JPH06298112A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve maneuverability by judging the angle of lateral slip from the yaw rate and lateral acceleration estimated from car speed and the front wheel steering angle, actual yaw rate and actual lateral acceleration, and when the angle of the lateral slip is judged large, decreasing the objective rear wheel steering angle variation quantity to actual yaw rate variation quantity. CONSTITUTION:A rear wheel steering angle calculating means calculates an objective rear wheel steering angle from the car speed detected by a car speed detecting means, front wheel steering angle detected by a front wheel steering angle detecting means, and the actual yaw rate detected by a turning state detecting means according to setting control rule, and the result is outputted to a control means to steer the rear wheels. While the angle of lateral slip is not large, a turning state estimating means estimates a yaw rate and lateral acceleration from the detected car speed and steering angle before detection. A slip judging means judges whether the angle of lateral slip is large or not from the estimation result and the actual yaw rate outputted by the turning state detecting means and actual acceleration. If it is large, the variable quantity of the objective rear wheel steering angle to the variable quantity of the actual yaw rate is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle rear wheel steering control apparatus for controlling a rear wheel steering angle based on a front wheel steering angle, a vehicle speed and an actual yaw rate in a vehicle equipped with a mechanism for steering rear wheels. Regarding

[0002]

2. Description of the Related Art Conventionally, as a rear wheel steering control device for improving motion performance, steering performance and stability while a vehicle is running, for example, as disclosed in Japanese Patent Laid-Open No. 3-176279. , The target yaw rate is calculated from the detected actual front wheel steering angle and the vehicle speed, and the target rear wheel steering angle is calculated so that the target yaw rate and the actual yaw rate as the actual behavior of the vehicle always match. Steer,
There is known a so-called yaw rate feedback control.

When the target yaw rate is calculated in such a conventional apparatus, a predetermined vehicle model preset by the vehicle specification data such as vehicle weight and wheel base is used. Is generally set on the assumption that the cornering force of the wheel (tire) and the side slip angle of the vehicle body are in a proportional relationship. That is, the tires are sufficiently grounded on the road surface, and the condition is set on the assumption that the vehicle can turn only by the amount the vehicle driver operates the steering wheel.

[0004]

However, it is generally known that when the side slip angle of the vehicle body increases, the tire largely slips (slip) and the proportional relationship between the cornering force and the side slip angle cannot be established. There is.

Therefore, when the tire slips in the above conventional device, the actual vehicle state and the vehicle model for calculating the yaw rate do not match, and, for example, the so-called spin state in which the front wheels and the rear wheels slip in opposite directions. Then
The actual yaw rate becomes extremely larger than the target yaw rate, and in a so-called drift condition in which the front wheel and the rear wheel slip in the same direction, the actual yaw rate becomes extremely smaller than the target yaw rate. There was a problem that the rear wheel was steered more than necessary because the difference between the rear wheel and the rear wheel became extremely large.

As a result, the behavior of the vehicle becomes severe when the wheels slip, and there is a problem in that the behavior of the vehicle cannot be stabilized unless the vehicle driver repeatedly corrects and steers the steering wheel. . The present invention has been made in view of these problems, and an object of the present invention is to provide a rear wheel steering control device for a vehicle that can improve the maneuverability of the vehicle when the sideslip angle of the vehicle body is increased.

[0007]

SUMMARY OF THE INVENTION That is, the present invention as set forth in claim 1 made in order to solve the above-mentioned problems, the rear wheel steering mechanism for steering the rear wheels of the vehicle as shown in FIG. An actuator for displacing the rear wheel steering mechanism, a vehicle speed detecting means for detecting a vehicle speed, a front wheel steering angle detecting means for detecting a steering angle of a front wheel of a vehicle steered by a vehicle driver, and a vehicle generated by turning the vehicle. As the behavior of, at least a turning state detecting means for detecting an actual yaw rate, and at least the vehicle speed, the front wheel steering angle, and the actual yaw rate,
According to a predetermined control rule set in advance, rear wheel steering angle calculation means for calculating a target rear wheel steering angle according to the traveling state of the vehicle,
In a rear-wheel steering control device for a vehicle, comprising: a control unit that drives and controls the actuator so that the steering angle of the rear wheels becomes the target rear-wheel steering angle, at least the vehicle speed and the front-wheel steering angle A turning state estimating means for estimating a yaw rate or / and a lateral acceleration that may occur in the vehicle when the vehicle side slip angle is not large; an estimation result of the turning state estimating means; and an actual yaw rate and / or an actual yaw rate occurring in the vehicle. Slip determination means for determining whether or not the lateral slip angle of the vehicle body is large based on the lateral acceleration, and when the slip determination means determines that the lateral slip angle of the vehicle body is large, the target after-target yaw rate change amount is changed. A rear wheel steering control device for a vehicle, comprising: a control law changing means for changing the control law so that a change amount of a wheel steering angle is reduced.

According to a second aspect of the present invention, in the vehicle rear wheel steering control device according to the first aspect, the control law changing means determines by the slip determining means that the vehicle side slip angle is large. A rear-wheel steering control device for a vehicle is characterized in that the control law is changed so that the target rear-wheel steering angle is calculated from the vehicle speed and the front-wheel steering angle when the vehicle is operated. .

Still further, the present invention according to claim 3 is the rear wheel steering control device according to claim 1, wherein the turning state estimating means is generated in the vehicle when the side slip angle of the vehicle body is not large. The maximum value and the minimum value of the possible yaw rate are estimated, the slip determination means compares the estimated maximum value and the minimum value with the actual yaw rate detected by the turning state detection means, and the actual yaw rate is When it is outside the range from the maximum value to the minimum value, it is determined that the side slip angle of the vehicle body is large, the control law changing means,
When the slip determination means determines that the vehicle side slip angle is large, when the actual yaw rate is greater than the maximum value, the target rear wheel steering angle is calculated from the maximum value, the vehicle speed, and the front wheel steering angle. As calculated, when the control law is changed and the actual yaw rate is smaller than the minimum value, the target rear wheel steering angle is calculated from the minimum value, the vehicle speed, and the front wheel steering angle. A rear wheel steering control device for a vehicle is characterized in that the control law is changed.

