Bi-level web sensitive retractor

A reel type safety seat belt retractor in which a pawl is triggered to engage a ratchet wheel, serving as a reel flange, by an inertial device sensitive to an accelerated movement of the reel, wherein the inertial device has two levels of sensitivity, a low level to prevent the triggering of the pawl under all normal conditions of belt withdrawal for buckling, and a second level of high sensitivity which prevails after the belt webbing has been buckled about the passenger. This is accomplished by means of a biasing spring shared by both a webbing follower and the inertial device, and by a clutch which rotated when the webbing in initially withdrawn to restrain the webbing follower and the attached spring bias in a condition of high tension for the low level of sensitivity. When the clutch rotates to release the webbing follower as the belt is buckled, the follower moves toward the diminished roll of webbing, reducing the tension on the shared spring bias and providing a high level of sensitivity for the protection of the buckled passenger.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to vehicle safety belt retractors and more 
particularly to those which permit withdrawal of the seat belt for 
buckling or to accommodate the body movements of the individual using the 
belt, but which lock to restrain the wearer when conditions require it in 
the interests of safety. 
2. Description of the Prior Art 
Many reel-type safety seat belt retractors are known which employ an 
inertial device for triggering a pawl into locking engagement with the 
ratchet teeth on the reel in response to neccelerated rotation of the reel 
in the unwind direction. Also different methods have been suggested for 
permitting the belt to be withdrawn for belting without activating the 
inertial device. This is commonly accomplished by designing the inertial 
device to respond only to relatively high rates of acceleration of the 
reel. This entails a compromise between sensitivity and convenience, often 
to the detriment of both. 
Retractors have been suggested wherein the sensitivity of the triggering 
device gradually increases as the webbing -S withdrawn, being related to 
the amount of webbing extended. The suggested methods are usually complex, 
expensive to manufacture, and add to the possibility of retractor failure. 
Electrical and hydraulic methods of achieving a change in sensitivity 
related to the amount of webbing extended, are known. It is a 
characteristic of this arrangement, that the further the belt is withdrawn 
for buckling, the greater the chance that the locking mechanism will be 
inadvertently triggered. It also follows that the sensitivity would be 
greater for a stout person than for a slim person or child. 
It is an object of this invention to provide a safety seat belt retractor 
in which the locking of the reel of webbing is triggered by an inertial 
sensing device having two levels of sensitivity, a low level which is in 
effect when the user withdrawn the webbing for buclking up, at which time 
the triggering of the locking mechanism would be an unneccessary 
annoyance; and a high level of sensitivity which prevails after the user 
is buckled up, and a ready response to any sudden accelerating motion of 
the reel is required to protect the user. It is also an object of this 
invention to achieve this bi-level sensitivity simply, without complicated 
and expensive additional structures. 
SUMMARY OF THE INVENTION 
The present invention is directed to a safety seat belt retractor having a 
rotatable reel to which a seat belt is attached. The reel is journaled in 
a support adapted for attachment to the frame of a vehicle. The reel has 
as a flange, at least one ratchet wheel biased in the wind direction, and 
a pawl adapted to engage the ratchet wheel in the unwind direction in 
response to the action of an inertial device sensitive to an accelerating 
rate of rotation of the reel. 
The novelty of the retractor of my invention lies in the fact that the 
inertial device has two levels of sensitivity. There is a low level of 
sensitivity by which applies when the webbing is first withdrawn for 
buckling, to avoid the annoyance of having the locking mechanism triggered 
inadvertently as the webbing is being withdrawn for buckling. Locking of 
the reel would then only occur should the belt be withdrawn with unusual 
vigor. The second level is one of high sensitivity, and prevails after the 
user has buckled up, and is dependent on the sensitivity of the retractor 
should he become involved in a collision. 
There are many different types of inertial devices. One of the most common 
and effective, and the one preferred in the retractor of my invention, 
consists of an inertial wheel with an attached pinion which is concentric 
thereto. The frame in which this wheel is journaled is rotatable about the 
shaft of the reel which extends through the sidewall of the support. At 
the end of this shaft there is a gear with which the pinion of the 
inertial wheel meshes. An arm of the rotatable frame encompasses an arm of 
the pawl bar making controlling contact to move the pawl bar toward or 
away from the ratchet wheel. The rotatable frame is biased to maintain the 
bar out of engagement with the ratchet wheels. When the webbing is 
extended to buckle the passenger, and extends and retracts with the 
ordinary body movements of the passenger, the gear meshed with the pinion 
turns the inertial wheel without moving the frame in which it is 
journaled, because of the spring bias. On the other hand, if the passenger 
lurches forward, as would be the case were the vehicle involved in a 
collision, the inertial wheel, in accordance with Newton's laws of motion, 
would resist change, and the gear would "walk" up the pinion, causing the 
frame to rotate to a limited degree, moving the pawl bar into locking 
engagement with the ratchet wheel. 
