Electric vehicle lower structure

Abstract

The present invention provides an electric vehicle lower structure which has a simple shape and which comprises a battery bottom cover for protecting a battery sufficiently. Provided is an electric vehicle lower structure comprising a battery tray (20) and a battery bottom cover (60A) which is provided under the battery tray (20) and which covers the bottom surface of the battery tray (20), wherein: the battery tray (20) includes a battery mounting region and a battery non-mounting region; and the battery bottom cover (60A) is an integrally molded body of fiber-reinforced plastic, has a connection portion which is connected to the battery non-mounting region, and has a protruding portion which protrudes downward of a vehicle so as to correspond to the battery mounting region.

Description

Electric vehicle undercarriage

[0001] The present invention relates to an undercarriage of an electric vehicle.

[0002] Electric vehicles are equipped with batteries as their power source. For example, Patent Document 1 discloses a battery structure for electric vehicles. The battery structure includes a battery case for at least one battery module, a top belt, a bottom belt, and a protector that connects them.

[0003] Patent Document 2 describes a battery housing for a vehicle battery, which includes at least one module receiving portion, which is surrounded by at least a side wall and an intermediate floor, and which is protected from the intrusion of objects from below by an underride guard disposed below the intermediate floor.

[0004] The battery pack described in Patent Document 3 is installed under the floor panel, and the pack outer cloth is attached to the bottom of the battery pack. The battery undercover is located under the pack outer cloth and is composed of side cover pieces and a center cover piece arranged in the vehicle width direction.

[0005] US Patent No. 5,949,999 provides an energy storage device and structure including a plurality of energy storage cells, each having a lateral area and spaced a specified distance apart.

[0006] In Patent Document 5, a vehicle is provided with a locker, a floor panel, a battery pack, a bracket, and an undercover to protect the battery pack. The battery pack has a tray, a partition plate, and multiple battery cells, and the undercover is disposed below the tray, and the undercover is partially displaced upward and disposed below the partition plate.

[0007] International Publication No. 2018 / 149762 International Publication No. 2018 / 153781 Japanese Patent Application Publication No. 2020-044880 US2019 / 0372173 Japanese Patent Application Publication No. 2022-065523

[0008] However, the battery undercover described in Patent Document 1 has a complex structure made up of a skin core, making it difficult to manufacture. In addition, because the structure of the battery undercover is uniform throughout, the rigidity of the battery undercover is excessive in areas of the battery tray where rigidity is high.

[0009] In Patent Documents 2 and 3, the undercover for protecting the lower part of the battery tray has a structure that combines multiple layers of rigid and strong members. This makes it possible to reduce the weight, but the complex structure makes it difficult to produce.

[0010] The invention described in Patent Document 4 has a recess in the tray that corresponds to the battery position, but this is an invention of a battery tray, and there is insufficient consideration given to a battery under-cover to protect the battery tray.

[0011] In the invention described in Patent Document 5, although the battery undercover is partially connected to the non-battery area, it has a generally simple flat shape, and therefore, when fiber-reinforced plastic is used as the battery undercover, the weight increases in order to ensure rigidity.

[0012] Therefore, the present invention provides a lower structure for an electric vehicle that has a simple shape and is equipped with a battery undercover for protecting the battery to a necessary and sufficient extent.

[0013] As a result of extensive investigations, the present inventors have found that the above problems can be solved by the following means, and have arrived at the present invention.

[0014] 1. An understructure for an electric vehicle comprising a battery tray and a battery undercover provided below the battery tray and covering the bottom surface of the battery tray, wherein the battery tray has a battery mounting area and a battery non-mounting area, and the battery undercover is an integrally molded body made of fiber reinforced plastic, has a connection part that connects to the battery non-mounting area, and has a convex part facing downward toward the vehicle to correspond to the battery mounting area. 2. The understructure for an electric vehicle according to paragraph 1, wherein α expressed by the following formula (1) satisfies 0 < α < 2.00. where p is the pitch (mm) of the connection portions and h is the height (mm) of the convex portions. 3. The understructure for an electric vehicle according to claim 2, wherein the convex portions have a repeating structure, and the pitch is the distance between the centers of adjacent circumscribing circles when circumscribing circles of the convex portions are drawn. 4. The understructure for an electric vehicle according to any one of claims 2 or 3, wherein the pitch p of the connection portions is 3 mm or more and 1500 mm or less, and the height h of the convex portions is 3 mm or more and 20 mm or less. 5. The understructure for an electric vehicle according to any one of claims 1 to 4, wherein the battery provided in the battery tray is a battery in which single cells are directly arranged. 6. The understructure for an electric vehicle according to any one of claims 1 to 5, wherein the rigidity of the connection portions is less than the rigidity of the convex portions.

