JPS6364871A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent the oversteering action caused by changing a rear wheel to be rapidly steered in the time of a reverse phase, by providing a hysteresis setting part, which sets a steering ratio characteristic in the time of deceleration to be displaced to a direction of the same phase as compared with the basic steering ratio characteristic in the time of acceleration and low speed, in a four-wheel steering device. CONSTITUTION:A bevel gear 48 is mounted to a rotary shaft 46, and a bevel gear 49, mounted onto an output shaft 50a of a stepping motor 50, is meshed with said bevel gear 48. If a sector gear 45 is turned by actuating the stepping motor 50, a holder 31 changes a tilt angle for the reference surface, and a steering angle thetaR of rear wheels 2L, 2R is controlled. While the sector gear 45, if it is turned from the neutral position, changes steering ratio so as to be controlled in the same phase steering both front and rear wheels to be directed to the same direction. The stepping motor 50 is actuated so as to be controlled by an output from a control unit with a built-in microcomputer.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention steers front wheels and rear wheels in accordance with the operation of a steering ring wheel, and changes the steering ratio of the front and rear wheels in accordance with the vehicle speed. The present invention relates to an improvement of a four-wheel steering system for a vehicle configured to vary according to steering ratio characteristics.

(Prior art) A four-wheel steering system for a vehicle normally sets the steering ratio of the front and rear wheels in opposite phases to 1IiIlvs during low-speed turns and sets the steering characteristics to tend to oversteer, thereby increasing the turning performance of the vehicle and improving the turning performance during high-speed turns. Based on a predetermined steering ratio characteristic set in advance according to the vehicle speed, the steering ratio is controlled in the same phase and the steering characteristic is set in a direction to strengthen understeer, thereby increasing the running stability of the vehicle. It is configured to change the steering angle of the rear wheels relative to the front wheels.

By the way, in a vehicle equipped with the four-wheel steering 'IAN, when decelerating during a turn, the steering ratio is reduced, that is, the rear wheels are steered in the opposite phase to the front wheels, resulting in oversteer, which causes the vehicle body to A tuck-in phenomenon, in which the vehicle body suddenly turns inward, or a scoop-in phenomenon, in which the vehicle body spins, may occur.

In order to prevent the occurrence of this tuck-in phenomenon, for example, as shown in Japanese Unexamined Patent Publication No. 60-85066, conventional methods have been used to adjust the steering ratio of the rear wheels to the front wheels according to the vehicle speed only when the vehicle is traveling substantially straight. and maintains the steering angle of the rear wheels constant when the vehicle is in a turning state,
Alternatively, as shown in Japanese Unexamined Patent Publication No. 60-85067, when the vehicle speed suddenly changes, a delay circuit or the like is used to change the steering angle of the rear wheels with a predetermined delay. It is.

However, with the former configuration, if the front wheels and rear wheels are in the same phase and decelerate in a high-speed turning state, the rear wheels will remain in the same phase even if the vehicle shifts to a low speed state.
If it is not possible to improve the turning performance and the front and rear wheels are in opposite phases when accelerating at low speeds,
The problem is that the rear wheels are held in an opposite phase state even when the vehicle shifts to a high speed state, making it impossible to improve the running stability of the vehicle, and that the original characteristics of the four-wheel steering system are not demonstrated in these states. There is.

In addition, in the latter configuration, when the vehicle is suddenly accelerated, the steering angle of the rear wheels changes gradually, making it impossible to obtain the desired steering ratio even in high-speed turns, which increases driving stability. In addition, there is a problem in that the steering ratio characteristics change depending on the amount of change in vehicle speed per unit time such as deceleration, so the driver cannot accurately grasp the steering ratio characteristics. there were.

(Object of the Invention) The present invention was made based on the above technical background, and at low speeds, the steering ratios of the front and rear wheels are set in opposite phases! The four-wheel steering system maintains the functions of a four-wheel steering system, such as being able to improve the vehicle's turning performance, and also increasing the running stability of the vehicle by keeping the above-mentioned steering ratio in the same phase when in 8th gear. Even when the vehicle decelerates during a turn, it is possible to prevent the car body from tucking in or digging into the car, and the steering ratio characteristics do not change depending on deceleration, etc. A four-wheel steering system that changes the steering angle of the wheels and allows the driver to accurately grasp the steering ratio characteristics.
The purpose is to obtain t.

