Hybrid side skirts for a motor vehicle and manufacturing method thereof

Abstract

Hybrid side skirts (102) for a motor vehicle, comprising: a pultruded profile part (100) comprising a continuous fiber-reinforced thermoplastic polymer (512) with a heat distortion temperature of at least 200 °C; and a connecting part (104) attached to an end portion (110) of the pultruded profile part (100), which comprises steel; and at least one metal bracket (106) which is fastened to the pultruded profile part (100) and within a convex profile section (111) of the pultruded profile part (100); and at least one crash body (114) fastened to the pultruded profile part (100), which crash body comprises steel and / or a thermoplastic polymer, wherein the pultruded profile part (100) is fastened to an Ω-profile steel beam (710), and wherein the crash body (114) is bonded to a hollow profile section (706) and an outer wall (103) of the convex profile section (111) in such a way that it extends from the outer wall (103) of the pultruded profile part (100) to an opposite inner wall (713) of the Q-profile steel beam (710) in such a way that a gap (714) remains.

Description

Prior ArtThe present invention relates to a hybrid side sill for a motor vehicle, and more particularly to a hybrid side sill having a resin portion and a metal portion. In further aspects, the present invention relates to a motor vehicle body having a hybrid side sill and a method for manufacturing a hybrid side sill.Typically, the two side sections of a motor vehicle body comprise a roof edge in the upper region of the motor vehicle body, a side sill in the lower region of the motor vehicle body, and columns which connect the roof edge and the side sill in order to form a framework for the passenger compartment. The side sills thus contribute to the cabin framework and determine the rigidity of the motor vehicle body both during normal use and in an accident with frontal impact, oblique impact or side impact, in which the side sill is generally subjected to an overload. For example, when another vehicle collides with its side, deformation of the cabin framework of a motor vehicle must be limited to a minimum, whereby the reinforcement of the side sill plays a decisive role.In motor vehicles manufactured at present, side sills are typically made of steel and are equipped with additional parts such as crash boxes for absorbing impact energy. Steel, while having the required strength and rigidity, is also heavy, thereby contributing significantly to the overall weight of the motor vehicle. To reduce weight, some cars recently sold include side sills made of carbon fiber reinforced plastics such as epoxy and vinyl ester. However, due to the different physical properties of these materials as compared to steel, existing automobile body production lines cannot be used or must be modified in a complex manner.For example, while in conventional manufacturing methods a motor vehicle body with side sills made of steel is first assembled to form a so-called green body, which subsequently undergoes painting and firing at a temperature of about 190° C., side sills comprising epoxy or vinyl esters, which are stable only up to a temperature of about 120° C., can be mounted on the motor vehicle body only in a separate mounting process after completion of the firing and, in addition, require a separate painting process using a non-fired paint of generally lower durability.DE 10 2012 024 836 A1 discloses an in side part for a motor vehicle body having an outer side part which faces an exterior of the vehicle, an inner side part which is fastened to the outer side part and faces an interior of the vehicle and having a foam as filler, and a corresponding method for producing such a side part. The outer side part is designed as a ductile component and the inner side part is at least partially filled with foam.DE 10 2005 043 698 A1 discloses a side sill of a motor vehicle body having a box profile which is composed of at least two partial shells and is reinforced in the region of the passenger compartment by a structural part, wherein the structural part is fixedly connected to the box profile. The structural part comprises a fiber-reinforced plastic part which is supported at least on one of the partial shells of the box profile.DE 10 2013 214 787 A1 describes a profile strip of a vehicle body, wherein the profile strip is designed with at least one shell component made of fiber-reinforced plastic and at least one pultrusion component.In addition, JP 2008-045 736 A also discloses a plastic element provided with a resin body part. The resin member is characterized in that a buffer part for distributing an external input load is provided on the side on which an external input load acts, and a reinforcing member capable of plastic deformation and fixed to the body part is provided on the side opposite to the side on which the external input load of the buffer part acts.There is thus a need to provide a side sill which at the same time has a favorable strength-weight ratio and can also be easily integrated with conventional production methods.Disclosure of the InventionThe above object is achieved by a hybrid side sill according to claim 1, by a motor vehicle body according to claim 5 and by a method for manufacturing