Patent Publication Number: US-2023143956-A1

Title: Steering device

Description:
FIELD 
     The present invention relates to a steering device. 
     BACKGROUND 
     A vehicle is provided with a steering device to transmit a steering wheel operation of a driver to the wheels. Such a steering device includes a steering shaft to which a steering hole is attached, and a cylindrical outer steering column that rotatably supports the steering shaft. The steering device may include a mechanism that can change a position of the steering wheel in an axial direction of the steering shaft. For example, a steering shaft disclosed in Patent Literature 1 has a lower shaft and an upper shaft that is slidably coupled to the lower shaft. The steering column includes a lower column that encloses the lower shaft and an upper column that is slidably coupled to the lower column. In a case in which a load is applied to the steering wheel in the axial direction, the upper shaft slides, and the steering wheel is displaced in the axial direction. In addition, the upper column slides following a slide of the upper shaft. 
     Furthermore, the upper column disclosed in Patent Literature 1 includes a clamp that is externally slidably fitted to the lower column, a cylindrical part that has a cylindrical shape and extends from the clamp toward the steering wheel, and a pair of protrusions that radially protrude outward from an outer peripheral surface of the clamp. A slit that extends in the axial direction is provided in the clamp. A bearing that supports the upper shaft is internally fitted to the cylindrical part. The pair of protrusions is disposed so that the slit of the clamp is interposed therebetween. In a case in which a compressive load acts on the pair of protrusions, a groove width of the slit of the clamp is narrowed. In other words, the clamp clamps the lower column disposed therein. As a result, the upper column is restricted not to slide on the lower column. The upper shaft supported by the cylindrical part is also restricted not to slide; thereby, a position of the steering wheel is secured. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2013-256193 
     SUMMARY 
     Technical Problem 
     Meanwhile, regarding both ends of the cylindrical part, one end side that is continuous with the clamp is opened, but the inside of the cylindrical part at the other end side near the steering wheel is blocked by the bearing and the upper shaft. Thus, the inside of the cylindrical part communicates with the external space through the slit of the clamp. However, in a case in which the lower column enters one end of the cylindrical part, the one end of the cylindrical part is blocked. In addition, the lower column enters the cylindrical part to compress air inside the cylindrical part. As a result, the air inside the cylindrical part passes through between an outer peripheral surface of the lower column and the inner peripheral surface of the cylindrical part and leaks to the external space. The outer peripheral surface of the lower column and the inner peripheral surface of the cylindrical part are slidable surfaces, and grease is applied on the surfaces. Therefore, the grease may be discharged to the external space along with the air that passes through between the lower column and the cylindrical part. In the above-mentioned Patent Literature 1, the upper column includes the cylindrical part and the clamp, but in a steering device in the related art, the lower column may include the cylindrical part and the clamp. In this case, the same problem as in the case in which the upper column enters the cylindrical part of the lower column occurs. 
     The present disclosure has been made in view of the above-mentioned problem, and an object thereof is to provide a steering device that can prevent grease from being discharged even though the lower column enters the inside of the cylindrical part of the upper column. 
     Alternatively, an object of the present disclosure is to provide a steering device that can prevent grease from. being discharged even through the upper column enters the inside of the cylindrical part of the lower column. 
     Solution to Problem 
     To achieve the above-mentioned object, a steering device according to one aspect of the present disclosure includes: a telescopic steering shaft that extends in a first direction; and a cylindrical outer steering column that rotatably supports the steering shaft, wherein the steering column includes a lower column, and an upper column having one end that is slidably attached to the lower column and another end on which a bearing that supports the steering shaft is provided, the upper column includes a clamp that is externally slidably fitted to the lower column and that has a slit extending in the first direction, and a cylindrical part that has a cylindrical shape and that has one end continuous with the clamp and another end blocked by the bearing being internally fitted, and the cylindrical part has an air hole that is spaced apart from the one end of the cylindrical part and that penetrates an outer peripheral surface and an inner peripheral surface of the cylindrical part. 
     The inside of the cylindrical part is always opened because of an air hole. Therefore, when the lower column enters the inside of the cylindrical part, air inside the cylindrical part is discharged to the outside of an external space through the air hole. Therefore, grease applied to the outer peripheral surface of the lower column and the inner peripheral surface of the cylindrical part is not discharged to the external space with air. 
     In the steering device, in a state where the steering shaft is shortened, the lower column and the air hole may overlap in a direction orthogonal to the first direction. 
     In the steering device according to a desirable aspect, the inner peripheral surface of the cylindrical part may include a first inner diameter part that is capable of being brought into slide-contact with an outer peripheral surface of the lower column, and a second inner diameter part having an inner diameter larger than that of the first inner diameter part, and the air hole may penetrate the second inner diameter part. 
     In a state where the lower column has entered the inside of the cylindrical part, the lower column is supported by a first inner diameter part. Therefore, the rattling of the upper column against the lower column is eliminated. When the lower column enters the inside of the cylindrical part, a gap is formed between the lower column and a second inner diameter part. Accordingly, the air hole is always opened, and the air inside the cylindrical part can be discharged reliably. 
     The steering device according to a desirable aspect includes a bracket including a first side plate and a second side plate that sandwich the clamp from a second direction orthogonal to the first direction; and a fastening mechanism that has a fastening shaft penetrating the first side plate and the second side plate to fasten the first side plate and the second side plate, wherein the upper column includes a pair of protrusions between which the slit is interposed, the protrusions protruding radially outward from the clamp and being pressed by the first side plate and the second side plate during fastening with the fastening mechanism, the pair of protrusions has long grooves into which the fastening shaft is inserted, and a penetration direction of the air hole is parallel to a penetration direction of the long grooves. 
