 of the first embodiment. is there.
In this comparative example, when the steering wheel 22 is turned back, at the time t0 when the steering angle θ becomes 0, the rear wheel turning angle is set to 0 and the yaw rate is returned to 0. However, in the subsequent scene 0tb, the rear wheel turning angle is set to the primary delay. The components are steered to the same phase side of the front wheel turning angle.
For this reason, the yaw rate change becomes large before and after the steering angle 0, and the vehicle behavior with respect to steering is uncomfortable.

FIG. 7 shows the rear wheel turning angle based on the first-order lag time constant τ (θ ^* ) calculated based on the processing in steps S103 to S105 without performing the processing in steps S106 and S107 of the first embodiment. It is an operation example when the target value δ _r ^* (S) is calculated.
In this case, the rear wheel turning angle changes with a delay with respect to the front wheel turning angle even when the steering angle θ becomes zero, so that a phase delay remains in the rear wheel turning angle and the yaw rate. For this reason, the driver feels that the rear wheels WR are not cut, and gives a sense of incongruity to the vehicle behavior with respect to steering. In addition, after the steering angle becomes zero, a state occurs in which the steering directions of the front wheels WF and the rear wheels WR are in phase, and the feeling of strangeness is further increased.

The overhang suppression performance at the time of starting from the above-described parallel parking state and the uncut portion of the rear wheel WR will be described based on FIGS. 9A and 9B.
FIG. 9A shows the trajectory of the vehicle body (trM), the trajectory in the center of the vehicle width direction of the front wheel WF (trF), and the trajectory of the center of the rear wheel WR in the vehicle width direction when starting from the above-described parallel parking state in the first embodiment. (TrR) is shown. Further, FIG. 9B shows a vehicle body trajectory (trM) in the vehicle width direction center of the front wheel WF when the rear wheel WR is simply turned in a reverse phase with respect to the front wheel WF when starting from the same parallel parking state. A trajectory (trF) and a trajectory (trR) at the center of the rear wheel WR in the vehicle width direction are shown.

As can be seen from a comparison of the trajectories (trM) of the vehicle bodies in FIGS. 9A and 9B, in the first embodiment of FIG. 9A, the vehicle rear portion overhangs with respect to the reference line DL1 at the time of initial steering at the time of starting, and the reference line at the time of reverse steering. The overhang with respect to DL2 is suppressed. On the other hand, in the comparative example of FIG. 9B, both the overhang (OVa) of the rear part of the vehicle with respect to the reference line DL1 at the time of the first steering at the start and the overhang (OVb) with respect to the reference line DL2 at the time of turnover are both more The amount of overhang is large.
Further, by turning the handle 22, in the example of FIG. 9A, the central locus (trR) of the rear wheel WR coincides with the central locus (trF) of the front wheel WF at the movement distance da. In contrast, in FIG. 9B, at this distance da, the rear wheel WR has a different trajectory from the front wheel WF due to the first-order lag, which causes a feeling of uncutness of the rear wheel WR.

