Rear structure of an automobile vehicle

Abstract

A rear structure (1) for an automobile vehicle (200) having a fuel tank (500) below the passenger seats and a powertrain (300) at the rear comprises a lower structure (11) and an upper structure (12), the lower structure and the upper structure together forming a closed hollow volume (10) along at least the area where the fuel tank is located, and the upper structure (12) is manufactured from a single metal blank.

Description

[Technical Field]

[0001] The present invention relates to a rear structure of an automobile vehicle having a power train at the rear and a fuel tank below a passenger seat. [Background technology]

[0002] This type of configuration is found in internal combustion vehicles with the engine located in the rear of the vehicle, and is also common in hybrid vehicles that have a fuel tank located under the passenger seats and an electric motor located in the rear, where the fuel tank is typically located between the battery pack and the rear electric motor. Summary of the Invention [Problem to be solved by the invention]

[0003] To protect passengers in the event of a rear or side collision, it is essential to ensure that the fuel tank is not damaged. Indeed, any damage within the fuel tank can lead to a fuel leak, which in turn can lead to fire and chemical hazards.

[0004] In the above arrangement, the fuel tank needs to be protected from intrusion of the heavy mass of the rear powertrain, particularly in the event of a rear collision.

[0005] Such rear impacts are the subject of, for example, the National Highway Traffic Safety Association (NHTSA) using Rear Moving Barrier Impact (FMVSS 301), in which a vehicle is impacted by a deformable barrier weighing 1368 kg, covering a 70% width offset, and traveling at an initial speed of 80 km / h. [Means for solving the problem]

[0006] The present invention provides an innovative rear structural design that absorbs at least a portion of the collision energy while ensuring adequate protection of the fuel tank, and optionally the rear battery pack, in an efficient manner without significantly increasing the overall weight, complexity, productivity and cost of vehicle manufacturing.

[0007] The object of the present invention is achieved by providing a rear structure for a motor vehicle according to claim 1, optionally comprising the features of claims 2 to 5 individually or according to any possible combination. The present invention further relates to a motor vehicle according to claim 6, optionally comprising the features of claim 7.

[0008] Other aspects and advantages of the present invention will become apparent on reading the following description, given by way of example and in no way limiting, made with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of an entire vehicle emphasizing the location of the rear structure of the present invention. [Figure 2] FIG. 1 is a bottom view of a vehicle highlighting the location of the rear structure of the present invention. [Figure 3] FIG. 2 is a perspective view of a lower rear structure according to an embodiment of the present invention. [Figure 4] FIG. 1 is a perspective view of a fully assembled lower and upper rear structure according to one embodiment of the present invention. [Figure 5] 5 shows cross sections AA and BB of the fully assembled lower and upper rear structures according to the invention in the direction defined in FIG. 4. [Figure 6] 1 is a set of still images taken from a crash simulation of a vehicle having a rear structure according to one embodiment of the present invention. [Figure 7] 1 is a series of three perspective views of three different embodiments of an upper rear structure according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the following description and claims, directional terms are defined according to the normal directions of the on-board vehicle.

[0011] In particular, terms such as "top," "up," "upper," "above," "bottom," "low," "lower," and "below" are defined according to the height of the vehicle. Terms such as "front," "back," "rear," "front," "forward," and "backward" are defined according to the longitudinal direction of the vehicle, i.e., the direction in which the vehicle moves forward when tracing a straight line. Terms such as "left," "right," and "transverse" are defined according to an orientation parallel to the width of the vehicle. The terms "inner" and "outer" should be understood according to the width of the vehicle, with "inner" being closest to the vehicle's central axis, i.e., closest to the inside of the vehicle, while "outer" is further away from said central axis of the vehicle and, in fact, closer to the outside of the vehicle. The same applies to the terms "distal" and "central," with the "distal" portion being closest to the outside of the vehicle and the "central" portion being closest to the center of the vehicle. The term "horizontal" refers to a planar orientation including longitudinal and lateral directions. The term "vertical" refers to any orientation including height.

[0012] In the following figures, all orientation and spatial references are made using an X, Y, Z coordinate system, with Z being the height of the vehicle, X being the length of the vehicle, and Y being the width of the vehicle. The X axis is oriented so that the X coordinate increases from front to rear, i.e., points further rearward on the vehicle have higher X coordinates than points further forward on the vehicle. Reference planes are represented in each figure. Where a figure is a 2D flat representation, axes that are outside the figure are represented by a dot in a circle when they are pointing towards the reader, and by a cross in a circle when they are pointing away from the reader, following established convention.

[0013] "Substantially parallel" or "substantially perpendicular" means a direction that does not deviate by more than 15° from the parallel or perpendicular direction.

