Floor frame for a motor vehicle body

Abstract

Floor frame (1) for a motor vehicle body, comprising at least one, preferably two longitudinal members (2) extending in the longitudinal direction (X) of the motor vehicle and at least two cross members (3) extending in the transverse direction (Y) of the motor vehicle, wherein the cross members (3) and longitudinal members (2) are profiled in their cross-section, characterized in that the floor frame (1) is manufactured from a one-piece tailored blank in a press stroke and the floor frame (1) has connection holes (5) for a battery carrier and that the cross member (3) has a lower tensile strength Rm and / or wall thickness in its end regions relative to the middle region of the cross member (3).

Description

[0001] The present invention relates to a floor frame for a motor vehicle body according to the features in the preamble of patent claim 1.

[0002] Motor vehicles are well known from the state of the art. These are powered by an internal combustion engine and increasingly by an electric motor. Such vehicles are also referred to as automobiles. They usually have a self-supporting vehicle body or chassis. Such a chassis is constructed from various sheet metal components. The sheet metal components are each manufactured individually, for example, the A-pillar, B-pillar, C-pillar, a sill, a floor panel, cross members, or longitudinal members. These are each formed as a one-piece shell component. The resulting precision of the individual component is high. The components are then joined together to form the self-supporting vehicle body. This joining process, in turn, creates tolerances.

[0003] WO 2020 / 058 037 A1 discloses a floor frame for a motor vehicle for accommodating a corresponding energy storage device. The floor frame is made of cross members and longitudinal members that are coupled together.

[0004] DE 10 2018 211 473 B3 discloses a battery housing for an electric vehicle. In this case, a tray is inserted into a surrounding frame and sealed with sealing lines.

[0005] The object of the present invention is to provide, based on the prior art, a floor frame for a motor vehicle which can be manufactured more simply and cost-effectively than the floor frame known in the prior art, while at the same time having a high level of precision in terms of the component accuracy to be achieved and, in addition, having improved rigidity behavior and improved crash properties compared to the components known in the prior art.

[0006] The above-mentioned object is achieved with a floor frame for a motor vehicle body having the features in claim 1.

[0007] Advantageous embodiments are the subject of the dependent claims.

[0008] The floor frame is for a self-supporting motor vehicle body or chassis. The floor frame is thus inserted into the body and joined, in particular welded, to it. The floor frame, in particular, creates an additional floor panel, which provides the floor panel itself. The floor frame thus serves as a stiffening structure for the motor vehicle body.

[0009] For this purpose, the floor frame has at least one longitudinal member, in particular two longitudinal members, extending in the longitudinal direction of the vehicle. The floor frame also has cross members extending in the transverse direction of the vehicle. Preferably, two cross members, in particular three cross members, are provided. The floor frame thus preferably has a ladder structure in plan view.

[0010] The cross members and the longitudinal members are themselves profiled in their cross-section, at least in some length sections. The floor frame is a single piece manufactured from a tailored blank, particularly preferably a tailored welded blank, in a single press stroke. This means that the tailored blank is initially provided as a sheet metal blank. The longitudinal member and cross member sections are therefore already provided and are then profiled in cross-section by the press stroke itself. The entire floor frame structure is therefore a single piece. In the case of a tailored rolled blank, for example, one-piece means one piece and made of the same material. In the case of a tailored welded blank, one-piece means that the individual sheet metal strips are first welded together to form the tailored welded blank and then the one-piece sheet metal blank is then formed in a single press stroke. A large-capacity press is used to produce the floor frame.The floor frame has a plan view size of more than 100 x 100 cm, preferably more than 150 x 100 cm.

[0011] According to the invention, the base frame is now characterized in that it has connection holes for a battery carrier. These can also be referred to as battery carrier connection holes. The area immediately adjacent to the battery carrier connection holes is reinforced by a greater wall thickness and / or greater tensile strength Rm.

[0012] Furthermore, the floor frame according to the invention is characterized in that the cross members have a smaller wall thickness and / or lower tensile strength at their outer ends or end regions relative to the transverse direction of the motor vehicle, in relation to a central region of the cross members and / or in relation to the longitudinal members.

[0013] This achieves two advantages according to the invention. First, the battery tray connection holes could be reinforced, so that a battery tray with a dead weight of several hundred kilograms, including the battery, can be securely mounted to the floor structure of the vehicle with a rigid and durable connection.