a hybrid side sill according to claim 6.According to the present invention, the hybrid side sill for an automobile includes a pultrusion type profile member including a continuous fiber-reinforced thermoplastic polymer having a heat distortion resistance of at least 200° C., and a terminal member including steel fixed to an end portion of the pultrusion type profile member. The reinforcing fibers may include, for example, carbon fibers, glass fibers, aramid fibers, or the like. Heat distortion temperature (HDT) is the temperature at which a polymer or plastic sample deforms under a predetermined load. It is determined by the test method set out in DIN EN ISO 75-1, -2, -3.The hybrid side sill further comprises at least one metal bracket attached to the pultrusion profile. This enables greater stability of the pultrusion profile part and the provision of additional functionality, such as for further connecting the side sill to the motor vehicle body. In this case, the at least one metal bracket is fastened in a convex profile section of the pultrusion profile part in a pushed-in manner, which enables particular stability and compactness.Furthermore, at least one crash body made of steel and / or a thermoplastic polymer, which contains endless or short reinforcing fibers, is fastened to the pultrusion profile part. This allows the side sill to absorb energy particularly effectively in the event of a side impact of the motor vehicle. Preferably, the at least one crash body is inserted into a convex profile section of the pultrusion profile part, which enables compactness and particular stability of the side sill during an impact.The pultrusion profile part is fastened to an Ω-profile steel beam, and the crash body is bonded to a hollow profile section and an outer wall of the convex profile section in such a way that it extends from the outer wall of the pultrusion profile part to an opposite inner wall of the Ω-profile steel beam in such a way that a gap remains.The pultrusion profile part having heat distortion resistance of at least 200° C. can be produced by means of a suitable conventional pultrusion process. For example, US 2014 / 0 316 063 A1 discloses a suitable method for producing a composite material, wherein the composite material comprises a collection of one or more synthetic reinforcing fibers impregnated with at least one thermoplastic polymer having a glass transition temperature T g of greater than or equal to 80° C. The method comprises: i) a step of impregnating the assemblage with a precursor composition in a molten state (after melting), wherein the impregnation is carried out at a temperature such that the viscosity of the precursor composition in the molten state does not exceed 100 Pa·s, wherein the precursor composition comprises: a) at least one prepolymer P(X) n of the thermoplastic polymer comprising a molecular chain P having n identical reactive functional groups X at its ends, wherein the prepolymer is of partially aromatic and / or partially cycloaliphatic structure and X is a reactive functional group of: OH, NH 2 or COOH, with n in the range of 1 to 3, b) at least one chain extender replaced by Y-A-Y having two identical functional groups Y, which can be reacted with at least one of the functional groups X, ii) a step of bulk polymerization by (poly)addition of the chain extender to the prepolymer in the molten state, the bulk polymerization resulting in the thermoplastic polymer by polyaddition.Because side sills of motor vehicles have a fundamentally elongate shape, the formation of the side sill including the pultrusion profile part makes it possible to form a large proportion of the side sill from the pultrusion profile part, so that, owing to the generally high strength-mass ratio of continuous-fiber-reinforced thermoplastic polymers, the entire side sill can be provided with a lower weight than a conventional steel side sill of corresponding thickness. Because the side sill of the present invention comprises the steel connector, fastening means such as bores, threads, etc. for fastening the side sill to the vehicle body can be provided with substantially the same freedom of design as in conventional steel side sills. For this reason, and because the heat distortion resistance of the pultrusion profile part is above 190° C., the side sill according to the invention can be combined with a motor vehicle body shell, i.e. with an unlampered motor vehicle body in a production stage before it passes through a painting and paint stoving process, as is usually carried out at a typical stoving temperature of 190° C.According to a further embodiment, the continuous fiber reinforced thermoplastic polymer has a heat distortion temperature of at least 220° C., which allows the side sill to withstand particularly high loads during a conventional paint stoving process without deforming. Preferably, the continuous fiber reinforced thermoplastic polymer has a heat distortion temperature of at least 230° C.According to a further embodiment, the thermoplastic polymer comprises a partially aromatic polyamide. Partially aromatic polyamides contain aromatic rings in their main chain, which gives them particularly high mechanical strength and heat resistance. Preferably, the thermoplastic polymer is a polyphthalamide (PPA) or high performance polyamide in which 60% or more moles of the carboxylic acid moiety of the repeating unit in the polymer chain is composed of a combination of terephthalic acid (TPA) and isophthalic acid (IPA).According to a further embodiment, the connection part is glued to the pultrusion profile part, which enables a simple and reliable connection between the connection part and the pultrusion profile part. The connecting part is preferably glued to the pultrusion profile part by means of a one-component epoxy adhesive which is easy to handle and has a particularly high strength and heat resistance compatible with a paint stoving process.The motor vehicle body according to the invention comprises at least one hybrid side sill, as described above, and is covered with a layer of paint which has been baked at a baking temperature of at least 190° C. In this way, a high-quality paint layer is provided over the entire vehicle body including the at least one side sill.According to one embodiment of the production process according to the invention, the pultrusion is formed by means of reactive pultrusion by polyaddition of chain extenders.That is, pultrusion is carried out using a pultrusion die in which polymerization reaction is carried out by polyaddition in the molten state of a prepolymer with a chain extender, for example, an oligomer. In this way it is possible to form the finished pultrusion profile with long chains of the thermoplastic polymer which confer high mechanical strength, while at pultrusion time the prepolymer can be provided in the molten state with low viscosity, which allows reliable wetting of the reinforcing fibers and thus a strong bond between the resulting thermoplastic polymer and the reinforcing fibers. Preferably, the chain extenders comprise at least one aromatic ring. This enables aromatic rings in the molecular main chains of the thermoplastic polymer to impart particularly high mechanical strength and heat resistance to the thermoplastic polymer.According to a further embodiment, a pultrusion die for carrying out the reactive pultrusion is heated to a die temperature between 200° C. and 30° C., in particular between 200° C. and 30° C. This allows the impregnating and polymerization conditions to be controlled to obtain a low impregnating viscosity.According to a further embodiment, at least one crash body, which comprises a fiber-reinforced thermoplastic polymer, is fastened to the pultrusion profile part. The at least one crash body is preferably formed by a pultrusion method, in particular by pull-winding or pull-braking, which enables a high ability to absorb impact energy with low weight.Brief Description of the FiguresFIG. 1 is a schematic front view of a pultrusion apparatus performing a profile pultrusion step of a manufacturing method according to an embodiment of the invention; FIG. 2 is an exploded diagram of an automobile hybrid side sill according to an embodiment illustrating an assembly step of the manufacturing method; FIG. 3 is a perspective drawing of a vehicle hybrid side sill according to an embodiment formed by the assembling step of FIG. 2 ; FIG. 4 is a schematic side view of a motor vehicle body including the side sill of FIG. 3, in accordance with one embodiment, passing through a paint dipping step of the manufacturing method; FIG. 5 is a schematic side view of the motor vehicle body of FIG. 4 as it passes through a bake lacquer step of the manufacturing process; and FIG. 6 is a schematic cross-sectional view of a side sill according to another embodiment of the invention, which has been installed as a component of a motor vehicle body in a manufacturing method according to an embodiment.Unless otherwise indicated, like reference numerals designate like elements throughout the figures.Detailed Description of EmbodimentsFIG. 3 shows a perspective view of a hybrid side sill 102 for a motor vehicle. The hybrid side sill 102 is elongated in shape and includes a pultruded profile part 100 that extends along most of the overall length of the hybrid side sill 102. The profile part 100 has an Ω-shaped profile and comprises a thermoplastic polymer reinforced by layers of carbon fibers and glass fibers (not shown) extending longitudinally over the entire length of the profile part 100. In the present embodiment, the thermoplastic polymer is assumed to be a polyphthalamide (PPA) or high performance polyamide. The material of the pultrusion profile part 100 has a heat distortion resistance of 220° C.The hybrid side sill 102 further includes a steel terminal 104 adhered to an end portion 110 of the pultrusion profile 100 using a one-component epoxy adhesive (not shown). In the connector 104, fastening means such as holes and slits for installing the hybrid side sill 102 to a vehicle body are formed. In addition, the hybrid side sill 102 comprises four metal brackets 106 glued into a convex profile portion 111 of the Ω-shaped profile of the pultrusion profile part 100 to stabilize the profile part 100 and absorb energy in case of a side impact.Referring next to FIGS. 1-5, a method of manufacturing the hybrid side sill 102 of FIG. 3 as well as a motor vehicle body 108 including the hybrid side sill 102 will be explained.FIG. 1 shows a schematic front view of a polyamide high-temperature pultrusion device 