     In a case in which the air hole and long grooves are formed by casting, releasing directions of molds for forming the air hole and the long grooves are unified in the same direction. In other words, the air hole and the long grooves for telescopic movement can be formed with a single mold, which facilitates the production of the upper column. 
     To achieve the above-mentioned object, a steering device according to one aspect of the present disclosure includes: a telescopic steering shaft that extends in a first direction.; and a cylindrical outer steering column that rotatably supports the steering shaft, wherein the steering column includes a lower column, and an upper column having one end that is slidably attached to the lower column and another end on which a bearing that supports the steering shaft is provided, the lower column includes a cylindrical part that has a cylindrical shape, and a clamp that protrudes from the cylindrical one end, that is externally slidably fitted to the upper column, and that has a slit extending in the first direction, and the cylindrical part has an air hole that is spaced apart from the one end of the cylindrical part and that penetrates an outer peripheral surface and an inner peripheral surface of the cylindrical part. 
     The inside of the cylindrical part is always opened because of an air hole. Therefore, when the upper column enters the inside of the cylindrical part, air inside the cylindrical part is discharged to the outside of an external space through the air hole. Therefore, grease applied to an outer peripheral surface of the upper column and the inner peripheral surface of the cylindrical part is not discharged to the external space with air. 
     In the steering device, in a state where the steering shaft is shortened, the upper column and the air hole may overlap in a direction orthogonal to the first direction. 
     In the steering device according to a desirable aspect, the inner peripheral surface of the cylindrical part may include a first inner diameter part that is capable of being brought into slide-contact with an outer peripheral surface of the upper column, and a second inner diameter part having an inner diameter larger than that of the first inner diameter part, and the air hole may penetrate the second inner diameter part. 
     In a state where the upper column has entered the inside of the cylindrical part, the upper column is supported by the first inner diameter part. Therefore, the rattling of the upper column against the lower column is eliminated. In a case in which the upper column enters the inside of the cylindrical part, a gap is formed between the upper column and the second inner diameter part. Accordingly, the air hole is always opened, and the air inside the cylindrical part can be discharged reliably. 
     Advantageous Effects of Invention 
     The steering device of the present disclosure can prevent grease from being discharged even though the lower column enters the inside of the cylindrical part of the upper column. Alternatively, the steering device can prevent grease from being discharged even though the upper column enters the inside of the cylindrical part of the lower column. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a side view of a steering device of the present embodiment. 
         FIG.  2    is a perspective view of the steering device of the present embodiment. 
         FIG.  3    is a side view of the steering device of the present embodiment. 
         FIG.  4    is a cross-sectional view of the steering device cut along an axis illustrated in  FIG.  3   . 
         FIG.  5    is a side view of an upper column of the present embodiment. 
         FIG.  6    is across-sectional view cut along VI-VI line illustrated in  FIG.  5   . 
         FIG.  7    is a bottom view of the upper column of the present embodiment. 
         FIG.  8    is a cross-sectional view cut along VII-VIII line illustrated in  FIG.  1   . 
         FIG.  9    is a cross-sectional view of the upper column of the present embodiment cut along the axis. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter the present invention is described in detail with reference to the drawings. The present invention is not limited to the following embodiment (hereinafter referred to as “embodiment”). In addition, components in the following embodiment include components capable of being readily assumed by those skilled in the art, components substantially identical, and components within the so-called equal range. Furthermore, the components disclosed in the following embodiment can be combined as appropriate. 
       FIG.  1    is a side view of a steering device of the present embodiment.  FIG.  2    is a perspective view of the steering device of the present embodiment.  FIG.  3    is a side view of the steering device of the present embodiment.  FIG.  4    is a cross-sectional view of the steering device cut along an axis illustrated in  FIG.  3   .  FIG.  5    is a side view of an upper column of the present embodiment.  FIG.  6    is a cross-sectional view cut along VI-VI line illustrated in  FIG.  5   .  FIG.  7    is a bottom view of the upper column of the present embodiment.  FIG.  8    is a cross-sectional view cut along VIII-VIII line illustrated in  FIG.  1   .  FIG.  9    is a cross-sectional view of the upper column of the present embodiment cut along the axis. 
     First, a basic configuration of a steering device  100  is described. As illustrated in  FIG.  1   , the steering device  100  includes a steering wheel  101 , a steering shaft  102 , a first universal joint  103 , an intermediate shaft  104 , a second universal joint  105 , and a pinion shaft  106 . 
     The steering wheel  101  is attached to one end  102   a  of the steering shaft  102  in a case in which a driver operates the steering wheel  101 , the steering shaft  102  rotates around an axis O, and an operation torque is applied to the steering shaft  102 . 
     A gearbox  110  is interposed between the other end  102   b  of the steering shaft  102  and the first universal joint  103 . An electric motor  120  is assembled with the gearbox  110  to provide an assist torque to the steering shaft  102 . In other words, the steering device  100  of the present embodiment is an electric power steering device that assists steering of the driver by using the electric motor  120 . The present invention may be applied to a steering device without the gearbox  110 . 
     One end of the intermediate shaft  104  is coupled to the first universal joint  103 . The pinion shaft  106  is coupled to the other end of the intermediate shaft  104  through the second universal obit  105 . As described above, the operation torque of the steering shaft  102  is transmitted to the pinion shaft  106  through the first universal joint  103 , the intermediate shaft  104 , and the second universal joint  105 . 
