JPS62247980A - Rear wheel steering control device for front and rear wheel steering car - Google Patents

Abstract

PURPOSE:To ensure the running stability of a vehicle by relaxing the change in a rear wheel steering angle by means of an output means comprising an electric control device when the rear wheel is steered by a predetermined angle in accordance with the change in a vehicle running condition related with the acceleration of the vehicle during cornering. CONSTITUTION:Each of a front wheel 2 and a rear wheel 4 is steered by each of a front and a rear wheel steering mechanism 3 and 5 depending on the rotation of a steering handle 1. And the rear wheel steering mechanism 5 is controlled by an electric control device 8 in such a way that the rear wheel steering angle is changed by a predetermined angle in response to the change in a vehicle running condition related with the acceleration of a vehicle during cornering based on each signal from a front wheel steering angle sensor 6 and an acceleration sensor 7. In the aforementioned device, the electric control device 8 is composed of a means 8a which judges the vehicle running condition based on both a front wheel steering angle and the quantity of acceleration, and a means 8b which outputs a control signal for the rear wheel steering mechanism 5 so that a rear wheel steering angle is gradually changed to a predetermined angle in response to the change in a judged vehicle running condition.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a front and rear wheel steered vehicle equipped with a front wheel steering mechanism and a rear wheel steering mechanism, and particularly relates to vehicle running conditions related to acceleration of the vehicle during turning. The present invention relates to a rear wheel steering control device for a front and rear wheel steered vehicle that controls a rear wheel steering mechanism to change a rear wheel steering angle by a predetermined angle in response to a change in the rear wheel steering angle.

[Prior art]

Conventionally, this type of control device includes a front wheel steering angle sensor that detects the front wheel steering angle and an acceleration sensor that detects the running acceleration of the vehicle, as shown in Japanese Patent Application Laid-open No. 57-60974, and the outputs of both of the sensors are If the vehicle is a rear-wheel drive (or front-wheel drive) vehicle, the rear wheels are in phase (or out of phase) with respect to the front wheels when the acceleration is detected. ) to prevent the vehicle from spinning (or drifting out) caused by the rear (or front) driving wheels slipping as the vehicle accelerates while turning. I have to.

[Problem that the invention seeks to solve]

However, in the conventional device described above, when acceleration of the vehicle during a turn 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. Further, when the turning or acceleration of the vehicle is canceled and the detection is no longer performed, the rear wheels are steered by a predetermined amount in the opposite direction to the above in order to restore the rear wheel steering at the time when the detection is no longer performed; As a result, the rear wheel steering angle abruptly changes by the predetermined amount in the same manner as described above, and in this case as well, the running stability of the vehicle deteriorates as in the above case.

The present invention has been devised in view of the above problem, and its purpose is to alleviate the deterioration of the running stability of the vehicle by alleviating the change in the rear wheel steering angle caused by the steering of the rear wheels. An object of the present invention is to provide a rear wheel steering control device for a vehicle with front and rear wheel steering, which prevents the above problems.

[Means for solving problems]

In order to solve this problem and achieve the above object, the structural features of the present invention are as shown in FIG. , a rear wheel steering mechanism 5 that steers the rear wheels 4, a front wheel steering angle sensor 6 that detects the front wheel steering angle, an acceleration sensor 7 that detects the running acceleration of the vehicle, and the front wheel steering angle sensor 6 and the acceleration sensor 7. an electric control device 8 that controls the rear wheel steering mechanism 5 to change the rear wheel steering angle by a predetermined angle in response to a change in the vehicle running state related to the acceleration of the vehicle during turning based on a signal from the In the rear wheel steering control device for a front and rear wheel steered vehicle, the electric control device 8 is configured to include a determining means 8a for determining the vehicle running state based on the detected front wheel steering angle and the magnitude of the detected acceleration; and an output means 8b for outputting a control signal for driving and controlling the rear wheel steering mechanism 5 so that the rear wheel steering angle gradually changes to the predetermined angle in response to changes in the running condition.

[Action of the invention]

In the present invention configured as described above, the determining means 8a
However, since the vehicle running state related to the acceleration of the turning vehicle is determined based on the front wheel steering angle and the vehicle running acceleration detected by the front wheel steering angle sensor 6 and the acceleration sensor 7, respectively, it is possible to determine whether the vehicle is turning. When the vehicle running state changes, such as when the vehicle accelerates during a turn or returns to a straight-ahead state after accelerating during a turn, the change is detected by the determining means 8a. In response to the detection of this change in vehicle running condition,
The output means 8b outputs a control signal for driving and controlling the rear wheel steering mechanism 5 to the rear wheel steering mechanism 5 so that the rear wheel steering angle gradually changes to a predetermined angle. The mechanism 5 gradually steers the vehicle to the predetermined angle.

