JPH0569845A - Vehicle turning limit judging device - Google Patents

Abstract

PURPOSE:To judge if steering wheels have reached a turning limit before skid limit by comparing a change rate of restoring torque to increase in a slip angle with a reference value. CONSTITUTION:A steering torque TH is detected by a steering torque sensor 42 (S2). After that, by subtracting a previous value from a present value of the steering torque TH, a steering torque differential DELTATH is calculated (S3). Next, a steering angle theta is detected by a steering angle sensor 40 and a lateral acceleration GY by a lateral acceleration sensor 44 (S4), respectively, and a steering angle differential PHItheta and a lateral acceleration differential DELTAGY are calculated, respectively (S5). Then, using the steering torque differential DELTATH, steering angle theta, steering angle differential DELTAtheta and lateral acceleration differential DELTAGY, it is judged if front wheels have reached turning limit (before skid limit) or not (S6).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for determining whether or not a steering wheel of a vehicle has reached a turning limit when the vehicle turns.

[0002]

2. Description of the Related Art Japanese Patent Application No. 3-15 previously filed by the applicant
In the specification of No. 2526, it is assumed that the vehicle is in a reference traveling state (for example, the vehicle is not subjected to any disturbance) from the steering angle of the steering wheel of the vehicle and the vehicle speed that is the traveling speed of the vehicle. Estimate the reference yaw rate, detect the actual yaw rate that occurs in the vehicle body, and determine the actual motion state of the vehicle (for example, whether the vehicle shows an oversteer tendency or an understeer tendency) from the relationship between the reference yaw rate and the actual yaw rate. Techniques for doing so are disclosed.

On the other hand, there is already known a vehicle motion control device which controls the motion of a vehicle and changes the vehicle motion characteristics by changing the control characteristics thereof. For example, a four-wheel steering controller,
The drive force transmission control device, the suspension control device, the power steering device, the anti-lock brake control device, the traction control device, etc. The respective devices will be schematically described below.

The four-wheel steering control device appropriately controls the rear-wheel steering angle of the vehicle in relation to the front-wheel steering angle, the vehicle speed, the actual yaw rate, etc., and changes the rear-wheel steering angle gain as a control characteristic. The driving force transmission control device controls the ratio of distributing the driving force of the engine to the front wheels and the rear wheels, and changes the driving force distribution ratio gain as a control characteristic. The suspension control device keeps the posture of the vehicle body horizontal regardless of the inclination of the road surface and the acceleration / deceleration of the vehicle, turning, etc., and changes the vehicle body roll angle suppression gain as a control characteristic. The power steering device assists the steering force applied to the steering wheel of the vehicle by the driver, and changes the assist amount gain as a control characteristic. The anti-lock brake control device controls the brake pressure of the wheels so that the wheels do not fall into a locked state during vehicle braking, and changes the brake pressure gain as a control characteristic. The traction control device reduces the drive force of the drive wheels so that excessive slip does not occur in the drive wheels when the vehicle starts and accelerates, and changes the drive force reduction amount gain as a control characteristic.

Then, the present applicant has asked the vehicle motion control device whether or not the turning state of the steering wheel has reached a limit in relation to the cornering force generated on the steering wheel, that is, the steering wheel turns. When it is determined that the limit has been reached and the technology that changes the control characteristics according to the result of the determination and the steering wheel has reached the turning limit, and that the turning limit has been reached We proposed a technology that estimates the friction coefficient of the road surface and changes the control characteristics accordingly.

Further, the applicant of the present invention has proposed the following method for determining whether or not the steering wheel has reached the turning limit. This is a method of utilizing the technique described in the above-mentioned Japanese Patent Application No. 3-152526 and determining that the turning limit has been reached if the deviation of the actual yaw rate from the reference yaw rate is larger than a threshold value.