(Effect of Embodiment 1)
The effects of the rear wheel steering control device of the first embodiment are listed below.
1) The rear wheel steering control device in the first embodiment is
A rear wheel steering device 30 for driving the rear wheel steering motor 31 as a driving means to steer the rear wheel WR;
A steering angle sensor 51 as a front wheel turning angle detection means for detecting a steering angle θ as a front wheel turning angle;
A rear wheel steering controller 40 as a control means for operating the rear wheel steering device 30 to steer the rear wheel WR with a first order delay with respect to the front wheel steering angle;
In the rear wheel steering control device with
The rear wheel turning controller 40 has a steady gain α (θ) set so that the rear wheel turning angle changes with a preset characteristic in accordance with the front wheel turning angle, and the front wheel turning angle with respect to the front wheel turning angle. Based on the product of the first-order-lag-derived component {1 / (1 + τ · S)} θ set to change the rear-wheel turning angle with a first-order lag, the rear-wheel turning angle target value δ _r ^* (S) is Seeking
In addition, when the absolute value of the steering angular velocity θ ^* as the front wheel turning angular velocity exceeds the angular velocity judgment value θ ₀ ^* as a preset threshold, the absolute value of the steering angular velocity θ ^* as the front wheel turning angular velocity is large. The first order lag-derived component is reduced as much as possible.
Therefore, when the steering wheel speed θ ^* is lower than the angular velocity judgment value θ ₀ ^*, such as at the start of steering, when the rear wheel WR is steered with a first order delay with respect to the front wheel turning angle, it is caused by the first order delay of the rear wheel WR. Ensure steering delay. Therefore, the rearward end of the vehicle body is prevented from projecting to the outside of the turn as compared with the simple front-rear phase, and handling performance can be ensured. Further, by keeping the primary delay constant in the steering angular velocity range lower than the angular velocity determination value θ ₀ ^*, it is possible to suppress the uncomfortable feeling that the primary delay amount changes in the low speed range.
On the other hand, in a scene where the steering angular velocity θ ^* (front wheel turning angle) is higher than the angular velocity judgment value θ ₀ ^* , the larger the absolute value of the steering angular velocity θ ^* , the smaller the first-order lag-derived component, and the front wheel turning angle becomes the angular velocity. Compared to a scene lower than the determination value θ ₀ ^{*, the} turning delay due to the primary delay of the rear wheel WR is reduced. Therefore, at the time of steering switching with high front wheel turning angular velocity, it is possible to suppress an unnatural change in the rear wheel turning angle due to a delay in turning of the rear wheel WR, thereby suppressing an unnatural change in the yaw rate behavior of the vehicle. It can suppress a sense of discomfort given to the person.
As described above, according to the present invention, it is possible to obtain an effect of reducing the uncomfortable feeling of the vehicle behavior due to the rear wheel turning delay when the front wheel turning angular velocity is high without impairing the handling performance.

2) The rear wheel steering control device of Embodiment 1
The rear wheel turning controller 40 sets the steady gain α to 0 when the absolute value of the steering angular velocity θ ^* as the front wheel turning angle is 0.
Therefore, when the steering angle θ is returned to 0 after steering, the rear wheel turning angle always returns to 0 when the steering angle θ is set to 0 regardless of the value of the steering angular velocity θ ^*. It is possible to eliminate the feeling of remaining (feeling that the rear part of the vehicle body moves sideways even though the steering angle θ is returned to 0). Therefore, an effect of further reducing the uncomfortable feeling of behavior with respect to steering can be obtained.

(Other embodiments)
Next, a motor unit according to another embodiment will be described.
In the description of the other embodiments, the same reference numerals as those in the first embodiment are assigned to the same components as those in the first embodiment, and the description thereof is omitted. Only the differences from the first embodiment will be described. .

(Embodiment 2)
Below, the rear-wheel steering control apparatus of Embodiment 2 of this invention is demonstrated.
The second embodiment is different from the first embodiment in part of the processing in the rear wheel steering control.
That is, in the second embodiment, as shown in the flowchart of FIG. 10, step S105b for calculating the first-order lag time constant τ (θ ^* ) and step S108b for setting the steady gain when the steering angle θ is larger than zero. The contents of this process are different from those of the first embodiment.

In step S105b, when the steering angular velocity θ ^* is other than 0, the first-order lag time constant τ (θ ^* ) is obtained from the constant value × the vehicle speed as in the first embodiment, but when the steering angular velocity θ ^* is 0, Based on the vehicle speed V and the constant length λ, the first-order lag time constant τ (θ ^* ) is calculated by the following equation (2).
τ = λ / V (2)
Here, the constant length λ may be set to any value. In the first embodiment, the constant length λ is shorter than the wheel base of the vehicle, for example, the same value as the constant value in the first embodiment. To do. Further, when the vehicle speed V = 0, division by 0 is avoided by using a minute value of V ≠ 0.

