The present invention relates to a seat belt retractor
having an improved web sensor.
An improved web sensor according to Claim 1 has improved
dynamic performance and activates the an inertial wheel and spring to initiate seat
belt lockup at different preset levels within a range of desired dynamic performance
levels specified by different end users and governmental regulations.
- Figure 1 is an exploded view of a seat belt retractor of the invention.
- Figure 2 is a cross-sectional view at section 2 - 2 of Figure 1.
- Figure 3 is an end plan view of a spool showing a web sensor pawl and thrust
washer installed thereon.
- Figure 4 shows an inertia wheel in a rest position upon the spool.
- Figure 5 is a cross-sectional view at section 5 - 5 of Figure 4.
- Figure 6 is a rear plan view of the inertia wheel.
- Figure 7 is a rear plan view of the lock ring.
- Figure 8 is a sectional view illustrating the components of the web sensor in
a configuration that would initiate seat belt or retractor lockup.
- Figures 9a, 9b, 9c and 9d show the front face of the inner disk with web sensor,
a spring and various pins.
Figure 1 is an exploded view of a seat belt retractor 20
incorporating the present invention and Figure 2 is a cross-sectional view taken
at section 2 - 2 of Figure 1. The seat belt retractor 20 includes many features
found in known emergency locking retractors (ELRs). The retractor 20 includes a
vehicle sensor 22, which comprises a housing 24, a movable mass 26 and a pivoting
movable sensor pawl 28 having at least one engagement tooth 29. The sensor pawl
28 is pivoted relative to the housing 24 about a pin 24a. The vehicle sensor 22
is fitted to or made a part of a lock ring 50 of known design. The lock ring 50
is, during non-emergency conditions, rotationally isolated from a shaft 102 that
is coaxial with a spool 100. In response to sensing a vehicle deceleration above
a set level, the mass 26 of the vehicle sensor 22 moves, causing the sensor pawl
28 to enter into locking engagement with a tooth 106 of the ratchet wheel 108, which
is rotatable with the spool 100. In the illustrated embodiment, the ratchet wheel
108 is cast as part of the spool 100. In the illustrated embodiment the spool 100
comprises die cast zinc or aluminum or a non-ferrous material. The lock ring 50
is piloted on the end of the shaft 102 and is rotatable about the shaft. Engagement
of the sensor pawl 28 with one of the teeth 106 couples the lock ring 50 to the
spool 100. Further rotation of the spool 100 in the direction indicated by arrow
110, a belt unwinding direction, causes a like rotation of the lock ring 50 in a
like direction. As described in conjunction with Figure 8, the lock ring 50 includes
a stub axle or hollow wall 53, which loosely receives the shaft 102 and serves as
The lock ring 50 has an arcuate cam slot 52 therein and
the retractor 20 includes a lock pawl 60, of known design, that is pivoted upon
a side 72 of the retractor frame 70 about an axis 74. The lock ring 50 is biased
to a rest position relative to the frame side 72 by a bias spring 51, as shown in
Figure 7. The lock pawl 60 is pivotally secured to the retractor frame 70 by a pin
61. The lock pawl 60 includes a pin 62 that functions as a cam follower. The pin
62 is slidingly received within the arcuate cam slot 52. Rotation of the lock ring
50 in the direction indicated by arrow 110 causes the arcuate cam slot 52 to move
relative to the pin 62. The arcuate cam slot 52 has walls that urge the lock pawl
60, in the direction indicated by arrow 112, into engagement with one or more teeth
116 of another ratchet wheel 114 of the spool 100. Upon engagement of the lock tooth
64 of the lock pawl 60 with a tooth 116 of the ratchet wheel 114, the spool 100
is locked against further rotation in the direction indicated by arrow 110. Either
of the ratchet wheels 108, 114 can be an integral part of the spool 100 or added
separately to the spool.
As is known in the art, the spool 100 is rotationally supported
relative to a U-shaped, typically metal retractor frame 70, in a known manner by
bushings in the spool or formed within plastic parts attached to the retractor frame.
The spool 100 includes a center portion 120 that secures an end 132 of a length
of seat belt webbing 130. The seat belt webbing is wound up about the center portion
120 of the spool 100. The seat belt retractor includes a rewind spring 105 that
can engage a spring arbor 105a located at an end of the spool 100 opposite the ratchet
wheels 108, 114. The rewind spring 105 under normal non-emergency situations, rotates
or rewinds the spool 100 in a direction opposite to the direction indicated by arrow
110 to retract and rewind the seat belt webbing 130 upon the spool.
