JPH07144653A - Controller of quantity of yawing momentum of vehicle - Google Patents

Abstract

PURPOSE:To enhance the feedback control following the quantity of yawing momentum by computing the maximum value of the objective quantity of momentum feasible with a vehicle concerned from a lateral accelerationn detection value, at running on an ice and snow road or the like. CONSTITUTION:This controller is provided with a car speed sensor 6, a steering angle sensor 8, a rear wheel steering angle sensor 9, a lateral acceleration sensor 11, a yaw rate sensor 12, and abnormality detection sensor 44 which detects the abnormality of each place of a rear-wheel steering gear 2, and the signals are inputted into a controller 3, severally. And, the standard quantity of yawing motion such as, for example, a standard yaw rate to becomes a standard is detected and set by specified operation formula, map retrieval, or the like, using each detection value, etc., of steering angle and car speed. Next, the control is performed so as to conform the quantity of yawning momentum detected with a yaw rate sensor to the objective quality of yawing momentum and in this case, the maximum value of the objective quantity yawing momentum feasible with a vehicle concerned, is computed based on the detection value of the friction state of the road face detected based on each sensor signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention calculates a target yawing momentum from an input acting on a vehicle, a physical quantity generated in the vehicle, and the like, and calculates a yawing momentum actually generated in the vehicle.
The present invention relates to a yawing momentum control device for a vehicle that performs feedback control so as to match the target yawing momentum, and particularly to a four-wheel steering device capable of individually controlling the steering angles of the front and rear wheels and the front and rear wheels, which enables this feedback control. Driving force distribution between the left and right wheels or the limiting force control device for the clutch, the braking force control device for the wheel cylinders provided on each wheel of the vehicle, and the roll rigidity between the left and right wheels It is applicable to a stabilizer control device or an active suspension device.

[0002]

2. Description of the Related Art For example, the four-wheel steering (hereinafter, simply referred to as 4WS)
The basic purpose of four-wheel steering in a vehicle is to improve the steering characteristics of the vehicle. Specifically, in today's four-wheel steering vehicles, when the steering wheel is steered to steer the front wheels that are steered wheels during low-speed traveling, a small turn is performed by so-called reverse-phase steering that steers the rear wheels in the opposite direction to the front wheels. The stability is improved by so-called in-phase steering in which the rear wheels are steered in the same direction as the front wheels when traveling at high speed. Further, in order to enhance the effect of the four-wheel steering, not only the rear wheels that are non-steering wheels but also the front wheels that are steered wheels are provided with a steering angle changing mechanism by a control means such as electronic / hydraulic so that the entire vehicle is Some proposals have been made to improve the steering characteristics in total. The steering characteristic-corresponding front and rear wheel control steering angle for controlling the steering characteristic of the vehicle according to the vehicle speed is detected by the vehicle speed sensor or the like, and an appropriate calculation formula or map is calculated based on the detected vehicle speed value. Calculated and set by search.

An example of a vehicle yaw momentum control device applied to such a four-wheel steering vehicle is disclosed in Japanese Patent Application Laid-Open No. 1-172071. In this four-wheel steering vehicle, for example, a yaw momentum such as a yaw rate occurring in the vehicle (hereinafter, simply referred to as an actual yawing momentum) is detected by a yaw rate sensor or the like, while the front-rear vehicle speed of the vehicle and the steering angle of the steering wheel are detected. The target yawing momentum such as the target yaw rate is calculated and set from these detected values by an appropriate calculation formula or map search, and the steering angle of the rear wheels for matching the actual yawing momentum with the target yawing momentum is set. , Based on the deviation between the actual yawing momentum and the target yawing momentum, it is calculated and set by an appropriate calculation formula or map search, and the actuator provided on the vehicle is driven to achieve the steering angle of the rear wheels. Feedback control is possible to improve the steering characteristics of the vehicle, especially regarding cornering characteristics. To. Specifically, the yaw momentum-corresponding rear wheel steering angle is obtained by adjusting the overall steering characteristic-corresponding rear wheel steering angle.

Here, when the relative steered angle between the front and rear wheels increases due to, for example, reverse-phase steering of the rear wheels, the yaw moment generated in the vehicle is promoted, and therefore the actual yaw rate actually generated in the vehicle. When the relative steering angle between the front and rear wheels decreases due to the in-phase steering of the rear wheels, etc., the yaw moment generated in the vehicle is suppressed, so the actual yawing momentum actually occurs in the vehicle. The actual yawing momentum, such as the actual yaw rate, is decelerated, so that the deviation between the target yawing momentum and the actual yawing momentum can be matched to a desired value.

In this way, in order to change the steering characteristics of the vehicle by controlling the turning angle of each wheel, in the four-wheel steering vehicle, attention is paid to the yawing momentum such as the yaw rate and the yaw angular acceleration. From this point of view, it can be handled as a yawing momentum control device. That is, the actual yawing momentum such as the yaw rate and the yaw angular acceleration actually generated in the vehicle can be detected via a sensor such as a yaw moment gyro mounted on the vehicle.
On the other hand, as is known, the target yawing momentum to be achieved in a vehicle is related to vehicle characteristics including tire characteristics, specifically, cornering power, wheel base, tread or these, with vehicle speed, steering angle or turning angle as variables. Can be obtained as a function relating to the stability factor and the like.
Further, this target yawing momentum also has vehicle speed, steering angle or steering angle, yawing momentum, etc. as variables, and overshoot and undershoot with respect to steady yawing momentum obtained as a function relating to vehicle characteristics such as stability factor. It can be obtained by performing a delay system calculation as a temporary delay system without a shoot. Specifically, this target yawing momentum simply increases with increasing steering angle or turning angle at a given vehicle speed. Then, feedback control is performed so that the target yawing momentum thus obtained matches the actual yawing momentum actually generated in the vehicle. At this time, in order to realize the target yawing momentum in the actual vehicle, for example, the deviation between the target yawing momentum and the actual yawing momentum is multiplied by a predetermined feedback control gain in consideration of the vehicle specifications and steering characteristics. There is. Incidentally, this feedback control gain is the same as the above-mentioned Japanese Patent Laid-Open No. 1-172071.
In the four-wheel steering vehicle disclosed in Japanese Patent Publication, a fixed value that is uniquely determined by vehicle specifications and vehicle characteristics is generally set.

Such a yawing momentum control device is
For example, the fastening force control device for the driving force distribution clutch between the front and rear wheels or the left and right wheels described in Japanese Patent Application Laid-Open No. 3-31030 previously proposed by the present applicant, and the Japanese Patent Application Laid-Open No. The active suspension and stabilizer control device capable of variable roll rigidity control described in Japanese Patent Application Laid-Open No. 5-193332, or the vehicle wheels described in Japanese Patent Application Laid-Open No. 5-24528 previously proposed by the present applicant. It is being widely applied to braking force control devices and the like for individually controlling the braking force.

[0007]

By the way, regarding the tire characteristics of a wheel with a pneumatic rubber tire, the friction coefficient of the road surface (hereinafter, also simply referred to as μ) is the same even for the same tire.
It is known that the cornering force changes depending on. In particular, the cornering force per unit side slip angle, that is, the maximum value of the cornering power and the cornering force, is greatly influenced by the road surface friction coefficient.
For example, when traveling on icy and snowy roads, since the road surface friction coefficient is extremely small, the tire cornering power and the maximum cornering force are also very small. Considering that the steering angle is proportional to the angle, it is clear that even if the steering angle of the steering wheel is increased, it is difficult for the vehicle to generate a sufficient yaw moment to turn the steering wheel.

However, in the conventional yawing momentum control device for a vehicle, it is considered that the target yawing momentum simply increases, if not linearly, as the steering angle and the turning angle increase. If
In the actual situation, the changes in the maximum values of the cornering power and the cornering force related to the road surface friction coefficient as described above are not taken into consideration. Therefore, under the condition of the road surface friction coefficient in which both the cornering power and the maximum cornering force are small, such as when running on the ice and snowy road surface, the driver can consciously or unconsciously change the steering angle of the steering wheel. The target yawing momentum is increased by increasing the value to turn the vehicle. On the other hand, the actual yawing momentum actually generated in the vehicle tends to be small in such a road surface friction coefficient state in which the maximum values of the cornering power and the cornering force are reduced. Therefore, in the conventional yawing momentum control device for a vehicle, when the deviation between the actual yawing momentum and the target yawing momentum is excessively large, when the feedback control is performed, the command value to the actuator is extremely high. As a result, the relative steered angle between the front and rear wheels reacts excessively to this command value with a predetermined delay.

On the other hand, in the yawing momentum control device developed in the four-wheel steering vehicle disclosed in Japanese Patent Laid-Open No. 60-161255 proposed by the applicant of the present invention, the yawing momentum control device depends on the road surface friction coefficient state. ， It is disclosed that the feedback control gain is changed. Specifically, under a road surface friction coefficient condition in which both the cornering power and the maximum cornering force become small, such as when traveling on the ice and snowy road surface,
The feedback control gain that is multiplied by the deviation between the actual yawing momentum and the target yawing momentum is reduced to suppress an excessive reaction of the relative steered angle between the front and rear wheels. However, even with this yawing momentum control device for a vehicle, as a result, a feedback that matches the target yawing momentum set so as to simply increase with an increase in the vehicle speed and the steering angle and the actual yawing momentum of the vehicle. Since control is exercised, there is no fundamental solution to the above problems.

The present invention has been developed in view of these problems. For example, when the vehicle is running under a road surface friction coefficient condition in which the maximum cornering power and the maximum cornering force are small, such as when traveling on the ice and snowy road surface. By setting the maximum feasible target yaw momentum, the yaw momentum tracking feedback control is limited to avoid meaningless feedback command value increase, and yawing momentum tracking feedback according to vehicle characteristics including tire characteristics is avoided. An object of the present invention is to provide a yawing momentum control device for a vehicle that enables control.

[0011]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has obtained the following findings and developed the present invention. That is, the road friction coefficient state that affects the maximum value of the cornering power and cornering force, which are the tire characteristics, is detected or estimated by some means, and the vehicle is implemented according to the detected value or estimated value of the road friction coefficient state. The maximum value of the possible target yawing momentum is set, and the target yawing momentum calculated simply from the input to the vehicle such as the vehicle speed and steering angle or the physical quantity generated in the vehicle does not exceed this maximum value. It was noted that the yawing momentum tracking feedback control according to the vehicle characteristics including the tire characteristics is enabled by calculating and setting the momentum. Here, the lateral acceleration generated in the turning state of the vehicle depends on the actual yawing momentum through the vehicle speed, the coefficient of friction between the tire and the road surface, the side slip angle of the tire, the maximum value of the cornering power and the cornering force incidental thereto. At the same time, we paid attention to the fact that when performing feedback control to track the target momentum, it serves as an evaluation index for vehicle behavior that occurs secondarily to the steering input.

