JPS63279976A - Steering device for vehicle - Google Patents

Abstract

PURPOSE:To achieve optimal turning condition corresponding to vehicle speed, in 4-wheel-steering vehicle, by applying brake onto a turning side rear wheel corresponding to vehicle speed. CONSTITUTION:A front wheel steering mechanism A, a hydraulic brake unit B for braking right and left rear wheels and an electric controller C for controlling the brake unit B electrically are provided to a vehicle. When front wheels FW1, FW2 are steered to the right by a front wheel steering mechanism 1 through turning of a steering wheel SW under driving of vehicle, a brake oil pressure applying means 6 provides brake oil pressure corresponding to an oil pressure control level determined through an oil pressure control level determining means 5 to a brake unit 16b for braking front wheel in steering direction so as to apply brake force onto the right rear wheel RW2. Consequently, a spring in a suspension mechanism for supporting the right rear wheel bends to steer the right rear wheel to the right with small angle thus reducing the turning radius.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a vehicle steering system, and more particularly to a vehicle steering system that corrects the steering of a vehicle by a front wheel steering mechanism according to the front wheel steering angle and vehicle speed. Regarding.

(Prior Art) Conventionally, this type of steering device is disclosed in, for example, Japanese Patent Application Laid-Open No. 55-914.
As shown in Japanese Patent No. 57 and Japanese Patent Application Laid-Open No. 59-81261, a front wheel steering mechanism is provided to steer the front wheels according to the rotation of a steering wheel, and the left and right rear wheels are connected in a steerable manner. It is equipped with a rear wheel steering mechanism that steers the vehicle in both left and right directions, and by controlling the rear wheel steering mechanism mechanically or electrically according to the front wheel steering angle and vehicle speed, the steering angle of the left and right rear wheels can be adjusted to the front wheel steering angle. The left and right rear wheels are steered so that the steering direction increases as , the steering of the vehicle by the front wheel steering mechanism is corrected and corrected. This improves the turning ability of the vehicle when traveling at low speeds, and also improves the running stability of the vehicle when traveling at high speeds.

(Problem to be Solved by the Invention) However, in the conventional device described above, in order to improve the turning ability of the vehicle when traveling at low speeds, it is necessary to largely steer the left and right rear wheels in the opposite phase to the front wheels. However, due to this large steering angle, there was a problem in that the rear wheel steering mechanism became large. Additionally, when the left and right rear wheels are steered in the opposite phase to the front wheels, side force is generated in the left and right rear wheels in the opposite direction to the front wheels at the moment of steering, and it takes time for side force to occur in the same direction as the front wheels. Because of the delay, the responsiveness of the vehicle body to the rotation of the steering wheel in the lateral direction becomes extremely poor, and the rear part of the vehicle body moves in the opposite direction to the steering direction of the vehicle, i.e., the left and right rear wheels move sideways. , the driver feels as if the left and right rear wheels are skidding. As a result of such movement responsiveness and the feeling of skidding, there is a problem in that it is difficult for the driver to drive the vehicle. Also,
Due to the movement of the rear part of the vehicle body in the opposite direction to the steering direction, the rear part of the vehicle body on the opposite side to the steering direction protrudes to the opposite side, making it unsuitable for turning the vehicle on narrow roads.

On the other hand, when driving at high speeds, the left and right rear wheels are steered in the same phase as the front wheels, which improves the vehicle's lateral movement response, but the vehicle only generates a very small moment in the steering direction, so the vehicle There has been a problem in that the driver has difficulty driving the vehicle when the vehicle is traveling at high speed and makes a large turn due to the poor eloquence.

The present invention has been devised in view of the above-mentioned problems, and its purpose is to maintain good turning ability of a vehicle during low-speed running and good running stability of the vehicle during high-speed running by the above-mentioned conventional device; It is an object of the present invention to provide a vehicle steering system that solves the above-mentioned driving problems and the problem of increasing the size of the rear wheel steering mechanism.

(Means for Solving the Problems) In order to solve the above problems and achieve the objects of the present invention, the structural features of the present invention are as shown in FIG. In a vehicle steering system equipped with a front wheel steering mechanism 1 that steers front wheels FW1 and FW2 accordingly, the left and right rear wheels RWI and RW2 are independently provided and applied to the left and right rear wheels RWI and RW2 according to the braking oil pressure applied thereto, respectively. A pair of left and right brake devices g2a and 2b that brake RW2, respectively, a front wheel steering angle detection means 3 that detects a front wheel steering angle, a vehicle speed detection means 4 that detects a vehicle speed, and a front wheel steering angle that increases as the detected front wheel steering angle increases. A hydraulic control value determining means 5 determines a hydraulic pressure control value that decreases as the detected vehicle speed increases, and the braking hydraulic pressure corresponding to the determined hydraulic pressure control value is used to steer the front wheels FWI, FW2 of the pair of left and right brake devices 2a, 2b. The reason is that a brake hydraulic pressure applying means 6 is provided to apply the braking pressure to the brake equipment W 2 a (or 2b) on the direction side.

(Operations and Effects of the Invention) In the present invention configured as described above, while the vehicle is running,
When the front wheel steering mechanism 1 steers the front wheels FWI, FW2 to the right (or left) by rotating the steering handle SW,
The brake oil pressure applying means 6 applies the brake oil pressure corresponding to the oil pressure control value determined by the oil pressure control value determining means 5 to the front wheels FW1.
Since it is applied to the steering direction side of FW2, that is, the right brake device 2b (or left brake device W 2 a ), the right rear wheel R
A braking force Fb as shown in FIG. 2 acts on W2 (or left rear wheel RWI). Also, due to this braking force Fb, the spring in the side of the suspension machine that supports the right rear wheel RW2 (or left rear wheel RWI) is bent, and the right rear wheel RW2 (or left rear wheel RWI) is moved in the right direction (or left direction), that is, the front wheel FW
I, FW2 is steered by a small angle θ° in the steering direction. With this steering, the right rear wheel RW2 (or left rear wheel RWI)
to the right (or left), i.e. front wheels FWI, FW2
A side force F3 is generated in the steering direction.

In such control, if the vehicle is running at low speed,
Since the vehicle speed detected by the vehicle speed detecting means 4 is small, the hydraulic control value determined by the hydraulic control value determining means 5 becomes large, and the front wheels FW1.
When the FW 2 is steered to a large steering angle, the front wheel steering angle detected by the front wheel steering angle detecting means 3 becomes large, and the determined hydraulic pressure control value becomes even larger. As a result, the braking force Fb of the rear wheel on the turning side of the vehicle, that is, the right rear wheel RW2 (or the left rear wheel RW1) increases. Also, at this time, a force F3 due to the forward movement of the vehicle is acting on the other rear wheels, that is, the left rear wheel RWL (or the right rear wheel RW2), and a large moment (F) is applied to the vehicle body in the vehicle turning direction.

10 Fb) d acts. On the other hand, front wheels FWI, FW2 have side forces F+, F2 (Fad+Fbd=F, ρl) that are balanced with this large moment (F, +Fb)d.
10F2ρ2) occurs in the opposite direction to the vehicle turning, so how many wheels FW1. FW2 has a slip angle θ1. θ2 occurs,
The vehicle is steered in the vehicle turning direction with respect to the central axes of the front wheels FWI and FW2 (dotted chain line), and the turning ability of the vehicle is improved.

In this way, when driving at low speeds, the braking force Fb is applied to improve the turning ability of the vehicle, and the front wheels FWI of the left and right rear wheels RWI and RW2.

The problem of the deterioration of the lateral movement response of the vehicle body and the feeling of sideslip given to the driver, which is the problem with the conventional device described above due to reverse phase steering for 1" W 2, has been solved, making it easier for the driver to drive the vehicle. Furthermore, the problem of the rear wheel steering mechanism increasing in size due to the reverse phase steering in the conventional device and the problem of the overhang of the rear part of the vehicle body on the opposite side to the steering direction are solved, so the vehicle steering device according to the present invention It is possible to realize this compactly, and at the same time, it also enables the vehicle to turn on narrow roads.