(Structure of the Invention) The present invention is configured to steer the front wheels and rear wheels in accordance with the operation of the steering wheel, and to change the steering ratio of the front and rear wheels in accordance with the steering ratio characteristic corresponding to the vehicle speed. In a four-wheel steering system for a vehicle that has been developed, the vehicle speed detection means for detecting the vehicle speed and the steering ratio characteristic during deceleration are displaced in the same phase direction compared to the basic steering ratio characteristics during acceleration and constant speed. a hysteresis setting section; a steering ratio setting section that determines the steering ratio of the front and rear wheels according to the output signal from the hysteresis setting section; and a rear wheel steering angle that controls the steering angle of the rear wheels according to the steering ratio. A control section is provided.

According to the above configuration, when the vehicle decelerates, the steering ratio characteristic shifts in the same phase direction according to the output signal from the hysteresis setting section, so that the rear wheels suddenly change from the same phase as the front wheels to the opposite phase. This will prevent this from happening.

(Example) FIGS. 1 and 2 schematically show the configuration of a four-wheel steering system for a vehicle, including front wheels 1L, 1R and rear wheels 2L.

2R is a front wheel steering mechanism 3 and a rear wheel steering mechanism 12, respectively.
is supported by.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms 4L.
, 4R, tie rods 5L, 5R, and a relay rod 6 that connects the left and right tie rods 5L, 5R. Further, a steering wheel 10 is connected to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7. That is, the steering mechanism 7 includes a rack 8 formed on the relay rod 6, and a steering shaft 11 to which a steering wheel 10 is connected to the upper end and a pinion 9 that meshes with the rack 8 is attached to the lower end. The left and right front wheels IL and 1R are configured to be steered in accordance with the operation of 10.

On the other hand, similarly to the front wheel steering mechanism 3, the rear wheel steering mechanism 12 has a relay rod 15 that connects the left and right knuckle arms 13L, 13R and the tie rods 14L, 14R.
and a hydraulic power steering mechanism 16.
It is equipped with This power steering mechanism 16 is
A power cylinder 17 is provided which is fixed to the vehicle body and has the relay rod 15 as a piston rod, and inside this power cylinder 17, two hydraulic chambers 17b and 17C are formed by a piston 17a which is integrally attached to the relay rod 15.
The hydraulic chambers 17b and 17C are divided into !
'18.19 is connected to the control valve 20. The control valve 20 also has an oil supply pipe 22 and an oil discharge pipe 23 leading to the reserve tank 21.
Two pipes are connected to each other, and a hydraulic pump 24 driven by an engine (not shown) is disposed in the oil supply pipe 22. The control valve 20 is a known spool valve type, and the relay rod 15
A cylindrical valve casing 20a is integrally attached to the valve casing 20a via a connecting member 25, and this valve casing 2Oa
It is equipped with a spool valve (not shown) fitted inside, and the spool valve 8! Pressure oil from the hydraulic pump 24 is supplied to one of the hydraulic chambers 17b (17c) of the power cylinder 17 in accordance with ll to assist the driving force for the relay rod 15. Note that the power cylinder 17
The relay rod 15 is placed in the 2° utral position (rear wheel 2
Return springs 17d and 17d are installed to bias the steering wheel L and 2R to a position where the steering angle θR is 0.

The relay rod 6 of the front wheel steering mechanism 3 is provided with a rack 26 that is separate from the rack 8 that constitutes the steering mechanism 7.
A binion 27 attached to the front end of a rotating shaft 28 extending in the longitudinal direction of the vehicle body is engaged with this rack 26, and the rear end of this rotating shaft 28 is connected to the rear wheel steering via a steering ratio υ control mechanism 29. It is connected to mechanism 12.

