JPH0761790B2 - Front and rear wheel steering vehicle rear wheel steering control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a front and rear wheel steering vehicle including a front wheel steering mechanism and a rear wheel steering mechanism, and more particularly to a vehicle traveling state related to acceleration of the vehicle during turning. The present invention relates to a rear wheel steering control device for controlling a rear wheel steering mechanism so as to change a rear wheel steering angle by a predetermined angle in response to the change of

[Prior art]

Conventionally, this type of control device is provided with a front wheel steering angle sensor for detecting a front wheel steering angle and an acceleration sensor for detecting a running acceleration of a vehicle, as disclosed in Japanese Patent Laid-Open No. 57-60974. Based on the above, the acceleration of the vehicle during turning is detected, and if the vehicle is a rear wheel drive type (or front wheel drive type) vehicle, the rear wheel is in phase (or in reverse phase) with respect to the front wheel when the acceleration is detected. ) Steering by a predetermined amount and the rear wheels (or front wheels) that are the driving wheels as the vehicle accelerates while turning.
The vehicle is prevented from spinning (or drifting out) caused by slipping.

[Problems to be solved by the invention]

However, in the above-mentioned conventional apparatus, when acceleration of the vehicle during turning is detected, the rear wheels are steered by a predetermined amount at the time of detection, and as a result, the rear wheel steering angle rapidly changes by the predetermined amount. Therefore, there is a problem that the running stability of the vehicle deteriorates in the process of this change. Also, when the vehicle is turned or accelerated is released and the detection is not performed, the rear wheels are steered by a predetermined amount in a direction opposite to the above in order to restore the rear wheel steering at the time when the detection is not performed, As a result, the steering angle of the rear wheels rapidly changes by the predetermined amount as described above, and in this case, the traveling stability of the vehicle deteriorates as in the case described above.

The present invention has been devised in view of the above problems, and an object of the present invention is to reduce the deterioration of the traveling stability of the vehicle by alleviating the change in the rear wheel steering angle due to the steering of the rear wheels. It is an object of the present invention to provide a rear wheel steering control device for preventing front and rear wheels.

[Means for Solving the Problems]

In order to achieve the above object, a structural feature of the present invention is that, as shown in FIG. 1, a front wheel steering mechanism 3 that steers front wheels 2 and a rear wheel 4 are steered according to rotation of a steering wheel 1. In a front and rear wheel steering vehicle including a rear wheel steering mechanism 5, a front wheel steering angle sensor 6 for detecting a front wheel steering angle, an acceleration sensor 7 for detecting a vehicle running acceleration, a vehicle speed sensor 7a for detecting a vehicle speed, A discriminating means 8a for discriminating whether or not the vehicle is in a turning acceleration state based on signals from the front wheel steering angle sensor 6 and the acceleration sensor 7, and a rear wheel when the discriminating means 8a discriminates that the vehicle is in a turning acceleration state. Steering angle is vehicle speed sensor 7a
The first calculation that sequentially calculates the control value for gradually changing the steering angle in small increments until it is changed by a predetermined angle irrelevant to the vehicle speed detected by After the means 8b and the determination means 8a determine that the vehicle is not in the turning acceleration state, the rear wheel steering angle changed by the predetermined angle is determined by the steering angle ratio depending on the vehicle speed detected by the vehicle speed sensor 7a. The control value for gradually changing the steering angle in small increments is sequentially calculated until it returns to the wheel steering angle, and then the rear wheel steering angle determined by the steering angle ratio depending on the vehicle speed detected by the vehicle speed sensor 7a. To the rear wheel steering mechanism 5, second calculating means 8c that keeps calculating the control values for steering the rear wheels, and control signals representing the respective control values calculated by the first calculating means 8b and the second calculating means 8c. Output sequentially and calculate first Providing output means 8d for steering control of the rear wheels 4 to the rear wheel steering angle corresponding to the control value calculated by the step 8b or the rear wheel steering angle corresponding to the control value calculated by the second calculating means 8c It is in.

