Steering column device

A steering column device includes a cylindrical inner tube, and a cylindrical outer tube which is fixed to the inner tube by being externally fitted to slide in an axial direction of the inner tube and being elastically reduced in diameter, wherein the outer tube is configured to have a first slit and a second slit to be reduced in diameter. A stress alleviation portion is provided at the second slit. A contour shape of the stress alleviation portion is set to include an elliptic arc-shaped portion of which a direction of a major axis is a direction intersecting the second slit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2019-166944 filed on Sep. 13, 2019, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a steering column device.

2. Description of Related Art

Conventionally, there is a steering column which rotatably supports a steering shaft of a vehicle. For example, a steering column of Japanese Unexamined Patent Application Publication No. 2009-6847 (JP 2009-6847 A) has a double pipe structure including an inner column and an outer column. A first slit which extends along an axis of the outer column and a second slit which is continuous with the first slit and extends in a circumferential direction of the outer column are provided in the outer column. Further, a pair of clamp portions which face each other with the first slit interposed therebetween is provided on the outer column. These clamp portions are sandwiched by column brackets fixed to a vehicle body. The inner column is tightened by reducing a diameter of the outer column due to elastic deformation of the clamp portions in directions in which they approach each other through an operation of a clamp device provided on the column bracket. Thus, relative movement between the inner column and the outer column in an axial direction is restricted.

SUMMARY

According to the steering column of JP 2009-6847 A, a rigidity when the diameter of the outer column is reduced is reduced by providing the first slit and the second slit in the outer column. A force required to reduce the diameter of the outer column and thus a force to operate the clamp device can be reduced by an amount that the rigidity of the outer column is reduced. Accordingly, operability of the clamp device is ensured.

However, when the diameter of the outer column is reduced, stress is concentrated on a distal end portion of the second slit. To alleviate the stress concentration at the distal end portion, a stress concentration alleviating portion is provided at the distal end portion of the second slit. The stress concentration alleviating portion opens in a circular shape having a diameter larger than a width of a portion of the second slit up to the distal end portion. A curvature of the distal end portion of the second slit becomes smaller by setting a diameter of the stress concentration alleviating portion to a value larger than the width of the portion of the second slit up to the distal end portion. Therefore, when the diameter of the outer column is reduced, the stress concentration on the distal end portion of the second slit is alleviated.

However, in the steering column of JP 2009-6847 A, the following may occur. For example, when a steering wheel is operated while rotation of a steering shaft is restricted by a steering lock device, a twisting force around an axis thereof is applied to the outer column. In this case, the stress may still be concentrated on the distal end portion of the second slit including the circular stress concentration alleviating portion.

The present disclosure provides a steering column device which is able to more appropriately alleviate stress concentration when a twisting force is applied to an outer tube.

A steering column device according to a first aspect of the present disclosure is a steering column device which rotatably supports a steering shaft. The steering column device includes a cylindrical inner tube, and a cylindrical outer tube which is fixed to the inner tube by being externally fitted to slide in an axial direction of the inner tube and being elastically reduced in diameter. The outer tube is configured to have a first slit which extends in an axial direction of the outer tube and a second slit which is continuous with the first slit and extends in a direction intersecting the first slit to be reduced in diameter. A stress alleviation portion which opens to have a width longer than a width up to an end portion of the second slit on a side opposite to the first slit is provided at the end portion. A contour shape of the stress alleviation portion is set to include an elliptic arc-shaped portion of which a direction of a major axis is a direction intersecting the second slit.

With such a configuration, it is possible to make a curvature of the end portion of the second slit smaller in a limited space by setting the contour shape of the end portion of the second slit to include the elliptic arc-shaped portion of which the direction of the major axis is the direction intersecting the second slit. Therefore, when a twisting force is applied to the outer tube for some reason, it is possible to more appropriately suppress stress concentration on the end portion of the second slit in the outer tube.

In the aspect, an opening portion into which an accessory component is inserted may be provided in the outer tube at a distance from the stress alleviation portion in the axial direction of the outer tube, and the stress alleviation portion may extend toward a side opposite to the opening portion in the axial direction of the outer tube.

