Seat belt retractor with comfort or tension reducing feature

A seat belt retractor adapted to be secured about a seated occupant comprising: a spool (54) having a length of seat belt (36) wound thereon for securement of the occupant, a portion of the seat belt forming a shoulder belt portion, the spool rotationally supported upon a frame (52); a tension reducing mechanism for controlling the amount of spring force transmitted from a rewind spring to the spool and hence the force applied to the shoulder of the occupant via the shoulder belt portion of the seat belt, the mechanism comprising: a cylindrical first spool (80) having an ungrooved, smooth body (81) operatively connected to the spool to rotate with the spool; a second reel (100) positioned remote from the first reel (80) having a tapered peripheral surface having a continuous spiral groove of varying diameter thereon, a rewind spring (160) operatively connected to the second reel for providing a rewind force to rewind the seat belt upon the spool; a flexible link (88) joining the first and second reel and for transmitting the force of the spring to the first reel, the link (88) wound about the second reel within the spiral groove and wound about the first reel (80).

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention generally relates to seat belt retractors and more 
particularly to a seat belt retraction mechanism capable of reducing the 
rewind force that acts on the shoulder of an occupant via the shoulder 
belt portion of the seat belt. 
Accordingly the invention comprises: a seat belt retractor adapted to be 
secured about a seated occupant comprising: a spool having a length of 
seat belt wound thereon for securement of the occupant, a portion of the 
seat belt forming a shoulder belt portion, the spool rotationally 
supported upon a frame; a tension reducing first means for controlling the 
amount of spring force transmitted from a rewind spring to the spool and 
hence the force applied to the shoulder of the occupant via the shoulder 
belt portion of the seat belt, the first means comprising: a cylindrical 
first spool, aligned to an a rotationally axis of the spool, having an 
ungrooved, smooth body operatively connected to the spool to rotate with 
the spool; a second reel positioned remote from the first reel including a 
tapered peripheral surface having a continuous spiral groove of varying 
diameter thereon, the second reel having an axis of rotation parallel to 
that of the first reel; a rewind spring operatively connected to the 
second reel for providing a rewind force to rewind the seat belt upon the 
spool; a flexible link joining the first and second reel and for 
transmitting the force of the spring to the first reel, the link wound 
about the second reel within the spiral groove and wound about the first 
reel. The link preferably extends away from the second reel, in a 
direction generally perpendicular to the axis of rotation of the second 
reel independent of the position of the link within the groove. This 
orientation avoids excess wear to the lip of the groove or groove segment 
and reduces associated acoustic noise. 
One advantage of the present invention is that as the flexible link, cable 
or cord is moved between an upper and a lower reel it will extend from the 
lower or first reel toward the upper or second reel in a general vertical 
manner. This is not true of the prior art as shown in U.S. Pat. No. 
5,628,470 or in U.S. Pat. No. 5,409,176, in which grooves are located on 
an upper reel. As the cable in these prior art retractors is repositioned 
between the upper and lower reels the cable will typically be inclined at 
an angle to the axis of both reels and grooves. This relationship causes 
the cable to rub upon the outer edges of the groove causing an audible 
noise and causing the wearing of the typically plastic reels. This is not 
the case in the present invention. 
It is an object of the present invention to provide a seat belt retractor 
with an improved tension reduction or comfort mechanism. 
Many other objects and purposes of the invention will be clear from the 
following detailed description of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Reference is briefly made to FIG. 1 which illustrates an exemplary 
three-point seat belt system 20. Illustrated in FIG. 1 is a seat 22 
located upon a vehicle floor 24. Also illustrated is the B-pillar 26 of 
the vehicle. The three-point safety belt system 20 comprises a retractor 
30, a web guide 32, a seat belt buckle 34 and a length of seat belt 
webbing 36, having a tongue 36 positioned thereon. The tongue 38 divides 
the seat belt 36 into a shoulder belt portion 36a and lap belt portion 
36b. The lower end 38 of the lap belt portion 36b is appropriately 
anchored to the vehicle floor. The anchor is shown generally as numeral 
40. 