[Action]

In the present invention configured as described above, the determining means 8a determines that the vehicle is in the turning acceleration state based on the front wheel steering angle detected by the front wheel steering angle sensor 6 and the traveling acceleration detected by the acceleration sensor 7. Then, the first calculating means 8b controls to gradually change the rear wheel steering angle by small angles until the rear wheel steering angle is changed by a predetermined angle irrelevant to the vehicle speed detected by the vehicle speed sensor 7a. The values are sequentially calculated, and thereafter the control value is maintained. Then, the output means 8d sequentially outputs a control signal representing the calculated control value to the rear wheel steering mechanism 5 to gradually steer the rear wheel 4 until it is changed by the predetermined angle. The mechanism 5 is controlled, and thereafter the steering of the rear wheels 4 is stopped. Therefore, when the vehicle is accelerated during turning, the rear wheels are gradually steered by a predetermined angle irrelevant to changes in the vehicle speed, and thereafter the same angle is maintained.

On the other hand, when it is determined by the determination means 8a that the vehicle is not in the turning acceleration state, the second calculation means 8c causes the second steering means 8c to change the rear wheel steering angle by a predetermined angle depending on the vehicle speed detected by the vehicle speed sensor 7a. The control value for gradually changing the steering angle in small increments is calculated sequentially until the steering angle returns to the rear wheel steering angle determined by the angular ratio, and then the steering angle ratio depends on the vehicle speed detected by the vehicle speed sensor 7a. The control value for steering the rear wheels is continuously calculated at the rear-wheel steering angle that is determined by the control. Then, the output means 8d sequentially outputs a control signal representing the calculated control value to the rear wheel steering mechanism 5 to steer the rear wheel 4 for a predetermined angle by the steering angle ratio depending on the vehicle speed. The rear wheel steering mechanism 5 is controlled so as to gradually return to the corner, and thereafter, the rear wheel steering mechanism 5 is controlled so that the rear wheels 4 are steered to the rear wheel steering angle determined by the steering angle ratio depending on the vehicle speed. Control. Therefore, when the turning acceleration state of the vehicle is released, the steering of the rear wheels by the predetermined angle is gradually returned to the rear wheel steering angle determined by the steering angle ratio depending on the vehicle speed.

[Effects of the Invention] As can be understood from the above description of the operation, when the vehicle is accelerated during turning and the rear wheels 4 are steered by a predetermined angle, and when the turning acceleration state of the vehicle is released, When the steering for a predetermined angle is returned to the rear wheel steering angle that is determined by the steering angle ratio that depends on the vehicle speed, the change in the rear wheel steering angle is moderated and becomes slower. Deterioration of the traveling stability of the vehicle due to this is prevented, and the traveling stability of the vehicle is improved.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. Second
The figure schematically shows a vehicle including a front wheel steering mechanism 20, a rear wheel steering mechanism 30, a rear wheel drive device 40, and an electric control device 50 for controlling the rear wheel steering mechanism 30.

The front wheel steering mechanism 20 includes a rack and pinion mechanism 21 and a pair of left and right relay rods connected to the rack portion of the mechanism 21.
22a and 22b are provided. Rack and pinion mechanism 21
The steering wheel 24 through the steering shaft 23 at its pinion portion.
The rotary motion of the steering wheel 24 is converted into the reciprocating motion of the relay rods 22a and 22b. The left and right relay rods 22a, 22b are respectively connected to the left and right front wheels 27a, 27b via the left and right tie rods 25a, 25b and the left and right knuckle arms 26a, 26b to steer the left and right front wheels 27a, 27b.

The rear wheel steering mechanism 30 includes a swing lever 32 for steering the left and right rear wheels 31a, 31b in conjunction with steering of the left and right front wheels 27a, 27b, and a linear actuator 33 for displacing a fulcrum 32a of the swing lever 32. And a relay rod 34 for interlocking the left and right rear wheels 31a, 31b. The oscillating lever 32 pivots a front connecting rod 35 connected to the left knuckle arm 26a to a force point 32b.
And an action point 32c pivotally attached to the rear connecting rod 36, and when the fulcrum 32a is between the force point 32b and the action point 32c, the action point 32c is displaced in the opposite direction to the force point 32b, and the fulcrum 32a is moved. Point of action 3
If it is on the opposite side of the force point 32b with respect to 2c, the point of action 32c is displaced in the same direction as the point of force 32b, and the fulcrum 32a becomes the point of action 32c.
When it is on the upper side, the action point 32c is not displaced, and the steering angle ratio is set by the ratio of the distance between the fulcrum 32a and the force point 32b based on the position of the fulcrum 32a and the distance between the fulcrum 32a and the action point 32c. I am trying to do it. The linear actuator 33 includes an actuator rod 33a connected to the fulcrum 32a, and the fulcrum 32a is displaced in the same direction by moving the actuator rod 33a in the lateral direction of the vehicle body. The relay rod 34 connects the left and right rear wheels 31a, 31b via the left and right tie rods 37a, 37b and the left and right knuckle arms 38a, 38b, respectively. A rear connecting rod 36 is connected to the left knuckle arm 38a, and rear wheels 31a and 31b are steered by the rear connecting rod 36 driven based on the swing of the swing lever 32.

