JPS63170171A - Four-wheel steering gear for vehicle - Google Patents

Abstract

PURPOSE:To aim at the promotion of properness in transition to a stable side control mode, by driving an actuator as long as the specified time at the time of detecting the actuator step-out by a comparison between a desired steering ratio and a detected steering ratio, and making it rejudge the transition to the stable side control mode on the basis of the subsequent state. CONSTITUTION:In this steering gear, there is provided with a steering ratio setting means 103 which sets each desired steering ratio of both front and rear wheels on the basis of the preset steering ratio characteristic, and an actuator 51 is driven by the output, then each steering ratio of these front and rear wheels is controlled so as to become the desired steering ratio. In this case, there is provided with a step-out detecting means 104 which detects a step-out state of the actuator by comparing the actual steering ratio controlled at the actuator 51 with the desired steering ratio. And, at the time of step-out detecting, the actuator 51 is driven as long as the specified time so as to cause the steering ratio to become the desired steering ratio by an actuator additional driving means 105, while afterward, when it is so judged that the steering ratio has not accorded with the desired steering ratio, a steering characteristic is compensated to a two-wheel steering state by a compensating means 106.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a four-wheel steering device that steers the front and rear wheels of a vehicle, and particularly 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 significantly 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 ratios are kept in the same phase and the steering characteristics are changed to understeer characteristics. This cover ensures the running stability of the vehicle.

As an example of this four-wheel steering system,
Japanese Patent No. 193770 proposes an actuator in which a stepping motor (pulse motor) is used to variably control the steering ratio of front and rear wheels.

Specifically, the movable member is connected to a rear wheel steering mechanism that steers the rear wheels of the vehicle and is movable in a predetermined movement axis direction, and the movable member swings with a swing center located on the movement axis of the moving member. A swinging arm called a swash plate, a connecting member that connects the swinging arm and the moving member, and a front wheel steering mechanism that steers the front wheels of the vehicle, and the connecting member is connected to the moving axis of the moving member. By providing a rotation imparting arm that rotates around the rotating member, and changing the inclination angle of the swinging center line of the swinging arm with respect to the movement axis of the moving member using a stepping motor,
It is designed to change the steering ratio of the front and rear wheels.

(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 above proposal, an excessive load is generated due to the stick of the gear mechanism that transmits the rotational force of the motor. The stepping motor goes out of step (
There is a risk that the target steering ratio may not be accurately obtained, and there is room for improvement in terms of stability.

For this reason, the actual steering ratio controlled by the stepping motor and the target steering ratio for the stepping motor are compared, and the difference is determined to be at a predetermined level set due to variations in detection accuracy of the steering ratio detection means. A possible countermeasure would be to forcibly correct the steering ratio to the stable side immediately when the detection width is exceeded, similar to the situation in which the stepping motor is out of step.

However, in reality, the running stability of a vehicle becomes a problem when the steering ratios of the front and rear wheels are in the opposite phase region and the steering characteristics become oversteer characteristics that are difficult to control. The risk at some point is relatively small. From this,
As described above, if the stepping motor is always uniformly corrected to the stable side during tax adjustment, it will inevitably switch to two-wheel steering, making it impossible to perform stable four-wheel steering control. Incidentally, such a problem similarly occurs even when an actuator such as a DC motor (direct current motor) is used in addition to the stepping motor.

(Objective of the Invention) The present invention has been made in view of the above points, and its purpose is not to immediately correct to the stable two-wheel steering control mode when the actuator step-out is detected, but to
By covering it so that the prescribed steps are taken in the meantime,
To avoid unnecessary correction to a two-wheel steering control mode when stability can be ensured even if a step-out occurs when the vehicle is running, and thereby to optimize the transition to a stable control mode.

(Means for solving the problem) In order to achieve this object, the solution taken by the present invention is to further drive the actuator to compensate for the step-out state when an actuator step-out is detected. The system is configured to determine whether to shift to a stable control mode based on the state of the drive speed.