〔Effect of the invention〕

As can be understood from the above operation explanation, when the vehicle running state related to the acceleration of the vehicle during turning changes and the rear wheels 4 are steered by a predetermined angle, the rear wheel steering angle due to the steering of the rear wheels 4 changes. Since the change is alleviated by the action of the output means 8b,
Unlike the conventional device described above, deterioration of the running stability of the vehicle due to sudden changes in the rear wheel steering angle is prevented, and the running 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 4o, and an electric control device 5o that controls the rear wheel steering mechanism 30.

The front wheel steering mechanism 20 includes a rack and binion mechanism 21 and a pair of left and right relay rods 22a and 22b connected to the rack portion of the mechanism 21. The rank and binion mechanism 21 is connected to the steering handle 24 via the steering shaft 23 at the sonobinion part.
4 is converted into reciprocating motion of the relay rods 22a and 22b. The left and right relay rods 22a, 22b are connected to the left and right tie rods 25a, 25b and the left and right knuckle arms 2.
It is connected to left and right front wheels 27a and 27b via 6a and 26b, respectively, and steers the left and right front wheels 27a and 27b.

The rear wheel steering mechanism 30 includes a swinging lever 32 for steering the left and right rear wheels 31a, 31b in conjunction with the steering of the left and right front wheels 27a, 27b, and a linear actuator for displacing the fulcrum 32a of the swinging lever 32. Eta 33 and left and right rear wheels 31
It is equipped with a relay rod 34 that interlocks a and 31b. The swing lever 32 includes a force point 32b to which a front connecting rod 35 connected to the left knuckle arm 26a is pivoted, and an action point 32C to which a rear connecting rod 36 is pivotally connected.
If a is between the force point 32b and the force point 32c, the force point 32c is displaced in the opposite direction to the force point 32b, and the fulcrum 32
When a is on the opposite side of the point of force 32b to the point of action 32c, the point of action 32C is displaced in the same direction as the point of force 32b, and when the fulcrum 32a is above the point of action 32C, the point of action 32c is not displaced. Then, based on the position of the fulcrum 32a, the distance between the fulcrum 32a and the point of force 32b, and the fulcrum 32a
He is trying to set a steering angle ratio by the ratio with the distance between two points of action 32C. The linear actuator 33 is at the fulcrum 32
The actuator rod 33a is connected to the vehicle body, and by moving the actuator rod 33a in the lateral direction of the vehicle body, the fulcrum 32a is displaced in the same direction. Relay rod 3
4 connects the left and right rear wheels 31a, 31b to left and right tie rods 37a,
37b and left and right knuckle arms 38a, 38b. A rear connecting rod 36 is connected to the left knuckle arm 38a, and the rear connecting rod 36, which is driven based on the swinging of the swinging lever 32, connects the rear wheel 31a.
, 31b are steered.

The rear wheel drive device 40 includes an accelerator pedal 41 disposed on the driver's seat, an engine 42 disposed on the front side of the vehicle body, and a differential mechanism 43. 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. The transmitted driving force is transmitted to the left and right rear wheels 31a, 31b via the differential mechanism 43 and left and right rear wheel drive shafts 45a, 45b connected between the left and right rear wheels 31a, 31b, respectively.
1b, and thereby the left and right rear wheels 31a, 31b are driven based on the output of the engine 42.

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

The vehicle speed sensor 51 picks up the rotation of the output shaft of the transmission and generates a pickup signal with 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. Ru. The depression amount sensor 52 detects the depression amount a of the accelerator pedal 41 and generates an analog signal representing the detected depression amount a, and this analog signal is converted into a digital signal by an analog-to-digital converter (hereinafter referred to as an A/D converter) 52a. The signal is converted into a signal and supplied to the microcomputer 54 as depression amount data. Front wheel steering angle sensor 53
detects the axial displacement amount of the relay lofts 22a, 22b or the rotational displacement amount of the steering shaft 23, and generates an analog signal representing a front wheel steering angle θf proportional to the detected displacement amount,
This analog signal is converted into a digital signal by the A/D converter 53a and supplied to the microcomputer 54 as front wheel steering angle data. In this case, front wheel steering angle θ
r takes a negative value corresponding to leftward steering of the left and right front wheels 27a, 27b, and takes a positive value corresponding to rightward steering.

