Helmet for protecting a head of a person

Abstract

The invention relates to a helmet (1) for protecting a head (2) of a person, the helmet (1) comprising: an outer layer having an outer surface (3) for receiving an impact to the helmet (1), the outer layer being coupled to an inner portion (40) of the helmet (1) via a reactive structure (7), wherein the inner portion (40) is configured to contact a head (2) of a person, wherein the reactive structure (7) is configured to provide for each location of a plurality of locations of the outer surface (3) a corresponding force for reducing a rotation of the helmet (1) upon an oblique impact on the location, wherein the reactive structure (7) is configured to provide a first force (F1) for reducing a rotation of the helmet (1) upon an oblique impact on a first location (L1) of the outer surface (3), the first location (L1) being comprised by said plurality of locations, and a different second force (F2) for reducing the rotation of the helmet (1) upon an oblique impact on a second location (L2) of the outer surface (3), the second location (L2) being different from the first location (L1) and comprised by said plurality of locations.

Description

[0001] Helmet for protecting a head of a person

[0002] Description:

[0003] The present invention relates to a helmet for protecting a head of a person.

[0004] Helmets have long been recognized as a critical safety gear, playing a pivotal role in safeguarding the human head from potentially devastating impacts. While traditional helmet designs have made significant strides in reducing the severity of head injuries, there remains an ongoing need for innovative improvements to enhance safety measures, address emerging risks, and protect users in a variety of demanding environments.

[0005] Existing helmets face challenges in terms of impact absorption, structural integrity, and adaptability to different types of impacts. In high-impact situations, such as sports collisions or industrial accidents, the head requires optimal protection to mitigate the risk of traumatic brain injuries. Moreover, some activities, such as biking or motorcycling, involve specific risks, such as rotational forces that are typically created upon oblique impacts onto the helmet. While these rotational forces are often responsible for severe head and neck injuries, only little is known in the prior art to control and act against these high-risk sources.

[0006] Based on this, it is subject of the present invention to provide a helmet for protecting a head of a person that is improved with respect to the prior art in that it reduces the rotation of the helmet upon an oblique impact.

[0007] This problem is solved by a helmet with the features of claim 1 .

[0008] Embodiments of the present invention are stated in the corresponding dependent claims and are described in the following.

[0009] The invention relates to a helmet for protecting a head of a person. The helmet comprises an outer layer having an outer surface for receiving an impact to the helmet. The outer layer is coupled to an inner portion of the helmet via a reactive structure, wherein the inner portion is configured to contact a head of a person. The reactive structure is configured to provide for each location of a plurality of locations of the outer surface a corresponding force for reducing a rotation of the helmet upon an oblique impact on the location, wherein the reactive structure is configured to provide a first force for reducing a rotation of the helmet upon an oblique impact on a first location of the outer surface, the first location being comprised by said plurality of locations, and a different second force for reducing the rotation of the helmet upon an oblique impact on a second location of the outer surface. The second location is different from the first location and comprised by said plurality of locations. In the context of the present invention, the term 'oblique impact' relates to impacts between the outer surface of the helmet and objects, particularly an impacting plane, with impact angles that are not equal to 90°. The impact angle is defined by the angle between an impact axis along which the impact occurs, which is typically defined by the relative motion between the helmet and the object, and a tangential plane extending tangentially to the outer surface of the helmet at the location of the impact.

[0010] For oblique impacts, helmet and head experience an impact torque that is inherent with the impact. The impact torque depends on the impact force and the geometrical arrangement of the center of mass of helmet and head combined with respect to the impact location. The impact torque causes a rotation of the helmet and the head, which may cause severe head and / or neck injuries of the person wearing the helmet due to the rotational acceleration and / or rotational velocity of the helmet upon impact. Therefore, in the context of the present invention, the term 'reducing a rotation of the helmet' is understood as reducing the rotational acceleration and / or the rotational velocity of the helmet and the head upon impact.

[0011] While above only a first and a second location are referred to as being part of said plurality of locations, the present invention can be extended to more than two locations of the outer surface of the helmet, for example a third, fourth, fifth, sixth, seventh, eight location, or more locations, wherein the reactive structure is configured to provide for each of these locations a corresponding force based on the above considerations to reduce the rotation of the helmet upon an oblique impact onto the respective location.

[0012] Particularly, the first force is configured to generate a first torque of the helmet for acting against a first impact torque of the helmet caused by an oblique impact on the first location so as to reduce the rotation of the helmet and wherein the second force is configured to generate a second torque of the helmet caused by an oblique impact on the second location so as to reduce the rotation of the helmet, wherein the first and the second torque are different from each other.

[0013] In particular, the first and the second torque are generated by force transmission, particularly by means of friction, between the impacting plane and the head of the person, which is realized by the helmet forming a mechanical connection between the impacting plane and the head during the impact. This force transmission can be controlled by means of the materials, mechanical interconnects, layers and / or structures that form the helmet. Typically, for oblique impacts, friction forces are oriented against a tangential component of the impact force, such that the first and the second torque are oriented against said impact torque. Consequently, the rotation of the helmet and the head upon impact, which results from the contributions of both the impact force and the first or the second torque, is reduced. In other words, the first and the second torque generated by the first and the second force can be controlled to reduce the resulting rotation of the helmet and the head upon impact, which lowers the risk of head and neck injuries.

