GB2118022A

GB2118022A - Cone pulley drive for seat belt tension control

Info

Publication number: GB2118022A
Application number: GB08310005A
Authority: GB
Inventors: Robert Boyson Heath
Original assignee: Rainsfords Metal Products Pty Ltd
Current assignee: Rainsfords Metal Products Pty Ltd
Priority date: 1982-04-14
Filing date: 1983-04-13
Publication date: 1983-10-26
Also published as: DE3313580A1; AU1345183A; GB8310005D0; FR2525112A1; JPS58203772A

Abstract

A cone pulley drive 22, 23, 30 is interposed between a spring shaft 24 of a seat belt retractor 10 which imparts retracting torsion, and a spool spindle 13 which carries a spool 14 on which seat belt webbing 15 is wound. <IMAGE>

Description

SPECIFICATION Cone pulley drive for seat belt tension control This invention relates to retraction means for the seat belt of a vehicle, for example for retracting the seat belt webbing in a passenger vehicle.

A problem which has been encountered and long recognised with seat belt retractors is that the retraction spring increases its retraction force over the useful range, approximately in accordance with HOOKES Law, that is, the more the belt webbing is withdrawn from the retractor, the higher the tension imparted by the spring, and this is further exacerbated by a reduction in the effective diameter of the spool, such that withdrawal of the seat belt greatly increases the tension on the seat belt webbing to the point where considerable discomfort occurs.

It is known that some efforts have been made to reduce the increase of restoring force imparted by the return spring of a retractor by utilising a retractor employing two spring spools, including a return spring having a transverse camber such that a substantially constant return force is imparted. This partiy solves the difficulty which has beset seat belt retractor manufacturers, but it does not resolve the problem associated with the reduction of effective diameter of the spool as the seat belt webbing is withdrawn, and the problem still remains that with all known prior art seat belt retractors, the tension increases as the seat belt webbing is withdrawn.This is generally annoying to most users, but gives rise to extreme discomfort in certain instances wherein the users may have physical disabilities, particularly where the sash portion of the seat belt webbing encounters a body with high tension.

The main object of this invention is to provide an improvement whereby the increase of tension upon seat belt webbing withdrawal is less than with prior art retractors, and wherein a seat belt retractor can be designed, if required, to actually have less tension on the belt webbing in its withdrawn state than when it is retracted or nearly retracted onto a spool.

Brief Summary of the Invention A cone pulley drive is interposed between a spring shaft of a seat belt retractor which imparts retracting torsion, and a spool spindle which carries a spool on which seat belt webbing is wound.

More specifically, in a seat belt retractor having a frame, a spool carried on a spool spindle which is rotatable in the frame, and a return spring having one end fixed with respect to the retractor frame and the other end coupled to a spring shaft, there is provided a spring shaft rotatable in bearings in the frame, said torsion imparting return spring being secured at one end to the frame and at the other end to the spring shaft, and drive means between said spool shaft and spring shaft, said drive means comprising a pair of pulleys at least one of which is on a shaft shaft, said pulleys including at least one spirally grooved cone pulley and a drive member coupling said pulleys.While in some instances use can be made of one flat pulley and one cone pulley for effecting drive between the two shafts, in one embodiment of this invention both the driving and driven pulleys are spirally grooved cone pulleys and the drive means is a spiral of flexible material retained at its ends on the respective pulleys.

With this arrangement, by merely varying the designed cone angle of the spirally grooved cone pulleys, the tension on the seat belt webbing can be varied to be greatest or least upon withdrawal of the webbing, depending upon design requirements. Thus it becomes possible to greatly reduce the tension imparted by the seat belt webbing against the body of a user, and to sufficiently increase the retracting tension during rewinding to ensure that the seat belt webbing is properly retracted by the retractor.

It will be obvious that the lay shaft can be coaxial with the spool spindle, or can be a journalled extension of the spool spindle, this being a mere mechanical equivalent. However, it is desirable in the construction of a seat belt retractor to maintain weight and size to a minimum, and in another aspect of this invention there is provided a pinion and gear drive between the spool spindle and the lay shaft reducing the rotational velocity of the lay shaft, increasing the force imparted by the return spring but reducing the number of turns required for the return spring and in turn reducing the size of the return spring.

Brief Description of the Drawings An embodiment of the invention is described hereunder in some detail, with reference to and as illustrated in the accompanying drawings, in which: Fig. 1 is an "exploded" view of the retraction means, Fig. 2 is an elevation of the drive means, and Fig. 3 is a graph which compares the belt tension and withdrawal.

