JPS6374772A - Rear wheel steering controller for front/rear wheel - Google Patents

Abstract

PURPOSE:To prevent spin or drift-out and improve the steering stability by permitting the steering control for rear wheels when each detection value of front wheel steering angle and accelerator opening degree is larger than each prescribed value and prohibiting the steering control except in the above-described case. CONSTITUTION:When a car is accelerated during turning, a judging means 8 judges the turning acceleration state on the basis of the fact that each detection value of the detecting means 6 and 7 for the front wheel steering angle and accelerator opening degree is larger than each prescribed value and permits the steering control for rear wheels RW by a control means 5. The control means 5 steering controls the rear wheels RW to the steering angle ratio corresponding to the difference of a the number of revolution detected by the front/rear wheel revolution speed detecting means 2 and 3 which a determining means 4 determines, in the cooperation with a rear wheel steering mechanism 1.Therefore, the spin or drift-out due to the slip of driving wheel in acceleration during turn is prevented, and steering stability can be improved. Further, when the car is not accelerated during turning, the judging means 8 prohibits the steering control for the rear wheels RW, and steering stability can be improved furthermore.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a rear wheel steering control device for a front and rear wheel steered vehicle, and particularly for preventing spin or driftout of the vehicle when the vehicle accelerates while turning. The present invention relates to a rear wheel steering control device for a front and rear wheel steered vehicle that controls the steering of the rear wheels.

[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. Spin (or drift-out) of the vehicle 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 vibrates in the lateral direction of the vehicle along with the vehicle body, making the acceleration detected by the sensor inaccurate. Furthermore, when the above acceleration is detected by a sensor that detects depression of the accelerator pedal,
There is a time delay between when the accelerator pedal is pressed and when the vehicle accelerates, and even when the accelerator pedal is pressed, the acceleration state of the vehicle differs depending on the driving condition of the vehicle, so there is a one-to-one correspondence between the acceleration of the vehicle and the pressing of the accelerator pedal. Otherwise, the detected acceleration will be inaccurate in this case as well.

Due to such inaccurate detection of vehicle acceleration, rear wheel steering control based on the above-mentioned sensor does not adequately prevent vehicle spin or drift-out due to slippage of the drive wheels when the vehicle accelerates during a turn. There was a problem.

Therefore, the present applicant submitted the following application:
No. 65), the slip state of the driving wheels that occurs when the vehicle accelerates is detected based on the difference in rotational speed between the driving wheels and non-driving wheels, that is, the difference in the rotational speed between the front wheels and the rear wheels. The front and rear wheels are designed to control the steering of the rear wheels by setting and controlling the steering angle ratio of the wheels, and to prevent the vehicle from spinning or drifting out based on the slip of the drive wheels when the vehicle accelerates during a turn. We proposed rear wheel steering control for steered vehicles.

According to this proposed device, when the vehicle is traveling on a normal road, spin or drift-out of the vehicle is appropriately controlled. However, if the vehicle is traveling on a rough road and the coefficient of friction between the drive wheels and the road surface is small, the difference in rotational speed between the drive wheels and the non-drive wheels will increase, regardless of the acceleration of the vehicle during turning. There are cases where the difference in rotational speed between the front wheels and the rear wheels becomes extremely large. In such a case, if the ratio of the steering angle of the rear wheels to the front wheels is set according to this rotational speed difference, the rear wheels will be largely steered regardless of the turning acceleration of the vehicle, which will actually worsen the steering stability of the vehicle. There's a problem.

The present invention was devised in view of the problems caused by the conventional device and the proposed device, and its purpose is to enable the proposed device to properly control rear wheel steering even when driving on rough roads. An object of the present invention is to provide a rear wheel steering control device for a front and rear wheel steered vehicle that more reliably prevents a vehicle from spinning or drifting out due to slippage of the drive wheels when the vehicle accelerates while turning.