[0014] A steel plate is a flat steel plate. It has a top and bottom surface, also called the upper and bottom sides or the top and bottom surfaces. The distance between these surfaces is designated as the plate's thickness. The thickness can be measured, for example, using a micrometer, the spindle and anvil of which are positioned on the top and bottom surfaces. The thickness of a molded part can also be measured in a similar manner.

[0015] The average thickness of a part or portion of a part means the overall average thickness of the material comprising the part after it has been initially formed from a flat sheet into a three-dimensional part.

[0016] A tailored welded blank is made by assembling several plates or cut-out blanks of steel, known as sub-blanks, together, for example by laser welding, to optimize the performance of the part in different areas thereof, reduce overall part weight, reduce overall part cost, and reduce material scrap. The sub-blanks that form the tailored welded blank can be assembled with or without overlap, for example, they can be laser butt welded (no overlap) or spot welded to each other (with overlap).

[0017] A flexible blank is a type of tailored welded blank in which at least some of the connections between different sub-blanks include regions where they are not rigid, allowing the sub-blanks to move in different directions during the forming operation in the corresponding regions.

[0018] In contrast to a tailored welded blank, a monolithic blank refers to a blank that consists of a single sub-blank, without several sub-blanks being joined together.

[0019] A tailored rolled blank is a multi-thickness blank obtained by differential rolling during the steel plate manufacturing process.

[0020] Ultimate tensile strength, yield strength, and elongation are measured according to ISO standard ISO 6892-1, published in October 2009. Tensile specimens are cut from the flat area. If necessary, smaller tensile test samples are taken to accommodate the entire flat area available on the part.

[0021] The bend angle is measured according to the VDA-238 bending standard. For the same material, the bend angle depends on the thickness. For simplicity, the bend angle values ​​in this specification are based on a thickness of 1.5 mm. If the thickness is different from 1.5 mm, the bend angle value should be normalized to 1.5 mm using the following calculation: α1.5 is the bend angle normalized to 1.5 mm, t is the thickness, and αt is the bend angle relative to the thickness t.

[0022] α1.5=(αt×√t) / √1.5 Cold stamping is a metal forming technique that involves pressing a metal sheet between an upper die and a lower die, called a cold stamping tool, to form a shaped part. For example, a cold stamping tool has a blank holder that allows the metal sheet to be held from its sides. For example, a cold stamping tool may consist of several steps, each including an upper and lower die, to generate complex shapes and / or perform additional operations, such as drilling holes in the part or trimming its sides. Other cold forming techniques include roll forming, which involves bending a continuous sheet between successive roll sets, and simple bending, which involves simply bending a steel sheet using a press and upper and lower bending tools.

[0023] Roll forming is a continuous metal forming process that takes sheet, strip, or coil and bends or forms it into a continuous cross section. This process takes place between successive pairs of rolls that change shape until the desired part is completed. The part is called the roll-formed part, and the direction in which the material is rolled, i.e., the direction separating two successive pairs of rolls, is called the roll-forming direction.

[0024] Hot stamping is a steel forming technique that involves heating a steel blank, or a preform made from a steel blank, to a temperature at which the microstructure of the steel is at least partially transformed to austenite, forming the blank or preform at high temperature by stamping, and simultaneously quenching the formed part to obtain a microstructure with very high strength, possibly with an additional quenching or tempering step in the heat treatment.

[0025] A multi-step hot stamping process is a specific type of hot stamping process consisting of at least two process steps, including at least one stamping step, performed at temperatures above 300°C. For example, a multi-step process can include a first stamping operation and a subsequent hot trimming operation, so that the finished part does not require further trimming at the end of the hot stamping process. For example, a multi-step process can include several consecutive stamping steps to produce parts with more complex shapes than can be achieved using a single stamping operation. For example, in a multi-step process, parts are automatically transferred from one operation to another, for example, using a transfer press. For example, the part remains in the same tool, which is a multi-purpose tool that can perform different operations, such as the initial stamping and subsequent in-tool trimming operations.

[0026] A partial-hardening hot stamping process is a hot stamping process in which the thermal profile experienced by the blank is intentionally tailored to be different in different regions of the blank in order to obtain different material properties in these different regions at the end of the hot stamping process. For example, this allows a single metal blank made of a single material to be used to produce hot-stamped parts with different levels of hardness and elongation in different regions of the final part. For example, this allows for the production of parts with soft and hard zones, where the soft zones can deform under impact loads to absorb energy, while the hard zones resist penetration by resisting deformation. There are several different techniques for implementing partial hardening. For example, the material can be heated to different temperatures in different regions of the blank, with the higher temperature zones being fully austenitic at the exit of the austenitizing furnace and resulting in a very hard microstructure after hot stamping, while the lower temperature zones have a dual-phase ferrite / austenite microstructure at the exit of the austenitizing furnace and resulting in a less hard microstructure after hot stamping. For example, the material may be quenched at different quenching rates in different areas of the blank during the hot stamping step itself, with areas quenched at a higher quenching rate having a higher hardness than areas quenched at a lower rate.