[0014] According to an embodiment, the first location and the second location each define a ratio d d2between a first distance d±and a second distance d2, the first distance d being the shortest distance from a pre-defined center of mass of helmet and head combined to a point on the perpendicular of a tangential plane of the respective location, and d2being the distance from the respective location to said point on the perpendicular, wherein the ratio differs for the first and the second location and wherein the first force is larger than the second force when the ratio defined by the first location is larger than the ratio defined by the second location and wherein the second force is larger than the first force when the ratio defined by the second location is larger than the ratio defined by the first location.

[0015] The first distance d forms a leverage arm of the impact torque while the second distance d2forms a leverage arm of the first or the second torque. As such, the rotation of the helmet may be reduced, and particularly zeroed by equalizing the impact torque at the first or the second location with the first or the second torque. This may be achieved by setting the first and the second force according to the ratio d d2at the first and the second location, respectively.

[0016] Particularly, the respective force at the respective location is proportional to the ratio d d2defined by the respective location.

[0017] According to an embodiment, the outer surface of the helmet is shaped such that the plurality of locations of the outer surface of the helmet comprise a ratio d d2between 0 and 0.3.

[0018] A positive ratio d d2denotes the case in which both the impact axis and the center of mass are oriented on the same side with respect to the respective perpendicular. In this case, the distance d is defined as positive, wherein d2is always positive irrespective of the orientation between the center of mass and the impact axis. For a positive ratio, the rotation of the helmet upon impact can be reduced by the reactive structure, since the impact torque and the torque generated by the reactive structure, particularly said first and second torque, comprise opposite senses. In turn, a negative ratio d d2denotes the case in which the impact axis and the center of mass are oriented on different sides with respect to the respective perpendicular, where d is negative while d2is still positive. Here, the torques comprise the same sense, which would result in an enhanced rotation of the helmet due to any kind of force transmission generated by the reactive structure. Therefore, for locations with a negative ratio, the force transmission is preferably as small as possible, particularly zero.

[0019] However, since the center of mass corresponds to the center of mass of the helmet and head combined, it is shifted slightly, typically by a few millimeters, downwards viewed from a top portion of the helmet, compared to a center of mass of only the helmet without the head, as the head is typically heavier than the helmet. For most locations of the outer surface of a normal-sized helmet of contemporary design, the corresponding ratio d. ld,2is positive and thus allows to reduce the rotation of the helmet upon impact. The center of mass of helmet and head combined can be determined by considering shape and weight of the helmet and assuming a typical human head and its weight, for instance a typical helmet such as a bicycle helmet can comprise a weight of about 300g. Particularly, the shape and weight of a headform (model of a human head) that is used for tests can be assumed, for example as defined by the National Operating Committee on Standards for Athletic Equipment (NOCSAE). For example, the headform can correspond to one of the headforms defined by Table 1 according to the STANDARD TEST METHOD AND EQUIPMENT USED IN EVALUATING THE PERFORMANCE CHARACTERISTICS OF HEADGEAR / EQUIPMENT - NOCSAE DOC ND 001-17m23, particularly to headform size 7 1 / 4 with a weight of 4.90 kg (cf. https: / / nocsae.org / wp-content / uploads / 2018 / 05 / ND001-17m23-Drop-Test-Method.pdf). More particularly, different helmet sizes can be based on different headform sizes, such as for example headform sizes 6 5 / 8, 7 1 / 4 and 7 5 / 8 of the headforms as defined by NOCSAE in said Table 1 above. These headform sizes can be used to shape a small, medium and large helmet, respectively. Alternatively, the headform is chosen larger than the headforms of a predefined percentile of the human population, such that the helmet can be worn by said percentile of the human population. Particularly, the helmet is shaped based on headforms that are larger than 95%, 50% and / or 5% of the human population, such that the helmet can be worn by 95%, 50% or 5% of the human population, respectively. These headform sizes can be used to shape a small, medium and large helmet, respectively.

[0020] For example, the outer surface of the helmet can be shaped such that the plurality of locations of the outer surface of the helmet comprises a distance d3between the respective location and the center of mass, wherein d3is between 120mm and 180mm, particularly within a range of 25%, more particularly 10% around at least one of the following distances: 144mm, 147mm, 171.9mm, 160mm, 126.6mm, 149.2mm.

[0021] Particularly, the outer surface of the helmet is shaped such that the plurality of locations of the outer surface of the helmet comprises an angle between the perpendicular of the respective location of the outer surface and a line extending through the respective location and the center of mass, wherein the angle is between 0 and 17°.

[0022] For example, said plurality of locations comprises locations, each location having an angle and a distance d3selected from the list comprised of: 12.3° and 144mm, 15.2° and 147mm, 3.8° and 160mm, 27.5° and 126.6mm, 15.4° and 149.2mm. According to an embodiment, the first and the second force are further proportional to a predefined absolute value of a pre-defined normal force component of an impact force due to the oblique impact.

