JP2005324655A - Vehicular rear wheel steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular rear wheel steering device capable of reducing the driving load of a driver when changing the lane or traveling following the lane. <P>SOLUTION: The vehicular rear wheel steering device comprises a camera 1, an image processor 2, a steering angle sensor 3, a vehicle speed sensor 4, a yaw rate sensor 5, a processor 6 and a rear wheel steering device 7. The processor 6 controls the rear wheel steering device 7 so as to maintain the constant yaw angle of a vehicle with respect to the lane irrespective of the steering by a driver. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of a vehicle rear wheel steering apparatus including a rear wheel steering mechanism.

As a conventional vehicle rear wheel steering device, for example, a device that stabilizes the steering characteristic of a vehicle by increasing the steering angle of the rear wheel in phase with the front wheel in accordance with deceleration is known (for example, , See Patent Document 1).
JP-A-5-69849

  However, in the above prior art, the driver must control the yaw angle and the lateral displacement at the same time by a series of steering wheel operations during lateral movement during lane change or lane following travel, and driving operability is poor. There was a problem that the driving load of the driver was high.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a vehicle rear wheel steering device that can reduce a driver's driving load during lane change or lane following traveling.

In order to achieve the above-mentioned object, in the present invention, in a vehicle rear wheel steering device including a rear wheel steering control means for controlling a rear wheel steering mechanism,
Lane recognition means for recognizing the lane ahead of the vehicle;
A yaw angle detection means for detecting a yaw angle with respect to the lane of the vehicle;
Provided,
The rear wheel steering control means performs the yaw angle maintenance control for controlling the rear wheel steering mechanism so as to keep the yaw angle with respect to the lane of the vehicle constant regardless of the driver's steering.

  In the present invention, the yaw angle with respect to the lane of the vehicle is maintained constant during lateral movement during lane change or lane following travel. Therefore, the driver only needs to pay attention to the lateral displacement and perform the steering operation, so that the driving operability is excellent and the driving load on the driver can be reduced.

  The best mode for carrying out the present invention will be described below based on the first embodiment.

First, the configuration will be described.
FIG. 1 is a configuration diagram of a vehicle rear wheel steering apparatus according to a first embodiment.
The vehicle rear wheel steering device according to the first embodiment includes a camera 1, an image processing device 2, a steering angle sensor 3, a vehicle speed sensor 4, a yaw rate sensor 5, a processor 6, and a rear wheel steering device 7. I have.

  The camera 1 captures the vehicle front image and outputs it to the image processing device 2. The image processing apparatus 2 estimates the lateral displacement of the vehicle with respect to the lane, the yaw angle with respect to the lane of the vehicle (hereinafter, “with respect to the lane of the vehicle” is omitted), and the road curvature, and outputs them to the processor 6. .

  The steering angle sensor 3 detects a steering angle (handle angle) and outputs it to the processor 6. The vehicle speed sensor 4 detects the vehicle speed (vehicle speed) of the host vehicle and outputs it to the processor 6.

  The processor 6 calculates a target rear wheel steering angle based on the lateral displacement, the yaw angle, the road curvature, the steering angle, and the vehicle speed, and outputs the target rear wheel steering angle to the rear wheel steering device 7. The rear wheel steering device 7 steers the rear wheel 8 so that the actual rear wheel steering angle matches the target rear wheel steering angle.

  FIG. 2 is a control block diagram showing the variation calculation unit 61 of the processor 6, and FIG. 3 is a control block diagram showing the target rear wheel steering angle calculation unit 62 of the processor 6.

  The variation calculation unit 61 includes a differentiator 61a, a steady turning state quantity calculator 61b, and three adders 61c, 61d, and 61e.

The differentiator 61a receives the lateral displacement y _cr and outputs a variation Δy′cr of the lateral displacement speed. The steady turning state quantity calculator 61b receives the road curvature ρ and the vehicle speed v, and outputs a steady state yaw angle φ _rρ , yaw rate φ ′ _ρ, and steering angle θ _ρ . The adder 61c is' a yaw rate φ steady state 'yaw rate φ enter the _[rho, and outputs the variation [Delta] [phi' of the yaw rate. The adder 61d inputs the yaw angle phi _Aruro the yaw angle phi _r and the steady state, outputs the variation [Delta] [phi _r of the yaw angle. The adder 61e inputs the steering angle theta _[rho steering angle theta and the steady state, outputs the variation Δθ of the steering angle.