The rear wheel drive device 40 is an accelerator pedal installed in the driver's seat.
41, an engine 42 arranged on the front side of the vehicle body, and a differential mechanism
It has 43 and. The driving force of the engine 42 controlled by the accelerator pedal 41 is transmitted to the differential mechanism 43 via a main drive shaft 44 connected between the engine 42 and the differential mechanism 43. This transmitted driving force is applied to the differential mechanism 43 and the left and right rear wheels 31a, 31b.
It is transmitted to the left and right rear wheels 31a, 31b via the left and right rear wheel drive shafts 45a, 45b which are respectively connected between the left and right rear wheels 31a, 31b.
Is driven based on the engine 42 output.

The electric control device 50 includes a vehicle speed sensor 51 that detects a vehicle speed V,
Depression amount sensor 52 for detecting the depression amount a of the accelerator pedal 41 and front wheel steering angle sensor 53 for detecting the front wheel steering angle θf.
And a microcomputer 54 that calculates a target steering angle ratio K based on the signals generated from these sensors 51, 52, 53 and outputs a control signal corresponding to this target steering angle ratio K, and this control signal A differential amplifier 55 that inputs and controls the linear actuator 33 is provided.

The vehicle speed sensor 51 picks up the rotation of the output shaft of the transmission and generates a pickup signal having a frequency proportional to the vehicle speed V. This pickup signal is converted into a rectangular wave signal by the waveform shaper 51a and supplied to the microcomputer 54. It The depression amount sensor 52 is a depression amount a of the accelerator pedal 41.
And an analog signal representing the detected stepping amount a is generated, and this analog signal is converted into a digital signal by an analog-digital converter (hereinafter referred to as A / D converter) 52a, and the microcomputer 54 as stepping amount data.
Is supplied to. The front wheel steering angle sensor 53 is the relay rod 22a,
An axial displacement amount of 22b or a rotational displacement amount of the steering shaft 23 is detected, and an analog signal representing a front wheel steering angle θf proportional to the detected displacement amount is generated. This analog signal is the A / D converter 53a. Is converted into a digital signal by and is supplied to the microcomputer 54 as front wheel steering angle data. In this case, the front wheel steering angle θf has a negative value corresponding to the leftward steering of the left and right front wheels 27a and 27b, and has a positive value corresponding to the rightward steering.

The microcomputer 54 is a read-only memory (hereinafter simply referred to as ROM) that stores a program corresponding to the flow chart shown in FIG. 3 and steering angle ratio pattern data for calculating the vehicle speed corresponding steering angle ratio Kv shown in FIG. 54a, a central processing unit (hereinafter simply referred to as CPU) 54b for executing this program, a writable memory (hereinafter simply referred to as RAM) 54c for temporarily storing data necessary for executing this program, and each sensor 51, Input / output interface (hereinafter simply referred to as I / O) for inputting signals supplied from 52, 53 5
4d, a bus 54e that connects the ROM 54a, the CPU 54b, the RAM 54c, and the I / O 54d in common. Further, the I / O 54d converts a digital signal representing the target steering angle ratio K output from the microcomputer 54 into an analog signal and supplies it to the non-inverting input of the differential amplifier 55 (hereinafter simply referred to as a digital analog converter).
D / A converter) 55a is connected.

The differential amplifier 55 inputs to its inverting input an analog signal representing the displacement amount of the actuator rod 33a, that is, the position sensor 56 for detecting the position of the fulcrum 32a, and supplies it to its non-inverting input and inverting input. The difference signal between the two signals is output to the linear actuator 33, and the linear actuator 33 is controlled so that the steering angle ratio set by the swing lever 32 becomes equal to the target steering angle ratio K.