The above steering ratio control 21It! The l structure 29 is a control rod 3 that is freely held WJvJ in the vehicle width direction with respect to the vehicle body.
0, and one end of this control rod 30 is connected to the spool valve of the control valve 20. The steering ratio control mechanism 29 also includes a swing arm 33 whose base end is swingably supported by a U-shaped holder 31 via a support pin 32, and the holder 31 is a casing fixed to the vehicle body. (not shown) on the control rod 3 above.
It is rotatably supported via a support shaft 35 having a rotation wheel line perpendicular to the axis of movement of zero. The support pin 32 of the swing arm 33 is located at the intersection of the two axes and extends in a direction perpendicular to the rotation axis.
By rotating it around, the support bin 32 at the tip
and the movement axis of the control rod 30,
In other words, the swing locus plane of the swing arm 33 centered on the support bin 32 is perpendicular to the movement axis (hereinafter referred to as the Yang quasi plane).
The angle of inclination made with respect to the base is changed.

Further, one end of a connecting rod 37 is connected to the distal end of the first dispatch arm 33 via a ball joint 36, and the other end of this connecting rod 37 is connected to the control rod 30 via a ball joint 38.
The control rod 30 is connected to the other end, and is configured to displace the control rod 30 in the vehicle width direction in response to displacement of the tip of the swing arm 33 in the vehicle width direction.

The connecting rod 37 is supported by a rotation imparting arm 40 via a ball joint 41 at a portion close to the ball joint 36 so as to be able to move WIvJ. The rotation imparting arm 40 is provided integrally with a large-diameter bevel gear 43 rotatably supported on the movement axis via a support shaft 42, and the bevel gear 43 has the above-mentioned shape as shown in FIG. A bevel gear 44 attached to the rear end of the rotating shaft 42 is meshed with the rotating shaft 42 to transmit rotation of the steering wheel 10 to the rotation imparting arm 40. Therefore, the suspension rotation imparting arm 40 and the connecting rod 37 rotate around the movement axis in accordance with the rotation angle of the steering wheel 10, and accordingly, the swing arm 33 swings around the support bin 32. If the support bin 32
When the axis of the control rod 30 coincides with the movement axis of the control rod 30, the ball joint 36 at the tip of the swing arm 33 only swings on the reference plane, and the control rod 30 is held stationary. If the axis of the bottle 32 is inclined with respect to the movement axis and the swing locus plane of the swing arm 33 deviates from the reference plane, the ball joint will be damaged as the swing arm 33 swings about the pin 32. 36 is displaced in the vehicle width direction, and this displacement causes the connecting rod 3
7 to a control rod 30, which is configured to move along the axis of movement and actuate the spool pulp of the control valve 20. That is, even if the swinging angle of the swinging arm 33 about the axis of the pin 32 is the same, the displacement of the control rod 30 in the left-right direction changes with the change in the inclination angle of the pin 32, that is, the rotational angle of the holder 31. and change.

In order to change the inclination angle of the support pin 32 with respect to the moving axis, that is, the inclination angle of the holder 31 with respect to the longitudinal plane, a sector gear 45 as a worm wheel is attached to the support shaft 35 of the holder 31, and a sector gear 45 as a worm wheel is attached to the rotary shaft 46. A worm gear 47 is engaged. A bevel gear 48 is attached to the rotating ring 46, and a bevel gear 49 is attached to the output shaft 50a of the stepping motor 50.
are engaged with each other, and by operating the stepping motor 50 and rotating the sector gear 45, the holder 31
The steering angle θR of the rear wheels 2L and 2R is controlled by changing the angle of inclination with respect to the reference plane of When the wheels are rotated clockwise, the steering ratio is controlled to be in the same phase so that the rear wheels 2L, 2R face in the same direction as the front wheels 1L, 1R.

Further, in the casing supporting the holder 31, there are stopper members 51 on the opposite phase side and the same phase side, which are made of pins on both left and right sides of the sector gear 45 as the rotation member and restrict the rotation range of the sector gear 45. 52 is attached, and when the sector gear 45 rotates to the opposite phase side, when the rotation angle from the neutral position is -17.5 degrees, for example, the sector gear 45 comes into contact with the opposite phase side stopper member 51. Further rotation is restricted, and sector gear 4
5 to the same phase side, when the rotation angle from the neutral position reaches, for example, 20 degrees, the sector gear 45 comes into contact with the stopper member 52 on the same phase side and moves 1J? It is configured to be regulated by υ1. The control position of the stepping motor 50 when the sector gear 45 comes into contact with the stopper member 51 on the opposite phase side is set as its initial position. Note that 39 is a rod stopper that restricts the maximum movement range of the relay rod 15 in the rear wheel steering mechanism 12.