FIG. 2 illustrates a cross sectional view of the seat belt retractor 30. 
The retractor 30 comprises a frame 50 having frame sides 52a and 52b, 
joining a rear frame portion 52c. A spool 54 is rotatably supported 
between the frame sides 52a and 52b. The spool 54 includes a central 
portion 56 about which the seat belt 36 is wound. The spool 54 includes a 
plurality of lock wheels 60a and 60b which are periodically locked by a 
locking pawl 64 such as during an emergency. The retractor 30 includes a 
web sensor 70 and a vehicle sensor 72, both of which are known in the art. 
Typically the web sensor 70 includes an inertial member which rotates 
outwardly as the spool accelerates linking the spool to a lock wheel, the 
motion of which causing the locking pawl 64 to engage one or more teeth 61 
on the lock wheel 60a and/or 60b. The vehicle sensor 72 typically 
comprises an inertial mass such as a rolling ball or standing man which 
similarly causes the lock pawl 64 to move into engagement with the lock 
wheel 60a and/or 60b. As illustrated, the lock pawl 64 is rotationally 
supported on one side of the frame 50. This lock pawl 64 may engage one or 
both of the lock wheels. The lock pawl 64 may be configured as a lock dog, 
pivoted on both sides of the frame 50 to simultaneously engages both lock 
wheel 60a and 60b. 
A spool shaft 74 extends through the spool 50 and is journaled at 76 
thereto. One end 74b of the spool shaft is rotationally supported, by a 
bearing 71 within an opening 72 in frame side 52b. The other end 74a can 
be directly supported within an opening in the frame by another bearing as 
described above or supported indirectly by a bearing 91 formed in a plate 
94 of a housing 90 (described below) which supports a cylindrical reel 80 
for rotation. 
A cylindrical, typically plastic reel, generally shown as 80 is 
rotationally fixed to end 74a of the shaft 74 so that it rotates with the 
shaft 70 and spool 54. The reel 80 and other associated mechanisms are 
enclosed within a housing 90. The housing 90 includes a mounting plate 94 
connected with frame side 52b, a top 94a, bottom 94b and an end plate or 
member 96. The cylinder 80 includes a recess 82 which is rotationally 
supported by an extending boss 98 formed on member 94a of the housing 90. 
Rotationally supported within the housing 90 is a tapered, typically 
plastic reel 100. The reel 100 includes a first end 102 rotationally 
supported by a boss 104 (which forms a spring arbor or fixed shaft 170) in 
housing 90. 
The reel 100 includes a stepped bore 150 which extends therethrough. The 
bore 150 is closed by a spring cap 106 having an opening 108 therein. The 
large end 152 of the stepped bore provides a housing for a rewind spring 
160. The shaft 170 includes a spring attachment part or slot 172 through 
which is received the inner end 162 of a rewind spring. The outer end 164 
of spring 160 is connected generally at location 166 to the walls of the 
larger diameter portion 152 of the reel 100. An extending end 109 of the 
shaft 170 extends through the opening 108 in the spring cap 106 to 
rotationally support the other end of the reel 100 (and spring cap 106). A 
flexible cable or wire 88 interconnects the cylinder 80 to the tapered 
reel 100. In the preferred embodiment the cable 88 is a flexible, twisted 
or breaded stainless steel wire having a diameter of about 0.34 to 0.86 
mm. 
Reference is briefly made to FIG. 3 which illustrates the feature of the 
cylinder 80 in greater detail. As can be seen, the cylinder 80 includes a 
constant radius center body 81 surrounded by end flanges 83a and 83b. The 
cable 88 is wound about a portion of the body 81. The shaft 74 is received 
in the central recess 85 of the reel 80. 
