Energy absorbing device, seat belt retractor and seat belt apparatus

To provide an energy absorbing device, a seat belt retractor, and a seat belt apparatus that can vary an energy absorbing amount depending on increase and decrease of rotation speed between relatively rotating objects and can improve durability. An energy absorbing device includes a casing connected to one object, an annular first clutch disc disposed in the casing, an annular second clutch disc disposed in the casing, and an annular clutch plate connected to the other object and having an engaging surface that faces both the first clutch disc and the second clutch disc, wherein the engaging outer teeth of the first clutch disc and the engaging inner teeth of the second clutch disc alternately engage with the engaging teeth of the clutch plate so as to absorb an energy generated by a relative rotation between one object and the other object.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage application of International Patent Application No. PCT/JP2015/054955, filed Feb. 23, 2015, which claims the benefit of priority to Japanese Patent Application No. 2014-049435, filed Mar. 12, 2014, the entireties of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an energy absorbing device, a seat belt retractor and a seat belt apparatus, and specifically, an energy absorbing device disposed between relatively rotating objects, a seat belt retractor having the energy absorbing device, and a seat belt apparatus having the seat belt retractor.

BACKGROUND ART

For example, in a retractor (including a rewinding function) for a long object such as a strip or a string, a winding drum (also called a drum or a spool) that retracts a long object rotates relative to a support unit that rotatably supports the winding drum. It is preferable to dispose an energy absorbing device between relatively moving objects since a large load is applied to the apparatus and the long object when the long object is fully extended or when the winding drum stops during retracting or rewinding of the long object in the apparatus which performs a relative movement. Typically, an example of such a retractor is a seat belt retractor used in a seat belt apparatus (for example, see Patent Literature 1 or 2).

Patent Literature 1 discloses a seat belt retractor in which a torsion bar and a wire are disposed between a winding drum and a ratchet gear which relatively rotate. This seat belt retractor can absorb an energy generated between the winding drum and the ratchet gear due to twisting deformation of the torsion bar and sliding deformation of the wire, and can change the energy absorbing properties by varying a withdrawing load necessary for sliding deformation of the wire.

Patent Literature 2 discloses a vehicular force limiter in which ring discs (1, 3) and an oscillation member (2) are disposed between relatively rotating objects. In the above limiter, when the oscillation member (2) rotates relative to the ring discs (1, 3), projections (5) formed on the oscillation member (2) come into contact with projections (7, 8) formed on the ring discs (1, 3) while oscillating alternately, thereby absorbing an energy generated between the relatively rotating objects. In particular, in the above limiter, a kinetic energy varies depending on a rotation speed of the oscillation member (2), and an energy absorbing amount can be increased with increase of the rotation speed of the oscillation member (2).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the seat belt apparatus having the seat belt retractor provided with the energy absorbing device described in Patent Literature 1 or 2, an occupant sitting in the vehicle may be a person with various builds such as a man or a woman, a person having a large build or a small build. Accordingly, even in the same seat belt apparatus, a load applied to the webbing or the retractor during a vehicle collision may vary.

In order to address the variation of the loads, a sensor that determines the build of an occupant or an energy absorbing device that can accommodate various loads needs to be disposed in the vehicle. Such a problem occurs not only in the seat belt retractor, but also in a retractor, for example, that retracts long objects of different thicknesses or types (such as fabrics and plates).

However, in the energy absorbing device described in Patent Literature 1, although the energy absorbing properties can be changed to two stages of the wire and the torsion bar, the energy absorbing properties cannot be changed steplessly.

Further, in the energy absorbing device described in Patent Literature 2, the energy absorbing amount can be changed depending on the rotation speed of the oscillation member to accommodate occupants of various builds. However, when the load is applied unevenly to the entire periphery of the oscillation member, load concentration occurs since the oscillation member reciprocates between the ring discs, which often causes damage to the oscillation member. Further, since the oscillation member oscillates while rotating, deformation due to counterforce from the ring disc may occur. This causes a problem of accumulation of metal fatigue and reduced durability.

The present invention has been made to overcome the above problems, and has an object to provide an energy absorbing device, a seat belt retractor and a seat belt apparatus that can vary an energy absorbing amount depending on increase and decrease of rotation speed between relatively rotating objects and can improve durability.

