JP3386858B2 - Vehicle steering system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering apparatus for a vehicle that steers the rear wheels when steering the front wheels, and more particularly, to a running state quantity other than the vehicle speed (for example, front wheel steering angle, yaw rate, etc.).
The present invention relates to the improvement of what determines the rear wheel steering control target value in consideration of the above.

[0002]

2. Description of the Related Art Generally, in a steering device for a vehicle of this type, the rear wheels are in the opposite phase to the steering direction of the front wheels in the low vehicle speed region, and the rear wheels are in the same direction as the steering direction of the front wheels in the high vehicle speed region. By steering in the same phase, the turning performance at low vehicle speed and the stability at high vehicle speed are ensured.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-108079, a basic term set to change according to the vehicle speed as described above is used as a running state quantity other than the vehicle speed. A target value for rear wheel steering control (for example, steering ratio of front and rear wheels, rear wheel steering angle, etc.) is determined by adding and subtracting a plurality of correction terms set based on the front wheel steering angle, the front wheel steering angular velocity, and the yaw rate. It is also known that the turning performance and the stability during turning are further harmonized for improvement.
In this case, each of the correction terms is a product of the function value of the corresponding running state quantity and the control gain, and the control gain is set to, for example, zero in the low vehicle speed region and a positive constant value in the high vehicle speed region. It may be set to a value that changes depending on the vehicle speed.

[0004]

However, in the above-mentioned prior art, when the vehicle is rapidly decelerated while turning, the basic term changes to the opposite phase side as the vehicle speed decreases and the yaw rate correction term becomes zero. The rear wheel steering angle changes from the same phase side to the opposite phase side. For this reason, there is a problem in that the vehicle falls into an oversteer state, which is more inward in the turning direction, and the stability deteriorates.

Therefore, in order to solve such a problem, it is conceivable to fix the target value for rear wheel steering control to a constant value and perform rear wheel steering at the time of sudden deceleration during turning. However, although the target value for the rear wheel steering control is determined in consideration of other running state quantities other than the vehicle speed, when the target value is fixed and the rear wheel steering is performed, Since the state quantity is not taken into consideration at all, it is not possible to perform a fine-grained rear wheel steering control in which the vehicle stability and the turning performance are harmonized. For example, when the yaw rate increases when the steering wheel is further steered in the turning direction or a spin state occurs during sudden deceleration during turning, the rear wheel steering control target value determined by taking the yaw rate into consideration The rear wheel steering is performed with a fixed value close to the opposite phase, and the behavior of the vehicle body cannot be sufficiently suppressed. Also, when the steering wheel is steered in the opposite direction to the turning direction during sudden deceleration during cornering, a fixed value closer to the same phase than the target value for rear wheel steering control determined by taking into account the front wheel steering angle and the front wheel steering angular velocity. The rear wheel steering is performed with the value, and the direction change of the vehicle becomes dull.

The present invention has been made in view of the above points, and an object thereof is to fix only the function value of the vehicle speed among the target values for the rear wheel steering control at the time of sudden deceleration during turning. Thus, a vehicle steering system capable of finely grained rear wheel steering control in which the stability and turning of the vehicle are harmonized is provided.

[0007]

In order to achieve the above object, the invention according to claim 1 is, as a vehicle steering device, a basic condition that changes according to a vehicle speed, but a traveling state of a vehicle other than the vehicle speed. A target value determining means for determining a rear wheel steering control target value by adding and subtracting a correction term set based on the amount is provided. The opposite phase is set to steer the rear wheels in the same phase as the steering direction of the front wheels in the high vehicle speed range.The correction term is a control that changes depending on the function value of the running state amount and the vehicle speed. It is assumed to be the product of the gain. And
Determination means for determining that the rapid deceleration state during turning traveling of the vehicle, with respect to the target value determining means when it is determined that the a rapid deceleration state during turning traveling the determination means, the fundamental term and the A correction means for fixing only the control gain in the correction term to a predetermined value and issuing a correction command so as to determine the rear wheel steering control target value is provided.