The microcomputer 54 is a read-only memory (hereinafter simply referred to as ROM) that stores a program corresponding to the flowchart shown in FIG. 3 and steering angle ratio pattern data for calculating the vehicle speed corresponding steering angle ratio Kv shown in FIG. 4. 5
4a and this pu. A central processing unit (hereinafter simply referred to as CPU) 54b that executes the program, and a writable memory that temporarily stores data necessary for executing this program (
(hereinafter simply referred to as RAM) 54c, and each sensor 51.52
An input/output interface (hereinafter simply referred to as Ilo) 54d that inputs signals supplied from the ROM 54
a, CPU54 b, RAM54 c and 11054
It consists of a bus 54e that commonly connects d. Also, l10
54d is a digital-to-analog converter (hereinafter simply referred to as a D/A converter) which converts the 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. ) 55
a is connected.

The differential amplifier 55 inputs to its inverting input an analog signal representing the position from a position sensor 56 that detects the displacement amount of the actuator rod 33a, that is, the position of the fulcrum 32a, and is supplied to its non-inverting input and inverting input. A difference signal between both 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-described embodiment configured as described above will be explained using the flowchart shown in FIG. First, to explain the outline of the operation, when the driver closes the ignition switch (not shown) to start the vehicle, the CPU
54b starts execution of the program in step 60, and in step 61, the vehicle speed corresponding steering angle ratio data stored in the RAM 54c and representing the vehicle speed corresponding steering angle Ku is transferred to the vehicle speed V.
The vehicle speed corresponding steering angle ratio -Ko (FIG. 4) when is zero is initialized, and a flag FLG, which is stored in the RAM 54C and represents the setting state of the target steering angle ratio, is initialized to "0". Note that this flag FLG represents a state in which the target steering angle ratio K is set to the vehicle speed corresponding steering angle ratio KV at "O",
"1" indicates a state in which the target steering angle ratio K is controlled to be set to a modified value Kv+α obtained by modifying the vehicle speed corresponding steering angle ratio Kv by a predetermined value α.

Further, this predetermined value α is the left and right rear wheels 31a, 3 which are driving wheels.
The value is set to a positive value to prevent the rear wheel drive vehicle from spinning during a turn due to the slip of 1b.

After the initial setting in step 61, the CPU 54b calculates the vehicle speed ■ based on the rectangular wave signal inputted from the waveform shaper 51a through the l1054d in step 62.
The data representing the calculated vehicle speed V is used as vehicle speed data RA
Store in M54C.

Next, in step 62.63, the CPU 54b reads the depression amount data representing the depression amount a of the accelerator pedal 41 and the front wheel steering angle data representing the front wheel steering angle θf from the A/D converters 52a and 53a through the l1054d. , the read pedal stroke amount data and front wheel steering angle data are stored in RAM5.
Each is stored in 4C. After storing various data through the processing in steps 62 to 64, the CPU 54b performs a "vehicle running state determination routine" consisting of steps 70 to 72 to determine whether the vehicle is turning based on the stored depression amount data and front wheel steering angle data. Based on the determination result, the target steering angle ratio K is determined based on the vehicle speed data stored in the "vehicle speed corresponding steering angle ratio setting routine" consisting of steps 80 to 84. Rudder angle ratio KV
or control the setting to "
In the "corrected steering angle ratio setting routine", the target steering angle ratio K is set to the corrected value KV+α of the vehicle speed corresponding steering angle ratio Kv, and the program proceeds to step 65.