[0015] By giving the battery undercover a simple shape and providing protrusions in optimal positions, it is possible to provide a lightweight battery undercover that is easy to produce and ensures rigidity and strength.

[0016] Perspective view of the battery box 10A of the first embodiment. Exploded perspective view of the battery box 10A. Cross-sectional view taken along the arrow III-III in FIG. 1. Cross-sectional view of the battery box 10B of another form. Cross-sectional view taken along the arrow V-V in FIG. 2. Perspective view of the battery box 110A of the second embodiment. Exploded perspective view of the battery box 110A. Cross-sectional view taken along the arrow VIII-VIII in FIG. 6. Cross-sectional view of the battery box 110B of another form. Cross-sectional view taken along the arrow X-X in FIG. 7. Perspective view of the battery box 210A of the third embodiment. Exploded perspective view of the battery box 210A. Cross-sectional view taken along the arrow XIII-XIII in FIG. 11. Cross-sectional view taken along the arrow XIV-XIV in FIG. 12. Cross-sectional view of the battery box 210B of another form. Explanatory diagram of the method for measuring the amount of deformation by applying a load to the battery under cover in Examples 1 to 12 and Comparative Examples 1 to 4. Explanatory diagram of the method for measuring the amount of deformation by applying a load to the battery under cover in Examples 13 to 24 and Comparative Examples 5 to 8. Diagram plotting the values of Examples 1 to 12 and Comparative Examples 1 to 4. The pitch p (mm) is plotted on the horizontal axis, and the amount of deformation per load (Displacement, mm / N) is plotted on the vertical axis, with the height h of the convex portion changed.

[0017] The embodiments of the present invention will be described below, but the present invention is not limited thereto. [First Embodiment] FIG. 1 is a perspective view of the battery box 10A of the first embodiment, and FIG. 2 is an exploded perspective view of the battery box 10A. FIG. 3 is a cross-sectional view taken along the arrow III-III in FIG. 1. The lower structure of the electric vehicle according to the embodiment of the present disclosure includes a battery tray 20 and a battery under cover 60A provided under the battery tray 20 and covering the bottom surface of the battery tray 20.

[0018] [Floor Panel] The battery box 10A in the present disclosure is preferably installed under the floor panel. The floor panel refers to the floor portion of the electric vehicle. It is the floor portion that spreads under the feet when entering the vehicle interior. The floor panel is also related to the safety of the vehicle. During a collision, the floor panel plays a role in protecting the occupants and improves safety by increasing the rigidity of the vehicle body. The floor panel supports the floor of the vehicle and ensures comfort and safety.

[0019] [Battery Tray] 1. General The battery 50 is stored in a battery box 10A that includes a battery tray 20 and a battery cover 40. The battery box 10A is installed, for example, on the floor panel under the seat or under the floor panel. When the battery capacity is large, it is preferable to place the battery box 10A under the floor panel in the lower part of the vehicle body.

[0020] The battery tray 20 stably and securely holds the battery 50, which functions as the power source for the vehicle, and secures the battery 50 to protect it from vibration and impact. The battery tray 20 is designed to fit the shape of the battery 50 and may be equipped with mounting fixtures or fixing devices to facilitate the installation and removal of the battery 50. Vents and a cooling fan to help cool the battery 50 may also be incorporated into the battery box 10A.

[0021] 2. Battery Mounting Area and Non-Battery Mounting Area The battery tray 20 in the present disclosure has a battery mounting area and a non-battery mounting area. The battery mounting area is an area on the underside of the battery tray 20 that corresponds to the battery 50 mounted on the battery tray 20, specifically, the area that corresponds to the battery housing section 22 that houses the battery 50. The non-battery mounting area is an area that does not correspond to the battery 50, specifically, the area that corresponds to the internal partition wall 21 that surrounds the battery housing section 22.