Therefore, the yawing momentum control device for a vehicle according to the first aspect of the present invention, as shown in the basic configuration diagram of FIG. 1, is a yawing momentum detecting means for detecting the yawing momentum actually occurring in the vehicle. And an input physical quantity detecting means for detecting an input acting on the vehicle or a physical quantity occurring in the vehicle, and an input detected value acting on the vehicle detected by the input physical quantity detecting means or a physical quantity detected value occurring in the vehicle A target yawing momentum calculation means for calculating a target yawing momentum to be achieved in the vehicle based on In a yawing momentum control device for a vehicle, which comprises a control means for controlling
The target yawing momentum calculation means includes a road surface friction coefficient state detection / estimation unit that detects or estimates the state of the road surface friction coefficient of the traveling road surface. It is characterized by comprising maximum value calculation means for calculating the maximum value of the target yawing momentum based on the state detection value or its estimated value.

A yawing momentum control device for a vehicle according to a second aspect of the present invention has a basic configuration diagram shown in FIG.
The road surface frictional state detection estimating means includes a lateral acceleration detecting means for detecting a lateral acceleration acting on the vehicle.

[0014]

In the yawing momentum control device for a vehicle according to the first aspect of the present invention, as shown in the basic configuration diagram of FIG. The yawing momentum (actual yawing momentum) such as the yaw rate is detected. On the other hand, the input physical quantity detecting means detects the steering angle through, for example, a steering angle sensor, and detects the vehicle front-rear vehicle speed through, for example, a vehicle speed sensor. A reference yawing momentum such as a reference yaw rate serving as a reference is calculated and set by a predetermined arithmetic expression or map search using the detected value and the vehicle speed detected value.

By the way, the road surface friction coefficient state detecting / estimating means detects or estimates the state of the friction coefficient of the road surface during traveling, for example, from an input to the vehicle or a physical quantity generated in the vehicle. Here, in the yawing momentum control device for a vehicle according to claim 2 of the present invention, as shown in the basic configuration diagram of FIG. 1, the lateral acceleration detecting means provided in the road surface friction coefficient state detecting and estimating means is applied to the vehicle. The acting lateral acceleration is detected. As described above, the lateral acceleration generated in the turning state of the vehicle is transmitted to the steering input through the vehicle speed, the coefficient of friction between the tire and the road surface, the side slip angle of the tire, the maximum value of the cornering power and the cornering force which accompany them. On the other hand, it becomes an evaluation index of vehicle behavior that occurs secondarily,
In accordance with this lateral acceleration detection value, the maximum value calculation means provided in the target yawing momentum calculation means, for example, a value obtained by dividing the lateral acceleration detection value by the vehicle speed detection value detected by the vehicle speed sensor or the like, The maximum value of the target yawing momentum (hereinafter, also simply referred to as the maximum yawing momentum) is calculated and set by multiplying by a predetermined proportional coefficient for unit conversion and correcting the time delay of the lateral acceleration with respect to the yawing momentum.

The maximum yawing momentum calculated and set in this manner is actually generated in consideration of the road surface friction coefficient state with respect to the target yawing momentum considered to occur in proportion to the vehicle speed and the steering angle as described above. From the actual yawing momentum, the lateral acceleration secondary to the steering input is divided by the vehicle speed detection value to obtain the maximum value of the target yawing momentum that can be steadily and actually achieved by the vehicle. Therefore, the target yawing momentum calculating means compares the maximum yawing momentum calculated and set by the maximum value calculating means with the reference yawing momentum, and when the reference yawing momentum is less than or equal to the maximum yawing momentum, the reference yawing momentum is calculated. Is set as the target yawing momentum, and when the reference yawing momentum exceeds the maximum yawing momentum, it is determined that the reference yawing momentum is a meaningless target value that cannot be actually achieved by the vehicle, and the maximum yawing momentum is determined. Set the momentum to the target yawing momentum.

On the basis of the target yawing momentum set in this way, the control means controls the yawing momentum detected by the vehicle (actual yawing momentum) so as to follow the target yawing momentum. The deviation of both yawing momentums is multiplied by a predetermined control gain, and the actuator provided to the vehicle is driven so that the deviation of both yawing momentums multiplied by this control gain becomes a predetermined value, for example, zero. Therefore, in the present invention, the target yawing momentum set as the target value is always a value that can be actually achieved by the vehicle on the basis of the friction coefficient state of the road surface, so that the control command value is meaninglessly large. By doing so, it is possible to prevent each actuator from acting excessively with a predetermined delay with respect to such an excessive command value.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a vehicle yaw momentum control device of the present invention will be described below with reference to the accompanying drawings. 2 to 7 show an embodiment in which the vehicle yawing momentum control device of the present invention is applied to a four-wheel steering vehicle capable of steering the rear wheels. Here, it is assumed that the basic steering characteristic improvement control contents in the above-described four-wheel steering vehicle are well known, and only the steering characteristic control for improving the cornering characteristic related to the yawing momentum will be described in detail.

First, FIG. 2 briefly shows the overall structure of a four-wheel steering vehicle. In the figure, 10FL and 10FR are left and right front wheels, and 10RL and 10RR are left and right rear wheels. Each of the wheels 10FL to 10RR is rotatably supported by at least a hub carrier that is swingably supported in the horizontal direction with respect to the vehicle. Of these, the front wheels 10FL, 10
For FR, tie rod 1 between both hub carriers
It is connected to the rack shaft of a known rack and pinion type steering gear device 14 via 3. A pinion (not shown) connected to a steering shaft 16 meshes with the rack shaft, and the steering wheel 15
It is configured such that the front wheel can be mechanically steered by rotating.

Reference numeral 2 in the same figure shows a rear wheel steering system mounted on a vehicle. In this rear wheel steering system 2, the rear wheels 10R
Both hub carriers are connected to the L and 10RR via a tie rod 18 and a steering shaft 20 for steering the rear wheels. The steering shaft 20 functions as a piston rod of a rear-wheel steering double-rod double-acting cylinder 22. Inside the rear-wheel steering cylinder 22, a left and right cylinder chambers 26L are formed by a piston 24 integrated with the steering shaft 20. 26R, and the steering shaft 20 is stroked according to the amount of oil supplied to these cylinder chambers 26L, 26R. A spring 28 having an equivalent elastic coefficient and a free length is provided in each of the cylinder chambers 26L and 26R. When the hydraulic pressure to each of the cylinder chambers 26L and 26R is released, the piston 24 is moved to the central portion of the cylinder 22. And is centered, and the rear wheels 10RL, 10RR are returned to the middle position.

Further, each cylinder of the rear wheel steering cylinder 22 is
Suction from the reservoir 34 into the binder chambers 26L, 26R
Hydraulic oil of a predetermined pressure from the hydraulic pump 30 and the control valve 32 and
And a cutoff valve 36. Specifically, oil
The pressure pump 30 is connected to the pump port P of the control valve 32.
The return port R of the control valve 32 is
Connected to the output port of the cutoff valve 36.
To S₁Connected to one cylinder chamber 26L of the cylinder 22
And the other output port S of the cutoff valve 36₂But
Connected to the other cylinder chamber 26R of the cylinder 22,
Furthermore, the two output ports A and B of the control valve 32 are
Two input ports N of the toff valve 36₁, N ₂Individually contact
Has been continued. Also, the hydraulic pump 30 may be installed in a vehicle, for example.
The reservoir 34 is driven to rotate by the mounted engine.
The hydraulic oil inside is discharged, and this is supplied to the control valve 32.
Of these, the hydraulic pump 32 and the reservoir 34 are
Installed side by side with a steering gear device
Also used as a power steering mechanism (not shown)
Good.

The cut-off valve 36 is a 4-port 2-position electromagnetic directional control valve having a function as a so-called fail-safe valve. In FIG. 2, a return spring 62 is arranged on the right side of the cutoff valve 36, and an electromagnetic solenoid 63 also arranged on the right side is excited by a drive signal CF from a controller which will be described later. There is. Therefore, in the normal state in which the electromagnetic solenoid 63 is not excited, the switch is in the right switching position in FIG. 2, and in this state, both input ports N ₁ and N _{2 of the} cutoff valve 36, that is, both output ports A of the control valve 32. , B
Becomes a communication state and the output hydraulic pressure of the control valve 32 is returned as it is, and both output ports S ₁ and S _{2 of} the cutoff valve 36, that is, both cylinder chambers 2 of the cylinder 22 are connected.
6L and 26R are in communication, and both cylinder chambers 26
Both cylinder chambers 2 by springs 28 in L and 26R
The hydraulic pressures in 6L and 26R are balanced so that the steering shaft 20 is centered, and the rear wheels 10RL and 10RR are in a straight traveling state, that is, in a non-steering state. Therefore, in a state where the control signal CF is not output, fail safe (failure compensation) is performed. ) Is done.
In addition, the spring 28 installed in the cylinder 22.
Has an elastic coefficient that does not easily deform due to the cornering force that normally occurs on the wheel during turning.

On the other hand, when the electromagnetic solenoid 63 of the cutoff valve 36 is excited by the drive signal CF from the controller, the cutoff valve 36 resists the elastic force of the return spring 62 and moves to the left switching position in FIG. Is switched to. In this state, one input port N ₁ of the cutoff valve 36 is in communication with the _one output port S ₁ and the other input port N ₂ is in communication with the other output port S ₂ , so that the control valve One output port A of 32 is communicated with the left cylinder chamber 26L of the cylinder 22, and at the same time, the other output port B of the control valve 32 is communicated with the right cylinder chamber 26R of the cylinder 22.

On the other hand, as can be understood from the above, the control valve 32 is composed of a 4-port 3-position, spring center type electromagnetic directional control valve having two input / output ports each, as shown in FIG. electromagnetic solenoid 60a of the left is excited by a drive signal CS ₁ from the controller to be described later, the electromagnetic solenoid 60b of the right is excited by a drive signal CS ₂ from the controller. Here, in a state where both electromagnetic solenoids 60a and 60b of the control valve 32 are not excited, the elastic forces of the return springs 61a and 61b on both sides of FIG. 2 are balanced and the control valve 32 is at the central switching position.
In this state, the pump port P and the return port R of the control valve 32 are in communication with each other, and the output ports A and B are in cutoff states. Therefore, in this state, the hydraulic pump 3
The discharge hydraulic pressure of 2 is returned to the reservoir 34 as it is, and when the cutoff valve 36 is in the operating state, the internal hydraulic pressures of the left and right cylinder chambers 26L and 26R of the cylinder 22 are respectively contained and the holding mode is set.