In step 65, the CPU 54b outputs the digital signal representing the target steering angle ratio K to the D/A converter 55a via the l1054d, and the D/A converter 55a converts this digital signal into an analog signal and converts the difference. The differential amplifier 55 controls the linear actuator 33 in cooperation with the position sensor 56 to set the fulcrum 32a so that the set steering angle ratio of the swing lever 32 becomes the target steering angle ratio K. Displace. After the processing in step 65, the CPU 54b returns the program to step 62, and thereafter executes steps 62 to 62.
64 processing, “vehicle running state determination routine” processing, “
The cyclic process consisting of the vehicle speed corresponding steering angle ratio setting routine, the corrected steering angle ratio setting routine, and the process of step 65 is continued, and the target steering angle ratio K is set according to the vehicle running state and vehicle speed. is calculated, and the set steering angle ratio of the swing lever 32 is set to the target steering angle ratio K. In addition, the above CPU5
The digital signal indicating the target steering angle ratio K output from the CPU 54b is stored in the CPU 54b until a new digital signal is output from the CPU 54b. In this state, depending on the rotation of the steering wheel 24, the left and right front wheels 27a,
When the left and right rear wheels 27b are steered, the left and right rear wheels 31a and 31b are rotated according to the set steering angle ratio of the swing lever 32.
It is steered in opposite phase or in phase with respect to 27b.

Next, a "vehicle running state determination routine" consisting of steps 70 to 72 executed during the above circulation process, and steps 80 to 72 are performed.
"Vehicle speed corresponding steering angle ratio setting routine" consisting of steps 84 and "corrected steering angle ratio setting routine" consisting of steps 90 to 92.
The processing will be explained in detail for each vehicle running state.

fl) After the vehicle starts, the flag FLG remains set to "0" due to the initial setting in step 61 above,
A case in which the vehicle is not in an accelerating state will be explained.

In this case, after updating various data in steps 62 to 64,
In step 70, the CPU 54b determines that rNOJ, that is, the depression iJa, is a predetermined value a based on the fact that the acceleration of the vehicle is large (i.e., the depression ia of the accelerator pedal 41 is small).

It is determined that the flag is not larger than F, and in step 71, the flag F is set.
Based on the fact that LG is “O” as mentioned above, rNO
It is judged as J, and the program advances to the "vehicle speed corresponding steering angle ratio setting routine". The predetermined value ao is set, for example, to a value corresponding to a depression amount of about 70% of the total depression amount of the accelerator pedal 41.

In this "vehicle speed corresponding steering angle ratio setting routine", CP
In step 80, U54b calculates the vehicle speed corresponding steering angle ratio Kv (fourth ) is calculated, and data representing the calculated steering angle ratio KV corresponding to vehicle speed is stored in the RAM 54C as steering angle ratio data corresponding to vehicle speed. Ste.

After the process in step 80, the CPU 54b proceeds to step 81 to calculate R based on the calculated vehicle speed corresponding steering angle ratio KV and the previous circulation process.
Absolute value l of the difference Kv- from the target steering angle ratio indicated by the target steering angle ratio data stored in AM54C KV-
It is determined whether Kl is smaller than a predetermined value β. In addition,
The predetermined value β indicates the maximum variation width in the target steering angle ratio, and when the vehicle is normally traveling, the vehicle speed corresponding steering angle ratio Kv changes due to a change in the vehicle speed V within the time required for the above-mentioned circulation process. It is set to a value slightly larger than the amount of change. 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 running normally, rYEsJ, that is, the absolute value 1Kv-
It is determined that Kl is less than β, and the CPU 54b stores the target steering angle ratio data in the RAM 54c in step 82 and expresses the target steering angle ratio K using the vehicle speed corresponding steering angle ratio K as calculated above.
In step 84, the flag FLG is set to "0", which is the same state as before, and the program proceeds to step 65. In step 65, as described above, a digital signal representing the target steering angle ratio K is output to the D/A converter 55a, and the set steering angle ratio at the swing lever 32 is set to the target steering angle ratio, that is, the steering angle corresponding to the vehicle speed. The setting is controlled to the ratio Kv (Fig. 4). As a result, in such a vehicle running state, when the vehicle speed ■ is small, the left and right rear wheels 31a, 31
b is steered in the opposite phase with respect to the left and right front wheels 27a and 27b,
As the vehicle speed V increases, the left and right rear wheels 31a and 31b are steered in the same phase with respect to the left and right front wheels 27a and 27b.

Furthermore, as the vehicle speed ■ suddenly drops due to reasons such as sudden braking of the vehicle, the steering angle ratio KV corresponding to the vehicle speed changes suddenly, and the above absolute value IKv
-Kl becomes equal to or greater than the predetermined value β, the CPU 54b determines rNOJ in step 81, and in step 83 converts the target steering angle ratio data representing the target steering angle ratio K to the following (Equation 1).
Updated by.