  The target rear wheel steering angle calculation unit 62 includes feedback coefficient units 62a, 62b, 62c, 62d, and 62e, and an adder 62f.

The feedback coefficient unit 62a outputs a value obtained by multiplying the yaw rate variation Δφ ′ by the feedback coefficient −k ₁ . The feedback coefficient unit 62b outputs a value obtained by multiplying the yaw angle variation Δφ _r by the feedback coefficient −k ₂ . The feedback coefficient unit 62c outputs a value obtained by multiplying the fluctuation amount of the lateral displacement speed Δy ′ _{cr by} the feedback coefficient −k ₃ . The feedback coefficient unit 62d outputs a value obtained by multiplying the fluctuation amount Δy _cr of the lateral displacement by the feedback coefficient −k ₄ . Feedback coefficient unit 62e outputs the value obtained by multiplying the feedback coefficient -k ₅ to variation Δθ of the steering angle.

The adder 62f inputs the steering angle theta _[rho output and the steady state of the feedback coefficient unit 62a to 62e, and outputs the target rear-wheel steering angle.

Next, the operation will be described.
[Target rear wheel steering angle calculation logic]
The target rear wheel steering angle calculation logic executed by the processor 6 will be described.

First, physical quantities are defined. The lateral displacement (more precisely, the lateral displacement of the center of gravity) is y _cr , the yaw angle is φ _r , the yaw rate is φ ′, the steering angle is θ, and the rear wheel steering angle is δ _r .

The state equation of the vehicle to be controlled is expressed by the following equation 1.

Each element of the matrix in Equation 1 is as follows.

However,
I: vehicle yaw moment of inertia, m: vehicle weight, lf: center of gravity to front wheel axle distance, lr: center of gravity to rear wheel axle distance, cf: front wheel cornering stiffness (for two wheels), cr: rear wheel cornering stiffness (For two wheels), v: vehicle speed, N: steering gear ratio

The steady state of Equation 1 is defined by Equation 2 below.

Since the lateral displacement speed y ′ _cr and the lateral displacement y _cr are both zero at steady state, Equation 2 is rewritten as Equation 3 below.

Δ _{rρ in} Equation 3 represents the rear wheel steering angle during steady turning on the curve of the road curvature ρ. By setting this according to the road curvature, the vehicle posture during steady turning changes (φ _{rρ in} Equation 3 changes). Here, _δrρ is set to zero. As a result, the vehicle posture during steady turning is the same as 2WS.

Subtracting Equation 3 from Equation 1 yields Equation 4 below.

Δ represents the variation from the steady value. Here, when the behavior of Δθ is modeled by a primary system driven by white noise, Equation 4 is rewritten as Equation 5 below.

Here, λ _θ represents a first-order lag coefficient, C _θ represents white noise intensity (intensity), and w represents white noise.

The target rear wheel steering angle δ _r ^* is expressed by the following formula 6.

The feedback coefficient [k ₁ k ₂ k ₃ k ₄ k ₅ ] is constituted by, for example, an optimal regulator so as to minimize the evaluation function J in the controlled object of Expression 5.

  For details of the optimal regulator, see, for example, the document "Introduction to Optimal Control" by Kanichiro Kato, Tokyo University Press 1987.

R in Equation 7 is a parameter for adjusting the strength of control. This is a coefficient (generally called a weight) for the yaw angle displacement (displacement relative to the steady value) Δφ _r , and the feedback coefficient is set so that Δφ _r is less likely to occur as this value is increased. Is done.

  Here, as shown in FIG. 4, the parameter R of the control strength may be set to be dependent on the vehicle speed v, and may be set so as to increase (increase the control) as the speed increases.

  Further, as shown in FIG. 5, the control strength parameter R may be set to depend on the steering angle θ, and may be set so as to decrease as the steering angle θ increases (so that the control is weakened).

  Furthermore, as shown in FIG. 6, the parameter R of the control strength may be set to depend on the steering angular velocity θ ′, and may be set so as to decrease (decrease control) as the steering angular velocity θ ′ increases.

  In addition, the rear wheel control may be temporarily stopped in situations where it is difficult or difficult to recognize the lane in which the host vehicle is traveling, such as a branch road.