     As illustrated in  FIG.  2   , the steering device  100  further includes a steering column  1 , a first bracket  70 , a second bracket  80 , and a fastening mechanism  90 , in addition to the above-mentioned components. Next, the details of each component of the steering device  100  will be described. The XYZ Cartesian coordinate system is used in the following description. An X axis is parallel to the axis O of the steering shaft  102 . A Y axis is parallel to a vehicle width direction of a vehicle on which the steering device  100  is mounted. A Z axis is perpendicular to both the X and Y axes. A direction parallel to the X axis is described as the X direction, a direction parallel to the Y axis is described as the Y direction, and a direction parallel to the Z axis is described as the Z direction. A direction toward the front of the vehicle in the X direction is a +X direction. In a case in which an operator faces the +X direction, the right direction is a +Y direction. The upward direction in the Z direction is a +Z direction. The X direction is sometimes referred to as a first direction, and the Y direction may be referred to as a second direction. 
     As illustrated in  FIG.  3   , the steering shaft  102  is assembled in a state or protruding from an end of the steering column  1  in a −X direction. As illustrated in  FIG.  4   , the steering shaft  102  has an upper shaft  108  that is a cylindrical shaft, and a lower shaft  109  that is a solid shaft. The steering wheel (see  FIG.  1   ) is attached to an end of the upper shaft  108  in the −X direction. An end of the upper shaft  108  in the +X direction is externally fitted to the lower shaft  109 . The end of the upper shaft  108  in the  4 −X direction and an end of the lower shaft  109  in the −X direction are spline-fitted to each other. Therefore, the upper shaft  108  can slide on the lower shaft  109  in the X direction. 
     An end of the lower shaft  109  in the +X direction enters the inside of a housing ill of the gearbox  110 . A torsion bar  112 , an output shaft  114  that is an outer cylinder of the torsion bar  112 , and a worm wheel  115  that is externally fitted to the output shaft  114  are provided inside the housing  111  of the gearbox  110 . The worm wheel  115  is engaged with a worm (not illustrated) that is coupled to the output shaft  114  of the electric motor  120 . Therefore, in a case in which the electric motor  120  is driven, a torque is applied to the output shaft  114 . 
     An outer peripheral surface at the end of the lower shaft  109  in the +X direction is brought into slide-contact with a seal member  118  fitted to an inner peripheral surface of the housing  111 . The end of the lower shaft  109  in the +X direction is coupled to an end of the torsion bar  112  in the −X direction. An end of the torsion bar  112  in the +X direction is coupled to the output shaft  114  by a fixing pin  113 . The first universal joint  103  is coupled to an end of the output shaft  114  in the +X direction. Therefore, a steering torque of the lower shaft  109  is transmitted to the intermediate shaft  104  (see  FIG.  1   ) through the torsion bar  112 , the output shaft  114 , and the first universal joint  103 . The torsion bar  112  twists in response to the steering torque of the lower shaft  109 , so that an angular difference in rotation between the lower shaft and the output shaft  5 . 
     In order to eliminate the angular difference rotation between the lower shaft  109  and the output shaft  114 , a torque detection groove  114   a  is formed at an end of the output shaft  114  in the −X direction. A cylindrical member  116  is disposed on an outer peripheral side of the torque detection groove  114   a,  The cylindrical member  116  is fixed to the end of the lower shaft  109  in the + direction and is integrally rotated with the lower shaft  109 . The cylindrical member  116  has a plurality of windows (not illustrated) penetrating in a radial direction. A torque sensor  117  is disposed on an outer peripheral side of the cylindrical member  116 . 
     The torque sensor  117  transmits a detection. result to a torque detection circuit board (not illustrated) that is provided inside the housing  111 , and the torque detection circuit board detects the angular difference in rotation between the lower shaft  109  and the output shaft  114 . The torque detection circuit board causes the electric motor  120  to be driven based on the detection result to provide a steering assist torque to the output shaft  114 . As a result, the same angle in rotation between the lower shaft  109  and the output shaft  114  is achieved. 
     As illustrated in  FIG.  2   , the first bracket  70  includes a pair of support pieces  71 . The support pieces  71  are spaced apart from each other in the Y direction. Each of the support pieces  71  includes an attachment plate  72  extending in the X direction and the Y direction and a support plate  73  extending in the X direction and the Z direction. The attachment plate  72  is fixed to a vehicle body by a bolt (not illustrated). A pivot shaft  74  extending in the Y direction is rotatably provided at an end of the support plate  73  in the −Z direction. The gearbox  110  is fixed to the pivot shaft  74 . Thus, the gearbox  110 , the steering shaft  102 , the steering column  1 , and the steering wheel  101  are supported by the first bracket  70  to be able to rotate around the pivot shaft  74  (see arrows A 1  and A 2  in  FIG.  1   ). 
     As illustrated in  FIG.  4   , the steering column  1  is an outer cylinder that extends in the X direction and surrounds the steering shaft  102 . The steering column  1  includes an upper column  2  and a lower column  3  disposed in the −X direction with respect to the upper column  2 . The lower column  3  has a cylindrical shape. An end of the lower column  3  in the +X direction is externally fitted to the housing Ill of the gearbox  110 . Here, an opening at an end of the housing  111  in the −X direction is sealed by the lower shaft  109  and the seal member  118 . The inside of the housing  111  of the gearbox  110  is excellent in sealing performance. Therefore, even though the air pressure inside the lower column  3  increases, it is difficult for air to enter the inside of the housing  111  through an opening at the end of the lower column  3  in the +X direction. 
