JP3137519B2 - Abnormality detection device for rear wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vehicle speed sensor by controlling an actuator provided in a rear wheel steering device.
The present invention relates to a rear wheel steering device that steers a rear wheel to a target steering angle determined according to a traveling state of a vehicle detected by various sensors such as a yaw rate sensor and a front wheel steering angle sensor. The present invention relates to an abnormality detection device for a rear wheel steering device that detects a steering abnormality.

[0002]

2. Description of the Related Art Conventionally, as an apparatus of this type, as disclosed in Japanese Patent Application Laid-Open No. 1-186474, for example, the absolute value of the difference between the target rear wheel steering angle and the actual steering angle is determined by the same target steering angle. If it does not converge within a predetermined value within a predetermined time after the steering to, the rear wheels are determined to be abnormal in steering.

[0003]

However, in the above-mentioned conventional device, the predetermined value is the response of the actuator,
Since it is not determined in consideration of the operation performance and the like, it is not possible to accurately determine the steering abnormality of the rear wheels. The present invention has been made in order to address the above-described problem, and an object of the present invention is to provide a rear-wheel steering device capable of accurately determining a rear-wheel steering abnormality by considering the responsiveness and operation performance of an actuator. An object of the present invention is to provide an abnormality detection device.

[0004]

In order to achieve the above-mentioned object, the structural features of the invention according to the first aspect include an actuator which is electrically driven to steer a rear wheel, and a driving state of a vehicle. Target steering angle determining means for determining a target steering angle for steering the rear wheel in accordance therewith, a rear wheel steering angle sensor for detecting the actual steering angle of the rear wheel, the determined steering target steering angle and the detected actual steering angle A steering control means for controlling the actuator in accordance with the angle and steering the rear wheel to the determined steering target steering angle, wherein the rear wheel steering device uses a transfer function representing the responsiveness of the actuator. Target steering angle conversion means for converting the determined steering target steering angle to a monitoring target steering angle; and abnormality determination for determining a steering abnormality based on the converted monitoring target steering angle and the detected actual steering angle. Means.

A structural feature of the invention according to claim 2 is that the abnormality judging means includes a first calculating means for calculating the rate of change of the converted monitoring target steering angle, and the detected actual steering angle. A second calculating means for calculating a change rate of the actual steering angle, wherein the change direction of the monitoring target steering angle and the change direction of the actual steering angle are the same, and When the value is larger than the absolute value of the calculated change rate of the target steering angle for monitoring by a predetermined value or more, or the direction of change of the target steering angle for monitoring and the direction of change of the actual steering angle are different and the calculated actual steering angle is different. And determining means for determining that the rear wheel is abnormal when the absolute value of the change rate of the rear wheel is not less than a predetermined value.

According to a third aspect of the present invention, there is provided a rear wheel steering apparatus including the actuator, a target steering angle determining unit, a rear wheel steering angle sensor, and a steering control unit . Target steering angle limiting means for limiting the target steering angle to a predetermined range in accordance with the operation capability of the actuator to provide a monitoring target steering angle, and the limited monitoring target steering angle and the detected actual steering angle. Abnormality determination means for determining a steering abnormality based on the above.

[0007]

According to the first aspect of the present invention, there is provided:
In the invention according to the steering target steering angle determined according target steering angle converting means the running state of the vehicle by using a transfer function representing the response of the actuator into a target steering angle for monitoring abnormality determining means Determines a steering abnormality based on the converted monitoring target steering angle and the detected actual steering angle. Therefore, according to the present invention, the responsiveness of the actuator is taken into consideration in determining whether the rear wheel is abnormally steered. Therefore, even if there is a delay between the time when the target steering angle is determined and the time when the rear wheel is actually steered, the actuator is not affected. The abnormality determination is performed within the range of the responsiveness, and the abnormality determination becomes accurate.

According to the second aspect of the present invention, the first and second calculating means monitor the rear wheels.
The rate of change of the target steering angle for use and the rate of change of the actual steering angle are calculated, respectively, and the abnormality determination means determines the steering abnormality of the rear wheels based on the two rates of change. In this abnormality determination, when the change direction of the monitoring target steering angle of the rear wheels is the same as the change direction of the actual steering angle, the absolute value of the change rate of the actual steering angle is the change rate of the monitoring target steering angle. When the absolute value of the change rate of the actual steering angle is not larger than the absolute value of the change rate of the monitoring target steering angle by a predetermined value or more when the absolute value of the change rate of the actual steering angle is larger than the absolute value of the Does not judge steering abnormality. Therefore, when the actuator as the actual steering angle and runaway goes beyond the steering target steering angle is a rear wheel is determined to be abnormal steering, actual steering by the actuator is large steering load of the rear wheels If the angle cannot follow the target steering angle for steering, it is not determined that the rear wheels are abnormal in steering. When the direction of change of the target steering angle for monitoring and the direction of change of the actual steering angle are different, when the absolute value of the rate of change of the actual steering angle is equal to or greater than a predetermined value, it is determined that the rear wheel is abnormal. Therefore, the actuator runs away and the rear wheel
If the opposite direction to the steering target steering angle as is steered also, a steering abnormality of the rear wheels is determined. Therefore, according to the present invention, even if the steering load of the rear wheel is temporarily large and the rear wheel does not follow the steering target steering angle and is not steered, the steering abnormality is not determined, and the malfunction of the actuator or the like is caused. An abnormal steering of the rear wheels is accurately determined.