[0023] The normal force contributes proportionally to the impact torque. Therefore, by setting the first and the second force proportional to the impact torque, the rotation of the helmet upon impact may be reduced. The normal force may for example be determined based on crash-testing standards, simulations and / or empirical data. A typical absolute value of such a pre-defined normal force can e.g. be in the range between 1 kN to 10 kN, more particularly within a range between 3 kN and 7 kN. For example, for a weight of helmet and head combined of 5 kg and an acceleration of 100 g during an oblique impact, with g=9.81m / s2, the corresponding normal force component is approximately 5 kN..

[0024] According to an embodiment, the first force is smaller than the product of the normal force and the ratio d. ld,2at the first location and wherein the second force is smaller than the product of the normal force and the ratio d di at the second location, wherein particularly the first force is larger than the second force when the ratio d. ld,2defined by the first location is larger than the ratio d. ld,2defined by the second location and wherein the second force is larger than the first force when the ratio d di defined by the second location is larger than the ratio d di defined by the first location.

[0025] According to an embodiment, the helmet comprises a plurality of panels, each panel forming a section of the outer surface of the helmet, wherein each panel is connected to the inner portion of the helmet by at least one respective reactive structure.

[0026] In an embodiment, the first location is comprised by a first panel and the second location is comprised by a second panel, wherein the first panel and the second panel are comprised by the plurality of panels.

[0027] According to another embodiment, for impacts onto the first panel, the reactive structure is configured to provide the first force and wherein for impacts onto the second panel, the reactive structure is configured to provide the second force. The reactive structure can comprise separated sections. Each section can be associated with one of the panels.

[0028] According to an embodiment, the reactive structure comprises a reactive layer coupling the outer layer, particularly the respective panel, to the inner portion of the helmet. As such, the reactive layer may be arranged between the outer layer, particularly the panel, and the inner portion of the helmet.

[0029] However, the reactive structure does not need to be arranged between the outer layer and the inner portion of the helmet. In an alternative embodiment, the reactive structure couples the outer layer, particularly the respective panel, and the inner portion of the helmet at a rim region of the helmet by establishing a lateral connection between the outer layer, particularly the respective panel, and the inner portion. The lateral direction corresponds to the direction in which the outer layer and the inner portion essentially extend. In another alternative embodiment, the reactive structure couples the respective panel and the inner portion at or circumferentially around an edge area of the respective panel. In these alternative embodiments, the reactive structure couples or connects the inner portion with the outer layer, particularly the respective panel laterally from their lateral sides, such that the inner portion and the outer layer, particularly the respective panel can be in physical contact with each other. Particularly, the reactive structure may at least partially embrace the inner portion and the outer layer or the respective panel, so as to provide the first and the second force.

[0030] Particularly, the reactive structure, particularly the reactive layer, may be laterally interrupted, such that the reactive structure / reactive layer comprises a plurality of separate sections. For example, in case of a plurality of panels, each panel may be connected to the inner portion of the helmet via a section of the reactive structure / reactive layer.

[0031] In an embodiment, the reactive layer comprises rollable elements, wherein the panel is connected to the inner portion via a connecting structure of the reactive layer, wherein upon impact with an impact force beyond said pre-determined failure force, the connecting structure is configured to fail, such that upon failure of the connecting structure, the panel moves with respect to the inner portion under rolling of the rollable elements.

[0032] In another embodiment, the reactive layer comprises rollable elements, wherein the respective panel is connected to the inner portion via a respective connecting structure of the reactive layer, wherein upon an impact with an impact force beyond said pre-determined failure force, the respective connecting structure is configured to fail, such that upon failure of the respective connecting structure, the respective panel moves with respect to the inner portion under rolling of the rollable elements.

[0033] To establish a mechanical connection between the rollable elements, the inner portion and / or the panel, particularly the respective panel, the connecting structure can comprise adhesive.

[0034] According to yet another embodiment, the first and the second force provided by the reactive layer are realized by failure of the respective connecting structure and a rolling resistance between the rollable elements, the inner portion and the respective panel.

[0035] In another embodiment, the first and the second force provided by the reactive layer are timedependent forces comprising a failure period during which the connecting structure fails and the first and the second force have a respective maximum corresponding to the failure force and a succeeding rolling resistance period during which the first and the second force are defined by the rolling resistance between the rollable elements, the inner portion and the respective panel.

[0036] Particularly, the pre-determined failure force is larger than the rolling resistance during the rolling resistance period.

[0037] In an embodiment, the connecting structure comprises at least one adhesive layer connecting the rollable elements with the inner portion and / or the respective panel. For example, the connecting structure comprises a first adhesive layer connecting the rollable elements with the inner portion and the connecting structure comprises a second adhesive layer connecting the rollable elements with the panel, particularly the respective panel. Alternatively, the connecting structure comprises a single adhesive layer that connects the rollable elements to the inner portion, wherein the inner portion and the panel, particularly the respective panel are separately fastened to each other. Vice versa, the connecting structure can comprise a single adhesive layer that connects the rollable elements to the panel, particularly the respective panel, wherein the inner portion and the panel, particularly the respective panel are separately fastened to each other.