     The upper column  2  is produced by casting. As illustrated in  FIGS.  3 ,  4 , and  5   , the upper column  2  includes a clamp  10  that is externally fitted to the lower column  3 , a cylindrical part  20  that extends from the clamp  10  in the −X direction, an attachment part  30  that is provided at an end of the clamp  10  in the +X direction, a pair of protrusions  40  (only one protrusion is illustrated in  FIGS.  3  and  5   ) that protrudes in the −Z direction from the outer peripheral surface of the clamp  10 , and contact ribs  50  (see  FIGS.  3  and  5   ) that extend in the X direction. 
     The cylindrical part  20  has a circular inner peripheral surface. An inner diameter of the cylindrical part  20  has a size enough to allow the lower column  3  to enter the inside. A bearing  21  is internally fitted to an end of the cylindrical part  20  in the −X direction. The cylindrical part  20  rotatably supports the upper shaft  108  by using the bearing  21 . In other words, an opening at the end of the cylindrical part  20  in the −X direction is blocked by the bearing  21  and the upper shaft  108 , so that sealing performance is excellent. In a case in which the bearing  21  has a seal (not illustrated) that prevents grease inside the bearing  21  from leaking out, the opening at the end of the cylindrical part  20  in the −X direction has further excellent sealing performance. Therefore, even though the air pressure inside the cylindrical part  20  increases, it is difficult for air to be discharged to the outside through the opening at the end of the cylindrical part  20  in the −X direction. Another configuration of the cylindrical part  20  will be described later. 
     As illustrated in  FIG.  6   , the clamp  10  is provided with a slit  11 . As illustrated in  FIG.  7   , the slit  11  of the clamp  10  extends in the X direction. Therefore, the clamp  10  has a circular arc-shaped cross-section and extends in the X direction. While no external force acts on the clamp  10 , the inner diameter of the clamp  10  is approximately the same in size as the outer diameter of the lower column  3 . In other words, the clamp  10  is slidable on the lower column  3 . 
     As illustrated in  FIG.  6   , the slit  11  of the clamp  10  is positioned in the −Z direction as viewed from the axis O. Therefore, a groove width of the slit  11  is along the Y direction. According to this, in a case in which a compressive load for fastening the clamp  10  from the Y direction acts on the clamp  10 , the clamp  10  deforms so that the groove width of the slit  11  is narrower. In other words, the clamp  10  clamps the lower column  3  disposed therein by reducing its diameter. As a result, a high frictional force acts between an inner peripheral surface of the clamp  10  and an outer peripheral surface of the lower column  3  to restrict the sliding of the upper column  2 . 
     As illustrated in  FIGS.  7  and  9   , a part of the attachment part  30  in the +Z direction includes a cut-out portion  31 . As illustrated in  FIG.  7   , the attachment part  30  wraps around the lower column  3  in an arc shape in the −Z direction. An attachment rib  32  is provided on an outer peripheral surface of the attachment part  30 , which faces the −Z direction. The attachment rib  32  has a female thread hole  33 . A bracket (not illustrated) that supports a harness or the like is attached to the female thread hole  33 . 
     A first expansion slit  12  and a second expansion slit  13  whose groove widths are circumferentially wider than that of the slit  11  are provided at both ends of the slit  11  of the clamp  10  in the X direction. Parts of the clamp  10 , which are not continuous with the adjacent cylindrical part  20  and the adjacent attachment part  30  in the X.-axis direction, increase because of the first expansion slit  12  and the second expansion slit  13 . As a result, the clamp  10  is less affected by the rigidity of the cylindrical part  20  and the attachment part  30  and is more easily deformed. 
     As illustrated in  FIG.  7   , the pair of protrusions  40  and  40  is disposed so that the slit  11  is interposed therebetween as viewed from the −Z direction. Hereinafter the one protrusion  40  of the pair of protrusions  40  and  40 , which is disposed in the −Y direction relative to the slit  11 , is referred to as a first protrusion  41 , and the other protrusion  40  of the pair of protrusions  40  and  40 , which is disposed in the +Y direction relative to the slit  11 , is referred to as a second protrusion  42 . The first protrusion  41  and the second protrusion  42  extend in the X direction with approximately the same length as that of the clamp  10 . As illustrated in  FIG.  5   , long grooves  43  and  44  extending in the X direction are provided. As illustrated in  FIG.  6   , the long grooves  43  and  44  penetrate in the Y direction. 
     As illustrated in  FIG.  6   , the contact ribs  50  each have a pair of first contact ribs  51  and  51 , and a 
     pair of second contact ribs  52  and  52 . The first contact ribs  51  protrude from the outer peripheral surface of the clamp  10 . The second contact ribs  52  are provided to protrude from outer surfaces of the first protrusion  41  and the second protrusion  42 , respectively. 
     As illustrated in  FIG.  5   , the first contact ribs  51  and the second contact ribs  52  extend in a straight line in the X direction. The first contact ribs  51  overlap the axis O as viewed from the Y direction. Each end of each first contact rib  51  in the −X direction is continuous with a second annular rib  23 . The second contact ribs  52  are positioned at the ends of the first protrusion  41  and the second protrusion  42  in the −Z direction, respectively, and extend along edges of the long grooves  43  and  44 . As described above, the first contact ribs  51  and the second contact ribs  52  are disposed so that the long grooves  43  and  44  are interposed therebetween. 