As shown in FIG. 3, the stepping motor 50 is configured to be operated υIIB by an output from a control unit 100 incorporating a microcomputer. That is, this control unit 100 includes a vehicle speed detecting section 102 that detects the traveling vehicle speed V of the vehicle based on the detection signal PCN of the vehicle speed sensor 101, and a vehicle speed detecting means consisting of the vehicle speed sensor 101 and the vehicle speed detecting section 102. It is determined whether the vehicle is in a deceleration state based on the actual driving speed V, and if the vehicle is in a deceleration state, the steering ratios of the front and rear wheels are determined to be the same based on the basic steering ratio characteristics, as described later. Hysteresis setting unit 10 that determines the exit vehicle speed V' so as to obtain hysteresis displaced in the phase direction.
3, and a steering ratio setting unit 10 that sets the steering ratio of the rear wheels 2 and 2R with respect to the front wheels 1L and IR according to this steering speed V'.
4, and a motor control section 105 as a rear wheel steering angle control section that outputs a l/1111 signal to the stepping motor 50 in accordance with the output signal from the steering ratio setting section 104.

Then, when the ignition key switch (not shown) is turned on, the control unit 100 turns on m*.
System 1 uses power supplied from the battery! The internal structure of the control unit 100 will be explained in detail with reference to FIG.
The CPLJ 106 includes a constant voltage circuit 108 that maintains the battery voltage (12V) at a constant voltage of 5V.
The CPtJl run detection unit 109 is activated by the output voltage from the CPU 106 and detects runaway of the CPU 106, and the output voltage is 4.5.
Voltage drop detection PIS1 that detects that the voltage has dropped below V
10 and a power-on reset section 11 that outputs a reset signal when the ignition key switch starts to be turned on.
It is reset upon receiving each output from 1.

Further, the output signal of the vehicle speed sensor 101 is input to an integral filter 113 via an interface 112, and after chattering is removed by the integral filter 113, the signal waveform is shaped by a waveform shaping circuit 114 and then supplied to the CPU 106. .

Furthermore, the control unit 100 includes a CPU 106
It has a stepping motor driver 115 that receives the output of the stepping motor 50 and drives the stepping motor 50.
In response to the current down command signal from the CPU 106, the output current from the battery power supply to the stepping motor 50 is reduced during the non-tJjtll of the motor 50 (motor output shaft 5
For example, when the rotation of 0a is stopped, each phase is 1
It has a current down section 116 that limits the current to 00mA.

Next, the CPU 10 of the control unit 100
Signal 11 performed at 6! The processing procedure will be explained below. FIG. 5 shows the main routine of the signal processing program. This routine performs the function of the steering ratio setting section 104. After starting by turning on the ignition key switch, the system is first initialized in step S1, and in the next step S2, the current number of steps MP of the stepping motor 50 is set to 580, and the target number of steps CP is set to O. At the same time,
Motor position initialization tI111! A flag F1 indicating execution of Il mode is set to Fl-1. The target step number CP is the control initial position of the stepping motor 50, that is, the position where the sector gear 45 is in contact with the opposite phase side stopper part 1c451 and the steering ratio is the maximum steering ratio on the opposite phase side. The current step number MP indicates the number of steps of the pulse signal applied to the motor 50 when controlling the motor 50 to its target control position. This shows the number of steps from the control initial position. The flag F1 is set to F1=1 in the motor position initialization control mode in which the motor 50 is controlled to initialize its lblIM1 position, but the flag F1 is set to F1=1 in the motor position initialization control mode in which the motor 50 is controlled to initialize its lblIM1 position. In the control mode, it is reset to Fl-0.

