WO1996013409A1

WO1996013409A1 - Method for locking and load limiting of a seat belt

Info

Publication number: WO1996013409A1
Application number: PCT/US1995/014273
Authority: WO
Inventors: Harold John Miller, Iii; Niels Dybro
Original assignee: Alliedsignal Inc.
Priority date: 1994-10-31
Filing date: 1995-10-10
Publication date: 1996-05-09
Also published as: AU4143996A

Abstract

A pretensioner usable with a seat belt to protect an occupant from injury comprising: a cable (40), movable in a belt tightening direction and in a belt loosening direction connected to the seat belt so that motion of the cable causes movement of the seat belt; a piston (112) for moving the cable and the belt a determinable amount in the tightening direction; a wedge housing (22) and wedges (30a, b) responsive to the motion of the cable in both the belt tightening direction for releasing the cable and responsive to motion of the cable in the loosening direction for locking upon the cable to prevent same from moving in the presence of a predetermined force applied to the belt.

Description

METHOD FOR LOCKING AND LOAD LIMITING OF A SEAT BELT

BACKGROUND AND SUMMARY OF THE INVENTION

The invention generally relates to a device for locking a cable in place and, more specifically, to a pretensioner of a safety restraint system to lock or controllably inhibit movement of a cable, seat belt and/or occupant.

A seat belt may comprise one or more of a torso belt and a shoulder belt. As is known in the art the torso and shoulder belt can be formed as a continuous loop or two separate belts. Seat belts and seat belt systems currently employ two (2) types of pretensioners or belt tighteners. One of these pretensioners or belt tighteners, is associated with the seat belt buckle in which the buckle is connected to the torso belt or to both the torso and shoulder belts. The other pretensioner is built into a seat belt retractor. The buckle pretensioner comprises a mechanism that pulls the seat belt buckle, and belt attached thereto, via a cable in a belt-tightening direction. The retractor pretensioner includes a mechanism that reverse winds the retractor in a direction to cause the seat belt to tighten. In many current safety restraint systems, the shoulder belt portion of the seat belt is connected to the retractor.

During an accident, various sensors associated with the safety restraint system generate one or more signals to activate the pretensioner thereby, causing the seat belt to tighten about the occupant. This tightening occurs very quickly and prior to the time the occupant begins to move forward due to the impact of the crash. As described therein the pretensioner, of the present invention includes a locking or clamping mechanism that prevents the webbing, after it is tightened, from moving from its pretensioned or tightened conditioned. In certain situations, it is desirable to permit the occupant to subsequently move forward in a controlled manner such that the occupant's motion dissipates some of the crash energy lessening the potential for injury. In these situations the occupant's motion is limited by the controlled movement of a cable.

It is an object of the present invention to provide an improved locking device usable within a pretensioner or belt tightener.

Accordingly, the invention comprises: a pretensioner to protect an occupant from injury comprising: a cable, movable in a belt tightening direction and in a belt loosening direction, operatively coupled (directly or via a retractor) to a seat belt so that motion of the cable causes movement of the seat belt. The device includes first means for moving the cable and the belt, a determinable amount in the tightening direction and locking means responsive to the motion of the cable in the belt tightening direction for releasing the cable and also responsive to motion of the cable in the belt loosening direction for locking upon the cable to prevent same from moving in the presence of a predetermined force applied to the belt. The locking means includes a wedge housing having a conical opening with a narrow end and a larger end. The opening is situated so that its narrow end faces the belt loosening direction. The locking means additionally includes a plurality of spaced wedges movable in the conical opening. Each wedge includes a conical outer wall and an inner wall defining an opening such that when these openings face each other they form a generally cylindrical shaped opening or channel for receipt of the cable. Bias means are provided to bias the wedges in the belt loosening direction into the conical opening of the wedge housing. Movement of the cable in the belt tightening direction causes the movement of the wedges, in the belt tightening direction, enlarging the cylindrical shaped opening or channel about the cable. Movement of the cable in the belt loosening direction causing the wedges to clamp upon and hold the cable therebetween.

In one embodiment of the invention each wedge includes a plurality of cable gripping teeth arranged on the inner wall of each wedge. The rake of the teeth can be direction in either the belt tightening or belt loosening directions. These teeth may be hardened in which case they firmly hold the cable, that is, after it was tightened, against further movement in the belt loosening direction. Alternately, the teeth may remain unhardened in which case some of them shear off at a predetermined level of shear force permitting the cable, belt and occupant to move in the belt loosening direction, in a controlled manner. As the cable shears the teeth, a relatively constant reaction force is generated which dissipates the crash energy.

Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGURE 1 is a cross-sectional view of some of the major components of the present invention.

FIGURE 2 is an isolated top plan view of a wedge housing. FIGURE 3 is an orthogonal view of two facing wedges.

FIGURE 4 is a partial cross-sectional view showing the details of one half of a wedge.

FIGURE 5 is a partial cross-sectional view showing the details of one half of an alternate wedge. FIGURE 6 shows the present invention incorporated into a buckle pretensioner.