[0010]

According to the present invention having the above-mentioned structure, the rear wheel steering angle calculating means detects at least the vehicle speed detected by the vehicle speed detecting means and the front wheel steering angle detecting means. From the front wheel steering angle and the actual yaw rate detected by the turning state detection means, a target rear wheel steering angle according to the running state of the vehicle is calculated according to a preset predetermined control rule, and the control means sets the rear wheel. The rear wheel is steered by driving and controlling an actuator for displacing the rear wheel steering mechanism so that the steering angle becomes the target rear wheel steering angle.

Then, the turning state estimating means generates the vehicle at least when the side slip angle of the vehicle body is not large based on at least the vehicle speed detected by the vehicle speed detecting means and the front wheel steering angle detected by the front wheel steering angle detecting means. Possible yaw rate and / or lateral acceleration, and the slip determination means determines a large lateral slip angle of the vehicle body from the estimation result of the turning state estimation means and the actual yaw rate and / or actual lateral acceleration actually generated in the vehicle. Whether the control law changing means determines that the side slip angle of the vehicle body is large by the slip determining means so that the change amount of the target rear wheel steering angle with respect to the change amount of the actual yaw rate becomes small. The rear wheel rudder angle calculation means changes the control law for calculating the target rear wheel rudder angle.

In the present invention, the state where the side slip angle of the vehicle body is large means that the vehicle body is in a so-called spin state or a drift state. Further, when it is determined by the slip determination means whether or not the lateral slip angle of the vehicle body is large by using the actual lateral acceleration generated in the vehicle, the turning state detection means may detect the actual lateral acceleration. .

Next, in the present invention according to claim 2, the control law changing means in the rear wheel steering control device according to claim 1 determines by the slip determining means that the vehicle side slip angle is large. When the target rear wheel steering angle is
As calculated from the vehicle speed detected by the vehicle speed detection means and the front wheel steering angle detected by the front wheel steering angle detection means,
Change the control law.

Therefore, according to the second aspect of the present invention, when the side slip angle of the vehicle body is large, the rear wheel steering angle is determined only by the vehicle speed and the front wheel steering angle which can be directly operated by the vehicle driver. The driver's will will be faithfully reflected in the steering of the rear wheels. Further, according to the invention described in claim 3, in the vehicle rear wheel steering control device according to claim 1, the turning state estimating means determines the maximum yaw rate that can occur in the vehicle when the side slip angle of the vehicle body is not large. The maximum and minimum values of the estimated yaw rate are estimated by comparing the maximum and minimum values of the estimated yaw rate with the actual yaw rate detected by the turning state detection means. When the value is outside the range from the minimum value to the minimum value, it is determined that the side slip angle of the vehicle body is large, and when the control law changing means determines that the side slip angle of the vehicle body is large by the slip determining means, the actual yaw rate is estimated. If it is larger than the maximum value, the control law is changed so that the target rear wheel steering angle is calculated from the maximum value, the vehicle speed, and the front wheel steering angle, and the actual yaw rate is smaller than the estimated minimum value. The Itoki changes the control law so that the target rear-wheel steering angle is calculated from the minimum value and the vehicle speed and front wheel steering angle.

Therefore, according to the third aspect of the present invention, the actual rear wheel steering angle for calculating the target rear wheel steering angle is calculated based on the maximum value and the minimum value of the yaw rate that can occur in the vehicle when the side slip angle of the vehicle body is not large. Since the yaw rate parameter will be limited, for example, even if the vehicle spins and the actual yaw rate becomes extremely large, or conversely the vehicle drifts and the actual yaw rate becomes extremely small, The wheel steering angle does not change extremely.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the present invention described in claim 2 is embodied in a vehicle rear wheel steering control device will be described below with reference to the drawings. 2 is a schematic configuration diagram for explaining the overall configuration of the device, and FIG. 3 is a schematic configuration diagram of the control device therein.

As shown in FIG. 2, the vehicle of this embodiment receives the electric command signals output from the rear wheel steering mechanism 1 and the control device 3 described later, and rotates in the forward and reverse directions to rotate the rear wheel steering mechanism. 1
And a DC servo motor 2 as an actuator for activating. The rear wheel steering mechanism 1 includes a torsion bar (not shown) whose one end is rotated by a DC servomotor 2 via a reduction gear 4, a pinion gear 5 attached to the other end of the torsion bar, a power piston 6, and a power piston 6. It comprises a rack 7 formed at one end of the piston 6 and meshing with the pinion gear 5, and a hydraulic valve 8 whose throttle area changes according to the torsion of the torsion bar.
The hydraulic valve 8 is in communication with the cylinder chamber of the power piston 6 and operates the power piston 6 according to the throttle area.

In the rear wheel steering mechanism 1 constructed as described above, when one end of the torsion bar is rotated by the DC servo motor 2, the torsion bar is twisted and, as a result, the throttle area of the hydraulic valve 8 changes. The hydraulic pressure is supplied in the direction that corrects the torsion of the torsion bar and the power piston 6
Will move.

Both ends of the power piston 6 thus moved are connected to a knuckle arm 10 via tie rods 9, respectively.
The rear wheel 11 is supported by 0 so as to be swingable in the left-right direction. Therefore, in the direction of arrow A in the figure, the power piston 6
The rear wheel 11 is steered to the left or right by moving the. And
At this time, the steering angle of the rear wheel 11 is such that the torsion bar is not twisted and the throttle area of the hydraulic valve 8 becomes “0”.
It is controlled as a position where the supply and discharge of hydraulic oil to the power piston 6 is stopped. In FIG. 2, 12 is a hydraulic pump that supplies hydraulic pressure to the power piston 6 via the hydraulic valve 8, and 13 is an oil tank.

Further, the vehicle rear wheel steering control system of this embodiment includes a rear wheel steering angle sensor 14, a vehicle speed sensor 15 as a vehicle speed detecting means, and a front wheel steering angle sensor 16 as a front wheel steering angle detecting means. A yaw rate sensor 17 and a lateral acceleration sensor 18 as turning state detecting means are provided.

