JPS6271761A - Rear-wheel steering controller for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To aim at preventing a spin due to a slip from occurring, by installing each revolving speed detecting device for both front and rear wheels, and a controlled variable setting device, setting a controlled variable which steers rear wheels according to the speed difference as well as an outputting device. CONSTITUTION:A car speed U is calculated out of a car speed sensor 51a by a central processing unit 52b and stored in a random access memory 52c, while a revolving speed data is stored into the RAM 52c by wheel revolving speed sensors 51b-51e. A smaller side of a front-wheel revolving speed is subtracted from a larger side of a rear-wheel revolving speed on the basis of the revolving speed data by the CPU 52b whereby a speed difference (g) is calculated and stored into the RAM 52c. Next, a car speed corresponding steering angle ratio K is calculated by the steering angle ratio pattern data stored in a read-only memory 52a on the basis of the car speed data by the CPU 52b, adding a functional value (f) to be increased in proportion as this speed difference (g) increases, thus the desired steering angle ratio K+f is calculated. With this constitution, steering control takes place as the same phase or opposite phase to front wheels according to a slip state in rear wheels so that a spin due to a slip is prevented from occurring without fail.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a front and rear wheel steering vehicle equipped with a front wheel steering mechanism and a rear wheel steering mechanism, and particularly relates to a front wheel steering vehicle equipped with a front wheel steering mechanism and a rear wheel steering mechanism. The present invention relates to a rear wheel steering control device for a front and rear wheel steered vehicle that controls the amount of steering of the rear wheels to prevent spin or drift out.

[Prior art]

Conventionally, this type of control device uses a sensor that detects the acceleration of a turning vehicle, a sensor that detects the longitudinal acceleration of the vehicle, a sensor that detects the lateral acceleration of the vehicle, or an accelerator, as shown in Japanese Patent Application Laid-Open No. 57-60974. It is detected by a sensor that detects pedal depression, and if the vehicle is a rear wheel drive type (or front wheel drive type), when the vehicle accelerates while turning, the rear wheels are moved relative to the front wheels based on the detected acceleration. The vehicle spins (or drifts) caused by the rear (or front) driving wheels slipping as the vehicle accelerates while turning. We are trying to prevent this.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional device, when the above-mentioned acceleration is detected by a sensor that detects the longitudinal acceleration of the above-mentioned vehicle, the sensor is usually provided in a part of the vehicle body, and this vehicle body is This causes a pitching phenomenon, and the sensor vibrates in the longitudinal direction of the vehicle together with the vehicle body, making the acceleration detected by the sensor inaccurate. Furthermore, when the above-mentioned acceleration is detected by a sensor that detects the lateral acceleration of the above-mentioned vehicle, the sensor is also usually installed in a part of the vehicle body, and this vehicle body causes a rolling phenomenon due to the unevenness of the road surface and the above-mentioned turning. The sensor moves in the lateral direction of the vehicle along with the vehicle body, and the acceleration detected by the sensor also becomes inaccurate. Furthermore, when the above acceleration is detected by a sensor that detects the depression of the accelerator pedal, there is a time delay between the depression of the accelerator pedal and the acceleration of the vehicle, and even if the accelerator pedal is depressed, the speed of the vehicle may vary depending on the driving condition of the vehicle. Since the acceleration conditions are different, there is no one-to-one correspondence between vehicle acceleration and accelerator pedal depression.
In this case as well, the detected acceleration will be inaccurate.

Due to such inaccurate detection of vehicle acceleration, the rear wheel steering control based on the above-mentioned sensor does not perform the same control properly, so the vehicle spins due to the slip of the drive wheels that occurs when the vehicle accelerates during a turn. Alternatively, drift-out may not be prevented, resulting in poor vehicle handling.

SUMMARY OF THE INVENTION In order to solve the above problem, an object of the present invention is to detect the slip state of the driving wheels that occurs when the vehicle accelerates by detecting the rotational speed difference between the driving wheels and the non-driving wheels, and to adjust the rear wheels according to the rotational speed difference. 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 performs steering control to reliably prevent the vehicle from spinning or drifting out due to slipping of the drive wheels that occurs when the vehicle accelerates while turning. It is.

