Steering apparatus for vehicle

There is provided a steering apparatus to ease an uncomfortable feeling given to an operator when a steering wheel is connected to a steering mechanism, on a fail. The apparatus includes a unit that varies an angular ratio of a steering angle of front wheels with respect to an operational angle of a steering wheel. The apparatus also includes a connection unit such as a electromagnetic clutch for connecting the steering wheel to the steering mechanism in order to fix the angular ratio, on a fail such as a failure of a steering motor. The apparatus also includes a rotational body which relatively rotates with respect to the steering wheel by an angular deviation upon this connection. Accordingly, since a real neutral position of the steering mechanism coincides with a neutral position recognized by a pattern on the rotational body being seen, it eases the uncomfortable feeling onto the operator.

CROSS-REFERENCE OF RELATED APPLICATION

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-018381 in Japan on Jan. 29, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a steering apparatus for a vehicle provided with an angular ratio varying device which can vary a ratio of a steering angle of a steerable vehicle wheel with respect to an operational angle of a steering member.

2. Description of Related Art

Steering of a vehicle is carried out by operating a steering mechanism in accordance with the operation of a steering member such as a steering wheel and varying a steering angle of a steerable vehicle wheel by the operation of the steering mechanism. In recent years, as a steering apparatus for a vehicle to carry out such a steering, one that is configured so as to be able to vary an angular ratio (=a steering angle/an operational angle) of the steering angle of the steerable vehicle wheel with respect to the operational angle of the steering member has been known (for example, refer to Japanese Patent Application Laid-Open No. 2003-252227).

The steering apparatus for a vehicle described in Japanese Patent Application Laid-Open No. 2003-252227 is a separation-type steering apparatus for a vehicle, namely, a so-called steer-by-wire system steering apparatus for a vehicle, which is configured in such a manner that a steering member to be operated by an operator and a steering mechanism operating so as to steer a steerable vehicle wheel are mechanically separated; attaching a steering motor to the steering mechanism, the steering motor is operated based on the operational direction and the operational angle of the steering member; and the steering force is added to the steering mechanism to carry out steering, namely, a so-called Steer-by-Wire System of steering apparatus for a vehicle. This steering apparatus for a vehicle can freely vary the angular ratio of the steering angle with respect to the operational angle without being mechanically restricted by operating the steering mechanism driving the steering motor.

According to the steering apparatus for a vehicle of the above-described Japanese Patent Application Laid-Open No. 2003-252227, a steering control unit imports an operational angle of the steering wheel that is detected by an operational angle sensor (Paragraph [0023]) and imports a real steering angle (a steering angle) of a wheel for steering to be steered that is detected by a real steering angle sensor (Paragraph [0020]). A steering angle control unit obtains a target steering angle by multiplying the imported operational angle by a predetermined control gain. The steering angle control unit carries out steering control operation by a feedback control based on a deviation between the target steering angle and the real steering angle. The control gain is determined as a value that is decreased depending on increase of a speed of a car or a value that is decreased depending on increase of a swing degree of a vehicle to be decided by a yaw rate or a lateral acceleration (Paragraphs [0026] and [0027]). As described above, in the steering apparatus for a vehicle of the above-described Japanese Patent Application Laid-Open No. 2003-252227, the angle ratio of the real steering angle (the steering angle) with respect to the operational angle can be varied by control of the steering angle control unit.

Varying a steering property in accordance with a running condition such as a difference in height of a speed of a car and a measure of the operational angle by varying the angular ratio of the steering angle with respect to the operational angle, the steering apparatus for a vehicle of the above-described Japanese Patent Application Laid-Open No. 2003-252227 can carry out steering suitable for the running condition. In addition, by varying only the steering angle of the steerable vehicle wheel, it is also possible to carry out active steering such as a motion control on a slip and avoidance of a danger of an obstacle.

However, in the steering apparatus for a vehicle as in the above-described Japanese Patent Application Laid-Open No. 2003-252227, in a case where an abnormality is caused in any of a control device for variably controlling an angular ratio and various sensors to be used for this control to be made into a fail condition, it is feared that steering is interfered by an inappropriate control to be carried out under this condition. Therefore, the steering apparatus for a vehicle in the above-described Japanese Patent Application Laid-Open No. 2003-252227 is configured so as to be capable of carrying out manual steering by arranging an electromagnetic clutch between the steering member and the steering mechanism and mechanically connecting the steering member to the steering mechanism due to the engagement operation of the electromagnetic clutch in the fail condition.

SUMMARY

However, in the steering apparatus for a vehicle as above described, since the angular ratios before or after connection are generally different when the steering member and the steering mechanism are mechanically connected in the fail condition, even if the steerable vehicle wheel returns to a straight position, in other words, even if the steering mechanism returns to a neutral position, it is feared that the steering member does not return to a reference position that has been determined in advance in accordance with the neutral position of the steering mechanism and this makes an operator feel an uncomfortable feeling.

Accordingly, an object is to provide a steering apparatus for a vehicle that can ease an uncomfortable feeling to be given to the operator by arranging a neutral indicator that becomes a predetermined rotational position when a steering mechanism is located on a neutral position in a steering member and coinciding a real neutral position of the steering mechanism to the neutral position to be recognized by the neutral indicator when the steering member is connected to the steering mechanism in the fail condition.

There is provided a steering apparatus for a vehicle according to an aspect, having a steering mechanism for being provided with a steerable vehicle wheel to be steered upon an operation of a steering member which is mechanically disconnected from the steering mechanism, comprising: a first controller capable of performing the operation of varying an angular ratio of a steering angle of the steerable vehicle wheel versus an operational angle of the steering member; a connection unit connecting the steering member to the steering mechanism such that the angular ratio is fixed, the connection unit being activated when the operation of the varying of the angular ratio is abnormal; a neutral indicator provided in the steering member, being relatively coaxially rotatable with respect to the steering member, and positioning in a predetermined rotational position when the steering mechanism positions in a neutral position; a rotation unit relatively rotating the neutral indicator with respect to the steering member; and a second controller capable of performing the operation of allowing the rotation unit to rotate the neutral indicator into the predetermined rotational position, in the case that the steering mechanism positions in the neutral position thereof, when the connection unit becomes active.

There is provided a displaying method for a steering position according to an aspect, the method being applied to a steering apparatus having a steering mechanism for being provided with a steerable vehicle wheel to be steered upon an operation of a steering member which is mechanically disconnected from the steering mechanism, the method comprising: providing a neutral indicator in the steering member, the neutral indicator being relatively coaxially rotatable with respect to the steering member, and the neutral indicator positioning in a predetermined rotational position when the steering mechanism positions in a neutral position; determining whether or not at least a part of the steering mechanism is in a fail condition; and allowing the rotation unit to rotate the neutral indicator into the predetermined rotational position, in the case that the steering mechanism positions in the neutral position thereof, when the determination represents the fail condition.

DETAILED DESCRIPTION

FIG. 1is a schematic view showing a structure of a steering apparatus for a vehicle according to an embodiment of the present invention.

The steering apparatus for a vehicle is provided with a steering mechanism1for steering front wheels10,10as steerable vehicle wheels that are arranged right and left of a vehicle body. The steering apparatus is also provided with a steering wheel2that is a steering member to be rotationally operated for steering and is arranged to be mechanically separated from the steering mechanism1. The steering apparatus is also provided with a steering motor3to be driven so as to add a steering force to the steering mechanism1in accordance with the operation of the steering wheel2and a steering control unit4.

The steering mechanism1is provided with a steering shaft11that is elongated in a horizontal direction of a vehicle body to be moved in a shaft length direction. The opposite ends of the steering shaft11are connected to knuckle arms12,12of the front wheels10,10via tie rods13,13, respectively. The steering mechanism1is configured so as to horizontally steer the front wheels10,10by pushing and pulling the knuckle arms12,12via the tie rods13,13due to movement in a horizontal direction of the steering shaft11.

A housing14supports the steering shaft11movably in a shaft length direction. The steering motor3is attached to the outside in a midstream of the housing14and an output shaft of the steering motor3is elongated to the inside of the housing14. The steering motor3transmits an output to the midstream of the steering shaft11via a motion conversion mechanism such as a ball screw mechanism. When the steering motor3is rotationally operated, this rotation is converted into a motion in a shaft length direction of the steering shaft11by the motion conversion mechanism. In accordance with this motion, the above-described steering is carried out.

The steering control unit4gives a control instruction to a driving circuit (not illustrated) of the steering motor3. The steering motor3is driven in accordance with this control instruction. On a connection portion between the steering shaft11and one tie rod13, a location sensor25for detecting a moving position of the steering shaft11moving in accordance with the steering is attached. A detection value of the moving position of the steering shaft11by the location sensor25is given to the steering control unit4as a detection value showing steering angles of the front wheels10,10. In addition, on the one tie rod13, a shaft force sensor26for detecting a shaft force to act in a shaft length direction is attached. A detection value of the shaft force by the shaft force sensor26is given to the steering control unit4showing a reaction force (hereinafter, referred to as a road surface reaction force) to be added to the steering mechanism1from a road surface in accordance with steering. In addition, a current sensor30for detecting the driving current of the steering motor3is attached to the steering motor3. A detection value of the driving current by the current sensor30is also given to the steering control unit4.

According to the embodiment, the steering control unit4is provided with an (auxiliary) control unit41. This control unit41can output a control instruction for carrying out engagement control and positioning to be described later in a fail condition to be described later. The steering control unit4can arbitrarily use a control instruction that is outputted by the control unit41as a control instruction to be outputted to each unit. In other words, the control unit41is a unit for a fail safe, which can act for at least a partial function of the steering control unit4, in the fail condition to be described later. Further, according to other embodiments, the control unit41may be an independent unit having a function that is equal to the steering control unit4. In this case, a plurality of control units may be arranged. The steering control unit4and the plurality of control units respectively output a control instruction. A control instruction that is selected from among these control instructions based on a principle of majority rule is given to each unit.

In addition, the steering wheel2is arranged being separated from the steering mechanism1. A steering shaft20is a rotating shaft of the steering wheel2. The steering wheel2is mounted on an arbitrary region of the vehicle body (not illustrated) via a column housing21for freely supporting the steering shaft20. A reaction motor22is mounted on a midstream part of the column housing21. This is rotationally driven so as to add a steering reaction force in accordance with the road surface reaction force. An output shaft of the reaction motor22is elongated to the inside of the column housing21. The output shaft of the reaction motor22transmits an output to a midstream part of the steering shaft20via a reduction mechanism such as a worm gear mechanism. When the reaction motor22is rotationally operated, a rotational force is reduces by the reduction mechanism to be given to the steering shaft20. This is given to the steering wheel2that is fixed on the upper end of the steering shaft20.

The steering control unit4gives a control instruction to a driving circuit (not illustrated) of the reaction motor22. The reaction motor22will be driven in accordance with this control instruction. On the midstream part of the column housing21, a rotation angle sensor27is arranged, and the rotation angle sensor27detects a rotation angle of the steering wheel2that is rotationally operated against the steering reaction force. A detection value of a rotation angle by the rotation angle sensor27is given to the steering control unit4as a detection value showing an operational angle of the steering wheel2that is rotated in accordance with steering. In addition, a running condition sensor28is mounted on each unit of the vehicle. To the steering control unit4, a detection value showing a running condition showing a speed of a car, a yaw rate, a lateral acceleration, and a longitudinal acceleration or the like is given.

The steering control unit4carries out the steering control to move the steering shaft11for performing steering by driving the steering motor3in accordance with the rotation operation of the steering wheel2. In this control, increasing and decreasing a current to be supplied to the reaction motor22in accordance with the road surface reaction force, a reaction force control to increase and decrease the steering reaction force to be added to the steering wheel2is carried out.

The steering control of the steering control unit4relevant to the steering motor3includes obtaining of a target steering angle, for example, by multiplying the operational angle of the steering wheel2to be detected by the rotation angle sensor27by a predetermined control gain and driving of the steering motor3based on the obtained target steering angle. The steering angles of the front wheels10,10on right and left sides to be detected by the location sensor25are used as feedback information on controlling the steering.

The running condition detected by the running condition sensor28will be used for selection of the control gain in this steering control. This steering control is determined so as to be made large or small in accordance with slowness or speedy of the speed of the car. This control gain is further determined as a value that is made smaller as a swing degree of a vehicle to be decided by a yaw rate or a lateral acceleration is made larger. In order to realize a steering property in accordance with the running condition, the steering motor3is controlled based on the target steering angle that is obtained by multiplying the road surface reaction force by such a control gain.

In addition, the reaction force control of the steering control unit4relevant to the reaction force motor22includes, for example, obtaining of a road surface reaction force to be added to the steering mechanism1based on the shaft force to be detected by the shaft force sensor26; calculation of the target steering reaction force to be added to the steering wheel2by multiplying the obtained road surface reaction by a predetermined control gain; and increase and decrease of the driving current of the reaction force motor22in accordance with this target steering reaction force.

Under this reaction force control, the running condition to be detected by the running condition sensor28is used for correction of the control gain. This correction is carried out, for example, so that the control gain is made larger as the speed of the car and the swing degree are made larger. Further, this correction is carried out so that the control gain is made larger as the deceleration degree to be obtained by the longitudinal acceleration is made larger. In addition, the operational angle of the steering wheel2to be detected by the rotation angle sensor27may be used for correction of the target steering reaction force. Thereby, an increase and decrease property of the driving current of the reaction force motor22is varied.

Due to this reaction force control, the rotational force of the reaction force motor22is added to the steering shaft20. This rotational force is added to the steering wheel2as a steering reaction force. This steering reaction force is obtained by correcting the road surface reaction force to be added to the steering mechanism1in practice in accordance with the running condition. Due to this steering reaction force, the operator who operates the steering wheel2can feel a good steering feeling.

On the midstream part of the housing14separated from the attaching position of the steering motor3, a pinion housing15is continued so as to cross this midstream part of the housing14, and a pinion shaft16is supported in the inside of this pinion housing15so as to be capable of being rotated around a shaft. On the lower part of this pinion shaft16, a pinion tooth (not illustrated) is formed, and the pinion tooth is engaged with a rack tooth formed across an arbitrary length on the outer face of the steering shaft11on a crossing part with the housing14.

On the other hand, a transmission shaft18is coupled to the upper end of the pinion shaft16projecting to the upper part of the pinion housing15via an intermediate shaft17provided with free junctions17a,17aon its opposite ends. This transmission shaft18is supported so as to be capable of being rotated around the shaft to be elongated upward toward the arrangement position of the steering wheel2.

In addition, the steering shaft20that is a rotational shaft of the steering wheel2projects to the lower part of the column housing21across an arbitrary length to be confronted against the upper end portion of the transmission shaft18, and an electromagnetic clutch5is located on this confronting portion.

The steering control unit4gives a control instruction to an excitation circuit of the electromagnetic clutch5(not illustrated). The electromagnetic clutch5is a publicly-known connection device, which is engaging-operated in accordance with the given control instruction. The steering control unit4carries out the engagement control to engage the electromagnetic clutch5in accordance with the determination of the fail condition. The determination of this fail condition will be described later. When the electromagnetic clutch5is in the engagement condition, the steering shaft20is mechanically connected to the transmission shaft18. The rotation of the steering shaft20in accordance with the rotational operation of the steering wheel2will be transmitted to the transmission shaft18via the electromagnetic clutch5. This rotation transmitted to the transmission shaft18, as described above, will be transmitted to the pinion shaft16via the free junctions17a,17aand the intermediate shaft17. This rotation transmitted to the pinion shaft16is converted into movement in a shaft length direction of the steering shaft11on the engagement portion between the pinion tooth and the rack tooth. In this way, since the transmission shaft18and the steering shaft20are mechanically connected by engagement of the electromagnetic clutch5, the rotational operation force of the steering wheel2is transmitted to the steering shaft11and manual steering becomes available.

FIG. 2is a view schematically showing the steering wheel2of the steering apparatus for a vehicle according to the present invention. As shown inFIG. 1andFIG. 2, the steering wheel2is configured by coupling a flat columnar hub2aand a circular rim2bthat are mounted on the same shaft on the upper end of the steering shaft20by a plurality of spokes (three inFIG. 2)2c.

In the hub2a, a motor for an indicator rotation (an indicator rotation device)60is fixed concentrically with the steering shaft20. An output shaft extending from one side of the motor60projects to the inverse side of the steering shaft20. On a projection end of the output shaft of this motor60, a rotational body (a neutral indicator)6is fitted and fixed. On the surface of the rotational body6, a pattern6asuch as a letter, a mark, a figure, and a picture are mentioned. This pattern6ais provided so as to allow the operator to recognize that the front wheels10,10are located in straight positions. In other words, this pattern6ais provided so as to allow the operator to recognize that the steering mechanism1is located on a neutral position.FIG. 2illustrates the condition that the steering mechanism1is located on a neutral position. The illustrated pattern6ais a combination of three marks (inFIG. 2, they are a circle, a triangle, and a circle, that is ∘Δ∘). When the steering mechanism1is located on the neutral position, these three marks are horizontally aligned on one line. The operator can recognize that the steering mechanism1is in a straight condition by viewing of the pattern6a.

The rotational body6is integrally rotated together with the motor60in accordance with the rotation of the steering wheel2. In a case where the motor60is rotationally driven, the rotational body6is relatively rotated for the steering wheel2.

The steering control unit4gives a control instruction to a driving circuit (not illustrated) of the motor60for the indicator rotation. The motor60for the indicator rotation will be driven in accordance with the given control instruction. The steering control unit4drives the motor60for the indicator rotation so as to relatively rotate the rotational body6for the steering wheel2. The steering control unit4drives the motor60for the indicator rotation so as to position the neutral position indicated by the pattern6amentioned on the rotational body6to coincide with the neutral position of the real steering mechanism1. Thereby, the neutral position of the real steering mechanism1is illustrated by the pattern6amentioned on the rotational body6.

According to the embodiment, it is assumed that, in a case where an abnormality is caused in any of the steering motor3, the steering control unit4, and various sensors to be used for this control, at least a part of the steering apparatus for a vehicle is in the fail condition. The steering control unit4carries out this positioning together with the above-described engagement control in the fail condition.FIG. 3is a flow chart showing operations of the steering control unit4when the steering apparatus, shown inFIG. 1, for a vehicle is in the fail condition. Further, the operation of the steering control unit4shown inFIG. 3will be carried out as the interrupt processing during the steering control and the reaction force control.

The steering control unit4determines presence or absence of the fail (step S1). For example, the fact that there is a fail in the steering motor3is determined in the following case, namely, the operational angle of the steering wheel2to be detected by the rotation angle sensor27is not 0; and the driving current of the steering motor3to be detected by the current sensor30is 0.

In step S1, when it is determined that there is no fail (step S1: NO), the processing is finished without carrying out the following operation. When it is determined that there is a fail (step S1: YES), proceeding to step S2, as described above, the engagement control to engage the electromagnetic clutch5will be carried out (step S2). By engagement of the electromagnetic clutch5, the steering wheel2is connected to the steering mechanism1, and the manual steering as described above becomes available.

Next, the operational angle of the steering wheel2to be detected by the rotation angle sensor27is imported (step S3). Further, the steering angles of the front wheels10,10on the right and left sides to be detected by the location sensor25are imported (step S4).

Next, using the steering angle imported in step S4, this steering angle is divided by the angular ratio that has been determined in advance on connection. The operational angle corresponding to this steering angle is obtained (step S5). The obtained operational angle is subtracted from the operational angle imported in step S3. Thereby, an angular deviation corresponding to a difference between the operational angle and the steering angle that present at this point of time will be calculated (step S6). This angular deviation is a difference between the position where the rotational body6should be located and the position where the rotational body6is located at the present.

Next, the steering control unit4gives a control instruction to a driving circuit (not illustrated) of the motor60for the indicator rotation so as to rotate the rotational body6just match as the angular deviation that is calculated in step S6(step S7). The motor60for the indicator rotation is driven in accordance with the control instruction to be given to the driving circuit and the rotational body6is rotated just match as the calculated angular deviation.

FIGS. 4A to 4Care explanatory views of operations of the steering wheel2and the steering mechanism1, that are caused by positioning operation. For convenience of explanation, the following conditions are supposed. Namely, as shown inFIG. 4A, three marks as the pattern6amentioned on the rotational body6are horizontally aligned on one line; the rotational body6is located on a predetermined rotational position corresponding to the neutral position of the steering mechanism1; the steering mechanism1is steered left; and the steering apparatus is in the fail condition. In this state, the electromagnetic clutch5is engaged in accordance with the fail determination. Further, due to the above-described positioning, only the rotational body6is rotated just match as the angular deviation that is obtained in step S6ofFIG. 3in the same left direction as that of the front wheels10,10. The rotational body6and the pattern6aof the rotational body6are made in the condition shown inFIG. 4B. After that, when the steering mechanism1returns to the neutral position, the steering wheel2connected to the steering mechanism1is rotated. Herewith, the rotational body6is rotated and the pattern6ais made into the condition shown inFIG. 4C. In this case, the neutral position shown by the rotational body6on which the pattern6ais mentioned coincides with a real neutral position of the steering mechanism1. Further, the condition shown inFIG. 4Amay be available when the active steering such as a motion control on a slip and avoidance of a danger of an obstacle is carried out.

As described above, according to the steering apparatus for the vehicle of the present invention, on the fail such as a failure of the steering motor3, mechanically connecting the steering wheel2to the steering mechanism1by the electromagnetic clutch5, the angular ratio of the front wheels10,10with respect to the operational angle of the steering wheel2is fixed, the rotational body6is relatively rotated for the steering wheel2by just match as a difference between the operational angle and the steering angle on this connection, and the real neutral position of the steering mechanism1is allowed to coincide with the neutral position to be recognized by the rotational body6on which the pattern6ais mentioned, so that it is possible to ease an uncomfortable feeling to the operator.

In addition, since the angular ratio on this connection is obtained when the steering wheel2is connected to the steering mechanism1, it is possible to immediately coincide the real neutral position of the steering mechanism1with the neutral position to be recognized by the rotational body6.

Further, since the rotational body6, on which the pattern6a, such as a letter, a mark, a figure, and a picture are mentioned, is defined to be the neutral indicator of the steering mechanism1, it is possible to ease an uncomfortable feeling to the operator by a simple structure.

Further, according to the present embodiment, arranging the rotational body6, on which the pattern6ais mentioned, and the motor60for the indicator rotation on the steering wheel2and rotating the rotational body6by the motor60for the indicator rotation, the neutral position of the steering mechanism1to be recognized by the pattern6ais allowed to coincide with the real neutral position of the steering mechanism1. However, the present invention is not limited to this and providing an image display unit in the steering wheel2, the neutral position of the steering mechanism1to be recognized by an image to be displayed on this image display unit may be allowed to coincide with the real neutral position of the steering mechanism1. In this case, the image display unit itself provided in the steering wheel2may be configured so as to be relatively rotated for the steering wheel2or only the image to be displayed on the image display unit may be configured so as to be relatively rotated for the steering wheel2.

In addition, according to the present embodiment, the electromagnetic clutch5is used as a connection device for connecting the steering wheel2to the steering mechanism1so as to fix the angular ratio between the operational angle of the steering wheel2and the steering angles of the front wheels10,10, however, the present embodiment is not limited to this and a clutch such as a friction clutch using a frictional force of a junction face and a positive clutch using a joint portion such as a nail may be used.

Further, according to the above-described embodiments, an example to apply the present invention to the Steer-by-Wire System of steering apparatus for a vehicle has been described. Further, various modified examples that are not limited to the above-described embodiments are available. For example, a modified example may be configured so that the angular ratio between the operational angle of the steering wheel and the steering angle of the steerable vehicle wheel are variable. According to this modified example, it is possible to fix the angular ratio by connecting the steering wheel to the steering mechanism on the fail. This modified example may include the steering apparatus for the vehicle that is configured so as to be capable of carrying out the manual steering in this way on the fail. Further, the present invention can be put into practice by variously modified formations within a range of the matters described in the scope of claims.

According to the embodiments, since the neutral indicator is relatively rotated for the steering member when the steering member is mechanically connected to the steering mechanism by means of the connection device on a fail condition (on an abnormal condition) such as a failure of a steering motor, the neutral position of the steering mechanism coincides with the neutral position to be recognized by the neutral indicator provided in the steering member and this makes it possible to ease an uncomfortable feeling given to the operator.

According to the embodiments, since the neutral indicator arranged in the steering member when the steering member is mechanically connected to the steering mechanism is relatively rotated by just match as a difference between the operational angle of the steering member when they are connected and the steering angle of the steerable vehicle wheel, it is possible to immediately coincide the neutral position of the steering mechanism with the neutral position to be recognized by the neutral indicator that is arranged in the steering member.

According to the embodiments, since the detected steering angle and operational angle are imported when the steering member is connected to the steering mechanism; the steering angle on the connection and a difference between the operational angle calculated by using the angular ratio and the operational angle on the connection are calculated; and the neutral indicator is rotated by just match as a difference that is calculated by issuing the operation instruction to the rotating device, it is possible to immediately coincide the neutral position of the steering mechanism with the neutral position to be recognized by the neutral position that is arranged in the steering member.

According to the embodiments, since the rotational body, on which a pattern, for example, a letter, a mark, a figure, and a picture are mentioned, is defined to be a neutral indicator, it is possible to ease an uncomfortable feeling to the operator by a simple structure.