Underbody for motor vehicle

Abstract

The invention relates to a motor vehicle underbody intended to define the lower part of a vehicle passenger compartment, said underbody comprising: - A pair of side members extending along the longitudinal direction of the vehicle; - A floor, in particular a central floor, extending transversely between the side members; - At least one elongated seat crossmember disposed on the upper face of the floor and extending transversely between the side members, said crossmember comprising a central portion and two lateral portions, each fixed at its end to the corresponding side member, at least one of the two lateral portions exhibiting ductile behavior and being capable of being plastically deformed, in whole or in part, under the effect of a lateral impact with an energy exceeding a predetermined value. Figure 2a

Description

Title of the invention: Underbody for motor vehicle technical field

[0001] The present invention relates to a chassis for a motor vehicle and a motor vehicle equipped with such a chassis. Technological background

[0002] The underbody of a motor vehicle, also called the "underbody structure", corresponds to the lower load-bearing part of the vehicle's body.

[0003] As is known per se, the underbody of a vehicle comprises several structural elements designed to ensure both the rigidity of the chassis and the protection of the occupants. The underbody includes a floor supported by two longitudinal members arranged on either side of the vehicle, as well as transverse cross members, in particular the front and rear seat cross members.

[0004] In the case of hybrid or electric vehicles, the underbody also supports essential elements for hybrid propulsion, such as the high-voltage battery pack, often installed under the central floor, between the front and rear seats.

[0005] Securing electrical components, such as batteries, as well as protecting occupants, is a major issue.

[0006] In particular, during a side impact, also known as a "pole impact," the presence of the propulsion battery pack raises a specific issue. Indeed, deformation of the underbody structure could lead to deformation of the batteries and damage to some of their cells, which presents significant risks, including electrocution or chemical burns for passengers.

[0007] This results in an increased need to improve the underbody structures in order to ensure optimal protection of the batteries and the passenger compartment. Summary of the invention

[0008] The invention aims to meet this need and relates to a motor vehicle underbody, in particular a central part of said underbody, intended to delimit a lower part of a vehicle passenger compartment, said underbody comprising: - A pair of lateral longitudinal members extending along the longitudinal direction of the vehicle; - A floor, in particular a central floor, extending transversely between the stringers, - At least one elongated seat crossmember positioned on the upper surface of the floor and extending transversely between the side rails, said cross member comprising a central portion and two lateral portions each fixed at their end to the corresponding spar, at least one of the two lateral portions exhibiting ductile behavior and being capable of being plastically deformed in whole or in part under the effect of a lateral shock of an energy greater than a predetermined value.

[0009] The seat crossmember according to the invention has several key advantages for vehicle safety and performance.

[0010] During a side impact, the rigid central portion provides increased structural resistance, helping to preserve the integrity of the passenger compartment and protect the occupants, while the ductile side portions deform more easily to absorb the impact energy and dissipate it gradually before it reaches the passenger compartment.

[0011] The ability of ductile portions to absorb and dissipate energy reduces the force transmitted to passengers during a side impact. This progressive deformation reduces the severity of the impact felt in the passenger compartment, thus decreasing the risk of serious injury to the occupants.

[0012] Furthermore, in hybrid or electric vehicles, the battery is often located under the floor, particularly near the seats, making it vulnerable in a side impact. The presence of the aforementioned side sections helps protect the battery by absorbing some of the impact energy before it reaches the area where the battery is housed. This reduces the risk of damage to the battery, preventing potential hazards such as fires, chemical leaks, or the risk of electrocution.

[0013] Furthermore, the incorporation of ductility directly into the structure of the seat crossmember ensures a compact design of the base.

[0014] A "side impact" or "pole impact" is a collision in which a vehicle is struck on one of its sides, rather than head-on or from the rear. This type of accident generally occurs when two vehicles collide perpendicularly, for example at an intersection, or when a vehicle collides with a fixed object, such as a pole or a tree.

[0015] “Ductile behavior” refers to the ability of lateral portions to deform significantly before breaking, while absorbing energy. Unlike a brittle portion, which breaks suddenly when subjected to stress, a portion exhibiting ductile behavior undergoes gradual plastic deformation under the effect of external forces, allowing it to change shape without fracturing immediately.

[0016] The predetermined value can be in the range of 20 to 30 kJ for a shock at approximately 29 to 32 km / h.

[0017] The seat crossbar may include an elongated beam, in particular made of a metallic material chosen, for example, from steel or aluminum. The beam may presenting a cross-section in the shape of an inverted U with a horizontal wall extending transversely and two lateral walls.

[0018] The beam can have a constant thickness along its longitudinal axis.

[0019] The beam may have a variable thickness along its longitudinal axis.

[0020] Preferably, the beam comprises the central portion and the aforementioned lateral portions.

[0021] The lateral portions may be symmetrical to each other with respect to a median plane of the seat cross member or beam.

