JPH089333B2 - Front and rear wheel steering vehicle rear wheel steering control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering control device for a front and rear wheel steering vehicle including a rear wheel steering device that steers rear wheels according to a steering state of front wheels and a vehicle speed. .

[Prior art]

Conventionally, a device of this type has a ratio of a steering angle of a rear wheel to a steering angle of a front wheel based on a vehicle speed detected by a vehicle speed sensor, as disclosed in, for example, Japanese Patent Laid-Open No. 60-78870. The steering angle ratio that changes is determined, and the steering angle of the rear wheels is controlled according to the determined steering angle ratio.
Further, in this device, when the vehicle speed sensor fails, the steering of the rear wheels is stopped to ensure the maneuverability of the vehicle.

[Problems to be solved by the invention]

However, since the vehicle speed sensor in the above conventional device normally detects the rotation of the output shaft of the transmission,
If one of the driving wheels runs idle, the detected vehicle speed becomes inaccurate, and accordingly, the steering control of the rear wheels by the device also becomes inaccurate. In view of the above points, the applicant of the present application, in the previous application (Japanese Patent Application No. 60-291157 "Vehicle speed determination method of a vehicle"), detects the rotation speeds of a plurality of wheels, respectively, and based on the detected rotation speeds. A method of calculating the vehicle speed and steering-controlling the rear wheels based on the calculated vehicle speed was proposed. According to this method, for example, even if one of the drive wheels spins, the vehicle speed can be calculated by excluding the rotational speed of the wheel, so that the calculated vehicle speed becomes accurate, and the steering control of the rear wheels can be performed. Although it will be accurate, if the vehicle speed is calculated excluding the rotational speed of the wheel that is idling as described above while the vehicle is turning, there will be a difference between the previously calculated vehicle speed and the newly calculated vehicle speed. There is a problem in that the steering angle of the wheels is discontinuously controlled, and the steerability of the vehicle deteriorates.

Further, in the above conventional device, only one vehicle speed sensor is provided, and if this one sensor fails, the steering control of the rear wheels is not performed, so the front and rear of the vehicle There was a problem that the function as a wheel steering vehicle was not fully exhibited. Further, if the rear wheels are being steered when the control of the rear wheel steering is stopped due to the breakdown of the vehicle speed sensor, the steering angle of the rear wheels suddenly returns to zero, which deteriorates the steerability of the vehicle. There was a problem of doing.

The present invention has been devised in view of the above problems, and an object of the present invention is to accurately detect the vehicle speed to improve the steering control system of the rear wheels, and to provide the discontinuous control of the rear wheel steering angle and the same steering angle. SUMMARY OF THE INVENTION It is an object of the present invention to provide a rear wheel steering control device for a front and rear wheel steering vehicle, which prevents the deterioration of the above-mentioned steerability due to a sudden change in the vehicle steering wheel and allows the front and rear wheel steering vehicle to sufficiently exhibit its function.

[Means for solving the problem]

In order to achieve the above-mentioned object, the structural feature of the present invention is, as shown in FIG. 1, a front and rear wheel steering device 1 provided with a rear wheel steering device 1 for steering a rear wheel RW according to a steering state of a front wheel FW and a vehicle speed. In a wheel steering vehicle, a plurality of rotation detection sensors 2a, 2b that continuously detect each rotation of a plurality of wheels FW (RW) and output a plurality of output signals representing each rotation, and a plurality of rotation detection sensors Vehicle speed calculation means 3 for repeatedly calculating a vehicle speed that changes with time based on the output signals from 2a and 2b,
A vehicle speed corresponding steering angle ratio determining means 4 for repeatedly determining a vehicle speed corresponding steering angle ratio which is a steering angle ratio of the rear wheels RW to the front wheels FW based on the latest calculated vehicle speed, and which changes according to the same vehicle speed; The latest vehicle speed corresponding to the latest vehicle speed that is repeatedly determined is compared with the currently set steering angle ratio of the rear wheel RW to the front wheel FW, and when the difference between the two steering angle ratios is smaller than a predetermined value. Determine the steering angle ratio as the target steering angle ratio,
When the difference between the two steering angle ratios is greater than or equal to the predetermined value, the target steering angle ratio is determined by changing the previous target steering angle ratio by a predetermined small value toward the latest vehicle speed corresponding steering angle ratio. The steering angle ratio determining means 5 and a control signal corresponding to the determined target steering angle ratio are output to the rear wheel steering device 1 to output the rear wheels RW.
The rear wheel steering control device is configured by the control means 6 for controlling the rear wheel steering device so as to steer the vehicle according to the target steering angle ratio.