Further, according to the third aspect of the present invention, the target steering angle limiting means limits the target steering angle for steering determined according to the running state of the vehicle within a predetermined range according to the operation capability of the actuator. Then, the monitoring target steering angle is determined, and the abnormality determination unit determines a steering abnormality based on the limited monitoring target steering angle and the detected actual steering angle. Therefore, according to the present invention, since the operation performance of the actuator is considered in the determination of the abnormal steering of the rear wheel, even if the target steering angle for steering is determined to be a value equal to or more than the operation performance of the actuator, the range of the operation performance of the actuator is determined. The abnormality determination is performed within the range, and the abnormality determination becomes accurate.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a front wheel steering mechanism 10 for steering left and right front wheels FW1 and FW2, and a rear wheel steering mechanism 20 for steering left and right rear wheels RW1 and RW2. And an electric control device 30 for electrically controlling the rear wheel steering mechanism 20.

The front wheel steering mechanism 10 includes a steering handle 11 for steering left and right front wheels FW1 and FW2 by a turning operation.
The handle 11 is fixed to the upper end of the steering shaft 12.
The lower end of the steering shaft 12 meshes with the rack bar 14 in the steering gear box 13. The rack bar 14 is supported in the steering gear box 13 so as to be displaceable in the axial direction, and tie rods 15a, 15
b and the left and right front wheels FW1, FW2 are steerably connected via the knuckle arms 16a, 16b.

The rear wheel steering mechanism 20 has an electric motor 21 such as a brushless motor as an actuator for steering the rear wheels. The electric motor 21 has two field windings connected in parallel, and if at least one of the windings is energized, the motor 21 is driven to rotate. Electric motor 2
The rotating shaft 1 is connected to a relay rod 23 supported in a steering gear box 22 via a speed reduction mechanism so as to be displaceable in the axial direction.
Is displaced in the axial direction according to the rotation of. The speed reduction mechanism in this case is preferably set to zero so as to reduce the reverse efficiency, so that the electric motor 21 is not unnecessarily driven to rotate by an external input from the relay rod 23 side. I have. A tie rod 2 is provided at both ends of the relay rod 23.
The left and right rear wheels RW1 and RW2 are connected via the knuckle arms 25a and 25b and the left and right rear wheels RW1 and RW2 are steered according to the axial displacement of the relay rod 23.

The electric control device 30 includes a vehicle speed sensor 31, a yaw rate sensor 32, a front wheel steering angle sensor 33, and a rear wheel steering angle sensor 34. The vehicle speed sensor 31 detects the vehicle speed V by measuring the rotation of an output shaft of a transmission (not shown), and outputs a detection signal indicating the vehicle speed V. The yaw rate sensor 32 detects a yaw rate γ around the vertical axis of the center of gravity of the vehicle body and outputs a detection signal representing the yaw rate γ. The front wheel steering angle sensor 33 detects the steering angle θf of the left and right front wheels FW1 and FW2 by measuring the rotation angle of the steering shaft 12, and outputs a detection signal representing the steering angle θf. Rear wheel steering angle sensor 34
Detects the steering angle θr of the left and right rear wheels RW1 and RW2 by measuring the rotation angle of the rotating shaft of the electric motor 21 and outputs a detection signal representing the steering angle θr. The yaw rate γ, the front wheel steering angle θf, and the rear wheel steering angle θr are positive in the left rotation direction and negative in the right rotation direction.

These sensors 31 to 34 are connected to a microcomputer 35. The microcomputer 35 includes a CPU, a ROM, a RAM, an I / O, a timer, and the like, and executes a program shown in the flowchart of FIG. 2 stored in the ROM. Microcomputer 35
Are connected to drive circuits 36a and 36b and a warning lamp 37. The drive circuits 36a and 36b are controlled by the microcomputer 35 to control the rotation of the electric motor 21 by passing the drive current from the battery 38 to the respective field windings of the electric motor 21. The voltage from the battery 38 is also supplied to the sensors 31 to 34, the microcomputer 35, and the warning lamp 37. The warning lamp 37 is provided near the driver's seat, and warns the driver of abnormal steering of the left and right rear wheels RW1 and RW2 by lighting.

Next, the operation of the embodiment configured as described above will be described with reference to the flowchart shown in FIG. When an ignition switch (not shown) is turned on, the microcomputer 35 starts executing the program in step 100 of FIG.
Is initialized to “0”. The flag FLG indicates "0" indicating a normal steering state of the left and right rear wheels RW1 and RW2, "2" indicates an abnormal steering state of the rear wheels RW1 and RW2, and "1" indicates the abnormal state determination. Indicates that the period is in progress. After the initial setting, it is determined in step 104 whether the flag FLG is "2". in this case,
Since the flag FLG has been set to "0" by the initial setting, "NO" is determined in step 104, and the program proceeds to step 106.

In step 106, each sensor 31
To 34, each detection signal representing the vehicle speed V, the yaw rate γ, the front wheel steering angle θf, and the rear wheel steering angle θr is input. Next, at step 108, a yaw rate proportional coefficient K1 (FIG. 3) that changes according to the vehicle speed V from a table provided in the ROM.
(A) and the steering angle proportional coefficient K2 (see FIG. 3 (B)) and read out these coefficients K1, K2 and yaw rate γ.
Then, the target steering angle θr * of the left and right rear wheels RW1 and RW2 is calculated by executing the calculation of the following equation 1 using the front wheel steering angle θf.

[0017]

After calculating the target rear wheel steering angle θr *, in step 110, the deviation θ between the target rear wheel steering angle θr * and the input rear wheel steering angle θr is calculated.
r * -θr is calculated and a control signal representing the deviation θr * -θr is output to the drive circuits 36a and 36b. Drive circuits 36a, 3
Reference numeral 6b supplies a drive current supplied from the battery 38 in accordance with the control signal to each field winding of the electric motor 21. As a result, the electric motor 21 rotates in accordance with the target rear wheel steering angle θr *, and the rotation is transmitted to the relay rod 23 to displace the rod 23 in the axial direction according to the rotation. The axial displacement of the relay rod 23 is transmitted to the left and right rear wheels RW1 and RW2 via the tie rods 24a and 24b and the knuckle arms 25a and 25b.
1, RW2 are steered to the target rear wheel steering angle θr *.

