JPH0557950B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering device that steers the front and rear wheels of a vehicle. Concerning countermeasures at the time of detection.

(Prior art) In recent years, this type of four-wheel steering system for vehicles has attracted attention as a device that can greatly change the driving characteristics of the vehicle. The steering ratio is controlled to be in the opposite phase and the steering characteristics are changed to oversteer characteristics to improve the turning performance of the vehicle.At the same time, at high vehicle speeds or at small steering angles, the steering ratio is kept in the same phase and the steering characteristics are changed to understeer characteristics. This is to ensure the running stability of the vehicle.

As an example of this four-wheel steering device, Japanese Patent Application Laid-open No. 193770/1983 proposes a system in which the actuator for variable control of the steering ratio of the front and rear wheels is a stepping motor (pulse motor). There is.

Specifically, it has a moving member that is connected to a rear wheel steering mechanism that steers the rear wheels of a vehicle and is movable in a predetermined movement axis direction, and a swing center located on the movement axis of the moving member. A rocking arm called a rocking swash plate, a connecting member that connects the rocking arm and the moving member, and a front wheel steering mechanism that steers the front wheels of the vehicle, which connects the connecting member to the moving member. A rotation imparting arm that rotates around a movement axis is provided, and the steering ratio of the front and rear wheels is changed by changing the inclination angle of the swing center line of the swing arm with respect to the movement axis of the moving member using a stepping motor. It is intended to do so.

(Problem to be Solved by the Invention) However, when a stepping motor is used to change the steering ratio of the front and rear wheels as in the proposed example above, an excessive load is generated due to the stays of the gear mechanism that transmits the rotational force of the motor. When this happens, there is a risk that the stepping motor will go out of synch (idle) and the target steering ratio cannot be obtained accurately, so there is room for improvement in terms of vehicle running stability. There is.

For this reason, a steering ratio detection means is provided to detect the actual steering ratio controlled by the stepping motor, and the detected actual steering ratio is compared with a target steering ratio for the stepping motor. When the difference exceeds a detection width of a predetermined level set due to variations in detection accuracy of the steering ratio detection means, it is assumed that the stepping motor is out of synchronization, and the stepout is detected. A possible countermeasure is to forcibly correct the steering ratio to the stable side at the time of adjustment.

However, in this case, motor step-out is detected by comparing the magnitude of the target steering ratio based on the output signal of the stepping motor and the detected steering ratio, so there is a limit to how fast the step-out detection speed can be increased. However, there is a problem in that it is difficult to immediately detect a step-out and control the control mode accordingly. Incidentally, such a problem similarly occurs even when an actuator other than a stepping motor is used, such as a DC motor (direct current motor).

(Object of the Invention) The present invention has been made in view of the above points, and its purpose is to correct the out-of-step state of an actuator such as a stepping motor with the target steering ratio of the front and rear wheels as described above. By making a judgment based on other appropriate state quantities instead of making a judgment by comparing the magnitude with the actual detected steering ratio, even if the actuator loses synchronization, it can be detected immediately. The object is to be able to correct the control mode accordingly.

(Means for Solving the Problem) In order to achieve this objective, the solution in the present invention compares the actuation speed of the actuator with the actual speed of change of the steering ratio controlled by the actuator. I try to do that.

Specifically, as shown in FIG. 1, the configuration of the present invention is a four-wheel steering system for a vehicle that simultaneously steers the front and rear wheels according to the operation of a steering wheel. Steering ratio setting means 1 for setting a target steering ratio of front and rear wheels based on ratio characteristics
03 and the output of the steering ratio setting means 103,
an actuator 51 such as a stepping motor that controls the steering ratio of the front and rear wheels to the target steering ratio;
and.