The rear wheel steering angle sensor 14 includes a power piston 6
Is provided in the vicinity of, and outputs a signal according to the position of the power piston 6, and further, the rear wheel steering angle θr. The vehicle speed sensor 15 detects the rotation speed of the axle or the wheel and outputs a signal corresponding to the vehicle speed V. The front wheel steering angle sensor 16 is provided on the steering shaft 19, detects rotation of the steering shaft 19 due to operation of the steering wheel 20, and outputs a signal corresponding to the steering wheel angle θs. The yaw rate sensor 17 is composed of a gyro or the like and outputs a signal corresponding to the rotational angular velocity (yaw rate) γ of the vehicle centering on the center of gravity of the vehicle, and the lateral acceleration sensor 18
Is the lateral acceleration of the center of gravity of the vehicle (hereinafter simply referred to as lateral acceleration)
The signal corresponding to α is output.

Next, the control device 3 will be described with reference to FIG. 3. The control device 3 includes a microcomputer (hereinafter referred to as a microcomputer) 24, a waveform shaping circuit 25, an analog buffer 29, and an A / D converter 30. And a drive circuit 32. The waveform shaping circuit 25 waveform-shapes the signal from the vehicle speed sensor 15 to perform microcomputer 24
To take in. Further, the analog buffer 29 takes in signals from the rear wheel steering angle sensor 14, the front wheel steering angle sensor 16, the yaw rate sensor 17, and the lateral acceleration sensor 18, and outputs them to the A / D converter 30. Then, the A / D converter 30 converts the analog signal from the analog buffer 29 into a digital signal, and the microcomputer 2
Incorporate in 4. The drive circuit 32 is the microcomputer 2
A current corresponding to a current command value signal If, which will be described later, output from the motor 4 is supplied to the DC servo motor 2.

The control device 3 thus constructed, based on the signals from the above-mentioned respective sensors, is the actual rear wheel steering angle θr, the vehicle speed V, and the steering wheel angle θs (front wheel steering angle θf) in the vehicle. And yaw rate γ and lateral acceleration α are detected respectively, and a rear wheel steering angle command value θ0r as a target rear wheel steering angle corresponding to the running state of the vehicle is calculated from these values,
By driving and controlling the rear wheel steering mechanism 1 including the DC servo motor 2, the rear wheel steering angle θr is changed to the rear wheel steering angle command value θ0r.
The rear wheel steering control is performed to steer the rear wheels 11 so as to match with. That is, in the present embodiment, the control device 3 and the rear wheel steering mechanism 1 including the DC servomotor 2 constitute a so-called positioning servo system.

Next, the details of the rear wheel steering control executed by the control device 3 (in particular, the microcomputer 24) configured as above will be described. The contents and units of each symbol used in the following description are shown in [Table 1] and [Table 2] below.

[0025]

[Table 1]

[0026]

[Table 2]

First, FIG. 4 is a flowchart showing the rear wheel steering control, which is executed by interruption processing at every predetermined time (for example, every 5 msec). As shown in FIG. 4, when the rear wheel steering control of the present embodiment is started, first, in step (hereinafter referred to as S) 110, the steering wheel angle θs, the vehicle speed V, and the rear wheel steering angle θr are detected. To do. Also, this S
At 110, the front wheel steering angle θf is calculated by dividing the steering wheel angle θs by the overall steering ratio N. In subsequent S120, the yaw rate γ and the lateral acceleration α are detected. In the following description, the yaw rate γ and the lateral acceleration α detected in this way are respectively referred to as the actual yaw rate γ and the actual lateral acceleration α.
Say.

Then, in subsequent S130, from the vehicle speed V detected or calculated in S110, the front wheel steering angle θf and the rear wheel steering angle θr, when the side slip angle of the vehicle body is not large, that is, the vehicle body is in a spin state or a drift state. If it is not, a process as a turning state estimating means for calculating the yaw rate γk and the lateral acceleration αk that may occur in the vehicle is executed. Hereinafter, the yaw rate γk and the lateral acceleration αk calculated in this way are referred to as a standard yaw rate γk and a standard lateral acceleration αk, respectively.

Here, a method of calculating the standard yaw rate γk and the standard lateral acceleration αk will be described. First, front wheel 3
4 and yaw rates generated when steering only the rear wheels 11 are γkf and γkr, respectively, and similarly, lateral accelerations generated when steering only the front wheels 34 and only the rear wheels 11 are αkf and αkr, respectively. The standard yaw rate γ k and the standard lateral acceleration α k are respectively expressed by the function γ of the Laplace operator s.
When expressed by k (s) and αk (s), the following expressions (1) and (2) are obtained.

[0030]

[Equation 1]

G2f (s) is input to the front wheel steering angle θf.
, The transfer function for the yaw rate γkf, G2
r (s) is the transfer function for the yaw rate γkr when the input is the rear wheel steering angle θr, G3f (s) is the transfer function for the lateral acceleration αkf when the input is the front wheel steering angle θf, G3r (s) Is the transfer function for the lateral acceleration αkr when the input is the rear wheel steering angle θr, and these are
It is determined by the various data of the vehicle and the vehicle speed V shown in the above table.

Here, the expressions (1) and (2) are shown by the transfer characteristics of the system, but in the present embodiment, they are calculated by strict discretization by the 0th-order holder. . Therefore,
For these transfer function calculation methods, input u (s),
Description will be given using a general formula when the output is y (s).

Now, the transfer function G as shown in the following equation (3)
When there is (s),

[0034]

[Equation 2]

Dividing the numerator and denominator of G (s) by α 2 respectively gives the following equation (4).

[0036]

[Equation 3]

When the transfer function G (s) of the equation (4) is converted into the state equation (controllable standard form), the following equation (5) is obtained.

[0038]

[Equation 4]

When the state equation of equation (5) is discretized using a 0th-order holder at a sampling period h (interruption period of this processing), the following equation (6) is obtained.

[0040]

[Equation 5]

When the equation (1) is applied to the equations (4) to (6), the transfer functions G2f (s) and G2r (s) are obtained.
Are respectively expressed by the following equations (7) and (8), and the standard yaw rate γk is obtained by the equation (9). Similarly, when the equation (2) is applied to the equations (4) to (6), the transfer functions G3f (s) and G3r (s) are obtained by the following equations (10) and (11), respectively. Thus, the reference lateral acceleration αk can be calculated as shown in equation (12).

[0042]

[Equation 6]

Thus, the standard yaw rate γk and the standard lateral acceleration α are calculated from the vehicle speed V, the front wheel steering angle θf, and the rear wheel steering angle θr.
After calculating k and the subsequent S140, the target yaw rate γ0 is calculated from the vehicle speed V detected in S110 and the front wheel steering angle θf based on the following equation (13).