Several factors effect the sensitivity of the inertial sensing device, such 
as the weight and dimension of the inertial wheel and the relative 
diameters of the driving gear and pinion. These factors are fixed, but the 
biasing means such as a spring is also an important factor. The strength 
of the spring and its degree of extension are important, the latter factor 
being one that can be readily altered. 
In most inertial devices of this type, one end of the spring is attached to 
the support wall or to a pin extending therefrom. The other end is 
attached to the rotatable frame of the inertial device, and several 
openings for the attachment of the spring are usually provided so that the 
sensitivity of the inertial device can be adjusted to meet the local 
requirements. The greater the tension on the spring, the less sensitive 
the sensing element becomes. 
In the retractor of my invention, one end of the biasing spring is, as 
usual, attached to the rotatable frame of the inertial device, but the 
other, rather than being attached to the sidewall, is attached to the end 
of a webbing follower which slides in a groove in the near side wall of 
the support. This groove goes from a point in or near the edge of the 
sidewall toward the point of spring attachment on the rotatable frame. The 
other end of this webbing follower pivots in the opposite sidewall, and a 
portion of the follower extends toward the reel and is biased toward the 
reel for sliding contact therewith. This bias is supplied by the same 
spring that provides bias for the rotatable frame of the inertial device, 
thus both webbing follower and inertial device share the same biasing 
spring. When the reel of webbing is substantially full, therefore, the 
shared biasing spring is under considerable tension, rendering the 
inertial device relatively insensitive to an accelerating rate of rotation 
of the reel in the unwind direction. When the roll of webbing on the reel 
has been substantially diminished by the withdrawal of webbing from the 
retractor, the bias becomes slight, rendering the inertial device more 
sensitive to an accelerating rate of retation of the reel in the unwind 
direction. 
This improvement, without any additional structure, provides a continuous 
change of sensitivity, with the sensitivity greatest as the webbing is 
extended. However, the retractor of my invention has additionally, a 
clutch positioned for limited retation with the ratchet wheel. The clutch 
is sandwiched between the ratchet wheel and the side wall of the support, 
and is biased toward the ratchet wheel for rotation therewith. The clutch 
has an arm extending in the general direction of the webbing follower and 
is of such a length, that it can rotate beneath the webbing follower when 
the webbing follower is held against its bias by a substantially full roll 
of webbing on the reel. The length of the arm of the clutch, however, is 
also such that it cannot pass beneath the webbing follower when the 
follower has moved toward the reel in response to a diminishing roll of 
webbing. Therefore, when the webbing is initially withdrawn for buckling, 
the arm of the clutch rotates beneath the webbing follower, and a further 
projection on the arm strickes the webbing follower, thus positioning the 
extended arm beneath the webbing follower and halting further rotation of 
the clutch in the unwind direction. This position of the arm prevents the 
follower from remaining in sliding contact with the diminished roll of 
webbing, and maintains the shared biasing spring extended in a relatively 
high degree of tension. When, however, in buckling, the webbing is 
permitted to retract slightly, as normally occurs during the buckling 
operation, the clutch rotates in the winding direction sufficient to 
release the webbing follower. The webbing follower then, in response to 
its bias, moves toward the diminished roll of webbing, reducing the 
tension of the shared spring bias and increasing the sensitivity of the 
inertial device to any accelerating rate of rotation of the reel in the 
unwind direction. 
In my reference to "webbing", I mean any form of safety belt or strap that 
may be employed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT WITH REFERENCE TO THE 
DRAWINGS 
With reference to FIGS. 1, 2 and 3, my invention is directed to a seat belt 
retractor of the type having a flanged rotatable reel 1 for belt webbing 2 
journaled in a support wall 3, and spring biased toward a fully wound 
condition by biasing means 4. An extension of the reel shaft connects to 
an inertial device 5 for tripping the locking pawl bar 6 into locking 
engagement with ratchet teeth 7 on the periphery of the flanges of the 
webbing reel 1, when a sudden pull is applied to webbing 2. 
The inertial device is sensitive to a sudden increase in the rate of 
acceleration of the reel in the unwind direction. 
