A webbing retractor which, by causing relative rotation between a prime mover rotating body and a rotating disc, connects the prime mover rotating body and a driven shaft which is connected to a take-up shaft of a webbing belt. A planet gear is pivotally supported at a plate having a braking piece and meshes with a sun gear. The plate is supported so as to be swingable around the sun gear. When the sun gear is driven to rotate at greater than a predetermined speed, the planet gear begins to circle around the sun gear against urging force of a spring attached to the plate, and makes the plate rotate such that the braking piece slidingly contacts the friction ring. Due to this braking, the rotating disc connected to the friction ring rotates relative to the prime mover rotating body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese patent Application No. 2002-202970, 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 retractor which structures a seat belt device for restraining, by an elongated, strip-shaped webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle or the like.

2. Description of the Related Art

A seat belt device which restrains, by an elongated, strip-shaped webbing belt, the body of a vehicle occupant who is seated in a seat of a vehicle, is equipped with a webbing retractor which is fixed to the vehicle body at the side of the seat. The webbing retractor has a spool (take-up shaft) whose axial direction runs, for example, substantially along the longitudinal direction of the vehicle. The proximal end side, in the longitudinal direction, of the webbing belt is anchored at the spool. The spool can take the webbing belt up in the form of a roll around the outer peripheral portion of the spool. When the seat belt device is not being used, the webbing belt can be accommodated in a state of being taken-up on the outer peripheral portion of the spool.

An urging member, such as a spiral spring or the like which urges the spool in a take-up direction in which the spool takes up the webbing belt, is provided at the webbing retractor. Due to the urging force of this urging member, the webbing belt is taken up and accommodated. In the state in which the webbing belt is applied to the body of a vehicle occupant, slack or the like of the webbing belt is eliminated by the urging force of the urging member.

On the other hand, a mechanism has been conceived in which, by taking-up a predetermined amount of the webbing belt onto the take-up shaft in a state of rapid deceleration of the vehicle or the like, the slight looseness known as “slack” or the like can be eliminated, and the force for restraining the body of the vehicle occupant by the webbing belt is increased such that the body of the vehicle occupant is held even more reliably. In such a mechanism, generally, the state of a rapid deceleration of the vehicle is sensed by an acceleration sensor, and the take-up shaft is forcibly rotated in the take-up direction on the basis of an electric signal from the acceleration sensor.

In contrast, a structure has been thought of in which the distance to another vehicle or an obstacle which is ahead is detected by a distance sensor or the like. When the distance to the vehicle or the obstacle which is ahead is less than a given value, a motor is operated, and the take-up shaft is rotated in the take-up direction by the torque of the motor.

Even in such a structure in which the take-up shaft is rotated in the take-up direction by the torque of a motor when the distance to a vehicle or an obstacle which is ahead is less than a given value, usually, the spool is rotated in the take-up direction by the urging force of the aforementioned urging member such as a spiral spring or the like. When the webbing belt is pulled out, the spool is rotated against the urging force of the urging member such as a spiral spring or the like. Thus, a clutch is provided between the motor and the spool so that the rotation of the spool at the time of usual taking-up and pulling-out of the webbing belt is not transmitted to the output shaft of the motor. Only in cases in which the motor is operated is the output shaft of the motor mechanically connected to the spool.

As a clutch mechanism used in such a structure, there is a structure in which an inertial mass body called an inertial plate is provided so as to be freely rotatable around the axis of the spool. In such a clutch mechanism, the inertial plate is provided so as to be able to rotate relative to both a driven shaft which is integral with the spool and a rotating body of a prime mover which rotates by receiving the rotation of the output shaft of the motor.

However, the other end of an urging member, such as a compression coil spring or the like whose one end is directly or indirectly engaged with the rotating body of the prime mover, is engaged with the inertial plate. When the rotating body of the prime mover rotates due to the torque of the motor, and, accompanying this rotation, the compression coil spring attempts to rotate, the urging force of the compression coil spring rotates the inertial plate.

However, the inertial plate attempts to maintain a stopped state by the inertia thereof. Thus, for example, when the rotating body of the prime mover suddenly rotates, relative rotation arises between the rotating body of the prime mover and the inertial plate which is attempting to maintain the stopped state by inertia. Interlockingly with this relative rotation, a connecting member, such as a pawl or the like which rotates together with the rotating body of the prime mover, is moved, and the connecting member is made to engage with the driven shaft. The torque of the motor is transmitted to the driven shaft, and consequently, to the spool.

However, in a structure using such an inertial plate, there is the condition that the rotating body of the prime mover must be rotated suddenly by the torque of the motor.

In order to satisfy such a condition, the rotating body of the prime mover and the output shaft of the motor must be directly connected without the torque of the motor being decelerated by a reduction gear or the like.

However, in the case of such a structure, if the clutch mechanism does not have a reduction mechanism, the rotation of the rotating body of the prime mover is transmitted to the driven shaft as well without being decelerated. Thus, the taking-up and the like of the webbing belt are carried out excessively rapidly.

SUMMARY OF THE INVENTION

In view of the aforementioned, an object of the present invention is to provide a webbing retractor which generates relative rotation between a prime mover rotating body and a rotating body such as an inertial plate or the like so as to reliably transmit rotation of the prime mover rotating body to a driven shaft, such that taking-up of a webbing belt by the driving force of a driving mechanism can be carried out.

A first aspect of the present invention is a webbing retractor for an elongated, strip-shaped webbing belt used for application to a body of a vehicle occupant, the webbing retractor comprising: a take-up shaft for taking the webbing belt up around itself, which take-up shaft is rotatably held, and to which one end of the webbing belt is anchored; a driven shaft connected to the take-up shaft; a prime mover rotating body rotatably supported relative to and coaxially with the driven shaft; a rotating member supported coaxially with both the prime mover rotating body and the driven shaft, and rotatable relative to both the prime mover rotating body and the driven shaft; an urging member, attached to the prime mover rotating body, for urging the rotating member in a direction of rotation of the prime mover rotating body when the prime mover rotating body is rotated; connecting members for connecting the prime mover rotating body and the driven shaft, by interlocking with relative rotation of the rotating member with respect to the prime mover rotating body, so as to transmit rotation of the prime mover rotating body to the driven shaft; a driving mechanism, including a drive source, for driving rotation of the prime mover rotating body in a predetermined direction; and a braking mechanism for braking rotation of the rotating member such that relative rotation of the rotating member with respect to the prime mover rotating body arises.

A second aspect of the present invention is a webbing retractor for a webbing belt, the webbing retractor having a take-up shaft, and by rotating the take-up shaft in one direction, the webbing retractor takes-up and accommodates, on the take-up shaft and from a proximal end side, a webbing belt which is elongated and strip-shaped and which is applied to a body of a vehicle occupant so as to restrain the body and which has a distal end and a proximal end, and due to the webbing belt being pulled toward a distal end side, the webbing retractor rotates the take-up shaft in another direction, and the webbing belt, which is taken-up on the take-up shaft, is pulled out, the webbing retractor comprising: a driven shaft connected to the take-up shaft coaxially and integrally; a prime mover rotating body which is substantially ring shaped and which is provided coaxially with the driven shaft so as to be able to rotate relative to the driven shaft; a rotating member which is able to rotate relative to and coaxially with both the prime mover rotating body and the driven shaft; an urging member which is attached to the prime mover rotating body and rotates together with the prime mover rotating body, and which urges the rotating member in a direction of rotation of the prime mover rotating body; connecting members which, interlockingly with relative rotation of the rotating member with respect to the prime mover rotating body, mechanically connect the prime mover rotating body and the driven shaft, and transmit rotation of the prime mover rotating body to the driven shaft; a driving mechanism having an output shaft which is connected one of directly and indirectly to the prime mover rotating body, and the driving mechanism rotates the output shaft by driving force of the driving mechanism; and a braking mechanism which, interlockingly with rotation of the output shaft, applies frictional force to the rotating member and impedes rotation of the rotating member.

The webbing retractor of the above-described aspect may further comprise a rotation transmitting mechanism which is provided between the output shaft and the prime mover rotating body, and which receives rotation from the output shaft and rotates, and which transmits rotation of the rotation transmitting mechanism to the prime mover rotating body.

In the webbing retractor having the above-described structure, the webbing belt, which is taken up onto the take-up shaft from the proximal end side thereof, is pulled from the distal end side thereof. The webbing belt is pulled-out while the take-up shaft is rotated in the pull-out direction, which is one direction around the axis thereof. By applying the pulled-out webbing belt to the body of a vehicle occupant, the body of the vehicle occupant is restrained by the webbing belt.

Further, when the state in which the pulled-out webbing belt restrains the body of the vehicle occupant is cancelled, and further, the take-up shaft is rotated in the take-up direction which is opposite to the aforementioned pull-out direction, the webbing belt is taken-up and accommodated in the form of a roll on the outer peripheral portion of the take-up shaft.

On the other hand, in the present webbing retractor, when the driving mechanism drives and the output shaft of the driving mechanism rotates and the rotation of the output shaft is transmitted to the prime mover rotating body and the prime mover rotating body, which is connected directly or indirectly to the output shaft, rotates. When the prime mover rotating body rotates, the urging member, which is attached to the prime mover rotating body, rotates in the direction of rotation of the prime mover rotating body.

The urging member urges the rotating member in the direction of rotation of the prime mover rotating body. Accordingly, basically, the rotating member can rotate coaxially with and relative to the prime mover rotating body and the driven shaft. However, when the urging member rotates accompanying the rotation of the prime mover rotating body, the urging member pushes the rotating member in the direction of rotation of the prime mover rotating body, and thereby attempts to rotate the rotating member in the direction of rotation of the prime mover rotating body.

Here, in the present webbing retractor, when the driving mechanism drives and the output shaft of the driving mechanism rotates, the braking mechanism operates, and the braking mechanism applies frictional force to the rotating member. This frictional force works to impede rotation of the rotating member. Thus, as described above, even if the urging member attempts to rotate the rotating member in the direction of rotation of the prime mover rotating body by the urging force of the urging member, the rotation of the rotating member is restricted by the frictional force which the braking mechanism applies to the rotating member. In this way, relative rotation arises between the prime mover rotating body and the rotating member.

When relative rotation arises between the prime mover rotating body and the rotating member, the connecting members mechanically connect the prime mover rotating body and the driven shaft. In this way, the rotation of the prime mover moving body is transmitted to the driven shaft, and the driven shaft, and accordingly, the take-up shaft, rotate. In this way, if the driven shaft rotates in the take-up direction for example, the webbing belt is taken up onto the take-up shaft by the driving force of the driving mechanism. If the driven shaft rotates in the pull-out direction, slack arises in the webbing belt which is wound on the take-up shaft, and the force by which the webbing belt restrains the body of the vehicle occupant decreases.