[Operation of the invention]

In the present invention configured as described above, the vehicle speed calculation means 3 repeatedly calculates the vehicle speed that changes over time based on the output signals from the plurality of rotation detection sensors 2a and 2b, and the vehicle speed corresponding steering angle ratio determination means 4 is obtained. Repeatedly determines the vehicle speed corresponding steering angle ratio that changes according to the vehicle speed based on the latest vehicle speed repeatedly calculated. Then, the latest vehicle speed corresponding rudder angle ratio determined repeatedly and the currently set rear wheel RW
If the difference from the steering angle ratio with respect to the front wheels FW is smaller than a predetermined value, the target steering angle ratio determination means 5 determines the latest vehicle speed corresponding steering angle ratio as the target steering angle ratio. Further, if the difference between the latest steering speed ratio corresponding to the vehicle speed repeatedly determined and the steering angle ratio of the rear wheel RW to the front wheel FW that is currently set is equal to or more than a predetermined value, the target steering angle ratio determining means 5 determines the previous time. The target rudder angle ratio is determined as a target rudder angle ratio that is changed by a predetermined small value in the direction approaching the latest vehicle speed corresponding rudder angle ratio. As a result, even if the vehicle speed drastically changes and the vehicle speed-corresponding steering angle ratio also drastically changes, the change in the target steering angle ratio is alleviated, and the control means 6 sends a control signal corresponding to the alleviated target steering angle ratio. The rear wheel RW is output to the rear wheel steering device 1 to steer the rear wheel RW according to the target steering angle ratio, and the front wheel FW of the rear wheel RW is output.
To the target steering angle ratio.

〔The invention's effect〕

As can be understood from the above description of the operation, according to the present invention, the vehicle speed is calculated based on the rotation of a plurality of wheels, so that even if one wheel spins, the calculated vehicle speed does not become inaccurate. Accurate steering control of the rear wheels.
Even if the vehicle speed is calculated by excluding the rotational speed of the wheel that is idling as described above while the vehicle is turning, the vehicle speed previously calculated by the target steering angle ratio determination unit 5 and the newly calculated vehicle speed are obtained. Since the steep change in the target steering angle ratio based on the difference between the two is relaxed, the steered angle of the rear wheels RW does not suddenly change, and the deterioration of the steerability of the vehicle is better prevented.

Further, the rotation sensors 2a, 2b are provided in plural, and even if one of the plurality of sensors 2a, 2b fails, the vehicle speed can be calculated based on the output signals from the remaining sensors, so that the rear wheels can be calculated. The functions of the front and rear wheel steering vehicle that steer-controls the RW according to the vehicle speed are fully exerted. Also in this case, the calculated vehicle speed changes abruptly with a change from the calculation of the vehicle speed based on the output signals from the plurality of rotation sensors 2a, 2b to the calculation of the vehicle speed based on the output signals from the remaining sensors. However, since the steering angle of the rear wheels RW does not change abruptly, the deterioration of the steerability of the vehicle is better prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 schematically shows the entire front and rear wheel steering vehicle according to the present invention. This front and rear wheel steering vehicle is a front wheel steering device A that steers the left and right front wheels FW1 and FW2, a rear wheel steering device B that steers the left and right rear wheels RW1 and RW2, and an electric control device that electrically controls the rear wheel steering device B. It has C and.

The front wheel steering system A has a steering wheel 11. The steering wheel 11 is connected to the left and right front wheels FW1, FW2 via the steering shaft 12, the rack and pinion mechanism 13, the relay rod 14, the left and right tie rods 15a, 15b and the left and right knuckle arms 16a, 16b.
The left and right front wheels FW1 and FW2 are steered according to the rotation of the handle 11. A control valve at the bottom of the steering shaft 12
17 is attached to the steering shaft 12 for supplying the hydraulic oil discharged by the hydraulic pump 18 and supplied through the conduit P1.
The hydraulic oil is supplied to one oil chamber of the power cylinder 21 according to the steering torque that acts on the hydraulic cylinder, and the hydraulic oil from the other oil chamber of the cylinder 2 is discharged to the reservoir 22 via the conduit P2. The power cylinder 21 has a relay rod 14 depending on the supply and discharge of the hydraulic oil.
Is driven to assist the steering of the left and right front wheels FW1 and FW2.

The rear wheel steering system B has a step motor 23,
23 is controlled by the electric control device C to drive the steering shaft 24 in rotation. The steering shaft 24 is connected to the left and right rear wheels RW1, RW2 via the rack and pinion mechanism 25, the relay rod 26, the left and right tie rods 27a, 27b and the left and right knuckle arms 28a, 28b,
The left and right rear wheels RW1 and RW2 are steered according to the rotation of the coaxial shaft 24. A control valve 31 is attached to an intermediate portion of the steering shaft 24, and the valve 31 controls the hydraulic oil discharged by the hydraulic pump 32 and supplied through the conduit P3 according to the steering torque acting on the steering shaft 24. The oil is supplied to one oil chamber of the power cylinder 33, and the working oil is discharged from the other oil chamber of the power cylinder 33 to the reservoir 22 via the conduit P4. The power cylinder 33 drives the relay rod 26 in accordance with the supply and discharge of the hydraulic oil to assist the steering of the left and right rear wheels RW1 and RW2.