     As illustrated in  FIG.  8   , the second bracket  80  includes a pair of attachment plates  81  and  81 , an upper plate  82 , a first side plate  83 , and a second site plate  84 . The second bracket  80  may be referred to simply as a bracket. 
     The pair of attachment plates  81  is plate-like members that are disposed to be spaced apart from each other in the Y direction so that the steering column  1  is interposed therebetween. The attachment plates  81  are coupled to the vehicle body by using release capsules  85 . Each of the release capsules  85  is disposed at an end of each of the attachment plates  81  in the −X direction. Each of the release capsules  85  is integrated with each of the attachment plates  81  by using each of resin members  86 , The release capsules  85  are fixed to a member on the vehicle body side by bolts or the like. In a case in which a load in the +X direction acts on the steering column because of a secondary collision of the vehicle (see arrow D 1  in  FIG.  1   ), the resin members  86  are sheared and only the attachment plates  81  move in the +X direction; thereby, the second bracket  80  is released from the vehicle body. 
     The upper plate  82  is a plate-like member that couples the pair of attachment plates  81  and  81  to each other. The first side plate  83  and the second side plate  84  are plate-like members that extend in the X direction and the Z direction. The first side plate  83  is disposed in the −Y direction relative to the clamp  10 . The second side plate  84  is disposed in the +Y direction relative to the clamp  10 . In other words, the first side plate  83  and the second side plate  84  are spaced apart from each other in the Y direction so that the clamp  10  of the steering column  1  is interposed therebetween. The first side plate  83  and the second side plate  84  are integrated with the pair of attachment plates  81  and  81 , and the upper plate  82  by welding. The first side plate  83  and the second side plate  84  are formed with arc grooves  83   a  and  84   a  that extend in the Z direction, respectively. The arc grooves  83   a  and  84   a  have an arc shape centered on the pivot shaft  74  (see  FIGS.  1 ,  2 , and  3   ). A protruding plate  87  that protrudes in the −Y direction is provided at an end of the first side plate  83  in the X direction. Therefore, the first side plate  83  has a higher rigidity in the Y direction than the second side plate  84  does. 
     The fastening mechanism  90  is a device that fastens the clamp  10  to apply a compressive load to the clamp  10 . The fastening mechanism  90  has a fastening shaft  91 , an operation lever  92 , a fixed cam  93 , a rotating cam  94 , a nut  95 , a spacer  96 , and a thrust bearing  97 . 
     The fastening shaft  91  is a rod-shaped member. The fastening shaft  91  is inserted, from the −Y direction toward the +Y direction, into the arc groove  83   a  of the first side plate  83 , the long grooves  43  and  44  of the clamp  10 , and the arc groove  84   a  of the second side plate  84  in this order, and extends in the Y direction. An end of the fastening shaft  91  in the −Y direction is provided with a head  91   a  The operation lever  92  is coupled near the end of the fastening shaft  91  in the −Y direction. The operation lever  92  extends from the fastening shaft  91  in the −X direction and can be operated by the driver in the vehicle (see  FIGS.  1  and  2   ). In a case in which the driver rotates the operation lever  92  around the fastening shaft  91 , the fastening shaft  91  is rotated in conjunction with the rotation of the operation lever  92 . 
     The fixed cam  93  and the rotating cam  94  are disposed between the first side plate  83  and the operation lever  92  in a state of being penetrated by the fastening shaft  91 . The fixed cam  93  is adjacent to the first side plate  83 . A part of the fixed cam  93  is fitted to the arc groove  83   a  of the first side plate  83 . Accordingly, the fixed cam  93  is not rotated in conjunction with the fastening shaft  91 . The rotating cam  94  is adjacent to the operation lever  92 . The rotating cam  94  is coupled to the operation lever  92  and is integrally rotated with the operation lever  92 . Tilted planes are provided on surfaces of the fixed cam  93  and the rotating cam  94 , which face each other, along the peripheral direction. In a case in which the rotating cam  94  is rotated by operation of the operation lever  92 , the tilted plane of the fixed cam  93  rides up or goes down on the tilted plane of the rotating cam  94 . As a result, a distance in the Y direction between the fixed cam  93  and the rotating cam  94  changes. 
     An end of the fastening shaft  91  in the +Y direction is provided with a male thread  91   b.  This male thread  91   b  is screwed with the nut  95 . As a result, the fastening shaft  91  is prevented from falling out of the arc grooves  83   a  and  84   a  and the long grooves  43  and  44 . The spacer  96  and the thrust bearing  97  are disposed between the second side plate  84  and the nut  95  in a state of being penetrated by the fastening shaft  91 . The spacer  96  is brought into contact with the periphery of the arc groove  84   a,  which is a part of the second side plate  84 . The thrust hearing  97  is disposed between the nut  95  and the spacer  96 . 
     As described above, in a case in which the fixed cam  93  and the rotating cam  94  are spaced apart from each other in the Y direction by the operation of the operation lever  92 , the head  91   a  of the fastening shaft  91  is pressed in the −Y direction, and the nut  95  moves toward the −Y direction. Accordingly, a distance in the Y direction between the fixed cam  93  and the spacer  96  is reduced, and a frictional force between the fixed cam  93  and the first side plate  83 , and a frictional force between the spacer  96  and the second side plate  84  increase. As a result, the movement of the fastening shaft  91  in the Z direction along the arc grooves  83   a  and  84   a  is restricted. Therefore, the movement of the upper column  2  in the Z direction, which is penetrated by the fastening shaft  91 , is also restricted, and a position of the steering wheel  101  in the Z direction is secured. 
     The first side plate  83  and the second side plate  84  are fastened in the Y direction by the fixed cam  93  and the spacer  96 . Thus, inner surfaces of the first side plate  83  and the second side plate  84  are brought into contact with the pair of second contact ribs  52  of the upper column  2 . The first side plate  83  and the second side plate  84  press the pair of second contact ribs  52  to be compressed against each other. As a result, a compressive load is applied to the first protrusion  41  and the second protrusion  42  in the Y direction. The groove width of the slit  11  of the clamp  10  is narrower to clamp the lower column. As a result, the upper column  2  is secured to the lower column  3 , and the movement of the steering wheel  101  in the X direction is restricted. 
     The first side plate  83  and the second side plate  84  press the pair of first contact ribs  51  and  51  in addition to the pair of second contact ribs  52  and  52 . As a result, a compressive load acts on the pair of second contact ribs  52  and  52  to be able to reduce the diameter of the clamp  10 . The first contact ribs  51  are spaced apart from the fastening shaft  91  on which a fastening force acts. Therefore, the compressive load acting on the first contact ribs  51  is smaller than the compressive load acting on the second contact ribs  52 . On the other hand, even though the compressive load is applied to the second contact ribs  52 , the first protrusion  41  and the second protrusion  42  are tilted so that only the ends of the first protrusion  41  and the second protrusion  42  in the −Y direction are close to each other; thereby, the slit of the clamp  10  may not be narrowed. In other words, the compressive load can be applied to the clamp  10  by using the first contact ribs  51  without using the first protrusion  41  and the second protrusion  42 . Therefore, during the operation of the operation lever  92 , the clamp  10  reliably clamps the lower column  3 . 
     By contrast, in a case in which the operation lever  92  is operated to bring the fixed cam  93  and the rotating cam  94  closer to each other in the Y direction, the distance in the Y direction between the fixed cam  93  and the spacer  96  is increased. Thus, a frictional force between the fixed cam  93  and the first side plate  83  is reduced. Accordingly, a frictional force between the spacer  96  and the second side plate  64  is reduced. As a result, the fastening shaft  91  is allowed to move in the Z direction along the arc grooves  83   a  and  84   a  In a case in which a load in the Z direction is applied to the steering wheel  101 , the steering column  1 , the steering shaft  102 , and the gearbox  110  are rotated around the pivot shaft  74  in directions of arrow A 1  or arrow A 2  (see  FIG.  1   ). As a result, a position of the steering wheel  101  in the Z direction is changed. 
     Fastening on the first contact rib  51  and second contact rib  52  by the first side plate  83  and the second side plate  84  is released. Therefore, the groove width of the slit  11  of the clamp  10  is widened, and clamping onto the lower column  3  is released. In a case in which a load in the X direction is applied to the steering wheel  101 , the upper column  2  and the upper shaft  108  slide in the X direction. As a result, a position of the steering wheel  101  in the X direction is changed (see arrow B 1  and arrow B 2  in  FIG.  1   ). 
     Next, the details of the cylindrical part  20  of the upper column  2  will be explained. As illustrated in  FIG.  5   , a first annular rib  22  and a second annular rib  23  that are disposed to be spaced apart from each other in the X direction are provided on an outer peripheral surface  20   a  of the cylindrical part  20 . Four straight linear ribs  24   a ,  24   b,    24   c,  and  24   d  (see  FIG.  7    regarding the linear rib  24   d ) that extend in the X direction are provided at a 90-degree interval on the outer peripheral surface  20   a  of the cylindrical part  20  and between the first annular rib  22  and the second annular rib  23 . Thus, the rigidity of the cylindrical part  20  is very high. 
     Here, as illustrated in  FIG.  1   , during the secondary collision, a load toward the front of the vehicle acts on the steering wheel  101  (see arrow D 1  in  FIG.  1   ). Therefore, as illustrated in  FIG.  5   , a compressive load (see arrows D 2   FIG.  5   ) acts on a wall in the direction as viewed from the axis O in the cylindrical part.  20 . In addition, a tensile load (see arrows D 3  in  FIG.  5   ) acts on a wall the direction as viewed from the axis O in the cylindrical part  20 . In a case in which the cylindrical part  20  is deformed, the lower column  3  may not be able to enter the inside of the cylindrical part  20 . In other words, in the event of the secondary collision, it is not possible to absorb the collision energy by shortening the steering shaft  102 . As described above, the linear ribs  24   a  and  24   c  are ribs for improving the rigidity against the compressive load and the tensile load acting on the cylindrical part  20  during the secondary collision. 
     As illustrated in  FIGS.  5  and  9   , the cylindrical part  20  has an air hole  25  that penetrates the outer peripheral surface  20   a  and an inner peripheral surface  20   b  of the cylindrical part  20 . The air hole  25  is provided in the wall of the cylindrical part  20 , which is positioned in the +Y direction as viewed from the axis O, and is adjacent to the linear rib  24   b.  Thus, even though the air hole  25  is provided in the cylindrical part  20 , the rigidity of the wall of the cylindrical part  20 , which is disposed in the +Z direction or − direction as viewed from the axis O is not reduced. 