From this state, when the electromagnetic solenoid 60a on the left side of FIG. 2 is excited by the drive signal CS ₁ of the controller, the control valve 32 is actuated against the elastic force of the return spring 61a on the left side of FIG. It becomes the right switching position in the figure,
In this state, the pump port P of the control valve 32 is in communication with the other output port B, and the return port R is in communication with one output port A. Therefore, in this state, when the cut-off valve 36 is in the operating state, the discharge pressure from the hydraulic pump 30 supplies the operating oil to the right cylinder chamber 26R of the cylinder 22 and the piston 24 of the steering shaft 20.
Is moved to the left in FIG. 2, resulting in the left cylinder chamber 26R
Since the hydraulic oil inside is returned to the reservoir 34, the rear wheels 10
RL and 10RR are in the right cut mode.

On the other hand, the drive signal CS _{2 of the} controller
When the electromagnetic solenoid 60b on the right side of FIG. 2 is excited by this, the control valve 32 moves to the left switching position in the figure against the elastic force of the return spring 61b on the right side of the figure. The pump port P and the one output port A are in communication with each other, and the return port R and the other output port B are in communication with each other. Therefore, in this state, when the cut-off valve 36 is in the operating state, the discharge pressure from the hydraulic pump 30 supplies the working oil to the left cylinder chamber 26L of the cylinder 22 so that the piston 24 of the steering shaft 20 moves as shown in FIG. Since the hydraulic oil in the right cylinder chamber 26R is moved to the right and returned to the reservoir 34 as a result, the rear wheel 10R
L and 10RR are in the left cut mode.

As will be described later in detail with respect to the controller, the steering shaft 16 of the vehicle is provided with a steering angle sensor 8 (input physical quantity detecting means) for detecting the steering angle of the steering wheel 15. As shown in FIG. 3, from the sensor 8, the controller 3 obtains a steering angle detection value θ that is a voltage signal that is positive when the steering wheel 15 is turned to the right and negative when the steering wheel 15 is turned to the left. Output to.

Further, the vehicle is provided with a vehicle speed sensor 6 (input physical quantity detecting means) for detecting the vehicle front-rear speed (vehicle speed). A vehicle speed detection value V consisting of a voltage signal that is sometimes negative is output to the controller 3. Further, near the steering shaft 20 of the rear wheels 10RL, 10RR, there is provided a rear wheel steering angle sensor 9 for detecting the actual rear wheel steering angle of the rear wheels 10RL, 10RR from the position of the steering shaft 20. This rear wheel steering angle sensor 9 is turned left or right depending on the magnitude of the actual rear wheel steering angle from the middle position of the rear left and right wheels 10RL, 10RR and when both the rear wheels 10RL, 10RR are turned right. The actual rear wheel steering angle detection value δ _RR , which consists of a voltage signal that becomes negative when the vehicle is on, is output to the controller 3.

Further, the vehicle has a lateral acceleration sensor 11 for detecting a lateral centrifugal acceleration (lateral acceleration) acting on the vehicle.
(Lateral acceleration detecting means) is provided, and outputs a lateral acceleration detection value Yg consisting of a voltage signal that is positive in right turn and negative in left turn to the controller 3 according to the magnitude of the lateral acceleration. . Further, the vehicle is provided with a yaw rate sensor 12 (yawing momentum detecting means) for detecting a yaw rate (hereinafter referred to as an actual yaw rate) occurring in the vehicle, and according to the magnitude of the yaw rate, a right turn is made. The actual yaw rate detection value ψ ′, which is a voltage signal that becomes negative in positive and left turns, is output to the controller 3.

Further, the vehicle is provided with an abnormality detection sensor 44 for detecting an abnormality in each part of the rear wheel steering device 2, and an abnormality of the sensor of the rear wheel steering device 2, a controller described later, or each actuator. When is detected, the abnormality detection signal FS is output to the controller 3.
As shown in FIG. 3, the controller 3 (control means) has an input interface circuit 40a having at least an A / D conversion function, a central processing unit (CPU) 40b, a storage device (ROM, RAM) 40c, and a D / A conversion function. A microcomputer 40 having an output interface circuit 40d etc. having a drive signal CS ₁ for the pressure control valve 32
And a drive circuit 42 for supplying a drive signal CS ₂ to the pressure control valve 32, and a drive circuit 43 for supplying a drive signal CF to the cutoff valve 36. Although the detailed contents of the four-wheel steering control for improving the steering characteristic during normal cornering by the controller 3 will not be described here in detail, the vehicle speed detection value from the vehicle speed sensor 6 and the steering angle obtained from the steering angle sensor 8 are described. According to the detected value, the detected steering angular velocity value, the detected steering angular acceleration value, etc., the steering characteristic is changed to the weak understeer direction in the low speed region of the vehicle by performing the rear wheel steering in the same phase as the steering of the front wheel by the steering wheel 15. The turning performance is improved by controlling the steering characteristics so that the steering characteristics are strengthened in the understeer direction in the middle and high speed ranges to improve the stability of the vehicle at the time of turning and at the time of lane change and improve the convergence of cornering. Furthermore, when a fast steering input is given mainly in the low speed range, the rear wheels are momentarily reverse-phase steered immediately after the start of steering, thereby improving the yaw rate rise necessary for turning and improving the responsiveness to steering. That is, it is possible to improve the turning stability, and after that, by performing the in-phase steering of the rear wheels, it is possible to improve the running stability during cornering. The calculation of the steering angle change amount in the normal rear wheel steering control is performed according to an individual calculation process (not shown) performed by the microcomputer 40 in the controller 3, and the rear wheel steering control component δ _RO. The storage device 40 of the microcomputer 40
It is updated and stored in c.

Then, in the microcomputer 40 of the controller 3 of the present embodiment, the reference yaw rate ψ ^'* ₀ is set on the basis of the steering angle detection value θ and the vehicle speed detection value V according to the arithmetic processing of FIG. 4 which will be described in detail later. calculated setting, the lateral acceleration ^'calculates sets a ^* max, the maximum yaw rate ^[psi' maximum yaw rate [psi based on a detection value Yg towards either smaller ^* max and the reference yaw rate [psi ^'* ₀ and compared to the the ^'set as ^*, the target yaw rate ^[psi' target yaw rate [psi calculates the yaw rate difference ε between ^* and the actual yaw rate detected value [psi ^', the yaw rate corresponding rear wheel steering angle [delta] _R ^* in accordance with the yaw rate difference ε The rear wheel steering angle δ _R is calculated by adding the rear wheel steering control amount δ _RO related to the improvement of the normal steering characteristics to the yaw rate corresponding rear wheel steering angle δ _R ^* to calculate the rear wheel steering angle δ _{R. R} and the actual rear wheel steering angle A deviation γ from the detected value δ _RR is calculated, and when the rear wheel steering angle deviation γ is positive, it is determined that the rear wheels 10RL and 10RR need to be right-turned, and the control signal S _CS1 is driven as described above. When the rear wheel steering angle deviation γ is negative, it is determined that the rear wheels 10RL and 10RR need to be turned left, and the control signal S _CS2 is directed to the drive circuit 42. If the rear wheel steering angle deviation γ is zero, the rear wheels 10R
When it is judged that it is not necessary to increase L and 10RR, the output of the control signal S _CS1 or the control signal S _CS2 is stopped.

Further, in the microcomputer 40 of the controller 3 of the present embodiment, the control signal S _CF is sent to the drive circuit 43 on the basis of the abnormality detection signal FS from the abnormality detection sensor 44 in accordance with a calculation process (not shown). Output. The drive circuits 41 and 42 convert the control signals S _CS1 and S _CS2 output from the microcomputer 40 into drive signals CS ₁ and CS ₂ to the proportional solenoids 60a and 60b of the pressure control valve 32, and output the drive signals CS ₁ and CS _2. It is for.

The drive circuit 43 is for converting the control signal S _CF output from the microcomputer 40 into a drive signal CF for the cutoff valve 36 and outputting the drive signal CF. Next, the basic principle of the arithmetic processing performed in the controller of this embodiment will be described.

First, the principle of performing feedback control so that the actual yawing momentum actually generated in the vehicle follows the target yawing momentum obtained from the input acting on the vehicle or the physical amount generated in the vehicle will be described. First, before the target yaw rate ψ ^'* and the target yaw angular acceleration ψ ^"* set as the target yaw momentum, the reference yaw rate ψ ^{' *} as the reference yaw momentum that becomes the reference ^.
Two calculation methods of ₀ will be described.

First, as described above, this reference yaw rate ψ ^'* ₀ is defined by the following equation 1 using the vehicle speed V and the steering angle θ as variables according to _the known vehicle motion equation and the vehicle specifications as coefficients.
Given by the formula. ψ ^{′ *} = V / R R = K _S · L / tan (θ / N) (1) where R is the turning radius, L is the wheel base, and N is the steering gear ratio. Further, K _S is a stability factor, and this stability factor K _S is a coefficient showing the vehicle behavior stability that appears in turning characteristics, etc. Generally, the larger the stability factor K _{S, the} more the steering characteristics tend to be understeer. To be done.

The reference yaw rate ψ ^'* ₀ can also be calculated by using the steady-state yaw rate H ₀ . Generally, this steady-state yaw rate H ₀ uses the vehicle speed V, the steering angle θ as variables, and the stability factor K _S , the steering gear ratio N, and the wheel base L as coefficients to obtain the following 2
Given by the formula. H ₀ = V / (L · (1 + K _S V ² )) · (θ / N) ……… (2) And the standard yaw rate ψ ^'* ₀ is this steady-state yaw rate H
It is also known that it can be obtained by performing a first-order lag system operation using a first-order lag time constant τ with respect to _{0 according} to the following three equations.

Ψ ^'* ₀ = H ₀ / (1 + τs) (3) However, s represents a Laplace operator (Laplacian). Here, it is of course possible to calculate the reference yaw rate ψ ^'* ₀ according to the above equations 1, 2 and 3, but it is difficult to avoid that the calculation load becomes considerable. Therefore, in the present embodiment, the correlation between the steering angle detection value θ, which is the steering input according to these calculation formulas, and the reference yaw rate ψ ^'* ₀ is shown in the control map of FIG. 5 using the vehicle speed detection value V as a parameter. The reference yaw rate ψ ^'* ₀ is calculated and set by linearly interpolating the control map according to the read vehicle speed detection value V. According to this, it is possible to reduce at least the calculation load related to the complicated calculation of each calculation formula and shorten the processing time. In this control map, in consideration of the fact that the steering angle detection value θ becomes positive when turning to the right and negative when turning to the left in the above equations 1 or 2 and 3, it is assumed that the steering angle detection value θ is at the time of turning to the right according to each sign. The reference yaw rate ψ ^'* _{0, which} is negative when turning to the left or right, is set.