The invention according to claim 2 is dependent on the invention according to claim 1, and shows one mode thereof. That is, the target value determining means has a yaw rate, a front wheel steering angle, and a front wheel steering angular velocity as the traveling state quantity of the vehicle, and adds or subtracts these correction terms from the basic terms to determine the rear wheel steering control target value. The control gain in the yaw rate correction term is set to zero in the low vehicle speed region and set to a positive constant value in the medium vehicle speed and high vehicle speed regions, and the control gain and the steering angular velocity correction term in the steering angle correction term are set. The medium control gains are both set to zero in the low vehicle speed region and the high vehicle speed region, and set to a positive constant value in the medium vehicle speed region.

The inventions described in claims 3 and 4 are both dependent on the invention described in claim 2, and more specifically show the correction content of the correction means which is one of the components. That is, in the invention according to claim 3, the correction means provides the target value determination means with the control gains in the basic term and the yaw rate correction term when it is determined that the vehicle is in the rapid deceleration state during turning. Is fixed to a predetermined value, and a correction command is issued to determine the rear wheel steering control target value. Further, in the invention according to claim 4, the correction means, when it is determined that the vehicle is in a rapid deceleration state during turning, is directed to the target value determination means, the control gain in the basic term and the yaw rate correction term, and the control gain. The control gain in the steering angle correction term and the control gain in the steering angle speed correction term are each fixed to a predetermined value, and a correction command is issued so as to determine the rear wheel steering control target value.

The invention according to claim 5 is dependent on the invention according to claim 3 or 4, and the predetermined value is a corresponding basic term or control gain at the time when it is determined that the vehicle is in a sudden deceleration state during turning. It is the same as the value of.

The invention according to claim 6 is dependent on the invention according to claim 4, and the predetermined value for the control gain in the steering angular velocity correction term is determined to be a rapid deceleration state during turning. The value is a value corrected by a predetermined amount in the direction in which the rear wheel steering angle is in the opposite phase to the value of the control gain in the steering angle speed correction term at the time point.

The invention according to claim 7 is dependent on the invention according to claim 3, wherein the predetermined value is the value of the corresponding basic term or control gain at the time when it is determined that the vehicle is in a sudden deceleration state during turning. Instead, the value is corrected by a predetermined amount in the direction in which the rear wheel steering angle is closer to the same phase.

[0013]

With the above construction, in the invention according to claim 1,
When the vehicle decelerates suddenly during turning, the judgment means judges that, and the correction means which receives the judgment result of the judgment means issues a correction command to the target value determination means. In the formula for calculating the target value for wheel steering control, only the function value of the vehicle speed, that is, the basic term that changes according to the vehicle speed and the control in the correction term that is set based on the running state amount of the vehicle other than the vehicle speed The gain and the gain are fixed at predetermined values. As a result, the rear wheel steering angle does not suddenly change from the in-phase side to the anti-phase side as the vehicle speed decreases and the oversteer state does not occur. In addition, at this time, when the traveling state amount other than the vehicle speed changes, the target value for the rear wheel steering control changes accordingly, and the fine-grained rear wheel steering that balances the stability and turning of the vehicle. Control is performed.

According to the third aspect of the present invention, the calculation formula of the target value for steering control has a correction term set based on the yaw rate, and the control gain in the correction term is a basic term when the vehicle is suddenly decelerated during turning. When the steering wheel is further steered in the turning direction or a spin state occurs during sudden deceleration during turning, the target value for rear-wheel steering control is increased as the yaw rate increases. The rear wheels are changed in the direction toward the same phase, and the unstable behavior of the vehicle body is suppressed. Here, as in the invention according to claim 7, the rear wheel steering angle is in phase with the predetermined value from the value of the corresponding basic term or control gain at the time when it is determined that the vehicle is in a sudden deceleration state during turning. If the value is corrected by a predetermined amount in the direction toward the side, the rear wheels will be steered more toward the same phase,
The effect of suppressing the unstable behavior of the vehicle body is enhanced.

