Steering device

A steering device according to an aspect of the present invention includes an outer shaft, an inner shaft, an outer column, and an inner column. The inner shaft has a sliding portion configured to be capable of being inserted into the outer shaft, and a bearing-mounting portion that is connected to the sliding portion in an axial direction thereof and is configured not to be capable of being inserted into the outer shaft. In the bearing-mounting portion, rear bearings are disposed with an interval therebetween in the axial direction.

TECHNICAL FIELD

The present invention relates to a steering device.

Priority is claimed on Japanese Patent Application No. 2017-116603, filed Jun. 14, 2017, the contents of which are incorporated herein by reference.

BACKGROUND ART

Some steering devices include a telescopic function. The telescopic function adjusts a position of a steering wheel in a front-to-rear direction in accordance with physical differences and a driving posture of drivers. This type of steering device includes an outer column mounted on a vehicle body, and an inner column which is inserted into the outer column to be movable relative to the outer column. For example, in a configuration of Patent Literature 1 below, an outer shaft is rotatably supported in an inner column via a bearing. A steering wheel is attached to a rear-end portion of the outer shaft. An inner shaft is rotatably supported in an outer column via a bearing. The inner shaft is inserted into the outer shaft.

According to the configuration of Patent Literature 1, during a telescopic operation, the inner column and the outer shaft move in an axial direction thereof relative to the outer column and the inner shaft, respectively. In the configuration of Patent Literature 1, the outer shaft is positioned further rearward in the vehicle body and is supported by bearings at both end portions thereof in the axial direction. For this reason, in the configuration of Patent Literature 1, it is recognized that vibrational stiffness can be enhanced.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

On the other hand, in a steering device, there is still room for improvement in that a desired vibrational stiffness needs to be obtained when a stroke amount at the time of telescopic operation and secondary collapse (a stroke at the time of secondary collision) is secured.

Aspects of the present disclosure have been made in view of the circumstances described above, and provide a steering device which can obtain a desired vibrational stiffness while securing a stroke amount.

Solution to Problem

In order to solve the above problem, the present disclosure has adopted the following aspects.

(1) A steering device according to an aspect of the present disclosure includes an outer shaft, an inner shaft which is inserted into the outer shaft to be movable relative to the outer shaft in a shaft axis direction thereof and to which a steering wheel is attached, an outer column configured to rotatably support the outer shaft around the shaft axis via a front bearing, and an inner column configured to rotatably support the inner shaft around the shaft axis via a rear bearing, the inner column being inserted into the outer column to be movable relative to the outer column in the shaft axis direction. The inner shaft has an insertable region configured to be capable of being inserted into the outer shaft, and a non-insertable region which is connected to the insertable region in the shaft axis direction and is configured not to be capable of being inserted into the outer shaft. The rear bearing has a first bearing and a second bearing which are disposed with an interval therebetween in the shaft axis direction in the non-insertable region.

The steering device according to the present aspect is configured such that the outer shaft is rotatably supported in the outer column, and the inner shaft is rotatably supported in the inner column. According to this configuration, even if a mounting member such as a key lock collar is externally fitted to the outer shaft positioned further forward in a vehicle body, the mounting member can be inhibited from being disposed on a movement trajectory of the inner column and the inner shaft. For this reason, at the time of a stroke during a telescopic operation, a secondary collapse or the like, interference between the inner column or the inner shaft and the mounting member can be inhibited. Thus, as compared with the configuration in the conventional technique in which the inner shaft is rotatably supported in the outer column positioned on a front side of the vehicle body, and the outer shaft is rotatably supported in the inner column positioned on a rear side of the vehicle body, stroke amounts of the inner column and the inner shaft can be secured.

In particular, in the present aspect, the first bearing and the second bearing are disposed in the non-insertable region which is configured not to be capable of being inserted into the outer shaft during the telescopic operation or the secondary collapse. According to this configuration, interference between a bearing positioned furthest forward among the bearings in the vehicle body and the outer shaft and members surrounding the outer shaft at the time of the stroke can be inhibited. A displacement of the inner shaft is inhibited, and the inner shaft is stably supported. Thus, vibrational stiffness can be improved.

Therefore, in the present aspect, it is possible to obtain a desired vibrational stiffness while securing the stroke amount.

(2) In the steering device according to the above aspect (1), at least one of the front bearing, the first bearing, and the second bearing may be a resin bush.

