Abstract:
Provided is a locking device, the fastening strength of which does not vary. A hook is provided with a recess having a first stopper surface and a second stopper surface which extend in the direction of a rotating shaft. A pawl is provided with a projection having a first contact surface capable of contacting the first stopper surface, and a second contact surface capable of contacting the second stopper surface. The provided locking device is one in which the first and second contact surfaces are convexly curving surfaces which project outward toward the first and second stopper surfaces.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a locking device. 
       BACKGROUND ART 
       [0002]    An example of a background locking device will be described with reference to  FIGS. 6 and 7 .  FIG. 6  is a view showing a locked state of the background locking device, and  FIG. 7  is a view showing an unlocked state of the background locking device. 
         [0003]    The locking device is attached to each of a moving-side member and a fixed-side member. The moving-side member is, for example, a seat, a door, a trunk lid or an engine hood, which is provided to be rotatable relative to a floor of a vehicle. The fixed-side member is, for example, a vehicle body. The locking device is a device that is capable of suppressing the relative movement between the moving-side member and the fixed-side member. 
         [0004]    The locking device includes a base  1  and a striker  3 . The base  1  is provided in one of the moving-side member and the fixed-side member, and the striker  3  is provided in the other one. The base  1  is provided with a groove  1   a  into which the striker  3  is able to enter. 
         [0005]    A hook  7  is rotatably provided in one side of the base  1 . A pawl  9  is rotatably provided in the other side of the base  1 . The groove  1   a  is provided between one side and the other side of the base  1 . The hook  7  is formed with a groove  7   a  into which the striker  3  is able to enter. The hook  7  is formed with a convex portion  7   b.    
         [0006]    The pawl  9  is formed with a concave portion  9   a  with which the convex portion  7   b  of the hook  7  can be engaged. The concave portion  9   a  has a shape that is spread toward its opening. 
         [0007]    A spring  11  is caused to exert a force on the hook  7  and the pawl  9 . One end of the spring  11  is locked to the hook  7 , and the other end thereof is locked to the pawl  9 . The spring  11  urges the hook  7  in an unlocked position direction (in the drawing, a direction of an arrow UL). The spring  11  urges the pawl  9  in a direction (in the drawing, a direction of an arrow K) in which the convex portion  9   a  is engaged with the concave portion  7   b  of the hook  7 . 
         [0008]    In the state shown in  FIG. 6 , the hook  7  is in a locked position where the striker  3  is prohibited from being detached from the groove  7   a . This state is a locked state where the concave portion  9   a  is engaged with the convex portion  7   b , and the rotation of the hook  7  is thus prohibited. 
         [0009]    In the state shown in  FIG. 7 , the engagement between the concave portion  9   a  and the convex portion  7   b  is released. This state is an unlocked state where the hook  7  is in an unlocked position and where the striker  3  is able to enter the groove  7   a.    
         [0010]    Next, an operation of the locking device configured as described above will be described. 
         [0011]    When the pawl  9  is rotated, from the locked state shown in  FIG. 6 , in a direction opposite to the direction of the arrow K against an elastic force of the spring  11 , the engagement between the concave portion  9   a  and the convex portion  7   b  is released. The hook  7  is further rotated, by the elastic force of the spring  11 , to the unlocked position where the striker  3  is able to enter the groove  7   a . In this way, the locking device becomes the unlocked state shown in  FIG. 7 , where the convex portion  7   b  is abutted against a portion other than the concave portion  9   a.    
