JP2528455B2 - 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 in particular, variably controls the steering ratio of the front and rear wheels according to the vehicle speed. To improve the so-called vehicle speed-sensitive type.

(Prior Art) In recent years, a four-wheel steering system for a vehicle of this type has been drawing attention as a vehicle that can greatly change the traveling characteristics of the vehicle. Among them, what is called a vehicle speed sensitive type that controls the steering ratio using the vehicle speed as a parameter is basically the steering of the front and rear wheels at a low vehicle speed, as shown in, for example, Japanese Utility Model Publication No. 61-80168. While controlling the ratio to the opposite phase to improve the turning performance of the vehicle by making the steering characteristic oversteer characteristic, at the time of high vehicle speed, the steering ratio is kept in the same phase and the steering characteristic is made understeer characteristic to improve the running stability of the vehicle. It is something that has been secured.

By the way, in such a vehicle speed-sensitive four-wheel steering system, the vehicle speed is used as a parameter to determine the turning ratio of the front and rear wheels. Therefore, if a vehicle speed detecting means such as a vehicle speed sensor for detecting the vehicle speed fails, There is a characteristic that the wheel steering control cannot be reliably executed. Therefore, a fail-safe system is provided which detects a failure of the vehicle speed detecting means and holds the two-wheel steering control state in which the steering ratio becomes zero in order to ensure traveling stability when the failure occurs.

When detecting the failure of the vehicle speed detecting means, the average value of the number of pulses of the pulse signal emitted from the vehicle speed detecting means is determined on a regular basis, and when the average value decreases and decreases to an extent that is not normally considered. It is determined that the vehicle speed detecting means is out of order.

(Problems to be solved by the invention) However, such a sudden decrease in the average value of the number of pulses is not limited to when the vehicle speed detection means fails, but is also caused by braking on a so-called low μ road such as a snow road. It also occurs when the locks and the rotation stops. That is,
Since the locked state of the wheel during braking cannot be accurately identified as the failure of the vehicle speed detection means, the system will operate under the situation where the phase-safe system is not originally necessary, and such a problem enhances the marketability. The above solution is preferable.

(Objects of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to provide a vehicle speed-sensitive four-wheel steering device that controls according to vehicle speeds of front and rear wheels as described above. Focusing on the fact that there is a difference in the output signal characteristics of the vehicle speed detecting means between the failure state of the detecting means and the locked state of the wheels during braking, the failure state of the vehicle speed detecting means is determined based on the difference. By making the distinction, it is possible to accurately identify the failure of the vehicle speed detecting means from the lock of the wheel at the time of braking, thereby improving the commercialability of the four-wheel steering device.

(Means for Solving the Problems) In order to achieve this object, the solution means taken by the present invention is such that when the wheels are locked and stopped due to braking, the vehicle speed rises due to the subsequent release of the lock stop. However, when the vehicle speed detecting means is out of order, no signal is output from the vehicle speed detecting means no matter how much time has passed thereafter. On the other hand, when it is considered that the vehicle speed detecting means has failed, the output characteristic of the vehicle speed detecting means thereafter is monitored for a predetermined time, and the failure of the vehicle speed detecting means is judged according to the presence or absence of the output signal. I am trying.

Specifically, the present invention is premised on a vehicle speed-sensitive four-wheel steering device in which the steering ratios of the front and rear wheels of a vehicle are controlled to have opposite phases when the vehicle speed is low and to have the same phase when the vehicle speed is high.

That is, as shown in FIG. 1, the vehicle speed detecting means 102 for detecting the vehicle speed V, the steering ratio changing means 32 for changing the steering ratio of the front and rear wheels, and the output signal of the vehicle speed detecting means 102 are inputted, The steering ratio changing means is such that the steering ratios of the front and rear wheels become the target steering ratio K determined based on a predetermined steering ratio characteristic.
And a turning ratio control means 103 for controlling the operation of 32. 4
In the wheel steering system, when the vehicle speed V decreases by a predetermined amount or more, the steering ratio control means 103 keeps the steering ratios of the front and rear wheels at the steering ratio K corresponding to the vehicle speed V before the decrease. While controlling the steering ratio changing means 32, the vehicle speed V is monitored until a predetermined time elapses from the time when the vehicle speed V drops to V = 0, and the vehicle speed V is maintained at V = 0 during the predetermined time. The failure determination unit outputs a signal for setting the steering ratio K to K = 0 when the vehicle is turned on, and outputs a signal for continuing the four-wheel steering control when the vehicle speed V is not maintained at V = 0.
104 is provided.