In the invention of claim 4, the rear wheel steering control target value calculation formula has correction terms set based on the front wheel steering angle and the front wheel steering angular velocity, respectively, and the control gain in these correction terms is included. When the steering wheel is steered in the opposite direction to the turning direction during sudden deceleration during turning, the target value for rear wheel steering control is the steering wheel operation, that is, the front wheel steering. The rear wheels change in the direction in which the rear wheels are in the opposite phase depending on the angle and the magnitude of the front wheel steering angular velocity, and the direction change or turning of the vehicle is enhanced.
Here, as in the invention according to claim 6, the control in the steering angular velocity correction term at the time when it is determined that the predetermined value for the control gain in the steering angular velocity correction term is in the rapid deceleration state during turning traveling. When the value is corrected by a predetermined amount in the direction in which the rear wheel steering angle is closer to the antiphase than the gain value, the rear wheels are steered toward the antiphase and the turning performance of the vehicle is further enhanced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a vehicle steering system according to an embodiment of the present invention. The steering apparatus A is mechanically connected to a front wheel steering mechanism 11 that steers the left and right front wheels 1 and 2, and is mechanically connected to the front wheel steering mechanism 11 via a transmission shaft 12, and is interlocked with front wheel steering by the front wheel steering mechanism 11. , The left and right rear wheels 3 and 4 are input from the front wheel steering mechanism 11 to the front wheel steering angle θF
And a rear wheel steering mechanism 13 that steers to a predetermined target rear wheel steering angle TGθR, and is provided in the rear wheel steering mechanism 13 and is expressed as a ratio of the rear wheel steering angle θR to the front wheel steering angle θF. A steering ratio variable mechanism 14 for setting and changing the steering ratio θs and a control unit 15 for controlling the steering ratio variable mechanism 14 are provided.

Reference numeral 21 denotes a vehicle speed sensor for detecting the vehicle speed V, and 22
Is a yaw rate sensor for detecting the yaw rate ψ ′ of the vehicle,
Reference numeral 23 is a steering ratio sensor for detecting a steering ratio θs set by the steering ratio variable mechanism 14, and 24 is a front wheel steering angle θF from the steering shaft rotation angle of the front wheel steering mechanism 11 or the like.
Is a front wheel steering angle sensor for detecting
The detection signals of 24 are input to the control unit 15.

The control unit 15 uses the detection signals of the vehicle speed V, the yaw rate ψ'and the front wheel steering angle θF, and the front wheel steering angle change rate obtained by differentiating the front wheel steering angle θF, that is, the front wheel steering angular velocity θ'F2. A target steering ratio T for the steering ratio variable mechanism 14 is calculated by adding and subtracting the obtained signal calculation values.
Gθs (rear wheel steering control target value) is determined, and when the target steering ratio TGθs exceeds a predetermined allowable range set according to the vehicle speed, the target steering ratio TGθs is set to a value within the allowable range. It is supposed to be fixed. Then, the target rear wheel steering angle TGθR is calculated by the following equation TGθR = θF · TGθs1 using the corrected target steering ratio TGθs1.

The target steering ratio TGθs is obtained by the following equation (1) TGθs = -G1f1 (V) θs.ST + G2K2 (θF2) J2 (│θ'F2│) f2 (V ) .Theta.YAW-G3.K3 (.theta.F2) .f3 (V) .theta.s.STD + G4.f4 (V) (1).

In the above equation (1), the first term on the right side is the steering angle correction term, the second term is the yaw rate correction term, the third term is the steering angular velocity correction term, and the fourth term is according to the vehicle speed. It is a basic term that is the basis for performing rear wheel steering control. By setting the target steering ratio TGθs in this manner, when the front wheels are steered from the straight traveling state based on the vehicle speed-sensitive rear wheel steering control, the rear wheels are opposite to the front wheels in the initial stage of the steering. While steering to the opposite phase side to improve turning performance,
After that, as the yaw rate is generated, the rear wheels can be steered to the same phase side where the direction is the same as that of the front wheels to perform directional stability control (phase inversion control).

In the above formula (1), G1, G2, G3 and G4
Is a constant, and other variables are calculated as follows based on the vehicle speed V, the yaw rate ψ ′ and the front wheel steering angle θF, as shown in FIG.