The operation of the above embodiment configured as described above will be described with reference to the flowchart of FIG. First, the outline of the operation will be described. When the driver closes an ignition switch (not shown) to start the vehicle, the CPU 54b
Starts the execution of the program in step 60, and in step 61 stores the vehicle speed corresponding steering angle ratio data stored in the RAM 54c and representing the vehicle speed corresponding steering angle Ku, to the vehicle speed corresponding steering angle ratio − when the vehicle speed V is zero. RAM54c with initial setting to Ko (Fig. 4)
The flag FLG stored in the memory and indicating the setting state of the target steering angle ratio K
Is initialized to “0”. The flag FLG is "0".
Indicates that the target steering angle ratio K is set and controlled to the vehicle speed corresponding steering angle ratio Kv, and the target steering angle ratio K is set to "1" when the target speed steering angle ratio Kv is set to the vehicle speed corresponding steering angle ratio Kv.
Represents a state of being set and controlled to a correction value Kv + α, which is a correction value obtained by correcting Further, the predetermined value α is set to a positive value that prevents the rear-wheel drive vehicle from spinning during turning due to the slip of the left and right rear wheels 31a and 31b that are drive wheels.

After the initial setting of step 61, the CPU 54b calculates the vehicle speed V based on the rectangular wave signal input from the waveform shaper 51a through the I / O 54d in step 62, and obtains data representing the calculated vehicle speed V. It is stored in the RAM 54c as vehicle speed data. next,
The CPU 54b executes the I / O 54 from the A / D converters 52a and 53a in steps 62 and 63.
The depression amount data indicating the depression amount a of the accelerator pedal 41 and the front wheel steering angle data indicating the front wheel steering angle θf are read via d, and the read depression amount data and the front wheel steering angle data are stored in the RAM 54c. Step 62 like this
After storing various data by the processing of ~ 64, the CPU 54b is related to the acceleration of the vehicle during turning based on the stored depression amount data and front wheel steering angle data in the "vehicle traveling state determination routine" including steps 70 to 72. The vehicle traveling state is determined, and based on the determination result, the target steering angle ratio K is set to the vehicle speed corresponding steering angle ratio Kv based on the stored vehicle speed data in the "vehicle speed corresponding steering angle ratio setting routine" including steps 80 to 84. Although the setting is controlled, or the target steering angle ratio K is set to the vehicle speed corresponding steering angle ratio in the "corrected steering angle ratio setting routine" including steps 90 to 92.
The correction value Kv + α of Kv is set and controlled, and the program proceeds to step 65.

In step 65, the CPU 54b outputs a digital signal representing the target steering angle ratio K to the D / A converter 55a via the I / O 54d, and D / A converter 55a
The A converter 55a converts this digital signal into an analog signal and supplies it to the differential amplifier 55.
By controlling the linear actuator 33 in cooperation with 56,
The fulcrum 32a is displaced so that the set steering angle ratio of the rocking lever 32 becomes the target steering angle ratio K. After the processing of step 65, the CPU 54b returns the program to step 62, and thereafter steps 62 to 64.
Processing, a "vehicle traveling state determination routine" processing, a "vehicle speed corresponding steering angle ratio setting routine" processing, a "corrected steering angle ratio setting routine" processing, and a circulation processing consisting of the processing of step 65 is continuously executed, The target steering angle ratio K is calculated according to the vehicle traveling state and the vehicle speed V, and the set steering angle ratio K of the rocking lever 32 is set to the target steering angle ratio K. The digital signal indicating the target steering angle ratio K output from the CPU 54b is stored in the I / O 54d until a new digital signal is output from the CPU 54b. In this state, when the left and right front wheels 27a, 27b are steered in response to the turning of the steering wheel 24, the left and right rear wheels 31
The a and 31b are steered in anti-phase or in-phase with the left and right front wheels 27a and 27b in accordance with the set steering angle ratio of the swing lever 32.

Next, a "vehicle traveling state determination routine" consisting of steps 70 to 72, a "vehicle speed corresponding steering angle ratio setting routine" consisting of steps 80 to 84, and a step 90 which are executed during the circulation processing.
The processing of the "corrected steering angle ratio setting routine" consisting of ~ 92 will be described in detail for each vehicle traveling state.