[Means for solving problems]

In solving this problem, the structural features of the present invention are as follows:
As shown in FIG. 1, a front wheel steering mechanism 3a that steers the front wheels 2a according to the rotation of the steering handle l, a rear wheel steering mechanism 3b that steers the rear wheels 2b, and a rear wheel steering mechanism 3b that steers the rear wheels 2b (or the front wheels 2a). In a rear wheel (or front wheel) drive type front and rear wheel steered vehicle equipped with a rear wheel drive device 4 (or front wheel drive device 4) that drives,
Front wheel rotation speed detection means 5a detects the rotation speed of the front wheel 2a, and rear wheel rotation speed detection means 5b detects the rotation speed of the rear wheel 2b.
and control to increase as the difference between the detected front wheel rotation speed and the rear wheel rotation speed increases, and to steer the rear wheels 2b in the same phase (or opposite phase) direction with respect to the front wheels 2a in accordance with the steering of the front wheels 2a. control amount determining means 6 for determining the determined control amount; and output means 7 for outputting a control signal corresponding to the determined control amount to the rear wheel steering mechanism 3b and controlling the steering of the rear wheels 2b in accordance with the control amount. There is a particular thing.

[Function and effect of the invention]

In the present invention configured as described above, the front wheel rotation speed detection means 5a detects the rotation speed of the front wheel 2a which is a non-driving wheel (or a driving wheel), and the rear wheel rotation speed detection means 5b detects the rotation speed of the front wheel 2a which is a non-driving wheel (or a driving wheel).
The control amount determining means 6 detects the rotation speed of the rear wheel 2b which is a non-driven wheel), and the control amount determining means 6 determines a control amount according to the difference between the two rotation speeds. 2a, and based on this control amount, the output means 7 and the rear wheel steering mechanism 3b steer the rear wheels 2a in the same phase (or in opposite phase).
Steer b. As a result, the control amount represents the slip state of the rear wheel 2b (or front wheel 2a), which is the driving wheel, accompanying vehicle acceleration, and the rear wheel 2b is in phase (or Since the steering control is performed in opposite phases, the vehicle is prevented from spinning (or drift out)
This is reliably prevented, and as a result, the handling stability of the vehicle is improved.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a front wheel steering mechanism 20 of a vehicle to which the present invention is applicable;
A rear wheel steering mechanism 30, a rear wheel drive device 40, and an electric control device 50 that controls the rear wheel steering mechanism 30 are shown.

The front wheel steering mechanism 20 includes a rack and pinion mechanism 21 and a pair of left and right relay rods 22a and 22b connected to a rack portion of the mechanism 21. The rank and pinion mechanism 21 is connected at its pinion portion to a steering handle 24 via a steering shaft 23.
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 the 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 swing lever 32 for steering the rear wheels 31a, 31b in conjunction with the steering of the front wheels 27a, 27b.
A linear actuator 33 for displacing the movable fulcrum 32a of the swing lever 32, left and right rear wheels 31a,
31b is provided. The swinging 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, and the fulcrum 32a has a force point 32b and an action point 32C. If the fulcrum 32a is on the opposite side of the force point 32b with respect to the force point 32C, the force point 32c is displaced in the same direction as the force point 32b. , furthermore, when the fulcrum 32a is on the point of action 32c, the point of action 32
C is not displaced, and the steering angle ratio is set based on the position of the fulcrum 32a based on the ratio of the distance between the fulcrum 32a and the point of effort 32b and the distance between the fulcrum 32a and the point of action 32c. The linear actuator 33 is a movable fulcrum 32
The movable 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 to the left and right tie rods 37.
a, 37b, and left and right knuckle arms 38a, 38b, and a rear connecting rod 36 is connected to the left knuckle arm 38a, and the rear wheels 31a, 31b are steered by the swinging of the swinging lever 32. .

The rear wheel drive device 40 includes an engine 41 disposed on the front side of the vehicle body and a differential mechanism 42, and the driving force of the engine 41 is transmitted through a main drive shaft 43 connected between the engine 41 and the differential mechanism 42. is transmitted to the differential mechanism 42 via. This transmitted driving force is transmitted to the differential mechanism 42 and the left and right rear wheels 31a, 31.
The power is transmitted to the left and right rear wheels 31a, 31b via the left and right rear wheel drive shafts 44a, 44b connected between the rear wheels 44a, 44b, respectively, and thereby the left and right rear wheels 31a, 31b are driven based on the output of the engine 41.

