Abstract:
An extendable and contractable steering column apparatus includes an outer column through which an inner column is slidably inserted, a lock housing portion formed on the outer column, and a locking mechanism that includes a pair of movable pieces slidably fitted within a bore formed in the lock housing portion. The locking mechanism shifts the pair of movable pieces toward each other so as to press the inner column and shifts the pair of movable pieces away from each other so as to release the pressure on the inner column, in response to swinging of an operating lever. The cross section of the bore of the lock housing portion is non-circular and the cross sections of said pair of movable pieces are also non-circular correspondingly.

Description:
This application claims the benefit of Japanese Patent Application No. 2002-321482 which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a telescopically length adjustable steering column apparatus for adjusting the position of a steering wheel in the length direction of a vehicle by extending and contracting telescopically the whole length of a steering column through which a steering shaft is inserted in accordance with the physical constitution or the position of the driver. 
   2. Related Background Art 
   As a steering apparatus for a vehicle, there is a telescopically extendable and contractable steering column apparatus (a so-called telescopic steering column apparatus) for adjusting the position of a steering wheel in the length direction of a vehicle by extending and contracting telescopically the whole length of a steering column, through which a steering shaft is inserted, in accordance with the physical constitution or the position of the driver. 
   In the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 6-78155 (Japanese Utility Model Registration No. 2588338), a lock housing portion is formed on an outer column through which an inner column is slidably inserted and a pair of movable pieces are fitted in a cylinder bore formed in the lock housing portion. That apparatus is provided with a locking mechanism for shifting the pair of movable pieces toward each other so as to press the inner column and shifting the pair of movable pieces away from each other to release the pressure on the inner column in response to swinging of an operating lever by the driver. 
     FIG. 4  is a side view showing the lock housing portion of the extendable steering column apparatus disclosed in Japanese Utility Model Application Laid-Open No. 6-78155 (Japanese Utility Model Registration No. 2588338). In this apparatus, the cylinder bore b formed in the lock housing portion a has a circular cross section and the pair of movable pieces c slidably fitted in the cylinder bore also have circular cross sections correspondingly. 
   However, in the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 6-78155 (Japanese Utility Model Registration No. 2588338), since the lock housing portion a has a circular cross section and the pair of movable pieces c also have circular cross sections, in the case that a torque is exerted on the movable piece c when the operating lever is swung, the movable piece is sometimes rotated. 
   In the case that the movable pieces c has been rotated due to swinging of the operating lever, the movable piece may bite the inner column at the time of adjustment of the telescopic position. 
   In addition, in the case that the cross sections of the cylinder bore b and the movable pieces c are circular, the pressing surfaces (or the friction surface) in which the movable pieces c press the inner column are unstable, so that the pressing force (or the holding force) as a frictional force becomes unstable. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above-described situations. An object of the present invention is to avoid rotation of the movable pieces positively so as to prevent the movable pieces from biting the inner column at the time of adjustment of the telescopic position while increasing the surface area in which the movable pieces press the inner column so as to provide an extendable and contractable steering column apparatus in which the pressing force (or the retaining force) is stabilized. 
   In order to attain the above-described object, an extendable and contractable steering column apparatus according to the present invention includes an outer column through which an inner column is slidably inserted, a lock housing portion formed on the outer column, and a locking mechanism that includes a pair of movable pieces slidably fitted within a bore formed in the lock housing portion to shift the pair of movable pieces toward each other so as to press the inner column and to shift the pair of movable pieces away from each other so as to release the pressure on the inner column, in response to swinging of an operating lever, wherein the cross section of the bore of the lock housing portion is non-circular and the cross sections of said pair of movable pieces are also non-circular correspondingly. 
   As per the above, according to the present invention, the cross sectional shape of the bore in the lock housing portion is non-circular and the cross sectional shapes of the pair of movable pieces are also non-circular correspondingly. With this feature, rotation of the pair of movable pieces can be avoided reliably even if a torque is exerted on the pair of movable pieces when the operating lever is swung, so that the movable pieces can be prevented from biting the inner column upon adjustment of the telescopic position. 
   In addition, since the cross sectional shapes of the bore and the movable pieces are non-circular, the area of the pressing surfaces (or friction surfaces) in which the movable pieces press the inner column can be increased. Therefore, the pressing force (i.e. the holding force) as a frictional force can be stabilized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view showing an extendable steering column apparatus according to an embodiment of the present invention. 
       FIG. 2  is a cross sectional view taken along line II-II in  FIG. 1 . 
       FIG. 3A  is an enlarged side view showing a lock housing shown in  FIG. 1 . 
       FIG. 3B  is an enlarged side view showing a lock housing as an modification of the embodiment of the present invention. 
       FIG. 4  is an enlarged side view showing a lock housing portion according to a prior art. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1  is a side view showing an extendable steering column apparatus according to an embodiment of the present invention.  FIG. 2  is a cross sectional view taken along line II-II in  FIG. 1 .  FIG. 3A  is an enlarged side view showing a lock housing shown in  FIG. 1 .  FIG. 3B  is an enlarged side view showing a lock housing as an modification of the embodiment of the present invention. 
   As shown in  FIGS. 1 and 2 , an outer column  1  is formed as a long tube extending in the axial direction by die cast molding using aluminum or injection molding using a synthetic resin etc. The outer column  1  is supported on the lower portion of the dashboard of a vehicle with integrally molded supporting brackets  2  projecting from both sides of the outer column  1  by means of bolts (not shown) via resin capsules  30 . 
   Inside the outer column  1 , there is inserted an inner column  3  in the form of a long tube extending in the axial direction that can slide in the axial direction. A length adjustable, that is, extendable and contractable steering shaft  4  is rotatably supported in the interior of the inner column  3 . 
   A lock housing portion  5  projecting below the outer column  1  is provided on the lower part of the supporting brackets  2 . The lock housing portion  5  is integrally molded with the supporting brackets  2 . The lock housing portion  5  has a bore  6  extending through the lock housing portion  5  in the width direction of the vehicle. 
   A first movable piece  7  is inserted in one of the half portions of the bore  6  (the right half in  FIG. 2 ) so that the first movable piece  7  can slide in the bore  6 . A first bevel  7   a  is formed at the upper portion of the first movable piece  7  at a position near the center of the lock housing portion  5  so that the first bevel  7   a  presses the outer circumferential surface of the inner column  3 . 
   A second movable piece  8  is inserted in the other half portion of the bore  6  (the left half in  FIG. 2 ) so that the second movable piece  8  can slide in the bore  6 . A second bevel  8   a  is formed at the upper portion of the second movable piece  8  at a position near the center so that the second bevel  8   a  presses the outer circumferential surface of the inner column  3 . 
   The first and second bevels  7   a  and  8   a  may be either planar surfaces or curved surfaces that follow the shape of the outer peripheral surface of the inner column  3 . 
   A locking mechanism for the first and second movable pieces  7  and  8  has the following structure. The first movable piece  7  has a threaded screw hole  9  having an internal thread. The second movable piece  8  has a through-hole  10  coaxial with the threaded screw hole  9 . A screw rod  11  is inserted through the threaded screw hole  9  of the first movable piece  7  and the through-hole  10  of the second movable piece  8 . 
   The screw rod  11  has a screw portion  11   a  having an external thread to be threaded in the threaded screw hole  9  at one end and an inverse screw portion  11   b  having an inverse external thread at the other end. The inverse screw portion  11   b  has a thread with a relatively large pitch such as a double-start thread. 
   A lock nut  12  is screwed on the portion of the screw rod  11  at one end thereof that projects beyond the outer surface of the first movable piece  7 . The lock nut is tightly secured to the outer surface of the first movable piece  7  so as to retain the screw rod  11  non-rotatable relative to the first movable piece  7 . The screw rod has a pair of planar surfaces  13  parallel to each other formed on the outer circumferential surface of the screw rod at the aforementioned end thereof to facilitate the tight securing operation. 
   A adjusting nut  14  is screwed on the inverse screw portion  11   b  projecting beyond the outer surface of the second movable piece  8  at the other end of the screw rod  11 . A base end portion of an operating lever  15  is connected and fixed to the adjusting nut  14  by welding or the like means. 
   An compression spring  16  is provided between the first and second movable pieces  7  and  8 . The screw rod  11  passes through the compression coil spring  16 . With the biasing force of the compression coil spring  16 , both the movable pieces are positively spaced apart from each other upon telescopic adjustment of the position of the steering wheel. The compression coil spring  16  is not essential to this structure, and it may be provided as circumstances demand. 
   In the extendable and contractable steering column apparatus having the above-described structure, when the operating lever  15  is swung in one direction to rotate the adjusting nut  14  in one direction for attaining securing at the telescopically adjusted position, since the adjusting nut  14  is screwed on the inverse screw portion  11   b  of the non-rotatable screw rod  11 , a tensile force acts on the non-rotatable screw rod  11  toward the left in  FIG. 2  by the effect of the feed screw mechanism while a reverse force acts on the adjusting nut  14  toward the right in  FIG. 2 . 
   Consequently, the non-rotatable screw rod  11  is shifted toward the left in  FIG. 2 , which causes the first movable piece  7  to shift toward the left in  FIG. 2 . On the other hand, the second movable piece  8  is shifted in the right in  FIG. 2  by the reverse force of the adjusting nut  14 . Thus, the first movable piece  7  and the second movable piece  8  are shifted toward each other, so that the bevels  7   a  and  8   a  of both the movable pieces  7  and  8  press the outer peripheral surface of the inner column  3 . As a result, securing at the telescopically adjusted position can be attained. 
   On the other hand, upon telescopically adjusting the position of the steering wheel, the operating lever is swung in the direction reverse to the above to rotate the adjusting nut  14  in the reverse direction. Then, a pressing force toward the right in  FIG. 2  acts on the non-rotatable screw rod  11  by the effect of the feed screw while an reaction force toward the left in  FIG. 2  acts on the adjusting nut  14 . 
   Consequently, the non-rotatable screw rod  11  is shifted toward the right in  FIG. 2  by a tensile force, which causes the first movable piece  7  to shift toward the right in  FIG. 2 , while the second movable piece  8  is shifted toward the left in  FIG. 2  by a reverse force of the inner column  3 . Thus, the first movable piece  7  and the second movable piece  8  are shifted away from each other, so that the bevels  7   a  and  8   a  of both the movable pieces  7  and  8  are detached from the outer peripheral surface of the inner column  3 . In this process, the compression spring  16  facilitates the shifting away movement of the movable pieces  7  and  8 . As a result, securing of the telescopic position is released and telescopic adjustment of the position of the steering wheel is allowed. 
   In this embodiment, as shown in  FIGS. 1 and 3A , the cross sectional shape of the bore  6  of the lock housing portion  5  is triangular (that is, non-circular), and the cross sectional shapes of the pair of movable pieces  7  and  8  are also triangular (non-circular) correspondingly. 
   The shapes of the cross sections of the bore  6  and the movable pieces  7  and  8  need only to be non-circular, and they may be quadrangular as shown in  FIG. 3B  or other shapes. 
   With the above-described feature, rotation of the pair of movable pieces  7  and  8  can be avoided reliably even if a torque is exerted on the pair of movable pieces when the operating lever  15  is swung, so that the movable pieces  7  and  8  can be prevented from biting the inner column  3  upon telescopic adjustment of the position of the steering wheel. 
   In addition, since the cross sectional shapes of the bore  6  and the movable pieces  7  and  8  are non-circular, the area of the pressing surfaces (or friction surfaces) in which the movable pieces  7  and  8  press the inner column can be increased. 
   Specifically, in the case that the cross sectional shapes of the bore  6  and the movable pieces  7  and  8  are triangular, the axial length of the area in which the movable pieces  7  and  8  are in contact with the inner column is D 1  as shown in  FIG. 3A , and in the case that the cross sectional shapes are quadrangular, the axial length of the area in which the movable pieces  7  and  8  are in contact with the inner column is D 2  as shown in  FIG. 3B , while in the case that the cross sectional shapes are circular, the axial length of the area in which the movable pieces  7  and  8  are in contact with the inner column is d as shown in  FIG. 4 . As will be apparent from those drawings, D 1  is larger than d and D 2  is larger than d. 
   Therefore, with the non-circular cross sectional shapes of the bore  6  and the movable pieces  7  and  8 , the area of the pressing surfaces (or the friction surfaces) in which the movable pieces  7  and  8  press the inner column  3  can be increased as compared to the case of the circular cross sectional shapes, so that the pressing force (i.e. the holding force) as a frictional force can be stabilized. 
   The cross sections of the movable pieces may be non-circular such as elliptic. The screw rod and the movable pieces may be arranged above the inner column. 
   It should be noted that the present invention is not limited to the details of the above-described embodiment and various modifications can be made to the embodiment. For example, while the above description of the embodiment has been made in connection with the telescopically length adjustable steering column, the present invention can also be applied to the tilt adjustable and telescopically length adjustable steering column. 
   As per the above, according to the present invention, the cross sectional shape of the bore in the lock housing portion is non-circular and the cross sectional shapes of the pair of movable pieces are also non-circular correspondingly. With this feature, rotation of the pair of movable pieces can be avoided reliably even if a torque is exerted on the pair of movable pieces when the operating lever is swung, so that the movable pieces can be prevented from biting the inner column upon the telescopic adjustment of the position of the steering wheel. 
   In addition, since the cross sectional shapes of the bore and the movable pieces are non-circular, the area of the pressing surfaces (or friction surfaces) in which the movable pieces press the inner column can be increased. Therefore, the pressing force (i.e. the holding force) as a frictional force can be stabilized.