Patent Publication Number: US-2011055993-A1

Title: Helmet including a protective shell with variable rigidity

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to foreign French patent application No. FR 09 04270, filed on Sep. 8, 2009, the disclosure of which is incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to the field of protective helmets and, more particularly, helmets carrying an optical system for projecting images onto a visor. 
     BACKGROUND OF THE INVENTION 
     In the field of aeronautics and notably of military aircraft, pilots generally wear a protective helmet. Protective helmets comprise a protective shell made of a high-performance composite material, surrounding a thick and rigid inner protective layer. The inner protective layer is intended to protect the pilot&#39;s skull against impacts, while the protective helmet is intended to protect the pilot against perforation aggressions such as ballistic aggressions. Helmets for military aircraft pilots are also intended to carry an opto-electronic system. The mounting and integration of a system of this type on a pilot&#39;s helmet is problematic for the following reasons. 
     A visualisation function and a collimator are mounted in order to display visual information on the visor. The visualisation function is implemented by way of an image source, such as a cathode-ray tube or a flat-screen display, located on the top of the head. The collimation optical system is mounted on the top of the front for the image projection onto the visor. To do this, the surface of the visor is treated with a layer of reflective material allowing synthetic sighting and navigation images or images originating from a thermal camera for flights in low-visibility conditions to be displayed in the pilot&#39;s field of view. For reasons relating to optical precision and quality of the displayed image, it is important for the visor of the helmet and the optical system to present little play in maintaining their positions relative to one another. However, the environment of the aircraft cockpit presents numerous stresses in terms of vibrations and substantial thermal deviations, for example. The helmet is also subject to deformations when it is donned or when an oxygen mask is attached. 
     Solutions are known which entail the integration of the mechanical structure of an opto-electronic system and the associated visor. For example, European patent EP 0651952B1 describes a mechanical structure supporting the optical system and the visor. This solution allows the optical system to be isolated from deformations of the protective helmet and includes heavy and unwieldy mechanical fittings positioned on the top of the helmet. This solution significantly increases the mass of the optical system assembly and consequently presents a danger to the pilot and also reduces the ease of use of the helmet. 
     The French patent FR 2717045A1 describes a helmet including a mechanical structure allowing an optronic equipment to be mounted on the shell of the helmet. This rigid mechanical structure is connected to the helmet via an assembly of deformable connections. Its purpose is to permit the necessary deformations of the helmet, while retaining a rigid part which allows the optronic equipment to be isolated from these deformations of the helmet. Similarly, this rigid mechanical structure mounted on the shell of the helmet increases the mass of the optronic system. 
     A head tracking system (HTS) may also be added to the pilot&#39;s helmet. The lightest HTS function is the electromagnetic HTS. For the aforementioned same reasons of precision, the optical and HTS functions are attached to a mechanical structure independent from the deformations of the protective helmet. Thus, the visualisation system is isolated from the deformations of the helmet occurring when it is donned and from the stresses due to the oxygen mask and the retention system on the shell of the helmet under a load factor. The HTS function sensor is attached to the mechanical structure of the optical system for reasons of precision, i.e. on the front and the top of the helmet. Some helmets integrate an electro-optical head tracking system whose LEDs (Light Emitting Diodes) are located at the back and the side of the helmet. The advantage of this principle is to shift the mass of the HTS function towards the back for better balance, but the main disadvantage is the greater mass of the mechanical structure of the visual system. In fact, the surface of the structure is extended towards the back to maintain the LEDs in a precise and stable position in relation to the optical system. In this case, the mechanical structure of the visual system resembles a second shell superimposed on the protective shell. 
     Finally, it is important to remember that the mass and the centring of the helmet visor are critical safety parameters. In fact, too high a mass may cause injuries to the cervical spine in the event of repeated stresses linked to load factors or in the event of an ejection. The centre of mass of the helmet affects its stability on the pilot&#39;s head during manoeuvres and in the event of an ejection where a centring which is too far forward and/or too high, may cause irreversible injuries. As a result, it is necessary, as far as possible, to reduce the mass of the helmet and to align the centre of gravity of the helmet with the centre of gravity of the wearer&#39;s head. In parallel, the electronic systems mounted on the helmet need to be isolated from the deformations of the helmet for reasons of precision of the optical functions. 