After the processing of step 110, step 1
A transfer function G (s) representing the response of the electric motor 21 at 12
The simulated value θr # of the target rear wheel steering angle θr * by the motor 21 is calculated by executing the following equation 2 using

[0019]

(Equation 2)

Equation (2) takes into account the secondary delay and dead time of the electric motor 21, a and b are coefficients predetermined according to the characteristics of the electric motor 21, and τ is a predetermined coefficient. Is a constant, and s is a Laplace operator. Therefore, the simulated value θr # represents the control steering angle of the left and right rear wheels RW1, RW2 in consideration of the delay of the electric motor 21.

Simulated value θ of the target rear wheel steering angle θr *
After the calculation of r #, the flag FLG is set to "0" at step 114.
Is determined. In this case, the flag FLG is kept at "0" as described above,
Is determined to be "YES" at step 116
Proceed to In step 116, it is determined whether or not the absolute value | θr−θr # | of the difference θr−θr # between the rear wheel steering angle θr and the calculated simulated value θr # is equal to or greater than a predetermined value C1. If the left and right rear wheels RW1, RW2 are normally steered and the absolute value | θr−θr # | is less than a predetermined value C1,
At step 116, “NO” is determined, and the program returns to step 104. Thereafter, the left and right rear wheels RW1, RW2
Is normally steered, the circulation processing consisting of steps 104 to 116 is repeatedly executed, and the left and right rear wheels RW
1 and RW2 are steered following the target rear wheel steering angle θr *.

On the other hand, for some reason, the absolute value | θ
When r−θr # | is equal to or greater than the predetermined value C1, “YES” is determined in step 116, and the program proceeds to step 118. In step 118, the flag FLG is set to "1".
And the program returns to step 104. Therefore, after the processing of the following steps 104 to 112, it is determined “NO” in step 114, and the program proceeds to steps 120 to 124. After calculating the rate of change dθr / dt of the rear wheel steering angle θr and the rate of change dθr # / dt of the simulated value θr # in steps 120 and 122, the two rates of change dθr / dt, dθr # / dt in step 124. Is included in the abnormal range indicated by hatching in FIG. This abnormal range is a range defined as follows. When the change direction of the simulated value θr # and the change direction of the rear wheel steering angle θr are the same, the change rate dθr /
The absolute value of dt | dθr / dt | is the rate of change of the simulated value θr #
When the absolute value | dθr # / dt | of the dθr # / dt is larger than the predetermined value C2 by more than the predetermined value C2, the abnormal range is determined. When the change direction of the simulated value θr # and the change direction of the rear wheel steering angle θr are different, the change rate dθr / dt of the rear wheel steering angle θr
Is abnormal when the absolute value | dθr / dt | If "NO" in step 124, that is, if it is determined that the change rates dθr / dt and dθr # / dt do not belong to the abnormal range, the flag FLG is returned to “0” in step 126, and the program is executed in step 104. Return to Accordingly, in this case, the processing of steps 104 to 116 (or steps 104 to 118) is executed again, and the left and right rear wheels RW1, RW2 are steered to the target steering angle θr *.
On the other hand, “YES” in step 124, that is, the change rate d
If it is determined that θr / dt and dθr # / dt belong to the abnormal range, at step 128, the absolute value | θr−θr # | of the difference θr−θr # between the rear wheel steering angle θr and the simulated value θr # Is greater than or equal to a predetermined value C4. The predetermined value C4 is the predetermined value C1
If the absolute value | θr−θr # | is not equal to or greater than the predetermined value C4, “NO” is determined in the step 128, and the program returns to the step 104, and the steps 104 to 114, The circulation process consisting of 120 to 124 and 128 is repeatedly executed. Therefore, in this case as well,
The left and right rear wheels RW1, RW2 are controlled to be steered to the target steering angle θr *, but during this circulation processing, the change rates dθr / dt, d
whether θr # / dt is in the abnormal range and the absolute value | θr
It is determined each time whether −θr # | is equal to or greater than a predetermined value C4. If the rate of change dθr / dt, dθr # / dt escapes from the abnormal range during this circulation processing, “NO” is determined in step 124, and the flag FLG is returned to “0” in step 126, and then the program Is returned to step 104, and the above-mentioned steps 104 to 116 (or steps 104 to 118) are performed.
Will be executed again.

Steps 104 to 114, 12
If the absolute value | θr−θr # | is greater than or equal to the predetermined value C4 during the processing of 0 to 124 and 128, “YES” in step 128.
And the program proceeds to step 130. In step 130, the flag FLG is changed to "2" and the program returns to step 104. As a result, in this case, "YES" is determined in the step 104, and after the processes in the steps 132 and 134 are executed, the execution of the program is terminated in the step 136. In step 132, a lighting control signal is output to the warning lamp 37. Since the warning lamp 37 lights up in response to the lighting control signal,
The driver can visually recognize that an abnormality has occurred in the steering of the left and right rear wheels RW1, RW2. In step 134, the drive circuits 36a and 36a are driven until the left and right rear wheels RW1 and RW2 return to the neutral position or until a predetermined maximum time has elapsed.
A control signal for returning the rear wheels RW1 and RW2 to the neutral position is output to 36b. Since the electric motor 21 has two field windings, the right and left rear wheels RW1 and RW2 are provided as long as abnormalities such as disconnection and short circuit do not occur simultaneously in both windings.
Is steered back to the neutral position. In this case, it is necessary to detect the rear wheel steering angle θr, but it is unlikely that the rear wheel steering angle sensor 34 will fail, and at the same time, the rear wheel steering angle sensor 34
May be provided, and in many cases, the left and right rear wheels RW1, RW2 return to the neutral position. If the rear wheels RW1 and RW2 do not return to the neutral position even after such neutral return control of the left and right rear wheels RW1 and RW2, the drive control of the electric motor 21 is stopped after the maximum time has elapsed.