[0044]

[Equation 7]

Here, S (V) and K6 (V) are constants (gains) determined by the vehicle speed V and the data of the vehicle such as the stability factor K representing the understeer or oversteer characteristic of the vehicle. ), Which is determined by searching the data map prepared in advance according to the vehicle speed V at that time. Further, s is a Laplace operator and T is a time constant. Also, (H (s) = ATs + 1 / Ts +
In 1), when the steering wheel angle θs changes stepwise, the target yaw rate γ0 is the front wheel steering angle θf (steering wheel angle θ
s), instead of being proportional to, it changes in a first-order manner during a transition, and then a steady value {S (V) · (1-K6
(V) · θf / L)},
It is a transfer function for providing a transient characteristic. By adding such a transient characteristic, the steering wheel 2
The responsiveness of the rear wheel steering when 0 is operated stepwise,
It achieves both stability at regular times.

Like the equations (1) and (2), the equation (13) is also shown by the transfer characteristics of the system in which the input is the front wheel steering angle θf and the transfer function is G1 (s). But in reality,
The target yaw rate γ 0 is also converted into the state equation expression by converting the transfer function H (s) in the same manner as the equations (1) and (2).
It is calculated by performing discretization using a 0th-order holder.

Then, in step S140, the target yaw rate γ0 is calculated, and then in step S150, the actual yaw rate γ0 is calculated.
Based on the actual lateral acceleration α, the reference yaw rate γk and the reference lateral acceleration αk, it is determined whether or not the side slip angle of the vehicle body is large, that is, whether or not the wheels are largely slipped and the vehicle body is in the spin state or the drift state. Then, the process as the slip determination means is executed.

This slip determination is performed by, for example, the following (1
4) to (19) are calculated, and (20) becomes
If it continues for 100 msec or more, it is determined that the vehicle side slip angle is large, and conversely, equation (20) continues for 20 msec.
If the state where only less than the condition is satisfied continues for 150 msec or more, it is determined by determining that the side slip angle of the vehicle body is not large (the grip force of the wheel is recovered).

[0049]

[Equation 8]

That is, in this embodiment, the difference between the actual yaw rate γ and the reference yaw rate γk is positive or negative continuously between the previous time and this time, and the absolute value of the difference at this time is a predetermined value. Threshold value X1 (for example, 2.74 × 10 ^-3 rad / se
c) or more, or the difference between the actual lateral acceleration α and the reference lateral acceleration αk is positive or negative continuously between the previous time and this time, and the absolute value of this time difference is a predetermined value. Threshold X2
When it is (for example, 0.372 m / s ² ) or more, it is determined that the side slip angle of the vehicle body is large.

When it is determined in S150 that the side slip angle of the vehicle body is not large (the wheels are gripping), the gain P for obtaining the rear wheel steering angle command value θ0r described later is obtained in S160. (V) is searched and set from a data map provided in advance. The gain P (V)
Like S (V) and K6 (V) described above, is a constant that is determined according to the vehicle speed V at that time, and by searching from a data map provided in advance according to the vehicle speed V at that time, It is determined.

On the other hand, when it is determined in S150 that the side slip angle of the vehicle body is large, the process proceeds to S170 and the process as a control law changing means for setting the gain P (V) to 0 is executed. Then, when the gain P (V) is set in S160 or S170, the process proceeds to S180, and as the rear wheel steering angle calculation means for calculating the rear wheel steering angle command value θ0r based on the following equation (21). The process of is executed.

[0053]

[Equation 9]

That is, when it is determined in S150 that the vehicle side slip angle is not large, the gain P
Since a constant corresponding to the vehicle speed V is set as (V),
The feedforward control term (K6
(V) · θf) and feedback control term (P (V) ·
(Γ-γ 0)) and the vehicle speed V and the front wheel steering angle θ
Since the rear wheel steering angle command value θ0r is calculated according to f and the actual yaw rate γ, 0 is set as the gain P (V) when it is determined that the side slip angle of the vehicle body is large. Only the feedforward control term (K6 (V) · θf) in the equation remains, and the rear wheel steering angle command value θ0r is calculated from only the vehicle speed V and the front wheel steering angle θf.

Then, in subsequent S190, based on the rear wheel steering angle command value θ0r thus calculated and the rear wheel steering angle θr detected in S110, a generally known rear wheel is eliminated so as to eliminate the difference. A positioning servo calculation is performed, and in accordance with the calculation result, in S200, a current command value signal If is calculated, and a process as a control unit that supplies a current to the drive circuit 32 to drive the DC servo motor 2 is executed.

Here, FIG. 5 shows a control block diagram of the above-mentioned rear wheel steering control. As shown in FIG. 5, in the rear wheel steering control device of this embodiment, the reference yaw rate γk and the reference yaw rate γk are calculated from the vehicle speed V, the front wheel steering angle θf, and the rear wheel steering angle θr according to the equations (1) and (2). The lateral acceleration αk is calculated, and from the calculation result and the actual yaw rate γ and the actual lateral acceleration α (14)
Based on equation (20), it is determined whether or not the vehicle side slip angle is large. Then, when it is determined that the side slip angle of the vehicle body is not large, the rear wheel steering angle command value θ0r is calculated from the equations (13) and (21), and when it is determined that the side slip angle of the vehicle body is large, (21) In the formula, switching is performed so as to calculate the rear wheel steering angle command value θ0r without adding the feedback control term (P (V) · (γ−γ0)) to the feedforward control term (K6 (V) · θf). Is going.

That is, in the rear wheel steering control system of this embodiment, when it is determined that the vehicle side slip angle is not large, the rear wheel steering angle command value θ0r is calculated from the vehicle speed V, the front wheel steering angle θf and the actual yaw rate γ. When the yaw rate feedback control to be calculated is performed and it is determined that the vehicle side slip angle is large, the value of the gain P (V) in the expression (21) is set to 0.
Thus, the control law is apparently changed so that the feedforward control is performed.