First, variables f1 (V) and f2 of each term on the right side
(V), f3 (V), and f4 (V) are vehicle speed-sensitive control gains, and from the vehicle speed V, maps m10, m5, m13,
It is calculated by m1. Of the above maps, maps m10 and m13 have characteristics such that the variables f1 (V) and f3 (V) are 0 in the low vehicle speed and high vehicle speed regions, respectively, and are positive constant values in the medium vehicle speed region. Also, map m5
Has a characteristic that the variable f2 (V) is 0 in the low vehicle speed region and is a positive constant value in the medium vehicle speed and high vehicle speed regions. Furthermore, the remaining map m1 is a variable f4 (V)
In the low vehicle speed range, a large negative value (that is, the opposite phase of the steering direction of the front wheels), and in the medium vehicle speed range from negative to positive (that is, in-phase in the same direction as the front wheel steering direction) as the vehicle speed increases. The value changes to a large positive value in the high vehicle speed range.

Next, the variable θs.ST of the first term on the right side is a steering angle correction value, and after the front wheel steering angle θF is offset by map m8 to θF1, this θ is calculated by map m11.
A hysteresis is added to F1 to obtain θF2, and the absolute value thereof is calculated from | θF2 | by a map m9. The addition of the offset in the map m8 is to prevent unnecessary control by providing the dead zone in the small steering angle region, and the addition of the hysteresis in the map m11 is the hunting for the control. This is to prevent the occurrence of. The map m9 is the variable θ
s.ST is 0 in the small rudder angle region, a value proportional to the rudder angle in the medium rudder angle region, a positive constant value in the large rudder angle region, and 0 when an abnormality occurs in the larger rudder angle region. It is a characteristic to be.

Next, the variable .theta.s.YAW of the second term on the right side is a yaw rate correction value, and after the yaw rate .psi. 'Is offset by the map m2 into .psi.'1, the map m3 is obtained.
Thus, the map m4 is used to calculate from ψ'2 in which hysteresis is added to ψ'1. The reason for adding the offset and hysteresis is the same as in the case of the variable θs.ST. The map m4 has characteristics that the variable θs.YAW is set to a value proportional to ψ'2 in the small yaw rate region, a positive constant value in the medium yaw rate region, and 0 in the large yaw rate region when an abnormality occurs.

The variable K2 (θF2) of the second term on the right side is
It is a control gain for steering angle sensitivity, and is calculated from θF2 obtained in map m11 by map m6.
The map m6 has a characteristic in which the variable K (θF2) is set to a value substantially proportional to θF2 in the small front wheel steering angle region and a value in which the increase rate decreases as the front wheel steering angle increases.

Further, the variable J2 (| θ 'of the second term on the right side)
F2 |) is the control gain of the steering angular velocity sensitivity, which is obtained by differentiating θF2 obtained in the map m11 and taking the absolute value | θ′F2
The map m7 is calculated from |. In the map m7, the variable J2 (| θ'F2 |) is changed to | θ'F2
In the region where | is small, that is, in the small front wheel steering angular velocity region, a small value is set, in the middle front wheel steering angular velocity region, a large value is set, and in the large front wheel steering angular velocity region, values are set to be smaller than those in the small front wheel steering angular velocity region.

Next, the variable θs.STD of the third term on the right side is a steering angular velocity correction value, and is calculated by a map m12 from a value θ'F2 obtained by differentiating θF2 obtained by the map m11. . In the map m12, the variable θs.STD is set to a value proportional to θ′F2 in the small front wheel steering angular velocity range, a positive constant value in the middle front wheel steering angular velocity range, and 0 when an abnormality occurs in the large front wheel steering angular velocity range. It is a characteristic.

The variable K3 (θF2) of the third term on the right side is
It is a control gain of steering angle sensitivity, and is calculated from the map m14 from θF2 obtained from the map m11.
The map m14 has a characteristic in which the variable K3 (θF2) is set to a value substantially proportional to θF2 in the small front wheel steering angle region and a value in which the increase rate decreases as the front wheel steering angle increases.