[0038] In another embodiment, the adhesive layer does not need to be continuous and can comprise a plurality of adhesive spots, each spot connecting at least one rollable element with the inner portion or connecting at least one rollable element with the respective panel. Thus, the force provided by the reactive structure can be controlled based on a spatial density of adhesive spots on the inner portion or the respective panel, wherein a larger spatial density gives rise to a larger force and wherein a smaller spatial density gives rise to a smaller force.

[0039] According to yet another embodiment, each rollable element can be integrally connected to the inner portion and / or to the respective associated panel.

[0040] In an embodiment, the first and the second panel are separated from each other, such that the first and the second panel are configured to be moved with respect to each other.

[0041] Exemplary embodiments are described below in conjunction with the Figures. The Figures are appended to the claims and are accompanied by text explaining individual features of the shown embodiments of the present invention. Each individual feature shown in the Figures and / or mentioned in the text of the Figures may be incorporated (also in an isolated fashion) into a claim relating to the present invention.

[0042] Figs. 1a, 1b schematically illustrate an embodiment of a helmet according to the invention, wherein in Fig. 1a, the helmet is impacting on an impacting plane at a first location of the outer surface of the helmet and wherein in Fig. 1 b, the helmet is impacting on the impacting plane at a second location of the outer surface of the helmet;

[0043] Fig. 2 shows six different impacts of a helmet according to an embodiment of the invention onto an impacting plane, wherein respective distances d1and d2describing the displacement between the respective impact location and the center of mass are indicated;

[0044] Fig. 3 shows an example embodiment of the reactive structure according to the invention;

[0045] Fig. 4 shows an embodiment of a helmet according to the invention, comprising a plurality of panels; and

[0046] Fig. 5 shows a graph that illustrates the time-dependent force dynamics provided by a reactive structure according to an embodiment of the invention.

[0047] Figs. 1a and 1b schematically illustrate an embodiment of a helmet 1 according to the invention. The shown helmet 1 is arranged on a head 2 of a person, such that the helmet 1 is configured to protect the head 2 of the person in case of an impact onto the helmet 1 . The helmet 1 is indicated by its outer surface 3 in this illustration. Figs. 1a and 1 b each sketch the helmet 1 as it impacts onto an impacting plane 30. The impact comprises an impact force, wherein a corresponding impact axis F0 is exemplarily oriented as indicated with respect to the impacting plane 30.

[0048] In Fig. 1a, the impact occurs at a first location L1 of the outer surface 3 of the helmet 1 and in Fig. 1 b, the impact occurs at a different second location L2 of the outer surface 3 of the helmet 1 , wherein for both impacts, the impact angle, that is, the angle between the impact axis F0 and the impacting plane 30 or a respective tangential plane 6 extending tangentially to the outer surface 3 at the respective location of the impact, is the same. In the moment of the impact, the respective tangential plane 6 of the first and the second location L1 , L2 is coincident with the impacting plane 30, cf. Fig. 1a and in Fig. 1 b. Consequently, the normal force FN of the impact force, that is, its component acting normal to the impacting plane 30, is the same for an impact onto the first location L1 and an impact onto the second location L2.

[0049] Generally, for oblique impacts, i.e. , with impact angles not equal to 90°, helmet 1 and head 2 experience an impact torque that is inherent with the impact. The impact torque depends on the impact force and the geometrical arrangement of the center of mass 4 of helmet 1 and head 2 combined with respect to the impact location. In particular, the impact torque scales with the normal force FN and a first distance d1, which is the shortest distance from the center of mass 4 to a point P on the perpendicular 5 of the tangential plane 6 of the respective location. Particularly, the impact torque can be written as Timp= FNd . The impact torque contributes to a potentially harmful rotation of the helmet 1 and the head 2 upon impact, which may cause severe head and / or neck injuries of the person wearing the helmet 1. In Figs. 1a and 1 b, both the impact axis FO and the center of mass 4 are oriented on the same side with respect to the respective perpendicular s. The impact torque is thus oriented counterclockwise, which would, in the absence of other torques, cause the helmet 1 and the head 2, and thus the center of mass 4, to rotate counterclockwise upon impact. As can be understood from comparing Figs. 1a and 1 b, the impact torque in Fig. 1 b is larger than the impact torque in Fig. 1a, due to the larger distance d , which forms a leverage arm of the impact torque, while FN is identical in both cases.

