A power transmission mechanism (19) for transmitting power from a motor (34) to a spindle (12) having a clutch housing (50), a pawl (41) engageable with the clutch housing (50), a gear wheel (57) which holds the pawl (41) and rotates with the rotation of the motor (34), an outer gear cover (26), and a friction ring (42) engaging with the pawl (41) and held on the outer gear cover (26) by frictional force. The friction ring (42) is provided with a protruding portion (42a) which engages with an engagement groove (41b) of the pawl (41), and a plurality of contact pieces (42b) in contact with an outer peripheral surface of a small diameter ring portion (26c) of the outer gear cover (26) and press radially against the outer peripheral surface towards an inner side The friction ring can be easily coupled to the outer gear cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national phase application of PCT International Application No. PCT/JP2016/063585, filed May 2, 2016, which claims the benefit of priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-013571, filed Jan. 27, 2016, and Japanese Patent Application No. 2015-116092, filed Jun. 8, 2015, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a seatbelt retractor, and particularly to a seatbelt retractor capable of retracting slack of a seatbelt by rotating a spindle using an electric actuator.

BACKGROUND

In conventional seatbelt retractors, a sudden deceleration state of a vehicle is detected by a sensor, whereupon a spindle is rotated in a retraction direction by a motor. When there is a possibility of a collision, a seatbelt is retracted by a prescribed amount so as to lightly restrain an occupant often (referred to as “pretensioning”) and, when a collision occurs, an explosive pretensioner is operated so as to forcibly retract the seatbelt referred to as pretensioning, whereby the occupant is securely protected.

Further, in seatbelt retractors, a power transmission mechanism for transmitting power from a motor to a spindle is provided with a clutch mechanism which transmits power from the motor to the spindle/interrupts the transmission of power from the motor to the spindle in order to prevent rotation on a spindle side from being transmitted to the motor due to the operation of the pretensioner.

For example, in the seatbelt retractor described in Japanese Patent Publication No. 2011-162157, a pawl arranged in a pawl sliding groove of a gear wheel is used to engage/disengage a clutch housing and a gear wheel arranged so as to oppose each other, thereby switching between transmission and interruption of power of a motor which rotates the gear wheel. In addition, the pawl is held, via a friction ring, in an outer gear cover which houses the clutch housing and the gear wheel. As shown inFIG. 11(a)toFIG. 11(c)provided with this specification, the prior art teaches a friction ring142for holding a pawl has a plurality of claw portions142b, each having a substantially hemispherical protruding portion142cwhich protrudes towards an outer side in a radial direction. The claw portions142bare pressed against a convex portion126aprovided on an outer gear cover126and the protruding portions142care brought into contact with an inner peripheral surface of the convex portion126a, whereby the friction ring142is held on the outer gear cover126due to frictional force.

SUMMARY OF INVENTION

However, in the above-described prior art reference, when the claw portions142bof the friction ring142are coupled to the convex portion126aof the outer gear cover126, the claw portions142bmust be temporarily contracted and then set, necessitating a contraction operation and requiring, to a certain extent, a high level of worker skill during assembly of the retractor.

The present invention has been made in view of the circumstance outlined above, and an object thereof is to provide a seatbelt retractor in which a friction ring can be easily coupled to an outer gear cover.

The object described above of the present invention is achieved by the following configuration:In a first aspect of the invention, a seatbelt retractor is provided with;a spindle for retracting a seatbelt,an electric actuator which generates power for rotating the spindle, anda power transmission mechanism which is capable of transmitting power from the electric actuator to the spindle,the power transmission mechanism includinga clutch housing which rotates together with the spindle and includes a portion to be engaged,a pawl which includes a first engaging portion that is capable of engaging with the portion to be engaged of the clutch housing,a gear wheel which includes a holding portion for holding the pawl so as to be movable, is disposed so as to oppose the clutch housing, and rotates in accordance with the rotation of the electric actuator,an outer gear cover which houses the clutch housing and the gear wheel, anda friction ring which engages with the pawl while allowing relative movement of the pawl in a radial direction and is held on the outer gear cover due to frictional force, whereina clutch mechanism, which switches between a mode in which power from the electric actuator can be transmitted to the spindle and a mode in which the transmission of power from the electric actuator to the spindle can be interrupted, by engagement/disengagement between the portion to be engaged of the clutch housing and the first engaging portion of the pawl, andthe friction ring is provided with another engaging portion which engages with a second engaging portion of the pawl so as to allow relative movement of the pawl in the radial direction, and a plurality of contact pieces which come into contact with an outer peripheral surface of a cylindrical portion formed on the outer gear cover and press against the outer peripheral surface towards an inner side in the radial direction.