[Means for solving problems]

In order to solve the above problems and achieve the purpose of the present invention,
The structural feature of the present invention is as shown in FIG.
a rear wheel steering mechanism 1 for steering W; a front wheel rotation speed detection means 2 for detecting the rotation speed of the front wheels FW; a rear wheel rotation speed detection means 3 for detecting the rotation speed of the rear wheels RW; determining means 4 for determining the ratio of the steering angle of the rear wheels RW to the front wheels FW according to the difference between the rotation speed of the rear wheels and the rotation speed of the rear wheels; and a control means 5 which outputs an output to the mechanism 1 and controls the steering of the rear wheels RW so that the rear wheel steering angle becomes a ratio of the determined steering angle,
A rear wheel steering control device for a front and rear wheel steered vehicle that prevents the vehicle from spinning or drifting out during turning acceleration, comprising a front wheel steering angle detection means 6 that detects a front wheel steering angle, and an accelerator opening that detects an accelerator opening. a detecting means 7; and a determining means 8 for allowing the steering control of the rear wheels by the control means 5 when both the detected front wheel steering angle and the accelerator opening are larger than a predetermined value, and prohibiting the steering control otherwise. This is because we have established this.

[Action/effect of the invention]

In the present invention configured as described above, when the vehicle is accelerated while turning, the determining means 8 determines the front wheel steering angle and the accelerator position detected by the front wheel steering angle detecting means 6 and the accelerator opening detecting means 7, respectively. Based on the fact that both opening degrees are larger than the predetermined values, it is determined that the vehicle is in a turning acceleration state and the control means 5 is allowed to control the steering of the rear wheels RW. The ratio of the steering angle determined by the determining means 4, that is, the rotation speed difference between the front wheel rotation speed and the rear wheel rotation speed detected by the front wheel rotation speed detection means 2 and the rear wheel rotation speed detection means 3 is determined by the cooperation of The rear wheels RW are steered according to the steering angle ratio.

This prevents the vehicle from spinning or drifting out due to the slip of the drive wheels when the vehicle accelerates during a turn, similar to the proposed device described above, and improves the steering stability of the vehicle.

Further, if the vehicle is not accelerated while turning, the determining means 8, contrary to the above, determines that the vehicle is not in a turning acceleration state and prohibits the control means 8 from controlling the steering of the rear wheels RW. Even if the vehicle is traveling on a rough road and the front wheels FW or rear wheels RW, which are drive wheels, slip regardless of the turning acceleration of the vehicle, the control means 8 does not perform steering control of the rear wheels RW.

As a result, in such a case, the rear wheels RW are not steered according to the rotational speed difference (this results in the problem that the rear wheels RW are steered regardless of the turning acceleration of the vehicle, as in the above-mentioned proposed device). This problem is solved, and the vehicle maneuverability becomes even better than that of the above-mentioned proposed device.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 2 schematically shows a front and rear wheel steered vehicle according to the present invention. This front and rear wheel steering vehicle includes a front wheel steering mechanism 10 that steers the left and right front wheels FWl and FW2, a rear wheel steering mechanism 20 that steers the left and right rear wheels RWI and RW2, a drive device 30 that drives the left and right rear wheels RWI and RW2, and a rear wheel. It consists of an electric control device 40 that electrically controls the steering mechanism 20.

The front wheel steering mechanism 10 has a steering shaft 12 that rotates in response to rotation of a steering handle 11. A pinion gear 13 is provided at the lower end of the coaxial 12, and the gear 13 is connected to a relay rod 14.
It meshes with the rank portion 14a of. Both ends of the relay rod 14 are connected to the left and right front wheels FW1. FW
2 are connected, and the front wheels FWI and FW2 are steered in accordance with the rotation of the steering handle 11.

