Seat belt retractor

A seat belt retractor incorporated in a seat back that does not create noise, even with the vibration of a vehicle. A reel is supported by a frame, and reel rotation is prevented by a locking mechanism. In the locking mechanism, rotation of a gear wheel is prevented by an acceleration sensor, and a trigger is pivoted through a clutch wheel to engage a tooth portion with teeth on a lock ring, thereby stopping rotation of an intermediate wheel. Ratchets are supported by a ratchet wheel associated with the intermediate wheel. Since the ratchet wheel rotates even after stopping rotation of the intermediate wheel, the ratchets move outward whereby a stopper is pressed down. This cancels the engagement between a rack on a sensor holding portion and a rack of the stopper.

BACKGROUND OF THE INVENTION 
The present invention relates to a retractor for a seat belt device 
installed in a vehicle, more particularly, to a seat belt retractor 
suitable for being incorporated in a seat back of a seat. Incorporating a 
seat belt retractor in a seat back provides various advantages such as it 
is not necessary to mount a seat belt anchoring member on a center pillar 
of the vehicle body. 
A typical seat belt retractor comprises a locking mechanism for locking a 
reel when a vehicle accelerates more than a predetermined value. When the 
typical seat belt retractor is incorporated in the seat back, the typical 
seat belt retractor is tilted according to the tilt of the seat back, 
causing the locking mechanism of the typical seat belt retractor to lock. 
Therefore, in this case, the typical seat belt retractor needs a mechanism 
for preventing the seat belt retractor from becoming locked due to seat 
back tilt. Europe Patent No. 351,551 discloses a seat belt retractor 
including such a mechanism. 
FIG. 25 is a structural view of the seat belt retractor of the Europe 
Patent, which is provided with an activating mechanism 204 having a gear 
wheel 202 to lock a reel rotatably supported by a frame 200. The 
activating mechanism 204 constitutes one part of a locking mechanism (not 
shown). 
The gear wheel 202 has teeth 206 facing an acceleration sensor 208. The 
acceleration sensor 208 comprises a weight 210 allowed to tilt, a casing 
212 holding the weight 210, a lever 214 laid on the weight 210, and an 
actuator 215. The pivot end of the lever 214 is supported by the casing 
212. The pivot end of the actuator 215 is rotatably supported by the frame 
200. As the weight 210 tilts, the lever 214 is pushed up so that a tip 
215a of the actuator 215 is also pushed up, such that the tip 215a of the 
actuator 215 engages one of the teeth 206. This actuates the activating 
mechanism 204 with the result that the locking mechanism (not shown) is 
actuated. 
The casing 212 is pivotally supported by a shaft 218. The casing 212 is 
provided with a weight 220 for keeping the casing 212 oriented vertically. 
The weight 220 is fan shaped and is provided with a rack 222 extending 
along the periphery thereof. A contact 224 is pressed against the rack 222 
by a torsion spring 226. The contact 224 can be rotated around a bar 228. 
As the seat back is tilted, the weight 220 pivots around the shaft 218 so 
as to maintain the vertical orientation of the casing 212. The contact 224 
engages the rack 222 to damp rocking movement of the weight 220. 
In the conventional seat belt retractor as mentioned above, when the weight 
220 reacts to a large acceleration, the contact 224 and the rack 222 slip 
with respect to each other to allow the movement of the weight 220. In the 
conventional seat belt retractor, slippage between the contact 224 and the 
rack 222 creates noise. Since the conventional seat belt retractor is 
incorporated in the seat back near an occupant's ear, slippage causes an 
unpleasant noise at the occupant's ear. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a seat belt retractor 
which does not cause such noise. 
A seat belt retractor according to the present invention comprises a reel 
for winding up a seat belt, and a locking mechanism for preventing the 
rotation of the reel when acceleration over a predetermined value is 
exerted. The locking mechanism comprises: a mass which tilts according to 
the acceleration to activate the locking mechanism; a casing capable of 
pivoting, the casing holding the mass; and a casing holder engaging the 
casing to prevent the pivotal movement of the casing, and wherein the 
casing holder releases the casing when the locking mechanism is activated 
to prevent rotation of the reel. 
