Adaptive knee airbag for a vehicle occupant restraint system

Abstract

Knee airbag (10) for a vehicle occupant restraint device, which can assume an unfolded operating position between a fixed vehicle component (12) and the legs (14; 16) of a vehicle occupant, with a gasbag coat (18), at least one outflow opening (20) formed therein, and a control device for selectively releasing the outflow opening (20), wherein the control device is arranged inside the knee gas bag (10) and is configured to release or block the outflow opening (20) depending on the expansion of the knee gas bag (10) in a specific expansion direction, wherein the control device has a retaining strap (26) which can limit the unfolding of the knee gas bag (10) in the direction of expansion, wherein the control device further comprises a flap (22) for selectively closing the outflow opening (20) and a pulling element (24) which is coupled on one side to the retaining strap (26) and on the other side to the flap (22), wherein one end of the traction element (24) is detachably attached in a fold (28) of the tether strap (26).

Description

[0001] The invention relates to a knee airbag for a vehicle occupant restraint device. The invention further relates to a vehicle occupant restraint device with such a knee airbag.

[0002] The inflation and deflation behavior of airbags is tested using crash test dummies in impact tests. Crash test dummies are life-size mannequins modeled after the human body. To adequately account for the different anatomical characteristics of real people in the simulations, the tests are generally conducted with three different dummies: The "50th percentile man," with a height of 175 cm and a weight of 78 kg, is intended to represent a generally "normal" sized vehicle occupant; the "95th percentile man," with a height of 188 cm and a weight of 101 kg, represents a tall vehicle occupant; and the "5th percentile woman," with a height of 152 cm and a weight of 54 kg, represents a short vehicle occupant. Due to the different physical characteristics, the normal seating positions of the various dummies vary accordingly during the crash tests.

[0003] From DE 10 2004 009 013 A1, a side-impact restraint device for protecting an occupant seated in a motor vehicle is known, comprising a gas bag that adapts to the occupant's body shape. The gas bag deploys between a side structure of the vehicle and the occupant and has a first discharge opening located in a region of the gas bag facing the occupant. The vertical position of the discharge opening is chosen such that it is not covered by the upper body of a small occupant, but is covered by that of a large occupant. Thus, a smaller occupant experiences a lower internal pressure within the gas bag than a larger occupant.

[0004] EP 1 279 565 A1 discloses a generic knee airbag for an occupant protection device, in which a vent hole is provided in an upper end section. The vent hole interacts with a passenger airbag located above the knee airbag. When the vehicle occupant's legs strike the deployed knee airbag and the vent hole is initially not covered by the passenger airbag, gas can escape from the vent hole. This dampens the impact on the vehicle occupant. However, as soon as the deployed passenger airbag covers the vent hole, the gas escape from the vent hole is restricted, thus maintaining a minimum internal pressure in the knee airbag for a longer period of time.

[0005] US Patent 7,954,850 B2 discloses a passenger airbag featuring a primary retaining strap with a tear seam and a secondary, actively controlled retaining strap. The secondary retaining strap is connected to a cover flap for a vent. If a small occupant is present in the passenger seat, the control device actively releases the secondary retaining strap, thereby also opening the vent and limiting the internal pressure of the passenger airbag to such an extent that the tear seam of the primary retaining strap does not open. If a normal-sized occupant is detected, the secondary retaining strap is not released, and the vent is closed by the cover flap, resulting in a sufficiently high internal pressure to cause the tear seam of the primary retaining strap to open.Furthermore, it is provided that if the normal vehicle occupant is in a strongly forward-leaning position (out of position), the second retaining strap will not be tensioned by limiting the deployment of the airbag, and the outflow opening will remain open, thus limiting the internal pressure of the passenger airbag so that the tear seam of the first retaining strap is not released.

[0006] US 2010 / 0001498A1 also shows a passenger-side airbag featuring a vent with a cover flap, the cover flap being connected to a first and a second retaining strap. The retaining straps are arranged such that whether a baby car seat is on the passenger seat or a vehicle occupant is leaning too far forward (out of position), the respective retaining strap is not tensioned, thus releasing the vent, allowing gas to escape and reducing the internal pressure.

