GB2413993A

GB2413993A - Seat belt pretensioner

Info

Publication number: GB2413993A
Application number: GB0410631A
Authority: GB
Inventors: Fredrik Wigstrom
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2004-05-12
Filing date: 2004-05-12
Publication date: 2005-11-16
Also published as: GB0410631D0

Abstract

A pretensioner arrangement for pretensioning a safety-belt 3 is embodied in a retractor which incorporates a rotatably mounted spool 1 having a drum 2 on which the safety-belt is wound. A grooved flange (5) is formed integrally with the drum. A wedge member (11) is provided on one end of a relatively stiff wire cable (10), the wedge member (11) being located adjacent the groove there being one turn of wire which passes around the flange and over the wedge member. A piston (8) and gas generator (9) unit applies tension to the wire cable (10) thus drawing the wedge member into frictional engagement with the flange (5) and rotating the flange to wind in safety-belt.

Description

24 1 3993

DESCRIPTION OF INVENTION

"IMPROVEMENTS IN OR RELATING TO A PRETENSIONER" THE PRESENT INVENTION relates to a pretensioner and more particularly relates to a pretensioner incorporated in a retractor reel.

It has been proposed previously to provide a pretensioner to tension a seat belt provided in a motor vehicle in the event that an accident is detected. It has been found that if tension is applied to a seat belt during the initial instants of an accident situation, the seat belt will become tightened around the seat occupant, thus tending to minimise any forward movement of the seat occupant relative to the seat as the vehicle decelerates.

Various types of pretensioner have been proposed previously, including pretensioners which apply a force to move a buckle to which part of the seat belt is connected. A second type of pretensioner actually rotates a spool within a retractor reel associated with the seat belt to "wind in" part of the seat belt.

The present invention relates to a retractor of this second type.

A difficulty faced by the designer of a pretensioner associated with a retractor spool was that, of course, the retractor spool must operate in the normal way before the pretensioner is actuated. Thus the spool must be free to rotate in either direction, a seat belt is withdrawn from the retractor or wound back into the retractor. It is only when the pretensioner is actuated that the spool of the retractor should be positively wound in a direction to effect "winding in" of the seat belt. There is, therefore a requirement for a connection between the components of the pretensioner and the spool of the retractor which permits the spool to rotate freely during ordinary use, but which also permits the spool to be driven in a "winding in" direction when the pretensioner is actuated.

The present invention seeks to provide an improved pretensioner.

According to this invention there is provided a pretensioner arrangement for pretensioning a safety-belt, arrangement comprising a rotatable spool to which part of the safety-belt is connected and on to which the safetybelt may be wound, the spool incorporating a part which has a peripheral groove, there being an elongate element, the elongate element being associated with an arrangement to apply force or tension to the end of the elongate element, the other end of the elongate element being connected to a wedge member being configured to effect frictional engagement with the said groove, the wedge member being located adjacent to the groove, the elongate element extending from the wedge member to effect at least one complete turn around the part of the spool defining the peripheral groove and passing over the wedge member so that the force or tension applied to the elongate element would cause the wedge member to be driven in to frictional engagement with the peripheral groove.

Preferably the wedge member is formed of deformable material. The material may be rubber or an equivalent material.

Conveniently the elongate element passing over the wedge member is received within a channel formed in the wedge member.

Advantageously the channel has a dimension which is slightly less than the diameter of the elongate element.

Conveniently the elongate element has a degree of stiffness such that the said at least one turn and the wedge member are initially held so that the spool may rotate freely. The elongate element is frictionally engaged by the wedge member where the elongate element is received within the channel in the wedge member.

Conveniently the elongate element is a wire cable.

Preferably the arrangement to apply force to one end of the elongate element is a gas generator and piston arrangement.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic and partly exploded view of the principled operative part of a pretensioner incorporated in a seat belt retractor, FIGURE 2 is an enlarged part sectional view of part of a flange of the retractor, and the wedge of the embodiment of Figure 1, and Figure 3 is a perspective view showing the flange being gripped by the wedge.

Referring initially to Figure 1 of the accompanying drawing, a spool 1 of a seat-belt retractor is illustrated, the spool 1 incorporating a generally cylindrical drum 2 upon which a terminal part of the seat belt 3 is wound. The spool is provided with a trunnion 4 by means of which, together with an opposed trunnion (not shown) the spool may be mounted rotatably in position.

The spool may be a generally conventional spool but the spool is provided, at one end, with a flange 5, the flange 5 having a peripheral V or U section groove 6, the groove being shown most clearly in Figures 2 and 3.

A pretensioner which is to rotate the spool l to "wind in" safety-belt in the event that an accident should occur has components which co-operate with the grooved flange 5. The pretensioner incorporates a cylinder 7, the cylinder 7 containing a piston 8. Extending from the cylinder is a gas generator chamber 9 which is to contain a pyrotechnic charge. The pyrotechnic charge is associated with a squib which ignites the pyrotechnic charge in response to an appropriate signal. The pyrotechnic charge then generates gas which is injected into the cylinder.

The gas generator chamber 9 is positioned so that when the pyrotechnic charge is ignited, the gas is injected in to the cylinder 7 at a point between a closed end thereof and the piston 8, thus tending to drive the piston along the cylinder 7. A relatively stiff wire cable 2 has one end connected to the piston and extends through a seal in the closed end of the cylinder. The wire cable 10 is connected, at the other end thereof, to a wedge member 11. The end of the wire cable 10 is securely bonded or otherwise secured to the wedge member 11.