FIGURE 7 illustrates the present invention within a retractor pretensioner. FIGURE 8 shows data associated with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGURE 1 illustrates many of the major components of the invention and shows a belt-locking device generally shown as 20 comprising a wedge housing 22 having a conically-shaped bore 23 having a side wall 24. We have found that the cone angle. A, of the walls to the vertical should be in the range of approximately 10 to 40 degrees. A twenty degree angle has been used during testes and displays good performance results. Fitted within the bore are radial wedges 30a and 30b formed as two facing, spaced cone halves. More specifically, each wedge 30a and 30b includes a conically shaped outer surface 32 conformally shaped to the bore 23 and one half ('/-) of a cylindrically-shaped bore or passage 34; the diameter of which is generally equal to the diameter, D, of a standard twisted aircraft cable 40. A typical diameter of these cables for the present application is in the range of about 0.01875 inch (4.76 mm) to 0.25 inch (6.35 mm). As can be seen the cable 40 extends through the wedges. Each wedge, 30a and 30b, is biased into the housing 22 by a spring 42 that is received about a boss 31 of each wedge. The angled wall 24 of the wedge housing lightly urges each wedge 30a,b against the cable 40. As can be appreciated, for a given wedge housing geometry, the distance that each wedge extends into the bore 23 will vary with the diameter of the cable 40. One end 44 of the cable 40 is attached to a movable, force-applying device such as a piston 112 of a pretensioner. The other end 48 of the cable 40 is attached to the mechanism 50 to be tightened or rather moved in a belt tightening direction (see arrow 52) such as a seat belt buckle or a clutch incorporated within a retractor.

Upon the activation of the pretensioner (see FIGURES 6 and 7) the piston 112 pulls the cable 40 in the belt tightening direction shown by arrow 52. Because the wedges lightly engage the cable the motion of the cable (in the belt tightening direction) urges the wedges 30a and 30b downward, as viewed in FIGURE 1, against the biased force of spring 42. The motion of the piston and cable 40 reduces slack in the seat belt against the occupant. After piston 112 has moved a predetermined amount, it will stop. This is typical of known belt and retractor pretensions. Thereafter, the forces generated during a crash cause the occupant to move or to tend to move forward against the tightened seat belt (lap belt and/or shoulder belt) . The occupant loads the lap belt, or shoulder belt of the seat belt, applying an upward directed load in the belt loosening direction, as seen in FIGURE 1 and as indicated by arrow 54, on the cable 40. This occupant-generated load causes the cable 40 to move oppositely from its pretensioned position. As the cable motion reverses direction, the forces generated by spring 42 immediately urge the wedges into the housing 22 reducing the spacing therebetween and closing them about the cable. The outward movement of the cable, in the belt loosening direction, in combination with the positive engagement between the cable and the interior bore 34 of the wedges 30a,b resulting from the inward thrust generated by the sloped side 24 of the bore 23 and the inherent friction between the cable and wedges further urges the wedges into bore 23. This combined action causing the wedges 30 to self-lock about the cable 40. Reference is made to FIGURES 4 and 5 which are partial sectional views through one of the wedges, such as 30a. As can be seen from FIGURE 4, the interior wall of the bore or passage 34 is serrated defining a plurality of rows 61 with spaced teeth 60. The teeth can be evenly or unevenly spaced. As can be seen the rake of the teeth 60 in FIGURE 5 is opposite that of FIGURE 4.

Depending upon the physically characteristics of the teeth 60 the cable 40 can be forcibly held in place or permitted to controllably slip relative to the teeth and wedge housing. The purpose of the controlled slippage will be clear from the description below. In one embodiment of the invention the strength, hardness, number of teeth, cone angle, material choice, etc., are sufficient to hold the cable in place against the loads generated during an accident. In this embodiment the teeth would be case hardened (hardness rating of Rc36 -Rc44) and made from 4130 steel. In a alternative embodiment of the invention the teeth are not hardened and the material is chosen such that the shear capability of the teeth is less than those frictional forces applied to the wedges through the cable. As an example the wedges and teeth can be made of 4130 steel having a shear strength of about 32 KSI. When the applied forces exceed the shear capability of the teeth in contact with the cable, and the cable begins to slip. At this point one or more sets of teeth are sheared away as the cable 40 slides therethrough. FIGURE 8 illustrates actual test data of a locking mechanism of FIGURE 1 utilizing shearable teeth. As can be seen, the positive lock between the cable and the wedges occurs at approximately 0.25 inch (6.25 mm) of reverse motion (in the belt loosening direction) or displacement of the cable. This quick locking is extremely advantageous as it initiates the control over the occupant early in the crash event. As the cable continues to be pulled through the wedges in response to the occupant-generated loading, the wedge/cable interface generates a relatively constant retarding force level due to the inherent frictional losses of the system. As can be seen in FIGURE 8 this constant force is about 600 pounds, however, depending on the design of the individual parts of the invention this force can be made to vary, from about 350 pounds to over 2000 pounds. The desired amount of retarding force will vary with the application of the invention. Because the interior teeth 60 are sheared away the interior of the bore 34, at the location of the sheared teeth, conform to the outside diameter of the cable 40 enhancing the friction force generating capability therebetween. These friction forces dissipate the crash energy and permit the occupant to move forward in a controlled manner.

