Flat battery box for electric or hybrid vehicles, equipped with a rigid cover.

Abstract

A traction battery casing for an electric or hybrid motor vehicle, forming a generally rectangular flat assembly, comprising a metal cover plate (14) fixed by its perimeter to the top of this casing, which has ribs (16) formed in its thickness, arranged along axes forming concentric rounded closed contours (22), each closed contour having several arc-shaped ribs (16) separated from each other by flat intermediate zones (24), between two adjacent closed contours (22) the flat intermediate zones (24) forming non-overlapping angular sectors. Figure 3

Description

Title of the invention: FLAT BOX FOR A TRACTION BATTERY FOR AN ELECTRIC OR HYBRID VEHICLE EQUIPPED WITH A RIGIDIFIED COVER

[0001] The present invention relates to a flat battery box for a traction battery of an electric or hybrid motor vehicle equipped with a cover, as well as a motor vehicle comprising such a battery box.

[0002] Certain electric or hybrid motor vehicles include a battery powering an electric traction machine which is installed flat under the floor of the vehicle to use a large available surface area, while arranging its mass in the lower part of the body in order to obtain a center of gravity of the vehicle located at a low height.

[0003] A known type of electric vehicle battery, presented in particular by document CN-U-218300105, comprising a flat rectangular shape elongated in the longitudinal direction of the vehicle, comprises a box having a lower container receiving the electrochemical elements, and a cover formed by a substantially flat sheet covering the entire battery, which has a contour fixed on an upper edge of the container to seal the box.

[0004] Generally speaking, to limit the mass of the vehicle and its cost, and to optimize the interior volume available in the battery box, the cover is made from a relatively thin metal sheet. In order to improve the rigidity of the cover, in particular to reduce the amplitude of the first-order vertical oscillations of its central part, the sheet has a network of stamped ribs giving it greater rigidity, without increasing the mass.

[0005] In particular, the battery cover comprises in its central part longitudinal ribs extending over a large part of the length of this cover, which are framed on each side by continuous curved ribs which start from a lateral edge and return to it. At each end of the longitudinal ribs, a curved transverse rib connects the two lateral edges together.

[0006] Furthermore, for their approval, motor vehicles undergo standardized side impact tests on a small diameter post, which concentrate the force on a reduced surface area on the side of the vehicle. In particular, the battery box trays generally have rigid side edges arranged near the sides of the vehicle, in order to protect the battery contained inside in the event of an impact on this vehicle.

[0007] In this case, even if the box is not deformed, transmissions can be obtained of energy in the cover of the box, causing vibrations of its central part along a vertical axis which are poorly limited by the network of ribs of the cover presented in the prior art document.

[0008] A vibration of the cover of too great an amplitude can cause problems of contact between the sheet metal of this cover and the electrochemical elements contained inside, and cause damage including risks of electrical damage and fire.

[0009] The present invention aims in particular to avoid these problems of the prior art.

[0010] To this end, it proposes a traction battery box for an electric or hybrid motor vehicle forming a substantially rectangular flat assembly, comprising a metal cover sheet fixed by its contour to the top of this box, which has ribs made in its thickness, this box being remarkable in that the ribs are arranged along axes having concentric rounded closed contours, each closed contour comprising several arcuate ribs separated from each other by flat intermediate zones, and in that between two neighboring closed contours the flat intermediate zones form angular sectors which do not overlap.

[0011] An advantage of this battery box is that in the event of a side impact on the vehicle which is reflected on the side of the battery box cover, energy transmission is obtained mainly through the flat surfaces of the sheet metal of this cover, which enters the first outer contour through an intermediate zone between two arcuate ribs of this first contour.

[0012] The flat intermediate zones of the second contour having an angular offset, the vibrational energy must first propagate in a circumferential direction before reaching a flat intermediate passage zone inside this next contour. Then for each passage in the next contour the energy must in the same way first propagate circumferentially.

[0013] A baffle system is thus produced which, with the propagations imposed in the circumferential direction between two contours, begins by widely dispersing the energy over the entire surface of the cover before it reaches its center. The energy arriving at the center of the cover is greatly attenuated, it gives a low vibration amplitude which protects the battery in the box.

[0014] It is possible to use a cover sheet having a limited thickness, which reduces the mass and costs, and to position the cover as close as possible to the battery, which makes it possible to optimize the volume of the compartment. Protection of the battery elements located inside is provided in a simple and effective manner, without adding a stiffening component to the cover, which would increase the mass and costs.

[0015] The electric or hybrid vehicle traction battery box according to the invention may additionally include one or more of the following characteristics, which may be combined with each other.