In a second aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the frictional force acts between the outer peripheral surface of the cylindrical portion of the outer gear cover and the contact pieces of the friction ring.

In a third aspect of the present invention, a seatbelt retractor is provided as described above further wherein; each of the contact pieces extends in an axial direction from an inner diameter side of an annular plate portion of the friction ring, and includes a contact portion which extends in a tangential direction of the outer peripheral surface of the cylindrical portion, and the contact portions press against the outer peripheral surface of the cylindrical portion towards the inner side in the radial direction.

In a fourth aspect of the present invention, a seatbelt retractor is provided as described above further wherein; an opening is formed in each of the contact pieces.

In a fifth aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the opening is formed at least between an inner diameter side end portion of the annular plate portion and the contact portion in the extension direction of the contact piece.

In a sixth aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the outer gear cover is provided with another cylindrical portion which is formed concentrically with the cylindrical portion on an outer side of the cylindrical portion in the radial direction, and the gear wheel is fitted to the other cylindrical portion so as to be freely rotatable.

In a seventh aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the second engaging portion is an engagement groove formed in the pawl, and the other engaging portion is a protruding portion formed on the friction ring.

In an eighth aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the protruding portion is inclined with respect to a horizontal plane of an annular plate portion of the friction ring in a direction separating from the engagement groove.

In a ninth aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the friction ring is heavier than one of the pawls.

In the tenth aspect of the present invention, a seatbelt retractor is provided as described above further wherein; the portion to be engaged of the clutch housing is an inner tooth formed on an inner peripheral side of the clutch housing, and the first engaging portion of the pawl is a structure which is capable of meshing with the inner tooth.

With the seatbelt retractor of the present invention, a power transmission mechanism for transmitting power from an electric actuator to a spindle is provided with a clutch housing, a pawl which is capable of engaging with the clutch housing, a gear wheel which holds the pawl and rotates in accordance with the rotation of the electric actuator, an outer gear cover, and a friction ring which engages with the pawl and is held on the outer gear cover due to frictional force. The friction ring is provided with another engaging portion which engages with a second engaging portion of the pawl, and a plurality of contact pieces which come into contact with an outer peripheral surface of a cylindrical portion of the outer gear cover and press against the outer peripheral surface towards an inner side in the radial direction. Accordingly, the friction ring can be easily coupled to the outer gear cover while the pawl is held due to the contact between the outer peripheral surface of the cylindrical portion and the contact pieces and, as a result, automation of the coupling operation can be easily addressed. Moreover, as contact between the outer peripheral surface of the cylindrical portion and the contact pieces is tangential contact, resistance to abrasion is improved and durability is enhanced.

DETAILED DESCRIPTION

Next, a seatbelt retractor according to one embodiment of the present invention will be described in detail with reference to the drawings.

As shown inFIG. 1andFIG. 2, a seatbelt retractor10of the present embodiment includes a spindle12for retracting a seatbelt (not shown), a retraction spring device13for biasing the spindle12in a seatbelt retraction direction, a locking mechanism14for locking a withdrawal operation of the seatbelt in accordance with acceleration detected by an acceleration sensor (not shown), a motor34, that is, an electric actuator which generates power for rotating the spindle12, a pretensioner15which generates other power for rotating the spindle12, and a power transmission mechanism19which is capable of transmitting power from the motor34to the spindle12.

Both ends of the spindle12are held so as to be rotatable by the retractor frame11. A torsion bar (not shown), which constitutes an energy absorption mechanism, is provided in the spindle12. The torsion bar is connected, at a first end side thereof (left end side inFIG. 1), to the spindle12, and is connected, at a second end side thereof (right end side inFIG. 1), to a tread head (not shown) to which force from the pretensioner15is input.

The pretensioner15forcefully ejects balls (not shown) using gas generated due to the ignition of a combustible material, whereby the balls move along grooves of a pinion (not shown). Rotation of the pinion is transmitted to the tread head, the torsion bar, and the spindle12via the locking mechanism14, whereby the seatbelt is retracted.