[0007]

In order to appropriately change the control characteristics in the vehicle motion control device according to the turning state of the steering wheel, the steering wheel may reach the skid limit, that is, reach the skid limit. It is desirable to change the control characteristic from the time when the property occurs. This is because even if the control characteristic is changed after the steering wheel reaches the skid limit, the vehicle tends to not respond quickly accordingly. The state where the steering wheel reaches the skid limit generally means that the cornering force generated on the steering wheel reaches a peak value and the change rate of the cornering force with respect to the increase in the slip angle of the steering wheel (hereinafter, simply the change of the cornering force. Rate) means 0.

However, when the turning limit judgment method proposed by the applicant is adopted, it is judged that the steering wheel reaches the turning limit only when the steering wheel actually reaches the skid limit. , It is not judged that the steering wheel has reached the turning limit before reaching the skid limit. In this judgment method, the change rate of the cornering force is 0.
This is because the fact that the deviation of the actual yaw rate from the reference yaw rate becomes larger than the threshold value is used.

As described above, the turning limit judging method proposed by the present applicant has a problem that it is difficult to judge whether or not the steering wheel has reached the turning limit before the skid limit. Therefore, a vehicle motion control device that changes the control characteristic according to the determination result by the turning limit determination method, or estimates the friction coefficient of the road surface accordingly and changes the control characteristic accordingly, changes the behavior of the vehicle. The problem arises that it is difficult to control sufficiently quickly and with high precision.

In view of such circumstances, the present invention has been made to make it possible to determine whether or not the steering wheel has reached the turning limit before the skid limit.

[0011]

SUMMARY OF THE INVENTION The gist of the present invention is (a) a restoring torque-related parameter detecting means for detecting a restoring torque generated in a steering wheel of a vehicle or a parameter that changes accordingly, and (b) Wheel slip angle related parameter detection means for detecting the slip angle of the steering wheel or a parameter that changes accordingly, and (c) the detected restoring torque or the parameter that changes accordingly, the detected slip angle or the corresponding slip angle. It is an object of the present invention to provide a vehicle turning limit determination device that includes a turning limit determination unit that determines that the steered wheels have reached the turning limit when the rate of change of the changing parameter with respect to the increase is smaller than the reference value.

The "restoring torque" in the present invention means, for example, the moment about the axis of the kingpin due to the cornering force acting on the tire contact surface of the steering wheel.

Further, as the "parameter changing according to the restoring torque" in the present invention, for example, the steering torque applied to the steering wheel by the driver, the pressure generated in the power cylinder of the power steering device, or the like can be selected.

Further, for example, the lateral acceleration generated in the vehicle body, the yaw rate generated in the vehicle body, or the like can be selected as the "parameter changing according to the slip angle" in the present invention.

[0015]

[Function] The restoring torque generated in the steering wheel is shown in FIG.
As shown in the graph in Fig. 3, the restoring torque changes in a curve that is convex upward as the slip angle of the steering wheel increases, but the restoring torque is before the cornering force generated on the steering wheel reaches the peak value, that is, the steering torque. The peak value is reached before the wheel reaches the skid limit. In other words, before the steering wheel reaches the skid limit, the restoring torque,
The rate of change with increasing slip angle becomes zero.

Based on this fact, in the vehicle turning limit determining apparatus according to the present invention, the restoring torque-related parameter detecting means detects the restoring torque generated in the steered wheels of the vehicle or the parameter that changes accordingly, and the wheel slip occurs. The angle-related parameter detection means detects the slip angle of the steering wheel or a parameter that changes accordingly, and the turning limit determination means detects the restoring torque or the parameter that changes accordingly, the detected slip angle or it If the rate of change for the increase of the parameter that changes accordingly is smaller than the reference value,
It is determined that the steering wheel has reached the turning limit. The reference value can be selected to be 0 or a value close thereto, for example.