         [0012]    In the unlocked state shown in  FIG. 7 , the hook  7  is rotated in the locked position direction against the elastic force of the spring  11  when a surface in the vicinity of an opening of the groove  7   a  of the hook  7  is pressed by the striker  3 . Further, the convex portion  7   b  of the hook  7  and the concave portion  9   a  of the pawl  9  are engaged, and the hook  7  is thus prohibited from rotating in the unlock direction. Then, the striker  3  becomes the locked state where the striker  3  is not able to be detached from the groove  7   a  of the hook  7  (e.g., see Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Patent Publication No. 4325794 
       
     
       SUMMARY OF THE INVENTION 
     Problem to be Solved 
       [0014]    In the locking device configured as described above, due to variations in the dimensional accuracy or assembly accuracy of the hook  7  or the pawl  9 , the contact position between the convex portion  7   b  and the concave portion  9   a  is varied when the convex portion  7   b  enters the concave portion  9   a . For example, an entry depth of the convex portion  7   b  into the concave portion  9   a  becomes shallow if the convex portion  7   b  is greater than its original shape. Therefore, the engagement strength between the hook  7  and the pawl  9  is varied, and thus there is a possibility that a sufficient engagement strength is not obtained. Therefore, the present invention is to provide a locking device where the engagement strength is hard to be varied. 
       Solution to Problem 
       [0015]    According to the present invention, there is provided a locking device including a base; a hook provided on the base so as to be rotatable around a rotation axis; and a pawl provided on the base so as to be rotatable around an axis parallel to the rotation axis, wherein the hook has a groove into which a striker is able to enter, the hook is rotatable from an unlocked position where the striker is able to enter the groove to a locked position where the striker is prohibited from being detached from the groove, and the hook is pressed in the unlocked position direction, wherein the pawl prohibits the rotation of the hook by being in contact with the hook located in the locked position, and the pawl is pressed in a direction to be urged against the hook, wherein a concave portion is provided in one of the hook and the pawl and has a first stopper surface and a second stopper surface facing the first stopper surface which are extending in the rotation axis direction, wherein a convex portion is provided in the other of the hook and the pawl and has a first contact surface that can be brought into contact with the first stopper surface and a second contact surface that can be brought into contact with the second stopper surface, wherein when the convex portion enters the concave portion, the first contact surface is brought into contact with the first stopper surface and the second contact surface is brought into contact with the second stopper surface, so that the rotation of the hook is prohibited by the pawl, and wherein the first contact surface is a convex curved surface projected toward the first stopper surface, and the second contact surface is a convex curved surface projected toward the second stopper surface, as seen from the rotation axis direction. 
       Effects of Invention 
       [0016]    According to the present invention, a locking device where the engagement strength is hard to be varied is provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an exploded perspective view of a locking device of an illustrative embodiment. 
           [0018]      FIG. 2  is a view showing an unlocked state of the locking device shown in 
           [0019]      FIG. 1 , as seen from II direction in  FIG. 1 . 
           [0020]      FIG. 3  is a view showing a locked state of the locking device shown in  FIG. 2 . 
           [0021]      FIG. 4  is an enlarged view of a pawl shown in  FIG. 1 . 
           [0022]      FIG. 5  is an enlarged view of a convex portion shown in  FIG. 4 . 
           [0023]      FIG. 6  is a configuration view showing a locked state of a background locking device. 
           [0024]      FIG. 7  is a configuration view showing an unlocked state of the background locking device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    An illustrative embodiment of the present invention will be described with reference to the drawings.  FIG. 1  is an exploded perspective view of a locking device of an illustrative embodiment.  FIG. 2  is a view showing an unlocked state of the locking device shown in  FIG. 1 , as seen from II direction in  FIG. 1 .  FIG. 3  is a view showing a locked state of the locking device shown in  FIG. 2 . 
         [0026]    The locking device is attached to each of a moving-side member and a fixed-side member. The moving-side member is, for example, a seat, a door, a trunk lid or an engine hood, which are provided to be rotatable relative to a floor of a vehicle. The fixed-side member is, for example, a vehicle body. The locking device is a device that is capable of suppressing the relative movement between the moving-side member and the fixed-side member. 
         [0027]    The locking device includes a base  151  and a striker  153  (see  FIG. 3 ). The base  151  is attached to one of the moving-side member and the fixed-side member, and the striker  153  is attached to the other of the moving-side member and the fixed-side member. The base  151  is provided with a groove  151   a  into which the striker  153  is able to enter. The base  151  includes a hook  157  and a pawl  161 . The hook  157  and the pawl  161  are provided on the base  151  so as to be rotatable around rotation axes parallel to each other. 
