A webbing take-up device enabling a reduction in size of an overload release mechanism and easy adjustment of an operation torque of the overload release mechanism is provided. In the overload release mechanism of this webbing take-up device, rotary force of a large diameter gear is transmitted to a small diameter gear via plural annular friction springs. The friction springs are disposed between an inner periphery face of a main body portion of the large diameter gear and a tubular portion of the small diameter gear, side by side along an axial direction of the two gears. Consequently, a radial direction enlargement of the large diameter gear and small diameter gear due to space for disposing the friction springs may be restrained. Moreover, the operation torque of the overload release mechanism may be adjusted stepwise by changing the number of the friction springs to be used, in accordance with requirements.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese Patent Application No. 2009-241443 filed Oct. 20, 2009, the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a webbing take-up device that takes up and accommodates a webbing for occupant restraint on a take-up spool, and more particularly to a webbing take-up device capable of turning the take-up spool with driving force of a motor.

2. Related Art

A webbing take-up device is disclosed in, for example, WO2006-123750. In this webbing take-up device, a motive power transmission mechanism (a deceleration mechanism) is provided between a take-up spool and a motor. The motive power transmission mechanism includes a torque limiter mechanism (an overload release mechanism). This torque limiter mechanism includes a large diameter side gear that is turned by driving force of the motor, and a small diameter side gear that is disposed at an inner side of the large diameter side gear and turns interlockingly with the spool. A plural number of limit springs are assembled, side by side in a circumferential direction, to an outer periphery portion of the small diameter side gear. The limit springs have structures that engage with protrusions/depressions formed at an inner periphery portion of the large diameter side gear. Relative rotations between the large diameter side gear and the small diameter side gear are allowed by resilient deformation of the limit springs.

Now, in a webbing take-up device as described above, for reasons such as the need to improve a degree of freedom of layout when the overload release mechanism is disposed at the deceleration mechanism and the like, a reduction in size of the overload release mechanism has been required. There have also been required for that it be made possible to easily adjust an operation torque of the overload release mechanism (a torque required for relatively turning the large diameter side gear and the small diameter side gear) in accordance with changes in the layout as mentioned above.

SUMMARY OF THE INVENTION

In consideration of the above circumstances, an object of the present invention is to provide a webbing take-up device that both enables a reduction in size of an overload release mechanism and enables easy adjustment of the operation torque of an overload release mechanism.

A webbing take-up device of a first aspect includes: a take-up spool that takes up a webbing for vehicle occupant restraint; a motor; and an overload release mechanism that is interposed between the take-up spool and the motor, wherein the overload release mechanism includes: a first rotating body that is rotated interlockingly with one of the take-up spool or the motor; a second rotating body that is provided coaxially with the first rotating body and relatively rotatably with respect to the first rotating body, and that is rotated interlockingly with the other of the take-up spool or the motor, an inner periphery portion of the second rotating body opposing an outer periphery portion of the first rotating body; and a plurality of friction springs that are each formed by a spring member in an annular shape, that are disposed between the outer periphery portion of the first rotating body and the inner periphery portion of the second rotating body and side by side along an axial direction of the first and the second rotating bodies, that suppress relative rotation with respect to one of the first rotating body or the second rotating body by friction generated between the friction springs and the one of the first rotating body or the second rotating body, and that prevents relative rotation with respect to the other of the first rotating body or the second rotating body by engaging with the other of the first rotating body or the second rotating body.

In the webbing take-up device of the first aspect, the overload release mechanism is provided with the first rotating body, which is turned interlockingly with the one of the take-up spool or the motor, and the second rotating body, which is turned interlockingly with the other of the take-up spool or the motor. The plural friction springs are provided between the first rotating body and the second rotating body. Rotary force is transmitted between the first rotating body and the second rotating body via these friction springs. Thus, rotation of the motor is transmitted to the take-up spool and the take-up spool is turned.

When a relative rotary force acts between the first rotating body and the second rotating body, which relative rotary force is above a maximum static friction force generated between the one of the first rotating body or the second rotating body and the plural friction springs, the plural friction springs relatively turn with respect to the one of the first rotating body or the second rotating body, and the first rotating body and second rotating body relatively rotate. Therefore, the take-up spool can turn independently of the motor.