The electric control device C is a wheel speed sensor 41a, 41b, 41c, 41.
d, a front wheel steering angle sensor 41e and a rear wheel steering angle sensor 41f. Wheel speed sensors 41a, 41b, 41c, 41d are left and right front wheels F
By picking up each rotation of W1, FW2 and left and right rear wheels RW1, RW2, the rotation speed Nf1, Nf of each wheel FW1, FW2, RW1, RW2
Pickup signals having frequencies proportional to 2, Nr1 and Nr2 are output. These sensors 41a, 41b, 41c, 41d are respectively connected to waveform shapers 42a, 42b, 42c, 42d, each shaper 42a, 42b, 42c, 42d waveform shaping the pickup signal, Revolving speed signals composed of rectangular wave signals having frequencies proportional to the rotating speeds Nf1, Nf2, Nr1 and Nr2, respectively, are output.

The front wheel steering angle sensor 41e is mounted on the steering shaft 12 and is coaxial 1
By detecting the rotation angle of 2, the analog signal representing the steering angle θf of the left and right front wheels FW1, FW2 is output. An analog-digital converter (hereinafter referred to as an A / D converter) 42e is connected to the front wheel steering angle sensor 41e, and the converter 42e performs front-wheel steering downward θf by performing analog-digital conversion on the analog signal. Outputs steering angle data. The rear wheel steering angle sensor 41f is assembled to the relay rod 26, and by detecting the displacement of the rod 26, it outputs an analog signal representing the steering angle θr of the left and right rear wheels RW1, RW2. An A / D converter 42f is connected to the rear wheel steering angle sensor 41f, and the converter 42f is based on an analog signal representing the rear wheel steering angle θr in the same manner as the A / D converter 42e described above. Rear wheel steering angle data in digital format representing the same steering angle θr is output. In addition,
The front wheel steering angle θf and the rear wheel steering angle θr are positive (or negative) and represent the steering of the left and right front wheels FW1 and FW2 and the left and right rear wheels RW1 and RW2 to the right (or left), respectively. Front wheel FW1, FW
2 and the left and right rear wheels RW1 and RW2 are not steered.

These waveform shapers 42a, 42b, 42c, 42d and A / D converter 42
A microcomputer 43 is connected to e and 42f. The computer 43 has a read-only memory (hereinafter referred to as ROM) 43b commonly connected by a bus 43a, a central processing unit (hereinafter referred to as CPU) 43c, and a writing unit. It consists of a possible memory (hereinafter referred to as RAM) 43d, a timer 43e, and an input / output interface (hereinafter referred to as I / O) 43f. The ROM 43a stores a program corresponding to the flowchart of FIG. 3 and also stores, in the form of a table, the vehicle speed corresponding steering angle ratio Kv that changes from negative to positive as the vehicle speed V shown in the graph of FIG. 4 increases. The vehicle speed-corresponding steering angle ratio Kv and the target steering angle ratio K described later represent the ratio of the steering angles of the left and right rear wheels RW1 and RW2 to the left and right front wheels FW1 and FW2. Wheels RW1 and RW2 are in phase (or opposite phase) to the left and right front wheels FW1 and FW2
That is, it means that they are steered in the same direction (or opposite directions), and at zero it means that the left and right rear wheels RW1, RW2 are not steered regardless of the steering of the left and right front wheels FW1, FW2. The CPU 43c executes the program, the RAM 43d temporarily stores data and flags necessary for the execution of the program, a timer
43e measures the time according to the instruction from the CPU 43c. I / O43
f is connected to the waveform shapers 42a, 42b, 42c, 42d and the A / D converters 42e, 42f, and the same shapers 42a, 42b, 42c, 42d and the same converters 42e, 4f.
Each rotation speed signal from 2f, the front wheel steering angle data and the rear wheel steering angle data are respectively taken into the microcomputer 43, and the rotation control data representing the rotation speed of the step motor 23 formed by the execution of the program is stored in the microcomputer 43. It is output from the computer 43 and has a function of storing this control data.

A drive circuit 44 is connected to this I / O 43f.
Reference numeral 44 outputs a drive pulse train signal for controlling the number of rotation steps of the step motor 23 based on the rotation control data supplied.

The operation of the embodiment configured as described above will be described with reference to the flowchart of FIG. When the ignition switch (not shown) is closed, the CPU 43c starts executing the program in step 50 and initializes the first to fourth flags F1, F2, F3, F4 to "0" in step 51, respectively. The target steering angle ratio data representing the target steering angle ratio K is set to the vehicle speed corresponding steering angle ratio −K ₀ (see FIG. 4) when the vehicle speed V is zero, and the first to fourth old vehicle speeds are set. V1 _old , V2 _old , V3 _old , V4 _old
Initially, the first to fourth old vehicle speed data representing the above are each set to "0". The first to fourth flags F1, F2, F3, F4 are "0".
Normal state of first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _new described later, which are newly calculated based on the respective rotation speed signals from the wheel rotation speed sensors 41a, 41b, 41c, 41d. Respectively, and "1" indicates the first to fourth new vehicle speeds V1 _new , V2 _new , V3
_new , V4 _new Indicates an abnormal state. Further, the first to fourth old vehicle speeds V1 _old , V2 _old , V3 _old , V4 _old correspond to the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _new , respectively, and are calculated previously. Represents what has been done.

