DE19856162A1 - Energy absorbing plastic structural member for energy absorbing components in vehicles has structural members in absorption direction and made of liquid crystal polymer - Google Patents

Abstract

The energy absorber has adjacent structural elements extending in the direction of expected loading and made of either a thermotropic liquid crystal polymer (LCP) or a mixture of two or more of these materials. Structural element wall thickness is not less than 1mm. Independent claims are included for: (a) the energy absorbing component (1) which deforms under a given loading when absorbing energy and includes the claimed structural members; (b) an injection molding process for the energy absorbing structural member; and (c) use of the energy absorbing component for cushioning in vehicles.

Description

The invention relates to an energy-absorbing structural element according to the preamble of claim 1, an energy absorbing Component according to the preamble of claim 11 and a method for the production of the structural element or the component according to Preamble of claim 13.

Are energy absorbing components or energy absorbers for short known in principle. These are components that pass through their geometry and dimensions are designed so that they at a given load, e.g. B. in the event of an impact, deform with absorption of energy. they consist of energy-absorbing structural elements used in stress Direction essentially arranged side by side are. Conventional energy absorbers and their structural elements consist mainly of aluminum or steel or foams or Elastomers and fiber composites. There are also honeycombs structures known as "honeycombs".

Energy absorber with honeycomb structures made of resin soaked Cardboards are known from publication WO-A-9525646. On Protective pad with a deformable honeycomb core made of polyurethane foam, urea resin foam or paper impregnated with synthetic resin  honeycomb is known from DE-AS 12 31 586. A foam Upholstered body with one foamed into a foam mass Honeycomb grate made of cardboard soaked in plastic for the accident Protective interior of vehicles is from DE-AS 13 00 040 known.

Press-molded energy absorbers made of thermoplastic resins or thermoplastic or thermosetting elastomers for automotive Bumpers are known from DE 25 09 265 C2. US 5,098,124 describes absorbers with gas-filled spring-loaded cells.

From DE 41 15 456 A1 an injection molding process is also known Production of microcellular, elastic molded articles from Po known polyurethane foam.

All known non-metallic energy absorbers, which are made of struc door elements are composed of cardboard tigt or foamed from plastics or press-formed. Disadvantageous the fact is that with these processes no filigree cavity Structures or no energy absorbers with complicated external ones Geometries can be produced. For the manufacture of such construction Parts are in and of themselves the injection molding process. Thermoplastic plastics that ver in the injection molding process Let work, but are too tough for this application. Your Flow properties are sufficient to produce the desired ones here complicated geometries are not made from wall thicknesses below 1 mm not feasible, which leads to large block lengths and thus to rela tiv low use of such elements leads. Indeed who which they have only occasionally used in the area of automotive bumpers  puts. Especially in the vehicle interior, where energy absorbers such. B. in Head impact area itself is urgently needed the very limited installation space makes their use.

Honeycomb structures can only be produced economically in blocks. However, there are only a few in particular in a motor vehicle set options for such cuboid elements.

The well-known fiber composite materials, which are very good in themselves Have crash properties and a high energy consumption difficult to find components for complex load requirements to process. In addition, there is no cheap and reliable Process for processing these materials with dishes or oriented fibers for those for large series production typical high quantities.

The invention is therefore based on the disclosure, an energy absorber beier structural element or a composed of it to provide a gieabsorbing component that is as high as possible he specific energy consumption and also with complex External geometry are inexpensive to manufacture. Task of the Erfin is also a method of making such a structure elements and components.

The solution to the problem is an energy-absorbing one Structural element with the features of claim 1, an energy absorbent component with the features of claim 11 and / or a method for their production with the features of claim 13.  

Liquid crystalline polymers or LCPs contain rigid molecules segments, the so-called mesogens, which are in the liquid state, i.e. H. in solution or in the melt, string together and parallel align with each other. This creates a state of order that between the perfect order in the crystal and the total Un order lies in ordinary liquids and therefore as "liquid crystalline" or "mesomorph" is referred to.