On the other hand, if the vehicle is traveling at high speed, the vehicle speed detection means 4
The vehicle speed detected by
2 is also not steered significantly, so the front wheel steering angle detected by the front wheel steering angle detecting means 3 becomes small. As a result, the hydraulic pressure side m determined by the hydraulic control value determining means 5
The value becomes small, and a small braking force F is applied to the rear wheel on the turning side of the vehicle.
b is applied, and by this braking force Fb, the rear wheels are steered in the same phase as the front wheels FWI and FW2, as described above. In this case, the braking force Fb is small, but since the vehicle speed is high, the side force F3 is large to some extent, ensuring the same responsiveness to the lateral movement of the vehicle as in the conventional system, improving the running stability of the vehicle, and reducing the braking force. The moment acting on the vehicle body as described above based on the power Fb (F, +F'
b) d improves the turning performance of the vehicle. This makes it easier for the driver to drive the vehicle even when the vehicle is traveling at high speed and makes a large turn.

(Example) a. First Example The first example of the present invention will be described with reference to the drawings.
FIG. 3 schematically shows the entirety of a vehicle equipped with a steering system according to the present invention. This vehicle has front left and right wheels FWI according to the rotation of the steering wheel SW.

Front wheel steering device 1jlA that steers FW2 and left and right rear wheels RW
l, hydraulic braking device B that brakes RW2, and the same braking device B
and an electric control device C that electrically controls the.

The front wheel steering mechanism A has a steering shaft 11 that rotates in response to rotation of the steering handle SW. The steering shaft 11 includes a rack and pinion mechanism 12, a relay rod 13, and left and right tie rods 1.
It is connected to the left and right front wheels FW1 and FW2 via 4a and 14b and left and right knuckle arms 15a and 15b, so that the left and right front wheels FWI and FW2 are steered in response to rotation of the steering handle SW.

The hydraulic braking device B includes a pair of left and right brake devices 16a, 16.
It has b. Left and right brake devices 16a.

16b brakes the rotation of the left and right rear wheels RWI, RW2 by braking the rotation of the left and right drive shafts 17a, 17b, respectively, with a braking force corresponding to the applied braking oil pressure. The left and right drive shafts 17a and 17b transfer the driving force distributed by the differential gear 18 to the left and right rear wheels RWI.
, RW2, respectively, and the same shafts 17a, 1
Left and right joints 21a and 21b are interposed near the ends of 7b to allow the left and right rear wheels RWI and RW2 to swing. Note that the left and right springs 22a and 22b equivalently represent the spring force within the suspension mechanism of the left and right rear wheels RWI and RW2.

The left and right brake devices 16a and 16b each have an electromagnetic switching valve 2.
3.24 via hydraulic pump 25. Accumulator 26
and a hydraulic power source consisting of a reservoir 27. The electromagnetic switching valve 23 includes electromagnetic solenoids 23a, 23b and springs 23c, 23d. When both types of magnetic solenoids 23a, 23b are in a non-excited state, the biasing force of both springs 23c, 23d causes the electromagnetic switching valve 23 to be in the first state (third state). (center position in the figure), and prohibits the supply of hydraulic oil from the hydraulic pump 25 to the left brake device 16a, and also prohibits the discharge of hydraulic oil from the brake device 16a to the reservoir 27. Further, when the electromagnetic solenoid 23a is excited, the electromagnetic switching valve 23 is set to the second state (the right position in FIG. 3), and the left brake device 16a is transferred from the hydraulic pump 25 to the
/\ hydraulic oil supply is allowed. Electromagnetic solenoid 23b
When energized, the electromagnetic switching valve 23 is set to the third state (left position in FIG. 3), allowing discharge of hydraulic fluid from the left brake device 16a to the reservoir 27.

The electromagnetic switching valve 24 includes electromagnetic solenoids 24a, 24b and springs 24c, 24d. When both types of magnetic solenoids 24a, 24b are in a non-energized state, the biasing force of both springs 24c, 24d causes the electromagnetic switching valve 24 to be in a first state (first state). 3
(center position in the figure) to prohibit the supply of hydraulic oil from the hydraulic pump 25 to the right brake device 16b, and also prohibit the discharge of hydraulic oil from the brake device 16b to the reservoir 27. Furthermore, when the electromagnetic solenoid 24a is energized, the electromagnetic switching valve 24 is set to the second position B (the right position in FIG. 3), allowing hydraulic oil to be supplied from the hydraulic pump 25 to the right brake device 16b. . Electromagnetic solenoid 2
4b is energized, the electromagnetic switching valve 24 is set to the third position B (the left position in FIG. 3), allowing hydraulic oil to be discharged from the right brake device 16b to the reservoir 27.

The electric control device C has a vehicle speed sensor 31a, a front wheel steering angle sensor 31b, and oil pressure sensors 31c and '31d. The vehicle speed controller 31a picks up the rotation of the right front wheel FW2 and outputs a vehicle speed signal having a frequency proportional to the rotational speed of the right front wheel FW2, that is, the vehicle speed. The front wheel steering angle sensor 31b detects the rotation angle of the steering shaft 11 and outputs a front wheel steering angle signal representing the steering angle θf of the left and right front wheels FWI, FW2. In addition, when this front wheel steering angle θf is positive (or negative), it represents the rightward (or leftward) steering of the left and right front wheels FWI, FW2, and when it is zero, it represents the left and right front wheels FWI.
, represents the state in which FW2 is not steered.

The oil pressure sensors 31c and 31d are connected to the left and right brake devices 16, respectively.
It detects the oil pressures PLD+PRD applied to the oil pressures PLO and PRD, and outputs oil pressure signals representing the oil pressures PLO and PRD.

The outputs of these sensors 31a to 31d are connected to a microcomputer 32, which includes a read-only memory (hereinafter referred to as ROM) 32b and a central processing unit (hereinafter referred to as C
PU is >32c.

A submersible memory (hereinafter referred to as RAM) 32d.

It consists of an input interface circuit 32e and an output interface circuit 32f. The ROM 32b stores programs corresponding to the flowcharts shown in FIGS. 4 to 6, and also controls the brake oil pressure P chamber, which decreases as the vehicle speed increases, as shown in FIG. 7, and the front wheel steering angle θf, as shown in FIG. The hydraulic coefficient 09, which increases as the absolute value Iθfl increases, is stored as a first and second table, respectively.

The CPU 32c executes the program, and the RAM 32d
temporarily stores data necessary for executing the program. The input interface circuit 32e connects each sensor 31
It has a format converter such as an A/D converter that converts each detection signal from a to 31d into digital data suitable for program processing. The output interface circuit 32f has a storage function for storing control data formed by program processing, and outputs the control data stored in the circuit 32. This output interface circuit 32
Excitation control circuits 33 and 34 are connected to f, and the excitation control circuit 33 controls each electromagnetic solenoid 2 of the electromagnetic switching valve 23.
3a, 23b, and the excitation control circuit 34 controls each electromagnetic solenoid 24a, 2 of the electromagnetic switching valve 24.
4b is energized or de-energized.

The operation of the first embodiment configured as described above will be explained with reference to the flowcharts of FIGS. 4 to 6. When the ignition switch (not shown) is closed in order to run the vehicle, this opening causes the CPU 3
2c starts execution of the main program at step 100 in FIG. After starting execution of this program, CP
In step 101, the U32c takes in a vehicle speed signal from the vehicle speed sensor 31a via the input interface circuit 32e, calculates the vehicle speed ■ based on the collected vehicle speed signal, and stores vehicle speed data representing the vehicle speed V in the RAM 32d.
The steering wheel 102 reads the front wheel steering angle signal from the front wheel steering angle sensor 31b via the input interface circuit 32e, and converts the read front wheel steering angle signal into the front wheel steering angle θ.
It is stored in the RAM 32 d as front wheel steering angle data representing f.