That is, the steering angular velocity θ ^* becomes 0 when the steering is increased stepwise or maintained at a constant steering angle θ. At this time, when the time constant gain is set to 1, there is a risk of insufficient delay at extremely low speed or excessive delay at high vehicle speed. Therefore, in the second embodiment, when the steering angular velocity θ ^* is 0, the first-order lag time constant τ (θ ^* ) is set in inverse proportion to the vehicle speed V.
That is, the time required for the rear wheel WR to travel increases as the vehicle speed V decreases, and decreases as the vehicle speed V increases. Therefore, the value obtained by dividing the constant length λ by the vehicle speed V is defined as the first-order lag time constant τ (θ ^* ) (Equation (2)). The rear wheel WR can be steered.

  In step S108b which proceeds when the steering angle is not 0 in step S106, the steady gain α (θ) is set to the horizontal axis which is the magnitude of the steering angle and the vertical which is the steady gain α (θ) as shown in FIG. 11A. The relationship with the axis is convex upward. That is, as indicated by the dotted line in the figure, the steady gain α with respect to the steering angle θ is set to be larger than the linear function set so that the rear wheel WR has the maximum rear wheel turning angle when the front wheel WF is turned. ing. Note that, in the same manner as in the first embodiment, the rear wheel WR is set to be cut to the maximum rear wheel turning angle when the front wheel WF is fully steered. The calculated vehicle body speed may be used so that the turning angle during full turning decreases as the vehicle speed increases.

(Operation of Embodiment 2)
Next, the operation of the second embodiment will be described.
First, the operation by setting the first-order lag time constant τ (θ ^* ) according to the vehicle speed V will be described.
The first-order lag time constant τ (θ ^* ) is obtained by multiplying the constant value by the time constant gain.
This time constant gain is set to 1 when the steering angular velocity θ ^* is 0.
The steering angular velocity θ ^* becomes 0 other than when traveling straight, for example, when the front wheel WF is started with full steering, or when stepped steering is performed to change the steering angle θ stepwise. In addition, it may occur during steering.

When the first-order lag time constant τ (θ ^* ) is set constant regardless of the vehicle speed V during this steering operation, the rear wheel turning angle is not sufficiently delayed when the vehicle speed V is extremely low, and conversely when the vehicle speed V is high. The delay of the rear wheel turning angle may be excessive with respect to the appropriate value indicated by the dotted line.
When the delay in turning the rear wheel WR is insufficient as in the former, the rear wheel WR enters inside the locus of the front wheel WF, and the delay in turning the rear wheel WR is excessive as in the latter. In such a case, the rear wheel WR bulges outward with respect to the locus of the front wheel WF.

In contrast, in the second embodiment, when the steering angular velocity θ ^* is 0, the first-order lag time constant τ (θ ^* ) is obtained by multiplying the value obtained by dividing the constant length λ by the vehicle speed V by the time constant gain. did. Therefore, even if the vehicle speed slightly increases or decreases in the low speed region, substantially the same vehicle locus and vehicle body rear end overhang amount can be obtained. Therefore, it is possible to further improve the low speed handling performance while reducing the uncomfortable behavior.

Next, characteristics of the steady gain α (θ) with respect to the steering angle (front wheel turning angle) will be described.
If the characteristic of the steady gain α (θ) with respect to the front wheel turning angle is linear as shown by the dotted line in FIG. 11A, when the handle 22 is cut, the characteristic is in a large steering angle region as shown by the dotted line in FIG. 11B. The rear wheel turning angle suddenly increases. For this reason, there is a possibility that the behavior of the rear wheel WR with respect to steering may be uncomfortable.
Therefore, as shown by the solid line in FIG. 11A, when the characteristic of the steady gain α (θ) with respect to the front wheel turning angle is a characteristic that is convex upward with respect to the linear function, the characteristic is shown by the solid line in FIG. 11B. Thus, the rear wheel turning angle gradually increases from a small steering angle range. For this reason, the increase in the rear wheel turning angle in the large steering angle region can be made gentler than the rear wheel turning angle characteristic shown by the dotted line in the figure, and the rear wheel turning angle characteristic shown by the dotted line in the figure can be reduced. The uncomfortable feeling of WR behavior can be reduced.