[0017]

Therefore, according to the present invention, it is possible to detect that the turning state of the steering wheel is close to the limit before the steering wheel reaches the skid limit, and it is judged by the vehicle turning limit judging device according to the present invention. If the vehicle motion control device is operated using the result, the effect of improving the control accuracy of the motion characteristics of the vehicle can be obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below in detail with reference to the drawings. A vehicle turning limit determination apparatus that is an embodiment of the present invention is provided in a vehicle equipped with the power steering apparatus shown in FIG. The power steering device is of a hydraulic type, a separator type, a rack and pinion type, or a vehicle speed sensitive type, but these are well known and will be briefly described.

That is, in this power steering system, a steering wheel 10 operated by a driver passes through a steering shaft 12, a steering gear box 14, a control rack (an element that functions as a so-called tie rod) 16, a knuckle arm 18, and a spindle 20. It is connected to the left and right front wheels 22 which are the steering wheels of the vehicle. The knuckle arm 18 and the spindle 20 are adapted to rotate integrally with each other around the axis of the kingpin 24. Further, a steering torque T applied by the driver to the steering wheel 10 by an oil pump (not shown) driven by an engine (not shown) of the vehicle and a control valve (not shown) provided in the steering gear box 14. The hydraulic pressure (right cutting pressure P _R and left cutting pressure P _L ) having a height corresponding to the difference between _H and the restoring torque T _T generated in the left and right front wheels 22 is supplied to the power cylinder 30, whereby the steering torque T _H. While being assisted, the left and right front wheels 22 are deflected according to the steering angle θ of the steering wheel 10. Further, in this power steering device, the right cutting pressure P _R and the left cutting pressure P _L are changed according to the vehicle speed by a solenoid valve (not shown).

As shown in FIG. 3, the present vehicle turning limit determination device is constructed by connecting a steering angle sensor 40, a steering torque sensor 42 and a lateral acceleration sensor 44 to a turning limit determination computer (hereinafter simply referred to as a computer) 50. Has been done. The steering angle sensor 40 detects the steering angle θ of the steering wheel 10 with the right turn steering of the steering wheel 10 as positive and the left turn steering as negative. The steering torque sensor 42 outputs the steering torque T _H of the steering wheel 10 to the right for steering the steering wheel 10 to the right.
Left turn steering is detected as negative. The lateral acceleration sensor 44 detects the lateral acceleration G _Y generated in the vehicle body as positive whether it is rightward or leftward. The ROM of the computer 50 stores various programs including the turning limit determination program shown in the flowchart of FIG. Then, the computer 50 uses C
PU uses the ROM turning limit judgment program for various sensors,
The turning limit determination is performed by using the RAM or the like.

The operation of the computer 50 will be described in detail. When the vehicle is powered on and the computer 50 is powered on, the computer 50 executes the turning limit determination program of FIG. In this program,
In step S1 (hereinafter simply referred to as S1; the same applies to other steps), scheduled initialization is performed, and subsequently in step S2, the steering torque T _H is detected by the steering torque sensor 42. Then, in S3, the steering torque differential ΔT _H is calculated by subtracting the previous value from the current value of the steering torque T _H.

Subsequently, in S4, the steering angle sensor 40
Steering angle θ, lateral acceleration sensor 44 lateral acceleration G
_Y is respectively detected, and in S5, in the same manner as in S3, the steering angle differential Δθ and the lateral acceleration differential Δ
G _Y is calculated respectively. Thereafter, in S6, the steering torque differential [Delta] T _H, the steering angle theta, using a steering angle differential Δθ and lateral acceleration differential .DELTA.G _Y, whether the front wheel 22 has reached a turning limit (skid limit forward) is determined.

There is a relationship represented by the graph of FIG. 4 between the absolute value of the steering torque T _H and the lateral acceleration G _Y. That is, the absolute value of the steering torque T _H increases in a convex curve as the lateral acceleration G _Y increases, reaches a peak value before the front wheels 22 reach the skid limit, and the steering torque T _H
The change rate of the absolute value of _H with respect to the increase of the lateral acceleration G _Y is 0.
There is a relationship that becomes. In this step, this relationship is used to determine whether or not the front wheels 22 have reached the turning limit before the skid limit.