As described above, according to the above-described embodiment, the simulated value obtained by converting the target rear wheel steering angle θr * determined in step 112 according to the processing of step 108 in accordance with the response of the electric motor 21. rear wheel RW according to θr #
Since the abnormality of the steering of the rear wheels RW1 and RW2 is delayed, the abnormality of the steering is accurately detected even if the steering of the rear wheels RW1 and RW2 by the motor 21 is delayed. In addition, it is determined whether or not it is necessary to perform the processing for determining a steering abnormality of the left and right rear wheels RW1 and RW2 consisting of steps 120 to 130 by the processing of step 116. The processing of ~ 130 was not performed. Therefore, in this case, the microcomputer 35 can perform the steering control of the left and right rear wheels RW1 and RW2 and other controls (not shown) with a sufficient time margin.

In the determination processing routine of steps 120 to 124, the change rates dθr / dt and dθr # / dt are as shown in FIG.
The steering abnormality of the left and right rear wheels RW1, RW2 is determined based on whether or not they belong to the abnormal range indicated by hatching. According to this, when the change direction of the simulated value θr # of the left and right rear wheels RW1 and RW2 is the same as the change direction of the actual rear wheel steering angle θr, the change rate dθr / dt of the rear wheel steering angle θr is provided. Value | dθr / dt | is the rate of change dθr # / d of the simulated value θr #
When the absolute value of t is larger than the absolute value | dθr # / dt | by a predetermined value C2 or more, the steering abnormality of the left and right rear wheels RW1 and RW2 is determined, and the absolute value | dθr / dt | is a predetermined value from the absolute value | dθr # / dt | When it is not larger than C2, the steering abnormality is not determined. Therefore, an abnormality occurs in each of the sensors 31 to 33, or the electric motor 21 runs away, and the actual rear wheel steering angle θr becomes the target rear wheel steering angle θ.
When the simulated value of r * exceeds the simulated value θr #, the left and right rear wheels RW1 and RW2 are determined to be abnormal in steering, but the steering load of the rear wheels RW1 and RW2 is large and the actual steering angle is reduced. If it is impossible to follow the target rear wheel steering angle θr *, it is not determined that the steering is abnormal. The simulated value θr
When the change direction of ## and the change direction of the rear wheel steering angle θr are different, the absolute value | dθr / dt | of the rate of change dθr / dt of the rear wheel steering angle θr
When is equal to or more than the predetermined value C3, the steering abnormality of the left and right rear wheels RW1, RW2 is determined. Therefore, even when an abnormality occurs in each of the sensors 31 to 33, or when the electric motor 21 runs away and the left and right rear wheels RW1 and RW2 are steered in the opposite direction to the simulation value θr #, the steering abnormality is also detected. Is determined. As a result, according to the above-described embodiment, if the left and right rear wheels RW1 and RW2 touch the curb or get stuck in the rut and temporarily become unable to steer, it is not determined that the steering is abnormal, and thereafter, Since the steering control of the left and right rear wheels RW1 and RW2 is continued, the steering function of the left and right rear wheels RW1 and RW2 is not unnecessarily limited.

Further, according to the above embodiment, step 1
Even if the steering abnormality of the left and right rear wheels RW1 and RW2 is determined by the processing of steps 20 to 124, the difference θr between the rear wheel steering angle θr and the simulated value θr # is determined by the processing of steps 128 and 130.
If the absolute value | θr−θr # | of −θr # is less than the predetermined value C4, the steering control of the rear wheels RW1 and RW2 is continued and the absolute value | θr−θr # | For the first time, the steering of the left and right rear wheels RW1, RW2 is stopped. As described above, when the absolute value | θr−θr # | is less than the predetermined value C4 and there is no problem in running the vehicle, the electric motor 21 waits for normal return, and the motor 21 returns to normal to change the rate dθr. / d
If t, dθr # / dt escapes from the abnormal range, the left and right rear wheels RW
1, RW2 steering is resumed. As a result, the steering functions of the left and right rear wheels RW1, RW2 are no longer restricted.

Next, first to third modifications of the above embodiment will be described.

A. First Modification Example A first modification example will be described. This modification has the same configuration as that of the above embodiment, but the microcomputer 35 executes a program corresponding to the flowcharts of FIGS. Is executed every predetermined time.

The execution of this program is started at step 200, and by the processing of steps 202 to 206 similar to the processing of steps 106 to 110 of the above embodiment, the rear wheel R
W1 and RW2 are steered to the target steering angle θr *.

After the steering control of the rear wheels RW1 and RW2, the microcomputer 35 executes a target steering angle limiting routine in step 208. Details of the target steering angle limiting routine are shown in the flowchart of FIG. 6, and the microcomputer 35 executes the routine at step 300.
, And the determined target rear wheel steering angle θr * is changed to the left and right rear wheels RW1, RW2 by the processing of steps 302 to 308.
Predetermined upper limit value θrmax representing the maximum steering angle to the left and right
And the lower limit value -θrmax. That is, if the target rear wheel steering angle θr * exceeds the upper limit value θrmax in the positive direction, the target rear wheel steering angle θr * is changed to the upper limit value θrmax, and the target rear wheel steering angle θr * is set to the lower limit value −θrmax. Direction, the target rear wheel steering angle θr * is changed to the lower limit −θrmax, and the target rear wheel steering angle θ
If r * is between the upper limit value θrmax and the lower limit value −θrmax, the target rear wheel steering angle θr * is kept as it is.