After this initialization, in step 52, the CPU 43c sends front wheel steering angle data and rear wheel steering angle data representing the front wheel steering angle θf and the rear wheel steering angle θr from the A / D converters 42e and 42f via the I / O 43f. Each is read, and the read both steering angle data are stored in the RAM 43d. After the processing of step 52, the CPU 43c sends each rotation speed signal from the waveform shapers 42a, 42b, 42c, 42d to the I / O 43 in step 53.
Input each via f, and the left and right front wheels F based on each rotation speed signal
Number of revolutions of W1, FW2 and left and right rear wheels RW1, RW2 Nf1, Nf2, Nr1, Nr2
And the calculated rotation speeds Nf1, Nf2, Nr1, Nr
Based on 2, the traveling distance of each wheel FW1, FW2, RW1, RW2 per unit time, that is, the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _{new for} each wheel FW1, FW2, RW1, RW2 And calculate the first
The first to fourth new vehicle speed data representing the fourth to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , and V4 _new are stored in the RAM 43d.

After the processing of step 53, the CPU 43c, at step 54, is based on the following conditions 1 and 2, and the abnormality of the calculated first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _new , that is, the wheel speed sensor. 41a, 41b, 41c, 41d abnormality or each wheel FW1, FW2, R
When there is an abnormality of W1 and RW2 by detecting the idling or locked state of the vehicle, the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4
_Set the first to fourth flags F1, F2, F3, F4 corresponding to _new to "
Set to 1 ".

Condition 1: 1st to 4th new vehicle speed V1 calculated in step 53
_{If new} , V2 _new , V3 _new , and V4 _new are equal to or lower than a predetermined vehicle speed that may be present in vehicle traveling, it is determined to be normal, and if they exceed the predetermined vehicle speed, it is determined to be abnormal.

Condition 2: 1st to 4th new vehicle speeds V1 calculated in step 53
_new , V2 _new , V3 _new , V4 _new and first to fourth old vehicle speeds V1 _new , V2 _new , V3 _new , represented by the first to second old vehicle speed data
If each difference from V4 _new is within the predetermined range, it is determined to be normal, and if it is outside the predetermined range, it is determined to be abnormal.

The calculated first to fourth new vehicle speeds V1 _new , V2 _new ,
If V3 _new and V4 _new are normal, the first to fourth flags F1, F
2, F3, F4 remain set to “0”.

After the process of step 54, the CPU 43c determines the first to fourth flags F1, F2, F3 and F4 based on the first to fourth flags F1, F2, F3 and F4 in steps 60 and 61.
Whether any two or more of the new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _new are abnormal, and the first to fourth new vehicle speeds V1
It is determined whether or not any one of _new , V2 _new , V3 _new , and V4 _new is abnormal.

First, the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4
_The case where all _new are normal will be described. In this case, the first to fourth flags F1, F set in step 54
Since 2, F3 and F4 are all "0", the CPU 43c executes steps 60 and 61.
It is determined to be “NO” in each, and the first to fourth in step 62
The vehicle speed V is calculated by averaging the two central values of the new vehicle speeds V1 _new , V2 _new , V3 _new , and V4 _new , and the vehicle speed data representing the calculated vehicle speed V is stored in the RAM 43d. After the processing in step 62, the CPU 43c stores the first to fourth old vehicle speed data stored in the RAM 43d in step 63 and representing the first to fourth old vehicle speeds V1 _old , V2 _old , V3 _old , and V4 _old , respectively. Fourth new vehicle speed V1
Update with _new , V2 _new , V3 _new , V4 _new and advance the program to step 70. It should be noted that the updating process of step 63 is performed in the next first to fourth new vehicle speed V1 in step 54.
_This is because the first to fourth old vehicle speed data are used for the abnormality determination of _new , V2 _new , V3 _new , V4 _new .