In this embodiment a seat belt retractor 10 is provided with a retractor frame 11 comprising two portions, one portion having bearings 12 in which a spool spindle 13 is journalled, the spool spindle 13 carrying on it a spool 14 with seat belt webbing 1 5 wound around it so that the webbing can be withdrawn by a user pulling the webbing off the spool, but the spool spindle is biased to a return or retraction direction by means of a flat helical return spring 1 6.

The spool spindle 1 3 extends at one end from the retractor frame and has at that extending end a driving pinion 1 8 which meshes with a relatively large driven gear 1 9 carried on a lay shaft 20, the lay shaft being journalled for rotation in bearings 25 in the retractor frame 1 The lay shaft also carries on it a spirally grooved cone pulley 22 wherein the cone angle converges in the opposite direction from the convergence of a second spirally grooved cone pulley 23 being carried on the spring shaft 24.

The spring shaft 24 is journalled for rotation in bearings 21 carried by the retractor frame 11 and having a slot 26 in one end which engages the radially inner end of the flat helical return spring 1 6, the radially outer end of which is anchored with respect to the retractor frame on the projecting pin 28.

Between the two spirally grooved cone pulleys there is provided a tension member 30, in this embodiment being formed from a moulding of polymeric material (for example nylon) and having heads 31 on its respective ends. As shown in Fig. 2, the tension spiral is a flat helical spiral as moulded, but is wound over the two cone pulleys 22 and 23, the heads engaging in respective head-receiving apertures 32 in the larger diameter ends of the pulleys. Since the flat helical return spring always operates in one direction, the tension member 30 is always under tension, but upon rotation of the spring shaft the member moves axially along the spirally grooved cone pulleys thereby varying the torque ratio between the lay shaft and the spring shaft.Since the driven gear is larger than the driving gear the flat helical spring needs to exert a greater returning force against the spring shaft than when a simple 1:1 ratio is used, and this therefore requires the use of a relatively thicker spring steel, but since the rotational movement of the spring shaft is less, fewer spring turns are required. Since fewer convolutions of the tension member 30 are required on the cone pulleys than if there were no reudiction, the cone pulley length is proportionately reduced.

The above embodiment has been described with respect to a lay shaft and this is a preferred construction, but obviously the spool spindle itself can carry on it the driven spirally grooved cone pulley. Similarly, it is not necessary for both the driving and driven pulleys to be spirally grooved cone pulleys but one of these can if required be a cylindrical pulley, and it is not always necessary that both pulleys should have spiral grooves.

The tension member has been described as a spirally formed member, and this is particularly desirable since it is easily assembled upon assembly of the retractor, but again it will be seen that other equivalent arrangements can be used and for example can be made of a woven belt, a flat steel band, a circular steel wire, or other equivalent filaments for imparting the return spring tension to the spool spindle.

The housing 35 at one end of the frame 11 contains a locking mechanism which forms no part of this invention. One suitable device which senses acceleration and locks the spool against extraction of webbing upon vehicle impact is described in our Australian Patent Application No. 82188/82.

Figure 3 illustrates graphically the belt tension during withdrawal and retraction. The continuous line illustrates one result achieved by this invention, and it may be noted that a higher tension exists at the retraction end of the graph than when the belt is fully withdrawn. The dotted line illustrates corresponding prior art conditions by way of contrast.

Although the above has been described with respect to separate lay and spool shafts, if the cone pulley length is increased these may be constituted in a single shaft, and the use of gearing can thereby be avoided.

Claims

1. In a seat belt retractor having a retractor frame, a spool carried on a spool spindle which is rotatable in the frame, and a return spring for imparting torsion to the spool spindle, retraction means comprising: a spring shaft rotatable in bearings in the frame, said torsion imparting return spring being secured at one end to the frame and at the other end to the spring shaft, and driven means between said spool shaft and spring shaft, said drive means comprising a pair of pulleys, at least one of which is on a said shaft, said pulleys including at least one spirally grooved cone pulley and a drive member coupling said pulleys.

2. In a seat belt retractor, retraction means according to Claim 1, further comprising: a lay shaft also carried by journals in the frame, said at least one spirally grooved cone pulley on one of the lay and spring shafts, a co-operating pulley on the other of these shafts, and a drive member between said pulleys, and drive means between the lay shaft and the spool spindle.

3. In a seat belt retractor, retraction means according to claim 2 wherein there are two spirally grooved cone pulleys, one on the lay shaft and the other on the spring shaft, and wherein said drive member comprises a tension member extending between the cone pulleys, said tension member terminating in heads at its respective ends, which said heads engage complementary surface in respective said cone pulleys.

4. In a seat belt retractor, retraction means according to claim 3 wherein said tension member is a moulded spiral of polymeric material.

5. In a seat belt retractor, retraction means according to claim 2 wherein said drive means comprise a relatively large gear on the lay shaft meshing with a relatively small pinion on the spool shaft.