The rear wheel steering mechanism 20 rotates the front connecting rod 2 at the power point 21a.
It has a swing lever 21 connected to the left knuckle arm 16a via 2a. The swing lever 21 swings around the fulcrum 21b in response to the displacement of the force point 21a, and moves to the point of action 21c.
is displaced according to the ratio of each distance from the fulcrum 21b to the force point 21a and the application point 21c, and the fulcrum 21b is moved by the linear actuator 23 to the actuator rod 2.
3a, the left and right front wheels FW1. Set the steering angle ratio of the left and right rear wheels RWI and RW2 with respect to FW2. An operating point 21c of the swing lever 21C is connected to a left knuckle arm 24a connected to the left rear wheel RWI via a rear connecting rod 22b. The left knuckle arm 24a is the left tie rod 2
5a to the left end of the relay rod 26, and the right end of the relay rod 26 is connected to the right rear wheel R via the left tie rod 25b.
It is connected to the right knuckle arm 24b to which W2 is connected.

The drive device 30 includes an engine 32 whose output is controlled according to the amount of depression of an accelerator pedal 31 .

The driving force from the engine 32 is transmitted to a differential device 36 via a clutch device 33, a transmission 34, and a propeller shaft 35. Ring RWI, RW
2 are connected, and the rear wheels RWl and RW2 are driven according to the output of the engine 32.

The electric control device 40 is a wheel rotation speed sensor 41a.

4lb, 41c, 41d, a vehicle speed sensor 41e1, a front wheel steering angle sensor 41f, and an accelerator opening sensor 41g. Wheel rotation speed sensors 41a, 41b.

41c and 41d are wheels FWI, FW2. RWI.

By pick-amping each rotation of RW2, wheel F
W1. FW2. Each rotation speed Nf of RWI and RW2 1. N
f2. Pick-up signals with frequencies proportional to Nrl and Nf2 are output. Wheel rotation speed sensor 41a, 41
waveform shapers 42a, 42b, 4
2c and 42d are connected to each other, and the same shaper 42a,
42b, 42c, 42d are the respective sensors 41a, 4
l b, 41 c.

Each pickup signal from 41d is converted into a square wave signal. The vehicle speed sensor 41e outputs a pink amplifier signal with a frequency proportional to the vehicle speed V by picking up the rotation of the output shaft of the transmission 34.

A waveform shaper 42e is connected to the vehicle speed sensor 41e, and the shaper 42e converts the pickup signal from the sensor 41e into a rectangular wave signal. Front wheel steering angle sensor 41
By detecting the rotation angle of the steering shaft 12 or the displacement amount of the relay rotor 4, f outputs an analog signal representing the steering angle θf of the left and right front wheels FWI, FW2. An analog-digital converter (hereinafter referred to as an A/D converter) 42r is connected to the front wheel steering angle sensor 41f, and the converter 42f
is the analog signal from the sensor 41f as the steering angle θr.
Convert to front wheel steering angle data in digital format.

Note that when this steering angle θf is positive (or negative), the left and right front wheels FW
1. This indicates that FW2 is steered to the right (or left), and zero indicates that the front wheels FWI and FW2 are not steered.

The accelerator opening sensor 41g outputs an analog signal representing the accelerator opening a by detecting the amount of depression of the accelerator pedal 31 or the opening of a throttle valve (not shown). A/D converter 42g for accelerator opening 41g
is connected, and the converter 42g converts the analog signal from the sensor 41g into digital accelerator opening data representing the accelerator opening a. Note that as the accelerator opening degree a increases from zero, it indicates that the accelerator pedal 31 has been depressed deeply.

