Description

The invention relates to a vehicle seat comprising an airbag unit at the rear side of its backrest and an airbag unit adapted for the use in such a vehicle seat.

The use of frontal airbags protecting a passenger in case of a frontal crash or a laterally offset frontal crash is widespread in today's automotive technology. Almost every modern car has a frontal airbag for the driver and a frontal airbag for the front seated passenger. The frontal airbag for the driver is usually located in the hub area of the steering wheel and the frontal airbag for the front seated passenger is usually located inside the instrument panel. In most cases the frontal airbag for the passenger shows a relatively large volume for the following reasons: First, it is often desired that the passenger frontal airbag does provide a good protection even for a non-belted passenger. Second, many belting systems for the front seated passenger have a force limiter for the belt in order to reduce the forces applied to the thorax of the passenger. Due to this the belt often does not hold the passenger at the end of the restraining process, such that he/she "falls" into the passenger airbag without any belt restrainment.

Since many years there exists the idea to implement a frontal airbag into the rear side of a front seat in order to give enhanced protection for a rear seated occupant. Such an idea if for example disclosed in DE 10 2015 004 807 A1 or US 2013/0341975 A. Generic DE 2 058 608 A1 shows a vehicle seat with an airbag module at or in the rear side of a backrest of a front seat. The deployed airbag of this airbag unit basically extends rearwards (in regards to the vehicle direction) and upwards from its connection to the backrest. Despite the fact, that the idea of providing a frontal airbag at the rear side of the backrest of a front seat exists since many years, this concept has not yet entered the practice.

Starting from this it is the task of this invention to provide a vehicle seat with an airbag unit in or at its backrest for protecting a rear seated passenger that can be practically used with good results.

This task is solved by a vehicle seat showing the features of claim 1 . An airbag unit adapted for the use in such a vehicle seat is defined in claim 16.

The basic idea of the invention is to design the airbag such that it restrains exclusively the head of the rear seated occupant and that it can move and/or tilt to some extend at least in the vehicle forward direction and to use mainly the headrest as a support. In order to provide these properties, the airbag skin (when fully deployed but free of outer forces) has an impact surface that defines an impact plane and a support surface that defines a support plane with the impact plane and the support plane enclosing an angle (denoted as first angle) between 5° and 90°, such that the upper region of the airbag has a basically wedge-shaped cross section.

Unlike a "classical" airbag for the front seated passenger the inventive airbag for the rear seated passenger does not restrain the thorax but only prevents the head from being bent too far into the direction of the chest and/or to the side.

It turned out that the relative small and high positioned airbag according to the invention gives very good additional protection due to the geometry and belt characteristics that are typical for the rear seated passenger. Especially the fact that the inventive airbag is supported mainly by the headrest of the front seat (which may be integral or designed as a separate element) some drawbacks that might occur in connection with large airbags can be avoided. The airbag, especially its impact surface can move both, into the longitudinal direction of the vehicle as well as (at least to some extent) in its transversal direction, such that too high forces in the neck of the passenger are avoided in many load cases.

Further, the small volume and high position of the airbag has additional ad- vantages: Due to the small volume the airbag can be deployed quickly without the need of a very strong inflator. This alone reduces the risk of injuries caused by the airbag in an out-of-position-constellation. Additionally, the airbag unit can be designed such that the airbag does not affect a baby carrier placed on the rear seat. In a preferred embodiment the first angle is between 10° and 60°, so it is an acute angle. As has already been mentioned, the volume enclosed by the airbag skin is relatively small, preferably less than 45 litres, or even more preferred less than 35 litres. Since the airbag is designed to restrain exclusively the head of the occupant, the impact plane defined by the impact surface is preferably parallel to the vertical plane or is inclined towards the vertical plane in such a way that the impact plane points upwards and towards the rear. In order to avoid that the head slips off the relatively small impact surface, the impact area should be basically flat. The preferred geometry of the impact surface is a square with an edge length of about 20 cm.

Since it is desired that the airbag can move to some extend when the head of the passenger coupled to the impact surface, it is preferred that at least a section of the support surface is located at the height of the headrest but displaced from the same in the longitudinal direction of the vehicle such that a gap exists between the headrest and the support surface. As will be described in detail, the outer skin of the airbag can be manufactured from a single cutting which is closed by means of only two seams. This does not only make the production very rational, this also gives an easy possibility to give the outer skin of the airbag the desired shape. Additionally at least one shaping tether can be used.