[0022] 3. Battery Tray Material There are no particular limitations on the material of the battery tray 20 in the present disclosure, and it may be made of metal such as iron or aluminum, or fiber-reinforced plastic.

[0023] 4. Cell-to-Pack Format The battery 50 mounted on the battery tray 20 is preferably a battery in which single cells are directly arranged. In contrast to a battery that combines "cells," the smallest unit that functions as a battery, to form "modules," and then uses the combined modules as a "pack," a cell-to-pack battery box eliminates the need for modules and mounts the combined cells directly as a pack on the vehicle. This is also known as "moduleless technology." Another approach is "cell-to-chassis," in which the battery box system itself is incorporated into the vehicle structure. Compared to using modules, the cell-to-pack format offers cost benefits by improving energy density through more efficient use of space and reducing the number of required parts.

[0024] [Battery Undercover] The lower structure of an electric vehicle according to the present disclosure includes a battery undercover 60A that covers the bottom surface of the battery tray 20. The battery undercover 60A is designed to deform and absorb impact energy when struck by an object such as a stone, gravel, or metal fragment from the road.

[0025] Conventional battery undercovers for protecting battery boxes (including battery trays) often have complex shapes, making them extremely difficult to manufacture. Furthermore, the battery undercover extends to areas of the battery tray or battery box that are highly rigid, resulting in excessive rigidity. Conversely, if the battery undercover were to have a simple, flat shape, the weight would increase in order to ensure the required rigidity.

[0026] 1. Connection Portion The battery undercover 60A of the present disclosure has a connection portion 61A that connects to the non-battery area of ​​the battery tray 20. Here, the "non-battery area" refers to an area of ​​the underside of the battery tray 20 that does not correspond to the battery 50 mounted on the battery tray 20. For example, the non-battery area is an area of ​​the underside of the battery tray 20 that corresponds to the internal partition wall 21. The connection portion 61A of the battery undercover 60A depicted in FIG. 3 is connected to an area of ​​the underside of the battery tray 20 where no battery 50 is mounted. In this way, connecting the battery undercover 60A to the non-battery area utilizes the strength and rigidity of the battery tray 20 and reduces impact on the battery 50. For example, the internal partition wall 21 of the battery tray 20 can absorb impact from the battery undercover 60A.

[0027] In the present disclosure, the connection portion 61A preferably has a flat shape. This is because the bottom surface of a battery tray is generally flat. There are no particular limitations on the method for joining the battery tray 20 and the connection portion 61A, and examples of such methods include fastening with bolts and nuts, welding, adhesion with an adhesive, joining with clips and clamps, joining with rings and pins, press-fit joining, rivet joining, and riveting, which joins parts using a combination of rivets and adhesive.

[0028] 2. Convex Portion The battery undercover 60A of the present disclosure has a convex portion 62A facing downward toward the vehicle to correspond to the battery mounting area, and preferably satisfies the requirement that the rigidity of the connection portion 61A is less than the rigidity of the convex portion 62A. The convex portion 62A may be solid, or there may be a space between the convex portion 62A and the battery tray 20 (e.g., as shown in FIG. 3 ). However, from the perspective of easy molding, it is preferable that there be a space between the convex portion 62A and the battery tray 20. "To correspond to the battery mounting area" may refer to a battery undercover 60A in which one convex portion 62A is provided for one battery mounting area, or a battery undercover 60B in which one convex portion 62B is provided for multiple battery mounting areas, as shown in FIG. 4.

[0029] For example, the battery undercover 60A in Fig. 3 has a convex portion 62A facing downward toward the vehicle, which prevents the battery 50 from being affected by an impact even if the battery undercover 60A is subjected to the impact, thereby protecting the battery 50. Meanwhile, the connection portion 61A is connected to the non-battery mounted area, so that even if an impact is received, it is unlikely to have a negative effect on the battery 50. In other words, by satisfying the requirement that the rigidity of the connection portion 61A is less than the rigidity of the convex portion 62A, it is possible to easily achieve both impact resistance and connection to the battery tray 20 without making the battery undercover 60A a complex structure.

