Patent Publication Number: US-8978214-B2

Title: Seatbelt buckle apparatus

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a seat belt buckle device that secures a tongue plate provided at a seat belt in a vehicle. 
     2. Related Technology 
     A seat belt is a safety device for preventing an occupant from bumping against the inner wall of a vehicle and injuring himself in the event of an accident or the like by restraining the occupant&#39;s body in the vehicle seat. A seat belt (webbing) is accommodated by winding on a seat belt retractor (retractor) in the center of a B pillar. The webbing unwound upward from the retractor is supported by a seat belt anchorage (anchorage) in the upper portion of the B pillar and folded back to the interior of the vehicle. A tongue plate is attached to the webbing pulled out from the anchorage. When the tongue plate is inserted into the seat belt buckle (buckle), the webbing applied to the chest and stomach of the occupant restraints the occupant&#39;s body. 
     When the tongue plate is inserted into the buckle, the latch hole of the inserted tongue plate is latched inside the buckle by a latch member provided inside the buckle, thereby securing the tongue plate. 
     Meanwhile, the seat belt can be taken off by the occupant of the vehicle by pushing the release button of the buckle. The pushed release button slides toward the interior of the buckle. As a result, the latch member (or a lock bar that pushes the latch member toward the tongue plate) rises from the tongue plate, the latching of the latch hole is released, and the tongue plate is discharged. Such a configuration of the buckle makes it possible to latch and unlatch the tongue plate easily. 
     Where a vehicle is subjected to an impact caused by an accident or the like when the seat belt is worn, the webbing is initially locked against pulling out of the retractor. Since the webbing is instantaneously picked up by a pre-tensioner provided in the retractor or the like, the seat belt tightly holds the occupant&#39;s body. Where the webbing is picked up by the pre-tensioner or the webbing then receives and stops the load from the occupant, the buckle is pulled to the tongue side. Alternatively, the buckle is pulled in the direction opposite that of the tongue by the action of the buckle pre-tensioner. 
     When the buckle moves in the direction of pulling from the initial position (tongue direction or the direction opposite thereto), the release button, which can slide inside the buckle, attempts to become stationary in the initial position under the inertia. Further, after the buckle movement has been stopped, the release button attempts to slide under the inertia in the movement direction of the buckle. Under such inertia action, the release button slides into the buckle and the secured tongue plate can be released during an accident. Accordingly, a counterweight acting as a weight with respect to the release button has been provided inside the buckle so as to prevent the release button from sliding under the inertia. 
     For example, the buckle disclosed in Japanese Patent Application Publication No. 2005-144138 is provided with a latch member, that latches (fixes) the tongue, and a release button, for releasing the latching of the tongue by the latch member, as the elements for fixing and releasing the tongue. Such a buckle is further provided with an inertia lever (counterweight) that is rotatably provided on a rotating shaft and abuts on the release button, thereby preventing the movement of the release button in the release direction thereof (direction in which the abovementioned latch is released). According to Japanese Patent Application Publication No. 2005-144138, the counterweight reliably maintains the latching of the buckle and the tongue even against the inertia force both in the release direction and non-release direction of the release button. 
     However, in order to dispose the rotatable counterweight, such as described in Japanese Patent Application Publication No. 2005-144138, in a buckle, it is necessary to provide the space allowing the counterweight to rotate in the buckle. This contradicts a recent trend toward miniaturization of the buckle that is aimed at improving the appearance and securing a free space inside the vehicle cabin. In particular, as the counterweight is increased in length, the jumping height thereof during rotation increases and a wider space is necessary for the rotation thereof. Thus, although the counterweight is necessary to prevent the unexpected release of the tongue plate in the event of collision, the presence of the counterweight limits the miniaturization of the buckle. 
     SUMMARY 
     It is an object of the present invention to resolve the above-described problem and to provide a seat belt buckle device in which the jumping height of the counterweight can be restricted and miniaturization can be advanced. 
     In order to resolve the above-described problems, the representative configuration of the seat belt device in accordance with the present invention is a seat belt buckle device that secures or fixes a tongue plate provided at a seat belt, including an outer case into which the tongue plate is inserted; a latch member that rotates in response to the insertion of the tongue plate into the outer case and latches the tongue plate; a release button that releases the latching of the tongue plate by the latch member by sliding into the outer case; and a counterweight that is rotated by a force received from the release button and resists to the sliding of the release button, wherein the counterweight has: a first rotating shaft that causes the counterweight to rotate with respect to the outer case; and a second rotating shaft that is engaged with a bearing groove formed in the release button and receives the force that rotates the counterweight due to the sliding of the release button, and the second rotating shaft has a portion, a part of an outer circumferential surface of which is missing, with this portion being configured to come into contact with the bearing groove of the release button when the release button slides into the outer case. 