According to the present aspect, the steering device can be simplified.

(3) In the steering device according to the aspect (1), the first bearing may be positioned forward from the second bearing in the vehicle body. A first stopper which comes into contact with an outer ring of the first bearing in the shaft axis direction may be formed in a portion of the inner column positioned forward from the first bearing in the vehicle body. A second stopper which comes into contact with an outer ring of the second bearing in the shaft axis direction may be formed in a portion of the inner column positioned rearward from the second bearing in the vehicle body.

According to the present aspect, since positional deviations of the first bearing and the second bearing relative to the inner column in the shaft axis direction can be inhibited, a steering shaft can be prevented from coming off.

In particular, since the steering shaft is prevented from coming off by the stopper formed on the inner column, it is unnecessary to separately use a stop ring or the like for fixing the outer ring. Therefore, the number of components can be reduced.

(4) In the steering device according to any one of the above aspects (1) to (3), the non-insertable region may be formed to be larger in diameter than the insertable region.

According to the present aspect, since rigidity of the inner shaft can be enhanced, vibrational stiffness can be enhanced.

In addition, in the present aspect, since only the non-insertable region is formed to have a larger diameter, an increase in weight accompanying enlargement of the diameter can be inhibited as much as possible, as compared with a case in which the entire inner shaft is formed to have a larger diameter.

(5) In the steering device according to any one of the aspects (1) to (4), the insertable region may be formed in a hollow cylindrical shape. The non-insertable region may be formed in a solid cylindrical shape.

According to the present aspect, since rigidity of the inner shaft can be enhanced, vibrational stiffness can be enhanced.

In particular, in the present aspect, since only the non-insertable region is formed to be solid, an increase in weight accompanying being formed to be solid can be inhibited as much as possible, as compared with a case in which the entire inner shaft is formed to be solid.

(6) In the steering device according to any one of the above aspects (1) to (5), a key lock collar configured to restrict rotation of the outer shaft relative to the outer column in a locked state may be externally fitted to the outer shaft. An outer diameter of the key lock collar may be smaller than an inner diameter of the inner column.

According to the present aspect, regardless of the place where the key lock collar is disposed, interference between the inner column and the key lock collar can be reliably inhibited at the time of a stroke of the inner column. Thus, a stroke amount of the inner column can be secured.

(7) A steering device according to an aspect of the present disclosure includes a front shaft, a rear shaft which is positioned rearward from the front shaft in a vehicle body and is configured to be movable relative to the front shaft in a shaft axis direction, and to which a steering wheel is attached, a front column configured to rotatably support the front shaft around the shaft axis via a front bearing, and a rear column configured to rotatably support the rear shaft around the shaft axis via a rear bearing and is configured to be movable relative to the front column in the shaft axis direction. The rear bearing has a first bearing and a second bearing which are disposed with a predetermined interval therebetween in the shaft axis direction. A distance between the first bearing and the second bearing in the shaft axis direction may be set to be 40 mm or less.

(8) A steering device according to an aspect of the present disclosure includes a steering shaft having a rear-end portion to which a steering wheel is attached, a rear bearing configured to support the steering shaft, a front bearing configured to support the steering shaft in front of the rear bearing, and a steering column configured to rotatably support the steering shaft around a shaft axis via the rear bearing and the front bearing. The rear bearing has a first bearing and a second bearing which are disposed with a predetermined interval therebetween in the shaft axis direction. A distance between the first bearing and the second bearing in the shaft axis direction may be set to be 40 mm or less.

As a result of the present inventor's studies for achieving the objects mentioned above, it was found that a rate of change in vibrational stiffness in a case where the distance between the first bearing and the second bearing is longer than 40 mm was smaller than a rate of change in vibrational stiffness in a case where the distance is 40 mm or less. That is, it was found that if the distance exceeds a predetermined range, regardless of the distance being increased thereafter, no significant improvement of vibrational stiffness can be expected.

Therefore, according to the present aspect, by setting the distance between the first bearing and the second bearing to be 40 mm or less, a desired vibrational stiffness can be obtained. By setting the distance between the first bearing and the second bearing to be 40 mm or less, the stroke amount when the front shaft and the front column and the rear shaft and the rear column move in the shaft axis direction can be secured.

Advantageous Effects of Invention

According to each aspect of the present disclosure, a desired vibrational stiffness can be obtained while securing the stroke amount.

DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG.1is a cross-sectional view of a steering device1.

As shown inFIG.1, the steering device1is mounted on a vehicle. The steering device1controls a steering angle of a vehicle wheel in accordance with a rotating operation of a steering wheel2. Also, in the following description, unless otherwise described, directions such as forward, rearward, upward, downward, left, and right indicate the directions in a state in which they are applied to a vehicle. In this case, in the drawings, an arrow UP indicates an upward direction, and an arrow FR indicates a forward direction.

The steering device1mainly includes a column unit11and a steering shaft12. The column unit11and the steering shaft12are each formed in a tubular shape extending along an axis O. Therefore, in the following description, a direction in which the axis O of the column unit11and the steering shaft12extends may be simply referred to as an axial direction (a shaft axis direction), a direction orthogonal to the axis O may be referred to as a radial direction, and a direction around the axis O may be referred to as a circumferential direction.

The steering device1of the present embodiment is mounted on the vehicle with the axis O intersecting a front-to-rear direction. Specifically, the axis O of the steering device1extends upward in the rearward direction. However, in the following description of the steering device1, for the sake of convenience, a direction toward the steering wheel2in the axial direction is simply referred to as a rear side, and a direction toward a side opposite to the steering wheel2is simply referred to as a front side. Also, regarding the radial direction, a direction in the vertical direction in a state in which the steering device1is attached to the vehicle is simply referred to as a vertical direction.

The column unit11has an outer column (a front column)21and an inner column (a rear column)22.

The outer column21is formed in a tubular shape extending along the axis O. The outer column21is attached to a vehicle body via a bracket (not shown). An outer ring of a front bearing28is fitted (press-fitted) into a front-end portion of the outer column21inside the outer column21.

The inner column22is formed in a tubular shape extending along the axis O. Specifically, the inner column22has a column small-diameter portion24, a column large-diameter portion25, and a connection portion26. The column large-diameter portion25is positioned behind the column small-diameter portion24. The connection portion26connects the column small-diameter portion24to the column large-diameter portion25.

An outer diameter of the column small-diameter portion24is smaller than an inner diameter of the outer column21. The column small-diameter portion24is inserted into the outer column21from behind the outer column21. The inner column22is configured to be movable relative to the outer column21in the axial direction while an outer circumferential surface of the column small-diameter portion24slides on an inner circumferential surface of the outer column21.

FIG.2is an enlarged cross-sectional view of the steering device1.

As shown inFIG.2, the connection portion26connects a rear end edge of the column small-diameter portion24and a front end edge of the column large-diameter portion25. In the illustrated example, an outer diameter of the connection portion26gradually increases toward the rearward direction. However, the connection portion26may be orthogonal to the axis O.

The column large-diameter portion25extends rearward from a rear end edge of the connection portion26. An outer diameter of the column large-diameter portion25is larger than the inner diameter of the outer column21. In the inner column22of the present embodiment, the column small-diameter portion24is an insertable region configured to be capable of being inserted into the outer column21. In the inner column22, the column large-diameter portion25and the connection portion26form a non-insertable region which cannot enter into the outer column21.

A front-end portion of the column large-diameter portion25constitutes a thickened portion25aof which an inner diameter is larger than that of a portion positioned behind the front-end portion (hereinafter referred to as a thinned portion25b). A stepped surface (a first stopper)25corthogonal to the axis O is formed at a boundary between the thickened portion25aand the thinned portion25b. Also, if the column large-diameter portion25is configured to have at least the stepped surface25c, dimensions of the outer diameter and the inner diameter can be changed as appropriate.

As shown inFIG.1, the steering shaft12includes an outer shaft (a front shaft)40and an inner shaft (a rear shaft)41.

The outer shaft40is formed in a hollow cylindrical shape extending along the axis O. The outer shaft40is inserted into the outer column21. A gap is formed between an outer circumferential surface of the outer shaft40and the inner circumferential surface of the outer column21in the radial direction. A rear-end portion of the outer shaft40enters into the inner column22. A front-end portion of the outer shaft40is press-fitted to an inner ring of the front bearing28described above. Thus, the outer shaft40is supported in the outer column21via the front bearing28to be rotatable around the axis O. The front-end portion of the outer shaft40protrudes forward from the outer column21. The front-end portion of the outer shaft40(a portion protruding forward from the outer column21) is connected to, for example, a steering gear box (not shown) or the like via a universal joint (not shown) or the like.

A key lock collar45is externally fitted to an axially intermediate portion of the outer shaft40(fitted to the outer circumferential surface of the outer shaft40). The key lock collar45is formed in a tubular shape. An outer diameter of the key lock collar45is smaller than an inner diameter of the column small-diameter portion24. Grooves46extending in the axial direction are formed in the key lock collar45. A plurality of grooves46are formed at intervals in the circumferential direction. In the outer column21, a slit48penetrating the outer column21is formed in a portion positioned below the key lock collar45. At the time of ignition off or the like in the vehicle, a locking member (not shown) enters into any one of the grooves46through the slit48(a locked state). Thus, rotation of the steering shaft12relative to the column unit11is restricted.

The inner shaft41is formed in a hollow cylindrical shape extending along the axis O. Specifically, in the inner shaft41, a sliding portion (an insertable region)51, a bearing-mounting portion (a non-insertable region)52, and a wheel connection portion (a non-insertable region)53are formed consecutively from the front to the rear. In the present embodiment, the sliding portion51, the bearing-mounting portion52, and the wheel connection portion53are formed to have a uniform diameter.

The sliding portion51is inserted into the outer shaft40from behind. The inner shaft41is configured to be movable relative to the outer shaft40in the axial direction while an outer circumferential surface of the sliding portion51slides on an inner circumferential surface of the outer shaft40with the movement of the inner column22relative to the outer column21in the axial direction. In addition, for example, a male spline (not shown) is formed on the outer circumferential surface of the sliding portion51. The male spline engages with a female spline (not shown) formed on the inner circumferential surface of the outer shaft40. Thus, the inner shaft41moves relative to the outer shaft40in the axial direction while its rotation relative to the outer shaft40is restricted. However, a structure for a telescopic operation and a structure for a rotation restriction of the steering shaft12can be changed as appropriate.

The wheel connection portion53protrudes rearward from the inner column22. The steering wheel2is connected to the wheel connection portion53.

As shown inFIG.2, rear bearings61and62are mounted at both end portions of the bearing-mounting portion52in the axial direction. Thus, the inner shaft41is configured to be rotatable relative to the inner column22around the axis O.

The rear bearings61and62are a first bearing61and a second bearing62positioned behind the first bearing61. Inner rings of the respective rear bearings61and62are press-fitted into the bearing-mounting portion52with a spacer65interposed between the respective rear bearings61and62. The spacer65is formed in a tubular shape surrounding a circumference of the inner shaft41. Both end faces of the spacer65in the axial direction come into contact with the inner rings of the respective rear bearings61and62. Also, the spacer65may be formed integrally with the inner shaft41.

The outer rings of the rear bearings61and62are press-fitted into the thinned portion25bof the column large-diameter portion25. The outer ring of the first bearing61comes into contact with the above-described stepped surface25cfrom behind. On the other hand, a caulking portion (a second stopper)67formed at a rear-end portion of the column large-diameter portion25abuts the outer ring of the second bearing62from behind.

In the present embodiment, a distance D between the rear bearings61and62(an interval between the rear bearings61and62) is preferably set to be 40 mm or less, and is more preferably set to be 20 mm or more and 40 mm or less.

Also, the steering device1of the present embodiment includes a telescopic adjustment mechanism (not shown). The telescopic adjustment mechanism switches between a locked state that restricts the movement of the inner column22(inner shaft41) relative to the outer column21(outer shaft40) in the axial direction and an unlocked state that allows the movement in the axial direction. For example, in the locked state, the telescopic adjustment mechanism fastens the inner column22via the outer column21. Thus, the movement of the inner column22relative to the outer column21is restricted.

On the other hand, in the unlocked state, the telescopic adjustment mechanism releases the fastening of the inner column22. Thus, the movement of the inner column22relative to the outer column21is allowed. For example, in the unlocked state, by pushing the steering wheel2forward, the steering wheel2moves forward together with the inner column22and the inner shaft41. In the unlocked state, by pulling the steering wheel2rearward, the steering wheel2moves rearward together with the inner column22and the inner shaft41. Then, by switching the telescopic adjustment mechanism to the locked state again, a position of the steering wheel2in the front-to-rear direction can be set to an arbitrary position.

In the case of a secondary collision, a collision load directed forward is applied to the steering wheel2from the driver. When the collision load is equal to or more than a predetermined value, the steering wheel2moves forward relative to the outer column21(outer shaft40) together with the inner column22and the inner shaft41. At this time, the collision load applied to the driver at the time of the secondary collision is relieved by a sliding resistance between the outer column21and the inner column22.

On the other hand, in the configuration of Patent Literature 1 mentioned above, the inner shaft is rotatably supported in the outer column disposed further forward in the vehicle body, and the outer shaft is rotatably supported in the inner column disposed further rearward in the vehicle body. In this case, if a mounting member such as a key lock collar is mounted forward in the vehicle body, the mounting member and the outer shaft may interfere with each other when the inner column (outer shaft) moves forward. For this reason, in the configuration of Patent Literature 1, it is difficult to secure a stroke amount in the telescopic operation and a secondary collapse.

Therefore, the present embodiment is configured such that the outer shaft40is rotatably supported in the outer column21disposed on the front side of the vehicle body, and the inner shaft41is rotatably supported in the inner column22disposed on the rear side of the vehicle body.

According to this configuration, the mounting member (for example, the key lock collar45or the like) can be inhibited from being disposed on a movement trajectory of the inner column22or the inner shaft41. For this reason, interference between the inner column22or the inner shaft41and the mounting member at the time of the stroke such as during the telescopic operation or the secondary collapse can be inhibited. Thus, the stroke amount of the inner column22and the inner shaft41can be secured as compared to the conventional technique.

In particular, in the present embodiment, the rear bearings61and62are mounted on the bearing-mounting portion52with an interval therebetween in the axial direction.

According to this configuration, in a rear portion of the inner shaft41, the plurality of rear bearings61and62can be mounted on a portion which is configured not to be capable of being inserted into the outer shaft40at the time of the telescopic operation or the secondary collapse. Thus, interference between the first bearing61and the outer shaft40and members surrounding the outer shaft40can be inhibited at the time of the stroke. A displacement of the inner shaft41is inhibited by the rear bearings61and62, and the inner shaft41is stably supported. Thus, vibrational stiffness can be improved.

Therefore, in the present embodiment, a desired vibrational stiffness can be obtained while securing the stroke amount.

In the present embodiment, the outer diameter of the key lock collar45is configured to be smaller than an inner diameter of the inner column22.

According to this configuration, regardless of the place where the key lock collar45is disposed, interference between the inner column22and the key lock collar45can be reliably inhibited at the time of the stroke of the inner column22. Thus, the stroke amount of the inner column22can be secured.

Second Embodiment

Next, a second embodiment of the present disclosure will be described.FIG.3is an enlarged cross-sectional view of a steering device100according to the second embodiment. The present embodiment is different from the above-described embodiment in that the bearing-mounting portion52is formed to have a diameter larger than that of the sliding portion51. In the following description, components the same as those of the above-described embodiment are denoted by the same reference signs, and the description thereof will be omitted.

In the steering device100shown inFIG.3, the inner shaft41has a tubular portion101and a solid portion102. The tubular portion101constitutes the sliding portion51. The solid portion102is joined to a rear-end portion of the tubular portion101. The solid portion102constitutes the bearing-mounting portion52and the wheel connection portion53. That is, in the present embodiment, the sliding portion51is formed in a hollow cylindrical shape as in the first embodiment described above. On the other hand, the bearing-mounting portion52and the wheel connection portion53are formed integrally in a solid cylindrical shape.

The bearing-mounting portion52has small-diameter portions (a first small-diameter portion110and a second small-diameter portion111) positioned at both end portions in the axial direction, and a large-diameter portion112positioned between the small-diameter portions110and111.

Outer diameters of the small-diameter portions110and111are larger than an outer diameter of the sliding portion51.

A first boundary surface114orthogonal to the axis O is formed at a boundary between the first small-diameter portion110and the large-diameter portion112.

On the other hand, a second boundary surface115orthogonal to the axis O is formed at a boundary between the second small-diameter portion111and the large-diameter portion112.

The inner ring of the first bearing61is externally fitted to the first small-diameter portion110(fitted to an outer circumferential surface of the first small-diameter portion110). The inner ring of the first bearing61comes into contact with the first boundary surface114from the front. On the other hand, the outer ring of the first bearing61comes into contact with the above-described stepped surface25cfrom behind.

The inner ring of the second bearing62is externally fitted to the second small-diameter portion111(fitted to an outer circumferential surface of the second small-diameter portion111). The inner ring of the second bearing62comes into contact with the second boundary surface115from behind. On the other hand, the outer ring of the second bearing62abuts the caulking portion67from the front.

Also in the present embodiment, the distance D between the rear bearings61and62(a length of the large-diameter portion112in the axial direction) is preferably set to be 40 mm or less, and is more preferably set to be 20 mm or more and 40 mm or less.

Also, a method for assembling the inner shaft41to the inner column22is as follows.

First, the first bearing61is press-fitted into the first small-diameter portion110. Next, the inner shaft41is press-fitted into the inner column22from behind. The inner shaft41is press-fitted until the outer ring of the first bearing61abuts the stepped surface25c. Thus, the first bearing61is press-fitted into the inner column22.

Subsequently, the second bearing62is press-fitted between the second small-diameter portion111and the thinned portion25bof the inner column22from behind. Then, the rear-end portion of the inner column22is caulked to form the caulking portion67. Thus, the inner shaft41is rotatably assembled to the inner column22.

With this configuration, a positional deviation of the rear bearings61and62relative to the inner column22in the axial direction can be inhibited and the inner shaft41can be prevented from coming off.

In particular, since the steering shaft12is prevented from coming off by the stepped surface25cand the caulking portion67which are formed in the inner column22, it is unnecessary to separately use a stop ring or the like for fixing the outer ring. For this reason, the number of components can be reduced.

A diameter of the wheel connection portion53is gradually reduced rearward from a rear end edge of the second small-diameter portion111, and then the wheel connection portion53further extends rearward. The steering wheel2is connected to a rear-end portion of the wheel connection portion53.

In the present embodiment, the bearing-mounting portion52is configured to be formed by the solid portion102.

According to this configuration, rigidity of the bearing-mounting portion52can be improved, so that vibrational stiffness can be further improved.

In particular, in the present embodiment, only the bearing-mounting portion52and the wheel connection portion53are formed by the solid portion102. Thus, in the present embodiment, it is possible to inhibit an increase in weight accompanying the adoption of the solid portion102as much as possible, as compared to a case in which the entire inner shaft41is formed to be solid.

In the present embodiment, an outer diameter of the bearing-mounting portion52is configured to be larger than the outer diameter of the sliding portion51.

According to this configuration, since rigidity of the inner shaft41can be improved, vibrational stiffness can be improved.

Moreover, in the present embodiment, only the bearing-mounting portion52is formed to have a larger diameter. Thus, in the present embodiment, it is possible to inhibit an increase in weight accompanying the increase in diameter as much as possible, as compared to a case in which the entire inner shaft41is formed to have a large-diameter.

In addition, although the case where the bearing-mounting portion52and the wheel connection portion53are formed to be solid have been described in the second embodiment described above, the present disclosure is not limited only to this configuration. At least one of the bearing-mounting portion52and the wheel connection portion53may be hollow.

In the second embodiment described above, although the configuration in which the inner shaft41is formed to be solid and is enlarged in diameter in order to secure rigidity of the inner shaft41has been described, the present disclosure is not limited to this configuration, and a part of the inner shaft41may be formed to have a thicker thickness.

Here, the present inventor studied a relationship between the distance D between the rear bearings61and62and vibrational stiffness by using a simulation.FIG.4is a graph showing the relationship between the distance D and vibrational stiffness. Also, inFIG.4, a solid line indicates vibrational stiffness in the horizontal direction, and a broken line indicates vibrational stiffness in the vertical direction.

As shown inFIG.4, it can be understood that vibrational stiffness increases as the distance D increases. However, a rate of change in vibrational stiffness in the range where the distance D is longer than 40 mm is smaller than a rate of change in vibrational stiffness in the range where the distance D is 40 mm or less. That is, it can be understood that, if the distance D exceeds a predetermined range, even when the distance D increases therefrom, no significant improvement in the vibrational stiffness can be expected.

Therefore, as in the present embodiment, even when the portion of the inner shaft41positioned behind the sliding portion51is set to be the bearing-mounting portion52, it is unnecessary to secure a pretty large length of the bearing-mounting portion52in the axial direction in order to secure vibrational stiffness.

Since a required vibrational stiffness varies depending on a vehicle where it is mounted, the distance D may be set appropriately. In the present embodiment, the distance D between the rear bearings61and62is set to be 20 mm or more and 40 mm or less. Thus, interference between the first bearing61and a mounting member can be inhibited, and a desired vibrational stiffness can be obtained while securing the stroke amount. The distance D is more preferably set to be 25 mm or more and 35 mm or less. As a result, a balance between a weight of the bearing-mounting portion52and vibrational stiffness is improved, and vibrational stiffness can be enhanced without excessively increasing the weight. The steering shaft12is not limited to the configuration including the outer shaft40and the inner shaft41. Even in a configuration consisting of a single steering shaft, a desired vibrational stiffness can be obtained by setting the distance D between the rear bearings61and62in the same manner. That is, even in a configuration in which the steering shaft is rotatably supported in a steering column via the rear bearings61and62and the front bearing28, the rear bearings61and62may be spaced apart at a distance D.

Third Embodiment

Next, a third embodiment of the present disclosure will be described.FIG.5is an enlarged cross-sectional view of a steering device200according to the third embodiment. The present embodiment is different from the embodiments described above in that a resin bush is used for at least one of the rear bearings61and62(the first bearing61in the present embodiment).

In the steering device200shown inFIG.5, the inner shaft41is formed in a hollow cylindrical shape throughout the entire shaft in the axial direction. The inner shaft41has a tubular portion201and a support portion202. The tubular portion201constitutes a sliding portion51.

The support portion202extends rearward from a rear-end portion of the tubular portion201. The support portion202constitutes the bearing-mounting portion52and the wheel connection portion53.

The bearing-mounting portion52has tapered portions (a first tapered portion210and a second tapered portion211) positioned at both end portions in the axial direction, and a large-diameter portion212positioned between the tapered portions210and211.

The first tapered portion210is gradually enlarged in diameter toward the rear. A front-end portion of the first tapered portion210is connected to a rear-end portion of the tubular portion201. A rear-end portion of the first tapered portion210is connected to a front-end portion of the large-diameter portion212.

The second tapered portion211is gradually enlarged in diameter toward the front. A front-end portion of the second tapered portion211is connected to a rear-end portion of the large-diameter portion212.

A reduced diameter portion215whose outer diameter is reduced as compared to its front portion (an enlarged diameter portion214) is formed at the rear-end portion of the large-diameter portion212. A rear end face (a stepped surface between the enlarged diameter portion214and the reduced diameter portion215) of the enlarged diameter portion214constitutes a second boundary surface221orthogonal to the axis O.

The inner column22has a column large-diameter portion225, a connection portion226and a column small-diameter portion227. The column large-diameter portion225is positioned in front of the column small-diameter portion227. The connection portion226connects between a rear-end portion of the column large-diameter portion225and a front-end portion of the column small-diameter portion227.

An outer diameter of the column large-diameter portion225is smaller than the inner diameter of the outer column21. The column large-diameter portion225is inserted into the outer column21from behind the outer column21.

As shown inFIG.5, the first bearing61in the present embodiment is a resin bush. The first bearing61is formed in a multi-stepped cylindrical shape disposed coaxially with the axis O. Specifically, the first bearing61has a shaft support portion231, a connection cylinder232, and a column support portion233.

The shaft support portion231is formed to be smaller in diameter than the column support portion233. The shaft support portion231surrounds a front-end portion of the large-diameter portion212(the enlarged diameter portion214). Sliding support portions235are formed on an inner circumferential surface of the shaft support portion231. The sliding support portions235bulge out from the inner circumferential surface of the shaft support portion231inward in the radial direction. A plurality of sliding support portions235are disposed at intervals in the circumferential direction. Each sliding support portion235slidably supports an outer circumferential surface of the large-diameter portion212. Therefore, the shaft support portion231rotatably supports the inner shaft41via the sliding support portions235. Also, the shaft support portion231may directly support the inner shaft41.

The connecting cylinder232is gradually enlarged in diameter toward the rear. The connection cylinder232may connect the shaft support portion231and the column support portion233via a step.

An inner diameter of the column support portion233is larger than an outer diameter of the inner shaft41. An outer diameter of the column support portion233is equal to or less than the inner diameter of the inner column22(column small-diameter portion227). Therefore, an outer circumferential surface of the column support portion233approaches or abuts an inner circumferential surface of the inner column22(column small-diameter portion227). Positioning convex portions240are formed on the column support portion233. The positioning convex portions240are formed in hemispherical shapes which bulge out from the column support portion233outward in the radial direction. The positioning convex portions240are fitted into positioning holes241formed in the inner column22. Thus, rotation of the first bearing61relative to the inner column22around the axis O is restricted. In the present embodiment, a plurality of positioning convex portions240are disposed at intervals in the circumferential direction.

A front slit250and a rear slit251are formed in the first bearing61. Each slit250and251extends in the axial direction. The slits250and251are alternately (by turns) disposed in the circumferential direction.

The front slit250opens at a front end face of the shaft support portion231and reaches a front portion of the column support portion233through the connection cylinder232.

The rear slit251opens at a rear end face of the column support portion233and reaches a rear portion of the shaft support portion231through the connection cylinder232.

In the first bearing61, portions positioned between the front slits250adjacent to each other in the circumferential direction (mainly the shaft support portion231and the connection cylinder232) are configured to be elastically deformable in the radial direction.

In the first bearing61, portions positioned between the rear slits251adjacent to each other in the circumferential direction (mainly the column support portion233and the connection cylinder232) are configured to be elastically deformable in the radial direction.

The inner ring of the second bearing62is press-fitted into the reduced diameter portion215of the inner shaft41. The inner ring of the second bearing62abuts the second boundary surface221from behind.

The outer ring of the second bearing62is press-fitted into the inner column22. The caulking portion67abuts the outer ring of the second bearing62from behind.

Also in the present embodiment, the distance D between the rear bearings61and62(the distance between the rear bearings230and62) may be set to be 40 mm or less.

In the present embodiment, in addition to achieving effects similar to those of the above-described embodiments, a configurational simplification can be achieved by adopting the resin bush for the first bearing61.

In the embodiment described above, although the case where the resin bush is adopted for the first bearing61has been described, the present disclosure is not limited to this configuration. The resin bush may be configured to be adopted to at least one of the front bearing28and the rear bearings (the first bearing61and the second bearing62). In the case of using the resin bush for the second bearing62, for example, the second bearing62may be assembled to the inner shaft41with the shaft support portion231facing rearward.

As described above, although the preferred embodiments of the present disclosure have been described, the present disclosure is not limited to these embodiments. Additions, omissions, substitutions, and other modifications of the configuration are possible without departing from the spirit of the present disclosure. The present disclosure is not limited by the foregoing description, but is only limited by the scope of the appended claims.

For example, in the embodiments described above, although the configuration in which the axis O intersects in the front-to-rear direction has been described, the present disclosure is not limited to this configuration. The axis O may coincide with a longitudinal direction of the vehicle3or may be inclined in a lateral direction thereof.

In the embodiments described above, although the configuration in which the outer column21supports the outer shaft40and the inner column22supports the inner shaft41behind the outer column21has been described, the present disclosure is not limited to this configuration. For example, the outer column21may support the inner shaft41, and the inner column22may support the outer shaft40behind the outer column21.

The outer column (rear column)21may be configured to be positioned behind the inner column (front column)22. In this case, the outer column21may support any one of the outer shaft40and the inner shaft41(rear shaft). The inner column22may support the other one of the outer shaft40and the inner shaft41(front shaft).

In the embodiments described above, the configuration in which the rear bearings61and62are disposed at the rear portion of the inner column22positioned on the rear side of the vehicle body has been described. However, when the outer column21is disposed on the rear side of the vehicle body, a configuration in which two front bearings are provided may be adopted. Also in this case, the distance between the front bearings is preferably set to be 40 mm or less, more preferably 20 mm or more and 40 mm or less, and further preferably 25 mm or more to 35 mm or less. Thus, a desired vibrational stiffness can be obtained while securing the stroke amount.

In the embodiments described above, although the configuration in which the key lock collar45is externally fitted to the outer shaft40has been described, the present disclosure is not limited to this configuration. For example, the steering device1may not have the key lock collar45. A mounting member other than the key lock collar45may be externally fitted to the outer shaft40.

In addition, it is possible to replace components in the above-described embodiments with known components as appropriate without departing from the spirit of the present disclosure, and the above-described modified examples may be combined as appropriate.

REFERENCE SIGNS LIST