[Problems with conventional vehicles]
FIG. 7 is a diagram showing vehicle behavior when a lane change of a vehicle including rear wheel steering is performed.
First, when steering is started in (a), the vehicle changes the yaw angle with respect to the lane, and at the same time, the center of gravity starts to move sideways. The behavior of the yaw angle and lateral G is affected by vehicle characteristics such as vehicle weight, yaw moment of inertia, cornering stiffness of front and rear tires, center of gravity, and other factors, as well as vehicle speed and road surface μ.

  Further, in a vehicle having rear wheel steering (hereinafter referred to as a 4WS vehicle), the behavior thereof is changed by control of rear wheel steering. For example, in a 4WS vehicle that cuts the rear wheels in phase with the front wheels, the generation of the yaw angle can be kept small. That is, as shown in FIG. 8, the lane change can be performed in a state similar to walking.

However, it is impossible with the conventional method to steer the rear wheels so as not to generate the yaw angle. If it is not generated, as shown in FIG. 9, the vehicle must run with a side slip angle generated during cornering.
In summary, in a conventional vehicle (including 4WS), a yaw angle is generated in the stage (a).

  Next, after the lateral movement of (b), the vehicle as shown in (c) enters a state where it converges to another lane. The driver should make the vehicle center of gravity point coincide with the target lateral position (for example, the center line of the target lane), and at that time, the yaw angle with respect to the lane of the vehicle body is a steady value (zero for straight lines, steady side slip angle for cornering) It is necessary to operate the handle so that Since two physical quantities must be controlled by a series of steering wheel operations, the driving load is increased.

  In a very slow lane change, the yaw angle change in (b) does not occur so much, so the driver can concentrate on paying attention to the lateral position control, but if the lane change becomes abrupt, (b) The change in yaw angle at this time increases, and the driving load on the driver increases.

  Lane tracking can also be regarded as a kind of lane change in a large sense, and it can be said that a similar driving load is given to the driver. Even a slight lateral position correction causes a yaw angle, so the driver must control the yaw angle and lateral displacement at the same time.

[Yaw angle maintenance control action]
On the other hand, in the vehicle rear wheel steering device according to the first embodiment, by controlling the rear wheel steering device 7 so that the yaw angle displacement Δφ _r does not occur, the lane change or the lateral movement during the lane following traveling is performed. The driving load on the driver is reduced.

FIG. 10 shows an example of correction steering during curve traveling in the vehicle rear wheel steering apparatus according to the first embodiment.
Now, it is assumed that the driver is required to shift the vehicle lateral position to the right by a predetermined value (the discussion of the curve is a general consideration including the straight line portion, and the description of the straight line portion is omitted here). For reasons, only the right steering is considered, and the left steering is omitted).
In the steady state of (a), it is assumed that the yaw angle is θ _rρ .

In order to shift the vehicle to the right, when the driver turns the steering wheel to the right, the rear wheels are steered so that yaw angle fluctuation does not occur. That is the state (b), and as a result of control, the yaw angle is maintained at _φrρ . Although the lateral displacement speed changes depending on how the steering wheel is turned, the yaw angle does not change.

As shown in (c), at the moment when the lateral displacement speed becomes zero, the yaw angle is maintained at the steady-state value φ _rρ , so that no lateral displacement occurs again.

  Thus, the driver only needs to pay attention to the lateral displacement, and the driving operability is improved.

[Change of yaw angle maintenance control strength according to vehicle speed]
The effect of setting the parameter R depending on the vehicle speed v will be described. In general, at low speeds, there are many situations in which a vehicle cannot run along a lane. For example, when guiding a vehicle out of the lane, the driver does not attempt to drive the vehicle along the lane. On the other hand, driving on a highway along a lane is the main situation. Therefore, the control is weakened (or not controlled) at low speeds, and enhanced at high speeds, so that it has excellent operability.

[Change effect of yaw angle maintenance control strength according to steering angle]
The effect of setting the parameter R depending on the steering angle θ will be described. Control that keeps the yaw angle at a steady value is effective when following a lane or changing lanes. However, there are accident vehicles, etc., and emergency avoidance etc. can not be run along the lane. By restricting the control to the minute steering region, it is possible to achieve both the drivability at the time of lane tracking and lane change and the emergency avoidance.