     Where the abovementioned configuration is compared with that in which the second rotating shaft has a round cross section, although the distance through which the release button is caused to slide when the seat belt is taken off is the same in both configurations, the rotation amount of the first rotating shaft can be reduced. Thus, the jumping height of the counterweight when the latching of the tongue plate is released can be reduced. As a result, the outer case can be reduced in thickness and a smaller outer case can be designed. 
     The second rotating shaft of the counterweight may come into contact with the bearing groove of the release button by an outer circumferential surface except the portion, a part of an outer circumferential surface of which is missing when the seat belt buckle device fixes the tongue plate, and come into contact with the bearing groove of the release button by the portion, a part of an outer circumferential surface of which is missing when a sliding distance of the release button into the outer case is the largest. 
     The abovementioned counterweight is a member that functions as a weight that rotates and offers resistance to the sliding of the release button. In a state in which the seat belt buckle device fixes the tongue plate, that is, when the counterweight functions as a weight, the portion of the second rotating shaft in which part of an outer circumferential surface is missing is not in contact with the release button. With such a configuration, the portion of the second rotating shaft in which part of an outer circumferential surface is missing does not affect the counterweight functions and can reduce the aforementioned jumping height. 
     The seat belt buckle device may further include a lock bar that receives a force from the tongue plate, rotates the latch member toward the tongue plate and latches the latch member, wherein the counterweight has a latching portion that latches the lock bar at a position in which the latch member is latched onto the tongue plate. 
     With such a configuration, by using the counterweight that rotates relative to the outer case it is possible to aid the latching of the tongue plate with the latch member. As a result, the latched state of the tongue plate in the seat belt buckle device can be maintained more reliably. 
     The counterweight may be made from a metal and may have an inertia mass larger than that of the release button. With such a configuration, the counterweight can reliably prevent the release button from sliding into the buckle under inertia. 
     In accordance with the present invention, it is possible to provide a seat belt buckle device in which the jumping height of the counterweight can be restricted and miniaturization can be advanced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the internal configuration of the seat belt buckle device according to the present embodiment. 
         FIG. 2  is an exploded view of the seat belt buckle device shown in  FIG. 1 . 
         FIGS. 3(   a ) and  3 ( c ) are perspective views of the counterweight from opposite sides thereof and  FIG. 3(   b ) is a side view of the shaft of the counterweight. 
         FIGS. 4(   a )- 4 ( d ) are sectional views taken along the A-A line in  FIG. 1 ; these views illustrating the operation of the seat belt buckle device from the initial state to the latched state. 
         FIGS. 5(   a )- 5 ( d ) are sectional views of the release operation of the seat belt buckle device from the latched state. 
         FIG. 6  illustrates the comparison of the seat belt buckle device according to the present embodiment and a seat belt buckle device of a comparative example. 
         FIG. 7  illustrates the state of contact of the counterweight and the release button in the latched state. 
     
    
    
     DETAILED DESCRIPTION 
     The preferred embodiments of the present invention will be described below in greater detail with reference to the appended drawings. The dimensions, materials, and other specific numerical values are exemplified to facilitate the understanding of the invention and are not intended to limit the present invention, unless specifically indicated otherwise. Meanwhile in the description of the invention and drawings, the elements having substantially the same function and structure are denoted by the same reference numerals and the redundant explanation thereof will be omitted. In addition, the elements that are not directly related to the invention will not be shown. 
     (Seat Belt Buckle Device) 
       FIG. 1  illustrates the internal configuration of the seat belt buckle device according to the present embodiment.  FIG. 2  is an exploded view of the seat belt buckle device shown in  FIG. 1 . The seat belt buckle device (referred to hereinbelow as “buckle  100 ”) is a device that fixes a tongue plate  102  provided at the seat belt. The buckle  100  is disposed inside the vehicle cabin so as to be positioned close to the hips of the occupant seating on a seat. 
     An outer case  110  of the buckle  100  is provided with an opening  112  for inserting the tongue plate  102  and disposing a release button  180 . A tongue insertion port  114  (see  FIG. 1 ) is formed at the portion of the opening  112  outside the portion where the release button  180  is disposed. The tongue plate  102  can be fixed (latched) to the buckle  100  by inserting the tongue plate into the tongue insertion port  114 , and the latching of the tongue plate  102  can be released by pushing the release button  180 . A lower case  116  is fixed by a screw  118  to the lower side of the outer case  110 . 