In the seat belt retractor according to the present invention, the casing 
may pivot freely when an acceleration activating the locking mechanism is 
exerted. Normally, the casing does not pivot, so noise is not created. 
The casing holder preferably comprises: a first engaging member disposed on 
the opposite side of the axis of the reel through the casing; a second 
engaging member disposed on the casing and capable of engaging the first 
engaging member; and an engagement canceler for moving the first engaging 
member apart from the second engaging member to cancel the engagement 
between the first engaging member and the second engaging member when the 
locking mechanism is activated. 
The engagement canceler preferably comprises: a wheel member capable of 
changing the diameter thereof and disposed coaxially with the reel; and a 
facing member facing the outer periphery of the wheel member, wherein the 
facing member is connected to the first engaging member, the facing member 
is pressed and moves radially with respect to the axis of the reel when 
the wheel member changes the diameter thereof so that the first engaging 
member moves apart from the second engaging, member to cancel the 
engagement therebetween. 
The wheel member preferably comprises: a ratchet wheel rotating integrally 
with the reel, a plurality of ratchets rotatably supported by pivot shafts 
around the outer periphery of the ratchet wheel in such a manner that the 
ratchets are capable of projecting from the outer periphery of the ratchet 
wheel. The pivot shafts projects perpendicularly to a face of the ratchet 
wheel. 
The ratchet wheel preferably acts on a facing member disposed near the 
periphery of the ratchet wheel. The facing member is pressed by the 
ratchets in such a direction as to move with respect to the axis of the 
ratchet wheel. 
It is preferable that the facing member is a plate extending in an arc 
shape along the outer periphery of the ratchet wheel and is biased toward 
the axis of the ratchet wheel by a biasing member. 
It is preferable that the first engaging member comprises: a concave 
arcuate face extending along a part of a circle centered on the axis of 
the ratchet wheel; and a first rack formed on the concave face, while the 
second engaging member comprises a second rack engaging the first rack. 
It is preferable that the casing is capable of pivoting around the axis of 
the ratchet wheel and is supported by a member having an arm portion 
extending in the radial direction of the ratchet wheel whereby the casing 
is capable of moving to a position vertically below the axis of the 
ratchet wheel when the engagement between the racks is canceled. 
It is preferable that the reel is rotatably supported by the frame and the 
casing is pivotally supported on the frame. 
Further, the casing is preferably provided with a dead mass to keep the 
casing in a vertical orientation. 
It is also preferable that the second engaging member is a rack formed on a 
bottom outer face of the dead mass, the bottom outer face being curved in 
an arc shape, and wherein the first engaging member is a protrusion for 
engaging the rack, the protrusion being disposed to confront the rack and 
connected to the plate. 
According to the present invention, it is preferable that the seat belt 
retractor further comprises an intermediate wheel confronting the ratchet 
wheel. 
The intermediate wheel rotates with the ratchet wheel without any 
restriction by the acceleration sensor when acceleration detected by the 
acceleration sensor is less than a predetermined value. The intermediate 
wheel has ratchet guide pins around the periphery thereof projecting from 
a face confronting the ratchet wheel, the ratchet guide pins being in 
contact with the ratchets. 
Rotation of the intermediate wheel is stopped and the ratchets are 
projected outward by the ratchet guide pins when the acceleration sensor 
detects acceleration over the predetermined value.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Hereinafter, preferred embodiments will be described with reference to 
attached drawings. FIGS. 1 through 20 show the structure of a seat belt 
retractor according to a preferred embodiment. 
As shown in FIG. 1, a frame 10 has a pair of side walls 12, 14 extending 
parallel to each other, and a back plate 16 for connecting the side walls 
12 and 14. The frame 10 is provided with a reel 20 for winding up a seat 
belt 18 and a locking mechanism 22 for locking the winding of the reel 20 
at an emergency. 
The side walls 12, 14 are provided with holes 26, 28 coaxially formed with 
each other, and on which inner circumferences are provided teeth 26a, 28a, 
respectively. 
The reel 20 has a shaft, projecting from the center of the left-side 
surface in FIG. 1, to which the central end of a return spring 24 is 
connected through a bush shaft 50a. The other end of the return spring 24 
is fixed to the side wall 12 through covers 25a, 25b. As the seat belt 18 
is withdrawn, the reel 20 rotates in such a direction that the return 
spring 24 is compressed. When the seat belt 18 is released, the reel 20 
rotates by the biasing force of the return spring 24 so as to 
automatically wind up the seat belt 18 onto the reel 20. It should be 
noted that the reel 20 rotates in a direction of the arrow A.sub.1 when 
the seat belt 18 is withdrawn. 
The reel 20 has flanges 30, 32 at both sides, which are provided with holes 
30a, 32a, respectively, through which a pawl pin 34 is inserted. 
The pawl pin 34 has a rectangular end on the left side in FIG. 2. As also 
shown in FIGS. 2 and 3, the left end of the pawl pin 34 is inserted into a 
rectangular hole 36b of a left pawl 36 and fixed by a screw 40. 
A right pawl 38 has a round hole 38b at the rear end side thereof, into 
which a right-side portion of the pawl pin 34 is rotatably inserted. 
Both pawls 36, 38 are provided with teeth 36a, 38a, respectively, which 
engage the teeth 26a, 28a of the aforementioned frame 10 to prevent the 
rotation of the reel 20 in the direction Al allowing withdrawal of the 
belt. The right pawl 38 has a guide pin 42 projecting outwardly relative 
to the reel 20. 
The pawl pin 34 is provided with an arm 44 extending perpendicularly to the 
longitudinal direction of the pawl pin at the right end in FIG. 1. The arm 
44 is provided with an arm guide pin 46 projecting from the distal end 
thereof and extending parallel to the pawl pin 34. 
The aforementioned locking mechanism 22 has a ratchet wheel 52 provided 
with a central hole 52a into which a shaft 50 projecting from the center 
of the right end face of the reel 20 is rotatably inserted as shown in 
FIGS. 2 through 7. The ratchet wheel 52 is provided with a plurality of 
pivot shafts 52b disposed circumferentially at equal intervals and 
projecting perpendicular to the face of the ratchet wheel 52. Ratchets 54 
have holes 54a (FIG. 8) at the rear ends, respectively, into which 
respective pivot shafts 52b are inserted. 
After placing the ratchets 54 on the pivot shafts 52b, a disk-like 
intermediate wheel 56 is disposed so as to sandwich the ratchets 54 with 
the ratchet wheel 52. The shaft 50 is received in a central hole 56a of 
the intermediate wheel 56. The intermediate wheel 56 is provided with 
circumferentially elongated holes 58 disposed around the periphery 
thereof, wherein the number of the elongated holes 58 is the same as the 
number of pivot shafts 52b so that the tips of the pivot shafts 52b are 
inserted into respective elongated holes 58. 
The intermediate wheel 56 is provided with a convex shaft 62 for supporting 
a pivotal trigger 60 (FIG. 9, FIG. 10). The convex shaft 62 is inserted 
into a hole 60a of the arc-like trigger 60. 
A compression coil spring 64 is disposed between the intermediate wheel 56 
and the trigger 60. That is, the intermediate wheel 56 has a small 
projection 66 extending parallel to the face of the wheel 56 and the 
trigger 62 has a small projection 68 facing the small projection 66 so 
that the spring 64 is disposed between both projections 66, 68. The 
trigger 60 is provided with a tooth portion 70 at an end thereof opposite 
to the small projection 68 of the trigger 60 with respect to the hole 60a. 
The tooth portion 70 engages internal teeth 76 of a lock ring 74 so as to 
prevent rotation of the intermediate wheel 56. The compression coil spring 
64 compresses the trigger 60 so that the tooth portion 70 is normally 
positioned apart from the internal teeth 76. 
The lock ring 74 has a ring-like portion where the internal teeth 76 are 
formed on the inner periphery thereof. The lock ring 74 is installed to 
the side wall 14 of the frame 10 in such a manner that the ring-like 
portion surrounds the outer peripheries of the wheels 52, 56. The numeral 
74a designates through holes into which bolts are inserted for mounting 
the lock ring 74 to the side wall 14. 
As shown in FIGS. 4, 6, 7, and 8, the left side face, in FIG. 1, of the 
intermediate wheel 56 is provided with ratchet guide pins 80 for guiding 
the ratchets 54 to pivot outwardly and ratchet stopping pins 82 for 
preventing the ratchets from pivoting excessively outward and returning 
the ratchets 54 to the initial positions. 
The ratchet guide pins 80 are in contact with inner surfaces of the 
ratchets 54, respectively, which are supported by the ratchet wheel 52. 
The ratchet stopping pins 82 are in contact with outer surfaces of the 
ratchets 54, respectively, as shown in FIG. 8A when there is no rotational 
phase shift between the ratchet wheel 52 and the intermediate wheel 56. 
When there is no rotational phase shift between the ratchet wheel 52 and 
the intermediate wheel 56, the ratchets 54 are each sandwiched between 
pins 80 and 82 to prevent pivoting. When the ratchet wheel 52 rotates in 
the direction A.sub.1 in FIG. 8 (in the belt withdrawing direction) with 
the rotation of the intermediate wheel 56 being prevented, rotational 
phase shifts are caused between the wheels 52 and 56. Therefore, the 
ratchets 54 are pushed up by the ratchet guide pins 80 to pivot outward as 
shown in FIG. 8B. Thus, a stopper 130 to be described later is pressed in 
such a direction as to move away from the shaft 50. 
The ratchet wheel 52 and the intermediate wheel 56 are provided with holes 
84 and 86, respectively, through which the pawl pin 34 is inserted. The 
hole 84 is a round hole having a diameter slightly larger than that of the 
pawl pin 34. The hole 86 of the intermediate wheel 56 is an elongated hole 
which is circumferentially elongated to allow the rotational phase shift 
between the wheels 52 and 56. The hole 86 is formed in such a manner as to 
extend along a part of a circle around the central hole 56a of the 
intermediate wheel 56 to have equal radii from the central hole 56a. 
The intermediate wheel 56 is provided with an elongated hole 88 adjacent to 
the hole 86, and a further elongated hole 90 adjacent to the elongated 
hole 88. The arm guide pin 46 at the end of the arm 44 of the pawl pin 34 
is inserted into the elongated hole 88. The guide pin 42 of the right pawl 
38 is inserted into the elongated hole 90. 
The elongated holes 88, 90 extend in an oblique direction between the 
circumferential direction and the radial direction. Specifically, the 
elongated hole 88 is formed in such a manner as to extend along a part of 
a circle around the central hole 56a of the intermediate wheel in a 
position near the hole 86 and to diverge away from the central hole 56a 
further from the hole 86. The elongated hole 90 is also formed obliquely 
in such a manner as to diverge away from the central hole 56a further from 
the hole 88. 
Since the elongated hole 86 extends along a part of a circle centered 
around the central hole 56a and the elongated hole 88 is formed obliquely, 
rotational phase shift between the wheels 52 and 56 is caused by rotating 
the ratchet wheel 52 in the direction A.sub.1 (the belt withdrawing 
direction) when the intermediate wheel 56 is stopped. At this point, the 
pawl pin 34 moves in the elongated hole 86 in the direction A.sub.1. 
Movement of the pawl pin 34 causes the arm 44, with the arm guide pin 46 
inserted into the elongated hole 88, to move away from the central hole 
56a (the shaft 50) and causes the pawl pin 34 to rotate around the axis of 
the pawl pin 34 in the direction P.sub.1 shown in FIGS. 2 through 6. 
Therefore, the left pawl 36 also rotates in the direction of P.sub.1 with 
the pawl pin 34 so that the teeth 36a engages the teeth 26a on the frame 
10. 
Since the elongated hole 90 is formed obliquely in the same manner as the 
elongated hole 88, when rotational phase shift between the wheels 52 and 
56 is caused by rotating the ratchet wheel 52 in the direction A.sub.1 and 
the intermediate wheel 56 is stopped, the guide pin 42 of the right pawl 
38 moves in the elongated hole 90 away from the elongated hole 88 and the 
guide pin 42 moves away from the shaft 50. Therefore, the right pawl 38 
rotates around the pawl pin 34 axis in the direction P.sub.1 so that the 
teeth 38a of the right pawl 38 engage the teeth 28a on the frame 10. 
The right and left pawls 36, 38 engage the teeth 26a, 28a, thereby 
preventing the rotation of the reel 20 and preventing the withdrawal of 
the belt 18. As for right and left pawls 36 and 38, one of the pawls first 
engages one of the teeth 26a, 28a and then the other pawl engages the 
other one of the teeth 26a, 28a after a little delay. 
The time delay between the engagements secures the engagements between the 
pawls 36, 38 and the teeth 26a, 28a of the frame 10. 
Because the central hole 52a of the ratchet wheel 52 is fitted on the shaft 
50, and the pawl pin 34 into the hole 84, the ratchet wheel 52 must rotate 
integrally with the reel 20 so that no rotational phase shift is possible 
between the ratchet wheel 52 and the reel 20. 
As for the intermediate wheel 56, the shaft 50 is inserted into the central 
hole 56a of the intermediate wheel 56 so as to allow relative rotational 
phase shift with respect to the reel 20 and the ratchet wheel 52. 
Therefore, a coil spring 94 is disposed in a concave 96 of the flange 30 
of the reel 20 to bias the intermediate wheel 56 in a direction to cancel 
the rotational phase shift. 
The intermediate wheel 56 has a projecting piece 98 standing at a right 
angle on the face confronting the reel 20 as shown in FIGS. 3, 4, and 6. 
The projecting piece 98 is inserted into the concave 96 through a window 
hole 100 of the ratchet wheel 52 such that the projecting piece 98 is 
inserted between the spring 94 and an internal wall 96a (FIG. 4) of the 
concave 96. 
When the engagement between the pivotal trigger 60 and one of the internal 
teeth 76 of the lock ring 74 prevents rotation of the intermediate wheel 
56, so as to cause rotational phase shift between the reel 20 and the 
ratchet wheel 52 with respect to the intermediate wheel 56, the spring 94 
is compressed. As the force locking (preventing the rotation of) the 
intermediate wheel 56 is removed, the intermediate wheel 56 rotates in 
such a manner as to negate the rotational phase shift between the wheels 
52 and 56 due to the biasing force of the spring 94. 
The shaft 50 is inserted into the central hole 56a of the intermediate 
wheel 56, and the distal end of the shaft 50 is rotatably engaged with a 
central hole 104a of the gear wheel 104 (shown in FIGS. 11 through 13). 
The gear wheel 104 is provided with teeth 104b around the outer periphery 
thereof. One of the teeth 104b can be engaged by a lever 108 of an 
acceleration sensor 106. 
As shown in FIG. 13, the sensor 106 comprises a casing 110 and a mass 112 
loosely supported in the casing 110 in such a manner as to tilt. The mass 
112 contacts the lower face in the longitudinal middle of the lever 108. 
The lever 108 is pivotally supported by the casing 110. When the mass 112 
tilts, the tip of the lever 108 is pushed up to engage one of the teeth 
104b. The engagement between the tip of the lever 108 and the teeth 104b 
prevents rotation of the gear wheel 104. 
As shown in FIGS. 11 and 12, a clutch wheel 116 is disposed inside the gear 
wheel 104. The clutch wheel 116 is fitted with a C-shape spring 118 bent 
in an arc shape and disposed in such a manner as to extend along the outer 
periphery of the clutch wheel 116. The spring 118 is bent at both ends 
118a in the radial direction. Both ends 118a are engaged to projections 
116a disposed on the face at the reel 20 side of the clutch wheel 116. 
The arc-like portion of the C-like spring 118 is positioned at the 
periphery of the clutch wheel 116 so as to elastically contact the inner 
periphery of the gear wheel 104. 
When rotation of the gear wheel 104 is not prevented by the lever 108, the 
clutch wheel 116 rotates integrally with the gear wheel 104 due to the 
frictional force of the spring 118. When rotation of the gear wheel 104 is 
prevented by lever 108, the clutch wheel 116 is subjected to the same 
frictional force from the gear wheel 104 but allowed to rotate. 
As shown in FIG. 12, the clutch wheel 116 is provided with a starting pin 
120 disposed perpendicularly on the face confronting the intermediate 
wheel 56. The starting pin 120 contacts a side face of the trigger 60 near 
the tooth portion 70, as shown in FIG. 12B. 
As shown in FIG. 13, a bush 122 mounted on the tip of the shaft 50 
pivotally supports a sensor holder 124. 
The sensor holder 124 comprises an elongated, plate-like arm portion 126 
having a supporting hole 126a at an upper end which is fitted on the bush 
122, and a sensor holding portion 128 integrally disposed on a lower end 
of the arm portion 126. The sensor holding portion 128 has a bottom (outer 
surface) which is curved in a convex arc shape and provided with a male 
rack 128a. 
The lock ring 74 guides a stopper 130 which is allowed to move in the 
radial direction for positioning the sensor. That is, the lock ring 74 has 
a pair of side walls 132 extending from the bottom of the ring-like 
portion the lock ring 74. The rectangular frame-like stopper 130 is 
slidably disposed between the side walls 132 and 132. The stopper 130 has 
a bottom (inner surface) which is concaved in an arc shape and provided 
with a female rack 130a capable of engaging the male rack 128a. 
The upper surface (outer surface) of the stopper 130 has a concave arc 
shape. The upper surface of the stopper 130 faces the ratchet wheel 52 and 
the ratchets 54. The stopper 130 is biased toward the ratchet wheel 52 by 
a spring 136. 
The stopper 130 is biased as mentioned above so that the upper surface of 
the stopper 130 slides against the ratchet wheel 52 and the ratchets 54. 
To minimize the friction produced by the sliding, the stopper 130 has a 
solid lubricant layer (not shown) formed on the upper surface. 
It should be noted that a cover case 134 (FIG. 1) is mounted on the side 
wall 14 of the frame 10 to cover the entire locking mechanism 22. 
The description of the operation of the seat belt retractor as structured 
above is as follows. 
In a normal state of a vehicle (for example, when the vehicle is stopping 
or driving at a fixed speed), the mass 112 of the acceleration sensor 106 
is vertically oriented and the tip of the lever 108 is spaced apart from 
the teeth 104b of the gear wheel 104. When the seat belt 18 is withdrawn, 
the reel 20 and the shaft 50 freely rotate with the ratchet wheel 52, the 
intermediate wheel 56, the gear wheel 104, and the clutch wheel 116 so 
that the seat belt is smoothly withdrawn. When the seat belt 18 is 
released or a buckle is released, the seat belt 18 is smoothly wound onto 
the reel 20 by the return spring 24. 
The ratchets 54 are positioned inward as shown in FIG. 14 and the female 
rack 130a of the stopper 130 is engaged with the male rack 128a of the 
sensor holding portion 128 by the spring 136. 
When the vehicle is subjected to large acceleration or deceleration by a 
collision or the like, the locking mechanism 22 is activated to prevent 
the withdrawal of the seat belt 18. A large acceleration exerted on the 
locking mechanism 22 causes the mass 112 to tilt. Thus, the distal end of 
the lever 108 is pushed up and engages one of the teeth 104b of the gear 
wheel 104, thereby preventing rotation of the gear wheel 104 (FIG. 16A 
through FIG. 18C). 
During a collision, an occupant's body tends to move forward toward the 
front of the vehicle pulling on the seat belt 18 so that the reel 20 
rotates in the belt withdrawing direction (A.sub.1). Since the reel 20 and 
the ratchet wheel 52 must integrally rotate, and the intermediate wheel 56 
is pressed by the spring 94, the wheels 52 and 56 rotate whenever the reel 
20 rotates. The trigger 60 disposed on the intermediate wheel 56 also 
rotates integrally with the intermediate wheel 56. 
The clutch wheel 116 contacts the inner periphery of the gear wheel 104 due 
to the C-like spring 118, and slides with friction on the inner periphery 
of the gear wheel 104. Since the starting pin 120 projecting from the face 
of the clutch wheel 116 contacts the side face of the trigger 60 near the 
tooth portion 70, the trigger 60 on the intermediate wheel 56 is subjected 
to a reaction force in the opposite direction by the starting pin 120 when 
the intermediate wheel 56 rotates. The biasing force of the spring 64 
against the trigger 60 is smaller than the force produced by the sliding 
friction between the clutch wheel 116 (the C-like spring 118) and the gear 
wheel 104. Therefore, the trigger 60 is pressed by the starting pin 120 to 
rotate about the supporting shaft 62 in the direction of B1 shown in FIGS. 
10 through 12 and 17 through 19. The tooth portion 70 of the trigger 60 
engages one of the internal teeth 76 of the lock ring 74 to stop rotation 
of the intermediate wheel 56. 
Even after rotation of the intermediate wheel 56 is stopped, the reel 20 
and the ratchet wheel 52 continue to rotate. The guide pin 42 of the right 
pawl 38 moves within the elongated hole 90 whereby the right pawl 38 
rotates in the direction P.sub.1 (FIG. 4) and the teeth 38a of the right 
pawl 38 engage the teeth 28a of the hole 28 in the frame 10. In addition, 
the pawl pin 34 moves within the elongated hole 86 and the arm guide pin 
46 moves within the elongated hole 88 so that the pawl pin 34 rotates in 
the direction P.sub.1 (FIGS. 2 and 3) and the left pawl 36 also rotates in 
the direction P.sub.1 such that the teeth 36a of the left pawl 36 engage 
the teeth 26a of the hole 26 in the frame 10. 
Therefore, the reel 20 is locked stopping the withdrawal of the seat belt 
18, thus protecting the occupant. 
When the intermediate wheel 56 is stopped from rotating by the trigger 60 
and the ratchet wheel 52 still rotates, the ratchets 54 pivot outward as 
shown in FIG. 8 and FIG. 19. The inward face of each ratchet 54 contacts a 
ratchet guide pin 80, pivoting ratchets 54 outward in the direction R1 
upon rotation of the ratchet wheel 52. The stopper 130 disposed below the 
outer periphery of the ratchet wheel 52 is pressed down by the ratchets 54 
as shown in FIG. 15, whereby the female rack 130a of the stopper 130 
separates from the male rack 128a of the sensor holder 124. 
When the seat belt 18 is rapidly withdrawn, rotation of the clutch wheel 
116 and the gear wheel 104 is delayed with respect to the reel 20 because 
of inertia. The starting pin 120 presses the trigger 60 in the direction 
B1 so that the tooth portion 70 of the trigger 60 engages the internal 
teeth 76 of the lock ring 74. As a result, the pawls 36 and 38 engage the 
teeth 26a and 38a, respectively, to stop the withdrawal of the seat belt 
18. 
When the force withdrawing the seat belt 18 is canceled, the rotational 
phase shift between the ratchet wheel 52 and the intermediate wheel 56 is 
canceled by the spring 94 as shown in FIG. 20. The ratchets 54 return 
inwardly, the stopper 130 is pressed upward by the spring 136, and the 
racks 130a and 128a engage each other. 
When the angle of the seat back of the vehicle seat is changed, the seat 
belt retractor with the sensor holder 124 is tilted. As a result, the mass 
112 of the acceleration sensor 106 tilts with respect to the sensor holder 
124 so that the tip of the lever 108 engages the teeth 104b of the gear 
wheel 104. Therefore, when the seat belt 18 is first attempted to be 
withdrawn after changing the angle of the seat back, the reel 20 is 
prevented from rotating by the operation of the locking mechanism 22, and 
the seat belt 18 cannot be withdrawn. 
Since the stopper 130 is pressed down by the ratchets 54, the female rack 
130a of the stopper 130 and the male rack 128a of the sensor holder 124 
are separated from each other. The top inner surface of the stopper 130 
comes into contact with the lever 108 so that the lever 108 is pushed down 
by the top inner surface, whereby the teeth 104b of the gear wheel 104 
move apart from the tip of the lever 108. The sensor holder 124 pivots on 
the bush 102 such that the arm portion 126 is vertically oriented. 
Therefore, by loosening the seat belt 18 after that, the rotational phase 
shift between the ratchet wheel 52 and the intermediate wheel 56 is 
canceled by the spring 94 so that the ratchets 54 pivot inward, the 
stopper 130 is pressed upward by the spring 136, and the racks 128a and 
130a re-engage each other again. Since cancellation of the rotational 
phase shift between the ratchet wheel 52 and the intermediate wheel 56 
returns the right pawl 38 and the left pawl 36 to their normal positions, 
the seat belt 18 can be smoothly withdrawn after that. 
Since the sensor holder 124 is stopped relative to the stopper 130 by the 
engagement between the racks 128a and 130a, the sensor holder 124 cannot 
move even when a large acceleration is exerted on the sensor holder 124. 
Therefore, no noise is created. 
FIG. 21 through FIG. 24 show another embodiment. In this embodiment, the 
structure of the acceleration sensor 106A is different from the structure 
of the acceleration sensor 106. 
Similar to the acceleration sensor 106, a mass 112 is supported by a casing 
138. The acceleration sensor 106A comprises a dead mass 140 disposed on 
the lower surface of the casing 138 for vertically orienting the casing 
138. The casing 138 is pivotally supported on a housing 142. The housing 
142 has an L-shaped bracket 144 so that the casing 138 is disposed between 
a body 146 of the housing 142 and the bracket 144 of the housing 142. 
Projections 150, 148 from the casing 138 are supported on the body 146 and 
the bracket 144, respectively. 
The projection 150 penetrates an intermediate hole 153 of a stopper 152. 
The stopper 152 is vertically oriented and has a protrusion 154 at the 
lower end. The protrusion 154 is disposed below the dead mass 140 when 
assembled, and is capable of engaging a rack 140a formed on the arc-like 
bottom of the dead mass 140. 
The stopper 152 is integrally provided with an arc-like guide plate 156 at 
the upper end. The guide plate 156 has a concave upper surface which faces 
the aforementioned ratchet wheel 52 and ratchets 54. The stopper 152 is 
biased upward by a spring 160 so that the guide plate 156 slides on the 
outer periphery of the ratchet wheel 52. 
Levers 162 and 164 are disposed above the mass 112. The lever 162 is 
supported by the casing 138 through shafts 162a, 162b, and the lever 164 
is supported by the housing 142 through shafts 164a, 164b. The tip of the 
lever 164 is capable of engaging one of the teeth 104b of the gear wheel 
104. 
When the mass 112 tilts, the tip of the lever 164 engages the teeth 104b of 
the gear wheel 104 so as to lock the reel 20. 
When the angle of the seat back is changed, the mass 112 also tilts, and 
the tip of the lever 164 engages the teeth 104b of the gear wheel 104 so 
as to lock the reel 20. When the seat belt 18 is first withdrawn, the 
guide plate 156 is pressed down by the ratchets 54 so that the protrusion 
154 moves apart from the rack 140a. Then, the casing 138 is returned to 
the vertical orientation by pivotal movement caused by the dead mass 140. 
When the tension exerted on the seat belt 18 is canceled, after that, the 
reel 20 can again freely rotate. 
In the embodiment of FIG. 21 through FIG. 24, since the protrusion 154 
normally engages the rack 140a due to the spring 160, the casing 138 and 
the related members do not rock so that no noise is created. 
In FIG. 22A and FIG. 23, the numeral 170 designates springs for absorbing 
the impact of the dead mass 140 and for preventing the impact noise. 
Alternatively, rather than the pawls 36, 38 engaging the teeth 26a, 28a on 
the frame 10, the pawls may be mounted on the frame 10 and the reel 20 may 
have a wheel including teeth which engage the pawls. 
According to the seat belt retractor of the present invention, the 
acceleration sensor returns to the vertical oriented position regardless 
of how the angle of the seat back is changed. In addition, the rocking 
members of the acceleration sensor are fixed not to rock in the normal 
state so that no noise is created, even with the vibration of the vehicle 
during driving.