Conventionally, this reference yaw rate ψ ^'* _{0 is used as it} is or almost as it is as the target yaw rate, that is, the target yawing momentum, but the drawbacks related thereto are as described above. On the other hand, as is known, in the tire characteristics of a wheel with a general pneumatic rubber tire, although the cornering force normally increases almost linearly with an increase in the sideslip angle, the rate of increase gradually becomes small, and then from a certain value. It tends to decrease depending on the wheel load.
However, even with the same tire, if the friction coefficient state of the road surface during running changes, the tire characteristics related to the cornering force also change. Specifically, for example, on a snowy or snowy road surface or a wet tile road surface, the coefficient of friction between the tire and the road surface is extremely small. -The maximum value of the cornering force in the cornering force correlation is also small, and its inclination, that is, the cornering force and the cornering power per unit skid angle are also small. On the other hand, on a concrete road surface or a dry asphalt road surface, the coefficient of friction between the tire and the road surface is relatively large, and therefore, even if the sideslip angle of the wheel increases, the tire retains grip power,
The maximum value of the cornering force in the side slip angle-cornering force correlation becomes relatively large, and the inclination and the cornering power also become large.

By the way, the relationship between the lateral acceleration Yg during the vehicle motion and the yaw rate ψ ', which is the yaw momentum, is that when the two are running in a steady balance, the yaw rate ψ' = V / R lateral acceleration Yg = V ² / R = ψ ′ · V where R is the turning radius and V is the vehicle speed. Considering the transient aspect, the time relationship between the two is that the steering input by the steering wheel steering of the driver causes cornering force on the front wheels, which causes yawing motion, and the vehicle has a sideslip angle. The cornering force of
Lateral acceleration occurs. Therefore, if the cornering force changes with the change of the road surface friction coefficient state, some change also occurs in the lateral acceleration. Specifically, when the cornering power is small because the road friction coefficient state is small, the rise of the cornering force with respect to the steering input is small, so the lateral acceleration generated in the vehicle is also small, and the maximum value of the cornering force is Since it is small, the maximum lateral acceleration generated in the vehicle is small. On the other hand, when the cornering power is large because the state of the road surface friction coefficient is large, the rise of the cornering force with respect to the steering input is large, so that the lateral acceleration generated in the vehicle also becomes relatively large and the cornering force Since the maximum value is large, the tire retains its grip force even in deep turns and the maximum lateral acceleration generated in the vehicle becomes relatively large.

Based on the above principle, in this embodiment, the maximum yaw rate achievable by the vehicle and the maximum yaw rate ψ ^'*
Max is calculated based on the following four equations using the lateral acceleration detection value Yg from the lateral acceleration sensor 11 and the vehicle speed detection value V from the vehicle speed sensor 6. ψ ^'* max = k · Yg / V (4) Here, considering the proportionality coefficient k used in the above equation 4, from the time relationship between the yaw rate, which is the yawing momentum, and the lateral acceleration as described above, It can be seen that the lateral acceleration always has a time delay with respect to the yawing momentum. Therefore, the maximum yaw rate ψ ^'* max, which is the maximum yawing momentum calculated from the lateral acceleration in the above equation 4, is multiplied by a proportional constant larger than "1" in addition to the predetermined unit conversion coefficient,
It is necessary to correct the time delay. Therefore, the proportional coefficient k is set to a value that satisfies these requirements.
This proportionality coefficient k is such that the absolute value of the reference yaw rate │ψ ^'* ₀ │ is the absolute maximum yaw rate when a sufficient grip force is secured as normal tire characteristics expected on high μ roads. It is set to a value that does not exceed the value | ψ ^'* max |.

From the above, the above-mentioned reference yaw rate ψ^'* ₀
Is the maximum yaw rate ψ^'*If the value exceeds max,
Quasi-yaw rate ψ^'* ₀Target yaw rate to be achieved in the vehicle
ψ^'*Even if it is set to, it is a meaningless target value, and this
As described above, control hunting occurs with
is there. Therefore, the absolute value of the reference yaw rate | ψ^'* ₀| Is before
Absolute value of maximum yaw rate | ψ^'*When max is exceeded
Is the maximum yaw rate ψ^'*Eyes to achieve max in vehicle
Target yaw rate as standard yawing momentum ψ ^'*Set to
By doing so, the inconvenience is avoided. Specifically,
Situations other than steady state or quasi-steady state, such as
Such as when the vehicle goes into extreme oversteer
In an abnormal situation, the yaw rate, which is the yawing momentum,
The acceleration does not match and the lateral acceleration detection value Yg is
The yawing momentum remains constant in the maximum state
The actual yaw rate detection value ψ'may increase.
However, even in such a case, the maximum of the yawing momentum is
Maximum maximum yaw rate ψ^'*max is road friction coefficient or
Is regulated by its lateral acceleration,
It becomes smaller than the actual yaw rate detection value ψ '
It can be seen that it acts in the direction of suppressing abnormal operation.

Next, the deviation between the target yaw rate ψ ^'* as the target yaw momentum set as described above and the actual yaw rate detection value ψ'as the actual yaw momentum occurring in the vehicle becomes zero. In order to perform the feedback control as described above, the deviation is calculated as the yaw rate difference ε by the following five equations, respectively. ε = ψ '− ψ' ^* (5) The yaw rate-corresponding rear wheel steering angle δ _R ^* for making the yaw rate difference ε thus calculated to be zero is calculated from the calculation formula considering the vehicle specifications. Although it is possible to uniquely calculate the yaw rate difference ε, here, the yaw rate corresponding rear wheel steering angle δ _R ^* is calculated and set from the control map shown in FIG. 6. Primary increasing upward curves in the control map, the a yaw rate difference ε and the yaw rate corresponding rear wheel steering angle [delta] _R ^* correlation by the vehicle computing equation in consideration of the specifications, the yaw rate corresponding rear wheel steering angle [delta] _R ^* In the positive region, the rear wheels 10RL, 1
0RR is turned to the right, and the rear wheels 10RL and 10RR are turned to the left in a region where the yaw rate-corresponding rear wheel steering angle δ _R ^* is negative. When the yaw rate difference ε is equal to or greater than the positive predetermined value + ε ₁ , the yaw rate corresponding rear wheel steering angle δ _R ^* is set to the positive predetermined value + δ _R
^* Held in _1, to hold the yaw rate corresponding rear wheel steering angle [delta] _R ^* to a predetermined negative value - [delta _R ^* ₁ when the yaw rate difference ε is a predetermined negative value-epsilon ₁ or less. Predetermined values for these rear wheel steering angles δ _R ^* corresponding to yaw rate + δ _R ^* ₁ , −δ
_R ^* ₁ is, so to speak, the upper and lower limit values of the rear wheel steering angle δ _R ^* corresponding to the yaw rate. Here, if the absolute value of the yaw rate-corresponding rear wheel steering angle | δ _R ^* | is carelessly increased as the absolute value of the yaw rate difference | ε | The yaw moment may be extremely suppressed or greatly promoted, resulting in unstable vehicle behavior. Therefore, in the present embodiment, in order to restrict the change in the yaw moment to the extent that the occupant does not feel the instability of the vehicle behavior, the yaw rate corresponding rear wheel steering angle δ _R ^*
Predetermined value + [delta] _R ^* ₁ as upper and lower limit values of, and set the -δ _R ^* _1.

The rear wheel steering angle δ _R ^* corresponding to the yaw rate,
The rear wheel steering angle δ _R is calculated by the following six equations by adding the rear wheel steering control amount δ _RO . δ _R = δ _RO + δ _R ^* (6) Further, this rear wheel steering angle δ _R and the actual rear wheel steering angle detection value δ
The deviation from _RR and the rear wheel steering angle deviation γ are calculated according to the following seven equations.

Next, in order to calculate and output the movement amount of the piston 24 in the cylinder 22 for controlling the yawing momentum of the vehicle and its control signal based on the principle of the invention as described above, the microcomputer 40 of the controller 3 executes the calculation. The arithmetic processing performed will be described with reference to the flowchart of FIG. This calculation process has a predetermined cycle ΔT.
This is executed as a timer interrupt process for each (for example, 20 msec). First, in step S1, the steering angle detection value θ from the steering angle sensor 8 and the vehicle speed detection value V from the vehicle speed sensor 6 are read.

Next, in step S2, the lateral acceleration detection value Yg from the lateral acceleration sensor 11 is read. Next, in step S3, the actual yaw rate detection value ψ ′ from the yaw rate sensor 12 is read. Next, in step S4, the actual rear wheel steering angle detection value δ from the rear wheel steering angle sensor 9 is detected.
Read _RR .

Next, in step S5, the latest rear wheel steering control component δ _RO calculated by the individual calculation process and stored in the storage device 40c is read. Next, in step S6, the reference yaw rate ψ ^{'* is} appropriately linearly interpolated from the control map of FIG. 5 using the vehicle speed detection value V and the steering angle detection value θ read in step S1.
₀ is calculated and set.

Next, in step S7, the lateral acceleration detection value Yg read in step S2 and step S2 are read.
Using the vehicle speed detection value V read in step 1, the maximum yaw rate ψ ^'* max is calculated according to the above equation (4). Next, the process proceeds to step S8, and the absolute value of the reference yaw rate | ψ ^'* ₀ | calculated and set in step S6 is the same as in step S7.
The absolute value of the maximum yaw rate calculated in step │ψ ^'* max │ is determined, and the absolute value of the reference yaw rate │ψ ^{' *} is determined ^.
_{If 0} | is less than or equal to the absolute value | ψ ^'* max | of the maximum yaw rate, the process proceeds to step S9, and if not, the process proceeds to step S10.

In step S9, step S6
Absolute value of the reference yaw rate calculated and set in ｜ ψ ^'* ₀ ｜
But the absolute value of the maximum yaw rate calculated in the step S7 | ψ ^'* max | been judged not to exceed, the reference yaw rate ^[psi' sets ^* ₀ to the target yaw rate [psi ^'*, in step S11 Transition. On the other hand, in step S10, the absolute value | ψ ^'* ₀ | of the reference yaw rate calculated and set in step S6 exceeds the absolute value | ψ ^{' *} max | of the maximum yaw rate calculated in step S7. Then, the maximum yaw rate ψ ^'* max is set to the target yaw rate ψ ^{' *} , and the process proceeds to step S11.

In the step S11, the step S
9 or the target yaw rate ψ set in step S10^'*
And the actual yaw rate detection value ψ ′ read in step S3
The yaw rate difference? Of Next
To step S12 and calculate in step S11.
Using the issued yaw rate difference ε, the control matrix shown in FIG. 6 is used.
Yaw rate corresponding rear wheel steering angle δ_R ^*Calculate setting
Set.