Solution to Problem

According to an aspect of the present invention, an energy absorbing device disposed between relatively rotating objects includes: a casing connected to one object; a first clutch disc of an annular shape disposed to be reciprocatable in a rotation axis direction in the casing; a second clutch disc of an annular shape disposed inside the first clutch disc to be reciprocatable in the rotation axis direction in the casing; and a clutch plate of an annular shape connected to the other object and having an engaging surface that faces both the first clutch disc and the second clutch disc, wherein the clutch plate has engaging teeth with ridges and grooves arranged in a circumferential direction of the engaging surface, the first clutch disc has engaging outer teeth on a surface which faces the engaging surface so as to be engageable with the engaging teeth, the second clutch disc has engaging inner teeth on a surface which faces the engaging surface so as to be engageable with the engaging teeth, and the engaging outer teeth and the engaging inner teeth alternately engage with the engaging teeth so as to absorb an energy generated by relative rotation between one object and the other object.

The energy absorbing device may include a plurality of oscillation members arranged in a circumferential direction to be able to oscillate inwardly and outwardly in a radial direction between the first clutch disc, the second clutch disc, and the casing so that the oscillation members oscillate to alternately reciprocate the first clutch disc and the second clutch disc in the rotation axis direction.

The casing may include a plurality of partition members that partition the disposed positions of the oscillation members. Further, the partition member may include a projection that partitions the disposed position of the first clutch disc and the disposed position of the second clutch disc. The first clutch disc may include a locking section that protrudes inward in a radial direction and is disposed between the partition members, and the second clutch disc may include locking sections that protrudes outward in a radial direction and is disposed between the partition members.

The clutch plate may be disposed in the casing to be rotatable relatively to the casing, and the casing may include a cover plate that regulates movement of the clutch plate in the rotation axis direction.

Further, according to another aspect of the present invention, a seat belt retractor includes: a spool that retracts a webbing that restrains an occupant; and a base frame that rotatably holds the spool, wherein an energy absorbing device is disposed between the base frame or a component fixed to the base frame and the spool, and the energy absorbing device is the energy absorbing device according to the above aspect of the present invention.

Further, according to another aspect of the present invention, a seat belt apparatus includes: a webbing that restrains an occupant; a seat belt retractor that retracts the webbing; a belt anchor that fixes the webbing to a vehicle body; a buckle provided on a side face of the seat; and a tongue disposed on the webbing, wherein the seat belt retractor is the seat belt retractor having the energy absorbing device according to the above aspect of the present invention.

Advantageous Effects of Invention

According to the energy absorbing device, the seat belt retractor, and the seat belt apparatus of the present invention, for the relatively rotating clutch plates, the first clutch disc and the second clutch disc are alternately reciprocated in a rotation axis direction so that the engaging outer teeth and the engaging inner teeth alternately engage with the engaging teeth. Accordingly, it is possible to increase and decrease the reciprocation speed of the first clutch disc and the second clutch disc depending on increase and decrease of the relative rotation speed of the clutch plates, and to vary the energy absorbing amount depending on increase and decrease of rotation speed between relatively rotating objects.

Further, according to the present invention, since the rotating component (clutch plate) and the reciprocating component (first clutch disc and second clutch disc) perform the respective functions, a counterforce generated during actuation can be distributed to the respective components, thereby reducing accumulation of metal fatigue and improving durability. Moreover, since only one surface of the first clutch disc and the second clutch disc engages with the clutch plate, the structural strength of the first clutch disc, the second clutch disc, and the clutch plate can be easily improved, thereby improving the durability of the energy absorbing device.

DESCRIPTION OF EMBODIMENTS

With reference toFIGS. 1 to 9, an embodiment of the present invention will be described below.FIG. 1is a development view of components of an energy absorbing device according to an embodiment of the present invention.FIG. 2is an assembly view of components of the energy absorbing device shown inFIG. 1, in whichFIG. 2(A)is a plan view andFIG. 2(B)is a sectional view taken along the line B-B ofFIG. 2(A).FIG. 3is a front view of a clutch plate, in whichFIG. 3(A)shows a first example,FIG. 3(B)shows a second example, andFIG. 3(C)shows a third example.