         [0028]    As shown in  FIG. 1 , the base  151  is a substantially plate-like member having a front surface and a back surface. The base  151  has a right portion and a left portion, which are provided across the groove  151   a.    
         [0029]    A hook  157  is provided on the front surface of the left portion of the base  151 . The hook  157  is formed with a through hole  157   h . Furthermore, the base  151  is also formed with a through hole  151   h . A diameter of the hole  151   h  is set to be substantially equal to a diameter of the hole  157   h  of the hook  157 . 
         [0030]    A bushing  145  is provided on the back surface of the base  151 . The bushing  145  has a cylindrical portion  145   a  that is inserted into the hole  151   h  of the base  151 , and an attaching portion  145   b . The attaching portion  145   b  is formed in a base portion of the cylindrical portion  145   a . An outer diameter of the cylindrical portion  145   a  that is abutted against the back surface of the base  151  is set to be slightly smaller than those of the hole  157   h  of the hook  157  and the hole  151   h  of the base  151 . 
         [0031]    The cylindrical portion  145   a  is inserted through the hole  151   h  of the base  151  and the hole  157   h  of the hook  157 . A leading end of the cylindrical portion  145   a , which has passed through the hole  157   h  of the hook  157 , is crimped. Therefore, the hook  157  is rotatable relative to the base  151 . 
         [0032]    In the present embodiment, the position of the hook  157  shown in  FIG. 2  is defined as an unlocked position, and the position of the hook  157  shown in  FIG. 3  is defined as a locked position. 
         [0033]    The pawl  161  is rotatably provided on the front surface of the right portion of the base  151 . The pawl  161  is formed with a through hole  161   h . The base  151  is also formed with a through hole  151   i . A diameter of the hole  151   i  is set to be substantially equal to a diameter of the hole  161   h  of the pawl  161 . 
         [0034]    A bushing  147  is provided on the back surface of the base  151 . The bushing  147  has a cylindrical portion  147   a  that is inserted into the hole  151   i  of the base  151 , and an attaching portion  147   b . The attaching portion  147   b  is formed in a base portion of the cylindrical portion  147   a  and abutted against the back surface of the base  151 . An outer diameter of the cylindrical portion  147   a  is set to be slightly smaller than those of the hole  161   h  of the pawl  161  and the hole  151   i  of the base  151 . 
         [0035]    The cylindrical portion  147   a  is inserted through the hole  151   i  of the base  151  and then inserted through the hole  161   h  of the pawl  161 . Further, a leading end of the cylindrical portion  147   a , which has passed through the hole  161   h  of the pawl  161 , is crimped. Therefore, the pawl  161  is rotatable relative to the base  151 . 
         [0036]    The hook  157  is formed with a groove  157   a  into which the striker  153  is able to enter. Further, on a peripheral portion of the hook  157 , a first convex portion  157   b  and a second convex portion  157   c  are formed along a rotation direction of the hook  157  into the unlocked position. A concave portion  157   d  is formed between the first convex portion  157   b  and the second convex portion  157   c . The concave portion  157   d  has a shape that is spread toward its opening. A width w (see  FIG. 2 ) of the concave portion  157   d  is gradually thinned toward the inside from a peripheral surface. 
         [0037]    A convex portion  161   a  is formed on a surface of the pawl  161  facing the hook  157 . The convex portion  161   a  can be locked/unlocked from the concave portion  157   d  of the hook  157 . Further, a concave portion  161   b , into which the second convex portion  157   c  of the hook  157  is able to enter, is formed on a surface of the pawl  161  facing the hook  157 . * 
         [0038]    A spring  171  for urging the hook  157  in the unlocked position direction (a direction of an arrow UL in  FIGS. 2 and 3 ) is provided between the base  151  and the hook  157 . Further, a spring  173  for urging the pawl  161  in a direction (a direction of an arrow E in  FIGS. 2 and 3 ) to be engaged with the hook  157  is provided between the base  151  and the pawl  161 . In the present embodiment, the springs  171 ,  173  are spiral springs. 