These waveform shapers 42a to 42e and A/D converter 4
A microcomputer 42 is connected to 2f and 42g, and the computer 43 includes a read-only memory (hereinafter referred to as ROM) 43b, a central processing unit W (hereinafter referred to as CPU) 43c, and a central processing unit W (hereinafter referred to as CPU) 43c, which are commonly connected to each other via a bus 43a.
It is composed of a writable memory (hereinafter referred to as RAM) 43d and an input/output interface (hereinafter referred to as I10) 43e. The ROM 43b stores a program corresponding to the flowchart shown in FIG. 3, and as shown in FIG. Store the angle ratio data in the form of a table. Note that this steering angle ratio KV corresponding to vehicle speed and the target steering angle ratio described later include that the left and right rear wheels RWI, RW2 are the left and right front wheels FWI, F at jL (or positive).
This means that the left and right rear wheels RW1. RW2 is left and right front wheel FW
1. The aim is not to be steered independently of the steering of FW2. The CPO43C starts executing the program when an ignition switch (not shown) is opened, continues executing the program until the switch is opened, and stores the program in the RAM.
43d temporarily stores variables necessary for executing the program. ■1043d is each waveform shaper 42a to 42e
It takes in signals and data from the and A-reconverters 42f and 42g according to the execution of the program, and stores and outputs the data formed according to the execution of the program to the outside.

A digital-to-analog converter (hereinafter referred to as a D/A converter) 44 is connected to the l1043e of the microcomputer 43, and the converter 44 converts the supplied digital data into an analog signal and converts the signal into a linear actuator. 23 is supplied to a non-inverting input of a differential amplifier 45 that controls driving of the differential amplifier 23.

A position sensor 46 is connected to the inverting input of the differential amplifier 45, and the sensor 46 is connected to the actuator rod 23a.
By detecting the amount of displacement, an analog signal representing the position of the fulcrum 21b of the drive lever 21, that is, the steering angle ratio set by the lever 21, is supplied to the inverting input of the differential amplifier 46. .

The operation of the embodiment configured as above will be explained with reference to the flowchart of FIG. When the driver closes the ignition switch (not shown) to start the vehicle, the CPU 43C starts executing the program in step 100, and in step 101, the CPU 43C starts executing the program.
The pickup signal from 1e is passed through waveform shapers 42e and 1
1043e, calculates vehicle speed ■ based on the acquired signal, and stores vehicle speed data representing this vehicle speed ■ in RAM 4.
Store in 3d. After the processing in step 101, the CPU 43
C is the front wheel steering angle θf and the accelerator opening detected in steps 102 and 103 by the front wheel steering angle sensor 41f and the accelerator opening sensor 41g, respectively, and converted into digital format by the A/D converters 42f and 42g, respectively. a
Front wheel steering angle data and accelerator opening data representing each are taken in via l1043e, and these data are
Store in AM43d. After processing step 103, C
In step 104, the PO 43C reads vehicle speed corresponding steering angle ratio data representing the vehicle speed corresponding steering angle ratio KV corresponding to the vehicle speed V represented by the same data from the ROM 43b and stores it in the RAM 43 (I) based on the stored vehicle speed data. is stored as vehicle speed-corresponding steering angle ratio data.

Next, in step 105, the CPU 43C determines, based on the stored front wheel steering angle data and accelerator opening degree data, that the front wheel steering angle θf and the accelerator opening degree a expressed by the data are set to a predetermined steering angle θfo and a predetermined opening degree, respectively. It is determined whether the degree is greater than the degree ao.

In this case, the predetermined steering angle θfo and the predetermined opening degree a.

are the left and right rear wheels RWl, which are the driving wheels when the vehicle turns and accelerates;
The value is set to such a value that there is a possibility that RW2 slips and the vehicle spins.