Next, by performing the processing of steps 310 to 316, the target rear wheel steering angle θr * is set to the upper limit value θr + Mvmax · Δt and the lower limit value θr−Mvmax ·
Restrict within the range of Δt. Here, θr is the left and right rear wheel RW
1, RW2, the current actual steering angle, Mvmax is the maximum speed indicating the limit of the speed performance of the electric motor 21, and Δt is the execution time of the program of FIG. 2 (including the target steering angle limiting program of FIG. 6 ). Since it represents the interval, the upper limit value θr + Mvmax · Δ
t and the lower limit value θr−Mvmax · Δt indicate both the positive and negative limit steering angles at which the left and right rear wheels RW1 and RW2 can be steered by the execution of the next program in view of the speed performance of the electric motor 21. In the processing of these steps 310 to 316, the target rear wheel steering angle θr * determined and restricted by the processing of the previous steps 204, 302 to 308 and the current processing of steps 204, 302 to 308, and By dividing the difference from the limited target rear wheel steering angle θr * by the time interval Δt, a change speed dθr * / dt of the target rear wheel steering angle θr * is calculated, and the change speed dθr * / dt and the electric motor are calculated. The respective maximum velocities Mvmax and -Mvmax on both the positive and negative sides are compared.
Then, the change speed dθr * / dt is each maximum speed Mvma
x, if −Mvmax is exceeded in the positive and negative directions, the target rear wheel steering angle θr
* Is changed by executing the following equations 3 and 4, and the change speed dθr *
If / dt is between the maximum speeds Mvmax and -Mvmax, the target rear wheel steering angle θr * is kept as it is.

[0032]

[Equation 3] θr * = MIN [θr *, θr + Mvmax · Δt]

[0033]

[Equation 4] θr * = MAX [θr *, θr−Mvmax · Δt] The operator MIN [] in the above equation 3 selects the smaller value in parentheses, and the operator MAX [] in the above equation 4 Means to select the larger value in parentheses. The reason for using such an operator is that the target rear wheel steering angle θr * has already been set to the upper limit value θr + Mvmax ·
This is because it may be limited to the range of Δt and the lower limit value θr−Mvmax · Δt.

Next, the processing of step 318 to 324, the upper limit value θr + dθr / dt · Δt + 1/2 · Mamax · Δt 2 and the lower limit value in consideration with the target rear wheel steering angle [theta] r * acceleration performance of the electric motor 21 θrd + dθr / dt · Δt−1 / 2 · Mamax · Δt ² Here, θr and Δt are as described above, dθr / dt is the change speed of the current actual steering angle θr of the left and right rear wheels RW1 and RW2, and Mamax is the maximum acceleration that indicates the limit of the acceleration performance of the electric motor 21. Therefore, the upper limit value θr + d
θr / dt · Δt + 1/ 2 · Mamax · Δt 2 and the lower limit value θr + dθr / d
t · Δt−1 / 2 · Mamax · Δt ² is determined by the acceleration performance of the electric motor 21 by the execution of the next program.
1, the limit steering angles on both the positive and negative sides capable of steering RW2. In these steps 318 to 324, the target rear wheel steering angular velocity dθr * / dt calculated in the previous step 310 and the target rear wheel steering angular velocity dθr * / dt calculated in the current step 310 are executed. Is divided by the time interval Δt to obtain the acceleration d ² θ of the target rear wheel steering angle θr *.
r * / dt ² and calculate the same acceleration d ² θr * / dt ² and electric motor 21
The maximum accelerations Mamax and -Mamax on both the positive and negative sides are compared. If the acceleration d ² θr * / dt ² exceeds each of the maximum accelerations Mamax and −Mamax in the positive and negative directions, the target rear wheel steering angle θr * is changed by executing the following equations 5 and 6, and the acceleration d ² θr If * / dt ² is between the maximum accelerations Mamax and −Mamax, the target rear wheel steering angle θr * is kept as it is.

[0035]

[Equation 5] θr * = MIN [θr *, θr + dθr / dt · Δt + 1/2
・ Mamax ・ Δt ² ]

[0036]

Equation 6 θr * = MAX [θr *, θr + dθr / dt · Δt−1 / 2
• Mamax · Δt ² ] The operator MIN [] and the operator MA in the above Expressions 5 and 6
X [] is as described above, and also in this case, step 3
02 to 308 or the processing of steps 310 to 316, the target rear wheel steering angle θr * has already become the upper limit value θr + dθr / dt · Δt + 1.
/ 2 · Mamax · Δt ² and lower limit value θr + dθr / dt · Δt−1 / 2 ·
Consideration is given to the possibility of being restricted to the range of Mamax · Δt ² .

When the execution of the target steering angle limiting routine in step 208 (FIG. 5) is completed, in step 210,
Similarly to the above equation 2, by executing the calculation of the following equation 7 using the transfer function G (s) representing the response of the electric motor 21, the simulation value θr of the target rear wheel steering angle θr * by the electric motor 21 is obtained.
# Calculate

[0038]

(Equation 7)

After the processing of the step 210, in order to determine the abnormality of the steering system such as the electric motor 21, step 212 is executed.
The absolute value | θr of the difference between the calculated simulated value θr # and the detected actual steering angles θr of the left and right rear wheels RW1 and RW2.
It is determined whether or not # −θr | is less than a small predetermined value A, and at step 214 simulated value θr #
Absolute value of the difference | dθ between the differential value dθr # / dt of the actual steering angle θr of the left and right rear wheels RW1 and RW2 (change speed) dθr / dt.
It is determined whether or not r # / dt−dθr / dt | is smaller than a small predetermined value B. In these determinations, the absolute value | θr # −
θr | is smaller than the predetermined value A and the absolute value | dθr # / dt−dθr / dt
If | is less than the predetermined value B, both steps 212 and 214
In step 216, the execution of the program is temporarily terminated. Then, after a lapse of a predetermined time, the execution of the program is started again from step 200, and the left and right rear wheels RW1, RW2 are steered to the target rear wheel steering angle θr *.

