Seatbelt retractor and seatbelt assembly including same

A seatbelt retractor is provided that can be formed in a smaller size yet properly operated, and capable of smoothly providing seatbelt tension, and a seatbelt assembly including such a seatbelt retractor. The seatbelt retractor includes a frame, a seatbelt, a spool that takes up the seatbelt, the spool being rotatably supported by the frame, a lock mechanism that allows the spool to rotate in a non-activated state and restricts, upon being activated, the spool from rotating in the seatbelt withdrawal direction, and an energy absorption mechanism that limits the load applied to the seatbelt to thereby absorb and alleviate energy of the occupant, and the energy absorption mechanism includes a first torsion bar concentrically enclosed in the spool with one end portion retained by the spool and the other end portion disposed to be locked by the lock mechanism, and disposed to be rotated by torsional force, a second torsion bar eccentrically enclosed in the spool with one end portion 24a disposed to be locked by the lock mechanism, and disposed to be rotated by torsional force, and a moving member that rotates interlocked with the spool, and moves between the first position for retaining the other end portion of the second torsion bar and the second position spaced from the other end portion of the second torsion bar.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Patent Application of International Patent Application Number PCT/JP2014/069593, filed on Jul. 24, 2014, which claims priority of Japanese Patent Application Number 2013-190085, filed Sep. 13, 2013, which are hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a technical field of a seatbelt retractor that allows a seatbelt to be retracted and withdrawn, and more particularly to a seatbelt retractor including an energy absorption mechanism (hereinafter, EA mechanism as the case may be) configured to limit, when restricting the withdrawal of the seatbelt in an emergency case, such as collision, where a large deceleration force is exerted on the vehicle while the seatbelt is worn by the occupant, a load applied to the seatbelt using an energy absorbing member such as a torsionally deformable torsion bar, to thereby absorb and alleviate the energy of the occupant, and to a seatbelt assembly including such a seatbelt retractor.

BACKGROUND ART

A seatbelt assembly conventionally equipped in a vehicle such as an automobile is designed to bind the occupant with the seatbelt in the emergency case, to prevent the occupant from being thrown out of the seat.

Such a seatbelt assembly includes a seatbelt retractor that retracts the seatbelt. In the seatbelt retractor, the seatbelt is wound around a spool when not in use, and withdrawn to be worn by the occupant when in use. In an emergency case as cited above, a locking device of the seatbelt retractor is activated so as to restrict the spool from rotating in the direction to withdraw the belt, thereby restricting the withdrawal of the seatbelt. Thus, the seatbelt binds the occupant in the emergency case.

In relation to the seatbelt retractor of the conventional seatbelt assembly, when the seatbelt binds the occupant in an emergency case such as vehicle collision, large vehicle deceleration is generated and hence the occupant is urged to move forward by large inertia. Accordingly, the seatbelt is subjected to a large load and the occupant is subjected to a large amount of energy from the seatbelt. Although such energy is not a critical issue to the occupant, it is preferable that the energy is limited.

Therefore, conventionally a torsion bar is provided in the seatbelt retractor, so as to limit the load applied to the seatbelt in an emergency case that happens while the seatbelt is worn by the occupant, thus to absorb and alleviate the energy.

However, in the conventional seatbelt retractors only a single load limit is specified with respect to a case of collision. Actually, the energy imposed on the occupant varies depending, for example, on the body weight of the occupant. Therefore, setting different load limits, instead of just one, in accordance with the situation of the emergency case to cope with the large energy that varies depending on the situation allows the occupant to be bound more effectively and more properly.

Accordingly, seatbelt retractors that allows setting of various limits to the load applied to the seatbelt have been proposed (see, for example, PTL 1).

The seatbelt retractor according to PTL 1 includes a pair of EA mechanisms having different EA characteristics, and one or both of the EA mechanisms are activated depending on the situation of the emergency case. Selectively activating the pair of EA mechanisms allows the load limit on the seatbelt to be set in two stages, depending on the situation of the emergency case.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

However, the structure of the seatbelt retractor according to PTL 1 requires a large space. For example, the second torsion bar described in PTL 1 is located on an outer side of the outer circumference of the shaft, which leads to an increase in size of the seatbelt retractor.

The present invention has been accomplished in view of the foregoing situation, and provides a seatbelt retractor configured to allow different load limits on the seatbelt to be set depending on the situation of the emergency case, yet formed in a smaller size, and a seatbelt assembly that includes such a seatbelt retractor.

In an aspect, the present invention provides a seatbelt retractor including a frame, a seatbelt, a spool that takes up the seatbelt, the spool being rotatably supported by the frame, a lock mechanism that allows the spool to rotate in a non-activated state and restricts, upon being activated, the spool from rotating in a seatbelt withdrawal direction, and an energy absorption mechanism that limits a load applied to the seatbelt to thereby absorb and alleviate energy of an occupant. The energy absorption mechanism includes a first torsion bar concentrically enclosed in the spool with one end portion retained by the spool and the other end portion disposed to be locked by the lock mechanism, and disposed to be rotated by torsional force, a second torsion bar eccentrically enclosed in the spool with one end portion disposed to be locked by the lock mechanism, and disposed to be rotated by torsional force, and a moving member that rotates interlocked with the spool, and moves between a first position for retaining the other end portion of the second torsion bar and a second position spaced from the other end portion of the second torsion bar.

In the seatbelt retractor according to the present invention, the energy absorption mechanism may include a first gear that retains the other end portion of the first torsion bar, the first gear being disposed to be locked by the lock mechanism, and a second gear meshed with the first gear and retaining the one end portion of the second torsion bar.

In the seatbelt retractor according to the present invention, the energy absorption mechanism may include a pressing member that moves the moving member to the first position and the second position, a drive mechanism that drives the pressing member, and a housing movably supporting the pressing member and accommodating therein the drive mechanism.

In the seatbelt retractor according to the present invention, the housing may include a cam portion spaced from the pressing member before the drive mechanism is activated, and contacted by the pressing member when the drive mechanism is activated.

The seatbelt retractor according to the present invention may further include an occupant information acquisition unit that acquires occupant information, and a control unit that decides whether the information acquired by the occupant information acquisition unit satisfies a predetermined condition, and moves the moving member, depending on a decision result, to the first position for retaining the other end portion of the second torsion bar and the second position spaced from the other end portion of the second torsion bar.

The seatbelt retractor according to the present invention may further include a pretensioner mechanism that rotates the spool in a seatbelt retracting direction in an emergency case, and the control unit may decide whether the information acquired by the occupant information acquisition unit satisfies the predetermined condition, after activating the pretensioner mechanism in the emergency case.

In another aspect, the present invention provides a seatbelt assembly including at least a seatbelt for binding an occupant, a seatbelt retractor that withdrawably retracts the seatbelt and restricts the seatbelt from being withdrawn upon being activated in an emergency case, a tongue slidably supported by the seatbelt withdrawn from the seatbelt retractor, and a buckle attached to a vehicle body or a vehicle seat to be removably engaged with the tongue. In the seatbelt assembly, one of the foregoing seatbelt retractors is employed as the seatbelt retractor.

The seatbelt retractor thus configured according to the present invention includes the frame, the seatbelt, the spool that takes up the seatbelt, the spool being rotatably supported by the frame, the lock mechanism that allows the spool to rotate in a non-activated state and restricts, upon being activated, the spool from rotating in the seatbelt withdrawal direction, and the energy absorption mechanism that limits the load applied to the seatbelt to thereby absorb and alleviate energy of the occupant, and the energy absorption mechanism includes the first torsion bar concentrically enclosed in the spool with one end portion retained by the spool and the other end portion disposed to be locked by the lock mechanism, and disposed to be rotated by torsional force, the second torsion bar eccentrically enclosed in the spool with one end portion disposed to be locked by the lock mechanism, and disposed to be rotated by torsional force, and the moving member that rotates interlocked with the spool, and moves between the first position for retaining the other end portion of the second torsion bar and the second position spaced from the other end portion of the second torsion bar. Therefore, the seatbelt retractor can be formed in a smaller size, yet can be properly operated, and is capable of smoothly providing the seatbelt tension.

In the seatbelt retractor according to the present invention, the energy absorption mechanism includes the first gear that retains the other end portion of the first torsion bar, the first gear being disposed to be locked by the lock mechanism, and the second gear meshed with the first gear and retaining the one end portion of the second torsion bar. Therefore, the first torsion bar and the second torsion bar can be securely connected to each other.

In the seatbelt retractor according to the present invention, the energy absorption mechanism includes the pressing member that moves the moving member to the first position and the second position, the drive mechanism that drives the pressing member, and the housing movably supporting the pressing member and accommodating therein the drive mechanism. Therefore, the pressing member can be driven to move the moving member by the drive mechanism mounted in the solid housing, and thus the components interact more properly with each other to perform accurate operations.

In the seatbelt retractor according to the present invention, the housing includes the cam portion spaced from the pressing member before the drive mechanism is activated, and contacted by the pressing member when the drive mechanism is activated. Moving thus the moving member by bringing the pressing member into contact with the cam portion allows a more accurate operation to be performed.

The seatbelt retractor according to the present invention further includes the occupant information acquisition unit that acquires occupant information, and the control unit that decides whether the information acquired by the occupant information acquisition unit satisfies the predetermined condition, and moves the moving member, depending on the decision result, to the first position for retaining the other end portion of the second torsion bar and the second position spaced from the other end portion of the second torsion bar. Therefore, the seatbelt retractor can be controlled in accordance with the condition of the occupant, thus to be more properly operated.

The seatbelt retractor according to the present invention further includes the pretensioner mechanism that rotates the spool in the seatbelt retracting direction in an emergency case, and the control unit may decide whether the information acquired by the occupant information acquisition unit satisfies the predetermined condition, after activating the pretensioner mechanism in the emergency case. The mentioned configuration enables the seatbelt to be quickly retracted in the emergency case.

The seatbelt assembly including the foregoing seatbelt retractor, which can be formed in a smaller size, allows the components of the seatbelt assembly to be arranged with a higher degree of designing freedom.

DESCRIPTION OF EMBODIMENTS

Hereafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1is a schematic perspective view showing a seatbelt assembly including a seatbelt retractor according to an embodiment of the present invention.

As shown inFIG. 1, the seatbelt assembly1according to this embodiment is a known three-point seatbelt assembly. The seatbelt assembly1includes a vehicle seat2, a seatbelt retractor3provided close to the vehicle seat2, a seatbelt4withdrawably retracted in the seatbelt retractor3and including a seatbelt anchor4afixed to a vehicle floor or the vehicle seat2, a guide anchor5that guides the seatbelt4withdrawn from the seatbelt retractor3to the shoulder of an occupant, a tongue6slidably supported by the seatbelt4guided from the guide anchor5, and a buckle7fixed to the vehicle floor or the vehicle seat, and in which the tongue6is removably inserted. The wearing action and releasing action of the seatbelt4of the seatbelt assembly1are also the same as those of the known seatbelt assemblies.

FIG. 2is an exploded perspective view of the seatbelt retractor according to this embodiment.

As shown inFIG. 2, the seatbelt retractor3according to this embodiment includes a frame11, a spool12, a spring chamber13, an EA mechanism20, a deceleration sensor40, a pretensioner mechanism50, and a lock mechanism60.

The frame11includes a back plate11a, and left and right sidewalls11b,11cextending from the respective side edges of the back plate11aorthogonally thereto, thus having a channel-shaped cross section. The left and right sidewalls11b,11cof the frame11each include a circular opening.

The spool12includes an intermediate portion12a, a first flange12battached to one end of the intermediate portion12a, a second flange12cattached to the other end of the intermediate portion12a, and a shaft portion12dprojecting from the second flange12c. The spool12is disposed so as to rotatably penetrate through the openings of the respective sidewalls of the frame11.

One end of the seatbelt4shown inFIG. 1is fixed to the outer circumferential surface of the intermediate portion12a, so that the seatbelt4can be wound therearound. The intermediate portion12aalso includes a groove12a1formed in the axial direction.

The first flange12bincludes a first hole12b1formed in a central region, and a second hole12b2formed at a position deviated from the axial center of the spool12. The first hole12b1includes a first stepped portion12b11where the diameter is reduced, formed halfway in the axial direction, and the second hole12b2includes a second stepped portion12b21where the diameter is reduced, formed halfway in the axial direction. The first hole12b1and the second hole12b2partially overlap.

The second flange12cincludes a third hole12c1formed so as to oppose the second hole12b2of the first flange12b. In addition, a plurality of column-shaped guide portions12c2are provided around the shaft portion12dof the second flange12c. The guide portions12c2serve to guide a release ring25to be subsequently described when the release ring25moves in the axial direction, and may be formed in different shapes without limitation to the column shape.

The spring chamber13includes a non-illustrated spring having one end connected to the shaft portion12dof the spool12and the other end attached to a case, so as to bias the spool12in a belt retracting direction.

FIG. 3andFIG. 4are perspective views each showing a part of the EA mechanism20of the seatbelt retractor according to this embodiment.FIG. 5is a perspective view showing a housing of the EA mechanism20of the seatbelt retractor according to this embodiment.FIG. 6is a side view showing the EA mechanism20of the seatbelt retractor according to this embodiment.FIG. 7is a front view showing the EA mechanism20of the seatbelt retractor according to this embodiment.FIG. 8is a cross-sectional view taken along a line A-A inFIG. 6.FIG. 9is a cross-sectional view taken along a line B-B inFIG. 7.FIG. 10is a cross-sectional view taken along a line C-C inFIG. 7.FIG. 11is an enlarged cross-sectional view of a portion indicated by D inFIG. 8.

The EA mechanism20includes a first torsion bar21, a first gear22, a second gear23, a second torsion bar24, the release ring25, a housing26, a lever ring27, a micro gas generator28, an O-ring29, and a piston30. The release ring25corresponds to the moving member, the lever ring27corresponds to the pressing member, and the micro gas generator28corresponds to the drive mechanism.

The first torsion bar21is concentrically accommodated inside the intermediate portion12aof the spool12. One end portion21aof the first torsion bar21is retained by the second flange12cof the spool12so as to rotate interlocked with the spool12. The other end portion21bof the first torsion bar21is retained by a first recess22aof the first gear22so as to rotate interlocked with the first gear22.

The first gear22includes the first recess22aformed on the inner side so as to retain the other end of the first torsion bar21, and first gear teeth22bformed along the outer circumference of the portion corresponding to the first recess22a. The first gear22also includes a shaft portion22cformed on the opposite side of the first recess22a. The first gear22is attached to the first torsion bar21so as to cover the one end of the intermediate portion12ainside the first hole12b1of the first flange12bof the spool12. The spool12and the first gear22are assembled so as to rotate relative to each other.

The second gear23includes second gear teeth23aformed along the outer circumference of one end portion in the axial direction, and a second recess23bformed inside the other end portion. The second gear23is accommodated inside the second hole12b2of the first flange12bof the spool12. The second gear teeth23aare meshed with the first gear teeth22bof the first gear22, in the region where the first hole12b1and the second hole12b2overlap. The second recess23bretains one end of the second torsion bar24.

The second torsion bar24is accommodated in the groove12a1formed in the intermediate portion12aof the spool12, at a position deviated from the axial center of the spool12. One end portion24aof the second torsion bar24is retained by the second recess23bof the second gear23, and the other end portion24bis disposed so as to penetrate through the third hole12c1of the second flange12cand normally retained by the release ring25. In addition, the second torsion bar24includes a minor-diameter portion24csmaller in diameter than the other end portion24b, formed on the inner side the other end portion24bin the axial direction.

The release ring25includes a central hole25athrough which the shaft portion12dprojecting from the second flange12cof the spool12is passed. The release ring25also includes a retention hole25bfor retaining the second torsion bar24formed so as to oppose the third hole12c1of the second flange12c, and a plurality of minor holes25cformed around the central hole25a, through each of which the guide portion12c2of the second flange12cis passed.

The release ring25is movable in the axial direction of the spool12. When the retention hole25bof the release ring25and the other end portion24bof the second torsion bar24are engaged with each other, the second torsion bar24is retained so as to rotate interlocked with the release ring25. Accordingly, the second gear23that rotates interlocked with the second torsion bar24is disabled from rotating.

When the release ring25moves in the axial direction so that the retention hole25bof the release ring25comes to the position opposite the minor-diameter portion24cof the second torsion bar24and that the second torsion bar24and the release ring25are separated from each other, the second torsion bar24freely rotates with respect to the release ring25. Accordingly, the second torsion bar24is allowed to rotate interlocked with the second gear23.

The housing26includes a through hole26a. The through hole26aincludes an annular stepped portion26bformed along the inner circumferential surface, and the annular stepped portion26bincludes a plurality of cam portions26ceach including a sloped surface26c1extending in the circumferential direction, and a top surface26c2located at the uppermost portion of the sloped surface26c1. In addition, an annular protruding portion26dis formed along the outer circumference of the through hole26a. The annular protruding portion26dincludes a gap, and a lever stroke region26eis provided on the outer side of the gap, for a lever portion27bof the lever ring27to move therein. The housing26also includes a communication hole26gcommunicating between the outer surface26fof the housing26and the lever stroke region26e, and a gas generator mounting base26his attached to the communication hole26g.

The lever ring27includes a ring portion27a, the lever portion27b, and a cutaway portion27c, and is located adjacent to the release ring25. The ring portion27ais an annular portion concentrically placed in the housing26and superposed on the release ring25. The lever portion27bradially protrudes outward from the outer circumference of the ring portion27a, and located in the lever stroke region26eof the housing26. An abutment27b1to be pressed by the piston30of the micro gas generator28is provided at an end portion of the lever portion27b. The cutaway portion27cis formed on the outer circumference of the ring portion27aat a position corresponding to the cam portion26cof the housing26.

The micro gas generator28includes the piston30located thereinside, and is mounted on the gas generator mounting base26hvia the O-ring29.

In addition, the seatbelt retractor3includes a deceleration sensor40, a pretensioner mechanism50, and a lock mechanism60. These may have known configurations.

The lock mechanism60includes a lock pawl61and a locking base62. The lock pawl61is rotatably attached to the sidewall of the frame11. The locking base62integrally coupled with the shaft portion22cof the first gear22. Thus, the locking base62and the first gear22rotate in an interlocked manner. The lock pawl61is meshed with the locking base62upon rotating, to thereby lock the rotation of the locking base62and the first gear22.

Hereunder, an operation of the seatbelt retractor3according to this embodiment will be described.

In the seatbelt retractor3according to this embodiment, first the pretensioner mechanism50and the lock mechanism60are activated once the deceleration sensor40detects large vehicle deceleration generated in an emergency case.

Then the EA mechanism20is activated, in which case the EA mechanism20according to this embodiment is configured to perform in two modes, namely a first operation mode and a second operation mode.

The first operation mode, in which the micro gas generator28is not activated, will be described first.

In the first operation mode, the EA mechanism20assumes the state illustrated inFIG. 3toFIG. 11, because the micro gas generator28is not activated. After the pretensioner mechanism50is activated and the spool12rotates in the retracting direction, the spool12is urged to rotate in the belt withdrawal direction because the seatbelt4is about to be withdrawn by the inertia of the occupant. However, the locking base62and the first gear22attached to the first flange12bof the spool12are locked by the lock pawl61.

Accordingly, the first torsion bar21, having one end portion21aretained by the spool12and the other end portion21bretained by the first gear22, suffers distortion. In other words, the first torsion bar21allows the seatbelt4to be withdrawn by a predetermined amount, while being subjected to a force limiter load, thereby absorbing the energy.

Since the second gear23moves together with the spool12, the second gear23is meshed with the first gear22so as to rotate. Accordingly, the second torsion bar24, having one end portion24aretained by the second gear23and the other end portion24bretained by the release ring25, suffers distortion. Thus, the second torsion bar24allows the seatbelt4to be withdrawn by a predetermined amount, while being subjected to the force limiter load, thereby absorbing the energy.

As described above, in the first operation mode of the seatbelt retractor3according to this embodiment, in which the micro gas generator28is not activated, both of the first torsion bar21and the second torsion bar24act to absorb the energy.

The second operation mode in which the micro gas generator28is activated will now be described.

FIG. 12is a perspective view showing a part of the EA mechanism20of the seatbelt retractor according to this embodiment, in a state after the micro gas generator is activated.FIG. 13is a perspective view showing the housing of the EA mechanism20of the seatbelt retractor according to this embodiment, in a state after the micro gas generator is activated.FIG. 14is a cross-sectional view taken along a line B-B inFIG. 7, showing a state after the micro gas generator is activated.FIG. 15is a cross-sectional view taken along a line C-C inFIG. 7, showing a state after the micro gas generator is activated.FIG. 16is an enlarged cross-sectional view of the portion indicated by D inFIG. 8, showing a state after the micro gas generator is activated.

In the second operation mode, the EA mechanism20assumes the state illustrated inFIG. 12toFIG. 16, because the micro gas generator28is activated. After the pretensioner mechanism50is activated and the spool12rotates in the retracting direction, the spool12is urged to rotate in the belt withdrawal direction because the seatbelt4is about to be withdrawn by the inertia of the occupant. However, the locking base62and the first gear22attached to the first flange12bof the spool12are locked by the lock pawl61.

Accordingly, the first torsion bar21, having one end portion21aretained by the spool12and the other end portion21bretained by the first gear22, suffers distortion. In other words, the first torsion bar21allows the seatbelt4to be withdrawn by a predetermined amount, while being subjected to a force limiter load, thereby absorbing the energy.

In the second operation mode, the micro gas generator28is activated so as to shoot the piston30. The piston30presses the abutment27b1of the lever portion27bof the lever ring27. Accordingly, the lever ring27starts to rotate because the lever portion27bhas been pressed. Then the ring portion27aof the lever ring27moves along the sloped surface26c1of the cam portion26cformed in the annular stepped portion26bof the housing26, formed in the cutaway portion27c, and climbs up to the top surface26c2.

At this point, the lever ring27which has moved presses the release ring25, so that the release ring25is moved in the axial direction. Then the retention hole25bof the release ring25moves to the position corresponding to the minor-diameter portion24cof the second torsion bar24, and the other end portion24bof the second torsion bar24is separated from the release ring25, so as to freely rotate with respect to the release ring25. Accordingly, the second torsion bar24and the second gear23are allowed to rotate interlocked with each other, and hence the second torsion bar24is not subjected to distortion. In other words, the force limiter load is not applied to the second torsion bar24.

Thus, in the second operation mode of the seatbelt retractor3according to this embodiment, in which the micro gas generator28is activated, only the first torsion bar21acts to absorb the energy.

Hereunder, the control of the seatbelt retractor according to this embodiment will be described.

FIG. 17is a block diagram showing a system configuration of the EA mechanism of the seatbelt retractor according to this embodiment.

Referring toFIG. 17, in the seatbelt retractor according to this embodiment a control unit77controls the operation of the pretensioner mechanism50and the micro gas generator28in accordance with the situation of emergency cases, on the basis of output signals from a seat weight sensor71, a seat slide position sensor72, an acceleration sensor73, a front satellite sensor74, a belt withdrawal sensor75, and an occupant information acquisition unit70such as a buckle switch76. The control unit77is constituted of a CPU or the like.

FIG. 18is an operation flowchart of the seatbelt retractor according to this embodiment.FIG. 19is an operation flowchart of the EA mechanism of the seatbelt retractor according to this embodiment.

First, it is decided whether an emergency case has occurred, at step1(ST1). The decision of the emergency case is made depending on whether the acceleration sensor73has detected sudden deceleration exceeding a predetermined threshold, originating from collision or the like. In the case where it is decided at step1that the emergency case has not occurred, the operation returns to step1.

In the case where it is decided at step1that the emergency case has occurred, the pretensioner mechanism50is activated at step2(ST2).

Then EA mechanism operation mode selection is performed at step3(ST3).

In the EA mechanism operation mode selection, first, occupant information is acquired at step31(ST31). The occupant information may be acquired from the sensors shown inFIG. 17.

At step32, it is decided whether the occupant information acquired at step31satisfies a predetermined condition (ST32). For example, it may be decided whether the load acquired by the seat weight sensor71is equal to or higher than a predetermined value, or smaller than that.

In the case where the predetermined condition is satisfied at step32, the first operation mode in which the micro gas generator28is not activated is selected at step33(ST33). In the case where the predetermined condition is not satisfied at step32, the second operation mode in which the micro gas generator28is activated is selected at step34(ST34). Upon selecting the operation mode of the EA mechanism, the EA mechanism operation mode selection is finished.

For example, in the case where the weight acquired by the seat weight sensor71is heavier than the predetermined value, the first operation mode is selected, and in the case where the weight acquired by the seat weight sensor71is lighter than the predetermined value, the second operation mode is selected.

Then the operation of the pretensioner mechanism50is finished at step4(ST4).

At step5, the EA mechanism20is activated in the operation mode selected at the EA mechanism operation mode selection process of step3(ST5).

At step6, the operation of the EA mechanism20is finished (ST6).

FIG. 20is a graph showing the load applied to the stroke in the first operation mode of the EA mechanism of the seatbelt retractor according to this embodiment.FIG. 21is a graph showing the load applied in the second operation mode to the stroke of the EA mechanism of the seatbelt retractor according to the embodiment.

Thus, the seatbelt retractor3according to this embodiment is configured to switch the load limit of the seatbelt4in an emergency case, utilizing the second torsion bar24to be selectively activated depending on the information known in advance (for example, occupant's weight information, seat-slide position information), collision prediction information, and information regarding the situation of the emergency case, such as information on severeness of the collision (for example, collision velocity information, collision acceleration/deceleration information, information on the form of the collision).

More specifically, when the first gear22is restricted from rotating in the seatbelt withdrawal direction so that the spool12rotates in the seatbelt withdrawal direction relative to the first gear22, it is selected whether the load applied to the seatbelt4is limited by both of the first torsion bar21and the second torsion bar24, or only by the first torsion bar21.

Therefore, the load limit of the seatbelt in the emergency case such as collision can be determined on the basis of the situation of the emergency case and the information such as the body size of the occupant present in the emergency case. Such an arrangement enables the occupant to be bound more effectively and more properly, in the emergency case.

Further, since the second torsion bar24is located inside the spool12, the seatbelt retractor3can be formed in a smaller size in the vertical direction. Therefore, a larger effective space can be secured inside the vehicle interior.

Here, although the micro gas generator28is employed as driving mechanism for pressing the lever portion27bof the lever ring27in the foregoing embodiment, the present invention is not limited to such a configuration. The lever portion27bmay be pressed by a different drive mechanism, for example by an electromagnetic solenoid that employs electromagnetic force to press the lever portion27b. In this case, the electromagnetic solenoid may be controlled by the control unit77in the same way as described above.

The seatbelt retractor configured as above according to the foregoing embodiment includes the frame11, the seatbelt4, the spool12that takes up the seatbelt4, the spool12being rotatably supported by the frame11, the lock mechanism60that allows the spool12to rotate in a non-activated state and restricts, upon being activated, the spool12from rotating in the seatbelt withdrawal direction, and the energy absorption mechanism20that limits the load applied to the seatbelt4to thereby absorb and alleviate energy of the occupant, and the energy absorption mechanism20includes the first torsion bar21concentrically enclosed in the spool12with one end portion21aretained by the spool12and the other end portion21bdisposed to be locked by the lock mechanism60, and disposed to be rotated by torsional force, the second torsion bar24eccentrically enclosed in the spool12with one end portion24adisposed to be locked by the lock mechanism60, and disposed to be rotated by torsional force, and the release ring25that rotates interlocked with the spool12, and moves between the first position for retaining the other end portion24bof the second torsion bar24and the second position spaced from the other end portion24bof the second torsion bar24. Therefore, the seatbelt retractor can be formed in a smaller size, yet can be properly operated, and is capable of smoothly providing the seatbelt tension.

In the seatbelt retractor according to the present invention, the energy absorption mechanism20includes the first gear22that retains the other end portion of the first torsion bar21, the first gear22being disposed to be locked by the lock mechanism60, and the second gear23meshed with the first gear22and retaining the one end portion24aof the second torsion bar24. Therefore, the first torsion bar21and the second torsion bar24can be securely connected to each other.

In the seatbelt retractor according to the present invention, the energy absorption mechanism20includes the lever ring27that moves the release ring25to the first position and the second position, the micro gas generator28that drives the lever ring27, and the housing26movably supporting the lever ring27and accommodating therein the micro gas generator28. Therefore, the lever ring27can be driven to move the release ring25by the micro gas generator28mounted in the solid housing26, and thus the components interact more properly with each other to perform accurate operations.

In the seatbelt retractor according to the present invention, the housing26includes the cam portion26cspaced from the lever ring27before the micro gas generator28is activated, and contacted by the lever ring27when the micro gas generator28is activated. Moving thus the release ring25by bringing the lever ring27into contact with the cam portion26callows a more accurate operation to be performed.

The seatbelt retractor according to the present invention further includes the occupant information acquisition unit70that acquires occupant information, and the control unit77that decides whether the information acquired by the occupant information acquisition unit70satisfies the predetermined condition, and moves the release ring25, depending on the decision result, to the first position for retaining the other end portion24bof the second torsion bar24and the second position spaced from the other end portion24bof the second torsion bar24. Therefore, the seatbelt retractor can be controlled in accordance with the condition of the occupant, thus to be more properly operated.

The seatbelt retractor according to the present invention further includes the pretensioner mechanism50that rotates the spool12in the retracting direction of the seatbelt4in an emergency case, and the control unit may decide whether the information acquired by the occupant information acquisition unit70satisfies the predetermined condition, after activating the pretensioner mechanism50in the emergency case. The mentioned configuration enables the seatbelt4to be quickly retracted in the emergency case.

The seatbelt assembly including the seatbelt retractor3according to the foregoing embodiment, which can be formed in a smaller size, allows the components of the seatbelt assembly to be arranged with a higher degree of designing freedom.

The present invention is applicable to a seatbelt retractor for a seatbelt assembly equipped in a vehicle such as an automobile, and particularly suitable to a seatbelt retractor that restricts the seatbelt from being withdrawn in an emergency case such as collision, while limiting a load applied to the seatbelt thereby absorbing and alleviating the energy of the occupant.