Next, in step 103, the CP LJ 32c determines the left and right front wheels FWI,
It is determined whether or not FW2 is traveling substantially straight. Now, left and right front wheels FW1. If the FW2 is running substantially straight, the absolute value 1θf1 of the front wheel steering angle θf is less than the predetermined minute steering angle value θfO, so the CPU 32c determines rNo,
That is, it is determined that the absolute value 1θf1 is not larger than the minute steering angle value θ0, and the program proceeds to steps 104 and 105. At steps 104 and 105, the CPU 32C outputs control data for exciting the electromagnetic solenoids 23b and 24b to the output interface circuit 32f. The output interface circuit 32f stores control data and outputs the control data to the excitation control circuits 33 and 34, respectively, and the excitation control circuits 33 and 34 output the control data to the electromagnetic solenoid 23.
b, 24b are each excited. Note that at this time, the electromagnetic solenoids 23a and 24a are controlled to be de-energized.

Due to such excitation control, the electromagnetic switching valves 23 and 24 are set to the third state (left position in FIG. 3), so the left and right brake devices 16a and 16b are set to the electromagnetic switching valves 23.
4 to the reservoir 27, and the left and right rear wheels RWI, R
W2 is not braked. In this way, the left and right rear wheels RW
As a result of not braking I and RW2, the vehicle travels substantially straight, like a normal vehicle. Step 104 above,
After the process in step 105, the CPU 32c returns the program to step 101, and continues to execute the cyclic process in steps 101>105 as long as the vehicle is traveling substantially straight.

During the circulation process, when the steering wheel SW is rotated to the right and the vehicle starts turning to the right, the CPU 32
c determines in step 103 that rYESJ, that is, the absolute value 1θf1 of the front wheel steering angle θf is larger than the minute steering angle value θ0, and the program is executed in steps 106, 107.
．． Proceed to step 108. In this step 106, the first table (Fig. 7) in the ROM 32b is referred to based on the vehicle speed data stored in the RAM 32d through the processing in step 101, and the brake oil pressure P corresponding to the vehicle speed is derived. be done. Further, in step 107, the second table (Fig. 8) in the ROM 32b is checked based on the front wheel steering angle data stored in the RAM 32d by the processing in step 102, and the hydraulic coefficient CP corresponding to the front wheel steering angle θf is determined. In step 108, the derived brake oil pressure PL and oil pressure 1! The target brake oil pressure P$ is calculated by executing the following calculation based on I Cp.

P$=CP-Pl Note that the target brake oil pressure data representing the calculated target brake oil pressure P is stored in the RAM 32d in step 108.
is memorized.

Next, in step 109, the CPU 32c determines whether or not the front wheel steering angle θf is positive based on the front wheel steering angle data stored in the RAM 32d through the processing in step 102 described above. Since the vehicle is currently turning to the right, the front wheel steering angle θf is positive, and the CPU 32c determines YES in step 109, and in step 110, similarly to the process in step 104, the electromagnetic solenoid By energizing 23b, the electromagnetic switching valve 23 is set to the third position.
Set to state. As a result, similarly to the above case, no braking force is applied to the left rear wheel RWI. This step 110
After processing, the CPU 32c executes the right brake control subroutine corresponding to the flowchart of FIG. 5 in step 111, and sets the oil pressure PRD in the right play valve device 16b to the target brake oil pressure P.

In this right brake control subroutine, the CPU3
2c starts executing a subroutine program in step 200, and in step 201 reads a hydraulic signal representing the right brake hydraulic pressure pao from the hydraulic pressure sensor 31d via the input interface circuit 32e, and in step 202, the right brake hydraulic pressure is It is determined whether the absolute value IPRD-P$1 of the difference between pyto and the target brake oil pressure pg calculated by the process of step 108 is less than a predetermined minute oil pressure value ΔP. Now, if the right brake hydraulic pressure PRD and the target brake hydraulic pressure P$ are not equal, the CPU 32C returns rNo in step 202, that is, the absolute value IP
It is determined that aoP*l is not less than the minute oil pressure value ΔP, and the program proceeds to step 203, where it is determined whether the target brake oil pressure P is greater than the right brake oil pressure PRD. In this case, if the target brake oil pressure P is larger than the right brake oil pressure PRD, the CPU 32c determines p@>p in the same step 203. rYES based on
, and in step 204 the electromagnetic solenoid 24
Control data for exciting a is output to the output interface circuit 32f. Output interface circuit 32
f stores the control data and outputs the control data to the excitation control circuit 34, which excites the electromagnetic solenoid 24a.

Note that at this time, the electromagnetic solenoid 24b is controlled to be de-energized. As a result, the electromagnetic switching valve is set to the second position B (right position in Figure 3) and supplies hydraulic oil from the hydraulic pump 25 to the right brake device 16b, so that the right brake hydraulic pressure PRD in the device 16b is Rise.

Further, if the target brake oil pressure P is less than the right brake oil pressure PRD, the CPU 32c controls the
Based on s<Pan, it is determined that rNo, and step 20
In step 5, the electromagnetic solenoid 24b is energized in the same manner as in step 105, thereby setting the electromagnetic switching valve 24 to the third state (the left position in FIG. 3). This results in
Since the right brake device 16b communicates with the reservoir 27,
The right brake hydraulic pressure PRD in the device 16b decreases.

On the other hand, at the time of determination in step 202, if the right brake oil pressure PAN and the target brake oil pressure P are approximately equal, the CPU
32C determines "YES" in step 202, that is, the absolute value IPaoP*l is less than the minute oil pressure value ΔP, and advances the program to step 206. At step 206, the CPU 32c controls both electromagnetic solenoids 24a.
, 24b are output to the output interface circuit 32f and control data for de-energizing them. The output interface circuit 32f stores the control data and outputs the control data to the excitation control circuit 34, and the excitation control circuit 34 connects both electromagnetic solenoids 24a.

24b is controlled to be de-energized. As a result, the electromagnetic switching valve 24 is set to the first position B (the center position in FIG. 3), prohibiting the supply of hydraulic oil from the hydraulic pump 25 to the right brake device 16b, and disabling the hydraulic fluid from the device 16'b to the reservoir 27. This also prohibits the discharge of hydraulic oil to the right brake device 16.
The brake oil pressure PRD in b is kept at the previous value.

After processing steps 204, 205, and 206 described above, C
The PU32c finishes executing the right brake control subroutine in step 207, and returns the program to step 101.
(FIG. 4), and thereafter, as long as the vehicle is turning right, the circulation process consisting of steps 101 to 103 and 106 to 111 continues to be executed. During such cyclic processing, C
The PU 32c controls the right brake device 16b by processing steps 204 to 206 of the right brake control subroutine.
The hydraulic pressure PRD is controlled to be raised, lowered, or held, and the hydraulic pressure PRD is controlled to be set to the target brake hydraulic pressure P$.

By applying the right brake oil pressure PRD, the right brake device 16b brakes the right rear wheel RW2 with a braking force Fb corresponding to the target brake oil pressure P. This braking force Fb is the second
As shown in the figure, since it acts on the rear of the vehicle, the
The rod 22b is bent, and the outer portion of the drive shaft 17b rotates rearward from the right joint 21b. As a result of this rotation, the right rear wheel RW2 is steered slightly to the right, as shown in FIG. 2, and a side force Fs is generated on the rear right wheel RW2.

This side force Fs is generated by the rotation of the steering wheel SW, that is, the left and right front wheels FW1. Since this occurs almost simultaneously with the steering of FW2, the vehicle is accelerated in the lateral direction in proportion to the side force F5, resulting in good lateral movement response of the vehicle. This will be explained using the graph of FIG. The graph shows the phase characteristics of the acceleration per front wheel steering angle (lateral acceleration/steering angle) with respect to the steering speed (frequency) of the left and right front wheels FWI, FW2, in the case of the first embodiment (solid line), and in the case of the conventional example (solid line). Left and right rear wheels RWI with wheel steering mechanism.

When RW2 is steered in the same phase as the left and right front wheels FWI and FW2 (solid line), when only the left and right front wheels FWI and FW2 are steered (dashed line), and when the left and right rear wheels RWI and RW2 are steered in the same phase as the left and right front wheels by the conventional rear wheel steering mechanism The cases where the steering is performed in the opposite phase to FWI and FW2 (dotted chain line) are shown respectively.

In other words, as can be understood from this graph, the first
According to the embodiment, the response of the vehicle in the lateral direction is almost the same as when the left and right rear wheels RWI, RW2 are steered in the same phase as the left and right front wheels FWI, FW2 by the conventional rear wheel steering mechanism. , by the same mechanism, the left and right rear wheels RW 1
, When RW 2 is steered in the opposite phase to the left and right front wheels FWI, FW2, and the left and right front wheels FWI.

This is better than when only FW2 is steered.

On the other hand, in this case, as shown in FIG. 2, the force F3 due to the forward movement of the vehicle is acting on the left rear wheel RWI in the front direction of the vehicle body, and the braking force Fb and the force F3 act on the vehicle body (F,
A moment +Fb)d acts in the vehicle turning direction, and this moment 1-(F.

Since +Fh)d occurs almost simultaneously with the steering of the left and right front wheels FWI and FW2, the yaw rate response of the vehicle body is improved. This will be explained using the graph of FIG. The graph shows the yaw rate per unit steering angle (yaw rate/
The phase characteristics of the steering angle) with respect to the steering speed (frequency) of the left and right front wheels FWl and FW2 are shown in the case of the first embodiment (solid line).
, when only left and right front wheels FWI, FW2 are steered (dashed line)
, when the left and right rear wheels RWI and RW2 are steered in the opposite phase to the left and right front wheels FWI and FW2 using a conventional rear wheel steering mechanism (
), and the left and right rear wheels RW1. by the conventional rear wheel steering mechanism. RW2 with left and right front wheels FW1. The cases where steering is performed in the same phase as FW2 (broken line and two-dot chain line) are shown. That is, as can be understood from this graph, according to the first embodiment, the yaw rate responsiveness of the vehicle body is as follows: RW1, R
W2 to left and right front wheels FW1. This is better than when the FW2 is steered in the same phase to the opposite phase.

In controlling the right brake hydraulic pressure PRD having such characteristics, if the vehicle is running at a low speed, the vehicle speed V calculated in step 101 (FIG. 4) is small, so the vehicle speed V calculated in step 106 is not determined in step 106. brake hydraulic pressure P,
becomes larger. Furthermore, based on the front wheel steering angle θf read in step 102, the hydraulic coefficient CP determined in step 107 is the absolute value 1θf1 of the front wheel steering angle θf.
As it gets thicker, it gets bigger, so step 1 above
Target brake oil pressure PI (-Cp
-Pl) becomes a larger value as the absolute value 1θf (increases), and the braking force Fb for the right rear wheel RW2 increases.As a result, the moment (F, +Fb)d increases, and the above (effects of the invention) As explained in the section, left and right front wheels FWI.

FW2 has a slip angle θ1. θ2 occurs and the vehicle's turning performance improves. At this time, the right rear wheel RW2 is the left and right front wheel FW.
Since the steering is in the same phase as I and FW2, the rear part of the vehicle does not move laterally, and since the vehicle speed is small, a small side force FS exists, and this side force FS causes the t As described above, since the responsiveness of the vehicle in the lateral direction is also good, the driver can turn the vehicle in a small manner without feeling any discomfort.

On the other hand, if the vehicle is running at a high speed, the brake oil pressure P becomes small because the vehicle speed (2) is high. Moreover, since the left and right front wheels FWI and FW2 are not significantly steered during high-speed running, the target brake oil pressure P is small and the braking force Fb for the right rear wheel RW2 is small. As a result, although the moment (P, +Fb) d is small, it acts to rotate the vehicle body in the turning direction, so that the maneuverability of the vehicle is improved. On the other hand, the side force Fs generated due to the braking force Fb is large to some extent because the vehicle speed ■ is high, and the lateral acceleration of the vehicle is also large to some extent, and as mentioned above, the responsiveness of the lateral acceleration is also good. Therefore, running stability during high-speed running is improved.

Next, a case where the left and right front wheels FWI and FW2 are steered to the left will be described. In this case, step 102 above
Since the front wheel steering angle θf read in (FIG. 4) is negative, the CPU 32c, after processing steps 106-108,
The determination in step 109 is "NO" and the program proceeds to steps 112 and 113. In step 112, the electromagnetic switching valve 24 is switched to the third state (left position in Figure 3). the result,
No braking force is applied to the right rear wheel RW2.

Further, in step 113, the left brake control subroutine (Fig. 6) is executed, and in the same manner as in the case of the right brake control subroutine described above, a braking force corresponding to the target brake oil pressure P is applied to the left rear wheel RW1. be done. Note that the left brake control subroutine includes steps 210-2.
17, and the processing of steps 210 to 217 corresponds to the processing of steps 200 to 207 of the right brake control subroutine (FIG. 5).

By applying this braking force Fb, the left rear wheel RWI is steered to the left, that is, in the same manner as the left and right front wheels FWI, FW2, and the left and right front wheels FWI, FW2 act in the same manner as if they were steered to the right, so that the vehicle can turn left. In this case, the same effect as in the case of turning to the right can be achieved.

b. Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 11 schematically shows the entire vehicle according to the second embodiment. In addition to the vehicle of the first embodiment, this vehicle has RWI rear wheels.

It has a rear wheel steering mechanism for interlocking and steering RW2. This rear wheel steering gear is RWI for the left and right rear wheels.

It has a relay rod 41 that connects RW2, and the same rod 4
Both ends of 1 are connected to left and right rear wheels RWI, Pj-W2 via left and right tie rods 42a, 42b and left and right arms 43a, 43b.
ip! Each is connected to I. Spring 44a, 4
Similarly to the springs 22a and 22b of the first embodiment, 4b equivalently indicates the spring force within the side of the suspension machine. The remaining portions in FIG. 11 are the same as those in the first embodiment, and are given the same reference numerals as in FIG. 3, and their explanation will be omitted.

According to the second embodiment, as in the first embodiment, one of the left and right rear wheels RWI and RW2 is controlled to move from the left and right front wheels FWI by the braking force of the brake devices 16a and 16b.
, FW2, this steering is performed by the relay rod 41, the left and right tie rods 42a, 42b, and the left and right arms 43a.

43b, and the other rear wheel is also steered in the same phase with respect to the left and right front wheels FW1 and FW2, similarly to the one rear wheel. As a result, left and right front wheels FWI,
Simultaneously with the steering of FW2, both the left and right rear wheels RWI and RW2 generate a side force Fs in the direction in which the left and right front wheels FWI and FW2 are steered, thereby improving the responsiveness of the vehicle in the lateral direction.

C6 Third Embodiment Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 1-2 schematically shows the entire vehicle according to the third embodiment. In addition to the second embodiment, this vehicle is equipped with a power cylinder 45 for driving a relay rod 41 and electromagnetic switching valves 46 and 47 for controlling supply and discharge of hydraulic oil to and from the cylinder 45 in the rear wheel steering mechanism. There is.

The power cylinder 45 is divided into left and right oil chambers 45b and 45c by a piston 45a fixed to the relay rod 41. The electromagnetic switching valve 46 includes electromagnetic solenoids 46a, 46
b and springs 46c and 46d, and when both types of magnetic solenoids 46a and 46b are in a de-energized state, both springs 4C>c and set to the first state (center position in FIG. 12) by the urging force of 46d. The passages communicating with the respective oil chambers 45b and 45c of the power cylinder 45 are blocked. Further, when the electromagnetic solenoid 46a is excited, the electromagnetic switching valve 46 is set to the second state (the right position in FIG. 12), and the hydraulic pump 25 is connected to the left oil chamber 4 of the power cylinder 45.
5b, and also allows hydraulic oil to be discharged from the right oil chamber 45c of the cylinder 45 to the reservoir 27. When the electromagnetic solenoid 46b is energized, the electromagnetic switching valve 46 is set to the third position R (the left position in Fig. 12), prohibiting communication of the hydraulic pump 25 and reservoir 27 with the power cylinder 45, and disabling the hydraulic pump 25 and the reservoir 27 from communicating with the power cylinder 45. Communication between the left and right oil chambers 45b and 45a is allowed.

The electromagnetic switching valve 47 includes electromagnetic solenoids 47a, 47b and springs 47c, 47d, and when both types of magnetic solenoids 47a, 47b are in a non-excited state, the biasing force of both springs 47c, 47d causes the electromagnetic switching valve 47 to be in the first state (the twelfth state).
(center position in the figure) to cut off each oil passage communicating with each oil chamber 45b, 45C of power cylinder 45. Also,
When the electromagnetic solenoid 47a is excited, the electromagnetic switching valve 4
7 is set to the second state B (right position in FIG. 12), and the right oil chamber 45C/\ of the power cylinder 45 is connected from the hydraulic pump 25.
The hydraulic oil is allowed to be supplied from the left oil chamber 45b of the cylinder 45 to the reservoir 27. When the electromagnetic solenoid 47b is excited, the electromagnetic switching valve 47 is set to the third state (the left position in FIG. 12), and the power cylinder 4 of the hydraulic pump 25 and the reservoir 27 is
5, and the left and right oil chambers 4 of the same cylinder 45 are prohibited.
51), allows communication between 45C.

Also, a spring 48a connected to the relay rod 41
, 48b is the same as the spring 44a of the second embodiment.
, 44b, and when the braking force Fb is applied to the left and right rear wheels RWI and RW2, the left and right rear wheels RWI and RW2 are set to a steering angle that should originally be steered by the target brake hydraulic pressure P*. It is designed to be steered slightly more than before.

Further, in order to control this rear wheel steering mechanism, the electric control device C is equipped with a rear wheel steering angle sensor 31e and excitation control circuits 35 and 36 in addition to those in the second embodiment. The rear wheel steering angle sensor 31e determines the left and right rear wheels RWI based on the variable position of the relay rod 41.

The steering angle θro of RW2 is detected, and a rear wheel steering angle signal representing the steering angle θrD is output to the input interface circuit 32e. Note that this rear wheel steering angle θrQ is positive (or negative)
Left and right rear wheels RW1. This indicates rightward (or leftward) steering of RW2, and zero indicates a state in which rear wheels RWI and RW2 are not steered.

Excitation control circuits 35 and 36 are output interface circuits 3
2f, each electromagnetic solenoid 46 a +' 46 b of the electromagnetic switching valve 46.47 is connected to the control data from the output interface circuit 32f.

47a and 47b are controlled to be energized or de-energized.

Furthermore, the microcomputer 32 controls the first and second
In addition to controlling the electromagnetic switching valves 23' and 24 as in the embodiment, the electromagnetic switching valves 46 and 47 are also controlled.
The ROM 32b in the computer 32 stores programs and data different from those in the first and second embodiments. That is, the ROM 32b stores a program corresponding to the flowchart in FIG. 13, which is a partial modification of the flowchart in FIG. 4, a program corresponding to the flowchart in FIGS.
A program corresponding to the flowchart in FIG. 5 is stored. The ROM 32b also stores the brake oil pressure Pl (seventh
In addition to storing the oil pressure coefficient Cp (Fig. 8) as the first and second tables, as shown in Fig. As shown by the solid line in Fig. 17, the rear wheel steering angle θr1 is "0" in the low vehicle speed region of less than about 40 km/h, and "1" in the high vehicle speed region of about 40 km/h or more. The steering angle coefficient Cθ is stored as third and fourth tables. The remaining parts are the same as those in the second embodiment, so the same reference numerals as in FIG. 11 are given and the explanation thereof will be omitted.

The operation of the third embodiment configured as described above will be explained with reference to the flowcharts of FIGS. 13, 5, 6, 14, and 15. Now, if the left and right front wheels FWI and FW2 are running substantially straight, the CPU 32C performs the processing of steps 101 to 105 in FIG. 13 to turn the left and right rear wheels RWI in the same manner as in the above case.

Avoid applying braking force to RW2. After the processing in step 105, the CPO 32C executes the rear wheel neutral return control subroutine (FIG. 14) in step 121 to bring the left and right rear wheels RWI, RW2 into the neutral state, that is, to set the rear wheel steering angle θrD to approximately "0". ”.

In this rear wheel steering control subroutine, CPO32
C starts executing the subroutine program in step 300, and in step 301, the rear wheel steering angle sensor 31
A rear wheel steering angle signal representing the rear wheel steering angle θr'D is read from the input interface circuit 32e through the input interface circuit 32e, and is stored in the RAM 32d as rear wheel steering angle data. Next, in step 302, the CPU 32C determines the rear wheel steering angle θ.
It is determined whether the absolute value 1θTo l of m"D is less than the minute steering angle value Δθr, that is, whether the left and right rear wheels RWI, RW2 are in a neutral state. Now, the left and right rear wheels RW1, RW
2 is in the neutral state, the CPU 32C performs step 3 above.
02 is determined as “YES”, and steps 303 and 304
Electromagnetic solenoid 46a.

Control data for controlling the solenoid 46b to be de-energized and control data for controlling the electromagnetic solenoids 47a and 47b to be de-energized are output to the output interface circuit 32f.

The output interface circuit 32f stores these control data and outputs them to the excitation control circuits 35 and 36, respectively, and the excitation control circuits 35 and 36 control the electromagnetic solenoid 46a,
46b and electromagnetic solenoids 47a and 47b are controlled to be de-energized. As a result, the electromagnetic switching valves 46 and 47 are each set to the first state (center position in FIG. 12), and each oil passage communicating with each oil pressure 45b, 45c of the power cylinder 45 is cut off, so that the cylinder 45 is Displacement of the relay rod 41 is prohibited. As a result, the left and right rear wheels RWI and RW2 are maintained in a neutral state.

Further, if the left and right rear wheels RWI and RW2 are being steered to the right, the CPU 32C determines rNo in step 302 above.
That is, it is determined that the absolute value 1θro l is not less than the minute steering angle value Δθr, and in step 305 the rear wheel steering angle θr
Determine whether o is positive. In this case, left and right rear wheels R
WI and RW2 are being steered to the right and the rear wheel steering angle θr
Since D is positive, the CPU 32C executes step 305 above.
rYES is determined, and step 306 switches the electromagnetic switching valve 47 to the first position in the same manner as in step 304 above.
state (center position in Fig. 12).

As a result, the switching valve 47 no longer controls the supply and discharge of hydraulic oil to the power cylinder 45.
In step 307, the PU32C activates the electromagnetic solenoid 46a.
Control data is output to the output interface circuit 32f to excite the . The output interface circuit 32f stores the control data and outputs it to the excitation control circuit 35, and the excitation control circuit 35 excites the electromagnetic solenoid 46a. As a result, the electromagnetic switching valve 46 is in the second state (first state).
2), the hydraulic oil from the hydraulic pump 25 is supplied to the left oil chamber 45b of the power cylinder 45, and the hydraulic oil from the right oil chamber 45c of the same cylinder 45 is supplied to the reservoir 2.
Discharge at 7. As a result, the power cylinder 45 displaces the relay rod 41 to the right, and this displacement causes the left and right rear wheels to RWI.

RW2 is steered to the left, that is, to the neutral direction.

