JPS6364873A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent a rear wheel from rapidly changing from the same phase with a front wheel to the reverse phase, by obtaining the steering ratio characteristic to be displaced in the same phase while a width of this displacement to be set, so that in the more deceleration range is a vehicle the displacement width increases the larger in accordance with an output signal from a displacement width setting part, when the vehicle is in deceleration. CONSTITUTION:A stepping motor 50, which controls the steering characteristic of a rear wheel, is actuated to be controlled by an output from a control unit 100. The control unit 100 is equipped with a hysteresis setting part 102, which obtains an arithmetic car speed V' so as to acquire the hysteresis, displacing steering ratio of front and rear wheels in a direction of the same phase from the basic steering ratio characteristic, when a vehicle is placed in a deceleration condition, and a displacement width setting part 103 which increases a displacement width alpha of the hysteresis, provided in the arithmetic car speed V' in the time of deceleration, such that in the lower speed range is the vehicle the displacement width increases the larger in accordance with a car speed. In this way, the lower in the speed range is the vehicle the larger the displacement width alpha of the hysteresis increases, accordingly, a steering device, reducing a frequency of the front and rear wheels being placed in the reverse phase even in case of the vehicle decreasing its speed when it is turned, improves the running stability.

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 wheel, and changes the steering ratio of the front and rear wheels to a steering ratio corresponding to the vehicle speed. The present invention relates to an improvement of a four-wheel steering system for a vehicle configured to change according to characteristics.

(Prior art) A four-wheel steering system for a vehicle usually controls the steering ratios of the front and rear wheels to be in opposite phases during low-speed turns and sets the steering characteristics to tend to oversteer, thereby increasing the turning performance of the vehicle and improving steering performance during high-speed turns. The front wheels are adjusted based on a predetermined steering ratio characteristic set in advance according to the vehicle speed so as to increase the running stability of the vehicle by setting the steering ratio in the same phase and setting the steering characteristic in a direction that increases understeer. It is configured to change the steering angle of the rear wheels relative to the vehicle.

By the way, in a vehicle equipped with the above-mentioned four-wheel steering system, when the vehicle decelerates 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 and the vehicle body. A tuck-in phenomenon in which the vehicle suddenly turns inward or a scoop-in phenomenon in which the m-body spins may occur, and this tendency is particularly noticeable in low speed ranges where the front and rear wheels are in opposite phases. In order to prevent the occurrence of the above-mentioned tuck-in phenomenon, for example, as shown in Japanese Unexamined Patent Publication No. 60-85066, the steering ratio of the rear wheels to the front wheels is adjusted according to the vehicle speed only when the vehicle is traveling substantially straight. The steering angle of the rear wheels is maintained constant when the vehicle is in a turning state, or when the vehicle speed suddenly changes as shown in Japanese Patent Application Laid-Open No. 60-85067. In conventional systems, the steering angle of the rear wheels is changed with a predetermined delay using a delay circuit or the like.

However, with the former configuration, when accelerating at a low speed with the front wheels and rear wheels in opposite phases, the rear wheels remain in the opposite phase even when the vehicle shifts to high speed, resulting in stable vehicle running. There is a problem in that the characteristics inherent to the four-wheel steering system cannot be exhibited in this state.

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. There was a problem that it was insufficient.

(Object of the Invention) The present invention has been made based on the above-mentioned technical background, and it is possible to increase the turning performance of the vehicle by setting the steering ratio of the front and rear wheels to opposite phases at low speeds, and to improve the turning performance of the vehicle at high speeds. While maintaining the four-wheel steering system's ability to increase vehicle running stability by keeping the above-mentioned steering ratios in the same phase, even when decelerating during a turn, the vehicle body is prone to tuck-in and wedge-in phenomena. 4 vehicles that can prevent
The aim is to obtain a wheel steering device.

(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, the vehicle speed detection means for detecting vehicle speed and the steering ratio characteristic during deceleration are displaced in the same phase direction as compared to the steering ratio characteristic during acceleration and at constant speed. a displacement width setting section that increases the displacement width of the hysteresis according to the vehicle speed [lower speed ranges]; and a hysteresis setting section that makes the steering ratio characteristic have hysteresis corresponding to the vehicle speed according to an output signal from the displacement width 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;
A rear wheel steering angle control section is provided.

