Front structure for electric vehicle

Abstract

To provide a design that optimizes energy absorption capacity of a tunnel nose and ensures that the tunnel nose is prevented from being pressed down toward a battery pack.SOLUTION: A front part structure 1 for an electric vehicle includes a lower dash panel 3, a seat cross member 9, and a tunnel nose 15. The tunnel nose absorbs energy at a front part thereof while resisting penetration at a rear part thereof, and thus energy absorption of a component during a front collision is optimized to prevent a battery pack from being damaged due to downward pressure effect of the lower dash panel.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a front structure for a motor vehicle with an electric powertrain, hereinafter referred to as an electric vehicle. The present invention further relates to a method for manufacturing such a front structure. [Background technology]

[0002] Environmental concerns and regulations related to increasing atmospheric carbon dioxide levels and local air pollution levels are driving the rise of electric vehicles. Compared to traditional internal combustion engine vehicles, electric vehicles have smaller engines, no fuel tanks, and no exhaust systems. On the other hand, electric vehicles have large battery packs that are not present in internal combustion engine vehicles.

[0003] These significant differences are resulting in a change in the global architecture of automotive vehicles. Electric vehicle designs must accommodate new powertrains and take advantage of the extra space provided by smaller engines and the absence of exhaust systems and fuel tanks. Meanwhile, electric vehicles must also take into account new requirements such as the additional weight of the battery pack and the need to protect it in the event of an accident.

[0004] In an internal combustion engine, the passenger compartment floor structure includes a tunnel that houses the exhaust system, located below the floor panel. The tunnel extends between the front seats and through the center of the rear floor panel. The tunnel is connected to the lower dash panel structure by a front section, commonly called the nose, that bends upward to accommodate the shape of the exhaust manifolds in the engine compartment.

[0005] For electric vehicles, the lack of an exhaust system means that such a tunnel is unnecessary. However, it may be interesting to retain part of the tunnel, i.e., the front section or nose, to accommodate creating space for equipment related to the battery pack located under the floor panel. For example, it may be interesting to house the electronic power management system in the tunnel nose. Furthermore, the tunnel nose can provide access points to the electronic power management system and the battery pack itself, which is one of the safety requirements related to the battery pack.

[0006] The front structure of a vehicle must be able to withstand a frontal collision by absorbing energy within the vehicle structure and ensuring that no intrusion occurs within the critical area occupied by the vehicle occupants. In the case of electric vehicles, further requirements are placed on the behavior of the battery pack in the event of a collision. Indeed, if the battery pack is breached, dangerous chemicals may be released from the battery cells, leading to health and fire hazards.

[0007] One such frontal crash test is Federal Motor Vehicle Safety Standard 208 (FMVSS 208), which requires a vehicle to impact a rigid barrier spanning the full width of the vehicle at a speed of 56 km / h.

[0008] The presence of the aforementioned separate tunnel nose poses challenges to the integrity of the battery pack during a frontal collision. In fact, the lower dash panel to which the tunnel nose is attached tends to push the nose downward during a frontal collision. This is primarily due to the fact that the lower dash panel is tilted vertically, with the top of the lower dash panel located closer to the front of the vehicle than the bottom of the lower dash panel. Under the impact of a collision, the front crash management system tends to push the upper portion of the lower dash panel forward, thereby correcting the lower dash panel toward the vertical. This, in turn, has the effect of pushing the rear of the nose downward toward the battery pack, which can lead to catastrophic failure of the battery pack and serious complications for the safety of passengers and rescue teams. Summary of the Invention [Problem to be solved by the invention]

[0009] One of the objectives of the present invention is to overcome these limitations by proposing a design that optimizes the energy absorption capacity of the tunnel nose while ensuring that the tunnel nose is not forced downwards towards the battery pack. [Means for solving the problem]

[0010] To this end, the present invention relates to a front structure for an electric vehicle, comprising a lower dash panel, a seat cross member extending generally laterally and attached at both ends to a transverse reinforcing structure of the vehicle, and a tunnel nose, the front structure comprising: a front portion attached to at least the lower dash panel; a rear portion attached to at least the seat cross member; Equipped with The product of the average thickness and ultimate tensile strength of the rear portion is greater than or equal to the product of the average thickness and ultimate tensile strength of the front portion, and the front portion is made from a material having a failure strain of at least 0.6 and a critical bend angle of at least 75°.