The CPU 43c executes RA in step 70 and step 62.
Based on the vehicle speed data stored in M43d, by referring to the table of RAM43b, determine the corporate rule corresponding steering angle ratio Kv (Fig. 4) corresponding to the vehicle speed V, and in step 71, the vehicle speed corresponding steering angle It is determined whether or not the absolute value | Kv−K | of the difference between the ratio Kv and the target steering angle ratio K set to −K ₀ by the initial setting in step 51 is less than a predetermined small value β. In this case, the vehicle is stopped immediately after the ignition switch is turned on, and the steering angle ratio Kv corresponding to the vehicle speed also becomes -K ₀ .
In step 71, it is determined to be "YES", and the CPU 43c sets the target steering angle ratio data representing the target steering angle ratio K to the vehicle speed corresponding steering angle ratio Kv in step 72, and executes the program in step 73.
Proceed to. At the same step 73, the CPU 43c executes the calculation of K.theta.f-.theta.r based on the front wheel steering angle data and the rear wheel steering angle data stored in the RAM 43d by the processing of step 52, and the target rear wheel steering angle K.theta.f and the present value are obtained. The steering angle difference K · θf−θr from the rear wheel steering angle θr is calculated, and the steering angle difference K · θf− is calculated.
The rotation control data for the step motor 23 corresponding to θr is output to the I / O 43f. The I / O 43f stores this rotation control data until new rotation control data is supplied, and outputs it to the drive circuit 44 at the same time.

The drive circuit 44 outputs a drive pulse train signal corresponding to the rotation control data to the step motor 23 to control the rotation of the step motor 23. By this rotation control, the step motor 23 rotationally drives the steering shaft 24, and the left and right rear wheels are driven according to the rotation of the coaxial shaft 24.
RW1 and RW2 are steered to the target rear wheel steering angle K · θf. When steering the left and right rear wheels RW1 and RW2, steering torque acts on the steering shaft 24, so that the power cylinder 33 assists the steering of the rear wheels RW1 and RW2.

After the processing of step 73, the CPU 43c first resets the timer 43e in step 74, and thereafter continuously determines whether or not the time measured by the timer 43e has reached the minute time Δt, thereby executing the program The progress is delayed by Δt time, and after this Δt time has elapsed, the program is returned to step 52,
After that, the circulation process consisting of steps 52 to 54, 60 to 63, 70 to 74 is continuously executed. As a result, the left and right rear wheels RW1, RW2 are steered to the vehicle speed corresponding steering angle ratio Kv set to −K ₀ in step 70.

When the vehicle is started in this state, step 53
1st to 4th new vehicle speeds V1 _new , V2 _new , V3 _new ,
V4 _new gradually rises. These first to fourth new vehicle speeds V
The increase of 1 _new , V2 _new , V3 _new , V4 _new is gentle as long as the vehicle is traveling normally, and the first to fourth flags F1, F2, F3, F4 are set to "1" in step 54. Never set,
In steps 61 and 62, it is determined as "NO" as described above, and in step 62, the first to fourth new vehicle speeds V1 _new , V2 _new ,
The vehicle speed V is calculated based on V3 _new and V4 _new , and in step 70, the vehicle speed corresponding steering angle ratio Kv is determined based on the calculated vehicle speed V. The vehicle speed V and the steering angle ratio Kv corresponding to the vehicle speed are the first
Through, as long as the fourth new vehicle speeds V1 _new , V2 _new , V3 _new , and V4 _new all change smoothly, they change smoothly. This allows
In step 71, since it is determined to be "NO" as in the case described above, even if the vehicle starts running, the CPU 43c
Continue to execute the circulation process consisting of 52-54, 60-63, 70-74. Then, the left and right rear wheels RW1 and RW2 are moved to the fourth position according to the vehicle speed V.
Steering control is performed at a steering angle ratio Kv corresponding to the vehicle speed that changes as shown in the graph of the figure.

Next, a case will be described in which any one of the wheel rotation speed sensors 41a, 41b, 41c, 41d fails, or one of the wheels FW1, FW2, RW1, RW2 idles and locks. In this case, the first to fourth new vehicle speeds calculated in step 53
Any one of V1 _new , V2 _new , V3 _new , V4 _new will show an extremely large value, or one of the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _new Since one of them shows a value greatly different from the corresponding first to fourth old vehicle speeds V1 _old , V2 _old , V3 _old , V4 _old , the above steps 52-
During the circulation process consisting of 54, 60 to 63, 70 to 74, the CPU 43c causes the first to fourth new vehicle speeds V1 _new , V2 which show an abnormal value at step 54.
First to fourth flags F1, F2, F corresponding to _new , V3 _new , V4 _new
Either one of 3 and F4 is set to "1", it is determined "NO" in step 60 and "YES" in step 61, and the program proceeds to step 64.

In step 64, the CPU 43c determines whether or not the front wheel steering angle θf represented by the front wheel steering angle data stored in the RAM 43d is close to zero. In this decision,
If the vehicle is in a straight traveling state, the CPU 43c determines “YES”, that is, the front wheel steering angle θf is a value close to zero, and advances the program to step 65. If the vehicle is in a turning state, the CPU 43c determines If "NO", that is, the front wheel steering angle θf is not a value approximated to zero, the program is determined to be step 66.
Proceed to. In step 65, the CPU 43c causes the first to fourth new vehicles corresponding to the three flags which are not set to "1" by the processing of step 54 among the first to fourth flags F1, F2, F3, F4. The median value of the three values among the speeds V1 _new , V2 _new , V3 _new , and V4 _new is adopted as the vehicle speed V, and vehicle speed data representing the vehicle speed V is stored in the RAM 43d. In step 66, it is determined whether either the first flag F1 or the fourth flag F4 is set to "1". In this determination, if the first or fourth new vehicle speed V1 _new , V4 _new shows an abnormal value and the first or fourth flags F1, F4 are "1", C
PU43c determines “YES” in the same step 66, and proceeds to the step
At 67, the average value of the second and third new vehicle speeds V2 _new , V3 _new (V2 _new
+ V3 _new ) / 2 is calculated and the average value is stored in the RAM 43d as vehicle speed data representing the vehicle speed V. In addition, the second or third new vehicle speed V2 _new , V3 _new shows an abnormal value,
If the flags F2, F3 are "1", the CPU 43c makes a "NO" determination at step 66, and at step 67 the average value of the first and fourth new vehicle speeds V1 _new , V4 _new (V1 _new + V4 _new ) / 2 is calculated and the average value is stored in the RAM 43d as vehicle speed data representing the vehicle speed V. It should be noted that the processing of these steps 66 to 68 reduces the calculation error of the vehicle speed V due to the difference in the turning radii of the wheels FW1, FW2, RW1, RW2 during turning of the vehicle, so that the first to the first which does not include an abnormal value. 4 New vehicle speed V1 _new , V2 _new , V3 _new , V4
_new , which is the average value of the corresponding wheels located on the diagonal line, that is, the average value of those corresponding to the wheels with the maximum turning radius and the minimum turning radius in turning the vehicle, or the wheel whose turning radius is the central binary value It means to calculate the average value of what was done.

After each of these steps 65, 67, 68, the CPU 43c proceeds to step 63 to determine the above-described first to fourth old vehicle speeds V1 _old , V2 _old , V3.
The first to fourth old vehicle speed data representing _old and V4 _old are updated, and based on the vehicle speed V calculated by the processing of steps 65, 67, and 68 in step 70, as described above, the vehicle speed corresponding steering angle ratio Kv
Is determined and the program proceeds to the determination processing in step 71. In this determination process, the steering angle ratio Kv corresponding to the vehicle speed and the RAM 43d
If the absolute value | Kv−K | of the difference from the previous target steering angle ratio K represented by the target steering angle ratio data stored in the above is smaller than the small value β, the CPU 43c proceeds to the same step 71 as described above. As described above, after determining in step 72 to 74 that the program is returned to step 52, steps 52 to 54, 60, 61, 64,
A vehicle speed corresponding steering angle that changes according to the vehicle speed V calculated by the processing of step 65 (67 or 68) by repeatedly executing the circulation processing consisting of 65 (66, 67 or 66,68), 63, 70 to 74. The steering of the left and right rear wheels RW1 and RW2 is controlled according to the ratio Kv. On the other hand, from the calculation processing of the vehicle speed V in step 62 to step 65 (67 or 6
8) Changes in the calculation method of the vehicle speed V due to the change to the calculation processing of the vehicle speed V or the first to fourth new vehicle speeds V1 _new , V2 _new , V3 adopted for calculating the vehicle speed V due to the change _new , V4
By changing to _new , the calculation method changes or the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 especially during turning of the vehicle.
_When the calculated vehicle speed V changes abruptly due to the change of _{new and} the vehicle speed corresponding steering angle ratio Kv determined in step 70 changes abruptly, the CPU 43c returns “NO” in step 71, that is, the absolute value | Kv−. If it is determined that K | is β or more, the program proceeds to step 75. CPU43c, in step 75, RAM43d
The target steering angle ratio K is set to K + (Kv-K) / m by the calculation based on the previous target steering angle ratio K represented by the target steering angle ratio data stored in and the vehicle speed corresponding steering angle ratio Kv. Update
The target steering angle ratio data representing the updated target steering angle ratio K is stored in the RAM 4
Remember in 3d. In this case, m is a predetermined large value,
As a result, the new target steering angle ratio K approaches the vehicle speed corresponding steering angle ratio Kv by (Kv-K) / m. After this step 75, CPU4
3c performs the same processing as in step 73 above, and the left and right rear wheels RW1,
The steering of RW2 is controlled according to the updated target steering angle ratio K. Next, the CPU 43c delays the progress of the program by .DELTA.t time as described above in step 74, and then returns the program to step 52, and thereafter, the previous steering angle ratio data stored in the RAM 43d. Steps 52 to 54,60,61,64,65 (66,67 or 66,68) until the absolute value | Kv−K | of the difference between the target steering angle ratio K and the vehicle speed corresponding steering angle Kv becomes less than β. , 63,70,71,
The circulation process consisting of 75, 73 and 74 is continued, and the target steering angle ratio K is gradually approached to the vehicle speed corresponding steering angle ratio Kv by (Kv-K) / m every Δt time by the process of steps 75 and 74. When the absolute value | Kv−K | becomes less than β by this circulation processing, the CPU 43c determines “YES” in step 71, and updates the target steering angle ratio K to the vehicle speed corresponding steering angle Kv in step 72. , After the processing of steps 73 and 74, the above steps 52 to 54, 60, 61, 64, 65 (66, 67 or 6
6, 68), 63, 70-74 are continuously executed to steer the left and right rear wheels RW1, RW2 to a vehicle speed corresponding steering angle ratio Kv that changes in accordance with the vehicle speed V.

Finally, a case will be described in which any two or more of the wheel rotation speed sensors 41a, 41b, 41c, 41d fail, or any two or more of the wheels FW1, FW2, RW1, RW2 idle and lock. In such a case, any two or more of the first to fourth new vehicle speeds V1 _new , V2 _new , V3 _new , V4 _new calculated in step 53 will show extremely large values, or the first To 4th new vehicle speed V1 _new , V2 _new , V3 _new , V4 _new corresponding to any two or more respectively 1st to 4th old vehicle speed V1 _old , V2
Since it will show a value greatly different from _old , V3 _old , V4 _old , the above steps 52 to 54,60 to 63,70 to 74, or step
52 to 54,60,61,64,65 (66,67 or 66,68), 63,70,71,72
During the cyclic processing consisting of (75), 73, and 74, the CPU 43c executes step 54.
1st to 4th new vehicle speeds V1 _new , V2 _new , V3 showing abnormal values at
Set two or more of the first to fourth flags F1, F2, F3, F4 corresponding to _new , V4 _new to "1", and then "YES" in step 60.
Then, the program proceeds to step 76.

The CPU 43c sets the steering angle ratio Kv corresponding to the vehicle speed to "0" in step 76, and advances the program to the determination processing in step 71.
Also in this case, as in the case described above in step 71,
The absolute value | Kv−K | of the difference between the vehicle speed corresponding steering angle ratio Kv set to “0” and the previous target steering angle ratio K represented by the target steering angle ratio data stored in the RAM 43d is smaller than the small value. It is determined whether it is smaller than the value β. In this case, the previous target steering angle ratio K represented by the target steering angle ratio data stored in the RAM 43d is close to “0”, and the absolute value | Kv−K | is smaller than the small value β. For example, the CPU 43c performs the same step 71.
In step 72, the vehicle speed corresponding steering angle ratio Kv set to “0” is set as the target steering angle ratio K, and after the processing in steps 73 and 74, steps 52 to 54, 60, The circulation process consisting of 76, 71 to 74 is repeatedly executed to control the steering of the left and right rear wheels RW1, RW2 in accordance with the target steering angle ratio K set to "0". On the other hand, the previous target steering angle ratio K represented by the target steering angle ratio data stored in the RAM 43d is not close to "0", and the absolute value | Kv-K | is not less than the small value β. If so, the CPU 43c makes a “NO” determination at step 71, and at step 75 sets the previous target steering angle ratio K represented by the target steering angle ratio data stored in the RAM 43d to “0”. The target steering angle ratio K is updated to K + (Kv−K) / m, that is, (1-1 / m) · K, by the calculation based on the set vehicle speed corresponding steering angle ratio Kv, and the updated target steering angle ratio is calculated. The target steering angle ratio data representing the ratio K is stored in the RAM 43d. As a result, the new target steering angle ratio K approaches the vehicle speed corresponding steering angle ratio Kv (= “0”) by −K / m. After the processing of step 75, the CPU 43c causes the above step 73
By the processing of (1), the steering of the left and right rear wheels RW1, RW2 is controlled according to the updated target steering angle ratio K. Next, the CPU 43c delays the progress of the program by .DELTA.t time as described above at step 74, returns the program to step 52, and thereafter, the RAM 43d.
The absolute value | Kv-K | (= | K |) of the difference between the previous target steering angle ratio K and the vehicle speed corresponding steering angle ratio Kv (= 0) represented by the target steering angle ratio data stored in Step 52 ~ until
Continuing the circulation process consisting of 54, 60, 76, 71, 75, 73, 74, the target rudder angle ratio K is reduced by −K at every Δt time by the process of steps 75, 74.
/ m gradually approaches "0". By this circulation processing,
When the absolute value | K | becomes less than β, the CPU 43c proceeds to step 71
In step 72, the target steering angle ratio K is updated to the vehicle speed corresponding steering angle ratio Kv, that is, “0”, and in step 7
After the processing of 3,74, the circulation processing including the above steps 52 to 54, 60, 76, 71 to 74 is continuously executed and the left and right rear wheels RW1 and RW2 are steered by the steering angle ratio "0", that is, the rear wheel steering angle θf is set to " Steering control is performed to "0".