An outer gear cover26, to which a motor assembly16is attached and in which the power transmission mechanism19is housed, is attached to the left side surface of the retractor frame11in the drawing. Further, the retraction spring device13is attached to the left side surface of the outer gear cover26.

The motor assembly16, which is located below the retractor frame11, is constituted by a motor case31, a motor34, a first gear35, a drive circuit board37, and a case cover38. Note that the first gear35is attached to the rotating shaft of the motor34and meshes with a second gear70of the power transmission mechanism19.

In the power transmission mechanism19, the second gear70, which meshes with the first gear35, is attached to a first end of a support shaft71, a third gear72is attached to a second end of the support shaft71, and the third gear72meshes with a final gear58formed on the outer peripheral surface of a gear wheel57. The support shaft71is held so as to be freely rotatable in the outer gear cover26by a pair of bearings73. Note that, in the present embodiment, the gear assembly is constituted by the first gear35, the second gear70, the third gear72, and the final gear58.

Further, as shown inFIG. 1andFIG. 2, a clutch mechanism46, which constitutes the power transmission mechanism19, is constituted by the gear wheel57, which has the final gear58formed on the outer peripheral surface thereof, a pair of pawls41, a friction ring42, a cover ring43, a gear cover44, and a clutch housing50.

As shown inFIG. 3andFIG. 4, the clutch housing50includes a boss portion51, an square shaft52which extends in the axial direction from the center of the boss portion51, a circular portion53provided with inner teeth53a, that is, portions to be engaged for the pawls41to engage with, which are formed on an inner peripheral surface thereof, a flange portion54formed outward from the boss portion51in the radial direction, and a plurality of thin fracturing portions55which connect the circular portion53and the flange portion54at a plurality of locations (four locations in the present embodiment) in the circumferential direction.

A male spline12aof the spindle12is spline-fitted to a female spline51aformed in a spindle12side of the boss portion51. As a result, the clutch housing50rotates integrally with the spindle12. Further, a spring core (not shown) of the retraction spring device13is fitted to the square shaft52of the clutch housing50so as to constantly bias the spindle12in the retraction direction.

The gear wheel57has a large diameter side cylindrical portion60, which includes the final gear58formed on an outer peripheral surface thereof, an inwardly directed collar portion61which extends towards an inner diameter side from a portion of the large diameter side cylindrical portion60that is closer to the other end thereof in the axial direction (closer to the outer gear cover26), and a small diameter side cylindrical portion62which extends from an inner diameter portion of the inwardly directed collar portion61towards the retractor frame11and has a shorter length in the axial direction than the large diameter side cylindrical portion60.

As shown inFIG. 3, the circular portion53of the clutch housing50is inserted, from the retractor frame11side towards the inwardly directed collar portion61, between the small diameter side cylindrical portion62and the large diameter side cylindrical portion60, so that the clutch housing50is housed in the gear wheel57. As a result, the inner peripheral surface of the large diameter side cylindrical portion60opposes the outer peripheral surface of the circular portion53of the clutch housing50so as to be freely rotatable relative thereto, and the outer peripheral surface of the small diameter side cylindrical portion62opposes the inner teeth53aformed on the inner peripheral surface of the clutch housing50so as to be freely rotatable relative thereto.

The inner peripheral surface of the small diameter side cylindrical portion62is fitted, so as to be freely rotatable, onto a large diameter ring portion26bwhich is formed concentrically with the clutch housing50and extends from the side wall26aof the outer gear cover26towards the direction of the clutch housing50. Note that a small diameter ring portion26c, which has a smaller diameter than that of the large diameter ring portion26b, is formed concentrically thereto on the side wall26aof the outer gear cover26on an inner diameter side of the large diameter ring portion26b.

As shown inFIG. 7, a pair of pawl sliding grooves62aare formed in the outer peripheral portion of the small diameter side cylindrical portion62of the gear wheel57, the pawl sliding grooves62aserving as holding portions for holding the pair of pawls41at an end surface of the small diameter side cylindrical portion62on a gear cover44side. The pair of pawl sliding grooves62aeach include an opening62b, which opens such that an engaging portion (first engaging portion)41aof the pawl41faces the inner teeth53aof the clutch housing50at a counter position (position rotated by 180°) to the outer peripheral surface of the small diameter side cylindrical portion62, and extend from the openings62bin mutually opposing directions so as to conform to the shape of the pawls41.