The electric control device 50 includes a vehicle speed sensor 51 that detects the vehicle speed U.
a, and each wheel 27a, 27b, 31a.

Wheel rotation speed sensor 51b that detects the rotation speed of wheel rotation speed 31b.
, 51c, 51d, 51e, and each of these sensors 51a
, 51b, 51c, 51d, and 51e, * is calculated for the target steering angle based on the signals generated from 51b, 51c, 51d, and 51e.
A microcomputer 5 that outputs a control signal corresponding to
2, and by inputting this control signal, the linear actuator 3
A differential amplifier 53 is provided to control 3.

The vehicle speed sensor 51a picks up the rotation of the output shaft of the transmission and generates a pick amplifier signal with a frequency proportional to the vehicle speed U, and this pickup signal is converted into a rectangular wave signal by the waveform shaper 54a and supplied to the microcomputer 52. be done. Wheel rotation speed sensors 51b, 51c, 51d,
51e is each wheel 27a, 27b, 31a
, 3 l b pick up each rotation of each wheel 2
7a, 27b, 31a.

31b, each of which has a frequency proportional to the number of rotations, and these pickup signals are passed through the waveform shapers 54b, 54c, 54d, 54, respectively.
e converts the signal into a rectangular wave signal and supplies it to the microcomputer 52.

The microcomputer 52 includes a read-only memory (hereinafter simply referred to as ROM) 52a that stores a program corresponding to the flowchart shown in FIG. A central processing unit (hereinafter simply referred to as CPU) 52b that executes the program, a writable memory (hereinafter simply referred to as RAM) 52c that temporarily stores data necessary for executing this program, and each sensor 51a, 51b, 51c, 5
A turnout interface (hereinafter simply referred to as Ilo) 52d that inputs signals supplied from 1d and 51e, and RO
M52a, CPU52b, RAM52C and l105
A bus 52e commonly connects the 2d. Also, l1
At 052d, a digital-to-analog converter (hereinafter simply referred to as D/A converter) converts the digital signal representing * to the target steering angle ratio outputted from the microcomputer 52 into an analog signal and supplies it to the non-inverting input of the differential amplifier 53. (called a vessel)
55 is connected.

The differential amplifier 53 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.

The operation of the above-described embodiment configured as described above will be explained using the flowchart shown in FIG. When the driver closes the ignition switch (not shown) to start the vehicle, the CPU 52b starts executing the program in step 60, and in step 61, the CPU 52b starts executing the program.
The vehicle speed U is calculated based on the pick amplifier signal supplied from A through the waveform shaper 54a and l1052d, and vehicle speed data representing this vehicle speed U is stored in the RAM 52C.In step 62, each wheel rotation speed sensor 51b, 51c , 51
d, 51e to waveform shapers 54b, respectively.

54 c, 54 d, 54 e and -l105
The rotation speed NrL of each wheel 27a, 27b, 31a, 31b based on the pickup signal supplied via 2d.

Nf2. Calculate Nrl and Nf2, and calculate each rotation speed N
f1. Nf 2. Nr 1. Wheel rotation speed data each representing Nf2 is stored in the RAM 52C. After the above calculation, C
In step 63, the PU 52b determines the rear wheel rotation speed Nrl based on the wheel rotation speed data.

The front wheel rotation speed Nfl is determined from the larger value of Nf2.

By subtracting the smaller value of Nf2, a front and rear wheel rotational speed difference g is calculated, and rotational speed difference data representing this front and rear wheel rotational speed difference g is stored in the RAM 52G.

As described above, the calculation of the front and rear wheel rotational speed difference g is based on the slip condition that occurs in the left and right rear wheels 31a and 31b, which are drive wheels, when a rear wheel drive type vehicle equipped with the rear wheel drive device 40 accelerates. It means to detect.

In addition, in the above calculation, the front wheel rotation speed difference g is calculated from the larger value of the rear wheel rotation speeds Nrl and Nr2 to the front wheel rotation speed Nfl.
, Nf2, the front wheel rotation speed Nfl is calculated from the average value of the rear wheel rotation speeds Nrl and Nr2.

It may be calculated by subtracting the average value of Nf.