In the above (Equation 1), the value on the left side is the current step 8.
The value on the right side represents the target steering angle ratio updated by the process in step 3, and the value on the right side represents the target steering angle ratio before being updated, that is, the target steering angle ratio that was set by the previous circulation process. The target steering angle ratio has a value that approaches the vehicle speed corresponding steering angle ratio Kv by 1/m of the above-mentioned absolute value IKv-Kl.

In addition, the value m is the change in target steering angle ratio (KV-K)/m,
In relation to the timing of updating to the same steering angle ratio, the value is set to a value that does not deteriorate the running stability of the vehicle. Then, in each circulation process, the target steering angle ratio K asymptotically approaches the vehicle speed corresponding steering angle ratio Kv by 1/the absolute value lKv-KIOm. However, in this case, if the vehicle speed {circle around (2)} changes, the vehicle speed corresponding steering angle ratio Kv in the process of step 80 also changes accordingly. As a result of the target steering angle ratio K asymptotic to the vehicle speed corresponding steering angle ratio KV, the absolute value IK
When v-Kl becomes less than the predetermined value β, rYESJ is determined in step 81 as described above, and the target steering angle ratio Kv is set to the vehicle speed corresponding steering angle ratio Kv.

In this way, as the vehicle speed V suddenly decreases, the vehicle speed corresponding steering angle ratio KV
If there is a sudden change in the target steering angle ratio, (K v - K)/m
The vehicle speed-corresponding steering angle ratio Kv is gradually approached (therefore, the steering angles of the left and right rear wheels 31a, 31b do not change suddenly (therefore, the running stability of the vehicle is improved).

(2) Next, a case will be described in which the accelerator pedal 41 of the vehicle, which is traveling substantially straight in the state of (1) above, is depressed deeply and the vehicle accelerates. In this case, after updating various data in steps 62 to 64, the CPU 54b determines in step 70 that rYESJ, that is, the depression amount a is larger than the predetermined value ao, based on the fact that the acceleration of the vehicle is large, that is, the depression amount a is large. In step 72, the absolute value 1θf1 of the front wheel steering angle θf is equal to the predetermined angle θ.
A comparison is made to determine whether or not the value is greater than or equal to fo. Predetermined angle θf.

is set to a value of about 5 degrees, and in this case, the vehicle is traveling substantially straight, so the CPU 54b executes step 7.
2 is “NO”, that is, the absolute value of the front wheel steering angle θr is 1θ [
1, it is determined that the angle is not greater than the predetermined angle θto, 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 target steering angle ratio K is set and controlled in the same way as in the case (i) above, so the left and right rear wheels
1 a.

31b is also steered in the same manner as in the case (1) above.

(3) Next, a case where the vehicle is in an acceleration state and in a turning state will be described. In this case, step 63.
Since the absolute value 1θf1 of the depression amount a and the front wheel steering angle θf set in step 64 is large, the CPU 54b
At step 0, it is determined that rYEsJ, that is, the depression amount a, is greater than the predetermined value ao, and at step 72, it is determined that the absolute value 1θf1 of the front wheel steering angle θf is greater than or equal to the predetermined angle θfo.
Proceed the program to the "corrected steering angle ratio setting routine."

In this "corrected steering angle ratio setting routine", the target steering angle ratio and the vehicle speed corresponding steering angle ratio Kv are initially set to the same value by the process of steps 80 and 82 of the previous circulation process, so The CPU 54b determines K<KV at step 90.
+α is determined to be rYEsJ, and in step 91, target steering angle ratio data representing the target steering angle ratio K is updated using the following (Formula 2).

Slightly +-... (Formula 2) The above (Formula 2) also increases the target steering angle ratio K by α/n in each circulation process, as in the case of (Formula 1) above. . Note that the value n is similar to the value m in (Equation 1) above, so that the change α/n in the target steering angle ratio can degrade the driving stability of the vehicle in relation to the update timing of the target steering angle ratio. However, the same value n moves the left and right rear wheels 31a, 31b to the left and right front wheels 27a, 27 faster than in the case of (Equation 1) above.
In order to steer in the same phase direction with respect to b, it is set slightly smaller than m (n<m). After the process in step 91, the CPU 54b goes to step 92 to flag FLC4-.
"1", and in step 65 a digital signal representing the target steering angle ratio K is output to the D/A converter 55a, and the program returns to step 62.