Specifically, the steering wheel 10 is currently being turned over and the steering torque differential Δ
The absolute value of the change rate of the steering angle torque T _H obtained by dividing T _H by the lateral acceleration derivative ΔG _Y is the predetermined threshold value (0
Alternatively, it is determined whether or not the value is sufficiently smaller than that value), and if so, it is determined that the front wheels 22 have reached the turning limit.

The determination as to whether or not the steering wheel 10 is currently being turned up is made by using the product of the steering angle θ and the steering angle differential Δθ, and if the product is greater than 0, the turning is increased. It is determined to be during steering.

When one execution of S2 to S6 is completed as described above, the process returns to S2 again and the computer 50
After that, the turning limit determination is periodically repeated.

As shown in FIG. 3, the present vehicle turning limit determination device includes a four-wheel steering control device (represented by "4WS" in the drawing) 60 and a driving force transmission control device ("4WD" in the drawing) as a vehicle motion control device. 62) and a warning means 64 for warning the driver that the front wheels 22 have reached the turning limit.

The four-wheel steering control system 60 controls the rear-wheel steering angle δ _R in proportion to the front-wheel steering angle δ _F , and the rear-wheel steering control in order to suppress the rotation of the vehicle body. Angle δ _R
In conjunction with yaw rate feedback control, which controls the vehicle in accordance with the yaw rate γ generated in the vehicle body, the rear wheel steering angle δ _R
To control. That is, the rear wheel steering angle δ _R is expressed by the following equation using the front wheel steering angle δ _F and the yaw rate γ. δ _R = K _F · δ _F + K _B · γ However, here, both K _F and K _B are control coefficients.

Further, the four-wheel steering control device 60 appropriately controls the kinetic characteristics of the vehicle in relation to the vehicle speed V by changing the control coefficients K _F and K _B in accordance with the vehicle speed V. The four-wheel steering control device 60 is connected to the vehicle turning limit determination device described above, and is supplied with a turning limit determination signal from the vehicle turning limit determination device. And
The four-wheel steering control device 60 receives the control coefficient K during the normal time when the signal indicating that the front wheels 22 have reached the turning limit is not supplied thereto.
_B is changed in relation to the vehicle speed V as shown by the broken line graph in FIG. 5, while the control coefficient K _{B is changed} to the vehicle speed V at the turning limit when the signal indicating that the front wheels 22 have reached the turning limit is supplied. In relation to, change as shown by the solid line graph in the figure. When the front wheels 22 reach the turning limit, the value of the control coefficient K _B multiplied by the yaw rate γ is made larger than when the front wheels 22 have not reached the turning limit, thereby increasing the ratio of the running stability to the steering response of the vehicle. ..

The driving force transmission control device 62 appropriately controls the ratio of the driving force of the vehicle engine to the front wheels 22 and the rear wheels (not shown) in relation to the friction coefficient of the road surface. Specifically, the driving force of the engine is set to the front wheel 2
The control hydraulic pressure in the center differential (not shown) that is distributed to the two front wheels and the rear wheel is such that the higher the control hydraulic pressure, the more the drive power of the engine is distributed to the front wheels 22.
The higher the value obtained by subtracting the rear wheel speed V _R from the second wheel speed V _{F, the} higher the control. That is, the control oil pressure P is expressed by the following equation using the wheel speed V _F of the front wheels 22 and the wheel speed V _{R of the} rear wheels. P = K · [V _F -V _R] However, K wherein is control coefficient.

The driving force transmission control device 62 is also connected to the vehicle turning limit determination device, and a turning limit determination signal from the vehicle turning limit determination device is supplied. Then, the drive force transmission control device 62 sets the control coefficient K to the normal value during a normal time when the signal indicating that the front wheels 22 have reached the turning limit is set to the normal value, while the signal indicating that the front wheels 22 have reached the turning limit is transmitted. At the supplied turning limit, the control coefficient K is set to a specific value larger than the normal value. When the front wheels 22 reach the turning limit, the value of the control coefficient K is made larger than when the front wheels 22 have reached the turning limit,
As a result, the ratio of the running stability to the steering response of the vehicle is increased.

