Seat belt retractor assembly

An improved seat belt retractor of the emergency locking variety is described. The primary improvement resides in providing a spur gear component which is insert molded directly onto one of the toothed sprockets of the retractor spool. By eliminating the two-piece prior art assembly, and molding the spur gear directly onto the toothed sprocket, the spur gear strength characteristics are vastly improved. Moreover, the relative positioning between the teeth of the spur gear and those of the toothed sprocket may be controlled with a very high degree of accuracy. This design further eliminates the required step of assembling the spur gear and sprocket together, and avoids problems of these components becoming separated during assembly or use.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a motor vehicle seat belt retractor and 
particularly, to such a retractor having an improved inertia sensitive 
actuator mechanism. 
Most motor vehicles are equipped with seat belt systems which act to 
restrain the occupants when the vehicle is subjected to high rates of 
deceleration which may occur, for example, during a motor vehicle 
collision. Many seat belt retractors are of the so-called emergency 
locking variety. These retractors employ an inertia sensitive actuator 
which prevents seat belt webbing from being withdrawn from the retractor 
when the vehicle is subjected to deceleration forces above a predetermined 
level, thereby restraining the vehicle occupant. During normal operating 
circumstances, however, the seat belt webbing may be freely withdrawn from 
the retractor, enabling freedom of movement by the vehicle occupants. 
The inertia sensitive actuator mechanism of a conventional emergency 
locking retractor includes a spur gear which is attached to one of a pair 
of toothed sprockets. These toothed sprockets are connected to a rotating 
belt support shaft. The function of the spur gear is to engage a pawl of 
the inertia sensitive actuator when the vehicle is subjected to high level 
deceleration. Once engaged, the inertia sensitive actuator causes 
engagement between a locking lever and the toothed sprocket thereby 
preventing continued seat belt webbing withdrawal from the retractor 
assembly. The spur gear must be accurately positioned with respect to the 
toothed sprocket. Inaccurate positioning between components can lead to a 
mechanical failure of the spur gear and/or the remaining components of the 
inertia sensitive actuator. As a means of accurately positioning the teeth 
of the spur gear relative to the toothed sprockets, it is current practice 
to include one or more locating tabs on the spur gear which engage bores 
or indentations formed by the end surface of the toothed sprocket. It is 
therefore necessary for an operator to carefully position the parts during 
assembly. 
In accordance with this invention, an improved seat belt retractor of the 
emergency locking variety is described. The principal improvement in the 
retractor design resides in providing a spur gear component which is 
molded directly to one of the toothed sprockets of the retractor. By 
molding these parts together, precise positioning therebetween can be 
maintained with a high degree of accuracy. Further, the strength of the 
spur gear is substantially increased due to its integration with the 
toothed sprocket. In addition to strengthening the spur gear itself, the 
connection between the spur gear and toothed sprocket becomes much more 
secure. Finally, due to the vastly increased strength and dimensional 
control characteristics inherent in the design according to this 
invention, a broader range of materials may be employed to form the spur 
gear component as compared with prior art designs.

DETAILED DESCRIPTION OF THE DRAWINGS 
A prior art seat belt retractor is shown assembled in FIG. 1 and is 
generally designated there by reference character 10. Retractor assembly 
10 includes retractor frame 12 to which rotatable spool 14 is mounted. 
Spool 14 includes a belt support shaft 16 terminating laterally in a pair 
of radially extending toothed sprockets 18 and 20. Tortion spring assembly 
22 acts upon belt support shaft 16 to rotatably bias spool 14 so that a 
belt webbing retracting force is applied when webbing 24 is withdrawn from 
retractor 10. One end of seat belt webbing 24 is attached to belt suppport 
shaft 16 and becomes rolled onto spool 14 as it is rotated. Retractor 
frame 12 includes one or more mounting holes 26 for fasteners which permit 
secure attachment of retractor 10 to the associated vehicle. Locking bar 
28 is particularly shown by FIGS. 2 and 3, and is movable between a normal 
non-engaged position to an engaged position wherein the locking bar 
engages one of the teeth of toothed sprockets 18 and 20. Locking bar 28 is 
caused to move to an engaged position by inertia sensitive actuator 30 
which includes housing 32 attached to frame 12, and internally disposed 
weighted element 34. Weighted element 34 moves to a tilted position once 
retractor assembly 10 (and the associated motor vehicle) are exposed to 
deceleration forces above a predetermined level (or when retractor frame 
12 is tilted from its installed position). Once weighted element 34 is 
caused to move to a tilted pposition, locking lever 36 becomes raised due 
to contact between the weighted element and lug 38 of the locking lever. 
Locking lever 36 rotates about pivot 40 between the normal and engaged 
positions. 