(1) After starting the vehicle, the flag FLG is set to the above step 61.
The case where the vehicle is still set to “0” by the initial setting and the vehicle is not in the acceleration state will be described. In this case, after updating the various data in steps 62 to 64, the CPU 54b
In step 70, the acceleration of the vehicle is not large, that is, the depression amount a of the accelerator pedal 41 is small,
It is determined that "NO", that is, the depression amount a is not larger than the predetermined value ao, and it is determined to be "NO" based on the flag FLG being "0" in step 71, and the program is set to " Car speed corresponding steering angle ratio setting routine ". In addition,
The predetermined value ao is set to a value corresponding to a depression amount of about 70% of the total depression amount of the accelerator pedal 41, for example.

In this "vehicle speed corresponding steering angle ratio setting routine", CPU5
Step 4b is step 80, in which the vehicle speed-corresponding steering angle ratio Kv (FIG. 4 is determined based on the vehicle speed data representing the vehicle speed V stored in the RAM 54c by the processing of step 62 and the steering angle ratio pattern data stored in the ROM 54a. ) Is calculated, and the data representing the calculated steering speed ratio Kv corresponding to the vehicle speed is stored as RAM 54c in the RAM 54c.
Remember. After the processing of step 80, the CPU 54b executes step 81.
The absolute value | Kv-K of the difference Kv-K between the calculated vehicle-speed corresponding steering angle ratio Kv and the target steering angle ratio K indicated by the target steering angle ratio data stored in the RAM 54c by the previous circulation processing. It is determined whether or not | is smaller than the predetermined value β. The predetermined value β indicates the maximum change range of the target steering angle ratio K, and when the vehicle is traveling normally, the steering angle ratio corresponding to the vehicle speed is changed by the change of the vehicle speed V within the time required for the circulation processing. It is set to a value slightly larger than the amount by which Kv changes. Further, in relation to the predetermined value α for correcting the vehicle speed corresponding steering angle ratio Kv, the predetermined value β has a relationship of β <α. Since the predetermined value β is set to such a value, as long as the vehicle is traveling normally, the determination in step 81 is “YES”, that is, the absolute value | Kv−K | is less than β. The CPU 54b updates the target steering angle ratio data stored in the RAM 54c and representing the target steering angle ratio K in step 82 with the calculated vehicle speed corresponding steering angle ratio Kv, and in step 84, the flag FLG.
To the same state as before, and the program proceeds to step 65. In step 65, as described above, the digital signal representing the target steering angle ratio K is converted into the D / A converter 55a.
Is output to the target steering angle ratio K, that is, the steering angle ratio Kv (FIG. 4) corresponding to the vehicle speed. As a result, in such a vehicle traveling state, when the vehicle speed V is low, the left and right rear wheels 31a, 31b become the left and right front wheels 27a, 27b.
On the other hand, the left and right rear wheels 31a, 31b are steered in phase with respect to the left and right front wheels 27a, 27b as the vehicle speed V increases.

In addition, the vehicle speed-corresponding steering angle ratio Kv changes abruptly as the vehicle speed V suddenly drops due to sudden braking of the vehicle, and the absolute value | Kv−K |
Becomes equal to or larger than the predetermined value β, the CPU 54b determines “NO” in the above step 81, and updates the target steering angle ratio data representing the target steering angle ratio K in the following step (Equation 1).

In the above (Equation 1), the value K on the left side is the current step 83.
Represents the target steering angle ratio updated by the process
Represents the target rudder angle ratio before being updated, that is, the target rudder angle ratio set by the previous circulation processing. Therefore, the target rudder angle ratio K updated by the lump is m minutes of the absolute value | Kv−K | The value approaches 1 to the vehicle speed corresponding steering angle ratio Kv. The value m is set to such a value that the change (Kv-K) / m of the target steering angle ratio K does not deteriorate the running stability of the vehicle in relation to the update timing of the steering angle ratio K. . Then, the absolute value | Kv−K |
The target steering angle ratio K gradually approaches the vehicle speed corresponding steering angle ratio Kv by 1 / m. However, in this case, if the vehicle speed V changes, the vehicle speed corresponding steering angle ratio Kv by the processing of step 80 also changes accordingly. When the absolute value | Kv−K | becomes less than the predetermined value β as a result of the target steering angle ratio K approaching the vehicle speed corresponding steering angle ratio Kv in this way, it is determined as “YES” in step 81 as described above. The target steering angle ratio Kv is set to the vehicle speed corresponding steering angle ratio Kv. In this way, when the vehicle speed corresponding steering angle ratio Kv changes abruptly as the vehicle speed V rapidly drops, the target steering angle ratio K gradually approaches the vehicle speed corresponding steering angle ratio Kv by (Kv-K) / m. Rear wheels 31a, 31b
The steering angle does not change suddenly and the running stability of the vehicle becomes good.

