Description

The invention relates to an airbag module according to the preamble of claim 1 and to an elastic connecting element for use in such an airbag module according to claim 17.

This invention relates especially to a driver airbag module. Such a driver airbag module always comprises an accommodation unit defining an accommodation space in which an airbag is stored, and an inflator unit for inflating this airbag. Most often this inflator unit is at least partially located inside the airbag. Usually the accommodation unit comprises a base and a cover being attached to this base; the base is often called “housing”. In most cases the inflator unit comprises a flange and this flange is directly or indirectly attached to the base.

It is known in the prior art to use the inflator unit as a damper mass of a vibration damper unit such that vibrations that are transferred to the steering wheel via the steering column are damped. In this case at least one elastic connecting element is provided which connects the inflator unit to the base. Two basic concepts are known for this:

In one concept, only a single, annular-shaped elastic connecting element is provided whose diameter basically conforms to the diameter of the flange of the inflator unit.

In another concept, at least three elastic connecting elements are provided. These connecting elements are basically in form of elastic pins that extend in axial direction from a base-side first end to an inflator-side second end. ln both cases, the inflator oscillates basically in the radial plane.

For example generic EP 2 847 486 B1 shows such a pin-shaped elastic connecting element connecting a mass to another element. For this purpose, this connecting element has a first annular groove and second annular groove, such that each connecting element can be snapped to the mass (here: the inflator unit) as well as to the other element (here: the base) which each comprise respective holes. In the following, the section of a connecting element at the first annular groove which is located inside a base-side hole is referred to as first section and the section of a connecting element at the second annular groove which is located inside an inflator-side hole is referred to as second section. Each connecting element further comprises an axial hole being used for assembly purposes.

The vibration damper unit being formed by the inflator unit and the connecting elements has at least one resonance frequency (usually more than one) which depends inter alia on the geometry and mass of the inflator unit and the geometry and elastic properties of the connecting elements. It is usually desired to tune the resonance frequencies of the damper unit to the expected frequencies of the steering wheel.

Often, a diffusor having a dome section spanning over the inflator unit is provided. The dome section of the diffusor hinders the oscillating inflator unit from coming in contact to the airbag. The diffusor is usually made of metal and comprises a flange section and the dome section.

Starting from this prior art it is an object of the invention to improve a generic airbag module in such a way that an easy and cost-effective possibility for tuning the resonance frequencies of the damper unit is provided.

This task is solved by an airbag module with the features of claim 1 . An elastic connecting element for use in such an airbag module is defined in claim 17. As it is known from the prior art, each connecting element has a main outer surface which is rotation-symmetrical around a first axis - which extends in the axial direction - at least in the first section and in the second section such that it can be attached to the base and to the inflator unit in any rotational orientation. Usually, the cross section through the outer surface is circular at least in these sections. Most often it is preferred that each connecting element has a main outer surface which is completely rotation-symmetrical around this first axis.

According to the invention at least one of the connecting elements has an axial hole (meaning that it extends in the axial direction) which is not rotation- symmetrical in respect to the first axis and/or has a non-circular cross-section. Usually it is preferred that all of the connecting elements have such an axial hole.

Because the axial hole is not rotation-symmetrical and/or has a non-circular cross section, the elastic properties of the elastic element regarding a radial displacement of its second end relative to its first end are not the same in all radial directions and consequently the oscillation behavior of the damper unit depends on the orientation of the connecting element. So, the resonance frequencies can be tuned just by turning the connecting element around its first axis. Since at least three elastic connecting elements are needed, one has three degrees of freedom if all connecting elements have an inventive axial hole. So, many different oscillation behaviors can be achieved by using the same elastic elements which makes the production of the connecting elements of course very efficient.

Even though it is preferred that all elastic connecting elements have offset and/or non-circular holes, it needs to be mentioned that an inventive effect would also take place if only one such elastic connecting element was used.

The space between the dome section of the diffusor and the inflator unit can of course not be used as a packaging space, so it is to some extend “wasted space”. So, there is the demand of making this “wasted space” as small as possible. This of course means that the dome section should be rather close to the inflator unit. Without additional measures, there it the risk that the flange of the inflator unit comes into contact to the dome section of the diffusor when the inflator unit vibrates. Since the flange of the inflator unit to which the elastic connecting elements are coupled as well as the diffusor are usually made of metal, this would lead to an undesired noise.