In this way, in the present webbing retractor, when the driving mechanism drives, relative rotation of the rotating member with respect to the prime mover rotating body can be reliably generated by the braking mechanism. In this way, the driving force (torque) of the driving mechanism can be reliably transmitted to the take-up shaft.

Further, in the webbing retractor of the above-described aspect, the braking mechanism may be structured so as to include a friction member which is substantially ring shaped and which is exposed to an exterior of the prime mover rotating body in a state in which the friction member is mechanically connected to the rotating member; and a braking member which is attached to one of the output shaft and the rotation transmitting member, and which, interlockingly with rotation of the one of the output shaft and the rotation transmitting member, moves so as to approach the friction member and slidingly contacts the friction member.

In the webbing retractor having the above-described structure, the friction member, which is exposed to the exterior of the prime mover rotating body, is mechanically connected to the rotating member. When the rotating member attempts to rotate, the friction member also attempts to rotate together therewith.

Here, when the driving mechanism drives and the output shaft rotates, the braking member, which is provided at the output shaft or is provided at the rotation transmitting mechanism disposed between the output shaft and the prime mover rotating body, moves so as to approach the friction member, interlockingly with the rotation of the output shaft or the rotating transmitting mechanism. In this way, the braking member slidingly contacts the friction member.

When the rotation of the friction member is restricted due to the frictional force which is applied from the braking member which slidingly contacts the friction member, rotation of the rotating member, to which the friction member is connected, is restricted indirectly. In this way, relative rotation arises between the prime mover rotating body and the rotating member.

Namely, in the present webbing retractor, in a way, braking force with respect to the rotating member, which is caused by the frictional force from the braking member, is applied indirectly to the rotating member via the friction member.

In the webbing retractor of the second aspect of the present invention, the braking mechanism can be structured so as to include a friction member which is provided at the exterior of the prime mover rotating body, and which is mechanically connected to the rotating member; a brake spring which is formed in a substantial ring shape in which a take-up direction side end portion and a pull-out direction side end portion around an axis of the driven shaft are apart from one another, and the brake spring has a spring property (elasticity), and an inner peripheral portion of the brake spring slidingly contacts the friction member; and a diameter forcibly reducing mechanism at which is anchored an end portion of the brake spring at one of the take-up direction side and the pull-out direction side, and which, interlockingly with rotation of the output shaft for rotating the take-up shaft in the other of the take-up direction and the pull-out direction, rotates the brake spring in the one direction with respect to the friction member, and reduces the diameter of the brake spring due to friction between the friction member and the brake spring.

In the webbing retractor having the above-described structure, the friction member, which is exposed at the exterior of the prime mover rotating body, is mechanically connected to the rotating member. When the rotating member attempts to rotate, the friction member also attempts to rotate together therewith.

The inner peripheral portion of the ring-shaped brake spring slidingly contacts the friction member. The end portion of the brake spring at one of the take-up direction side and the pull-out direction side is anchored at the diameter forcibly reducing mechanism. Here, in order to explain the present invention such that it can be understood more easily, explanation will be given with “the one” of the take-up direction and the pull-out direction being the “pull-out direction”, and “the other” being the “take-up direction”.

When, in order to rotate the take-up shaft in the take-up direction, the driving mechanism is operated and the output shaft rotates, interlockingly with the rotation of the output shaft, the diameter forcibly reducing mechanism makes the brake spring rotate in the pull-out direction relative to the friction member.

When relative rotation arises in this way, frictional force arises between the brake spring and the friction member. The frictional force works to impede rotation of the brake spring. Thus, in a case in which the pull-out direction side end portion is forcibly rotated in the pull-out direction with respect to the friction member, or in a case in which the pull-out direction side end portion of the brake spring does not attempt to rotate regardless of the fact that the take-up direction side end portion of the brake spring is rotated in the take-up direction due to the friction member attempting to rotate in the take-up direction, the brake spring reduces the gap which is formed between the pull-out direction side end portion and the take-up direction side end portion. The diameter of the entire brake spring is thereby reduced against the elasticity of the brake spring.

Due to the diameter of the brake spring being reduced, the brake spring tightens around the friction member. In this way, the frictional force between the friction member and the brake spring increases.

The frictional force, which has increased in this way, works to restrict rotation of the friction member in the take-up direction. Due to rotation of the friction member in the take-up direction being restricted by the frictional force, rotation in the take-up direction of the rotating member, to which the friction member is connected, is restricted. In this way, relative rotation arises between the prime mover rotating body and the rotating member.

The braking mechanism may be structured so as to include a lever. The end portion of the brake spring at one of the take-up direction side and the pull-out direction side is anchored at the distal end side of the lever. The proximal end side of the lever is indirectly connected to the driving mechanism. The lever may be rotated by the driving force of the driving mechanism, and may pull the brake spring toward the other of the take-up direction side and the pull-out direction side.

In the webbing retractor having the above-described structure, for example, when the prime mover rotating body rotates in the take-up direction (which is the other of the take-up direction and the pull-out direction) due to the driving force of the driving mechanism, and the rotating member thereby attempts to rotate in the take-up direction, accompanying this, the friction member connected to the rotating member attempts to rotate in the take-up direction. Moreover, the friction member attempts to rotate the brake spring in the take-up direction due to the friction between the friction member and the brake spring.

On the other hand, as described above, when the driving mechanism drives and the output shaft rotates, the lever rotates in the pull-out direction due to the rotation of the output shaft. Due to the rotation of the lever in the pull-out direction, the pull-out direction side end portion of the brake spring which is anchored at the distal end side of the lever, is pulled in the pull-out direction, and the brake spring attempts to rotate in the pull-out direction.

In this way, due to the brake spring and the friction member attempting to rotate in mutually opposite directions, the frictional force between the brake spring and the friction member suddenly increases. The frictional force, which has increased in this way, works to restrict rotation of the friction member in the take-up direction. Due to the rotation of the friction member in the take-up direction being restricted by this frictional force, the rotation in the take-up direction of the rotating member, to which the friction member is connected, is restricted. In this way, relative rotation arises between the prime mover rotating body and the rotating member.

Or, the webbing retractor may have a frame which directly or indirectly supports the take-up shaft, and the diameter forcibly reducing mechanism may be structured such that the one side end portion of the brake spring is anchored at the frame.

In the webbing retractor having the above-described structure, for example, when the prime mover rotating body rotates in the take-up direction (which is the other of the take-up direction and the pull-out direction) due to the driving force of the driving mechanism, and the rotating member thereby attempts to rotate in the take-up direction, accompanying this, the friction member connected to the rotating member attempts to rotate in the take-up direction. Moreover, the friction member attempts to rotate the brake spring in the take-up direction due to the friction between the friction member and the brake spring.

Here, in the present webbing retractor, the end portion of the brake spring at the pull-out direction (the one of the take-up direction and the pull-out direction) side is anchored at the frame which directly or indirectly supports the take-up shaft. Thus, even if the brake spring attempts to rotate in the take-up direction, the end portion of the brake spring at the pull-out direction side cannot rotate following this rotation.

Accordingly, due to the brake spring attempting to rotate in the take-up direction in the state in which the pull-out direction side end portion thereof is anchored, the gap formed between the pull-out direction side end portion and the take-up direction side end portion of the brake spring narrows. The diameter of the entire brake spring is thereby reduced in opposition to the elasticity of the brake spring.

Due to the diameter of the brake spring being reduced, the brake spring tightens around the friction member. In this way, the frictional force between the friction member and the brake spring increases.

The frictional force, which has increased in this way, works to restrict rotation of the friction member in the take-up direction. Due to rotation of the friction member in the take-up direction being restricted by this frictional force, rotation in the take-up direction of the rotating member, to which the friction member is connected, is restricted. In this way, relative rotation arises between the prime mover rotating body and the rotating member.

In this way, in the above-described webbing retractor, the frame can be included in the diameter forcibly reducing mechanism, and the brake spring can be anchored at the frame, and the rotating member can be made to rotate relative to the prime mover rotating body. Moreover, due to the frame being included in the diameter forcibly reducing mechanism, there is no need to provide a separate, special member for forming the diameter forcibly reducing mechanism, and the webbing retractor can be made compact and lightweight.

Note that, in the above description, for convenience of explanation, “the one” of the take-up direction and the pull-out direction was the “pull-out direction”, and “the other” was the “take-up direction”. However, the present invention is established even if, conversely, “the one” is the “take-up direction” and “the other” is the “pull-out direction”. In this case, the phrases of “pull-out direction” and “take-up direction” in the above explanation are merely reversed, and detailed description of such a case will therefore be omitted.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention may have the following features.

In the webbing retractor of one embodiment, the driven shaft is rotatably connected integrally with the take-up shaft. The urging member has one end and another end and is elastically deformable, and the one end is attached to the prime mover rotating body, and the other end is held at the rotating member so as to be able to push the rotating member. The urging member has a coil spring.

The driven shaft has a peripheral surface, and the connecting members are held at the prime mover rotating body so as to be able to approach and move away from the driven shaft, and when the prime mover rotating body is rotated, the connecting members contact the peripheral surface of the driven shaft due to the relative rotation, and connect the prime mover rotating body and the driven shaft. The following structure is possible: a plurality of teeth are formed at the peripheral surface of the driven shaft, and the connecting members have pawl shapes which can engage with any of the teeth, and at least one of the connecting members contacts the tooth of the driven shaft so as to engage with the tooth, and connects the prime mover rotating body and the driven shaft.

In the webbing retractor of another embodiment, the connecting members are roller-shaped, and due to the relative rotation, the connecting members are pressed by the peripheral surface of the driven shaft and connect the prime mover rotating body and the driven shaft, and rotation of the prime mover rotating body is thereby transmitted to the driven shaft.

In the webbing retractor of one embodiment, due to the braking mechanism applying frictional force to the rotating member, rotation of the rotating member is braked. The braking mechanism may brake the rotating member when the prime mover rotating body is driven to rotate at greater than a predetermined speed. The braking mechanism may connect such that power can be transmitted from the driving mechanism, i.e., motion of the braking mechanism for braking operation is transmitted from the driving mechanism. The braking mechanism may brake the rotating member interlockingly with driving and rotating of the prime mover rotating body by the driving mechanism.