The target steering ratio TGθs is determined by adding / subtracting the signal operation value obtained by multiplying the constant and the variable for each term on the right side of the above equation. If this addition / subtraction value takes an abnormal value, Since the target steering ratio TGθs also becomes an abnormal value, when the target steering ratio TGθs exceeds the permissible range (hatched portion in the map m15) set according to the vehicle speed V according to the map m15, this target steering ratio TGθs T
Gθs is corrected to an upper limit value or a lower limit value (curve shown by a broken line in the map m15) within the above allowable range. The curve shown by the solid line in the map m15 is the variable f4 (V) shown in the map m1.

With the configuration shown in FIG. 2 as described above, the target value determining means for determining the target steering ratio TGθs, which is the target value for rear wheel steering control, according to the invention of claim 1 is based on the above equation (1). 31 is configured, and the target value determining means 3
1 is provided in the control unit 15.

As a feature of the present invention, the control unit 15 is adapted to add a correction to the determination of the target steering ratio TGθs based on the above equation (1) when the vehicle is in a sudden deceleration state while turning. This correction process is
This is performed according to the flowchart shown in FIG.

In FIG. 3, first of all, step S1
After reading the vehicle speed V from the vehicle speed sensor 21 and the front wheel steering angle θF from the front wheel steering angle sensor 24, the vehicle deceleration -V 'is calculated in step S2. This deceleration-V 'is calculated by dividing the difference between the previous value of the vehicle speed V and the current value by the cycle time.

Then, in step S3, the vehicle speed V is a predetermined value V
It is determined whether or not 0 or more, and it is determined in step S4 whether or not the deceleration -V 'is a predetermined value -V'0 or more (-V'≤-V'0), and further step S5. Front wheel steering angle θF
Is greater than a predetermined value θF0. When all of these determinations are YES, the flag F is set to "1" in step S6, and then in step S7, the fourth term (basic term) and the second term (yaw rate correction) on the right side in the above equation (1). Item) vehicle speed sensitive control gain f4 (V), f2
(V) is the current control gain f4 (Vn), f2
It is fixed to (Vn), and the values obtained by multiplying the fixed control gains f4 (V) and f2 (V) by 1.2 in steps S8 and S9 respectively are replaced with new control gains f4 (V) and f2 (V). , Return.

On the other hand, when the determination in step S3 is NO, the process directly returns. In addition, the above step S4
Alternatively, if the determination in S5 is NO, it is determined in step S10 whether the flag is "1". This judgment is YES
If it is, it is determined in step S11 whether or not the time is up, and in step S12, it is determined whether or not the vehicle speed V is 0. If both of the determinations are NO, the process directly returns.

When the determination at step S10 is NO, or when the determinations at steps S11 and S12 are YES,
After resetting the flag F to "0" in step S13, the fixing of the control gains f4 (V) and f2 (V) is released,
To return.

In the above flow chart, step S
The determination means 32 for determining the rapid deceleration state during turning of the vehicle is constituted by 1 to S5, and step S6 is performed.
When the determination means 32 determines in S14 that the vehicle is in a decelerating state during turning, the target value determination means 31
On the other hand, the control gain f4 (V) of the basic term and the vehicle speed sensitive control gain f2 (V) of the yaw rate correction term are fixed to predetermined values, respectively, and the target steering ratio TGθs is determined by the equation (1). A correction unit 33 that issues a correction command is configured. Since the basic term is the product of the control gain f4 (V) and a constant, fixing the control gain f4 (V) fixes the basic term.