(Operation) According to the present invention, the vehicle speed V is detected by the vehicle speed detection means 102 while the vehicle is traveling, and the steering ratio control means 103 receives an output signal from the vehicle speed detection means 102 in the present invention. The changing means 32 is operated and controlled, and the turning ratio changing means is changed.
The turning ratio of the front and rear wheels is controlled according to the vehicle speed V by the operation of 32, and is changed so as to have the opposite phase at the low vehicle speed and the same phase at the high vehicle speed.

Then, when the vehicle speed V detected by the vehicle speed detecting means 102 suddenly drops below a predetermined level, the operation of the steering ratio changing means 32 is first controlled by the operation of the failure determination unit 104 in the steering ratio control means 103. Thus, the steering ratios of the front and rear wheels are maintained at the steering ratio K corresponding to the vehicle speed before the decrease. Thereafter, the failure determination unit 104 monitors the vehicle speed V detected by the vehicle speed detecting means 102 from the time when the vehicle speed V drops to V = 0 until a predetermined time elapses.
At this time, the vehicle speed V
Is decreased by a predetermined value or more, the vehicle speed V is returned to the value of V ≠ 0 during a predetermined time thereafter and is not maintained at V = 0. At that time, it is considered that the wheels are locked by the braking, and the four-wheel steering control is continued thereafter.

However, when the vehicle speed detecting means 102 is out of order,
After the elapse of a predetermined time, the vehicle speed V is still maintained at V = 0. At this time. It is considered that the vehicle speed detecting means 102 is out of order, and a signal that the steering ratio K becomes K = 0 is output to the steering ratio changing means 32 and the like, and the vehicle is held in the two-wheel steering state.

Therefore, by determining whether or not the vehicle speed V has risen to V ≠ 0 after the vehicle speed V has drastically decreased in this way, it is determined whether or not there is a failure in the vehicle speed detecting means 102. The failure of can be accurately identified with respect to the locked state of the wheels due to braking.

(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 four wheels of a four-wheel steering type vehicle according to an embodiment of the present invention. Left and right front wheels 1 _L and 1 _R are provided by a front wheel steering mechanism 3 and left and right wheels. The rear wheels 2 _L and 2 _R are linked by a rear wheel steering mechanism 12, respectively.

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 steering mechanism 7. That is, a rack 8 is formed on the relay rod 6, and a pinion 9 meshing with the rack 8 is attached to the lower end of a steering shaft 11 having a steering wheel 10 connected to the upper end thereof. The left and right front wheels 1 _L and 1 _R are steered according to the operation.

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 includes a power cylinder 17 fixed to the vehicle body and having the relay rod 15 as a piston rod, and the inside of the power cylinder 17 is a piston 17 integrally attached to the relay rod 15.
It is divided into two hydraulic chambers 17b and 17c by a, and the hydraulic chambers 17b and 17c in the cylinder 17 are connected to the control valve 20 via hydraulic pipes 18 and 19, respectively. Also,
The control valve 20 is connected to two pipes, an oil supply pipe 22 and an oil discharge pipe 23 that reach a reserve tank 21, and the oil supply pipe 22 is provided with a hydraulic pump 24 driven by an in-vehicle engine (not shown). Has been done. The control valve 20 is configured by a known spool valve type, and has a tubular valve casing 20a integrally attached to the relay rod 15 via a connecting member 25, and the inside of the valve casing 20a. A spool valve (not shown) that is fitted is provided, and hydraulic oil from the hydraulic pump 24 is supplied to one hydraulic chamber 17b (17c) of the power cylinder 17 in response to movement of the spool valve to drive the relay rod 15. It is to assist power.

Further, in the power cylinder 17 of the power steering mechanism 16, the relay rod 15 is biased to a neutral position (position where the turning angles θ _{R of the} rear wheels 2 _L and 2 _R become zero) via a piston 17a. The pair of return springs 17d, 17d are compressed. 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, positioned in the neutral position of the piston 17a by the biasing force of the 17d, the rear wheels 2 _L, 2 turning angle of _R theta _R always theta _R
= 0, the steering characteristic of the vehicle is set to the two-wheel steering state.

The rack is attached to the relay rod 6 of the front wheel steering mechanism 3.
In addition to 85, a rack 29 is formed. 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, and the rear end of the rotary shaft 31 has a steering ratio changing mechanism 32.
It is linked to the rear wheel steering mechanism 12 via the.