(Effect of Embodiment 2)
In addition to the effects 1) to 3) described in the first embodiment, the rear wheel steering control device according to the second embodiment has the effects listed below.
2-1) The rear wheel steering control device in Embodiment 2 is
The rear-wheel steering controller 40 has a non-linear characteristic in which the steady-state gain α (θ) with respect to the absolute value of the steering angle θ as the front-wheel steering angle increases toward the increase side with respect to a linear function with respect to the steering angle θ (see FIG. 11A)).
When the characteristic of the steady gain α (θ) with respect to the steering angle θ (front wheel turning angle) is linear, when turning the handle 22, the rear wheel turning angle suddenly increases in the large steering angle region. The behavior may make the driver feel uncomfortable.
On the other hand, when the characteristic of the steady gain α (θ) is a non-linear convex upward as described above, the rear wheel turning angle gradually increases from a small steering angle θ to a characteristic close to the linear characteristic. As a result, the increase in the rear wheel turning angle in the large steering angle region can be moderated. Therefore, it is possible to reduce giving the driver a feeling of strangeness with respect to the steering.

2-2) In the rear wheel steering control device of the second embodiment,
When the steering angular velocity θ ^* as the front wheel steering angular velocity is 0, the rear wheel steering controller 40 determines the primary delay time constant τ (θ ^* ) as the primary delay-derived component based on the wheelbase length of the vehicle. It is obtained based on a value obtained by dividing a preset constant length λ by a vehicle speed V.
Therefore, when the vehicle is traveling with the front wheel WF being steered while maintaining the steering angular velocity θ ^* = 0, even if the vehicle speed slightly increases or decreases in the low speed region, the same vehicle trajectory and vehicle body rear end overhang amount can be obtained. It is done. Therefore, the effect of further improving the low speed handling performance can be obtained while reducing the uncomfortable behavior.

(Embodiment 3)
First, the configuration of the rear wheel steering control device of the third embodiment will be described.
The third embodiment is an example in which the present invention is applied to a configuration in which a variable mechanism is provided between the handle 22 and the front wheel rack and pinion 21, and the rear wheel WR is easily steered to full steering.

  As shown in the overall system diagram of FIG. 12, the rear wheel steering device of the third embodiment is obtained by adding a variable gear ratio mechanism 301 and a front wheel rack stroke sensor 302 to the configuration of the first embodiment.

The variable gear ratio mechanism 301 is a variable mechanism capable of steering gear ratio is a ratio of the steering angle θ and the front wheel turning angle [delta] _f. In the third embodiment, the gear ratio is set to slow in a region where the steering angle θ is small, and the gear ratio is set to quick in a region where the steering angle θ is large. In addition, the steering gear ratio may be changed according to the vehicle speed V.

The results have the variable gear ratio mechanism 301, the relationship between the steering angle θ and the front wheel turning angle [delta] _f may not uniquely determined. Therefore, in the third embodiment, the value of the front wheel rack stroke sensor 302 is measured, and the front wheel turning angle δ _f is calculated from the measured value.

Next, rear wheel turning angle control in the third embodiment will be described based on the flowchart shown in FIG. The difference from the second embodiment is that the front wheel turning angle δ _f is used instead of the steering angle θ, and the rear wheel turning angle target value is determined in steps S301 to S304 following steps S107c and S108c. It is a flow of processing.

In step S101c～S105c, instead of the steering angle θ in the first and second embodiments, it is used a front wheel steering angle [delta] _f. In the first embodiment, it is used as the equivalent of the steering angle θ to the front wheel turning angle [delta] _f, no substantial differences in the use of the front wheel steering angle [delta] _f in the third embodiment.