The warning means 64 is also connected to the vehicle turning limit judging device, and a turning limit judging signal is supplied from the vehicle turning limit judging device. And the warning means 64
Is inactive during normal times when no signal is supplied to it that the front wheels 22 have reached the turning limit, while the front wheels 2
When a signal indicating that 2 has reached the turning limit is supplied, at the turning limit, it is activated and informs the driver that the front wheels 22 have reached the turning limit by light, sound or the like.

As is apparent from the above description, in the present embodiment, it is judged whether or not there is a possibility that the front wheels 22 will reach the skid limit, so that the four-wheel steering control device 60 can be operated. The responsiveness of the vehicle behavior based on the operation and the responsiveness of the vehicle behavior based on the operation of the driving force transmission control device 62 are improved.

Further, in this embodiment, the warning means 6 indicates that the front wheel 22 has reached the turning limit before the skid limit.
4 is transmitted to the driver, so that the driver uses the front wheel 2
There is also an effect that the maneuver for early avoiding that 2 reaches the skid limit can be started.

As is clear from the above description, in this embodiment, the steering torque sensor 42 and the computer 5 are used.
The portion 0 for executing S2 in FIG. 1 constitutes a restoring torque related parameter detecting means of a type for detecting the steering torque T _H as the “parameter changing according to the restoring torque” in the present invention, and the lateral acceleration sensor 44 and a portion of the computer 50 that executes S4 in the figure detect the wheel slip angle related parameter of the type in which the lateral acceleration G _Y is detected as the "parameter that changes according to the slip angle of the steering wheel" in the present invention. The steering angle sensor 4 constitutes the means.
0, and S3, S5, and S of FIG.
6 is the lateral acceleration G of the steering torque T _H.
This constitutes a turning limit determination means of the type that uses the absolute value of the rate of change with respect to the increase in _Y.

Another embodiment will be described. Since this embodiment has many parts in common with the previous embodiment, only different parts will be described in detail. Further, the vehicle turning limit determination device according to the present embodiment also includes the above-described power steering device, 4
The vehicle is provided with a wheel steering control device 60, a driving force transmission control device 62, and a warning means 64.

As shown in FIG. 6, the present vehicle turning limit determination device includes the steering angle sensor 40 and the lateral acceleration sensor 44.
And the right cutting pressure P _R generated in the power cylinder 30.
Various sensors including a right cutting pressure sensor 100 for detecting the left cutting pressure and a left cutting pressure sensor 102 for detecting the left cutting pressure P _L are connected to a turning limit determination computer (hereinafter, simply referred to as a computer) 110. The ROM of the computer 110 stores various programs including the turning limit determination program represented by the flowchart of FIG.

In the turning limit judgment program of FIG. 7, first, in S11, scheduled initialization is performed,
Then, in S12, the right cutting pressure P _R and the left cutting pressure P _L are detected by the right cutting pressure sensor 100 and the left cutting pressure sensor 102, respectively. After that, in S13, the hydraulic pressure difference P _R -P _L is calculated by subtracting the left cutting pressure P _L from the right cutting pressure P _R , and the previous value is subtracted from the current value of the hydraulic pressure difference P _R -P _L in S14. As a result, the hydraulic pressure differential Δ (P _R −P _L ) is calculated.

Subsequently, in S15, the steering angle sensor 4
The steering angle θ is detected by 0 and the lateral acceleration G _Y is detected by the lateral acceleration sensor 44, and the steering angle differential Δθ and the lateral acceleration differential ΔG _Y are calculated in S16.
Then, in S17, the hydraulic pressure differential Δ (P _R −
P _L ), the steering angle θ, the steering angle differential Δθ, and the lateral acceleration differential ΔG _Y are used to determine whether or not the front wheels 22 have reached the turning limit.