         [0039]    Next, shapes of the concave portion  157   d  and the convex portion  161   a  will be described. 
         [0040]    The concave portion  157   d  of the hook  157  has a first stopper surface  157   s  extending in a rotation axis direction of the hook  157  and a second stopper surface  157   t  facing the first stopper surface  157   s . The rotation axis direction of the hook  157  is a direction perpendicular to a paper surface of  FIGS. 2 and 3 . The rotation direction of the hook  157  is the direction of the arrow UL and an opposite direction thereof in  FIGS. 2 and 3 . The first stopper surface  157   s  and the second stopper surface  157   t  are opposed to each other via a space. The first stopper surface  157   s  and the second stopper surface  157   t  are planar surfaces. The first stopper surface  157   s  is inclined with respect to the second stopper surface  157   t  such that the concave portion  157   d  is spread toward its opening. 
         [0041]    As shown in  FIGS. 4 and 5 , the convex portion  161   a  of the pawl  161  has a first contact surface  161   s  and a second contact surface  161   t . The first contact surface  161   s  can be brought into contact with the first stopper surface  157   s . The second contact surface  161   t  can be brought into contact with the second stopper surface  157   t . The first contact surface  161   s  and the second contact surface  161   t  are convex curved surfaces projected toward the concave portion  157   d , as seen from the direction parallel to the rotation axes of the hook  157  and the pawl  161 . As seen from the direction of the rotation axis, the first contact surface  161   s  is a convex curved surface projected toward the first stopper surface  157   s  and the second contact surface  161   t  is a convex curved surface projected toward the second stopper surface  157   t.    
         [0042]    Since the first stopper surface  157   s  and the second stopper surface  157   t  are planar surfaces, the radius of curvature thereof is infinite. Namely, the curvature of the first stopper surface  157   s  is set to be greater than that of the first contact surface  161   s , and the curvature of the second stopper surface  157   t  is set to be greater than that of the second contact surface  161   t.    
         [0043]    In the present embodiment, a leading end portion of the convex portion  161   a  of the pawl  161  is configured by an arcuate surface centered on a center axis O 2 , as seen from the rotation axis direction. A portion of the arcuate surface is configured by the first contact surface  161   s , the second contact surface  161   t , and a top surface  161   w  (see  FIG. 5 ) that connects the first contact surface  161   s  and the second contact surface  161   t . Further, the second contact surface  161   t  is formed at a position close to a rotation center axis O 1  of the pawl  161  than the first contact surface  161   s.    
         [0044]    In the present embodiment, the concave portion  157   d  has a connecting surface  157   w  (see  FIGS. 2 and 3 ) that connects the first stopper surface  157   s  and the second stopper surface  157   t.    
         [0045]    As shown in  FIG. 3 , the convex portion  161   a  enters the concave portion  157   d . When the first contact surface  161   s  is in contact with the first stopper surface  157   s  and the second contact surface  161   t  is in contact with the second stopper surface, further entry of the convex portion  161   a  into the concave portion  157   d  is stopped. In this state, the top surface  161   w  faces the connecting surface  157   w  without being in contact with the connecting surface  157   w.    
         [0046]    A first avoiding portion  161   u  having a concave shape is formed adjacent to the first contact surface  161   s . The first avoiding portion  161   u  is set such that a distance r 2  to the rotation center axis of the pawl  161  is set to be shorter than a distance r 1  from the first contact surface  161   s  to the rotation center axis O 1  of the pawl  161 . 
         [0047]    A second avoiding portion  161   v  is formed adjacent to the second contact surface  161   t  and has a concave shape. The second avoiding portion  161   v  is set such that a distance r 4  to the rotation center axis of the pawl  161  is set to be longer than a distance r 3  from the second contact surface  161   t  to the rotation center axis O 1  of the pawl  161 . 