Next, processing in steps S301 to S304 will be described.
The processing in steps S301 to S304 is an example in which the rear wheel turning angle (provisional value) is cut at an upper limit value corresponding to full turning in order to facilitate full turning of the rear wheel WR. is there.
In step S301, the front wheel turning angle [delta] _f, first-order lag time constant τ (δ _f ^*), steady-state gain β rear wheel turning angle provisional value as a product derived from the component primary delay with the ^{_{(δ f) pδ r * (}} S ) Is calculated by the following equation (3), and then the process proceeds to step S302. Note that this rear wheel turning angle provisional value pδ _r ^* (S) corresponds to the rear wheel turning angle in the first and second embodiments.
pδ _r ^* (S) = − β · {1 / (1 + τ · S)} δ _f (S) (3)
Here, what with a minus sign on the right side, with respect to the front wheel turning angle [delta] _f, indicates that the steered rear wheel steering angle in the opposite phase direction of the front wheel turning angle.

In the next step S302, determines whether the magnitude of the rear wheel steering angle provisional pδ _r ^* (S) exceeds the upper limit value set in advance, when has been exceeded the process proceeds to step S303, exceeds If not, the process proceeds to step S304.

In step S303 the rear wheel steering angle provisional pδ _r ^* (S) proceeds when exceeds the upper limit value, sets the rear wheel turning angle provisional pδ _r ^* (S) = the upper limit.
The subsequent step S304, the rear wheel turning angle provisional pδ _r ^* (S) to the rear wheel steering angle target value δ _r ^* (S). That is, if the rear wheel turning angle provisional value pδ _r ^* (S) does not exceed the upper limit value, the rear wheel turning angle provisional value pδ _r ^* (S) is directly used as the rear wheel turning angle target value δ _r ^* (S). If the rear wheel turning angle provisional value pδ _r ^* (S) exceeds the upper limit value, the upper limit value becomes the rear wheel turning angle target value δ _r ^* (S).
Here, the upper limit value set in step S303 is set to the full turning angle (maximum turning angle) of the rear wheel turning angle. Therefore, compared to the first and second embodiments, the front wheel turning angle is a turning angle before the full turning angle, and the rear wheel turning angle target value is a full turning equivalent value.

(Operation of Embodiment 3)
Next, the operation of the third embodiment will be described.
FIG. 14B is a comparative example with respect to the third embodiment, and shows a case where the upper limit cut by the rear wheel turning angle target value calculation unit 340 is not performed.
That is, in this comparative example, the front wheel turning angle δf is the maximum turning angle (full turning), and the rear wheel turning angle δr is the maximum turning angle. In this case, since it takes time until the first-order delay converges completely, there are many scenes where the rear wheel WR cannot be used up to the maximum turning angle.

On the other hand, in the second embodiment, as shown in FIG. 14A, correction is made to cut the portion where the provisional value of the rear wheel turning angle δ _r ^* (S) exceeds the upper limit, and the maximum rotation is performed at this upper limit. The steering angle was adjusted. For this reason, the tendency for the rear wheel turning angle target value of the first-order delay to become the maximum turning angle increases, and the number of scenes that can be used up to the maximum increases. Therefore, it is possible to obtain an effect that the low speed handling performance can be further improved while suppressing the uncomfortable feeling of the vehicle behavior.

(Effect of Embodiment 3)
In the third embodiment, in addition to the effects 1) to 3) and 2-1) 2-2) described in the first and second embodiments, the following effects can be obtained.
3-1) The rear wheel steering control device of Embodiment 3 is
The rear wheel turning controller 40 obtains a rear wheel turning angle provisional value pδ _r ^* (S) by a product of the steady gain β and the first order lag-derived component {1 / (1 + τ · S)} δ _f . absolute value of the rear wheel steering angle provisional pδ _r ^* (S) is, if exceeded the wheel steering angle limit value after preset, the rear wheel turning angle provisional value was corrected to cut the excess amount Pideruta and determines the rear wheel steering angle target value δ _r ^* (S) based on the _r ^* (S).
In Embodiment 3, when the absolute value of the rear wheel turning angle provisional value pδ _r ^* (S) exceeds the rear wheel turning angle upper limit value, the excess amount is cut, and this upper limit value is determined as the maximum turning angle. Thus, the rear wheel turning angle target value δ _r ^* (S) is set. Therefore, even if a primary delay is given to the rear wheel steering angle, the steering wheel is easily steered to the maximum steering angle, and there is an effect of further improving the low-speed maneuverability while reducing the uncomfortable behavior.