The steering ratio changing 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 changing 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. If 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 remains stationary. However, if the axis of the pin 35 is tilted with respect to the movement axis l _{1 and} the swing locus surface of the swing arm 36 is displaced 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 ie front and rear wheels 1 _L , 2 _R
(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 perpendicular to the center line of the rotating shaft 47 of the worm gear 48 (at this time, the ball joint 38 at the tip of the swing arm 36).
Rotates the upper reference surface, the rear wheels 2 _L, 2 turning angle of _R theta _R is theta _R =
When it is rotated in one direction (from 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.

The support shaft 37 of the holder 34 is provided with a turning ratio sensor 101 composed of a potentiometer that detects the actual turning ratio controlled by the stepping motor 51 based on the rotation angle of the sector gear 46. . Further, on the casing supporting the holder 34, stopper members 52, 53 on the opposite phase side and the same phase side, which are pins for restricting the rotation range of the sector gear 46, are attached to the left and right sides of the sector gear 46, respectively. The control position of the stepping motor 51 when 46 abuts on 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
The detection signals from the vehicle speed sensor 102 for detecting (vehicle speed) and the steering ratio sensor 101 are input, and the signal processing function of the microcomputer of the control unit 100 controls the operation of the steering ratio changing mechanism 32. Then, the steering ratios of the front and rear wheels 1 _L , 2 _L are controlled to a target steering ratio determined based on a predetermined steering ratio characteristic.

In addition, as shown in FIG. 4 and FIG. 5, the steering ratio characteristic is such that the steering ratios of the front and rear wheels 1 _L , 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. When the vehicle speed V reaches a predetermined value while the ratio becomes negative, the steering ratio becomes zero, and the steering angles θ _{R of the} rear wheels 2 _L , 2 _R are irrespective of the steering of the front wheels 1 _L , 1 _R. With θ _R = 0, the vehicle enters the normal two-wheel steering state. When driving at higher speeds, the rear wheels 2 _L , 2 _R are in the same direction as the front wheels 1 _L , 1 _{R in} order to improve the grip of the rear wheels 2 _L , 2 _R during cornering and improve running stability. That is, the steering ratio is set to be positive by steering in the same phase. Then, by comparing the vehicle speed V detected by the vehicle speed sensor 102 with the steering ratio characteristic, the target steering ratio corresponding to the vehicle speed V is determined. FIG. 4 shows the characteristics of the rear wheel steering angle with respect to the steering angle of the steering wheel (the turning angle of the steering wheel 10) when the vehicle speed changes, and FIG. 5 shows the steering ratio characteristics with respect to the vehicle speed at the predetermined steering wheel steering angle. There is.

Here, a signal processing procedure performed for controlling the operation of the stepping motor 51 and the electromagnetic on-off valve 28 in the microcomputer of the control unit 100 will be schematically described with reference to FIG.

First, in step S ₁ after the start, the vehicle speed sensor 10
The vehicle speed V detected by 2 is read, and then step S
_{At 2} , it is determined whether the vehicle speed V is V = 0. Where V =
0 When YES is determined, reduction of [Delta] V _E of the vehicle speed V is determined whether less than a predetermined value-.alpha. (deceleration is large) proceeds to step S _3, the judgment is [Delta] V _E <- when the YES of α determines the vehicle speed V becomes V = 0 at step S ₄ and the vehicle speed decrease of [Delta] V _E is whether state immediately becomes greater than the predetermined value-.alpha.. If this determination is NO, the process directly proceeds to step S ₇ , while if YES, the process proceeds to step S ₅ to set the flag F to F = 1, and then step S ₆
After the timer T _M is set to the predetermined time T _M = b (for example, 20 seconds), the process proceeds to step S ₇ . The flag F is for identifying the control mode under that condition as F = 1 when the vehicle speed V is drastically reduced at a speed equal to or higher than a predetermined value and becomes V = 0. The in the step S ₇ timer T _M is T _M =
If it is YES at T _M = 0, the process proceeds to step S ₁₀ to set the target turning ratio K of the front and rear wheels 1 _L , 2 _L to K = 0.
After being set to (turning ratio for two-wheel steering), the stepping motor 51 is controlled so that the actual turning ratio of the front and rear wheels 1 _L , 2 _L becomes the target turning ratio K in step S ₁₁ . .
On the other hand, when the determination in step S ₇ is NO when T _M ≠ 0, the timer is updated to T _M = T _M −1 in step S ₈ and
After fixing the target turning ratio K of the front and rear wheels 1 _L , 2 _L in S ₉ , the process proceeds to the above step S ₁₁ to change the actual turning ratio of the front and rear wheels 1 _L , 2 _{L to} the fixed target turning ratio of the above. controls to K, repeats subsequent steps S ₂ ... a return to the first step S ₁ after the step S _11.