[0014] A thinner wall thickness and / or lower tensile strength in the end areas of the cross members provides high rigidity in the event of a crash, particularly in a side-on collision, while at the same time deforming the end area like a crash box, thus dissipating energy. In contrast, a central area of ​​the cross members themselves, relative to the longitudinal direction of the cross member, is softer or more ductile. A crumple zone can form here, whereby the passengers sitting on the left or right side of the vehicle are safely protected in the resulting passenger compartment of the vehicle body thanks to the higher external rigidity of the cross member.

[0015] Furthermore, the longitudinal members are preferably arranged offset inward relative to the transverse direction of the vehicle. As a result, the ladder-like structure is designed as a cross-like structure because the longitudinal members project outward.

[0016] Alternatively, or as a preferred design variant, the longitudinal members are arranged on the outside relative to the transverse direction of the vehicle. In this case, the longitudinal members can also be designed as a sill shell or sill half-shell. The vehicle sills, which are oriented in the vehicle body and thus in the longitudinal direction of the vehicle, are arranged on the outside of the floor frame and preferably form the vehicle sill on the inside as an existing part of a half-shell.

[0017] In the case of a tailored welded blank, the longitudinal members and cross members can form a double layer in a coupling or intersection area. The sheet metal blank can then be prepared easily and cost-effectively using spot welding.

[0018] Preferably, the sheet metal blank is made from a pre-coated starting material, in particular a hardenable steel material, which is pre-coated, for example, with an aluminum-silicon coating. Especially when using hot forming and press hardening technology, the provided floor frame can thus exhibit improved corrosion protection properties.

[0019] Alternatively, the tailored welded blank can be formed, at least in sections, from individual sheets that butt together, forming the transition areas from the cross member to the longitudinal member. These are then welded together using butt welding, for example, using a laser welding process.

[0020] Furthermore, by applying hot forming and press hardening technology, a high tensile strength Rm is formed in the high-strength region. This strength is then particularly preferably formed as a tensile strength greater than 980 MPa, in particular greater than 1,350 MPa. At least in some regions, the tensile strength can also be greater than 1,500 MPa, in particular greater than 1,800 MPa, and most preferably greater. In particular, this can provide high rigidity through the floor frame. If the floor frame itself is coupled to a floor panel, the floor panel can in turn provide sufficient ductility, so that the floor frame and floor panel achieve high rigidity, in particular torsional rigidity, of the motor vehicle body, while at the same time ensuring particularly high crash performance in the event of a crash.

[0021] The longitudinal members and / or cross members are particularly preferably U-shaped in their respective cross-sections, at least in some length sections, and very particularly preferably in the shape of a hat profile. Thus, outwardly projecting flanges are formed at the ends of the webs of the U-shaped profile. These can be provided as connection areas to a floor panel. The flanges themselves are particularly preferably soft, as so-called soft zones, thus having a tensile strength of preferably 500 MPa to 850 MPa. If spot welds are used here, tearing of the floor panel joined thereto or, in the case of the longitudinal members, the other sill shells, is prevented, thus providing high ductility through high strength, at least in some areas of the cross-section in the U-shaped area, while at the same time high rigidity and good crash safety are provided.

[0022] Further advantages, features, properties, and aspects of the present invention are the subject of the following description. Preferred embodiments are illustrated in schematic figures. These serve to facilitate understanding of the invention. They show: Fig. 1 in plan view with respective cross-sectional views of a floor frame, Fig. 2 an analogous design variant according to Fig. 1, Fig. 3 an alternative design variant of the floor frame according to the invention, Fig. 4 an alternative design variant to Fig. 2, Fig. 5 a plan view of a sheet metal blank for producing a floor frame according to Fig. 1, Fig. 6 an alternative design variant for the production of a floor frame according to Fig. 2, Fig. 7 alternative sheet metal blanks for the production of a floor frame as a tailored welded blank with butt joints, Fig. 8 alternative sheet metal blanks for the production of a floor frame with a respective overlapping area, which has a double layer designed as a tailored welded blank with spot welds, Fig. 9 a cross-sectional view of a resulting motor vehicle sill, Fig. 10 a plan view of a floor frame analogous to Fig. 4 and Fig. 11a -e different cross-sectional views of a tailored welded blank in which two butt-jointed sheets are covered with a patch.

