Abstract:
A steering apparatus exhibits favorable lever operability and generates a powerful steering column fastening and fixing force during tilt and telescopic adjustment. It has a simple structure includes: a column supporting member; a fixed bracket having, fixed side portions; a lock bolt that penetrates the respective fixed side portions of the fixed bracket together with the column supporting member; a main driving cam; a driven cam; an intermediate cam; and an operating lever. The lock bolt penetrates the main driving cam, the driven cam, and the intermediate cam, the main driving cam is rotated by the operating lever, the driven cam is attached to the fixed side portions to be incapable of rotating, the intermediate cam is disposed between the main driving cam and the driven cam, and the intermediate cam is caused to approach and separate from the main driving cam and the driven cam.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a steering apparatus that exhibits favorable lever operability and generates a powerful steering column fastening and fixing force during tilt and telescopic adjustment while having an extremely simple structure. 
     2. Description of the Related Art 
     A conventional steering apparatus having a tilt and telescopic adjustment function includes a lock mechanism with which locking is achieved by rotating a spindle that penetrates a side plate of a fixed bracket fixed to a vehicle using an operating lever so as to press the side plate of the fixed bracket. Japanese Patent Application Publication No 2004-210265 is available as this type of steering apparatus. 
     To summarize the content of Japanese Patent Application Publication No. 2004-210265 (reference symbols provided in the description of Japanese Patent Application Publication No. 2004-210265 are used as is), a connecting rod  50  is inserted into and connected to guide slots  33  serving as tilt adjustment elongated holes formed in fixed brackets  31 ,  32  and a through hole  43  formed in a movable bracket  40 . A first stopper  51  and a second stopper  52  are provided on either end of the connecting rod  50  to prevent the fixed brackets  31 ,  32  and the movable bracket  40  from separating from each other. Further, a rotary member  70  disposed on the connecting rod  50  to be capable of rotating and conveyance members  81 ,  82  for fixing and releasing the movable bracket  40  to and from the fixed brackets  31 ,  32  are provided. 
     When the rotary member  70  is rotated in one direction, the inside conveyance member  81  and the outside conveyance member  82  move so as to separate to an inner side and an outer side of the rotary member  70 , respectively. However, outward movement of the connecting rod  50  is restricted by the stoppers  51 ,  52 , and therefore, during movement of the conveyance members  81 ,  82 , a fixing unit  60  moves in its entirety to the first fixed bracket  31  side by the distance moved by the respective conveyance members  81 ,  82  so as to press the first fixed bracket  31 . As a result, the movable bracket  40  is brought into close contact with the fixed brackets  31 ,  32  and supported fixedly thereby. 
     When the rotary member  70  is rotated in an opposite direction, a pressure applied to a tilting portion  84  by a pressing portion  73  is released together with the pressure on the first bracket  31 , and therefore the movable bracket  40  is not fixed to the fixed brackets  31 ,  32  any further. 
     SUMMARY OF THE INVENTION 
     In Japanese Patent Application Publication No. 2004-210265, the pressing portions  73  formed on corresponding surfaces on either side of the rotary member  70  pass over the tilting portions  84  formed on the respective conveyance members  81 ,  82  simultaneously during locking, and therefore tightening a lever  72  may feel heavy, leading to deterioration of an operation feeling. Similarly during unlocking, the pressing portions  73  formed on the corresponding surfaces on either side of the rotary member  70  move over the tilting portions  84  formed on the respective conveyance members  81 ,  82  simultaneously, and therefore the lever  72  may return too rapidly. 
     Further, the conveyance member  82  is fixed to the first stopper  51  and therefore, in a case where the connecting rod  50  and the first topper  51  are fastened using a screwing method by rotating the first stopper  51 , the conveyance member  82  rotates together with the first stopper  51 . Hence, a male screw  50   a  and a female screw  51   a  must be formed on the connecting rod  50  and the first stopper  51 , respectively, to ensure that a first cam surface  85  of the conveyance member  82  is in alignment with a second cam surface  74  of the rotary member  70  when the connecting rod  50  and the first stopper  51  are fastened. Therefore, initial setting is complicated. 