     A metal frame  120  is provided inside the buckle. As shown in  FIG. 2 , the frame  120  has a square U-shaped cross-section and is provided with a pair of side walls  122  and a bottom wall  124  provided between the side walls  122 . The upper surface of the bottom wall  124  constitutes the insertion path for the tongue plate  102  inside the buckle. 
     A latch member  140  is provided in the upper portion inside the square U-shaped frame  120 . The latch member  140  rotates following the movement of the tongue plate  102  inserted into the outer case  110  and latches onto the tongue plate  102 . The latch member  140  is made from a metal and has a latch protrusion  142  that protrudes in the direction to the bottom wall (direction Z 2  in the figure) of the frame  120  at the end portion on the tongue insertion port  114  side (Y 2  side in the figure). Where the tongue plate  102  is inserted into the outer case  110 , the latch protrusion  142  is inserted into a latch hole  104  provided in the tongue plate  102  and then inserted into an orifice  126  provided in the bottom wall  124  of the frame  120 . 
     The latch member  140  has a support arm  144  that projects toward both side walls  122  (direction X 1  in the figure and the direction X 2  in the figure) of the frame  120  at the end portion on the side (Y 1  side in the figure) opposite that of the latch protrusion  142 . The support arm  144  engages with a support hole  128  provided at the side wall  122  of the frame  120 . As a result, the latch member  140  can rotate toward the bottom wall  124  (direction Z 2  in the figure) of the frame  120  and in the opposite direction (direction Z 1  in the figure) about the support arm  144 . 
     An opening  146  is provided in the center of the latch member  140 . A spring latching projecting portion  148  that projects in the direction to the latch protrusion  142  (direction Y 2  in the figure) is provided at the edge of the opening  146  on the support arm  144  side thereof (Y 1  side in the figure). An ejector spring  170  that is disposed between the latch member  140  and a cantilever  160  is connected to the spring latching projecting portion  148 . 
     An ejector  150  is provided between the latch member  140  and the bottom wall  124  of the frame  120 . The ejector  150  is configured to be capable of sliding in the attachment-detachment direction of the tongue plate  102  on the bottom wall of the frame  120 . Where the tongue plate  102  is inserted into the outer case  110 , the ejector  150  is brought into contact with the end portion of the tongue plate  102  and pushed there against and slides from the tongue insertion port  114  side toward the rear side (Y 1  side in the figure) inside the outer case  110 . Further, where the latching of the tongue plate  102  by the latch member  140  is released, the ejector  150  is biased by the ejector spring  170  and slides from the rear side inside the outer case  110  toward the tongue insertion port  114 . As the ejector  150  slides in this case, the tongue plate  102  is pushed out of the outer case  110 . 
     The ejector  150  is provided with a base portion  152  of a substantially U-like shape and arm portions  154  extending from both ends of the base portion  152  toward the side wall of the frame  120  (the X 1  direction in the figure and the X 2  direction in the figure). The arm portions  154  are inserted into slits  130  formed between the side wall  122  and the bottom wall  124  of the frame  120 . Since the arm portions  154  can move inside the slits, the ejector  150  has a configuration that can slide in the attachment-detachment direction of the tongue plate  102  on the bottom wall of the frame  120 . The base portion  152  is provided with a pushed portion  156  that is the surface on the tongue insertion port side and comes into contact with the end portion of the tongue plate  102  and a holding hole  158  that comes into contact with the cantilever  160  on the inner side of the substantially U-like shape. 
     The cantilever  160  is a member that uses the repulsion force of the ejector spring  170  to push the latch member  140  by a lock bar  172  toward the tongue plate  102 . The cantilever  160  has a shaft  162  that engages with the holding hole  158  of the ejector  150  and is configured to be rotatable about the shaft  162 . A bar latching portion  164  formed as a curved surface is provided at the distal end of the cantilever  160 . The bar latching portion  164  passes through the opening  146  and is positioned above the latch member  140  to latch onto the lock bar  172  that is also positioned above the latch member  140 . A spring holding protruding portion  166  for connecting to the ejector spring  170  is provided on the surface of the cantilever  160  on the side opposite that of the bar latching portion  164  (rear surface in  FIG. 2 ). 
     The ejector spring  170  is disposed between the spring latching projecting portion  148  of the latch member  140  and the spring holding protruding portion  166  of the cantilever  160 . Since the ejector spring  170  is disposed in a compressed state, repulsion forces acting in the direction of pulling the latch member  140  and the cantilever  160  apart from each other act at all times. 