FIG. 4 shows the details of the construction of the tapered reel 100. The 
outer walls or outer peripheral surface 180 of reel 100 has a tapered 
configuration. This surface 180, interior of a small outer flange 182, 
includes a first generally flat section 190 adjacent to a second section 
192 having a rapidly increasing radius which transitions to a third 
section 194 having a slope which changes more gradually than the slope of 
section 192. Sections 192 and 194 preferably include a tapered, spiral 
groove 200 which begins at the end of section 190 and extends through to 
the end 196 of section 194. In the embodiment shown in FIG. 6 the first 
section 192 is conical which aids in the shaping of the torque profile 
transmitted to the spool during the time that most of the webbing remains 
rewound upon the spool 54. FIG. 4 shows adjacent groove portions 202a-202h 
of various segments of the spiral groove 200. Each groove segment is 
separated by a wall 204 having a circular or radiused contour 206. The 
inner surface 208 between adjacent groove segments 202a-202n comprises 
smooth, circular or radiused section contour 208. 
As mentioned above, the cable 88 connects the cylinder 80 and tapered reel 
100. One end 88a of the cable 88 is secured to reel 100 and is threaded 
through the spiral groove 200 in a counter-clockwise direction as viewed 
in FIG. 5. The other end 88b of the cable 88 is secured to and wrapped 
about the cylindrical reel 80 in a clockwise direction also shown in FIG. 
5. In this manner as the seat belt 36 is extended see arrow 300, the spool 
54 will rotate in the direction as shown by arrow 302, reel 80 will rotate 
in the same direction as shown by arrow 304 and reel 100 which also rotate 
in the same direction shown by arrow 306. The direction of rotation is 
reversed as the seat belt is retracted. 
Reference is again made to FIG. 2 which shows the retractor 30 with its 
seat belt 36 completely retracted. The retraction of the seat belt 36 is 
achieved as the force of the rewind spring 160 is communicated to the 
cable 88 and then to the reel 80, rewinding the spool 54. As can be 
appreciated, in this condition the cable 88 is maintained tightly wound 
about the reel 100 and reel 80. The rewind spring 160 continually 
maintains a determinable amount of tension on the cable 88 to keep it 
taut. When the seat belt 36 is withdrawn or protracted from spool 54 reel 
80, fixedly connected therewith, will rotate with the spool 54. The 
rotation of the reel 80 is communicated to the cable 88 which in turn 
causes reel 100 to rotate against the action of the rewind spring 160. 
As the webbing 36 is protracted, the cable 88 will unwind from the outer 
most, narrow diameter groove segments 202h, 202i, etc., of the reel 100 
and be displaced upon reel 80. As can be appreciated, as the cable 88 
moves from section 190 to section 192 it is supported on groove segments 
having increasing diameters while being supported at its other end on a 
constant diameter reel 80. This interrelationship effectively provides for 
a variable gear ratio between the spring and spool 54 changing the torque 
transmitted therebetween. As is known in the art, as a typical flat spring 
is wound tight, as happens in a conventional seat belt retractor, the 
rewind force applied to the belt increases. This force is applied via the 
shoulder belt to the shoulder of the seated occupant of course once the 
seat belt has been secured about the occupant. In some prior systems the 
amount of force acting on the shoulder has been objectionable to some 
occupants. In the present invention the cable 88 is design to be 
repositioned on the reel 100 at a diameter which (in combination with the 
diameter of reel 80) will reduce the amount of transmitted spring torque 
seen by the spool and hence by the occupant. The torque at this position 
(amount of bet protraction) must however, not be reduced to a level in 
which the rewind spring 106 cannot rewind the extended length of seat belt 
to its stored, generally vertical position. 
In the present embodiments approximately five or six revolutions of cable 
88 are wound about section 190, to generate a sufficient transmitted 
spring force to insure that the seat belt can be completely rewound on the 
spool (see FIG. 2). As the seat belt is protracted from the spool the 
cable 88 is displaced into the grooves 202a-202e of section 192 taking 
about five added revolutions to move the cable 88 to groove segment 202e 
which is the position corresponding to full seat belt protraction. The 
added revolutions of the cable 88 about the groove segments in section 194 
are provided mainly for the storage of excess cable. These groove segments 
can optionally be eliminated. 
Many changes and modifications in the above described embodiment of the 
invention can, of course, be carried out without departing from the scope 
thereof. Accordingly, that scope is intended to be limited only by the 
scope of the appended claims.