Now, assuming that the front wheel steering angle θf is zero, cpU43c
is "NO" in step 105 above, that is, the same steering angle θ
It is determined that f is not larger than the predetermined steering angle θfo, and the program proceeds to step 106. In step 106, the CPU 43c sets the vehicle speed corresponding steering angle ratio Kv expressed by the vehicle speed corresponding steering angle ratio data as the target steering angle ratio based on the stored vehicle speed corresponding steering angle ratio data, and in step 107, the CPU 43c sets the vehicle speed corresponding steering angle ratio Kv as the target steering angle ratio. Target steering angle ratio data representing K is output to 11043e. l1043e stores this target steering angle ratio data and outputs it to the D/A converter 44.
supplies an analog signal corresponding to the same data to the non-inverting input of the differential amplifier 45. The amplifier 45 is a position sensor 46
The linear actuator 23 is driven and controlled in cooperation with the fulcrum 21b of the actuator 23 to set the target steering angle ratio K.
(= steering angle ratio Kv corresponding to vehicle speed), that is, if the steering angle ratio K is negative, the position is between the force point 21a and the point of application 21c, and as the steering angle ratio K approaches zero, point 21
If the position is close to c and the steering angle ratio is positive, the point of action 21
c as a reference, and as the steering angle ratio K approaches zero, it is displaced to a position closer to the point of action 21C. After the process in step 107, the CPU 43C returns the program to step 101, and as long as the front wheel steering angle θf is zero, the CPU 43C repeatedly executes the circulation process consisting of steps 101 to 107 to adjust the swing lever 21 as described above. The position of the fulcrum 21b, that is, the steering angle ratio set by the lever 21, is set to the target steering angle ratio K (=vehicle speed corresponding steering angle ratio KV). In this case, the left and right front wheels FWI and FW2 are not steered, so the swing lever 21 does not swing, and the point of action 21c is always at the reference position, so the left and right rear wheels RWI, FW2 are not steered.
RW2 is not steered. As a result, the vehicle travels straight ahead.

In addition, left and right front wheels FW1. The FW2 moves rightward (
or to the left).

In this case as well, the CPU 43 c determines rNOJ in step 105 based on 1θf1≦θfo, and executes the circulation process consisting of steps 101 to 107 to change the set steering angle ratio by the swing lever 21 to the target steering angle ratio. Angular ratio K (=
The vehicle speed corresponding steering angle ratio Kv) is set. On the other hand, swing lever 2
1 swings by a small angle counterclockwise (or clockwise) as the left and right front wheels FW1 and FW2 are steered. At this time, the vehicle speed V is small and the target steering angle ratio K (vehicle speed corresponding steering angle ratio Kv)
If is negative, the fulcrum 21b is the point of effort 21a as described above.
and the point of action 21c, the swing lever 21
Due to the counterclockwise (or clockwise) rocking, the left and right rear wheels RWI, RW2 are steered in the left direction (or right direction), that is, in the opposite phase with respect to the left and right front wheels FWI, FW2. In addition, if the vehicle speed V is large, the target steering angle ratio K (vehicle speed corresponding steering angle ratio KV)
If is positive, the fulcrum 21b is the point of action 21 as described above.
Since it is located on the opposite side to the point of force 21a with reference to c, the left and right rear wheels RWI, RW2 are moved in the right direction (or left direction), that is, the left and right front wheels, by the counterclockwise (or clockwise) rocking of the rocking lever 21. FWI and FW2 are steered in the same phase. In this way, the left and right rear wheels RWI, RW2 are set at the vehicle speed V.
However, in this case, since the front wheel steering angle θf is extremely small, the left and right rear wheels RW1. R.W.
The steering angle of No. 2 is also extremely small, and the vehicle only travels with a slight change in direction.

Furthermore, even if the left and right front wheels FWI and FW2 are steered and the front wheel steering angle θf becomes large (1θfl>θfo) and the vehicle starts turning, the amount of depression of the accelerator pedal 31 is small and the accelerator opening a is set to the predetermined opening. If it is less than ao, CPO
43G determines rNOJ based on asao in step 105, as described above, and executes a circular process consisting of steps 101 to 107. In this case as well, left and right rear wheels RWI
, RW2, same as above, left and right front wheels FWI, FW at low speed.
Since the steering control is performed in the opposite phase to FW2, and the steering control is performed in the same phase to the left and right front wheels FWI and FW2 at high speeds, the tight turning performance of the vehicle during turning is improved at low speeds, and the steering control is performed in the same phase at high speeds. In this case, the running stability of the vehicle during turning is improved.