On the other hand, if the left and right rear wheels RWI, RW2 are being steered to the left, the CPO 32C determines [N01] in steps 302 and 305, and in step 308, the electromagnetic switching valve 46 is turned on by the same process as step 303. is set in the first shape R (center position in FIG. 12). As a result, the switching valve 46 no longer controls the supply and discharge of hydraulic oil to and from the power cylinder 45. Next, the CPU 32c
At the knob 309, the output interface circuit 32f and the excitation control circuit 36 are processed in the same manner as in step 307 above.
The electromagnetic switching valve 47 is placed in the second state (12th
Set to the right position in the figure. As a result, the hydraulic bonder 25
The hydraulic oil from the power cylinder 45 is supplied to the right oil chamber 45c of the power cylinder 45, and the hydraulic oil from the left oil chamber 451 of the power cylinder 45 is discharged to the reservoir 27, so the cylinder 45 moves the relay rod 41 to the left. This displacement causes the left and right rear wheels RWI, RW2 to be steered in the right direction, that is, in the neutral direction.

In this way, if the rear wheel steering angle θrD is approximately "0", the left and right rear wheels RW1. Keep the steering of RW2 in the previous state, and otherwise left and right rear wheels RWI.

Step 303 described above for controlling the steering of RW2 in the neutral direction.
After processing steps 304, 307, and 309, the CPU 32c returns the program to step 101 (FIG. 13) in step 310. Thereafter, as long as the left and right front wheels FWl and FW2 are in a substantially straight-ahead state (1θfl<θ.), the CPU 32c continues to execute the circulation process of steps 101 to IO5, 121, and in step 121 executes the program process of the rear wheel return control subroutine. By executing this, the rear wheel steering angle θrD becomes “0”.
Since the left and right rear wheels RWI, RW2 are steered so that the steering angle θrD of the left and right rear wheels RWI, RW2 is reliably fixed to approximately “0”.

During the above circulation process, when the vehicle starts turning to the right,
In step 103, the CPU 32C determines that rYEs, that is, the absolute value 1θf1 of the front wheel steering angle θf is the minute steering angle value θ1.
．． The braking force Fb corresponding to the target brake oil pressure P$ is applied to the right rear wheel RW2 through the processes of steps 106 to 108 and 109 to 111, as in the first and second embodiments. . However, in this case, since the biasing forces of the springs 48a and 48b are set smaller than those in the first and second embodiments, the left and right rear wheels RW
I and RW2 are steered to a slightly greater angle than the desired steering angle due to the target brake oil pressure P being zero.

In the case of this third embodiment, after the process in step 108, the CPU 32c in step 122 stores the target brake oil pressure data in the ROM 3 based on the target brake oil pressure data stored in the RAM 32d.
Referring to the third table (Fig. 16) in 2b, set the same oil pressure P.
Deriving the rear wheel steering angle θr1 corresponding to $, step 12
In step 3, based on the vehicle speed ■, the steering angle coefficient C corresponding to the vehicle speed ■ is determined by referring to the fourth table (Fig. 17) in the ROM 321).
θ is derived, and in step 124, a target rear wheel steering angle θγ number is calculated by executing the following calculation based on the rear wheel steering angle θr1 and the steering angle coefficient Cθ thus derived.

θrl = Cθ・θr1 As a result, the target rear wheel steering angle θr becomes "0" in the low vehicle speed range of less than about 40 km/h, and becomes the target brake oil pressure P* in the high vehicle speed range of about 40 km/h or more. This corresponds to the steering angle that should originally be set. Note that the target rear wheel steering angle data representing the calculated target rear wheel steering angle No. 01 is stored in the RAM in step 124.
32 d.

After the processing in step 124, the CPU 32c executes the processing in steps 109 to 111 described above, and advances the program to step 125. At step 125, the CPU
32c reads the rear wheel steering control subroutine (FIG. 15) and executes the program of the same routine. In this rear wheel steering control subroutine, the CPU 32c starts executing the program of the routine in step 400, and reads the rear wheel steering angle θrD in step 401 in the same manner as in step 301 above. Next, in step 402, the CPU 32c determines whether the front wheel steering angle θf read in the process of step 102 (FIG. 13) is positive. In this case, the vehicle is in a right-turning state and the front wheel steering angle θf is positive, so the CPU 32c determines rYES in step 402, and in step 403, the electromagnetic Switching valve 47
is set to the first state. As a result, the electromagnetic switching valve 47
denotes each oil chamber 45b of the power cylinder 45.

Since each oil passage communicating with the power cylinder 45c is cut off, there is no need to control the supply and discharge of hydraulic oil to the power cylinder 45.

After the processing in step 1103, the CPU 32C determines in step 404 whether or not the absolute value 1θr−θro l of the difference between the target rear wheel steering angle θjl and the rear wheel steering angle θrD is less than the minute steering angle value Δθr. That is, left and right rear wheels RW1.
It is determined whether RW2 is being steered to approximately the target rear wheel steering angle θr$. Now, if the left and right rear wheels RWI and RW2 are being steered approximately to the target rear wheel steering angle θr, the CPU 32c
is rYESJ, that is, the absolute value 1 in step 404.
It is determined that θr - θrol is less than the minute steering angle value Δθr, and in step 405, the electromagnetic switching valve 46 is set to the first state (center position in FIG. 12) in the same manner as in step 303 above. As a result, the electromagnetic switching valve 46 shuts off each oil passage communicating with the left and right oil chambers 45b and 45c of the power cylinder 45, so that the cylinder 45 is connected to the relay rod 41.
The left and right rear wheels RWI, RW2 are maintained at the target rear wheel steering angle θ1 by inhibiting displacement of the left and right rear wheels RWI, RW2.

In addition, the left and right rear wheels RWI and RW2 are set to the target rear wheel steering angle θr$
If the steering wheel is steered more to the right than the minute steering angle value Δθr, the CPU 32c determines in step 404 that rNOJ, that is, the absolute value 101-1-θr,l is not less than the minute steering angle value 601, and in step 406 rYES, that is, it is determined that the rear wheel steering angle θr0 is larger than the target rear wheel steering angle θ71, and in step 407, the above step 307 is determined.
The electromagnetic switching valve 46 is set to the second state (the right position in FIG. 12) in the same way as in the process of FIG. By setting the electromagnetic switching valve 46 to the second state, as in the case described above, the hydraulic oil from the hydraulic pump 25 is supplied to the left oil chamber 45b of the power cylinder 45, and the hydraulic oil is supplied from the right oil chamber 45c of the power cylinder 45. As the hydraulic oil is discharged into the reservoir 27, the power cylinder 45
displaces the relay rod 41 to the right, and moves the left and right rear wheels RW.
I, RW2 is steered to the left, that is, in the direction of the target rear wheel steering angle θr$.

On the other hand, the left and right rear wheels RWI and RW2 are at the target rear wheel steering angle θγ$
If the vehicle has been steered to the left more than the minute steering angle value Δθr by 1, the CPU 32c determines in step 404 that rNOJ, that is, the absolute value 101-$-θro 1 is not less than the minute steering angle value 601, and proceeds to step 406. Then, it is determined that the rear wheel steering angle θrD is not larger than the target rear wheel steering angle θr, and in step 408, the electromagnetic solenoid 46b is excited in cooperation with the output interface circuit 32f and the excitation control circuit 35. Due to this excitation, the electromagnetic switching valve 46 is set to the third state (the left position in FIG. 12), and the left and right oil chambers 45b, 45c of the power cylinder 45 communicate with each other via the switching valve 46.

In such a case, the left and right rear wheels r (Wl, RW2 are adjusted to the steering angle that should originally be set in relation to the biasing forces of the springs 48a and 48b by applying the braking force F5 to the right rear wheel RW2 based on the target brake oil pressure P number. (Target rear wheel steering angle θrs
), the left and right rear wheels RWI, RW2 are steered to the right by the braking force Fb, that is, in the direction of the target rear wheel steering angle θr$.

In addition, with this steering, the relay rod 41 is displaced to the left, and the hydraulic oil in the left oil chamber 45b of the power cylinder 45 flows into the right oil chamber 45c of the same cylinder 45 via the electromagnetic switching valve 46.