[0011] Yield strength, ultimate tensile strength, and uniform and total elongation are measured according to ISO standard ISO 6892-1, published October 2009.

[0012] By applying the above-mentioned invention, it is possible to control the deformation of the tunnel nose during a frontal collision and avoid damage to the battery pack. The described invention also makes it possible to optimize the amount of energy absorbed by giving the front part the role of energy absorption.

[0013] According to other optional features of the front structure according to the invention, considered alone or according to any possible technical combination, there is provided: The material from which the tunnel nose is manufactured has a minimum ultimate tensile strength of at least 700 MPa in part.

[0014] The front part has at least one geometric change part that locally changes its cross-section.

[0015] At least part of the tunnel nose is produced by hot stamping a material that has a tensile strength of at least 1000 MPa after hot stamping.

[0016] The composition of the aforementioned press-hardened steel is, by weight percentage, 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%, 0.002% ≤ B ≤ 0.004%, and the balance is iron and inevitable impurities resulting from processing.

[0017] At least part of the tunnel nose is produced by cold stamping a material that has a tensile strength of at least 950 MPa.

[0018] At least part of the tunnel nose is produced by cold stamping a material that has a chemical composition, by weight percentage, of 0.13% < C < 0.25%, 2.0% < Mn < 3.0%, 1.2% < Si < 2.5%, 0.02% < Al < 1.0%, 1.22% < Si + Al < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05%, with the balance being Fe and inevitable impurities, and has a microstructure containing 8% - 15% retained austenite, and the balance is ferrite, martensite, and bainite, and the total of the martensite fraction and the bainite fraction is included between 70% and 92%.

[0019] At least a part of the tunnel nose is manufactured by cold stamping a material, and the material has a chemical composition containing, by weight percentage, 0.15% < C < 0.25%, 1.4% < Mn < 2.6%, 0.6% < Si < 1.5%, 0.02% < Al < 1.0%, 1.0% < Si + Al < 2.4%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, the balance being Fe and inevitable impurities, has a microstructure containing 10% - 20% retained austenite, and the balance is ferrite, martensite and bainite.

[0020] The tunnel nose is formed by stamping a tailored welded blank.

[0021] The tunnel nose is formed by stamping a tailored rolled blank.

[0022] The present invention further provides a method for manufacturing the aforementioned rear structure 1, comprising: providing a blank; stamping the blank into the shape of the tunnel nose; attaching the tunnel nose to the lower dash panel; attaching the tunnel nose to the seat cross member; and a method comprising the above steps.

[0023] Other aspects and advantages of the present invention will become apparent upon reading the following description given by way of example and made with reference to the accompanying drawings.

Brief Description of the Drawings

[0024] [Figure 1] An overall perspective view of a vehicle according to the present invention. [Figure 2] An overall perspective view of the front structure according to the present invention. [Figure 3] An individual perspective view of the tunnel nose according to the present invention. [Figure 4A]4A and 4B show rear crash test simulations of a vehicle according to the present invention using the FMVSS 208 standardized crash described above, with FIG. 4A showing the situation before the crash occurs. Each figure consists of a top view and a perspective view from the front of the passenger compartment. [Figure 4B] 4A and 4B show rear crash test simulations of a vehicle according to the present invention using the FMVSS 208 standardized crash described above, with FIG. 4B showing the situation 100 ms after the crash. Each figure consists of a top view and a perspective view from the front of the passenger compartment. DETAILED DESCRIPTION OF THE INVENTION

[0025] In the following description, the terms "upper," "lower," "front," "rear," "lateral," and "longitudinal" are defined according to the normal directions of the vehicle on which they are mounted. More specifically, the terms "upper" and "lower" are defined according to the elevation direction of the vehicle, the terms "front," "rear," and "longitudinal" are defined according to the fore-aft direction of the vehicle, and the term "lateral" is defined according to the width of the vehicle. "Substantially parallel" or "substantially perpendicular" means a direction that can deviate from the parallel or perpendicular directions by no more than 15°.