In the webbing retractor of one embodiment, the rotating member has a friction member which is attached to the rotating member and rotates integrally with the rotating member, and the braking mechanism has a braking member which slidingly contacts the friction member, and the braking mechanism brakes due to the braking member slidingly contacting the friction member. The following structure is possible: the friction member is substantially ring shaped, and the braking member is substantially shaped as a ring having one end and another end, and the braking member is disposed so as to surround one portion of an outer peripheral surface of the friction member, and in a state in which the one end of the braking member is held at the outer peripheral surface of the friction member, the other end of the braking member is connected to the driving mechanism and is pulled in a direction of decreasing a diameter of the braking member when the driving mechanism operates.

The webbing retractor of another embodiment further comprises a frame which is fixed, and the friction member is substantially ring shaped, and the braking member is substantially shaped as a ring having one end and another end, and the braking member is disposed so as to surround one portion of an outer peripheral surface of the friction member, and in a state in which the one end of the braking member is held at the outer peripheral surface of the friction member, the other end of the braking member is anchored at the frame so as to be pulled in a direction of decreasing a diameter of the braking member when the friction member is rotated.

In the webbing retractor of one embodiment, the prime mover rotating body has an external gear which is ring shaped and has external teeth for connection to the driving mechanism such that the external gear can be driven and rotated; a base portion having a holding portion for holding the plurality of connecting members, the base portion being pivotally supported coaxially with the rotating member; and at least one torque limiter provided between the external gear and the base portion, so as to be able to transmit torque in a predetermined range to the base portion from the external gear.

The webbing retractor of one embodiment further comprises a control unit controlling operation of the driving mechanism, and when a rate of change in deceleration at a time when the vehicle decelerates is greater than or equal to a predetermined value, the control unit effects control so as to cause the driving mechanism to operate. Further, when a distance to an obstacle which is positioned ahead of the vehicle is less than a predetermined value, the control unit effects control so as to cause the driving mechanism to operate.

STRUCTURE OF FIRST EMBODIMENT

(Overall Structure of Webbing Retractor10)

A front sectional view showing the overall structure of a webbing retractor10relating to a first embodiment of the present invention is shown inFIG. 1. As shown inFIG. 1, the webbing retractor10has a frame12. The frame12has a back plate14which is substantially plate-shaped. The webbing retractor10is mounted to a vehicle body by the back plate14being fixed to the vehicle body by unillustrated fasteners such as bolts or the like. A pair of leg plates16,18extend parallel to one another from the transverse direction ends of the back plate14. A spool20, which serves as a take-up shaft and is manufactured by die casting or the like, is disposed rotatably between the leg plates16,18.

The spool20is structured by a spool main body22and a pair of flange portions24,26, and is formed in a drum-shape on the whole. The spool main body22is substantially hollow cylindrical. The pair of flanges24,26are formed in substantial disc shapes at the end portions of the spool main body22.

The proximal end portion of a webbing belt28, which is formed in the shape of an elongated strip, is fixed to the spool main body22between the flange portions24,26. When the spool20is rotated in one direction around the axis thereof, the webbing belt28is taken-up in the form of a roll on the outer peripheral portion of the spool main body22from the proximal end side of the webbing belt28. Further, if the webbing belt28is pulled from the distal end side thereof, the webbing belt28, which is taken-up on the outer peripheral portion of the spool main body22, is pulled-out. Accompanying this, the spool20rotates opposite to the direction of rotation at the time of taking-up the webbing belt28. (Hereinafter, for convenience of explanation, the direction of rotation at the time of taking-up the webbing belt28will be called the “take-up direction”, and is denoted by arrow A in the related drawings. The direction of rotation of the spool20at the time when the webbing belt28is pulled out will be called the “pull-out” direction for convenience of explanation, and is denoted by arrow B in the related drawings.)

The flange portion24one end side of the spool20, which is at the side opposite the flange portion26side of the spool20, passes substantially coaxially through a circular hole30, which is formed in the leg plate16, and projects to the exterior of the frame12. A case32is disposed at the outer side of the frame12at the leg plate16side. The case32is disposed so as to oppose the leg plate16along the axial direction of the spool20, and is fixed to the leg plate16. The case32is, on the whole, open toward the leg plate16side. The one end side of the spool20which passes through the circular hole30enters into the inner side of the case32, and is rotatably supported by the case32.

Moreover, a spiral spring34is disposed at the interior of the case32. The end portion, at the outer side in the direction of the spiral, of the spiral spring34is anchored on the case32. The end portion, at the inner side in the direction of the spiral, of the spiral spring34is anchored on the spool20. When the spool20is rotated in the pull-out direction from a neutral state in which no particular load is applied, urging force in the take-up direction arises, and the spiral spring34urges the spool20in the take-up direction. Accordingly, basically, when the tensile force applied to the webbing belt28for pulling the webbing belt28out from the spool20is released, the urging force of the spiral spring34rotates the spool20in the take-up direction, and the webbing belt28is taken-up onto the spool20.

On the other hand, the flange portion26side other end side of the spool20, which is opposite the flange portion24side thereof, passes substantially coaxially through an internal teeth ratchet hole36formed in the leg plate18, and projects at the exterior of the frame12. A lock mechanism38is provided at the outer side of the frame12at the leg plate18side. The lock mechanism38has a case40. The case40is disposed so as to oppose the leg plate18along the axial direction of the spool20, and is fixed to the leg plate18. Respective members forming the lock mechanism38, such as an inertial plate or an external gear, an acceleration sensor, and the like (all of which are unillustrated), are accommodated at the inner side of the case40. Due to the spool20rotating suddenly in the take-up direction, the inertial plate within the case40rotates relative to the spool20, or the acceleration sensor detects a state of rapid deceleration of the vehicle and the inertial plate is forcibly rotated within the case40relative to the spool20.

A pair of lock plates42are provided at the inner side of the ratchet hole36. The lock plates42are supported by a lock base which is provided within the case40and rotates integrally with the spool20. When the inertial plate within the case40rotates in the pull-out direction relative to the lock base, the inertial plate is guided by guide portions formed at the lock base, and approaches the inner peripheral portion of the ratchet hole36. External teeth formed at the lock plates42mesh with the internal teeth formed at the inner peripheral portion of the ratchet hole36. Due to the external teeth formed at the lock plates42meshing with the internal teeth formed at the inner peripheral portion of the ratchet hole36in this way, rotation of the lock base in the pull-out direction is restricted, and accordingly, rotation of the spool20is restricted.

On the other hand, a motor44serving as a drive source is disposed beneath the spool20between the leg plate16and the leg plate18. The motor44is electrically connected via a driver46to a battery48mounted in the vehicle. Due to current from the battery48flowing to the motor44via the driver46, the motor44rotates an output shaft50in the forward direction or the reverse direction. The driver46is connected to an ECU52formed by a microcomputer or the like. The ECU52is connected to a forward observation sensor54.

The forward observation sensor54is provided in a vicinity of the front end portion of the vehicle, and emits infrared rays toward the region in front of the vehicle, and receives the infrared rays which have been reflected by another vehicle or an obstacle which has stopped or is traveling in front of the vehicle. (Hereinafter, such objects, including vehicles which are traveling or have stopped, will be called “obstacles” for convenience of explanation.) The ECU52computes the distance to the obstacle ahead on the basis of the time required for the forward observation sensor54to receive light from the time the forward observation sensor54emitted the infrared rays.

On the basis of an electrical signal outputted from the forward observation sensor54, the ECU52operates the driver46and controls the motor44.

On the other hand, a gear56is provided coaxially and integrally with the distal end portion of the output shaft50of the motor44. The gear56meshes with a gear62which has external teeth and which forms a braking mechanism60. As shown inFIGS. 2,3A and3B, the braking mechanism60has a frame64. The frame64has a pair of side walls66which are parallel to and oppose the leg plates16,18of the frame12. The side walls66are connected integrally to the rear surface side of the frame12by a back wall68. On the whole, the frame64is formed, in plan view, in a substantially concave shape which opens toward the front surface side of the frame12.

The gear62is provided such that the center of rotation thereof is positioned between the side walls66, and is rotatably supported by a shaft70which passes through the side walls66and is supported at the leg plate16of the frame12. The gear62has a larger diameter than and more teeth than the gear56. Accordingly, the rotation of the gear56is decelerated by being transmitted to the gear62. Moreover, a gear72is disposed at the side of the gear62opposite the side at which the back wall68of the frame64is provided.

The gear72meshes with the gear62in a state in which the gear72is pivotally supported by a shaft74whose both ends are supported at the side walls66. Accordingly, the gear72can rotate around the gear62due to the rotation of the gear62being transmitted thereto. Moreover, the shaft74which pivotally supports the gear72extends to the interior of the frame12. A weight76, which is formed in the shape of a solid cylinder and which is substantially coaxial with the shaft74, is fixed integrally to this distal end portion of the shaft74. The weight76is integral with the gear72via the shaft74. The self-weight of the gear72and the weight of the weight76are applied to the gear72.

On the other hand, one end of a tension coil spring78is anchored on the back plate68of the frame64. The other end of the tension coil spring78is fixed to the leg plate16at a position which is lower than the one end of the tension coil spring78. The urging force of the tension coil spring78is greater than the gravity based on the weight of the weight76and the self-weight of the gear72which are applied to the gear72. The urging force is applied such that the rear wall68side of the frame64is pulled downward against the gravity applied to the gear72.

Further, a braking piece80, which is shaped as a plate having a narrow width and which serves as a braking member, extends from the top end portion of the rear wall68. The braking piece80structures a clutch90which serves as a clutch mechanism and will be described later. The braking piece80restricts rotation of a friction ring170due to friction at the time when the braking piece80abuts the outer peripheral portion of the friction ring170which structures the clutch mechanism and serves as a friction member.

On the other hand, as shown inFIG. 1, the clutch90is provided at the radial direction side of the gear62. Hereinafter, the clutch90will be described with reference toFIGS. 4 through 7.

As shown inFIG. 4, the clutch90has a base plate92serving as an intermediate rotating body. The base plate92is formed in the shape of a hollow cylinder which has a bottom and whose axial direction dimension is extremely short (or in the shape of a shallow tray). A substantially ring-shaped peripheral wall96, which serves as an intermediate peripheral wall, is formed along the outer peripheral portion of a disc-shaped base portion94of the base plate92. A cover98, which is shaped as a thin disc, is attached to the open end at one axial direction end side of the base plate92(the arrow C direction side inFIG. 4), such that the open end of the base plate92is basically closed.