     Existing solutions have hitherto proposed the implementation of additional mechanical structures, thereby increasing the rigidity of the structure of the helmet but, conversely, increasing the mass. In designing a visor helmet, the person skilled in the art is therefore faced with a dilemma between, on the one hand, isolating the display equipment in order to maintain good optical precision and, on the other hand, reducing the mass of the helmet. Moreover, it is necessary for the helmet to have reversible deformation capabilities sufficient for the comfort of the pilot when the latter dons the helmet or attaches the oxygen mask. These deformations must not be passed on to the structure which holds the optical system in place. 
     SUMMARY OF THE INVENTION 
     The invention overcomes the aforementioned problems and dispense with a heavy and unwieldy mechanical structure for mounting electronic equipment such as a visor projection device and a head tracking device. 
     More precisely, the invention relates to a helmet including a protective shell, characterised in that the protective shell is made up of an upper part disposed in the top part of the helmet and a lower part, the upper part being made of a “sandwich” composite material including two skins, disposed on either side of a core, themselves including a plurality of composite tissue layers, the lower part being made of a monolithic composite material. 
     According to one preferred embodiment, the helmet includes an inner protective layer disposed in the top part of the helmet, and advantageously the upper part of the protective shell is disposed opposite the inner protective layer and the lower part extends towards the bottom of the helmet beyond the inner protective layer. The upper part of the protective shell preferably covers more or less the entire parietal, frontal and upper occipital part of the neurocranium of the wearer. 
     Advantageously, the monolithic composite material of the lower part is formed with at least one skin of sandwich composite material of the upper part of the shell, said skin being extended beyond the core. The monolithic composite material is preferably formed by the two skins extended beyond the core, the two skins then being bonded to one another through polymerisation. 
     Advantageously, the tissue layers of the lower part of the shell include fibres whose orientation is offset by around 45° in relation to a vertical axis of the plane of symmetry of the helmet. 
     According to one preferred embodiment, the edge of the core of the sandwich composite material in the area between the upper part and the lower part of the protective shell is wedge-shaped. 
     According to a first embodiment of the helmet including a head equipment mounted on the protective shell, said equipment is fixed onto the outer surface of the sandwich composite material skin. 
     According to a second embodiment of the helmet, at least one head equipment is fixed between the two sandwich composite material skins, a part of the core of said composite material being hollowed in order to insert said head equipment. 
     According to a third embodiment of the helmet, the upper part of the protective shell includes two sub-parts, a rear sub-part connected to the lower part of the protective shell and fixed to the inner protective layer and an immovable front sub-part, fixing elements mounted on said sub-parts allowing said sub-parts to be joined together and separated. 
     According to any one of the last two embodiments, the core of the composite material of the front sub-part of the upper part of the protective shell includes a material thickness greater than the core of the composite material of the rear sub-part. 
     According to one particular embodiment, the helmet is a helmet for a military aircraft pilot comprising a visor, and the head equipment is a device for projecting images onto said visor and, advantageously, the projection device and the visor are mounted on the front part of the upper part of the protective shell. Advantageously, for this last embodiment, a second head equipment is a head tracking system. 
     According to any one of the preceding embodiments, the core of the first composite material is a foam material intended for impact protection. 
     The protective shell of the helmet has a structure which reacts differently to stresses according to the stressed areas of the helmet. The high rigidity of the upper part of the shell, due to the use of a sandwich composite material, eliminates the need for an additional mechanical structure to be used to hold one or more electronic equipments as well as the visor in place. In this way, the invention proposes a solution allowing the mass of the helmet to be reduced and the positioning of the centre of gravity of the helmet assembly in relation to the centre of gravity of the head of the wearer to be improved. 
     The lower part has reversible deformation capabilities allowing the pilot&#39;s comfort to be improved when donning the helmet and when using the oxygen mask to hold the headphones in place, and also when adjusting the retention system. The elasticity and suppleness of the material of the lower part of the protective shell allow the helmet to react to stresses without transmitting the structural deformations to the electronic equipment. In fact, the rigidity of the upper part of the shell is much greater than that of the lower part and allows said electronic equipment to be isolated from any deformation. Thus, the precision required for the positioning and holding in place of the electronic equipment and the visor in working mode is improved and is sufficient to obtain a good display quality. 
     The protective shell comprising two parts which have deformation capabilities that are variable according to the areas of the helmet and, more particularly, a substantial rigidity on the upper part allows electronic equipment to be mounted directly on the protective shell. Thus, it is not necessary to use an additional mechanical structure or a high-rigidity double protective shell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood and other advantages will become evident from reading the non-limiting description which follows, referring also to the attached drawings, in which: 
         FIG. 1  is a perspective view of the helmet according to the invention, showing the upper and lower part of the protective shell. Stresses are exerted on the shell and the lower part is shown in places as a double line to symbolise the deformations of the lower part of the shell. 
         FIG. 2  shows a first embodiment of the helmet according to a section implemented in the plane of symmetry of the helmet. The section allows the materials that make up the protective shell of the helmet to be shown. The helmet is donned on the head of a wearer and an electronic equipment is mounted on the outer surface of the protective shell. 
         FIG. 3  shows a second embodiment in which the electronic equipment is integrated within the sandwich material. The upper part of the protective shell includes a front sub-part and a rear sub-part. 
         FIG. 4  shows a third modular embodiment of the helmet including an immovable front sub-part of the protective shell supporting the electronic equipment. The layers of material that make up the protective shell are shown transparently. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is intended in particular for military aircraft pilots&#39; helmets to hold the electronic equipment in place on the protective shell. However, the scope of the invention is not limited to this type of helmet and applies to any type of protective helmet, with or without head equipment. 
     In the embodiment described below, the invention proposes a technical solution for maintaining the necessary precision for electronic systems for projecting an image on a visor. The protective shell comprising a plurality of parts having variable deformation capabilities allows the equipment and the visor to be isolated from the stresses linked to the use of the helmet.  FIG. 1  shows with arrows the mechanical stresses acting on a helmet. Most of the time, these mechanical stresses act on the lower part  2  of the helmet when it is placed on the head of the wearer. In this case, this involves in particular the lower lateral working parts. In fact, once it is in place, the wearer tends to remove the sides of the helmet. The oxygen mask is similarly attached to this lower part. The pilot&#39;s movements cause deformations on the lower part of the protective shell. The deformations acting on the helmet may be oriented towards the front, the rear, or in the lateral direction. The constitution of the lower part  2  of the protective shell offers properties of increased flexibility and suppleness in these directions. The nature of the material of the lower part is shown in more detail in the description which follows. 
     The upper part  1  of the protective shell is implemented according to a structure which differs from the structure of the lower part  2 . The shell has a structural junction between the upper part  1  and the lower part  2 . This junction is positioned more or less on the edge of the inner protective layer. However, said junction may be located either slightly higher or slightly lower than the edge of the inner protective layer. Generally, the rigid inner protective layer more or less covers the parietal, frontal and upper occipital part of the neurocranium of the wearer, as these are critical areas to be protected.  FIG. 1  does not show this inner protective layer. This will be shown in the following figures. The section A-A implemented in the plane of symmetry of the helmet, shown in  FIG. 2 , describes the layers of the materials forming the protective shell. 
     Description of the First Embodiment of the Helmet: 
       FIG. 2  shows a first embodiment of the helmet according to the section A-A. The helmet is made up of an upper part  1  and a lower part  2 . The upper part  1  is implemented in a “sandwich” composite material. A “sandwich” composite material refers collectively to a material formed from two layers, also referred to as skins, which may be identical or different, closely connected via an intermediate substance also referred to as a core. The upper part  1  of the shell includes a first skin  12  and a second skin  13  disposed on either side of a core  11 . The lower part  2  is implemented in a composite material comprising the extension of the skins  12  and  13  towards the bottom part of the helmet. The extended parts of the two skins of the sandwich are directly connected for the purpose of forming a monolithic composite material. The term monolithic refers to a layer of material in general, or the layer of the shell in the present embodiment, comprising a plurality of folds associated with and joined directly to one another, with no intermediate core. 
     The helmet includes a rigid inner protective layer  3  serving as a shockproof protective layer. This layer is rounded in shape, disposed in the top part of the helmet. The upper part  1  is disposed opposite the inner protective layer  3 . The lower part  2  of the shell corresponds to the part which extends towards the bottom of the helmet and which is not opposite the inner protective layer  3 . This protective layer is generally covered with a foam layer  4  in contact with the head of the wearer to improve the comfort of the wearer. A non-rigid, supple foam  9  providing comfort and support for the head is fixed to the lower part of the protective shell. 
     This paragraph describes the constitution of the upper part  1  of the shell. The sandwich material includes the skin  12  and the skin  13  disposed on either side of the core  11 . The skins  12  and  13  comprise a plurality of layers (also referred to as folds), themselves including a plurality of stratified layers of composite carbon and aramid or polyethylene tissues. Thus, the skins  12  and  13  offer high performance in terms of elasticity and resistance to perforation. Other types of material can be used to form the folds in order to obtain similar or higher performances. The number of folds forming the skins  12  and  13  depends on the stresses imposed for the military applications of the helmet. On the upper part  1  of the helmet, the folds of the skins  12  and  13  comprise a plurality of pieces of crossed-fibre tissue  17  and  18 .  FIG. 2  shows an enlarged sample of the disposition of the pieces of tissues oriented in the longitudinal and transverse direction in relation to the plane of symmetry of the helmet (section view A-A). The two skins  12  and  13  are indirectly connected by the shockproof foam core  11 . The core  11  may be made from the same material as the inner shockproof foam  3  or from a material having more or less similar properties in terms of rigidity, deformation and shock-resistance performance. The formation of the sandwich composite material with a high-rigidity core and composite skins offering high performance in terms of suppleness and resistance to perforation allows a protective shell to be obtained which offers good performance in terms of both rigidity and perforation. This part of the shell offers the advantage of a high resistance to external stresses and notably to the stresses of deformation. 
     Consequently, the main advantage of this structure of the upper part  1  of the protective shell is the possibility of fixing to it the electronic image projection equipment  7 , a head tracking equipment in any place on this part of the shell and also the visor  6 . The high rigidity of this part of the shell allows high optical precision to be obtained and the same mechanical holding structure to be used for these three helmet equipments. In prior solutions, the different equipment is fixed onto separate mechanical structures which, when deformations of the shell occur, may present a shift in positioning, resulting in a degradation of the precision of the head-tracking calculations and the quality of the images displayed on the visor. To protect the electronic equipment, an additional protective shell  8  is positioned on the top. However, it is not necessary for this shell to have a high rigidity capability. 
     The upper part  1  of the protective shell includes means for fixing electronic and optical equipment, said fixing means being positioned between the two skins  12  and  13  of the upper part  1  of the protective shell and being fixed with the aid of a resin with a density and rigidity greater than the core  11  in order to transmit the stresses to the two skins  12  and  13 . According to the embodiment, these fixing means are tapped to receive fixing screws or comprise feet or bores for positioning the optical equipment requiring good precision. These fixing means are generally made of metal or a composite material. 
     This paragraph describes the constitution of the lower part  2  of the shell. The lower part  2  of the protective shell is made of a monolithic composite material. This material comprises a plurality of stratified layers of composite carbon-fibre and aramid-fibre, glass or polyethylene tissues. Other types of material with similar or higher performances may of course be used without, however, being excluded from the scope of the invention. This part of the shell is formed with the extension of at least one of the skins  12  and  13  beyond the core of the sandwich material of the upper part  1 . However, the lower part is preferably formed with the two skins  12  and  13  together which are directly bonded to one another through polymerisation. Thus, this part of the shell offers the same performances in terms of resistance to perforation as the upper part of the shell. However, the orientation of the fibres of the tissues of this part of the shell differs from that of the fibres of the tissues of the upper part. An enlargement of the fibres  21  and  22  is shown in  FIG. 2 . Fibres  21  are disposed in parallel and offset at an angle of around 45° in relation to a vertical axis  23  of the plane of symmetry of the helmet. Fibres  22  are also disposed in parallel, offset at an angle of around 45° in relation to the vertical axis  23  and perpendicular to the fibres  21 . This offset in the orientation of the fibres in relation to a vertical axis of the plane of symmetry of the helmet allows the suppleness of the composite to be increased. In fact, when the wearer dons the helmet, he removes the sides of the shell, perpendicular to the plane of symmetry, in particular to put on headphones. 
     The advantage of the structure of the lower part  2  is that it is less rigid than that of the upper part  1  of the shell. The suppleness in this area of the helmet improves comfort when the helmet is donned and offers reversible deformation capabilities which allow the working life of the shell to be increased. The lower part of the shell is thus subjected to stresses without transmitting them to the more rigid upper part. The helmet retention system is also fixed onto this lower part and is also the cause of deformations of the shell. For reasons of comfort and in order to increase the working life of the shell, it is advantageous for this area of the helmet to have suppleness capabilities. The same applies to the holding in place of the oxygen mask. This area of the helmet also integrates headphones  5  for which it is preferable for shell suppleness facilities to be provided for. 