Then, the process proceeds to step S13 and the above-mentioned step is performed.
Rear wheel steering angle corresponding to yaw rate calculated and set in step S12
δ_R ^*And the rear wheel steering control read in step S5
Min δ _R0From the above, the rear wheel steering angle δ_RCalculate
It Then, the process proceeds to step S14, and step S1 is performed.
Rear wheel steering angle δ calculated in 3_RAnd in step S4
Real rear wheel steering angle detection value δ read_RRFrom the above 7
Then, the rear wheel steering angle deviation γ is calculated.

Next, in step S15, the value of the rear wheel steering angle deviation γ calculated in step S14 is determined. If the rear wheel steering angle deviation γ is a positive value, the process proceeds to step S16. If the rear wheel steering angle deviation γ is a negative value, the process proceeds to step S17, and if the rear wheel steering angle deviation γ is zero, the process proceeds to step S18. In the step S16, it is determined that the rear wheels 10RL and 10RR need to be turned to the right with respect to the rear wheel steering angle δ _R calculated in the step S13, and the control valve 32 is turned to the right for the rear wheels. Drive circuit 41 for obtaining the drive signal of
The control signal S _CS1 is output toward and returns to the main program.

On the other hand, in step S17, the rear wheel 1 is set with respect to the rear wheel steering angle δ _R calculated in step S13.
It is determined that 0RL and 10RR need to be left-turned, and a control signal S _CS2 is output to the drive circuit 42 in order to obtain a drive signal for left-turning the rear wheel to the control valve 32. Return to the main program. Then, in step S18, it is determined that the actual rear wheel steering angle detection value δ _RR of the rear wheels 10RL, 10RR matches the rear wheel steering angle δ _R calculated in step S13, and each control signal S _CS1 , Stops the output of S _CS2 and returns to the main program.

Next, the operation of the vehicle yawing momentum control device of this embodiment will be described based on the behavior of the vehicle.
Here, a description will be given from the state where the piston 24 of the rear wheel steering cylinder 22 is centered at the center position by the springs 28 in both cylinder chambers 26L and 26R. Further, this state is also described as the rear wheels 10RL and 10RR being in a moderate state.

Now, it is assumed that the cutoff valve 36 is in the ON state and the vehicle is traveling straight at a constant speed on a high μ road having a flat and flat road surface and a sufficient friction coefficient. During constant-speed straight traveling on such a high μ good road, the actual yaw rate detection value ψ ′ read from the yaw rate sensor 12 in step S3 is zero or approximately every sampling time at which the arithmetic processing of FIG. 4 is performed. It is zero. Further, even if the vehicle speed detection value V detected by the vehicle speed sensor 6 becomes a certain value,
Since the steering angle detection value θ detected by the steering angle sensor 8 is zero or substantially zero, the reference yaw rate ψ ^{′ *} ₀ calculated and set in step S6 of the calculation process of FIG. 4 is also zero or substantially zero. Similarly, even if the vehicle speed detection value V detected by the vehicle speed sensor 6 reaches a certain value, the lateral acceleration detection value Yg detected by the lateral acceleration sensor 11 is zero or substantially zero. The maximum yaw rate ψ ^'* max calculated in step S7 of the calculation process is also zero or substantially zero. Therefore, step S8
In ～S10, the reference yaw rate [psi ^'* ₀ or maximum yaw rate ^{[psi' 'is} set to ^*, in any event the target yaw rate ^[psi' smaller ^* max Kano any absolute value target yaw rate [psi ^* is It is set to zero or near zero. Then, since the actual yaw rate detection value ψ ′ is zero or substantially zero, as shown in FIG.
The yaw rate difference ε calculated in step S11 of the calculation process of 0 becomes zero or substantially zero, and the yaw rate corresponding rear wheel steering angle δ _R ^* calculated and set in step S12 also becomes zero or substantially zero. Here, since the steering angle of the steering wheel is zero or substantially zero, the rear wheel steering control amount δ _R0 calculated and set by an individual calculation process not described in detail is also zero or substantially zero. The rear wheel steering angle δ _R calculated in step S13 of the calculation process is also zero or substantially zero. Further, as described above, since the piston 24 of the rear wheel steering cylinder 22 is in the central position and both the rear wheels 10RL and 10RR are in a straight middle state, the actual rear wheels read in step S4 of the arithmetic processing of FIG. Since the steering angle detection value δ _{RR is} also zero or substantially zero, and therefore the rear wheel steering angle deviation γ calculated in step S14 is also zero or substantially zero, the steps S15 to S15 are performed.
Moving to 18, neither the control signal S _CS1 nor the control signal S _CS2 is output.

Therefore, which solenoid 6 of the control valve 32
Since 0a and 60b are not excited, the control valve 32 is held in the central switching position, whereby the hydraulic oil due to the discharge pressure from the hydraulic pump 30 is directly returned to the reservoir 34, and the piston 24 of the rear wheel steering cylinder 22 is returned. The centered state is maintained at the center position and the normal constant-speed straight traveling state is maintained.

On the other hand, it is assumed that the constant-speed straight traveling on the high μ good road is changed to the constant-speed rightward traveling. At this time, it is assumed that the turning radius in the constant-speed right turning state is relatively large with respect to the vehicle speed. Further, in order to facilitate understanding, the rear wheel steering control component δ _{R0 that} is individually performed in the above-described calculation process is assumed to be gradually and simply increased numerically with respect to an increase in steering input. The number of times gradually increases in the positive direction,
In the left turn, that is, in the left turn, the explanation will proceed with the assumption that it gradually increases in the negative direction. On such a high μ road, both cornering power and cornering force as tire characteristics are relatively large. Further, since the turning radius is comparatively large, the steering angle detection value θ read in the step S1 becomes relatively moderately large and the maximum value thereof is also comparatively small every sampling time when the arithmetic processing of FIG. 4 is performed. Will be a value. Therefore, the reference yaw rate ψ ^'* ₀ calculated and set from the control map of FIG. 5 in the same step S6 for each sampling time when the arithmetic processing of FIG. 4 is performed relatively slowly increases in the positive direction, and the steering angle detection is performed. Since the reached maximum value of the value θ is relatively small, the reference yaw rate ψ ^'* ₀ at the end of steering cutoff becomes a relatively small positive value.

Further, since the road has a high μ, the cornering force of each wheel increases reliably and relatively gently as the steering angle increases, and as the cornering force increases, the arithmetic processing of FIG. 4 is performed. The lateral acceleration detection value Yg read in step S2 at each sampling time
Since the vehicle is turning to the right, it increases in the positive direction relatively slowly, and since the vehicle is traveling at a constant speed, the lateral acceleration detection value Yg after the end of the steering cut is a relatively small positive value. Therefore, the maximum yaw rate ψ ^'* max calculated in step S7 of the calculation process of FIG. 4 is also a relatively small positive value.

Then, in the calculation process of FIG. 4, the absolute value of the reference yaw rate |
ψ ^'* ₀ ｜ and the absolute value of the maximum yaw rate │ ψ ^{' *} max ｜ are compared, but as described above, the maximum yaw rate ψ ^'* ma
The proportional coefficient k of the four equations used to calculate x is the absolute value | ψ ^'* ₀ | of the standard yaw rate when the tire characteristics normally assumed on a high μ road ensure a sufficient grip force. Since the absolute value of the maximum yaw rate │ψ ^'* max │ is not exceeded, the process proceeds from step S8 to step S9, and the reference yaw rate ψ ^{' *} ₀ is set to the target yaw rate ψ ^'*. It

Here, as described above, the reference yaw rate ψ ^'*
_Since the target yaw rate ψ ^'* set to ₀ is relatively moderately increased, the feedback control for matching the actual yaw rate detection value ψ' with the target yaw rate ψ ^'* is performed. The calculation process of FIG. 4 is performed. The yaw rate difference ε calculated in step S11 becomes a relatively small negative value for each sampling time. Then, in step S12, the yaw rate corresponding rear wheel steering angle δ _R ^* calculated and set according to the control map of FIG. 6 according to the yaw rate difference ε of this relatively small negative value also becomes a relatively small negative value. At this time, since the yaw rate difference ε will be sufficiently smaller than the negative predetermined value −ε ₁ , the yaw rate corresponding rear wheel steering angle δ _R ^* is held at the negative upper limit −δ _R ^* _1. There will be no.

Then, step S13 of the arithmetic processing of FIG.
The rear wheel steering angle δ _R calculated at each sampling time
Is a value obtained by _{adding the} rear wheel steering control amount δ _R0 from the expression 7 to the yaw rate corresponding rear wheel steering angle δ _R ^* which is a relatively small negative value. Next, in step S14, the rear wheel steering angle deviation γ is calculated from the equation 7 using the actual rear wheel steering angle detection value δ _RR read in step S4. the rear wheel steering control amount [delta] _RO is a small positive value to a small, relatively small negative value in a yaw rate corresponding rear wheel steering angle [delta] _R ^* a wheel steering angle after the sum [delta] _R is a moment to this, negative May be. On the other hand, since the actual rear wheel steering angle detection value δ _RR immediately before the start of the right steering cut is substantially zero, the rear wheel steering angle deviation γ becomes a negative value for a moment. Therefore, in such a case, step S15
To S17, the control signal S _CS2 is output to the drive circuit 42. Therefore, the drive circuit 4
2, the drive signal CS ₂ is output toward the solenoid 60b on the right side of the control valve 32, which excites the solenoid 60b to switch the control valve 32 to the left switching position in FIG. The hydraulic oil accompanying the discharge pressure is supplied to the left cylinder chamber 26L of the rear wheel steering cylinder 22, so that the piston 24 is moved to the right in FIG. 2, whereby the steering shaft 20 is moved to the right and the rear left and right wheels are moved. 10RL, 1
0RR is left-turned for a moment around the kingpin axis (not shown). As a result, the relative steered angle between the front and rear wheels is momentarily increased, the yaw moment generated in the vehicle is promoted accordingly, and at the same time, the yaw rate is accelerated and quickly rises, and the vehicle obtains good turning performance.