     Furthermore, in a case where the connecting rod  50  and the first stopper  51  are fastened using a screwing method by rotating the second stopper  52 , it is difficult to fix the rotating second stopper  52  in the guide slot  33  of the fixed bracket  32 . Hence, positioning during fastening is difficult in both cases, and therefore a fastening ability is poor. An object of (a technical problem to be solved by) the present invention is to improve the operation feeling of locking and unlocking operations during tilt and telescopic adjustment, and to improve the fastening ability of an apparatus. 
     As a result of much committed research undertaken by the inventor to solve the problem described above, the problem was solved by providing, as a first aspect of the present invention, a steering apparatus including: a column supporting member for supporting a steering column; a fixed bracket having, on respective width direction sides thereof, fixed side portions that sandwich the column supporting member; a lock bolt that penetrates the respective fixed side portions of the fixed bracket together with the column supporting member; a main driving cam; a driven cam; an intermediate cam; and an operating lever, wherein the lock bolt penetrates the main driving cam, the driven cam, and the intermediate cam in an axial direction, the main driving cam is rotated by the operating lever, the driven cam is attached to the fixed side portions to be incapable of rotating, the intermediate cam is disposed between the main driving cam and the driven cam, and the intermediate cam is caused to approach and separate from the main driving cam and the driven cam in the axial direction by rotating the main driving cam. 
     Further, the problem described above was solved by providing, as a second aspect of the present invention, the steering apparatus according to the present invention, wherein a separation distance between the main driving cam and the intermediate cam is equal to a separation distance between the driven cam and the intermediate cam. Furthermore, the problem described above was solved by providing, as a third aspect of the present invention, the steering apparatus according to the present invention, wherein a separation distance between the main driving cam and the intermediate cam is different to a separation distance between the driven cam and the intermediate cam. 
     In the first aspect of the present invention, a lock mechanism is constituted by the main driving cam, the driven cam, and the intermediate cam, and the intermediate cam is provided between the main driving cam and the driven cam. Further, axial direction separation and approach operations between the main driving cam and the intermediate cam and axial direction separation and approach operations between the intermediate cam and the driven cam can be performed in two-stage rotation operations. Due to this two-stage operation, lift amounts generated during separation can be divided into smaller amounts, and therefore an operating load of the operating lever can be reduced during both locking and unlocking. As a result, a favorable operation feeling can be obtained in the operating lever. Further, the operating lever can be prevented from returning too rapidly during unlocking, and therefore an unlocking operation can be performed favorably. 
     In the second aspect of the present invention, the separation distance between the main driving cam and the intermediate cam is made equal to the separation distance between the driven cam and the intermediate cam. Therefore, the main driving cam and driven cam can be formed with identical shapes and the respective axial direction side faces of the intermediate cam can be formed with identical cam surface shapes, enabling a reduction in manufacturing cost and easy assembly. 