On the other hand, the absolute value | θr # −θr | is greater than or equal to a predetermined value A or the absolute value | dθr # / dt−dθr / dt | is greater than or equal to a predetermined value B due to an abnormality in the steering system such as the electric motor 21. Then, the program proceeds to steps 218 and 220 by the determination processing of steps 212 and 214. Step 2
Steps 18 and 220 are performed in step 13 of FIG.
2 and 134.
8, 220, the warning lamp 37 is turned on, and the left and right rear wheels RW1, RW2 are controlled to return to the neutral position. After the processing of steps 218 and 220, step 2
Execution of the subsequent program is stopped by the process of 22, and thereafter, the steering control of the left and right rear wheels RW1, RW2 is stopped.

As described above, according to this modification, the target rear wheel steering angle θr * of the left and right rear wheels RW1 and RW2 is calculated by the processing of step 204 according to the running state of the vehicle. The target rear wheel steering angle θr * calculated by the processing of the target steering angle restriction routine is limited to a predetermined range. Specifically, the target rear wheel steering angle θ is obtained by the processing of steps 302 to 308 of the target steering angle restriction routine of FIG.
r * is limited to a change range corresponding to the maximum steering angle θrmax of the left and right rear wheels RW1, RW2, and the target rear wheel steering angle θr * is an upper limit based on the limit of the speed performance of the electric motor 21 by the processing of steps 310 to 316. θr + Mvmax · Δt and lower limit value θr
−Mvmax ・ Δt, and the range from step 318 to
324, the target rear wheel steering angle θr * is
Upper limit value θr + dθr / dt · Δt based on the limit of acceleration performance of 1
+ 1/2 · Mamax · Δt ² and lower limit value θrd + dθr / dt · Δt−1 /
It is limited to the range of 2 · Mamax · Δt ² .

The target rear wheel steering angle θr * limited in accordance with the operation performance of the electric motor 21 as described above is determined by the processing of step 210 by further considering the response performance of the electric motor 21 by the target rear wheel It is converted into a simulated value θr # of the steering angle θr *. Then, steps 212 and 21
The absolute value | θr # −θr of the difference between the limited and converted simulated value θr # and the actual rear wheel steering angle θr by the process of FIG.
And the absolute value | dθr # / dt−dθr / dt | of the difference between the differential value dθr # / dt of the simulated θr # and the differential value (change speed) dθr / dt of the actual rear wheel steering angle θr. Since the abnormality of the steering system such as the electric motor 21 is determined, the abnormality of the steering system is determined based on the simulated value θr # and the actual steering angles θr of the rear wheels RW1 and RW2. Even if * is set to a value equal to or greater than the response performance and operating performance of the electric motor 21, the above determination is performed within the range of the response performance and operating performance, and the determination is performed with high accuracy.

B. Second Modification The second modification is a modification of the target steering angle restriction routine of the first modification. The modified target steering angle limiting routine is shown in detail in the flowchart of FIG.
The microcomputer 35 starts execution of the same routine in step 400, and in step 402, the left and right rear wheels RW
1, the rotational speed Mv (= dθr / dt) of the electric motor 21 is calculated by differentiating the actual steering angle θr of RW2. next,
In step 404, the maximum acceleration Ma of the electric motor 21 corresponding to the absolute value | Mv | is determined by referring to a table (FIG. 8) provided in the microcomputer 35 based on the absolute value | Mv | of the rotational speed Mv. To determine. This table is determined in advance by actual measurement results based on the rotation speed-acceleration (torque) characteristics of the electric motor 21.
The maximum acceleration Ma indicating the limit of the electric motor 21 corresponding to the rotation speed Mv is shown.

After the determination of the maximum acceleration Ma, step 4
At 06 and 408, the upper limit value θrmax and the lower limit value θrmin of the target rear wheel steering angle θr * are calculated by executing the calculations of the following equations 8 and 9.

[0045]

[Equation 8] θrmax = θr + Mv · Δt + 1/2 · Ma · Δt ²

[0046]

Equation 9] Shitarmin = Since θr + Mv · Δt-1/ 2 · Ma · Δt 2 also Delta] t in the number 8,9 is the time interval in which the program as in the above embodiment is performed, the upper limit value rmax and the lower limit value θrmin indicates the positive and negative limit steering angles at which the left and right rear wheels RW1, RW2 can be steered by the execution of the next program in light of the acceleration performance of the electric motor 21.

After the processing in steps 406 and 408, in steps 410 and 412, as shown in FIG.
Target rear wheel steering angle θ determined by the process of step 204 of FIG.
It is determined whether or not r * is between the upper limit value θrmax and the lower limit value θrmin. The target rear wheel steering angle θr * is the upper limit value θrmax and the lower limit value θrm
If it is between in, in steps 410 and 412, “Y
ES ”, and the target steering angle limiting routine is terminated in step 418 while the target rear wheel steering angle θr * is maintained at the determined value. If the target rear wheel steering angle θr * exceeds the upper limit θrmax in the forward direction, “NO” is determined in step 410 and the target rear wheel steering angle θr * is determined by the processing in step 414.
To the upper limit value θrmax. If the target rear wheel steering angle θr * exceeds the lower limit value θrmin in the negative direction, “NO” is determined in step 412, and the target rear wheel steering angle θr * is changed to the lower limit value θrmin by the process of step 414. .

Then, similarly to the above embodiment and the first modification, the limited target rear wheel steering angle θr * is
Is converted into a simulated value θr # of the target rear wheel steering angle θr * by the motor 21 in consideration of the response performance of the motor 21, and the converted simulated value θr # and the actual steering angle θr of the rear wheels RW1, RW2.
, The abnormality of the steering system is determined, so that the determination can be accurately performed.