After that, the process advances to step S3, and the flag F1 is set to Fl-
Determine whether it is 1 or not. When this determination is Fl-1, that is, when performing the position initialization iI11wa mode of the motor 50, the process proceeds to step S4, and it is determined whether the target number of steps CP for the motor 50 is equal to the current number of steps MP, If this determination is CP≠MP, the process directly returns to step S3. Also, the judgment is CP-M
When the initialization of the control position of the motor 50 is completed at P, the process proceeds to step S5, where the target step number CP and current step number MP of the motor 50 are set to CP-MP-0,
Then, the flag F1 is reset to Fl-0, and the flag F2 for identifying that the control position initialization of the motor 50 has been executed once is set to F2-1, and then the process returns to step S3.

On the other hand, when it is determined in step S3 that the vehicle is not Fl-1 and the motor 50 is to be controlled to change the steering ratio, the process proceeds to step S6, where the running vehicle speed V detected by the vehicle speed detection unit 102 is O (stopping state). If the determination is YES, it is further determined in step S7 whether the flag F2 is F2-0.

When the determination at step S7 is F2≠0, the process returns to step S3, but when the determination is F2-0 and the traveling vehicle speed V is 0 and the vehicle is stopped, the motor 50
If it is confirmed that the control position initialization has not been executed, the flag F1 is set to Fl-1 in step S8, and the current step number M of the motor 50 is set in the next step S9.
After setting P and the target step number CP to MP-580 and CP-0 corresponding to the control initial position, the process returns to step S3.

Further, in the above step S6, when it is determined that the running vehicle speed V is not O and the vehicle is in a running state, the process proceeds to step Sw, and the operation is calculated based on the above running vehicle speed V in the second interwoven routine mentioned above. Vehicle speed V',
After reading out the target step number CP fat (V') of the motor 50 by comparing it with a control data table showing basic steering ratio characteristics corresponding to the vehicle speed stored in the ROM 107 in advance, in the next step S11 Both of the above flags F1. F
2 are reset to Fl-F2-0, and then the process returns to step S3. The control data table for the basic steering ratio characteristics stored in the ROM 107 is such that the front and rear wheels 1L, 2L (
If the steering ratio (IR, 2R) changes and the vehicle speed is low,
In order to improve the turning performance of the vehicle, the rear wheels 2L and 2R are steered in the opposite direction to the front wheels 1L and 1R, that is, in the opposite phase, so that the steering ratio becomes negative, while the vehicle speed is, for example, about 671v.
/ When the timing is wrong, the steering ratio becomes zero and the front wheels 1L,
Regardless of the steering of 1R, the steering angle θR of rear wheels 2L and 2R is θR.
-0 and the vehicle enters normal two-wheel steering. Furthermore, when the vehicle speed is high, the rear wheels 2L and 2 when cornering
1" (in order to improve the grip force and increase running stability, the rear wheels 2L and 2R are steered in the same direction as the front wheels IL and 1R, that is, in the same phase, so that the steering ratio becomes positive. It is set.

FIG. 7 shows a first interactive routine that interrupts the main routine when the time set in the timer built in the CPU 106 has elapsed.
The function of section 105 is fulfilled. In this first interwoven routine, in the first step S12, the motor 5 is
It is determined whether the target step number CP of 0 is equal to the current step number MP. When this determination is CP-MP, that is, there is no need to output a pulse signal to the motor 50, and the motor 5
0 in its control position, step 5tl
By proceeding to step I and outputting a current down command signal to the current down section 116, the voltage applied to the motor 50 is lowered to suppress the amount of heat generated, and then, at step S%, the above-mentioned timer is activated to generate the next interrupt process. After setting, the process returns to the step after the interrupt in the main routine.

Further, when the determination in step S12 is that CP≠MP, the process proceeds to step S15 to cancel the output of the current down command signal to the current down section 116, and then proceeds to step Ss to control the target step number of the motor 50. The magnitude relationship between CP and the current step number MP is determined. When this determination is CP>MP, the process advances to step Sv and the motor 50 is rotated by 1 in the same phase direction of the steering ratio.
Switch the excitation phase so that it moves by a step, and then set the current step number MP to MP4-MP+ in step Sss.
After updating to 1, the process moves to step S14. On the other hand, when the determination in step Sw is CP<MP,
Proceeding to step S19, the excitation phase is switched so that the motor 5o moves by one step in the opposite phase direction of the steering ratio.
In step S20, the current step number MP is MP-MP-1.
After updating to , move on to step S above.

