U.S. patent application number 09/985924 was filed with the patent office on 2002-05-09 for seat belt retractor.
This patent application is currently assigned to TAKATA CORPORATION. Invention is credited to Kanamori, Yasushi, Mishina, Joji, Shiotani, Masahiro.
Application Number | 20020053621 09/985924 |
Document ID | / |
Family ID | 32912752 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020053621 |
Kind Code |
A1 |
Shiotani, Masahiro ; et
al. |
May 9, 2002 |
Seat belt retractor
Abstract
A seat belt retractor which achieves more stable performance of
a pretensioner is provided. The seat belt retractor includes a
spool for winding up a belt thereon. The spool has a shaft portion,
a spool gear, and a spring-biased shaft projection which are
disposed to project from a face of the spool. A spool bearing (or
ring-like collar) is fitted around the shaft portion of the spool.
The spool bearing is made of a material having high hardness and
high rigidity such as SUS or SC. By this spool bearing, the spool
is prevented from being directly subjected to load, like a
bearing.
Inventors: |
Shiotani, Masahiro;
(Koka-gun, JP) ; Mishina, Joji; (Koka-gun, JP)
; Kanamori, Yasushi; (Nagahama, JP) |
Correspondence
Address: |
Michael D. Kaminski
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W., Suite 500
Washington
DC
20007-5109
US
|
Assignee: |
TAKATA CORPORATION
|
Family ID: |
32912752 |
Appl. No.: |
09/985924 |
Filed: |
November 6, 2001 |
Current U.S.
Class: |
242/374 |
Current CPC
Class: |
B60R 22/4628 20130101;
B60R 22/4676 20130101; B60R 2022/468 20130101; B60R 2022/287
20130101; B60R 2022/4642 20130101 |
Class at
Publication: |
242/374 |
International
Class: |
B60R 022/46 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2000 |
JP |
JP2000-337391 |
Claims
What is claimed is:
1. A seat belt retractor comprising: a spool for winding up a seat
belt rotatably held in a frame; a bearing attached to a portion of
said spool held by said frame; a clutch mechanism arranged on one
end of said spool; a pretensioner disposed adjacent to said clutch
mechanism; and wherein said spool is made of light alloy, and said
bearing is made of steel.
2. The seat belt retractor of claim 1, wherein said pretensioner
comprises: a gas generator; a plurality of serial driving members
positioned to be accelerated by gas generated from said gas
generator; a path for guiding said driving members; a first
rotational member having a plurality of levers, wherein said
driving members collide with said levers so as to apply rotational
torque to said first rotatable member; a second rotational member
fixed to said spool; and a clutch mechanism formed by said first
rotational member and said second rotational member, wherein said
second rotational member being a pinion having external teeth; said
first rotational member being a ring gear having internal teeth
capable of meshed with the external teeth of said pinion and the
levers around the outer periphery thereof; said clutch mechanism
becomes in its coupled state where the internal teeth of said ring
gear are meshed with the external teeth of said pinion thereby
allowing said accelerated driving members to push the levers of
said ring gear so as to move said ring gear; said clutch mechanism
being in its decoupled state before the activation of pretensioner
and switching into its coupled state by the rotation of said first
rotational member when the pretensioner is activated.
3. A seat belt retractor comprising: a rotatable spool for winding
and unwinding a seat belt; a pretensioner operably connected to the
spool for rotating the spool to wind the seat belt; wherein the
pretensioner includes an opening for retaining the spool; and
wherein a bearing is positioned in the opening between the
pretensioner and the spool.
4. The retractor of claim 3, wherein the bearing comprises a
material having a greater hardness than the spool.
5. The retractor of claim 3, wherein the opening is formed in a
plate of the pretensioner.
6. The retractor of claim 3, wherein the bearing comprises a
collar.
7. The retractor of claim 3, wherein the spool includes a shaft
that extends through the opening.
8. The retractor of claim 7, wherein the bearing is positioned
between the shaft and the opening.
Description
[0001] The present invention relates to a seat belt retractor which
winds up a seat belt for restraining an occupant to a vehicle seat.
More particularly, the present invention relates to a seat belt
retractor which achieves more stable performance of a
pretensioner.
[0002] Vehicles such as automobiles are equipped with seat belt
devices for restraining rapid movement of the occupants due to
acceleration occurred at a vehicle collision to ensure the safety
of occupants. Such a seat belt device includes a seat belt
retractor which has a spool for winding a belt thereon and a spring
for retracting the belt inside the seat belt retractor and locks
the withdrawal of the belt when impact is applied, thereby
restraining the occupant. In recent years, most seat belt
retractors for vehicles have been provided with pretensioners. The
purpose of a pretensioner is to remove slack in the seat belt in
the event of a collision involving the vehicle. The pretensioner
operates by rapidly rotating the spool in the belt-winding
direction to apply tension to the seat belt.
[0003] A seat belt retractor may include the following components:
an aluminum spool for winding a belt thereon; a torsion bar fixed
to the spool to extend along the axis of the spool; a pretensioner
which is arranged on the other side of the base to rapidly rotate
the spool in the belt-winding direction in the event of a vehicle
collision; a clutch mechanism comprising a pinion fitted onto a
spool gear of the spool and a ring gear within the pretensioner;
and a return spring which is disposed on an outer surface of the
pretensioner to bias the spool in the belt-winding direction.
[0004] The pretensioner may include the following components: a
pipe; a pretensioner cover; a pretensioner plate made of steel, the
cover and plate being arranged on both sides of the pipe; a gas
generator fixed at the proximal end of the pipe; a piston, and a
plurality of balls which are arranged inside the pipe; a guide
block fitted in the other end (distal end) of the pipe.
[0005] In the seat belt retractor, the ring gear is held to the
pretensioner cover by the pins before the activation of the
pretensioner. In this state, the ring gear and the pinion are out
of mesh and have a predetermined clearance therebetween.
[0006] Therefore, the spool can freely rotate. When the gas
generator is activated to generate gas, the piston and the
plurality of balls within the pipe of the pretensioner are pushed
by the pressure of gas. The pins are sheared by the pressing force
of the balls and the holding of the ring gear is released and
internal teeth of the ring gear and external teeth of the pinion
are meshed together. As the external teeth of the ring gear are
forced by the balls so as to rotate the ring gear, the spool is
rotated via the pinion coupled with the ring gear thereby causing
the belt to be pretensioned.
[0007] A shaft portion of the spool is inserted into and held by a
hole of the pretensioner plate. When the ring gear and the pinion
couple together, the spool is strongly pressed against the
pretensioner plate due to the large impact of the ring gear and
pinion. As a result, the shaft portion of the spool may be deformed
because the spool is made of aluminum while the pretensioner plate
is made of steel. The power of the pretensioner may be reduced due
to the deformation of the shaft of the spool.
[0008] The present invention was made to solve the aforementioned
problems and the object of the invention is to provide a seat belt
retractor which enables to stabilize the performance of the
pretensioner.
SUMMARY OF THE INVENTION
[0009] To solve the aforementioned problems, a seat belt retractor
of the present invention comprises: a spool for winding up a seat
belt; a clutch mechanism arranged on one end of the spool; a
pretensioner disposed adjacent to the clutch mechanism; and a frame
holding the spool rotatably, and is characterized in that the spool
is made of light alloy, and a bearing made of steel is attached to
a portion of the spool held by the frame.
[0010] According to the present invention, when great impact is
applied during the clutch mechanism becomes in its coupled state,
the impact is transmitted to the spool through the bearing.
Therefore, the spool is prevented from being deformed, thereby
further stabilizing the performance of the pretensioner.
[0011] In the seat belt retractor of the present invention, the
pretensioner comprises: a gas generator; a plurality of serial
driving members which will be accelerated by gas generated from the
gas generator; a path for guiding the driving members; a first
rotational member having a plurality of driving points (levers),
wherein the driving members collide with the driving points so as
to apply rotational torque to the first rotatable member; a second
rotational member fixed to the spool; and a clutch mechanism
defined by the first rotational member and the second rotational
member, wherein the second rotational member is a pinion having
external teeth; the first rotational member is a ring gear having
internal teeth capable of meshed with the external teeth of the
pinion and the levers around the outer periphery thereof; the
clutch mechanism becomes in its coupled state where the internal
teeth of the ring gear are meshed with the external teeth of the
pinion by that the accelerated driving members push the levers of
the ring gear so as to move the ring gear; the clutch mechanism is
in its decoupled state before the activation of pretensioner and
becomes in its coupled state by the rotation of the first
rotational member when the pretensioner is activated (in the event
of a vehicle collision).
[0012] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only, and are not restrictive of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other features, aspects and advantages of the
present invention will become apparent from the following
description, appended claims, and the accompanying exemplary
embodiments shown in the drawings, which are briefly described
below.
[0014] FIG. 1 is an exploded perspective view showing a seat belt
retractor according to an embodiment of the present invention.
[0015] FIG. 2(A) is a sectional view, taken along the axis of a
spool, showing a clutch mechanism portion of the seat belt
retractor of FIG. 1 and FIG. 2(B) is a sectional view taken along
in the radial direction of the shaft portion of the spool.
[0016] FIGS. 3(A)-3(D) are sectional views each showing a variation
of the clutch mechanism portion of the seat belt retractor.
[0017] FIG. 4 is a frontal sectional view of a pretensioner of the
seat belt retractor according to the embodiment of the present
invention, showing the state before the activation.
[0018] FIG. 5 is a frontal sectional view of the pretensioner,
showing the state just after the activation.
[0019] FIG. 6 is an exploded perspective view showing one example
of a seat belt retractor.
[0020] FIG. 7 is a sectional view, taken along the axis of a spool,
showing a clutch mechanism portion of the seat belt retractor of
FIG. 6.
DETAILED DESCRIPTION
[0021] FIGS. 6 and 7 disclose an example of a seat belt retractor.
In these drawings, some parts are not illustrated because these are
not necessary for describing the present invention.
[0022] The seat belt retractor shown in FIG. 6 comprises the
following components: a base 101; a spool 102 for winding a belt S
thereon which is made of aluminum; a torsion bar 103 fixed to the
spool 102 to extend along the axis of the spool 102; locking
mechanisms 104, 105 which are arranged on one side (the right side
in FIG. 6) of the base 101 to prevent the rotation of the spool 102
in the belt withdrawing direction during the emergency locking
operation;
[0023] a retainer 106 for supporting one end (the right end in FIG.
6) 103a of the torsion bar 103 via the locking mechanisms 104, 105;
a pretensioner 100 which is arranged on the other side (the left
side in FIG. 6) of the base 101 to rapidly rotate the spool 102 in
the belt-winding direction in the event of a vehicle collision; a
clutch mechanism comprising a pinion 120 fitted onto a spool gear
119 of the spool 102 and a ring gear 118 within the pretensioner
100; and a return spring 108 which is disposed on an outer surface
of the pretensioner 100 to bias the spool 102 in the belt-winding
direction.
[0024] The pretensioner 100 comprises the following components: a
pipe 111; a pretensioner cover 109 made of aluminum and a
pretensioner plate 110 made of steel which are arranged on both
sides of the pipe 111; a gas generator 112 fixed at the proximal
end of the pipe 111; a stopper spring 113, a piston 114, and a
plurality of balls 115 which are arranged inside the pipe 111; a
guide block 116 fitted in the other end (distal end) of the pipe
111.
[0025] In the seat belt retractor, the ring gear 118 is held to the
pretensioner cover 109 by the pins 47 before the activation of the
pretensioner 100. In this state, the ring gear 118 and the pinion
120 are out of mesh and have a predetermined clearance
therebetween. Therefore, the spool 102 can freely rotate. When the
gas generator 112 is activated to generate gas, the piston 114 and
the plurality of balls 115 within the pipe 111 of the pretensioner
100 are pushed by the pressure of gas. As a result, the pins 117
are sheared by pressing force of the balls 115, whereby the holding
of the ring gear 118 is released and internal teeth 118b of the
ring gear 118 and external teeth 120a of the pinion 120 are meshed
with each other, that is, the coupled state of the clutch
mechanism. As the external teeth 118a of the ring gear 118 are
forced by the balls 115 so as to rotate the ring gear 118, the
spool 102 is rotated via the pinion 120 coupled with the ring gear
118. In this manner, the belt S is pretensioned.
[0026] As shown in FIG. 7, a shaft portion 122 of the spool 102 is
inserted into and thus held by a hole 110a of the pretensioner
plate 110 of the pretensioner 100.
[0027] Since the shaft portion 122 of the spool 102 is directly
held by the pretensioner plate 11. The spool 102 is forced against
the pretensioner plate 110 due to the impact produced when the ring
gear 118 and the pinion 120 mesh together (coupled with each
other). As a result, the shaft portion 122 of the spool 102 may be
deformed because the spool 102 is made of aluminum while the
pretensioner plate 110 is made of steel. The power transmitting
function of the pretensioner 100 may be reduced due to the
deformation of the spool 102.
[0028] As shown in FIG. 2A the present invention is characterized
by a spool bearing 30 interposed between a spool 2 for winding a
belt S thereon and a pretensioner plate 31 of a pretensioner 10. In
addition, as shown in FIG. 1, the basic structure of the seat belt
retractor includes the following components: a base 1; the spool 2
for winding the belt S thereon; a torsion bar 3 fixed to the spool
2 to extend along the axis of the spool 2; locking mechanisms 4, 5
for preventing the rotation of the spool 2 in the belt withdrawing
direction during the emergency locking operation; and a retainer 6
for supporting one end 3B of the torsion bar 3 via the locking
mechanisms 4, 5; a deceleration detecting device 7 for detecting
deceleration of a vehicle; a pretensioner 10 for rapidly rotating
the spool 2 in the belt-winding direction in the event of a vehicle
collision; and a clutch mechanism additionally provided for the
pretensioner 10; and a return spring 8 for biasing the spool 2 in
the belt-winding direction.
[0029] Hereinafter, description will be made as regard to the
structure of the seat belt retractor according to the embodiment of
the present invention.
[0030] As shown in FIG. 1, the base or frame 1 comprises a pair of
side walls 1A, 1B arranged in parallel, and a back plate 1C
connecting the side walls 1A, 1B.
[0031] The base 1 is, for example, a press product made of a steel
plate. The spool 102 on which the belt S is wound is disposed
between the both side walls 1A and 1B of the base 1. Further
disposed on the side wall 1A is the deceleration detecting device
7.
[0032] As shown in FIG. 1, the spool 2 has a drum-like shape. A
shaft portion 2A, a spool gear 2B, and a spring-biased shaft
projection 2C are disposed to project from the left end face (the
left side in FIG. 1) of the spool 2. As best seen in FIG. 2(A), a
spool bearing (or ring-like collar) 30 is fitted around the shaft
portion 2A of the spool 2. The spool bearing 30 is made of a
material having high hardness and high rigidity such as SUS or SC.
Also, the bearing may be made of SPCC or SPHC. The above materials
are commonly referred to as follows: SUS--stainless steels;
SC--carbon steels for machine structural use;
[0033] SPCC--cold rolled plates; and SPHC--hot rolled plates. The
surface of the spool bearing 30 may be covered with a low friction
coating.
[0034] As shown in FIG. 2(B), ribs 2a are formed at three locations
around the outer periphery of the shaft portion 2A of the spool 2.
The ribs 2a are in contact with the inner surface of the spool
bearing 30. Therefore, the spool bearing 30 and the spool 2 are
strongly coupled to each other just like one unit, thereby
preventing the backlash of the spool 2 during the normal operation
(during rotation for withdrawing or winding up the belt S). The
spool bearing 30 prevents the spool 2 from being directly subjected
to load.
[0035] The spool gear 2B of the spool 2 projects outside from the
side wall 1B of the base 1. As shown in FIG. 2(A), a pinion 20
composing a clutch mechanism inside the pretensioner 10 is fitted
around the spool gear 2B. The spring-biased shaft projection 2C is
inserted into a bush hole 8A (see FIG. 1) of a cover of the return
spring 8. The return spring 8 applies a biasing force onto the
spring-biased shaft projection 2C. The spool 2 is also provided
with a hole 2D extending in the axial direction thereof as shown in
FIG. 1. The torsion bar 3 is arranged inside the hole 2D.
[0036] As shown in FIG. 1, the torsion bar 3 comprises a bar
portion 3A and hexagonal ends 3B, 3C on the both ends of the bar
portion 3A. In the assembled state, one of the hexagonal ends 3B
(the right end in FIG. 1) is fitted and fixed to a central portion
of the back surface (a hidden surface in FIG. 1) of the locking
mechanism 4. The other hexagonal end 3C is fitted and fixed to a
portion inside the spool gear 2B of the spool 2. The torsion bar 3
is twisted for limiting the belt load in the event of a vehicle
collision, providing Energy Absorption (EA).
[0037] The locking mechanisms 4, 5 and the retainer 6 shown in FIG.
1 are arranged on the side wall 1A side of the base 1 when the seat
belt retractor is assembled. The deceleration detecting device 7
shown in FIG. 1 is mounted on the side wall 1A of the base 1.
[0038] The pretensioner 10 will now be described with reference
mainly to FIG. 1, FIG. 4, and FIG. 5. The pretensioner 10 comprises
a pipe 11. The pipe 11 is interposed between the pretensioner cover
41 and the pretensioner plate 31 and, in this state, is attached to
the outside of a side wall of the base 1. The pipe 11 is a curved
steel pipe which may, for example, be bent into the desired shape.
As best seen in FIG. 4 and FIG. 5, the pipe 11 continuously extends
from the proximal end 11A at the bottom side in the drawings to a
straight portion 11B. The portion between the proximal end 11A and
the straight portion 11B is bent at approximately 90.degree. from
the proximal end 11A toward the upper right. The pipe 11 further
continuously extends from the straight portion 11B to a
semi-circular portion 11C at the top side in the drawings. The pipe
11 further extends downwardly from the semi-circular portion 11C to
a straight portion 11D. Formed in the straight portion 11D is a
cut-out 11a facing an area surrounded by the pipe 11. One or more
of external teeth 18a of the ring gear 18, described later, are
partially positioned inside the cut-out 11a.
[0039] The ring gear 18 is arranged in the area surrounded by the
pipe 11 (this area will be referred to as "the inner area of the
pipe 11"). The ring gear 18 is held at a predetermined position in
the inner area of the pipe 11 by two pins 42 of the pretensioner
cover 41. Also arranged inside the ring gear 18 is the pinion 20.
The pinion 20 has external teeth 20a formed around the outer
periphery thereof and internal teeth 20b formed around the inner
periphery thereof. The pinion 20 is fixedly fitted around the spool
gear 2B of the spool 2 (see FIG. 2(A)).
[0040] Formed around the inner periphery of the ring gear 18 are
inner teeth 18b capable of meshing with the external teeth 20a of
the pinion 20. The inner diameter of the ring gear 18 is larger
than the outer diameter of the pinion 20. As a result, a clearance
is ensured between the internal teeth 18b of the ring gear 18 and
the external teeth 20a of the pinion 20 so that the ring gear 18
and the pinion 20 are out of mesh in the state shown in FIG. 4.
Therefore, the spool 2 can freely rotate, in spite of the existence
of the pretensioner 10. This state means the decoupled state of a
clutch mechanism composed of the ring gear 18 and the pinion
20.
[0041] The ring gear 18 has a plurality of external teeth 18a
(i.e., driving points or levers) formed around the outer periphery
thereof. The external teeth 18a project outwardly just like
projections (the number of the teeth is seven in the illustrated
example). The respective external teeth are generally spaced.
However, one tooth marked by numeral 18a' is offset. The offset
tooth 18a' is positioned inside the cut-off 11a of the straight
portion 11D of the pipe 111 and is in contact with the front-most
ball 15-1 (described later) in the pipe 11.
[0042] Formed at the proximal end 11A of the pipe 11 is a
generator-housing portion 11E of which diameter is slightly larger
than that of the pipe 11. A gas generator 12 is housed in the
generator-housing portion 11E. The gas generator 12 ignites
explosive therein according to a signal outputted from a collision
detecting means (not shown) in the event of an accident such as a
vehicle collision so as to supply gas pressure into the pipe 11.
The gas generator 12 is fixed by a crimped flange portion 11e after
being inserted in the generator-housing portion 11E.
[0043] Arranged inside the pipe 11 are, in the order from the gas
generator 12, a coil spring 13, a piston 14, and a plurality of
balls 15 (fifteen balls are shown in the illustrated example)
positioned in series. Each ball 15 (i.e., driving member) is a
sphere made of metal such as steel. Each ball 15 may be surfaced
with low frictional coating. The outer diameter of the ball 15 is
slightly smaller than the inner diameter of the pipe 11, thus
allowing relative smooth movement of the balls inside the pipe 11.
The front-most ball 15-1 is in contact with the external tooth 18a'
of the ring gear 18.
[0044] The piston 14 is made of resin such as silicone rubber. The
piston 14 is deformed to increase its diameter after the discharge
of gas so that the piston 14 comes in close contact with the inner
surface of the pipe 11, thereby achieving sealing function for
preventing gas from leaking to the distal end (the other end)
side.
[0045] The coil spring 13 is disposed between the gas generator 12
and the piston 14 to bias the piston 14 in a direction toward the
distal end. Because of the biasing force of the coil spring 13, the
front-most ball 15-1 is in contact with the external tooth 18a' of
the ring gear 18.
[0046] A guide block 16 is attached to the end of the straight
portion 11D of the pipe 11 by a vis or fastener 22. The guide block
16 is a cylindrical member having a slant end face which is formed
by obliquely cutting. This slant end face functions as a guide
face. The guide face comprises a first guide face 16a and a second
guide face 16b. The first guide face 16a is formed at the top end
of the guide block into an arc shape substantially concentrical
with the ring gear 18. During the actuation of the pretensioner,
balls 15 are forced out of the pipe 11 and then collide with the
first guide face 16a. The second guide face 16b is a flat face
which extends in such a way as to gradually increase the distance
from the ring gear 18. The vis 22 also has the function of fixing
the pipe 11 to the pretensioner plate 31
[0047] The guide block 16 has a through opening 16c which extends
from one side to the opposite side along the width direction of the
guide face. The through opening 16c is formed in a portion
substantially beneath the second guide face 16b. Because of this
through opening 16c, most of the second guide face 16b is a thin
plate so that the second guide face 16b has poor rigidity. The
first guide face 16a has high rigidity because it is supported by
the side walls of the guide block 16 itself.
[0048] As shown in FIG. 1, the pretensioner plate 31 is interposed
between the pipe 11 and the outside of the side wall 1B of the base
1. The pretensioner plate 31 is provided with a through hole 32 at
substantially the center thereof. As shown in FIG. 2(A), the shaft
portion 2A of the spool 2 around which the spool bearing 30 is
fitted is positioned inside the through hole 32.
[0049] The peripheral edge of the through hole 32 of the
pretensioner plate 31 may be formed to have a wider area as shown
in FIGS. 3(A)-3(D). Therefore, the contact area between the
peripheral edge of the through hole 32 of the pretensioner plate 31
and the outer periphery of the spool bearing 30 can be increased,
thereby reducing the bearing stress.
[0050] FIG. 3(A) is a sectional view showing an example in which
the peripheral edge of the through hole 32 of the pretensioner
plate 31 is formed to have a T-shaped section.
[0051] FIG. 3(B) is a sectional view showing an example in which
the peripheral edge of the through hole 32 of the pretensioner
plate 31 is covered by a ring member 35 having a channel-shaped
section which is made of metal (preferably iron). It should be
noted that the ring member 35 may extend radially outward a
distance indicated by a mark L in FIG. 4 (where force is exerted
during the activation of the pretensioner), and may extend axially
along the whole periphery of the through hole 32. This
configuration facilitates assembly of the ring member 35 to the
through hole 32.
[0052] FIG. 3(C) is a sectional view showing an example in which
the peripheral edge of the through hole 32 of the pretensioner
plate 31 is bent toward the ring gear 18. FIG. 3(D) is a sectional
view showing an example in which the peripheral edge of the through
hole 32 of the pretensioner plate 31 is bent in a direction
opposite to that in FIG. 3(C).
[0053] The pretensioner cover 41 shown in FIG. 1 is an aluminum
product made of die casting and is provided with a through hole 42
formed at substantially the center thereof. The spring-biased shaft
projection 2C of the spool 2 is inserted into the through hole 42.
The pretensioner cover 41 has a pipe guide 43 formed on a pipe-side
surface thereof. As shown in FIG. 4 and FIG. 5, the pipe guide 43
supports the inner area of the pipe 11 and guides the semi-circular
portion 11 C of the pipe 11. The pretensioner cover 41 further
includes two pins 47 studded to the pipe-side surface thereof. The
ring gear 18 is held in its predetermined position in the inner
area of the pipe 11 by the two pins 47. The pretensioner cover 41
is provided with a ball receiving portion 45 formed on a lower part
thereof. Balls 15 forced out of the pipe 11 are received and
gathered in the ball receiving portion 45.
[0054] The return spring 8 shown in FIG. 1 is housed in a cover.
The cover for the return spring 8 has a bush hole 8A formed at the
center thereof. The spring-biased shaft projection 2C of the spool
2 is fitted in the bush hole 8A not to allow relative rotation
because they are engaged with each other through splines. The spool
2 is always biased in the belt-winding direction by the return
spring 8.
[0055] Hereinafter, the operation of the pretensioner 10 having the
aforementioned structure will be described with regard to the
characteristics of the present invention. When the pretensioner is
not actuated (in the normal state), the ring gear 18 is held in its
predetermined position in the inner area of the pipe 11 by the two
pins 47 (see FIG. 1) of the pretensioner cover 41. In this state,
the ring gear 18 is not meshed with the pinion 20 as shown in FIG.
4. Therefore, the spool 2 freely rotates regardless of the
pretensioner 10.
[0056] As a vehicle collision is detected, a signal is transmitted
to the gas generator 12. According to this signal, as shown in FIG.
5, the gas generator 12 is activated to supply gas pressure into
the pipe 11. The piston 14 which is located nearest to the gas
generator 12 is pushed by the gas pressure. The plurality of balls
15 are subsequently pushed by the pushing force of the piston 14.
Thus, the force is transmitted to the front-most ball 15-1 (which
is in contact with the external tooth 18a' of the ring gear 18).
During this, the gas pressure deforms and increase the diameter of
the piston 14 so that the piston 14 functions as seal relative to
the inner surface of the pipe 11, thereby preventing gas from
leaking to the distal end side.
[0057] The force transmitted through the balls 15 is exerted on the
ring gear 18. As a result of this, the pins 47 (see FIG. 1) are
sheared so as to release the ring gear 18. Therefore, the ring gear
18 moves to the pinion 20, causing the internal teeth 18b of the
ring gear 18 to mesh with the external teeth 20a of the pinion 20.
The ring gear 18 is rotated about the shaft of the pinion 20 by the
force of the balls 15 pushing the external teeth 18a. Before the
ring gear 18 starts to move, the front-most ball 15-1 is in contact
with the external tooth 18a' of the ring gear 18 thereby applying
torque to the external tooth 18a', to ensure the rotation of the
ring gear 18.
[0058] While the ring gear 18 and the pinion 20 are meshed with
each other, the ring gear 18 is pushed by the driving force of the
balls 15, causing great impact to be exerted to the spool 2 side.
The impact is transmitted to the spool 2 through the spool bearing
30. The impact is not directly exerted to the spool 2, thereby
preventing the shaft portion 2A of the spool 2 from being
deformed.
[0059] As the balls 15 are subsequently pushed out by the gas
pressure, each ball 15 falls in corresponding one of the
depressions formed between the external teeth 18a of the ring gear
18. As shown in FIG. 5, one depression of the ring gear 18
corresponds to and is engaged with two balls 15. The engagements of
the balls 15 rotates the ring gear 18 in the counter-clockwise
direction in FIG. 5. The external teeth 20a of the pinion and the
internal teeth 18b of the ring gear 18 mesh together causing the
rotation of the ring gear 18 to be transmitted to the pinion 20. As
a result, the ring gear 18 and the pinion 20 move with each other.
The pinion 20 is fitted to the spool gear 2B of the spool 2,
causing the spool 2 to rotate with the pinion 20, thereby
immediately taking up some length of the seat belt S (see FIG. 1)
in the belt-winding direction. The balls 15 are forced out of the
pipe 11 through the end opening 21b of the pipe 11 and are gathered
into the ball receiving portion 45 of the pretensioner cover 41. As
described above, the present invention can stabilize the
performance of the pretensioner.
[0060] The priority application, Japanese Patent Application No.
2000-337391, is hereby incorporated by reference herein in its
entirety.
[0061] Given the disclosure of the present invention, one versed in
the art would appreciate that there may be other embodiments and
modifications within the scope and spirit of the invention.
Accordingly, all modifications attainable by one versed in the art
from the present disclosure within the scope and spirit of the
present invention are to be included as further embodiments of the
present invention. The scope of the present invention is to be
defined as set forth in the following claims.
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