A distinction is made between main chain and side chain LCP. At the main chain LCP are the rigid mesogens in the Po lymer chain. In the side chain LCP, the mesogens are over one Connection structure attached to the polymer.

The thermotropic LCP are for processing in the injection molding process suitable which has a liquid crystalline order in the melt demonstrate.

The structural elements and components according to the invention have the Advantage that they have finer structures, e.g. B. thinner wall thicknesses and / or smaller light spaces, as such from conventional chen plastics. This is because the fluidity and the pseudoplastic behavior of liquid crystalline polymers Manufacture of such delicate structures by injection molding allow. The structural elements and Components have a lower component weight than those made from conventional chen plastics with improved functionality. With egg reduced material usage and a short block length (e.g. 10%) is the most useful for energy consumption  re deformation path larger. A high energy consumption (40 kJ / kg and more) can be realized.

The method according to the invention is simple and inexpensive. It uses known substances, namely liquid crystalline polymers back, the one for the production of filigree structures in the Injection molding process suitable flow behavior and pseudoplastic show this behavior. The inventive method makes itself furthermore take advantage of the phenomenon that the special morphology of this Compound class leads to the molecules of this ver bond class automatically in a certain orientation judge. This is particularly pronounced in the longitudinal direction of the tub the individual structural elements. Since this is in the body shop is generally the direction of stress at the same time, he this gives a high degree of rigidity in this direction structural elements according to the invention. Because of this self-amplification kung is already at the beginning of a deformation or an opening bounces a higher level of force, i.e. a higher specific Energy absorption than in the case of structural elements and components conventional plastics. It also results from this compared to structural elements and components from conventional ones Plastics a steeper increase in the force / deformation curve, or the absorption characteristic for sudden loads.

About these effects, especially the directional force veau, to make the most of it, a broad orientation of the Structural elements in the direction of force can be guaranteed. This is with the injection molding process using suitable mold design Sliders, core pulls, etc. possible.  

Due to the individual design of the structural elements set the desired orientation of the molecules. The brittle Speed or toughness is easy due to the choice of materials adjustable. The rework, e.g. B. Trigge processing for defining a force application point on the structure element can be omitted. The method according to the invention offers a very high design freedom and the execution of filigra NEN energy absorbers, e.g. B. for the interior of motor vehicles.

According to the invention, the component according to the invention is used le when padding the inside of the A-, B- and / or C- Pillars, the rearview mirror, the dashboard, the airbagver clothing, the inner door panels (side impact protection), the roof frame, as impact protection for knees and feet and / or for the upper, middle and lower seat impact areas in the In Interior of a motor vehicle preferred.

Advantageous further developments result from the dependent claims chen. In particular, there are particularly small wall thicknesses or through knife realizable, the size and weight of the structural elements and reduce components and use them in tight spaces make suitable. The fine structures allow a better out Direction of the mesogens in the melt and thus a larger one Degree of self-amplification with the effects described above.

Main chain LCP are preferably used, especially those which contain reinforcing fibers such as glass fibers as fillers. This creates an additional reinforcing effect.  

With regard to the geometry of the structural elements according to the invention there is a wide selection of hollow bodies with different shapes cross sections, but also waveforms and trapezoidal shapes suitable. The selection depends on the type of application you require turn away.

The following is an embodiment of the present invention described in more detail.

As liquid crystalline polymers (LCP) to be processed thermotropic main chain LCP selected. These are thermoplastic processable and show ordered liquid crystalline structures in the melt. Will the liquid crystalline polymer melt Subject to shear and stretching currents, as is the case with all processes ren for thermoplastic processing is the order the rigid molecules or parts of molecules to form fibers and Fibrils. This order becomes when the polymer melt cools down frozen. Fiber layers are then in the matrix of the polymer embedded from the same polymer. Therefore they are called Polymers also as "self-reinforcing" polymers. What fiber structure adjusts in this way depends on the geometry of the component, in particular the wall thickness, the flow shape and the flow history, is therefore by parameters of the process processing method, in particular by determining the flow channels and gate layers, controllable.