Further, the decision in step S ₂ is negative (NO) of the V ≠ 0 is the flag F is cleared to F = 0 the process proceeds to step S _12, then the decision in step S ₃ is [Delta] V _E ≧-.alpha. NO
The flag F proceeds to step S ₁₃ with the time of F =
1 or to determine whether said the process proceeds to step S _7, it is determined NO, and the map of the steering ratio characteristic of the above target turning ratio K in step S ₁₄ when it is determined where F = 1 and after more read, steering ratio of the front and rear wheels 1 _L, 2 _L proceeds to step S ₁₁ is actuated controls the stepping motor 51 so that the target steering angle ratio K read above.

That is, the flow of steps S ₁ ~S _4, S ₆ is one in which the vehicle speed V starts counting the predetermined time b from the point when the decreased by more than a predetermined. In addition, steps S ₂ , S ₃ ,
The flow from S ₁₃ , S _{7 to} S ₉ , S ₁₁ is
This is for fixing the target turning ratio K of the front and rear wheels 1 _L , 2 _L. Furthermore, flow of the step _{S 2, S 3, S 13} , S 7, S 10, S 11 the vehicle speed V during the predetermined time b has the front and rear wheels 1 _L, 2 _L when held in the V = 0 2 with the target turning ratio K set to K = 0
The wheel steering state is maintained, and steps S ₁ , S ₂ , S ₁₂
Similarly, the flow from S ₁₄ to S ₁₁ is similar to the vehicle speed V during the predetermined time b.
When V ≠ 0 and there is a rise, the front and rear wheels
The target turning ratios K of 1 _L and 2 _L are read from the map of turning ratio characteristics, and normal four-wheel steering control is continued.
When the steering ratio of the front and rear wheels 1 _L and 2 _L is set to zero and the two-wheel steering state is maintained, the stepping motor 51 may be controlled and the electromagnetic opening / closing valve 28 may be turned on.

Therefore, in the present embodiment, the steps in the above flow
The _{S 1, S 2, S 14} , S 11, the output signal of the vehicle speed sensor 102, the steering ratio of the front and rear wheels 1 _L, 2 _L is, the target that has been determined based on a predetermined steering ratio characteristic The turning ratio control means 103 is configured to control the operation of the stepping motor 51 of the turning ratio changing mechanism 32 so that the turning ratio becomes K.

Pursuant to the steps S ₁ to S _13, so that the vehicle speed V is held to the steering ratio K of the steering ratio of the front and rear wheels 1 _L, 2 _L corresponding to the reduction previous vehicle speed V when decreased by more than a predetermined While controlling the steering ratio changing mechanism 32, the vehicle speed V is monitored until the predetermined time b elapses from the time when the vehicle speed V decreases to V = 0, and the vehicle speed V is V = 0 during the predetermined time b. When the vehicle speed V is not maintained at V = 0, the failure determination unit 104 outputs a signal for setting the steering ratio K to K = 0, and when the vehicle speed V is not maintained at V = 0, outputs a signal for continuing the four-wheel steering control. The failure determination unit 104 constitutes a part of the turning ratio control means 103.

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

In the traveling state of the vehicle, the vehicle speed V at that time is detected by the vehicle speed sensor 102, and a detection signal is output from the vehicle speed sensor 102 to the control unit 100. The steering ratio control means 103 of the control unit 100 controls the steering ratio. The target turning ratio K corresponding to the vehicle speed V is calculated by comparison and comparison with the characteristics, and a pulse signal corresponding to the target turning ratio K 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. A connecting rod that rotates around the moving axis l ₁ in conjunction with the steering of _L and 1 _R
The movement direction and the movement distance of the control rod 33 with respect to the movement of 39 change, and the rear wheels 2 _L , 2 _R are moved to the front wheels 1 _L , 1 _R in accordance with the movement of the control rod 33. is steered so as to be K, by this, the four-wheel 1 _L to 2 _R is antiphase steering ratio at low speed of the vehicle is controlled so that the steering ratio is respectively in phase at the time of high speed . The steering of the rear wheels 2 _L , 2 _R is performed by a power steering mechanism that is operated by the hydraulic oil supplied from the hydraulic pump 24.
It is assisted by 16 power cylinders 17.