     In the third aspect of the present invention, the separation distance between the main driving cam and the intermediate cam is made different to the separation distance between the driven cam and the intermediate cam. In so doing, the lift amount can be increased without impairing the operating feeling during locking and unlocking. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sectional view showing main parts of a steering apparatus in a locked condition, according to the present invention,  FIG. 1B  is an enlarged view of a part (α) of  FIG. 1A , and  FIG. 1C  is an enlarged view of the part (α) of  FIG. 1A  in an unlocked condition; 
         FIG. 2A  is a perspective view of main driving cam,  FIG. 2B  is a side view of the main driving cam,  FIG. 2C  is a perspective view of an intermediate cam,  FIG. 2D  is a side view of the intermediate cam,  FIG. 2E  is a perspective view of a driven cam, and  FIG. 2F  is a side view of the driven cam; 
         FIG. 3  is an enlarged view showing main parts of an embodiment of the present invention in which a column supporting member is integrated with a steering column; 
         FIG. 4  is a stroke diagram showing operations for switching the main driving cam, intermediate cam, and driven cam according to the present invention from the unlocked condition to the locked condition and from the locked condition to the unlocked condition; and 
         FIG. 5A  is an enlarged view showing main parts of a second embodiment of the present invention,  FIG. 5B  is a schematic view showing a main driving cam and an intermediate cam according to the second embodiment in a separated condition, and  FIG. 5C  is a schematic view showing the intermediate cam and a driven cam according to the second embodiment in a separated condition. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1A , a steering apparatus according to the present invention is mainly constituted by a fixed bracket  1 , a steering column  2 , a column supporting member  3 , a lock bolt  4 , a main driving cam  5 , a driven cam  6 , an intermediate cam  7 , and an operating lever  8 . The fixed bracket  1  is mainly constituted by fixed side portions  11 , a connecting portion  12 , an attachment portion  13 , and so on. The two fixed side portions  11  are substantially flat plate-shaped sites that oppose each other in parallel. Tilt adjustment elongated holes  11   a  are formed in the two fixed side portions  11  in a substantially vertical direction to serve as sites penetrated by the lock bolt  4 , as will be described below. 
     The two fixed side portions  11  are connected by the connecting portion  12  in an upper portion location thereof using welding means or the like. The connecting portion  12  is formed in a substantially trapezoidal gate shape, an arch shape, or the like when viewed from the front. Further, the horizontally shaped attachment portions  13  are formed to face outward from an upper end location of the two fixed side portions  11 . The fixed bracket  1  is fixed to a frame member or the like on a front portion of a traveling vehicle such as an automobile via the attachment portions  13 . 
     The steering column  2  is constituted by an outer column  21  and an inner column  22 , and a steering shaft is housed in the interior of the inner column  22  to be free to rotate in a periaxial direction. The outer column  21  is supported either fixedly or to be capable of moving in an axial direction by the column supporting member  3 . The column supporting member  3  exists in a plurality of types. A first type is a movable bracket having movable side portions  31  on either width direction side, wherein the two movable side portions  31  are connected by a connecting portion  32  so as to be formed integrally. Telescopic adjustment elongated holes  31   a  are formed in the movable side portions  31 . Further, the outer column  21  is fixed to respective upper end edges of the two movable side portions  31 . 
     The two movable side portions  31  of the movable bracket are disposed between the two fixed side portions  11  of the fixed bracket  1 . The lock bolt  4  is inserted into the tilt adjustment elongated holes  11   a  and the telescopic adjustment elongated holes  31   a , whereby the movable bracket type column supporting member  3  and the steering column  2  are connected to the fixed bracket  1  to be capable of tilt and telescopic adjustment (see  FIG. 1A ). 
     A second type of the column supporting member  3  is formed integrally with the outer column  21  and fixed to the fixed bracket  1  while clutching the inner column  22 . This column supporting member  3  is formed mainly from an aluminum alloy and so on by casting, extrusion molding, or the like, and is mainly constituted by a clutching main body portion  33  and two fastening pieces  35  (see  FIG. 3 ). The clutching main body portion  33  is formed in a substantially cylindrical shape, and a clutching inner peripheral surface thereof is formed in a substantially hollow cylindrical shape so as to clutch the inner column  22 . A dividing groove portion  34  is formed on a diametrical direction lower portion side of the clutching main body portion  33 , and the two fastening pieces  35  are formed in locations on respective width direction sides of the dividing groove portion  34 . 