That is, 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 in accordance with the operation of a steering wheel. Based on the target steering ratio f (V) of the front and rear wheels
and an actuator 51 such as a stepping motor that receives the output of the steering ratio setting means 103 and controls the steering ratio of the front and rear wheels to the target steering ratio f (V). In addition, an out-of-step detection means 104 is provided for detecting an out-of-step state of the actuator 51 by comparing the actual steering ratio controlled by the actuator 51 with the target steering ratio f (V).

Roughly speaking, upon receiving the output of this step-out detection means 104, when the actuator 51 steps out, the steering ratio K reaches the above-mentioned value '+H'I.
The actuator 5
Actuator additional drive means 10 for driving 1 between predetermined parts
5, the steering ratio K is set to the target steering ratio f by driving the actuator 51 in the actuator additional drive means 105.
(V), the correction means 106 corrects the steering characteristics of the vehicle to a two-wheel steering state when it is determined that they do not match.

(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 based on the steering ratio characteristics by the steering ratio detection means 103 by the operation of the actuator 51. The steering ratio is controlled to be f (V).

Then, the actual steering ratio K controlled by this actuator 51 is compared with the target steering ratio f (V) for the actuator 51 in the tax adjustment detection means 104, and the difference in f (V) between the two steering ratios is determined. When is larger than a predetermined level, it is determined that the actuator 51 is in the adjusted state.

When such step-out is detected, the actuator additional drive means 105 additionally drives the actuator 51 for a predetermined time so that the actual steering ratio K becomes the target steering ratio f(■), and the actuator 51 is driven. As soon as the actual steering ratio K matches the target steering ratio f (V), the steering characteristics of the vehicle are maintained in the four-wheel steering state. When the steering ratio K does not match the target steering ratio f(V), it is determined that the actuator 51 is in a tax adjustment state that cannot be corrected, and the correction means 106 forcibly changes the steering characteristics of the vehicle to a two-wheel steering state. Correction controlled.

Therefore, even if the step-out detection means 104 detects that the actuator 51 is out of step, the steering control mode is not immediately shifted to the stable two-wheel steering control mode, and the steering ratio is adjusted by additionally driving the actuator 51. K is the target steering ratio f
(V), it is possible to avoid unnecessary transition to a stable control mode in a steering ratio range in which running stability of the vehicle is ensured.

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

In FIG. 2, 1L to 2R are four wheels of the vehicle, and the left and right front wheels IL and 1R are linked by a front wheel steering mechanism 3, and the left and right rear wheels 2L and 2R are linked by a rear wheel steering mechanism 12. ing.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms 4L.
, 4R, tie rods 5L, 5R, and a relay rod 6 that connects the left and right tie rods 5L, 5R. In addition, a steering wheel 1 is connected to this front wheel steering device fS3 via a rack and pinion type steering mechanism 7.
0 is linked. The relay rod 6 has a rack 8 formed thereon, and a steering shaft 11 to which a steering wheel 10 is connected at the upper end.
A pinion 9 that engages with the rack 8 is attached to the lower end of the vehicle, and is configured to steer the left and right front wheels IL and 1R in accordance with the operation of the steering wheel 10.

On the other hand, the rear wheel steering device 'ti 12 is the front wheel steering device E.
3, the left and right suspension arms 13L, 13R and tie rods 14L, 14R, and the tie rod 1
It has a relay rod 15 that connects 4L and 14R, and is further provided with a hydraulic power steering mechanism 16. The power steering device 4M16 includes a power cylinder 17 that is fixed to the vehicle body and covers the relay rod 15 with a piston rod, and inside the power cylinder 17 is a piston 1 that is integrally attached to the relay rod 15.
7a into two hydraulic chambers 17b and 17c, and the hydraulic chambers 17b and 17C in the cylinder 17 are connected to the control valve 2 via hydraulic piping 18 and 19, respectively.
Connected to 0. In addition, the control valve 20
Two pipes, an oil supply pipe 22 and an oil discharge pipe 23, leading to a reserve tank 21 are connected to the oil supply pipe 22, and a hydraulic pump 24 driven by an on-vehicle engine (not shown) is disposed in the oil supply pipe 22. The control valve 20 is constructed of a known spool valve type, and includes a cylindrical valve casing 20a integrally attached to the relay rod 15 via a connecting portion 'rA 25;
A spool valve (not shown) fitted in the valve casing 2Oa is depicted, and one hydraulic chamber 17b (1) of the power cylinder 17 is moved as the spool valve moves.
7c) is supplied with pressure oil from the hydraulic pump 24 to assist the driving force for the relay rod 15.

