JPS63151577A - Four-wheel steering apparatus for vehicle - Google Patents

Abstract

PURPOSE:To prevent the steering characteristics of a steering ratio from being varied from the basic characteristics due to the initialization of an actuator by forcedly maintaining the steering characteristics of a vehicle in a fixed characteristic from the starting of the initalization of the actuator to the completion thereof. CONSTITUTION:A four-wheel steering apparatus is provided with an initializing means 103, which positions the control position of an actuator 51 at a fixed initial position when the ignition key switch of a vehicle is set to ON, and a steering ratio controlling means 104 which, after the initializing means 103 is operated, sets a target steering ratio for the front and rear wheels according to a fixed steering ratio characteristic, and at the same time, operates the actuator 51 so that the steering ratios for the front and rear wheels attain to the target steering ratio. If the key switch is set to OFF before it is set to ON under a coasting operation or the like, the initialization of the actuator is started as the key switch is restored to the ON state, and then, a solenoid valve 28 is operated so that the steering ratio characteristics of the vehicle is switched to the twowheel steering characteristics, and further, such a condition is continued until the initialization of the actuator is completed.

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. This invention relates to measures for correcting four-wheel steering control.

(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. It is designed to ensure the running stability of the vehicle.

As an example of this four-wheel steering device,
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) By the way, due to the characteristics of the above-mentioned stepping motor, it is necessary to perform so-called initialization in which the control position is positioned at a predetermined initial position prior to actual operation control. This is normally performed when the vehicle's ignition key switch is turned on.

Since this ignition key switch is turned on when the vehicle is stopped, the initial position of the stepping motor is set to the maximum value on the opposite phase side corresponding to when the steering ratio is vehicle speed = 0. is possible.

However, when the initial position of the motor upon turning on the ignition key switch of the vehicle is set to the maximum value on the opposite phase side of the steering ratio, the following problem occurs. In other words, if the ignition key switch is turned OFF to perform coasting operation while the vehicle is running, and then turned ON again, or if a contact failure occurs in the ignition system for some reason and the ignition key switch is turned OFF. If the ON state is returned to the ON state, the stepping motor will be initialized and the steering ratio will change to the maximum value on the opposite phase side, even though the vehicle is running. There is a risk that the steering characteristics of the vehicle may change from the basic characteristics, resulting in a situation that is difficult for the occupants to deal with. In particular, in the latter case of poor contact, etc., the motor is initialized without the occupant being aware of it, which causes a great sense of anxiety to the occupant, so it is preferable to improve the system in order to ensure safety.

Incidentally, even when an actuator other than the above-mentioned stepping motor is used, such as a DC motor, the same problem as above occurs.

(Object of the invention) The present invention has been made in view of the above points, and its object is to turn off the ignition key switch while the vehicle is running.
When the initialization of the actuator starts with switching from the ON state to the ON state, the steering characteristics of the vehicle are forcibly maintained at the predetermined characteristics until the initialization is completed, thereby initializing the actuator. The purpose of this invention is to eliminate the change in steering characteristics from the basic characteristics due to the steering ratio changing to the maximum value on the opposite phase side, thereby further improving the running safety of the vehicle.

(Means for Solving the Problem) In order to achieve this object, the solution of the present invention is to change the steering characteristics of the vehicle to the two-wheel steering characteristics when the actuator is initialized while the vehicle is running. The above correction is canceled after the initialization is completed.

Specifically, as shown in FIG. 1, the present invention provides a four-wheel steering system for a vehicle that steers both the front and rear wheels.
An actuator 51 such as a stepping motor that changes the steering ratio of the front and rear wheels, and an initialization means 10 that positions the control position of the actuator 51 to a predetermined initial position when the ignition key switch of the vehicle is turned on.
3, after the initialization means 103 operates, the target steering ratios of the front and rear wheels are set based on the predetermined steering ratio characteristics, and the above-mentioned steps are performed so that the steering ratios of the front and rear wheels become the target steering ratio. It is assumed that the steering ratio control means 104 for controlling the operation of the actuator 51 is provided.

First, a two-wheel steering control means 28 is provided which is separate from the steering ratio control means 104 and maintains the steering characteristics of the vehicle at a two-wheel steering characteristic where the steering ratio is zero.

Roughly speaking, a running detecting means 105 that detects that the vehicle is running, an output signal of the running detecting means 105, and an ON/OFF signal of the ignition key switch are input, and when the vehicle is running, the ignition key switch is activated. When changing from OFF state to ON state, the above 2.
The initialization means 10 operates the wheel steering control means 28 and the ignition key switch is turned on.
After the initialization of the actuator 51 in step 3 is completed, an ignition OFF operation means 106 is provided which stops the operation of the two-wheel steering control means 28.

(Function) With the above configuration, in the present invention, when the ignition key switch is turned on while the vehicle is stopped,
The actuator 51 is initialized by the operation of the initialization means 103, and its control position is determined, for example, so that the steering ratio becomes the maximum value on the opposite phase side, and after this initialization is completed, the four-wheel steering control is performed. It will be done. That is, the target steering ratio of the front and rear wheels is set in the steering ratio control means 104 based on the steering ratio characteristics, and the actuator 51 is actuated and controlled by the output signal of this steering ratio control means, thereby steering the front and rear wheels. The ratio is controlled so that it becomes the target steering ratio.

However, when the vehicle is running, this is detected by the running detection means 105, and in that running state,
When the ignition key switch returns from the OFF state to the ON state, the initialization means 1
03 is operated as it is, and the control position of the actuator 51 is positioned at the initial position. Simultaneously with the start of this initialization, the ignition OFF operating means 106 is operated. The two-wheel steering control means 28 is actuated by the operation of the ignition OFF operation means '106, and the two-wheel steering control means 28 causes the steering characteristics of the vehicle to change when the vehicle is turned, regardless of the operation of the steering ratio control means 104. The two-wheel steering characteristic is forcibly maintained such that the ratio is zero.

When the initialization of the actuator 51 by the initialization means 103 is completed in response to the ON state of the ignition key switch, the two-wheel steering fril control means 28 is stopped, and the steering ratio control means 104 is activated to control the vehicle. The steering control characteristics return to the original four-wheel steering characteristics.

Therefore, even if the ignition key switch changes from the OFF state to the ON state and the actuator 51 is initialized due to an operation by the occupant or a poor contact while the vehicle is running, the steering ratio corresponds to the initial position of the actuator 51. There is no change in the steering ratio, the steering ratio is always zero, and the two-wheel steering characteristics are maintained, thereby improving and maintaining the running safety of the vehicle.

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

In FIG. 2, IL to 2R are the four wheels of the vehicle, and the left and right front wheels 1L and IR 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 and tie rods 5L, 5r<, and a relay rod 6 that connects the left and right tie rods 5L, 5R. In addition, this front wheel steering mechanism 3 has a rack and pinion type steering wheel connected to the steering wheel 1 via a mechanism 7.
0 is linked. That is, the relay rod 6 has a rack 8 formed thereon, and a steering shaft 11 with a steering wheel 10 connected to its upper end.
A pinion 9 that meshes with the rack 8 is attached to the lower end of the vehicle, and the left and right front wheels 1L and IR are steered in accordance with the operation of the steering wheel 10.

On the other hand, similar to the front wheel steering mechanism 3, the rear wheel steering mechanism 12 includes left and right knuckle arms 13L, 13R, tie rods 14L, 14R, and tie rods 14L, 14R.
It has a no-rod 15 that connects the R's, and is further provided with a hydraulic power steering mechanism 16. The power steering mechanism 16 includes a power cylinder 17 that is fixed to the vehicle body and has the relay rod 15 as a piston rod, and inside the power cylinder 17, two hydraulic chambers are formed by a piston 17a that is integrally attached to the relay rod 15. The hydraulic pressure 117b and 17C in this cylinder 17 are respectively connected to the control valve 20 via hydraulic pipes 18 and 19. 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 constructed of a known spool valve type, and includes a cylindrical valve casing 20a integrally attached to the relay rod 15 via a connecting member 25, and a cylindrical valve casing 20a inside the valve casing 20a. The relay rod 15 is driven by supplying pressure oil from the hydraulic pump 24 to one hydraulic chamber 17b (17c) of the power cylinder 17 according to the movement of the spool valve (not shown). It assists in power.

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 18.1
9 are connected to a normally closed electromagnetic on-off valve 28 (fail-safe solenoid valve) via hydraulic piping 26 and 27, respectively, and when this electromagnetic on-off valve 28 is opened, both hydraulic chambers 17b of the power cylinder 17 are opened. , 17c, the piston 17a is positioned at the neutral position by biasing the return springs 17d, 17d, and the rear wheel 2
L.

The steering angle θR of 2R is always set to θR=O, so that the steering characteristic of the vehicle is in 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 two ranks, and the rear end of the rotating shaft 31 is connected to the rear wheel rotation through a steering ratio control mechanism 32. It is linked to the rudder mechanism 12.

The steering ratio control mechanism 32, as shown in detail in FIG.
The control rod 33 is slidably held on the movement axis g1 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. In addition, the steering ratio control mechanism 3
2 includes a swinging arm 36 whose base end is swingably supported by a U-shaped holder 34 via a support pin 35, and the boulder 34 is attached to a casing (not shown) fixed to the vehicle body. It is rotatably supported via a support shaft 37 having a rotation axis f12 orthogonal to the movement axis g1 of the rod 33. The support pin 35 of the swing arm 36 is located at the intersection of the two axes ρ1 and 12, and extends in a direction perpendicular to the rotation axis fI2.
Rotation axis, l! 2) By rotating it around, the inclination angle formed by the support pin 35 at the tip and the movement axis Ω1 of the control rod 33, that is, the swing locus plane of the swing arm 36 about the support pin 35 becomes the movement axis. The angle of inclination made with respect to a plane perpendicular to Jh (hereinafter referred to as a reference plane) is changed.

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 33 via a ball joint 40. The third end of the swing arm 36 is connected to the other end.
The control rod 33 is moved in the left-right direction in response to displacement in the left-right direction in the figure.

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 rotation arm 41 and the connecting rod 39 rotate around the movement axis 11 by an amount corresponding to the rotation angle of the steering wheel 10, and the swing arm 36 swings around the support pin 35 accordingly. In this case, when the axis of the pin 35 coincides with the movement axis fl+ 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 inclined with respect to the movement axis ρ and the swing locus plane of the swing arm 36 deviates from the reference plane, the swing arm 36 will not swing around the pin 35. As the ball joint 38 moves, the ball joint 38 is displaced in the left-right direction in FIG. , is configured to disturb the operation of the spool valve of the control valve 20. In other words, even if the swing angle of the swing 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 will change as the inclination angle of the pin 35, that is, the rotation angle of the holder 340 changes. and change.

The axis of movement of the support pin 35, l! In order to change the inclination angle with respect to 1, 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, and a worm gear 4B on the rotating shaft 47 is attached to the sector gear 46. are engaged.

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 IL, 2L (IR, 2R>) by changing the inclination angle with respect to the reference plane. For example, the center line of the sector gear 46 is the worm gear 48.
(At this time, the ball joint 38 at the tip of the swing arm 36 rotates on the reference plane, and the steering angle OR of the rear wheels 2L and 2R is θR.)
= O) when rotating in one direction, the steering ratio of the front and rear wheels 1L and 2L is changed from the rear wheels 2L and 2R to the front wheels 1L and 1R.
On the other hand, when the wheels are rotated in the other direction, the steering ratio is changed so that the rear wheels 2L and 2R are facing the front wheels I.
It is configured to be controlled to have the same phase and direction in the same direction as L and IR.

The support shaft 37 of the holder 34 is provided with a steering ratio sensor 101 consisting of a potentiometer that detects the actual steering ratio controlled by the stepping motor 51 based on the rotation angle of the sector gear 46. It is being In addition, stopper members 52 and 53 on the opposite phase side and the same phase side, which are made of pins that restrict the rotation range of the sector gear 46, are attached to the casing that supports the holder 34 on both the 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
The control unit 100 is configured to be operated and controlled by the output from a control unit 100 containing a microcomputer, and the control unit 100 includes a vehicle speed sensor 102 that detects the traveling speed V (vehicle speed) of the vehicle and the steering ratio sensor 101. A detection signal and an ON/OFF signal of an ignition key switch (not shown) are input.

Here, in the microcomputer of the control unit 100, the stepping motor 51 and the
faI? Communication performed to control the operation of the f1 closing valve 28 @
The processing procedure will be schematically explained based on FIG. 6.

First, in the first step S1 after starting, it is detected that the ignition key switch is in the ON state, and in the next step S2, it is determined whether the vehicle is running based on the output signal of the vehicle speed sensor 102. Here, if the determination is No due to the stopped state of the vehicle, step Ss e
Proceed to 31G and perform normal four-wheel steering control.

To explain this normal four-wheel steering control, when the ignition key switch is turned on, first, in step S9, the stepping motor 51 is initialized, and its control position is set to, for example, a position where the steering ratio is on the opposite phase side. Position it so that it reaches the maximum value. Next, after the initialization of the stepping motor 51 is completed, the process proceeds to step 310, where the original four-wheel steering control is performed. That is, this control compares the vehicle speed V detected by the vehicle speed sensor '102 with the steering ratio/characteristic set in advance according to the vehicle speed (2), and adjusts the speed of the front and rear wheels 1L, 2L corresponding to the vehicle speed V. In addition to determining the target steering ratio, an operation command signal (pulse signal) is output to the stepping motor 51 so that the steering ratios of the front and rear wheels IL and 2L become the determined target steering ratio. The steering ratio control mechanism 32 is driven by the stepping motor 51.
By rotating the sector gear 46 to change the inclination angle of the holder 34 with respect to the reference plane and changing the steering angle OR of the rear wheels 2L and 2R, the steering ratio of the front and rear wheels IL and 2L is variably controlled to the target value. do.

As shown in Figs. 4 and 5, the above steering ratio characteristics 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 vehicle In order to improve the steering performance, the rear wheels 2L and 2R are steered in the opposite direction to the front wheels 1L and 1R, that is, in the opposite phase, so that the steering ratio becomes negative (opposite phase), while the vehicle speed V remains at a predetermined level. When the value is reached, the steering ratio becomes zero, and the steering ratio is the rear wheel 2L regardless of whether the front wheels 1L or 1R are steered.

The steering angle θR of 2R is maintained at θR=O, and the vehicle enters the normal two-wheel steering state. Furthermore, when driving at high speeds, in order to improve the grip of the rear wheels 2L and 2R during cornering and increase running stability, the rear wheels 2L and 2R are
It is steered in the same direction as R, that is, in the same phase, and the steering ratio is positive (
the same phase). FIG. 4 shows the characteristics of the rear wheel steering angle with respect to the steering wheel angle (rotation angle of the steering wheel 10) when the vehicle speed changes, and FIG. ing.

Further, the output signal of the steering ratio sensor 101 is input as a feedback signal, and the stepping motor 51 is controlled by this feedback signal so that the actual steering ratio matches the target steering ratio. Further, when the actual steering ratio controlled by the stepping motor 51 does not match the target steering ratio, it is assumed that the stepping motor 51 is in a so-called tax adjustment (idling), and the electromagnetic on-off valve 28 is turned on. Accordingly, the steering ratio of the front and rear wheels 1L and 2L is maintained at zero, and the system is configured to shift to a fail-safe mode.

When the vehicle is running and the determination is YES in step S2, that is, when the ignition key switch changes from the OFF state to the ON state while the vehicle is running, the process does not proceed to steps 39 and 310, but step 83
~Execute S8. First, in step S3, the electromagnetic on-off valve 28 (fail-safe solenoid valve) is turned on to forcibly maintain the steering characteristics of the vehicle in a two-wheel steering state.

Next, the process proceeds to step $4, where the stepping motor 51 is initialized in the same manner as described above, and its control position is set to the initial position corresponding to the maximum steering ratio on the opposite phase side. After such initialization, the process proceeds to step S5, where the stepping motor 51 is driven so that the steering ratio changes from the maximum value on the opposite phase side to zero, and then, in step S6, the electromagnetic on-off valve 28 is turned off. to return to the four-wheel steering control state, roughly drive the stepping motor 51 to the control position corresponding to the target steering ratio at that point in step S7, and then resume the original four-wheel steering control in step S8. fully executed. The four-wheel steering control in step S8 is performed using the stepping motor 5 in step Sho.
This is the same as the four-wheel steering control performed after initialization in step 1.

Therefore, in this embodiment, the initialization means 103 is configured to position the control position of the stepping motor 51 to the initial position when the ignition key switch is turned on in steps 34 and 39 in the control routine described above. be done.

Further, in steps Ss and Sho, after the initialization means 103 is activated, the target steering ratios of the front and rear wheels IL, 2L are set based on the steering ratio characteristics corresponding to the turtle speed V, and the target steering ratios of the front and rear wheels IL, 2L are set. A steering ratio control means 104 is configured to control the operation of the stepping motor 51 so that the steering ratio of 2L becomes the target steering ratio.

Then, the [i on-off valve 28 (fail-safe solenoid valve), which is separate from the steering ratio control means 104, maintains the steering characteristics of the vehicle at the two-wheel steering characteristics where the steering ratio is zero. A two-wheel steering control means is constructed.

Furthermore, in step $2, the running detection means 105 is configured to detect that the vehicle is running based on the vehicle speed (2) detected by the vehicle speed sensor 102.

Further, in steps 83.35 to S7, the output signal of the running detection means 105 and the ON/OFF signal of the ignition key switch are input, and when the ignition key switch changes from the OFF state to the ON state while the vehicle is running, , the electromagnetic on-off valve 28 as the two-wheel steering control means is turned on, and the stepping motor 51 is turned on as the initialization of the stepping motor 51 by the initialization means 103 is completed due to the ON state of the ignition key switch. After the steering ratio maintained by the operation of the N-magnetic on-off valve 28 is adjusted to a control position at which it becomes zero, the ignition-off operating means 10 stops the operation of the electromagnetic on-off valve 28 and restores four-wheel steering control.
6 are configured.

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

First, when the ignition key switch is turned on in order 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 vehicle speed V at that time is detected by the vehicle speed sensor 102, and the vehicle speed V at that time is detected by the vehicle speed sensor 102.
A detection signal is output from 02 to the control unit 100, and the control unit 100 determines the vehicle speed V by comparing it with the steering ratio characteristics stored in advance.
A target steering ratio corresponding to the target steering ratio is calculated, and a drive pulse signal corresponding to the target steering ratio is output to the stepping motor 51 to drive the motor 51. Driven by the motor 51, the sector gear 46 of the steering ratio control mechanism 32 rotates, and the tilt of the swing locus plane of the swing arm 36 that is fast connected to the sector gear 46 is changed with respect to the reference plane. The control rod 33 controls the movement of the connecting rod 39 that rotates around the movement axis Jh in conjunction with the operation of the steering wheel 10, that is, the steering of the front wheels 11.1R.
The moving direction and moving distance of the control rod 33 changes, and the rear wheels 2L, 2R change the front wheels 1L, 2R according to the movement of the control rod 33.
The vehicle is steered while being assisted by the power cylinder 17 of the power steering mechanism 16 so as to achieve the target steering ratio calculated above for 1R.
The wheels 1L to 2R 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.

Additionally, while the vehicle is running, if the ignition key switch is turned OFF and then turned ON due to coasting, or if the ignition key switch changes from OFF to ON due to poor contact in the ignition system, etc. When the ignition key switch returns to the ON state, the stepping motor 51 is initialized in the same way as when the vehicle is stopped, and its control position is set to the initial position. Before initialization is started, the electromagnetic on-off valve 28 (fail-safe solenoid valve) is turned on to switch the steering ratio characteristic of the vehicle to the two-wheel steering characteristic,
This two-wheel steering characteristic continues until initialization of the stepping motor 51 is completed. When the initialization of the stepping motor 51 is completed, the stepping motor 5
1 was maintained by the ON operation of the electromagnetic on-off valve 28.

The steering ratio is adjusted to a control position of zero, and then the electromagnetic on-off valve 28 is turned off to return to the original four-wheel steering control.

Therefore, in this case, when the ignition key switch changes from the OFF state to the ON state while the vehicle is running and the stepping motor 51 is initialized, the steering characteristics of the vehicle are forced to 2 during the initialization. Since the wheel steering characteristics are maintained, the steering ratio does not change to the maximum value on the opposite phase side when the stepping motor 51 is initialized, and therefore the running safety of the vehicle can be further improved.

Further, when the initialization of the stepping motor 51 is completed, the control position of the stepping motor 51 is once maintained by the operation of the electromagnetic on-off valve 28.

After the steering ratio is adjusted to a control position of zero, it is gradually positioned to the control position corresponding to the target steering ratio, so the steering ratio suddenly changes as the two-wheel steering state returns to four-wheel steering control. This can reduce the discomfort felt by the occupants.

Furthermore, as the two-wheel steering control means uses the electromagnetic on-off valve 28 for switching to fail-safe mode when the stepping motor 51 loses synchronization, there is no need for a dedicated means to execute the two-wheel steering control. Therefore, the device configuration can be simplified.

In the above embodiment, the stepping motor 51 was used as the actuator for controlling the steering ratio of the front and rear wheels IL and 2L, but the present invention is also capable of controlling the steering ratio using another actuator such as a DC motor. Of course, it can also be applied to wheel steering devices.

(Effects of the Invention) As explained above, according to the present invention, four-wheel steering of a vehicle is performed in which the actuator for controlling the steering ratio of the front and rear wheels is initialized in accordance with the ON state of the ignition key switch. In the device, when the ignition key switch changes from the OFF state to the ON state while the vehicle is running and initialization of the actuator is executed, the original 4 is forcibly set while the actuator is being initialized.
By interrupting wheel steering control, switching to 2-wheel steering control, and returning 4-wheel steering control after initialization, the ignition key switch can be turned on due to passenger operation or poor contact while the vehicle is running. Even when the actuator is initialized by Further improvement can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block 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 groove and a steering ratio control mechanism. 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. The 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, 2L, 2R...rear wheel, 3...
・Front wheel steering mechanism, 12... Rear wheel steering mechanism, 28...
Electromagnetic on-off valve, 32... Steering ratio control mechanism, 51... Stepping motor, 100... Control unit, 102... Vehicle speed sensor, 103... Initialization means,
104... Steering ratio control means, 105... Running detection means, 106... Ignition OFF operating means. This place

Claims (1)

[Claims] (1) An actuator that changes the steering ratio of the front and rear wheels, an initialization device that positions the control position of the actuator to a predetermined initial position when the ignition key switch is turned on, and operation of the initialization device. a steering ratio control means that sets a target steering ratio for the front and rear wheels based on a predetermined steering ratio characteristic, and controls the operation of the actuator so that the steering ratio of the front and rear wheels becomes the target steering ratio; A four-wheel steering system for a vehicle comprising: two-wheel steering control means for maintaining the steering characteristic of the vehicle at a two-wheel steering characteristic in which the steering ratio is zero, in a system separate from the steering ratio control means; a running detection means for detecting that the vehicle is running; an output signal of the running detection means; and an ON state of the ignition key switch.
- When an OFF signal is input and the ignition key switch changes from the OFF state to the ON state while the vehicle is running, the two-wheel steering control means is activated, and the initialization means associated with the ON state of the ignition key switch is activated. an ignition O that stops the operation of the two-wheel steering control means after the initialization of the actuator is completed;
1. A four-wheel steering device for a vehicle, characterized in that a FF operation means is provided.