     The two fastening pieces  35  are formed to oppose each other in an orthogonal direction to an axial direction of the inner column  22  and in a width direction of the clutching main body portion  33 , and fastening holes  35   a  are formed respectively in the two fastening pieces  35 . The lock bolt  4  is inserted into the two fastening holes  35   a  and the tilt adjustment elongated holes  11   a  in the two fixed side portions  11  of the fixed bracket  1  such that the fixed bracket  1  and the column supporting member  3  formed integrally with the outer column  21  are connected to be capable of tilt and telescopic adjustment. 
     Next, the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  will be described. A plurality of embodiments exists with regard to the constitutions of the cams. In a first embodiment, the main driving cam  5  is formed from a cam base portion  51  and a plurality of cam operating portions  52  (see  FIG. 1  and  FIGS. 2A and 2B ). The cam base portion  51  is formed substantially in a disc shape, and an attachment hole  51   a  is formed in a center of the cam base portion  51 . 
     The attachment hole  51   a  is press-fitted to a press-fitting region of the lock bolt  4  such that the main driving cam  5  is capable of rotating in a periaxial direction of the lock bolt  4  together therewith. The plurality of cam operating portions  52  are formed in a circumferential direction in an appropriate region on an outer periphery of one side face of the cam base portion  51  (see  FIGS. 2A and 2B ). 
     An inclined surface  52   a , a top surface  52   b , and a cam projecting portion  52   c  are formed continuously in each cam operating portion  52 . The inclined surface  52   a  is formed as an inclined surface that retreats gradually from a surface of the cam base portion  51 , and the flat surface-shaped top surface  52   b  is formed on an apex of the inclined surface  52   a . Further, the cam projecting portion  52   c  is formed on a circumferential direction outer side of the inclined surface  52   b . The cam projecting portion  52   c  is formed to have a substantially rectangular shape when a peripheral side face thereof is seen from the outside. The plurality of cam operating portions  52  in which these components forma single set are formed at equal intervals around the outer periphery of the cam base portion  51 . 
     More specifically, the outer periphery of the cam base portion  51  is divided into four equal parts, and a single cam operating portion  52  is formed in each of four divided regions obtained as a result. With this configuration, four cam operating portions  52  are formed on the single cam base portion  51  (see  FIGS. 2A and 2B ). The number of cam operating portions  52  is not necessarily limited to four, and three or less or five or more portions may be provided instead. A non-circular bulging portion  53  is formed concentrically with the center of the cam base portion  51  on an opposite side face of the cam base portion  51  to the side on which the cam operating portions  52  are formed (see  FIG. 2B ). The bulging portion  53  is formed in an elongated circular shape, a rectangular shape, an elliptical shape, a circular shape partially formed in a flat surface shape, or the like. The bulging portion  53  is attached by being inserted into a fixing hole  81   a  provided in a rocking central portion  81  of the operating lever  8 , whereby the operating lever  8  and the main driving cam  5  rotate integrally. 
     The driven cam  6  is formed in an identical shape to the main driving cam  5 . The driven cam  6  is formed from a cam base portion  61  and a plurality of cam operating portions  62  (see  FIG. 1  and  FIGS. 2E and 2F ). An inclined surface  62   a , a top surface  62   b , and a cam projecting portion  62   c  are formed continuously in each cam operating portion  62 . An attachment hole  61   a  is formed in a center of the cam base portion  61 . The attachment hole  61   a  is attached to a bolt shaft portion  41  of the lock bolt  4  to be capable of spinning. 
     A non-circular bulging portion  63  is formed concentrically with the center of the cam base portion  61  on an opposite side face of the cam base portion  61  to the side on which the cam operating portions  62  are formed. The bulging portion  63  has a substantially identical shape to the bulging portion  53  of the main driving cam  5 . The bulging portion  63  of the driven cam  6  is disposed in the tilt adjustment elongated hole  11   a  formed in the fixed bracket  1  such that the driven cam  6  is incapable of rotating. 