[Change effect of yaw angle maintenance control strength according to steering angular velocity]
The effect of setting the parameter R depending on the steering angular velocity θ ′ is similar to the steering angle θ dependency, focusing on the fact that the steering angular velocity at the time of emergency avoidance increases, and by limiting the control when the steering angular velocity is small, It is possible to achieve both the drivability at the time of lane tracking and lane change and the above emergency avoidance.

  Since this control is based on the premise that the lane of the host vehicle can be recognized, erroneous steering can be effectively prevented by actively stopping the control in situations where the host lane is difficult to recognize, such as a high-speed branch road.

Next, the effect will be described.
In the vehicle rear wheel steering apparatus according to the first embodiment, the following effects can be obtained.

  (1) The processor 6 controls the rear wheel steering device 7 so as to keep the yaw angle with respect to the lane of the vehicle constant regardless of the driver's steering. The yaw angle with respect to the lane is maintained constant. Therefore, the driver only needs to pay attention to the lateral displacement and perform the steering operation. Therefore, the driver is excellent in driving operability and does not impose a driving load on the driver.

  (2) Since the processor 6 weakens the control strength of the yaw angle maintenance control at low speed or stops the control, the processor 6 can perform the optimum rear wheel steering according to the vehicle speed.

  (3) Since the processor 6 performs the yaw angle maintenance control when the front wheel steering angle is in the minute steering region, it is possible to achieve both operability during lane tracking and lane change and emergency avoidance.

  (4) Since the processor 6 weakens the control strength of the yaw angle maintenance control or temporarily stops the control as the absolute value of the front wheel steering angular velocity increases, the operability and emergency avoidance at the time of lane tracking or lane change Can be compatible.

  (5) Since the processor 6 temporarily stops the yaw angle maintenance control when the lane recognition means does not recognize the lane, the processor 6 is caused by erroneous steering by the rear wheel steering device 7 when the yaw angle with respect to the lane of the vehicle cannot be detected. Deterioration of vehicle behavior can be prevented.

1 is a configuration diagram of a vehicle rear wheel steering apparatus according to a first embodiment. FIG. 4 is a control block diagram showing a variation calculation unit 61 of the processor 6. FIG. 3 is a control block diagram showing a target rear wheel steering angle calculation unit 62 of a processor 6. FIG. It is an example of setting parameter R according to the vehicle speed. It is an example of setting of parameter R according to a steering angle. It is a setting example of the parameter R according to the steering angular velocity. It is a figure which shows the vehicle behavior at the time of the vehicle general lane change including rear-wheel steering. It is a figure which shows the vehicle behavior of a 4WS vehicle. It is a figure which shows generation | occurrence | production of a skid angle. FIG. 6 is a diagram illustrating an operation of the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera 2 Image processing apparatus 3 Steering angle sensor 4 Vehicle speed sensor 5 Yaw rate sensor 6 Processor 61 Fluctuation calculation part 62 Target rear-wheel steering angle calculation part 7 Rear-wheel steering apparatus

Claims (5)

In the vehicle rear wheel steering device including the rear wheel steering control means for controlling the rear wheel steering mechanism,
Lane recognition means for recognizing the lane ahead of the vehicle;
A yaw angle detection means for detecting a yaw angle with respect to the lane of the vehicle;
Provided,
The rear wheel steering control means performs the yaw angle maintenance control for controlling the rear wheel steering mechanism so as to keep the yaw angle with respect to the lane of the vehicle constant regardless of the driver's steering. apparatus. In the vehicle rear wheel steering apparatus according to claim 1,
The vehicle rear wheel steering device according to claim 1, wherein the rear wheel steering control means weakens the control strength of the yaw angle maintenance control at a low speed or stops the control. In the vehicle rear wheel steering device according to claim 1 or 2,
The vehicle rear wheel steering device according to claim 1, wherein the rear wheel steering control means performs yaw angle maintenance control when the front wheel steering angle is in a minute steering region. In the vehicle rear wheel steering device according to any one of claims 1 to 3,
The vehicle rear wheel steering apparatus characterized in that the rear wheel steering control means weakens the control strength of the yaw angle maintenance control or temporarily stops the control as the absolute value of the front wheel steering angular velocity increases. The vehicle rear wheel steering device according to any one of claims 1 to 4,
The vehicle rear wheel steering device, wherein the rear wheel steering control means temporarily stops the yaw angle maintenance control when the lane recognition means does not recognize the lane.

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