(2) Next, a case will be described in which the accelerator pedal 41 of the vehicle that is traveling substantially straight in the state of (1) is deeply depressed to accelerate the vehicle. In this case, after updating the various data in steps 62 to 64, the CPU 54b
In step 72, it is determined that the vehicle acceleration is large, that is, the stepping amount a is large, and therefore "YES", that is, the stepping amount a is larger than the predetermined value ao.
It is determined whether or not the absolute value | θf | of f is greater than or equal to the predetermined angle θfo. The predetermined angle θfo is set to a value of about 5 degrees. In this case, the vehicle is in a straight-ahead state, so CP
U54b is “NO” in the same step 72, that is, the front wheel steering angle θf
The absolute value of | θf |
The program advances to the "vehicle speed-corresponding steering angle ratio setting routine". In this "vehicle speed-corresponding steering angle ratio setting routine", the target steering angle ratio K is set and controlled in the same manner as in the case (1), so that the left and right rear wheels 31a, 31b are also steered in the same manner as in the case (1). To be done.

(3) Next, a case where the vehicle is in an accelerating state and in a turning state will be described. In this case, steps 63, 64
Since the absolute value │θf│ of the depression amount a and the front wheel steering angle θf set in step 6 are large, the CPU 54b returns "YES" in step 70.
That is, it is determined that the depression amount a is larger than the predetermined value ao, and it is determined in step 72 that the absolute value | θf | of the front wheel steering angle θf is equal to or larger than the predetermined angle θfo, and the program is set to the “corrected steering angle ratio setting routine”. Proceed to.

In this "corrected steering angle ratio setting routine", the target steering angle ratio K and the vehicle speed corresponding steering angle ratio Kv are initially set to the same value by the processing of steps 80 and 82 of the previous circulation processing. In step 90, the CPU 54b determines “YE based on K <Kv + α”.
Then, in step 91, the target steering angle ratio data representing the target steering angle ratio K is updated by the following (formula 2).

Similarly to the case of the above-mentioned (Formula 1), the above-mentioned (Formula 2) also increases the target steering angle ratio K by α / n for each circulation process.
The value n is the same as the value m in the above (Equation 1), and the change α / n of the target steering angle ratio K does not deteriorate the running stability of the vehicle in relation to the update timing of the steering angle ratio K. However, the same value n is slightly smaller than m in order to steer the left and right rear wheels 31a, 31b in the in-phase direction with respect to the left and right front wheels 27a, 27b faster than in the case of (Equation 1) above. (N <m) is set. After the processing of step 91, the CPU 54b sets the flag FLG to "1" in step 92, outputs the digital signal representing the target steering angle ratio K to the D / A converter 55a in step 65,
Return the program to step 62.

Then, as long as the vehicle is in the accelerating state and the turning state as described above, the CPU 54b executes the steps 70 and 72.
Is determined to be YES, and the target steering angle ratio K is increased by α / n for each circulation processing by the processing of steps 90 and 91 similar to the above. When the target steering angle ratio K becomes K ≧ Kv + α during this circulation processing, the CPU 54b determines “NO” in step 90, does not execute the processing of step 91, and advances the program to step 92. Through the processing of these steps 90 to 92, the target steering angle ratio K gradually increases from the vehicle speed corresponding steering angle ratio Kv before executing the "correction steering angle ratio setting routine" to the correction value Kv + α by α / n. In this case, the vehicle speed corresponding steering angle ratio Kv is maintained at the same value even if the vehicle speed V changes due to non-execution of step 80. As a result, if the vehicle in turn is accelerating,
Since the left and right rear wheels 31a, 31b are steered by a steering angle ratio corresponding to a predetermined value α in the in-phase direction with respect to the steering direction of the left and right front wheels 27a, 27b rather than the steering angle set by the vehicle speed corresponding steering angle ratio Kv, The left and right rear wheels 31a, which are the driving wheels, as the vehicle inside accelerates,
The spin of the vehicle caused by the slip of 31b is better prevented. Further, since the steering correction of the left and right rear wheels 31a and 31b is performed gradually by α / n, the change in the rear wheel steering angle due to the steering correction is alleviated and the running stability of the vehicle due to the sudden change in the rear wheel steering angle is reduced. Is better prevented.