On the other hand, when the accelerator pedal 31 is depressed during such a turn and the vehicle is accelerated, the CPU 43C determines rY based on 1θfl>θfo and a>ao in step 105.
It is determined to be EsJ and the program proceeds to step 111. In step 111, the CPU 43C detects each wheel rotation speed sensor 41a, 41b.

The pickup signals from 41C and 41d are transferred to the waveform shaper 4.
2a, 42b, 42c, 42d and! 1043e, and each wheel rotation speed N is determined based on each of the acquired signals.
f1+Nf2. Nrl and Nr2 are calculated, and in step 112, the smaller value of the front wheel rotational speeds Nf1 and Nf2 is subtracted from the larger value of the rear wheel rotational speeds Nr1 and Nr2, thereby calculating the front and rear wheel rotational speed difference g. do. The calculation of this front and rear wheel rotational speed difference g is performed using the left and right rear wheels RWI as described above.
.

This means detecting a slip state that occurs in the left and right rear wheels RW1 and RW2, which are drive wheels, during acceleration of a rear wheel drive vehicle equipped with a drive device 30 that drives RW2. In addition, in the above calculation, the front and rear wheel rotational speed difference g is expressed as the rear wheel rotational speed Nr.
The front wheel rotation speed Nfl, N is determined from the larger value of l and Nr2.
Although the calculation was made by subtracting the smaller value of f2, it is also possible to calculate by subtracting the average value of the front wheel rotation speeds Nfl and Nf2 from the average value of the rear wheel rotation speeds Nrl and Nr2. good.

After the processing in step 112, the CPU 43C executes step 1.
13, based on the front and rear wheel rotation speed difference g calculated above, the function value f (g
), for example, by calculating f (g) = α・g, and adding this function value f (g) to the vehicle speed corresponding steering angle ratio KV, the target steering angle ratio K (=+f (g)) can be set. calculate. 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. The larger the slip ratio of rear wheels RWI and RW2, the more the left and right rear wheels RWI determined by the vehicle speed corresponding steering angle ratio KV.
, the steering angle of RW2 is thicker (corrected) in the in-phase direction with respect to the left and right front wheels FWI, FW2.This means that
The steering angle ratio characteristic shown by the solid line in FIG. 4 changes like the steering angle ratio characteristic shown by the broken line in the figure, and the degree of change becomes larger as the above-mentioned slip ratio becomes larger. In addition, the above function value f
(g) is determined by the relationship between the slip rate of the left and right rear wheels RWI, RW2 and the spin of the vehicle, and is not limited to the above relationship. For example, if the above function f (g) is When it is smaller than a predetermined value, f (g) = α・
g, and when g is equal to or greater than a predetermined value, f(g)=β
・g” (however, 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 in-phase side is the same amount of change in the same left g. , and the same-left g becomes thick (then the amount of correction to the in-phase side becomes large with respect to the same amount of change of the same-left g.

After the processing in step 113, the CPU 43C executes step 1
07, as described above, by outputting the target steering angle ratio data representing the target steering angle ratio K, the set steering angle ratio by the swing lever 21 is controlled to be set to the target steering angle ratio K, and this state is As long as steps 101-105, 111-113.
107 continues to be executed. In this case, the target steering angle ratio is the vehicle speed corresponding steering angle ratio KV by the correction amount f (g)
Since the left and right rear wheels RWI and RW2 of the vehicle in question are set to values corrected by , the left and right rear wheels RWI and RW2 of the vehicle in question are steered in the same phase direction by the corrected iff(g) compared to control based only on the vehicle speed corresponding steering angle ratio KV.

The effects of such steering control will be explained with reference to the drawings in relation to the turning state of the vehicle.

FIG. 5 shows a left-turning state of the vehicle, and FIG. 6 shows the yaw rate of the vehicle and the number of rotations of each wheel Nfl in such a case.

