Winding – tensioning – or guiding – Reeling device – With spring motor
Reexamination Certificate
1999-09-02
2001-03-27
Jillions, John M. (Department: 3653)
Winding, tensioning, or guiding
Reeling device
With spring motor
Reexamination Certificate
active
06206314
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a seat belt retractor, and more particularly, to a seat belt retractor wherein a force for withdrawing a seat belt is substantially uniform even when a withdrawing amount of the seat belt is increased.
Conventionally, in a seat belt retractor equipped in a motor vehicle, a seat belt (hereinafter referred to as a webbing in case of indicating a belt itself to be wound) is wound around a reel by spring driving force of a spiral spring or the like built in the seat belt retractor. In this type of the seat belt retractor, as a withdrawing amount of the webbing is increased, the spiral spring is wound so as to increase an urging-force thereof. Thus, there has been a situation that a force of withdrawing the webbing is increased as the amount of withdrawal of the webbing is increased.
To solve the aforementioned situation, a seat belt retractor has already been developed, which includes a tension reducing mechanism for reducing the force of withdrawing the webbing as disclosed in Japanese Patent No. 2,711,428. The tension reducing mechanism of the seat belt retractor is explained hereunder by referring to FIG.
7
. As shown in
FIG. 7
, a belt reel
51
of a seat belt retractor
50
is axially supported by a base frame (not shown) through a rotational shaft
59
. A webbing
57
is arranged to be wound on an outer peripheral surface of the belt reel
51
. Further, a housing
61
for the tension reducing mechanism is fixed on an outer side wall of the base plate (not shown). A shaft end
59
a
of the rotational shaft
59
extends to an inside of the housing
61
attached adjacent to the base frame. A first rope pulley
52
in a shape of a truncated cone is fixed to the shaft end
59
a
extending inside the housing
61
. A spiral guide groove
55
is incised on an outer peripheral surface of the first rope pulley
52
.
Furthermore, a second rope pulley
54
is accommodated in the housing
61
in a state that the second rope pulley
54
is axially supported through a rotational shaft
62
. As in the first rope pulley
52
, the second rope pulley
54
is formed in a shape of a truncated cone and provided with a spiral guide groove
58
on an outer peripheral surface thereof. The rotational shaft
62
is disposed parallel to the rotational shaft
59
at a position laterally spaced away therefrom with a predetermined distance. As shown in
FIG. 7
, a hollow chamber
63
, which has a cylindrical shape and is coaxial with the rotational shaft
62
, is formed in the second rope pulley
54
. The spiral spring
56
is situated inside the hollow chamber
63
. One end of the spiral spring
56
is fixed to the second rope pulley
54
supported by the rotational shaft
62
, and the other end of the spiral spring
56
is fixed to a bearing boss
65
formed in the hollow chamber
63
of the second rope pulley
54
.
Further, a rope
53
extends between the first rope pulley
52
and the second rope pulley
54
. In a condition that the webbing
57
is completely wound, one end of the rope
53
is fixed to a fixing end (not shown) at a largest diameter position of the guide groove
58
of the second rope pulley
54
such that the rope
53
is spirally wound in the entire periphery or length of the guide groove
58
, and the other end of the rope
53
is fixed to a fixing end
67
of a largest diameter portion of the guide groove
55
of the first rope pulley
52
.
In the tension reducing mechanism thus structured, an urging force for winding generated in case of winding up the spiral spring
56
is transmitted to the second rope pulley
54
as a rotational force or torque for winding the end portion of the rope
53
wound in the guide groove
58
of the second rope pulley
54
. At this time, as shown in
FIG. 7
, the rope
53
extends from the smallest diameter portion of the second rope pulley
54
to the largest diameter portion of the guide groove
55
of the first rope pulley
52
. When the webbing
57
in the wound state is withdrawn against a winding force shown by an arrow K in the figure, the first rope pulley
52
of the tension reducing mechanism rotates in a direction of an arrow A in the figure, so that the rope
53
is gradually wound on the first rope pulley
52
. At this time, the rope
53
is wound on the first rope pulley
52
while being held in the guide groove
55
. In accordance therewith, the rope
53
wound in the guide groove
58
is gradually unwound from the second rope pulley
54
.
As described above, the rope
53
held in the guide grooves
55
and
58
respectively formed on the outer peripheral surfaces of the first rope pulley
52
and the second rope pulley
54
transmits the rotations of the rope pulleys
52
and
54
therebetween. In this case, by adequately setting the cone shapes of the first rope pulley
52
and the second rope pulley
54
, a rotational ratio of the first rope pulley
52
to the second rope pulley
54
can be controlled, so that the force for withdrawing the webbing can be made constant or reduced regardless of a withdrawal amount of the webbing.
In the seat belt retractor shown in
FIG. 7
, however, since the tension reducing mechanism is formed of two rope pulleys in the shape of the truncated cone having the spiral guide groove, there have been a problem that assembling the rope pulleys with the housing is poor, and a problem that the miniaturizing the entire apparatus is difficult because the roller pulley itself can not be miniaturized.
Also, in the seat belt retractor, by winding the rope on the outer peripheral surface of the rope pulley in the shape of the truncated cone, the force for withdrawing the webbing is reduced with a long unwinding stroke. However, since the rope is wound several times on the outer peripheral surface of the truncated cone with a gentle lead angle, a ratio of decreasing a radius of the wound rope is small at the time of unwinding the rope, so that a change in the force of withdrawing the webbing can not be taken greatly.
Further, since the rope winding surface is inclined as a result of the shape of the truncated cone, it is necessary to form the deep guide groove so as not to allow the rope to be loosened and disengaged from the guide grooves in case of winding after the seat belt is suddenly withdrawn.
Accordingly, an object of the invention is to solve the aforementioned problems in the conventional retractor and to provide a seat belt retractor which is good in assembly and includes a compact tension reducing mechanism to achieve a high reliability in withdrawing the seat belt.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
To achieve the above object, a seat belt retractor of the present invention is formed of a first reel coaxially connected to a rotational axis of a reel shaft for winding a webbing therearound so as not to rotate relatively to the reel shaft; a second reel having a rotational shaft disposed parallel to and spaced away laterally from the first reel which winds a rope member including one end fixed to a predetermined position of the first reel; and urging force providing means accommodated inside the second reel. When the first reel is rotated by withdrawing the webbing, the rope member is wound around the first reel to cause a rotation of the second reel, by which the urging force providing means provides a force of urging the second reel in a direction of winding the webbing against this rotation of the second reel. In the seat belt retractor, by changing a rotational ratio of the first reel to the second reel, a force for withdrawing the webbing is decreased in accordance with an amount of withdrawal of the webbing.
The first reel is formed in a shape of a cylindrical drum, and the second reel is provided with a small diameter reel portion, a large diameter reel portion, and a transition portion connecting the small diameter reel portion and the large diameter reel portion. The rope member transferred from the first
Kosugi Noriyuki
Mizuno Isamu
Shiotani Masahiro
Tanji Hiromasa
Jillions John M.
Kanesaka & Takeuchi
Takata Corporation
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