Further, FIG. 8 shows a second interwoven routine that performs interrupt processing at a constant cycle, and this routine fulfills the function of the hysteresis setting section 103. That is, in this second interwoven routine, first, in step 821, the current traveling vehicle speed V is determined in the vehicle speed detecting section 102 based on the detection signal PCN of the vehicle speed sensor 101.

Next, in step S22, it is determined whether the traveling vehicle speed ■ is larger or smaller than the previous calculated vehicle speed V' obtained and stored in the previous interrupt processing, and the current traveling vehicle speed ■ is larger than the previous calculated vehicle speed V'. If it is determined that the values are greater than or equal to each other, and it is confirmed that the vehicle is in an acceleration state or a constant speed state, in step S23, the value of the traveling vehicle speed ■ is output as is as the calculated vehicle speed V', and the calculated vehicle speed V is ′ to v
After updating to ′←■, the process returns to the main routine described above.

As a result, when the vehicle is accelerating or running at a constant speed, the stepping motor 50 operates at tlJ so that the steering ratio corresponds to the basic steering ratio characteristic shown by the solid line in FIG.
(2) The steering angle θR of the rear wheels 2L and 2R is set to a predetermined value. That is, in a low-speed turning state, the rear wheels 2L, 2R are steered so that they are in the opposite phase with respect to the front wheels 1L, 1R, resulting in good retrospectivity.
The wheels R are steered so that they are in the same phase, improving driving stability.

Further, if it is determined in step 822 that the current traveling vehicle speed V is smaller than the previous calculated vehicle speed V', and it is confirmed that the vehicle is in a deceleration state, step 32
In step 4, it is determined whether the traveling vehicle speed (2) is larger or smaller than a value V'-α obtained by subtracting a predetermined hysteresis width α from the previous calculated vehicle speed V′. As a result of this determination, if it is confirmed that the traveling vehicle speed V is greater than or equal to the above iv' - α, the calculated vehicle speed V' is not updated and the steering ratio is maintained at the previous state. do. Then, the deceleration progresses roughly, and when it is determined in step 324 that the traveling vehicle speed ■ has become smaller than the value V'-α, the calculated vehicle speed ■' is updated to v'←V+α in step 825, and the current The steering angle θR of the rear wheels 2L and 2R is adjusted according to the steering ratio corresponding to a vehicle speed that is higher than the traveling vehicle speed ■ by an amount corresponding to the hysteresis width α.
Set.

As a result, when decelerating, as shown by arrow a in Figure 6,
Section corresponding to the above hysteresis width α, front wheel IL, 1R
After the steering ratio of the rear wheels 2L and 2R is maintained constant, the basic steering ratio characteristic is shifted parallel to the lower speed side, as shown by the arrow, and the steering ratio during deceleration is shown by the broken line. Rear wheel 2L depending on characteristics.

The steering angle θR of 2R is set. That is, at the same vehicle speed, the steering ratio characteristic when the vehicle is reduced "a" is displaced in the same phase direction compared to the basic steering ratio characteristic during acceleration or constant speed.

In this manner, when the vehicle decelerates, the front wheels 1L, IR, and rear wheels 2L are adjusted according to the steering ratio characteristics during deceleration that are displaced in the same phase direction as compared to the basic steering ratio characteristics described above.

Since the steering ratio of 2R is set, even when the vehicle speed decreases from a fast turning state, the rear wheels 2 are turned.

2R is prevented from being abruptly steered in the opposite phase direction. Therefore, the vehicle is maintained in an understeer state for a predetermined period of time, improving driving stability, and the occurrence of the tuck-in phenomenon and the scooping-in phenomenon of the vehicle is reduced.

