Force Limitation in a Vehicle Occupant Restraining System

The invention relates to a method for limiting the force exerted on a vehicle occupant by a safety belt in an occupant restraining system in the event of a vehicle impact, and to a force limiter, with which the method may be performed.

In the course of a restraining process force peaks occur in the belt webbing which increase the risk of injury. Therefore force limiters have been developed which are arranged in the path of force flow in the belt system and smooth out force peaks by plastic deformation of material.

Optimum protection of an occupant may be achieved by combined use of a safety belt and an inflatable restraining element (or airbag). In the case of such a combined restraining system after a certain forward displacement of the occupant there will be contact between the belt and the inflated restraining element. It has now been found that at the latest from the occurrence of such contact and thereafter the characteristic, which represents the force as a function of the forward displacement, should possess a decreasing tendency so that the restraining force applied by the belt is reduced.

In the case of conventional force limiters the characteristic of the force is set at a fixed value along the forward displacement path by the design of the equipment. Dependent on the size and/or weight of the occupant's body a different form of such characteristic would however be desirable for minimum risk of injury.

The present invention provides a method of limiting the restraining force acting on the occupant in an occupant restraining system in the event of a vehicle impact, which renders possible an optimization of the characteristic representing the force as a function of the forward displacement. In accordance with the invention a parameter is derived from the occupant representing his body size and/or weight and the level of force limitation is set in a fashion dependent on such parameter. For a smaller body size or a lower weight of the occupant a lower force level is set than for larger or heavier persons so that independently of the features of the body of the occupant the full forward displacement path of the force limiter is always available.

In the case of a restraining system which is combined with an inflatable restraining element the setting of the force level is performed in accordance with the invention in such a manner that in the characteristic representing the force as a function of the forward displacement in a section of the path, after the completion of which contact between the belt webbing and the inflated restraining element is expected to occur, the characteristic possesses a decreasing tendency.

Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of several embodiments thereof in conjunction with the accompanying drawings.

FIG. 1 is a graph of a characteristic representative of the force as a function of the forward displacement path.

FIG. 2a shows a first working embodiment of a force limiter.

FIG. 2b shows the characteristic thereof.

FIG. 3a shows a second working embodiment of a force limiter.

FIG. 3b shows the characteristic thereof.

FIG. 4a shows a third working embodiment of a force limiter.

FIG. 4b shows the characteristic thereof.

FIG. 5a shows a fourth working embodiment of a force limiter.

FIG. 5b shows the characteristic thereof.

FIG. 6a diagrammatically illustrates a drum shaft of a belt retractor with an integrated force limiter in accordance with a fifth embodiment of the invention.

FIG. 6b shows the respective characteristic.

FIGS. 6c to 6f show details of this working embodiment of the force limiter .

In the course of forward displacement of an occupant wearing a belt the belt force F will initially increase steeply, but after a short displacement s.sub.1 is limited to a value F.sub.1 by a force limiter operating on the basis of plastic material deformation. In the ideal case the force will remain at this value F.sub.1 for a long path part. In a restraining system, which in addition to the belt possesses an inflatable restraining element (airbag), after a certain forward displacement the belt will engage the inflated restraining element. At this point in time, which corresponds to a path part s.sub.3 in the graph of FIG. 1, the characteristic should possess a distinctly downwardly sloping tendency so that the sum of the belt force and the supporting force due to the inflated restraining element does not assume an excessive value. Even prior to reaching the path part s.sub.3, i.e. at s.sub.2, the characteristic consequently passes into a downwardly sloping part.

However, for large or heavy persons a greater force level will be desired than for smaller or lighter persons. In the case of known force limiters such a behavior can not be produced.

In the embodiment depicted in FIG. 2a a force limiter has two fitting parts 10 and 12, which may be extended with plastic deformation of their material and are arranged so that they are functionally connected in parallel. The fitting parts 10, 12 are coupled at one end by an attachment pin 14, and at the opposite end by a pyrotechnic rivet 16. The pyrotechnic rivet 16 possesses an electrical fuse and may be fired by the application of an electrical pulse to two leads. The fitting part 12 is then uncoupled from the fitting part 10. The operation of the pyrotechnic rivet 16 takes place selectively in the course of a crash in a fashion dependent on the weight or size of the vehicle occupant. In the case of a low weight and/or a small size merely the fitting part 10 is to be effective as a force limiting means. This results in the characteristic marked in broken lines in FIG. 2b, which is at a lower level than the characteristic in a continuous line, which corresponds to the parallel arrangement of the two fitting parts 10 and 12.