This orientation of the polymer molecules leads to being liquid crystalline polymers show pronounced anisotropic properties.  

In general, the mechanical property values are strongly directional dependent. E.g. are strength and stiffness in orientation direction much higher than across. The thermal expansion and the shrinkage are perpendicular to the orientation direction is sometimes much higher than parallel to it. The Anisotropy can be reduced with fillers. With that stands in addition to the chemical modification of the polymers, a second possibility Possibility to modify the material properties supply. In this way, the poly has a wide range of modifications properties possible.

For the present invention, it is particularly advantageous that the liquid crystalline polymers have a very high elasticity modulus as well as a very high tensile strength and rigidity in flow have direction. In the flow direction they also show a very high toughness, especially notched impact strength. Take the values even increase with decreasing wall thickness. This is because the Molecules are more oriented in thin walls. Based on this the miniaturization of the energy absorbers or Reduction of the wall thickness of the hollow structural elements.

Furthermore, liquid crystalline polymers have very small thermi cal expansion coefficients that can be adjusted so that ver with those of metals, glasses or ceramics are comparable. In addition, they show a low swine dung, a small heat of fusion, d. H. high solidification speed speed, low flow viscosity of the melt, low water uptake high chemical resistance and very low ignition availability even without flame retardant additives.  

Main chain LCPs have melt temperatures from 300 ° C to 400 ° C. The absorbers according to the invention therefore withstand temperatures over 200 ° C without stressing the material.

Liquid crystalline polymers can be made with the usual tools and machines processed and separated according to the known methods or be added. They are with the usual ones for polyester Adhesives can be glued and can be ultrasonically welded. she can also be galvanized or metallized by spraying the.

All of these properties are for the preferred application of the Invention advantageous in motor vehicles.

For the exemplary embodiment, the main chain LCP from Hoechst of the type Vectra with the type designations B 130, K 130, L 130 and E 130i selected. All of these types have a glass fa water content of 30%. Glass fibers are among the fillers that the pronounced anisotropy of the properties described above mitigate liquid crystalline polymers.

As the geometry of the energy-absorbing elements according to the invention a conical tube was chosen. The diameter at the tapered The end was 5 mm. The length was once 100 mm and once 45 mm. The total angle was 3 ° to 6 °. On the side with the small diameter, the force should be applied. On the Triggering could therefore be dispensed with because of the load-bearing Cross section increased with the path of destruction.  

The structural elements according to the invention were sprayed casting machine of the type Arburg 270 M Allrounder 350-90. It is a fully hydraulic programmable Machine with a screw length of 600 mm, a screw diameter of 25 mm, a nozzle diameter of 2 mm and a Injection pressure at the nozzle up to 1860 bar.

The liquid crystalline polymers were initially in the form of granules. The granules were dried in a drying oven at 160 ° C. for 4 to 5 hours dries.

The plasticizing unit on the injection molding machine was processing temperature typical for liquid crystalline polymers be preheated from 300 ° C to 350 ° C. The wall temperature of the Tool was at 50 ° C to 180 ° C, preferably 80 ° C to 120 ° C set.

During injection molding, the screw speed was set so that complete plasticization of the mass 1 to 2 seconds before opening of the tool. Common values were at 10 to 20 m / min. There was a dynamic pressure when plasticizing generally not necessary. A snail decompression was if necessary, kept to a minimum.

The injection pressure was generally 300 to 900 bar, preferably wise 600 to 800 bar, starting with lower values en and the pressure was gradually increased. The optimal spritz However, pressure in individual cases depends on the respective LCP type and on  the design of the molded part, the tool and the machine parts conditions.

The liquid crystalline polymers were injected with high speeds from 60 to over 100 ccm / min. preferably 80 to 90 ccm / min and thus short injection times processed.