Furthermore, a steering ratio speed detecting means 104 for detecting the actual changing speed ds/dt of the steering ratio controlled by the actuator 51, and a steering ratio speed detecting means 104 for detecting the changing speed ds/dt of the actual steering ratio controlled by the actuator 51; dt and the operating speed dm/dt of the actuator 51 to detect the out-of-step state of the actuator 51, and receiving the output of the out-of-step detection means 105, determines the steering specific speed. ds／dt
A correction means 106 is provided for forcibly correcting the steering characteristics of the vehicle to a predetermined characteristic such as a two-wheel steering characteristic when the difference between the actuator 51 and the operating speed dm/dt of the actuator 51 is larger than a predetermined value.

(Function) With the above configuration, in the present invention, when the vehicle is running, the steering ratio of the front and rear wheels of the vehicle is set to the target determined by the steering ratio setting means 103 based on the steering ratio characteristics by the operation of the actuator 51. The steering ratio is controlled to be the same. The actual steering ratio change speed controlled by this actuator 51
ds/dt is detected by the steering specific speed detection means 104, and the steering specific speed ds/dt detected by the steering specific speed detection means 104 and the operating speed of the actuator 51 are detected by the step-out detection means 105.
dm/dt are compared, and when the difference between both speeds ds/dt and dm/dt is greater than the set value, actuator 5
1 is determined to be an out-of-step state, and the correction means 106 performs processing such as forcibly changing the steering characteristics of the vehicle to a two-wheel steering state.

At that time, in the step-out detection means 105,
The out-of-step state of the actuator 51 is detected by comparing the operating speed dm/dt of the actuator 51 and the actual speed of change of the steering ratio ds/dt. It is possible to correct the two-wheel steering characteristics and execute control with good responsiveness.

(Example) Hereinafter, an example of the present invention will be described based on the drawings from FIG. 2 onwards.

In Fig. 2, 1 _L to 2 _R are the four wheels of the vehicle, and the left and right front wheels 1 _L and 1 _R are the front wheel steering mechanism 3.
Furthermore, the left and right 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 _4L , _4R and 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 linked to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7.
That is, the relay rod 6 is formed with a rack 8, while the upper end steering wheel 1 is formed with a rack 8.
A pinion 9 that engages with the rack 8 is attached to the lower end of the steering shaft 11 to which the steering wheel 10 is connected, and is configured to steer the left and right front wheels 1 _L and 1 _R in accordance with the operation of the steering wheel 10. .

On the other hand, similarly to the front wheel steering mechanism 3, the rear wheel steering mechanism 12 has left and right knuckle arms 13 _L , 1
3 _R and tie rods 14 _L and 14 _R , and a relay rod 1 that connects the tie rods 14 _L and 14 _R.
5, and further includes a hydraulic power steering mechanism 16. The power steering mechanism 16 is fixed to the vehicle body and connected to the relay rod 1.
The inside of the power cylinder 17 is divided into two hydraulic chambers 17b and 17c by a piston 17a integrally attached to the relay rod 15. 17b, 17c
are connected to a control valve 20 via hydraulic pipes 18 and 19, respectively. Furthermore, two pipes, an oil supply pipe 22 and an oil discharge pipe 23, leading to a reserve tank 21 are connected to the control valve 20, and a hydraulic pump 24 driven by an on-vehicle engine (not shown) is connected to the oil supply pipe 22. It is arranged. The control valve 20 is
Consists of a known spool valve type,
A cylindrical valve casing 2 is integrally attached to the relay rod 15 via a connecting member 25.
0a, and a spool valve (not shown) fitted in the valve casing 20a, and the power cylinder 17 is moved in response to movement of the spool valve.
A hydraulic pump 24 is installed in one of the hydraulic chambers 17b and 17c.
The drive force for the relay rod 15 is assisted by supplying pressure oil from the relay rod 15.