After each process of steps 405, 407, 4.08 above, C
The PU 32c ends the execution of the rear wheel steering control subroutine in step 420, returns the program to step 101 (FIG. 13), and returns steps 101 to 103 and 106 to 10.
8,122-124 degrees 109-111,125 continues to be executed. During this circulation process, the rear wheel steering control subroutine is delayed in step 125, and the left and right rear wheels RWI, RW2 are controlled in step 40 in FIG.
The rear wheels are steered to the target rear wheel steering angle θjl by feedback control consisting of steps 4 to 408. As a result, as in the first and second embodiments, the circulation process applies braking force Fh to the right rear wheel RW2, and in the low vehicle speed region, the left and right rear wheels Rwt, Rw2 are steered. The angle θro is “
The rear wheel steering angle θr that should be set to "0" and that should be originally set in accordance with the target brake oil pressure P$ in the high vehicle speed region.
It is steered accurately to l. As a result, in the low vehicle speed region, the left and right rear wheels RWI and RW2 are the left and right front wheels FWI.

Since the vehicle is not steered in the same phase as FW2, the vehicle's movement response in the lateral direction I\ is different from that of the left and right front wheels FW1. Although the result is about the same as when only FW2 is steered (broken line in FIG. 9), the vehicle's turning performance is improved compared to the first and second embodiments. In addition, in a high vehicle speed region, the left and right rear wheels RW 1 and RW 2 have a rear wheel steering angle that corresponds to the target brake hydraulic pressure PI, regardless of differences in braking force due to the driving road surface, variations in spring force within the suspension machine, etc. Since the vehicle is reliably steered to θr1, the running stability of the vehicle is always stable and good. In addition, in this third embodiment, the steering by the power cylinder 45 is performed by the braking force Fb of the left and right rear wheels R.
Since it acts to correct the steering of WI and RW2, it does not require a very large driving force.

Next, a case where the left and right front wheels FWI and FW2 are steered to the left will be described. In this case, since the front wheel steering angle θf is negative, the CPU 32c performs step 101 in FIG.
~103,106~108°122~124,109,
Execute a circular process consisting of 112, 113, 125,
The same braking force Fb as in the first and second embodiments is applied to the left rear wheel RWI, and the left and right front wheels FWI, FW are applied to the left rear wheel RWI.
Similarly to the case of right steering in No. 2, the left rear wheel RW1 is steered to the target rear wheel steering angle θr. However, in this case, in the rear wheel steering control subroutine (FIG. 15) that is read and executed in step 125, steps 400 to 402, 413 to 418, and 420 are performed because the front wheel steering angle θf is negative.
processing is executed.

That is, the CPU 32C uses the step 413 to set the electromagnetic switching valve 46 to the first state in the same manner as in step 303 above, thereby causing the switching valve 46 to control the left and right rear wheels RW1. While prohibiting the steering control of RW2, the electromagnetic switching valve 47 is controlled in steps 414 to 418 to RWI the left and right rear wheels.

The steering angle θrQ of RW2 and the target rear wheel steering angle θrl are set. Note that in this case, since the rear wheel steering angle θrD is negative, in steps 414 and 416, the above step 4 is
Unlike the judgment in 04,406, 1θr$10θro
A conditional determination is made that l<, θr, θrD, θrne. Further, in step 415, the electromagnetic switching valve 47
By setting the left and right rear wheels RWI, RW2 to the first state (center position in FIG. 12) as in step 405, the left and right rear wheels RW2 are maintained at the target rear wheel steering angle θr$, and in step 417, the electromagnetic switching valve 47 is set to the first state. By setting the electromagnetic switching valve 47 to the second state (the right position in FIG. 12), the left and right rear wheels RWI, RW2 are steered to the right, contrary to step 407, and in step 418, the electromagnetic switching valve 47 is set to the third state (the right position in FIG. 12). 1
Step 40 above by setting the left position in Figure 2).
8, the left and right rear wheels RW 1 and RW 2 are steered to the left.

As described above, when the left and right front wheels FWI and FW2 are steered to the left, the application of braking force to the left and right rear wheels RWI and RW2 is controlled and the left and right rear wheels FW1. Since steering control is performed in the same phase direction with respect to FW2, it is expected that the same improvement in the turning performance of the vehicle and the driving stability of the vehicle as described above will be achieved.

In the above embodiment, as shown by the solid line in FIG. 17, the steering angle coefficient Cθ discontinuously changes from "0" to "1" at the boundary between the low vehicle speed region of about 40 km/h and the high vehicle speed region. However, as shown by the broken line in FIG. 17, the steering angle coefficient Cθ changes from "0" to "0" near the boundary.
It may be made to change continuously up to 1''. In this case, the continuously changing steering angle coefficient Cθ is stored in the ROM 321).
What is necessary is to store it in the fourth table in the table.

According to this modified example, since the steering angle coefficient Cθ changes continuously near the boundary between the low vehicle speed region and the high vehicle speed region, the vehicle speed V changes across the boundary while the vehicle is turning. However, the rear wheel steering angle θr(, , ) does not change suddenly, and the running stability of the vehicle is improved.

d. Fourth embodiment Next, RWI of the left and right rear wheels in the third embodiment.

The steering control of RW2 is simplified, and the left and right rear wheels RWI and RW2 are set to a steering angle rQ only in the low vehicle speed region.

A fourth embodiment of the present invention in which control is performed will be described.

The vehicle according to the fourth embodiment has a cylinder 51, an electromagnetic switching valve 52, and an excitation control circuit 37 in place of the power cylinder lt5, electromagnetic switching valve 46, 47, and excitation control circuit 35, 36 of the third embodiment. has. cylinder 51
Similar to the power cylinder 45 above, the relay rod 41
Left and right oil chambers 5 partitioned by a piston 51a fixed to the
1b, 51c, but the left and right oil chambers 51b, 51c do not communicate with the hydraulic pump 25 or the reservoir 27, and the oil chambers 51b, 5]c are filled with hydraulic oil.

The electromagnetic switching valve 52 includes an electromagnetic solenoid 52a and a spring 52bt! - When the solenoid 52a is not excited, it is set to the first state (left position in FIG. 18) by the biasing force of the spring 52b, and communication between the left and right oil chambers 51b and 51c of the cylinder 51 is prohibited. Further, when the electromagnetic solenoid 52a is excited, the electromagnetic switching valve 52 is set to the second state (the right position in FIG. 12), and the cylinder 5
The left and right oil chambers 51b and 51c of 1 are communicated with each other. The excitation control circuit 37 is connected to the output interface circuit 32f, and controls excitation and de-excitation of the electromagnetic solenoid 52a according to control data from the output interface circuit 32f. Along with these changes, the programs and data stored in the ROM 32b of the microcomputer 32 are also different, and the programs include a program corresponding to flowchart 1 in FIG. 19, which is a partially modified version of the flowchart in FIG. Programs corresponding to the flowcharts shown in FIGS. 5 and 6 above and programs corresponding to the flowchart shown in FIG. 20 are stored, and the data include the brake oil pressure P.
Only the hydraulic coefficient z (FIG. 7) and the hydraulic coefficient Cp (FIG. 8) are stored as the first and second tables. In addition,
In this case, the spring 44a in the rear wheel steering device IID,
44b is applied to the left and right rear wheels R, W1. R and W2 are set to such an extent that the steering angle is adjusted to the steering angle that should originally be steered, that is, larger than that of the third embodiment and approximately the same as that of the second embodiment. Note that the remaining parts are the same as those in the third embodiment, so the first
The same reference numerals as in FIG. 2 are used, and the explanation thereof will be omitted.

The operation of the fourth embodiment, which has an elliptical structure as described above, will be explained.

Also in this fourth embodiment, step 101 in FIG.
.about.113 and the left and right brake control subroutines shown in FIGS. 5 and 6, the left and right rear wheels R, W1. Application of braking force Fb to RW2 is controlled. On the other hand, in this fourth embodiment, during the circulation process consisting of steps 101 to 113 (FIG. 19),
The CPU 32C performs step 13 after processing step 102.
1, the rear wheel steering port/turn subroutine (Fig. 20) is executed, and the left and right rear wheels RW1. Controls the steering lock of RW2.