FIG. 2 illustrates the normal position of the components of inertia 
sensitive actuator 30. When, however, weighted element 34 moves toward a 
tilted position, locking lever 36 is caused to rotate in a clockwise 
direction, with respect to the orientations shown by FIGS. 2 and 3. Once 
slightly rotated, actuator pawl 42 of locking lever 36 engages a tooth of 
spur gear 44 which is also rotatable with spool 14. Rotation of spool 14 
causes continued rotation of locking lever 36 until the locking lever 
contacts the underside of locking bar 28, urging it into engagement with a 
tooth of toothed sprockets 18 and 20. Actuator pawl 42 and spur gear 44 
are provided to augment the rotational urging forces applied to locking 
lever 36 as weighted element 34 becomes tilted. Such augmentation results 
in improved reliability and accuracy of retractor locking and provides 
positive engagement between locking bar 28 and toothed sprockets 18 and 
20. 
FIG. 4 illustrates spool 14 and spur gear 44 according to prior art 
designs. As shown by that Figure, spur gear 44 is a separate component 
typically made from a polymeric plastic material which is connected to 
toothed sprocket 18 by engagement between a plurality of protruding bosses 
(not shown) and holes or depressions 46 within the outer surface of 
toothed sprocket 18. The bosses and holes 46 are located such that when 
they are in registry with one another, the teeth of toothed sprocket 18 
and those of spur gear 44 are in a predetermined angularly alingned 
condition. Typically, this alignment is provided by positioning bosses and 
holes 46 such that the two parts engage only when they are in a desired 
angular relationship. As is evident from a description of the operation of 
the inertia sensitive actuator mechanism 30 described above, this precise 
relationship between the positions of toothed sprocket 18 and spur gear 44 
must be maintained. Otherwise, excessive rotation of spur gear 44 would 
occur prior to engagement between locking bar 28 and toothed sprockets 18 
and 20, thereby presenting the potential for mechanical failure of spur 
gear 44 and/or actuator pawl 42. 
In accordance with this invention, an integrated spur gear and toothed 
sprocket assembly 48 is shown with reference to FIGS. 5, 6 and 7. The spur 
gear portion 50 of assembly 48 is formed by molding directly onto modified 
toothed sprocket 52, as shown by cross-sectional view FIG. 6. During 
molding, the material which makes up spur gear 50 flows into and engages a 
plurality of bores or slots 54 provided through toothed sprocket 52. 
Enhanced reinforcement of the teeth of spur gear 50 and firm engagement 
between the spur gear and toothed sprocket 52 may be provided by forming a 
continuous ring 56 of material on the reverse side of modified toothed 
sprocket 52 from the side having spur gear 50. As best shown by FIGS. 6 
and 7, ring 56 communicates with each of slots 54. 
Integral spur gear and toothed sprocket assembly 48 is preferably formed by 
first assembling the toothed sprockets onto belt support shaft 16 and then 
inserting toothed sprocket 52 within an injection molding die cavity. 
Alternately, assembly 48 could be formed and later attached to belt 
support shaft 16. Regardless of the assembly sequence, positioning means 
are provided within the mold cavity to positively locate the teeth of 
toothed sprocket 52 with respect to the teeth of the spur gear 50. Once 
this location step is completed, heated polymeric plastic material is 
injected under pressure within the die cavity until the material flows to 
form spur gear 50. Once the material has cooled sufficiently, the assembly 
is removed from the injection molding die. 
Integral spur gear and toothed sprocket assembly 48 provides a number of 
significant advantages over the two-piece construction according to prior 
art designs as shown by FIG. 4. Since spur gear 50 is formed directly onto 
toothed sprocket 52, accurate relative positioning between the teeth of 
these two structure is achieved. Additionally, since slots 54 are provided 
for each of the teeth of spur gear 50, the strength of these individual 
teeth is increased significantly over the prior art spur gear 44 
construction where spur gear 44 is connected to toothed sprocket 18 only 
by projections near the center of the spur gear. Also, due to the firm 
engagement between spur gear 50 and modified toothed sprocket 52, these 
two parts are firmly attached to each other and problems of their becoming 
separated during assembly or in use are eliminated. Designers of seat belt 
retractors were limited to selecting materials for conventional spur gears 
which had superior dimensional stability characteristics. This design 
limitation was imposed due to the existence of some relative movement 
between the spur gear and sprocket and more significantly, due to 
deflection of the unsupported teeth of the spur gear as it is subjected to 
the broad range of environmental conditions within a motor vehicle 
interior. Unfortunately, materials selected for this application, such as 
Nylon, tend to be brittle and therefore subject to mechanical failure. Due 
to the substantial increase in the strength of the spur gear component and 
the greater control over relative positioning of components inherent in 
the design of integral assembly 48 according to this invention, a broader 
range of materials can be employed to form the spur gear component. The 
material for spur gear 50 may be chosen for its low cost and formability 
characteristics rather than primarily for its dimensional stability. For 
example, "Hytrel" (Trademark of Du Pont Company) polymeric plastic 
material has been found suitable for use in practicing this invention. 
This material is unsuitable for use in forming prior art spur gears since 
it is hydroscopic and tends to change dimensionally with humidity changes. 
Finally, by providing integral spur gear and toothed sprocket assembly 48 
according to this invention, manufacturing costs and steps can be reduced 
since the separate step of assembling the two components is eliminated. 
While the above description constitutes the preferred embodiments of the 
present invention, it will be appreciated that the invention is 
susceptible to modification, variation and change without departing from 
the proper scope and fair meaning of the accompanying claims.