The shaft 102 shown in Figures 1 and 2 can be made as an
integral part of the spool, or alternately can be configured as an extending end
of a torsion bar (not shown) or separate axle, which is located within a center
bore or passage (not shown) of the spool 100. The shaft 102 is received in a recess
78 (see Figure 2) in a protective plastic cover 76 that is attached to the retractor
frame 70 and covers the lock ring 50. The recess 78 acts as a bushing. Other known
ways of supporting the shaft are within the scope of the invention. The center of
the lock ring 50 can be rotationally supported on the hollow wall 53 of the lock
The seat belt retractor 20 includes a web sensor 200. The
web sensor 200 comprises an inertia wheel 202; a torsion spring 204 having legs
206a, 208a, each with an end 206, 208; and a web sensor pawl 210 having a body 212
with an opening or bore 214 therein. The web sensor pawl body 212 includes two lock
teeth 220, 222. The web sensor pawl body 212. Located near the opening 214 is an
extending leg 216 that acts as a mechanical stop to limit the inward rotation of
the web sensor pawl 210. The web sensor pawl body 212 includes a pin 234 that acts
as a cam follower. The web sensor pawl 210 is rotationally supported on a pin 230.
The pin 230 has a flat side 232 and is provided as an integral formation of the
spool 100. In Figure 1 the ratchet wheel 108 forms a cup-shaped structure 150 at
the end or side of spool 100. The pin 230 extends from a bottom 152 of the cup-shaped
The retractor 20 includes a thrust washer 160 that is received
about the shaft 102 and fits in a narrow recess 153 in the bottom 152 of the cup-shaped
structure 150. The thrust washer 160 reduces sliding friction between the spool
100 and the inertia wheel 202. The placement of the thrust washer 160 and the web
sensor pawl 210 is also shown in Figure 3. The bottom 152 of the cup-shaped structure
150 includes another integrally formed projection 154 that cooperates with a leg
216 of the web sensor pawl 210. The counterclockwise rotation, or inward motion,
of the web sensor pawl 210, in relation to Figure 3, is stopped upon engagement
of the leg 216 with the projection 154.
The inertia wheel 202 of the web sensor 200 is shown in
Figure 4 assembled upon the spool 100. The web sensor pawl is positioned below the
inertia wheel 202 in this figure. Figure 4 shows a partially assembled seat belt
retractor. Figure 5 is a cross-sectional view at section 5 - 5 of Figure 4. Figure
6 illustrates the inner or front surface (the opposite side) of the inertia wheel
The inertia wheel 202 can be a zinc casting or a formed
metal and includes a front or outer surface 302 and a rear or inner surface 304
and a number of intermediate features. Both the front and rear surfaces are stepped
by including a variety of different elevations or planes. The front surface 302
is formed with a cavity or depression 306. Within the cavity are a plurality of
integrally formed pins 308 (308a - 308e) as shown in Figures 4 and 9a - 9d. The
position and purpose of the pins will be discussed below. Each pin 308a - 308e can
be inserted in the inertia wheel. The wheel 202 includes an axle 310 having a center
bore. In Figure 5 a part of the shaft 102 extends through the bore 312 of the axle
310. The inertia wheel 202, i.e. the axle 310, includes wings 314, 316 that are
located proximate the front surface 302 of the inertial wheel 202. The wings 314,
316 prevent the outward creep of the center or spiral-coiled portion 205 of the
torsion spring 204 that is installed about the axle 310. An annular groove 320 extends
about the axle 310 and the center or spiral-coiled portion 205 of the torsion spring
204 is received therein. A spring leg 206a includes a bent end 206 that envelops
a portion of the selected pin as shown in Figure 1.
In Figure 4 the bent end 206 of the spring leg 206a is
positioned about a pin 308e. The other leg 206b of the torsion spring 204 extends
tangentially outward from the coiled portion 205 into an oblong opening 340 formed
in the inertia wheel 202. The spring leg 206b has a bent portion 207a that elevates
the end of leg 206b from the corresponding end of the center coiled portion 205,
enabling the end of the spring leg 206b to be received within a notch or ledge 342
formed in the inertia wheel. In Figures 5 and 6 a small annular projection or lip
344 is formed at a surface 304 to reduce the area in contact with the thrust washer
160 and reduce the rotational friction acting on the rear surface 304 of the inertia
Reference is again made to Figure 4 and in particular the
relationship between the inertia wheel 202 and shaft 102, as well as the inertia
wheel 202 and the cup-shaped structure 150 formed by ratchet wheel 108. A first
annular space 354 is located between the hollow axle 310 and the shaft 102, and
a second annular space 356 is located between the outer circumference of a wheel
202 and the cup-shaped structure 150 that is the inner wall of ratchet wheel 108.
Figure 7 is a plan view of the features formed on the rear
face of the lock ring 50. The lock ring 50, at its center, includes a hollow axle
53, also shown in Figure 2, which is received about the end of the axle 102 and
functions as a bushing to stabilize the axial position of the axle 102. The hollow
axle 53 is positioned within the hollow annular space 354 as shown in Figure 2.
The lock ring 50 further includes an extending cylindrical wall 55. The inner surface
of the cylindrical wall 55 is formed as a ratchet wheel 56 having a plurality of
teeth 57. On assembly, the cylindrical wall 55 is positioned within the space 356,
with the ratchet teeth 57 facing the inertia wheel 202. On assembly, the ratchet
wheel 108 is positioned about the wall 55 and slightly spaced therefrom. The lock
ring 50, at its outer edge, includes another cylindrical wall 59. A ratchet wheel
114 is positioned inside and spaced from the cylindrical wall 59. The lock ring
50 includes an outer wall or outer side face 59a that envelops the web sensor 20
and provides protection for the web sensor as shown in Figure 1.
In Figure 8 the outer wall or face portion 59a of the lock
ring 50, that is above section line 9 - 9 of Figure 2, has been removed to more
clearly show the inertia wheel and ratchet wheels.
The inertia wheel 202 includes a cam slot 315, which is
also shown in Figure 4. With the inertia wheel 202 installed upon the spool 100,
the cam follower 234 of the web sensor pawl 210 is received within the cam slot
315. The leg 206b of the torsion spring 204 is positioned on the flat side face
231 of the pin 230 facing the cam slot 315. In this manner the inertial wheel 202
is biased to rotate in a counterclockwise manner as shown in Figure 4. The inertia
wheel 202 will achieve a steady state position under the bias of the torsion spring
204 when end 341 of the opening 340 bottoms against a generally opposite side of
the pin 230, as shown in Figure 4. In this orientation, the cam follower or pin
234 of the pawl 210 rests near the innermost depth of the cam slot 315. In this
orientation, as a consequence of the cam follower 234 being in the above orientation,
the web sensor pawl 210 is rotated away from the ratchet teeth 57 of the ratchet
wheel 55, so that the web sensor pawl teeth 222 are free from engagement with the
During normal, non-emergency operation of the seat belt
retractor, the torsion spring 204 will maintain the inertia wheel 202 in the condition
illustrated in Figure 4 wherein the sensor pawl 208 is disengaged from the lock
ring 50. During a vehicle crash, as the vehicle rapidly decelerates, a vehicle occupant
who is wearing his or her seat belt will tend to move forward and thereby rapidly
protract the belt webbing 130 from the spool 100. The protraction of belt webbing
causes the spool 100 to rapidly rotate in an unwinding direction as indicated by
arrow 110 of Figure 1.
During the initial rapid movement of the spool 100 in response
to the rapid withdrawal of the belt webbing 130, the inertia wheel 202 will tend
to stay in its pre-crash orientation. Consequently, the rotation of the spool 100
in concert with the tendency of the inertia wheel 202 to stay in place creates a
relative displacement rotation between the spool and the inertia wheel. This relative
rotation between the spool and the inertia wheel causes the cam follower 234 to
move outwardly relative to a cam slot 315 as the inertia wheel rotates. This motion
then causes the web sensor pawl 210 to rotate about the pivot pin 230, urging the
lock teeth 220, 222 to engage and lock with corresponding teeth or a tooth 57 of
the lock ring 50. The above action thereby rotationally couples the lock ring 50
to the spool 100. Further rotation of the lock ring 50 moves a lock pawl 60 into
locking engagement with the teeth 116 of the lock wheel or a ratchet 114 formed
on and movable with the spool 100. With the lock pawl 60 engaged with the lock teeth
116, the retractor is once again locked from further rotation, preventing further
pay-out of the seat belt webbing.
Depending upon governmental or customer supplied specifications,
it may be desirable to have the web sensor activate when the web acceleration, as
indicated by the rotational acceleration of the spool 100, is between 0.3 - 0.70
g; then the spring leg 206a is positioned on the pin 308e, which positioning changes
the bias force produced by the torsion spring 204, which acts upon the inertia wheel
202. The selected bias force keeps the inertial wheel in place at a rest position
until the acceleration equals or exceeds the desired level. If the desired lockup
acceleration level is between 0.8 and 2.0 g, the spring leg 206a is secured at a
pin 308d. If it is desired that the web sensor activate in the vicinity between
1.0 and 3.0 g, the spring is secured at a pin 308c. If it is desired the web sensor
activates in the vicinity of 3.0 g, the spring is secured at a pin 308b. If the
maximum range is in the vicinity of 4.5 g, the spring leg 206a is secured to a pin
308a. In the various figures, each pin 308a - 308e is located at the radius from
the center of inertia wheel 202; the spacing between adjacent pins 308a - 308e varies.