Absolute value of hydraulic pressure difference P _R -P _L and lateral acceleration G _Y
There is a relationship represented by the graph of FIG.
That is, the absolute value of the hydraulic pressure difference P _R −P _L increases in a convex curve as the lateral acceleration G _Y increases, reaches a peak value before the front wheel 22 reaches the skid limit, and the hydraulic pressure difference P
There is a relation that the rate of change of the absolute value of _R− P _L with respect to the increase of the lateral acceleration G _Y becomes zero. In this step, this relationship is used to determine whether or not the front wheels 22 have reached the turning limit before the skid limit.

Specifically, the steering wheel 10 is currently being turned up, and the hydraulic pressure differential Δ (P
Whether the absolute value of the change rate of the steering angle torque T _H obtained by dividing _R −P _L ) by the lateral acceleration derivative ΔG _Y is less than or equal to a predetermined threshold value (0 or a value sufficiently close to it). Is determined, and if so, it is determined that the front wheels 22 have reached the turning limit.

When one execution of S12 to S17 is completed as described above, the process returns to S12 again, and the computer 110 thereafter periodically repeats the turning limit determination.

Therefore, also in this embodiment, as in the previous embodiments, the effect of improving the control response of the vehicle behavior and the effect of accelerating the skid avoidance start time can be obtained.

As is apparent from the above description, in this embodiment, the right cutting pressure sensor 100 and the left cutting pressure sensor 102, and the portion of the computer 110 which executes S12 in FIG. As a parameter that changes in accordance with the restoring torque ", a restoring torque related parameter detecting means of the type that detects the hydraulic pressure difference P _R -P _L is configured,
The lateral acceleration sensor 44 and the part of the computer 110 that executes S15 in the figure detect the lateral acceleration G _Y as the "parameter that changes according to the slip angle of the steering wheel" in the present invention. The steering angle sensor 40 and the part of the computer 110 that executes S13 to S17 in the figure constitute a related parameter detecting means, and indicate the absolute value of the rate of change of the hydraulic pressure difference P _R −P _L with respect to the lateral acceleration G _Y. That is, the turning limit determination means of the type used is constructed.

Another embodiment will be described. Since this embodiment has many parts in common with the previous two embodiments, only different parts will be described in detail. In addition, the vehicle turning limit determination device according to the present embodiment is also provided in the vehicle including the power steering device, the four-wheel steering control device 60, the driving force transmission control device 62, and the warning means 64.

As shown in FIG. 9, the present vehicle turning limit determining apparatus includes a steering angle sensor 40, a steering torque sensor 42,
Various sensors including a lateral acceleration sensor 44, a right cutting pressure sensor 100, and a left cutting pressure sensor 102 that detects a left cutting pressure P _L are connected to a turning limit determination computer (hereinafter, simply referred to as a computer) 150. The ROM of the computer 150 stores various programs including the turning limit determination program shown in the flowchart of FIG.

In the turning limit judgment program of FIG. 10, first, in S21, a scheduled initial setting is performed, and subsequently, in S22, the steering torque sensor 42,
The steering torque T _H , the right cutting pressure P _R, and the left cutting pressure P _L are detected by the right cutting pressure sensor 100 and the left cutting pressure sensor 102, respectively. Then, in S23, the restoring torque T _T generated in the left and right front wheels 22 is calculated from the steering torque T _H , the right turning pressure P _R and the left turning pressure P _L.

In the power steering system described above, the restoring torque T _T which is the sum of the restoring torques generated in the front wheels 22, that is, the moment around the axis of the kingpin 24 due to the cornering force acting on the tire contact surface of the left and right front wheels 22 is , The king pin 24 by the operating force applied from the power cylinder 30 to the control rack 16
Is equal to the sum of the moment M _P about the axis of the king pin 24 and the moment M _G about the axis of the king pin 24 due to the operating force applied to the control rack 16 from the steering gear box 14. In addition, the moment M _P is the hydraulic pressure difference P _R −
P _L is equal to the product of the pressure receiving area A of the power cylinder 30 and the length L of the knuckle arm 18, and the moment M _G is equal to the product of the steering torque T _H and the total steering gear ratio N. In short, the restoring torque T _T is expressed by the following equation, using the steering torque T _H and the hydraulic pressure difference P _R −P _L , T _T = N · T _H + L · A · [P _R −P _L ]. , S23, the restoring torque T _T is calculated using this equation.