Nf2. It shows changes in Nrl, Nf2, and the slip angle of the vehicle. Assuming that the vehicle starts turning to the left at time to in FIG. 6 and turns at approximately constant speed until time t1, the yaw rate and wheel rotation speed Nf 1. Nf
2. Nrl, Nf2 and slip angle change smoothly. Then, at time t1, when the vehicle is accelerated by depressing the accelerator pedal 31 while keeping the rotating position of the steering wheel 110 in the previous state, the left and right rear wheels RWI and RW2, which are the driving wheels, slip. Left and right rear wheels RWI
, RW2 rotation speed Nr 1. Nr 2 increases rapidly, but the left and right front wheels FW1. which are non-driving wheels. FW2 rotation speed N
fl and Nf2 do not increase that much.

Note that the rotation speed Nr1 of the left rear wheel RWI is the right rear wheel RW2.
(This 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 rate of the wheel on the inside of the turn is larger than the rotation speed Nr2 of the wheel on the outside of the turn.) This is because the slip rate of the wheels of
The reason why Nfl is larger than the rotational speed Nfl of the left front wheel FWI is because the turning radius of the right front wheel FW2 becomes wider than the turning radius of the left front wheel FWI as the vehicle turns to the left. Then, the slip rate of the left and right rear wheels RW1 and RW2 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 representing the slip state of the left and right rear wheels RWI, RW2 is calculated by the calculation in step 112 of the flowchart in FIG. The function value f becomes larger as g becomes larger.
(g) is calculated, and the left and right rear wheels RWI and RW2 are changed to the left and right front wheels FWI using this function value f (g).

Since correction control is performed to steer FW2 in the same phase direction, the spin caused by the slip of the left and right rear wheels RWI and RW2 is prevented, and the steering stability of the vehicle is improved. In addition, when the vehicle turns to the right, the left and right front wheels
WI, FW2. The operation is the same as in the above case, except that the steering directions of the left and right rear wheels RWI and RW2 are reversed.

Further, in this embodiment, steps 102, 103.
Through the process of step 105, the turning acceleration state of the vehicle is detected based on the front wheel steering angle θf and the accelerator opening a, and only at the time of this detection, steering control is performed according to the difference g between the front and rear wheels. When the vehicle is driving on a rough road, the left and right rear wheels, which are the driving wheels, RWI, RW, regardless of the turning acceleration of the vehicle.
Even if the steering wheel 2 slips, the steering control will not be performed, and it is possible to better prevent deterioration of the steering stability of the vehicle due to the steering control unrelated to turning acceleration.

In the above embodiment, the vehicle speed ■ is detected by the vehicle speed sensor 41e, but this vehicle speed sensor 41e
omitted, wheel rotation speed sensors 41 a, 4 l
Each wheel FW1 by b, 41 c, 41 d,
FW2. Each rotation speed Nfl of RWI and RW2.

Nf2. Calculate the total average value of Nrl, Nf2, or calculate the respective rotational speeds Nfl, N of the left and right front wheels FWI, FW2, which are non-driving wheels.
It is also possible to calculate the vehicle speed ■ by a method such as calculating the average of f2.

Next, a second embodiment of the present invention will be described. FIG. 7 shows a part of the rear wheel steering mechanism 20 and the electric control device 40 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 20
is left and right rear wheels RWI.

A linear actuator 27 is provided that directly drives a relay rod 26 that interlocks RW2. Electric control device 4
0 is equipped with a D/A converter 44 and a differential amplifier 45 similar to those in the first embodiment, and the inverting input of the differential amplifier 45 detects the displacement position of the relay rod 26 and outputs signals to the left and right rear wheels. A position sensor 47 that generates an analog signal representing the steering angle θr of RWI and RW2 is connected. Note that the remaining parts are the same as those of the first embodiment, except that the program described later is different.