In the embodiment depicted in FIG. 3 a fitting part 20, placed in the force path of the belt system, is provided with a slot 22 into which an adjustable pin 24 fits. The pin 24 possesses a shank varying in diameter. In the illustrated working embodiment of the invention such shank is conical. By displacement of the pin 24, for example by means of a cable 26 coupled with the driver's seat, the external diameter of the pin is changed which is effective for fitting into the slot 22 and the material of the fitting part 20 will be plastically deformed. FIG. 3b diagrammatically shows two characteristics which may be produced in this manner.

In the case of the embodiment illustrated in FIG. 4a a belt buckle 30 is anchored by means of a cable 32, which possesses a casing 34 of aluminum, to the vehicle body. The casing 34 is curved and deflected by three pins 36, 38 and 40. The pins 36 and 38 are rigidly fixed to the vehicle body, whereas the pin 40 may be set so that it causes a greater or less curvature of the bent part of the casing 34. The setting of the position of the pin 40 may also be performed with the setting of the seat position in the case of this embodiment. Dependent on the setting of the pin 40 there will be one of the characteristics shown in FIG. 4b.

In the embodiment of FIG. 5a a belt buckle 50 is connected via a cable 52 with the piston 54 of a piston and cylinder unit, whose cylinder 56 is connected with a pyrotechnic gas generator 58. The piston 54 possesses a conical section, on which two roller elements 60 and 62 bear, which engage the inner wall surface of the cylinder 56. FIG. 5a shows the piston and cylinder unit after operation of the gas generator 58 to tighten the belt webbing. From this position rearward movement of the piston 54 may only take place when the cylinder wall is plastically deformed by the roller elements 60 and 62. The resistance to deformation of the cylinder wall is varied by a sleeve 64 slipped onto same having a variable wall thickness over its length. A two armed lever 66 engages the sleeve 64 and is pivotally mounted, its end remote from the sleeve 64 bearing a wheel 68 running on a ramp on the floor of the vehicle. Since the piston and cylinder unit illustrated in FIG. 5a is mounted with the belt buckle 50 on a vehicle seat, the overall arrangement is entrained on displacement of the vehicle seat with the result that the slope of the lever 66 is changed and accordingly the longitudinal position of the sleeve 64 on the cylinder wall is also changed. FIG. 5b shows by way of example two characteristics resulting from setting of the sleeve 64.

In the embodiment of FIG. 6 the belt spool 70 of a belt retractor is provided at its two end surfaces with a convolute groove 72. Two ratchet wheels 74 mounted on the end surfaces of the belt spool 70 are each coupled with the belt spool 70 by means of a pin 76, which on the one hand fits into the groove 72 and on the other hand runs in an oblique groove 78 in the inner side of the ratchet wheels 74. The groove 72 has an outer, part-circular section 72a, an inner, also part-circular section 72b and an intermediate section 72c, which interconnects the sections 72a and 72b. At the start the pins 75 are located at the outer end 72d of the groove.

In the locked condition of the belt retractor the ratchet wheels 74 are held on the frame of the retractor in a manner preventing rotation. When a high torque is exerted via the belt webbing on the belt spool 70, the belt spool 70 will be rotated in relation to the ratchet wheels 74, the pins 76 the extending into the groove 72 and the lateral walls of the groove 72 being plastically deformed, since the pin 76 is wider than the groove 72. On the outer section 72a of the groove there is a radius R.sub.1, which leads to the substantially constant force level F.sub.1 in the graph of FIG. 6b. After approximately one complete revolution of the belt spool 70 the pins 75 will respectively fit into the intermediate section 72c of the groove 72 so that now, owing to the progressively increasing effective leverage, with which the force F engages the periphery of the belt spool 70, there will be a downwardly sloping part of the characteristic in FIG. 6b. The inward movement of the pins 76 is rendered possible by the radial component of the groove 78. As soon as the internal section 72b of the groove 72 with the radius R.sub.2 is reached, the force will be limited to a lower level F.sub.2 in the characteristic in accordance with FIG. 6b.

FIG. 6e diagrammatically indicates that the depth of penetration of the pins 76 into the groove 72 may be adjusted. The adjustment may for instance be performed in a fashion dependent on the height the belt webbing still coiled on the belt spool 70, since such measure indirectly provides information about the size of the vehicle occupant. Dependent on the depth of penetration of the pins 76 into the groove 72 there will be greater or smaller values for the forces F.sub.1 and F.sub.2, as shown in FIG. 6b by a broken line.

As lastly will be seen from the FIG. 6f, the pins 76 are provided with an angled elongated guide runner 80 to serve for reliable location of the pins.