Further, during the control of the turning ratios of the front and rear wheels 1 _L , 2 _L , when the vehicle speed V sharply decreases to V = 0, another control mode is executed. First, as the vehicle speed V decreases,
The target turning ratio K of the front and rear wheels 1 _L , 2 _L is maintained at the target turning ratio K before the vehicle speed decreased. In parallel with this, the vehicle speed V
There is started counting of the predetermined time b by the timer T _M from the time of reduction, during the counting of the timer T _M, the vehicle speed V
Is maintained at V = 0. That is, when the vehicle is traveling on a low μ road such as a snowy road and the wheels 1 _L to 2 _R (specifically, vehicle speed detecting wheels) are locked and stopped by braking, the vehicle speed sensor 102 determines that the vehicle speed V is V = 0. However, when the wheels 1 _L to 2 _R are locked, the braking is released for a predetermined time b, and the vehicle speed V rises to a value other than V = 0 again. . Therefore, during such a predetermined time b, V
When there is a rise to ≠ 0, it can be considered that the wheels 1 _L to 2 _R are in the lock stopped state, and at this time, the vehicle speed sensor 102
Since it is not a failure of the above, the four-wheel steering control is continued as it is, and immediately after the rising of the vehicle speed V is detected, the front and rear wheels 1 _L , 2
The turning ratio of _L is controlled so as to become the target turning ratio K corresponding to the vehicle speed V.

However, when the vehicle speed sensor 102 itself is out of order, a signal other than the vehicle speed V = 0 (a signal of V ≠ 0) is not output from the vehicle speed sensor 102 at all during the upper predetermined time b. Therefore, in this state, it can be determined that the vehicle speed sensor 102 is out of order, and at that time, the target turning ratio K of the front and rear wheels 1 _L , 2 _L is forcibly K after the elapse of the predetermined time b.
Is corrected to = 0, and the steering characteristic of the vehicle is maintained in the two-wheel steering state.

Therefore, in this embodiment, when the signal of the vehicle speed V = 0 is output from the vehicle speed sensor 102, it is determined whether the cause is the failure of the vehicle speed sensor 102 or the lock stop of the wheels 1 _L to 2 _R. It is possible to accurately identify and switch the control thereafter according to each of the states, so that the commercialability of the four-wheel steering device can be greatly improved.

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, in a four-wheel steering system for a vehicle speed-sensitive vehicle in which the front and rear wheels are steered by operating a steering wheel, when the vehicle speed drops sharply. , The steering ratio is maintained at the steering ratio corresponding to the vehicle speed before the decrease, and it is determined whether or not the vehicle speed has risen for a predetermined time after the decrease, and if there is a vehicle speed rise, the wheels involved in braking are It is considered that it is due to the lock stop state of, and while continuing the four-wheel steering control as it is,
When the vehicle speed does not rise, it is regarded as a failure of the vehicle speed detecting means, and the turning ratio is maintained in the two-wheel steering state, so that the failure of the vehicle speed detecting means is accurately identified as the wheel lock stop state. Can be detected by the
The product characteristics of the wheel steering device can be greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. FIG. 2 and the following drawings 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 is a perspective view of a rear wheel steering mechanism and a steering ratio variable mechanism. Fig. 4 is a skeleton diagram showing the state, Fig. 4 is a characteristic diagram illustrating the characteristic of the rear-wheel steering angle with respect to the steering angle when the vehicle speed changes, and Fig. 5 is a characteristic diagram showing the turning ratio characteristic with respect to the vehicle speed when the steering angle is a predetermined steering angle. FIG. 6 is a flow chart showing the control procedure for the stepping motor processed in the control unit. 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 changing mechanism, 51 …… Stepping motor, 100 …… Control unit, 102
…… Vehicle speed sensor, 103 …… Turning ratio control means, 104 …… Failure discrimination section.

Claims (1)

(57) [Claims] 1. A vehicle speed-sensitive four-wheel steering system in which the steering ratios of the front and rear wheels of a vehicle are controlled in opposite phases at low vehicle speeds and at the same phase at high vehicle speeds. The detection means, the turning ratio changing means for changing the turning ratio of the front and rear wheels, and the output signal of the vehicle speed detecting means are input, and the turning ratio of the front and rear wheels is determined based on a predetermined turning ratio characteristic. And a turning ratio control means for operating and controlling the turning ratio changing means so that the target turning ratio becomes a desired turning ratio.The turning ratio control means turns the front and rear wheels when the vehicle speed decreases more than a predetermined value. The steering ratio is controlled so that the steering ratio is maintained at the steering ratio corresponding to the vehicle speed before the decrease, and the vehicle speed is monitored until a predetermined time elapses from the time when the vehicle speed decreases to zero,
A fault that outputs a signal that makes the steering ratio zero when the vehicle speed is maintained at zero during the predetermined time, and outputs a signal that continues the four-wheel steering control when the vehicle speed is not maintained at zero. A four-wheel steering system for a vehicle, which has a discrimination section.