550 for producing the pultrusion profile part 100 of the hybrid side sill 102. Pultrusion apparatus 550 comprises a fiber material storage device 552 in which fiber material for the layers of reinforcing fibers is stored on respective spools 501, an alignment device 554 which aligns the fiber material according to the intended relative arrangement of the reinforcing fibers within the pultrusion profile part 100 to be produced, a preheating device 520 which preheats the fiber material, a heated extruder 604 which has a screw shaft 602 disposed in the interior and is connected to a hopper 601 which contains solid granules of an oligomer 606 required to form a molten precursor 510 of thermoplastic polymer 512, a pultrusion die 522 which is equipped with a heater 521 and has an internal profile corresponding to the desired external profile of pultrusion profile part 100 to be produced, a drawing device 524, which draws a composite strand 525 formed from the fiber material and thermoplastic polymer resin from the pultrusion die 522 and thus drives the production process, and a cutting device 526 for cutting the composite strand 525 into segments of a desired length of the pultrusion profile part 100 to be produced.For preparation for operation, the fiber material stored on the bobbins 501 is successively passed through the aligning device 554, the preheating device 520, the pultrusion die 522, the drawing device 524, and the cutting device 526. Furthermore, the hopper 601 is filled with the granulate of the oligomer 606 required for forming the thermoplastic polymer 512, which is selected such that the individual oligomers (short polymers) 606 each comprise at least one aromatic ring. The extruder 604 is heated to a temperature sufficiently high to provide the oligomers 606 in a liquid state, e.g., to a temperature 10 K or more above the melting temperature of the granules of the oligomer 606.In order to initiate a pultrusion step for producing the pultrusion profile part 100, the fiber material is continuously or intermittently drawn out of the pultrusion die 522 by the drawing device 524, which results in the withdrawal of fiber material in corresponding amounts from the storage device 552. After alignment is completed in the alignment device 554, the fiber material is preheated while passing through the preheating device 520 to enter the pultrusion die 522 at an elevated temperature. Simultaneously, pellets of oligomer 606 are introduced from hopper 601 into extruder 604, where they are melted to form a molten precursor 510, which is fed into pultrusion die 522 at a position near its entrance 560, into which the fiber material is drawn by the action of puller 524. Preferably, the melting and transport of the molten precursor 510 to the pultrusion die 522 are at a sufficiently low temperature to prevent further polymerization of the oligomers 606 to a significant extent and thus maintain a low viscosity, which is believed to be 2 Pa·s in the present embodiment, of the molten precursor 510.Upon entering pultrusion die 522, molten precursor 510 impregnates the fiber material, penetrating even minute voids between the fibers due to its low viscosity, and thoroughly wetting the surface of the fibers. While the puller 524 continues to draw the fiber material with the molten precursor 510 impregnated into the fibers through the pultrusion die 522, the heater 521 maintains a temperature profile within the pultrusion die 522 that causes the molten precursor 510 to fully polymerize along the path of the impregnated fiber material through the pultrusion die 522 by polyaddition of oligomers 606, with polymerization first beginning near the surface of the fibers because the fiber material has been preheated in the preheater 520. In the present embodiment, it is assumed that a die temperature of 350° C. is maintained along the path of the impregnated fiber material through the pultrusion die 522 to enable polymerization by polyaddition of the oligomers 606 within a polymerization time of 30 s. As a result, a composite strand 525 having the composition and profile of the pultrusion profile 100 to be produced continuously exits the pultrusion die 522 at its exit 561 where it is cut by the cutter 526 to provide the pultrusion profile 100 repetitively.The oligomers 606 from which the molten precursor 510 is to be formed can be prepared in various ways provided that no polymerization occurs during their transport as the molten precursor 510 in the molten state and the molten precursor 510 is capable of undergoing in situ polymerization to a thermoplastic polymer resin by polyaddition of the oligomers 606 after entry into the pultrusion die 522, resulting in a composite strand 525 having a desired heat distortion temperature of at least 200° C., in the present embodiment assumed 220° C. For example, as in the present embodiment, oligomers can be selected to form a polyphthalamide (PPA) or high performance polyamide.In alternative embodiments of the manufacturing process, more than two components, such as a prepolymer and a chain extender to be polyadded to the prepolymer, may be mixed to form the molten precursor.FIG. 2 shows a subsequent side sill assembly step of the method for manufacturing the hybrid side sill 102. In the assembly step, the steel connector 104 is bonded to an end portion 110 of the pultrusion profile 100 using a one-component epoxy adhesive (not shown). Furthermore, the four metal brackets 106 are glued into the convex profile section 111 of the profile of the pultrusion profile part with the aid of the one-component epoxy adhesive. The hybrid side sill 102 resulting from the assembly step of FIG. 2 is shown in FIG. 3.After the manufacture of the hybrid side sill 102 is completed, the hybrid side sill 102 is assembled with additional parts into an automobile body 108 shown in FIG. 4 using the fasteners in the connector 104 and / or in one or more of the metal brackets 106. For example, the connector 104 and / or one or more of the metal brackets 106 may be welded or screwed to other parts of the motor vehicle body 108. FIG. 4 shows the motor vehicle body 108 resulting from the motor vehicle body assembly step while it passes through a later paint dipping step of the method for manufacturing the motor vehicle body. In the paint dipping step, the vehicle body 108 including the hybrid side sill 102 is lowered into a paint container 700 to be dipped into a liquid paint 112 contained in the paint container 700. After complete dipping, the motor vehicle body 108 is pulled out of the paint container 700.FIG. 5 is a schematic side view of the motor vehicle body 108 of FIG. 4 as it passes through a subsequent paint stoving step of the manufacturing process. In the paint stoving step, the vehicle body 108 covered with paint 112 is placed in a stoving furnace 702 in which a prescribed stoving temperature of 190° C. is maintained for a prescribed stoving duration.FIG. 6 is a schematic cross-sectional view of another hybrid side sill 102 in a mounted condition as part of a motor vehicle body 108, with a portion of a closed vehicle door 116 also shown. FIG. 6 illustrates only a portion of the motor vehicle body 108 proximate to the hybrid side sill 102. While the pultrusion profile part 100 of the hybrid side sill 102 has a substantially Ω-shaped cross section as in the embodiment of FIG. 3, a hollow profile section 706 is additionally formed in the cross section, which protrudes from an outer wall 103 thereof into the convex profile section 111 and encloses an internal rectangular cavity 704. In the present embodiment, the closed configuration of the hollow profile portion 706 provides greater inertia and torsional strength to the hybrid side sill 100, so as to enable high overall performance of the hybrid side sill 102.The hybrid side sill 102 is fastened to an Ω-section steel beam 710 of the motor vehicle body 108 by bonding foot portions 708 of the pultrusion profile part 100 of the hybrid side sill 102 to foot portions 709 of the Ω-section steel beam 710 using, for example, one-component epoxy adhesive in such a way that the convex profile portion 111 of the pultrusion profile part 100 merges with an opposite convex profile portion 711 of the Ω-section steel beam 710 to form a common interior 111, 711. The Ω-section steel carrier 710 is in turn connected to further steel parts 712 of the motor vehicle body 108 by welding. An upper side wall 716 of the pultrusion profile part 716 forms an upper surface of the hybrid side sill 102, which in a complete motor vehicle is opposite a base surface of the vehicle door 116 in the closed state.Furthermore, a cylindrical crash body 114, which is produced separately by pull-winding or pull-brazing from an endless fiber-reinforced thermoplastic polymer having a heat distortion resistance of at least 200° C., is bonded to the hollow profile section 706 and the outer wall 103 of the convex profile section 111 of the pultrusion profile part 100 of the hybrid side sill 102 in such a way that it extends from the outer wall 103 of the pultrusion profile part 100 of the hybrid side sill 102 almost as far as an opposite inner wall 713 of the Ω-profile steel beam 710, where only a small gap 714 remains. If the motor vehicle suffers a side impact, the crash body 114 absorbs impact energy by gradually deforming as the outer wall 103 of the pultrusion profile part 100 of the hybrid side sill 102 is pressed in the direction of the inner wall 713 of the Ω-profile steel beam 710.The cylindrical shape of the crash can 114 may have a circular cross-section, a rectangular cross-section, an elliptical cross-section, or the like. Further, the crash can is not limited to a cylindrical shape, but may be formed with a plurality of cavities extending in parallel through the internal space 111, 711, for example. In alternative embodiments, the crash can 114 may also be made of a metal such as steel or injection molded from a thermoplastic polymer, with or without added short length glass fibers. The injection molding may be performed separately from the pultrusion profile 100, or as an overmolding step in which the crash can 114 is attached and formed in place as an overmolded element on the pultrusion profile 100.In addition, elements of the hybrid side sill 102 of FIG. 6 may be combined with elements of the above-described embodiments without departing from the invention. For example, crash bodies 114 may be mounted in a pultrusion profile part 100 having a simple Ω-shaped cross section, or metal brackets 106 may be mounted in a pultrusion profile part 100 as shown in FIG. 6.

Claims

A hybrid side sill (102) for a motor vehicle, comprising: a pultrusion profile part (100) comprising an endless fiber reinforced thermoplastic polymer (512) having a heat distortion resistance of at least 200°C; and a terminal part (104) comprising steel attached to an end portion (110) of the pultrusion profile part (100); and at least one metal bracket (106) attached to the pultrusion profile part (100) and within a convex profile portion (111) of the pultrusion profile part (100); and at least one crash body (114) which is fastened to the pultrusion profile part (100) and has steel and / or a thermoplastic polymer, wherein the pultrusion profile part (100) is fastened to an Ω-profile steel beam (710), and wherein the crash body (114) is bonded to a hollow profile section (706) and an outer wall (103) of the convex profile section (111) in such a way that it extends from the outer wall (103) of the pultrusion profile part (100) to an opposite inner wall (713) of the Q-profile steel beam (710) in such a way that a gap (714) remains.The hybrid side sill (102) of claim 1, wherein the continuous fiber reinforced thermoplastic polymer (512) has a heat distortion temperature of at least 220°C, more preferably at least 230°C.Hybrid side sill (102) according to claim 1 or 2, wherein the thermoplastic polymer (512) comprises a partially aromatic polyamide, in particular a polyphthalamide.Hybrid side sill (102) according to claim 1 or 3, wherein the connection part (104) is glued to the pultrusion profile part (100), in particular using a one-component epoxy glue.Motor vehicle body (108) having a hybrid side sill (102) according to Claim 1, which is covered with a layer of paint (112) baked at a stoving temperature of at least 190°C.A method of manufacturing a hybrid side sill (102) for a motor vehicle, comprising the steps of: forming a pultrusion profile part (100) comprising an endless fiber reinforced thermoplastic polymer (512) having a heat distortion temperature of at least 200°C; and securing a terminal part (104) comprising steel to an end portion (110) of the pultrusion profile part (100) and at least one metal bracket (106) to the pultrusion profile part (100) and within a convex profile portion (111) of the pultrusion profile part (100); Fastening at least one crash body (114) to the pultrusion profile part (100), which crash body comprises steel or / and a thermoplastic polymer, wherein the pultrusion profile part (100) is connected to an Ω-profile steel carrier (710), wherein the crash body (114) is bonded to a hollow profile section (706) and an outer wall (103) of the convex profile section (111) in such a way that it extends from the outer wall (103) of the pultrusion profile part (100) to an opposite inner wall (713) of the Ω-profile steel carrier (710) in such a way that a gap (714) remains.Method according to claim 6, wherein the pultrusion profile part (100) is formed by reactive pultrusion which comprises polyaddition of chain extenders, in particular oligomers (606).The process of claim 7 wherein the chain extenders comprise at least one aromatic ring.The method of claim 7 or 8, wherein a pultrusion die (522) is heated to a temperature of at least 340 °C for conducting the reactive pultrusion.Method according to one of claims 6 to 9, wherein the connection part (104) is fastened to the pultrusion profile part (100) by adhesive bonding, in particular using a one-component epoxy adhesive.Method according to Claim 10, further comprising a step of forming the at least one crash body (114) by pultrusion, in particular by pull-winding or pull-forming.The method of any of claims 6 to 11, further comprising the steps of: installing the hybrid side sill (102) in an automobile body (108); coating the automobile body (108) with paint (112); and baking the paint coated automobile body (108) at a baking temperature of at least 190°C.

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