[0050] However, upon impact, another torque is generated by a force transmission, particularly by means of friction, between the impacting plane 30 and the head 2 of the person, which is realized by the helmet 1 forming a mechanical connection between the impacting plane 30 and the head 2 during the impact. This force transmission can be controlled by means of the materials, mechanical interconnects, layers and / or structures that form the helmet 1. In the embodiment of Figs. 1a and 1 b, the helmet 1 is configured such that for an impact onto the first location L1 , the torque generated by said force transmission corresponds to a first torque generated by a first force F1 and for an impact onto the second location L2, this torque corresponds to a second torque generated by a second force F2, cf. Fig. 1a and Fig. 1b. Both the first and the second force F1 , F2 are oriented against a tangential component FT of the impact force, such that the first and the second torque are oriented against said impact torque. Consequently, the rotation of the helmet 1 and the head 2 upon impact, which results from the contributions of both the impact force and the first or the second torque, is reduced. In other words, the first and the second torque generated by the first and the second force F1 , F2 can be controlled to reduce the resulting rotation of the helmet 1 and the head 2 upon impact, which lowers the risk of head 2 and neck injuries. The second force F2 is chosen larger than the first force F1 to account for the larger distance d for the second location L2 compared to the first location L1 .

[0051] A different first and second force F1 , F2 of the helmet 1 for impacts on the first and the second location L1 , L2 can be realized by a reactive structure 7 of the helmet that couples the outer surface 3 to an inner portion of the helmet 1 contacting the head 2, and form what is referred to as a reactive structure 7 the helmet 1. The reactive structure 7 may comprise different materials, structures, layers and / or mechanical interconnections that are configured to realize the first force F1 for an impact onto the first location L1 and the second force F2 for an impact onto the second location L2.

[0052] Besides the first and the second force F1 , F2, the first and the second torque also scale with a respective distance d2from the respective location L1 , L2 to said point P on the respective perpendicular 5. Particularly, the first and the second torque may be written as Tt= FLd2, with i=1 ,2 for the first and the second location L1 , L2 and d2determined at the first and the second location L1 , L2, respectively. With these considerations, the resulting rotation of the helmet 1 and the head 2 may be further reduced, particularly zeroed, by choosing the first and the second force F1 , F2 provided by the reactive structure 7 such that the first and the second torque generated by the force transmission at the respective location equal the impact torque at the respective location L1 , L2. This is the case when the respective force scales with the product of the normal force and a respective ratio between d and d2at the respective location, particularly wherein the first force is F1= F^d^d^ and with d and d2determined at the first location L1 and wherein the second force is F2=w(di / d2) with d and d2determined at the second location L2.

[0053] While the above explanations are made for two locations on the outer surface 3 of the helmet 1 , the inventive concept may be extended to more than two locations of the outer surface 3 of the helmet 1 , for example a third, fourth, fifth, sixth, seventh, eight location, or more locations, wherein the reactive structure 7 is configured to provide for each of these locations a corresponding force based on the above considerations to reduce the rotation of the helmet 1 upon an oblique impact onto the respective location.

[0054] Fig. 2 shows six different impacts of a helmet 1 according to an embodiment of the invention onto an impacting plane 30. Every impact occurs on a different location of the outer surface 3 of the helmet 1 , wherein the locations are numbered from one to six. For every location, the impact is shown in a front view (left of the two columns) as well as a side view (right of the two columns) onto the impacting plane 30. For each impact location, the corresponding distances d and d2are indicated together with the ratio d d2at the respective location. The respective force provided by the reactive structure 3 for an impact onto the respective location is preferably based on the respective ratio, wherein higher ratios correspond to higher forces and wherein lower ratios correspond to lower ratios. As such, the force realized by the reactive structure 7 may be determined based on the shape of the outer surface 3 of the helmet 1 , particularly based on the geometrical arrangement of the outer surface 3 with respect to the center of mass 4 which defines the distances d and d2, respectively. As can be seen in Fig. 2, five out of the six locations comprise a positive ratio (— > 0). Only location 3 comprises a negative ratio (— < 0). A positive ratio denotes the case in which both the impact axis F0 and the center of mass 4 are oriented on the same side with respect to the respective perpendicular 5, as shown in the examples of Fig. 1a and 1b. In this case, the distance d1is defined as positive, wherein d2is always positive irrespective of the orientation between the center of mass 4 and the impact axis F0. For a positive ratio, the rotation of the helmet 1 upon impact can be reduced by the reactive structure 7, since the impact torque and the torque generated by the reactive structure 7, particularly said first and second torque, comprise opposite senses. In turn, a negative ratio denotes the case in which the impact axis F0 and the center of mass 4 are oriented on different sides with respect to the respective perpendicular 5, cf. location 3 in Fig. 2 which comprises a negative dl twhile d2is positive. Here, the torques comprise the same sense, which would result in an enhanced rotation of the helmet due to any kind of force transmission generated by the reactive structure 7. Therefore, for locations with a negative ratio, the force transmission is preferably as small as possible, particularly zero.

[0055] However, since the center of mass 4 corresponds to the center of mass 4 of the helmet 1 and head 2 combined, it is shifted downwards viewed from a top portion of the helmet 1 , compared to a center of mass 4 of only the helmet 1 without the head 2. Consequently, for most locations of the outer surface 3 of a normal-sized helmet 1 of contemporary design, the corresponding ratio is positive and thus allows to reduce the rotation of the helmet 1 upon impact, cf. locations 1 and 2 as well as locations 4 to 6 in Fig. 2.

[0056] Fig. 3 shows an example embodiment of the reactive structure 7 according to the invention. In this embodiment, the reactive structure 7 comprises a reactive layer 70 comprising rollable elements 11 , such as rolls and / or spherical bodies. Fig. 3 represents a cut view through the helmet 1 , with the respective panel 8 forming the outer surface 3 of the helmet 1. The respective panel 8 is connected to the inner portion 40 of the helmet 1 via a respective connecting structure 10 of the reactive layer 70 of the respective panel 8. The inner portion 40 is configured for contacting the head 2 of the person wearing the helmet 1 .

[0057] As such, the reactive layer 70 is sandwiched between the respective panel 8 and the inner portion 40. In case the helmet 1 comprises a single panel 8, the helmet 1 can comprise just a single reactive layer 70 underneath it. In the following, the embodiment will be described in the context of multiple panels 8. The panels 8 are preferably configured as stiff layers which can be achieved by selecting an appropriate material and shape. Particularly, a curved shape of the panels 8 as shown in Fig. 4 contributes to said stiffness. Particularly, the panels 8 can be formed out of polycarbonate and can comprise a thickness in the range from 0.25 mm to 20 7 mm, preferably 0.4 to 1 mm. Other materials for the panels 8 are also conceivable. The reactive layer 70 comprises a lower layer 12 arranged between the rollable elements 11 and the inner portion 40. Preferably, as the panels 8 the lower layer 12 is also adapted to be stiff in the sense described above. The inner portion 40 may comprise an energy absorbing layer configured to absorb energy of an impact on the helmet 1 , particularly in a normal direction of the outer surface 3 of the helmet, i.e. along the direction of the normal force FN.

[0058] The inner portion 40, particularly the energy absorbing layer, can be formed out of an expanded polystyrene foam (EPS) and can be bonded to an inner surface 13a of the lower layer 12 by an adhesive 20, e.g. acrilux or other suitable thermo-softening adhesives. The lower layer 12 preferably comprises a thickness in the range from 0.25 mm to 20 mm and may also be formed out of polycarbonate.

[0059] The plurality of rollable elements 11 preferably remain rigid during normal use of the helmet 1 , when no impact occurs, and are configured to roll for impacts with corresponding tangential forces FT, cf. Figs. 1a and 1b, beyond a pre-determined impact threshold over an outer surface 13b of the lower layer 12. The impact threshold corresponds to a pre-defined tangential force on the respective panel 8 that, if exceeded upon an oblique impact, caused the rollable elements 11 to roll. In a preferred embodiment, the rollable elements 11 comprise a diameter of about 2 mm.

[0060] Fig. 3 shows only one such reactive layer 70, but such a reactive layer 70 is preferably present under each panel 8.

[0061] Particularly, the respective connecting structure 10 comprises a substrate film 14 with the plurality of rollable elements 11 arranged thereon. Particularly, the rollable elements 11 are bonded to the substrate film 21 via a first adhesive layer 21 that is preferably configured to undergo brittle failure so as to allow the rollable elements 11 to roll on the substrate film 14 and thus over the lower layer 12 and with respect to the inner portion 40 of the helmet 1 when said impact threshold is exceeded. Preferably, the substrate film 14 comprises a thickness smaller than 200 pm and can be formed out of a polymer such as PVC. Other materials are also conceivable. Furthermore, the substrate film 14 can comprise adhesive 20 such as a pressure sensitive adhesive (PSA) arranged on a side of the substrate film 14 facing away from the rollable elements 11.

[0062] Furthermore, the rollable elements 11 can be bonded to an inner surface 8a of the respective panel 8 by a second adhesive layer 22 applied to the respective panel 8. As the first adhesive layer 21 , the second adhesive layer 22 is preferably configured to undergo brittle failure beyond said pre-determined impact threshold. Preferably, the respective connecting structure 10, particularly its adhesive layers 21 ,22, is or are configured to hold the respective panel 8 such that said pre-determined impact threshold required to activate rolling of the rollable elements 11 of the reactive layer 70 is about 0.1 kN or higher. Upon brittle failure, the rollable elements 11 engage with the stiff panel 8 and the stiff lower layer 12, which ensures a well-controlled rolling resistance.

[0063] A helmet 1 comprising multiple panels 8 is shown in Fig. 4. For each of the panels 8, a respective resulting force is determined based on the above procedure. Each panel 8 is connected via a respective reactive structure 7 to the inner portion of the helmet 1 , wherein the respective reactive structure 7 provides the respective resulting force. The respective reactive structure 7 may for example be based on the embodiment of Fig. 3. As can further be seen in Fig. 4, gaps 9 separate neighbored panels 8 of the helmet 1. As such, upon impacts beyond said pre-determined impact threshold, neighbored panels 8 are configured to be moved with respect to each other and with respect to the inner portion 40 contacting the head 2 of the person. Particularly, as a consequence of the curvature of the panels 8, neighbored panels 8 may be configured to move on top of each other upon impact.

[0064] Fig. 5 shows a graph that illustrates the time-dependent force dynamics provided by a reactive structure 7 with a reactive layer 70 comprising a connecting structure 10 with adhesive layers 21 ,22 that bond rollable elements 11 between the respective panel 8 and the inner portion 40 of the helmet, for example according to the embodiment shown in Fig. 3.

[0065] The force dynamics shows on the x-axis the time dependence and on the y-axis the force provided by the reactive structure 7 and is governed by two distinct regimes. The time axis describes the time passed upon an impact of the helmet 1 onto an impacting plane 30. In a first regime, immediately upon impact, the impact force acts on the adhesive layers 21 ,22 that bond the rollable elements 11 between the respective panel 8 and the inner portion. Once the impact force reaches a pre-determined impact failure force FF corresponding to said impact threshold, the adhesive layers 21 ,22 undergo brittle failure. Now, the adhesive layers 21 ,22 are no longer configured to hold the respective panel 8 and the inner portion 40 together. The adhesive layers 21 ,22 break and cause the rollable elements 11 to roll, whereby the respective panel 8 and the inner portion 40 are moved with respect to each other. The rolling of the rollable elements 11 represents a second regime with an essentially constant force provided by the reactive layer 70 by means of a constant rolling resistance FR.

[0066] Particularly, to realize the first or the second force F1 ,F2, the failure force FF and the rolling resistance FR may be chosen such that the average of the time-dependent force dynamics over an impact time timpcorresponds to the first or the second force F1 ,F2. For example, the impact time timpis between 2.5ms and 7.5ms, particularly between 4ms and 6ms, more particularly 5ms. As such, the forces realized by a respective reactive structure 7 may be controlled by adjusting the failure force FF and the rolling resistance FR. Particularly, the failure force FF may be varied by means of different types of adhesive, different densities of adhesive and / or different geometries of the adhesive layers 21 ,22. The rolling resistance FR may be varied by means of different types of rollable elements 11 , particularly with different geometries, including variations from a perfectly spherical shape, and / or by changing the materials, particularly the surfaces of layers that the rollable elements 11 engage with upon brittle failure of the adhesive layers 21 ,22.

[0067] List of reference signs

[0068] Helmet 1

[0069] Head 2

[0070] Outer surface 3

[0071] Center of mass 4

[0072] Perpendicular 5

[0073] Tangential plane 6

[0074] Reactive structure 7

[0075] Panel 8

[0076] Inner surface of the panel 8a

[0077] Gap 9

[0078] Connecting structure 10

[0079] Rollable elements 11

[0080] Lower layer 12

[0081] Inner surface of the lower layer 13a

[0082] Outer surface of the lower layer 13b

[0083] Substrate film 14

[0084] Adhesive 20

[0085] First adhesive layer 21

[0086] Second adhesive layer 22

[0087] Impacting plane 30

[0088] Inner portion 40

[0089] Reactive layer 70

[0090] Impact axis F0

[0091] First force F1

[0092] Second force F2

[0093] Failure force FF

[0094] Normal force FN Rolling resistance FR

[0095] First location L1

[0096] Second location L2

[0097] Point on the perpendicular P

Claims

Claims1. A helmet (1) for protecting a head (2) of a person, the helmet (1) comprising: an outer layer having an outer surface (3) for receiving an impact to the helmet (1), the outer layer being coupled to an inner portion (40) of the helmet (1) via a reactive structure (7), wherein the inner portion (40) is configured to contact a head (2) of a person, wherein the reactive structure (7) is configured to provide for each location of a plurality of locations of the outer surface (3) a corresponding force for reducing a rotation of the helmet (1) upon an oblique impact on the location, wherein the reactive structure (7) is configured to provide a first force (F1) for reducing a rotation of the helmet (1) upon an oblique impact on a first location (L1) of the outer surface (3), the first location (L1) being comprised by said plurality of locations, and a different second force (F2) for reducing the rotation of the helmet (1) upon an oblique impact on a second location (L2) of the outer surface (3), the second location (L2) being different from the first location (L1) and comprised by said plurality of locations.

2. The helmet (1) according to claim 1 , wherein the first force (F1) is configured to generate a first torque of the helmet (1) for acting against a first impact torque of the helmet (1) caused by an oblique impact on the first location (L1) so as to reduce the rotation of the helmet (1) and wherein the second force (F2) is configured to generate a second torque of the helmet (1) caused by an oblique impact on the second location (L2) so as to reduce the rotation of the helmet (1), wherein the first and the second torque are different from each other.

3. The helmet (1) according to claim 1 or 2, wherein the first location (L1) and the second location (L2) each define a ratio d d2between a first distance d1and a second distance d2, the first distance d being the shortest distance from a pre-defined center of mass (4) of helmet (1) and head (2) combined to a point (P) on the perpendicular (5) of a tangential plane (6) of the respective location, and d2being the distance from the respective location to said point (P) on the perpendicular (5), wherein the ratio d d2differs for the first and the second location (L2) and wherein the first force (F1) is larger than the second force (F2) when the ratio d d2defined by the first location (L1) is larger than the ratio d d2defined by the second location (L2) and wherein the second force (F2) is larger than the first force (F1) when the ratio d d2defined by the second location (L2) is larger than the ratio d d2defined by the first location (L1).

4. The helmet (1) according to claim 3, wherein the respective force at the respective location is proportional to the ratio defined by the respective location.

5. The helmet (1) according to claim 3 or 4, wherein the outer surface (3) of the helmet (1) is shaped such that the plurality of locations of the outer surface (3) of the helmet (1) comprise a ratio between 0 and 0.3.

6. The helmet (1) according to one of the claims 3 to 5, wherein the outer surface (3) of the helmet (1) is shaped such that the plurality of locations of the outer surface (3) of the helmet (1) comprises a distance d3between the respective location and the center of mass (4), wherein d3is between 120mm and 180mm, particularly within a range of 25%, more particularly 10% around at least one of the following distances: 144mm, 147mm, 171.9mm, 160mm, 126.6mm, 149.2mm.

7. The helmet (1) according to one of the preceding claims, wherein the outer surface (3) of the helmet (1) is shaped such that the plurality of locations of the outer surface (3) of the helmet (1) comprises an angle between the perpendicular (5) of the respective location of the outer surface (3) and a line extending through the respective location and the center of mass (4), wherein the angle is between 0 and 17°.

8. The helmet (1) according to claim 6 or 7, wherein said plurality of locations comprises locations, each location having an angle and a distance d3selected from the list comprised of: 12.3° and 144mm, 15.2° and 147mm, 3.8° and 160mm, 27.5° and 126.6mm, 15.4° and 149.2mm.

9. The helmet (1) according to one of the preceding claims, wherein the first and the second force (F2) are further proportional to a pre-defined absolute value of a predefined normal force (FN) component of an impact force due to the oblique impact.

10. The helmet (1) according to one of the preceding claims, wherein the first force (F1) is smaller than the product of the normal force (FN) and the ratio d- d^ at the first location (L1) and wherein the second force (F2) is smaller than the product of the normal force (FN) and the ratio d d2at the second location (L2), wherein particularly the first force (F1) is larger than the second force (F2) when the ratio d l2defined by the first location (L1) is larger than the ratio d2defined by the second location (L2) and wherein the second force (F2) is larger than the first force (F1) when the ratio d2defined by the second location (L2) is larger than the ratio d l2defined by the first location (L1).

11. The helmet (1) according to one of the preceding claims, wherein the helmet (1) comprises a plurality of panels (8), each panel (8) forming a section of the outer surface (3) of the helmet (1), wherein each panel (8) is connected to the inner portion (40) of the helmet (1) by a at least one respective reactive structure (7).

12. The helmet (1) according to claim 11 , wherein the first location (L1) is comprised by a first panel (8) and wherein the second location (L2) is comprised by a second panel (8), wherein the first and the second panel (8) are comprised by the plurality of panels (8).

13. The helmet (1) according to claim 11 or 12, wherein for impacts onto the first panel (8), the reactive structure is configured to provide the first force (F1) and wherein for impacts onto the second panel (8), the reactive structure (7) is configured to provide the second force (F2).

14. The helmet (1) according to one of the preceding claims, wherein the reactive structure (7) comprises a reactive layer (70) coupling the outer layer to the inner portion (40) of the helmet (1).

15. The helmet (1) according to one of the claims 11 to 13 and according to claim 14, wherein the reactive layer (70) comprises rollable elements (11), wherein the respective panel (8) is connected to the inner portion (40) via a respective connecting structure (10) of the reactive layer (70), wherein upon an impact with an impact force beyond a pre-determined failure force (FF), the respective connecting structure (10) is configured to fail, such that upon failure of the respective connecting structure (10), the respective panel (8) moves with respect to the inner portion (40) under rolling of the rollable elements (11).

16. The helmet (1) according to claim 15, wherein upon impact, the first and the second force (F 1 , F2) provided by the reactive layer (70) are realized by failure of the respective connecting structure (10) and a rolling resistance (FR) between the rollable elements (11), the inner portion (40) and the respective panel (8).

17. The helmet (1) according to claim 15 or 16, wherein the first and the second force (F1 ,F2) provided by the reactive layer (70) are time-dependent forces comprising a failure period during which the connecting structure (10) fails and the first and the second force (F1 ,F2) have a respective maximum corresponding to the failure force (FF) and a succeeding rolling resistance period during which the first and the second force (F1 ,F2) are defined by the rolling resistance (FR) between the rollable elements (11), the inner portion (40) and the respective panel (8).

18. The helmet (1) according to one of the claims 15 to 17, wherein the pre-determined failure force (FF) is larger than the rolling resistance (FR) during the rolling resistance period.

19. The helmet (1 ) according to one of the claims 15 to 18, wherein the connecting structure(10) comprises at least one adhesive layer (21 ,22) connecting the rollable elements(11) with the inner portion (40) and / or the respective panel (8).

20. The helmet (1 ) according to one of the claims 15 to 19, wherein the connecting structure (10) integrally connects the rollable elements (11) with the inner portion (40) and / or with the respective panel (8).

21. The helmet (1) according to claim 20, wherein the first panel (8) and the second panel (8) are separated from each other, such that the first and the second panel (8) are configured to be moved with respect to each other.

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