     The intermediate cam  7  is disposed between the main driving cam  5  and the driven cam  6  in the axial direction of the lock bolt  4  (see  FIG. 1  and  FIGS. 2C and 2D ). The intermediate cam  7  is formed from a cam base portion  71 , main cam operating portions  72 , and driven cam operating portions  73 . An attachment hole  71   a  that is penetrated by the lock bolt  4  is formed in a diametrical center of the cam base portion  71 . A main base surface  71   f  and a driven base surface  71   r  exist on respective axial direction side faces of the cam base portion  71  such that the main base surface  71   f  opposes a cam surface of the main driving cam  5  and the driven base surface  71   r  opposes a cam surface of the driven cam  6 . 
     The main cam operating portions  72  are formed on the main base surface  71   f , and the driven cam operating portions  73  are formed on the driven base surface  71   r . The main cam operating portion  72  is constituted by an inclined surface  72   a , a top surface  72   b , and a cam projecting portion  72   c . The driven cam operating portion  73  is similarly constituted by an inclined surface  73   a , a top surface  73   b , and a cam projecting portion  73   c . The main cam operating portion  72  and the driven cam operating portion  73  are formed in an identical shape. 
     The main driving cam  5 , the driven cam  6 , and the intermediate cam  7  are disposed on an outer side of the fixed side portion  11  on one side of the fixed bracket  1  via the lock bolt  4  and arranged in order of the driven cam  6 , the intermediate cam  7 , and the main driving cam  5  from the fixed side portion  11 . The operating lever  8  is disposed on one axial direction end side of the lock bolt  4 , and the lock bolt  4  is attached to the fixed bracket  1  on the other axial direction end side by a fastening tool  9  such as a nut or a washer. 
     Further, the main driving cam  5  rotates together with the operating lever  8 , whereas the driven cam  6  is attached to the tilt adjustment elongated hole  11   a  in the fixed side portion  11  to be incapable of rotating. The intermediate cam  7  is free to spin relative to the lock bolt  4 . Hence, according to the present invention, the main driving cam  5  and the intermediate cam  7  separate from and approach each other through relative rotation, and the intermediate cam  7  and the driven cam  6  separate from and approach each other through relative rotation. 
     When the main driving cam  5  and the intermediate cam  7  are close and the intermediate cam  7  and the driven cam  6  are close, an axial direction interval between the main driving cam  5  and the driven cam  6  reaches a minimum interval Lmin (see FIG.  1 C). This condition corresponds to an unlocked condition during tilt and telescopic adjustment. Further, when the main driving cam  5  and the intermediate cam  7  are separated and the intermediate cam  7  and the driven cam  6  are separated, the axial direction interval between the main driving cam  5  and the driven cam  6  reaches a maximum interval Lmax (see  FIG. 1B ). This condition corresponds to a locked condition during tilt and telescopic adjustment. 
     Next, fastening and fixing according to the present invention will be described on the basis of  FIG. 4 . First, during a locking operation, the operating lever  8  is rotated downward, or in other words clockwise, such that the lock bolt  4  rotates together with the main driving cam  5  (see ( 1 ) in  FIG. 4 ). Note that black dots in  FIG. 4  indicate respective positions of the main driving cam  5 , the driven cam  6 , and the intermediate cam  7 , and displacement of the positions of the black dots indicates that the main driving cam  5  and the intermediate cam  7  have rotated by a predetermined amount in directions indicated by arrows. The driven cam  6  is incapable of rotating relative to the fixed side portion  11 . Therefore, in a first stage, the main driving cam  5  and the intermediate cam  7  rotate simultaneously in a clockwise direction relative to the unrotatable driven cam  6 . 