Next, to explain the operation and effect of the above embodiment, in the normal turning traveling state, the control unit 15 uses the target steering angle TGθs based on the equation (1).
The target steering angle TGθs is corrected to a value within the allowable range, and the steering ratio variable mechanism 14 is controlled so that the actual steering ratio θs by the steering ratio variable mechanism 14 becomes the corrected target steering ratio TGθs1. . As a result, under the control of the control unit 15, in the rear wheel steering mechanism 13, the target rear wheel steering angle TGθR, which is the product of the corrected target steering ratio TGθs1 and the front wheel steering angle θF, is changed to the actual rear wheel steering angle. θR
Feedback control is performed so that At this time, the above equation (1) is based on the basic term that changes according to the vehicle speed, and the front wheel steering angle as the traveling state amount of the vehicle other than the vehicle speed,
Since the target steering angle TGθs is determined by adding and subtracting a plurality of correction terms set based on the front wheel steering angular velocity and the yaw rate, it is possible to achieve both turning performance and stability during turning. it can.

On the other hand, when the vehicle is suddenly decelerated during turning,
In the above equation (1), the basic term (specifically, its control gain f4 (V)) and the control gain f2 of the yaw rate correction term
And (V) are fixed to predetermined values, respectively, and the target steering angle TGθs is determined based on the equation (1). Therefore, the target steering ratio TGθs or the target rear wheel steering angle TGθR does not suddenly change from the in-phase side to the anti-phase side as the vehicle speed decreases, and it is possible to prevent the oversteer state.

In addition, when the steering wheel is further steered in the turning direction or a spin state occurs during sudden deceleration during turning, the target steering angle TGθs is the yaw rate ψ ′ or the yaw rate correction value θs.YAW. Since it changes in the direction toward the same phase with the increase, the unstable behavior of the vehicle body can be suppressed. In particular, in the case of the embodiment, when the control gain f4 (V) of the basic term and the control gain f2 (V) of the yaw rate correction term are fixed to predetermined values, it is determined that the vehicle is in a sudden deceleration state during turning. Corresponding control gain value f4 (Vn) at
Since the rear wheel steering angle is fixed to a value 1.2 times in the direction closer to the same phase than f2 (Vn), the rear wheels are steered closer to the same phase, and the vehicle The effect of suppressing stable behavior can be further enhanced.

FIG. 4 is a flow chart showing a modification of the correction process for determining the target steering ratio.

In the case of this modification, as in the case of the embodiment, first, in step S21, the vehicle speed V and the front wheel steering angle θF are set.
After reading and, in step S22, the vehicle deceleration-V '
Is calculated. Then, in step S23, the vehicle speed V is the predetermined value V
It is determined whether or not 0 or more, and it is determined in step S24 whether or not the deceleration −V ′ is equal to or greater than the predetermined value −V0. Further, in step S25, the front wheel steering angle θF is greater than the predetermined value θF0. Determine whether or not. And all of these judgments are YES
In the case of, the flag F is set to "1" in step S26, and then in step S27, the first term on the right side of the equation (1) to
Each vehicle speed sensitive control gain f1 (V) to f4 (V)
Are respectively the current control gains f1 (Vn) to f4 (Vn
), The value obtained by multiplying the fixed control gain f3 (V) of the third term (steering angular velocity correction term) by 1.2 in step S27 is replaced with a new control gain f3 (V), and the process returns.

On the other hand, if the determination in step S23 is NO, the process directly returns. In addition, the above step S24
Alternatively, if the determination in S25 is no, it is determined in step S30 whether the flag is "1". This judgment is YES
In case of, it is judged in step S31 whether or not the time is up, and in step S32, it is judged whether or not the vehicle speed V is 0. If both of the judgments are NO, the routine directly returns.

When the determination in step S30 is NO, or when the determinations in steps S31 and S32 are YES,
After resetting the flag F to "0" in step S33, the control gains f1 (V) to f4 (V) are released from being fixed in step S34, and the process returns.

In the above flow chart, step S
21 to S25 constitute the judgment means 32 'for judging that the vehicle is in the rapid deceleration state while the vehicle is turning.
At 26 to S28 and S30 to S34, when it is judged by the judging means 32 'that the vehicle is in a decelerating state during turning, the control gain f4 (V) of the basic term is supplied to the target value determining means 31 (see FIG. 2). And vehicle speed sensitive control gains f1 (V) to f3 of the steering angle correction term, the yaw rate correction term, and the steering angle speed correction term.
The correction means 33 'is configured to issue a correction command so that (V) and (V) are fixed to predetermined values and the target steering ratio TGθs is determined.