Next, the CPU 52b reads the steering angle ratio pattern data stored in the ROM 52a based on the stored vehicle speed data, and adjusts the vehicle speed according to the steering angle ratio pattern shown by the solid line in FIG. 4 based on the relationship with the calculated vehicle speed U. Determine the steering angle ratio K. As a result, the vehicle speed corresponding steering angle ratio is set to a value that continuously changes from a negative value with a large absolute value to a positive value with a large absolute value as the vehicle speed U increases. Note that when the steering angle ratio is negative (or positive), the left and right rear wheels 31a, 31b
This means that the wheels are steered in opposite phase (or in phase) with respect to the left and right front wheels 27a and 27b. After calculating the steering angle ratio corresponding to the vehicle speed, the CPL 152b in step 65 calculates a function value f(g) that increases as the front and rear wheel rotation speed difference g increases, based on the stored wheel rotation speed data, for example, f (
g) = α・g, and add this value f (g) to the vehicle speed corresponding steering angle ratio K to set the target steering angle ratio *
(−+f (g)) is calculated. Note that the coefficient α is a positive constant, and according to the above calculation, the target steering angle ratio * increases as the front and rear wheel rotation speed difference g increases; Left and right rear wheels 31a
, 31b has a large slip ratio (I see, this means that the steering angles of the left and right rear wheels 31a, 31b determined by the vehicle speed corresponding steering angle ratio K are largely corrected in the same phase direction with respect to the left and right front wheels 27a, 27b. .

As a result, the steering angle ratio pattern characteristic shown by the solid line in FIG. 4 changes like the steering angle ratio pattern characteristic shown by the broken line in FIG. 4, and the degree of change increases as the slip ratio increases. , and the above function f (g) is the left and right rear wheels 31a
, 31b and the spin of the vehicle, and is not limited to the above relationship. For example, the function f (g) is determined by the relationship f (g) when the front and rear wheel rotation speed difference g is smaller than a predetermined value. = α·g, and when g is equal to or greater than a predetermined value, it may be defined as f (g) = β·gL (where β is a positive constant). According to this, when the front and rear wheel rotational speed difference g is small, the amount of correction to the same phase side is small relative to the same amount of change in the same left g, and when the same left g increases, the amount of correction to the same phase side is the same as the same left g. It increases with the amount of change.

After the calculation in step 65, the CPU 52b outputs a digital signal representing * to the calculated target steering angle ratio to the D/A converter 55 via the l1052d in step 66. converts this digital signal into an analog signal and supplies it to the differential amplifier 53, which controls the linear actuator 33 in cooperation with the position sensor 56 to determine the set steering angle of the swing lever 32. The fulcrum 32a is displaced so that the ratio becomes * to the target steering angle ratio.

Next, the program returns to step 61 again, and thereafter the C
The PU 52b continues to execute the circulation process of steps 61 to 66, calculates * as the target steering angle ratio according to the vehicle speed U and the front and rear wheel rotational speed difference g, and sets the set steering angle ratio of the swing lever 32 to the above target. Set the steering angle ratio to *.

Note that the digital signal indicating the target steering angle ratio output from the CPU 52b is stored in the l1052d until a new digital signal is output from the CPU 52b.

In such a state, assuming that the steering wheel 24 is in a neutral state, the steering angles of the left and right front wheels 27a and 27b are zero, and the swing lever 32 does not swing, so the steering of the left and right rear wheels 318, 31b is The angle is also zero, and the vehicle is traveling straight. On the other hand, when the steering wheel 24 of the vehicle is turned to the left (or right), the left and right front wheels 27a, 27b are steered to the left (or right), and this steering force is applied to the left knuckle arm 26a, the front connecting rod 35, swing lever 3
2. Rear connecting rod 36, left knuckle arm 38a, left tie rod 37a1, relay rod 34, right tie rod 3
7b and the right knuckle arm 38b to the left and right rear wheels 3L.
a, 31b, and the left and right rear wheels 31a, 31b are steered according to the steering angle ratio set by the swing lever 32. Therefore, when the vehicle speed U is small, the left and right rear wheels 31
a, 31b are steered in opposite phase to the left and right front wheels 27a, 27b, that is, in the right direction (or left direction), and when the vehicle speed U is high, the left and right rear wheels 31a, 31b are steered in the same phase, that is, in the left direction (or left direction) with respect to the left and right front wheels 27a, 27b. (to the right).

As a result, the vehicle turns left (or right) with a small turning radius when the vehicle speed U is low, and turns left (or right) with a large turning radius when the vehicle speed U is high.