Therefore, according to the rear wheel steering control system of this embodiment, the side slip angle of the vehicle body becomes large and the actual yaw rate γ is increased.
Is not reflected in the steering angle of the rear wheels 11, so that the actual yaw rate γ becomes extremely large by spinning the vehicle, or the actual yaw rate γ changes by drifting the vehicle. Even if it becomes extremely small, the rear wheel 11
The rudder angle of does not change extremely, the behavior of the vehicle becomes gentle, and the vehicle driver can easily stabilize the posture of the vehicle by the smooth steering wheel operation.

When the vehicle side slip angle becomes large, the rear wheel steering angle command value θ0r is determined only by the vehicle speed V and the front wheel steering angle θf which can be directly manipulated by the vehicle driver. Since the intention is faithfully reflected in the steering of the rear wheels 11, the steering angle of the rear wheels 11 does not change extremely more than expected by the vehicle driver, and the vehicle driver has a large side slip angle. It becomes possible to quickly get accustomed to the control of the rear wheel 11 when the vehicle is in a state of being struck, and the steering of the rear wheel 11 can be positively used to quickly stop the sideslip of the wheel.

If the control law is changed depending on whether the side slip angle of the vehicle body is large or not, the rear wheel steering angle command value θ0r may change greatly at the moment of the change. Therefore, in this embodiment, for example, FIG.
As shown in FIG. 6, when it is determined that the side slip angle of the vehicle body has increased and the control law 1 is switched to the control law 2 (time t1 in FIG. 6), the rear wheel steering calculated by each of the control laws 1 and 2 is calculated. The difference Δθ0r between the angle command values θ0r is set to a constant speed Δ
The control law 2 is smoothly switched while decreasing with θ (deg / sec). By performing such control, even if there is a large difference between the rear wheel steering angle command value θ0r calculated by the control law 1 and the control law 2, the vehicle driver can feel the sense of incongruity without feeling uncomfortable. It becomes possible to switch.

In the above embodiment, the standard yaw rate γk is calculated from the vehicle speed V, the front wheel steering angle θf and the rear wheel steering angle θr.
And the reference lateral acceleration αk were calculated, and it was determined from these values and the actual yaw rate γ and the actual lateral acceleration α whether or not the lateral slip angle of the vehicle body was large. It is also possible to calculate only one of α k and determine from this and the actual yaw rate γ or the actual lateral acceleration α that the lateral slip angle of the vehicle body is large.

Furthermore, in the above-mentioned embodiment, when it is determined that the vehicle side slip angle is large, the gain P (V) in the equation (21) is set to 0, and the feedback control term (P (V). (Γ−γ0)) was deleted to substantially change the control law for calculating the rear wheel steering angle command value θ0r, but when the side slip angle of the vehicle body is large and when it is not, You may change to a completely different control law.

Then, as a second embodiment, a rear wheel steering control device in which the control law itself is changed will be described. The second embodiment is different from the first embodiment only in the rear wheel steering control executed by the control device 3,
Only this point will be described.

As shown in FIG. 7, in the rear wheel steering control of this embodiment, S1 of FIG. 4 is performed by the processing of S210 to S230.
Just like 10 to S130, the vehicle speed V, the front wheel steering angle θf,
The rear wheel steering angle θr, the actual yaw rate γ, and the actual lateral acceleration α are detected, and the standard yaw rate γk and the standard lateral acceleration αk are calculated based on the equations (1) to (12). And then S
At 240, (14)-
Based on the equation (20), it is determined whether or not the vehicle side slip angle is large. In this embodiment, the target yaw rate γ0 is not calculated because the control law of the first embodiment is not used.

If it is determined in S240 that the vehicle side slip angle is not large, then in S250,
The rear wheel steering angle command value θ0r is calculated based on the following equation (22). Note that KB (V) is also the vehicle specification data and vehicle speed V
Is a constant determined from the above, and is determined by searching from a data map provided in advance.

[0066]

[Equation 10]

On the other hand, when it is determined in S240 that the vehicle side slip angle is large, the process proceeds to S260, and the rear wheel steering angle command value θ0r is calculated based on the following equation (23).

[0068]

[Equation 11]

The expression (23) is the same as the feedforward term of the expression (21) in the first embodiment. Then, when the rear wheel steering angle command value θ0r is calculated in S250 or S260, the process proceeds to S270, and in S280 following this S270, the rear wheel steering angle command is performed in the same manner as in S190 and S200 of FIG. The rear wheel positioning servo calculation is performed based on the value θ0r and the rear wheel steering angle θr, and the current command value signal If is calculated based on the calculation result, and the current is supplied to the drive circuit 32.

Here, FIG. 8 shows a control block diagram of the rear wheel steering control. As shown in FIG. 8, in the rear wheel steering control system of the second embodiment, it is determined whether or not the side slip angle of the vehicle body is large as in the case of the first embodiment, but if the side slip angle of the vehicle body is not large. When the determination is made, the rear wheel steering angle command value θ0r is calculated by the formula (22), and conversely, when it is determined that the vehicle side slip angle is large, the rear wheel steering angle command value θ0r is calculated by the formula (23). It is carried out.

That is, in the rear wheel steering control system of this embodiment, when it is determined that the vehicle side slip angle is not large, as in the first embodiment, the vehicle speed V, the front wheel steering angle θf, and the actual yaw rate γ are determined. The yaw rate feedback control for calculating the rear wheel steering angle command value θ0r is performed, and when it is determined that the side slip angle of the vehicle body is large, the feed forward for calculating the rear wheel steering angle command value θ0r only from the vehicle speed V and the front wheel steering angle θf. Although the control law is changed so that the control is performed, the change of the control law is not performed by changing the value of the gain, but is performed by switching between different control laws. Even if the control law itself is switched in this way, the behavior change of the rear wheel 11 when the wheel slips sideways can be suppressed just as in the rear wheel steering control device of the first embodiment.

The embodiment embodying the invention described in claim 2 has been described above. Next, as a third embodiment, the rear wheel steering of the vehicle embodying the invention described in claim 3 will be described. The control device will be described. In this third embodiment, the lateral acceleration sensor 18 is not provided because the actual lateral acceleration α is not used to determine whether or not the lateral slip angle of the vehicle body is large, and it is executed by the control device 3. Only the rear wheel steering control that is performed is different from the above-described first and second embodiments, so only this rear wheel steering control will be described.