Then, as long as the vehicle is in the acceleration state and turning state as described above, the CPU 54b determines rYEsJ in steps 70 and 72, and sets the target steering angle ratio by the processing in steps 90 and 91 similar to the above. K is increased by α/n for each circulation process. During this circulation process, if the relationship of target steering angle ratio K≧KV+α is established, the CPU 54b makes a "NO" determination in step 90, does not execute the process in step 91, and advances the program to step 92.

Through the processing of steps 90 to 92, the target steering angle ratio gradually increases by α/n from the vehicle speed corresponding steering angle ratio KV before executing the "corrected steering angle ratio setting routine" to the corrected value KV+α. In this case, the steering angle ratio KV corresponding to the vehicle speed is maintained at the same value even if the vehicle speed ■ changes due to non-execution of step 80.

As a result, when the vehicle in question accelerates while turning, the left and right rear wheels 31a and 31b are set to a predetermined value in the same phase direction with respect to the steering direction of the left and right front wheels 27a and 27b, rather than the steering angle set by the vehicle speed corresponding steering angle ratio KV. Since the vehicle is steered by the steering angle corresponding to α, it is possible to prevent the vehicle from spinning, which is caused by the left and right rear wheels 31a and 31b, which are the drive wheels, slipping as the vehicle accelerates during a turn. Further, since the steering correction of the left and right rear wheels 31a, 31b is performed gradually by α/n, changes in the rear wheel steering angle due to the steering correction are alleviated, and the vehicle movement caused by sudden changes in the rear wheel steering angle is reduced. Deterioration of running stability is better prevented.

(4) Next, a case will be described in which the acceleration of the vehicle is canceled from the state of (3) above while the vehicle is turning. In this case, as the acceleration is released, the accelerator pedal 41
Since the depression amount a is released and the depression amount a set in step 63 becomes smaller, the CPU 54b performs step 7.
0, it is determined that rNOJ, that is, the depression amount a is not larger than the predetermined value aO, and in step 71, the flag FLG is set to "
1''. In this judgment, as explained in (3) above, the flag FLG is set at step 9.
Since it is set to “1” by the process in step 2, CPU5
4b is determined to be rYEsJ and the program is executed at step 72.
Proceed to. In this case, the vehicle is still turning and the absolute value 1θf1 of the front wheel steering angle θr is a large value, so
The CPU 54b determines in step 72 that rYEsJ, that is, the same absolute value 1θr1 is greater than or equal to the predetermined angle θfo, and advances the program to the "corrected steering angle ratio setting routine" consisting of steps 90 to 92, so that the steering angle of the vehicle is The ratio is set in the same manner as in the case (3) above, and the left and right rear wheels 31a, 31b are also steered in the same manner as in the case (3) above. As a result, even if the acceleration of the vehicle in question is canceled while turning, the steering angle ratio will not be changed, and unless the front wheel steering angle is changed, the rear wheel steering angle will not change, and the vehicle in question while turning is It is possible to continue turning while maintaining the same state, improving driving stability when turning.

(5) Next, when the vehicle is returned to a substantially straight-ahead state from the state in which the acceleration of the vehicle in (4) above is canceled, or the vehicle is returned to a substantially straight-ahead state from the turning acceleration state in (3) above. The case where it is restored will be explained. In this case, in the "vehicle running state determination routine", the CPU 54b determines in step 72 after the processing of step 70.71 or after the processing of step 71 that the absolute value 1θf1 of the front wheel steering angle θf set in step 64 is small. Based on rNOJ
That is, it is determined that the absolute value 1θf1 is not 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 process as in the case (1) above to set the steering angle ratio of the vehicle to the target steering angle ratio, that is, to the vehicle speed corresponding steering angle ratio Kv. do. In this case, normally the target steering angle ratio is initially determined by steps 90 to 9 that have been executed up to now.
2, the steering angle ratio corresponding to the vehicle speed is set to the value obtained by adding the predetermined value α to the steering angle ratio KV. The relationship between the corresponding steering angle ratio is 1Kv - KI × β
It is determined that there is no As a result, the target steering angle ratio is changed by (KV-K)/m in each circulation process by the process of step 83, and gradually approaches the vehicle speed corresponding steering angle ratio Kv. This prevents the rear wheel steering angle from changing suddenly as described above, and improves the running stability of the vehicle. At this time, the vehicle V has become large, and the vehicle speed corresponding steering angle ratio Kv and the target steering angle ratio K, which was set in the "corrected steering angle ratio setting routine" consisting of steps 90 to 92, coincidentally become approximately the same. If so, the CPU 54 b selects rYES in step 81.
J is determined, and the target steering angle ratio K is set to the vehicle speed corresponding steering angle ratio KV through the process of step 82.