The wedge member is made of rubber or a similar deformable material.

The wedge member 11, as can be seen most clearly from Figure 2, is an elongate element of uniform U or V cross-section. The element is of "U" or "V" external form and also internal form. Thus the exterior of the wedge member presents two side faces 12, 13 which converge inwardly towards a generally rounded bottom 14. Each side face may be provided with ribbing, such as the ribs 15.

The part of the wedge member opposed to the rounded base 14 is provided with a channel 16 which is of "U" shaped form, the channel 16 being dimensioned to receive an intermediate part of the wire lO. Preferably the width of the channel adjacent the base of the channel is slightly less than the diameter of the wire cable.

It is to be appreciated that the wire cable lO is loosely wound around the grooved flange 5, with the wedge member located adjacent to the groove 6 and with part of the wire cable 10 passing over the wedge member and being received in the channel 16 formed in the wedge member 1 1.

Due to the inherent stiffness of the wire cable 10 and due to the frictional engagement between the intermediate part of the wire cable 10 and the channel 16, the wedge member is initially held only in very loose engagement with the groove 6 in the flange 5, or may even be held spaced above the groove 6. There is one complete turn of wire cable which is loosely accommodated within the peripheral recess 6 provided on the flange 5.

It is to be appreciated, therefore, that during ordinary use of the retractor the spool 1 may rotate freely. However, when the pyrotechnic charge within the chamber 9 is ignited gas is generated which causes the piston 8 may move very rapidly along the cylinder thus applying a very substantial force to the wire cable 10. This substantial force initially causes the wedge member 11 to be driven radially inwardly, as indicated by the arrow 17 in Figure 1 to engage firmly the groove 6 provided in the peripheral of the flange 5. Continued force applied to the wire cable 10 will cause the wire cable to slide through the channel 16 provided in the wedge member 11 whilst further driving the wedge member in to the channel. As the wire is driven in to the base of the channel 16, the upper parts of the side wall 12 and 13 of the wedge member will be driven apart, as the wedge member is made of deformable material, thus further enhancing the frictional grip between the ribbed outer walls 12 and 13 of the wedge member 11 and the peripheral recess 6 provided in the flange 5.

Thus a very secure grip is effected between the wedge member and the flange 5, and further tension applied to the wire cable 10 as the piston 8 continues to move within the cylinder 7 will tend to cause the entire spool 1 to rotate in a sense which "winds in" safety-belt 3.

Whilst in the described embodiment, as shown in Figure 1, there is one quarter of a turn of wire cable 10 between the wedge member and the point where the wire cable 10 leaves the flange 5, a number of turns may be provided so that the spool may be driven through a number of revolutions to wind in a substantial length of safety-belt.

It is to be appreciated that the described arrangement is a very simple and incorporates a minimum number of parts, enabling the arrangement to be manufactured at low cost. However, the arrangement provides a satisfactory operating characteristic.

Whilst the invention has been described with reference to an embodiment in which the wedge member which is made of rubber or similar deformable material, it is envisaged that alternate materials may be used. In certain embodiments the wedge member may be formed of steel. In the situation described, certain steels may provide a very desirable operating characteristic. A further possibility is to use a wedge which has a steel core provided with an outer covering of plastic or rubber material. If a wedge of this type is utilised, the outer covering may be provided with frangible retaining portions provided to retain the wedge at a position slightly spaced above the groove during normal use of the apparatus. Thus the wedge may comprise a wedged shaped steel core provided with a thin covering of plastic or rubber material. The covering of plastic material may incorporate a plurality of frangible extensions in the form of"legs" which loosely engage the groove during normal use, without imparting any significant frictional forces on the groove as the spool of the retractor rotates. The legs are formed of frangible material so that, should tension be applied to the wire cable, the wedge will be forced inwardly towards the groove and the frangible legs will snap and break off, thus allowing the plastic or rubber coated steel core to engage the groove with an adequate frictional engagement.

When used in this Specification and Claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS: 1. A pretensioner arrangement for pretensioning a safety-belt, the

arrangement comprising a rotatable spool to which part of the safety-belt is connected and on to which the safety-belt may be wound, the spool incorporating a part which has a peripheral groove, there being an elongate element, the elongate element being associated with an arrangement to apply force or tension to the end of the elongate element, the other end of the elongate element being connected to a wedge member being configured to effect frictional engagement with the said groove, the wedge member being located adjacent to the groove, the elongate element extending from the wedge member to effect at least one complete turn around the part of the spool defining the peripheral groove and passing over the wedge member so that the force or tension applied to the elongate element would cause the wedge member to be driven in to frictional engagement with the peripheral groove.
2. A pretensioner according to Claim 1 wherein the wedge member is formed of deformable material.
3. A pretensioner according to Claim 1 or 2 wherein the elongate element passing over the wedge member is received within a channel formed in the wedge member.
4. A pretensioner according to Claim 3 wherein the elongate element has a degree of stiffness such that the said at least one turn and the wedge member are initially held so that the spool may rotate freely.

S
5. A pretensioner according to any one of the preceding Claims wherein the elongate element is a wire cable.
6. A pretensioner according to any one of the preceding Claims wherein the arrangement to apply force to one end of the elongate element and is a gas generator and piston arrangement.
7. A pretensioner substantially as herein described with reference to and as shown in the accompanying drawings.
8. Any novel feature or combination of features disclosed herein.