As shown inFIGS. 1, 2(A), and2(B), an energy absorbing device1according to an embodiment of the present invention is an energy absorbing device disposed between relatively rotating objects and includes a casing2connected to one object, an annular first clutch disc3disposed to be reciprocatable in the rotation axis direction in the casing2, an annular second clutch disc4disposed inside the first clutch disc3to be reciprocatable in the rotation axis direction in the casing2, and an annular clutch plate5connected to the other object and having an engaging surface50that faces both the first clutch disc3and the second clutch disc4, wherein the clutch plate5has engaging teeth51with ridges and grooves arranged in a circumferential direction of the engaging surface50, the first clutch disc3has engaging outer teeth31on a surface which faces the engaging surface50so as to be engageable with the engaging teeth51, and the second clutch disc4has engaging inner teeth41on a surface which faces the engaging surface50so as to be engageable with the engaging teeth51, and the engaging outer teeth31and the engaging inner teeth41alternately engage with the engaging teeth51so as to absorb an energy generated by a relative rotation between one object and the other object.

Further, a plurality of oscillation members6are arranged in a circumferential direction to be able to oscillate inwardly and outwardly in a radial direction between the first clutch disc3, the second clutch disc4and the casing2so that the oscillation members6oscillate to alternately reciprocate the first clutch disc3and the second clutch disc4in the rotation axis direction. Further, a component that alternately reciprocates the first clutch disc3and the second clutch disc4in the rotation axis direction is not limited to the oscillation members6shown in the figure, but may be spring members disposed between the first clutch disc3and the casing2and between the second clutch disc4and the casing2.

The casing2has a bottomed cylindrical shape that can house the first clutch disc3and the second clutch disc4having a circular outer shapes. Further, the casing2has a double cylindrical shape having a cylindrical outer wall21and a cylindrical inner wall22. It should be noted that the shape of the casing2shown in the figure is a mere example, and is not limited to a cylindrical shape as far as the casing2can house the first clutch disc3and the second clutch disc4. The center portion of the casing2(an inner diameter part of the inner wall22) may be hollow or solid.

The casing2includes a plurality of partition members23that partition the disposed positions of the respective oscillation members6. The partition members23are the wall members connected to the outer wall21and the inner wall22and are formed radially. Accordingly, a plurality of projections and recesses can be formed alternately in the circumferential direction of the casing2such that oscillation members6are housed in the recesses24formed in gaps between the respective partition members23.

Further, the partition member23includes a projection23athat partitions the disposed position of the first clutch disc3and the disposed position of the second clutch disc4. The projection23ais formed at a substantially center of the partition member23that connects the outer wall21and the inner wall22, and the partition member23has a substantially T-shaped cross section. A housing space23bfor the first clutch disc3is formed outside the projections23abetween the partition members23and the outer wall21, and a housing space23cfor the second clutch disc4is formed inside the projections23abetween the partition members23and the inner wall22.

The first clutch disc3is an annular plate member housed in the housing space23bformed by a plurality of partition members23and is provided with the engaging outer teeth31on a surface opposite to a contact surface with the partition member23. A surface of the partition member23has a plurality of radially formed grooves which provide ridges and grooves arranged in the circumferential direction, thereby forming the engaging outer teeth31. The first clutch disc3may have locking sections32that protrude inward in the radial direction and are disposed between the respective partition members23.

Accordingly, when the first clutch disc3is housed in the housing space23b, the locking sections32are disposed adjacent to the projections23aof the partition members23. The locking sections32lock the projections23a, therefore suppress rotation of the first clutch disc3in the circumferential direction.

The second clutch disc4is an annular plate member housed in the housing space23cformed by a plurality of partition members23and is provided with the engaging inner teeth41on a surface opposite to a contact surface with the partition member23. A surface of the partition member23has a plurality of radially formed grooves which provide ridges and grooves arranged in the circumferential direction, thereby forming the engaging inner teeth41. The second clutch disc4may have locking sections42that protrude outward in the radial direction and are disposed between the respective partition members23.

Accordingly, when the second clutch disc4is housed in the housing space23c, the locking sections42are disposed adjacent to the projections23aof the partition members23. The locking sections42lock the projections23a, therefore suppress rotation of the second clutch disc4in the circumferential direction. With this configuration, the first clutch disc3and the second clutch disc4are prevented from rotating relatively to the casing2.

The clutch plate5is an annular plate member having the engaging surface50that faces the engaging outer teeth31of the first clutch disc3and the engaging inner teeth41of the second clutch disc4. As shown inFIGS. 3(A) to 3(C), a surface of the engaging surface50has a plurality of radially formed grooves which provide ridges and grooves arranged in the circumferential direction, thereby forming the engaging teeth51. The clutch plate5is not limited to an annular shape and may be a disc shape.

In the engaging outer teeth31, the engaging inner teeth41, and the engaging teeth51, the teeth (or grooves) are formed in the same phase so that the engaging outer teeth31of the first clutch disc3and the engaging inner teeth41of the second clutch disc4mesh with the engaging teeth51of the clutch plate5.

As shown in the first example inFIG. 3(A), the engaging teeth51of the clutch plate5may be formed on the entire surface of the engaging surface50. Further, as shown in the second example inFIG. 3(B), the engaging surface50may have a flat section53on which the engaging teeth51are not formed on a portion that faces the inner wall22of the clutch plate5. Further, as shown in the third example inFIG. 3(C), the engaging surface50may have a flat section54on which the engaging teeth51are not formed on a portion that faces the projection23aof the partition member23.

Further, the clutch plate5is disposed in the casing2to be rotatable relatively to the casing2, and the casing2includes a cover plate25that regulates movement of the clutch plate5in the rotation axis direction. The cover plate25is, for example, an annular member that can be housed in the casing2, and includes a plurality of projections25aon the outer periphery. Further, notches21ain which the projections25aof the cover plate25can be inserted are formed on the edge of the outer wall21of the casing2.

Further, it is preferable that a surface of the clutch plate5(back surface52) opposite to the engaging surface50is provided so as to decrease friction resistance to the inner surface of the cover plate25fixed to the casing2.

Further, the shape or fixing method of the cover plate25is not limited to the configuration shown in the figure and, for example, the cover plate25may be in a disc shape, a lid member that can be threaded in the casing2, or a configuration that can be fixed to the inner wall22.

The oscillation member6has a substantially plate shape that can be housed in the recess24of the casing2, and has a support point60which is slidable while being in contact with the bottom of the casing2, a first force point61that transmits a drive force while being in contact with the first clutch disc3, and a second force point62that transmits a drive force while being in contact with the second clutch disc4. The support point60may be a shape that protrudes in a shaft shape or in a spherical shape. Further, a recess26that supports the support point60may be formed on the bottom of the casing2that faces the support point60.

Portions of the first force point61and the second force point62which is in contact with the first clutch disc3and the second clutch disc4may have a protruding curved section. With this configuration, a stress generated by contact between the oscillation member6and the first clutch disc3, the second clutch disc4can be decreased. Further, since the support point60, the first force point61, and the second force point62are in contact with the casing2, the first clutch disc3, and the second clutch disc4, respectively, a substantially uniform load can be distributed to the entire circumference during reciprocation of the first clutch disc3and the second clutch disc4so as to prevent the concentration of stress and damage to the engaging teeth50, the engaging outer teeth31, and the engaging inner teeth41.

In the assembled state of the above components as shown inFIG. 2(B), when the second force point62of the oscillation member6is inclined to be in contact with the bottom of the casing2, the first force point61is inclined in the direction toward the clutch plate5. In this state, the engaging outer teeth31of the first clutch disc3mesh with the engaging teeth51of the clutch plate5. Similarly, although not shown in the figure, when the first force point61of the oscillation member6is inclined to be in contact with the bottom of the casing2, the second force point62is inclined in the direction toward the clutch plate5. In this state, the engaging inner teeth41of the second clutch disc4mesh with the engaging teeth51of the clutch plate5.

Next, with reference toFIGS. 4 to 6, an operation of the above energy absorbing device1will be described.FIG. 4is a view of an operation of the energy absorbing device during rotation of the clutch plate, in whichFIG. 4(A)shows a first clutch disc engagement state,FIG. 4(B)shows a relative rotation start state, andFIG. 4(C)shows a second clutch disc engagement state.FIG. 5is a view of an operation of the energy absorbing device during rotation of the casing, in whichFIG. 5(A)shows a first clutch disc engagement state,FIG. 5(B)shows a relative rotation start state, andFIG. 5(C)shows a second clutch disc engagement state.FIG. 6is a diagram which shows a relationship between a rotation rate of the relative rotation and a load generated by the energy absorbing device.

The explanatory views shown inFIGS. 4(A) to 4(C)show an operation when the casing2is fixed and the clutch plate5rotates, while the explanatory views shown inFIGS. 5(A) to 5(C)show an operation when the clutch plate5is fixed and the casing2rotates. Further, the oscillation member6is not shown inFIG. 4andFIG. 5.

As shown inFIG. 4(A), it is assumed that the engaging teeth51of the clutch plate5engage with the engaging outer teeth31of the first clutch disc3. In this state, when the clutch plate5rotates in the up direction in the figure, a relative rotation is generated among the first clutch disc3, the second clutch disc4, and the clutch plate5since the first clutch disc3and the second clutch disc4are housed in the casing2so as not to rotate.

As shown inFIG. 4B, as the engaging teeth51of the clutch plate5moves, the engaging outer teeth31of the first clutch disc3are pushed in the direction away from the clutch plate5. Further, at the same time, as the first clutch disc3is pushed in the direction away from the clutch plate5due to the operation of the oscillation member6, the second clutch disc4moves in the direction toward the clutch plate5.

Finally, in the state in which the engaging outer teeth31of the first clutch disc3and the engaging teeth51of the clutch plate5are disengaged, the engaging inner teeth41of the second clutch disc4engage with the engaging teeth51of the clutch plate5as shown inFIG. 4(C). As the clutch plate5rotates, the first clutch disc3and the second clutch disc4alternately reciprocate in the rotation axis direction so that the engaging outer teeth31and the engaging inner teeth41alternately engage with the engaging teeth51.

Then, as shown inFIG. 5(A), it is assumed that the engaging teeth51of the clutch plate5engage with the engaging outer teeth31of the first clutch disc3. In this state, when the casing2rotates in the up direction in the figure, a relative rotation is generated among the first clutch disc3, the second clutch disc4, and the clutch plate5since the first clutch disc3and the second clutch disc4are housed in the casing2so as not to rotate.

Since the movement of the clutch plate5in the axis direction is regulated, as the engaging outer teeth31of the first clutch disc3moves, the engaging outer teeth31of the first clutch disc3are pushed in the direction away from the clutch plate5as shown inFIG. 5(B). Further, as the first clutch disc3is pushed in the direction away from the clutch plate5due to the operation of the oscillation member6, the second clutch disc4moves in the direction toward the clutch plate5.

Finally, in the state in which the engaging outer teeth31of the first clutch disc3and the engaging teeth51of the clutch plate5are disengaged, the engaging inner teeth41of the second clutch disc4engage with the engaging teeth51of the clutch plate5as shown inFIG. 5(C). As the casing2rotates, the first clutch disc3and the second clutch disc4alternately reciprocate in the rotation axis direction so that the engaging outer teeth31and the engaging inner teeth41alternately engage with the engaging teeth51.

According to the above configuration of the energy absorbing device1of the present embodiment, when a relative rotation rate of the clutch plate5to the casing2increases, a reciprocation rate (oscillating rate) of the first clutch disc3and the second clutch disc4increases accordingly, thereby a kinetic energy (E=½·mV2) of the first clutch disc3and the second clutch disc4increases.

Accordingly, a vertical resistance N when the first clutch disc3and the second clutch disc4come into contact with the clutch plate5increases, and a friction force (F=μN) generated among the engaging outer teeth31, the engaging inner teeth41, and the engaging teeth51increases. In addition, a friction force generated to the wall surface of the casing2due to reciprocation of the first clutch disc3and the second clutch disc4also increases. As a result, the kinetic energy generated by a relative rotation of the clutch plate5can be converted into a friction force by reciprocation of the first clutch disc3and the second clutch disc4, thereby absorbing the kinetic energy of the clutch plate5.

Particularly, in the energy absorbing device1according to the present embodiment, an energy absorbing amount (N) varies to the relative rotation rate (m/s) as shown inFIG. 6so that the energy absorbing amount can be decreased when the rotation rate is small, and the energy absorbing amount can be increased when the rotation rate is large. Further, inFIG. 6, although the energy absorbing amount to the rotation rate is indicated by the quadratic curve in which the energy absorbing amount increases with increase of acceleration of the rotation rate, it may have a proportional relation in which the energy absorbing amount increases with increase of the rotation rate.

Further, in the energy absorbing device1according to the present embodiment, since only one surface of the first clutch disc3and the second clutch disc4engages with the clutch plate5, the structural strength of the first clutch disc3, the second clutch disc4, and the clutch plate5can be easily improved, thereby improving the durability of the energy absorbing device1. For example, the thickness of the first clutch disc3, the second clutch disc4and the clutch plate5can be easily changed, and the back surface of the first clutch disc3, the second clutch disc4and the clutch plate5can be easily reinforced.

Next, with reference toFIGS. 7 to 9, a seat belt retractor and a seat belt apparatus having the above energy absorbing device1will be described.FIG. 7is an overall configuration view of a seat belt apparatus according to the present embodiment.FIG. 8is a cross sectional view of a seat belt retractor according to the present embodiment.FIG. 9is a development view of components of a shaft unit of the seat belt retractor shown inFIG. 8.

A seat belt apparatus100shown inFIG. 7includes a webbing101that restrains an occupant (not shown in the figure) to a seat S, a seat belt retractor102that retracts the webbing101, a guide anchor103that is provided on a vehicle body and guides the webbing101, a belt anchor104that fixes the webbing101to the vehicle body, and a buckle105provided on the side face of the seat S, and a tongue106disposed on the webbing101.

The seat belt apparatus100shown in the figure is a so-called passenger seat belt apparatus, and in many cases, a pillar P is disposed adjacent to the seat S. The seat belt retractor102is disposed, for example, in the pillar P, and the guide anchor103is disposed on a surface of the pillar P. In such a seat belt apparatus100, the webbing101is withdrawn and the tongue106is fitted in the buckle105to restrain an occupant to the seat S by using the webbing101.

Other configuration of the seat belt apparatus100than the seat belt retractor102is the same as that of the conventional seat belt apparatus, and the detailed description thereof is omitted. Further, the seat belt apparatus100is not limited to a passenger seat, and may be a seat belt apparatus for a driver's seat or a seat belt apparatus for a rear seat. The guide anchor103may be omitted in a seat belt apparatus for a rear seat.

The seat belt retractor102shown inFIG. 8includes a spool121that retracts a webbing (not shown in the figure) that restrains an occupant, a base frame122that rotatably holds the spool121, and an energy absorbing device1disposed between the base frame122or a component fixed to the base frame122and the spool121. Further, the shaft unit shown inFIG. 9is the seat belt retractor102ofFIG. 8while the base frame122, a spring unit123described below, part of a lock mechanism124and an acceleration sensor126described below are omitted.

The seat belt retractor102includes the base frame122that is substantially U-shaped and rotatably supports the spool121, the spring unit123disposed at one end of the spool121, the lock mechanism124disposed on the other end of the spool121, a torsion bar125inserted through the center of the spool121, and the acceleration sensor126that detects an acceleration of the vehicle. Further, although the figure does not show a pre-tensioner that instantly retracts the webbing at the time of a vehicle collision to eliminate a gap between the occupant and the webbing, the seat belt retractor102according to the present embodiment may or may not include a pre-tensioner.

The spring unit123includes a spring core123athat forms a shaft of a spiral spring (not shown in the figure), and a spring cover123bthat houses the spiral spring. The spring core123ais connected to one end of the torsion bar125. The torsion bar125is rotatably supported by a bearing122adisposed on the base frame122. Further, a push nut122bmay be disposed on the outside of the bearing122afor prevention of falling off.

The lock mechanism124includes a locking base124adisposed on an end of the torsion bar125, a pawl124bdisposed on the locking base124ain a swingable manner, a lock gear124cdisposed on an end of the torsion bar125so as to be adjacent to the outside of the locking base124a, a flywheel124ddisposed on the lock gear124cin a swingable manner, and a retainer124ethat houses the above components and rotatably supports the torsion bar125.

The acceleration sensor126is disposed adjacent to the lock mechanism124and includes projections that are engageable with teeth formed on the outer periphery of the lock gear124cwhen detecting an acceleration generated in the vehicle due to a vehicle collision or the like.

When the acceleration sensor126detects an acceleration generated in the vehicle due to a vehicle collision or the like, rotation of the lock gear124cis suppressed, and accordingly, the flywheel124dswings. The flywheel124dis configured to swing the pawl124bwith swing of the flywheel124d. When swings, the pawl124bprotrudes in an outer diameter direction of the locking base124aand engages with the teeth formed on the opening of the base frame122. This engagement of the pawl124ballows the locking base124ato be fixed to the base frame122.

When the webbing is further withdrawn and a predetermined load is generated in the operated state of the lock mechanism124, the spool121connected to the webbing rotates relative to the locking base124a. Here, the torsion bar125twists to absorb an energy generated in the webbing. Further, a maximum torsion rotation speed of the torsion bar125is regulated by a stopper125afitted on the outer periphery of the shaft of the locking base124a, thereby preventing the torsion bar125from tearing. Alternatively, a collar125bfor backlash prevention may be disposed between the stopper125aand the spool121.

The above described seat belt retractor102has the same configuration as that of the conventional seat belt retractor, for example, as described in Japanese Unexamined Patent Application Publication No. 2012-30636, and detailed description thereof is omitted.

In addition to the above configuration, the seat belt retractor102according to the present embodiment includes a fixation ring102afixed to the locking base124aand an energy absorbing device1disposed between the spool121and the fixation ring102a. As shown inFIG. 8, the casing2of the energy absorbing device1is fixed to the spool121, and the clutch plate5is fixed to the fixation ring102a. Further, as shown inFIG. 9, the clutch plate5has inner teeth on the inner periphery thereof, and the fixation ring102ahas outer teeth which engage with the inner teeth of the clutch plate5.

Accordingly, when the lock mechanism124operates to generate relative rotation between the locking base124aand the spool121, the clutch plate5and the casing2generate relative rotation. As a result, the energy absorbing device1operates to absorb an energy generated in the webbing.

Moreover, since the seat belt retractor102shown in the figure includes the torsion bar125fixed to the bearing122a, the energy absorbing device1operates simultaneously with actuation of the torsion bar125. Thus, using the energy absorbing device1and the torsion bar125together reduces a burden to the energy absorbing device1, thereby reducing the size and weight of the energy absorbing device1.

In general, an occupant sitting in a vehicle may be a person with a large build (such as a man) or a small build (such as a woman and a child). When a predetermined load is applied, the seat belt retractor102having only the conventional torsion bar uniformly operates regardless of whether the occupant is a person with a large build or a small build. For example, when the occupant is a person with a large build, speed reduction is less likely to occur when the upper body of the occupant moves forward due to a vehicle collision or the like. On the other hand, when the occupant is a person with a small build, speed reduction is more likely to occur when the upper body of the occupant moves forward due to a vehicle collision or the like.

Accordingly, if the operation condition of the torsion bar is set depending on whether the occupant has a large build or a small build, a sensor or the like that determines the build of the occupant is separately needed. To the contrary, the seat belt retractor102having the energy absorbing device1according to the present embodiment can increase or decrease the energy absorbing amount in accordance with the withdrawing speed of the webbing depending on a build of the occupant without using a sensor or the like that determines a build of the occupant, since the energy absorbing amount can be increased or decreased depending on the relative rotation speed.

Although the torsion bar125is provided in the above described embodiment, the torsion bar125may not be provided. For example, by providing a shaft (not shown in the figure) made of metal or resin having the substantially same shape as that of the torsion bar125so that the shaft is freely rotatable to the bearing122a, the spool121can rotate relative to the shaft even if the lock mechanism124operates. In such a configuration, it is possible to actuate the energy absorbing device1by relative rotation of the locking base124aand the spool121.

The present invention is not limited to the above described embodiment. As a matter of course, various modifications can be made without departing from the spirit of the present invention, and for example, the casing2can be fixed to the locking base124aand the clutch plate5can be fixed to the spool121.