As mentioned above, although the cooling device of the drive unit of the present invention has been described based on the embodiment, the specific configuration is not limited to this embodiment, and the invention according to each claim of the claims Design changes and additions are permitted without departing from the gist of the present invention.
In the embodiment, the front-wheel drive vehicle using the drive motor as the vehicle drive means has been described, but the vehicle drive means and drive type are not limited to this. That is, other means such as an engine can be used as the drive means of the vehicle, and the rear wheel drive, the four wheel drive, the left and right independent drive, etc. can be used as the drive type.
In the embodiment, in setting the time constant gain according to the front wheel turning angular velocity (steering angular velocity), the time constant gain is set as a linear function according to the front wheel turning angular velocity (steering angular velocity). However, the present invention is not limited to this. In short, the higher the front wheel turning angular velocity (steering angular velocity), the lower the time constant gain. In that case, the time constant gain may be lowered in a multiple-order function or may be lowered stepwise.
In FIG. 3, the dotted line indicates the case where the angular velocity determination value θ ₀ ^* is set to a value near 0. In this case, the time constant gain is set to 1 when the steering angular velocity θ ^* is close to 0, and the time constant gain is set to approach 0 as the steering angular velocity becomes larger than 0. It may be linear or may be set stepwise.

20 Front wheel steering device 30 Rear wheel steering device 40 Rear wheel steering controller (control means)
51 Steering angle sensor (front wheel turning angle detection means)
A Rear wheel steering control device WF Front wheel WR Rear wheel α (θ) Steady gain β (θ) Steady gain δ _f Front wheel steering angle δ _f ^* Front wheel steering angular velocity
pδ _r ^* (S) Rear wheel turning angle provisional value δ _r ^* (S) Rear wheel turning angle target value θ ^* ₀ Angular velocity judgment value θ Steering angle θ ^* Steering angular velocity λ Constant length τ (δ _f ^* ) Primary delay time constant

Claims (5)

A rear wheel steering device for driving the driving means to steer the rear wheels;
Front wheel turning angle detection means for detecting the front wheel turning angle;
Control means for operating the rear wheel steering device to steer the rear wheel with a first order delay with respect to the front wheel steering angle;
In the rear wheel steering control device with
The control means includes a steady-state gain that is set so that the rear wheel turning angle changes with a preset characteristic in accordance with the front wheel turning angle, and a first order delay of the rear wheel turning angle with respect to the front wheel turning angle. The rear wheel turning angle is determined based on the product of the first-order lag-derived component set to be changed at
In addition, when the absolute value of the front wheel turning angular velocity exceeds a preset threshold value, the first-order lag-derived component is reduced as the absolute value of the front wheel turning angular velocity increases. In the rear wheel steering control device according to claim 1,
The said control means sets the said steady gain to 0, when the absolute value of the said front-wheel steering angle is 0, The rear-wheel steering control apparatus characterized by the above-mentioned. In the rear wheel turning control device according to claim 1 or 2,
The control means is characterized in that the steady-state gain with respect to the absolute value of the front wheel turning angle has a non-linear characteristic that is convex on the increase side with respect to a linear function linear with respect to the front wheel turning angle. . In the rear-wheel steering control device according to any one of claims 1 to 3,
When the front wheel turning angular speed is 0, the control means is based on a value obtained by dividing a primary delay time constant as a component derived from the primary delay by a vehicle speed by a constant length preset based on a wheelbase length of the vehicle. A rear-wheel steering control device characterized by being obtained. In the rear wheel steering control device according to any one of claims 1 to 4,
The control means obtains a provisional value of a rear wheel turning angle by a product of the steady gain and the component derived from the first order lag, and an absolute value of the provisional value of the rear wheel turning angle exceeds a preset rear wheel turning angle upper limit value. In this case, the rear wheel turning control device determines the rear wheel turning angle target value based on the provisional value of the rear wheel turning angle that has been corrected to cut the excess.