The left-turning state of the vehicle, the yaw rate of the vehicle in this state, and the number of revolutions Nf of the wheels 27a, 27b, 31a, and 31b.1. Nf 2. The temporal changes in Nr 1°Nf2 and the slip angle of the vehicle are shown in FIGS. 5 and 6. Time t in FIG.

Assuming that the vehicle starts turning to the left at time t1 and turns at approximately constant speed until time t1, the yaw rate and wheel rotation speed Nf1. Nf 2. Nrl, Nf2 and slip angle change smoothly. Then, at time t1, when the vehicle is accelerated while keeping the rotational position of the steering wheel 24 in the previous state, the left and right rear wheels 31a, 3, which are the drive shafts,
1b slips, and the rotation speed of the left and right rear wheels 31a and 31b is Nrl.

Nf2 increases rapidly, but the left and right front wheels 2, which are non-driving wheels,
The rotational speeds Nfl and Nf2 of 7a and 27b do not increase that much. Note that the rotation speed Nr1 of the left rear wheel 31a is the same as that of the right rear wheel 31b.
The reason why the rotational speed is higher than Nr2 is because the load applied to the wheel on the inside of the turn is smaller than the load on the wheel on the outside of the turn due to the centrifugal force when the vehicle turns, so the slip ratio of the wheel on the inside of the turn is higher than that of the wheel on the outside of the turn. This is because the slip rate of the front right wheel 27b is higher than that of
The reason why Nfl becomes larger than the rotational speed Nfl of the left front wheel 27a is because the rotation radius of the right front wheel 27b becomes larger than the rotation radius of the left front wheel 27a as the vehicle turns left. In this way, when the vehicle accelerates while turning, the slip ratio of the left and right rear wheels 31a, 31b increases, and the vehicle tends to oversteer.
The yaw rate and slip angle may suddenly increase and the vehicle may spin. Therefore, in the above embodiment, the front and rear wheel rotational speed difference g, which represents the slip state of the left and right rear wheels 31a and 31b, is calculated by the calculation in step 63 of the flowchart in FIG. The larger g is, the thicker it is (the function value f
(g) is calculated, and correction control is performed using this function value f (g) so that the left and right rear wheels 318.31b are steered in the same phase direction with respect to the left and right front wheels 272.27b.
The spin caused by the slips of 1a and 31b is prevented, and the maneuverability of the vehicle is improved. In addition, when the vehicle turns right, the left and right front wheels 27a as in the case of the left turn.

27b, and the left and right rear wheels 31a, 31b are steered in opposite directions, but the operation is the same as in the above case.

Note that the vehicle speed sensor 51a in the above embodiment is omitted, and each wheel 27a, 27b, 31a, 31 is provided with wheel rotation speed sensors 51b, 51c, 51d, and 51e.
Each rotation speed Nf of b 1. Nf 2. Calculate the total average value of Nr 1°Nf2 or calculate the left and right front wheels 27a, which are non-drive axles,
It is also possible to calculate the vehicle speed U by a method such as calculating the average of the respective rotational speeds Nfl and Nf2 of the engine 27b.

Next, a second embodiment of the present invention will be described. FIG. 7 shows a portion of a rear wheel steering mechanism 30 and an electric control device 50 which are a modification of the first embodiment shown in FIG. The same parts as in the example are given the same reference numerals. Rear wheel steering mechanism 30
are the left and right rear wheels 31a.

31b, and a linear actuator 39 that directly drives the rods 34a, 34b. left and right relay rods 34a,
34b connects to the left and right rear wheels 313.3 via the left and right tie rods 37a, 37b and the left and right knuckle arms 38a, 38b.
1b, and steer the left and right rear wheels 31a, 31b in conjunction with each other. The electric control device 50 includes a D/A converter 55 and a differential amplifier 53 similar to those in the first embodiment, and the inverting input of the differential amplifier 53 is connected to the right relay rod 3.
A position sensor 57 detects the displacement position of the left and right rear wheels 31a and 4b and generates an analog signal representing the steering angle δr of the left and right rear wheels 31a and 31b.
is connected. Furthermore, as shown by the broken line in FIG. 2, this electric control device 50 includes a front wheel steering angle sensor 58 that detects the rotation angle of the steering shaft 23 and generates an analog signal representing the steering angle δf of the left and right front wheels 27a, 27b. , an A/D converter 59 that converts this analog signal into a digital signal and supplies it to the microcomputer 52. In addition,
The remaining parts are the same as in the first embodiment except for a different program, which will be described later.