In addition, the relay rod 15 is placed in the power cylinder 17 via the piston 17a at the neutral position (the position where the steering angle θ _R of the rear wheels 2 _L and 2 _R is zero).
A pair of return springs 17d, 1 biasing the
7d has been reduced. In addition, the above hydraulic piping 1
8 and 19 are connected to a normally closed electromagnetic on-off valve 28 via hydraulic piping 26 and 27, respectively, and when this electromagnetic on-off valve 28 is opened, the oil pressures in both oil pressures 17b and 17c of the power cylinder 17 are equalized. The piston 17a is positioned at the neutral position by the biasing force of the return springs 17d and 17d, and the steering angle θ _R of the rear wheels 2 _L and 2 _R is always set to θ _R = 0, so that the steering characteristics of the vehicle are in a two-wheel steering state. It is made to be.

In addition to the rack 8 constituting the steering mechanism 7, another rack 29 is formed on the relay rod 6 of the front wheel steering mechanism 3, and the rack 29 has a pinion 30 attached to the front end of a rotating shaft 31 extending in the longitudinal direction of the vehicle body. are engaged with each other, and the rotating shaft 31
The rear end is linked to the rear wheel steering mechanism 12 via a steering ratio control mechanism 32.

As shown in detail in FIG. 3, the steering ratio control mechanism 32 has a control rod 33 that is slidably held on a movement axis _l1 in the vehicle width direction relative to the vehicle body. One end of the door 33 is connected to the spool valve of the control valve 20. Further, the steering 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 connected to a casing ( (not shown)
The control rod 33 is rotatably supported via a support shaft 37 having a rotation axis _l2 perpendicular to the movement axis _l1 of the control rod 33. The support pin 35 of the swing arm 36 is located at the intersection of the two axes l ₁ and l ₂ and extends in a direction perpendicular to the rotation axis l ₂ . ₂ ) By rotating it around, the inclination angle between the support pin 35 at its tip and the movement axis _l1 of the control rod 33,
In other words, the swinging arm 36 centered on the support pin 35
The plane in which the oscillation locus plane of is orthogonal to the movement axis l ₁ (hereinafter referred to as
The angle of inclination made with respect to a reference plane (referred to as a reference plane) is changed.

Further, a connecting rod 3 is connected to the tip of the swing arm 36 via a ball joint 38.
One 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 moved in the left-right direction in accordance with the displacement 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 thereof close to the ball joint 38. This rotation imparting arm 41 is
It is provided integrally with a large diameter bevel gear 44 rotatably supported on the movement axis _l1 via a support shaft 43,
A bevel gear 45 attached to the rear end of the rotating shaft 31 is meshed with the bevel gear 44 so as to transmit rotation of the steering wheel 10 to the rotation imparting arm 41. Therefore, the rotation arm 41 and the connecting rod 39 rotate about the movement axis _l1 by an amount corresponding to the rotation angle of the steering wheel 10, and the swing arm 36 rotates around the support pin 35 accordingly. When the axis of the pin 35 coincides with the movement axis _l1 of the control rod 33, the ball joint 38 at the tip of the swing arm 36 only swings on the reference plane. , the control rod 33 is held stationary, but the axis of the pin 35 is the axis of movement l ₁
If the swing locus plane of the swing arm 36 deviates from the reference plane by tilting to This displacement is transmitted via the connecting rod 39 to the control rod 33, which moves along the axis of movement _l1 to actuate the spool valve of the control valve 20. It is configured to allow That is, even if the swing angle of the swing arm 36 about the axis of the support pin 35 is the same, the tilt angle of the displacement pin 35 in the left-right direction of the control rod 33, that is, the rotation angle of the holder 34, will change. It changes accordingly.