In addition, the relay rod 15 is placed in the neutral position (rear wheel 2L) through the piston 17a in the power cylinder 17.
, 2R, a pair of return springs 17d bias the steering angle θR to a position where the steering angle θR is zero.

17d has been reduced. In addition, the above hydraulic piping” 8.1
9 are connected to a normally open electromagnetic on-off valve 28 via hydraulic pipes 26 and 27, respectively, and when this electromagnetic on-off valve 28 is opened, both pressure chambers 17b of the power cylinder 17,
The return spring 17d uses the same pressure as the oil pressure in 17c.
, 17d positions the piston 17a at a neutral position, and the steering angle θR of the rear wheels 2L and 2R is always set to θR=0, so that the steering characteristic of the vehicle is brought into a two-wheel steering state.

The relay rod 6 of the front wheel steering mechanism 3 is equipped with a rack 2 other than the rack 8 constituting the steering mechanism 7.
9 is formed, and a pinion 30 attached to the front end of a rotating shaft 31 extending in the longitudinal direction of the vehicle body is engaged with the rack 29, and the rear end of the rotating shaft 31 is connected to the rear end via the steering ratio control I mechanism 2. It is linked to the wheel steering opening groove 12.

As shown in detail in FIG. 3, the steering ratio control mechanism 32 includes a control rod 33 that is movably held on a movement axis rQfJl in the vehicle width direction with respect to the vehicle body. One end of the control rod 33 is connected to the spool valve of the control valve 20. Further, the steering ratio controller 8S32 has a base end movably attached to a U-shaped holder 34 via a support pin 35. Supported swinging arm 36
The holder 34 has a casing (
movement of the control rod 33 @II (not shown)
It is rotatably supported via a support shaft 37 having a rotation axis fJ2 perpendicular to line B1. The support pin 35 of the swing arm 36 is connected to both axes, l! 1. Located at the intersection of ρ2, the rotation axis, l! It extends in the direction perpendicular to 2,
By rotating the holder 34 around the support shaft 37 (rotation axis N2), the movement axis of the support pin 35 at the tip and the control rod 33, l! 1, that is, the angle of inclination that the swinging locus plane of the swinging arm 36 centered on the support pin 35 makes with respect to a plane perpendicular to the movement axis 11 (hereinafter referred to as W i:% plane). It is made to do.

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 control rod 39 via a ball joint 40.
The control rod 33 is connected to the other end, and is configured to displace the control rod 33 in the left-right direction in response to 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 thereof close to the ball joint 38 . The rotation imparting arm 41 is provided integrally with a large-diameter bevel gear 44 rotatably supported on the movement axis 11 via a support shaft 43, and the bevel gear 44 is attached to the rear end of the rotation shaft 31. A bevel gear 45 attached to the steering wheel 10 is meshed with the bevel gear 45 so that the rotation of the steering wheel 10 is transmitted to the rotation imparting arm 41. Therefore, the arm 41 and the three connecting rods rotate by an amount corresponding to the rotation angle of the steering wheel 10, and the moving axis, l! When the swing arm 36 swings around the support pin 35, the axis of the pin 35 becomes the movement axis of the control rod 33, l! 1, the ball joint 38 at the tip of the swing arm 36 only swings on the reference plane, and the control rod 33
is held stationary, but if the axis of the pin 35 is inclined with respect to the movement @ line gl and the swing locus plane of the swing arm 36 deviates from the reference plane, the swing arm 3 around this pin 35 will move.
6, the ball joint 38 is displaced to the right in FIG.
9 to the control [1-rule rod 33, which =
The control rod 33 is configured to move along the axis of movement, Il+, to actuate the spool valve of the control valve 20. Support pin 3
Even if the vibration angle of the swing arm 36 about the axis 5 remains the same, the displacement of the control rod 33 in the left-right direction changes as the inclination angle of the pin 35, that is, the rotation angle of the holder 34 changes.

In order to change the inclination angle of the support pin 35 with respect to the movement axis p1, that is, the inclination angle of the holder 34 with respect to the reference plane, a sector gear 46 as a worm wheel is attached to the support shaft 37 of the holder 34. A worm gear 48 on a rotating shaft 47 is engaged with the worm gear 46 .

Further, a bevel gear 49 is attached to the rotating shaft 47,
This bevel gear 49 has a bevel gear 50 attached to the output shaft 51a of a stepping motor 51 as an actuator.
are engaged with each other, and by operating the stepping motor 51 and rotating the sector gear 46, the holder 34
Controls the steering angle θR of the rear wheels 2L, 2R, that is, the steering ratio (rear wheel steering angle θR/front wheel steering angle θF) of the front and rear wheels 1L, 2L (1R, 2R) by changing the inclination angle with respect to the reference plane. death,
For example, if the sector gear 46 is the center line of the worm gear 4,
8 rotations! ! 1147, the ball joint 38 at the tip of the moving arm 36 rotates about the reference plane, and the steering angle θR of the rear wheels 2L and 2R is θR= When the steering ratio of the front and rear wheels IL and 2L is rotated in one direction from 0 to When the vehicle is rotated in the direction, the steering ratio is controlled so that the rear wheels 2L, 2R are in the same phase as the front wheels IL, IR in the same direction.

Further, the support shaft 37 of the holder 34 is provided with a steering ratio sensor 101 comprising a potentiometer that detects the actual steering ratio R controlled by the stepping motor 51 based on the rotation angle of the sector gear 46. ing. In addition, on the mounting that supports the holder 34, there are pins J on both left and right sides of the sector gear 46 that regulate and control the rotation range of the sector gear 46: stoppers on the opposite phase side and the same phase side. Members 52 and 53 are attached so that 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 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
The control unit 100 includes a vehicle speed sensor 102 that detects the traveling speed V (vehicle speed) of the vehicle, and an output from the steering ratio sensor 101. Each detection signal 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 with reference to FIG.

First, in the first step S1 after starting, the vehicle speed sensor 1 is
02 is input, and in the next step S2, the front and rear wheels IL, 2L (1R,
2R) is set. 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 1L and 2L depending on the vehicle speed V, and when the vehicle speed V is low, the turning of the vehicle changes. To improve sex,
When the rear wheels 2L and 2R are steered in the opposite direction to the front wheels 1m and 1R, that is, in the opposite phase, the steering ratio becomes negative, and the vehicle speed V
When reaches a predetermined value, the steering ratio becomes zero and the front wheel 1
Regardless of the steering of L and 1R, the steering angles θR of the rear wheels 2L and 2R are maintained at 0R=O, and the vehicle enters the normal two-wheel steering state.

Furthermore, in the case of high-speed driving, the rear wheel 2L for cornering
In order to improve the grip of 2R and increase running stability, the rear wheels 2L and 2R are steered in the same direction as the front wheels 1m and 1R, that is, in the same phase, so that the steering ratio is positive. has been done. Then, the vehicle speed sensor 1
The target steering ratio f (V) corresponding to the vehicle speed V is determined by comparing the vehicle speed V detected at 02. Furthermore, the fourth
The figure shows the characteristics of the rear wheel steering angle with respect to the steering wheel angle (rotation angle of the steering wheel 10) that changes when the vehicle speed changes.
FIG. 5 shows steering ratio characteristics with respect to vehicle speed at a predetermined steering angle.

After this, in step S3, the front and rear wheels 1L.

The stepping motor 51 is driven so that the steering ratio of 2L becomes the target steering ratio f (V) set above.

In other words, by rotating the J stiff sector gear 46 to drive the stepping motor 51, changing the inclination angle with respect to the block 4 (surface) of the holder 34, and changing the turning angle OR of each wheel 2L, 2R, The steering ratio of the front and rear wheels 1L and 2L is variably controlled to a target value f (V).Furthermore, in step S4, a signal indicating the actual steering ratio of the front and rear wheels detected by the steering ratio sensor 101 is sent. In the next step S5, it is determined based on this detected steering ratio K whether the steering ratio is in the opposite phase side region (the lower region of the characteristic diagram shown in FIG. 5).This determination is YES. , step S
Proceeding to step 6, the magnitude of the steering ratio detected by the steering sensor 101 and the target value f (V) is determined, and f (
When it is determined that NO9 of V)≦, that is, the steering ratio is on the same phase side (upper side in the figure) than the steering ratio characteristic line L in FIG. Continue normal steering control. Also, the determination is YES if f'(V)>K.

In other words, when it is determined that the steering ratio is on the opposite phase side (lower side) than the steering ratio characteristic line L, the electromagnetic on-off valve 2B is opened in step S8, and the power cylinder 17 is opened.
By setting the turning angle θR of the rear wheels 2L and 2r to on=o by the biasing force of the return springs 17d and 17d inside, the steering characteristic of the vehicle is forcibly maintained at the two-wheel steering control characteristic. mode.

On the other hand, in step S5, the steering ratio is in the same phase side region (fifth
If it is determined that the upper region 1gC of the characteristic diagram shown in the figure is present, the process proceeds to step S9, and similarly to step S6, the steering ratio detected by the steering ratio sensor 101 is set to the target value "(
■) Determine the size.

If it is determined that I' (V)≦ is NO, the process advances to step 312 and normal control regarding four-wheel steering is continued, while if f (V)>K is YES, step SIG Then, the stepping motor 51 is additionally driven by the difference between both steering ratios f(V). By this additional drive of the stepping motor 51, the actual steering ratio K is adjusted to the target steering ratio f (V). In step 3o, the target steering ratio f
(V) and the actual steering ratio, and when this judgment is determined as f(V)≦No, the actual steering ratio K is adjusted to the target steering by the)B addition drive of the stepping motor 51. It is assumed that the ratio f (V) matches, and the step S12 described above is performed.
Proceed to.

Furthermore, when it is determined in step So that f (V)>K is YES, it is assumed that the steering ratio K has not been adjusted to the target steering ratio f (V) despite the additional drive of the stepping motor 51. Then, the process proceeds to step S13, and it is determined whether or not the procedures of steps 31G and So have been repeated a predetermined number of times N or more. Through such a flow, the additional driving of the stepping motor 51 is continued for a predetermined period of time. If the determination in step 313 is No, the process returns to step SIG, whereas if the result is YES, the process proceeds to step 314, where the steering characteristics of the vehicle are forced by operating the electromagnetic on-off valve 28 in the same manner as in step S8. Generally, the two-wheel steering control characteristics are maintained.

Therefore, in this embodiment, the target steering ratio f (V) of the front and rear wheels 1L and 2L is determined in steps S+ and S2 in the above-described control routine based on the preset steering ratio characteristics.
A steering ratio setting means 103 is configured to set the steering ratio.

Further, in the same step Ss, 39, when the actual steering ratio K controlled by the stepping motor 51 is in the same phase side region, the target steering ratio f is set to the actual steering ratio K controlled by the stepping motor 51.
(V) to detect the step-out state of the stepping motor 51.

Further, in step SIO* S++ + 313, the output of the step-out detection means 104 is received, and when the stepping motor 51 is out of step, the steering ratio K is set to the target steering ratio f(
An additional actuator driving means 105 is configured to drive the stepping motor 51 for a predetermined period of time so as to achieve the following.

Further, in step Sll*814, the additional drive of the stepping motor 51 by the actuator additional drive means 105 causes the steering ratio K to become the target steering ratio f (V).
A correction means 106 is configured to forcibly correct the 1h steering behavior of the vehicle to a 2-wheel steering state when the 1h steering behavior does not match.

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

First, when an ignition key switch is turned on to drive a vehicle that is not in use, the initial control position of the stepping motor 51 is determined accordingly. Thereafter, when the vehicle shifts to a running state, the next vehicle speed 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, and the steering ratio of the control unit 100 is 52 In the constant means 103, a target steering ratio f (V) corresponding to the vehicle speed V is calculated by comparison with the steering ratio characteristic, and a pulse (No. 8 is a stepping motor) corresponding to this target steering ratio f (V) is calculated. 51 to drive the motor 51. The drive of the -E-taper 51 causes the sector gear 46 to be driven.
is rotated and connected to the sector gear 46 so that the swing locus plane of the swing arm 36 (Q') is changed in inclination with respect to the reference plane,
This change changes the moving direction and moving distance of the control rod 33 in response to the movement of the connecting rod 39, which rotates around the movement axis fJ1 in conjunction with the operation of the steering wheel 10, that is, the steering of the front wheels IL and 1R. The movement of the control rod 33 caused trouble, and the rear wheel 2
Adjust the power steering height 1 so that L and 2R have the steering ratio f (V) calculated above for the front wheel 11.1R.
The vehicle is steered while being assisted by the power cylinder 17 of No.6. As a result, the four wheels 1L to 2R of the vehicle are controlled so that the steering ratios are in opposite phases when the vehicle speed is low, and the steering ratios are in the same phase when the vehicle speed is high.

During control of the stepping motor 51, the actual steering ratio K is detected by the steering ratio sensor 101 based on the rotation angle of the sector gear 46, and the detected steering ratio is detected by the step-out detection means 104 in the control unit 100. The magnitude of the ratio and the target steering ratio f (V>) is determined, and when the steering ratio K is greater than or equal to the target steering ratio f (V), it is determined that the stepping motor 51 is not out of step. , the above-described control is continued as it is, and the steering characteristics of the vehicle are controlled to be the four-wheel steering characteristics.

On the other hand, when the actual steering ratio K is smaller than the forward steering ratio f (V), it is determined that the stepping motor 51 is out of step. In that case, the subsequent processing differs depending on the above-mentioned steering ratio range, and when the steering ratio is in the opposite phase range where it is likely to be dangerous for the vehicle to run, the process is performed in order to ensure the running stability of the vehicle. , it will immediately go into failsafe mode. That is, the electromagnetic on-off valve 28 is opened and the return spring 1 in the power cylinder 17 is opened.
The steering angle θ of the rear wheels 2L and 2R is determined by the urging forces of 7d and 17d.
R is maintained at 0R=O, the steering characteristics of the vehicle are forcibly maintained under two-wheel steering control, and the running stability of the vehicle can be improved by this two-wheel steering control.

On the other hand, when the steering ratio is in the same phase range where stability can be ensured, the actuator additional drive means 105 drives the stepping motor 51 for a predetermined time so that the steering ratio K becomes the target steering ratio f (V). After this additional driving of the stepping motor 51, the magnitude of the steering ratio and the target steering ratio f (V) is determined again, and the steering ratio K is set to the target steering ratio f (V).
Once the steering ratio K matches the target steering ratio f(V), additional driving of the stepping motor 51 causes the steering ratio K to match the target steering ratio f(
It is assumed that the correction has been made to V), and the steering characteristics of the vehicle are maintained as they are as four-wheel steering characteristics.

However, an additional layer of the stepping motor 51 due to the actuator additional drive means 105! Even after vI, when the steering ratio K is still smaller than the target steering ratio f (V),
It is assumed that the stepping motor 51 is in a state where an uncorrectable step-out condition such as motor rotation has occurred, and the electromagnetic on-off valve 28 is opened by shifting the steering control to the 7-fail safe mode by the operation of the correction means 106. The steering characteristics of the vehicle are forcibly maintained under two-wheel steering control.

Therefore, in this embodiment, when the steering ratios of the front and rear wheels 1L and 2L are in the same phase range where the degree of instability is low in terms of vehicle running, even if the stepping motor 51 is out of synchronization, the steering characteristics immediately change to 2. Without shifting to the fail-safe mode in which the wheel steering state is maintained, the steering ratio K is temporarily set to the target steering ratio f (
The stepping motor 51 is additionally driven for a predetermined time so that the steering ratio K becomes the target steering ratio f.
Since the transition to the fail-safe mode is made only when (V) does not match, the steering control of the vehicle does not unnecessarily transition to the fail-safe mode, and therefore the transition to the fail-safe mode can be optimized. .

In the above embodiment, when the stepping motor 51 is additionally driven when the stepping motor 51 detects the tax adjustment,
In the control routine of the control unit 100,
Although the additional driving time of the stepping motor 51 is set to a constant value by the number of repetitions of steps S+o and 3o, even if the additional driving time is set by a timer, J:<, the same effect as in the above embodiment is obtained. You can aim for the effect. For example, in the control routine described in section 2, a step for starting a timer may be added after step S9, and the correction may be made such that the elapsed time between the timer units is determined in step 313.

Further, in the above embodiment, the case where the steering ratio of the front and rear wheels 1L to 2R of the vehicle is variably controlled in accordance with the vehicle speed V has been exemplified. The present invention can also be applied to a four-wheel steering system that is directly driven by a stepping motor depending on the steering angle of the steering wheel.

Further, in the above embodiment, the stepping motor 51 is used as an actuator for controlling the steering ratio of the front and rear wheels 1L, 2L.
However, the present invention can also be applied to a four-wheel steering system in which the steering ratio is controlled by other actuators such as a DC motor.

(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 steering ratio and target steering ratio are compared to detect the adjustment state of the actuator. The actuator is further driven so that the steering ratio becomes the target steering ratio, and the steering characteristics of the vehicle are corrected to the two-wheel steering state only when the two steering ratios do not match even after this drive. When the steering ratio adjustment of the actuator is detected in the steering ratio range where driving stability can be ensured, it is possible to avoid unnecessary correction of the steering characteristics of the vehicle to the two-wheel steering state. This makes it possible to appropriately shift the steering control to the fail-safe mode.

[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, FIG. 2 is a plan view schematically showing the overall configuration of a four-wheel steering device, and FIG. 3 is a rear wheel steering mechanism and steering ratio control la structure. Figure 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 Figure 5 shows the steering ratio characteristics with respect to the vehicle speed at a predetermined steering angle. Characteristic diagram,
FIG. 6 is a flowchart showing the control procedure for the stepping motor and the electromagnetic on-off valve processed in the control unit. 1L, 1r<... front wheel, 2, 2rs... rear wheel,
3... Front wheel steering mechanism, 12... Rear wheel steering mechanism, 28
... Solenoid on-off valve, 32 ... Steering ratio control mechanism, 51.
...Stepping motor, 100...J control unit, 101...Steering ratio sen 1, '102...
Vehicle speed sensor, 103... Steering ratio setting means, 104...
- Step-out detection means, 105... Actuator additional drive means, 106... Correction means, K... Detection steering ratio, f
(V)...Target steering ratio.

Claims (1)

[Claims] (1) 4 vehicles in which the rear wheels are steered along with the front wheels
A wheel steering device, comprising: a steering ratio setting means for setting a target steering ratio of 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 an actuator that controls the actual steering ratio controlled by the actuator and the target steering ratio. Out-of-step detection means for detecting an out-of-step state of the actuator by comparison; and an out-of-step detection means that receives the output of the out-of-step detection means and operates the actuator for a predetermined time so that the steering ratio becomes the target steering ratio when the actuator is out of step. The present invention further comprises: an additional actuator drive means for driving the actuator; and a correction means for correcting the steering characteristic of the vehicle to a two-wheel steering state when the steering ratio does not match the target steering ratio due to driving of the actuator by the additional actuator drive means. 4 featured vehicles
Wheel steering device.