So, in a preferred embodiment, a protrusion extends between the two grooves radially from the main outer surface of each connecting element in order to avoid that the flange hits the dome section. This protrusion preferably extends completely around the elastic connecting element, such that the elastic connecting element can be attached to the inflator unit in any rotational position. The radial length of the protrusion is chosen such that it extends over the edge of the flange of the inflator unit, such that the elastic protrusion hits the dome section, not the flange. This effect could in principal also be achieved by making the section of the elastic connecting element between the two grooves thick enough, but this would often lead to a too stiff elastic connecting element and additionally it would then often be impossible to mount the elastic connecting element to the base and to the inflator unit.

It is preferred that the protrusion is close to the flange and thus closer to the sec- ond annular groove than to the first annular groove.

It is further preferred that the protrusion is comprised of a plurality of protrusion sections since this further eases the assembly process. Although such a protrusion is especially useful in connection with an inventive elastic element, it is to be noted that it would also be useful in cases where the elastic connecting element has an axial hole being completely symmetrical in respect to the first axis, or even no axial hole at all. The invention will now be described by means of preferred embodiments in view of the figures. The figures show: Figure 1 all elements of a first embodiment of an inventive airbag module in a strongly schematic sectional view,

Figure 2 one elastic connecting element of Figure 1 in an enlarged representation,

Figure 3 the elastic connecting element of Figure 2 in a plane view from the side,

Figure 4 the elastic connecting element of Figure 3 in a plane view from the bottom from direction R in Figure 3,

Figure 5 what is shown in Figure 1 after first assembly steps have been performed,

Figure 6 what is shown in Figure 5 after another assembly step,

Figure 7 the completely assembled airbag module,

Figure 8 the retainer with attached elastic connecting elements in a more detailed perspective view,

Figure 9 the detail D of Figure 7, and

Figures 10 to 13 alternative embodiments of an elastic connecting element in a representation according to Figure 4.

Figure 1 shows all elements of an embodiment of the inventive airbag module in a strongly schematic sectional view. A base 10 (sometimes also referred to as housing) is provided, to which all other elements are directly or indirectly mounted. This base 10 comprises several holes, namely a central hole (without reference number), holes 12 for diffusor studs and base-sides attachment holes 16.

A cover 20 is provided in such a way that the base 10 and the cover 20 define an accommodation space for a folded airbag 60. Cover 20 and base 10 therefore form an accommodation unit.

An inflator unit 30 is comprised of a gas generator 32 and a retainer 33 which holds the gas generator 32. This retainer 33 has a flange 34 with inflator-side attachment holes 36. In other embodiments it would also be possible that a flange extends directly from the gas generator, but providing a retainer has the advantage that the flange 34 is to some extend heat-isolated from the gas generator 34 which is usually a pyrotechnic gas generator.

Elastic connecting elements 40 are provided in order to connect the inflator unit 30 to the base 10. As it will be described later in detail each of those elastic connecting elements 40 has two grooves for engaging into attachment holes 16 and 36.

Finally, a diffusor 50 is provided. This diffusor 50 has a dome section 52 spanning over the gas generator 42 and separating the gas generator 42 from the airbag 60, and a flange section 54 being attached to the base 10 via studs 70. These studs 70 can be separate parts or can be integral with the diffusor. Nuts 72 or rivets are provided for securing the studs 70.

Figures 2 to 4 show one of the elastic connecting elements 40 in different representations, wherein Figure 2 is an enlarged view of one of the elastic connecting elements 40 shown in Figure 1 , meaning that it is a cross sectional view. Figure 3 is a side view and Figure 4 is a view from the bottom. The elastic connecting element 40 is a one-pieced element consisting of a - for example rubberlike - elastic material. This elastic connecting element 40 extends from a first end 40a to a second end 40b. The end section near the second end 40b is basically cone-shaped. A first annular groove 45 is provided near the first end and a second annular groove 46 is provided under the cone-shaped end section. The first annular groove 45 has the shape of a fluting. The section of the elastic connecting element 40 on the inside of the first annular groove 45 is referred to as first section and the section on the inside of the second annular groove 46 is referred to as the second section. As one can especially see from Figure 3, the elastic connecting element 40 has a main outer surface 41 with protrusion sections 48 extending from this main outer surface 41 . This main outer surface 41 is completely rotation-symmetrical around a first axis A1 meaning that all sections taken through this main outer surface 41 perpendicular to the first axis A1 are circles having their center points on the first axis. This of course also applies to the outer surface of the first section 45a and the outer surface of the second section 46a.