         [0048]    A first protrusion  151   b , a second protrusion  151   c , a third protrusion  151   d  and a stopper protrusion  151   s , which are projected to the direction of the hook  157 , are provided around the hole  151   h  on the front surface of the base  151 . The hook  157  that rotates is supported at the top of at least three protrusions of these four protrusions. With respect to the dimensions in the rotation axis direction of the hook  157 , a height from the front surface of the base  151  to the top of these four protrusions is set to be greater than a thickness of the spring  171 . 
         [0049]    The base  151  is provided with a hole  151   j  that penetrates through the base  151 . As shown in  FIG. 1 , the hook  157  is provided with a protrusion  157   e  that is projected to the direction of the base  151 . A height of the protrusion  157   e  is set to a height where the protrusion does not abut against the base  151 . Moreover, the protrusion  157   e  is formed at a position in which the protrusion  157   e  can pass through above the hole  151   j  of the base  151  and can be abutted against the stopper protrusion  151   s  on the base  151  when the hook  157  is rotated in the direction of the arrow UL. 
         [0050]    A fourth protrusion  151   e , a fifth protrusion  151   f  and a sixth protrusion  151   g , which are projected to the direction of the pawl  161 , are also formed around the hole  151   i  on the front surface of the base  151 . The pawl  161  that rotates is supported at the top of these three protrusions. For the dimensions in the rotation axis direction of the pawl  161 , a height from the front surface of the base  151  to the top of these three protrusions is set to be greater than a thickness of the spring  173 . 
         [0051]    The base  151  is formed with a hole  151   k  that penetrates through the base  151 . As shown in  FIG. 1 , the pawl  161  is formed with a protrusion  161   e  that is projected to the direction of the base  151 . A height of the protrusion  161   e  is set to a height in which the protrusion does not abut against the base  151 . Moreover, the protrusion  161   e  is formed at a position in which the protrusion  161   e  passes through above the hole  151   k  of the base  151  when the pawl  161  is rotated. 
         [0052]    An inner end of the spring  171  is locked to the first protrusion  151   b  of the base  151 , and an outer end thereof is locked to the protrusion  157   e  of the hook  157 . The spring  171  urges the hook  157  in the unlocked position direction. 
         [0053]    An inner end of the spring  173  is locked to the fourth protrusion  151   e  of the base  151 , and an outer end thereof is locked to the protrusion  161   e  of the pawl  161 . The spring  173  urges the pawl  161  in a direction to be pressed against the hook  157 . 
         [0054]    Next, an operation of the configuration described above will be described. In the state of  FIG. 3  where the hook  157  is in the locked position, the concave portion  157   d  and the convex portion  161   a  are engaged, and hence, the hook  157  is prohibited from rotating in the unlock direction. When the convex portion  161   a  is engaged with the concave portion  157   d , the first contact surface  161   s  is in contact with the first stopper surface  157   s  and the second contact surface  161   t  is in contact with the second stopper surface  157   t . In this state, the pawl  161  prohibits the rotation of the hook  157 . This state is a locked state where the striker  153  is not able to be detached from the groove  157   a  of the hook  157 . 
         [0055]    Here, when the pawl  161  is rotated in the direction opposite to the direction of the arrow E against the elastic force of the spring  173 , the pawl  161  is detached from the hook  157 . Then, the engagement between the concave portion  157   d  and the convex portion  161   a  is released. The hook  157  is rotated in the unlocked position direction shown in  FIG. 2  by the elastic force of the spring  171 . In this way, the striker  153  is in the unlocked state where the striker can be detached from the groove  157   a  of the hook  157 . 
         [0056]    In the present embodiment, the stopper protrusion  151   s  is provided on the front surface of the base  151 . When the protrusion  157   e  of the hook  157  that rotates in the unlocked position direction is abutted against the stopper protrusion  151   s , further rotation of the hook  157  in the unlocked position direction is prohibited. 