As can be understood from the above description of the operation, according to the present embodiment, in the normal case, the plurality of wheel rotation speed sensors 41a,
Using the pickup signals from 41b, 41c, 41d, the vehicle speed V is calculated by the process of step 62, and the sensors 41a, 41a,
When the rotation of any one of the wheels 41b, 41c, 41d does not correspond to the vehicle speed V due to the idling or locking of any one of the wheels, the wheel rotation speed sensor corresponding to the wheel is excluded. Since the vehicle speed V is calculated by the processing of steps 64-68 using the pickup signals from the sensors 41a, 41b, 41c, 41d, the vehicle speed V is calculated at the same time when the sensor fails. The calculated vehicle speed V becomes accurate. By calculating the vehicle speed V and improving its accuracy, the steering control of the left and right rear wheels RW1, RW2 is performed even if any one of the wheel rotation speed sensors 41a, 41b, 41c, 41d fails, so that the front and rear wheel steering vehicle is controlled. And the steering control can be performed well.

In addition, a sudden change in the calculated vehicle speed V due to a change in the calculation processing of the vehicle speed V from the calculation processing of the vehicle speed V in step 62 to steps 64-68, or two from the wheel rotation speed sensors 41a, 41b, 41c, 41d. Left and right rear wheels that are recognized as abnormal pickup signals
When the steering speed control of RW1 and RW2 is stopped and the steering angle ratio Kv corresponding to the vehicle speed changes abruptly, the steep control of the left and right rear wheels RW1 and RW2 is controlled by the process of steps 71 and 75 to mitigate this abrupt change. Therefore, the steering angles θ _{r of} the rear wheels RW1 and RW2 do not change abruptly, and the deterioration of the steerability of the vehicle is better prevented.

In the above embodiment, steps 61, 62, 64-68.
Although the vehicle speed V is calculated by a relatively simple method by the processing described in (1), for example, as already proposed by the same applicant in Japanese Patent Application No. 60-291157, further factors such as vehicle acceleration and The vehicle speed V may be calculated in consideration of deceleration. Further, in the above embodiment, each wheel FW1, FW2, RW1, RW
4 wheel rotation speed sensors 41a, 41b, 41c, 4 corresponding to 2 respectively
Although the vehicle speed V is calculated using 1d, the present invention is also applicable to a case where only two wheel speed sensors are provided. In this case, step 54 of the above embodiment
If the signal from each sensor is abnormal, the vehicle speed V is calculated by averaging the two vehicle speeds calculated from both signals, and one signal is abnormal. In this case, the vehicle speed calculated from the other signal is set to the vehicle speed V.
It should be made to act as.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the configuration of the invention described in the claims, FIG. 2 is an overall schematic diagram of a vehicle showing one embodiment of the present invention, and FIG. 3 is executed by a second microcomputer. FIG. 4 is a flow chart of a program according to the present invention, and FIG. Explanation of symbols A ... front wheel steering device, B ... rear wheel steering device, C ... electric control device, FW1, FW2 ... front wheels, RW1, RW2 ... rear wheels, 41a, 41
b, 41c, 41d …… Wheel speed sensor, 41e …… Front wheel steering angle sensor, 41f …… Rear wheel steering angle sensor, 43 …… Microcomputer.

Front Page Continuation (72) Inventor Takashi Shigematsu 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Norio Koda 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (56) Reference References: JP-A-60-85067 (JP, A), JP-A-61-148763 (JP, U)

Claims (1)

[Claims] 1. A front and rear wheel steering vehicle including a rear wheel steering device for steering rear wheels according to a steering state of front wheels and a vehicle speed, wherein each rotation of a plurality of wheels is continuously detected to represent each rotation. A plurality of rotation detection sensors that respectively output a plurality of output signals, a vehicle speed calculation unit that repeatedly calculates a vehicle speed that changes over time based on each output signal from the plurality of rotation detection sensors, and the latest calculated repeatedly. A vehicle speed corresponding steering angle ratio determining means for repeatedly determining a vehicle speed corresponding steering angle ratio which is a steering angle ratio of the rear wheels to the front wheels based on the vehicle speed and changes according to the same vehicle speed, and the latest vehicle speed corresponding steering angle which is repeatedly determined. Compare the ratio and the steering angle ratio of the rear wheel to the front wheel that is currently set,
When the difference between the two steering angle ratios is smaller than a predetermined value, the latest steering angle ratio corresponding to the vehicle speed is determined as the target steering angle ratio, and when the difference between the two steering angle ratios is equal to or more than the predetermined value, the previous target steering angle ratio is set. Target rudder angle ratio determining means for deciding as a target rudder angle ratio a value changed by a predetermined small value in a direction approaching the latest vehicle speed corresponding rudder angle ratio, and a control signal corresponding to the determined target rudder angle ratio. And a control means for controlling the rear wheel steering device so as to steer the rear wheel according to the target steering angle ratio by outputting to the rear wheel steering device. Steering control device.