[0030] In a preferred embodiment of the present disclosure, the connecting portion 61A has a flat plate shape, and the protruding portion 62A has a convex shape. In this case, the structural rigidity of the protruding portion 62A can be easily made higher than the structural rigidity of the connecting portion 61A having a flat plate shape. In other words, the protruding portion 62A has a small amount of deformation when subjected to a load, while the flat connecting portion 61A has a large amount of deformation when subjected to a load, but this is not a major problem. In this specification, the structural rigidity of the connecting portion 61A and the protruding portion 62A may be simply referred to as the rigidity of the connecting portion 61A and the rigidity of the protruding portion 62A.

[0031] The battery undercover 60A, including the connecting portion 61A and the protruding portion 62A, is integrally molded. Therefore, although the connecting portion 61A and the protruding portion 62A are made of the same material, the protruding portion 62A has higher rigidity. Because the battery undercover 60A has a simple shape consisting of the connecting portion 61A and the protruding portion 62A, it can be formed from a single sheet of plate material. For example, the battery undercover 60A can be formed by forming the protruding portion 62A on a metal plate using press molding or the like.

[0032] 3. Relationship between the Pitch p of the Connection Portions and the Height h of the Protrusions 3.1 The pitch of the connection portions 61A is illustrated at p in Figure 5. Figure 5 is a cross-sectional view taken along the V-V arrow in Figure 2. In Figures 2 and 5, the connection portions 61A have a repeating structure, and the repeating interval is the pitch p of the connection portions 61A. Furthermore, as shown at h in Figure 5, the height h of the protrusions 62A is the length of the protrusions 62A in the vertical direction of the vehicle (Z-axis direction). As shown in Figure 5, h is the distance from the bottom surface of the battery undercover 60A to the bottom of the protrusions 62A, and does not include the plate thickness of the battery undercover 60A.

[0033] 3.2 Formula (1) In the battery undercover 60A of the present embodiment, it is preferable that α expressed by the following formula (1) satisfies 0<α<2.00.

[0034] In the formula, p is the pitch (mm) of the connection portions, and h is the height (mm) of the protrusions. The range within which the desired rigidity is achieved is defined by the value of α. As described above, if α is within a specific range, it is possible to effectively increase the rigidity of the battery undercover 60A and reduce its weight.

[0035] In the above formula (1), increasing the height h of the convex portion 62A means increasing α. If the height h of the convex portion 62A is reduced and α becomes 0, the convex portion 62A will have a completely flat plate shape, failing to provide structural rigidity to the battery undercover 60A. Conversely, if the height h is large and the pitch p is small, i.e., if α is 2.00 or greater, the convex portion 62A will have a deeply tapered shape, making molding the battery undercover 60A difficult. The larger the value of α, the greater the amount of deformation upon impact and the greater the amount of impact absorption. However, because the design space under the battery undercover is limited, α is preferably less than 2.00. Furthermore, if the height h is too high, it will be difficult to place the battery undercover in the lower part of the vehicle. Thus, the height h and pitch p do not have an independent effect.

[0036] The value of α is more preferably 0<α<1.50, more preferably 0<α<1.00, more preferably 0<α<0.70, more preferably 0<α<0.50, more preferably 0<α<0.25, more preferably 0.05≦α<0.20, and more preferably 0.05≦α<0.10.

[0037] 4. Height h The height h is preferably more than 0 mm and not more than 20 mm. The height h is more preferably more than 0 mm and not more than 10 mm, even more preferably more than 0 mm and not more than 6 mm, still more preferably 0.1 mm or more and not more than 4 mm, and most preferably 0.3 mm or more and not more than 4 mm.

[0038] 5. Pitch p The pitch p is a multiple of the pitch of the non-battery-mounted region, and p is preferably 3 mm or more and 1500 mm or less. The lower limit of the pitch p is more preferably 5 mm or more, more preferably 10 mm or more, more preferably 15 mm or more, more preferably 20 mm or more, and more preferably 25 mm or more. The upper limit of the pitch p is more preferably 500 mm or less, more preferably 300 mm or less, more preferably 150 mm or less, and more preferably 30 mm or less.