         [0057]    In the case of the unlocked state shown in  FIG. 2 , the hook  157  is rotated in the locked position direction against the elastic force of the spring  171  when a surface  157   n  in the vicinity of an opening of the groove  157   a  of the hook  157  is pressed by the striker  153 . Then, the concave portion  157  is engaged with the convex portion  161   a , and hence, the hook  157  is prohibited from rotating in the unlock direction. In this way, the locking device is in the locked state where the striker  153  is not able to be detached from the groove  157   a  of the hook  157 . 
         [0058]    Next, a method of assembling the locking device configured as described above will be described with reference to  FIGS. 1 to 3 . 
         [0059]    First, the cylindrical portion  145   a  of the bushing  145  is inserted into the hole  151   h  from the back surface of the base  151 . Further, the cylindrical portion  147   a  of the bushing  147  is inserted into the hole  151   i  from the back surface of the base  151 . At this time, the cylindrical portion  145   a  and the cylindrical portion  147   a  are projected from the front surface of the base  151 . 
         [0060]    Subsequently, the spring  171  is placed on the front surface of the base  151  and the inner end of the spring  171  is locked to the first protrusion  151   b . Further, in the state where the elastic force is generated in the spring  171 , the outer end of the spring  171  is held by a rod-shaped jig that is inserted through a round hole  151   j  from the back surface of the base  151 . Subsequently, the hook  157  is placed on the spring  171  and the jig is extracted. At this time, the outer end of the spring  171  is locked to the protrusion  157   e  of the hook  157 . 
         [0061]    Further, the spring  173  is placed on the front surface of the base  151 , and the inner end of the spring  173  is locked to the fourth protrusion  151   e . Further, in the state where the elastic force is generated in the spring  173 , the outer end of the spring  173  is held by a rod-shaped jig that is inserted through a round hole  151   k  from the back surface of the base  151 . Then, the pawl  161  is placed on the spring  173 , and the jig is extracted. At this time, the outer end of the spring  173  is locked to the protrusion  161   e  of the pawl  161 . 
         [0062]    In this way, the locking device described above is obtained. 
         [0063]    According to the above configuration, the following effects can be achieved. 
         [0064]    (1) The hook  157  is provided with the concave portion  157   d  that has the first stopper surface  157   s  and the second stopper surface  157   t , which extends in the rotation axis direction of the hook  157 . The pawl  161  is provided with the convex portion  161   a  that has the first contact surface  161   s  that can be brought into contact with the first stopper surface  157   s  and the second contact surface  161   t  that can be brought into contact with the second stopper surface  157   t . The first contact surface  161   s  and the second contact surface  161   t  are convex curved surfaces which are projected toward the concave portion  157   d , as seen from the rotation axis direction of the hook  157  and the pawl  161 . 
         [0065]    Therefore, even when the variations in the dimensional accuracy or assembly accuracy of the hook  157  or the pawl  161  occur, the contact position between the first contact surface  161   s  and the first stopper surface  157   s  and the contact position between the second contact surface  161   t  and the second stopper surface  157   t  are hard to be changed. 
         [0066]    For example, even when the convex portion  161   a  is greater than its original shape due to manufacturing error, since the first contact surface  161   s  and the second contact surface  161   t  are convex curved surfaces, the contact point between the first stopper surface  157   s  and the first contact surface  161   s  is hard to be deviated in a depth direction of the concave portion  157   d.    
         [0067]    On the contrary, unlike the present embodiment, for example, in the case where both the first stopper surface and the first contact surface are planar surfaces, the contact point between the first stopper surface and the first contact surface is significantly deviated to a shallow position when the convex portion to be engaged with the concave portion is greater than its original shape, due to manufacturing error, so that the engagement strength is greatly lowered. 
         [0068]    For such reasons, variations in the engagement strength between the hook  157  and the pawl  161  are hard to occur. 