As shown in FIG. 9, when the rear wheel steering control of this embodiment is started, first, at S310, the steering wheel angle θ is reached.
s, the vehicle speed V, and the rear wheel steering angle θr are detected, the front wheel steering angle θf is calculated from the steering wheel angle θs, and the actual yaw rate γ is detected in subsequent S320. Then, in subsequent S330,
From the following equations (24) to (26), the standard yaw rate γk that can occur in the vehicle when the side slip angle of the vehicle body is not large
The processing as a turning state estimating means for calculating the maximum value γkmax and the minimum value γkmin of is executed. Hereinafter, these are simply referred to as the maximum value γkmax and the minimum value γkmin.

[0074]

[Equation 12]

Here, the maximum value γkmax and the minimum value γkm
A method of calculating in will be described. First, the above (1)
In the equation, the rear wheel steering angle θr is given by the equations (13) and (21)
Substituting the rear wheel steering angle command value θ0r calculated by the equation, the reference yaw rate γk is expressed by the equation (24). That is, in the rear-wheel steering control, the rear-wheel steering angle θr is controlled so as to match the rear-wheel steering angle command value θ0r. Therefore, the standard yaw rate γk can be expressed without the rear-wheel steering angle θr as a parameter. You can do it. In the equation (24),
T1 is a time constant determined by the vehicle specification data and the vehicle speed V, and γ1 is the final value of the standard yaw rate γk for the front wheel steering angle θf.

Since T1 and γ1 respectively use the front / rear equivalent cornering powers CF and CR depending on the friction coefficient μ of the road surface as parameters, the maximum value γkmax and the minimum value γkmin of the standard yaw rate γk are estimated in advance. Maximum value C of front / rear equivalent cornering power CF, CR corresponding to maximum and minimum values of friction coefficient μ
By Fmax, CRmax and minimum values CFmin, CRmin, (2
It can be calculated as in equations (5) and (26).

As in the equations (1) and (13), the equations (25) and (26) have the input as the front wheel steering angle θf and the transfer functions as G4 (s) and G5 (s). Although it is shown by the transfer characteristic of the system, in practice, the transfer functions G4 (s) and G5 (s) are converted into the state equation representation as in the case of the equations (1) and (13). , Is calculated by performing the discretization by the 0th-order holder.

Thus, the maximum value γkmax and the minimum value γkm
After the in is calculated, in the subsequent S340, the vehicle speed V detected in S310 as in S140 of the first embodiment (FIG. 4).
And the front wheel steering angle θf, based on the above equation (13),
Calculate the target yaw rate γ 0.

Then, in the subsequent S350, it is determined whether or not the actual yaw rate γ is smaller than the minimum value γkmin, and when it is determined that the actual yaw rate γ is not smaller than the minimum value γkmin, the following S360 is performed. , It is determined whether or not the actual yaw rate γ is larger than the maximum value γkmax. When it is determined that the actual yaw rate γ is not larger than the maximum value γkmax, the actual yaw rate γ is substituted into the algebra γ ′ for calculating the rear wheel steering angle command value θ0r in S400, which will be described later, in S370. .

On the other hand, when it is determined in S350 that the actual yaw rate γ is smaller than the minimum value γkmin, the process proceeds to S380, the minimum value γkmin is substituted into the algebra γ ′, and S3
When it is determined at 60 that the actual yaw rate γ is larger than the maximum value γkmax, the maximum value γkmax is substituted into the algebra γ ′.

When a value is assigned to the algebra γ'in any of S370 to S390, the process proceeds to S400 and the rear wheel steering angle command value θ0r is calculated. In addition, this S40
At 0, the rear wheel steering angle command value θ0r is calculated using the algebra γ ′ instead of the actual yaw rate γ in the equation (21).

That is, by the processes of S350 and S360, a process as a slip judging means for judging whether or not the actual yaw rate γ is within the range from the maximum value γkmax to the minimum value γkmin is executed, and S380 and S390. When the actual yaw rate γ is larger than the maximum value γkmax, the maximum value γkmax, the vehicle speed V, and the front wheel steering angle θf
Therefore, when the actual yaw rate γ is smaller than the minimum value γkmin, the control law changing means is switched to calculate the rear wheel steering angle command value θ0r from the minimum value γkmin, the vehicle speed V and the front wheel steering angle θf. Is being executed.

Then, in this way, the rear wheel steering angle command value θ0
After calculating r, in subsequent S410 and S420, the rear wheel positioning is performed based on the rear wheel steering angle command value θ0r and the rear wheel steering angle θr, just like S190 and S200 in the first embodiment (FIG. 4). Servo calculation is performed, a current command value signal If is calculated based on the calculation result, and a current is supplied to the drive circuit 32.

Here, FIG. 10 shows a control block diagram of the rear wheel steering control. As shown in FIG. 10, in the rear wheel steering control device of the third embodiment, the vehicle speed V and the front wheel steering angle θf.
From equations (25) and (26), the maximum value γkmax and the minimum value γkmin of the reference yaw rate γk are calculated, and the calculated result and the actual yaw rate γ are compared, and the actual yaw rate γ is calculated from the maximum value γkmax. If it is within the range up to the minimum value γkmin, it is determined that the side slip angle of the vehicle body is not large, and conversely, if the actual yaw rate γ is outside the range, it is determined that the side slip angle of the vehicle body is large. Then, when it is determined that the side slip angle of the vehicle body is large, and the actual yaw rate γ is larger than the maximum value γkmax, in equation (21),
This maximum value γkmax is used instead of the actual yaw rate γ to calculate the rear wheel steering angle command value θ0r, and conversely, the actual yaw rate γkmax is calculated.
Is smaller than the minimum value γkmin, in the equation (21), the rear wheel steering angle command value θ0r is switched using the minimum value γkmin instead of the actual yaw rate γ.

In other words, in the rear wheel steering control system of this embodiment, when the actual yaw rate γ is out of the range from the maximum possible yaw rate γkmax to the minimum possible yaw rate γkmin, the vehicle side slip angle becomes large. When it is determined that the vehicle body is in the spin state or the drift state in this way, the maximum value γkmax or the minimum value γkmin is fixed to the parameter of the actual yaw rate for calculating the rear wheel steering angle command value θ0r. By substituting as, the control law is substantially changed.

Therefore, according to the rear wheel steering control system of the present embodiment, for example, the actual yaw rate γ becomes extremely large due to the spinning of the vehicle, or the actual yaw rate γ becomes extremely small due to the drift of the vehicle. Even if the steering angle of the rear wheels 11 does not change extremely, the behavior of the vehicle becomes gentle, and when it is determined that the side slip angle of the vehicle body is large, the rear wheel steering angle command value θ0r is calculated. Since the parameter of the actual yaw rate is fixed to the maximum value γkmax or the minimum value γkmin, the steering angle of the rear wheel 11 is substantially determined only from the vehicle speed V and the front wheel steering angle θf. , First
Also, similarly to the rear wheel steering control device of the second embodiment, the intention of the vehicle driver can be faithfully reflected in the steering of the rear wheels 11.

In this embodiment, by substituting the maximum values CFmax, CRmax and the minimum values CFmin, CRmin of the front / rear equivalent cornering powers CF, CR into the reference yaw rate γk expressed by the equation (24), Based on the obtained equations (25) and (26), the reference yaw rate γ is obtained.
The maximum value γkmax and the minimum value γkmin of k are calculated. For example, as shown in the following equations (27) and (28), a predetermined coefficient Rmax is added to the reference yaw rate γk obtained by the equation (24). (1 <Rmax), Rmin (0 <Rmin <
The maximum value γkmax and the minimum value γkmin may be simply calculated by multiplying each by 1).

[0088]

[Equation 13]

Further, as shown in the following equations (29) to (31), the intermediate values γ ^ for calculating the target yaw rate γ0 are multiplied by predetermined coefficients Rmax and Rmin, respectively, to obtain the maximum values γkmax and The minimum value γkmin may be calculated.

[0090]

[Equation 14]

Here, even if the friction coefficient μ of the road surface is the same, the wheels are less likely to skid at low speeds, and conversely, the wheels are likely to skid at high speeds. The coefficient of friction μ of changes with the vehicle speed V. Therefore, in order to calculate the maximum value γkmax and the minimum value γkmin of the standard yaw rate γk, the maximum values CFmax, CRmax and the minimum values CFmin, CRmin of the front / rear equivalent cornering powers CF, CR and the above-mentioned predetermined coefficients Rmax, Rm.
By setting in as a function of the vehicle speed V, the maximum value γkmax and the minimum value γkmin can be calculated more accurately.

Even if the maximum value γkmax and the minimum value γkmin are calculated by any of the above-mentioned methods, the front wheel steering angle θf
When is 0, both maximum value γkmax and minimum value γkmin are 0
Therefore, for example, even when a yaw occurs due to a disturbance such as a side wind when the vehicle is traveling straight (when the front wheel steering angle θf = 0), the algebra γ ′ in FIG. However, the actual yaw rate γ is not reflected in the steering of the rear wheels 11.

Therefore, as a countermeasure against this, the following (3
As shown in equation (2), the smaller of the value (γk-Δγ) obtained by subtracting the predetermined value Δγ from the reference yaw rate γk calculated by equation (24) and the minimum value γkmin is the true minimum value used for control. γkmin, or a value (γk +) obtained by adding a predetermined value Δγ to the reference yaw rate γk calculated by the equation (24).
The larger one of Δγ) and the maximum value γkmax may be set as the true maximum value γkmax used for control.

[0094]

[Equation 15]

Then, in this way, the true maximum value γkm
If ax and the minimum value γkmin are set, when the vehicle goes straight, that is, when the front wheel steering angle θf is 0, the range of the value substituted into the algebra γ ′ is from the shaded range in FIG. This is one of the functions of the yaw rate feedback rear wheel steering control because it spreads in the shaded area in FIG. 11 (B).
It is possible to achieve both the disturbance suppression function when the vehicle goes straight and the vehicle behavior suppression function when the wheels skid according to the present invention.

The third embodiment described above is an apparatus for calculating the rear wheel steering angle command value θ0r based on the control law used in the first embodiment, that is, the equation (21). The present invention was applied. Therefore, as a fourth embodiment, a case will be described below in which the rear wheel steering angle command value θ0r is calculated based on the control law used in the second embodiment, that is, the equation (22).

Since the fourth embodiment is different from the above-described third embodiment only in the rear wheel steering control executed by the control device 3, only this point will be described. As shown in FIG. 12, in the rear wheel steering control of the present embodiment, S510 to S530.
By the processing of step S310 to step S330 of FIG. 9, the vehicle speed V, the front wheel steering angle θf, the rear wheel steering angle θr, and the actual yaw rate γ are detected, and the expressions (24) to (26) or (2) are detected.
From equations (7) and (28) or equations (29) to (31),
The maximum value γkmax and the minimum value γkmin of the standard yaw rate γk that can occur in the vehicle when the sideslip angle of the vehicle body is not large are calculated. Then, in subsequent S540 to S580, FIG.
Just as in S350 to S370, the actual yaw rate γ is compared with the maximum value γkmax and the minimum value γkmin in magnitude, and the actual yaw rate parameter for calculating the rear wheel steering angle command value θ0r is calculated according to the comparison result. Substitute each value into the algebra γ ′ as. In this embodiment, the target yaw rate γ0 is not calculated because the same control law as in the second embodiment is used.

When a value is assigned to the algebra γ'in any of S560 to S580, the process proceeds to S590 and the rear wheel steering angle command value θ0r is calculated. In addition, this S59
At 0, the rear wheel steering angle command value θ0r is calculated using the algebra γ ′ instead of the actual yaw rate γ in the equation (22). When the rear wheel steering angle command value θ0r is calculated, the subsequent S60
At 0 and S610, the current command value signal If is calculated in exactly the same manner as S410 and S420 of FIG. 9, and the current is supplied to the drive circuit 32.

Here, FIG. 13 shows a control block diagram of the rear wheel steering control. As shown in FIG. 13, the rear wheel steering control device of the fourth embodiment is the same as the rear wheel steering control device of the third embodiment except that the rear wheel steering angle command value θ0r is obtained based on the equation (22). Exactly the same.

Also, the rear wheel steering control system of this embodiment can obtain the same effect as that of the system of the third embodiment.

[0101]

As described above, according to the present invention as set forth in claim 1, when it is determined that the side slip angle of the vehicle body is large, that is, the vehicle body is in the spin state or the drift state, the change amount of the actual yaw rate is determined. On the other hand, the control law for calculating the target rear wheel steering angle is changed so that the amount of change in the rear wheel steering angle becomes small.