Structural elements according to the invention with the wall thicknesses were obtained 0.6 mm and 0.425 mm. These elements were on a testing machine of type Zwick 1456 under quasi static conditions on groove degree of compression, compression length, absorbed energy, crashed mass and specific energy consumption at a certain load (Crash load) examined, with continuous destruction before the side with the smaller diameter. To do that Force-displacement diagrams added. This became the specific one Energy consumption calculated. The results are in Table 1 for a 45 mm long cone with 0.6 mm wall thickness and in Table 2 for an equally long cone with a wall thickness of 0.425 mm poses.  

Table 1

Energy absorption of the energy absorption elements with a length of 45 mm and a wall thickness of 0.6 mm

Table 2

Energy absorption of the energy absorption elements with a length of 45 mm and a wall thickness of 0.425 mm

In general, the energy absorption elements resulted from the Material Vectra E 130i the best results because of this particular which is flowable. This material is characterized by a ge wrestle brittleness and high toughness.

In the elements according to the invention, the energy was reduced by Fal bumps as well as broken material of various sizes taken. The specific energy consumption was between 25 and 40 kJ / kg. These values are above the values of metallic ones Elements and extend to the level of fiber composite material close up.

The geometry of the energy absorption elements is limited not on the manufactured and tested in the embodiment conical tube. Other shapes, such as cylinder, wave, trapezoid or zigzag shapes as well as other cross sections of the tubes such as Triangles, squares, cuboids, trapezoids, rhombuses, hexagons and the like. the like are feasible.

The fields of application of the elements according to the invention in motor vehicles The area is preferably where complex structures at ge limited space should be realized. These are in it line of the ABC pillar, rear-view mirror, interior door covering areas (side impact protection), airbag cover, knee and footrest impact protection, dashboard and seat impact areas above, in the middle and bottom.

In the following description, some preferred out management examples described. The drawings show:  

Fig. 1 a crash absorber with cylindrical elements;

FIG. 2 is a crash box;

FIG. 3 shows an energy absorber with shaft structure;

FIG. 4 shows an energy absorber according to FIG. 3 with supporting webs between the shafts;

FIG. 5 shows an energy absorber with a honeycomb structure; and

Fig. 6 shows an energy absorber with a double-sided conical hollow structure.

In Fig. 1 a first embodiment of a total designated crash absorber is illustrated. This crash absorber 1 has a base plate 2 , on which a plurality of cylindrical elements 3 are arranged. The elements 3 are made neither as separate elements 3 and are then with the base plate 2 , z. B. connected by gluing, welding or the like, or they are made together with the bottom plate 2 in one piece. The wall thickness of the hollow elements 3 is 0.3 mm to 1 mm and their diameter is 5 mm to 20 mm. The arrangement of the elements 3 on the base plate 2 is regular in both the longitudinal and transverse directions. However, they can also be staggered, ie arranged on a gap. The elements 3 all have the same length.

FIG. 2 shows an exemplary embodiment of a crash box 4 in which two crash absorbers 1 according to FIG. 1 are inserted one into the other in the direction of arrow 5 . The open sides of the crash absorber 1 interlock. The elements 3 of one crash absorber 1 lie in the gaps 6 of the other crash absorber 1 . In this way, the elements 3 support each other in a crash ge.

In the exemplary embodiment in FIG. 3, the elements 3 have a wave shape, the waves 7 running parallel to one another. The axial directions of the wave crests or valleys run orthogonal to the level of the base plate 2 . In the embodiment of FIG. 4, the shafts 7 are connected to one another via support webs 10 . In this way the rigidity is increased transversely to the axial direction. The support webs 10 are all arranged in mutually parallel planes, which in turn gives the component an orientation.

In the exemplary embodiment in FIG. 5, the elements 3 have a honeycomb shape, the honeycomb 11 lying against one another with their walls 12 . This has the advantage that, due to the small wall thickness of the walls 12, very high orientations are achieved.

Finally, FIG. 6 shows an energy absorber 1 with a hollow structure, the cavities 13 and 14 having an elongated shape and being conical. The cavities 13 and 14 are nested in such a way that they always lie on a gap. This is possible because the cone of the cavities 13 runs in the opposite direction to the cone of the cavities 14 . This absorber 1 also has small wall thicknesses.