[0022] The lateral portions may have an identical length, measured along the longitudinal axis of the seat cross member.

[0023] The lateral portions may each have a length less than 30% of the total length of the seat cross member.

[0024] Preferably, each lateral portion is a single piece. Preferably, the seat crossmember is configured to achieve ductile behavior without requiring the addition of add-on parts. The present invention eliminates the need for add-on parts on the seat crossmember by directly integrating structural characteristics into the crossmember design to achieve the desired ductility. This simplifies manufacturing, reduces weight and costs, while ensuring optimal performance in terms of safety and energy absorption during a side impact.

[0025] Preferably, the seat cross member is free of added parts intended to impart ductile behavior. As mentioned above, ductility is advantageously integrated directly into the structure of the cross member, without requiring additional or added parts.

[0026] The lateral portions may each comprise a ductile material, preferably metallic.

[0027] The ductile material can be a steel, in particular one chosen from among high-strength borated steels (PHS - Press Hardened Steel). A steel suitable for such an application could be Ductibor 500 steel, marketed by ArcelorMittal.

[0028] The ductile material can be aluminium.

[0029] In some embodiments, the central portion and the lateral portions are made of different materials.

[0030] The central portion may comprise a sheet metal material, such as steel, in particular a very high yield strength (VHS) or ultra-high yield strength (UHSS) type steel. A steel suitable for such an application may be Usibor 1500 steel marketed by ArcelorMittal.

[0031] The seat crossmember, in particular the beam, is obtained by assembling parts. The lateral portions can each be connected to the central portion by butting, welding or screwing, so as to form said seat crossmember.

[0032] Preferably, the seat cross member, in particular the beam, is monolithic, with the lateral and central portions being made from a single piece of material. In other words, the central portion and the lateral portions advantageously take the form of a single, unified block.

[0033] The seat cross member, in particular the beam, can be obtained by a stamping process, in particular hot or cold stamping.

[0034] The lateral portions may have a plurality of openings made at predefined locations so as to obtain said ductile behavior. The presence of such openings promotes deformation in the lateral portions. The perforated lateral portions can thus behave as "fuse-like" zones that will deform ductilely to absorb the shock, while the central portion remains rigid and ensures structural integrity.

[0035] The openings may have a rounded contour, in particular a substantially circular or oval shape. This helps to avoid stress concentrations at the corners, which improves the ability of the lateral portions to deform gradually without cracking.

[0036] The size of the openings is preferably proportional to the thickness and material of the seat cross member, in particular the beam.

[0037] The perforations can be formed by laser cutting, punching, or water jet. Preferably, the perforations are formed by laser cutting.

[0038] Preferably, the base comprises two seat cross members having one or more of the characteristics described above.

[0039] The cross members can be joined together at their central sections, for example at mid-length, by a bar. This stiffens the central area where the batteries are located. This ensures that, even if the ductile sections deform upon impact, the central area remains intact and continues to protect the batteries.

[0040] The invention also relates to a motor vehicle comprising the underbody according to the invention.

[0041] The vehicle may be of hybrid or electric type.

[0042] The vehicle preferably includes one or more battery packs, in particular located under the floor. Brief description of the figures

[0043] The following description, with reference to the accompanying drawings, given by way of non-limiting examples, will clearly explain what the invention consists of and how it can be implemented. In the accompanying figures:

[0044] [Fig-1] [Fig.1] is a schematic and partial view of a portion of a vehicle according to the invention,

[0045] [Fig.2a] and [Fig.2b] Figures 2a and 2b illustrate a base according to the invention,

[0046] [Fig.3a] [Fig.3a] is a top view of the central part of the base of the [Fig.2a]

[0047] [Fig.3b] [Fig.3b] is a bottom view of the central part of [Fig.3a],

[0048] [Fig.4a] [Fig.4a] shows in isolation, in top view, the seat crossbeams according to the invention,

[0049] [Fig.4b] [Fig.4b] is a detail of [Fig.4a], and

[0050] [Fig.4c] The [Fig.4c] is a view from below of the seat crossbeams of the [Fig.4a]. Description of method(s) of implementation

[0051] In the figures, and unless otherwise specified, identical elements shall bear the same reference symbols.

[0052] Figure 1 shows a motor vehicle 1 according to the invention. The vehicle is of the hybrid or electric type and, for this purpose, comprises one or more propulsion battery packs 50. The vehicle also comprises a passenger compartment area 7 arranged to accommodate the seats and occupants of the vehicle. The vehicle 1 further comprises a subframe 10 forming the lower part of the motor vehicle 1.

[0053] As illustrated in Figures 2a and 2b, the underbody 10 comprises three floors 12a, 12b, and 12c, respectively front, central, and rear, which extend substantially along the longitudinal direction of the vehicle, from front to rear. The central floor 12b is arranged to delimit the lower part of the passenger compartment 7 of the vehicle 1. The battery pack(s) 50 are located beneath the central floor 12b.

[0054] As can be seen in Figures 3a and 3b, the underbody 10 comprises a pair of lateral longitudinal members 14 extending parallel to the longitudinal axis X of the vehicle 1, and between which the central floor 12b extends transversely.

[0055] The base 10 further comprises two seat cross members 20 each arranged on the upper face of the central floor 12b and extending transversely between the side rails 14. As illustrated in particular in [Fig.1], the two seat cross members each have a longitudinal axis Yt perpendicular to the longitudinal axis X of the floor 12b and serve as support for the slides 5 of the vehicle seats 1.

[0056] In the illustrated example, each seat cross member 20 comprises a monolithic beam 22 of elongated shape made of metallic material, chosen for example from steel or aluminum. Preferably, beam 22 is made of steel. As can be seen in Figures 4a and 4c, beam 22 has a cross-section in the general shape of an inverted U with a horizontal wall 22a extending transversely and two lateral walls 22b extended by flanges 22c. In the illustrated example, the beam has a constant thickness along its longitudinal axis Yt.

[0057] Each beam 22, and therefore each seat crossbeam 20, comprises a central portion 24 arranged above the battery block(s) 50 and two lateral portions 26 fixed each at their end 27 to the corresponding spar 14.

[0058] As can be seen in particular in [Fig. 4b], each lateral portion 26 has a plurality of openings 28 made in the wall of the beam 22, for example by laser cutting. The openings 28 have rounded contours and are arranged in predefined locations to obtain ductile behavior. These openings 28 facilitate the deformation of the lateral portions. They act as "fuse zones," deforming ductilely to absorb the impact, while the central portion remains rigid, thus preserving structural integrity.

[0059] The lateral portions 26 are thus able to be plastically deformed in whole or in part under the effect of a lateral shock of an energy greater than a predetermined value.

[0060] The predetermined value may for example be in the range of 20 to 30 kJ for a shock at approximately 29 to 32 km / h, for tests carried out in accordance with safety standards such as the Euro NCAP side impact test or FMVSS 214.

[0061] The ductile lateral portions 26 extend over a length Ld less than 30% of the length L of the seat crossmember. As can be seen in [Fig. 1], the lateral portions 26 do not extend to the location of the battery pack(s) 50. Indeed, excessive deformation in this area could lead to risks to the integrity of the batteries, or even fires.

[0062] The central portion 24 of the seat crossmember 20 is located in relation to the battery block(s) 50. By its rigidity, it ensures that the batteries are not subjected to stress or deformation, which is essential for their safety.

[0063] In addition, the central portions of the two cross members are connected to each other by a bar which strengthens the protection of the battery block(s) by insulating and protecting the battery cells from impacts.

[0064] The underbody 10 further includes crash boxes 40 below the central floor 12b between the longitudinal members 14 and the battery blocks 50.

[0065] The invention is not limited to the example just described.

Claims

Demands

1. Underbody (10) of a motor vehicle (1) intended to delimit a lower part of a passenger compartment (7) of the vehicle, said underbody (10) comprising: - A pair of side rails (14) extending along the longitudinal direction of the vehicle (X); - A floor (12b), in particular a central floor, extending transversely between the side rails (14), - At least one seat cross member (20) of elongated shape disposed on the upper face of the floor (12b) and extending transversely between the side rails (14), said cross member (20) comprising a central portion (24) and two lateral portions (26) each fixed at their end (27) to the corresponding side rail, at least one of the two lateral portions (26) exhibiting ductile behavior and being capable of being plastically deformed in whole or in part under the effect of a lateral impact of an energy greater than a predetermined value.

2. Base according to the preceding claim, the lateral portions (26) each having a length (Ld) less than 30% of the total length (L) of the seat cross member.

3. Base according to claim 1 or 2, the lateral portion(s) (26) comprising a ductile material, preferably metallic, for example steel or aluminium.

4. Base according to any one of the preceding claims, the central portion (24) and the lateral portions (26) being made of different materials.

5. Base according to the preceding claim, the seat cross member (20) being obtained by assembling parts, the lateral portions (26) being connected each to the central portion (24) by butting, welding or screwing, so as to form said seat cross member (20).

6. Base according to any one of claims 1 to 4, the seat cross member (20) being monolithic, the lateral portions (26) and the central portion (24) being made of material.

7. Base according to the preceding claim, the seat cross member (20) being obtained by stamping.

8. Base according to claim 5 or 6, the lateral portions (26) comprising a plurality of openings (27) made at predefined locations so as to obtain said ductile behavior, in particular formed by cutting, the openings preferably having a rounded contour.

9. Base according to any one of the preceding claims, the base (10) comprising two seat crossbeams (20), preferably the seat crossbeams being joined together at their central portions (24), for example at mid-length, by a bar (29).

10. Motor vehicle (1), in particular of hybrid or electric type, comprising the underbody (10) according to any one of the preceding claims, and one or more battery packs (50) arranged under the floor (12b).

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