(4) Next, a case where the acceleration of the vehicle is released from the state of the above (3) while the vehicle is turning will be described. In this case, the accelerator pedal 41
Since the stepping amount of is released and the stepping amount a set in step 63 becomes smaller, the CPU 54b sets "N" in step 70.
It is determined that "O", that is, the depression amount a is not larger than the predetermined value ao, and it is determined at step 71 whether the flag FLG is "1". In this determination, as described in (3) above, the flag FLG is set to "1" by the processing of step 92, so the CPU 54b determines "TES" and advances the program to step 72. In this case, since the vehicle is still turning and the absolute value | θf | of the front wheel steering angle θf is a large value, the CPU 54b determines “YES” in step 72, that is, the absolute value | θf | is equal to or greater than the predetermined angle θfo. Since the program proceeds to the “corrected steering angle ratio setting routine” consisting of steps 90 to 92, the steering angle ratio of the vehicle is set in the same way as in the case of (3) above, and the right and left rear Ring 31
The steering wheels a and 31b are also steered in the same manner as in the above case (3). As a result, even if the acceleration of the vehicle being turned is released, the steering angle ratio is not changed, and if the front wheel steering angle is not changed, the rear wheel steering angle is not changed, and the vehicle being turned is It is possible to continue turning while maintaining the same state, which improves running stability during turning.

(5) Next, when the vehicle is further returned to the substantially straight traveling state from the state where the acceleration of the vehicle is released in the above (4), or the vehicle is brought to the substantially straight traveling state from the turning acceleration state of the above (3). The case where it is restored will be described. In this case, in the "vehicle traveling state determination routine", the CPU 54b executes the step 7
After the processing of 0, 71 or the processing of step 71, in step 72, the absolute value of the front wheel steering angle θf set in step 64 |
Based on the fact that θf | is small, “NO”, that is, the same absolute value |
It is determined that θf | is not equal to or greater than the predetermined value θfo, and the program proceeds to the “vehicle speed-corresponding steering angle ratio setting routine”. In this "vehicle speed-corresponding steering angle ratio setting routine", the CPU 54b performs the same processing as in the case of (1) above to set the steering angle ratio of the vehicle to the target steering angle ratio K, that is, the vehicle speed corresponding steering angle ratio Kv. . In this case, normally, the target steering angle ratio K is a value obtained by first adding a predetermined value α to the vehicle speed corresponding steering angle ratio Kv by the processing of the "steering angle ratio correction routine" that has been executed so far from Steps 90 to 92. Is set to "NO" in the judgment at step 81.
That is, the relationship between the target steering angle ratio K and the vehicle speed-corresponding steering angle ratio is | Kv−K
It is determined that | <β is not satisfied. The result is the target steering angle ratio K
Is changed by (Kv-K) / m for each circulation process by the process of step 83 and gradually approaches the vehicle speed corresponding steering angle ratio Kv.
As a result, the rear wheel steering angle does not suddenly change as described above, and the running stability of the vehicle becomes good. At this time, the target steering angle ratio K set by the "corrected steering angle ratio setting routine" including the vehicle speed corresponding steering angle ratio Kv and steps 90 to 92 is about 1 by chance. If so, the CPU 54b determines “YES” in step 81, and sets the target steering angle ratio K to the vehicle speed corresponding steering angle ratio Kv by the processing in step 82.

Further, in this "vehicle speed-corresponding steering angle ratio setting routine", after the processing in steps 82 and 83, the flag FLG is set in step 84.
Is changed to "0", the flag FLG is returned to the initial state in this state.

As can be understood from the above description of the operation, according to the above-described embodiment, the vehicle traveling state related to the acceleration of the vehicle while turning is determined by the process of the "vehicle traveling state determination routine" including steps 70 to 72. If the steering angle ratio Kv corresponding to the vehicle speed is corrected or the correction is released according to the determination,
Since the steering angle ratio is gradually corrected by the processing of the "vehicle speed corresponding steering angle ratio setting routine" consisting of steps 80 to 84 or the "corrected steering angle ratio setting routine" consisting of steps 90 to 92,
The gradual change of the steering angle ratio prevents the rear wheel steering angle from changing suddenly, and the running stability of the vehicle becomes good.