     The air hole  25  extends in the Y direction. In other words, the air hole  25  is formed in parallel to a penetration direction of the long grooves  43  and  44  of the lower column  3 . Here, the long grooves  43  and  44  are formed by casting. In detail, the long groove  43  is formed by using a mold released from the upper column  2  the −Y direction. (see arrow C 1  in  FIG.  6   ). The long groove  44  is formed by using a mold released from the upper column  2  in the +Y direction (see arrow C 2  in  FIG.  6   ). Therefore, releasing directions of the mold for forming the air hole  25  and the mold for forming the long groove  44  are unified, and the air hole  25  and the long groove  44  can be formed with a single mold. 
     As illustrated in  FIG.  9   , the inner peripheral surface  20   b  of the cylindrical part includes a flange  26  that restricts the movement of the bearing  21  in the +X direction, a first inner diameter part  27  that is brought into slide-contact with the outer peripheral surface of the lower column  3 , and a second inner diameter part  28  having an inner diameter larger than that of the first inner diameter part  27 . 
     The flange  26  is provided near the end of the cylindrical part  20  in the −X direction. The first inner diameter part  27  is provided near the end of the cylindrical part  20  in the +X direction. The first inner diameter part  27  extends in the +X direction, and is provided across the inner peripheral surface of the clamp  10 . In this first inner diameter part  27 , the outer peripheral surface of the lower column  3  is a slidable surface in a state where the diameter of the clamp  10  is not reduced. The inner peripheral surface of the clamp  10  is provided with a third inner diameter part  14  which is spaced apart from the first inner diameter part  27  in the +X direction, and of which an inner diameter is the same as the inner diameter of the first inner diameter part  27 . In other words, a fourth inner diameter part  15  formed to have a larger diameter than the inner diameters of the first inner diameter part  27  and the third inner diameter part  14  is provided between the first inner diameter part  27  and the third inner diameter part  14 . As a result, a clamping force of the clamp  10  is concentrated to the first inner diameter part  27  and the third inner diameter part  14  in a state where the diameter of the clamp  10  is reduced. The second inner diameter part  28  is positioned in the center of the cylindrical part  20  in the X direction. The air hole  25  is positioned in the center of the cylindrical part  20  in the X direction and is spaced apart from the end of the cylindrical part  20  in the +X direction. The air hole  25  then penetrates the second inner diameter part  28 . 
     Next, a relationship between the cylindrical part  20  and the lower column  3  will be explained with reference to  FIG.  9   . The dashed lines indicated by reference signs  3 A,  3 B, and  3 C indicate end surfaces of the lower column  3  in the −X direction. When a length of the steering shaft  102  is the longest length in the X direction, the upper column  2  slides in the −X direction. In this case, the lower column  3  does not enter the inside of the cylindrical part  20 , as indicated by reference sign  3 A in  FIG.  9   . Thus, the end of the cylindrical part  20  in the +X direction is opened. Air inside the cylindrical part  20  flows from and to the external space through the air hole  25  or the slit  11  of the clamp  10 . 
     Subsequently, in a state where the length of the steering shaft  102  is shortened in the X direction, and the upper column  2  slides in the −X direction, the lower column  3  enters the inside of the cylindrical part  20 , as indicated by reference sign  3 B in  FIG.  9   . Accordingly, the inside of the cylindrical part  20  is then continuous with the inside of the lower column  3  via an opening at the end of the lower column  3  in the −X direction (see  FIG.  4   ). In a space formed of the inside of the cylindrical part  20  and the inside of the lower column  3 , the end in the +X direction is blocked by the lower shaft  109 , the seal member  118 , and the gearbox  110 . In addition, in the space formed of the inside of the cylindrical part  20  and the inside of the lower column  3 , the end in the −X direction is blocked by the bearing  21  and the upper shaft  108 . On the other hand, the inside of the cylindrical part  20  communicates with the external space through the air hole  25 . Therefore, in a case in which the air pressure in the space formed of the inside of the cylindrical part  20  and the inside of the lower column  3  increases, the air inside the cylindrical part  20  is discharged to the external space through the air hole  25 . 
     Subsequently, when the length of the steering shaft  102  is the shortest length in the X direction, an entry amount of the lower column  3  that enters the inside of the cylindrical part  20  increases, as indicated by reference sign  3 C in  FIG.  9   . In a case in which the entry amount of the lower column  3  is greater than a predetermined amount, the outer peripheral surface of the lower column  3  faces the air hole  25 . In other words, the lower column  3  and the air hole  25  overlap in a direction. orthogonal to the axis O. Here, an outer diameter of the second inner diameter part  28  is larger than an outer diameter of the first inner diameter part  27 , and a gap is generated between the second inner diameter part  28  and the outer peripheral surface of the lower column  3 . Therefore, the air inside the cylindrical part  20  flows from and to the external space through the air hole  25  and the gap formed between the second inner diameter part  28  and the outer peripheral surface of the lower column  3 . As described above, according to the present embodiment, the air inside the cylindrical part  20  to be discharged to the external space does not pass through between the lower column  3  and the first inner diameter part  27 . 
     As explained above, the steering device  100  of the embodiment includes the telescopic steering shaft  102  that extends in the first direction, and the cylindrical outer steering column  1  that rotatably supports the steering shaft  102 . The steering column includes the lower column  3 , and the upper column  2  having one end that is slidably attached to the lower column  3  and the other end on which the bearing  21  that supports the steering shaft  102  is provided. The upper column  2  includes the clamp  10  that is externally slidably fitted to the lower column  3  and that has the slit  11  extending in the first direction, and the cylindrical part  20  that has a cylindrical shape and that has one end continuous with the clamp  10  and the other end blocked by the bearing  21  being internally fitted. The cylindrical part  20  has the air hole  25  that is spaced apart from the one end of the cylindrical part  20  and that penetrates the outer peripheral surface  20   a  and the inner peripheral surface  20   b.    