A novel feature of this seat belt retractor is the additional structure 
provided to permit the webbing to be withdrawn from the retractor for 
buckling without the annoyance of having the reel lock in response to 
inertial device 5, no matter how far the belt is extended on the first 
pull, and no matter how rapidly it is manually withdrawn. I say 
"manually", bacause the pawl and ratchet can still engage, if the 
acceleration is as great as would be encountered in a collision, where the 
webbing was suddenly subjected to an acceleration in the order of 3 g's or 
more. This feature insures that the retractor would act to restrain a 
passenger even if for some reason the mechanism was blocked from behaving 
in the manner intended. 
The ability of the retractor to permit withdrawal of the webbing without 
normally triggering the locking mechanism is made possible by increasing 
the bias applied to the inertial device by biasing means 8 during this 
period of initial withdrawal of the webbing. This is achieved by attaching 
a spring to the inertial device and the other end, which in retractors of 
the prior art is generally fixed on the support, to a movable webbing 
follower 9. 
When the reel is substantially full of webbing as when the webbing is 
initially withdrawn, the distance subtended by the spring is at a maximum, 
thus maximizing the degree of applied bias, and greatly reducing the 
sensitivity of the inertial device to any accelerated rate of withdrawal 
of the webbing. As the diameter of the roll of webbing is substantially 
reduced with the withdrawal of the belt, the webbing follower, a portion 
of which is in sliding contact with the surface of the roll of webbing, 
moves toward the shaft of the reel, and in so doing, lessens the distance 
subtended by the spring, between the inertial device and the webbing 
follower, thus reducing the bias and making the inertial device more 
sensitive and responsive. The material of construction of this webbing 
follower 9, is not critical, but nylon or Teflon is preferred, said 
follower preferably being shaped for strength and rigidity. The webbing 
follower of FIGS. 1,2 and 3 extends into an opening 11 in the side support 
wall most distant from the inertial device 5. The side support wall most 
distant from the inertial device 5. The webbing follower extends beyond 
the opposite wall, with its end 10 extending through slot 12 which starts 
at the outer edge of the support wall and slopes in the direction of that 
part of the inertial device to which the biasing spring 8 is attached. The 
other end of spring 8 is attached to the end of the webbing follower that 
extends beyond slot 12, thus biasing the follower toward the reel. The end 
of the follower in the slot can easily slide in the slot in a line either 
toward or away from the inertial device. Preferably the slot is lined with 
a polymeric material such as nylon or Teflon to increase the ease of 
slippage of the end of the webbing follower within said slot. 
A portion 13 of the webbing follower extends toward the roll of webbing on 
the reel for sliding contact therewith. With this arrangement it can be 
seen that, as the webbing is withdrawn, the sensitivity of the inertial 
device to any sudden extension of the webbing, increases. In other words, 
initially, the webbing can be withdrawn with little danger of triggering 
the locking mechanism, but the further the webbing is extended, the 
greater becomes the chance of triggering the locking mechanism. To 
forestall such an eventuality, the retractor of this invention also has a 
clutch 14 which is rotatable on the shaft of the reel, and is positioned 
between the sidewall of the support and the face of the adjacent toothed 
reel flange 15 hereinafter called the ratchet wheel. The clutch 14 is 
biased against the ratchet wheel for rotation therewith. The clutch has an 
extending arm having an outer edge 16, preferably shaped as an arc segment 
having approximately the radius as measured from its curved surface to the 
center of the shaft. This outer edge is at such a distance from the shaft 
of the reel that it can pass beneath the webbing follower 9 when said 
follower is restrained outwardly against its bias 8 by a substantially 
full roll of webbing on the reel, but said outer edge is at a distance 
from the shaft such that it cannot pass beneath the webbing follower when 
the roll of webbing on the reel has been appreciably reduced as a result 
of the belt having been withdrawn for buckling. Although the shape of the 
outer edge of the extending arm of the clutch is preferably that of an arc 
segment, actually this outer edge can be a step, shoulder, or any shape 
which behaves in the manner described. Adjacent to this arc segment, and 
positioned to follow the arc segment as the clutch rotates in the unwind 
direction, is a projection 17, extending beyond the arc segment to a 
distance such that it cannot rotate beneath the webbing follower in any of 
its positions, thus when the webbing is first withdrawn, the arc segment 
16 of the clutch rotates beneath the webbing follower 9, and is held there 
when the projection or stop strikes the webbing follower, halting further 
rotation of the clutch, the surface of which is then in sliding contact 
with the ratchet wheel. As more webbing is withdrawn from the reel, the 
arm of the clutch retains the webbing follower in a fixed position, with 
the biasing spring extended. This maintains the inertial device in a 
condition of low sensitivity. 