     The driven cam operating portions  73  of the intermediate cam  7  rotating together with the main driving cam  5  accordingly move away from the cam operating portions  62  of the unrotatable driven cam  6  such that an axial direction separation interval is generated between the intermediate cam  7  and the driven cam  6 . In other words, a stroke is performed from ( 1 ) to ( 2 - 1 ) in  FIG. 4 . The cam projecting portions  73   c  of the rotating intermediate cam  7  and the cam projecting portions  62   c  of the unrotatable driven cam  6  then come into contact with each other in a cam axial rotation direction (a circumferential direction). As a result, the rotation of the intermediate cam  7  is stopped by the driven cam  6  such that the separation interval between the intermediate cam  7  and the driven cam  6  reaches a maximum. 
     When the operating lever  8  continues to be operated as is after the rotation of the intermediate cam  7  has been stopped in the manner described above, the main driving cam  5  rotates clockwise relative to the stopped intermediate cam  7  in a second stage. In other words, a stroke is performed from ( 2 - 1 ) to ( 3 ) in  FIG. 4 . During this stoke, the main cam operating portions  72  of the stopped intermediate cam  7  and the cam operating portions  52  of the rotating main driving cam  5  move relative to each other. More specifically, the cam operating portions  52  of the main driving cam  5  move in the axial direction away from the main cam operating portions  72  of the intermediate cam  7  such that a separation interval is generated in the axial direction between the intermediate cam  7  and the main driving cam  5 . 
     The cam projecting portions  72   c  of the intermediate cam  7  and the cam projecting portions  52   c  of the main driving cam  5  then come into contact with each other in the cam axial rotation direction (the circumferential direction). As a result, the rotation of the main driving cam  5  relative to the intermediate cam  7  is stopped such that the separation interval between the main driving cam  5  and the intermediate cam  7  reaches a maximum. Thus, a total axial direction interval between the main driving cam  5 , the intermediate cam  7 , and the driven cam  6  reaches a maximum, and as a result, the fixed bracket  1  and the steering column  2  are locked during tilt and telescopic adjustment (see ( 3 ) in  FIG. 4 ). 
     Next, a second fastening and fixing pattern according to the present invention will be described. When the operating lever  8  is rotated downward, or in other words clockwise, the lock bolt  4  rotates together with the main driving cam  5 . Here, similarly to the first pattern, the driven cam  6  is incapable of rotating. Hence, in a first stage, the main driving cam  5  rotates in the clockwise direction alone relative to the intermediate cam  7  and the driven cam  6 . The intermediate cam  7  does not rotate, and the driven cam  6  is incapable of rotating. 
     As a result, first, the cam operating portions  52  of the initially rotating main driving cam  5  move in the axial direction away from the main cam operating portions  72  of the stopped intermediate cam  7  such that the main driving cam  5  and the intermediate cam  7  separate from each other. In other words, condition ( 1 ) shifts to condition ( 2 - 2 ) in  FIG. 4 . The cam projecting portions  52   c  of the rotating main driving cam  5  and the cam projecting portions  72   c  of the non-rotating intermediate cam  7  then come into contact with each other in the cam axial rotation direction (or the circumferential direction). As a result, the separation interval between the main driving cam  5  and the intermediate cam  7  reaches a maximum such that the intermediate cam  7  is rotated by the rotation of the main driving cam  5 . When the operating lever  8  continues to be rotated as is, the main driving cam  5  and the intermediate cam  7  begin to rotate relative to the unrotatable driven cam  6  simultaneously in a second stage. 
     The driven cam operating portions  73  of the intermediate cam  7  rotating together with the main driving cam  5  then move relative to the cam operating portions  62  of the unrotatable driven cam  6 . Accordingly, the cam projecting portions  72   c  of the rotating intermediate cam  7  and the cam projecting portions  62   c  of the driven cam  6  come into contact with each other in the cam axial rotation direction (or the circumferential direction). As a result, the rotation of the main driving cam  5  and the intermediate cam  7  is stopped by the unrotatable driven cam  6  such that the respective separation intervals between the main driving cam  5 , the intermediate cam  7 , and the driven cam  6  reach the maximum intervals, whereby the locked condition is established. In other words, condition ( 2 - 2 ) shifts to condition ( 3 ) in  FIG. 4 . Thus, the total axial direction interval between the main driving cam  5 , the intermediate cam  7 , and the driven cam  6  reaches a maximum, and as a result, the fixed bracket  1  and the steering column  2  are locked during tilt and telescopic adjustment. 