The operation of the second embodiment configured as described above will be explained with reference to the flowchart of FIG. The target rear wheel steering angle is calculated by multiplying the target steering angle ratio by * and the front wheel steering angle δf read from the front wheel steering angle sensor 58, and *.delta.f is calculated. The signal is output to the D/A converter 55 in FIG. The D/A converter 55 converts this digital signal into an analog signal and supplies it to the differential amplifier 53, and the differential amplifier 53 cooperates with the position sensor 57 to convert the rear wheel steering angle δr into the target rear wheel steering angle. *・δf. This achieves the same effect as the first embodiment.

In the first and second embodiments described above, the steering angles of the left and right rear wheels 31a, 31b, which are determined according to the vehicle speed U, are corrected and controlled based on the difference g between the front and rear wheels. The left and right rear wheels 31a according to.

This can also be applied to vehicles in which the steering angle of 31b is not controlled. That is, the left and right rear wheels 31a, 31 are determined only by the function value f (g) determined according to the difference g in the rotational speed of the front and rear wheels.
b may be controlled in the same phase direction with respect to the left and right front wheels 27a and 27b.

Further, in the first and second embodiments described above, 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, during acceleration, the slip rate of the left and right front wheels 27a, 27b, which are drive wheels, becomes high, and the rotational speeds Nfl, Nf of the left and right front wheels 27a, 27b increase.
2 is the rotation speed N of the left and right rear wheels 3La and 31b, which are non-driving wheels.
As the slip ratio becomes larger than rl and Nr2, the vehicle in question tends to understeer while turning, and as the slip ratio becomes higher, it drifts out. Therefore, in this case, in step 63 of the flowchart in FIG.
, left and right rear wheels 312 from the larger Nf2 (or average value)
．． 31b rotation speed Nr1. The calculation is made by subtracting the smaller one (or the average value) of Nr2, and in the calculation at step 65, *crab*=−f (
It is calculated according to the relationship g).

As a result, the target steering angle ratio * changes as shown by the dashed line in FIG. 4, and when the vehicle in question accelerates while turning, the left and right rear wheels 31a and 31b change to the left and right front wheels 27a.

Since the correction control is performed in the opposite phase direction with respect to 27b, drift-out during turning acceleration in a front-wheel drive vehicle is prevented. Furthermore, in this case as well, the left and right rear wheels 3
The steering angle 18.31b may not change depending on the vehicle speed U.

[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 a first embodiment of the invention, and FIG. Figure 4 is a characteristic graph showing the steering angle ratio to vehicle speed, Figure 5 is a diagram showing the turning state of the vehicle, and Figure 6 is a graph showing the yaw rate and wheels when turning a rear-wheel drive vehicle. A diagram showing the change characteristics of rotational speed and slip ratio, and FIG. 7 are partial schematic diagrams of a vehicle showing a second embodiment of the present invention. 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
．． 39... Linear actuator, 40... Rear wheel drive device, 41... Engine, 50... Electric control device, 51a... Vehicle speed sensor, 5 l b, 51 c
, 51 d, 51 e - Wheel rotation speed sensor, 52... Microcomputer, 56.57...
- Position sensor, 58... Front wheel steering angle sensor.

Claims (1)

[Claims] Equipped with a front wheel steering mechanism that steers the front wheels according to rotation of the steering wheel, a rear wheel steering mechanism that steers the rear wheels, and a rear wheel drive device (or front wheel drive device) that drives the rear wheels (or front wheels). In a rear wheel (or front wheel) drive type vehicle with front and rear wheel steering,
A front wheel rotation speed detection means detects the rotation speed of the front wheels, a rear wheel rotation speed detection means detects the rotation speed of the rear wheels, and the rotation speed increases as the difference between the detected front wheel rotation speed and the rear wheel rotation speed increases. and a control amount determining means for determining a control amount for steering the rear wheels in the same phase (or opposite phase) direction with respect to the front wheels in response to the steering of the front wheels, and a control signal corresponding to the determined control amount to the rear wheel steering mechanism. 1. A rear wheel steering control device for a front and rear wheel steering vehicle, comprising: an output means for outputting an output and controlling the steering of the rear wheels according to the control amount.