In order to change the inclination angle of the support pin 35 with respect to the moving axis _l1 , that is, the inclination angle of the holder 34 with respect to the reference plane, a sector gear 4 as a worm wheel is attached to the support shaft 37 of the holder 34.
6 is attached, and a worm gear 48 on a rotating shaft 47 is meshed with this sector gear 46.
Further, a bevel gear 49 is attached to the rotating shaft 47, and a bevel gear 50 attached to an output shaft 51a of a stepping motor 51 as an actuator is meshed with this bevel gear 49. By operating and rotating the sector gear 46, the inclination angle of the holder 34 with respect to the reference plane is changed to change the steering angle θ _R of the rear wheels 2 _L , 2 _R , that is, the front and rear wheels L _L , 2 _L , 1 _R , 2. The steering ratio of _R (rear wheel steering angle θ _R /front wheel steering angle θ _F ) is controlled, and the sector gear 46 is, for example, placed at a neutral position where its center line is perpendicular to the center line of the rotating shaft 47 of the worm gear 48 (this position is At this time, the ball joint 38 at the tip of the swing arm 36 rotates on the reference plane, and the steering angle θ _R of the rear wheels 2 _L and 2 _R becomes θ _R = 0). When the steering ratio of the front and rear wheels 1 _L and 2 _L is changed to the rear wheels 2 _L and 2 _R
On the other hand, when the rear wheels _2L and _2R are rotated in the opposite direction, the steering ratio is the same as that of the front wheels _{1L and 1R .} The configuration is such that control is performed in the same phase in both directions.

Further, the support shaft 37 of the holder 34 is provided with a potentiometer as a steering ratio detection means for detecting the rotation angle s of the sector gear 46 corresponding to the actual steering ratio controlled by the stepping motor 51. A steering ratio sensor 101 is provided. The casing that supports the holder 34 is provided with anti-phase and same-phase stopper members 52 and 53, which are made of pins that restrict the rotation range of the sector gear 46, on both left and right sides of the sector gear 46. The control position of the stepping motor 51 when the stepping motor 46 comes into contact with the stopper member 52 on the opposite phase side is set as its initial position. Further, in FIG. 3, 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 electromagnetic on-off valve 28 are configured to be operated and controlled by the output from a control unit 100 incorporating a microcomputer, and this control unit 100 has a running speed V (vehicle speed) of the vehicle. Vehicle speed sensor 102 to detect and the steering ratio sensor 1
Each detection signal from 01 is input.

Here, the signal processing procedure performed in the microcomputer of the control unit 100 to control the operation of the stepping motor 51 and the electromagnetic on-off valve 28 will be schematically explained based on FIG.

First, in the first step _S1 after the start, the signal of the vehicle speed V detected by the vehicle speed sensor 102 is input, and in the next step _S2 , the signal is adjusted according to the vehicle speed V based on the steering ratio characteristic set and stored in advance. Set target steering ratios for front and rear wheels 1 _L , 2 _L , 1 _R , and 2 _R. That is, as shown in FIGS. 4 and 5, the steering ratio characteristics described above change the steering ratios of the front and rear wheels 1 _L and 2 _L depending on the vehicle speed V, and when the vehicle speed V is low, the vehicle In order to improve the turning performance of the vehicle, the rear wheels 2 _L and 2 _R are steered in the opposite direction to the front wheels 1 _L and 2 _R , so that the steering ratio becomes negative, while the vehicle speed V When reaches a predetermined value, the steering ratio becomes zero and the front wheels _1L ,
Regardless of the steering of 1 _R , the steering angle θ _R of rear wheels 2 _L and 2 _R is θ _R =
0 and the vehicle enters normal two-wheel steering.
Furthermore, when driving at high speeds, the rear wheels _{2L and 2R} are moved in the same direction as the front wheels 1L and _1R in order to improve the grip force of the rear wheels _2L and _2R during cornering and increase running stability. In other words, the wheels are steered in the same phase, and the steering ratio is set to be positive. Then, the vehicle speed V detected by the vehicle speed sensor 102 is compared with this steering ratio characteristic to determine the target steering ratio corresponding to the vehicle speed V. In addition, FIG. 4 shows the characteristics of the rear wheel steering angle with respect to the steering wheel steering angle (rotation 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 when a predetermined steering wheel steering angle is applied. ing.