Subsequently, the restoring torque differential ΔT _T is calculated in S24, and the steering angle sensor 40 is calculated in S25.
Steering angle θ, lateral acceleration sensor 44 lateral acceleration G
_Y is detected, and the steering angle differential Δ
θ and lateral acceleration differential ΔG _Y are calculated respectively. Then, in S27, it is determined whether or not the front wheels 22 have reached the turning limit using the restoration torque differential ΔT _T , the steering angle θ, the steering angle differential Δθ, and the lateral acceleration differential ΔG _Y.

There is a relationship represented by the graph of FIG. 11 between the absolute value of the restoring torque T _T and the lateral acceleration G _Y.
That is, the absolute value of the restoring torque T _T increases in a convex curve as the lateral acceleration G _Y increases, reaches a peak value before the front wheel 22 reaches the skid limit, and the absolute value of the restoring torque T _T , The rate of change with respect to the increase of the lateral acceleration G _Y becomes 0. In this step, this relationship is used to determine whether or not the front wheels 22 have reached the turning limit before the skid limit.

Specifically, the steering wheel 10 is currently being turned over and the restoring torque differential Δ is present.
It is determined whether or not the absolute value of the change rate of the restoring torque T _T obtained by dividing T _T by the lateral acceleration differential ΔG _Y is less than or equal to a predetermined threshold value (0 or a value sufficiently close to 0). ,
If so, it is determined that the front wheels 22 have reached the turning limit.

When one execution of S22 to S27 is completed as described above, the process returns to S22 and the computer 150 thereafter periodically repeats the turning limit determination.

As is clear from the above description, in the present embodiment as well as in the previous two embodiments, the effect of improving the control response of the vehicle behavior and the effect of accelerating the skid avoidance start time are obtained. can get.

As is clear from the above description, in the present embodiment, the steering torque sensor 42 and the right-turn pressure sensor 1 are
00 and the left cutting pressure sensor 102, and the computer 15
10 and the portion that executes S22 of FIG. 10 constitute the restoring torque related parameter detecting means of the type that detects the restoring torque T _T as the “restoring torque” in the present invention, and the lateral acceleration sensor 44 and the computer 150. , S2 in the figure
5 executes a wheel slip angle-related parameter detecting means for detecting the lateral acceleration G _Y as the "parameter that changes according to the slip angle of the steering wheel" in the present invention. The part of the computer 150 that executes S23 to S27 in FIG.
This constitutes a turning limit determination means of the type that uses the absolute value of the rate of change of the restoring torque T _T with respect to the lateral acceleration G _Y.

Each of the vehicle turning limit determination devices according to the above-described embodiments is a four-wheel steering control device 60 and a driving force transmission as a vehicle motion control device that changes control characteristics according to the determination result. It was provided in a vehicle equipped with a control device 62, but with them,
Instead of these, it may be provided in a vehicle equipped with a vehicle motion control device other than them, that is, for example, the above-mentioned suspension control device, anti-lock brake control device, traction control device and the like.

Further, in any of the embodiments described in detail above, when the steering wheel reaches the turning limit, the vehicle motion control device changes the control characteristic from the normal time to the turning limit time, and then the turning state of the steering wheel. It was said that the control characteristics would not be changed regardless of the height of the skid limit that is expected to be reached if, for example, the height of the turning limit is judged and the control characteristics are changed accordingly. It can also be one. An example will be described below.

Lateral acceleration G when the restoring torque T _T or a parameter that changes accordingly reaches a peak value
There is a proportional relationship between _Y and the coefficient of friction μ between the front wheels 22 and the road surface (this is an example of a parameter corresponding to the height of the turning limit). That is, there is a relation represented by the equation μ = a · G _Y. However, in this equation, a is a constant of proportionality, which is a value of around 1.5.

Therefore, based on this relationship, means for estimating the friction coefficient μ from the lateral acceleration G _Y when it is determined that the front wheels 22 have reached the turning limit is provided, and the vehicle motion control device is estimated. The control characteristic is changed according to the friction coefficient μ so that the lower the friction coefficient μ, the higher the ratio of the running stability to the steering response of the vehicle.

Although some embodiments of the present invention have been described in detail with reference to the drawings, various modifications other than these will be made based on the knowledge of those skilled in the art without departing from the scope of the claims. Of course, the present invention can be implemented in an improved mode.

[Brief description of drawings]

FIG. 1 is a flowchart showing a turning limit determination program used by a vehicle turning limit determination device that is an embodiment of the present invention.

FIG. 2 is a diagram conceptually showing a configuration of a power steering device provided in a vehicle provided with the vehicle turning limit determination device of FIG.

FIG. 3 conceptually shows the configuration of the vehicle motion control device of FIG. 1, and a four-wheel steering control device (represented by “4WS” in the figure) and a driving force transmission control device (FIG. 3) provided in the vehicle. Is represented by “4WD” in FIG. 4) and a warning unit.

FIG. 4 is a graph for explaining a relationship between a lateral acceleration G _Y generated in a vehicle body and a steering torque T _H applied to a steering wheel by a driver.

5 is a graph for explaining a relationship between a vehicle speed V and a control coefficient K _B used by the four-wheel steering control system of FIG.

FIG. 6 conceptually shows a configuration of a vehicle turning limit determination apparatus which is another embodiment of the present invention, and a four-wheel steering control apparatus (indicated by “4WS” in the figure) provided in the vehicle, It is a figure which shows the relationship with a driving force transmission control apparatus (it represents with "4WD" in a figure), and a warning means.

7 is a flowchart showing a turning limit determination program used by the turning limit determination computer in FIG.

8 is a graph for explaining a relationship between a lateral acceleration G _Y generated in the vehicle body and a hydraulic pressure difference P _R -P _L generated in the power cylinder of FIG. 2.

FIG. 9 conceptually shows a configuration of a vehicle turning limit determination device which is still another embodiment of the present invention, and a four-wheel steering control device (“4W” in the figure) provided in the vehicle.
S "), drive force transmission control device (" 4W "in the figure)
It is a figure which shows the relationship with D)) and a warning means.

10 is a flowchart showing a turning limit determination program used by the turning limit determination computer in FIG.

FIG. 11 is a graph for explaining the relationship between the lateral acceleration G _Y generated on the vehicle body and the restoring torque T _T generated on the steered wheels.

FIG. 12 is a graph for explaining characteristics of changes in each of the cornering force and the restoring torque generated in the steering wheel of the vehicle with respect to the slip angle of the steering wheel.

[Explanation of symbols]

 22 front wheel 40 steering angle sensor 42 steering torque sensor 44 lateral acceleration sensor 50, 110, 150 turning limit determination computer 100 right cutting pressure sensor 102 left cutting pressure sensor

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area B62D 137: 00

Claims (1)

[Claims] 1. A restoring torque related parameter detecting means for detecting a restoring torque generated in a steering wheel of a vehicle or a parameter changing in accordance therewith, and a wheel slip detecting a slip angle of the steering wheel or a parameter changing in accordance therewith. The angle-related parameter detection means, and the steering wheel when the rate of change of the detected restoring torque or the parameter that changes accordingly with respect to the increase of the detected slip angle or the parameter that changes accordingly is smaller than the reference value. A vehicle turning limit determination device, comprising: a turning limit determining means for determining that the vehicle has reached a turning limit.