The invention will now be described by means of a preferred embodiment in view of the figures. The figures show:

Figure 1 A very schematic representation of a front seat comprising an airbag unit according to the invention, a rear seat and a passenger / dummy seated on the rear seat;

Figure 2 The items shown in Figure 1 with the airbag of the airbag unit being fully deployed;

Figure 3 A top view from direction R in Figure 2;

Figure 4 The detail D of Figure 2 and geometrical planes relevant for the invention;

Figure 5 The same as Figure 2, meaning a very early point in time of a frontal crash or a laterally offset frontal crash;

Figure 6 What is shown in Figure 5 at a later point in time;

Figure 7 What is shown in Figure 6 at an even later point in time;

Figure 8 What is shown in Figure 7 at an even later point in time;

Figure 9 A cutting for manufacturing an airbag skin of an airbag as is shown in Figures 2 to 8 and

Figure 10 The cutting of Figure 9 with signs and arrows indicating the sewing process. Figure 1 shows very schematically a front seat 5 and rear seat 40 of a motor vehicle, especially a passenger car. The front seat 5 has a backrest 10 having a front side 12 pointing to the front of the vehicle and a rear side 14 pointing to the rear of the vehicle. The rear side 14 basically defines a plane. This plane is typically inclined towards the vertical (Z) direction in an angle between 15 and 30 degrees especially between 20 and 25 degrees. It should be noted that the invention will only properly work if the inclination of the backrest is within its typical range. Especially if the backrest 10 is inclined too far towards the horizontal plane (as is usually not the case if the rear seat 40 is occupied) the airbag unit provided in the backrest 10 (which will be described later) will not give the desired protection to a passenger 50 seated on the rear seat 40.

A headrest 16 extends from the upper end of the backrest 10. In the embodiment shown this headrest 16 is an element separate from the backrest 10 and is comprised of a bolster 17 and at least one support element (usually in form of a stud) 18 connecting this bolster 6 to the backrest 10. It needs to be emphasised here that in other embodiments of the invention (not shown in the pictures) the headrest 16 could also be integral with the backrest 10.

An airbag unit 20 is located in or at the rear side 14 of the backrest 10 at its upper end region (under the headrest 16). This airbag unit 20 comprises an inflator 24 (usually in form of a gas generator) and an airbag 30. The airbag 30 has (as every airbag) an outer skin and may also comprise one or more tethers for shaping this outer skin (not shown). As no tethers are shown in the described embodiment, the term "airbag" will sometimes be used instead of the term "outer skin of the airbag" for the sake of linguistic simplicity. The airbag unit 20 may comprise a housing 22 into which the airbag 30 is folded. The outer skin of the airbag is directly or indirectly attached to the backrest, from example to its frame.

Figure 2 shows the same as Figure 1 but with the airbag 30 being fully deployed, but free of outer forces (meaning that the passenger 20 has not yet hit the airbag 30). The backrest 10 is within its standard inclination range between 15° and 30° to the vertical. The position and shape of the airbag 30 (meaning its outer skin) is now described in more detail in view of Figures 2 to 4. As one can see especially from Figure 2 the major part (usually more than 80% in view of the volume) of the fully deployed airbag 30 is located above its lowest attachment to the backrest 10 (in order to show this a horizontal plane HP cutting the lowest attachment point is drawn in Figure 2). This means that the airbag 30 basically extends to the rear end upwards. The airbag 30 encloses a volume of less than 45 litres and preferably less than 35 litres. At least the upper part of the airbag 30 has a basically triangular- or wedge-shaped cross section with a support surface 32 positioned above the attachment of the airbag 30 to the backrest 10 basically rear of the headrest 16 but (in the state before the passenger hits the airbag) remote from the same such that there is a gap G between this support surface 34 and the headrest 16. The support surface 32 can be looked at as being basically flat such that it defines a support plane SP.