[0016] Advantageously, the system of ribs has symmetry with respect to a longitudinal axis and a transverse axis of the rectangular assembly.

[0017] In particular, each closed contour may comprise two to four ribs.

[0018] In this case, the first closed contour arranged towards the center may comprise two ribs, the following closed contours each comprising four ribs.

[0019] Advantageously, on each closed contour, along the circumferential direction the length of the ribs is greater than the length of the flat intermediate zones.

[0020] Advantageously, each rib has a height of between 10 and 20 mm.

[0021] Advantageously, each rib has in its cross section a width between 30 and 50mm.

[0022] Advantageously, the radial distance between two neighboring closed contours is between 100 and 150 mm.

[0023] Advantageously, the cover sheet made of steel has a surface area greater than 1m2 and a thickness less than 1mm.

[0024] The invention also relates to an electric or hybrid motor vehicle comprising a battery integrated in a box comprising any one of the preceding characteristics, remarkable in that this box is arranged flat under the floor of the vehicle between the front and rear axles.

[0025] The invention will be better understood and other characteristics and advantages will appear more clearly on reading the description below given by way of example, with reference to the appended drawings in which:

[0026] [Fig.l] is a top view of a side impact test on an electric vehicle comprising a battery box according to the invention;

[0027] [Fig.2] is a cross-sectional view of this battery box;

[0028] [Fig.3] is a top view of the cover of this box; and

[0029] [Fig.4] is a view detailing in cross section a rib of this cover.

[0030] Throughout the document the upper or above orientation is relative to the vertical direction for a vehicle placed on horizontal ground.

[0031] [Fig.l] shows an electric motor vehicle 2 arranged along a longitudinal axis A, which comprises a traction battery integrated in a sealed box 8 comprising a substantially rectangular flat shape arranged under the floor of the vehicle, between the front and rear axles. The lateral edges of the battery box 8 arrive at a small distance from the sides of the vehicle 2 in order to occupy a major part of the surface of the floor.

[0032] A standardized vehicle side impact resistance test bench 2 comprises a vertical bar 4 rigidly connected to a mass 6 which is projected with a speed V on the side of the vehicle, with a small angle to its transverse direction. We obtain a penetration of the bar 4 on the side of the vehicle 2, with a transmission of energy which is absorbed by the different components arranged on this side which deform.

[0033] Figures 2 and 3 show the battery box 8 comprising a lower sheet 10, two lateral side members 12 formed by aluminum profiles having closed cells in order to present a high resistance, and an upper cover sheet 14 comprising ribs 16. The box 8 receives electrochemical battery cells 18 which are fixed on the floor sheet 10.

[0034] The cover plate 14 has on its periphery a series of holes 20 receiving tightening screws on the contour of the box 8 in order to ensure a seal on this contour, to protect the interior cells 18 from projections and impacts.

[0035] The cover plate 14 has a central point of ribs O arranged at the intersection of the longitudinal axis A, and a transverse axis B which is slightly offset from the middle of its longitudinal direction. The cover plate 14 has five circles 22 forming concentric circular axes of ribs 16, centered on the central point O, which are spaced apart at a constant radial distance. The fifth outermost circle 22e extends beyond the lateral sides of the cover plate 14, the fourth circle 22d arranged just before is complete.

[0036] Generally speaking, the ribs 16 can be arranged according to concentric closed contours, such as ovals which would make it possible to better cover the rectangular shape of the cover 14.

[0037] Each circle 22 comprises several ribs 16 each forming an arc of a circle, which are separated from each other by flat intermediate zones 24 covering a portion of an angular sector. All of the ribs 16 are symmetrical with respect to the longitudinal axis A and the transverse axis B.

[0038] The first inner circle 22a comprises two ribs 16 arranged symmetrically on each side of the transverse axis B, leaving between them two intermediate zones 24 centered on the transverse axis B. The second circle 22b comprises four ribs 16 centered on the longitudinal axis A and the transverse axis B, leaving between them four intermediate zones 24 centered on the diagonals between these axes. The intermediate zones 24 of the second circle 22b are angularly offset relative to the intermediate zones of the first circle 22a, without angular overlap, so as to obtain an angular overlap between the ribs 16 of these two circles.

[0039] The third circle 22c has four ribs 16 which are arranged along the diagonals. The fourth circle 22d has four ribs 16 which are centered on the longitudinal axis A and transverse axis B. The fifth circle 22e has four ribs 16 which are centered on the diagonals.

[0040] In this way, along the radial directions, between two neighboring circles 22, flat intermediate zones 24 are obtained, forming angular sectors which do not overlap, and therefore ribs 16 forming angular sectors having ends which systematically overlap.

[0041] [Fig. 4] shows a cross-section of the grooves 16, comprising from the general lower level of the cover plate 14 an elevation having two slightly inclined flat sides closing upwards, a flat top, and connecting radii between these surfaces.

[0042] Advantageously, the ribs 16 have a height H of between 10 and 20 mm, a width W of between 30 and 50 mm, and a distance between two neighboring concentric circles 22 of between 100 and 150 mm, for a cover having a surface area of ​​more than 1 m2 which is formed with a steel sheet less than one millimeter thick.

[0043] During the standardized lateral impact shown [Fig.l], a deformation of the vehicle body is obtained, and an impact on the lateral side member 12 on this side of the battery box 8, which depending on the intensity of the impact can transmit energy to the cover plate 14. The cover plate 14 forming a substantially flat assembly having a large surface area, has a vertical vibrational natural mode of its central part which will be excited with the energy received.

[0044] The flat parts of the cover sheet 14 between two circles 22, and angularly between two ribs 16 forming the intermediate zones 24, can vibrate more easily due to their flexibility while transmitting the energy by propagation, whereas the various highly rigid ribs 16 constitute obstacles to this propagation.

[0045] The energy coming from the lateral impact of the post 4 on the side of the battery box is partly transmitted to the cover 14, outside the fourth circle 22d directly towards one of its ribs 16 arranged between the two spaced ribs of the fifth circle 22e. The direction of propagation of the energy will then abut on the rib 16 of the fourth circle 22d located opposite, to move away on each side in a circumferential direction 30.

[0046] Arriving at the level of the first intermediate zone 24d of the fourth circle 22d, the direction of propagation of the energy 32 will divide into a circumferential direction which continues straight ahead, and a radial direction which enters at the intermediate of this fourth circle. The entry into this fourth circle 22d following the radial direction will in turn come up against the ribs 16 of the third circle 22c arranged opposite the intermediate zones 24d of the fourth circle, to have to divide again into two opposite circumferential directions.

[0047] We thus realize from the fourth circle 22e, at each passage towards the interior of the following circle a division of the propagation of the energy which leaves according to the two di opposite circumferential sections. The energy received on one side of the cover 14 is distributed laterally with respect to the direction of the shock, without being able to directly and quickly access its center O. The central part of the cover 14 receives a low level of energy, its natural vibration mode is little excited with a limited oscillation amplitude.

[0048] It is thus possible to produce a cover 14 with a sheet of limited thickness, and to arrange it near the internal electrochemical elements 18 while ensuring their protection, which makes it possible to reduce the mass and the costs of this cover, and optimizes the use of the internal volume of the box 8.

Claims

Claims

1. Traction battery box for an electric or hybrid motor vehicle forming a substantially rectangular flat assembly, comprising a metal cover sheet (14) fixed by its contour to the top of this box (8), which has ribs (16) made in its thickness, characterized in that the ribs (16) are arranged along axes forming concentric rounded closed contours (22), each closed contour (22) comprising several arcuate ribs (16) separated from each other by flat intermediate zones (24), and in that between two neighboring closed contours (22) the flat intermediate zones (24) form angular sectors which do not overlap.

2. Battery box according to claim 1, characterized in that the rib system (16) has symmetry with respect to a longitudinal axis and a transverse axis of the rectangular assembly.

3. Battery box according to claim 1 or 2, characterized in that each closed contour (22) comprises two to four ribs (16).

4. Battery box according to claim 3, characterized in that the first closed contour arranged towards the center (22a) comprises two ribs (16), the following closed contours each comprising four ribs (16).

5. Battery box according to any one of the preceding claims, characterized in that on each closed contour (22) in the circumferential direction the length of the ribs (16) is greater than the length of the flat intermediate zones (24).

6. Battery box according to any one of the preceding claims, characterized in that each rib (16) has a height of between 10 and 20 mm.

7. Battery box according to any one of the preceding claims, characterized in that each rib (16) has in its cross section a width of between 30 and 50 mm.

8. Battery box according to any one of the preceding claims, characterized in that the radial distance between two neighboring closed contours (22) is between 100 and 150 mm.

9. Battery box according to any one of the preceding claims, characterized in that the cover sheet (14) made of steel has a surface area greater than 1m2 and a thickness less than 1mm.

10. Electric or hybrid motor vehicle comprising a battery integrated in a box (8) according to any one of the preceding claims, characterized in that this box (8) is arranged flat under the floor of the vehicle (2) between the front and rear axles.