JPH0820309A - Retractor for seat belt - Google Patents

Abstract

PURPOSE:To provide a retractor for a seat belt having the strength not impairing the function as a ratchet wheel and preventing the occurrence of noise by molding the ratchet teeth section of a ratchet wheel member supported on a retractor shaft out of a soft plastic. CONSTITUTION:A lock member 15 formed with a lock section 15a to be coupled with the internal teeth of a latch cup and a flange 14 constituting a lock means 31 together with a sensor spring 16 are fixed to a winding shaft in this retractor. A ratchet wheel member 50 containing a ratchet tooth section 55 having the teeth 55a connected to the sensor arm of a vehicle body acceleration detecting means is provided outside the lock member 15. The winding shaft is emergency- locked by the outputs of a webbing extracting acceleration detecting sensor and a vehicle body acceleration detecting sensor. The ratchet tooth section 55 is made of a soft plastic, and the occurrence of high-frequency noise is suppressed when the teeth 55a collide with the sensor arm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seat belt retractor (winding device), and more particularly to a seat belt retractor having an emergency lock mechanism including a webbing pull-out acceleration sensor and a vehicle body acceleration sensor. It is about improvement.

[0002]

2. Description of the Related Art A seat belt for safely holding an occupant of a vehicle on a seat is composed of a webbing, a buckle, a mounting device, and a retractor. The retractor is a device that automatically retracts the webbing when the seatbelt is not used, and is a winding device that prevents damage to the webbing and allows the length of the webbing to be freely changed when the seatbelt is used. Such retractors include automatic lock type retractors and emergency lock type retractors, but in general, in order to solve the problem of excessively restraining the occupant and giving the wearer a feeling of pressure,
An emergency lock that effectively and safely restrains the occupant with an emergency lock mechanism that physically locks the retractor by inertial sensing means that responds to sudden acceleration, collision, or deceleration, and that reduces the feeling of pressure from normal webbing Formula retractors are used. Further, as an inertial sensing mechanism used in such an emergency lock type retractor, a vehicle body acceleration sensing sensor used to lock the webbing drawer when the vehicle body receives a shock or is greatly tilted, and the webbing pullout acceleration has a predetermined value. There is a webbing pull-out acceleration sensing sensor used for locking the webbing pull-out when the above is reached.

An example of an emergency lock type retractor equipped with both a conventional vehicle body acceleration sensor and a webbing pull-out acceleration sensor is disclosed in, for example, Japanese Patent Laid-Open No. 51-1350.
There is an emergency lock type retractor disclosed in Japanese Patent No. 17. According to this publication, as shown in FIGS. 10 to 12, the ratchet wheel and the clutch mechanism, which are these inertial members, have an outer peripheral edge 101 having ratchet teeth 100 with which a sensor arm 111 of a vehicle body acceleration sensor (not shown) meshes. Flat surface 102 extending from the center toward the center
A ridge portion 103 arranged along the outer peripheral edge on a flat surface, a holding portion 104 extending inward from the outer peripheral edge of the ridge portion toward the central axis of the ratchet wheel, the holding portion 104 and the flat surface. Locking part 1 formed between 102 and
Plastic ratchet wheel 106 with
And a clutch plate 107 fitted in the locking portion,
Clutch plate 10 in the thrust direction of the winding shaft
7 (shown by an imaginary line in FIG. 11) for urging the holding member 104 toward the holding portion 104. As this urging means, as shown in FIG. 11, a plurality of elastic projections 1 which are projected from the flat surface of the ratchet wheel
08 (deformed in a direction along the flat surface 102 when mounted) or a disc-shaped leaf spring 109 arranged between the clutch plate 107 and the ratchet wheel 106 as shown in FIG.

[0004]

In the conventional ratchet wheel and clutch mechanism described above, the clutch plate and the ratchet wheel can be frictionally slidably rotated by the thrust urging means in the thrust direction. The ratchet wheel has a structure in which it is stacked in the thrust direction of the winding shaft, which has the drawback of increasing the size of the retractor. Further, in the conventional ratchet wheel and clutch mechanism, when the vehicle is traveling, especially when the vehicle is traveling on a bumpy road, the sensor arm 111 of the vehicle body acceleration detection sensor oscillates due to the vehicle vibration, and thus the ratchet teeth of the ratchet wheel. Collide with 100. As a result, there is a problem in that the ratchet wheel made of a relatively hard material in order to maintain a constant strength is struck by the sensor arm, causing an abnormal noise, which is annoying. As a countermeasure against this abnormal noise, it may be possible to form the entire ratchet wheel with a soft material, but in this case, the pressing force by the biasing means such as the elastic protrusion 108 and the leaf spring 109 described above is applied. There was a problem that the ratchet wheel itself was deformed in response to this and the function as the ratchet wheel was not fulfilled.