According to the above configuration, when the vehicle decelerates, the steering ratio characteristic is displaced in the same phase direction according to the output signal from the hysteresis setting section, and the width of this displacement is changed to a low speed according to the output signal from the displacement width setting section. By increasing the range, the rear wheels are prevented from rapidly changing from the same phase to the front wheels to the opposite phase.

(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 shaft 8 formed on the lever rod 6, and a steering shaft 11 to which a steering wheel 10 is connected at the upper end and a pinion 9 which meshes with the rack 8 at the lower end. The left and right front wheels 11.1R 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.
It further includes a hydraulic power steering 116. This power steering mechanism 16 includes a power cylinder 17 that is fixed to the vehicle body and has the relay rod 15 as a piston rod. Inside the power cylinder 17, two hydraulic chambers are formed by a piston 17a that is integrally attached to the relay rod 15. The hydraulic chambers 17b and 17C are divided into 17b and 17c, respectively.
8.19 to the control valve 20. The control valve 20 also has two oil supply pipes 22 and an oil discharge pipe 23 leading to the reserve tank 21.
The oil supply pipe 22 is connected to a hydraulic pump 24 driven by an engine (not shown). The control valve 20 is a known spool valve type, and includes a cylindrical valve casing 20a integrally attached to the relay rod 15 via a connecting member 25, and a valve casing 20a fitted into the valve casing 20a. The hydraulic pump 24 supplies pressure oil from the hydraulic pump 24 to one hydraulic chamber 17b (17c) of the power cylinder 17 according to the movement of the spool valve to assist the driving force to the relay rod 15. It is something. Incidentally, return springs 17d and 17d are installed in the power cylinder 17 to urge the lever rod 15 to a neutral position (at a position N such that the steering angle θR of the rear wheels 2L and 2R is O).

The relay 6 of the front wheel steering mechanism 3 has a rack 26 installed at a different position 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 the rack 26, and the rear end of this rotating shaft 28 has a steering ratio of IIIvA1m lateral 2
It is connected to the rear wheel steering mechanism 12 via 9.

The steering ratio control mechanism 29 has a control rod 30 that is slidably held in the vehicle width direction with respect to the vehicle body, and one end of the 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) via a support shaft 35 having a rotation wheel line perpendicular to the axis of movement of the control head 30. Support bin 32 of the swing arm 33
is located at the intersection of the two axes and extends in a direction perpendicular to the rotating wheel line, and by rotating the holder 31 around the support shaft 35, the axis of movement of the support pin 32 and the control rod 30 at the tip thereof is In other words, the angle of inclination made by the swing locus plane of the swing arm 33 centered on the support bin 32 with respect to a plane perpendicular to the movement axis (hereinafter referred to as the reference plane) is changed. There is.

Further, one end of a connecting rod 37 is connected to the tip of the swing arm 33 via a ball joint 36, and the other end of the connecting rod 37 is connected to the control rod 37 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 slidably supported by a rotation imparting arm 40 via a ball joint 41 at a portion thereof close to the ball joint 36 . This rotation imparting arm 40 has a support shaft 42 on the movement axis.
The bevel gear 43 is provided integrally with a large diameter bevel gear 43 rotatably supported via a bevel gear 43, and a bevel gear 44 attached to the rear end of the rotating shaft 42 is meshed with this bevel gear 43 as shown in FIG. The rotation of the steering wheel 1o is transmitted to the rotation imparting arm 40. Therefore, the rotation imparting arm 40 and the connecting rod 37 rotate around the movement axis in accordance with the rotation angle of the steering wheel 1o, and the swing arm 33 rotates around the support pin 3.
When the axis of the support pin 32 coincides with the axis of movement of the control rod 30, the ball joint 3 at the tip of the swing arm 33
6 only swings on the reference plane, and the control rod 30 is held stationary, but the axis of the bottle 32 is inclined with respect to the movement axis, and the swing locus plane of the swing arm 33 is moved from the reference plane. If it is misaligned, the ball joint 36 will be displaced in the Φ width direction as the swing arm 33 swings around the bin 32, and this displacement will be equal to 1 connecting rod 3.
7 to a control rod 30, which is configured to move along the axis of movement and actuate the spool valve of the control pulp 20. In other words, even if the swing angle of the swing arm 33 about the axis of the bin 32 is the same, the left-right displacement of the control rod 30 will change as the tilt angle of the bin 32, that is, the eye movement angle of the holder 31, changes. and change.

The inclination angle 1 with respect to the movement axis of the support bin 32 is
That is, in order to change the inclination angle of the holder 31 with respect to the reference plane, a worm gear 47 on a rotating shaft 46 is engaged with a sector gear 45 serving as a worm wheel on the support shaft 35 of the holder 31. Further, a bevel gear 48 is attached to the rotating wheel 46, and a bevel gear 48 is attached to the output shaft 50a of the stepping motor 50. 14
By operating the stepping motor 50 and rotating the sector gear A745, the inclination angle of the holder 31 with respect to the reference plane is changed and the rear wheels 2L, 2 are engaged with each other.
When the sector gear 45 is rotated clockwise when viewed from above the vehicle body from a neutral position where its center line is perpendicular to the center line of the rotating shaft 46 of the worm gear 47, The steering ratio is rear wheel 2L, 2R is front wheel IL, IR.
The structure is such that tIIIO is directed in the same direction and in the same phase.

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 comprised of bins that restrict the rotation range of the sector gear 45 on both left and right sides of the sector gear 45 as the rotation member. 52 is attached, and when 745 rotates to the opposite phase side to the sector gear, the rotation angle from the neutral position is -17.5 degrees, for example.
Then, the sector gear 45 is moved to the opposite phase side stopper member 51.
When the sector gear 45 comes into contact with the stopper member 52 on the same phase side and the rotation angle from the neutral position reaches 20'', for example, when the sector gear 45 rotates toward the same phase side, the sector gear 45 contacts the stopper member 52 on the same phase side. The control position of the stepping motor 50 when the sector gear 45 abuts against 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 by an output from a control unit 100 incorporating a microcomputer. That is, this control unit 1
00 indicates the actual traveling vehicle speed detected by a vehicle speed detecting section 101b that detects the traveling vehicle speed V of the vehicle based on the detection signal PCN of the vehicle speed sensor 101a, and a vehicle speed detecting means consisting of the vehicle speed sensor 101a and the vehicle speed detecting section 101b. Based on V, it is determined whether the vehicle is in a deceleration state, and if the vehicle is in a deceleration state, a hysteresis is obtained in which the steering ratio of the front and rear wheels is displaced from the basic steering ratio characteristic in the same phase direction as described later. a hysteresis setting section 102 that calculates the calculated vehicle speed ■' so that the calculated vehicle speed v' is calculated, a displacement width setting section 103 that increases the displacement width α of the hysteresis given to the calculated vehicle speed v' at the time of deceleration in accordance with the vehicle speed in the lower speed range; A steering ratio setting section 104 that sets the steering ratio of the rear wheels 2L and 2R with respect to the front wheels 1L and IR according to the speed V'; and this steering ratio setting section 104.
A motor control unit 105 is provided as a rear wheel steering angle i control unit that outputs a control signal to the stepping motor 50 in accordance with an output signal from the motor.

The control unit 100 operates using power supplied from the vehicle battery as a system power supply when an ignition key switch (not shown) is turned on, and its internal configuration will be specifically explained with reference to FIG. Then, control 0-) Lt l knee but 1
It is equipped with a CPU 106 as a 00haj1111 section and a ROM 107 for storing a predetermined control data, and the CPt
J106 is the battery voltage (12V) wo5 Vc7
) A cp that is activated by the output voltage from the constant voltage 11'8108 and detects one run of the CPU 106.
It receives outputs from a runaway detection section 109, a voltage drop detection section 110 that detects that the output voltage has decreased to 4.5V or less, and a power-on reset section 111 that outputs a reset signal when the ignition key switch is turned on. will be reset.

Further, the output signal of the vehicle speed sensor 101a is input to an integral filter 113 via an interface 112, and after chattering is removed by this integral filter 113, the signal waveform is shaped by a waveform shaping port +t8114.
06.

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 CPtJ 106, the output current from the battery power supply to the stepping motor 50 is reduced, for example, by 100 m for each phase while the motor 50 is not being controlled (when the rotation of the motor output shaft 50a is stopped).
It has a current down section 116 that limits the current to A.

Next, CPtJ1 of the control unit 100
The signal processing procedure performed in 06 will be explained.

FIG. 5 shows the main routine of the signal processing program. This routine performs the function of the steering ratio setting section 104. Turn on the ignition key switch
After starting by operation, 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, the target number of steps CP is set to 0, and the motor position is set. Set flag F1 indicating execution of initialization control mode to Fl.
Set to -1. The target step number CP is the initial control position of the stepping motor 500, that is, the sector gear 4.
5 is in contact with the opposite phase side stopper member 51 and the steering ratio is the maximum steering ratio on the opposite phase side. 50, and the current step number MP indicates the number of steps of the motor 50 from the current III pupil position control initial position. The flag F1 is set to Fl-1 in the motor position initialization control mode in which the motor 50 is set to 11111 for the initial flower at the lllll11 position, but the flag F1 is set to Fl-1 when the motor 50 is set to 11111 for the initial flower at the lllll11 position. Sensitivity t, II When in II mode, Fl-
Reset to 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 M control mode of the motor 50, the process advances 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 $3. Further, when the determination is CP-MP and the fiAi 11 position initialization of the motor 50 has been completed, the process proceeds to step S5, where the target step number CP and the current step number MP of the motor 50 are set to CP-MP-O,
Then, the flag F1 is reset to Fl-0, and the 7-lag F2 for identifying that the control position of the motor 50 has been changed to the initial Ifl is set to F2=1, and then the process proceeds to step S3. return.

On the other hand, if it is determined in step S3 that τF1-1 is not true and the motor 50- is to be turned to tllll to change the steering ratio, the process proceeds to step $6 and the vehicle speed detection unit 101b
It is determined whether or not the traveling vehicle speed (2) detected by the above is O (stopped state). If this determination is YES, it is further determined in step S7 whether or not the flag F2 is F2-0. If the determination in step S7 is F2≠0, the process returns to step S3, but the determination is F2-0, and the motor 500 control position initialization is not executed when the vehicle is stopped and the traveling vehicle speed V is O. If this is confirmed, the flag F1 is set to Fl-1 in step Sa, and the current step number MP and target step number CP of the motor 50 are set to MP-580 corresponding to the control initial position in the next step S9. , CP-0, and then returns to step S3.

Further, in step $8 above, when it is determined that the traveling vehicle speed ■ is not O and the vehicle is in a traveling state, the process proceeds to step Ss, and the calculation calculated based on the traveling vehicle speed ■ in the second interrelated routine described later is performed. Vehicle speed v′,
The value f(V') of the target step number CP of the motor 50 is determined by comparing it with the tI1111D data table showing the basic steering ratio characteristics corresponding to the vehicle speed stored in the ROM 107 in advance.
After reading out, in the next step S11, both flags F1
．． After both F2 are reset to Fl-F2=O, the process returns to step S3. The control data table for basic steering ratio characteristics stored in the ROM 107 is as follows:
As shown by the solid line in Figure 6, depending on the vehicle speed, the front and rear wheels are 1L,
When the steering ratio of 2L (IR, 2R) changes and the vehicle speed is low, in order to improve the turning performance of the 11 cars, the rear wheels 21
．． 2R is steered in the opposite direction to the front wheels 1L and 1R, that is, with an opposite phase, and the steering ratio becomes negative. On the other hand, when the vehicle speed reaches, for example, about 67 kl/hour, the steering ratio becomes zero, Regardless of the steering of the front wheels 1L and 1R, the steering angle θR of the rear wheels 2L and 2R is maintained at θR-0, and the vehicle enters a normal two-wheel steering state. Furthermore, when the vehicle speed is high, the rear wheels 2L and 2R are rotated in the same direction as the front wheels 1L and 1R, that is, in the same phase, in order to improve the grip force of the rear wheels 2L and 2R during cornering and increase driving stability. The steering ratio is set to be positive.

Further, 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 11 abilities as a person are fulfilled. In this first interwoven routine, first, in step S12, it is determined whether the target number of steps CP of the motor 50 is equal to the current number of steps MP. When this determination is CP-MP, that is, when the output of the pulse signal to the motor 50 is unnecessary and the motor 50 is held at the tIIlt10 position, step St
By proceeding to step 3 and outputting a current down command signal to the current down section 116, the voltage applied to the motor 50 is reduced to suppress the amount of heat generated, and then the above-mentioned timer is activated to generate the next interrupt process at step S%. After setting, the process returns to the step after the interrupt in the main routine.

When the determination in step S12 is 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 Sw+ to move the motor 50 to the target step. The magnitude relationship between the number CP and the current number of steps MP is determined. When this determination is CP>MP, the process proceeds to step Sv, where the excitation phase is switched so that the motor 50 moves by one step in the same phase direction of the steering ratio, and then, in step Su, the current step number MP is set to MP4-MP+.
After updating to 1, the process moves to step S14. on the other hand,
If the determination in step Sw is CP<MP, the process proceeds to step Stg, where the excitation phase is switched so that the motor 50 moves by one step in the opposite phase direction of the steering ratio, and the current step number MP is determined in step S20. MP+MP-
After updating to 1, proceed to step S%. .

In addition, FIG. 8 shows the second
This shows an interwoven routine in which the hysteresis setting section 102 and the displacement width setting section 103
function as. That is, in this second interwoven routine, first, in step S21, the vehicle speed sensor 1 is
Based on the detection signal PCN of 01a, the vehicle speed detecting section 101b calculates the current traveling vehicle speed. Then step 8
22, the magnitude of the above-mentioned running vehicle speed V and the previous calculated vehicle speed V' obtained and stored in the previous interrupt process is determined, and the current running vehicle speed ■ is determined as the previous 'lAi vehicle speed ■'
If it is determined that the vehicle is greater than or equal to , and it is confirmed that the vehicle is in an acceleration state or a constant speed state, in step 823, the value of the traveling vehicle speed V is calculated as the calculated vehicle speed V'
After updating the performance vehicle speed V' to V'←■, the process returns to the main routine.

As a result, when the vehicle is accelerating or running at a constant speed, the stepping motor 50 is controlled so that the steering ratio corresponds to the basic steering ratio characteristics shown by the solid line in FIG. The steering angle θR of wheels 2L and 2R is set to a predetermined value.

In other words, in a low-speed turning state, the rear wheels 2L and 2R are the front wheels IL.
, the rear wheels 2L and 2R are steered to be in the same phase when turning at high speeds, improving driving safety. do.

Further, if it is determined in step 822 that the current running 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 822
In step 4, the hysteresis displacement width α is determined according to the calculated vehicle speed V'. That is, the displacement width α of the hysteresis is previously stored in the ROM 107 as a &11III data table corresponding to the calculated vehicle speed V', and the value of this displacement width α is calculated based on the calculated nO1 speed v' as shown in FIG. Primary circle number h
(V'), and is set so that the smaller the value of the calculated vehicle speed V', the larger the value of the displacement width α.

Next, in step 325, it is determined whether the traveling vehicle speed (■) is larger or smaller than the value V'-α obtained by subtracting the displacement width α from the previous calculated vehicle speed (■'). As a result of this determination, the traveling vehicle speed V is set to the above value V'
If it is confirmed that the calculated vehicle speed V' is greater than or equal to -α, the calculated vehicle speed V' is not updated and the steering ratio is maintained at the previous state. Then, the deceleration progressed further,
When it is determined in step S25 that the running vehicle speed V has become smaller than the above value V'-α, the calculated vehicle speed v' is updated to v'←■+α in step S28, and the current running vehicle speed V is The steering angle θR of the rear wheels 2L and 2R is set in accordance with a steering ratio corresponding to a vehicle speed that is higher by an amount corresponding to the hysteresis width α.

As a result, when decelerating, as shown by arrow a in Figure 6,
The front wheel IL is a section corresponding to the hysteresis displacement width α determined according to the vehicle's performance WII speed V'.

After the steering ratio of the rear wheels 2L and 2R with respect to 1R is maintained constant, as indicated by the arrow, the steering ratio during deceleration is shifted to the lower speed side than the above basic steering ratio characteristic, as shown by the broken line. The steering angle θRtfi of the rear wheels 2L and 2R is set according to the characteristics. In other words, at the same vehicle speed, the steering ratio characteristics during deceleration will be displaced in the same phase direction compared to the basic steering ratio characteristics during acceleration or constant speed, and the amount of displacement will depend on the speed of the vehicle. The smaller it gets, the bigger it gets.

In this manner, when the 11 cars are decelerating, the front wheels IL, IR and the 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 steering ratio characteristics in the μ water.

Since the steering ratio of 2R is set and the displacement width of the steering ratio characteristic becomes larger in the lower speed range, even when the vehicle speed decreases in a turning state,
The frequency at which front loading is in the opposite phase is reduced, driving stability is improved, and the occurrence of tuck-in and scoop-in phenomena of the vehicle is suppressed.

In addition, when the vehicle shifts from the deceleration state to the acceleration state, as shown by arrow C in FIG. After the ratio is maintained, the steering ratios of the front and rear wheels are set according to the internal steering ratio characteristics shown by the solid line.

In addition, as shown in Figure 10, the 2.111jll data table for determining the above displacement width α is calculated as follows:
Various functions can be used, such as expressing the displacement width α as a quadratic function Q(V') of the velocity V', as long as the displacement width α increases as the value of the velocity V' decreases. . In the above embodiment, in order to obtain accurate steering characteristics and to be able to vary the steering angle of the rear shaft with good response, a stepping motor is used whose output shaft rotates according to the number of pulses of the input pulse signal. Although the four-wheel steering OFF of the oven-loop control method used has been described, the configuration of the present invention can also be adopted in a closed-loop-type four-wheel steering V 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 changes the steering ratio of the front and rear wheels with a steering ratio characteristic corresponding to the vehicle speed. In the four-wheel steering system for a vehicle constructed as described above, a hysteresis setting section is provided for displacing the steering ratio characteristic during deceleration in the same phase direction as compared to the basic steering ratio characteristic during acceleration and low speed. Since a displacement width setting section is provided that increases the displacement width in the lower speed range according to the vehicle speed, even when the vehicle is decelerated from a turning state, the frequency at which the front and rear wheels are in opposite phases is reduced, and oversteer conditions are suppressed. υ1,
This prevents the vehicle from being prone to tuck-in during deceleration, resulting in car crashes, and driving stability is further improved. Furthermore, during acceleration, etc., the rear wheel steering angle is set according to the above-mentioned basic steering ratio characteristics, so it is possible to improve the turning performance of the vehicle during low-speed turns, and to stabilize the running of the vehicle during high-speed turns. It is possible to demonstrate the original characteristics of a four-wheel steering vehicle, which is to improve performance.

[Brief explanation of the drawing]

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 CP in the control unit labeled -F.
A flowchart showing the main routine processed by U.
FIG. 6 is a characteristic diagram of vehicle speed and steering ratio, FIGS. 7 and 8 are flowcharts showing the first and second interwoven routines processed by the CPLJ, and FIGS.
FIG. 0 is a characteristic diagram showing the relationship between displacement width and vehicle speed. 1L, 1R...front wheel, 2L, 2R...rear wheel, 101
a...Vehicle speed sensor, 102...Vehicle speed detection section, 103
...Hysteresis setting section, 104... Steering ratio setting section, 105... Motor a, t+tin section (rear wheel steering angle control section).

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 that detects the vehicle speed, and a hysteresis displacement width that shifts the steering ratio characteristics during deceleration in the same phase direction compared to the basic steering ratio characteristics during acceleration and constant speed. a hysteresis setting section that makes the steering ratio characteristics have hysteresis corresponding to the vehicle speed according to an output signal from the displacement width setting section; The present invention is characterized in that it includes a steering ratio setting section that determines the steering ratio of the front and rear wheels according to an output signal, and a rear wheel steering angle control section that controls the steering angle of the rear wheels according to this steering ratio. Four-wheel steering system for vehicles.