With such a configuration, a rigidity between the second slit and the opening portion of the outer tube can be easily ensured as compared with a case in which the stress alleviation portion extends toward the opening portion side in the axial direction of the outer tube.

In the aspect, the accessory component may be a lock member which engages with a part of the steering shaft and restricts rotation of the steering shaft.

With such a configuration, when a torque is applied to the steering shaft while the rotation of the steering shaft is restricted by the lock member, a twisting force is applied to the outer tube. It is possible to appropriately suppress stress concentration on the end portion of the second slit by providing the stress alleviation portion at the end portion of the second slit.

In the aspect, the stress alleviation portion may extend toward both sides of a portion of the second slit up to the stress alleviation portion in a width direction. Such a configuration can be adopted when there is no opening portion near the second slit in the outer tube.

In the aspect, the stress alleviation portion and the portion of the second slit up to the stress alleviation portion may be smoothly continuous. With such a configuration, stress concentration on a peripheral edge portion of the second slit in the outer tube is suppressed.

In the aspect, a contour shape of the stress alleviation portion may be elliptical. It is conceivable to set the contour shape of the end portion of the second slit to a circular shape, and when it is assumed that the stress alleviation portions are provided in regions having the same size, a curvature of the elliptic arc in the direction of the major axis is smaller than the curvature of the arc. Therefore, it is possible to further reduce the curvature of the end portion of the second slit in a limited space by adopting the elliptical shape as the contour shape of the stress alleviation portion.

According to the steering column device of the present disclosure, it is possible to more appropriately alleviate stress concentration when a twisting force is applied to an outer tube.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a steering column device will be described. As shown inFIG. 1, the steering column device1rotatably supports a steering shaft2. A steering wheel3is connected to a first end portion of the steering shaft2. A second end portion of the steering shaft2engages with a rack shaft which extends in a right and left direction of a vehicle body via an intermediate shaft and a pinion shaft. Both end portions of the rack shaft are connected to right and left steered wheels via tie rods. A direction of steered wheels is changed in accordance with an operation of a steering wheel3.

The steering shaft2has an outer shaft11and an inner shaft12. The outer shaft11and the inner shaft12are connected to each other by, for example, spline connection. The outer shaft11and the inner shaft12are integrally rotatable and relatively movable in an axial direction of each other. The steering shaft2is provided obliquely to a forward and rearward direction X1of a vehicle so that the steering wheel3is located on the upper side.

The steering column device1has a steering column15fixed to a fixed portion13such as a frame of a vehicle body. The steering shaft2is inserted through the steering column15. The steering shaft2is rotatably supported by the steering column15via a bearing.

The steering column15has an outer tube16and an inner tube17. Each of the outer tube16and the inner tube17has a tubular shape. The outer tube16and the inner tube17are fitted to each other to be movable relative to each other in the axial direction of the steering shaft2. The inner tube17is inserted into the outer tube16from the side opposite to the steering wheel3. The outer tube16is fixed to the fixed portion13on the vehicle body side via a column bracket21.

As shown inFIG. 2, the column bracket21has an upper bracket22, a tilt bracket23, and two clamp brackets24aand24b. The upper bracket22has a flat plate shape which extends in the right and left direction of the vehicle body (the right and left direction inFIG. 2). Mounting seats22aare respectively provided at both ends of the upper bracket22. The upper bracket22is fixed to the fixed portion13of the vehicle body through the mounting seats22aand22a. Specifically, it is as follows.

That is, two bolts31and31are provided on the fixed portion13to protrude therefrom. The bolts31and31extend so that an axial direction Z1thereof intersects a vertical direction. The bolts31and31are provided one by one on the left side and the right side of the vehicle body with respect to the steering shaft2when seen in the axial direction of the steering shaft2. The bolt31is a stud bolt having male threads on both ends thereof. A first end portion of the bolt31is screwed into the fixed portion13. A second end portion of the bolt31passes through the mounting seat22a. The mounting seat22ais fixed to the fixed portion13by tightening a nut32on the second end portion of the bolt31. A washer33is interposed between the nut32and the mounting seat22a.

The tilt bracket23is fixed to the upper bracket22. The tilt bracket23has a square U-shape which opens to the side opposite to the upper bracket22. The tilt bracket23has a connecting plate41and two side plates42aand42b. The connecting plate41is fixed to a surface (a lower surface inFIG. 2) of the upper bracket22opposite to the fixed portion13of the vehicle body. The two side plates42aand42bare connected to both side edges of the connecting plate41in the right and left direction of the vehicle body when seen in the axial direction of the steering shaft2. The two side plates42aand42bextend toward the side opposite to the fixed portion13of the vehicle body (downward inFIG. 2). Long holes which extend in the axial direction Z1of the bolt31are provided in the two side plates42aand42b.

The two clamp brackets24aand24bare formed by bending a metal flat plate into a square U-shape. The two clamp brackets24aand24bare fixed to an outer peripheral surface of the outer tube16. The two clamp brackets24aand24bextend toward the side opposite to the fixed portion13of the vehicle body (downward inFIG. 2). The two clamp brackets24aand24bare located inside the two side plates42aand42bof the tilt bracket23in the right and left direction of the vehicle body when seen in the axial direction of the steering shaft2and are held in a state in which they are in contact with the two side plates42aand42b. Long holes which extend in the axial direction of the steering shaft2are provided in the two clamp brackets24aand24b.

The tilt bracket23and the two clamp brackets24aand24bare connected via a tightening shaft51configured of a bolt. The two clamp brackets24aand24bare supported by the tightening shaft51so that their positions can be adjusted relative to the tilt bracket23. The tightening shaft51extends in a direction intersecting the axial direction of the steering shaft2(the right and left direction inFIG. 2). The tightening shaft51passes through the long holes of the side plates42aand42bof the tilt bracket23and the long holes of the two clamp brackets24aand24b. A nut53is screwed into a tip end portion of the tightening shaft51having passed which is an end portion on the side opposite to a head portion52. On the tightening shaft51, a lever54is rotatably supported between the head portion52and one (the left side inFIG. 2) clamp bracket24a.

A first cam55is integrally provided on a side surface of a base end portion of the lever54on the clamp bracket24aside. Further, a second cam56is provided between the first cam55and one side plate42aof the tilt bracket23. The second cam56is provided in a state in which relative rotation with respect to the side plate42ais restricted. A plurality of protruding portions is provided at intervals on a peripheral edge portion of a side surface of the first cam55on the second cam56side. A plurality of protruding portions is also provided at intervals on a peripheral edge portion of a side surface of the second cam56on the first cam55side. A rotational position of the first cam55is switched between a first rotational position and a second rotational position by a rotation operation of the lever54. The first rotational position is a position at which the protruding portions of the first cam55engage between the protruding portions of the second cam56. The second rotational position is a position at which the protruding portions of the first cam55ride on the protruding portions of the second cam56.

When the rotational position of the first cam55is switched from the first rotational position to the second rotational position through the rotation operation of the lever54, the first cam55rotates relatively with respect to the second cam56, and the protruding portions of the first cam55ride on the protruding portions of the second cam56in accordance with such rotation. Since movement of the lever54in a direction along the tightening shaft51is restricted, the second cam56tries to move to the nut53side by an amount that the protruding portions of the first cam55ride on the protruding portions of the second cam56. In accordance with this, the two side plates42aand42bof the tilt bracket23are elastically deformed in directions in which they approach each other and are thus pressed against the two clamp brackets24aand24bbetween the second cam56and the nut53. Accordingly, the relative movement of the two clamp brackets24aand24bwith respect to the tilt bracket23is restricted.

Further, the two clamp brackets24aand24bare elastically deformed in the directions in which they approach each other via the two side plates42aand42bof the tilt bracket23. Here, a slit61is provided in a portion of the outer tube16between the two clamp brackets24aand24b. The slit61has a portion which extends from the first end portion to the second end portion in the axial direction of the outer tube16. Therefore, the outer tube16is elastically deformed in such a manner that a gap between the slits61is narrowed by narrowing a gap between the two clamp brackets24aand24b. That is, the outer tube16is elastically deformed so that an inner diameter thereof becomes smaller, and thus tightens an outer peripheral surface of the inner tube17. Accordingly, the relative movement of the outer tube16with respect to the inner tube17in the axial direction is restricted.

When a position of the steering wheel3is changed, the rotational position of the first cam55may be switched from the second rotational position to the first rotational position by the rotation operation of the lever54. The tightening of the two side plates42aand42bof the tilt bracket23in the direction in which they approach each other and the tightening of the two clamp brackets24aand24bin the direction in which they approach each other are released by fitting the protruding portions of the first cam55between the protruding portions of the second cam56. A distance between the two side plates42aand42band a distance between the two clamp brackets24a,24bare respectively increased by elastically returning the two side plates42aand42bof the tilt bracket23and the two clamp brackets24aand24bto their original positions.

Accordingly, a force with which the two side plates42aand42bof the tilt bracket23sandwich the two clamp brackets24aand24bis weakened. Therefore, the outer tube16to which the two clamp brackets24aand24bare fixed can move relatively with respect to the tilt bracket23in the vertical direction. The position of the steering wheel3in the vertical direction can be adjusted by moving the steering wheel3in the vertical direction. Further, the outer tube16can move relatively with respect to the inner tube17in the axial direction by releasing the tightening of the inner tube17by the outer tube16. The position of the steering wheel3in the axial direction can be adjusted by moving the steering wheel3in the axial direction.

Next, the outer tube16will be described in detail. As shown inFIG. 3, the slit61and a rectangular opening portion62are provided in a peripheral wall of the outer tube16. The opening portion62is located between the slit61and an end portion (a right end portion inFIG. 3) of the outer tube16on the steering wheel3side in the axial direction.

As shown inFIG. 4, a lock recessed portion63is provided in a peripheral wall of the outer shaft11. The lock recessed portion63extends in the axial direction of the outer shaft11. A position of the lock recessed portion63of the outer shaft11and a position of the opening portion62of the outer tube16are aligned with each other in the axial direction of the outer shaft11. Therefore, during one rotation of the outer shaft11, a state in which the lock recessed portion63and the opening portion62are aligned with each other in a rotation direction of the outer shaft11is formed.

In the state in which the lock recessed portion63of the outer shaft11and the opening portion62of the outer tube16are aligned with each other in the rotation direction of the outer shaft11, a lock member64of a steering lock device is inserted into the lock recessed portion63through the opening portion62. The lock member64moves between a lock position and an unlock position, for example, in conjunction with an operation of an ignition key. The lock position is a position at which a tip end of the lock member64is inserted into the lock recessed portion63of the outer shaft11through the opening portion62of the outer tube16. The unlock position is a position at which the tip end of the lock member64is pulled out of the lock recessed portion63or the opening portion62.

When the ignition key is turned from an ON position of a vehicle power supply to the lock position, the lock member64moves from the unlock position to the lock position. When the steering shaft2is about to rotate through the operation of the steering wheel3, an inner surface of the lock recessed portion63of the outer shaft11engages with the lock member64. Thus, the rotation of the steering shaft2and thus the steering wheel3is restricted. On the other hand, when the ignition key is turned from the lock position to the ON position of the power supply, the lock member64moves from the lock position to the unlock position. Accordingly, the rotation of the steering wheel3is allowed.

As shown inFIG. 3, the slit61has a first slit71and a second slit72. The first slit71and the second slit72are continuous with each other and have an L shape as a whole.

The first slit71extends in the axis of the outer tube16. The first slit71is provided in a range from an end portion (a left end portion inFIG. 3) of the outer tube16opposite to the steering wheel3to the vicinity of a center of the outer tube16in the axial direction. The end portion of the first slit71opposite to the steering wheel3is open. The second slit72extends in a direction which intersects the first slit71starting from an end portion (a right end portion inFIG. 3) of the first slit71on the steering wheel3side, here, in a circumferential direction of the outer tube16. In the axial direction of the outer tube16, the second slit72and the opening portion62are adjacent to each other with a predetermined interval therebetween.

As shown inFIG. 5, a stress alleviation portion72ais provided at an end portion of the second slit72. The end portion of the second slit72is an end portion of the second slit72on the side opposite to the first slit71. The stress alleviation portion72aopens in an elliptical shape having a major axis longer than a width of a portion of the second slit72up to the stress alleviation portion72a. The stress alleviation portion72aextends in the axial direction of the outer tube16toward the side opposite to the opening portion62(the left side inFIG. 5). That is, the stress alleviation portion72ais provided not to protrude to the opening portion62side (the right side inFIG. 5) based on the portion of the second slit72up to the stress alleviation portion72a. The stress alleviation portion72aand the portion of the second slit72up to the stress alleviation portion72aare continuous with each other via a smooth curved surface.

Now, after the adjustment of the position of the steering wheel3is completed, the rotational position of the first cam55is switched from the first rotational position to the second rotational position by the rotation operation of the lever54. In accordance with this operation, the two side plates42aand42bof the tilt bracket23are tightened in the directions in which they approach each other, and thus the relative movement of the two clamp brackets24aand24bwith respect to the tilt bracket23is restricted. Further, a diameter of a portion of the outer tube16in which the slit61is provided is reduced to tighten the outer peripheral surface of the inner tube17. Accordingly, the relative movement of the outer tube16with respect to the inner tube17in the axial direction is restricted.

Here, the slit61provided between the two clamp brackets24aand24bin the outer tube16has not only the first slit71which extends in the axial direction of the outer tube16but also the second slit72which extends in the circumferential direction of the outer tube16. Therefore, a rigidity when the diameter of the portion of the outer tube16in which the slit61is provided is reduced becomes lower than that of the other portions. Since an operating force of the lever54required to reduce the diameter of the outer tube16becomes smaller, the operability of the lever54improves.

Next, the operation of the stress alleviation portion72awill be described. When the ignition key is operated from the ON position of the vehicle power supply to the lock position, the lock member64is inserted into the lock recessed portion63of the outer shaft11through the opening portion62of the outer tube16, and thus the rotation of the steering shaft2is restricted. In this state, for example, when the steering wheel3is intended to be operated, a twisting force is applied to the outer tube16via the portion in which the opening portion62is provided. The twisting force is transmitted to the slit61as a torque around the axis of the outer tube16. At this time, stress may be concentrated on a tip end portion of the second slit72which is a portion of the outer tube16closest to the opening portion62in the slit61and extends in the circumferential direction of the outer tube16.

In this regard, the elliptical stress alleviation portion72ahaving a major axis longer than the width to the end portion is provided at the end portion of the second slit72. That is, it is possible to further reduce a curvature of the end portion of the second slit72in a limited space by setting a contour shape of the end portion of the second slit72to include an elliptic arc-shaped portion in which a direction intersecting with the second slit72is a direction of a major axis thereof. Therefore, when a twisting force is applied to the outer tube16, it becomes difficult for stress to be concentrated on the end portion of the second slit72including the stress alleviation portion72a. Incidentally, as the curvature of the elliptic arc which is the contour shape of the end portion of the second slit72becomes smaller, in other words, a radius of curvature of the elliptic arc becomes larger, the stress concentration at the end portion of the second slit72is further alleviated.

As shown as a comparative example inFIG. 6, it is also conceivable to set the contour shape of the end portion of the second slit72, that is, the stress alleviation portion72ato, for example, a circular shape having a diameter larger than the width of the portion of the second slit72up to the stress alleviation portion72a.

However, when it is assumed that, for example, the circular stress alleviation portion72aand the elliptical stress alleviation portion72aare provided in regions having the same size, the curvature of the arc becomes larger than the curvature of the elliptic arc in the direction of the major axis. Therefore, although it may be different according to the diameter of the circular stress alleviation portion72a, when the twisting force is applied to the outer tube16, the stress may be still concentrated on the end portion of the second slit72including the circular stress alleviation portion72a.

In order to further alleviate the stress concentration at the end portion of the second slit72, the diameter of the circular stress alleviation portion72amay be set to a larger value. However, as the diameter of the stress alleviation portion72ais set to a larger value, an opening area of the stress alleviation portion72abecomes wider, and thus the rigidity of the portion of the outer tube16in which the slit61is provided is reduced. Further, there is a limit to an increase in a size of the stress alleviation portion72adue to the space limitation on the outer peripheral surface of the outer tube16.

In this regard, it is possible to set the curvature of the end portion of the second slit72to be smaller in a limited space while suppressing an increase in the opening area of the stress alleviation portion72aby setting the contour shape of the stress alleviation portion72ato an elliptical shape.

As shown by a two-dot chain line inFIG. 7, in the case in which a circular shape is adopted as the contour shape of the stress alleviation portion72a, when it is intended to obtain a curvature similar to the curvature of the end portion of the second slit72obtained when the elliptical shape is adopted as the contour shape of the stress alleviation portion72a, the opening area of the circular stress alleviation portion72ais larger than the opening area of the elliptical stress alleviation portion72a.

Therefore, it is possible to more effectively alleviate the stress concentration at the end portion of the second slit72while suppressing an increase in the opening area of the stress alleviation portion72aby adopting an elliptical shape as the contour shape of the stress alleviation portion72a.

In addition, the stress alleviation portion72aextends toward the side opposite to the opening portion62in the axial direction of the outer tube16. Therefore, the rigidity of the portion of the outer tube16between the second slit72and the opening portion62is ensured as compared with the case in which the stress alleviation portion72aextends toward the opening portion62side.

Therefore, according to the embodiment, the following effects can be obtained. It is possible to further reduce the curvature of the end portion of the second slit72in a limited space by setting the contour shape of the end portion of the second slit72to include an elliptic arc-shaped portion having a direction intersecting the second slit72as the direction of the major axis. Therefore, when a twisting force is applied to the outer tube16, it is possible to more appropriately suppress the stress concentration on the end portion of the second slit72in the outer tube16.

Specifically, an elliptical shape is adopted as the contour shape of the stress alleviation portion72aprovided at the end portion of the second slit72. It is conceivable to set the contour shape of the end portion of the second slit72to a circular shape, and for example, when it is assumed that the circular stress alleviation portion72aand the elliptical stress alleviation portion72aare provided in the regions having the same size, the curvature of the elliptic arc in the direction of the major axis is smaller than the curvature of the arc. Therefore, it is possible to further reduce the curvature of the end portion of the second slit72in a limited space by adopting the elliptical shape as the contour shape of the stress alleviation portion72a. Therefore, when a twisting force is applied to the outer tube16, it is possible to more effectively alleviate the stress concentration on the end portion of the second slit72.

The stress alleviation portion72aextends toward the side opposite to the opening portion62in the axial direction of the outer tube16. Therefore, the rigidity of the portion of the outer tube16between the second slit72and the opening portion62can be ensured. A supporting rigidity of the steering shaft2in the outer tube16is also ensured.

The stress alleviation portion72aand the portion of the second slit72up to the stress alleviation portion72aare continuous via a smooth curved surface. Therefore, it is possible to suppress the stress concentration on the peripheral edge portion of the end portion of the second slit72.

The embodiment may be modified as follows. A plurality of lock recessed portions63may be provided at predetermined intervals in the outer shaft11in the circumferential direction thereof. The rotation of the steering shaft2is restricted by inserting the lock member64of the steering lock device into any one of the lock recessed portions63through the opening portion62of the outer tube16.

As a portion into which the lock member64of the steering lock device is inserted, a hole passing through a peripheral wall of the outer shaft11may be adopted instead of the lock recessed portion63. In the embodiment, although the second slit72extends in the circumferential direction of the outer tube16to be orthogonal to the first slit71, the second slit72may be provided to intersect the first slit71at a predetermined acute angle or obtuse angle.

The steering lock device may be not provided at the outer tube16according to use of a product, or the like. In this case, it is possible to adopt a configuration in which the opening portion62is omitted as the outer tube16. Even when the configuration is adopted, a twisting force may be applied to the outer tube16for some reason. In addition, when the configuration in which the opening portion62is omitted is adopted as the outer tube16, as shown inFIG. 8, an elliptical stress alleviation portion72amay be provided to protrude to both sides of the portion of the second slit72up to the stress alleviation portion72a. In this case, as shown inFIG. 9, the elliptical stress alleviation portion72aand a main portion of the second slit72may be continuous with a smooth curve. Even in this case, the same effect in the above embodiment can be obtained.

An opening portion for inserting another accessory member such as a wire harness may be provided at a position near the second slit72in the outer tube16, instead of the opening portion62for inserting the lock member64.

The contour shape of the stress alleviation portion72ais not limited to the elliptical shape. The contour shape of the stress alleviation portion72amay be set to include an elliptic arc-shaped portion of which a direction of a major axis is a direction intersecting the second slit72.