The airbag 30 further comprises an impact surface 34 which can also be looked at as being basically flat such that it defines an impact plane IP. The support plane SP and the impact plane IP enclose a first angle a which is between 5° and 90°, preferably between 10° and 60°. This is why the cross section of at least the upper area of the airbag 30 basically forms a triangle. As long as the backrest 10 is within its standard inclination range between 15° and 30° (usually between 20° and 25°) the angle β between the impact plane IP and the vertical plane VP (referred to as inclination angle) is between 0° and 45° such that the impact plane IP is either basically parallel to the vertical plane VP or points rearwards and upwards as is shown in Figure 4.

In the embodiment shown the impact surface 34 is basically a square with a side length of around 20 cm.

As is shown in Figure 3 the width (in Y direction) of the basically flat impact surface 34 exceeds the width of the base of the airbag 30 attached to the backrest 10 and the width of the headrest 16. The geometry just described leads to an overall geometry and crash behaviour as is described now in view of Figures 5 to 8:

Figure 5 shows the situation at the very beginning of the restraining process after a frontal crash or a laterally offset frontal crash has been detected. As is shown in Figure 5 the airbag 30 is fully deployed very quickly when the passenger 50 is still almost in his initial seating position. The impact surface 34 is located in front of the head 52 of the passenger 50 and the support surface 32 is located basically (more or less completely) rear of the headrest 16 with the gap G between the headrest 16 and the support surface 32.

As can be seen from Figure 6 the passenger 50 now starts to move with the head 52 moving quicker than the thorax 45, especially because the passenger 50 is (although not shown) belted.

Next, (as is shown in Figure 7) the head 52 hits the impact surface 34. After that the airbag 30 may tilt into the direction of the arrow shown in Figure 7 and deform until the support surface 32 abuts the headrest 16. So, the head 52 of the passenger 50 is restrained relatively softly. The restraining of the head avoids a bending of the neck too far into the direction of the chest but without applying too high forces to the neck of the passenger. After the support surface above has hit the headrest 16 the airbag 30 will continue to deform because gas is ventilated through at least one (not shown) ventilation opening of the airbag 30.

Because of the described geometry the airbag 30 in total or at least its impact surface 34 can also move to some extent in the transversal (Y direction) after the impact surface is hit by the head of the passenger such that the forces applied to the neck of the passenger stay relatively low even in case of laterally offset frontal crash.

Figure 9 shows a cutting 60 for manufacturing an airbag as described above from a single cutting by means of applying only two seams to this cutting which makes the manufacturing process of this airbag quite rational despite its quite complex three-dimensional shape. The cutting 60 of this embodiment is mirror symmetric as one can easily see. In the middle of its lower end (lower means here simply at the lower end of the drawing) this cutting 60 has a cut-out 62 which will form the blow mouth of the airbag after the finishing of the production process. Left and right of this cut-out 62 there are two edges 63a and 63b. Above the cut-out 62 and the two edges 63a and 63b there is a wider middle section 64, and a narrower end portion 65 extends from this wider middle section 64. The position 66 of the impact surface and the position 68 of the support surface are shown in Figure 9.

The sewing process is now described in view of Figure 10 which shows the cutting of Figure 9 with additional marks for clarifying this sewing process:

First, the two edges 63a and 63b are sewn together by means of a first seam, wherein it is preferred that these two edges are anti-parallel orientated (meaning that they show in different directions such that this first seam which is applied to these two edges is a shear seam). Now the remaining edges of the cutting (except the edges encircling the cut-out 62) are placed on one another like follows: Edge region 2a lies onto edge region 2a, edge region 2b lies on region 2b and so forth. The second seam starts at point A and is sewn until point B. By this second seam the cutting 60 is now (except the blow mouth) completely closed such that an airbag skin 30 as is shown in the figures is created.

list of reference numbers

5 front seat

10 backrest

12 front side

14 rear side

16 headrest

17 bolster

18 support element (stud)

20 airbag unit

22 housing

24 inflator (gas generator)

30 outer skin of airbag

32 support surface

34 impact surface

40 rear seat

50 passenger / dummy

52 head

54 thorax

60 cutting of airbag

62 cut-out

63a, b edges next to the cut-out

64 wider middle portion

65 narrower end portion

66 position of the impact surface

SP support plane

IP impact plane

VP vertical plane

HP horizontal plane

G gap

a first angle

β inclination angle