[0007] Furthermore, US patent 2012 / 0104737A1 also shows a passenger airbag with a vent opening that can be closed by a cover flap. For this purpose, the passenger airbag has a retaining strap that can be divided into several sections, with the strap connected at one end to the cover flap and at the other end to the airbag casing. One flap section of the retaining strap extends from the cover flap to a second attachment point on the airbag casing. From this second attachment point to a guide, a shaping section of the retaining strap extends, and from the guide to the first attachment point, a control section extends. The arrangement of the retaining strap sections can be designed such that, when an occupant is close to the airbag, the cover flap is opened or closed by tensioning the flap section.

[0008] The object of the invention is to enable the protective effect of an inflated knee airbag to be adapted to the body structure of a vehicle occupant.

[0009] This problem is solved by a knee airbag for a vehicle occupant restraint device with the features of claim 1. Advantageous and appropriate embodiments of the knee airbag according to the invention are specified in the associated dependent claims.

[0010] The knee airbag according to the invention for a vehicle occupant restraint device can assume an unfolded operating position between a fixed vehicle component and the legs of a vehicle occupant. The knee airbag comprises an airbag casing, at least one outflow opening formed therein, and a control device for selectively releasing the outflow opening. The control device is arranged inside the knee airbag and configured to release or block the outflow opening depending on the expansion of the knee airbag in a specific direction of expansion.

[0011] The invention is based on the fundamental idea that by adjusting the internal pressure of the knee airbag to the physical constitution of the respective vehicle occupant, improved protection can be achieved. Compared to complex "active" solutions, which require, for example, electronic occupant qualification and a multi-stage gas generator, a "passive" solution is significantly more cost-effective.

[0012] Based on this fundamental idea, the present invention is founded on the understanding that the distance between the lower part of the instrument panel, from which a knee airbag typically deploys, and the legs of the vehicle occupant in a normal seating position depends on the occupant's body size. This is also taken into account in crash tests with dummies: The aforementioned distance is smaller in tests with 5% dummies (corresponding to a small vehicle occupant) than in tests with a 50% dummy (corresponding to a normal-sized vehicle occupant).

[0013] The control device according to the invention for the knee airbag, for selectively releasing the discharge opening, ensures that the discharge opening opens or closes depending on the expansion of the knee airbag (towards the vehicle occupant). Thus, in the case of a small vehicle occupant, whose limited legroom restricts the expansion of the knee airbag, the discharge opening can be opened to cushion the impact on the knee airbag. Conversely, in the case of a vehicle occupant of average height, the greater leg spacing allows the airbag to fully expand towards the occupant, causing the control device to close the discharge opening. The internal pressure of the airbag then remains at a high level for a longer period.Thus, regardless of the vehicle occupant's constitution, the same amount of gas can always be used to inflate the knee airbag, as the internal pressure adjusts automatically. Occupant qualification or a multi-stage gas generator is not required for the solution according to the invention. Furthermore, the arrangement of the control unit inside the knee airbag has the advantage that no additional steps are necessary during installation.

[0014] Following the passive basic concept of the invention, a passive detection system is provided for the extent of the knee airbag's extension towards the vehicle occupant, which allows conclusions to be drawn about the distance between the occupant's legs and the instrument panel, and thus about their physique. According to the embodiment of the invention, the control device for this purpose has a retaining strap that can limit the deployment of the knee airbag in the relevant direction of extension. It is advantageous for the retaining strap, in particular its length, to be designed such that if the knee airbag is unimpeded (from the outside) in the direction of the vehicle occupant, only the internal retaining strap limits the deployment, which indicates a (normally) sized vehicle occupant. In contrast, for a small vehicle occupant, the deployment should not be limited by the retaining strap, but rather by the occupant's legs beforehand.With such an interpretation, the length of the restraint strap can thus serve as a criterion for distinguishing between a small and a (normal) large vehicle occupant.

[0015] To ensure this functionality of the retaining strap, a design is recommended in which the retaining strap is attached on one side to a section of the gasbag casing opposite the vehicle component and on the other side to a section of the gasbag casing opposite the vehicle occupant, in relation to the use position of the knee gasbag.

[0016] According to the invention, the control device selectively closes the exhaust opening by comprising a flap and a pull rod that is coupled to the retaining strap on one side and to the flap on the other. With such a design, the different behavior of the retaining strap described above for small and (normal) sized vehicle occupants can be effectively used for the automatic "operation" of the flap.

[0017] Within the framework of this control concept, an embodiment according to the invention is characterized in which one end of the tensioning element is detachably fastened in a fold of the retaining strap, preferably by a tear seam. With a small vehicle occupant, due to the limitation of the airbag expansion caused by the occupant themselves, the forces acting on the fold and the tear seam are so low that the tensioning element is held under tension in a position where it keeps the flap away from the exhaust opening. With a large vehicle occupant, however, the load on the retaining strap is so great that the tear seam ruptures and releases the tensioning element. When the tensioning element is no longer released, the flap automatically assumes a locking position in which it closes the exhaust opening.

[0018] To achieve this behavior of the flap, it can be designed so that one edge section of the flap is connected to the gasbag casing, while a free section of the flap is coupled to the tensioning device. If the tensioning device detaches from the tensioning strap, the previously held flap can then fold down automatically.

[0019] To ensure that the flap folds in the correct direction, i.e., towards the exhaust opening, a particular aspect of the invention provides that the edge section is attached to the airbag casing by means of a seam with a curved path. The curvature of the seam, in conjunction with the forces acting on the airbag casing during expansion or when the knee airbag is fully inflated, defines a clear folding direction. This practically eliminates the possibility of the flap pivoting in a direction opposite to the desired direction.

[0020] According to a particularly preferred design and arrangement of the flap, the seam essentially follows an arc of a circle surrounding the outflow opening, or a corresponding arc of an ellipse, or a similar angular shape. Such a seam shape ensures that the free section of the flap folds precisely onto the outflow opening and securely closes it.

[0021] Positioning the discharge opening in the upper region of the knee airbag, preferably in the upper third relative to the knee airbag's operating position, has the advantage that a traction element oriented more or less perpendicular to the length of the safety strap can be used. In a configuration where the traction element is coupled to the safety strap, this allows for optimal force transmission into the traction element. However, it is also possible, in principle, to position the discharge opening in the lower or another region of the knee airbag.

[0022] The invention also provides a vehicle occupant restraint device with a knee airbag according to the invention. In the vehicle occupant restraint device according to the invention, the knee airbag is installed such that the direction of expansion, i.e., the direction of airbag expansion, depending on which the outflow opening is opened or blocked, points from the fixed vehicle component towards the legs of the vehicle occupant.

[0023] Furthermore, with regard to the specific installation situation of the vehicle occupant restraint device according to the invention, it should be ensured that the length of the section of the retaining strap extending between the opposing walls of the knee airbag is greater than the minimum distance of the fixed vehicle component from the legs of a small vehicle occupant, but less than the corresponding distance from the legs of a normal-sized vehicle occupant.

[0024] Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. The drawings schematically show: - Fig. 1 an interaction of a small vehicle occupant with an inflated knee airbag according to the invention in a vehicle. - Fig. 2 an interaction of a normally sized vehicle occupant with an inflated knee airbag according to the invention in a vehicle; - Fig. 3 the connection of the traction element to the retaining strap of the knee airbag according to the invention in detail; - Fig. 4. The release of the traction element when the safety strap is under load; - Fig. 5 a top view of a spread-out knee gas bag according to the invention with released outflow openings; - Fig. 6 a top view of a spread-out knee gas bag according to the invention with blocked outflow openings; and - Fig. 7 a detailed view of the flap of a knee gas bag according to the invention.

[0025] In the Fig. 1 and Fig. Figure 2 shows a knee airbag 10 of a vehicle occupant restraint device in a motor vehicle, which has unfolded from a recess between the lower part of the instrument panel 12 of the vehicle and the legs 14 or 16 of a vehicle occupant. The Fig. 1 and Fig. The position shown in 2 of the knee gas bag 10 after complete inflation by a gas generator is hereinafter referred to as the operating position of the knee gas bag 10, to which the terms "top", "bottom", etc. refer.

[0026] The knee airbag 10 is essentially formed from an airbag casing 18 in which at least one exhaust opening 20 is formed, through which gas can escape from the knee airbag 10 under certain circumstances, which will be discussed in more detail later. The exhaust opening 20 is located in the upper region of the knee airbag 10, more precisely in the upper third with respect to the knee airbag 10's position in use.

[0027] The exhaust opening 20 can be covered by a flap 22 located inside the knee airbag 10. A flexible pull cord 24, for example in the form of a strap or cord, is used, among other things, to control the flap 22. One end of the pull cord 24 is connected to the flap 22, and the other end to a retaining strap 26, which is also located inside the knee airbag 10 and serves to limit the expansion of the knee airbag 10 towards the vehicle occupant. For this purpose, the retaining strap 26 is attached on one side to a section of the airbag casing 18 opposite the instrument panel 12 and on the other side to a section opposite the vehicle occupant.

[0028] The connection of the traction element 24 to the safety strap 26 is in Fig. Figure 3 shows in detail. The second end of the traction element 24 is sewn into or onto a fold 28 of the retaining strap 26. The seam 30 used for this purpose is a tear seam that cannot withstand a predetermined load and will tear open. In particular, when a certain force acts on the retaining strap 26 in its longitudinal direction and the fold 28 is pulled apart accordingly, the seam 30 tears open and releases the second end of the traction element 24, as shown in Figure 3. Fig. 4 shown.

[0029] The flap 22 for covering one or more outlet openings 20 is in the Fig. 5 and Fig. 6 in different positions and in Fig. Figure 7 shows in detail. The flap 22 has an edge section 32 that is connected to the gasbag casing 12. In the illustrated embodiments, the flap 22 is essentially rectangular in shape, sewn to the gasbag casing 12 on one side. The seam 34 used for this purpose is not straight, but curved in a special way. More precisely, the course of the seam 34 essentially corresponds to an arc of a circle surrounding the outflow opening 20 or to a corresponding arc of an ellipse. A corresponding angular shape is also possible and is likewise considered "curved." The free section 36 of the flap 22, which is not attached to the gasbag casing 18, is connected to the tensioning element 24.

[0030] Fig. Figure 5 shows the flap 22 in its initial state. The tensioned pull cord 24, which is attached to the retaining strap 26, holds the flap 22 away from the outflow openings 20. This position of the flap 22 can therefore also be referred to as the release position.

[0031] Fig. Figure 6 shows the flap 22 in a state where it is not held by the tensioning element 24. The tensile forces acting in the gasbag casing 18 when the knee gasbag 10 is deployed or held under tension ensure that the flap 22 is folded over the exhaust openings 20. The special curved shape of the seam 34 is responsible for pivoting the flap 22 in the correct direction. This position of the flap 22, in which it covers the exhaust openings, can therefore be described as the locking position.

[0032] Returning to the Fig. 1 and Fig. 2 now describes the different functionality of the knee airbag 10 for a small and a normal-sized vehicle occupant.

[0033] In Fig. Figure 1 depicts a situation with a small vehicle occupant (corresponding to a 5 percent dummy). In the seating position and posture typically used for crash tests, the legs 14, and in particular the knee 38, of the small vehicle occupant are at a certain minimum distance x from the instrument panel 12. The length of the section of the retaining strap 26 extending between the opposing walls of the knee airbag 10, with the fold 28 to which the tensioning element 24 is attached, is so much greater than the distance x that the deployment of the knee airbag 10 towards the vehicle occupant is limited not by the retaining strap 26, but by the vehicle occupant himself, more precisely by his legs 14. The retaining strap 26 is either not under tension or only under such low tension that the seam 30 does not tear.

[0034] This state corresponds to the initial state in which flap 22 is in the release position (see below). Fig. 3 and Fig. 5) This means that the tensioning element 24, attached to the retaining strap 26 and the free section 36 of the flap 22, is under tension and holds the flap 22 away from the exhaust opening(s) 20, allowing gas to escape from the knee airbag 10. This reduces the internal pressure of the knee airbag 10, thus dampening the impact of the knees 38 of the small vehicle occupant on the fully inflated knee airbag 10.

[0035] In Fig. 2 is the same situation as in Fig.Figure 1 shows the situation, but with a normal-sized vehicle occupant (corresponding to a 50 percent dummy). The minimum distance y of the legs 16 or knees 40 from the instrument panel 12, based on the usual crash test conditions, is greater here than the distance x. The length of the section of the retaining strap 26 with the fold 28 is dimensioned such that, under these conditions, when the knee airbag 10 unfolds, the section is stretched so strongly towards the vehicle occupant that the seam 30 tears open and releases the tensioning element 24.

[0036] Since the tensioning element 24 is no longer under tension, the tensile forces in the gasbag casing 18 and the course of the seam 34 ensure that the flap 22 folds onto the exhaust opening(s) 20 and closes them. This keeps the internal pressure of the gasbag largely constant in order to guarantee sufficient protection for a vehicle occupant of average size.

[0037] As already mentioned, the design and arrangement of the knee airbag 10 are based on the leg and knee positions of the respective crash test dummies (5 percent or 50 percent dummy), as determined by the sitting posture and position of the dummies that is generally used in the impact tests (no so-called OOP positions). Reference symbol list 10 Knee gasbag 12 Fixed vehicle component (instrument panel) 14 legs of a small vehicle occupant 16 legs of a normal-sized vehicle occupant 18 Gasbag coat 20 Outlet opening 22 flap 24 traction elements 26 tether strap 28 folds 30 tear seam 32 marginal section 34 seam 36 free section 38 knees of a small vehicle occupant 40 knees of a normal-sized vehicle occupant

Claims

[1] Knee airbag (10) for a vehicle occupant restraint device, which can assume an unfolded position of use between a fixed vehicle component (12) and the legs (14; 16) of a vehicle occupant, with a gasbag coat (18), at least one outflow opening (20) formed therein, and a control device for selectively releasing the outflow opening (20), wherein the control device is arranged inside the knee gas bag (10) and is configured to release or block the outflow opening (20) depending on the expansion of the knee gas bag (10) in a specific expansion direction, wherein the control device has a retaining strap (26) which can limit the unfolding of the knee gas bag (10) in the direction of expansion, wherein the control device further comprises a flap (22) for selectively closing the outflow opening (20) and a pulling element (24) which is coupled on one side to the retaining strap (26) and on the other side to the flap (22), wherein one end of the traction element (24) is detachably attached in a fold (28) of the tether strap (26). [2] Knee gas bag (10) according to claim 1, characterized by , that the retaining strap (26) is attached on one side to a section of the gasbag jacket (18) opposite the vehicle component (12) and on the other side to a section of the gasbag jacket (18) opposite the vehicle occupant, with reference to the position of use of the knee gasbag (10). [3] Knee gas bag (10) according to claim 1 or 2, characterized by , that the end of the traction element (24) is detachably fastened in the fold (28) of the tether strap (26) by a tear seam (30). [4] Knee gas bag (10) according to one of the preceding claims, characterized by, that the flap (22) has an edge section (32) which is connected to the gasbag mantle (18) and a free section (36) which is coupled to the traction element (24). [5] Knee gas bag (10) according to claim 4, characterized by , that the edge section (32) is attached to the gasbag jacket (18) by means of a seam (34) which has a curved course. [6] Knee gas bag (10) according to claim 5, characterized by , that the course of the seam (34) essentially corresponds to a circular arc of a circle surrounding the outflow opening (20) or a corresponding arc of an ellipse or a similar angular course. [7] Knee gas bag (10) according to one of the preceding claims, characterized by , that the outflow opening (20) is arranged in the upper area of ​​the knee gas bag (10), preferably in the upper third, with respect to the operating position of the knee gas bag (10). [8] Vehicle occupant restraint device with a knee airbag (10) according to one of the preceding claims, characterized by , that the direction of expansion points from the fixed vehicle component (12) to the legs (14, 16) of the vehicle occupant. [9] Vehicle occupant restraint device according to claim 8 with a knee airbag (10) according to claim 2, characterized by , that the length of the section of the restraint strap (26) extending between the opposite walls of the knee airbag (10) is greater than the minimum distance x of the fixed vehicle component (12) from the legs (14) of a small vehicle occupant, but less than the corresponding distance y from the legs (16) of a normal-sized vehicle occupant.

Images