[0039] 6. Definition of Pitch Because the protrusions 62A are provided to correspond to the battery mounting area, they have a repeating structure with a pitch equal to a multiple of the pitch of the battery mounting area. The pitch of the protrusions 62A is preferably equal to the pitch p of the connection portions 61A. The pitch of the protrusions 62A is the distance between the centers of adjacent circumscribing circles of the protrusions 62A. If multiple circumscribing circles can be drawn, the pitch of the protrusions 62A may be the distance between the centers of the smallest circumscribing circles that encompass the entire outer edge of the protrusions 62A. In addition, when drawing the circumscribing circles, the protrusions 62A are observed from the vertical direction of the electric vehicle (the Z-axis direction in Figures 1 and 2).

[0040] 7. Shape of the Convex Portion There are no particular limitations on the shape of the convex portion 61A when observed from the top-bottom direction of the electric vehicle (the Z-axis direction in FIGS. 1 and 2 ), but it may be circular, elliptical, or polygonal. In other words, the convex portion 61A may be conical, columnar, dome-shaped, pyramidal, ribbed, or curved. Furthermore, it is preferable that the convex portion 61A has a repeating structure, and the repeating structure may be wavy or random.

[0041] Second Embodiment Fig. 6 is a perspective view of a battery box 110A according to a second embodiment, and Fig. 7 is an exploded perspective view of the battery box 110A. Fig. 8 is a cross-sectional view taken along the line VIII-VIII in Fig. 6. Note that components similar to those in the first embodiment are designated by the same reference numerals with the same last two digits, and a description thereof will be omitted.

[0042] While the battery 50 in the first embodiment was cylindrical, the battery 150 in the second embodiment is rectangular. Accordingly, the shape of the battery accommodating portion 121 of the battery tray 120 corresponds to the shape of the battery 150. Furthermore, the shape of the protrusion 162A of the battery under-cover 160A is rectangular, similar to the shape of the battery 150 when viewed from above, and is a quadrangular pyramid.

[0043] 8 shows a battery undercover 160A in which one protrusion 162A is provided for one battery mounting area (area corresponding to the battery housing section 121). On the other hand, as shown in FIG. 9, a battery undercover 160B may be provided in which one protrusion 162B is provided for multiple battery mounting areas (areas corresponding to the battery housing section 121).

[0044] The pitch of the connection portions 161A is illustrated by p in Figure 10. Figure 10 is a cross-sectional view taken along the X-X arrow in Figure 7. In Figures 7 and 10, the connection portions 161A are structured to be repeated in the X and Y directions of Figure 7, and this repetition interval is referred to as the pitch p of the connection portions 161A. Furthermore, the height h of the protrusions 162A is the length of the protrusions 162A in the vertical direction of the vehicle (Z-axis direction), as shown by h in Figure 10. As shown in Figure 10, h is the distance from the lower surface of the battery undercover 160A to the bottom of the protrusions 162A, and does not include the plate thickness of the battery undercover 160A. The protrusions 162A have a repeating structure that is repeated at the same pitch p as the connection portions 161A. The pitch of the protrusions 162A is the distance between the centers of adjacent circumscribing circles of the protrusions 162A. When multiple circumscribing circles with different diameters can be drawn, the distance between the centers of the smallest circumscribing circles that encompass the entire outer edge of the convex portion 162 A may be used as the pitch of the convex portion 162 A. When drawing the circumscribing circles, the convex portion 162 A is observed from the vertical direction of the electric vehicle (the Z-axis direction in FIGS. 6 and 7 ).

[0045] Third Embodiment Fig. 11 is a perspective view of a battery box 210A according to a third embodiment, Fig. 12 is an exploded perspective view of the battery box 210A, Fig. 13 is a cross-sectional view taken along the line XIII-XIII in Fig. 11, and Fig. 14 is a cross-sectional view taken along the line XIV-XIV in Fig. 12. Note that components similar to those in the second embodiment are designated by the same reference numerals with the last two digits omitted, and a description thereof will be omitted. In this embodiment, as shown in Fig. 12, a battery undercover 260A has connection portions 261A extending in the Y direction and protrusions 262A extending in the Y direction alternately arranged in the X direction.

[0046] The pitch of the connection portions 261A is shown by p in Figure 14. In Figures 12 and 14, the connection portions 261A are configured to repeat in the X direction, and the repetition interval in the X direction is the pitch p of the connection portions 161A. Furthermore, as shown by h in Figure 14, the height h of the protrusions 162A is the length of the protrusions 262A in the vertical direction of the vehicle (Z-axis direction). As shown in Figure 14, the plate thickness of the battery undercover 260A is not included in the height h.