Engaging recesses100are formed at uniform intervals along the peripheral direction in the outer peripheral portion of the peripheral wall96. An external gear102serving as a prime mover rotating body is provided at the outer side of the peripheral wall96. The external gear102is formed in a substantial ring shape whose number of teeth is sufficiently larger than that of the gear62, and is disposed coaxially with respect to the base plate92. The inner diameter dimension of the external gear102is sufficiently larger than the outer diameter dimension of the peripheral wall96. An annular gap is formed between the inner peripheral portion of the external gear102and the outer peripheral portion of the peripheral wall96. As shown inFIGS. 5 through 7, a plurality of torque limiters104are disposed intermittently in the peripheral direction in this annular gap.

As shown inFIGS. 4 through 7, the torque limiters104are plate-shaped metal pieces having thin widths and having a spring property, and the widths thereof are smaller than the axial direction dimension of the external gear102. Engaging portions106, which can enter into the aforementioned engaging recesses100, are formed at the both longitudinal direction end portions of each of the torque limiters104. Further, an engaging projection108, which is bent as if to project out in a direction substantially opposite to the projecting direction of the engaging portions106, is formed substantially at the longitudinal direction center of each of the torque limiters104.

Engaging recesses110are formed at the inner peripheral portion of the external gear102in correspondence with the engaging projections108. Due to the engaging portions106entering into the engaging recesses100in the state in which the engaging projections108are in the engaging recesses110, the base plate92and the external gear102are connected substantially integrally via the torque limiters104. In this way, when the external gear102attempts to rotate relative to the base plate92around the axis of the base plate92, the torque limiters104also of course attempt to rotate integrally together with the external gear102.

However, due to the engaging portions106of the torque limiters104being in the engaging recesses100, when the engaging portions106attempt to rotate along the peripheral direction of the peripheral wall96, the engaging recesses100interfere with the engaging portions106such that rotation of the engaging portions106is restricted. In this way, relative rotation of the external gear102with respect to the base plate92is restricted, and basically, the external gear102and the base plate92are connected integrally.

However, as described above, because the torque limiters104are metal pieces having a spring property, if the torque generated by the relative rotation of the external gear102with respect to the base plate92is large enough to pull the engaging portions106out from the engaging recesses100against the spring force (urging force) of the torque limiters104, the interference of the engaging recesses100with the engaging portions106is released. Therefore, relative rotation of the external gear102with respect to the base plate92becomes possible.

On the other hand, an adapter112, which is substantially hollow cylindrical and serves as a driven shaft, is disposed substantially coaxially with the base plate92at the inner side of the base plate92. On the whole, the axial direction one end (the arrow D direction side inFIG. 4) of the adapter112is pivotally supported at a circular hole115formed in the center of the base portion94(the base plate92). A tubular portion114, which is hollow cylindrical and is formed coaxially at the other end of the adapter112, is pivotally supported at a circular hole116formed in the cover98.

A spacer118, which is formed in a ring shape and of a synthetic resin material, is disposed between the adapter112and the base portion94of the base plate92. The spacer118is pivotally supported by the tubular portion114of the adapter112. One axial direction end surface of the spacer118abuts the base portion94, whereas the other axial direction end surface abuts the end surface of the connecting portion where the main body portion of the adapter112is connected to the tubular portion114.

A fit-together hole120, which passes through along the axial direction of the adapter112, is formed in the adapter112. The other axial direction end of the spool20is fit into the fit-together hole120, such that the adapter112and the spool20are connected together coaxially and integrally. Further, a plurality of external teeth122, which is an odd number of teeth, are formed at uniform intervals at the outer peripheral portion of the adapter112.

Moreover, a pair of bosses124are formed at the base portion94of the base plate92at the radial direction outer side of the adapter112. Each boss124is formed as a substantially hollow cylinder, and stands erect from the base portion94toward one side in the axial direction thereof. These bosses124are formed so as to oppose one another across the circular hole115. A pawl130serving as a connecting member is provided at each boss124.

The pawl130has a main body132. The main body132is formed in the shape of a ring whose inner diameter dimension is extremely slightly larger than the outer diameter dimension of the boss124. Due to the main body132being fit together with the boss124such that the boss124passes through the main body132, the pawl130is pivotally supported so as to be freely rotatable around the boss124.

A connecting piece134is formed at a portion of the outer periphery of the main body132. The connecting piece134is formed so as to extend, with respect to the main body132, toward the spool20take-up direction side, in the state in which the main body132is pivotally supported at the boss124. Moreover, the connecting piece134is formed such that, due to the main body132rotating over a predetermined angle in the take-up direction around the boss124, the corner portion of a distal end134A abuts the outer peripheral portion of the adapter112between the external tooth122and the external tooth122of the adapter112.

The distal end134A of the connecting piece134is formed as an inclined surface which is inclined so as to correspond to the pull-out direction side surfaces of the teeth of the adapter112. Due to the distal end134A abutting and interfering with the external tooth122, rotation of the adapter112in the pull-out direction is restricted.

Here, as described above, the bosses124are formed so as to oppose one another across the circular hole115. Therefore, in a state in which the corner portions of the distal ends134A of the pawls130which have basically the same configurations contact the outer peripheral surface of the adapter112, the distal end134A of one of the pawls130is positioned, across the axial center of the adapter112, at the opposite side of the distal end134A of the other of the pawls130. Accordingly, if the total number of external teeth122formed at the outer peripheral portion of the adapter112is an even number and the external tooth122is formed at the opposite side, across the axial center of the adapter112, of any one of the external teeth122, the distal ends134A of the both pawls130both abut the external teeth122.

However, in the present embodiment, as mentioned above, the total number of the external teeth122formed at the outer peripheral portion of the adapter112is an odd number. Thus, in the state in which the distal end134A of the one pawl130is abutting the external tooth122, the distal end134A of the other pawl130has moved apart from the external tooth122along the peripheral direction of the adapter112(i.e., the distal end134A of the other connecting piece134is not contacting the external tooth122).

On the other hand, a releasing piece136extends from the outer peripheral portion of the main body132. The releasing piece136is formed at the side of the main body132approximately opposite the side at which the connecting piece134is formed. The outer side surface of the releasing piece136is an inclined surface which is directed toward the outer side in the radial direction of the base plate92with respect to the pull-out direction. By rotating the releasing piece136in the pull-out direction, the connecting piece134rotates in the direction of moving away from the outer peripheral portion of the adapter112.

Further, the clutch90is provided with a rotating disc140serving as a rotating member. The rotating disc140has a substantially plate-shaped base portion142whose direction of thickness runs along the axial directions of the base plate92and the adapter112. A circular hole144is formed in the base portion142. The inner diameter dimension of the circular hole144is formed to be extremely slightly larger than the outer diameter dimension of the tubular portion114formed coaxially with respect to the outer peripheral portion of the adapter112at the axial direction other end side of the adapter112. By carrying out assembly by making the tubular portion114pass through the circular hole144, the base portion142, and thus, the rotating disc140are pivotally supported at the adapter112so as to freely rotate around the adapter112.

Further, a pair of blocks146serving as a forcibly connecting mechanism are formed at the base portion94side surface of the base portion142. The blocks146are formed so as to oppose one another across the circular hole144. Among the two portions running along the outer periphery of the outer side of the circular hole144between the pair of blocks146, one of the bosses124is positioned at one portion, and the other boss124is positioned at the other portion which is at the opposite side of this one portion across the circular hole144.

A spring accommodating portion148is formed at the outer peripheral portion of one of the pair of blocks146(the outer peripheral surface of the block146which outer peripheral surface runs along the radial direction of the circular hole144). A compression coil spring150serving as an urging member is accommodated in the spring accommodating portion148.

The compression coil spring150is accommodated in the spring accommodating portion148in a state in which the compression coil spring150bends around the center of the circular hole144. The take-up direction side end portion of the compression coil spring150abuts a wall portion148A of the spring accommodating portion148. The pull-out direction side end portion of the compression coil spring150abuts an abutment wall152which extends from the inner peripheral portion of the peripheral wall96of the base plate92and which enters into the spring accommodating portion148.

The rotating disc140is pivotally supported at the tubular portion114of the adapter112. Therefore, basically, the rotating disc140freely rotates relative to not only the adapter112but to the base plate92as well. However, as described above, the take-up direction side end portion of the compression coil spring150abuts the wall portion148A of the spring accommodating portion148, and the pull-out direction side end portion of the compression coil spring150abuts the abutment wall152of the base plate92. Therefore, when the base plate92attempts to rotate in the take-up direction relative to the rotating disc140, the abutment wall152pushes the rotating disc140in the take-up direction via the compression coil spring150, and makes the rotating disc140rotate following the rotation of the base plate92. Thus, provided that torque, which is of a magnitude which can resist the urging force of the compression coil spring150, is not applied to the rotating disc140, rotation of the base plate92in the take-up direction relative to the rotating disc140is limited.

Moreover, a pressing piece154is provided at the inner peripheral portion of each block146. These pressing pieces154are disposed at the take-up direction sides of the pawls130, and can move relative to the blocks146(i.e., relative to the rotating disc140) along peripheral walls156formed at the blocks146so as to curve coaxially with respect to the circular hole144. Further, compression coil springs158are provided at the sides of the pressing pieces154opposite the sides at which the pawls130are provided. The compression coil springs158are disposed in states of being curved along the peripheral walls156. One end of the compression coil spring158is anchored at and connected to the end portion of the pushing piece154at the side opposite the side where the pawl130is provided. In contrast, the other end of the compression coil spring158is, in a state of abutting an abutment wall160which is formed at the rotating disc140at the side opposite the pushing piece154, anchored at and connected to a projection (not illustrated) which is formed so as to project from the abutment wall160toward the pushing piece154.

Inclined surfaces164are formed at the transverse direction outer ends of the connecting pieces134of the pawls130, in correspondence with the respective pushing pieces154. The inclined surface164is inclined outwardly in the radial direction of the base plate92with respect to the take-up direction. In the state in which the distal end134A does not contact the outer peripheral portion of the adapter112, the inclined surface164opposes (faces) the pushing piece154along the peripheral direction of the base plate92and the rotating disc140. The pushing piece154is formed so as to abut the inclined surface164due to the base plate92rotating by a predetermined amount in the take-up direction relative to the rotating disc140. When, from this state of abutment, the base plate92attempts to rotate even further in the take-up direction relative to the rotating disc140, the inclined surface164is pushed in the pull-out direction by the pushing piece154. Due to this pushing force, the pawl130rotates in the take-up direction around the boss124.