         [0069]    (2) Incidentally, in a case where the first stopper surface  157   s  and the second stopper surface  157   t  are planar surfaces and the first contact surface  161   s  and the second contact surface  161   t  are arcuate surfaces, it is easy to form the convex portion  161   a  and the concave portion  157   d . Further, with a simple shape, variations in the engagement strength between the hook  157  and the pawl  161  are hard to occur. 
         [0070]    (3) Further, in the locking device of the present embodiment, the first stopper surface  157   s  and the second stopper surface  157   t  have curvatures, and the curvature of the first stopper surface  157   s  is greater than the curvature of the first contact surface  161   s , and the curvature of the second stopper surface  157   t  is greater than the curvature of the second contact surface  161   t.    
         [0071]    Therefore, even when variations in the dimensional accuracy or assembly accuracy of the hook  157  or the pawl  161  occur, the contact position between the first contact surface  161   s  and the first stopper surface  157   s  and the contact position between the second contact surface  161   t  and the second stopper surface  157   t  are hard to be changed. 
         [0072]    (4) As described above, the first stopper surface  157   s  is inclined with respect to the second stopper surface  157   t  such that the concave portion  157   d  is spread toward its opening. 
         [0073]    The convex portion  161   a  can easily enter the concave portion  157   d  when the concave portion  157   d  is formed in such a shape. Further, variations in the engagement strength are liable to occur due to variations in the dimensional accuracy or the like when the concave portion  157   d  has such a shape. However, according to the present invention, for the reasons described above, it is possible to suppress the variations in the engagement strength. 
         [0074]    (5) The second contact surface  161   t  is formed at a position close to the rotation axis of the pawl  161  than the first contact surface  161   s . The first avoiding portion  161   u  is provided adjacent to the first contact surface  161   s . The second avoiding portion  161   v  is provided adjacent to the second contact surface  161   t.    
         [0075]    The distance r 2  from the rotation axis of the pawl  161  to the first avoiding portion  161   u  is shorter than the distance r 1  from the rotation axis of the pawl  161  to the first contact surface  161   s . The distance r 4  from the rotation axis of the pawl  161  to the second avoiding portion  161   v  is longer than the distance r 3  from the rotation axis of the pawl  161  to the second contact surface  161   t.    
         [0076]    Therefore, when the convex portion  161   a  is detached from the concave portion  157   d , the portion of the pawl  161  other than the first contact surface  161   s  and the second contact surface  161   t  is hard to be brought into contact with the concave portion  157   d  of the hook  157 , so that the convex portion  161   a  can be easily detached from the concave portion  157   d.    
         [0077]    (6) Further, in a case where the first avoid portion  161   u  and the second avoiding portion  161   v  are concave surfaces, it is possible to more reliably suppress the portion of the pawl  161  other than the first contact surface  161   s  and the second contact surface  161   t  from being brought into contact with the concave portion  157   d  of the hook  157 . 
         [0078]    (7) The concave portion  157   d  has the connecting surface  157   w  for connecting the first stopper surface  157   s  and the second stopper surface  157   t . The convex portion  161   a  has the top surface  161   w  facing the connecting surface  157   w . The connecting surface  157   w  and the top surface  161   w  have shapes that are not in contact with each other in the state where the first contact surface  161   s  is in contact with the first stopper surface  157   s  and the second contact surface  161   t  is in contact with the second stopper surface. 
         [0079]    Therefore, according to the contact between the first contact surface  161   s  and the first stopper surface  157   s  and the contact between the second contact surface  161   t  and the second stopper surface, the engagement strength between the hook  157  and the pawl  161  is determined and the variations in the engagement strength are hard to occur. 
         [0080]    (8) At this time, if the top surface  161   w  is a curved surface, the top surface  161   w  is hard to be brought into contact with the connecting surface  157   w.    
         [0081]    It is noted that the present invention is not limited to the above embodiments. The following modifications may be realized. 
         [0082]    In the above-described embodiment, an example has been described in which the concave portion  157   d  is provided in the hook  157  and the convex portion  161   a  is provided in the pawl  161 . However, the convex portion may be provided in the hook  157  and the concave portion may be provided in the pawl  161 . 