After that, in step _S3 , the operating speed dm/dt of the stepping motor 51 is set, and then the process proceeds to step _S4 , where the steering ratio of the front and rear wheels _1L and _2L reaches the target steering ratio set above. The stepping motor 51 is driven at the above-mentioned set speed dm/dt so that. That is, by driving the stepping motor 51, the sector gear 46 is rotated to change the inclination angle of the holder 34 with respect to the reference plane, and by changing the steering angle θ _R of the rear wheels 2 _L and 2 _R , the front and rear wheels 1 This is to variably control the steering ratio of _L and _2L to a target value.

Furthermore, in step _S5 , the signal of the rotation angle s of the sector gear 46 detected by the steering ratio sensor 101 (a value corresponding to the actual steering ratio of the front and rear wheels 1 _L and 2 _L ) is input, and the next step is started. In _S6 , the rotation speed ds/dt of the sector gear 46 as the speed of change of the steering ratio (steering ratio speed) is calculated based on the detected rotation angle S. After this, in step _S7 , the above steps are performed.
The operating speed dm/dt of the stepping motor 51 set in _S5 and the rotation speed calculated in step _S6
The absolute value of the difference from ds/dt |(dm/dt)−(ds/dt)| is calculated and the value is stored in memory a. Next, in step _S8 , it is determined whether the memory value a is larger than the first set value _a1 , and if a> _a1 , YES is determined.
If it is determined that the sector gear 46 hardly rotates even though a signal is being output to the stepping motor 51, it is assumed that the stepping motor 51 is completely out of step due to motor lock or the like. Proceeding to step _S9 , the electromagnetic on-off valve 28 is controlled to close the return spring 17 in the power cylinder 17.
By setting the steering angle θ _R of the rear wheels 2 _L and 2 _R to θ _R = 0 using the urging forces of d and 17 d, the steering ratio characteristic of the vehicle is forcibly changed to the two-wheel steering control characteristic as a fail-safe mode. to hold.

If it is determined in step _S8 that a≦ _a1 is NO, the process proceeds to step _S10 , where the memory value a is changed to a second set value _a2 smaller than the first set value _a1 . Compare the size with. When this determination is YES for a> _a2 , the stepping motor 51 is out of step, but it is considered that this is not a problem, and the process proceeds to step _S11 , where the rotation angle of the sector gear 46 is adjusted to the above level. Steering ratio sensor 10
Correction control is performed to drive the stepping motor 51 until the rotation angle s detected in step 1 is reached.

On the other hand, when it is determined in step _S10 that a≦ _a2 (NO), it is assumed that the stepping motor 51 is not out of step, and the routine advances to step _S12 to continue normal control regarding four-wheel steering.

Therefore, in this embodiment, the target steering ratios of the front and rear wheels 1 _L and 2 _L are set based on the steering ratio characteristics preset in steps S ₁ and S ₂ in the above-described control routine. A steering ratio setting means 103 is configured.

In addition, in the same step _S6 , the above-mentioned steering ratio sensor 1
A steering ratio speed detecting means 104 is configured to detect the rotational speed ds/dt of the sector gear 46 corresponding to the changing speed of the steering ratio detected by 01.

Furthermore, in steps S ₇ , S ₈ , and S ₁₀ , the rotational speed ds/dt (steering ratio speed) of the sector gear 46 detected by the steering ratio speed detection means 104 and the operating speed dm of the stepping motor 51 are determined. A step-out detection means 105 is configured to detect the step-out state of the stepping motor 51 by comparing the stepper motor 51 with /dt.

Further, in steps S ₉ and S ₁₁ , the output of the step-out detection means 105 is received, and the rotational speed ds/dt of the sector gear 46 and the operating speed of the stepping motor 51 are determined.
When the difference from dm/dt is larger than the first set value a ₁ , the steering characteristics of the vehicle are forcibly corrected to the two-wheel steering state, and when the difference is less than the first set value a ₁ , the second set value is adjusted. Stepping motor 5 when larger than a ₂
Correction means 1 configured to perform correction control for 1
06 is configured.