[0023] In the figures, the same reference symbols are used for identical or similar components, even if a repeated description is omitted for reasons of simplification.

[0024] Fig. 1 shows a floor frame 1 in plan view with respective cross-sectional views. The floor frame 1 has, as shown here, three longitudinal members 2 which are arranged oriented in the longitudinal direction X of the vehicle. The floor frame 1 also has two cross members 3. The cross members 3 are arranged oriented in the vehicle Y direction. In their respective cross sections, the cross members 3 themselves are arranged in a hat shape. They therefore have a U-shaped section and flanges 4 arranged at each end. The flanges 4 are preferably soft or in the form of a so-called soft zone. For coupling to a floor panel (not shown in detail), the flanges 4 are then ductile and would not tear off in the event of a crash. In particular, the U-shaped section is then particularly preferably designed with a higher strength so that sufficient rigidity in the cross section is achieved.

[0025] According to the invention, respective connection holes 5 can also be formed for a battery carrier (not shown in more detail). These connection holes 5 also have a greater wall thickness in the area adjacent to the connection holes 5. A battery carrier with a dead weight of several hundred kg can thus be coupled to the floor frame 1 securely and with permanent rigidity over the service life of a motor vehicle, without the need for additional, more extensive stiffening structures in the underbody area. Furthermore, and particularly preferably, in a respective end region 6, indicated schematically here by the circle, the cross member 3 has its wall thickness increased and / or its tensile strength increased. In the event of a side crash in the transverse direction Y of the motor vehicle, improved crash behavior is thus ensured.If a central region of the cross member 3 in the transverse direction Y of the vehicle is then made softer, a crumple zone remains which provides sufficient ductility.

[0026] Fig. 2 shows an analogous design variant according to Fig. 1. However, here three cross members 3 are shown and no central longitudinal member 2 is formed, thus only two outer longitudinal members 2 are provided, resulting in a ladder frame structure in plan view. The longitudinal members 2 are shown in their respective cross sections. These then have an L-shaped configuration on the outside in cross section. Here again, a flange 4 can protrude outwards in relation to the vehicle transverse direction Y. A longitudinal section through a cross member 3 is also shown along section line BB. This then has a trough-shaped configuration in longitudinal section. The outer L-shaped regions of the longitudinal member 2 can serve as an inner partial shell or half-shell for a sill (not shown in detail) of a motor vehicle body. An outer sill half-shell is then coupled to the longitudinal member 2 on the outside in relation to the vehicle transverse direction Y.The floor panel (not shown in detail), which is coupled to the floor frame 1, can then likewise provide an outer sill, at least partially in cross-section. The sill itself then extends in the vehicle's longitudinal direction X. In this case, the outer longitudinal member 2 of the floor frame 1 is particularly preferably designed with a high level of strength. The flange 4 of the longitudinal member 2 itself can in turn be designed to be ductile, as a soft zone. This ensures that sufficient rigidity is provided for a side crash, in particular also a lateral pole test. An outer sill shell (not shown in detail) can itself be ductile, so that the intensity of the initial contact is reduced in the event of a crash. The rigidity of the sill, however, is provided by the floor frame 1 and here a particularly high tensile strength of more than 1,000 MPa.

[0027] Fig. Figure 3 shows an alternative embodiment of the floor frame 1 according to the invention. A cross-like structure is formed here. The floor frame 1 is made with a longitudinal member 2 with a hat-shaped cross section and two cross members 3 arranged transversely thereto. In this case, the cross members 3 and the longitudinal members 2 are each hat-shaped.

[0028] Fig. 4 shows an alternative design variant to Fig. 2. The outer longitudinal members 2 are hat-shaped in their respective cross-sections, even in this case.

[0029] Fig. 5 shows a plan view of a sheet metal blank 7 for producing a floor frame 1 according to Fig. 1. The sheet metal blank 7 has strips that will later form the cross members 3, as well as sheet metal strips that will later form the longitudinal members 2. These are all manufactured butt-jointed at transition areas 8 and welded together in the area of ​​the dashed line to form a butt joint 9. For example, as a laser weld. This creates a tailored welded blank. The individual sheet metal sections can each be homogeneous in terms of wall thickness and / or material. However, the individual sheet metal sections can themselves vary in their longitudinal profile, for example, in wall thickness. Thus, the specific properties of the floor frame 1 to be produced later can be preset via the sheet metal blank 7 or the individual sheet metal strips of the sheet metal blank 7.

[0030] Fig. 6 shows an alternative design variant. In this case, for the production of a floor frame 1 according to Fig. 2. For this purpose, the sheet metal blank 7 has an overlap in the transition areas 8. This overlap makes it possible to perform the spot welds 10 shown. This process also produces a tailored welded blank. This tailored welded blank can be produced particularly easily and cost-effectively using spot welds 10.

[0031] What all design variants have in common is that a further centering in both the vehicle transverse direction Y and the vehicle longitudinal direction X is produced in a large press, so that the cross member 3 and / or longitudinal member 2 is not only a highly precise component in its cross-section, but all cross members 3 and all longitudinal members 2 are calibrated together in the forming press with respect to their position in the vehicle longitudinal direction X and vehicle transverse direction Y. The floor frame 1 and thus the connection structure of the floor in the rest of the vehicle body are thus optimally prepared.

[0032] Another special feature in Fig. 6 as a possible option is that the two metal strips, which are in the Fig. 2 form two cross members 3 relative to one another, are continuously connected to one another by an end-side overlap region and are connected to the longitudinal member 2. To produce the sheet metal blank 7, depending on the number of cross members 3 to be produced, centering can also be carried out cost-effectively and economically during the production of the sheet metal blank 7.

[0033] Fig. 7 and Fig. 8 show alternative sheet metal blanks 7 for producing a floor frame 1 according to Fig. 3, in each case of Fig. 7 as Tailored Welded Blank with butt joints and in case of Fig. 8 with a respective overlap area, which is a double layer formed as a tailored welded blank with spot welds 10.

[0034] Fig. 9 shows a cross-sectional view of a resulting motor vehicle sill 11. The sill 11 itself extends with its longitudinal course in the vehicle X-direction. The sill 11 is formed by the outer part of the longitudinal member 2 with the connecting flange 4. This forms an inner half-shell with respect to the vehicle transverse direction Y. Furthermore, an outer sill plate 12 is arranged. This likewise has a connecting flange 13. This is coupled to the connecting flange 4 of the longitudinal member 2. A lower connecting flange 14 of the sill plate 12 is coupled to the illustrated floor plate 15 along a downwardly angled floor flange 15-1. The motor vehicle sill 11 is thus formed as a hollow profile in cross-section. The sill plate 12 can be an unhardened sheet, thus having a tensile strength of approximately 400 MPa to 800 MPa.The longitudinal member 2 is designed as a high-strength component with a tensile strength Rm > 1,000 MPa, at least in the region of the web 16 relative to the vehicle vertical direction Z. The connecting flange 4 of the longitudinal member 2 is designed to be soft. The floor panel 15 is also designed to be soft or ductile. Thus, sufficient ductility is present in the joining areas between 4 and 13 and between 14 and 15, and tearing is avoided in the event of a crash. The lower region of the longitudinal member 2 relative to the vehicle vertical direction Z, indicated by the arrow at reference number 2, can also be designed to be ductile. However, sufficient rigidity is achieved by a high tensile strength Rm and / or greater wall thickness Rm in the region of the web 16. In particular, this rigidity counteracts deformation in the vehicle longitudinal direction X.In the event of a side crash in the vehicle's transverse direction Y, this also achieves a high level of rigidity, so that no intrusion into the passenger cell occurs.

[0035] Fig. 10 shows a plan view of a floor frame 1 analogous to Fig. 4. However, the ends 16 of the cross members 3 are designed to be extended relative to the longitudinal members 2 in the vehicle transverse direction Y. For this, but also all other variants, it can be provided that the end regions 6 or connecting regions of the cross members 3 and / or longitudinal members 2 are thinner in their wall thickness and / or have a reduced tensile strength compared to the remaining regions of the same cross member 3.

[0036] Fig. 11a - e show five different thickness transitions from a sheet metal blank as a tailored welded blank. In each case, a thin sheet 22 is butt-welded to a relatively thicker sheet 23 or, in the case of Fig. 11b a tailored rolled blank, in which the thickness transition occurs on both sides. In the area of ​​the thickness jump 24, a reinforcement patch 6 or patch is applied on one side. This patch 21 further reinforces the area of ​​the thickness transition. In the case of Fig. 11a and b as well as d and e, the reinforcement patch has a bend 25 in its cross-section, so that it compensates for the thickness jump 24 or thickness transition. In the case of Fig. 11c, one side of the thick sheet 23 and the thin sheet 22 is flat, so that the reinforcement patch 6 is also flat in its cross-sectional shape. In particular, a design variant according to Fig. 11d or 11e are preferred. The underside of thick sheet 23 and thin sheet 22 is also flat in cross-section. The thickness gap 24 is then covered by the patchwork sheet. The patch is applied before the actual hot forming process. This avoids undercuts, which would otherwise require, for example, slides or segmented tooling.

[0037] Fig. 11e shows the patched Tailored Welded Blank of Fig. 11d in the state after hot forming and press hardening. The previously existing gap between the patchwork sheet and the two sheets of the tailored welded blank is largely closed as a result of hot forming, preventing corrosion problems during subsequent cathodic dip coating of the body and during vehicle use.

[0038] The steel grades used can be used as examples below and can be used for all variants of this invention. In particular, different steel grades can be combined in a tailored welded blank. The corresponding strength ranges for hard or soft areas, or for strong or ductile areas, can be found in the table. All alloy components are given in wt. %, with the respective hardenable steel alloy then adding the remaining iron and melting-related impurities. Reference symbol: 1 floor frame 2 longitudinal members 3 cross members 4 Flange 5 connection hole 6 End area 7 Sheet metal blank 8 Transition area 9 Butt weld 10 spot welding 11 vehicle sills 12 sill plate 13 Connection flange to 12 14 connecting flange to 12 15 floor plate 15-1 Floor flange 16 bridge to 2 21 Patch 22 thin sheet metal 23 thick sheet metal 24 Thickness jump 25 Angulation X Longitudinal direction of the vehicle Y vehicle transverse direction Z Motor vehicle vertical direction

Claims

[1] Floor frame (1) for a motor vehicle body, comprising at least one, preferably two longitudinal members (2) which extend in the longitudinal direction (X) of the motor vehicle and at least two cross members (3) which extend in the transverse direction (Y) of the motor vehicle, wherein the cross members (3) and the longitudinal members (2) are profiled in their cross section, characterized by that the base frame (1) is produced from a one-piece tailored blank in one press stroke and the base frame (1) has connection holes (5) for a battery carrier and that the cross member (3) has a lower tensile strength Rm and / or wall thickness in its end regions relative to the central region of the cross member (3). [2] Floor frame (1) according to claim 1, characterized by that the longitudinal members (2) are arranged offset inwards with respect to the transverse direction (Y) of the motor vehicle or that the longitudinal members (2) are arranged on the outside. [3] Floor frame (1) according to claim 1 or 2, characterized by that the longitudinal beams (2) and the cross beams (3) form a double layer in a coupling area. [4] Floor frame (1) according to one of the preceding claims, characterized by that the tailored blank is a tailored welded blank and is formed at least in sections by butt-fitting transition regions (8) which are welded together. [5] Floor frame (1) according to one of the preceding claims, characterized by that a tensile strength Rm in the high strength areas greater than 1350 MPa is formed. [6] Floor frame (1) according to one of the preceding claims, characterized by that at least one longitudinal member (2) is U-shaped in cross-section, at least in length sections. [7] Floor frame (1) according to one of the preceding claims, characterized by that the cross members (3) are U-shaped in cross section at least in length sections. [8] Floor frame (1) according to one of the preceding claims, characterized by that the outer longitudinal members (2) are L-shaped in cross-section and have an outwardly projecting flange (4). [9] Floor frame (1) according to one of the preceding claims, characterized by that soft areas have a tensile strength Rm of less than 1000 MPa. [10] Floor frame (1) according to one of the preceding claims, characterized by that a longitudinal member (2) has different wall thicknesses in its longitudinal direction. [11] Floor frame (1) according to one of the preceding claims, characterized by that a patch is applied in the area of ​​a connection hole (5). [12] Floor frame (1) according to one of the preceding claims, characterized by that a reinforcement patch (21) is applied at least locally.

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