Each of the pair of pawls41includes an engaging portion41aat a first end side thereof, forms a curved shape which curves gently from the first end side thereof to a second end side thereof, and is held so as to be slidable in the pawl sliding groove62a. Each of the pair of pawls41moves, in the pawl sliding groove62a, between a first position P1(seeFIG. 7) at which the pawl41is located when the motor34is not in operation, and a second position P2(seeFIG. 9) at which the pawl41is located when the motor34is in operation and the engaging portion41ais engaged with the inner teeth53aof the clutch housing50.

Referring toFIG. 5andFIGS. 6(a) and 6(b), the friction ring42is provided with an annular plate portion42d, a pair of protruding portions (other protruding portions)42awhich protrude towards an outer side in the radial direction from counter positions (180° phase) on the outer diameter side of the annular plate portion42d, and a plurality (six in the present embodiment) of contact pieces42bwhich extend in the axial direction from the inner diameter side of the annular plate portion42d, and is formed from a single plate-shaped member. Each of the contact pieces42bis formed by bending, in the axial direction, a plate-shaped portion that extends towards an inner side from the inner diameter side of the annular plate portion42dand has a predetermined width. More specifically, each of the contact pieces42bis formed so as to have a substantially V-shaped cross section which extends in the axial direction while inclining slightly towards an inner side in the radial direction and then reverses so as to incline towards an outer side in the radial direction. The portion at which the inclination is reversed continues smoothly due to a curved surface42c. Accordingly, the curved surface42chas the same prescribed width as the contact piece42b, and is formed so as to extend linearly in the tangential direction of the outer peripheral surface of the small diameter ring portion26c.

The friction ring42presses against the outer peripheral surface of the small diameter ring portion26c, which is a non-driving portion formed on the outer gear cover26, towards an inner side in the radial direction due to the biasing force of the contact pieces42bthemselves. More specifically, the curved surfaces42cof the friction ring42make tangential contact with the outer peripheral surface of the small diameter ring portion26cdue to the elastic force of the contact pieces42b. As a result, when the contact pieces42bof the friction ring42are subject to a force in the rotational direction, frictional force is generated in a direction opposite to the rotational direction between the contact pieces42band the small diameter ring portion26cof the outer gear cover26, and the friction ring42is held on the small diameter ring portion26cdue to this frictional force. By simply pressing the friction ring42, having formed thereon each of the contact pieces42bhaving a substantially V-shaped cross section, straight towards the small diameter ring portion26cof the outer gear cover26from the axial direction, each of the contact pieces42bcomes into tangential contact with the outer peripheral surface of the small diameter ring portion26c, whereby the friction ring42is set on the outer gear cover26. For this reason, the coupling operation of the friction ring42to the outer gear cover26may be automated.

Further, the pair of protruding portions42aof the friction ring42are held in the respective engagement grooves (second engaging portions)41bof the pawls41(seeFIG. 7). Moreover, the side of the friction ring42is covered with a cover ring43(seeFIG. 3).

Further, the friction ring42is configured to be heavier than one of the pawls41. If the friction ring42is lighter than the weight of one of the pawls41then, when the friction ring42begins to rotate, friction ring42will be affected by the weight of the pawls41, making it difficult for the friction ring42to operate properly. Accordingly, the weight of the friction ring42is set to be heavier than one of the pawls41in order to facilitate proper operation thereof.

Next, operation of the seatbelt retractor10of the present embodiment will be described. When the possibility of a collision is detected by a monitoring sensor or the like (not shown), the motor34is driven by an ECU (not shown) prior to collision, thereby rotating the spindle12via the power transmission mechanism19and retracting the seatbelt. Further, when there is no longer a possibility of collision, the motor34is rotated in the opposite direction, thereby returning the seatbelt retractor10to a state in which the seatbelt can be withdrawn. During a collision, however, the pretensioner15operates so as to forcibly retract the seatbelt.

Here, operation of the clutch mechanism46will be described with reference toFIG. 7toFIG. 9. First, as shown inFIG. 7, when retraction by the motor34is not being performed, the pawl41is positioned at the innermost portion of the pawl sliding groove62a, the engaging portion41aof the pawl41is located further towards an inner diameter side than the inner teeth53aof the clutch housing50, and the clutch housing50and the pawl41are not engaged with each other. For this reason, only the clutch housing50, which is integral with the spindle12, is rotatable and normal retraction and withdrawal of the seatbelt is possible.

When the motor34rotates towards the retraction side, the driving force transmitted to the second gear70from the first gear35attached to the rotating shaft of the motor34is transmitted from the third gear72to the final gear58, and the gear wheel57rotates clockwise (arrow A) as shown inFIG. 8. At such time, each of the pawls41held due to engagement between the pair of protruding portions42aof the friction ring42and the engagement grooves41bis biased by the frictional force between the friction ring42and the small diameter ring portion26cof the outer gear cover26so as to remain in place. Accordingly, as the gear wheel57rotates in the clockwise direction, the pawl41moves relatively towards the opening62bfrom the innermost portion in the pawl sliding groove62a.

As shown inFIG. 9, when the gear wheel57rotates by a predetermined angle, the engaging portion41aof the pawl41moves beyond the opening62band engages with the inner teeth53aof the clutch housing50.

When the gear wheel57further rotates beyond the predetermined angle in the seatbelt retraction direction (arrow A), the gear wheel57, the clutch housing50, the friction ring42, and the pawl41integrally rotate in the retraction direction (arrow A) in a state where the engaging portion41aof the pawl41and the inner teeth53aof the clutch housing50are engaged, the power from the motor34is transmitted to the spindle12, and the seatbelt is retracted.

At this time, the contact pieces42bof the friction ring42slide on the outer peripheral surface of the small diameter ring portion26cof the outer gear cover26against the frictional force between the contact pieces42band the small diameter ring portion26c. However, the curved surface42cof the contact piece42b, which comes into contact with the outer peripheral surface of the small diameter ring portion26c, provides a larger contact area than in a conventional friction ring142(seeFIGS. 11(a) to 11(c)) in which contact is performed by a substantially hemispherical protruding portion142c. For this reason, even when the spring characteristics of each of the contact pieces42bvary, variation in contact area can be reduced and, as a result, variation in operating torque can be reduced.

Note that when the motor34rotates towards an unlocking side (withdrawal direction), the gear wheel57rotates counterclockwise (the direction opposite to the arrow A). In such a case, the pawl41remains in place due to the frictional force between the friction ring42and the small diameter ring portion26cof the outer gear cover26, hence the pawl41moves, in the pawl sliding groove62a, relatively towards the inner side from the opening62bas the gear wheel57rotates, and the engaging portion41aof the pawl41separates from the inner teeth53aof the clutch housing50and returns to the first position P1.

When the PP (pre-pretensioner) is operated (the motor34rotates in the retraction direction) and there is an input to the seatbelt in the withdrawal direction that is higher than a pre-set value in a state in which the engaging portion41aof the pawl41and the inner teeth53aof the clutch housing50are engaged, the thin fracturing portions55of the clutch housing50fracture so that only the boss portion51, the square shaft52integral with the boss portion51, and the flange portion54are rotatable, and transmission of power from the motor34to the spindle12is interrupted, thereby preventing the motor34from affecting the characteristics of the load limiter or the energy absorbing mechanism.

As described above, with the seatbelt retractor10of the present embodiment, the power transmission mechanism19which transmits power from the motor34to the spindle12is provided with the clutch housing50, the pawls41which are capable of engaging with the clutch housing50, the gear wheel57which holds the pawls41and rotates in accordance with the rotation of the motor34, an outer gear cover26, and a friction ring42which engages with the pawls41and is held on the outer gear cover26due to frictional force. The friction ring42includes the protruding portions42awhich engage with the engagement grooves41bof the pawls41, and a plurality of contact pieces42bthat come into contact with the outer peripheral surface of the small diameter ring portion26cof the outer gear cover26and press against the outer peripheral surface towards the inner side in the radial direction. Accordingly, the friction ring42can be easily coupled to the outer gear cover26while the pawls41are held due to the contact between the outer peripheral surface of the small diameter ring portion26cand the contact pieces42band, as a result, automation of the coupling operation can be easily addressed. Moreover, as contact between the outer peripheral surface of the small diameter ring portion26cand the contact pieces42bis tangential contact, resistance to abrasion is improved and durability is enhanced.

In particular, with the present embodiment, the frictional force described above acts between the outer peripheral surface of the small diameter ring portion26cof the outer gear cover26and the contact pieces42bof the friction ring42.

Further, the contact pieces42beach have a curved surface42cextending in the tangential direction of the outer peripheral surface of the small diameter ring portion26c, and the curved surface42cpresses against the outer peripheral surface of the small diameter ring portion26ctowards the inner side in the radial direction, hence the contact area between the outer peripheral surface of the small diameter ring portion26cand the curved surface42cis increased due to tangential contact and, even when there is variation among the spring characteristics of each of the respective contact pieces42b, variation in contact area can be reduced and, as a result, variation in operating torque can be reduced.

Further, as the contact pieces42bare formed by a bending process, processing is easier in comparison to when the conventional protruding portions142care provided.

Moreover, the outer gear cover26is provided with the large diameter ring portion26b, which is formed concentrically with the small diameter ring portion26c, on an outer side of the small diameter ring portion26cin the radial direction. As the large diameter ring portion26bis fitted, so as to be freely rotatable, to the gear wheel57as a bearing thereof, the coupling structure of the friction ring42and the outer gear cover26of the present embodiment can be designed without changing surrounding structures.

The seatbelt retractor described above is a preferred example of the present invention, and other embodiments can be implemented or executed by various methods. Unless specifically indicated in the specification of the present application, the present invention is not limited to the shapes, sizes, configuration arrangements, etc. of the detailed parts shown in the accompanying drawings. Moreover, the expressions and terms used in the specification of the present application are for the purpose of explanation and are not limited thereto unless specific indication is given to this effect.

FIGS. 10(a) and 10(b)show the friction ring42according to a modified example of the present invention. In this modified example, an opening42eis formed in each of the contact pieces42b. Due to this opening42e, it is possible to adjust the spring force of the contact pieces42bwhile securing contact area through tangential contact between the outer peripheral surface of the small diameter ring portion26cand the curved surface42c, and frictional contact force can be adjusted to an optimal level during the design phase. More specifically, as the spring force and, in turn, the frictional contact force can be reduced due to the openings42e, the operating torque of the friction ring42can be adjusted. More specifically, the opening42eis formed at least between the inner diameter side end42d1of the annular plate portion42dand the curved surface42c, that is, a contact portion, in the extension direction of the contact piece42b.

Note that, in this modified example also, the friction ring42is, in consideration of operability when rotation begins, formed so as to be heavier than one of the pawls41.

Further, the protruding portions42aof the friction ring42in this modified example are inclined with respect to the horizontal plane H of the annular plate portion42din a direction separating from the bottom surface of the engagement grooves41bof the pawls41(seeFIGS. 6(a) and 6(b)) or, in other words, are inclined upward (in a direction opposite to the extension direction of the contact pieces42b) with respect to the horizontal plane H of the annular plate portion42dinFIG. 10(b).

Were the protruding portions42ato be inclined downward (in the same direction as the extension direction of the contact pieces42b) with respect to the horizontal plane H of the annular plate portion42d, the contact pressure between the pawls41and the friction ring42would increase, and there is a possibility that the pawls41and the friction ring42would interfere with each other at times other than when necessary, and the movement of the pawls41would become unstable. For this reason, the contact pressure between the pawls41and the friction ring42can be reduced by inclining the protruding portions42aslightly upward with respect to the horizontal plane H of the annular plate portion42a.

Moreover, in the embodiment described above, the engagement groove41bformed in the pawl41and the protruding portion42aformed in the friction ring42are engaged with each other so as to allow relative movement of the pawl41with respect to the friction ring42in the radial direction, however, the present invention is not limited to such a configuration. In other words, in the present invention, as long as the second engaging portion of the pawl41and the other engaging portion of the friction ring42are engaged so as to allow relative movement of the pawl41with respect to the friction ring42in the radial direction, other configurations may also be used.

Moreover, in the embodiment described above, the engaging portion41aof the pawl41is a structure which is capable of meshing with the inner teeth53aformed on the inner peripheral side of the clutch housing50, such that power from the electric actuator can be transmitted to the spindle12, however, the present invention is not limited to such a configuration. In other words, in the present invention, as long as the portion to be engaged of the clutch housing50and the first engaging portion of the pawl41engage with/disengage from each other so that power from the electric actuator can be transmitted to the spindle12and power transmitted from the electric actuator to the spindle can be interrupted, other configurations may also be used.

In addition, in the embodiment described above, the pawl41is held, so as to be movable, by the pawl sliding groove62a, however, as long as a holding portion in the present invention holds the pawl41so as to be movable, other configurations may also be used, i.e. the configuration of the present invention is not limited to that which is described above.