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

First, in order to drive a vehicle that is out of service,
When the ignition key switch is turned on, the initial control position of the stepping motor 51 is determined accordingly. Thereafter, when the vehicle shifts to a running state, the vehicle speed V at that time is detected by the vehicle speed sensor 102, a detection signal is output from the vehicle speed sensor 102 to the control unit 100, and the steering ratio setting means 103 of this control unit 100 A target steering ratio corresponding to the vehicle speed V is calculated by comparison with the steering ratio characteristics, and a pulse signal corresponding to this target steering ratio is output to the stepping motor 51, so that the motor 51 adjusts to the set speed.
Driven by dm/dt. The sector gear 46 is rotated by the drive of this motor 51.
The slope of the swing locus plane of the swing arm 36 connected to the swing arm 36 is changed relative to the reference plane, and this change affects the operation of the steering wheel 10, that is, the front wheels _1L , _1R.
The direction and distance of movement of the control rod 33 relative to the movement of the connecting rod 39, which rotates around the moving axis _l1 , changes in conjunction with the steering of the rear wheel. 2 _L and 2 _R are steered while being assisted by the power cylinder 17 of the power steering mechanism 16 so that the front wheels 1 _L and 1 _R reach the target steering ratio calculated above. This allows the vehicle's 4
The wheels 1 _L to 2 _R are controlled so that when the vehicle speed is low, the steering ratios are in opposite phases, and when the vehicle speed is high, the steering ratios are in the same phase.

Also, during the control of the stepping motor 51, the steering ratio sensor 101 detects the front and rear wheels _1L ,
The above sector gear 4 corresponds to the actual steering ratio of _2L .
The rotation angle s of 6 is detected, the rotation speed ds/dt of the sector gear 46 is calculated by the steering ratio speed detection means 104 in the control unit 100, and the rotation speed ds/dt is calculated by the step-out detection means 105.
ds/dt and the operating speed of the stepping motor 51
Set values a ₁ , a ₂ (a ₁ >
a ₂ ), and if the absolute value of the difference a is less than the second set value a ₂ , the stepping motor 5
1, it is determined that there is no step out, and the above-mentioned control is continued as it is, and the steering characteristics of the vehicle are controlled to the four-wheel steering characteristics.

Furthermore, when the absolute value a of the difference is greater than the second set value _a2 but less than the first set value _a1 , it is determined that the stepping motor 51 is out of step to a degree that does not cause any trouble. , the steering characteristic of the vehicle is controlled to the four-wheel steering characteristic by the correction means 106, and the correction means drives the stepping motor 51 so that the rotation angle of the sector gear 46 becomes the value s detected by the steering ratio sensor 101. Control takes place.

However, when the absolute value a of the difference is larger than the first set value _a1 , the stepping motor 51 is in an uncorrectable out-of-step state due to motor lock, etc., and the stepping motor 51 is in an out-of-step state that cannot be corrected due to motor lock or the like. valve 2
8 is opened, the steering angle θ _R of the rear wheels 2 _L and 2 _R is maintained at θ _R = 0 by the biasing force of the return springs 17 d and 17 d in the power cylinder 17, and the steering characteristics of the vehicle are forcibly changed. It is maintained under two-wheel steering control.

In this case, the operating speed dm/dt of the stepping motor 51 is compared with the rotational speed ds/dt of the sector gear 46 corresponding to the actual steering ratio of the front and rear wheels _1L , _2L , and based on the result, Stepping motor 5
Since the presence or absence of a step-out condition is determined in step 1, the step-out condition is lower than when comparing the output value of the target steering ratio to the stepping motor 51 and the actual steering ratio (rotation angle S of the sector gear 46). When the ping motor 51 goes out of step, it can be quickly detected, and the steering characteristics of the vehicle can be immediately corrected to a two-wheel steering state.
Therefore, the running stability of the vehicle can be further improved.