However, in the constant-speed right-turn traveling with a relatively large turning radius, as described above, the yaw rate difference ε calculated in step S11 of the arithmetic processing of FIG. 4 continues to be a relatively small negative value. On the other hand, since the rear wheel steering control amount δ _R0 simply continues to increase in the positive direction with an increase in the steering input, the rear wheel steering angle δ _R calculated in step S13 is a positive value thereafter. When the actual rear wheel steering angle δ _RR is still zero or a small negative value, the rear wheel steering angle deviation γ calculated in step 14 becomes a positive value after becoming zero. Therefore, in the calculation process of FIG. 4, the process temporarily goes from step S15 to step S18 to stop the output of the control signal S _CS2 , and then goes from step S15 to step S16, where the control signal S _CS1 is It is output toward the drive circuit 41. Therefore, the drive signal CS ₁ is sent from the drive circuit 41 to the solenoid 60 to the left of the control valve 32.
a toward the solenoid 60a, so that the solenoid 60a
Is excited and the control valve 32 is switched to the right switching position via the switching position in the center of FIG. 2, and the hydraulic oil accompanying the discharge pressure of the hydraulic pump 30 is supplied to the right cylinder chamber 26R of the rear wheel steering cylinder 22. The piston 24 is moved to the left in FIG. 2, whereby the steering shaft 20 is moved to the left, and the rear left and right wheels 10RL and 10RR are cut right around the kingpin axis (not shown). Thereby, the rear wheels 10RL, 1
Since 0RR is steered in-phase with the turning direction of the front wheels 10FL and 10FR, the yaw moment generated in the vehicle is suppressed and the running stability of the vehicle is improved. Of course, in order to continuously execute the feedback control for matching the actual yaw rate detection value ψ'with the reference yaw rate ψ ^'* ₀ set to the target yaw rate ψ ^{' *} , a good yaw rate is generated in the vehicle and a transient Cornering characteristics are improved.

On the other hand, on the same high μ road, when the constant speed straight traveling is changed to the constant speed left turning traveling with a relatively large turning radius, the signs of the respective detection values except the vehicle speed detection value V are reversed, and The sign of the wheel steering control amount δ _R0 is also reversed, and therefore the signs of the reference yaw rate ψ ^'* ₀ and the maximum yaw rate ψ ^{' *} max are reversed, so that the target yaw rate ψ ^'* , the yaw rate difference ε, and the yaw rate corresponding rear wheel steering angle δ. The signs of _R ^* , the rear wheel steering angle δ _R , and the rear wheel steering angle deviation γ are reversed, the control signal S _CS1 and the control signal S _CS2 are replaced, and the control valve 32, the rear wheel steering piston 24, the rear wheel steering The rear wheel steering control is performed in the same manner as described above, except that the behaviors of the shaft 20 and the rear wheels 10RL, 10RR are reversed left and right.

Next, also on the high μ good road,
From a constant-speed right-turn running with a large turning radius to a relatively turning radius
It is assumed that the vehicle has shifted to a small constant-speed right turn drive. Turning like this
When moving to constant speed right turn with a small turning radius, the
Increase in steering angle detection value θ read in step S1 in the positive direction
The reference yaw rate calculated and set in step S6
Ψ^'* ₀Also increases in the positive direction, and the same due to the reduction of the turning radius.
Positive direction of lateral acceleration detection value Yg read in step S2
The maximum yaw calculated in step S7
Rate ψ^'*max also increases in the positive direction. However, high
The tire characteristics still maintain grip due to the μ good road
Therefore, the absolute value of the standard yaw rate | ψ^'* ₀｜ is the highest
Absolute value of large yaw rate | ψ^'*max │ not exceeded, figure
In the arithmetic processing of No. 4, through steps S8 to S9
The reference yaw rate ψ^'* ₀Is the target yaw rate ψ^'*Set to
To be done. This target yaw rate ψ^'*On the vehicle against
The actual yaw rate detection value ψ'being delayed should be further delayed.
Therefore, it is calculated in step S11 of the arithmetic processing of FIG.
The yaw rate difference ε is
The negative value is relatively larger than that when traveling in the right-turning direction.
In step S12, the yaw rate difference ε
Rear wheel steering angle δ corresponding to a relatively large negative yaw rate _R ^*Is arithmetic
Out set. On the other hand, in step S13, steering input
The rear wheel steering control component δ which becomes a large positive value as_R0
In addition, the rear wheel corresponding to the yaw rate, which is a relatively large negative value,
Steering angle δ_R ^*And rear wheel steering angle δ_RIs calculated. This
Here, the rear wheel steering control amount δ during turning_R0Is the front wheel 10F
It is supposed to be for in-phase control with L and 10FR
For example, the rear wheel steering angle δ_RFront and rear wheels to achieve by
The relative steering angle between them will be relatively large.

Therefore, at the moment when the right turning cut is further increased in order to shift from the constant speed turning running with a comparatively large turning radius to the constant speed turning running with a comparatively small turning radius, the straight running is carried out at that moment. The rear wheel steering angle deviation γ calculated in step S14 of FIG. 4 becomes a negative value for a moment as in the period when the transition from the vehicle to the turning travel is started. _CS2 is drive circuit 4
Is output to the 2, from the drive circuit 42 a drive signal CS ₂ to the solenoid 50b of the right side of the control valve 32 of FIG. 2 is output, the rear wheel 1 as a result, which has been right turn until it
0RL and 10RR are left-turned for a moment to increase the relative steered angle between the front and rear wheels, which promotes the yaw moment generated in the vehicle and at the same time accelerates the yaw rate to quickly start up, and the vehicle has good turning performance. To get

However, since the rear wheel steering control component δ _R0 continues to increase in the positive direction as the steering input increases, the rear wheel steering angle deviation γ calculated in step S14 of FIG.
After becoming zero, it becomes a positive value. Therefore, in the calculation process of FIG. 4, the process temporarily goes from step S15 to step S18 to stop the output of the control signal S _CS2 , and then goes from step S15 to step S16, where the control signal S
_CS1 is output to the drive circuit 41. Therefore, the drive signal CS ₁ is output from the drive circuit 41 to the solenoid 60a on the left side of the control valve 32, and the control valve 32 is switched to the right switching position via the central switching position in FIG. Axis 20 is moved to the left and rear left and right wheels 10R
L and 10RR are right-cut around a kingpin axis (not shown). As a result, the rear wheels 10RL, 10RR are steered in phase with the steering direction of the front wheels 10FL, 10FR, so that the yaw moment generated in the vehicle is suppressed and the running stability of the vehicle is improved. Of course, in order to continuously execute the feedback control for matching the actual yaw rate detection value ψ'with the reference yaw rate ψ ^'* ₀ set to the target yaw rate ψ ^{' *} , a good yaw rate is generated in the vehicle and a transient Cornering characteristics are improved.

Here, step S of the arithmetic processing of FIG.
Due to the yaw rate difference ε, which has a relatively large negative value at 11,
Therefore, in step S12, the rear wheel steering angle corresponding to the yaw rate is set.
δ_R ^*Is the negative predetermined value −δ_R ^* ₁Can also be held in
It is conceivable that this negative predetermined value −δ_R ^* ₁Is the yaw rate
Corresponding rear wheel steering angle δ_R ^*Is set as the lower limit of
The rear wheel steering angle δ corresponding to the yaw rate_R ^*Is the lower limit
Negative predetermined value −δ_R ^* ₁Even if held in
Vehicle behavior does not become unstable.

On the other hand, also on the high μ good road, when the constant speed turning traveling with the relatively small turning radius is changed to the constant speed turning traveling with the relatively large turning radius, the constant speed with the relatively large turning radius is obtained. The rear wheel steering, which is the opposite of the transition period from turning to constant-speed turning with a relatively small turning radius, is performed, and as a result, the relative steered angle between the front and rear wheels is momentarily reduced, and the yaw moment is suppressed. As a result, the steering characteristics of the vehicle are enhanced in the understeer direction, and then the relative steered angle between the front and rear wheels is achieved in accordance with the steering angle detection value θ required for the turning radius, thereby improving the traveling stability. . Of course, during this time,
^'Reference yaw rate ψ is set to ^{*' *} ₀ target yaw rate ψ
In order to continuously execute the feedback control for matching the actual yaw rate detection value ψ ′ with the above, a good yaw rate is generated in the vehicle, and the transient cornering characteristic is particularly improved.

Also on the high μ good road, in the constant speed left turning traveling with the different turning radii, the signs of the detected values and the calculated values in the constant speed right turning traveling with the different turning radii are reversed. Then, the control signal S _CS1 and the control signal S _CS2 are replaced, and the actuator and the rear wheels 10RL, 10R are replaced.
The same control as described above is executed except that the behavior of R is reversed between left and right.

Similarly, when the steering wheel is steered to the left and right at a high speed on a high μ road, for example, a slalom wheel, the turning travel with a relatively large turning radius is changed to the turning travel with a relatively small turning radius. After that, the vehicle makes a transition to a traveling with a comparatively large turning radius, and then to a traveling with a comparatively large turning radius in the opposite direction, and further to a traveling with a comparatively small turning radius in the opposite direction. The same control as above is executed by repeating the transition from the same to the turning traveling with a large turning radius.
The vehicle can run slalom quickly and stably.

Also on the high μ good road, when acceleration / deceleration is executed or an acceleration / deceleration input is applied irrespective of whether the vehicle is traveling straight or traveling, the vehicle speed detection value V resulting from the acceleration / deceleration is applied to the above-mentioned value. The same control as is executed. Next, constant-speed, right-turning traveling on a low μ road having a small friction coefficient state such as the above-mentioned snow and snow road surface will be considered. On such a low μ road, the maximum value of the cornering power and the maximum value of the cornering force as tire characteristics are small regardless of the size of the turning radius. Therefore, the cornering force as a tire characteristic does not sufficiently follow the increase of the steering input, and the maximum value of the cornering force is small for the excessive steering input, and the tire loses its grip force early. As a result, the lateral acceleration detection value Yg read in step S2 of the calculation process of FIG. 4 becomes a small positive value, and therefore the maximum yaw rate ψ ^'* calculated in step S7 of the calculation process of FIG. max has a small positive value.

On the other hand, the calculation shown in FIG. 4 is accompanied by an excessive steering input.
The steering angle detection value θ read in step S1 of the process is square
If it increases, the standard calculated and set in step S6
Yaw rate ψ^'* ₀Also increases in the positive direction, but the same step S
8 is the absolute value of the standard yaw rate | ψ^'* ₀｜ is the maximum yaw
Absolute value of │ψ^'*Is it judged that max is exceeded?
In this case, the process proceeds from step S8 to step S10.
The maximum yaw rate ψ ^'*max is the target yaw rate ψ^'*To
Is set.

Here, as described above, since the cornering force as a tire characteristic is generally small, the yaw moment generated in the vehicle is also small. Therefore, the actual yaw rate detected value ψ read in step S3 of the arithmetic processing of FIG. 'Is also a small positive value. From the above, there is no doubt that the yaw rate difference ε calculated in step S11 of the arithmetic processing of FIG. 4 is necessarily a small value. At this time, it is unclear whether the yaw rate difference ε is a positive value or a negative value depending on the vehicle behavior, but in any case, it is set in step S12 of the calculation process of FIG. 4 based on the yaw rate difference having a small value. The yaw rate-corresponding rear wheel steering angle δ _R ^* has a positive or small value. Therefore, the rear wheel steering angle δ _R calculated in step S13 is such that a small yaw rate difference ε achievable on this low μ road is generated with respect to the rear wheel steering control amount δ _RO read in step S5. Only the sum of the rear wheel steering angle δ _R ^* for small yaw rate can be obtained. Then, for this rear wheel steering angle δ _R , the actual rear wheel steering angle detection value δ _RR read in step S5 and the rear wheel steering angle deviation γ are calculated in step S1.
4 is calculated, the output or the output stop step in S15~S17 control signal S _CS1, S _CS2 so as to zero the wheel steering angle deviation γ After this is performed, according to the control signal S _CS1, S _CS2 Steering control of the rear wheels 10RL, 10RR is executed.

Here, even if the steering angle detection value θ increases due to the excessive steering input, the rear wheel steering angle δ _R corresponding to the yaw rate
^* Does not become a large value in either positive or negative. On the other hand, since the rear wheel steering control amount δ _R0 increases as the steering input increases, the achieved relative steering angle between the front and rear wheels becomes small. That is, the in-phase control with a relatively large steering angle is executed for the rear wheels 10RL and 10RR, the yaw moment of the vehicle is suppressed, the yaw rate is not accidentally accelerated, and running stability is ensured. . Of course, for the appropriate steering input other than the excessively rapid steering input, including this excessive steering input, the maximum yaw rate achievable on the low μ road surface is generated in the vehicle, and the appropriate steering input is generated. To maintain a proper driving line intended by the driver,
The vehicle is turned as much as possible even with an excessive steering input.

In this rear wheel steering control, the signs of the detected value and the calculated value are reversed even when the vehicle is traveling to the left and the control signal S
_Except that _CS1 and the control signal S _CS2 are reversed, and the behaviors of the actuator and the rear wheels 10RL, 10RR are reversed left and right, substantially the same as the above is executed. In order to facilitate understanding here, the yaw rate-corresponding rear wheel steering angle δ _R ^* achieved by the rear wheel steering control on this low μ road, the actual yaw rate detection value ψ ′ generated in the vehicle, and the target yaw rate ψ ^{′ *} The change will be described according to the time chart shown in FIG. Here, for easier understanding, it is assumed that the yaw rate-corresponding rear wheel steering angle δ _R ^* matches the actual rear wheel steering angle δ _RR .

[0075] Now, if you are a constant speed straight running from the time "0", it is assumed that the right cut the steering wheel at the time t _01. A cornering force is generated in the tire in response to this steering input, and a positive maximum yaw rate ψ ^'* max, which is a substantially constant value, is calculated according to a certain positive lateral acceleration detection value Yg generated and detected by this. Suppose On the other hand, as the detected steering angle θ due to the steering input increases in the positive region, the reference yaw rate ψ ^'* ₀ of a certain positive value calculated with the first-order delay is also calculated and set. Therefore, the time from time t ₀₁ to time t ₀₂ when the positive reference yaw rate ψ ^'* ₀ is less than or equal to the maximum positive yaw rate ψ ^{' *} max by the calculation process of FIG. 4 is the target yaw rate ψ ^'*. Is set to the reference yaw rate ψ ^'* ₀ .

On the other hand, the vehicle is delayed by this
Occurs, and as a result, the actual yaw rate increases in the positive region
The detected value ψ ′ is detected. Therefore, the time t₀₁Since
Tick t ₀₂The time until is calculated at least by the calculation process in Figure 4.
The yaw rate difference ε is reduced in the negative region,
After supporting the yaw rate according to the yaw rate difference ε that decreases in the range
Wheel steering angle δ_R ^*Is reduced in the negative region, so real rear wheel steering
Angle δ_RRIs in the negative direction, that is, the rear wheels 10RL and 10RR are on the left
Turned off and steered in reverse phase to detect the actual yaw rate
Value ψ^'*Is further accelerated.

However, as shown by the alternate long and short dash line in FIG.
Quasi-yaw rate ψ^'* ₀Is the maximum value as the steering input increases.
Rate ψ^'*Although it continues to increase beyond max,
In the calculation process, the reference yaw rate ψ^'* ₀Is the maximum
Yaw rate ψ^'*Time t that exceeds max₀₂From the target
Ψ^'*Is the maximum yaw rate ψ ^'*
max is set.

On the other hand, the yaw rate difference ε between the actual yaw rate detection value ψ ′ that continues to increase in the positive region and the target yaw rate ψ ^{′ *} set to the constant maximum yaw rate ψ ^{′ *} max is After t ₀₂ , it increases in the negative region.
Therefore, since the yaw rate-corresponding rear wheel steering angle δ _R ^* increases in the negative region according to the yaw rate difference ε increasing in this negative region, the actual rear wheel steering angle δ _RR gradually decreases in the negative region, that is, the rear wheel 10RL and 10RR gradually return to the normal state from the left turn, whereby the actual yaw rate detection value ψ ′ is gradually decelerated.

However, due to the vehicle inertia, the actual yaw rate detected value ψ ′ is the constant value of the maximum yaw rate ψ ^{′ *.}
For the target yaw rate ψ ^'* set to max, time t ₀₃
However, the yaw rate difference ε increases slightly in the positive range, but the yaw rate-corresponding rear wheel steering angle δ _R ^* increases slightly in the positive range. Since the actual rear wheel steering angle δ _RR gradually increases in the positive direction and is turned to the right, that is, in-phase steering is performed, as a result, the yaw moment generated in the vehicle is further suppressed and is substantially reduced. In addition, the actual yaw rate detection value ψ'is further gradually but gradually decelerated.

The actual yaw rate detection that continues to be decelerated in this way
The output value ψ ′ and the maximum yaw rate ψ that is the constant value.^'*to max
Set target yaw rate ψ^'*And the yaw rate difference ε is
Tick t ₀₄It exceeds the maximum positive value at and decreases further in the positive direction.
During this period as well, the actual yaw rate detection value ψ ′ is
Second, it continues to slow down little by little. And continue to slow down
The actual yaw rate detection value ψ ′ is determined by the inertia of the vehicle at time t.
₀₅And the maximum yaw rate ψ that is the constant value^'*set to max
Target yaw rate ψ^'*Slightly moreover
The yaw rate difference ε between the two is very small and negative.
It decreases in the area and time t₀₆Over the negative maximum and again
Increases in the negative region. Accompanying this, the actual yaw rate detection value
ψ'is the complement of the very small negative yaw rate difference ε.
Just correct, it will accelerate very slightly, and at time t₀₇so
The actual yaw rate detected value ψ'is the maximum yaw that is the constant value.
Rate ψ^'*Target yaw rate ψ set to max^'*Against
Match without overshooting.

During this time, the maximum yaw rate that can be achieved on the low μ road is generated in the vehicle, so that the vehicle keeps turning with a constant turning radius. Therefore, the steering wheel is turned to the right for proper steering input. It's good. Also,
Even if there is an excessive steering input, the driver recognizes the disagreement with the turning radius of the vehicle, and therefore the steering wheel may be slightly turned back by the surplus.

On the other hand, by the conventional rear wheel steering control in which the reference yaw rate ψ ^'* ₀ calculated and set with only the steering angle detection value θ and the vehicle speed detection value V as the variables is set to the target yaw rate ψ ^{' *} , The changes in the yaw rate-corresponding rear wheel steering angle δ _R ^* and the actual yaw rate detection value ψ ′ and the target yaw rate ψ ^{′ *} generated in the vehicle achieved on the low μ road will be described with reference to the time chart shown in FIG. Specifically, steps S7 to S9 are deleted in the calculation process of FIG. 4, and the reference yaw rate ψ ^'* calculated and set in step S6 is set ^.
It can be considered that ₀ is set as it is to the target yaw rate ψ ^'* .

[0083] in the same manner as described above, from the time "0" has been a constant speed straight-ahead running, it is assumed that the right cut the steering wheel at the time t _11. The target yaw rate ψ ^'* continues to increase in the positive region as the steering angle detection value θ increases in the positive region due to this steering input, and the yaw rate deviation ε with the actual yaw rate detection value ψ' that occurs later is negative. Continues to decline in the area of.
Accordingly, the yaw rate deviation ε eventually exceeds the negative predetermined value −ε ₁ in the control map of FIG. 6 and further decreases in the negative region at the time t ₁₂ , so that the yaw rate corresponding rear wheel steering angle δ _R ^* is concerned. At time t ₁₂ , the negative lower limit value −δ _R ^* ₁ is held.

The actual yaw rate detection that is occurring in the vehicle eventually
Outgoing value ψ'and target yaw rate ψ^'*And the yaw rate difference ε is
Tick t₁₃And exceeds the maximum negative value at
Meru. However, the relative steering angles of the front and rear wheels were large during this period.
The actual yaw rate detection value ψ'will continue to be held and will be accelerated rapidly.
The vehicle keeps trying to turn sharply in order to continue
For low μ roads such as
The maximum value of the ground is also small, so each tire will eventually grip
The driver loses power and begins to skid, and the driver is conscious or unconscious
Regardless of the target, time t₁₄Steering wheel in the opposite direction
The so-called counter steer is performed to switch back to. With this
At time t₁₄To target yaw rate ψ ^'*Is in the positive region
Although it begins to decrease, the actual yawley continues to accelerate rapidly.
The detected value ψ'is further accelerated by the vehicle inertia.
to continue.

Eventually, the yaw rate difference ε becomes the time t₁₅In the negative place
Fixed value −ε₁Since it increases sharply in the negative region beyond
-Rate compatible rear wheel steering angle δ_R ^*Is the time t₁₅After that, suddenly
The yaw rate detection value ψ'increases in the negative region and eventually increases.
And target yaw rate ψ^'*And the yaw rate difference between the two
Time t when ε becomes zero₁₆Rear wheel steering angle δ for yaw rate _R
^*Is also zero.

However, the target yaw rate ψ ^{'*, which} is set with a first-order lag from the steering wheel steering due to the abrupt counter-steering, decreases in the positive region thereafter,
Eventually it decreases in the negative region. On the other hand, the actual yaw rate detection value ψ ′ that has been continuously accelerated by the vehicle inertia continues to increase in the positive region, and thus the yaw rate difference ε between the two continues to increase in the positive region. Therefore, the rear wheel steering angle δ _R corresponding to the yaw rate
^* Continues to increase in the positive region after the time t ₁₆ ,
_{At the} time t ₁₇ , the yaw rate-corresponding rear wheel steering angle δ _R ^* is increased at the time t ₁₇ since it exceeds the positive predetermined value + ε ₁ and further increases in the positive region.
Is held at the positive upper limit value + δ _R ^* ₁ . Therefore, after the time t ₁₆ , the relative steered angle between the front and rear wheels is kept small, and the yaw moment generated in the vehicle continues to be suppressed, so that the actual yaw rate detection value ψ ′ continues to be rapidly decelerated.

[0087] begins to diminish in time beyond the maximum positive value the yaw rate difference ε is at time t ₁₈ 'and target yaw rate ^[psi' actual yaw rate detected value [psi generated in the vehicle and ^* also in the positive region. However, during this period, as described above, the actual yaw rate detection value ψ'continues to be rapidly decelerated, so the vehicle keeps on going straight ahead, and as a result, the actual yaw rate detection value ψ'of the vehicle begins to decrease in the positive region. When the driver recognizes the fact, the driver suddenly re-cuts the steering wheel in the forward direction, that is, the original turning direction at time t ₁₉ , consciously or unconsciously. Along with this, the target yaw rate ψ ^'* starts to increase in the negative region from the time t _19, but the actual yaw rate detection value ψ'which has been continuously decelerated rapidly.
Is further rapidly decelerated in the positive direction by the vehicle inertia.

Eventually, the yaw rate difference ε becomes the time t₂₀In the positive place
Fixed value + ε₁The sharp decrease in the positive region
-Rate compatible rear wheel steering angle δ_R ^*Is the time t₂₀After that, suddenly
Decreases sharply in the positive region, and eventually the actual yaw rate detection value ψ '
And target yaw rate ψ^'*And the yaw rate difference between the two
Time t when ε becomes zero_{twenty one}Rear wheel steering angle δ for yaw rate _R
^*Or the actual rear wheel steering angle detection value δ_RRIs also zero.

However, the target yaw rate ψ ^'* set by the first-order lag from the steering of the stearin wheel due to the rapid re-cutting increases in the negative region and thereafter increases in the positive region. On the other hand, the actual yaw rate detection value ψ ′ that has been continuously decelerated by the vehicle inertia continues to increase in the negative direction, so the yaw rate difference ε between the two continues to decrease in the negative region. Therefore, the yaw rate-corresponding rear wheel steering angle δ _R ^* continues to decrease in the negative region after the time t ₂₁ and exceeds the negative predetermined value −ε ₁ at the time t ₂₂ and further decreases in the negative region. The corresponding rear wheel steering angle δ _R ^* is held at the negative lower limit value −δ _R ^* ₁ at the time t ₂₂ . Therefore, the time t ₂₁ after, the relative turning angle between the front and rear wheels continues to be kept large, in order yaw moment generated in the vehicle is to continue to be promoted, the actual yaw rate detected value [psi 'continues to be abruptly accelerated.

[0090] begins to increase over time in the same negative region yaw rate difference ε is exceeds the maximum negative value at time t ₂₃ of the actual yaw rate detection value which is generated in the vehicle [psi 'and target yaw rate ^[psi' and ^*. However, during this period, as described above, the actual yaw rate detection value ψ ′ continues to be rapidly accelerated, so that the vehicle continues to make a sharp turn, and thereafter, this phenomenon continues at least until the vehicle exits the corner.

During this period, the driver not only has to continuously steer the steering wheel to the left and right in order to cope with the yaw rate that is being greatly accelerated and decelerated, but the vehicle may be understeered or oversteered. Its behavior becomes unstable. From the above, in the vehicle yaw momentum control device of the present invention,
Particularly, even on a low μ road, the maximum yawing momentum according to the road surface friction coefficient state is achieved, the turning traveling line is maintained, and the behavior of the vehicle is stabilized.

In the above embodiment, the maximum value of the target yaw rate is calculated and set from the lateral acceleration generated by the influence of the road surface friction coefficient state on the steering input, and this is calculated according to the steering input and the vehicle speed. Although the yaw rate limiter is used, the yaw momentum control device for a vehicle according to the present invention is not limited to this means. For example, as shown in FIG. A control map for setting the target yaw rate in consideration of the road surface friction coefficient state is searched and the target yaw rate is calculated and set according to the steering angle detection value θ and the lateral acceleration detection value Yg is used as a parameter. As shown in Fig. 3, the friction coefficient state of the road surface is detected or estimated from the lateral acceleration detection value generated in response to the steering input, and the road friction coefficient is determined according to the steering degree detection value θ. The target yaw rate ψ ^'* may be calculated and set by retrieving a control map using the number state as a parameter.

Further, in the above embodiment, the road surface friction coefficient state is detected or estimated from the lateral acceleration in which the influence of the road surface friction coefficient state is added to the steering input. However, the yawing momentum control of the vehicle of the present invention is performed. The device is not limited to detecting or estimating the road surface friction coefficient state from the lateral acceleration, and in addition to this, if the road surface friction coefficient state is detected or estimated from various physical quantities generated in the vehicle including the road surface friction coefficient state. Good.

Further, in the above-described embodiment, the case where the microcomputer is applied as the controller 3 has been described, but instead of this, electronic circuits such as a counter and a comparator may be combined and configured. Further, the supply source of the working fluid pressure is not limited to the oil pump individually provided in the system, but it is also possible to use the line pressure from the oil pump utilizing the rotational output of the engine.

Further, in this embodiment, a detector which is simply a vehicle speed sensor is used to detect the longitudinal speed of the vehicle.
If it is difficult to detect the vehicle speed with a high resolution, the pseudo vehicle speed is calculated and set from the wheel speed obtained with the existing wheel speed sensor, or the vehicle acceleration obtained from the acceleration sensor is integrated over time and used. It is also possible. Of course, it is also possible to combine auxiliary functions and configurations for performing normal four-wheel steering that is performed to improve steering characteristics during turning, or it is possible to combine none of these.

Further, in the above embodiment, the yawing momentum control device of the vehicle has been developed to the auxiliary steering control device including the four-wheel steering control device, and only the case where the auxiliary steering is performed only on the rear wheels has been described in detail. The yawing momentum control device for a vehicle according to the present invention sets the target yawing momentum and performs comparison control with the actual yawing momentum generated in the vehicle, including those performing auxiliary steering and those performing auxiliary steering to the front and rear wheels. The present invention can be applied to all control devices, for example, Japanese Patent Application Laid-Open No.
No. 31030 discloses a fastening force control device for a driving force distribution clutch between front and rear wheels or left and right wheels, and a roll rigidity variable control disclosed in Japanese Patent Laid-Open No. 5-193332 previously proposed by the present applicant. In an active suspension and stabilizer control device that enables the above, or a braking force control device that individually controls the braking force of each wheel of the vehicle described in Japanese Patent Application Laid-Open No. H5-242528 previously proposed by the present applicant. Is also widely deployable.

[0097]

As described above, according to the yaw momentum control device for a vehicle of the present invention, particularly under the condition of the road surface friction coefficient in which the cornering power and the maximum value of the cornering force are both small, such as when traveling on the ice and snow road surface, The maximum value of the target yawing momentum that can be actually achieved by the vehicle is always set based on the friction coefficient state of the road surface, thereby limiting the yawing momentum tracking control to avoid meaningless increase of the control command value, and at the same time, It is possible to avoid the actuator from acting excessively on such an excessive command value with a predetermined delay and to perform yawing momentum tracking control according to vehicle characteristics including tire characteristics.

At this time, since the lateral acceleration generated in the vehicle in response to the steering input is secondarily generated due to the influence of the road surface friction coefficient, the road surface friction coefficient is detected from the detected lateral acceleration value. Alternatively, estimating is an easy and reliable means even in an actual vehicle, and the accuracy of the yawing momentum tracking control is improved.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a vehicle yaw momentum control device of the present invention.

FIG. 2 is a schematic configuration diagram showing an example in which the vehicle yawing momentum control device of the present invention is applied to an auxiliary steering control device including a four-wheel steering control device.

FIG. 3 is a schematic configuration diagram showing an example of an auxiliary steering control device of FIG.

FIG. 4 is a flowchart showing a calculation process of an embodiment of the vehicle yaw momentum control device of the present invention.

FIG. 5 is a control map for calculating and setting a reference yaw rate using the vehicle speed detection value as a parameter for the steering angle detection value in the arithmetic processing of FIG.

FIG. 6 is a control map for calculating and setting a yaw rate-corresponding rear wheel steering angle with respect to a deviation between a target yaw rate and an actual yaw rate detection value in the calculation process of FIG. 4;

FIG. 7 is a time chart of rear wheel steering by yaw rate feedback control performed in the calculation processing of FIG.

FIG. 8 is a time chart of rear wheel steering by conventional yaw rate feedback control.

FIG. 9 is a control map for calculating and setting a target yaw rate using a lateral acceleration detection value as a parameter with respect to a steering angle detection value as another embodiment of the vehicle yawing momentum control device of the present invention.

FIG. 10 is a control map for calculating and setting a target yaw rate using a road surface friction coefficient state as a parameter with respect to a detected steering angle, as another embodiment of the vehicle yawing momentum control device of the present invention.

[Explanation of symbols]

 2 is a rear wheel steering device 3 is a controller 5FL, 5FR is a front multi-link suspension 6 is a vehicle speed sensor (input physical quantity detection means) 8 is a steering angle sensor (input physical quantity detection means) 9 is a rear wheel steering angle sensor 10FL to 10RR are front Left wheel to rear right wheel 11 is a lateral acceleration sensor (lateral acceleration detecting means) 12 is a yaw rate sensor (yawing momentum detecting means) 13 is a tie rod 14 is a steering gear device 15 is a steering wheel 16 is a steering shaft 18 is a tie rod 20 is a steering shaft 22 Is a rear wheel steering cylinder 24 is a piston 26L, 26R is a cylinder chamber 28 is a spring 30 is a hydraulic pump 32 is a control valve 34 is a reservoir 36 is a cutoff valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B62D 113: 00 137: 00

Claims (2)

[Claims] 1. A yawing momentum detecting means for detecting a yawing momentum actually occurring in a vehicle, an input physical quantity detecting means for detecting an input acting on the vehicle or a physical quantity occurring in the vehicle, and the input physical quantity detecting means. Target yawing momentum calculation means for calculating a target yawing momentum to be achieved in the vehicle based on the input detection value acting on the vehicle detected by the means or the physical quantity detection value generated in the vehicle,
A yawing momentum control device for a vehicle, comprising: a control means for performing control so that the target yawing momentum calculated by the target yawing momentum calculating means matches the yawing momentum detected by the yawing momentum detecting means. A road surface friction coefficient state detection estimating means for detecting or estimating the state of the road surface friction coefficient is provided, and the target yawing momentum calculating means has a road surface friction state detection value detected or estimated by the road surface friction coefficient state detection estimating means. Alternatively, a yawing momentum control device for a vehicle, comprising a maximum value calculating means for calculating the maximum value of the target yawing momentum based on the estimated value. 2. The yawing momentum control device for a vehicle according to claim 1, wherein the road surface frictional state detection estimating means includes a lateral acceleration detecting means for detecting a lateral acceleration acting on the vehicle.