     The air inside the cylindrical part  20  is discharged to the outside of the external space through the air hole  25 . In other words, the air inside the cylindrical part  20  is not discharged from between the outer peripheral surface of the lower column  3  and the inner peripheral surface of the cylindrical part  20 . Therefore, it is possible to prevent grease applied to the outer peripheral surface of the lower column  3  and the inner peripheral surface of the cylindrical part  20  from being discharged to the external space. 
     In the steering device  100  of the embodiment, in the state where the steering shaft  102  is shortened, the lower column  3  and the air hole  25  overlap in the direction orthogonal to the first direction. In addition, the inner peripheral surface  20   b  of the cylindrical part  20  in the steering device  100  of the embodiment includes the first inner diameter part  27  that can be brought into slide-contact with the outer peripheral surface of the lower column  3  and the second inner diameter part  28  of which the inner diameter is larger than that of the first inner diameter part  27 . The air hole  25  penetrates the second inner diameter part  28 . 
     The lower column that has entered the inside of the cylindrical part  20  is supported by the first inner diameter part  27 . Therefore, the rattling of the upper column  2  against the lower column  3  is restrained. In addition, the air hole  25  is always opened since the gap is formed between the lower column  3  and the second inner diameter part  28 . 
     The steering device  100  of the embodiment includes the bracket including the first side plate  83  and the second side plate  84  that sandwich the clamp  10  from the second direction orthogonal to the first direction; and the fastening mechanism  90  that has the fastening shaft  91  penetrating the first side plate  83  and the second side plate  84  and that fastens the first side plate  83  and the second side plate  84 . The upper column  2  includes the pair of protrusions  40  and  40  between which the slit  11  is interposed, the protrusions  40  and  40  protruding radially outward from the clamp  10  and being pressed by the first side plate  83  and the second side plate  84  during fastening with the fastening mechanism  90 . The pair of protrusions  40  and  40  includes the long grooves  43  and  44  into which the fastening shaft  91  is inserted. The penetration direction of the air hole  25  is parallel to the penetration direction of the long grooves  43  and  44 . 
     In a case in which the air hole  25  and the long groove  44  are formed by casting, the releasing directions of the mold for forming the air hole  25  and the mold for forming the long groove  44  are unified, and the air hole  25  and the long groove  44  can be formed with a single mold. Thus, the lower column  3  is easily manufactured. 
     Although the embodiment is explained as described above, the steering device of the present disclosure is applicable to a steering device in which a lower column includes a cylindrical part and a clamp, and an upper column enters the cylindrical part of the lower column. In other words, the steering device includes a telescopic steering shaft that extends in a first direction, and a cylindrical outer steering column that rotatably supports the steering shaft. The steering column includes the lower column, and the upper column having one end that is slidably attached to the lower column and the other end on which a bearing that supports the steering shaft is provided. The lower column includes a cylindrical part that has a cylindrical shape, and a clamp that protrudes from the cylindrical one end, that is externally slidably fitted to the upper column, and that has a slit extending in the first direction. The cylindrical part has an air hole that is spaced apart from the one end of the cylindrical part and that penetrates an outer peripheral surface and an inner peripheral surface of the cylindrical part. With such a steering device, when the upper column enters the cylindrical part of the lower column, the: air inside the cylindrical part is discharged to the outside of the external space through the air hole. Therefore, it is possible to prevent grease applied to the outer peripheral surface of the upper column and the inner peripheral surface of the cylindrical part from being discharged to the external space. 
     In a state where the upper column enters the cylindrical part of the lower column, and the steering shaft is shortened, the upper column and the air hole overlap in the direction orthogonal to the first direction. In this state, the inner peripheral surface of the cylindrical part includes the first inner diameter part that can be brought into slide-contact with the outer peripheral surface of the upper column, and the second inner diameter part having the inner diameter larger than that of the first inner diameter part. In addition, the air hole may penetrate the second inner diameter part. As a result, the upper column that has entered the inside of the cylindrical part is supported by the first inner diameter part. Therefore, the rattling of the upper column against the lower column is eliminated. In addition, the air hole is always opened since the gap is generated between the upper column and the second inner diameter part. 
     REFERENCE SIGNS LIST 
       100  Steering device 
       101  Steering wheel 
       102  Steering shaft 
       108  Upper shaft 
       109  Lower shaft 
       110  Gearbox 
       1  Steering column 
       2  Upper column 
       3  Lower column 
       10  Clamp 
       11  Slit 
       12  First expansion slit 
       13  Second expansion slit. 
       20  Cylindrical part 
       21  Bearing 
       25  Air hole 
       27  First inner diameter part 
       28  Second inner diameter part 
       30  Attachment part 
       40  ( 41 ,  42 ) Protrusion (first protrusion, second protrusion) 
       43 ,  44  Long groove 
       50  Contact rib 
       51  First contact rib 
       52  Second contact rib 
       70  First bracket 
       74  Pivot shaft 
       80  Second bracket (bracket) 
       83  First side plate 
       84  Second side plate 
       90  Fastening mechanism 
       91  Fastening shaft 
       92  Operation lever 
       93  Fixed Cam 
       94  Rotating Cam 
       95  Nut