[0047] 13 illustrates a battery undercover 260A in which one protrusion 262A is provided for one row of battery mounting areas in the Y direction (areas corresponding to one row of battery housing sections 221 in the Y direction). On the other hand, as shown in FIG. 15, a battery undercover 260B may be provided in which one protrusion 262B is provided for multiple rows of battery mounting areas in the Y direction (areas corresponding to multiple rows of battery housing sections 221 in the Y direction).

[0048] 7.1 Cell-to-pack case One protrusion may be provided for one battery cell, or one protrusion may be provided for multiple battery cells. For example, as shown in Figs. 4 and 9, one protrusion may be provided for two battery cells.

[0049] 7.2 When Modules Are Included One protrusion may be provided for one battery module, or one protrusion may be provided for multiple battery modules. That is, modules formed by combining cells, which are the smallest unit of a battery, may be arranged as in the battery 50 of the first embodiment and the battery 150 of the second embodiment and housed in the battery tray 20, 120. In this case, as shown in Figures 4 and 9, one protrusion may be provided for, for example, two battery modules.

[0050] [Battery Undercover: Integral Molded Body] The battery undercover is an integrally molded body made of fiber-reinforced plastic. Integral molding means that it is molded continuously without any seams and is not formed by joining separate components. This type of integral molding creates a structure in a single molding operation, preferably achieved by press molding. Because it is created by integral molding, separate parts can be processed as a single part, making it possible to reduce the unit price of the part. In addition, the number of assembly steps is reduced, and the reduced number of parts also makes it possible to reduce inventory costs.

[0051] [Battery Undercover: Resin] The resin contained in the battery undercover, which is a fiber-reinforced plastic, may be either thermosetting or thermoplastic.

[0052] 1. Thermoplastic Resin When the resin used is a thermoplastic resin, the type is not particularly limited, and a resin having a desired softening point or melting point can be appropriately selected and used. As the thermoplastic resin, one having a softening point in the range of 180°C to 350°C is usually used, but is not limited thereto.

[0053] Examples of thermoplastic resins include polyolefin resins, polystyrene resins, polyamide resins, polyester resins, polyacetal resins (polyoxymethylene resins), polycarbonate resins, (meth)acrylic resins, polyarylate resins, polyphenylene ether resins, polyimide resins, polyethernitrile resins, phenoxy resins, polyphenylene sulfide resins, polysulfone resins, polyketone resins, polyether ketone resins, thermoplastic urethane resins, fluorine-based resins, and thermoplastic polybenzimidazole resins.

[0054] The fiber-reinforced plastic of the present disclosure may contain only one type of thermoplastic resin, or two or more types. Examples of a combination of two or more thermoplastic resins include, but are not limited to, a combination of thermoplastic resins having different softening points or melting points, or a combination of thermoplastic resins having different average molecular weights.

[0055] When a thermoplastic resin is used, it is more preferable to use a polyolefin resin, and even more preferable to use a polypropylene resin.

[0056] 2. Thermosetting Resin The resin may be a thermosetting resin. When a thermosetting resin is used, it is preferably an unsaturated polyester resin, a vinyl ester resin, an epoxy resin, or a phenol resin. One type of resin may be used alone, or two or more types may be used in combination.

[0057] Furthermore, when a thermosetting resin is used as the resin of the present disclosure, it is preferable to use a sheet molding compound (sometimes referred to as SMC) containing reinforcing fibers. Due to its high moldability, sheet molding compounds can be easily molded into complex shapes. Sheet molding compounds have higher fluidity and formability than continuous fibers, making it easy to create ribs and bosses.

[0058] 3. Other Agents The resin may contain additives such as various fibrous or non-fibrous fillers such as organic or inorganic fibers, flame retardants, UV resistant agents, stabilizers, release agents, pigments, softeners, plasticizers, surfactants, etc., within the scope of the present disclosure. When a thermosetting resin is used, it may contain thickeners, curing agents, polymerization initiators, polymerization inhibitors, etc. One type of additive may be used alone, or two or more types may be used in combination.