C. Third Modified Example The third modified example is also a modification of the target steering angle restriction routine of the first modified example. The changed target steering angle limiting routine is shown in detail in the flowchart of FIG.
The microcomputer 35 starts the execution of this routine in step 500, and in step 502, the left and right rear wheels RW
1 and RW2 to calculate the rotational speed Mv (= dθr / dt) of the electric motor 21 by differentiating the actual steering angle θr, and in step 504, differentiate the rotational speed Mv to obtain the rotational acceleration Ma of the electric motor 21. Is calculated. Next, in step 506, based on the rotation speed Mv and the rotation acceleration Ma, the operation state of the electric motor 21 is determined with reference to a speed table (FIG. 10) and an acceleration table (FIG. 11) provided in the microcomputer 35. I do. The speed table shows actual measurement results of speed changes with respect to time corresponding to the following operation states S1 to S6 of the electric motor 21, and the acceleration table shows each operation state S1 to S6 of the motor 21.
2 shows the measurement results of the change in acceleration with respect to the time corresponding to each.

The operation state S1 shows a state in which the electric motor 21 rotating at the maximum speed in the forward direction is decelerated at the maximum deceleration until the rotation of the motor 21 stops. The operating state S2 indicates a state in which the electric motor 21 that has stopped rotating starts rotating in the forward direction at the maximum acceleration and the rotation of the motor 21 reaches the maximum speed in the forward direction. The operating state S3 indicates a state in which the electric motor 21 that has stopped rotating starts rotating in the negative direction at the maximum acceleration and the rotation of the motor 21 reaches the maximum speed in the negative direction. The operating state S4 indicates a state in which the electric motor 21 rotating at the maximum speed in the negative direction is decelerated at the maximum deceleration until the rotation of the motor 21 stops. The operating state S5 indicates a state in which the electric motor 21 continues to rotate in the forward direction at the maximum speed. The operating state S6 indicates a state in which the electric motor 21 continues to rotate in the negative direction at the maximum speed. As described above, the operating states S1 to S6 enumerate all cases in which the electric motor 21 operates, and the combinations of the positive and negative and zero of the rotational speed Mv and the rotational acceleration Ma indicate the operating states S1 to S6.
Therefore, the operation states S1 to S6 of the electric motor 21 are determined by the processing in step 506. For example,
If the rotation speed Mv and the rotation acceleration Ma are both positive, the electric motor 21 is determined to be in the operating state S2. If the rotation speed Mv is positive and the rotation acceleration Ma is zero, the electric motor 21 is determined to be in the operating state S5. .

Next, referring to the speed table (FIG. 10) based on the determined operating state S1 (or S2 to S6) and the rotation speed Mv of the electric motor 21 in step 508,
The time tx corresponding to the rotation speed Mv is determined. Next, at step 510, the same determined operating state S1 (or
S2 to S6) and the determined time tx, and referring to the steering angle change table (FIG. 12) provided in the microcomputer 35, the steering angle change Δθ (tx) corresponding to the time tx and Program execution time interval Δ from time tx
The steering angle change amount Δθ (tx + Δt) after t is determined. FIG.
The steering angle change amount table shows each operation state of the electric motor 21.
The change amounts Δθ of the steering angles of the left and right rear wheels RW1 and RW2 corresponding to S1 to S6 are values measured from the start to the end of each operating state. Therefore, the steering angle change amount Δθ (tx)
Represents the steering angle changed from the start of the determined operating state S1 (or S2 to S6) to the present, and the steering angle change amount Δ
θ (tx + Δt) indicates the steering angle until the next target rear wheel steering angle θr * is determined. After the processing in step 510, the steering angle change amount Δθ determined in step 512
The maximum steering angle change amount Δθx that can be changed from the present time of the left and right rear wheels RW1 and RW2 to the execution of the next program is calculated by executing the calculation of the following equation 10 using (tx), Δθ (tx + Δt).

[0052]

After calculating this maximum steering angle change amount Δθx, it is determined in step 514 whether or not the maximum steering angle change amount Δθx is equal to or greater than “0”. If the maximum steering angle change amount Δθx is “0” or more,
In step 516, the target rear wheel steering angle θr * is changed to the current actual steering angle θ.
It is determined whether or not the upper limit value θr + Δθx obtained by adding the maximum steering angle change amount Δθx to r has been exceeded in the forward direction. In the determination,
If the target rear wheel steering angle θr * does not exceed the upper limit value θr + Δθx, “YES” is determined in step 516, and the process proceeds to step 522 while maintaining the target rear wheel steering angle θr * at the previous value. Thus, the execution of the target steering angle restriction routine is terminated. If the target rear wheel steering angle θr * exceeds the upper limit value θr + Δθx, “NO” is determined in step 516, and in step 520, the target rear wheel steering angle θr * is set to the upper limit value θr + Δθ.
Restrict to x.

On the other hand, if the maximum steering angle change Δθx is less than “0”, the target rear wheel steering angle θr * is obtained by adding the maximum steering angle change Δθx to the current actual rear wheel steering angle θr in step 518. It is determined whether or not the lower limit value θr + Δθx has been exceeded in the negative direction. In the determination, the target rear wheel steering angle θr * is equal to the lower limit value θr +
If Δθx is not exceeded, “YE” is determined in step 518.
S ", the execution of the target steering angle restriction routine is terminated in step 522 while the target rear wheel steering angle θr * is maintained at the previous value. If the target rear wheel steering angle θr * exceeds the lower limit value θr + Δθx, at step 518, “N
O ", and at step 520, the target rear wheel steering angle θ
r * is limited to a lower limit value θr + Δθx.

In the same manner as in the above embodiment, the first and second modified examples, the limited target rear wheel steering angle θr * is determined by the target rear wheel steering angle Is converted into a simulated value θr # of the angle θr *, and the abnormality of the steering system is determined based on the converted simulated value θr # and the actual steering angles θr of the rear wheels RW1 and RW2. Will be done well.

In the first to third modifications,
The target rear wheel steering angle θr * is limited to a predetermined range according to the speed performance and the acceleration performance of the electric motor 21 from the current actual rear wheel steering angle θr. The target rear wheel steering angle θr * determined at the time of executing the previous program may be limited to a predetermined range according to the speed performance and the acceleration performance of the electric motor 21. In this case, in the first modified example, steps 314 and 31 in FIG.
6, θr of Equations 3 to 6 executed at 6, 322, 324
Change it to *. Further, in the second modified example, θr of the equations (8) and (9) executed in steps 406 and 408 may be changed to θr *. Further, in the third modified example, the calculation of the upper limit value and the lower limit value θr + Δθx in the determination processing of steps 516 and 518 in FIG.
The upper limit value and the lower limit value calculated using r * may be changed to θr * + Δθx.