In this modified example, as in the case of the above embodiment, when the vehicle is rapidly decelerated during turning, the control gain f4 (V) of the basic term and the vehicle speed response control gain f2 of the yaw rate correction term are obtained. (V) and (V) are each fixed to a predetermined value, so that the target steering ratio TGθ is reduced as the vehicle speed decreases
It is possible to prevent the s or the target rear wheel steering angle TGθR from abruptly changing from the in-phase side to the anti-phase side to fall into the oversteer state, and to suppress the unstable behavior of the vehicle body.

In addition, the control gain f4 of the above basic term
(V) and the yaw rate correction term vehicle speed sensitive control gain f2
In addition to (V), the vehicle speed-sensitive control gains f1 (V) and f3 (V) of the steering angle correction term and the steering angle speed correction term are also fixed to predetermined values, so that the steering handle during sudden deceleration during turning traveling. When the vehicle is steered in the opposite direction to the turning direction, the target steering ratio TGθs changes in the direction in which the rear wheels are in the opposite phase depending on the steering wheel operation, that is, the front wheel steering angle and the front wheel steering angular velocity. It is possible to change the direction or improve the turning ability. In particular, as in the modified example, the predetermined value for the control gain f3 (V) of the steering angular velocity correction term is calculated from the value of the control gain in the steering angular velocity correction term at the time when it is determined that the vehicle is in a sudden deceleration state during turning. Also, since the rear wheel steering angle is fixed to a value that is 1.2 times in the direction toward the opposite phase, the rear wheels are steered toward the opposite phase, and the turning performance of the vehicle is further enhanced. You can

[0048]

As described above, according to the vehicle steering system of the present invention, when the vehicle is suddenly decelerated during turning, only the function value of the vehicle speed in the formula of the rear wheel steering control target value is calculated. That is, the basic term that changes according to the vehicle speed and the control gain in the correction term that is set based on the running state amount of the vehicle other than the vehicle speed are fixed to predetermined values, respectively. It is possible to prevent the rear wheel steering angle from suddenly changing to the opposite phase side and falling into the oversteer state, and the target value for rear wheel steering control changes with changes in the running state amount other than the vehicle speed. As a result, it is possible to perform a fine-grained rear-wheel steering control that balances the stability and turning of the vehicle.

In particular, the invention according to claim 3 has a correction term set in the formula for calculating the target value for rear wheel steering control based on the yaw rate, and the control gain in this correction term is used to control suddenly during turning. When the steering wheel is steered further during sudden deceleration during turning, or if a spin state occurs, the target value for rear wheel steering control is set to As the number of rear wheels increases, the rear wheels change in the direction toward the same phase, and the unstable behavior of the vehicle body can be suppressed.

In the invention according to claim 4, the rear wheel steering control target value calculation formula has correction terms set based on the front wheel steering angle and the front wheel steering angular velocity, respectively, and the control gain in these correction terms is included. When the steering wheel is steered in the opposite direction to the turning direction during sudden deceleration during turning, the target value for rear wheel steering control is the steering wheel operation, that is, the front wheel steering. The rear wheels are changed in the direction in which the rear wheels are in the opposite phase depending on the angle and the magnitude of the front wheel steering angular velocity, and the turning performance of the vehicle can be enhanced.

According to the sixth aspect of the present invention, the predetermined value for the control gain in the steered angular velocity correction term in the fourth aspect of the present invention is the steering angular velocity at the time when it is determined that the vehicle is in a sudden deceleration state during turning. The control gain in the correction term is corrected by a predetermined amount in the direction in which the rear wheel steering angle is in the opposite phase, so the rear wheels can be steered more in the opposite phase, and the vehicle is turning. The sex can be enhanced.

Further, in the invention according to claim 7, the predetermined value in the invention according to claim 3 is set to the value of the corresponding basic term or control gain at the time when it is determined that the vehicle is in a sudden deceleration state during turning. Rather, the rear wheel steering angle is corrected by a predetermined amount in the direction in which the rear wheels are closer to the same phase, so the rear wheels can be steered closer to the same phase, and the effect of suppressing unstable behavior of the vehicle body can be further suppressed. Can be increased.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a vehicle steering system according to an embodiment of the present invention.