As one can see from Figures 2 and 4, an axial hole 44 extends from the first end 40a into the elastic element 40. In the first embodiment this axial hole 44 also has a circular cross section so that it defines an axis - the second axis A2 -. This second axis is parallel to but offset from the first axis A1. So, the axial hole 44 is offset to the first axis A1 .

Figure 5 shows the same elements as Figure 1 but after some assembly steps have been performed. The diffusor 50 has been placed into the airbag 60 in such a way that the studs 70 extend through attachment holes 64 of the airbag 60. Further, the elastic connecting elements 40 have been pushed through the base-side attachment holes 16 in a direction as indicated by the arrow in Figure 5 such that the edge regions of the base-side attachment holes 16 are located inside the first annular grooves 45, meaning that the first section of the connecting element is located inside this base-side attachment hole. ln the next step as shown in Figure 6, the inflator unit 30 is attached to the elastic connecting elements 40, meaning that now the elastic connecting elements 40 extend through the inflator-side attachment holes 36 such that the second sections of the elastic connecting elements are located inside the inflator-side attachment holes 36. As one can see (and this will be seen in detail in Figure 9), the protrusion sections 48 that are located on the outside, extend over the edge of the flange 34.

Finally, as shown in Figure 7, the diffusor 50 is attached to the base 10 so that also the airbag 60 is attached to the base and the cover 20 is mounted - for example snapped - to the base.

Figure 8 shows the retainer 33 which is attached to elastic connecting elements 40 in detail. It can be seen that four elastic connecting elements 40 are provided and this is preferred. It is further preferred that all elastic connection elements 40 are identical to one another.

Turing back to Figure 7 one can see that in the shown embodiment the elastic connecting elements 40 are attached to the base 10 in such a way that the axial holes 44 have an innermost position. This results in a certain vibration behavior of the damper unit being comprised of the inflator unit 30 and the elastic connecting elements 40. If for example all elastic connecting elements 40 are turned 180° around their first axis (which usually must be done before mounting the elastic connecting elements 40 to the base 10), the axial holes 44 would be in their outermost position leading to a different vibration behavior. It is easy to understand that because all four elastic connecting elements 40 can independently be turned 360°, the vibration behavior of the damper unit and thus its resonance frequencies can be tuned very finely despite the fact that in all cases the same elastic connecting elements 40 are used.

As it can be seen from Figure 9, the protrusion sections 48 hinder the flange 34 from hitting the diffusor 50, even if the inflator unit 30 oscillates with large amplitude. Because the protrusion sections 48 extend all around the elastic connecting elements 40, this effect is independent of the rotational orientation of each elastic connecting element.

Figures 10 to 12 show embodiments of an elastic connecting element 40 in which the axial hole 44 is not offset from the first axis A1 , but does not have a circular cross section. Here the tuning effect when turning the elastic connecting element 40 around its first axis A1 will not be as strong as in the first embodiment, but still the behavior of the damper unit will depend on the orientation of the axial hole 44, since their radial elastic properties are not isotropic.

Of course it is also possible to arrange a non-circular axial hole offset from the first axis A1 , as it is shown in Figure 13.

One sees that a possibility of tuning the oscillation behavior of the damper unit is achieved without the need of altering the elastic connecting elements. Thus the elastic connecting elements can be produced in large numbers which makes their production easy and cost-effective. Further, the oscillation behavior can easily be optimized in an experimental way.

List of reference numbers

5 airbag module 10 base 12 hole for diffusor studs

16 base-side attachment hole 20 cover 30 inflator unit 32 gas generator 33 retainer 34 flange 36 inflator-side attachment hole

40 elastic connecting element 40a first end 40b second end

41 main outer surface

44 axial hole

45 first annular groove 45a outer surface of first section 46 second annular groove

46a outer surface of first section 48 protrusion sections 50 diffusor 52 dome section of diffusor 54 flange section of diffusor

60 airbag 62 central hole 64 attachment hole 70 stud 72 nut