     The lock bar  172  is a member pushing the latch member  140  from above toward the tongue plate  102 . The lock bar  172  has a length equal to or greater than a width of the latch member  140 . The lock bar  172  is disposed to span between the guide holes  132  that are formed in a substantially L-like shape in both side walls  122  of the frame  120 . As described hereinabove, the bar latching portion  164  of the cantilever  160  latches onto the lock bar  172 , and the lock bar can move inside the guide hole  132  as the cantilever  160  rotates. 
     The release button  180  is provided in the opening  112  side (Y 2  side in the figure) of the frame  120  so as to cover both side walls  122  and the upper portions thereof. The release button  180  can freely slide in the attachment-detachment direction of the tongue plate  102  on the frame. The release button  180  has an operation section  182  to be exposed outside from the opening  112  and legs  184  extending into the buckle  100  from both ends of the operation section  182 . The distal ends of the legs  184  are connected by an arch-like portion. 
     The legs  184  of the release button  180  slide on the outer sides of the side walls  122  of the frame  120 . An operation recess  186  is provided on the inner side (side wall side of the frame  120 ) of each leg  184 . The end portion of the lock bar  172  protruding from the guide hole  132  of the frame  120  is inserted into the operation recess  186 . Where the release button  180  slides in the direction into the buckle  100 , the lock bar  172  is pushed in the direction into the buckle  100  (Y 1  side in the figure) by the surface of the operation recess  186  on the opening  112  side, comes into contact with the curved edge of the guide hole  132 , and moves upward along this edge. As a result, the pressure acting from the latch member  140  on the tongue plate  102  under the effect of the lock bar  172  is released and latching of the tongue plate  102  is released. 
     A guiding projecting portion  188  is provided on the inner side of each leg  184  on the surface facing the side wall  122  of the frame  120 . The guiding projecting portion  188  protrudes along the side wall  122  of the frame  120  and extends toward the distal ends of the operation section  182  and the leg  184 . The guiding projecting portion  188  is inserted in a long groove  134  formed in the side wall  122  of the frame  120 . When the release button  180  slides, the guiding projecting portion  188  is guided by the long groove  134 . Therefore, the release button  180  can slide parallel to the side wall  122  and the bottom wall  124  of the frame  120 . 
     A lower end portion  190  protruding in the direction into the buckle  100  is provided at the bottom wall side of the frame  120  in the operation section  182 . A bearing groove  192  extending toward the arms on both sides is formed in the lower end portion  190 . A second rotating shaft  204  of a counterweight  200  is engaged with the bearing groove  192 . An auxiliary groove  194  for receiving a thick portion  206  located in the vicinity of the second rotating shaft of the rotating counterweight  200  is provided in the bearing groove  192  on the operation section  182  side. 
       FIG. 3  illustrates the external appearance of the counterweight  200 . The counterweight  200  is a member playing the role of a weight acting against the release button  180 . As shown in  FIG. 3(   a ), the counterweight  200  has a first rotating shaft  202  and the second rotating shaft  204  and can rotate inside the outer case, following the sliding movement of the release button  180 . 
     The first rotating shaft  202  is inserted into the concave groove  136  provided in the side wall  122  of the frame  120  shown in  FIG. 2  and enables the rotation of the counterweight  200  with respect to the frame  120  and the outer case  110 . The second rotating shaft  204  is engaged with the bearing groove  192  provided in the lower end portion  190  of the release button  180 . The second rotating shaft  204  receives the force from the sliding release button  180 , rotates the counterweight  200  with respect to the release button  180 , and also rotates the counterweight  200  with respect to the outer case  110  about the first rotating shaft  202 . 
     Referring again to  FIG. 2 , in the event of an accident or the like, an inertia force acting in the direction into the buckle  100  (Y 1  direction in the figure) can be generated in the release button  180  connected to the second rotating shaft  204 . However, a comparatively weak force such as the inertia force of the release button  180  is canceled by the inertia force of the counterweight  200  that is received from the second rotating shaft  204 . Since the center of gravity of the counterweight  200  tries to rotate under the inertia in the direction into the buckle  100  (Y 1  direction in the figure) about the first rotating shaft  202 , an inertia force in the direction (Y 2  direction in the figure) opposite that of the rotation direction of the center of gravity is generated in the second rotating shaft  204 . Since the counterweight  200  thus offers the resistance to the sliding movement of the release button  180  inward the buckle  100 , the release button  180  cannot slide in the direction into the buckle  100  under the inertia. Therefore, the counterweight  200  prevents the tongue plate  102  from being unintentionally unlatched. 