As can be appreciated, these friction losses are dependent upon the material used, the number of teeth employed in the wedges, the hardness of the teeth, and the material shear strength. The following characterizes the wedges and cable used to achieve the results shown in FIGURE 8. material - 4130 steel with hardness of about Rc42, number of rows of teeth - 12 (although the rows of teeth can be between 8 to 20), tooth rake - about 25 degrees, which can be either in the belt tightening or loosening direction tooth depth - about 0.50 mm shear strength about 34 KSI. cone angle - 20 degrees (although the angle may vary between about 10 to 40 degrees) ,

Reference is briefly made to FIGURE 6 which illustrates a buckle pretensioner 100. The pretensioner includes a pressure tube 102 joined to a housing 104 such as by threads 103. Incorporated within the pretensioner housing 104 is the wedge housing 22. Situated within the wedge housing are the wedges 30a and 30b. Extending outwardly from the housing 104 is a pyrotechnic cartridge 106 of known variety, that generates products of combustion that are received within a bore or pressure cavity 110 of the housing 104. This cavity is closed at one side by the piston 112 and the products of combustion urge a piston 112 down the pressure tube. As the piston moves it pulls cable 40 about a pulley 114 thereby pulling a buckle 116 downward (relative to the seated occupant) in the belt tightening direction. When the buckle 116 and associated torso belt 117 and/or shoulder belt 206 are loaded by the occupant, the cable is moved in an opposite, belt loosening direction causing the wedges 30a,b to positively lock against the cable 40 as described above. Components 116, 117, 206 are shown in reduced size. As mentioned above the wedges 30a and 30b are biased by spring 42 which is fitted within the pretensioner.

FIGURE 7 shows a retractor pretensioner 200 comprising a housing 202. A portion of the housing is formed to provide an integral wedge housing 22. Also situated within the retractor housing 202 is the retractor reel or spool 204 upon which seat belt webbing 206 is wound. Typical of retractor pretensioners is a one¬ way clutch 210 which, when activated, causes the reel 204 to reverse wind. Connected to the clutch is the pretensioning cable 40 that is fed through the wedges 30a and 30b. As before the wedges are biased by spring 42 which is kept in place by a cap 212. Upon activation of the pretensioner, the cable is drawn in the direction of arrow 220 as an associated movable element, such as a piston, is powered outwardly. The motion of the cable reverse winds the reel 204. Subsequently, as the belt 206 is loaded by the occupant, the reel and clutch rotate in a clock-wise manner, thereby urging the cable 40 downward as viewed in FIGURE 7. Thereafter, the wedges 30a and 30b lock against the cable 40 in the manner as described above.

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.

Claims

1. A pretensioner usable with a seat belt to protect an occupant from injury comprising: a cable (40), movable in a belt tightening direction and in a belt loosening direction connected to the seat belt so that motion of the cable causes movement of the seat belt; first means (112) for moving the cable and hence the belt a determinable amount in the tightening direction; lock means responsive to the motion of the cable 0 in the belt tightening direction for disengaging the cable and responsive to motion of the cable in the belt loosening direction for locking upon the cable to prevent same from moving in the presence of a predetermined force applied to the belt. 5

2. The device as defined in Claim 1 wherein the lock means includes: a wedge housing (20) having a conical opening (22) having a narrow end and a larger end situated so 0 that its narrow end faces the belt loosening direction and the larger end faces the belt tightening direction, a plurality of spaced wedges (30a,b) movable in the conical opening (22) each wedge including a 5 conical outer wall (32) and an inner wall defining a belt receiving cylindrical opening (34) such that the opening of each wedge when positioned about the cable, forms a generally cylindrical shaped opening for receipt of the cable (40),

30 bias means (42) for biasing the wedges in the belt loosening direction into the conical opening of the wedge housing (20) such that movement of the cable in the belt tightening direction causes the movement ,-. of the wedges in the belt tightening direction to enlarge the cylindrical shape opening and that movement of the cable in the belt loosening direction causing the wedges to clamp upon and hold the cable therebetween.

3. The device as defined in Claim 2 wherein each wedge (30a,b) includes a plurality of cable gripping c teeth (60) arranged on the inner wall (34) .

4. The device as defined in Claim 3 wherein the teeth (60) are shearable at a predetermined shear force generated by the motion of the cable. 0

5. The device as defined in Claim 1 wherein the first means includes a piston (112) attached to an end of the cable and movable in the belt tightening direction. 5

6. The device as defined in Claim 4 wherein the teeth are arranged about the inner surface of each wedge in rows.

7. The device as defined in Claim 6 wherein the 0 teeth made of an unhardened metal.

8. The device as defined in Claim 3 wherein the teeth have a rake which is arranged in one the belt loosening and belt tightening direction.

9. The device as defined in Claim 1 wherein the 5 cable (40) is connected to a seat belt buckle.

10. The device as defined in Claim 1 wherein the cable in connect to a clutch (210) of a seat belt 0 retractor.

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