In the above embodiment, the stepping motor 51
operating speed dm/dt and rotation speed of sector gear 46
The out-of-step state of the stepping motor 51 is detected by comparing the speed with A method of detecting an out-of-step state of the stepping motor 51 by comparing the magnitude with the actual steering ratio can also be used. In this case, there is an advantage that an out-of-step state of the stepping motor 51 can be detected more reliably.

In addition, in the above embodiment, the front and rear wheels 1 _L and 2 _L of the vehicle are
Although the case where the application is applied to a four-wheel steering system in which the steering ratio of the steering wheel is variably controlled according to the vehicle speed V has been exemplified, the present invention is also applicable to a four-wheel steering system in which the rear wheels are directly driven by a stepping motor according to the steering angle of the front wheels. The present invention can also be applied to a four-wheel steering system.

Further, in the above embodiment, the stepping motor 51 was used as an actuator to control the steering ratio of the front and rear wheels 1 _L and 2 _L , but in the present invention, the steering ratio is controlled by another actuator such as a DC motor. It is also possible to apply the present invention to a four-wheel steering system.

(Effects of the Invention) As explained above, according to the present invention, in a four-wheel steering system for a vehicle in which the front and rear wheels are steered by operating a steering wheel, the steering ratio of the front and rear wheels is set in advance. Control is performed by operating an actuator such as a stepping motor based on the steering ratio characteristics, and the actual speed of change in the steering ratio is detected, and the actuator is determined by comparing the steering ratio speed with the size of the actuator. By detecting an out-of-step state and forcibly correcting the vehicle's steering characteristics to a two-wheel steering state, etc., when the actuator steps out, it can be detected quickly and immediately corrected to a two-wheel steering state, etc. Therefore, it is possible to improve the responsiveness of transition to the fail-safe mode when the actuator is out of synchronization.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention. 2 to 6 show embodiments of the present invention, and FIG. 2 is a plan view schematically showing the overall configuration of a four-wheel steering device;
Fig. 3 is a skeleton diagram showing the rear wheel steering mechanism and steering ratio control mechanism in a perspective state, Fig. 4 is a characteristic diagram illustrating the characteristics of the rear wheel steering angle with respect to the steering wheel angle when the vehicle speed changes, and Fig. 5 is a FIG. 6 is a characteristic diagram showing steering ratio characteristics with respect to vehicle speed at a predetermined steering angle of the steering wheel. FIG. 6 is a flowchart showing a control procedure for the stepping motor and the electromagnetic on-off valve processed by 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, 28...
Electromagnetic on-off valve, 32... Steering ratio control mechanism, 46...
Sector gear, 51...Stepping motor, 10
0... Control unit, 102... Vehicle speed sensor, 103... Steering ratio setting means, 104... Steering ratio speed detection means, 105... Step-out detection means, 1
06...Correction means, dm/dt...Motor operating speed,
ds/dt...Sector gear rotation speed.

Claims (1)

[Claims] 1. A four-wheel steering device for a vehicle configured to steer both the front wheels and the rear wheels, comprising a steering ratio setting means for setting a target steering ratio for the front and rear wheels based on preset steering ratio characteristics; , an actuator that receives the output of the steering ratio setting means and controls the steering ratio of the front and rear wheels to the target steering ratio; and a steering ratio that detects the actual steering ratio speed controlled by the actuator. a speed detecting means; a step-out detecting means for detecting a step-out state of the actuator by comparing the steering ratio speed detected by the steering ratio speed detecting means with the operating speed of the actuator; and the step-out detecting means. and a correction means for forcibly correcting the steering characteristics of the vehicle to a predetermined characteristic when the difference between the steering ratio speed and the operating speed of the actuator is larger than a predetermined value. A four-wheel steering system for vehicles that