Claims (23)

1. Energy-absorbing structural element made of plastic, in particular for an energy-absorbing component, in particular for motor vehicles, the structural elements in the energy-absorbing component being arranged side by side in the direction of stress in a substantially area-wide manner, characterized in that the structural element consists of a material which is essentially a Contains thermotropic liquid crystalline polymer (LCP) or a mixture of two or more thermotropic liquid crystalline polymers (LCP), where the wall thickness of the structural element is less than 1 mm. 2. Structural element according to claim 1, characterized in that it consists of a material that is essentially one or contains several thermotropic main chain LCP. 3. Structural element according to one of the preceding claims, since characterized in that the one or more LCP Contain fillers. 4. Structural element according to claim 3, characterized in that the LCP or the filler reinforcing fibers, in particular contain glass fibers.   5. Structural element according to one of the preceding claims, since characterized in that it is a hollow body delt whose diameter is less than 5 mm. 6. Structural element according to one of the preceding claims, since characterized in that the wall thickness of the structural element less than 0.5 mm and / or the diameter of the hollow structure is less than 3 mm. 7. Structural element according to one of the preceding claims, since characterized in that it is in the form of honeycombs, cells or Tubes or as a wave, zigzag or trapezoidal course is formed. 8. Structural element according to claim 7, characterized in that it is a tube with a round cross-section, square, cuboid, trapezoidal, diamond shaped or is hexagonal. 9. Structural element according to claim 8, characterized in that it is a conical tube. 10. Structural element according to one of the preceding claims, since characterized in that it produces by injection molding is cash. 11. Energy absorbing component, which is in a pre given load with absorption of energy defined ver  forms, the energy absorbing component with itself in Be Structural elements extending direction of stress which is essentially areas within the component are arranged side by side, characterized net that it consists of structural elements according to one of claims 1 until 10 is composed. 12. The component according to claim 11, characterized in that it Injection molding process can be produced. 13. Process for producing an energy absorbing structure turelements according to one of claims 1 to 10 and one ener Gi-absorbing component according to one of claims 11 to 12, characterized in that it is an Spritzgußver driving is using a material that is used in essentially a thermotropic liquid crystalline polymer (LCP) or a mixture of two or more thermotropic contains liquid crystalline polymers (LCP). 14. The method according to claim 13, characterized in that a or more main chain LCP can be used. 15. The method according to any one of claims 13 or 14, characterized ge indicates that LCP with one or more fillers be used. 16. The method according to claim 15, characterized in that as Use filler reinforcing fibers, especially glass fibers be det.   17. The method according to any one of claims 13 to 16, characterized records that the liquid crystalline polymers before Injection molding at least about 4 hours at about 160 ° C be dried. 18. The method according to any one of claims 13 to 17, characterized records that the liquid crystalline polymers at a tem temperature of about 300 to 350 ° C are melted. 19. The method according to any one of claims 13 to 18, characterized records that the casting tool to a wall temperature of about 50 to 180 ° C, preferably about 80 to 120 ° C preheated becomes. 20. The method according to any one of claims 13 to 19, characterized records that the screw speed to about 10 to 20 m / min. is preferably set to about 15 m / min. 21. The method according to any one of claims 13 to 20, characterized records that the spray pressure to about 300 to 900 bar preferably about 600 to 800 bar. 22. The method according to any one of claims 13 to 21, characterized records that the injection speed to about 60 to over 100 ccm / min. preferably about 80 to 90 cc / min. turned on is posed.   23. Use of an energy absorbing component after a of claims 11 to 12 or one by a method according to one of claims 13 to 16 producible energy absorption component for cushioning the inside of the A-, B and / or C pillars, the rearview mirror, the dashboard, the airbag trim, the inner door trim (Side impact protection), the roof frame, as impact protection for knees and feet and / or for the upper, middle or un teren seat impact areas in the interior of a motor vehicle.