In the above embodiment, the running acceleration of the vehicle is detected by the depression amount sensor 52 that generates a signal according to the depression amount of the accelerator pedal 41.
The acceleration sensor may be mounted on the vehicle body to detect the acceleration of the vehicle body by utilizing inertia. Alternatively, the acceleration may be calculated by differentiating the detected vehicle speed V by the program processing of the microcomputer 54.

Further, in the above-described embodiment, in order to gradually change the steering angle ratio set by the swing lever 32, the calculation processing of steps 83 and 91 is performed to reduce the change in the target steering angle ratio K. Circuit is microcomputer 54 and D / A converter 55a
May be provided between the D / A converter 55a and the differential amplifier 55 to reduce the level change of the control signal supplied to the differential amplifier 55. In this case, the microcomputer 54 need only output a digital signal representing the target steering angle ratio K to be finally set by the swing lever 32.

Further, in the above embodiment, the case where the present invention is applied to the rear wheel drive type vehicle has been described, but the present invention is also applied to the front wheel drive type vehicle. However, in a front wheel drive type vehicle, the slip ratios of the left and right front wheels, which are the drive wheels, become high during acceleration, and the vehicle during turning tends to understeer and drift out. Therefore, it is necessary to set the predetermined value α for correcting the vehicle speed corresponding steering angle ratio Kv in the processing of steps 90 and 91 (FIG. 3) to a negative value, that is, -α. As a result, when the vehicle that is turning is accelerated, the left and right rear wheels are corrected in opposite phases to the left and right front wheels, so drift-out during turning acceleration in a front-wheel drive vehicle is prevented. In this case as well, the change in the steering angle ratio is naturally relieved when the steering angle ratio is corrected or restored.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the configuration of the invention described in the claims, and FIG. 2 is a schematic diagram of a vehicle showing an embodiment of the present invention.
FIG. 3 is a flowchart corresponding to the program executed by the microcomputer of FIG. 2, and FIG. 4 is a characteristic graph showing the steering angle ratio with respect to the vehicle speed. Explanation of code 20 …… Front wheel steering mechanism, 24 …… Steering wheel, 27a, 27b…
… Front wheels, 30 …… Rear wheel steering mechanism, 31a, 31b …… Rear wheels, 32…
… Rotating lever, 33 …… Linear actuator, 40 …… Rear wheel drive, 41 …… Accelerator pedal, 42 …… Engine,
50 ... Electric control device, 51 ... Vehicle speed sensor, 52 ... Stepping amount sensor, 53 ... Front wheel steering angle sensor, 54 ... Microcomputer, 55 ... Differential amplifier, 56 ... Position sensor.

Claims (1)

[Claims] 1. A front-wheel steering angle for detecting a front-wheel steering angle in a front-rear wheel steering vehicle comprising a front-wheel steering mechanism for steering front wheels in response to turning of a steering wheel and a rear-wheel steering mechanism for steering rear wheels. A sensor, an acceleration sensor that detects the vehicle running acceleration, a vehicle speed sensor that detects the vehicle speed, and a determination that determines whether the vehicle is in a turning acceleration state based on signals from the front wheel steering angle sensor and the acceleration sensor. And the rear wheel steering angle when the vehicle is determined to be in the turning acceleration state by the determining means until the rear wheel steering angle is changed by a predetermined angle irrelevant to the vehicle speed detected by the vehicle speed sensor. The first control means for sequentially calculating the control value for gradually changing the control value, and thereafter maintaining the same control value; and when the determination means determines that the vehicle is not in the turning acceleration state. A control value for gradually changing the steering angle by a small angle until the rear wheel steering angle changed by a predetermined angle returns to the rear wheel steering angle determined by the steering angle ratio depending on the vehicle speed detected by the vehicle speed sensor. The second calculation means for continuously calculating the control value for steering the rear wheels to the rear wheel steering angle determined by the steering angle ratio depending on the vehicle speed detected by the vehicle speed sensor, A control signal representing each control value calculated by the first calculation means and the second calculation means is sequentially output to the rear wheel steering mechanism, and the rear wheel steering angle corresponding to the control value calculated by the first calculation means. Or a rear wheel steering control device for a front and rear wheel steering vehicle, comprising: output means for steering and controlling the rear wheels at a rear wheel steering angle corresponding to the control value calculated by the second calculating means.