At the take-up direction side end portion of each block146which runs along the peripheral direction of the rotating disc140, a pushing portion166is formed, and a releasing piece accommodating portion168is formed further toward the axial center of the rotating disc140than the pushing portion166. The pushing portion166is formed so as to correspond to the releasing piece136of the pawl130along the peripheral direction of the rotating disc140. The releasing piece136gradually curves toward the axial center of the base plate92from the portion thereof connected to the main body132(the proximal end portion thereof) toward the distal end side thereof. The (transverse direction) outer side surface of the releasing piece136as well is curved in a similar way.

Accordingly, when the base plate92rotates by a predetermined amount in the pull-out direction relative to the rotating plate140, the pushing portions166abut the (transverse direction) outer side surfaces of the releasing pieces136. In this state of abutment, when the base plate92is rotated further in the pull-out direction relative to the rotating disc140, the pushing portions166push the distal end portions of the releasing pieces136in the take-up direction. Here, the distal ends of the releasing pieces136are inclined surfaces which are inclined toward the outer side in the radial direction of the rotating disc140, with respect to the pull-out direction. Thus, due to the pushing portions166pushing the distal ends of the releasing pieces136, the pushing portions166rotate the pawls130in the pull-out direction around the bosses124and guide them to the releasing piece accommodating portions168.

Moreover, the friction ring170is disposed coaxially between the cover98and the base portion142of the rotating disc140. The friction ring170is formed in a ring shape on the whole. A pair of tongue-shaped attachment pieces172extend from the inner peripheral portion of the friction ring170so as to oppose one another across the center of the friction ring170. The attachment pieces172are integrally connected to the base portion142of the rotating disc140by fasteners such as screws or the like. In this way, the rotating disc140and the friction ring170are integral. The outer peripheral portion of the friction ring170corresponds to the distal end of the aforementioned braking piece80. Due to the frame64rotating in the pull-out direction around the shaft70, the distal end of the braking piece80slidingly contacts the outer peripheral portion of the friction ring170.

The external gear102of the clutch90having the above-described structure meshes together with the gear62.

OPERATION AND EFFECTS OF PRESENT EMBODIMENT

Next, the operation and effects of the present embodiment will be described by way of explaining the operation of the present webbing retractor10.

(Basic Operation of Webbing Retractor10)

First, the basic operation of the webbing retractor10will be described.

In the present webbing retractor10, in the state in which the webbing belt28is taken-up and accommodated in the form of a roll on the spool20, when the webbing belt28is pulled while an unillustrated tongue plate is pulled, the webbing belt28is pulled out while the spool20is rotated in the pull-out direction against the urging force of the spiral spring34which urges the spool20in the take-up direction. In this way, in the state in which the webbing belt28is pulled out, the vehicle occupant seated in a seat inserts the tongue plate in an unillustrated buckle device while pulling the webbing belt28around the front of his/her body, such that the tongue plate is held in the buckle device. The webbing belt28is thereby set in a state of being applied to the body of the vehicle occupant (hereinafter, this state will be referred to simply as the “applied state”).

When the webbing belt28is pulled out and the spool20is rotated in the pull-out direction in order to apply the webbing belt28to the body of a vehicle occupant, the spiral spring34is wound tighter, such that the urging force of the spiral spring34which urges the spool20in the take-up direction increases. Accordingly, in the aforementioned applied state, the urging force of the spiral spring34works to make the webbing belt28be taken up on the spool20. Thus, basically, the webbing belt28is fit to the body of the vehicle occupant due to this urging force, and the webbing belt28restrains and holds the body of the vehicle occupant by a force corresponding to the urging force at this time.

On the other hand, when holding of the tongue plate by the buckle device is released and the tongue plate comes out of the buckle device, the force for maintaining the webbing belt28in the state of being pulled-out against the urging force of the spiral spring34is cancelled. Thus, the spool20is rotated in the take-up direction by the urging force of the spiral spring34. The webbing belt28which has been pulled out is taken-up in the form of a roll onto the outer peripheral portion of the spool20due to the rotation of the spool20in the take-up direction. In this way, the webbing belt28is accommodated.

Here, because the spool20is fit together with the adapter112of the clutch90, when the spool20is rotated in order to pull-out or take-up the webbing belt28, the adapter112rotates. However, in this state, if the adapter112merely rotates, the base plate92and the rotating disc140do not rotate. Therefore, the pawls130do not rotate. Accordingly, the external gear102does not rotate. Accordingly, the rotation of the spool20is not transmitted to the output shaft50of the motor44via the external gear102and the gears62,56.

(Operation of Webbing Retractor10when Approaching an Obstacle Ahead)

On the other hand, while the vehicle is traveling, the forward observation sensor54detects the distance to an obstacle which is in front of the vehicle. An electric signal having a signal level corresponding to the distance to the obstacle is outputted from the forward observation sensor54. The electric signal outputted from the forward observation sensor54is inputted to the ECU52. At the ECU52, on the basis of the electric signal from the forward observation sensor54, it is judged whether or not the distance to the obstacle is less than a predetermined value.

Next, if it is judged at the ECU52that the distance to the obstacle is less than the predetermined value, the ECU52outputs a control signal to the driver46, and makes current flow to the motor44via the driver46. In this way, the motor44is driven to rotate forward at a speed of a predetermined value or more, and rotates the output shaft50forward.

The rotation of the output shaft50is, while being decelerated via the gears56,62, transmitted to the external gear102of the clutch90, and rotates the external gear102in the take-up direction at a rotational speed of a predetermined value or more. The external gear102is mechanically connected to the base plate92via the torque limiters104. Thus, due to the external gear102rotating in the take-up direction, the base plate92rotates integrally in the take-up direction.

When the base plate92rotates in the take-up direction, the abutment wall152pushes the take-up direction side end portion of the compression coil spring150, and the compression coil spring150pushes the wall portion148A of the spring accommodating portion148by urging force. The rotating disc140thereby attempts to rotate so as to follow rotation of the base plate92.

On the other hand, as described above, when the rotation of the output shaft50is transmitted to the gear62via the gear56, rotation is transmitted from the gear62to the gear72, and the gear72attempts to rotate downward around the gear62while rotating around the shaft74. However, the urging force of the tension coil spring78is applied to the frame64at which the shaft74, which pivotally supports the gear72, is supported. Thus, the gear72cannot rotate downward around the gear62. However, as described above, the output shaft50rotates at a rotational speed of a predetermined value or more, and this rotation is transmitted to the gear72. In this way, the resultant force of the force applied to the gear72around the gear62and the gravity based on the self-weight of the gear72and the weight of the weight76, exceeds the urging force of the tension coil spring78. The gear72, and consequently, the frame64, are rotated around the shaft70.

In this way, the braking piece80slidingly contacts the outer peripheral portion of the friction ring170. The friction, which is generated between the braking piece80and the outer peripheral portion of the friction ring170, restricts rotation of the friction ring170, and accordingly, of the rotating disc140which is integral with the friction ring170. In this way, relative rotation arises between the base plate92and the rotating disc140, and the base plate92can be rotated reliably in the take-up direction with respect to the rotating disc140.

In this way, when the base plate92rotates by a predetermined amount or more in the take-up direction relative to the rotating disc140, the pushing pieces154provided at the blocks146of the rotating disc140abut the connecting pieces134of the pawls130. In this state, when the base plate92attempts to rotate further in the take-up direction relative to the rotating disc140, the pushing pieces154push the inclined surfaces164of the connecting pieces134in the pull-out direction. The pushing forces applied to the inclined surfaces164act in the pull-out direction and toward the inner side in the radial direction of the rotating disc140and the base plate92. The portions of the forces, which portions act toward the radial direction inner sides, rotate the pawls130in the take-up direction around the bosses124. As shown inFIG. 6, due to the pawls130rotating in the take-up direction around the bosses124, the corner portions of the distal ends134A abut the outer peripheral portion of the adapter112. In this state, the pawls130rotate together with the base plate92in the take-up direction around the center of the base plate92, until the pawls130abut the external teeth122which are adjacent at the take-up direction sides.

Then, in this state, the distal ends134A abut the external teeth122. When the base plate92rotates further in the take-up direction, the distal ends134A of the pawls130push the external teeth122in the take-up direction, and rotate the adapter112, and accordingly, the spool20, in the take-up direction. Due to this rotation of the spool20, the webbing belt28is taken-up onto the spool20. In this way, looseness or so-called “slack” in the webbing belt28is eliminated, and the force by which the webbing belt28restrains the body of the vehicle occupant is improved. Even if the vehicle occupant thereafter carries out the operation of suddenly braking the vehicle such that a state of rapid deceleration of the vehicle arises, the webbing belt28reliably holds the body of the vehicle occupant.

In this way, when the motor44stops in the state in which slack has been eliminated, rotation of the base plate92in the take-up direction stops. When rotation of the base plate92stops, the compression coil spring150pushes the rotating disc140in the take-up direction by urging force, and rotates the rotating disc140in the take-up direction. When the rotating disc140rotates, the pushing portions166abut the releasing pieces136of the pawls130and push the releasing pieces136in the take-up direction. Due to the releasing pieces136receiving this pushing force, the pawls130rotate in the pull-out direction around the bosses124, and as shown inFIG. 5, the distal ends134A of the connecting pieces134move away from the outer peripheral portion of the adapter112. In this way, the mechanical connection between the base plate92and the adapter112, i.e., the mechanical connection between the output shaft50of the motor44and the compression coil spring150, is cancelled.

Here, in the present embodiment, as described above, the total number of the external teeth122of the adapter112is an odd number. In the state in which the distal end134A of one of the pawls130is abutting the external tooth122, the distal end134A of the other pawl130is apart from the external tooth122along the peripheral direction of the adapter112, and is positioned at an intermediate portion between the external tooth122, which is adjacent in the take-up direction along the peripheral direction of the adapter112, and the external tooth122which is adjacent in the pull-out direction.

Namely, in the present embodiment, in the state in which the distal ends134A of the both pawls130abut the outer peripheral portion of the adapter112, the interval from the distal end134A of one of the pawls130to the distal end134A of the other of the pawls130is not an integer multiple of the pitch of the external teeth122. Thus, as shown inFIG. 7, even if the distal end134A of one of the pawls130abuts the addendum of the external tooth122at the time when the both pawls130are rotating around the bosses124, the distal end of the other of the pawls130does not abut the addendum of the external tooth122, and abuts the outer peripheral portion of the adapter112between the external teeth122which are adjacent in the peripheral direction.

Accordingly, even if the distal end134A of one of the pawls130abuts the addendum of the external tooth122and cannot mesh with the external tooth122, the distal end134A of the other of the pawls130reliably meshes with the external tooth122if the base plate92rotates by substantially one-half of the pitch of the external teeth122. Thus, the rotation of the base plate92can reliably and swiftly be transmitted to the adapter112, and the torque of the motor44can be transmitted to the spool20.

Moreover, in the state in which the distal end134A of one of the pawls130abuts the addendum of the external tooth122, the connecting piece134abuts the pushing piece154in this state as is. Here, even if the pushing piece154is integral with the rotating disc140, further rotation of the base plate92in the take-up direction relative to the rotating disc140is restricted. In this state, because the interference of the pushing piece154with the distal end of the other of the pawls130is insufficient, the pushing piece154cannot rotate the other pawl130sufficiently in the take-up direction. As a result, there is the possibility that the distal end of the other of the pawls130cannot abut the external tooth122.

Here, in the present embodiment, as described above, the connecting piece134abuts the pushing piece154with the distal end134A of the one pawl130abutting the addendum of the external tooth122. In this state, when the base plate92attempts to rotate further in the take-up direction relative to the rotating disc140, as shown inFIG. 7, the distal end134A of the pawl130pushes the pushing piece154and displaces the pushing piece154in the take-up direction, against the urging force of the compression coil spring158. In this way, the base plate92rotates in the take-up direction relative to the rotating disc140.

Thus, the pushing piece154corresponding to the other pawl130interferes with the distal end134A of the other pawl130, and rotates the pawl130in the take-up direction. In this way, even if the connecting piece134abuts the pushing piece154in a state in which the distal end134A of the one pawl130abuts the addendum of the external tooth122, the other pawl130can be made to mesh with the external tooth122of the adapter112, and the rotation of the base plate92can be reliably transmitted to the adapter112.

On the other hand, as described above, by rotating the spool20in the take-up direction by the torque of the motor44, the force by which the webbing belt28restrains the body of the vehicle occupant is improved. However, until the slack is eliminated, in the state in which the webbing belt28is wound on the spool20, the body of the vehicle occupant is an obstruction, and basically, the webbing belt28cannot be taken-up any further on the spool20. In this state, if the spool20attempts to rotate further in the take-up direction and take-up the webbing belt28, the webbing belt28is tightened against the body of the vehicle occupant by a force which is greater than needed, which is not preferable.

Here, as described above, if the spool20attempts to take-up the webbing belt28any more than needed, the body of the vehicle occupant is an obstruction to the taking-up of the webbing belt28. Tensile force of a magnitude corresponding to the take-up force for the spool20to take the webbing belt28up is applied to the webbing belt28from the body of the vehicle occupant. This tensile force acts opposite to the direction in which the spool20takes up the webbing belt28. Thus, the spool20is stopped due to this tensile force being applied to the webbing belt28.

In this state, the torque of the motor44is applied to the spool20via the external gear102, the base plate92, the pawls130and the adapter112. Thus, in the state in which the spool20is stopped, the external teeth122of the adapter112restrict rotation of the pawls130around the center of the base plate92, and the pawls130restrict rotation of the base plate92in the take-up direction. Moreover, via the torque limiters104, the base plate92restricts rotation of the external gear102in the take-up direction.

Here, in this state in which the rotation of the external gear102is limited by the base plate92via the torque limiters104, if the external gear102attempts to rotate further in the take-up direction and the torque at this time exceeds the spring force of the torque limiters104, the engaging portions106of the torque limiters104come out from the engaging recesses100. In this way, the connection between the base plate92and the external gear102is temporarily cancelled, and only the external gear102rotates in the take-up direction until the engaging portions106enter into the other, adjacent engaging recesses100. In this way, due to the connection between the base plate92and the external gear102being cancelled, the transmission of the torque of the external gear102to the base plate92, i.e., the transmission of the torque of the motor44to the spool20, is cut-off. Thus, an increase in the restraining force applied by the webbing belt28can be suppressed.

As described above, the clutch90used in the present webbing retractor10not only has the function of transmitting torque, but also can cut-off the transmission of torque by the torque limiters104when an excessive torque is applied. Regardless of the fact that the above-described effects can be obtained, the widthwise dimension of the torque limiters104(the dimension thereof along the axial direction of the external gear102) is less than the axial direction dimension of the external gear102. The rotating disc140and the torque limiters104are therefore all disposed between the peripheral wall96of the base plate92and the external gear102along the radial direction of the external gear102.

Moreover, members such as the pawl130, the rotating disc140and the like as well are disposed between the peripheral wall96and the adapter112. These members are accommodated at the inner side of the external gear102. Thus, the thickness dimension (the axial direction dimension) of the clutch90is, in actuality, the axial direction dimension of the external gear102, and is extremely thin.

In this way, because the clutch90having the torque limiters104can be made thin, the present webbing retractor10can be made compact.

STRUCTURE OF SECOND EMBODIMENT

Next, another embodiment of the present invention will be described. Note that, in describing the respective embodiments hereinafter, regions which are basically the same as those of the previous embodiments (including the above-described first embodiment) are denoted by the same reference numerals, and detailed description thereof is omitted.

The structure of a webbing retractor290relating to a second embodiment of the present invention is shown in schematic front view inFIG. 8.

As shown inFIG. 8, the webbing retractor290relating to the present embodiment differs from the webbing retractor10relating to the above-described first embodiment in that the webbing retractor290does not have the braking mechanism60and the clutch90, and instead, is equipped with a braking mechanism300and a clutch350which serves as the clutch mechanism.

As shown inFIGS. 8 and 9, a gear56, which is provided coaxially and integrally at the distal end portion of the output shaft50of the motor44, meshes with an external gear302structuring the braking mechanism300. The number of teeth of the gear302is sufficiently larger than that of the gear56. The axial direction ends of the gear302are pivotally supported at the leg plate16of the frame12and a frame301of the braking mechanism300.

At the leg plate16side of the gear302, a gear304, which has a number of teeth which is sufficiently smaller than that of the gear302, is provided coaxially and integrally with respect to the gear302. Above the gear304, a gear306, which has more teeth than the gear304, is pivotally supported at the leg plate16and the frame301in a state in which the gear306meshes with the gear304. Moreover, above the gear306, the external gear102, which serves as a prime mover rotating body forming the clutch350which will be described later, meshes with the gear306. The rotation of the output shaft50is decelerated and transmitted to the external gear102via the gears56,302,304,306.

On the other hand, an arm308is provided at the leg plate16side of the gear304. The arm308is a plate-shaped member whose longitudinal direction runs along the rotation radial direction of the gear302and whose direction of thickness runs along the axial direction of the gear302. A substantially circular spring accommodating portion310is formed at the proximal end side, in the longitudinal direction, of the arm308(seeFIG. 10).

A friction spring312is accommodated in the spring accommodating portion310. The friction spring312is formed on the whole in a substantial ring shape. The inner peripheral portion of the friction spring312slidingly contacts a shaft portion314which is integral with the gear304. Further, the both peripheral direction ends of the friction spring312bend outwardly in the radial direction.

A wall portion316is formed in the spring accommodating portion310in correspondence with the region between the bent both ends of the friction spring312. When the friction spring312attempts to rotate around the shaft portion314with respect to the arm308, one of the both ends of the friction spring312interferes with the wall portion316, such that the friction spring312pushes the wall portion316in the direction of rotation thereof.

On the other hand, a shaft portion318is formed to project from the distal end side of the arm308toward the gear302. The proximal end portion of a lever320is pivotally supported at the shaft portion318so as to be freely rotatable around the shaft portion318. The lever320is a plate-shaped member whose longitudinal direction runs along the radial direction of the shaft portion318, and whose direction of thickness is along the axial direction of the gear302. A through hole322, which passes through in the direction of thickness, is formed at the longitudinal direction distal end side of the lever320. The pull-out direction side end portion of a brake spring324, which is formed in a substantial ring shape, is fit into the through hole322.

On the other hand, as shown inFIG. 11, the clutch350, which has the external gear102which structures the clutch350, is equipped with the base plate92. The base plate92is formed in the shape of a hollow cylinder which has a bottom and whose axial direction dimension is extremely short (or in the shape of a shallow tray). The substantially ring-shaped peripheral wall96is formed along the outer peripheral portion of the disc-shaped base portion94of the base plate92. The cover98, which is shaped as a thin disc, is attached to the open end at one axial direction end side of the base plate92(the arrow C direction side inFIG. 11), such that the open end of the base plate92is basically closed.

The engaging recesses100are formed at uniform intervals along the peripheral direction in the outer peripheral portion of the peripheral wall96. The external gear102, which is substantially ring-shaped and which has a number of teeth which is sufficiently larger than that of the gear302, is disposed coaxially with the base plate92at the outer side of the peripheral wall96. The inner diameter dimension of the external gear102is sufficiently larger than the outer diameter dimension of the peripheral wall96. An annular gap is formed between the inner peripheral portion of the external gear102and the outer peripheral portion of the peripheral wall96. The plurality of torque limiters104are disposed intermittently in the peripheral direction in this annular gap.

The torque limiters104are plate-shaped metal pieces having thin widths and having a spring property. The engaging portions106, which can enter into the aforementioned engaging recesses100, are formed at the both longitudinal direction end portions of each of the torque limiters104. Further, the engaging projection108, which is bent as if to project out in a direction substantially opposite to the projecting direction of the engaging portions106, is formed substantially at the longitudinal direction center of each of the torque limiters104.

The engaging recesses110are formed at the inner peripheral portion of the external gear102in correspondence with the engaging projections108. Due to the engaging portions106entering into the engaging recesses100in the state in which the engaging projections108are in the engaging recesses110, the base plate92and the external gear102are connected substantially integrally via the torque limiters104.

In this way, when the external gear102attempts to rotate relative to the base plate92around the axis of the base plate92, the torque limiters104also of course attempt to rotate integrally together with the external gear102. However, due to the engaging portions106of the torque limiters104being in the engaging recesses100, when the engaging portions106attempt to rotate along the peripheral direction of the peripheral wall96, the engaging recesses100interfere with (engage) the engaging portions106such that rotation of the engaging portions106is restricted.

In this way, relative rotation of the external gear102with respect to the base plate92is restricted, and basically, the external gear102and the base plate92are connected integrally.

However, as described above, because the torque limiters104are metal pieces having a spring property, if the torque generated by the relative rotation of the external gear102with respect to the base plate92is large enough to pull the engaging portions106out from the engaging recesses100against the spring force (urging force) of the torque limiters104, the interference (engagement) of the engaging recesses100with the engaging portions106is released, and relative rotation of the external gear102with respect to the base plate92becomes possible.

On the other hand, an adapter352, which is substantially hollow cylindrical and serves as a driven shaft and an inner side rotating body, is disposed substantially coaxially with respect to the base plate92at the inner side of the base plate92. The adapter352is formed, on the whole, in the shape of a thick ring whose direction of thickness (axial direction) runs along the axial direction of the base plate92. The above-described spool20is fit integrally and coaxially into the adapter352. The spacer118, which is formed in a ring shape and of a synthetic resin material, is fit into the base portion94side end portion of the adapter352. One axial direction end surface of the spacer118(the side in the direction opposite to the direction of arrow C inFIG. 11) abuts the base portion94.

A plurality (three in the present embodiment) of connecting rollers354, each of which serves as a connecting member, are disposed at the radial direction outer side of the adapter352. The connecting roller354is formed, on the whole, substantially in the shape of a solid cylinder. The axial direction of the connecting roller354is the axial direction of the adapter352, i.e., substantially the same direction as the axial direction of the spool20. Moreover, a lock piece356serving as a guiding member is provided between the connecting roller354and the peripheral wall96of the base plate92.

The lock pieces356are formed of a material which has relatively high strength (e.g., a material which has mechanical strength which is sufficiently higher than that of the material forming the base plate92). The lock pieces356are fixed integrally with the peripheral wall96in a state in which the lock pieces356are fit in piece mounting portions358which are formed at the inner peripheral portion of the peripheral wall96.

A guide surface360is formed at the surface of the lock piece356at the side thereof which faces the connecting roller354along the radial direction of the adapter352and the base plate92. The guide surface360is formed as an inclined surface or a curved surface whose distance from the outer peripheral surface of the adapter352gradually becomes shorter along the pull-out direction around the axial center of the adapter352. Due to the connecting rollers354rotating or moving in the pull-out direction so as to follow along the guide surfaces360, the connecting rollers354are forcibly made to approach the outer peripheral surface of the adapter352.

Moreover, in a vicinity of the pull-out direction side end portion of the guide surface360, the interval (distance) from the outer peripheral surface of the adapter352is set to be the same as or extremely slightly shorter than the outer diameter dimension of the connecting roller354. Thus, when the connecting roller354moves to a vicinity of the pull-out direction side end portion of the guide surface360, the connecting roller354contacts the outer peripheral portion of the adapter352.

Moreover, a rotating disc362serving as a forcibly connecting member is provided at the side of the connecting rollers354opposite the side at which the base portion94of the base plate92is provided. The rotating plate362has a plate-shaped base portion366in which is formed a circular hole364through which the spool20passes. Basically, the rotating plate362rotates freely around the axial center of the spool20relative to the spool20and the base plate92.

A plurality of peripheral walls368are formed at the periphery of the circular hole364of the base portion366. The peripheral walls368are formed at uniform intervals on an imaginary circumference which is concentric with the circular hole364. The number of the peripheral walls368which are formed is the same as the number of the connecting rollers354. The connecting rollers354are disposed between the peripheral walls368. A restricting wall370, which serves as a forcibly connecting mechanism, is formed at the pull-out direction side end portion (the end portion in the direction of arrow B inFIGS. 11 and 12) of the peripheral wall368around the axial center of the adapter352. When the connecting roller354attempts to move by a predetermined amount or more in the take-up direction around the axial center of the adapter352, the restricting wall370interferes with the outer peripheral portion of the connecting roller354so as to limit movement of the connecting roller354.

In contrast, a wedge-shaped portion372serving as a forcibly releasing mechanism is formed at the take-up direction side end portion (the end portion in the direction of arrow A inFIGS. 11 and 12) of the peripheral wall368around the axial center of the adapter352. The wedge-shaped portion372is formed in a taper shape whose thickness gradually decreases in the take-up direction. Due to the rotating plate362rotating in the take-up direction with respect to the connecting rollers354, the wedge-shaped portions372interfere with the outer peripheral portions of the connecting rollers354in a vicinity of the outer peripheral portion of the adapter352, and push the connecting rollers354in a direction of moving away from the outer peripheral portion of the adapter352.

A spring attaching portion374is formed at one of the plurality of the peripheral walls368. The compression coil spring150serving as an urging member is attached to the spring attaching portion374. The compression coil spring150is curved such that the axial direction thereof approximately runs along the inner peripheral configuration of the peripheral wall96. The take-up direction side end portion of the compression coil spring150abuts a wall portion374A of the spring attaching portion374, whereas the pull-out direction side end portion of the compression coil spring150abuts an abutment wall376formed at the inner peripheral portion of the peripheral wall96.

In this way, the rotating disc362basically is freely rotatable around the axial center of the adapter352relative to the adapter352and the base plate92. However, when the base plate92attempts to rotate in the take-up direction relative to the rotating disc362, the abutment wall376presses the other end portion of the compression coil spring150in the take-up direction. In this way, the increased urging force of the compression coil spring150pushes the wall portion374A in the take-up direction, and rotates the rotating disc362in the take-up direction.

Accordingly, when the base plate92attempts to rotate in the take-up direction relative to the rotating disc362, the rotating disc362attempts to follow the rotation of the base plate92due to the urging force of the compression coil spring150.

On the other hand, at the side of the cover98opposite the side at which the rotating disc362is disposed (i.e., at the outer side of the cover98), a friction ring378serving as a friction member is disposed coaxially with respect to the adapter352. The friction ring378is formed in a substantial ring shape on the whole. An annular accommodating groove380, which accommodates the aforementioned brake spring324, is formed in the outer peripheral portion of the friction ring378. The outer diameter dimension of the accommodating groove380at the floor portion of the accommodating groove380is substantially equal to the inner diameter dimension of the brake spring324. The inner peripheral portion of the brake spring324slidingly contacts the floor portion of the accommodating groove380.

A plurality (three in the present embodiment) of tongue-shaped attachment pieces382extend from the inner peripheral portion of the friction ring378. The attachment pieces382are integrally connected to the base portion366of the rotating disc362by fasteners such as screws or the like which pass through openings384formed in the cover98. In this way, the rotating disc362and the friction ring378are integral.

The external gear102of the clutch350having the above-described structure meshes with the gear306.

OPERATION AND EFFECTS OF SECOND EMBODIMENT

Next, the operation and effects of the present embodiment will be described by way of explaining the operation of the present webbing retractor290.

(Operation of Webbing Retractor290when Approaching an Obstacle Ahead)

In the present embodiment, when the vehicle is traveling, the forward observation sensor54detects the distance to an obstacle ahead of the vehicle. An electric signal, which has a signal level corresponding to the distance to the obstacle, is outputted from the forward observation sensor54.

The electric signal outputted from the forward observation sensor54is inputted to the ECU52. At the ECU52, on the basis of the electric signal from the forward observation sensor54, it is judged whether or not the distance to the obstacle is less than a predetermined value.

Next, when it is judged at the ECU52that the distance to the obstacle is less than a predetermined value, the ECU52outputs a control signal to the driver46, and makes current flow to the motor44via the driver46. In this way, the motor44is driven to rotate forward at a speed which is greater than or equal to a predetermined value, and the output shaft50is rotated forward. The rotation of the output shaft50is transmitted to the external gear102of the clutch350while being decelerated via the gears56,302,304,306, and rotates the external gear102in the take-up direction at a rotational speed of a predetermined value or more.

The external gear102is mechanically connected to the base plate92via the torque limiters104. Thus, due to the external gear102rotating in the take-up direction, the base plate92rotates integrally in the take-up direction.

When the base plate92rotates in the take-up direction, the abutment wall376presses the pull-out direction side end portion of the compression coil spring150, and further, the compression coil spring150presses the wall portion148A of the spring accommodating portion148by urging force. The rotating disc362thereby attempts to rotate so as to follow the base plate92.

On the other hand, as described above, when the rotation of the output shaft50is transmitted to the gear302via the gear56and the gear302rotates, the shaft portion314rotates. Due to the shaft portion314rotating, the frictional force generated between the shaft portion314and the inner peripheral portion of the friction spring312attempts to rotate the friction spring312. Due to the transmitted torque, the friction spring312pushes the wall portion316, and rotates the arm308around the shaft portion314(seeFIG. 10).

Due to the arm308rotating, the proximal end portion of the lever320rotates around the shaft portion314. In this way, the lever320rotates one end of the brake spring324(the end portion at the side engaged with the distal end of the lever320) in the pull-out direction (the direction of arrow B inFIGS. 10,11and12).

As described above, the inner peripheral portion of the brake spring324slidingly contacts the floor portion of the accommodating groove380of the friction ring378. Thus, due to the brake spring324rotating, frictional force is generated between the brake spring324and the floor portion of the accommodating groove380.

This frictional force works to restrict rotation of the brake spring324. Thus, the other end side of the brake spring324does not follow the rotation of the one end side. In this way, the brake spring324tightens against the floor portion of the accommodating groove380. The brake spring324attempts to rotate the friction ring378, and consequently, the rotating disc362which is integral with the friction ring378, in the pull-out direction. The base plate92rotates in the take-up direction relative to the rotating disc362due to this rotation of the rotating disc362itself in the pull-out direction and due to the torque received at the external gear102.

In this way, when the base plate92rotates in the take-up direction relative to the rotating disc362, the guide surfaces360of the lock pieces356fixed to the base portion94of the base plate92push the connecting rollers354and rotate the connecting rollers354in the take-up direction around the axial center of the adapter352. When the connecting rollers354rotate by a predetermined amount, the restricting walls370interfere with the outer peripheral portions of the connecting rollers354, such that the rotation of the connecting rollers354is restricted.

Due to the guide surfaces360further pushing the connecting rollers354in this state, the connecting rollers354are moved so as to approach the outer peripheral portion of the adapter352. Due to the guide surfaces360pushing the connecting rollers354until the connecting rollers354contact the outer peripheral portion of the adapter352, the connecting rollers354are sandwiched between the outer peripheral portion of the adapter352and the guide surfaces360. The connecting rollers354press-contact both the outer peripheral portion of the adapter352and the guide surfaces360(seeFIG. 13).

In this way, the rotation of the base plate92is transmitted to the adapter352via the lock pieces356and the connecting rollers354. The adapter352, and accordingly, the spool20which is integral with the adapter352, are rotated in the take-up direction.

The webbing belt28is taken-up onto the spool20due to the rotation of the spool20. In this way, looseness or so-called “slack” in the webbing belt28is eliminated, and the force by which the webbing belt28restrains the body of the vehicle occupant is improved. Even if the vehicle occupant thereafter carries out the operation of suddenly braking the vehicle such that a state of rapid deceleration of the vehicle arises, the webbing belt28reliably holds the body of the vehicle occupant.

In this way, when the motor44stops in the state in which slack has been eliminated, rotation of the base plate92in the take-up direction stops. When rotation of the base plate92stops, the compression coil spring150pushes the rotating disc362in the take-up direction by urging force, and rotates the rotating disc362in the take-up direction.

When the rotating disc362rotates, the wedge-shaped portions372push the outer peripheral portions of the connecting rollers354, and move the connecting rollers354away from the outer peripheral portion of the adapter352. In this way, the mechanical connection between the base plate92and the adapter352, i.e., the mechanical connection between the output shaft50of the motor44and the compression coil spring150, is cancelled (seeFIG. 12).

In this way, in the present embodiment, the wedge-shaped portions372forcibly move the connecting rollers354away from the outer peripheral portion of the adapter352. Thus, the state of press-contact between the connecting rollers354and the outer peripheral portion of the adapter352is not unnecessarily maintained due to frictional force or the like which arises between the connecting rollers354and the outer peripheral portion of the adapter352.

As described above, the connecting rollers354move by being pressed by the guide surfaces360of the lock pieces356, and press-contact the outer peripheral portion of the adapter352. However, when the connecting rollers354press-contact the outer peripheral portion of the adapter352due to sudden rotation of the base plate92, a great load is applied to the lock pieces356as well.

Here, in the present embodiment, the lock pieces356are basically structured as members which are separate from the base plate92. Thus, it is possible to improve the mechanical strength of only the lock pieces356. Therefore, even if the weight increases by forming the lock pieces356of a material having strength which can sufficiently withstand the aforementioned load, the increase in weight is limited to the lock pieces356alone.

Moreover, by improving the mechanical strength of the lock pieces356, the mechanical strength of the base plate92overall is not increased more than needed. Thus, a relatively light-weight material can be used for the entire base plate92, except for the lock pieces356. Thus, the entire clutch350can be made to be lighter weight.

Moreover, as described above, the connecting rollers354move by being pressed by the guide surfaces360. Thus, the period of time from the start of rotation of the base plate92to the time when the connecting rollers354press-contact the outer peripheral surface of the adapter352, differs slightly in accordance with the angle of inclination or the radius of curvature of the guide surfaces360.

Here, in the present embodiment, as described above, the lock pieces356are formed as separate members independent of the base plate92. Thus, plural types of lock pieces356, at which the angles of inclination or the radii of curvature of the guide surfaces360are different, are prepared and the type to be used is appropriately selected in accordance with the specifications or the requirements of the vehicle or the like. In this way, the setting of the period of time until the connecting rollers354press-contact the outer peripheral surface of the adapter352can be changed easily without changing the parts other than the lock pieces356, such as the base plate92or the like.

On the other hand, in the present embodiment, as described above, the rotation of the rotating disc362following the rotation of the base plate92is forcibly restricted by the braking mechanism300, and further, the rotating disc362is forcibly relatively rotated in the pull-out direction. In this way, relative rotation in the take-up direction of the base plate92with respect to the rotating disc362can be generated quickly and reliably. Thus, the mechanical connection between the base plate92and the adapter352due to the above-described movement of the connecting rollers354can be carried out quickly and reliably.

As described above, by rotating the spool20in the take-up direction by the torque of the motor44, the force by which the webbing belt28restrains the body of the vehicle occupant is improved. However, until the slack is eliminated, in the state in which the webbing belt28is wound on the spool20, the body of the vehicle occupant is an obstruction, and basically, the webbing belt28cannot be taken-up any further onto the spool20.

In this state, if the spool20attempts to rotate further in the take-up direction and take-up the webbing belt28, the webbing belt28tightens against the body of the vehicle occupant by a force which is greater than needed, which is not preferable.

Here, as described above, if the spool20attempts to take-up the webbing belt28any more than needed, the body of the vehicle occupant is an obstacle to the taking-up of the webbing belt28. Tensile force of a magnitude corresponding to the take-up force for the spool20to take the webbing belt28up is applied to the webbing belt28from the body of the vehicle occupant. This tensile force acts opposite to the direction in which the spool20takes up the webbing belt28. Thus, the spool20is stopped due to this tensile force being applied to the webbing belt28.

In this state, the torque of the motor44is applied to the spool20via the external gear102, the base plate92, the connecting rollers354and the adapter352. Thus, in the state in which the spool20is stopped, the connecting rollers354, which are nipped between the adapter352and the guide surfaces360, restrict rotation of the base plate92in the take-up direction via the lock pieces356. Moreover, via the torque limiters104, the base plate92restricts rotation of the external gear102in the take-up direction.

Here, in this state in which the rotation of the external gear102is limited by the base plate92via the torque limiters104, if the external gear102attempts to rotate further in the take-up direction and the torque at this time exceeds the spring force of the torque limiters104, the engaging portions106of the torque limiters104come out from the engaging recesses100. In this way, the connection between the base plate92and the external gear102is temporarily cancelled, and only the external gear102rotates in the take-up direction until the engaging portions106enter into the other, adjacent engaging recesses100.

In this way, due to the connection between the base plate92and the external gear102being cancelled, the transmission of the torque of the external gear102to the base plate92, i.e., the transmission of the torque of the motor44to the spool20, is cut-off. Thus, an increase in the restraining force applied by the webbing belt28can be suppressed.

Moreover, at the clutch350, the torque limiters104are disposed between the external gear102and the peripheral wall96, and the connecting rollers354and the rotating disc362are disposed between the peripheral wall96and the adapter352. Thus, the entire thickness dimension of the clutch350can be made to be about the axial direction dimension of the external gear102. In this way, the clutch350can be made thin, and the webbing retractor290can be made compact.

In the present embodiment, the ECU52drives the motor44via the driver46on the basis of the signal from the forward observation sensor54when the distance to an obstacle ahead is less than or equal to a given value. However, a structure is possible in which the motor44is driven in a case in which, for example, a state of rapid deceleration of the vehicle is detected by an acceleration sensor.

STRUCTURE OF THIRD EMBODIMENT

The basics of the structure of a webbing retractor390relating to the present embodiment are shown in front view inFIG. 14. The basics of the structure of the webbing retractor390are shown in exploded perspective view inFIG. 15. As shown in these figures, in the same way as the webbing retractor290relating to the above-described second embodiment, the webbing retractor390has the gears302,304,306.

However, the present webbing retractor390does not have the arm308and the lever320. Accordingly, in the present embodiment, the gears302,304,306do not structure the braking mechanism, and are merely a reduction gear train for decelerating the rotation of the output shaft50of the motor44and transmitting it to the external gear102.

In this way, the present webbing retractor390differs from the webbing retractor290relating to the second embodiment in that the webbing retractor390does not have the braking mechanism300. However, the present webbing retractor390does have the clutch mechanism350. Further, the webbing retractor390also has the friction ring378. As shown inFIGS. 14 and 15, a brake spring392, which forms the braking mechanism in the present embodiment, is accommodated in the accommodating groove380of the friction spring378instead of the brake spring324. The brake spring392is basically the same as the brake spring324. However, the pull-out direction side end portion of the brake spring392is directed in the direction opposite that of the brake spring324, and enters into a hole portion394formed in the leg plate16.

Namely, in the present embodiment, when the rotation of the output shaft50of the motor44is transmitted to the external gear102via the gears56,302,304,306and the external gear102rotates in the take-up direction, the abutment wall376attempts to rotate the compression coil spring150in the take-up direction. Moreover, the compression coil spring150presses the wall portion374A of the spring attaching portion374, and attempts to rotate the rotating disc362in the take-up direction. In this way, the friction ring378, which is integral with the rotating disc362, attempts to rotate in the take-up direction while following the brake spring392due to the frictional resistance.

However, the pull-out direction side end portion of the brake spring392is in the hole portion394formed in the leg plate16. Thus, rotation of the brake spring392itself is restricted. In this state, the brake spring392attempts, by friction, to restrict rotation of the friction ring378against the urging force of the compression coil spring150. Thus, relative rotation arises between the rotating disc362and the external gear102.

Due to relative rotation arising between the rotating disc362and the external gear102in this way, as explained in the second embodiment as well, the connecting rollers354are moved so as to approach the outer peripheral portion of the adapter352, and are nipped between the outer peripheral portion of the adapter352and the guide surfaces360. The connecting rollers354press-contact both the outer peripheral portion of the adapter352and the guide surfaces360(seeFIG. 13).

In this way, the rotation of the base plate92is transmitted to the adapter352via the lock pieces356and the connecting rollers354. The adapter352, and accordingly, the spool20which is integral with the adapter352, are rotated in the take-up direction.

Due to this rotation of the spool20, the webbing belt28is taken-up onto the spool20. In this way, looseness or so-called “slack” in the webbing belt28is eliminated, and the force by which the webbing belt28restrains the body of the vehicle occupant is improved. Even if the vehicle occupant thereafter carries out the operation of suddenly braking the vehicle such that a state of rapid deceleration of the vehicle arises, the webbing belt28reliably holds the body of the vehicle occupant.

In this way, in the present embodiment, the pull-out direction side end portion of the brake spring392is merely disposed in the hole portion394which is formed in the leg plate16. However, the brake spring392, by frictional resistance, restricts rotation of the friction ring378which is integral with the rotating disc362. Thus, effects which are similar to those of the braking mechanism60of the previously-described first embodiment and the braking mechanism300of the previously-described second embodiment can be obtained.

Moreover, in the present embodiment, in order to structure the braking mechanism, members other than the brake spring392, e.g., the arm308, the lever320, and the like, are not needed. Therefore, the webbing retractor390can be realized at a low cost, and can be made more compact and lighter weight.

As described above, in accordance with the present invention, at the time of driving of a driving mechanism, a braking mechanism forcibly restricts rotation of a rotating member which follows a prime mover rotating body, and relative rotation is forcibly generated between the prime mover rotating body and the rotating member. Thus, the prime mover rotating body and a driven shaft are reliably connected by connecting members which are interlocked with this relative rotation. The driving force of the driving mechanism can be reliably transmitted to a take-up shaft and can reliably rotate the take-up shaft.