In addition, if the vehicle speed decreases further, the steering ratio changes according to the steering ratio characteristic during deceleration, which is set parallel to the basic steering ratio characteristic described above, so turning during low-speed turns In addition, the driver can easily grasp the state of change in the steering ratio.

In other words, the basic steering ratio characteristics described above and the steering ratio characteristics during deceleration are parallel, and the rate of change in the steering ratio is constant depending on the deceleration, so the driver can easily understand this. It is.

Note that when the vehicle transitions from the deceleration state to the acceleration state, a constant steering ratio is maintained in the section corresponding to the hysteresis width α, as shown by arrow C in FIG. The steering ratios of the front and rear wheels are set according to the steering ratio characteristics.

In the above embodiment, in order to obtain accurate steering characteristics and to variable control the steering angle of the model shaft with good responsiveness, a stepping motor is used whose output shaft rotates according to the number of pulses of the input pulse signal. Although the oven loop l1Iltl11 type four-wheel steering device used has been described, the configuration of the present invention can also be adopted in a closed-loop type four-wheel steering device using a DC motor or the like.

In addition, in the above embodiment, the steering ratio of the front and rear wheels of the vehicle is controlled variably according to the vehicle speed, but the rear wheels are directly driven by a stepping motor or the like according to the vehicle speed and the steering angle of the front wheels. may be configured.

(Effects of the Invention) As explained above, the present invention steers the front and rear wheels according to the operation of the steering wheel, and also changes the steering ratio of the @I wheel with a steering ratio characteristic corresponding to the vehicle speed. In the four-wheel steering system for a vehicle configured in Even when decelerating from a fast turning situation,
This prevents the rear wheels from being abruptly steered in the opposite phase direction, resulting in an oversteer condition, which prevents the vehicle from causing tuck-in or digging-in phenomena during deceleration, further improving driving stability, and improving driving stability during acceleration. Since the steering angle of the rear wheels is set according to the above-mentioned basic steering ratio characteristics, it is possible to improve the turning performance of the vehicle when turning at low speeds, and it also improves the running stability of the vehicle when turning at high speeds. This allows the original characteristics of a wheel-steering vehicle to be demonstrated.

Moreover, the steering ratio characteristic does not change depending on deceleration, etc., and a certain correspondence can be established between the steering ratio characteristic during deceleration and the basic steering ratio characteristic. This has the advantage that the driver can easily understand this steering ratio characteristic.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a four-wheel steering device for a vehicle according to the present invention, FIG. 2 is a schematic perspective view of the above-mentioned steering device, and FIG. 3 is a block diagram showing the functions of a control unit.
Figure 4 is a block diagram showing the specific configuration of the control unit, and Figure 5 is the CPU in the control unit.
FIG. 6 is a characteristic diagram of vehicle speed and steering ratio, and FIGS. 7 and 8 are flowcharts showing the first and second interwoven routines processed by the CPU. It is. 1L, 1R...front wheel, 2L, 2R...rear wheel, 101
...Vehicle speed sensor, 102...Vehicle speed detection section, 103.
...Hysteresis setting section, 104... Steering ratio setting section,
105...-E -tat+Il 1!11 PIs(
II wheel steering angle ljlilDM). Patent Applicant: Mazda Co., Ltd. Agent: Patent Attorney: Etsushi Kotani, Patent Attorney: Chief 1) Masayuki, Patent Attorney: Yasuo Itaya, 2nd Series, 37th, 61st, Figure 7, Figure 8

Claims (1)

[Claims] 1. Four-wheel steering for a vehicle configured to steer the front and rear wheels in response to steering wheel operations and to change the steering ratio of the front and rear wheels in accordance with steering ratio characteristics corresponding to vehicle speed. The device includes a vehicle speed detection means for detecting vehicle speed, a hysteresis setting section for displacing the steering ratio characteristic during deceleration in the same phase direction as compared to the basic steering ratio characteristic during acceleration and constant speed, and the hysteresis A steering ratio setting section that determines the steering ratio of the front and rear wheels according to an output signal from the setting section, and a rear wheel steering angle control section that controls the steering angle of the rear wheels according to this steering ratio. A four-wheel steering device for a vehicle characterized by: