JP2506702B2 - 4-wheel steering system for vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a four-wheel steering device that steers the front and rear wheels of a vehicle, and more particularly to a measure for eliminating the scooping phenomenon during deceleration.

(Prior Art) In recent years, a four-wheel steering system for a vehicle of this type has attracted attention because it can greatly change the running characteristics of the vehicle. Basically, when the vehicle speed is low or the steering angle is large, the front and rear wheels can rotate. While controlling the steering ratio to the opposite phase and making the steering characteristics oversteer characteristics to improve the turning performance of the vehicle, at the time of high vehicle speed or small steering angle, the steering ratio is kept in phase and the steering characteristics are understeer characteristics. This is to ensure the running stability of the vehicle.

By the way, in such a four-wheel steering system, since the steering ratios of the front and rear wheels are controlled to be in the opposite phase at low vehicle speed and to be in the same phase at high vehicle speed, for example, a deceleration state such as turning the steering wheel while decelerating and running. Then, since the steering ratio, which had been the same phase until then, changes to the opposite phase, the steering wheel cuts more than expected, which is a behavior called so-called scooping. However, in order to correct this scooping phenomenon, it is necessary to return the turned handle in reverse, and it requires skill to perform it, so it is necessary to eliminate it from the viewpoint of safety.

As an example of a four-wheel steering system for suppressing such a scooping phenomenon during deceleration, there is a conventional one, for example, JP-A-60-85.
As disclosed in Japanese Patent No. 067, by delaying the output signal of the vehicle speed sensor that detects the vehicle speed, it is possible to artificially eliminate a sudden change in the vehicle speed and to mitigate a sudden change in the steering ratio during deceleration. What has been done is proposed.

(Problems to be Solved by the Invention) However, when the output signal of the vehicle speed sensor is delayed as in this proposed example, the vehicle speed signal is delayed not only when the vehicle is decelerated but also when it is accelerated. That is, since the steering ratios of the front and rear wheels change from the opposite phase to the same phase during acceleration, when turning during the acceleration, an operation to increase the steering wheel in reverse to the above deceleration is required for correction. . However, it is easy to increase the steering wheel, and therefore, if the vehicle speed signal is intentionally delayed for this reason, it is inevitable that the control becomes complicated.

Therefore, a steering ratio characteristic line dedicated for deceleration is added to the steering ratio characteristic for setting the steering ratio of the front and rear wheels to add a so-called hysteresis to the steering ratio characteristic in normal time and deceleration. However, there is a problem that the storage capacity of the entire device increases correspondingly.

(Object of the Invention) The present invention has been made in view of the above points, and an object thereof is to control a turning ratio in a turning ratio region having a predetermined turning ratio of front and rear wheels as a boundary during deceleration of a vehicle. By delaying, it is possible to delay the turning ratio to be in the opposite phase at the time of deceleration with one type of turning ratio characteristic line, thereby ensuring the responsiveness of the turning ratio control when the vehicle is not decelerating. At the same time, it is intended to surely eliminate the scooping phenomenon during deceleration without requiring a steering ratio characteristic line dedicated for deceleration.

(Means for Solving Problems) In order to achieve this object, the solution means of the present invention, when controlling the steering ratio of the front and rear wheels from the in-phase region to the anti-phase region at the time of deceleration of the vehicle, the rotation ratio is changed. At the time when the steering ratio becomes zero (the steering angle of the rear wheels becomes zero), the subsequent steering ratio control in the anti-phase region is delayed.

That is, as shown in FIG. 1, the present invention is a four-wheel steering system for a vehicle in which the front and rear wheels are simultaneously steered according to the operation of the steering wheel. The steering ratio characteristic storage means 103 for storing the steering ratio characteristics set in advance according to the vehicle speed V so as to be in the same phase at high vehicle speed, the vehicle speed detection means 102 for detecting the vehicle speed V, A steering ratio setting means 104 for inputting an output signal of the vehicle speed detection means 102 and setting a target steering ratio of front and rear wheels based on the steering ratio characteristics stored in the steering ratio characteristic storage means 103, Receiving the output of the turning ratio setting means 104,
An actuator 51 such as a stepping motor for controlling the steering ratio of the front and rear wheels to the target steering ratio is provided.

Further, deceleration detecting means 105 for detecting the deceleration state of the vehicle based on the output signal of the vehicle speed detecting means 102 is provided.

Further, when the output signal of the deceleration detection means 105 is input, the steering ratio shifts to the opposite phase side as the vehicle speed V decreases during vehicle deceleration at the time when the steering ratio of the front and rear wheels becomes zero. A turning ratio characteristic correcting means 106 for correcting the turning ratio characteristic of the turning ratio setting means 104 with respect to the actuator 51 is provided so as to delay by a predetermined time.

(Operation) According to the present invention, when the vehicle is traveling, the steering ratio setting means 104 stores the vehicle speed V detected by the vehicle speed detecting means 102 in the steering ratio characteristic storage means 103. The target steering ratio corresponding to the vehicle speed V is set by the comparison with the ratio characteristic, and the steering ratio of the front and rear wheels of the vehicle is set by the operation of the actuator 51 in response to the output signal of the steering ratio setting means 104. It is controlled so that the target turning ratio is achieved.

When the vehicle speed V is reduced to a decelerating state, the deceleration detecting means 105 detects it based on the output signal of the vehicle speed detecting means 102, and receives the output of the deceleration detecting means 105. The turning ratio characteristic of the turning ratio setting means 104 with respect to the actuator 51 is corrected by 106, and the shift of the turning ratio to the opposite phase side due to the decrease in the vehicle speed V reaches a predetermined time when the turning ratio becomes zero. Only delayed. As a result, the change of the steering ratio from the in-phase region to the anti-phase region is delayed, and even if the steering wheel is turned off and the vehicle turns at the same time as deceleration due to this delay, the scooping phenomenon does not occur, and therefore the vehicle Driving safety is ensured.

In that case, since the shift of the turning ratio to the opposite phase side is delayed based on one type of turning ratio characteristic stored in the turning ratio characteristic storage unit 103, the turning ratio characteristic is used as it is for deceleration. The control in the anti-phase region of time can be delayed, so that the hysteresis line dedicated for deceleration of the steering ratio characteristic becomes unnecessary.

Further, since the shift of the steering ratio to the opposite phase side is delayed at the time when the steering ratio becomes zero, the control becomes simpler and the occupant feels uncomfortable compared with the case where the steering ratio is delayed. Is avoided. Moreover, the steering ratio control in the same phase region during deceleration or during non-deceleration can be performed as usual,
The responsiveness of the steering ratio control can be secured.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings starting from FIG.

In FIG. 2, 1 _{L to} 2 _R are the four wheels of the vehicle, the left and right front wheels 1 _L and 1 _R are the front wheel steering mechanism 3, and the left and right rear wheels 2 _L and 2 _R are the rear wheel steering. Mechanisms 12 are linked together.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms.
4 _L , 4 _R and tie rods 5 _L , 5 _R and the left and right tie rods
The relay rod 6 connects 5 _L and 5 _{R to} each other. A steering wheel 10 is linked to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7. That is, the relay rod 6 has a rack 8
While the steering wheel 10
A pinion 9 that engages with the rack 8 is attached to the lower end of the steering shaft 11 that is connected to
The left and right front wheels 1 _L , 1 depending on the operation of the steering wheel 10.
It is designed to steer the _R.

On the other hand, the rear wheel steering mechanism 12 is similar to the front wheel steering mechanism 3 in that the left and right knuckle arms 13 _L and 13 _R and the tie rod 1 are used.
4 _L and 14 _R , a relay rod 15 that connects the tie rods 14 _L and 14 _{R to} each other, and a hydraulic power steering mechanism 16. The power steering mechanism 16 is
A power cylinder 17 fixed to the vehicle body and having the relay rod 15 as a piston rod is provided.
Inside is a piston integrally attached to the relay rod 15
The hydraulic chambers 17b and 17c in the cylinder 17 are divided into two hydraulic chambers 17b and 17c by the hydraulic pressure pipes 17 and 19a, respectively.
Connected to the control valve 20 via. Two pipes, an oil supply pipe 22 and an oil discharge pipe 23, which reach the reserve tank 21, are connected to the control valve 20, and a hydraulic pump 24 driven by an in-vehicle engine (not shown) is connected to the oil supply pipe 22. It is arranged. The control valve 20 is of a known spool valve type, and is a cylindrical valve casing 20a integrally attached to the relay rod 15 via a connecting member 25.
And a spool valve (not shown) fitted in the valve casing 20a, the pressure oil from the hydraulic pump 24 is supplied to one hydraulic chamber 17b (17c) of the power cylinder 17 according to the movement of the spool valve. It is supplied to assist the driving force for the relay rod 15.

A pair of return springs 17d for biasing the relay rod 15 to the neutral position (position where the turning angles θ _{R of the} rear wheels 2 _L , 2 _R become zero) are provided in the power cylinder 17 via the piston 17a. , 17d is disguised. Further, the hydraulic pipes 18 and 19 are communicated with the normally-closed electromagnetic opening / closing valve 28 via the hydraulic pipes 26 and 27, respectively, and when the electromagnetic opening / closing valve 28 is opened, both hydraulic chambers 17b of the power cylinder 17 are the return spring 17d and the hydraulic pressure in 17c as the pressure, position the piston 17a to the neutral position by the biasing force of the 17d, as always theta _{R =} 0 the turning angle theta _R of the rear wheels 2 _L, 2 _R steering characteristic of the vehicle The two-wheel steering state is set.

The relay rod 6 of the front wheel steering mechanism 3 has another rack other than the rack 8 constituting the steering mechanism 7.
29 is formed, and a pinion 30 attached to the front end of a rotary shaft 31 extending in the vehicle front-rear direction is meshed with the rack 29,
The rear end of the rotary shaft 31 is linked to the rear wheel steering mechanism 12 via a steering ratio control mechanism 32.

The steering ratio control mechanism 32, as shown in detail in FIG.
The control rod 33 is slidably held on the moving axis l ₁ in the vehicle width direction with respect to the vehicle body, and one end of the control rod 33 is connected to the spool valve of the control valve 20. Further, the turning ratio control mechanism 32 includes a swing arm 36 whose base end is swingably supported by a U-shaped holder 34 via a support pin 35, and the holder 34 is a casing fixed to the vehicle body ( (Not shown) has a support shaft 37 having a rotation axis l ₂ orthogonal to the movement axis l ₁ of the control rod 33.
It is rotatably supported via. Swing arm 36
Of the support pin 35 is located at the intersection of the two axes l ₁ and l ₂ and extends in the direction orthogonal to the rotation axis l _2, and rotates the holder 34 around the support shaft 37 (rotation axis l ₂ ). By moving it, the support pin 35 at the tip and the movement axis l ₁ of the control rod 33
A tilt angle formed by, that is, a swing locus surface of the swing arm 36 about the support pin 35 as a plane orthogonal to the movement axis l ₁ (hereinafter, referred to as
It is designed to change the angle of inclination with respect to the reference plane).

Further, one end of a connecting rod 39 is connected to the tip of the swing arm 36 via a ball joint 38, and the other end of the connecting rod 39 is connected to the other end of the control rod 33 via a ball joint 40. The control rod 33 is displaced in the left-right direction according to the displacement of the tip end of the swing arm 36 in the left-right direction in FIG.

The connecting rod 39 is slidably supported by a rotation imparting arm 41 via a ball joint 42 at a portion near the ball joint 38. The rotation imparting arm 41 is provided integrally with a large-diameter bevel gear 44 rotatably supported on the moving axis l ₁ via a support shaft 43,
The bevel gear 44 is a bevel gear attached to the rear end of the rotating shaft 31.
45 is meshed with each other and transmits the rotation of the steering wheel 10 to the rotation imparting arm 41. Therefore, the rotation imparting arm 41 and the connecting rod 39 rotate about the moving axis l _{1 by} an amount corresponding to the rotation angle of the steering wheel 10, and the swing arm 36 swings about the support pin 35 accordingly. When moved, when the axis of the pin 35 is aligned with the movement axis l ₁ of the control rod 33, the ball joint 38 at the tip of the swing arm 36 only swings on the reference plane, and the control rod 33 moves. Although it is held stationary, if the axis of the pin 35 tilts with respect to the movement axis l _{1 and} the swing locus surface of the swing arm 36 deviates from the reference plane,
As the swing arm 36 swings about the pin 35, the ball joint 38 is displaced in the left-right direction in FIG. 3, and this displacement is transmitted to the control rod 33 via the connecting rod 39, and the control is performed. Rod 33 is moving axis
It is configured to move along l ₁ to actuate the spool valve of control valve 20. That is,
Even if the swinging angle of the swinging arm 36 about the axis of the support pin 35 is the same, the displacement of the control rod 33 in the left-right direction is accompanied by a change in the inclination angle of the pin 35, that is, the rotation angle of the holder 34. Change.

A sector gear 46 as a worm wheel is attached to the support shaft 37 of the holder 34 in order to change the inclination angle of the support pin 35 with respect to the moving axis l _1, that is, the inclination angle of the holder 34 with respect to the reference plane. A worm gear 48 on a rotating shaft 47 is meshed with the. A bevel gear 49 is attached to the rotating shaft 47, and a bevel gear 49 has a stepping motor as an actuator.
The bevel gear 50 mounted on the output shaft 51a of the gear 51 is meshed, and by operating the stepping motor 51 to rotate the sector gear 46, the inclination angle of the holder 34 with respect to the reference plane is changed to change the rear wheel _2L. , 2 _R Steering angle θ _R, that is, front and rear wheels 1 _L , 2 _L
(1 _R , 2 _R ) steering ratio (rear wheel steering angle θ _R / front wheel steering angle θ _F )
For example, the sector gear 46 is moved to a neutral position where its center line is at a right angle to the center line of the rotary shaft 47 of the worm gear 48 (at this time, the ball joint at the tip of the swing arm 36).
38 is rotated on the reference surface, the rear wheels 2 _L, 2 turning angle of _R theta _R is theta _R
= 0), the front and rear wheels
The steering ratio of 1 _L , 2 _L is controlled to the opposite phase in which the rear wheels 2 _L , 2 _R face in the opposite direction to the front wheels 1 _L , 1 _R , while the steering ratio is changed in the opposite direction Are configured to control the rear wheels 2 _L , 2 _{R in the} same phase so as to face the same direction as the front wheels 1 _L , 1 _R.

Further, the support shaft 37 of the holder 34 is provided with a turning ratio sensor 101 composed of a potentiometer for detecting the actual turning ratio R controlled by the stepping motor 51 based on the turning angle of the sector gear 46. ing. The casing supporting the holder 34 has a sector gear.
Stop members 52, 5 on the opposite phase side and the same phase side, which are pins that restrict the rotation range of the sector gear 46 on both the left and right sides of 46
3, the control position of the stepping motor 51 when the sector gear 46 comes into contact with the stopper member 52 on the opposite phase side is set to its initial position. Further, in FIG. 3, reference numeral 54 is a rod stopper that restricts the maximum movement range of the relay rod 15 in the rear wheel steering mechanism 12.

The stepping motor 51 and the solenoid on-off valve 28 are the control unit 10 including a microcomputer.
Configured to be actuated by the output from 0,
This control unit 100 has a vehicle traveling speed V
Vehicle speed sensor 10 as vehicle speed detecting means for detecting (vehicle speed)
2 and the respective detection signals from the steering ratio sensor 101 are input.

As shown in FIG. 4, the control unit 100 has, as a signal processing function of the microcomputer, a steering ratio characteristic storage unit 103 for storing a steering ratio characteristic set in advance according to a vehicle speed V, and the steering ratio characteristic storage unit 103. Based on the steering ratio characteristic of the steering ratio characteristic storage unit 103, the steering ratio setting unit 104 for setting the target steering ratio of the front and rear wheels 1 _L , 2 _L corresponding to the vehicle speed V and the output signal of the vehicle speed sensor 102 Based on the deceleration detection unit 105 that detects the deceleration state of the vehicle based on the deceleration detection unit 105, the output signal of the deceleration detection unit 105 is input, and the steering ratio characteristic of the steering ratio setting unit 104 with respect to the stepping motor 51 is corrected when the vehicle is decelerated. The steering ratio characteristic correction unit 106 is provided.

As shown in FIGS. 5 and 6, the turning ratio characteristics stored in the turning ratio characteristic storage unit 103 are such that the turning ratios of the front and rear wheels 1 _L and 2 _L change according to the vehicle speed V. When the vehicle speed V is low, the rear wheels 2 _L , 2 _R are steered in the opposite direction to the front wheels 1 _L , 1 _R , that is, in the opposite phase, in order to improve the turning performance of the vehicle.
While steering ratio is negative (opposite phase), when the vehicle speed V reaches a predetermined value, the steering ratio is zero, the front wheels 1 _L, 1 rear wheel 2 irrespective of the turning of the _{R L,} 2 _R The steering angle θ _R is maintained at θ _R = 0 and the vehicle enters the normal two-wheel steering state. When driving at higher speeds, the rear wheels 2 _L , 2 _R are connected to the front wheels 1 _L , 2 _{R in} order to improve the grip of the rear wheels 2 _L , 2 _R during cornering and improve running stability.
It is set in the same direction as 1 _R , that is, in the same phase, and the steering ratio is positive (in phase). Incidentally, FIG. 5 shows the characteristics of the rear wheel steering angle with respect to the steering angle of the steering wheel (rotational angle of the steering wheel 10) when the vehicle speed changes, and FIG. 6 shows the steering ratio characteristics with respect to the vehicle speed at the predetermined steering wheel steering angle. There is.

Further, each output signal of the turning ratio characteristic storage unit 103 and the vehicle speed sensor 102 is input to the turning ratio setting unit 104, and in the turning ratio setting unit 104, the turning ratio characteristic storage unit 1
The vehicle speed V detected by the vehicle speed sensor 102 is collated with the steering ratio characteristic stored in 03, the target steering ratio corresponding to the vehicle speed V is determined, and the front and rear wheels 1 _L , 2 _L are steered. Step motor 51 so that the ratio becomes the target turning ratio determined above.
An operation command signal (pulse signal) is output to.
That is, by the sector gear 46 by the drive of the stepping motor 51 is rotated to change the angle of inclination with respect to the reference surface of the holder 34, changing the steering angle theta _R of the rear wheels 2 _L, 2 _R, front and rear wheels 1 _L , 2 _L steering ratio is variably controlled to the target value.

The output signal of the steering ratio sensor 101 is input as a feedback signal to the steering ratio setting unit 104,
The feedback signal controls the stepping motor 51 so that the actual turning ratio matches the target turning ratio. Further, when the actual turning ratio controlled by the stepping motor 51 does not match the target turning ratio, it is considered that the stepping motor 51 is out of synchronization (idling), and the electromagnetic opening / closing valve 28 is turned on. As a result, the steering ratios of the front and rear wheels 1 _L and 2 _L are maintained at zero and the mode shifts to the fail-safe mode.

Further, the deceleration detecting unit 105 determines that the vehicle is decelerating when the deceleration of the vehicle speed V detected by the vehicle speed sensor 102 is larger than a predetermined value.

Further, in the steering ratio characteristic correction unit 106, when the deceleration detection unit 105 determines that the vehicle is decelerating, the steering ratio changes from the same phase as the vehicle speed V decreases as shown in FIG. When changing to the opposite phase, the turning ratio is shifted to the opposite phase side by a predetermined time t at the time when the turning ratio becomes zero, and the turning ratio setting unit 104 with respect to the stepping motor 51 is delayed. The steering ratio characteristic is corrected to the steering ratio characteristic shown by the broken line in the figure. Since the influence of the scooping phenomenon is large when the vehicle is rapidly accelerated, the delay time t is preferably changed according to the deceleration of the vehicle, and is preferably set to be longer as the deceleration is increased.

 Next, the operation of the above embodiment will be described.

First, when the ignition key switch is turned on in order to drive the vehicle which is in the stopped state, the control initial position of the stepping motor 51 is positioned accordingly. After that, when the vehicle shifts to the traveling state, the vehicle speed V at that time is detected by the vehicle speed sensor 102, and the vehicle speed sensor 1
A detection signal is output from 02 to the control unit 100, and the steering ratio setting unit 104 of the control unit 100 compares and verifies with the steering ratio characteristic stored in the steering characteristic storage unit 103 to determine the vehicle speed V. The target turning ratio is calculated, and a pulse signal corresponding to this target turning ratio is output to the stepping motor 51 to drive the motor 51. By driving the motor 51, the sector gear 46 rotates to change the swing locus surface of the swing arm 36 connected to the sector gear 46 with respect to the reference plane. By this change, the operation of the steering wheel 10, that is, the front wheel 1 is performed. The movement direction and the movement distance of the control rod 33 with respect to the movement of the connecting rod 39 rotating around the movement axis l ₁ in association with the steering of _L and 1 _R are changed, and the rear wheels are moved according to the movement of the control rod 33. The power cylinder 17 of the power steering mechanism 16 assists and steers 2 _L and 2 _R so that the target steered ratio is calculated with respect to the front wheels 1 _L and 1 _R. Thus, 4-wheel 1L _L to 2 _R of the vehicle in the opposite phase steering ratio at the time of low vehicle speed, at the time of high vehicle speed is controlled so turning ratio is respectively in phase.

Then, when the vehicle speed V sharply decreases and the vehicle decelerates, the target turning ratio determined by the turning ratio setting unit 104 changes from the same phase to the opposite phase as the vehicle speed V decreases. The deceleration detection unit 105 detects the deceleration state of the vehicle based on the decrease in the vehicle speed V, and the turning ratio characteristic correction unit 106 that receives the output signal of the deceleration detection unit 105 causes the vehicle speed V to decrease.
The target steering ratio is maintained at zero as it is when the steering ratio that changes to the opposite phase side due to the decrease of the vehicle speed becomes zero, and after the elapse of a predetermined time t, the original steering ratio corresponding to the vehicle speed V. The change is gradually controlled toward. For this reason, even if the steering wheel 10 is operated to turn while decelerating,
As described above, the steered ratio does not suddenly change from the in-phase region to the anti-phase region, so that the occurrence of the scooping phenomenon is effectively suppressed, and the traveling safety of the vehicle can be improved.

At that time, in the turning ratio characteristics stored in the turning ratio characteristic storage unit 103, since the characteristics when the turning ratio changes to the opposite phase side are delayed, the original turning ratio characteristic line For example, it is not necessary to add a steering ratio characteristic line (hysteresis line) dedicated to deceleration, which is provided with hysteresis so that the in-phase region is expanded. Therefore, the storage capacity in the steering ratio characteristic storage unit 103 can be reduced. It is possible to reliably suppress the scooping phenomenon during deceleration without increasing the number.

Further, since the delay control of the steering ratio to the opposite phase side is started at the time when the steering ratio becomes zero, there is less discomfort to the occupant in driving compared to when starting from the same phase side, and the delay is delayed. Control can be performed easily.

Further, since only the steering ratio characteristic in the anti-phase region of the steering ratio is changed when the vehicle is decelerated, the in-phase region of the steering ratio and the steering ratio characteristic in the non-deceleration are kept as normal. The responsiveness can be secured by increasing the control speed of the steering ratio to the target steering ratio.

Incidentally, in the above embodiment, the stepping motor 51 is used as an actuator for controlling the steering ratio of the front and rear wheels 1 _L , 2 _L , but the present invention controls the steering ratio by another actuator such as a DC motor. It can also be applied to the four-wheel steering system described above.

(Effects of the Invention) As described above, according to the present invention, the steering ratios of the front and rear wheels are set in advance according to the vehicle speed by operating the steering wheel so that the steering ratio is in the opposite phase when the vehicle speed is low. In a four-wheel steering system for a vehicle, which is controlled based on the turning ratio characteristic, it detects when the vehicle is decelerating, and at the time of deceleration, the turning ratio shifts to the opposite phase side as the vehicle speed decreases. By delaying for a predetermined time from the time when the steering ratio becomes zero, the in-phase region during deceleration and the responsiveness of steering non-control during non-deceleration are ensured, and the steering ratio characteristics are exclusively for deceleration. While not requiring a hysteresis line, the control can be simplified and the scooping phenomenon that occurs when decelerating while turning the steering wheel can be reliably suppressed, and the traveling safety of the four-wheel steering vehicle can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. 2 to 6 show an embodiment of the present invention, FIG. 2 is a plan view schematically showing the overall construction of a four-wheel steering system, and FIG. 3 shows a rear wheel steering mechanism and a steering ratio control mechanism. FIG. 4 is a skeleton diagram showing a perspective view, FIG. 4 is a block diagram showing the configuration of the control unit, FIG. 5 is a characteristic diagram illustrating the characteristic of the rear wheel steering angle with respect to the steering wheel steering angle when the vehicle speed changes, and FIG. It is a characteristic diagram which shows the turning ratio characteristic with respect to the vehicle speed at the time of a steering angle. 1 _L , 1 _R ...... Front wheel, 2 _L , 2 _R ...... Rear wheel, 3 ...... Front wheel steering mechanism,
12 …… Rear wheel steering mechanism, 32 …… Turning ratio control mechanism, 51 …… Stepping motor, 100 …… Control unit, 101
…… Turning ratio sensor, 102 …… Vehicle speed sensor, 103 …… Turning ratio characteristic storage unit, 104 …… Turning ratio setting unit, 105 …… Deceleration detection unit, 106 …… Turning ratio characteristic correction unit, V ... vehicle speed, t ... delay time.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-85067 (JP, A) JP-A-62-181966 (JP, A) JP-A-62-181967 (JP, A) JP-A-60- 135389 (JP, A)

Claims (1)

(57) [Claims] 1. A four-wheel steering system for a vehicle, wherein not only the front wheels but also the rear wheels are steered. The vehicle speed detecting means detects the vehicle speed, and the front and rear wheels have opposite phases when the steering ratio is low. Steering ratio characteristic storage means for storing the steering ratio characteristic set in advance according to the vehicle speed so as to be in the same phase at high vehicle speed,
A steering ratio setting means for inputting an output signal of the vehicle speed detection means and setting a target steering ratio of front and rear wheels corresponding to a vehicle speed based on the steering ratio characteristic of the steering ratio characteristic storage means, and the steering ratio setting means. An actuator that receives the output of the ratio setting means and controls the turning ratio of the front and rear wheels to the target turning ratio, deceleration detecting means that detects the deceleration state of the vehicle based on the output signal of the vehicle speed detecting means, and the deceleration By inputting the output signal of the detection means, the steering is delayed so that the steering ratio shifts to the opposite phase side as the vehicle speed decreases when the vehicle decelerates for a predetermined time when the steering ratio becomes zero. A four-wheel steering system for a vehicle, comprising: a turning ratio characteristic correcting means for correcting a turning ratio characteristic of an actuator of a ratio setting means.