     The junction area  24  between the upper part and the lower part of the shell is determined by the edge of the core of the sandwich material. The thickness of the core  11  preferably reduces progressively in the direction towards the lower part  2 . The edge  14  of the core is then wedge-shaped. This particular form offers the advantage of avoiding concentrations of stress and shearing between the core  11  and the skins  12  and  13 . The entire outer layer of the protective shell, comprising the skin  12  of the upper part  1  and the composite material layer of the lower part  2 , forms a single polymerised unit. The composite material layer of the lower part  2  is formed with the skin  12  and/or the skin  13 . In the case where it is formed with the two skins, the latter are then polymerised in the lower part  2 . 
     Description of the Second Embodiment of the Helmet: 
       FIG. 3  shows a version of the helmet integrating the head equipment between the two sandwich material skins. The protective shell comprises three parts: a lower part  60  designed in the same way as the lower part of the helmet according to the first embodiment, and an upper part including a front sub-part  70  and a rear sub-part  50 . The helmet includes an inner protective layer  54  and a comfort foam  55  fixed onto the inner surface of the protective layer  54 . 
     The design of the lower part  60  is similar to that of the helmet described in the first embodiment. This part comprises a monolithic composite material whose fibres  63  and  62  of the composite tissue layers are oriented at around 45° in relation to a vertical axis in the plane of symmetry of the helmet. The lower part also has low rigidity properties. 
     The rear upper sub-part  50  comprises a sandwich composite material similar to that described in the first embodiment. This material includes a shockproof foam core  51  and two skins  52  and  53  comprising a plurality of composite tissue layers. The fibres  57  and  58  of the tissues are oriented in the longitudinal and transverse direction of the plane of symmetry of the helmet. 
     The front sub-part  70  of the helmet corresponds to the front upper part of the helmet onto which the head equipment, the display device  74 , the collimation device  76  and  77  and the visor  75  are fixed. This front sub-part is implemented in a sandwich composite material of the same type as that of the rear sub-part, this material including a skin  72  and a skin  73  disposed on either side of a core  71 . It therefore offers the same rigidity performances allowing the head equipment to be fixed directly onto the protective shell, the shell structure rigidity being sufficient to dispense with a dedicated mechanical structure. The image projection equipment  74  is inserted between the two skins  72  and  73 . Thus, it is not necessary to use a second shell to protect the electronic equipment. In this display device fixing variant, the thickness of the core  71  is greater than that of the core  51  of the rear sub-part. The area between the two skins  72  and  73  integrates the fixing parts of the visor, the collimation optical system  76  and  77  and the sensor or LEDs of the HTS function. The geometry of the inner and outer skins and the thickness of the core can be adapted according to the overall size of the optical elements and the HTS function inserted between the skins in such a way as to obtain smooth surfaces, in particular for an even distribution of the stresses on the inside of the helmet caused by an impact, and to avoid the risks of snagging with the cockpit on the outside. 
     It is in fact necessary for the surface of the protective shell in contact with the absorbent foam to be as smooth as possible in order to reduce the penetration of the shell into the absorbent foam (an angular-shaped shell will more easily penetrate the absorbent foam and will risk coming into contact with the head, subjecting the head to significant stress). 
     The density of the foam constituting the core can also be adapted according to its thickness. The greater the thickness, the lower the density of the absorbent foam and the lower the stress transmitted to the head in the event of an impact. 
     In this embodiment, the electronic equipment fixing means are fixed onto one of the skins  72  or  73  of the upper part of the shell to mount the equipment. 
     Description of a Third Embodiment of the Helmet: 
       FIG. 4  shows a modular version of the protective shell. The front sub-part  70  and the rear sub-part  50  are designed from the same materials as those of the upper part of the protective shell of the second embodiment. The head equipment is also inserted between the two sandwich material skins comprising the protective shell. Unlike the second embodiment of the helmet described above, the front sub-part  70  of the helmet may be separated from the rear sub-part  50 . The rear sub-part  50  is connected to the lower part  60  of the protective shell. The composite materials of the lower part  60  comprise the same materials as those of the skins of the material of the rear sub-part  50 , differing only in terms of the orientation of the tissue fibres which constitute these materials. Fixing elements  81 ,  82 ,  83  and  84  are mounted on the upper part of the protective shell. They allow the front sub-part  70  and the rear sub-part  50  to be joined and separated. The visor-fixing inserts are also mounted on the immovable front sub-part  70 . The advantage of this modular version of the shell is that a standard part of the helmet, comprising the rear sub-part and the lower part of the shell, can be implemented, and the front part of the helmet carrying the head equipment can easily be modified or replaced. 
     The invention is intended particularly for aircraft pilots&#39; helmets. However, it also applies to any protective helmet on which head equipment is or is not mounted, for example helmets in the automotive field.