     Next, unlocking will be described. When the operating lever  8  is rotated upward, or in other words counter-clockwise, the lock bolt  4  rotates together with the main driving cam  5 , whereby the main driving cam  5  and the intermediate cam  7  rotate counter-clockwise simultaneously relative to the unrotatable driven cam  6  in a first stage. In other words, condition ( 3 ) shifts to condition ( 2 - 2 ) in  FIG. 4 . Accordingly, the driven cam operating portions  73  of the rotating intermediate cam  7  move relative to the cam operating portions  62  of the driven cam  6 . 
     The cam projecting portions  73   c  of the rotating intermediate cam  7  and the cam projecting portions  62   c  of the unrotatable driven cam  6  then approach each other so as to come into contact in the cam axial rotation direction (or the circumferential direction). As a result, the rotation of the intermediate cam  7  is stopped by the driven cam  6 . Then, in a second stage, the main driving cam  5  rotates counter-clockwise relative to the stopped intermediate cam  7 . 
     The cam operating portions  52  of the rotating main driving cam  5  thus move relative to the main cam operating portions  72  of the stopped intermediate cam  7  in an approaching direction, whereby the cam projecting portions  72   c  of the intermediate cam  7  and the cam projecting portions  52   c  of the main driving cam  5  come into contact with each other in the cam axial rotation direction (or the circumferential direction). As a result, the rotation of the main driving cam  5  is stopped by the intermediate cam  7  such that the total axial direction interval between the main driving cam  5 , the intermediate cam  7 , and the driven cam  6  reaches a minimum, whereby the unlocked condition is established. In other words, condition ( 2 - 2 ) shifts to condition ( 1 ) in  FIG. 4 . 
     Next, a second unlocking pattern will be described. When the operating lever  8  is rotated upward, or in other words counter-clockwise, the lock bolt  4  rotates together with the main driving cam  5 . In a first stage, the main driving cam  5  rotates counter-clockwise alone relative to the intermediate cam  7  and the unrotatable driven cam  6 . The intermediate cam  7  does not rotate, and the driven cam  6  is incapable of rotating. In other words, condition ( 3 ) shifts to condition ( 2 - 1 ) in  FIG. 4 . The cam operating portions  52  of the rotating main driving cam  5  move relative to the main cam operating portions  72  of the stopped intermediate cam  7 . Accordingly, the cam projecting portions  52   c  of the rotating main driving cam  5  and the cam projecting portions  72   c  of the non-rotating intermediate cam  7  come into contact with each other in the cam axial rotation direction (or the circumferential direction). As a result, the separation interval between the main driving cam  5  and the intermediate cam  7  reaches a minimum such that the intermediate cam  7  is rotated by the rotation of the main driving cam  5 . 
     When the operating lever  8  continues to be rotated as is, the main driving cam  5  and the intermediate cam  7  rotate counter-clockwise simultaneously relative to the unrotatable driven cam  6  in a second stage. Accordingly, the driven cam operating portions  73  of the intermediate cam  7  move relative to the cam operating portions  62  of the driven cam  6 . The cam projecting portions  73   c  of the intermediate cam  7  and the cam projecting portions  62   c  of the driven cam  6  thus come into contact with each other in the cam axial rotation direction (or the circumferential direction). As a result, the rotation of the main driving cam  5  and the intermediate cam  7  is stopped by the unrotatable driven cam  6  such that the overall axial direction interval between the main driving cam  5 , the intermediate cam  7 , and the driven cam  6  reaches a minimum, whereby the unlocked condition is established. In other words, condition ( 2 - 1 ) shifts to condition ( 1 ) in  FIG. 4 . 