In this rear wheel steering lock subroutine', the CPU
32c starts executing the program of the same routine at step 500, and executes the above-mentioned step 30 at step 501.
Read the rear wheel steering angle θrO in the same manner as in step 1. Next, C.P.
The U32C determines whether or not the absolute value 1θrot of the rear wheel steering angle θrD read in step 502 is less than the minute steering angle value Δθr, that is, whether the left and right rear wheels RWI, RW2 are in a substantially neutral state.・The vehicle speed ■ calculated by the process of step 101 (FIG. 19) in the knob 503 is set to the predetermined vehicle speed V corresponding to the boundary between the low vehicle speed region and the high vehicle speed region.
+ (for example, about 40 km/h).

Now, if the left and right rear wheels RWI, RW2 are in a substantially neutral state and the vehicle speed V is less than the predetermined vehicle speed 71, the CPU 32c determines "YESJ" in each of steps 502 and 503, and disables the electromagnetic solenoid 52a in step 504. Interface circuit 32f that outputs control data for controlling excitation
Output to.

The output interface circuit 32f stores the control data and outputs it to the excitation control circuit 37, and the excitation control circuit 37 controls the electromagnetic solenoid 52a to be de-energized. As a result, the electromagnetic switching valve 52 is set to the first state (left position in FIG. 12), and the left and right oil chambers 51b, 51 of the cylinder 51
Communication between the two terminals c is prohibited, and displacement of the relay rod 41 is prohibited.

In this case, left and right rear wheels RW1. Since RW2 was previously in a substantially neutral state, the left and right rear wheels RW1. RW2 is maintained in a substantially neutral state. After processing step 504, the CP Ll 32c finishes executing the rear wheel steering lock subroutine in step 505, and advances the program to step 103 (FIG. 19).

With this control, when the vehicle is turned at low speed after starting, when the vehicle is stopped, the left and right rear wheels RWI
, RW2, no braking force Fb is applied to the rear of the vehicle, and the same rear wheels RWI.

Since the steering angle of RW2 is approximately "0", the left and right rear wheels Rwt and Rw2 of the turning vehicle are held at the steering angle "0", and the small turning performance of the vehicle is improved as in the case of the third embodiment. . Also, when the vehicle is turned after moving from high-speed straight running to low-speed straight running, the left and right rear wheels RWI and RW2 are adjusted to the steering angle [
0], the small turning performance of the vehicle is improved as described above.

On the other hand, if the absolute value 1θrD1 of the rear wheel steering angle θrD is equal to or greater than the minute steering angle value 661, or if the vehicle speed ■ is equal to or greater than the predetermined vehicle speed 71, the CPU 32c executes r at steps 502 and 503.
The determination is No, and step 506 executes the above step 5.
Similarly to the process in step 04, the electromagnetic solenoid 5
2a is excited. This causes the electromagnetic switching valve 52 to switch to the second
(the right position in FIG. 12), and the left and right oil chambers 51b and 51c of the cylinder 51 are communicated with each other. As a result, the left and right rear wheels RWI, RW2 can be steered by the braking force Fb. After the processing in step 504, the CPU 32c finishes executing the rear wheel steering lock routine in step 505 and advances the program to step 103 (FIG. 19).

Through such control, the RWI of the left and right rear wheels of a vehicle traveling at high speed is
, RW2 is steered to a steering angle corresponding to the target brake oil pressure 2 ports by applying the braking force Fb, so that the running stability of the vehicle at high speeds is as good as in the first to third embodiments. Moreover, after the left and right rear wheels RWI, RW2 are once steered in either the left or right direction, the above-mentioned step 5
As a result of the processing in step 02, the steering will not be locked until the same rear wheels RWI and RW2 return to a substantially neutral state, so the left and right rear wheels R
The steering will not be locked while WI and RW2 are being steered in either the left or right direction.

e. Modification In the first to fourth embodiments described above, when setting the brake oil pressure PLD+PRD in the left and right brake devices 16a and 16b to the target brake oil P, and when setting the left and right rear wheels RWI,
When setting the steering angle θrD of RW2 to the target rear wheel steering angle θr$, feed pack control by program processing of the microcomputer 32 is used. The feedback control may be performed outside the microcomputer 32 by outputting a signal representing the zero steering angle θr. In this case, the signal, the oil pressure sensors 31c, 31d, and the rear wheel steering angle sensor 31e
The output signal from the servo amplifier may be inputted to a servo amplifier, and the electromagnetic switching valves 23, 24, 46, 47 may be controlled by the output of the amplifier.

[Brief explanation of the drawing]

FIG. 1 is a diagram corresponding to the configuration of the present invention described in the claims, FIG. 2 is an operational explanatory diagram for explaining the present invention in detail, and FIG. 3 is a diagram according to the first embodiment of the present invention. An overall schematic diagram of the vehicle, Figures 4 to 6 are flowcharts of the program executed by the microcomputer in Figure 3, Figure 7 is a graph showing the relationship between vehicle speed and brake oil pressure, and Figure 8 is the front wheel steering angle. - A graph showing the relationship between oil pressure coefficients, Figure 9 is a phase characteristic diagram of lateral acceleration/steering angle, Figure 10 is a phase characteristic diagram of yaw rate/steering angle, and Figure 11 is a vehicle according to the second embodiment of the present invention. FIG. 12 is an overall schematic diagram of a vehicle according to a third embodiment of the present invention, and FIGS.
16 is a graph showing the relationship between target brake oil pressure and rear wheel steering angle, FIG. 17 is a graph showing the relationship between vehicle speed and steering angle coefficient, and FIG. 18 is a graph showing the relationship between vehicle speed and steering angle coefficient. 19 and 20, which are overall schematic diagrams of a vehicle according to a fourth embodiment of the present invention, are flowchart 1 of a program executed by the microcomputer shown in FIG. 18. Explanation of symbols A...Front wheel steering mechanism, B...Hydraulic braking device, C...
- Electric control device, D... Rear wheel steering mechanism, SW... Steering handle, FWI, FW2,,. Front wheel, RWl, RW2. ,, rear wheels, 16a, 16b--
- brake equipment, 22a, 22b, 44a; 441), 48a, 48b --- Spring, 23° 24.46, 47.5'2... Solenoid switching valve, 31a
...Vehicle speed sensor, 31b...Front wheel steering angle sensor, 3
1c, 31d...Oil pressure sensor, 31e...Rear wheel steering angle sensor, 32...Microcomputer, 41...
・Relay rod, 45...Power cylinder, 51...
·Cylinder. Applicant: Toyota Motor Corporation Representative, Patent Attorney: Teru (1 other person) Fig. 1 Fig. 2 + d--) Fig. 5 Fig. 6 Fig. 7 Electric power (kvn/h) Fig. 8 Left-〇-Front wheel several peaks of Fig. 9 Fig. 10 Fig. 16 Fig. 17 (k%/h> Vehicle speed V Fig. 20

Claims (1)

[Claims] In a steering system for a vehicle equipped with a front wheel steering mechanism that steers the front wheels according to the rotation of a steering wheel, the left and right rear wheels are independently provided and applied to the left and right rear wheels, respectively, and brake the left and right rear wheels according to the applied brake hydraulic pressure. a pair of brake devices, a front wheel steering angle detection means for detecting a front wheel steering angle, a vehicle speed detection means for detecting vehicle speed, and a hydraulic control value that increases as the detected front wheel steering angle increases and decreases as the detected vehicle speed increases. a hydraulic control value determining means for determining the determined hydraulic pressure control value, and a braking hydraulic pressure applying means for applying a braking hydraulic pressure corresponding to the determined hydraulic pressure control value to a brake device on the side in the steering direction of the front wheels among the pair of left and right brake devices. A vehicle steering device characterized by: