Self-Supporting Car Body Part
The present invention relates to a self-supporting car body part, and in particular to a shock and sound absorbent motor bonnet according to the preamble of Claim 1 , as well as to a suitable substructure for the manufacture of such a car body part
Motor bonnets such as are used in the field of motor vehicle manufacture essentially have a covering made of a thin metal sheet or a synthetic material and are stiffened with struts or similar structures In addition, modern motor vehicles are provided with acoustically effective linings in order to reduce the engine noises emitted towards the exterior
Such linings are well known in the art and are described, for example, in EP 0,352,993 The assembly disclosed in this publication concerns an acoustically effective part such as is used in the aeroplane industry In particular, this part comprises a core layer with a honeycomb structure, whose individual cavities communicate acoustically with each other via drainage openings This core layer is bounded on the one side by a perforated or open-celled cover layer in order to be acoustically effective This assembly is not suited in any way for shock absorbing functions
An analogue acoustically effective assembly is disclosed in FR-2,727, 189 This assembly also comprises a core layer having a honeycomb structure which can be filled with an open-celled foam, and which is provided on both sides with outer cover layers made of an open-celled synthetic foam This assembly is used for sound insulation in buildings and does not exhibit any particular shock absorbent properties
Analogue assemblies for use in any passenger vehicles are also known, for example, from DE-U- 296,07,262 The element disclosed in this publication is used as a roof liner in motor vehicles This element comprises a honeycomb layer as a core layer and on both sides of this core layer comprises a cover layer made of fibrous material These cover layers are melted onto the honeycomb layer and, due to the material bonding, result in an increased stiffness of the entire element This arrangement provides stability, provides an enhanced tensile strength but does not have any particular acoustic or shock absorbing properties
It is the aim of the modern motor vehicle industry to produce vehicle parts which comprise different physical properties in the same assembly, in order to be able to reduce the large number of different components having different technical functions and to reduce the weight Thus, for example, CH-692,731 discloses an ultralight package for use in vehicles, which
combines shock and sound absorbing properties This package is suitable for protecting passengers and is preferably used in the crash sensitive part of the foot space This package does not have any particularly stiffening properties and is only laid into the existing vehicle space
As a rule, known assemblies show either stiffening or acoustic or shock absorbing properties and are inserted additionally into the vehicles None of these elements combine the mentioned properties in a useful and desired manner
It is therefore the aim of the present invention to provide an acoustically effective substructure for the manufacture of a self-supporting car body part and in particular to provide a motor bonnet which leads to enhanced stiffening properties as well as to enhanced acoustic and shock absorbing properties of the motor bonnet manufactured with this substructure), in order to provide a car body part (in particular a motor bonnet) which does not require stiffening struts and headings which can lead to serious injuries, and in particular head injuries, in the case of crashes with other road users (pedestrians or animals)
This problem is solved by a self-supporting vehicle body part, and in particular by a motor bonnet, having the features of Claim 1 , as well as by a substructure for the manufacture of such a vehicle body part, comprising the features of Claim 5
The vehicle body part according to the invention comprises a substructure and an outer skin, whereby said substructure comprises a core layer, preferably a honeycomb-like core layer This core layer, on the noise emission side, comprises an open-celled first cover layer and a second cover layer on the outer skin side This substructure is attached to the outer skin by means of suitable attachment means According to the invention, the HPC-value of the entire self- supporting vehicle body part is less than 1000, and the air flow resistance of the cover layer on the noise emission side is between 200 and S000 Ns/m3
Said HPC-value is defined as follows
where.
a the resultant acceleration is a multiple of "g" t1 and t2 the two time instants (in seconds) during the impact, defining the beginning and the end of the recording for which the value of HPC is a maximum
Therefore, in order to determine the HPC-value, the accelerations in the x-, y- and z-directions are measured for the center of gravity of the pedestrian's head and the resultant acceleration is calculated The HPC-value can be determined based on the above formula, i e by integrating the resulting acceleration over time The HPC-value is a dimension-free value
Further embodiments of this vehicle body part and the corresponding substructure are within the normal expertise of the man skilled in the art
It is understood that the inventive car body part can be designed as a self-supporting motor bonnet, as a self-supporting trunk lid or as a self-supporting vehicle roof, and can be applied to any type of vehicle for road or rail transport
The invention is described in more detail by means of an exemplary embodiment and with the aid of the Figures
Fig 1 shows a schematic view of a vehicle body part according to the invention,
Fig 2 shows a schematic view of a vehicle body part according to the invention having local fixation means,
Fig 3 shows a schematic view of a vehicle body part according to the invention having additional shock absorbent elements, and
Fig 4 shows comparative measurement curves for the time-dependent progression of impact delay
Fig 5 shows a schematic view of a vehicle body part according to the invention comprising a substructure with locally arranged omega-shaped deformations, and
Fig 6 shows a schematic view of a vehicle body part as shown in Fig 5 comprising a substructure having locally compressed areas
The assembly according to the invention is schematically shown in Figure 1 This Figure shows a self-supporting vehicle body part 1 with a honeycomb-like core layer 2, which comprises an open-celled covering layer 3 on the engine compartment side and a covering layer 4 on the outer skin side, said covering layer 4 on the outer skin side being bonded to an outer skin 6 by means of a bonding or adhesive agent The assembly comprising the honeycomb-like core layer 2 and both covering layers 3, 4 is hereinafter called the substructure 7 The core layer 2 is preferably made of cardboard, aluminium, Nomex® or other deformable materials, in particular made of plastic materials such as PA, polyester, PL) It is evident that other suitable materials be used, such as recycled or corrugated cardboard or TS-foam (PU- or polyamide-based foam) or TP-foam (EPP, Notyl® EEF or similar) or metallic foams The two covering layers 3, 4 are preferably made of a fibrous material, in particular of a composite of several fibre types such as mineral fibres (glass fibres, ceramic fibres), natural fibres (for example cotton, jute, sisal, linen, hemp), animal fibres (wool etc ) metallic and/or synthetic or chemical fibres having a high melting resistance In a specific embodiment the honeycomb-like structure is made of aluminium and is glued to a metal-containing layer As a rule, the outer skin 6 comprises a steel or aluminium sheet The individual layers can be joined to each other either by means of fπctional connection (mechanically) and/or material connection (soldered, glued) The assembly according to the invention is dimensioned such that the desired shock absorbing requirements are fulfilled Particular attention is paid to the bending stiffness of the entire vehicle body part, i e the outer skin 6 and the substructures 7, in that thickness and choice of material of the outer skin 6 as well as thickness and composition of the substructure 7 are jointly taken into account Preferred values for the thickness of the core layer 2 are 20 ± 10 mm The diameter of the individual cells of this core layer 2 are in the range of between 5mm to 25 mm, and the compression resistance is in the range of between 100 KPa and 1000 KPa The outer skin 6 of the vehicle body part 1 can be made of a known phenolic material It goes without saying that glass fibres, basalt fibres and other fibrous materials (also thermoplastic polymers) can be used The area weight of this outer skin is in the range of between 500 g/m2 to 1500 g/m2 The bond between the substructure 7 and the outer skin 6 can be achieved by means of a sticky film weighing less than 150 g/m2, or by means of a thermoplastic film which begins to melt when the substructure 7 is polymerized Of course, other classic adhesives such as epoxy resins, melamines, urethanes, acrylics or urea formaldehyde condensates can be used, or the joining of the outer skin 6 with the substructure 7 can be achieved by a suitable final forming step It is understood that the substructure can be fixed to the metallic outer skin 6 by clips or line bonding or full surface bonding or a combination of line bonding and mechanical fixation, or by embedding under- support brackets and clips Furthermore, the substructure 7 can incorporate local fixation points