While the belt webbing is buckled about the user, however, the webbing is 
normally retracted slightly, and to a sufficient degree as to rotate the 
arc segment away from its position beneath the webbing follower. The 
webbing follower then springs forward to contact the diminished roll of 
webbing and in so doing reduces the bias of the spring attached to the 
inertial device, thus greatly increasing its sensitivity to any sudden 
extension of the webbing. 
The clutch 14 is not visible in the retractor as shown in FIG. 1, but is 
placed beside it. Its relation to the webbing follower is clearly shown in 
the drawing of FIG. 2. 
The retractor is termed "bi-level web sensitive" because of its low 
sensitivity to the acceleration of the reel when the webbing follower 9 is 
held stationary by clutch 14 when the webbing is first withdrawn, and its 
high sensitivity when the user is buckled up. The clutch has in this case 
released the webbing follower to move toward the reel, thereby reducing 
the tension on biasing spring 8, and producing the high level of 
sensitivity to any sudden extension of the webbing. 
FIG. 3 represents the webbing follower in its released position wherein the 
inertial device is highly sensitive and readily responsive. 
The clutch 8 is shown in FIG. 3 with biasing spring 18 pressing it in 
contact with ratchet wheel 15. 
FIG. 4 illustrates a different type of webbing follower, this one journaled 
in the sidewalls near the top of the support frame. Being constructed of 
rod, it has a central loop 13 for sliding contact with the roll of 
webbing. The controlling end of this webbing follower passes through a 
slot in the support wall for cooperation with the clutch in substantially 
the same manner as the webbing follower of FIG. 2. 
Although a spiral spring can be used with this version of the webbing 
follower, FIG. 5 shows the manner in which a leaf spring could serve as 
well. 
There are many varieties of webbing followers and biasing means that could 
be adapted for use in the safety belt retractor of my invention. 
To summarize the action of the retractor: as the webbing is initially 
withdrawn for buckling, the spring 8 is extended because the substantially 
full roll of webbing on the reel presses the webbing follower outwardly, 
at a considerable distance from the inertial device to which it is 
connected by this spring 8. Also, in manually withdrawing the webbing, the 
clutch is immediately rotated by its contact with the ratchet wheel, so 
that its arc segment 16 passes under the webbing follower where it comes 
to reset as stop 17 strikes the webbing follower. The high level of 
tension is therefore maintained by the extended spring 8, even after the 
roll of webbing diminishes in diameter as the webbing is withdrawn. The 
inertial device, now having a low level of sensitivity, does not normally 
annoy the user by triggering the locking mechanism as the webbing is 
withdrawn. 
In the buckling operation, the user inadvertently allows the webbing to 
retract slightly. Only a slight movement of the reel in the rewind 
direction is necessary to rotate the arc segment 16 free of its position 
beneath the webbing follower to respond to its bias and move toward the 
reel. The spring 8 therefore contracts. But the spring is shared by the 
inertial device 5 which now becomes highly sensitive to any sudden 
acceleration of the reel in the unwind direction, so that if the passenger 
lurches forward as would be the case in a collision, the inertial device 
triggers the locking mechanism and the webbing restrains the passenger. 
In our drawing the preferred inertial device comprises an inertial wheel 19 
journaled into a light frame 21 which is rotatable about the shaft of the 
reel. Gear 22 is keyed to the shaft. As the reel rotates, this gear, which 
meshes with a pinion attached to the inertial wheel, turns the wheel. If 
the motion of the reel is moderate, such as would be produced by the 
normal body motion of a belted passenger, any slight tendency for the 
frame 21 to rotate, is thwarted by the bias of spring 8. If the passenger 
suddenly lurches against the webbing, however, the inertia of the inertial 
wheel 19 offers enough resistance to immediate rotation to cause the gear 
22 to "walk up" the pinion. Since the pinion with attached inertial wheel 
is journaled in the rotatable frame, and off-center with respect to the 
point of rotation of the frame, the inertial device rotates counter 
clockwise. It can be seen in FIG. 2, that the encompassing arm 23 of the 
inertial device will then rock the extended arm 24 of the pawl bar, and 
thus rock the pawl bar 6 into locking engagement with the ratchet wheel 
15, causing the webbing to restrain the buckled passenger. 
While I have described the preferred embodiments of my invention, it will 
be understood that various modifications can be made in the seat belt 
retractor without departing from the spirit of the invention.