Now, in this webbing take-up device, a torque required for relatively rotating the first rotating body and the second rotating body (the operation torque of the overload release mechanism) can be adjusted by changing the number of friction springs in accordance with requirements. Therefore, adjustment of the operation torque of the overload release mechanism can be made simpler. Furthermore, the plural friction springs, which are formed in annular shapes, are disposed side by side along the axial directions of both of the first rotating body and the second rotating body, between the outer periphery portion of the first rotating body and the inner periphery portion of the second rotating body. Therefore, a radial direction enlargement of the first rotating body and the second rotating body due to space for disposing the friction springs may be restrained. Hence, the overload release mechanism may be reduced in size.

A webbing take-up device of a second aspect is the webbing take-up device of the first aspect in which the plurality of friction springs include a pair of coil springs, helix orientations of which are set to mutually opposite orientations, and the pair of coil springs receiving forces in directions approaching one another due to friction with the one of the first rotating body or the second rotating body during relative rotation in one direction around the axis with respect to the one of the first rotating body or the second rotating body.

In the webbing take-up device of the second aspect, when the pair of coil springs whose helix orientations are set to opposite orientations from one another relatively turn in the one direction around the axis with respect to the one of the first rotating body or the second rotating body, because of friction between the one of the first rotating body or the second rotating body and the pair of coil springs, the pair of coil springs are subject to forces in directions such that the pair of coil springs approach one another. Therefore, the pair of coil springs may be closely contacted with one another and the forces acting on the two coil springs counteract. Thus, mispositioning of the coil springs in the axial direction relative to the one of the first rotating body or the second rotating body may be prevented or suppressed.

In the above first and the second aspect, it is possible that a plurality of protruding portions are provided at the other of the first rotating body or the second rotating body, the protruding portions protruding in radial directions of the other of the first rotating body or the second rotating body and being respectively disposable between one end portions in a circumferential direction of the friction springs and the other end portions in the circumferential direction of the friction springs.

A webbing take-up device of a third aspect includes: a take-up spool that takes up a webbing for vehicle occupant restraint; a motor; and an overload release mechanism that is interposed between the take-up spool and the motor, wherein the overload release mechanism includes: a first rotating body that is rotated interlockingly with one of the take-up spool or the motor; a second rotating body that is provided coaxially with the first rotating body and relatively rotatably with respect to the first rotating body, and that is rotated interlockingly with the other of the take-up spool or the motor, an inner periphery portion of the second rotating body opposing an outer periphery portion of the first rotating body; and a friction spring that is formed by a spring member in an annular shape, that is disposed between the outer periphery portion of the first rotating body and the inner periphery portion of the second rotating body, that suppresses relative rotation with respect to one of the first rotating body or the second rotating body by friction generated between the friction spring and the one of the first rotating body or the second rotating body, and that prevents relative rotation with respect to the other of the first rotating body or the second rotating body by engaging with the other of the first rotating body or the second rotating body, wherein a plurality of friction springs can be disposed between the outer periphery portion of the first rotating body and the inner periphery portion of the second rotating body side by side along an axial direction of the first and the second rotating bodies.

In the webbing take-up device of the third aspect, the overload release mechanism is provided with the first rotating body, which is turned interlockingly with the one of the take-up spool or the motor, and the second rotating body, which is turned interlockingly with the other of the take-up spool or the motor. The friction spring(s) is/are provided between the first rotating body and the second rotating body. Rotary force is transmitted between the first rotating body and the second rotating body through the friction spring(s). Thus, rotation of the motor is transmitted to the take-up spool and the take-up spool is turned.

When a relative rotary force acts between the first rotating body and the second rotating body, which relative rotary force is above a maximum static friction force generated between the one of the first rotating body or the second rotating body and the friction spring, the friction spring relatively turns with respect to the one of the first rotating body or the second rotating body, and the first rotating body and second rotating body relatively turn. Therefore, the take-up spool can turn independently of the motor.

In this webbing take-up device, the friction springs may be plurally disposed between the outer periphery portion of the first rotating body and the inner periphery portion of the second rotating body. Therefore, a torque required for relatively rotating the first rotating body and second rotating body (the operation torque of the overload release mechanism) can be adjusted by changing the number of friction springs in accordance with requirements. Therefore, adjustment of the operation torque of the overload release mechanism can be made simpler. Furthermore, the plural friction springs formed in annular shapes can be disposed side by side along the axial directions of both of the first rotating body and the second rotating body, between the outer periphery portion of the first rotating body and the inner periphery portion of the second rotating body. Therefore, a radial direction enlargement of the first rotating body and the second rotating body due to space for disposing the friction springs may be restrained. Hence, the overload release mechanism may be reduced in size.