made of SMC or thermosettings or metallic reinforcements in order to fix hinges or hooks or to improve or to vary the stiffness of the substructure
The required stiffness of the inventive self-supporting vehicle body part 1 is essentially defined by the stiffening effect of the substructure 7 The expert will compile a suitable choice of designs, materials, thickness and stiffness of the individual layers In particular, the expert will consider to choose a suitable thickness, cell size, compression resistance or material for the honeycomb-like layer, whilst taking into consideration the nature of material, the surface weight, the bonding strength of the skin
The acoustic efficacy of the inventive vehicle body part 1 is essentially defined by the acoustic properties of the substructure 7 In particular, the open celled cover layer 3 has an air flow resistance of between 200 to 5000 Ns/m3
It is to be understood that in order to improve the absorptive capacity of kinetic energy during a possible impact situation, the substructure 7 can - at least locally - be provided with further honeycomb-like or foam layers 8 and additional fibrous layers 9, as is seen in Figure 3
It is within the scope of the expert to provide the vehicle body part 1 with further elements, and in particular with additional elements 1 1 for attaching hinges or other closure elements, as shown schematically in Figure 2 Furthermore, in predetermined regions the vehicle body part 1 can be provided with a thermal protection, in particular with an aluminium foil The use of metallic fibres, a conductive film or a metallic grid can provide a protection against electromagnetic waves (EMC protection)
Figure 4 shows measurement curves of the time-dependent progression of the impact delay for several different arrangements The critical HPC (head performance criteria) value is measured for the head of a child's body, the head weighing 3 5 kg (or for the head of an adult's body, the head weighing 4 8 kg), and at an impact velocity of 35 km/hr This value should be less than one thousand (HPC<1000) in order to meet the guidelines for shock absorption of the European automobile industry
Figure 5 shows a schematic view of a vehicle body part according to the invention comprising a substructure with a locally arranged omega-shaped deformation This design is useful to increase the stiffness of the entire vehicle body part The geometry of such a shaped substructure is adjusted such that the HPC-value remains below 1000 A local padding or local substructures 8 can be added
Figure 6 shows the vehicle body part as shown in Figure 5, comprising locally compressed areas 12, 13, which allows to vary the stiffness of the substructure In particular this further allows to decrease the first peak of the dynamic force deflection It is understood that the claimed substructure can be covered at least locally with an aluminium film to assure a good thermal resistance
In a preferred embodiment this substructure is covered by a nonwoven fabric or a foil, which can be removed after painting, if this vehicle body part is assembled before painting The expert will take into consideration to design the substructure comprising structural folds or to provide this substructure with fire-resistant, chemical-resistant and humidity-resistant additives
It is understood that the structure according to the invention can be designed and dimensioned in such a manner that future norms for the protection of pedestrians according to ACEA and/or EEC WG17 can be met, or that equivalent rules in other countries (USA, Japan etc ) are met The current rules concern only a crash on to a windscreen and are not mandatory or are merely facultatively applicable to motor bonnets It is understood that this vehicle body part can be designed as a headlmer which fulfils the FMVSS 201 regulations
The advantages of the inventive vehicle body part are immediately evident to the expert In particular the advantage is to be seen in the creation of a vehicle body part having sufficient stiffness to form a self-supporting vehicle body part, i e structural parts, and also having the required HPC values, whilst being acoustically efficient
Furthermore the present invention allows a more compact vehicle construction, in that the vehicle body part can be arranged closer to the engine block or to another rigid element (aggregate, battery, or similar) This is ensured, in particular, by an increased energy absorption caused by a deformation of the entire self-supporting vehicle body part, as well as by the progressive compression behaviour of the substructure In this way, the spacing between the engine block or any other rigid vehicle element can be reduced by 25% without exceeding the prescribed HPC-value (or HIC-value, i e head injury criteπum)