[0027] 1 and 2, the present invention relates to an automobile vehicle 200 having a rear powertrain 300 located at the rear of the vehicle and a fuel tank 500 located below the passenger seats. Optionally, the automobile vehicle may further include an energy storage unit 400, such as a battery pack or a hydrogen storage tank, at the rear in front of the fuel tank 500. The energy storage unit 400 may be disposed, for example, in front of the fuel tank 500 and behind a rocker assembly 700, as shown in FIG. 2.

[0028] The rear powertrain 300 may be, for example, an internal combustion engine, which is often associated with rear-wheel drive vehicles, or it may be, for example, an electric motor, such as in the case of a hybrid vehicle, which holds the fuel tanks mentioned above to power the combustion engine, but also has an electric motor powered by a separate energy storage unit.

[0029] The rear powertrain 300 has a very significant weight, for example in the case of an internal combustion engine it usually weighs more than 100 kg, and even in the case of an electric motor it is still very heavy.

[0030] In the event of a rear impact, the kinetic energy of the collision transmitted through the rear bumper assembly 600 can move the significant mass towards the fuel tank 500, potentially leading to fuel tank failure. It is an object of the present invention to provide an innovative rear structure 1 to prevent such failure.

[0031] 3 and 4, the rear structure 1 comprises a lower structure 11 and an upper structure 12. Figure 3 actually shows only the lower structure 11, while Figure 4 shows an embodiment of the upper and lower structures fully assembled.

[0032] The undercarriage 11 includes left and right lower longitudinal beams 11L, 11R having their front ends attached to a rocker assembly 700 and their rear ends attached to a rear bumper assembly 600. Each of the lower longitudinal beams 11L, 11R is generally U-shaped with a lower horizontal wall and two substantially vertical side walls.

[0033] Because the rocker assembly 700 is located at a lower height than the rear bumper assembly 600, the front ends of the lower longitudinal beams 11L, 11R are located at a lower height than the rear ends of the lower longitudinal beams. The lower longitudinal beams 11L, 11R extend longitudinally to form three separate sections extending at different heights: the left and right front sections 11LF, 11RF extend substantially horizontally at the same height as the rocker assembly 700 to which they are attached; the left and right rear sections 11LB, 11RB extend substantially horizontally at the same height as the rear bumper assembly 600 to which they are attached; and the left and right intermediate sections 11LM, 11RM are located between the front and rear sections. The height transition between the front and rear sections occurs within the left and right intermediate sections 11LM, 11RM. More specifically, the intermediate portion comprises a lower bend in a transition region 11LFM, 11RFM with a front portion and an upper bend transition region 11LBM, 11RBM with a rear portion - between said lower bend and said upper bend, the intermediate portion extends longitudinally at an angle in height to ensure a height transition between the front and rear portions.

[0034] A fuel tank 500, and optionally an energy storage unit 400, are disposed between the left and right longitudinal beams and extend along the front portions 11LF, 11RF and middle portions 11LM, 11RM of the lower longitudinal beams. A rear powertrain 300 is also located between the left and right longitudinal beams, but further rearward, at least partially along the rear portions 11LB, 11RB of the lower longitudinal beams. As shown in FIGS. 2 and 3 , the undercarriage 11 further includes a rear transverse beam 11TP attached to both the left and right rear portions 11LB, 11RB of the lower longitudinal beams 11L, 11R. The rear powertrain 300 is attached to the rear transverse beam 11TP. In certain embodiments, a lower subframe is also attached to the rear transverse beam 11TP. The lower subframe is not directly subject of the present invention and is therefore not shown in the accompanying drawings.

[0035] In certain embodiments, the undercarriage further comprises additional cross beams 11T attached to the front or middle portions of the left and right lower longitudinal beams. The additional cross beams 11T may have a structural role of increasing the rigidity of the undercarriage, and may also have a functional role of serving as attachment points for structures that help secure a fuel tank and / or energy storage unit to the vehicle. For example, the fuel tank and / or energy storage unit rests on a series of U-shaped straps (not shown) located below the fuel tank and / or energy storage unit and secured at their tips to two of the additional cross beams 11T.

[0036] The rear structure 1 further comprises an upper structure 12. The upper structure 12 comprises left and right upper closure plates 12L, 12R attached to the lower longitudinal beams 11L, 11R and forming left and right closed hollow volumes 10L, 10R together with the lower longitudinal beams. The lower structure and the upper structure are attached, for example, by spot welding the upper closure plates along flanges present at the top of the lower longitudinal beams. Other assembly means, such as MIG / MAG welding or bolting, are also possible.

[0037] The upper closure plates 12L, 12R and associated enclosed hollow volumes 10L, 10R extend longitudinally along the rear structure 1. The forward ends of the upper closure plates and associated hollow volumes are substantially longitudinally aligned with the forward ends of the lower longitudinal beams' front portions 11LF, 11RF. In other words, the forward ends of the upper closure plates and the forward ends of the lower longitudinal beams share substantially the same X-coordinate. Meanwhile, the rear ends of the upper closure plates and associated hollow volumes are longitudinally disposed between the forward ends of the lower longitudinal beams' rear portions 11LB, 11RB and the rear transverse beam 11TP. In other words, the X-coordinate of the rear ends of the upper closure plates is at least equal to or greater than the coordinate of the forward ends of the rear portions, but less than the X-coordinate of the rear transverse beam 11TP.

[0038] The hollow volumes 10L, 10R are shown in Figure 5. Cross section AA is taken at the front portions 11LF, 11RF of the lower longitudinal beam near the transition regions 11LFM, 11RFM between the front and middle portions. Cross section BB is taken at the middle portions 11LM, 11RM near the transition regions 11LBM, 11RBM between the middle and rear portions.

[0039] The superstructure 12 further comprises at least one upper cross member 12T mounted between the upper closure plates 12L, 12R. The presence of the upper cross member 12T increases the stiffness of the superstructure 12 and ensures that both upper closure plates 12L, 12R cooperate efficiently with each other in the event of a collision.

[0040] The superstructure 12 is further characterized by the fact that it is fabricated from a single metal blank. The metal blank can be a monolithic blank, a tailored welded blank (including the possibility of a flexible blank), or a tailored rolled blank. This additional feature provides the solution with productivity and cost advantages by streamlining the manufacturing process to only one forming operation, instead of several separate forming operations followed by several assembly operations in the case of a multi-part design. This additional feature also provides a structural advantage because the superstructure 12 is made from a single, integral part, with no assembly points between sub-parts that tend to become structural weak points in assemblies susceptible to failure when subjected to heavy crash loads or repeated cyclic stresses of fatigue-type loads.

[0041] The above-described rear structural design makes it possible to efficiently protect the fuel tank 400 and the possible energy storage unit 500, especially in the case of a rear collision.

[0042] The aforementioned upper and lower bends in the front-to-middle transition zones 11LFM, 11RFM and the rear-to-middle transition zones 11LBM, 11RBM are geometric discontinuities that create structural weaknesses in the event of a rear impact. The load path of the crash energy transmitted from the rear bumper assembly 600 first passes through the approximately horizontally oriented rear portions 11LB, 11RB of the lower longitudinal beam. The crash energy then strikes the upper bends and then the lower bends, exerting a force that tends to increase the angle of the straight portions of the middle portions 11LM, 11RM with the horizontal, causing both the upper and lower bends to act as hinges during deformation. This deformation reduces the longitudinal clearance of the front and middle portions of the longitudinal beam. Because this is the exact area where the fuel tank 500 and, optionally, the energy storage unit 400 are located, this movement could damage the sensitive fuel tank and energy storage unit. This is particularly important given the presence of a rear powertrain at the rear that is propelled against a fuel tank and energy storage unit.

[0043] The upper structure 12 formed by the lower longitudinal beams and the hollow volumes 10L, 10R define a reinforced area of ​​the rear structure 1. This reinforcement provides a significant amount of rigidity and resistance to deformation in the area where the fuel tank and, possibly, the energy storage unit are located. In particular, the closure plates 12L, 12R and the associated hollow volumes are present in the upper and lower flexures, thus significantly reinforcing these structural weak points and preventing them from acting as hinges during a rear impact. The presence of the integral upper transverse beam 12 connecting the upper closure plates further strengthens this vulnerable area and ensures excellent coordination between the two sides, especially when only one side of the rear structure is aligned with the impactor (i.e., offset laterally from the impactor). It also serves to stiffen the area to be protected and prevent intrusion in the event of a side impact.

[0044] Thanks to the fact that the rear cross beam 11TP, on which the rear powertrain 300 is mounted, is not included in the reinforced area, the reinforced area of ​​the rear structure 1 is protected from intrusion of the powertrain 300 in the event of a rear collision.

[0045] Because the superstructure 12 does not extend longitudinally beyond the lower rear transverse beam 11TP, an unreinforced area necessarily remains in the rear portions 11LB, 11RB of the lower longitudinal beams. This unreinforced area, over which the upper closure plates 12L, 12R do not extend, is available to deform by crushing under the load of a rear impact, thereby absorbing at least a portion of the impact energy. This is one of the technical advantages of the present design, which ensures protection of the fuel tank by the presence of the upper closure plates 12L, 12R and the associated rigidified, enclosed hollow volumes 10L, 10R, while leaving at least a portion of the rear portions of the lower longitudinal beams unreinforced to absorb the impact energy.

[0046] In a specific embodiment, at least a portion of the rear portions 11LB, 11RB of the lower longitudinal beams are made using steel having a tensile strength of at least 800 MPa on the formed part and a bend angle of at least 70°, preferably at least 75°, normalized to 1.5 mm. Advantageously, the high tensile strength and high bend angle allow for the absorption of a lot of energy by deformation without significant cracking.

[0047] In certain embodiments, the aforementioned effect of having anti-intrusion zones in the front and middle sections and deformable zones in the rear section is further enhanced by providing the lower longitudinal beam front sections 11LF, 11RF and middle sections 11LM, 11RM with higher resistance to deformation than the rear sections 11LB, 11RB. This can be achieved, for example, by using a material for manufacturing the front and middle sections that has a higher product of ultimate tensile strength through average thickness than the material used to manufacture the rear sections. This can be achieved by manufacturing the lower longitudinal beam using a tailored welded or tailored rolled blank in which, after forming the part, the product of thickness through tensile strength of the material for the front and middle sections is higher than that of the rear sections. Advantageously, this allows the rear sections to deform under the force of a rear impact, thus deflecting at least a portion of the energy of the collision, all the more so since they are further reinforced by the upper closure plates 12L, 12R, while ensuring that the front and middle sections undergo limited deformation. Deflecting impact energy not only protects the fuel tank and energy storage unit, but also the vehicle occupants.

[0048] In certain embodiments, the above combination of materials with higher deformation resistance in the front and middle portions of the lower longitudinal beam and lower deformation resistance in the rear portion can be further combined with an increase in deformation resistance when progressing from the rear portion of the rear portion to the front portion of the rear portion. For example, the lower longitudinal beam can be made using a tailored welded blank in its rear portion, with a first sub-blank at the rear of said rear portion having a lower tensile strength per average thickness than a second sub-blank at the front of said rear portion. Advantageously, this allows for plastic deformation at the onset of impact in the very rear portion of the lower longitudinal beam, allowing for progressive absorption of more energy as the impact energy reaches the front of the rear portion.

[0049] In a particular embodiment, patches are used to reinforce specific areas of the front and middle sections of the lower longitudinal beam. The patches are additional reinforcements that are fixed to the metal blank before forming, for example by spot welding. Advantageously, this allows for a local increase in stiffness and resistance to deformation without having to increase the overall thickness of the part.

[0050] In certain embodiments, the undercarriage 11 is fabricated by forming a single metal blank. In other words, the left and right lower longitudinal beams 11L, 11R, and rear cross beam 11TB, as well as a possible additional cross beam 11T, are all integrated into a single metal blank formed as the undercarriage. For example, a tailored welded or tailored rolled blank may be used. This provides the same productivity and structural advantages as those described for the integrally formed upper structure 12.

[0051] Referring to Figure 6, a crash test is simulated to demonstrate the effectiveness of the design of the present invention in the case of a rear impact. The NHTSA rear impact assessment described above is simulated, in which a vehicle is impacted by a deformable barrier weighing 1368 kg, covering a 70% width offset, and traveling at an initial speed of 80 km / h.

[0052] Each lower longitudinal beam 11L, 11R was fabricated by hot stamping a steel laser-welded blank with three sub-blanks: the first sub-blank, corresponding to the front and middle sections 11LF, 11LM, 11RF, and 11RM, had an average thickness of 1.5 mm and a tensile strength of 1500 MPa after hot stamping; the second sub-blank, corresponding to the front section of the rear section, had an average thickness of 1.6 mm, a tensile strength of 1000 MPa, and a 75° bend angle normalized to 1.5 mm after hot stamping; and the third sub-blank, corresponding to the rear section of the rear section, had an average thickness of 1.2 mm, a tensile strength of 1000 MPa, and a 75° bend angle normalized to 1.5 mm after hot stamping. The construction is summarized in the table below.

[0053] [Table 1] Table 1: Impact simulation - configuration of the lower longitudinal beam sub-blank

[0054] The rear cross beam 11TB is made by pressing steel plate with an average thickness of 1.0 mm and a tensile strength of 600 MPa.

[0055] The superstructure 12 used in the crash simulation was fabricated using a steel laser-welded blank consisting of left and right upper closure plates and upper cross beams located at the front ends of the left and right upper closure plates. The upper closure plates extended from the front of the front portion of the lower longitudinal beam to the front of the rear portion of the lower longitudinal beam. The sub-blanks corresponding to the upper closure plates were fabricated using material with a tensile strength of 1500 MPa after hot stamping and an average thickness of 1.5 mm. The sub-blanks corresponding to the upper cross beams were fabricated using material with a tensile strength of 1500 MPa after hot stamping and an average thickness of 1.0 mm.

[0056] 6 shows a set of still images taken from a crash test simulation, illustrating the progression of the simulation using side (left) and bottom (right) views. The impactor 8 is shown in a simplified form to focus on the deformation of the vehicle 200 upon impact.

[0057] The timestamps of the stills are expressed in seconds after the start of the test. The top still is taken at the start of the test, at test time t=0 seconds. The middle still is taken at t=0.21 seconds, just after the start of the impact. The bottom still is taken at t=0.68 seconds, at the maximum penetration depth of the impactor just before rebound. For clarity, the different elements of the vehicle and rear structure are not labeled in the stills. For reference, this is the same vehicle as in Figure 2, with the locations of the rear powertrain 300, fuel tank 400, energy storage unit 500, etc. all shown in detail.

[0058] As can be seen from the figure, and verified by a detailed analysis of the simulation, the elements provided within the reinforced zone bounded by the front and middle portions 11LF, 11RF, 11LM, 11RM of the lower longitudinal beams, and topped by the upper closure plates 12L, 12R, remain intact even with maximum impactor penetration. There is no damage to the fuel tank 400 or the energy storage unit 500. On the other hand, the rear portions 11LB, 11RB of the lower longitudinal beams are significantly deformed under the loads applied by the impactor 8—especially the rear portion 11LB of the left lower longitudinal beam, which is more severely impacted considering the 70% offset directed towards the left side of the vehicle. This allows a significant amount of energy to be absorbed and dissipated to protect the vital elements of the vehicle and also the vehicle occupants.

[0059] The fact that the left and right upper closure plates 12L, 12R are integrally connected by the upper transverse beam 12T also played an important role in ensuring the structural stability and anti-intrusion properties of the front and middle parts of the rear structure 1.

[0060] Several configurations of the location of the at least one upper cross beam 12T are possible, including, but not limited to, those shown in Figure 7. The upper cross beam can be located at the front end of the upper closure plate, as in the crash test simulation described above. It can also be located at the rear end of the upper closure plate. It is also possible to have two upper cross beams, one at each end of the upper closure plate.

[0061] Other configurations are possible, such as an upper transverse beam between the rear and front ends of the upper closure plate. The location of the at least one transverse cross beam can be adapted to suit the specific design needs of the vehicle, depending on the available space and the required resistance to deformation during a collision or the overall stiffness requirements of the vehicle.

[0062] In a particular embodiment, at least part of the rear structure 1 is made of hot-stamped steel sheet, and the blanks used to manufacture it comprise one of the following materials, combined in the form of a monolithic blank or a tailored rolled blank, or in the form of a tailored welded blank:

[0063] A steel having a composition, by weight, of 0.06% C≦0.1%, 1%≦Mn≦2%, Si≦0.5%, Al≦0.1%, 0.02%≦Cr≦0.1%, 0.02%≦Nb≦0.1%, 0.0003%≦B≦0.01%, N≦0.01%, S≦0.003%, P≦0.020%, and less than 0.1% Cu, Ni, and Mo, with the remainder being iron and unavoidable impurities resulting from refining. With this composition range, the yield strength of the corresponding zone after hot stamping is between 700 and 950 MPa, the tensile strength is between 950 and 1200 MPa, and the bending angle is greater than 75°. For example, this material is used in the zones corresponding to the rear portions 11LB and 11RB of the lower longitudinal beams, because it absorbs energy without cracking and because this zone does not need to resist penetration but can advantageously absorb part of the impact energy by deformation.

[0064] Steels with an ultimate tensile strength after hot stamping between 1300 MPa and 1650 MPa and a yield strength between 950 MPa and 1250 MPa.

[0065] - Steels with an ultimate tensile strength after hot stamping between 1300 MPa and 1650 MPa, a yield strength between 950 MPa and 1250 MPa, and a bending angle of more than 75 °.

[0066] A steel having a composition, in weight percent, of 0.20%≦C≦0.25%, 1.1%≦Mn≦1.4%, 0.15%≦Si≦0.35%, Cr≦0.30%, 0.020%≦Ti≦0.060%, 0.020%≦Al≦0.060%, S≦0.005%, P≦0.025%, and 0.002%≦B≦0.004%, with the remainder being iron and unavoidable impurities resulting from processing. With this composition range, the ultimate tensile strength of the corresponding zones of the part after hot stamping is between 1300 MPa and 1650 MPa, and the yield strength is between 950 MPa and 1250 MPa. For example, this steel composition is used in the zones corresponding to the front and middle sections 11LF, 11RF, 11LM, and 11RM of the lower longitudinal beams, and / or in the upper closure plates 12L and 12R and at least one upper transverse beam 12T. In fact, this steel grade has high anti-penetration properties.

[0067] - Steel with a tensile strength higher than 1800 MPa after press hardening.

[0068] A steel having a composition, in weight percent, of 0.24%≦C≦0.38%, 0.40%≦Mn≦3%, 0.10%≦Si≦0.70%, 0.015%≦Al≦0.070%, Cr≦2%, 0.25%≦Ni≦2%, 0.015%≦Ti≦0.10%, Nb≦0.060%, 0.0005%≦B≦0.0040%, 0.003%≦N≦0.010%, S≦0.005%, P≦0.025%, and the remainder being iron and unavoidable impurities resulting from processing. In this composition range, the tensile strength of the corresponding zone after hot stamping is higher than 1800 MPa. For example, this material is used for the front and middle parts 11LF, 11RF, 11LM, 11RM of the lower longitudinal beams and / or for the upper closure plates 12L, 12R and at least one upper transverse beam 12T in order to benefit from its high anti-intrusion properties.

[0069] A steel having a composition comprising, in weight percent, 0.15-0.25% C, 0.5-1.8% Mn, 0.1-1.25% Si, 0.01-0.1% Al, 0.1-1.0% Cr, 0.01-0.1% Ti, 0.001-0.004% B, P≦0.020%, S≦0.010%, N≦0.010%, and optionally one or more of the following elements in weight percent: Mo≦0.40%, Nb≦0.08%, Ca≦0.1%, with the remainder of the composition being iron and unavoidable impurities resulting from refining. In this composition range, the tensile strength of the corresponding zone after hot stamping is greater than 1350 MPa, and the bending angle is greater than 70°.

[0070] A steel having a composition comprising, in weight percent, 0.26-0.40% C, 0.5-1.8% Mn, 0.1-1.25% Si, 0.01-0.1% Al, 0.1-1.0% Cr, 0.01-0.1% Ti, 0.001-0.004% B, P≦0.020%, S≦0.010%, N≦0.010%, and optionally one or more of the following elements in weight percent: Ni≦0.5%, Mo≦0.40%, Nb≦0.08%, Ca≦0.1%, with the remainder of the composition being iron and unavoidable impurities resulting from refining. In this composition range, the tensile strength of the corresponding zone after hot stamping is greater than 1350 MPa, and the bending angle is greater than 70°.

[0071] A steel having a composition comprising, in weight percent, C: 0.2-0.34%, Mn: 0.50-1.24%, Si: 0.5-2%, P≦0.020%, S≦0.010%, N≦0.010%, and optionally one or more of the following elements in weight percent: Al:≦0.2%, Cr≦0.8%, Nb≦0.06%, Ti≦0.06%, B≦0.005%, Mo≦0.35%, with the remainder of the composition being iron and unavoidable impurities resulting from refining. In this composition range, the tensile strength of the corresponding zone after hot stamping is 1000 MPa or more, and the bending angle is greater than 55°.

[0072] A steel having a composition, by weight, of 0.13-0.4% C, 0.4-4.2% Mn, 0.1-2.5% Si, Cr≦2%, Mo≦0.65%, Nb≦0.1%, Al≦3.0%, Ti≦0.1%, B≦0.005%, P≦0.025%, S≦0.01%, N≦0.01%, Ni≦2.0%, Ca≦0.1%, W≦0.30%, V≦0.1%, and Cu≦0.2%, where the combination is 114-68*C-18*Mn+20*Si-56*Cr-60*Ni-36*Al+38*Mo+79*Nb-17691*B<20, with the remainder being iron and unavoidable impurities resulting from refining. For example, this composition is used when hot stamping parts using a multi-step process.

[0073] Steel coated with an aluminum-based metallic coating. Aluminum-based means a coating comprising at least 50% aluminum by weight. For example, the metallic coating is an aluminum-based coating containing 8-12% Si by weight. The metallic coating is applied, for example, by immersing the substrate in a molten metal bath. Advantageously, applying an aluminum-based metallic coating avoids the formation of surface scale during the heating step of the hot stamping process, which allows parts to be manufactured by hot stamping without a subsequent sandblasting operation. Furthermore, the aluminum-based coating also provides corrosion protection to the part during use in the vehicle.

[0074] Steel coated with an aluminum-based metallic coating comprising 2.0 to 24.0% by weight of zinc, 1.1 to 12.0% by weight of silicon, optionally 0 to 8.0% by weight of magnesium, and optionally an additional element selected from Pb, Ni, Zr or Hf, the weight content of each additional element being lower than 0.3% by weight, the remainder being aluminum and optionally unavoidable impurities. Advantageously, this type of metallic coating provides very good corrosion protection on the part as well as good surface aspects after hot stamping.

[0075] In a particular embodiment, at least one element of the rear structure is made by hot stamping a laser-welded blank comprising at least one sub-blank with an aluminum-based metal coating, said aluminum-coated sub-blank having been previously prepared by ablating at least part of the metal coating on the edges to be welded, advantageously removing part of the aluminum present in the coating, which would contaminate the weld seam and reduce its mechanical properties.

[0076] In a specific embodiment, at least one element of the rear structure is produced by hot stamping a laser-welded blank comprising at least one sub-blank having at least one side covered with an emissivity-increasing top layer. The emissivity-increasing top layer is applied to the outermost surface of the sub-blank. The emissivity-increasing top layer allows the surface of the sub-blank to have a higher emissivity compared to the same sub-blank not coated with the emissivity-increasing top layer. The emissivity-increasing top layer can be applied to either the top or bottom surface of the sub-blank. The emissivity-increasing top layer can also be applied to both sides of the sub-blank. If the sub-blank comprises a metal coating as described above, the emissivity-increasing top layer is applied on top of the metal coating. In fact, the emissivity-increasing top layer must cover the outermost surface of the sub-blank to increase the emissivity of the surface. Advantageously, the emissivity-increasing top layer allows for an increased heating rate of the sub-blank, thus increasing the productivity of the heating step of the hot stamping process. When using several sub-blanks of different thicknesses, said emissivity-increasing top layer is advantageously applied to the sub-blank with the greatest thickness in order to reduce the difference in heating time between the different sub-blanks and therefore increase productivity, increase the hot stamping process window and make it possible to obtain a final part with overall uniform surface properties.

Claims

1. A rear structure (1) for an automobile vehicle (200) having a fuel tank (500) below a passenger seat and a powertrain (300) at the rear, comprising: - a substructure (11) comprising itself, - left and right lower longitudinal beams (11L, 11R) attached at their front ends to a rocker assembly (700) and at their rear ends to a rear bumper assembly (600), each of which has a front portion (11LF, 11RF) extending substantially horizontally at the same height as the rocker assembly (700), a rear portion (11LB, 11RB) extending substantially horizontally at the same height as the rear bumper assembly (600), and an intermediate portion (11LM, 11RM) located between the front and rear portions; - rear transverse beams (11TP) attached to the left and right rear portions (11LB, 11RB) and on which the rear powertrain (300) is mounted; a substructure (11) comprising: a superstructure (12) comprising itself, - left and right upper closure plates (12L, 12R) respectively attached to the lower longitudinal beams (11L, 11R) and forming left and right closed hollow volumes (10L, 10R) together with the lower longitudinal beams, - the front ends of the upper closure plates (12L, 12R) being substantially aligned with the front ends of the front parts (11LF, 11RF) of the lower longitudinal beams, - the rear ends of the upper closure plates (12L, 12R) being longitudinally arranged between the front ends of the rear parts (11LB, 11RB) of the lower longitudinal beams and the rear transverse beam (11TP); - at least one upper cross member (12T) mounted between said upper closure plates (12L, 12R); a superstructure (12) comprising: Equipped with the superstructure (12) is manufactured from a single metal blank; A rear structure (1) for an automobile vehicle (200) having a fuel tank (500) below a passenger seat and a powertrain (300) at the rear.

2. 2. The rear section (1) according to claim 1, wherein at least a portion of the rear section (11LB, 11RB) of the lower longitudinal beam is made of steel having a tensile strength of more than 800 MPa and a bending angle of at least 70° normalized to a thickness of 1.5 mm.

3. 3. A rear structure (1) according to claim 1 or 2, wherein the undercarriage (11) is manufactured from a single metal blank.

4. A rear structure (1) according to any one of claims 1 to 3, wherein the front (11LF, 11RF) and middle (11LM, 11RM) portions of the lower longitudinal beam have a higher deformation resistance than the rear (11LB, 11RB) portions.

5. A rear structure (1) according to any one of claims 1 to 4, wherein the material used to manufacture the rear structure is steel, and at least the lower longitudinal beams (11L, 11R) and the upper structure (12) are manufactured by hot stamping.

6. An automobile vehicle (200) having a fuel tank (500) below a passenger seat and a powertrain (300) at the rear, and having a rear structure (1) according to any one of claims 1 to 5.

7. 7. The automotive vehicle (200) of claim 6, further comprising an energy storage unit (400) disposed forward of the fuel tank (500) and aft of the rocker assembly (700).

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