[0026] More specifically, the terms "fracture strain" and "critical bend angle" refer to the fracture strain and critical bend angle criteria defined by Pascal Dietsch et al. in "Methodology to assess fracture during crash simulation: fracture strain criteria and their calibration" in Metallurgical Research Technology Volume 114, Number 6, 2017. The critical bend angle defines the angle at which the first crack is detected on the backside of a sample deformed according to the standardized VDA-238-100 standard. The fracture strain is the associated equivalent strain in the material at the deformation point when the critical bend angle is reached.

[0027] Yield strength, ultimate tensile strength, and uniform and total elongation are measured according to ISO standard ISO 6892-1, published October 2009.

[0028] The average thickness of a part or portion of a part is the thickness of the corresponding area of ​​the sheet used to manufacture said part.

[0029] The term "controlled buckling" refers to a deformation mode of a part subjected to a compressive load, in which the part gradually absorbs the mechanical energy of the compressive load by forming a series of successive waves resulting from successive localized buckling deformations of the part. As a result, the length of the part measured in the direction of the compressive load is smaller than the initial length of the part in said direction after deformation. In other words, when a part responds to a compressive load by controlled buckling, it folds in on itself in the same way as a plastic bottle when a compressive load is applied between the top and bottom of the bottle.

[0030] 1 and 2, a description will be given of a front structure 1 of an electric vehicle 16 having a battery pack 2 located under a floor panel 4 of a passenger compartment 5. The front structure 1 includes at least: a lower dash panel 3 separating the passenger compartment 5 from the forward engine compartment 7; a seat cross member 9 extending generally laterally and attached at both ends to a lateral reinforcing structure 13 of the vehicle; A tunnel nose 15 located approximately at the center of the passenger compartment 5 in the width direction; Equipped with.

[0031] The front structure 1 is connected to lateral reinforcing structures 17 on both sides of the vehicle. The lateral reinforcing structures 17 comprise, for example, the following elements: side sills 8 extending longitudinally along the bottom of the vehicle body, front or A-pillars 10 arranged in front of the front doors with their lower parts connected to the side sills 8 and their upper parts rising to the roof of the vehicle, center or B-pillars 12 arranged between the front and rear doors, and rear or C-pillars 14 arranged behind the rear doors.

[0032] The lower dash panel 3 is a large panel that closes off the passenger compartment 5 at its lower front end. It is connected to the transverse reinforcing structure 17 on its sides and to the front end of the floor panel 4 at its bottom end. It typically features multiple openings 6 intended for the steering column or pedals for the driver. Its primary function is to separate the passenger compartment 5 from the engine compartment 7 and therefore does not have a primary structural role in the event of a frontal collision. It is typically made of a soft material with a low average thickness that can be deformed into the complex shapes required by vehicle designers for this component without adversely affecting the overall vehicle weight. For example, the lower dash panel 3 is typically made of a steel designed for deep drawing, with an average thickness between 0.5 mm and 0.9 mm and an ultimate tensile strength of less than 350 MPa.

[0033] The lower dash panel 3 is generally angled relative to the vertical, with the bottom of the lower dash panel 3 being further rearward than the top of the lower dash panel 3. This is due to the general shape of the engine compartment 7 and the need for chassis mechanical elements at the lower front of the vehicle.

[0034] The seat cross-member 9 is a structural component for reinforcing the overall vehicle rigidity and supporting the lateral reinforcing structure 17. In the particular embodiment shown in Figure 2, the seat cross-member 9 has a U-shaped cross section with two side walls and one top wall. It is also possible to design a tubular seat cross-member 9 or any other shape deemed appropriate for that function.

[0035] In certain embodiments, the seat cross member 9 is attached to the floor panel 4. For example, the seat cross member 9 is attached by welding to the top of the floor panel 4, as shown in FIG.

[0036] In the event of a lateral collision, the seat cross member 9 functions as an anti-intrusion component, protecting the driver and passengers from the intrusion of the impactor. Therefore, it is typically manufactured using very high-strength steel, which does not need to exhibit high ductility when installed in the vehicle because it is not expected to absorb energy by deforming under the impact, but rather to maintain its shape and length as much as possible. For example, the seat cross member is made of a material with an ultimate tensile strength of more than 1800 MPa and an average material thickness before forming of between 1.3 mm and 2.0 mm.

[0037] The seat cross members 9 are attached to the transverse reinforcing structures 17 on both sides of the vehicle. The seat cross members 9 are attached to the transverse reinforcing structures 17 by, for example, spot welding. For example, the seat cross members 9 are attached to the transverse reinforcing structures 17 by welding them onto the side sills 8.

[0038] 2 and 3 , tunnel nose 15 has two side walls 30 and a top wall 32. An interior volume defined by the interior of tunnel nose 15 can be used, for example, to house an electronic power management system for battery pack 2. In certain embodiments, tunnel feature opening 18, for example, in top wall 32, is intended to provide access to elements housed within the interior volume. Tunnel nose 15 comprises at least a front portion 21 and a rear portion 23. Front portion 21 is attached to at least lower dash panel 3, for example, by welding a flange 25 of tunnel nose 15 to lower dash panel 3. Rear portion 23 is attached to at least seat cross member 9, for example, by welding a flange 27 of the rear portion to seat cross member 9.

[0039] The tunnel nose 15 is designed so that the product of the average thickness and ultimate tensile strength of the rear portion 23 is equal to or greater than the product of the average thickness and ultimate tensile strength of the front portion 21. This product reflects the ability to deform under load. Because the rear portion 23 has a greater or equal thickness than the front portion 21, the front portion 21 tends to deform before the rear portion 23 when the part is subjected to a load, such as a compressive load applied at both ends. The tunnel nose 15 is also designed so that the front portion 21 is made from a material with a failure strain of at least 0.6 and a critical bend angle of at least 75°. This allows the front portion 21 to deform without fracture during a frontal collision, as described in more detail below.

[0040] In certain embodiments, tunnel nose 15 is further attached to floor panel 4 at a portion of front portion 21 and / or rear portion 23. For example, tunnel nose 15 is attached by spot welding flange 25 to floor panel 4.

[0041] For example, in the case of a frontal collision simulated by the aforementioned standardized crash test FMVSS 208, the impact force initially compresses the engine compartment 7, as shown in FIG. 4B. The compressed engine compartment 7 then applies a load to the lower dash panel 3, causing the lower dash panel 3 to deform, as seen in FIG. 4B. The load is also transmitted to the tunnel nose 15. Because the front portion 21 tends to deform before the rear portion 23, the front portion 21 is deformed by the transmitted impact force, as previously described. More precisely, the transmitted impact force F is counteracted by the reaction force R applied by the seat crossmember 9, as shown in FIG. 4B. Under the compressive load resulting from the combined action of mechanical forces F and R, the front portion 21 deforms by folding in on itself, thereby mechanically absorbing a large amount of energy from the collision. This contributes to the overall energy absorption of the front structure, which acts to protect the vehicle occupants as well as the battery pack 2.

[0042] Furthermore, by folding onto itself, the front portion 21 prevents the rear portion 23 from moving under the influence of the transmitted impact force F, thereby preventing the rear portion 23 from destroying the battery pack 2 located below the tunnel nose 15.

[0043] In the particular embodiment shown in Figures 3, 4A and 4B, the front portion 21 comprises a geometric change 22. The geometric change locally modifies the cross section of the front portion 21 and therefore acts as a trigger for deformation under compressive load. Advantageously, this allows the vehicle designer to control the location of the onset of deformation under compressive load.

[0044] In the particular embodiment shown in FIG. 3 , the rear portion 23 includes at its rear end a step 29 designed to fit the shape of the rear cross member 9. Indeed, since the volume below the floor panel 4 is generally occupied by the battery pack 2, it is advantageous to design the seat cross member 9 to be located above the floor panel 4. In such a case, it is advantageous to include at the rear end of the rear portion 23 a step 29 having a shape complementary to that of the seat cross member 9. This makes it possible to maximize the attachment surface between the rear portion 23 and the seat cross member 9, and also increases the support and resistance effect to counteract the impact force F transmitted by the resistance force R during a frontal collision.

[0045] In certain embodiments, the material from which tunnel nose 15 is made has an ultimate tensile strength of at least 700 MPa. Advantageously, this ensures structural stability for tunnel nose 15 and also ensures that tunnel nose 15 absorbs a significant amount of energy as it deforms during a crash.

[0046] In certain embodiments, at least a portion of the tunnel nose 15 is produced by hot stamping a material having a tensile strength of at least 1000 MPa after hot stamping. Advantageously, the use of hot stamping technology enables the production of complex shapes with high resistance and no springback problems after forming. Furthermore, by using a high-strength material having a mechanical resistance exceeding 1000 MPa in the final part, high energy absorption during a collision is ensured.

[0047] For example, the press-hardened steel described above has, by weight %, 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%, 0.002% ≤ B ≤ 0.004%, and the balance is iron and inevitable impurities resulting from processing.

[0048] In certain embodiments, at least a portion of the tunnel nose 15 is produced by cold stamping a material having a tensile strength of at least 950 MPa. Advantageously, by using a high-strength material having a mechanical resistance exceeding 950 MPa in the final part, high energy absorption during a collision is ensured. Furthermore, by using cold stamping instead of hot stamping as described in the previous embodiment, the manufacturing cost can be reduced.

[0049] For example, the tunnel nose 15 is produced by cold stamping a material having a chemical composition including, by weight %, 0.13% < C < 0.25%, 2.0% < Mn < 3.0%, 1.2% < Si < 2.5%, 0.02% < Al < 1.0%, 1.22% < Si + Al < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05%, the balance being Fe and inevitable impurities, and having a microstructure including 8% - 15% retained austenite, the balance being ferrite, martensite, and bainite, with the total of the martensite fraction and the bainite fraction being included between 70% and 92%.

[0050] In another example, the tunnel nose 15 is made by cold stamping a material having a chemical composition of 0.15% < C < 0.25%, 1.4% < Mn < 2.6%, 0.6% < Si < 1.5%, 0.02% < Al < 1.0%, 1.0% < Si + Al < 2.4%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5% by weight, the balance being Fe and inevitable impurities, and having a microstructure containing 10% - 20% retained austenite, the balance being ferrite, martensite and bainite.

[0051] According to a particular embodiment, the tunnel nose 15 is made by stamping a tailored welded blank. The tailored welded blank can be made of materials with different average thicknesses and strength levels for cold stamping. Alternatively, it can be made of materials with different average thicknesses and strength levels for hot stamping. Advantageously, by using different grades and average thicknesses, the designer can more flexibly optimize the performance and weight of the part. For example, the front portion 21 is made of a material having a lower average thickness and / or a lower ultimate tensile strength than the rear portion 23.

[0052] According to a particular embodiment, the tunnel nose 15 is made by stamping a tailored rolled blank. This offers similar advantages as in the case of the aforementioned tailored welded blank. For example, the front portion 21 is made of a material having a lower average thickness than the rear portion 23.

[0053] In a specific embodiment, tunnel nose 15 is fabricated from a material having an average thickness between 0.8 mm and 2.0 mm. For example, tunnel nose 15 is fabricated by hot stamping a tailored welded blank having a first portion corresponding to front portion 21 made of material having an average thickness of 1.1 mm and an ultimate tensile strength of greater than 1000 MPa after hot stamping, and a second portion corresponding to rear portion 23 having an average material thickness of 0.9 mm and an ultimate tensile strength of greater than 1500 MPa after hot stamping. The product of the average thickness and ultimate tensile strength of rear portion 23 can be verified to be 1200 MPa·mm, which is higher than the 1100 MPa·mm of front portion 21.

[0054] Next, a method for manufacturing the above-mentioned rear structure will be described, which comprises: providing a blank; stamping the blank into the shape of the tunnel nose; Steps for attaching the tunnel nose to the lower dash panel; attaching the tunnel nose to the seat cross member; Equipped with.

Claims

1. A front structure (1) for an electric vehicle (2) comprising: a lower dash panel (3) separating a passenger compartment (5) from a front engine compartment (7); a seat cross member (9) extending generally laterally and attached at both ends to a lateral reinforcing structure (17); and a tunnel nose (15), The tunnel nose (15) comprises a front portion (21) and a rear portion (23) located rearward of the front portion; The front portion (21) is attached to the lower dash panel (3), The rear portion (23) is attached to the seat cross member (9), the product of the average thickness and ultimate tensile strength of the rear portion (23) is greater than the product of the average thickness and ultimate tensile strength of the front portion (21), the front portion (21) being made of a material having a fracture strain of at least 0.6 and a critical bend angle of at least 75°; The material from which the tunnel nose (15) is made has an ultimate tensile strength of at least 700 MPa in part. Front structure (1).

2. 2. A front structure (1) according to claim 1, wherein the front part (21) is provided with at least one geometrical change (22) which locally changes its cross section.

3. 3. The front structure (1) according to claim 1 or 2, wherein at least a part of the tunnel nose (15) is made by hot stamping a material having a tensile strength of at least 1000 MPa after hot stamping.

4. The composition of the press hardened steel is, in weight percent:

4. The front structure (1) according to claim 3, wherein the contents of the alloy are: 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%, 0.002%≦B≦0.004%, and the remainder being iron and unavoidable impurities resulting from processing.

5. 3. The front structure (1) according to claim 1 or 2, wherein at least a part of the tunnel nose (15) is made by cold stamping a material having a tensile strength of at least 950 MPa.

6. at least a portion of the tunnel nose (15) is made by cold stamping a material having a chemical composition comprising, in weight percent, 0.13%<C<0.25%, 2.0%<Mn<3.0%, 1.2%<Si<2.5%, 0.02%<Al<1.0%, 1.22%<Si+Al<2.5%, Nb<0.05%, Cr<0.5%, Mo<0.5%, Ti<0.05%, the balance being Fe and unavoidable impurities, and having a microstructure comprising 8% to 15% retained austenite, the balance being ferrite, martensite and bainite; The front structure (1) according to claim 5, wherein the sum of the martensite and bainite fractions is comprised between 70% and 92%.

7. 6. The front structure (1) according to claim 5, wherein at least a portion of the tunnel nose (15) is made by cold stamping a material having a chemical composition comprising, in weight percent, 0.15%<C<0.25%, 1.4%<Mn<2.6%, 0.6%<Si<1.5%, 0.02%<Al<1.0%, 1.0%<Si+Al<2.4%, Nb<0.05%, Cr<0.5%, Mo<0.5%, the remainder being Fe and unavoidable impurities, and having a microstructure comprising 10% to 20% retained austenite, the remainder being ferrite, martensite and bainite.

8. A front structure (1) according to any one of claims 1 to 7, wherein the tunnel nose (15) is formed by stamping a tailored welded blank.

9. A front structure (1) according to any one of claims 1 to 7, wherein the tunnel nose (15) is formed by stamping a tailor rolled blank.

10. A method for manufacturing a front structure (1) according to any one of claims 1 to 9, comprising the steps of: providing a blank; stamping the blank into the shape of the tunnel nose (15); attaching the tunnel nose to the lower dash panel (3); attaching the tunnel nose to the seat cross member (9); A method for providing the above.

Images