A webbing take-up device of a fourth aspect is the webbing take-up device of any of the first to third aspects in which at least one protruding portion is provided at the other of the first rotating body or the second rotating body, the protruding portion protruding in a radial direction of the other of the first rotating body or the second rotating body and being disposable between one end portion(s) in a circumferential direction of the friction spring(s) and the other end portion(s) in the circumferential direction of the friction spring(s).

In the webbing take-up device of the fourth aspect, relative rotation of the friction spring with respect to the other of the first rotating body or the second rotating body is impeded by the protruding portion disposed between the circumferential direction one end portion and the circumferential direction other end portion of the friction spring abutting against the circumferential direction one end portion or the circumferential direction other end portion of the friction spring. Furthermore, in a case where the protruding portion is plurally provided, the plural protruding portions may be assigned one-to-one to the plural friction springs. Hence, a load inputted to the other of the first rotating body or the second rotating body from the friction springs during the relative rotation can be distributed between the plural protruding portions.

A webbing take-up device of a fifth aspect is the webbing take-up device of any of the first to fourth aspects in which each of the friction springs is formed from a linear spring member.

In the webbing take-up device of the fifth aspect, because the annular friction spring is formed from linear spring member, a space for disposing the plural friction springs may be kept small when the plural friction springs are disposed between the first rotating body and the second rotating body side by side along the axial direction thereof.

The spring member of the fifth aspect is not limited to a member with a circular cross-section (a wire-form member); the member with cross-section in square shape and the like may be used. If the cross-section of a spring member is a square shape, more cross-sectional area may be assured than with circular cross-section. Therefore, a torque generated between the one of the first rotating body or second rotating body and the friction spring may be more easily assured. Moreover, because a contact area between the one of the first rotating body or second rotating body and the friction spring is larger, surface pressure between the two is reduced and resistance to abrasion is improved.

In the above aspects, it is possible that relative rotation with respect to the other of the first rotating body or the second rotating body is prevented by the one end portion in the circumferential direction of the friction spring or the other end portion in the circumferential direction of the friction spring abutting against the at least one protruding portion.

As described above, in a webbing take-up device relating to the present invention, the overload release mechanism may be reduced in size and the operation torque of the overload release mechanism may be easily adjusted.

DETAILED DESCRIPTION OF THE INVENTION

First Exemplary Embodiment

Herebelow, a webbing take-up device10relating to a first exemplary embodiment of the present invention is described with reference toFIG. 1toFIG. 4.

As illustrated inFIG. 1, the webbing take-up device10includes a frame12that constitutes a support member. The frame12includes a plate-form rear plate14. The rear plate14is fixed to a vehicle body in the vicinity of, for example, a lower end portion of a center pillar of the vehicle, by unillustrated fastening members such as bolts or the like. Thus, this webbing take-up device10is attached to the vehicle body. A pair of leg plates16and18, which oppose one another substantially in a vehicle front and rear direction, are extended in parallel from two width direction ends of the rear plate14. A take-up spool20, which is formed in a substantially circular tube shape, is disposed between the leg plates16and18.

The axial direction of the take-up spool20is set to the direction of opposition of the leg plates16and18, and the take-up spool20is made rotatable around its own axis. A length direction base end portion of a long belt-form webbing22is anchored at the take-up spool20. By the take-up spool20rotating in a take-up direction (the direction of arrow A inFIG. 1), which is one way around the axis thereof, the webbing22is taken up from the base end side thereof onto an outer periphery portion of the take-up spool20in layers, and is stowed. When the webbing22is pulled from a distal end side thereof, the webbing22that has been taken up onto the take-up spool20is unwound. In accordance therewith, the take-up spool20rotates in an unwinding (pull-out) direction which is opposite to the take-up direction (the direction of arrow B inFIG. 1).

An unillustrated torsion shaft is disposed inside the take-up spool20, coaxially with the take-up spool20. An axial direction one end portion of the torsion shaft (the end portion at the side of the leg plate18) is coupled to the take-up spool20to be relatively non-rotatable, and the axial direction other end side passes through a through-hole formed in the leg plate16and protrudes to one side of the leg plate16(the opposite side of the leg plate16from the side at which the take-up spool20is disposed).

A sensor cover24made of resin is attached to the one side of the leg plate16. The sensor cover24is formed in a box shape that is open to the leg plate16side thereof. The axial direction other end side of the torsion shaft enters into the interior of the sensor cover24, and is turnably supported at an unillustrated bearing portion provided in the sensor cover24. A widely known locking mechanism, which is not illustrated, is accommodated in the interior of the sensor cover24. This locking mechanism restricts rotation of the torsion shaft in the unwinding direction during a sharp deceleration of the vehicle or the like.

A pretensioner mechanism26is also provided at the one side of the leg plate16. This pretensioner mechanism26includes a cylinder28, which is fixed to the leg plate16. A gas generator30is accommodated at a lower end portion of the cylinder28. When an unillustrated ignition device operates, this gas generator30produces high-pressure gas into the cylinder28. An unillustrated piston is accommodated in the inside of the cylinder28. When the gas is produced into the cylinder28, this piston protrudes from the cylinder28and forcibly turns the torsion shaft in the take-up direction.

A clutch housing32that constitutes a support member is attached to the other side of the leg plate18(the opposite side thereof from the side at which the take-up spool20is disposed). The clutch housing32is formed in a box shape that is open toward the opposite side thereof from the side at which the leg plate18is disposed, and the opening portion is closed off by a cover34. A circular through-hole36is formed in a side wall portion32A of the clutch housing32. This through-hole36is disposed to be concentric with the take-up spool20, and an adapter38is disposed at the inside of the through-hole36. This adapter38is formed in a hexagonal rod shape. The adapter38passes through a through-hole formed in the leg plate18, and is fixed to the axial direction one end portion of the torsion shaft, coaxially therewith. Consequently, the adapter38rotates integrally with the torsion shaft and the take-up spool20.

A circular rod-shaped shaft portion38A is coaxially and integrally provided at this adapter38. The shaft portion38A protrudes to the opposite side of the adapter38from the side thereof at which the take-up spool20is disposed. This shaft portion38A passes through a through-hole34A formed in the cover34and protrudes to the other side of the cover34(the opposite side of the cover34from the side at which the clutch housing32is disposed).

A spring cover40made of resin is provided at the other side of the cover34. This spring cover40is formed substantially in the shape of a circular tube with a floor, with the cover34side thereof being open. The spring cover40is attached to the leg plate18via the clutch housing32. The shaft portion38A of the adapter38is inserted into the interior of the spring cover40, and the shaft portion38A is turnably supported by an unillustrated bearing portion provided in the spring cover40.

An unillustrated spiral spring is accommodated in the interior of the spring cover40. A spiral direction outer side end portion of this spiral spring is anchored at the spring cover40, and a spiral direction inner side end portion is anchored at the shaft portion38A. This spiral spring urges the take-up spool20in the take-up direction, via the adapter38and the torsion shaft.

A clutch42is accommodated in the interior of the above-mentioned clutch housing32. The clutch42includes a gear wheel44. This gear wheel44is formed in the shape of a circular tube with a floor, with a short axial direction dimension and the other side thereof (the cover34side) being open. The opening portion of the gear wheel44is closed off by a circular disc-form cover46. Outer teeth are formed at an outer periphery portion of the gear wheel44. These outer teeth correspond with a gear80, which is mentioned below.

A substantially circular tube-shaped ratchet48is disposed at the inside of the gear wheel44to be coaxial with the gear wheel44. An axial direction one end portion of the ratchet48is axially supported to be rotatable at a circular hole formed in the gear wheel44, and an axial direction other end portion is axially supported to be rotatable at a circular hole formed in the cover46. Thus, the ratchet48is made relatively rotatable with respect to the gear wheel44and the cover46.

A fitting hole50with a hexagonal cross-section is formed in an axial center portion of the ratchet48. The adapter38fits into this fitting hole50. Thus, the ratchet48and the take-up spool20are relatively non-rotatably coupled, and the gear wheel44and the cover46are supported at the adapter38via the ratchet48. Plural ratchet teeth are formed with a constant pitch on an outer periphery portion of the ratchet48.

A pawl that swings due to, for example, centrifugal force, is accommodated at a radial direction outer side of the ratchet48. This pawl is supported at the gear wheel44, and meshes with the ratchet teeth of the ratchet48when the gear wheel44turns in the take-up direction. Thus, the gear wheel44and the ratchet48are mechanically coupled, and the clutch42is in a coupled state. This pawl disengages the state of meshing with the ratchet48when the gear wheel44turns in the unwinding direction. Thus, the state of coupling of the gear wheel44and the ratchet48is released, and the clutch42is in a disengaged state.

A speed reduction (deceleration) gear train52is accommodated at the inside of the above-mentioned clutch housing32. The speed reduction gear train52includes a spur gear54. The gear54is accommodated inside the clutch housing32in a state in which the axial direction thereof is aligned with the axial direction of the take-up spool20.

The gear54is fixed to an output shaft58of a motor56to which the clutch housing32is attached. A spur gear60with a larger diameter than the gear54is provided to sideward in a rotation radius direction of the gear54. A support shaft62is formed at the clutch housing32to correspond with the gear60. An axial direction of the support shaft62is aligned with the axial direction of the take-up spool20, and the gear60is rotatably supported at the support shaft62in a state of meshing with the gear54.

A spur gear64with a smaller diameter than the gear60is formed, coaxially and integrally with the gear60, to sideward in the axial direction of the gear60. A large diameter gear66(the second rotating body) with a larger diameter than the gear64is provided to sideward in the rotation radius direction of the gear64. This large diameter gear66structures an overload release mechanism65(a torque limiter mechanism).

As illustrated inFIG. 2andFIG. 3, the large diameter gear66includes a main body portion66A, which is formed in the shape of a circular tube with a floor, having a floor wall at the other side (the cover34side) thereof. The main body portion66A is disposed in a state in which an opening portion at the one side thereof opposes the side wall portion32A of the clutch housing32. A circular tube-shaped bearing portion66B is provided at the inside of the main body portion66A. The bearing portion66B protrudes from the floor wall of the main body portion66A toward the one side (the opening side) of the main body portion66A, and is provided coaxially and integrally with the main body portion66A. A support axis70, which is provided at the clutch housing32, is inserted into the inside of the bearing portion66B. An axial direction of the support axis70is aligned with the axial direction of the take-up spool20. Thus, the large diameter gear66is rotatably supported by the support axis70in a state in which spur gear outer teeth formed at the outer periphery portion of the main body portion66A mesh with the gear64. Thus, the large diameter gear66rotates interlockingly with the motor56.

A small diameter gear72(the first rotating body) is disposed at the one side of the large diameter gear66. This small diameter gear72includes a tubular portion72A formed in a circular tube shape. The bearing portion66B of the large diameter gear66is rotatably fitted into the inside of the tubular portion72A. Thus, the small diameter gear72is supported to be coaxial with and relatively rotatable with respect to the large diameter gear66.

A flange-form collar portion72B is coaxially and integrally provided at the one side of the tubular portion72A. The opening of the main body portion66A is closed off by this collar portion72B. A gear portion72C, which is formed with a smaller diameter than the large diameter gear66, is coaxially and integrally provided at the one side of the collar portion72B. The gear portion72C protrudes to outside (the one side) of the main body portion66A, and spur gear outer teeth are formed at an outer periphery portion thereof.

The spur gear80(seeFIG. 1), with a larger diameter than the gear portion72C, is provided to sideward in a rotation radius direction of the gear portion72C. A support shaft78is formed at the clutch housing32to correspond with the gear80. The axial direction of the support shaft78is aligned with (along) the axial direction of the take-up spool20. Thus, the gear80is rotatably supported at the support shaft78in a state of meshing with the gear portion72C. An unillustrated spur gear is coaxially and integrally formed at the other side of the gear80. This gear is meshed with the gear wheel44of the clutch42mentioned before. Thus, the small diameter gear72is turned interlockingly with the gear wheel44, and the small diameter gear72is turned interlockingly with the take-up spool20in a state of coupling with the clutch42.

An outer periphery face of the tubular portion72A and an inner periphery face of the main body portion66A oppose one another in the radial direction of the two portions, and an annular gap74is formed between the two portions. A plural number (in this case, two) of friction springs76are concentrically disposed in this gap74. The friction springs76are coil springs formed by curving or bending wire-form (linear) spring members into loops (helical forms). The friction springs76are disposed side by side along the axial direction of the large diameter gear66and the small diameter gear72. In this first exemplary embodiment, numbers of windings of the friction springs76are two windings.

The friction springs76are formed with an inner diameter dimension of the friction springs76when in a free state being smaller than an outer diameter dimension of the tubular portion72A. The friction springs76are mounted onto the outer periphery face of the tubular portion72A in an increased-diameter state. Consequently, the friction springs76are retained at the small diameter gear72by friction force generated between the friction springs76and the tubular portion72A, and relative rotation of the friction springs76with respect to the small diameter gear72is suppressed.

As illustrated inFIG. 4, a protruding portion66C that protrudes to the radial direction inner side is provided at the inner periphery portion of the main body portion66A. This protruding portion66C is disposed between a circumferential direction one end portion76A and a circumferential direction other end portion76B of each friction spring76. Consequently, relative rotation of each friction spring76with respect to the large diameter gear66is impeded by the circumferential direction one end portion76A or circumferential direction other end portion76B abutting against the protruding portion66C.

In the overload release mechanism65with the structure described above, when the large diameter gear66turns, rotary force of the large diameter gear66is transmitted through the friction springs76to the small diameter gear72, and the small diameter gear72rotates to follow the large diameter gear66. However, if a relative rotary force that acts between the large diameter gear66and the small diameter gear72exceeds a maximum static friction force that acts between the friction springs76and the tubular portion72A, then the tubular portion72A slides against the friction springs76, and the small diameter gear72relatively rotates with respect to the friction springs76and the large diameter gear66.

In this first exemplary embodiment, a maximum of ten of the friction springs76may be disposed in the gap74between the large diameter gear66and the small diameter gear72. A maximum of five of the friction springs76may be mounted onto the outer periphery face of the tubular portion72A. Thus, by changing the number of the friction springs76that are used, the operation torque of the overload release mechanism65(the torque required for relatively turning the large diameter gear66and the small diameter gear72, which is hereinafter simply referred to as the operation torque) can be adjusted stepwise.

Specifically, in this first exemplary embodiment, the friction springs76are constituted such that an operation torque of 1 N·m is generated by each one thereof. Thus, the operation torque is increased/reduced in steps of 1 N·m when the number of the friction springs76being used is increased/reduced by one. For example, if one friction spring76is mounted on the outer periphery face of the tubular portion72A, the operation torque is 1 N·m, and if four friction springs76are mounted on the outer periphery face of the tubular portion72A, the operation torque is 4 N·m.

In this first exemplary embodiment, the number of windings of each friction spring76is two. However, the number of windings of friction spring may be changed in other exemplary embodiments. For example, a constitution is possible in which a number of windings of friction springs is set to three and an operation torque of 1 N·m is produced by each friction spring. In this case, if two 3-winding friction springs are used, an operation torque of 2 N·m is produced. Further, constitutions are possible in which plural friction springs with different numbers of windings are mixed together, and the constitutions of the friction springs may be suitably changed.

Next, operation of the present first exemplary embodiment is described.

In the webbing take-up device10, when a control unit such as an ECU (electronic control unit) or the like (not illustrated) determines that a distance to an obstacle forward of the vehicle in which this webbing take-up device10is installed is less than a certain value, on the basis of detection results from a forward monitoring unit such as, for example, a radar ranging device, an infrared ranging device or the like (not illustrated), the control unit drives the motor56to forward-turn.

When the output shaft58is forward-turned by the forward-turning driving force of the motor56, the forward-turning of the output shaft58is transmitted through the gears54,60and64to the large diameter gear66of the overload release mechanism65, and the large diameter gear66turns one way around the axis (the direction of arrow C inFIG. 2toFIG. 4). As a result, the protruding portion66C of the large diameter gear66abuts against the circumferential direction one end portions76A of the plural friction springs76, and the plural friction springs76turn the one way around the axis to follow the large diameter gear66. Further, the small diameter gear72at which the plural friction springs76are mounted on the tubular portion72A turns the one way around the axis to follow the friction springs76and the large diameter gear66.

The turning of the small diameter gear72is transmitted through the gear80and the unillustrated gear to the gear wheel44of the clutch42, and the gear wheel44is turned in the take-up direction (the direction of arrow A inFIG. 1). When the gear wheel44turns in the take-up direction, the unillustrated pawl attached to the gear wheel44meshes with the ratchet teeth of the ratchet48, and the gear wheel44and the ratchet48are mechanically coupled. As a result, the ratchet48is turned in the take-up direction together with the gear wheel44.

The ratchet48is coupled to the take-up spool20via the adapter38and the torsion shaft. Therefore, the take-up spool20is turned in the take-up direction by the ratchet48turning in the take-up direction, and the webbing22is taken up onto the take-up spool20, from the length direction base end side thereof. As a result, a slight looseness in the webbing22that is applied to the body of an occupant, referred to as “slack”, is eliminated and restraint of the occupant by the webbing22is improved.

If an excessive tension (unwinding) force acts on the webbing22, for example, during the taking up of the webbing22as described above, a rotary force in the direction of the unwinding is inputted to the gear wheel44that is coupled to the take-up spool20, and a rotary force the other way around the axis (the direction of arrow D inFIG. 2toFIG. 4) is inputted to the small diameter gear72. If this rotary force is larger than the maximum static friction force that acts between the plural friction springs76and the tubular portion72A, the tubular portion72A slides (rubs with friction) against the plural friction springs76. Therefore, relative rotation of the small diameter gear72with respect to the large diameter gear66is allowed, and structural members that are at the motor56side relative to the large diameter gear66are cut off from the rotation of the take-up spool20. Thus, the take-up spool20can turn in the unwinding direction independently of the motor56.

In the overload release mechanism65of the present webbing take-up device10, the plural friction springs76formed in annular shapes are disposed in the gap74between the large diameter gear66and the small diameter gear72, side by side along the axial direction. Therefore, a radial direction enlargement of the large diameter gear66and small diameter gear72according to a space for disposing the friction springs76may be restrained. Thus, because the overload release mechanism65is reduced in size, a degree of freedom of layout when the overload release mechanism65is to be disposed at the speed reduction gear train52is improved.

In addition, the operation torque of the overload release mechanism65can be adjusted by changing the number of the friction springs76to be used in accordance with requirements. Therefore, adjustment of the operation torque of the overload release mechanism65when the layout is changed as mentioned above is simple.

In this first exemplary embodiment, the operation torque of the overload release mechanism65is provided by a friction force that acts between the plural friction springs76and the tubular portion72A (the small diameter gear72). Thus, during operation of the overload release mechanism65, the tubular portion72A of the small diameter gear72slides smoothly with respect to the plural friction springs76. Therefore, operation noise and vibrations and the like are suppressed.

In this first exemplary embodiment, each friction spring76is formed by a wire-form (linear) spring member being curved into an annular shape. Therefore, a space for disposing the friction springs76when the plural friction springs76are disposed side by side along the axial direction between the large diameter gear66and the small diameter gear72may be kept small. Moreover, assembly characteristics when the friction springs76are being assembled to the tubular portion72A of the small diameter gear72are excellent.

In this first exemplary embodiment, when the gear wheel44turns in the take-up direction, rotary force of the large diameter gear66is inputted to the circumferential direction one end portion76A of each friction spring76, and when the gear wheel44turns in the unwinding direction, the rotary force of the large diameter gear66is inputted to the circumferential direction other end portion76B of the friction spring76. Thus, the two circumferential direction end portions of the friction spring76are used as rotary force input portions, and consequently endurance of the friction spring76may be excellently assured.

The above-described first exemplary embodiment has a structure in which frictional force is generated between the outer periphery face of the tubular portion72A of the small diameter gear72and the friction springs76. However, the present invention is not to be limited thus. A structure is possible in which frictional force is generated between the inner periphery face of the main body portion66A of the large diameter gear66and friction springs. In this case, the protruding portion66C is omitted and a protrusion or the like is needed to be provided at the small diameter gear72such that the friction springs do not relatively rotate with respect to the small diameter gear72. (For example, a protruding portion166C (seeFIG. 9) such as like the protruding portion66C may be provided at the outer periphery face of the tubular portion72A of the small diameter gear72inFIG. 2.)

In this case, the friction springs76are formed with an outer diameter dimension of the friction springs76when in a free state being larger than a diameter dimension of the inner periphery face of the main body portion66A of the large diameter gear66. The friction springs76are mounted onto the inner periphery face of the main body portion66A of the large diameter gear66in a decreased-diameter state.

The above-described first exemplary embodiment has a structure in which the large diameter gear66that serves as the second rotating body is connected to the gear64at the motor56side and the small diameter gear72that serves as the first rotating body meshes with the gear80at the take-up spool20side. However the present invention is not to be limited thus. A structure is possible in which the first rotating body is connected to a rotation transmission member at the motor side and the second rotating body is connected to a rotation transmission member at the take-up spool side. The same applies to the other exemplary embodiments of the present invention that are described below.

Next, other exemplary embodiments of the present invention are described. Therein, structures and operations that are basically the same as in the first exemplary embodiment are assigned the same reference numerals as in the first exemplary embodiment and descriptions thereof are not given.

Second Exemplary Embodiment

FIG. 5illustrates structure of an overload release mechanism82, which is a structural member of a webbing take-up device relating to a second exemplary embodiment of the present invention, in an exploded perspective diagram.FIG. 6illustrates the overload release mechanism82in a sectional diagram.

This overload release mechanism82has basically the same structure as the overload release mechanism65relating to the first exemplary embodiment. However, in this overload release mechanism82, the two friction springs76are mounted onto the tubular portion72A of the small diameter gear72in a state in which the respective circumferential direction one end portions76A and circumferential direction other end portions76B are arranged at opposite sides from one another. The protruding portion66C provided at the large diameter gear66is disposed between the circumferential direction one end portion76A and circumferential direction other end portion76B of one of the friction springs76, and a protruding portion66D, provided at the large diameter gear66, is disposed between the circumferential direction one end portion76A and circumferential direction other end portion76B of the other of the friction springs76. This protruding portion66D has the same structure as the protruding portion66C, and the two protruding portions are disposed at mutually opposite sides of the large diameter gear66in the circumferential direction (sides that are opposite by 180°). That is, in this exemplary embodiment, a plural number (in this case, two) of the protruding portions66C and66D are assigned, one-to-one, to the plural number (in this case, two) of the friction springs76. In the present exemplary embodiment, structures apart from the structure described above have the same constitutions as in the first exemplary embodiment.

In this exemplary embodiment, when the small diameter gear72relatively rotates with respect to the large diameter gear66, the circumferential direction one end portion76A or the circumferential direction other end portion76B of the one friction spring76abuts against the protruding portion66C of the large diameter gear66, and the circumferential direction one end portion76A or the circumferential direction other end portion76B of the other friction spring76abuts against the protruding portion66D of the large diameter gear66. Therefore, a load (stress) inputted to the large diameter gear66from the two friction springs76is distributed between the protruding portion66C and the protruding portion66D. Hence, endurance of the large diameter gear66may be improved.

For the second exemplary embodiment described above, a case with two of the friction springs and of the protruding portions has been described. However, this is not to be limiting, and the numbers of friction springs and protruding portions may be suitably varied. How the plural protruding portions are assigned to the plural friction springs may be arbitrarily varied.

Third Exemplary Embodiment

FIG. 7illustrates partial structure of an overload release mechanism84, which is a structural member of a webbing take-up device relating to a third exemplary embodiment of the present invention, in a side view. This overload release mechanism84has basically the same structure as the overload release mechanism65relating to the first exemplary embodiment. However, in the overload release mechanism84, two (a pair of) friction springs76and86(coil springs) that are mounted on the tubular portion72A of the small diameter gear72have helix orientations thereof set to mutually opposite orientations.

The one friction spring76has the circumferential direction one end portion76A disposed at one end side of the protruding portion66C of the large diameter gear66(not illustrated inFIG. 7) and the circumferential direction other end portion76B disposed at the other end side of the protruding portion66C. The other friction spring86has a circumferential direction one end portion86A disposed at the one end side of the protruding portion66C of the large diameter gear66and a circumferential direction other end portion86B disposed in the vicinity of the circumferential direction other end portion76B of the one friction spring76and at the other end side of the protruding portion66C. In the present exemplary embodiment, structures apart from the structures described above have the same constitutions as in the first exemplary embodiment.

In this exemplary embodiment, when the small diameter gear72relatively turns the one way around the axis with respect to the large diameter gear66, the circumferential direction one end portions76A and86A of the friction springs76and86abut against the one end side of the protruding portion66C, and relative rotation of the friction springs76and86with respect to the large diameter gear66is impeded. If the rotary force that acts between the large diameter gear66and the small diameter gear72is larger than the maximum static friction force that acts between the friction springs76and86and the tubular portion72A, then the tubular portion72A slides (rubs with friction) against the friction springs76and86, and relative rotation of the small diameter gear72with respect to the large diameter gear66is allowed. At this time, forces in directions to approach one another act on the friction springs76and86due to the friction thereof against the outer periphery face of the tubular portion72A. Therefore, the friction springs76and86may be closely contacted and forces acting on the two counteract. Therefore, mispositioning of the friction springs76and86in the axial direction relative to the small diameter gear72may be prevented.

That is, as illustrated inFIG. 8A, if the small diameter gear72rotates relative to the friction spring76in a case where the helical friction spring76(coil spring) is mounted on the tubular portion72A of the small diameter gear72, the friction spring76is mispositioned in the axial direction of the small diameter gear72by a force component of the friction force that acts between the small diameter gear72and the friction spring76(seeFIG. 8B). Thus, in the present exemplary embodiment, the pair of friction springs76and86whose helix orientations are set to mutually opposite orientations are closely contacted and the mispositioning actions counteract, and the above-mentioned problem may be solved.

In the exemplary embodiments described above, it has been described that the friction springs76and86are formed of wire-form spring members (with circular cross-sections). However, the present invention is not to be limited thus. The cross-sectional shapes of the friction springs76and86may be suitably changed.

Hereabove, exemplary embodiments have been offered as examples to describe the present invention, but the present invention is not to be limited by the above exemplary embodiments; numerous modifications may be embodied within a technical scope not departing from the spirit of the invention. Obviously, rights to the present invention are not to be limited to the above exemplary embodiments.