FIG. 2 is a block diagram of a target steering ratio determination control unit.

FIG. 3 is a flowchart of a correction process for determining the target steering ratio.

FIG. 4 is a view corresponding to FIG. 3 showing a modified example.

[Explanation of symbols]

A steering device 31 Target value determination means 32, 32 'Judgment means 33,33 'correction means

Continuation of front page (51) Int.Cl. ⁷ identification code FI B62D 137: 00 B62D 137: 00 (56) References JP-A-4-108079 (JP, A) JP-A-4-118381 (JP, A) JP-A-2-175471 (JP, A) JP-A-63-151580 (JP, A) JP-A-2-274667 (JP, A) JP-A-5-69849 (JP, A) JP-A-5-185949 (JP, A) JP-A-6-171532 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B62D 6/00-6/06 B62D 7/14

Claims (7)

(57) [Claims] 1. A target value for determining a rear wheel steering control target value by adding or subtracting a correction term set based on a running state amount of a vehicle other than the vehicle speed to a basic term that changes according to the vehicle speed. A determining means is provided, and the basic term is to steer the rear wheels in a reverse phase opposite to the steering direction of the front wheels in the low vehicle speed range and to steer the rear wheels in the same phase in the same direction as the front wheel steering direction in the high vehicle speed range. In the steering device of the vehicle, which is defined as the product of the function value of the running state quantity and the control gain that changes according to the vehicle speed, the correction term is set to the rapid deceleration state during turning of the vehicle. Only the control gains in the basic term and the correction term for the target value determining means when it is determined by the determining means that the vehicle is in a sudden deceleration state during turning. Fixed to a predetermined value so that the target value for rear wheel steering control can be determined The vehicle steering system is characterized in that a correcting means for emitting positive command. 2. The target value determining means has a yaw rate, a front wheel steering angle, and a front wheel steering angular velocity as a vehicle running state quantity, and these correction terms are added to or subtracted from the basic terms to set target values for rear wheel steering control. The control gain in the yaw rate correction term is set to zero in the low vehicle speed range, and is set to a positive constant value in the medium and high vehicle speed ranges. The control gain in the angular velocity correction term is
2. The vehicle steering system according to claim 1, wherein both are set to zero in the low vehicle speed region and the high vehicle speed region and set to a positive constant value in the medium vehicle speed region. 3. The correction means, when it is determined that the vehicle is in rapid deceleration during turning,
3. The vehicle steering system according to claim 2, wherein the basic term and the control gain in the yaw rate correction term are each fixed to a predetermined value and a correction command is issued so as to determine a rear wheel steering control target value. 4. The correction means, when it is determined that the vehicle is in a sudden deceleration state during turning,
The control gain in the basic term, the yaw rate correction term, the control gain in the steering angle correction term, and the control gain in the steering angle speed correction term are fixed to predetermined values, respectively, and a target value for rear wheel steering control is determined. The steering apparatus for a vehicle according to claim 2, wherein a correction command is issued so that the steering device is operated. 5. The vehicle steering system according to claim 3, wherein the predetermined value is the same as the value of the corresponding basic term or control gain at the time when it is determined that the vehicle is in a sudden deceleration state during turning. 6. The predetermined value for the control gain in the steering angular velocity correction term is greater than the value of the control gain in the steering angular velocity correction term at the time when it is determined that the vehicle is in a sudden deceleration state during turning traveling.
The vehicle steering system according to claim 4, wherein the steering angle of the rear wheel is a value corrected by a predetermined amount in a direction in which the rear wheel steering angle is closer to the opposite phase. 7. The predetermined value is in a direction in which the rear wheel steering angle is closer to the same phase than the corresponding basic term or control gain value at the time when it is determined that the vehicle is in a sudden deceleration state during turning. The vehicle steering system according to claim 3, wherein the value is a value that is quantitatively corrected.