     The weight of the counterweight  200  is set such that the center of gravity does not rotate counterclockwise about the first rotating shaft  202  even under inertia. Therefore, the counterweight  200  cannot rotate under the inertia and cause the release button  180  to slide toward the lock bar  172 . 
     The counterweight  200  is made from a metal and configured to have an inertia mass larger than that of the release button  180 . Therefore, the counterweight  200  can reliably prevent the release button  180  from sliding into the buckle  100  under inertia. 
     The second rotating shaft  204  has a portion (a flat surface in the present embodiment) in which part of the outer peripheral surface is missing at a position that is in contact with the bearing groove  192  of the release button  180  preferably in a state in which the sliding distance of the release button into the outer case is the largest.  FIG. 3(   b ) is a side enlarged view of the second rotating shaft  204 . The second rotating shaft  204  illustrated by  FIG. 3(   b ) is shown in a posture such that the latching portions  212  of the counterweight  200  are positioned to face to the right and the second rotating shaft  204  is positioned vertically below the first rotating shaft  202 . As shown in  FIG. 3(   b ), the second rotating shaft  204  is provided with a first cut-out portion  208  and a second cut-out portion  210  as the portions in which part of the outer peripheral surface is missing. The first cut-out portion  208  is provided over almost the entire width of the second rotating shaft at a position on the left side and upper side of the second rotating shaft  204  in the posture shown in  FIG. 3(   b ). The second cut-out portion  210  is provided at the lower side of the second rotating shaft  204  in the posture shown in  FIG. 3(   b ). 
     As shown in  FIG. 3(   b ), the distances D 1 , D 3  between the points on the cut-out portions  208 ,  210  and the center of the second rotating shaft  204  are less than the respective distances D 2 , D 4  between the points on the outer circumference in the case of a virtual circle representing the second rotating shaft  204  that has no missing portions and the center of the second rotating shaft. Further, in the present embodiment, the cut-out portions  208 ,  210  are provided as flat surfaces (portions in which parts of the outer circumferential surface of the second rotating shaft  204  are missing), but such a shape is not limiting. The cut-out portions  208 ,  210  may also be curved surfaces, rather than flat surfaces, provided that they are pulled back from the outer circumferential surface of the second rotating shaft  204  toward the center of the circle. 
     As shown in  FIG. 3(   c ), the latching portions  212  that latch onto the lock bar  172  are provided at the distal end of the counterweight  200  on the inner side of the buckle  100 . The latching portions  212  latch onto the lock bar  172  at a position in a state in which the tongue plate  102  has latched onto the latch member  140 . Therefore, it is possible to use the counterweight  200  that can rotate with respect to the outer case  110  and aid the latching of the tongue plate  102  with the latch member  140 . As a result, the latched state of the tongue plate  102  in a seat belt buckle device can be maintained more reliably. 
     (Operation of Seat Belt Buckle Device) 
       FIGS. 4(   a )- 4 ( d ) are sectional views taken along the A-A line in  FIG. 1  and illustrate the operation of the seat belt buckle device from the initial state to the latched state. The A-A section in  FIG. 1  is the section in the Y 1 /Y 2  direction in the figure and the Z 1 /Z 2  direction in the figure. In  FIGS. 4(   a )- 4 ( d ), the elements that are irrelevant to the operation of the seat belt buckle device are omitted. The initial state, as referred to herein, is an unlatched state in which the seat belt is not worn and the tongue plate  102  is not latched onto the buckle  100 . The latched state, as referred to herein, is a state in which the occupant wears the seat belt and the tongue plate  102  is latched onto the buckle  100 . In the explanation below, the tongue insertion port side and opening  112  side are at the left side in the figure, and the buckle inner side is at the right side in the figure. 
       FIG. 4(   a ) illustrates the initial state of the buckle  100 . As shown in  FIG. 4(   a ), in the initial state, the ejector  150  is caused to slide toward the tongue insertion port side by the repulsion force of the ejector spring  170 . The cantilever  160  is in a state in which it is tilted clockwise about a shaft portion  162 . The cantilever  160  also pushes the lock bar  172  toward the opening  112 . Since the lock bar  172  is positioned in the upper portion of the guide hole  132  and pushed by the cantilever  160 , the lock bar comes into contact with a substantially vertical edge, as shown in  FIG. 4(   a ), which is the opening  112  side of the guide hole  132 . 