In addition, in this "vehicle speed corresponding steering angle ratio setting routine", after the processing in steps 82 and 83, the flag FLG is set to 10'' in step 84, so in this state, the flag FLG is returned to the initial state. .

As can be understood from the above explanation of the operation, according to the above embodiment, the vehicle running state related to the acceleration of the turning vehicle is determined by the processing of the "vehicle running state determination routine" consisting of steps 70 to 72. , if the vehicle speed corresponding steering angle ratio KV is modified or the modification is cancelled, the "vehicle speed corresponding steering angle ratio setting routine" consisting of steps 80 to 84 or the "correction" consisting of steps 90 to 92 is performed. As the steering angle ratio is gradually corrected through the process of "Steering angle ratio setting routine", the rear wheel steering angle does not suddenly change based on the gradual change in the steering angle ratio (this prevents the running stability of the vehicle from being changed). 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 detection may be performed using an acceleration sensor that detects the acceleration of the vehicle body. Further, the addition i[ may be calculated by differentiating the detected vehicle speed ■ by program processing of the microcomputer 54.

Further, in the above embodiment, in order to gradually change the steering angle ratio set by the swing lever 32, step 83.9 is performed.
Although the change in the target steering angle ratio is alleviated by the arithmetic processing in step 1, the integration circuit is connected to the microcomputer 54 and D/
It may also be provided between the A converter 55a or between the D/A converter 55a and the differential amplifier 55 to alleviate level changes in the control signal supplied to the differential amplifier 55. In this case, the microcomputer 54 only needs to 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 a rear wheel drive type vehicle has been described, but the present invention can also be applied to a front wheel drive type vehicle. However, in a front-wheel drive vehicle, when the vehicle accelerates, the slip ratio of the left and right front wheels, which are drive wheels, increases, and the vehicle tends to understeer and drift out while turning. Therefore, in the process of steps 90 and 91 (FIG. 3), it is necessary to set the predetermined value α for correcting the vehicle speed corresponding steering angle ratio Kv to a negative value, that is, to one α. As a result, when a turning vehicle accelerates, the left and right rear wheels are corrected in a direction opposite to the left and right front wheels, thereby preventing drift-out during turning acceleration in a front-wheel drive vehicle. In this case, of course, the change in the steering angle ratio is relaxed when correcting or returning the steering angle ratio.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to the configuration of the invention described in the claims, FIG. 2 is a schematic diagram of a vehicle showing an embodiment of the invention,
FIG. 3 is a flowchart corresponding to the program executed by the microcomputer in FIG. 2, and FIG. 4 is a characteristic graph showing the steering angle ratio with respect to vehicle speed. Explanation of symbols 20...Front wheel steering mechanism, 24...Steering handle, 2
7a, 27b...front wheel, 30...rear wheel steering mechanism, 3
1a, 31b... Rear wheel, 32... Rocking lever, 33
... Linear actuator, 40 ... Rear wheel drive device, 41 ... Accelerator pedal, 42 ... Engine, 5
0... Electric control device, 51... Vehicle speed sensor, 52.
・・Depression amount sensor, 53 ・・Front wheel steering angle sensor, 5
4...Microcomputer, 55...Differential amplifier,
56...Position sensor. Applicant Toyota Motor Corporation Representative Patent Attorney Teru Hase - (1 other person)

Claims (1)

[Claims] A front wheel steering mechanism that steers the front wheels according to rotation of a steering wheel, a rear wheel steering mechanism that steers the rear wheels, a front wheel steering angle sensor that detects the front wheel steering angle, and an acceleration sensor that detects the running acceleration of the vehicle. , the rear wheel steering mechanism is configured to change the rear wheel steering angle by a predetermined angle in response to a change in the vehicle running state related to the acceleration of the vehicle during turning based on the signals from the front wheel steering angle sensor and the acceleration sensor. In the rear wheel steering control device for a front and rear wheel steered vehicle, the electric control device is configured to control the electric control device by determining the vehicle running state based on the detected front wheel steering angle and the detected acceleration. and an output means for outputting a control signal for driving and controlling the rear wheel steering mechanism so that the rear wheel steering angle gradually changes up to the predetermined angle in response to the determined change in the vehicle running state. A rear wheel steering control device for a front and rear wheel steering vehicle, characterized by: