U.S. patent application number 09/755196 was filed with the patent office on 2001-07-19 for seat belt tension adjuster.
Invention is credited to Yano, Hideaki.
Application Number | 20010008261 09/755196 |
Document ID | / |
Family ID | 18535774 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008261 |
Kind Code |
A1 |
Yano, Hideaki |
July 19, 2001 |
Seat belt tension adjuster
Abstract
A seat belt tension adjuster adjusts tension on a seat belt
wound on a reel by a biasing spring. The tension adjuster includes
a biasing force adjusting mechanism situated between the reel and
the spring for adjusting a biasing force transmitted from the
spring to the reel depending on a rotational angular position of
the reel. The biasing force adjusting mechanism includes a cam for
gradually changing the biasing force based on the rotational
angular position of the reel. The tension adjuster can freely set
the withdrawing force and the winding force of the seat belt.
Inventors: |
Yano, Hideaki; (Tokyo,
JP) |
Correspondence
Address: |
KANESAKA AND TAKEUCHI
1423 Powhatan Street
Alexandria
VA
22314
US
|
Family ID: |
18535774 |
Appl. No.: |
09/755196 |
Filed: |
January 8, 2001 |
Current U.S.
Class: |
242/375.3 |
Current CPC
Class: |
B60R 2022/4413 20130101;
B60R 22/44 20130101 |
Class at
Publication: |
242/375.3 |
International
Class: |
B60R 022/44; B65H
075/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 17, 2000 |
JP |
2000-007376 |
Claims
What is claimed is:
1. A seat belt tension adjuster for adjusting tension on a seat
belt wound on a reel by a biasing spring to be used in a vehicle,
comprising: a biasing force adjusting mechanism situated between
the reel and the spring for adjusting a biasing force transmitted
from the spring to the reel depending on a rotational angular
position of the reel, said biasing force adjusting mechanism
including a cam for setting a biasing force adjusting ratio to be
an arbitrary function depending on the rotational angular portion
to thereby gradually change the biasing force based on the
rotational angular position of the reel.
2. A seat belt tension adjuster according to claim 1, wherein said
biasing force adjusting ratio is Fo / Fx, wherein Fx is an input
biasing force from the spring to the biasing force adjusting
mechanism and Fo is an output biasing force from the biasing force
adjusting mechanism to the reel.
3. A seat belt tension adjuster according to claim 1, wherein said
biasing force adjusting mechanism further includes a slit plate
having an input shaft to be connected to the spring and a first
slit extending in a radial direction from the input shaft, a lever
to be connected to the reel and having a second slit, and a pin,
said cam being disposed between the slit plate and the lever and
having a cam groove so that the pin is slidable situated in the
first and second slits through the cam groove.
4. A seat belt tension adjuster according to claim 3, further
comprising a base plate immovably attached to the lever, said slit
plate and cam being slidable relative to the base plate.
5. A seat belt tension adjuster according to claim 4, further
comprising a reduction gear mechanism to be arranged between the
biasing force adjusting mechanism and the reel for reducing
rotation transmitted from the reel to the biasing force adjusting
mechanism.
6. A seat belt tension adjuster according to claim 5, wherein said
base plate is fixed to the reduction gear mechanism.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to a device for adjusting
tension on a seat belt used in a vehicle or automobile, and more
particularly, to a mechanical seat belt tension adjuster which can
freely set the withdrawing force and the retracting force of the
seat belt.
[0002] A normal seat belt system currently installed in an
automobile has a tension spring employing a leaf spring. The leaf
spring is formed in a spiral shape and has an inside end connected
to a shaft of a reel for winding the seat belt and an outside end
fixed to a housing of a seat belt retractor. The biasing force of
the leaf spring exerts torque to the reel in a belt winding
direction.
[0003] In the aforementioned seat belt retractor, the tension on
the seat belt significantly varies with the withdrawn amount of the
seat belt. For example, when the seat belt is fully wound up, the
distortion of the leaf spring is the minimum and the biasing force
is thus weak, so that the tension on the seat belt is thus small.
On the other hand, when the seat belt is fully withdrawn, the
distortion of the leaf spring is the maximum, the biasing force is
thus strong, and the diameter of a circle formed by the seat belt
wound on the reel is small. Thus, the tension on the seat belt is
large. Due to the variation in the belt tension, the pressure by
the seat belt increases against a large occupant to make the
occupant uncomfortable. As conventionally pointed out, there is
also a problem that the retractor sometimes can not wind up the
seat belt completely.
[0004] It has been developed to provide a seat belt retractor which
can exert a constant tension in spite of the withdrawn amount of
the seat belt. For example, proposed by Japanese Unexamined Utility
Model Publication No. 58-203772 is a mechanism of equalizing the
biasing force of a spring by using cone pulleys. In this mechanism,
the biasing force of the spring is amplified and is then
transmitted to the reel in a position near the limit to which the
seat belt is wound up. On the other hand, the biasing force of the
spring is reduced and is then transmitted to the reel in a position
near the limit to which the seat belt is withdrawn. In this manner,
the tension on the seat belt can be constant in spite of the
withdrawn amount of the seat belt.
[0005] Bet tension adjusting devices having cone pulleys just like
the aforementioned publication are proposed by U.S. Pat. Nos.
5,730,385 and 5,803,400. Although these devices can equalize the
biasing force, these devices can not freely set the tension on the
seat belt. In addition, although these devices proposed by the
patents have switches to change from a light mode to a heavy mode
and vice versa, in which the tension values set in the respective
modes are significantly different from each other, these devices
can not smoothly adjust the magnitude of the tension between a
small value and a large value.
[0006] In considering the aforementioned problem of the variation
in a belt tension as the limit of the mechanical seat belt
retractor, there is an idea that a reel for a seat belt is driven
by a motor. In this case, the tension on the seat belt can be
freely set because the torque of the motor can be freely
controlled. Further, there is an idea that the rotational biasing
force for the reel is amplified or reduced by using an
electromagnet. However, the electric retractor requires a lot of
parts as compared to the mechanical retractor using only one leaf
spring. The electric retractor also requires wirings for
transmitting electrical power and control signals.
[0007] The present invention has been made with reference to the
aforementioned problems, and an object of the present invention is
to provide a mechanical seat belt tension adjuster which can free
set the withdrawing force and the winding force of the seat
belt.
SUMMARY OF THE INVENTION
[0008] To solve the aforementioned problems, the present invention
provides a seat belt tension adjuster for adjusting the tension on
a seat belt used in a vehicle comprising: a reel on which the seat
belt is wound; a spring for producing rotational biasing force to
be imparted to the reel; and a biasing force adjusting mechanism
arranged between the reel and the spring for adjusting the biasing
force to be transmitted from the spring to the reel depending on
the rotational angular position .omega. of the reel. The biasing
force adjusting mechanism includes a cam for setting a biasing
force adjusting ratio .alpha. to be an arbitrary function depending
on the rotational angular position .omega. when the biasing force
adjusting ratio .alpha. is Fo / Fx, i.e. Fo / Fr=.alpha., wherein
Fx is the input biasing force from the spring to the biasing force
adjusting mechanism and Fo is the output biasing force from the
biasing force adjusting mechanism to the reel.
[0009] Since the seat belt tension adjuster of the present
invention has the cam for setting the biasing force adjusting ratio
.alpha. to be an arbitrary function depending upon the rotational
angular position .omega. of the reel, the tension (withdrawing
force/winding force) of the seat belt can be freely set in spite of
variation in the biasing force of the tension spring. Since a
retractor of the present invention including the tension adjuster
is of a mechanical type, parts including a motor for obtaining
external power and wirings are not required.
[0010] In the seat belt tension adjuster of the present invention,
the spring may be a leaf spring, one end of which is fixed. The
biasing force adjusting mechanism comprises a slit plate having an
input shaft, to which the other end of the leaf spring is fixed to
a position apart from the center of the input shaft, and a slit
extending in the radial direction; and a pin slidably situated in
the slit. The cam is a cam plate having a cam groove in which the
pin slides.
[0011] The biasing force adjusting ratio .alpha. can be freely set
by suitably selecting the configuration of the cam groove of the
cam plate. The seat belt retractor according to the present
invention can be compact as compared to a conventional one having
cone pulleys.
[0012] The seat belt tension adjuster of the present invention may
further comprise a reduction gear mechanism arranged between the
biasing force adjusting mechanism and the reel for reducing the
rotation to be transmitted from the reel to the biasing force
adjusting mechanism.
[0013] Because of the reduction gear mechanism, the moving amount
of the leaf spring can be reduced. Accordingly, there is an
advantage of reducing the load of the leaf spring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is an exploded perspective view showing the structure
of a seat belt tension adjuster according to one embodiment of the
present invention;
[0015] FIGS. 2(A)-2(C) are plan views showing various examples of
the structures of the cam grooves formed in cam plates; and
[0016] FIG. 3 is a graph of S-F curves indicating the relation
between the withdrawn length "S" of the seat belt and the
withdrawing force "F" thereof.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] Hereinafter, the description will be made with reference to
the attached drawings. In the following description, directions
including "right and left" means directions indicated in the
drawings.
[0018] FIG. 1 is an exploded perspective view showing the structure
of a seat belt tension adjuster according to an embodiment of the
present invention. This seat belt tension adjuster comprises in a
broad aspect the following main components:
[0019] (1) a leaf spring 1 for generating tension on a seat
belt,
[0020] (2) a biasing force adjusting mechanism 3 composed of a slit
plate 11, a cam plate 13, a pin 15, and a lever 17,
[0021] (3) a reduction gear mechanism 4 of a planetary gearing
type, and
[0022] (4) a reel 5 onto which the seat belt 7 is wound.
[0023] The leaf spring 1 is formed in a spiral shape and has an
inside end connected to an input shaft 11a of the slit plate 11 of
the biasing force adjusting mechanism 3 for winding up the seat
belt. An outside end of the leaf spring 1 is fixed to a housing 2
of a seat belt retractor. The biasing force of the leaf spring 1
exerts torque to the reel 5 in a belt winding direction via the
biasing force adjusting mechanism 3 and the reduction gear
mechanism 4.
[0024] The slit plate 11 has a disk-like main body 11e. The main
body 11e has the input shaft 11a which is formed to stand on the
center of the main body 11e and to which the aforementioned spring
1 is connected. The input shaft 11a is provided at the core thereof
with an axial hole 11c opening to the rear surface of the slit
plate 11. Fitted in the axial hole 11c is a shaft 13a of the cam
plate 13 described later. The slit plate 11 also has a slit 11g
which extends in the radial direction. The slit 11g penetrates the
main body 11e. The pin 15 described later is slidably fitted in the
slit 11g.
[0025] The cam plate 13 has the disk-like main body 13e. The main
body 13e has the shaft 13a which is formed to stand on the center
of the main body 13e. The shaft 13a fits in the aforementioned
axial hole 11c of the slit plate 11, and the slit plate 11 and the
cam plate 13 are coaxial with each other to allow relative rotation
with each other. The shaft 13a is provided at the core thereof with
an axial hole 13c opening to the rear surface of the cam plate 13.
Fitted in the axial hole 13c is a small shaft 19a of a base plate
19 described later. The cam plate 13 is formed with a spiral cam
groove 13g. The cam groove 13g penetrates the main body 13e. The
pin 15 described later is slidably fitted in the cam groove
13g.
[0026] The pin 15 is cylindrical. One end portion of the pin 15 is
fitted in the slit 11g of the slit plate 11. A middle portion of
the pin 15 is fitted in the cam groove 13g of the cam plate 13. The
other end portion of the pin 15 is fitted in a slit 17e of the
lever 17 described later. Depending on the fitting position of the
pin 15 in the cam groove 13g, the position of the pin 15 in the
radial direction apart from the rotation center of the cam plate 13
is defined. The biasing force adjusting ratio .alpha. can be
obtained according to the radial position R2 of the pin 15. The
biasing force adjusting ratio will be described in detail
later.
[0027] The lever 17 is a substantially rectangular plate. The lever
17 is provided at the center thereof with an axial hole 17c which
is formed to penetrate the lever 17. Fitted in the axial hole 17c
is a large shaft 19c of the base plate 19 described later. The
lever 17 is provided at an upper portion thereof with a slit 17e
extending in the radial direction. The slit 17e penetrates the
lever 17. The other end portion of the pin 15 slides in the slit
17e. The lever 17 is also provided at a lower portion thereof with
a pin hole 17a which is formed to penetrate the lever 17. Fitted in
the pin hole 17a is a pin 19e of the base plate 19 described
later.
[0028] The base plate 19 is a circular plate. The base plate 19 has
the large shaft 19c and the small shaft 19a which are formed to
stand on the center of the base plate 19. The small shaft 19a is
formed to stand on the large shaft 19c. The small shaft 19a is
fitted in the axial hole 13c of the cam plate 13. The large shaft
19c is fitted in the axial hole 17c of the lever 17. The base plate
19 also has the pin 19e which is formed to stand on a lower portion
in the drawing (left surface in the drawing) of the base plate 19.
The pin 19e is fitted in the pin hole 17a of the lever 17. The base
plate 19 is provided on the outer periphery thereof with four key
grooves 19g equally spaced apart from each other at 90.degree.. The
key grooves 19g penetrate the base plate 19. Fitted in the key
grooves 19g are keys 21c with an internal gear 21, respectively, as
described later.
[0029] The internal gear 21 has a ring-like shape and internal
teeth 21a formed on the inner periphery thereof. The internal teeth
21a mesh with external teeth 23a formed on a planetary gear 23
described later. The internal gear 21 is provided on the peripheral
edge with the four keys 21c equally spaced apart from each other at
90.degree.. These keys 21c are fitted in the key grooves 19g of the
base member 19.
[0030] The planetary gear 23 has the external teeth 23a. The
external teeth 23a mesh with the internal teeth 21a of the internal
gear 21 and with external teeth 25a of a sun gear 25. An arm 24
which is fixed to the retractor housing 2 is held between the shaft
center of the planetary gear 23 and the axis of the sun gear 25.
The sun gear 25 has the external teeth 25a which mesh with the
external teeth 23a of the planetary gear 23. The sun gear 25 is
fixed to a shaft 5c which is formed to stand on an end surface of
the reel 5.
[0031] The reel 5 has a drum portion onto which the seat belt 7 is
wound. The reel 5 is provided at an end thereof with a flange 5a.
The shaft 5c for fixing the sun gear 25 is formed on the center of
the flange 5a.
[0032] The slit plate 11 and the cam plate 13 can rotate about the
small shaft 19a of the base plate 19. The lever 17 can not rotate
relative to the base plate 19 by the pin 19e. The pin 15 is fitted
in the slit 11g of the slit plate 11, the cam groove 13g of the cam
plate 13, and the slit 17e of the lever 17. As the lever 17 rotates
according to the rotational angle of the reel 5, the pin 15 also
moves according to the rotation of the lever 17. The slit plate 11
synchronizes with the lever 17 via the pin 15 to rotate together.
At this time, the cam plate 13 takes a rotational position
depending upon the engaging condition between the pin 15 and the
cam groove 13g.
[0033] Hereinafter, description will now be made as regard to the
biasing force adjusting ratio .alpha. of the seat belt tension
adjuster.
[0034] First, the leaf spring 1 exerts a biasing force Fr to the
shaft 11a of the slit plate 11. This force is transmitted to the
pin 15 fitted in the slit 11g. The pin 15 transmits the force to
the lever 17 and further transmits the force to the base plate 19
via the lever 17. Assuming that the current radial position of the
pin 15 is R2, an equation Fx.times.R1=Fp.times.R2 is obtained from
the balance of torque. Accordingly, an equation Fp=Fx.times.(R1/R2)
is obtained. That is, the force Fp transmitted from the pin 15 to
the lever 17 varies depending on the radial position R2 of the pin
15. Here, R2 is defined by the configuration of the cam groove 13g
of the cam plate 13 and the rotational angular position of the reel
5. Therefore, by suitably setting the configuration of the cam
groove 13g of the cam plate 13, the force Fp transmitted from the
pin 15 to the lever 17 can be freely set according to the
rotational angular position .omega. of the reel.
[0035] The lever 17 is prevented from rotating relative to the base
plate 19 by the pin 19e. Accordingly, the force transmitted from
the pin 15 to the lever 17 is directly transmitted to the base
plate 19. Therefore, the force transmitted to the base plate 19 can
also be freely set according to the rotational angular position
.omega. of the reel. In the same manner, the same force is
transmitted to the internal gear 21 which is fixed to the base
plate 19 by the keys.
[0036] Then, the force transmitted to the internal gear 21 is
transmitted to the reel 5 via the reduction gear mechanism 4
composed of the planetary gear 23 and the sun gear 25. By adjusting
the gear ratio of the reduction gear mechanism 4, the force
transmitted from the base plate 19 to the reel 5 can be set
optimally.
[0037] From the above description, the biasing force adjusting
ratio .alpha. of the seat belt tension adjuster is defined by the
radius R1 of the shaft 11a of the slit plate 11, the radial
position R2 of the pin 15, and the gear ratio Rc of the reduction
gear mechanism 4. Among them, the radius R1, the gear ratio Rc, and
the radius R3 are inherent in the device and thus can be designed
to obtain optimal biasing force. During the operation, these values
do not vary.
[0038] On the other hand, the radial position R2 of the pin 15
varies during the operation of the device. Therefore, according to
the variation of the R2 during the operation, the ratio .alpha.
between the input biasing force Fx from the spring to the biasing
force adjusting mechanism and the output biasing force Fo from the
biasing force adjusting mechanism to the reel can be changed during
the operation.
[0039] FIGS. 2(A)-2(C) are plan views showing various examples of
the configurations of the cam grooves formed in the cam plate 13.
These drawings are also seen as .omega.-R curves indicating the
relation between the rotational angular position .omega. of the
leaf spring 1 and the radial position R2 of the pin 15. By
employing these various configurations of the cam grooves, the
biasing force adjusting ratio .alpha. can be variously set.
[0040] The following description will be made as regard to the
variation in the belt tension with reference to FIG. 3.
[0041] FIG. 3 is a graph of S-F curves indicating the relation
between the withdrawn length "S" of the seat belt and the
withdrawing force "F".
[0042] A case of a conventional seat belt is shown by a solid line
41. This curve shows that the input biasing force of the leaf
spring 1 is increased as the seat belt is withdrawn.
[0043] Cases of the seat belt devices using the cam plate of the
present invention are shown by dashed lines 43 and chain
double-dashed lines 45. In these cases, even when the withdrawn
length is increased, the withdrawing force is substantially
constant. To obtain such results, it should be designed such that
the radial position R2 of the pin 15 is gradually increased as the
rotational angular position .omega. of the reel is increased. That
is, by forming the groove to achieve such design, a desired
withdrawing force can be obtained.
[0044] In the case shown by the chain double-dashed lines 45,
unlike the conventional seat belt system, the withdrawing force
(winding force) is greater at the initial stage of withdrawal (or
final stage of winding) of the seat belt, is smaller at the middle
stage, and is slightly greater at the final stage. Because of the
greater force at the final stage of winding the seat belt, the
withdrawn seat belt can be securely completely wound up. Therefore,
the seat belt retractor has excellent retracting property. Because
of the smaller force at the middle stage, excess force is not
required for wearing the seat belt. Because of the greater force at
the final stage, the seat belt can fit the occupant's body. Such
results also can be obtained by designing the configuration of the
cam groove to obtain the desired result.
[0045] Though the above description has been made as regard to the
seat belt retractor according to the one embodiment of the present
invention with reference to FIGS. 1-3, the present invention is not
limited thereto. By adjusting the biasing force adjusting mechanism
and the reduction gear mechanism, the belt tension can be freely
set to fit the occupant's body (slender, stout, tall, short, etc.)
and/or preference.
[0046] As apparent from the above description, according to the
present invention, the tension (withdrawing force/winding force) of
the seat belt can be freely set in spite of variation in the
biasing force of the tension spring depending upon the rotational
angular position .omega. of the reel. Since the retractor of the
present invention is of a mechanical type, parts including a motor
for obtaining external power and wirings are not required.
[0047] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
* * * * *