     Since the cantilever  160  is in the state in which it is tilted clockwise, the vertical position of the spring holding protruding portion  166  is closer than the vertical position of the spring latching projecting portion  148  of the latch member  140  to the bottom wall side of the frame  120 . Therefore, the ejector spring  170  is curved in a S-like shape. In this case, in the ejector spring  170 , the end surface S 1  on the spring holding protruding portion side and the end surface S 2  on the spring latching projecting portion side are not parallel to each other, and the end surface S 1  transmits a repulsion force from obliquely below the spring holding protruding portion side of the cantilever  160  as shown in  FIG. 4(   a ). 
     The latch member  140  is biased by the repulsion force of the ejector spring  170  in the clockwise direction about the support arm  144  (see  FIG. 2 ). As a result, the latch protrusion  142  of the latch member  140  separates from the bottom surface  124  of the frame  120  and an insertion path for the tongue plate  102  is ensured between the bottom wall  124  and the latch protrusion  142 . 
       FIG. 4(   b ) shows a state in which the tongue plate  102  is inserted into the buckle. The end portion of the tongue plate  102  comes into contact with the pushed portion  156  of the ejector  150 , and the ejector  150  is caused to slide in the insertion direction of the tongue plate  102 . In this case, the shaft portion  162  of the cantilever  160  slides together with the ejector  150  against the repulsion force of the ejector spring  170 . Meanwhile, the bar latching portion  164  of the cantilever  160  pushes the lock bar  172  by the repulsion force of the ejector spring  170 . Therefore, the cantilever  160  rotates counterclockwise about the lock bar  172  from the state shown in  FIG. 4(   a ) to the state shown in  FIG. 4(   b ). 
     In the state shown in  FIG. 4(   b ), the cantilever  160  rotates counterclockwise and therefore the vertical position of the spring holding protruding portion  166  gets close to the vertical position of the spring latching projecting portion  148  of the latch member  140 . In the state shown in  FIG. 4(   b ), the end surface S 1  is tilted counterclockwise from the state shown in  FIG. 4(   a ), and the end surface S 1  and the end surface S 2  are closer to being parallel to each other than in the state shown in  FIG. 4(   a ). Therefore, in the state shown in  FIG. 4(   b ), the S-like curved shape of the ejector spring  170  is released. 
       FIG. 4(   c ) shows a state in which the tongue plate  102  is further inserted into the buckle from the state shown in  FIG. 4(   b ). In this state, the ejector  150  further slides into the buckle  100 , and the cantilever  160  further rotates counterclockwise about the shaft portion  162 . In this case, the ejector spring  170  is curved to protrude upward. Therefore, the end surface S 1  of the ejector spring  170  transmits a repulsion force from obliquely above the spring holding protruding portion  166  side of the cantilever  160  to the cantilever  160 . 
     The bar latching portion  164  of the cantilever  160  pushes the lock bar  172  down along the substantially vertical edge of the guide hole  132  toward the corner of the guide hole  132 . The lock bar  172  that has been pushed down pushes the latch member  140  located therebelow, and the latch member  140  rotates about the support arm  144  (see  FIG. 2 ) toward the tongue plate  102 . As a result, the latch protrusion  142  is inserted into the latch hole  104  of the tongue plate  102  and then inserted into the orifice  126  of the bottom wall  124  of the frame  120 , and the tongue plate  102  is latched onto the buckle  100 . 
       FIG. 4(   d ) shows a state in which the release button  180  slightly slides in the direction of the opening from the state shown in  FIG. 4(   c ). In the state shown in  FIG. 4(   c ), the lock bar  172  that has been pushed down by the cantilever  160  and went over the corner of the guide hole  132  can move in the direction of the opening inside the guide hole  132 . The surface of the operation recess  186  of the release button  180  on the opening side is pushed in the direction of the opening by the lock bar  172  that has received the repulsion force of the ejector spring  170 . Therefore, the release button  180  slightly slides in the direction of the opening, and the counterweight  200  rotates clockwise about the first rotating shaft  202 . Because of such rotation, the latching portion  212  of the counterweight  200  comes into contact with the upper side of the lock bar  172  and latches there onto. In a state in which the latch member is latched onto the tongue plate, the lock bar can move horizontally (as shown in the figure) inside the guide hole  132 , but this movement is prevented by the latching portion of the counterweight. As a result, the latching of the tongue plate  102  is completed and the buckle  100  assumes the latched state. 
       FIGS. 5(   a )- 5 ( d ) illustrate the release operation performed from the latched state of the seat belt buckle device.  FIG. 5(   a ) illustrates a state in which the release button  180  is pushed from the latched state shown in  FIG. 4(   d ). Where the release button  180  is pushed by an occupant and the release button  180  slides in the direction into the buckle  100 , the counterweight  200  initially rotates counterclockwise about the first rotating shaft  202  and the latching of the lock bar  172  by the latching portion  212  is released. Then, the lock bar  172  is pushed by the surface of the operation recess  186  on the opening side in the direction into the buckle  100  and moves there into. In this case, since the lock bar  172  is pushed, the cantilever  160  and the ejector  150  also move in the direction into the buckle  100 . As a result, the ejector spring  170  is compressed. 
     Where the release button  180  is further pushed from the state shown in  FIG. 5(   a ), the lock bar  172  comes into contact with the curved edge of the guide hole  132  as shown in  FIG. 5(   b ). Further, as shown in  FIG. 5(   c ), the lock bar  172  rises along the curved edge of the guide hole  132 , while being pushed by the surface of the operation recess  186  on the opening side. 
     As shown in  FIG. 5(   c ), in a state in which the release button  180  has slid into the interior of the buckle  100 , the cantilever  160  rotates clockwise about the shaft portion  162  and assumes a tilted state. In this case, the vertical position of the spring holding protruding portion  166  is closer to the bottom wall side of the frame  120  than the vertical position of the spring latching projecting portion  148  of the latch member  140 . Therefore, the ejector spring  170  assumes an S-like curved shape. In this case, the end surface S 2  of the ejector spring  170  causes the latch member  140  to rotate in the clockwise direction about the support arm  144  (see  FIG. 2)  via the spring latching projecting portion  148 . As a result, the latch protrusion  142  of the latch member  140  rises from the latch hole  104  of the tongue plate  102 , and the latching of the tongue plate  102  is released. 
     The end surface S 1  of the ejector spring  170  pushes the cantilever  160  in the direction to the opening. Therefore, where the latching of the tongue plate  102  is released, the cantilever  160  and the ejector spring  170  slide with force in the direction to the opening under the effect of the ejector spring  170 , as shown in  FIG. 5(   d ). As a result, the tongue plate  102  is pushed out from the tongue insertion port  114 . Where the occupant removes the hand from the release button  180 , the surface of the operation recess  186  on the opening side is pushed toward the opening by the lock bar  172  that has received the repulsion force of the ejector spring  170 , the release button  180  slides toward the opening, and the buckle  100  returns to the initial state shown in  FIG. 4(   a ). 
     In  FIG. 6 , the seat belt buckle device according to the present embodiment is compared with a seat belt buckle device of a comparative example. As shown in  FIG. 6 , the buckle  100  according to the present embodiment is provided with the counterweight  200  having the first cut-out portion  208  at the second rotating shaft  204 . Meanwhile a second rotating shaft  14  of a counterweight  10  of the comparative example has a round cross section. 
     Both in the embodiment and the comparative example, the state shown in  FIG. 6  is assumed where the release button  180  is caused to slide completely into the buckle  100  when the latching of the tongue plate  102  is released. In this state, the second rotating shaft  204  of the present embodiment is brought into contact with a substantially vertical flat plate of the bearing groove  192  of the release button  180  by the first cut-out portion  208 . Comparing with the second rotating shaft  14  of the comparative example, although the sliding distance of the release button  180  is the same as in the comparative example, the distance of rightward movement ( FIG. 6 ) of the second rotating shaft  204  of the present embodiment is shorter due to the presence of the first cut-out portion  208 . Therefore, the rotation amount of the counterweight  200  of the present embodiment about the first rotating shaft  202  is reduced with respect to the rotation amount of the counterweight  10  of the comparative example about the first rotating shaft  12 . Therefore, in the present embodiment, the jumping height of the counterweight  200  is lower by the height h than the jumping height of the counterweight  10 . 
     Since the counterweight  200  is also provided with the second cut-out portion  210 , in the case where the first rotating shaft  202  and the second rotating shaft  204  are positioned substantially vertically, the distance between the center of the second rotating shaft  204  and a point on the second cut-out portion  210  located substantially vertically therebelow (distance D 3  in  FIG. 3 ) is shorter than the distance between the center of the second rotating shaft  14  and a point on the circumference located substantially vertically therebelow (distance D 4  in  FIG. 3 ). Since the second cut-out portion  210  is present, a gap is provided between the second rotating shaft and the bearing groove  192  and the interference with the bearing groove  192  is reduced. As a result, the release button  180  can be caused to slide smoothly. 
     With the above-described configuration, in the buckle  100  according to the present embodiment, the space for allowing the counterweight  200  to rotate can have a small width, the thickness of the outer case  110  (thickness in the Z 1  direction and Z 2  direction in  FIG. 1 ) can be reduced, and the buckle of reduced size can be designed. 
       FIG. 7  illustrates the contact of the counterweight  200  and the release button  180  in the latched state.  FIG. 7  is an enlarged view of the counterweight  200  in the buckle  100  in the latched state shown in  FIG. 4(   d ). 
     In the buckle  100  in the latched state, the counterweight  200  functions as a weight that rotates and offers resistance to the sliding of the release button  180 . In the latched state, the second rotating shaft  204  of the counterweight  200  is in contact with the bearing groove  192  of the release button  180  by the outer circumferential surface outside of the portions in which part of the outer circumferential surface is missing (cut-out portions  208 ,  210 ). For example, the second rotating shaft  204  shown in  FIG. 7  can be in contact with the bearing groove  192  at contact points P 1 , P 2  that are shown schematically in the figure. 
     The contact point P 1  is in contact with the bearing groove  192  when the release button  180  slides in the Y 1  direction shown in the figure (in the direction into the buckle  100 ). The release button  180  slides in this direction, for example, when an acceleration is applied to the buckle  100  in the Y 1  direction shown in the figure under the inertia occurring in the event of an accident or the like. In this case, the release button  180  is prevented from sliding in the Y 1  direction in the figure by the resistance offered by the second rotating shaft  204  to which a load is applied in the direction of clockwise rotation about the first rotating shaft  202  by the abovementioned acceleration in the Y 1  direction shown in the figure. Therefore, the latching of the tongue plate  102  is maintained. 
     The contact point P 2  is in contact with the bearing groove  192  when the release button  180  slides in the Y 2  direction shown in the figure (direction toward the tongue insertion port  114 ) or when the counterweight  200  rotates in the counterclockwise direction as shown in  FIG. 7 . The sliding of the release button  180  and the rotation of the counterweight  200  in those directions occur, for example, when an acceleration in the Y 2  direction shown in the figure is applied to the buckle  100  under the inertia. The weight and center of gravity of the counterweight  200  are designed such that the counterweight does not rotate in the counterclockwise direction and does not cause the release button  180  to slide in the Y 1  direction shown in the figure. In other words, the counterclockwise rotation of the counterweight  200  is prevented by the resistance offered by the release button  180  sliding in the Y 2  direction shown in the figure. Therefore, the latching of the tongue plate  102  is maintained. 
     In the latched state of the buckle  100 , that is, when the counterweight  200  functions as a weight, the portions (in particular, the first cut-out portion  208 ) of the second rotating shaft  204  in which part of the outer circumferential surface is missing are not in contact with the release button  180 . In other words, the first cut-out portion  208  is formed such that it is not in contact with the bearing groove  192  in the latched state of the buckle  100 . As described hereinabove, in the latched state, the second rotating shaft  204  is in contact with the bearing groove  192  by the outer circumferential surface outside the portion in which part of the outer circumferential surface is missing (portion outside the first cut-out portion  208 ). Even if the posture of the counterweight  200  is somewhat disturbed, the first cut-out portion  208  does not come into contact with the bearing groove  192  in the latched state. Therefore, although the second rotating shaft  204  is provided with the first cut-out portion  208 , no adverse effect is produced on the aforementioned functions of the counterweight  200 . 
     As explained hereinabove with reference to  FIG. 6(   a ), the first cut-out portion  208  of the second rotating shaft  204  comes into contact with the bearing groove  192  when the sliding distance of the release button  180  into the outer case  110  is the largest. With such a configuration, the portion of the second rotating shaft  204  in which part of the outer circumferential surface is missing produces no adverse effect on the aforementioned functions of the counterweight  200  and the jumping height of the counterweight can be reduced. 
     The preferred embodiments of the present invention are described hereinabove with reference to the appended drawings, but the above embodiments are merely preferred examples of the present invention, and other embodiments may be also implemented or executed using various methods. In particular, the present invention is not limited to the shapes, dimensions, and arrangement of the components illustrated in detail in the appended drawings, unless specific limiting description to the contrary is provided in the specification of the present application. Further, expressions and terms used in the specification of the present application are employed for descriptive purposes only, and the present invention is not limited to these expressions and terms unless specifically stated otherwise. 
     Therefore, it is clear that a person skilled in the art could conceive of various variation examples or modification examples without departing from the scope defined by the claims, and those variation examples and modification examples are also construed to be included in the technical scope of the present invention.