         [0083]    In the above-described embodiment, an example has been described in which the first stopper surface  157   s  and the second stopper surface  157   t  are planar surfaces. However, it may be a curved surface such as an arcuate surface, an elliptical surface, a parabolic surface, or may be a surface having fine irregularities. 
         [0084]    Although an example has been described, in which a leading end portion of the convex portion  161   a  of the pawl  161  is an arcuate surface centered on the center axis O 2  and a portion of the arcuate surface is the first contact surface  161   s  and the second contact surface  161   t , a portion other than the first contact surface  161   s  and the second contact surface  161   t  may not be an arcuate surface. 
         [0085]    Further, the first contact surface  161   s  and the second contact surface  161   t  may not be an arcuate surface centered on the center axis O 2  that is common. 
         [0086]    Although an example has been described, in which the first contact surface  161   s  and the second contact surface  161   t  are arcuate surfaces, the first contact surface and the second contact surface may have fine irregularities or may be a curved surface such as an elliptical surface or parabolic surface, other than the arcuate surface. 
         [0087]    Although the first avoiding portion  161   u  and the second avoiding portion  161   v  have been formed in a concave shape, the present invention is not limited thereto. The first avoiding portion  161   u  and the second avoiding portion  161   v  may be configured as stepped portions adjacent to the first contact surface  161   s  and the second contact surface  161   t.    
         [0088]    Further, the shape of the concave portion  157   d  is not limited to those illustrated. For example, the concave portion may have any one of a shape where the connecting surface  157   w  is a planar surface, or a shape where the connecting surface is a curved surface, or a valley shape where the connecting surface is omitted and the first stopper surface  157   s  and the second stopper surface  157   t  are adjacent to each other. Further, the shape of the convex portion  161   a  is not limited to those illustrated. The convex portion may have a shape where the top surface  161   w , which is located at a leading end than the first contact surface  161   s  and the second contact surface  161   t , is a planar surface, a curved surface, or a polygonal surface. 
         [0089]    In the above-described embodiment, an example has been described in which the curvature of the first stopper surface  157   s  and the curvature of the second stopper surface  157   t  are equal, the curvature of the first contact surface  161   s  and the curvature of the second contact surface  161   t  are equal, and the curvatures of the first stopper surface  157   s  and the second stopper surface  157   t  are greater than those of the first contact surface  161   s  and the second contact surfaced  161   t . However, the present invention is not limited thereto. 
         [0090]    For example, the curvature of the first stopper surface  157   s , the curvature of the second stopper surface  157   t , the curvature of the first contact surface  161   s  and the curvature of the second contact surface  161   t  may be set in descending order. Alternatively, the curvature of the first stopper surface  157   s , the curvature of the first contact surface  161   s , the curvature of the second stopper surface  157   t , and the curvature of the second contact surface  161   t  may be set in descending order. 
         [0091]    In the above-described embodiment, an example has been described in which the hook  157  and the pawl  161  are disposed on the front surface of the base  151  and the bushings  145  and  147  are inserted through the base  151  from the back surface. However, the present invention is not limited thereto. The hook  157  and the pawl  161  may be disposed on the front surface of the base  151  and the bushings  145  and  147  may be inserted through the base  151  via the hook  157  and the pawl  161  from the front surface. 
         [0092]    The present application is based upon Japanese Patent Application (Patent Application No. 2013-030639) filed on Feb. 20, 2013, the contents of which are incorporated herein by reference. 
       REFERENCE NUMERALS LIST 
       [0000]    
       
           151  Base 
           157  Hook 
           157   d  Concave Portion 
           157   s  First Stopper Surface 
           157   t  Second Stopper Surface 
           161  Pawl 
           161   a  Convex Portion 
           161   s  First Contact Surface 
           161   t  Second Contact Surface 
           161   u  First Avoiding Portion 
           161   v  Second Avoiding Portion 
           171 ,  173  Spring