Therefore, an object of the present invention is to solve the above-mentioned problems. When the sensor arm collides with the ratchet teeth due to vehicle vibration, the ratchet wheel does not produce an offensive high-frequency sound, and is relatively uncomfortable. It is an object of the present invention to provide a seat belt retractor having a low-frequency sound that prevents generation of abnormal noise and has strength that does not impair the function as a ratchet wheel.

SUMMARY OF THE INVENTION It is an object of the present invention to detect a webbing pull-out acceleration sensor and a vehicle body acceleration which are rotatably provided in response to a webbing pull-out operation and can detect the pull-out acceleration of the webbing. In a seat belt retractor having a vehicle body acceleration sensor configured to be capable, a wheel portion in which the webbing pullout acceleration sensor functions as an inertia member in the rotation direction of the retractor shaft and is supported by the retractor shaft, A ratchet wheel member having a ratchet tooth portion on its outer periphery is provided, and the vehicle body acceleration detection sensor is provided with a swingable sensor arm that meshes with the ratchet tooth portion, and the ratchet tooth portion is formed of soft plastic. For seat belts characterized by being It is achieved by the tractor.

[0006]

According to the above-mentioned structure of the present invention, since the ratchet tooth portion of the ratchet wheel member is formed of soft plastic, the sensor arm of the vehicle body acceleration detecting sensor has the ratchet tooth 10 of the ratchet wheel member when the vehicle vibrates.
Even if it collides with 0, the sound will have a relatively low frequency, and the sound pressure itself will also decrease. Moreover, in the ratchet wheel member, the portions other than the ratchet tooth portion are made of a material harder than the soft plastic forming the ratchet tooth portion, so that the strength as a component of the webbing pull-out acceleration detection sensor is maintained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a seat belt retractor according to the present invention will be described in detail below with reference to FIGS. In the exploded perspective views of the seatbelt retractor shown in FIGS. 1 and 2, most of the base 1 has a U-shaped cross section, and the through holes 1b are formed in the opposite side plates 1a so as to face each other. In the through hole 1b, a take-up shaft 4 having a take-up reel 2 around which webbing is wound is fixedly rotatably bridged via left and right plastic bushes 3. A well-known winding spring device 7 that constantly biases the winding shaft 4 in the webbing winding direction is disposed at one end of the winding shaft 4.

On the other hand, an emergency lock mechanism for preventing the webbing from being pulled out in an emergency is arranged at the other end of the winding shaft 4. This emergency lock mechanism has a latch plate 4a, which is a ratchet wheel fixed to the other end of the winding shaft 4, and a part of the winding shaft 4 is projected to the outside of the latch plate 4a. 9 and a latch cup 13 which is a latch member having inner teeth 13d are loosely fitted. The spring hanger 1 formed on the latch cup 13
A return spring 12 is attached to 3b and a spring hanger 9a formed on the tension plate 9, and a biasing force for rotating the latch cup 13 in the arrow X ₂ direction is applied.

The winding shaft 4 located outside the latch cup 13 has a lock portion 15 which engages with the inner teeth 13d.
Lock member 15 and sensor spring 1 in which a is formed
The flange 14 that constitutes the locking means 31 together with 6 is fixed. Further, on the outer side of the lock member 15, there is provided a ratchet wheel member 50, which is an inertia member loosely fitted to a tapping screw 20 screwed to the flange 14 via a plane washer 17, and the outer peripheral surface thereof is provided. , A sensor arm 2 of a vehicle body acceleration sensing means 32 described later.
Tooth 55 facing the belt pull-out direction for engaging 8
A plurality of a are formed. Further, since the friction spring 18 is slidably mounted on the wheel portion 51 provided inside the ratchet wheel member 50 and the friction spring 18 is engaged with the lock member 15, the ratchet wheel member 50. Is the winding shaft 4
It is possible to rotate integrally with and to be displaced relative to the winding shaft 4.

As shown in FIGS. 6 (a), 6 (b) and 6 (c), the wheel portion 51 of the ratchet wheel member 50 has a substantially circular shape, and a center hole 52 is formed in the center thereof.
Is provided, and the shaft portion 20a of the tapping screw 20 is provided.
Is pivotally supported by. The wheel portion 51 is provided with a groove portion 53 that accommodates the friction spring 18 in a frictionally slidable state. In addition, on the outer peripheral side of the wheel portion 51, at equal intervals in the circumferential direction of the wheel portion 51,
The two fitting portions 54 are provided, and the fitting projections 55 of the ratchet tooth portion 55 of the ratchet wheel member 50 described later are provided.
The wheel portion 51 and the ratchet tooth portion 55 are integrated with each other by fitting with b.

The wheel portion 51 is formed by injection molding of plastic that is harder than the ratchet tooth portion 55 that is made of soft plastic according to the present invention.
Materials are polyacetal (POM), polyamide (P
A), polypropylene (PP) or the like having a high specific gravity containing a metal compound such as zinc oxide, iron oxide or metal powder such as stainless powder or iron powder is used. Its specific gravity is 1.5 according to the required lock sensitivity.
It can be set freely within the range of up to 4.5.

Further, the ratchet tooth portion 55 of the ratchet wheel member 50 is a ring having a substantially circular shape, and the sensor arm 28 of the vehicle body acceleration sensing means 32, which will be described later, is provided on the outer circumference.
A tooth 55a that meshes with is provided over the entire circumference. Further, on the inner peripheral side of the ratchet tooth portion 55, the wheel portion 51
Are provided with four fitting protrusions 55b which are respectively fitted to the four fitting portions.

The ratchet tooth portion 55 is made of soft plastic as referred to in the present invention, such as polyacetal (PO).
M) containing 40% by weight of urethane, or a thermoplastic elastomer (TPEE). As a result, even if the tooth 55a collides with the sensor arm 28 of the vehicle body acceleration sensing means 32, its low elastic modulus deforms and absorbs energy at the time of collision of the sensor arm, thereby suppressing generation of high-frequency sound. I am able to do that. It is possible to further suppress the generation of sound by using soft plastic for the sensor arm. The wheel portion 51 and the ratchet tooth portion 55 are separately molded, and then integrally assembled by fitting and locking the fitting portion 54 and the fitting projection 55b by pushing in the winding axial direction. The member 50 is formed.

As shown in FIG. 2, the friction spring 18 is formed by forming a linear spring steel into an annular shape, and after temporarily bending both ends of the linear spring steel inward, both ends thereof are further bent in the same axial direction. It has a symmetrical shape in which the engaging portions 18a and 18b are formed. Then, these engaging portions 18
The a and 18b are engaged with holes 15b and 15c, which are a pair of locking portions provided in the lock member 15, respectively, and deformation of the friction spring 18 in the radial direction and the radial direction is restricted.

That is, the friction spring 18 mounted on the wheel portion 51 of the ratchet wheel member 50.
Since the intermediate portion thereof frictionally engages with the groove portion 53, the locking force between the lock member holes 15b and 15c whose action direction changes depending on the rotation direction of the lock member 15 that rotates together with the winding shaft 4, respectively. The engaging portions 18a and 18b of can be received in each rotation direction. Therefore, the diameter of the friction spring 18 does not expand or contract in the radial direction depending on the rotation direction of the winding shaft 4.
The friction spring 18 has the same frictional resistance with the ratchet wheel member 50 for each rotation direction, and does not generate excessive sliding resistance with the ratchet wheel member 50.

Further, a pawl 11 which is a pawl member which is engaged with the latch plate 4a to prevent the latch plate 4a from rotating in the webbing pull-out direction (arrow X ₁ direction) is engaged with the latch plate 4a via the pole pin 10. It is detachably supported on the outside of the side plate 1a. One end of the pole pin 10 is fitted into the through hole 33 formed in the side plate 1a and the other end is fitted into the through hole 9b of the tension plate 9, so that the pole pin 10 is engaged by the meshing load between the pole 11 and the latch plate 4a. It is prevented from falling. Therefore, the pole 11 can swing and rotate around the through hole 33. A pole guide protrusion 11b is provided on the pole 11 so as to protrude, and the pole guide protrusion 11b is inserted into a pole guide hole 13c formed on the outer peripheral portion of the latch cup 13.

Further, a sensor case 27 which constitutes a vehicle body acceleration sensing means 32 is fixed to the lower portion of the side plate 1a, and a ball weight 29 as a sensor main body is placed in the hollow portion and a protrusion 28a is provided. Sensor arm 28
Is swingably attached. The sensor cover 21 is provided outside the side plate 1a that covers these emergency lock mechanisms.
Is provided.

Next, the operating state of the seat belt retractor will be described. First, in a normal use state, as shown in FIG. 3, the latch cup 13 is moved in the webbing winding direction (arrow X ₂ by the urging force of the return spring 12 mounted on the spring hanger 13b and the spring hanger 9a of the tension plate 9). Direction), and the pole guide projection 11b engages with the pole guide hole 13c. The pole 11 is biased in the arrow Z ₂ direction that is not engaged with the latch plate 4a, and the lock member 15 is locked. Since the portion 15a is urged by the urging force of the sensor spring 16 to a position that does not mesh with the inner teeth 13d of the latch cup 13, the webbing can be pulled out freely.

When the locking operation starts due to the webbing pull-out acceleration (not shown) in an emergency such as a collision, the ratchet wheel member 50 receives an inertial force to take up the winding shaft 4.
There is a rotation delay with respect to the rotation of the webbing in the drawing direction. The engaging portion 18a of the friction spring 18 mounted in the groove portion 53 of the ratchet wheel member 50 is locked by the lock member 1 rather than the biasing force of the sensor spring 16.
When the force pushing the inner surface of the hole 15b of No. 5 in the direction in which the lock portion 15a meshes with the inner teeth 13d is predominant, the lock member 15 is moved in the direction in which the lock portion 15a meshes with the inner teeth 13d.
At this time, since the intermediate portion of the friction spring 18 is frictionally engaged with the mounting portion inner peripheral wall 19b of the ratchet wheel member 50 with an appropriate frictional force, the engaging portion 18a of the friction spring 18 and the hole of the lock member 15 are formed. 1
There is no possibility that an excessive force acts on 5b to disengage it, or the friction spring 18 falls off from the mounting portion of the ratchet wheel 50 member.

Further, when the winding shaft 4 rotates in the webbing pull-out direction, the lock portion 15a of the lock member 15 and the inner teeth 13d of the latch cup 13 mesh with each other as shown in FIG. 13 and the latch cup 13 is rotated integrally with the winding shaft 4 in the arrow X ₁ direction against the biasing force of the return spring 12. Then, as shown in FIG. 5, the pole guide protrusion 1
Paul guide holes 13c for engagement in 1b is to engage the engaging portion 11a in the latch plate 4a by rotating the pawl 11 in the arrow Z ₁ direction via the pawl guide protrusion 11b.
As a result, the pole 11 moves toward the arrow X ₁ of the latch plate 4a.
The rotation in the direction, that is, the pulling-out of the webbing is suppressed and locked.

When the vehicle undergoes a speed change more than a predetermined value in an emergency, the ball weight 29 rolls to swing the sensor arm 28, and the tip 28a of the ball weight 29 is toothed 55a of the tooth portion 55 of the ratchet wheel member 50. The ratchet wheel member 50 is prevented from rotating in the belt withdrawing direction. When the webbing is further pulled out while the ratchet wheel member 50 is prevented from rotating, a rotation delay occurs in the ratchet wheel member 50 with respect to the rotation of the winding shaft 4 in the webbing pull-out direction.
The locking means 31 operates to lock the drawer of the webbing as described above.

Hereinafter, FIGS. 7 (a), 7 (b) and 7 (c)
Second Embodiment A seat belt retractor according to a second embodiment of the present invention will be described in detail with reference to FIG. 7A is a plan view of a wheel member of a seat belt retractor based on the second embodiment, FIG. 7B is a sectional view taken along line bb in FIG. 7A, and FIG. It is CC sectional drawing in FIG. 7 (a). The same members as those shown in FIGS.
The same reference numerals are given and detailed description thereof is omitted.

The wheel portion 61 of the ratchet wheel member 60 in the second embodiment has a substantially circular shape, and a center hole 62 is provided in the center thereof, and is axially supported by the shaft portion 20a of the tapping screw 20. . The wheel portion 61 is provided with a groove portion 63 that accommodates the friction spring 18 in a frictionally slidable state. Further, on the outer peripheral side of the wheel portion 61, eight engaging protrusions 64 are provided at equal intervals in the circumferential direction of the wheel portion 61, and engage with an engaging step portion 65b of a ratchet tooth portion 65 described later. Thus, the wheel portion 61 and the ratchet tooth portion 65 are integrated.

The ratchet tooth portion 65 is a ring having a substantially circular shape, and the outer periphery of the tooth 65 engages with the sensor arm 28 of the vehicle body acceleration sensing means 32 described in the first embodiment.
a is provided over the entire circumference. Further, on the inner peripheral side of the ratchet tooth portion 65, an engagement step portion 65b that engages with each of the eight engagement protrusion portions 64 of the wheel portion 61 is provided.
The ratchet wheel member 60 including the wheel portion 61 and the ratchet tooth portion 65 is formed by double molding. That is, first, the wheel portion 61 is injection-molded, then the mold of the molding machine is appropriately replaced, and the ratchet tooth portion 65 is molded by injecting another resin. In this case, it is preferable to select the material so that the wheel portion 61 has a higher temperature between the resin temperature at the time of molding the wheel portion 61 and the resin temperature at the time of molding the ratchet tooth portion 65. The portion 61 is made of a polyacetal (POM) -based material having a relatively high mechanical strength, and the ratchet tooth portion 65 is made of a polyamide (PA) -based or polyethylene (PE) -based soft grade. Therefore, in the second embodiment of the present invention, since the ratchet wheel member 60 is formed by double molding, the wheel portion 61 and the ratchet tooth portion 65 are formed.
It is possible to provide the ratchet wheel member 60 so as to have two highly reliable functions without falling off, separation, dropping, and the like.

A third embodiment of the seat belt retractor according to the present invention will be described in detail below with reference to FIGS. 8 (a), 8 (b), 8 (c) and FIG. FIG. 8A is a plan view of a wheel member of a seat belt retractor based on the third embodiment, and FIG. 8B is a b- in FIG. 8A.
b sectional view, FIG. 8C is a sectional view taken along line cc in FIG. 8A, and FIG. 9 is a part of an exploded perspective view. The same members as those in FIGS. 1 to 7 are designated by the same reference numerals,
Detailed description thereof will be omitted.

The wheel portion 71 of the ratchet wheel member 70 in the third embodiment is made of a substantially circular metal plate, and a center hole 72 is provided in the center thereof, and is pivotally supported by the shaft portion 20a of the tapping screw 20. There is. The wheel portion 71 is provided with a connecting portion 73 projecting in the axial direction of the wheel portion 71, which engages with a hole 115b which is a locking portion provided in the lock member 115 and enables the lock member 115 to operate. . The connecting portion 73 is formed by pressing. By performing this press work, a waste hole is formed around the connecting portion 73, so that the wheel portion 7
1 is provided with a balance hole 74 on the opposite side of the center hole 72 for preventing an inertial unbalanced state corresponding to the waste hole.

Further, the ratchet tooth portion 77 of the ratchet wheel member 70 is a substantially circular ring, and all the teeth 77a that mesh with the sensor arm 28 of the vehicle body acceleration sensing means 32 described in the first embodiment are provided on the outer circumference. It is provided all around. Further, on the inner peripheral side of the ratchet tooth portion 77, a circular fitting groove 78 having a substantially U-shaped cross section for fitting the circular outer edge portion 75 of the wheel portion 71 is provided.
Has a structure that does not fall out of the ratchet teeth. Further, the circular outer edge portion 75 and the circular fitting groove 78 are both circular, so that they can relatively rotate and slide.

The ratchet tooth portion 77 is formed by insert-molding a metal wheel portion 71. Ratchet teeth 77
Is molded from plastic, and by utilizing the molding shrinkage force, the circular outer edge portion 75 of the metal wheel portion 71 is appropriately pressure-bonded. By allowing the ratchet teeth 77 to retain the crimping force, the rotary sliding resistance between the circular outer edge portion 75 and the circular fitting groove 78 is obtained. further,
On the inner peripheral side of the ratchet tooth portion 77, a crimping force adjusting hole 76 for adjusting the crimping force of the metal wheel portion 71 after the molding contraction is provided.

The ratchet teeth 65 are formed of polyacetal (POM) type soft grade or the like, so that even if the teeth 55a collide with the sensor arm 28 of the vehicle body acceleration sensing means 32, the elastic modulus thereof is low. , It is possible to suppress the generation of high frequency sound by deforming and absorbing the energy when the sensor arm collides. That is, according to the third embodiment of the present invention, it is possible to obtain relative rotational sliding between the circular outer edge portion 75 and the circular fitting groove 78 by insert molding of a metal plate, and the wheel portion. Since 71 is provided with the connecting portion 73 protruding in the axial direction thereof, the friction spring is unnecessary. Further, since the metal plate is insert-molded, the circular outer edge portion 75 of the wheel portion 71 and the circular fitting groove 78 of the ratchet tooth portion 77 having a substantially U-shaped cross section are fitted to each other. 71 and the ratchet teeth 77 do not fall off, separate, fall off, etc., and a highly reliable component can be provided.

[0030]

As described above, according to the present invention, since the ratchet teeth of the ratchet wheel member are formed of soft plastic, the sensor arm of the vehicle body acceleration detecting sensor is the ratchet wheel member ratchet wheel member when the vehicle vibrates. Even if it collides with a tooth, it produces a sound with a relatively low frequency, and the sound pressure itself also decreases. Moreover, in the ratchet wheel member, the portions other than the ratchet tooth portion are made of a material harder than the soft plastic forming the ratchet tooth portion, so that the strength as a component of the webbing pull-out acceleration detection sensor is maintained.

[Brief description of drawings]

FIG. 1 is a part of an exploded perspective view of a seat belt retractor according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of a remaining portion of the seat belt retractor shown in FIG.

FIG. 3 is a broken side view of a main part for explaining a webbing pullout locking operation of the seat belt retractor shown in FIGS. 1 and 2.

FIG. 4 is an enlarged view of a main part for explaining a webbing pullout lock operation of the seat belt retractor shown in FIGS. 1 and 2.

5 is an enlarged view of a main part for explaining a webbing pullout locking operation of the seat belt retractor shown in FIGS. 1 and 2. FIG.

6A is a plan view of a wheel member of a seat belt retractor according to a first embodiment of the present invention, FIG. 6B is a sectional view taken along line bb in FIG. 6A, and FIG. 6 is a sectional view taken along line cc in FIG.

7A is a plan view of a wheel member of a seat belt retractor according to a second embodiment of the present invention, FIG. 7B is a sectional view taken along line bb in FIG. 7A, and FIG. 6 is a sectional view taken along line cc in FIG.

8A is a plan view of a wheel member of a seat belt retractor according to a third embodiment of the present invention, FIG. 8B is a sectional view taken along line bb in FIG. 8A, and FIG. 6 is a sectional view taken along line cc in FIG.

FIG. 9 is a part of an exploded perspective view of a seat belt retractor according to a third embodiment of the present invention.

FIG. 10 is a front view of a conventional ratchet wheel and clutch mechanism.

11 is a sectional view taken along line XII-XII in FIG.

FIG. 12 is a cross-sectional view of another conventional ratchet wheel and clutch mechanism.

[Explanation of symbols]

 28 sensor arm 50 ratchet wheel member 55 ratchet tooth portion 60 ratchet wheel member 65 ratchet tooth portion 70 ratchet wheel member 77 ratchet tooth portion

Claims (1)

[Claims] 1. A webbing pull-out acceleration sensor which is rotatably provided in response to a webbing pull-out operation and is configured to detect a pull-out acceleration of the webbing, and a vehicle body acceleration sensor which is configured to detect a vehicle body acceleration. In a seatbelt retractor provided with a ratchet wheel member having a wheel portion supported by the retractor shaft and a ratchet tooth portion on the outer periphery, wherein the webbing pull-out acceleration detection sensor functions as an inertia member in the rotation direction of the retractor shaft. The vehicle body acceleration detecting sensor includes a swingable sensor arm that meshes with the ratchet tooth portion, and the ratchet tooth portion is formed of soft plastic for a seat belt. Retractor.