Further, in the above-described embodiment and each modified example,
The condition for judging a steering abnormality may be as follows. First, when the absolute value of the difference between the simulated value θr # of the target rear wheel steering angle θr * and the actual rear wheel steering angle θr is equal to or larger than a predetermined value, it is determined that the steering of the left and right rear wheels RW1 and RW2 is abnormal.

Even if it is not determined that the steering is abnormal, the absolute value of the difference between the change rate dθr # / dt of the simulated value θr # and the change rate dθr / dt of the actual rear wheel steering angle θr is not less than a predetermined value. At this time, it is determined that the steering of the left and right rear wheels RW1, RW2 is abnormal. However, in this case, the simulated value θr
The predetermined value which is the abnormality determination condition when the change direction of # is different from the change direction of the actual rear wheel steering angle θr is equal to or smaller than the predetermined value which is the abnormality determination condition when both change directions are different. Should be set to a value.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing a program executed by the microcomputer of FIG. 1;

FIG. 3A is a change characteristic diagram of a yaw rate proportional coefficient with respect to a vehicle speed, and FIG. 3B is a change characteristic diagram of a steering angle proportional coefficient with respect to a vehicle speed.

FIG. 4 is a graph showing an abnormal range and a normal range of rear wheel steering.

FIG. 5 is a flowchart corresponding to a program executed by the microcomputer of FIG. 1 according to a first modification;

FIG. 6 is a flowchart showing details of a target steering angle restriction routine of FIG. 5;

FIG. 7 is a flowchart illustrating details of a target steering angle restriction routine according to a second modification.

FIG. 8 is a graph showing a change characteristic of an acceleration with respect to a rotation speed of an electric motor.

FIG. 9 is a flowchart illustrating details of a target steering angle restriction routine according to a third modification.

FIG. 10 is a graph showing a time change characteristic of a rotation speed in each operation state of the electric motor.

FIG. 11 is a graph showing a time change characteristic of acceleration in each operation state of the electric motor.

FIG. 12 is a graph showing a time change characteristic of a steering angle change amount of a rear wheel in each operation state of the electric motor.

[Explanation of symbols]

FW1, FW2: front wheel, RW1, RW2: rear wheel, 10 ...
Front wheel steering mechanism, 20: rear wheel steering mechanism, 21: electric motor, 30: electric control device, 31: vehicle speed sensor, 32: yaw rate sensor, 33: front wheel steering angle sensor, 34: rear wheel steering angle sensor, 35: micro Computer, 36a, 36
b: drive circuit, 37: warning lamp.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hidemori Tsuka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Katsumi Fukaya 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kozo Fujita 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Shinichi Tagawa 2-1-1 Asahimachi, Kariya City, Aichi Prefecture Aisin Seiki Co., Ltd. (72) Inventor Katsuraya Hideki 2-1-1 Asahi-cho, Kariya-shi, Aichi Prefecture Aisin Seiki Co., Ltd. (72) Inventor Hiroshi Nakajima 2-1-1 Asahi-cho, Kariya-shi, Aichi Prefecture Aisin Seiki Co., Ltd. (72) Inventor Tsutomu Miyata Aichi 2-1-1 Asahi-machi, Kariya City Aisin Seiki Co., Ltd. (56) References JP-A-1-186474 (JP, A) JP-A-3 125669 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) B62D 6/00 B62D 7/14

Claims (3)

(57) [Claims] An actuator electrically driven to steer a rear wheel; target steering angle determining means for determining a steering target steering angle for a rear wheel according to a traveling state of a vehicle; wheel steering and angle sensor, steering target steering with the determined rear wheel by controlling the actuator in accordance with the actual steering angle that is the detection and steering target steering angle with the determined after detecting the actual steering angle of the wheels A steering control means for steering to an angle, a target steering angle conversion for converting the determined steering target steering angle into a monitoring target steering angle using a transfer function representing the response of the actuator. Means, and abnormality determination means for determining a steering abnormality based on the converted target steering angle for monitoring and the detected actual steering angle. 2. The method according to claim 1, wherein the abnormality determining means calculates a change rate of the converted monitoring target steering angle.
Calculating means; second calculating means for calculating the detected rate of change of the actual steering angle; and the direction of change of the monitoring target steering angle and the direction of change of the actual steering angle are the same, and the calculated actual steering angle is calculated. When the absolute value of the rate of change of the monitoring target steering angle is greater than the absolute value of the calculated rate of change of the monitoring target steering angle by a predetermined value or more, or the direction of change of the monitoring target steering angle and the direction of change of the actual steering angle are different and the An abnormality detection device for a rear wheel steering device, comprising: determination means for determining an abnormality in rear wheel steering when the calculated absolute value of the change rate of the actual steering angle is equal to or greater than a predetermined value. An actuator for steering the rear wheels 3. A is electrically driven, the target steering angle determining means for determining a steering eyes <br/> target steering angle of the rear wheels according to the running state of the vehicle, after wheel steering and angle sensor, steering target steering with the determined rear wheel by controlling the actuator in accordance with the actual steering angle that is the detection and steering target steering angle with the determined after detecting the actual steering angle of the wheels A steering control means for steering to an angle, wherein the determined target steering angle for steering is limited to a predetermined range according to the operation capability of the actuator, and the target is set as a target steering angle for monitoring. Abnormality detection of a rear wheel steering device, comprising: steering angle restriction means; and abnormality determination means for determining a steering abnormality based on the limited monitoring target steering angle and the detected actual steering angle. apparatus.