     Hence, during locking and unlocking according to the present invention, the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  are rotated in two stages. During locking, the cam projecting portions  72   c ,  73   c  formed respectively on the main base surface  71   f  and the driven base surface  71   r  on either axial direction side face of the intermediate cam  7  move in two stages rather than climbing the inclined surface  51  of the main driving cam  5  and the inclined surface  71  of the driven cam  6  simultaneously. As a result, an operating load of the operating lever  8  can be reduced such that a favorable operation feeling can be obtained in the operating lever  8 . Furthermore, the steering column  2  can be fastened and fixed rigidly without the need for an increase in cam size. 
     During unlocking, the cam projecting portions  72   c ,  73   c  formed on the respective side faces of the intermediate cam  7  descend in two stages rather than descending the inclined surface  52   a  of the main driving cam  5  and the inclined surface  62   a  of the driven cam  6  simultaneously, and therefore an initial operation of the operating lever  8  during unlocking does not feel heavy. Hence, a favorable operation feeling can be obtained in the operating lever  8 . Furthermore, by dividing the descending movement into two stages, the operating lever  8  can be prevented from returning too rapidly. 
     In the first embodiment of the present invention, described above, the cam operating portions  52  of the main driving cam  5  are shaped identically to the cam operating portions  62  of the driven cam  6 , and the main cam operating portions  72  and driven cam operating portions  73  of the intermediate cam  7  are likewise shaped identically to the cam operating portions  52  and cam operating portions  62 . In other words, a separation distance between the intermediate cam  7  and the main driving cam  5  is identical to a separation distance between the intermediate cam  7  and the driven cam  6 . 
     In a second embodiment, on the other hand, the cam operating portions  52  of the main driving cam  5  are shaped differently to the cam operating portions  62  of the driven cam  6  such that the separation distance between the main driving cam  5  and the intermediate cam  7  is different to the separation distance between the driven cam  6  and the intermediate cam  7 . In this embodiment, a height Ha from the cam surface of the cam base portion  51  of the main driving cam  5  to the top surface  52   b  of the cam operating portion  52  is different to a height Hb from the cam surface of the cam base portion  61  of the driven cam  6  to the top surface  62   b  of the cam operating portion  62 . 
     In an embodiment shown in  FIG. 5 , the height Ha from the cam surface to the top surface  52   b  of the cam operating portion  52  is greater than the height Hb from the cam surface of the cam base portion  61  of the driven cam  6  to the top surface  62   b  of the cam operating portion  62 , and therefore Ha&gt;Hb. Accordingly, a separation distance La between the main driving cam  5  and the intermediate cam  7  is set to be larger than a separation distance Lb between the intermediate cam  7  and the driven cam  6 . An opposite configuration may also be employed. 
     The main cam operating portions  72  and the driven cam operating portions  73  of the intermediate cam  7  are formed identically to the main cam operating portions  72  of the main driving cam  5  and the driven cam operating portions  73  of the driven cam  6 , respectively. For example, the separation distance between the main driving cam  5  and the intermediate cam  7  is formed to be larger than the separation distance between the driven cam  6  and the intermediate cam  7 . 
     Hence, even when the respective cam operating portions of the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  do not have identical shapes, the lever operability is not impaired as long as rotation is performed in two stages. Therefore, the respective cam operating portions of the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  may be formed in several variations such that a lift amount can be increased without increasing the size of the lock mechanism. 
     Further, in the embodiments described above, the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  are all formed with identical diameters. In so doing, component uniformity can be realized, making manufacture of the cams easy. However, the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  may have different diameters. For example, the driven cam  6  and the main driving cam  5  may have identical diameters while the diameter of the intermediate cam  7  alone is different, or the main driving cam  5 , the driven cam  6 , and the intermediate cam  7  may all have different diameters to each other. According to the present invention, various modifications and amendments may be implemented appropriately on the embodiments described above. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.