The operation of the second embodiment configured as described above will be explained with reference to the flowchart in FIG. 3.
Steps 101 to 107 or 1 similar to the first embodiment above
During the circulation process of 01-105, 111-113.107,
In step 107, a target rear wheel steering angle K·θf is calculated by multiplying the target steering angle ratio by the front wheel steering angle θf represented by the front wheel steering angle data stored in the RAM 43d.
A digital signal representing this target rear wheel steering angle K·θf is output to the D/A converter 44 shown in FIG. D/A converter 44
converts this digital signal into an analog signal and supplies it to the differential amplifier 45, and the differential amplifier 45 cooperates with the position sensor 47 to convert the rear wheel steering angle θr into the target rear wheel steering angle K・
Set to θf.

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 RWI, RW2, which are determined according to the vehicle speed (2), are corrected and controlled based on the difference g between the front and rear wheels. RWI left and right rear wheels depending on.

This is also applicable to vehicles in which the steering angle of RW2 is not controlled. That is, the left and right rear wheels RW1. R.W.
2 may be controlled in the same phase direction with respect to the left and right front wheels FWI and FW2.

Further, in the first and second embodiments described above, the case where the present invention is applicable to a rear wheel drive type vehicle has been described, but the present invention is also applicable to a front wheel drive type vehicle. However, in front-wheel drive vehicles, during acceleration, the slip rate of the left and right front wheels FWI, FW2, which are the drive shafts, becomes high, and the rotational speeds Nfl, Nf of the left and right front wheels FWI, FW2 increase.
2 is the rotation speed N of the left and right rear wheels RWI, RW2, which are non-driving wheels
As rl becomes larger than 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 112 of the flowchart in FIG.
, left and right rear wheels RWI from the larger Nf2 (or average value)
, by subtracting the smaller (or average value) of RW2 rotational speeds Nrl and Nr2, and in step 113, the target steering angle ratio K is calculated by the relationship: = = -f (g). Make it. 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 RWI, RW2 change to the left and right front wheels FW1. Since the correction control is performed in a direction opposite to FW2, drift-out during turning acceleration in a front-wheel drive vehicle is prevented. Furthermore, in this case,
The steering angles of the left and right rear wheels RWI and RW2 may not change depending on the vehicle speed (■).

[Brief explanation of the drawing]

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. Description of symbols FWI, FW2...Front wheel, RWI, RW2...Rear wheel, 10...Front wheel steering mechanism, 11...Steering handle,
20... Rear wheel steering mechanism, 21... Rocking lever, 23
．． 27... Linear actuator, 30... Drive device, 31... Accelerator pedal, 32... Engine,
40... Electric control device, 41 a, 4 l b,
41 c, 41 d...Wheel rotation speed sensor, 41e...Vehicle speed sensor, 41f...Front wheel steering angle sensor, 41g...Accelerator opening sensor, 43...
・Microcomputer, 46.47...Position sensor. Applicant Toyota Motor Corporation Representative Patent Attorney Teru Hase - (1 other person) Figure 1 Figure 6 1o1. 1 Figure 7

Claims (1)

[Claims] a rear wheel steering mechanism that steers the rear wheels, a front wheel rotation speed detection means that detects the rotation speed of the front wheels, a rear wheel rotation speed detection means that detects the rotation speed of the rear wheels, and the detected front wheel rotation speed and the rear wheel. determining means for determining a ratio of the steering angle of the rear wheels to the front wheels according to the difference in rotational speed; and a determining means for outputting a control signal corresponding to the determined steering angle ratio to the rear wheel steering mechanism to and a control means for controlling the steering of the rear wheels so that the steering angle becomes a ratio of the determined steering angle, and the rear wheel steering control device for a front and rear wheel steered vehicle prevents the vehicle from spinning or drifting out when accelerating a turn. There is a front wheel steering angle detection means for detecting a front wheel steering angle, an accelerator opening degree detection means for detecting an accelerator opening degree,
The vehicle is characterized by further comprising a determining means for permitting the steering control of the rear wheels by the control means when both the detected front wheel steering angle and the accelerator opening are larger than a predetermined value, and for inhibiting the steering control at other times. Rear wheel steering control device for front and rear wheel steered vehicles.