Therefore, according to the first aspect of the present invention, the extreme change in the actual yaw rate caused by the skidding of the wheels is not significantly reflected in the rear wheel steering angle.
For example, even if the vehicle spins and the actual yaw rate becomes extremely large, or conversely the vehicle drifts and the actual yaw rate becomes extremely small, the rear wheel steering angle does not change extremely and The behavior of the vehicle becomes gentle when the sideslip angle of the vehicle becomes large, and the vehicle driver can easily stabilize the posture of the vehicle by a smooth steering wheel operation.

Further, in the present invention as set forth in claim 2, when it is judged that the side slip angle of the vehicle body is large, the rear wheel steering angle is determined only by the vehicle speed and the front wheel steering angle which can be directly operated by the vehicle driver. As described above, the control law for calculating the target rear wheel steering angle is changed.

Therefore, according to the present invention described in claim 2,
Since the will of the vehicle driver is faithfully reflected in the steering of the rear wheels when the sideslip angle of the vehicle body becomes large,
The rear wheel rudder angle does not change more drastically than expected by the vehicle driver, and the vehicle driver can easily stabilize the posture of the vehicle by a smooth steering wheel operation. In addition, the vehicle driver can quickly get used to the control of the rear wheels when the sideslip angle of the vehicle body is large, so that the steering of the rear wheels can be positively used to quickly stop the sideslip of the wheels. become able to.

Further, in the present invention according to claim 3, when it is determined that the side slip angle of the vehicle body is large,
To calculate the target rear wheel steering angle so that the rear wheel steering angle is determined based on the maximum or minimum yaw rate that can occur in the vehicle when the vehicle side slip angle is not large, rather than the actual yaw rate. I am trying to change the control law.

Therefore, according to the third aspect of the present invention, for example, the vehicle spins and the actual yaw rate becomes extremely large, or conversely, the vehicle drifts and the actual yaw rate becomes extremely small. Even if the rear wheel rudder angle does not change extremely, the behavior of the vehicle becomes gentle, and when it is determined that the side slip angle of the vehicle body is large, the actual yaw rate for calculating the target rear wheel rudder angle is calculated. The parameter is fixed to the estimated maximum or minimum value of the yaw rate, so that the rear wheel steering angle is substantially determined only from the vehicle speed and the front wheel steering angle. As in the present invention, the intention of the vehicle driver can be faithfully reflected in the steering of the rear wheels.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an overall configuration of a rear wheel steering control device.

FIG. 3 is a schematic configuration diagram of a control device.

FIG. 4 is a flowchart showing rear wheel steering control in the first embodiment.

FIG. 5 is a control block diagram of rear wheel steering control in the first embodiment.

FIG. 6 is an explanatory diagram illustrating a switching process performed when switching control rules.

FIG. 7 is a flowchart showing rear wheel steering control in the second embodiment.

FIG. 8 is a control block diagram of rear wheel steering control in the second embodiment.

FIG. 9 is a flowchart showing rear wheel steering control in the third embodiment.

FIG. 10 is a control block diagram of rear wheel steering control in the third embodiment.

FIG. 11 is an explanatory diagram illustrating a process for achieving both the disturbance suppression function when the vehicle goes straight and the vehicle behavior suppression function when the wheels skid.

FIG. 12 is a flowchart showing rear wheel steering control in a fourth embodiment.

FIG. 13 is a control block diagram of rear wheel steering control in the fourth embodiment.

[Explanation of symbols]

1 ... Rear wheel steering mechanism 2 ... DC servo motor 3 ...
Control device 11 ... Rear wheel 14 ... Rear wheel steering angle sensor 15
... Vehicle speed sensor 16 ... Front wheel steering angle sensor 17 ... Yaw rate sensor 18
... Lateral acceleration sensor

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

Claims (3)

[Claims] 1. A rear wheel steering mechanism for steering a rear wheel of a vehicle, an actuator for displacing the rear wheel steering mechanism, a vehicle speed detecting means for detecting a vehicle speed, and a vehicle front wheel steered by a vehicle driver. Front wheel steering angle detection means for detecting the steering angle, as a vehicle behavior caused by the turning of the vehicle, at least a turning state detection means for detecting the actual yaw rate, and at least from the vehicle speed, the front wheel steering angle and the actual yaw rate, According to the set predetermined control rule, rear wheel steering angle calculation means for calculating a target rear wheel steering angle according to the traveling state of the vehicle, and the steering angle of the rear wheel is the target rear wheel steering angle, A rear-wheel steering control device for a vehicle, comprising: a control means for driving and controlling the actuator; and a rear-wheel steering control device for a vehicle, wherein: Based on the turning state estimating means for estimating the possible yaw rate and / or the lateral acceleration, and the estimation result of the turning state estimating means and the actual yaw rate and / or the actual lateral acceleration generated in the vehicle, is the lateral slip angle of the vehicle body large? Slip determining means for determining whether or not, when the slip determining means determines that the side slip angle of the vehicle body is large, the amount of change in the target rear wheel steering angle with respect to the amount of change in the actual yaw rate becomes small, A rear wheel steering control device for a vehicle, comprising: a control rule changing unit that changes the control rule. 2. The vehicle rear wheel steering control device according to claim 1, wherein the control law changing unit determines the vehicle speed and the front wheel when the slip determining unit determines that the side slip angle of the vehicle body is large. A rear wheel steering control device for a vehicle, characterized in that the control law is changed such that the target rear wheel steering angle is calculated from the steering angle. 3. The vehicle rear wheel steering control device according to claim 1, wherein the turning state estimating means estimates the maximum value and the minimum value of the yaw rate that can occur in the vehicle when the sideslip angle of the vehicle body is not large. The slip determination means compares the estimated maximum value and minimum value with the actual yaw rate detected by the turning state detection means, and the actual yaw rate is out of the range from the maximum value to the minimum value. When the actual yaw rate is larger than the maximum value, the control law changing means determines that the side slip angle of the vehicle body is large by the slip determining means. , The control law is changed so that the target rear wheel steering angle is calculated from the maximum value, the vehicle speed, and the front wheel steering angle, and the actual yaw rate is lower than the minimum value. When it is small, the control law is changed so that the target rear-wheel steering angle is calculated from the minimum value, the vehicle speed, and the front-wheel steering angle.