[0059] [Battery Undercover: Fiber Length of Reinforcing Fibers] The battery undercover contains reinforcing fibers, and the weight average fiber length of the reinforcing fibers is preferably 100 mm or less, and more preferably contains discontinuous reinforcing fibers of 1 mm or more and 100 mm or less. The weight average fiber length Lw of the reinforcing fibers is further preferably 3 mm or more and 80 mm or less, and even more preferably 5 mm or more and 60 mm or less.

[0060] If the weight-average fiber length Lw of the reinforcing fibers is 100 mm or less, the fluidity of the material is less likely to decrease when the battery undercover is manufactured by press molding, making it easier to produce the battery undercover in the desired shape. Furthermore, if the weight-average fiber length Lw is 1 mm or more, the mechanical strength of the resulting battery undercover is less likely to decrease, which is preferable.

[0061] That is, the reinforcing fibers contained in the battery undercover of the present disclosure are preferably discontinuous fibers. When discontinuous fibers are used, formability is improved compared to when only continuous fibers are used, making it easier to create complex molded bodies. Furthermore, by using discontinuous reinforcing fibers, no matter what direction stress is applied to the battery undercover from, it is unlikely that a direction will result in extremely weak mechanical properties.

[0062] In fiber-reinforced plastics made by injection molding, the weight-average fiber length of the reinforcing fibers is about 0.1 to 0.3 mm. Therefore, when the weight-average fiber length of the reinforcing fibers is set to 1 mm or more and 100 mm or less, it is preferable to make the molded body by press molding.

[0063] In the present disclosure, discontinuous reinforcing fibers having different fiber lengths may be used in combination. In other words, the discontinuous reinforcing fibers used in the present disclosure may have a single peak in the weight-average fiber length distribution, or may have multiple peaks.

[0064] [Battery undercover: number average fiber length L of reinforcing fibers ｎ and weight average fiber length L ｗ Generally, the fiber length of each reinforcing fiber is L ｉ Then, the number average fiber length L ｎ and weight average fiber length L ｗ is calculated by the following formulas (2) and (3). ｎ and weight average fiber length L ｗ The unit is mm.

[0065] Here, "I" indicates the number of reinforcing fibers measured, and i indicates a natural number from 1 to I.

[0066] When the fiber length is constant, the number-average fiber length and the weight-average fiber length are the same value. Reinforcing fibers can be extracted from fiber-reinforced plastics by, for example, performing a heat treatment at 500°C for about 1 hour and removing the resin in a furnace.

[0067] The average fiber length is, for example, the fiber length L of 100 fibers (I=100) randomly sampled from the battery undercover. ｉ (i is a natural number from 1 to 100) can be measured to the nearest 1 mm using a caliper or the like and calculated based on formula (1).

[0068] If short fibers that cannot be measured with a caliper are included, the resin is removed, and the resulting reinforcing fibers are placed in water containing a surfactant and thoroughly stirred with ultrasonic vibration. The stirred dispersion is randomly sampled with a measuring spoon to obtain evaluation samples, and the lengths of 3,000 fibers are measured using a Luzex® AP image analyzer manufactured by Nireco Corporation. Using the measured fiber lengths, the number-average fiber length Ln and weight-average fiber length Lw can be calculated in the same manner as in the above-mentioned formulas (1) and (2).

[0069] [Battery Undercover: Fiber Volume Ratio of Reinforcing Fibers] The fiber volume ratio Vf of the reinforcing fibers contained in the battery undercover is not particularly limited, but is preferably 20 to 70%, more preferably 25 to 60%, and even more preferably 30 to 55%. The fiber volume ratio (Vf, unit: volume %) is the ratio of the volume of the reinforcing fibers to the total volume including not only the reinforcing fibers and resin but also other additives. There are no limitations on the analysis of the reinforcing fiber volume ratio, but it is recommended to measure it as follows.

[0070] A sample was cut out from the battery undercover, and the resin was burned off in a furnace at 500°C for 1 hour. The masses of the sample before and after treatment were weighed to calculate the masses of the reinforcing fibers, resin, and other additives. Next, the specific gravity of each component was used to calculate the volume ratio Vf of the reinforcing fibers to the resin using the following formula (4): Vf = 100 × reinforcing fiber volume / (reinforcing fiber volume + resin volume + other additive volume) (4)

[0071] [Battery Undercover: Type of Reinforcing Fiber] In this specification, the reinforcing fiber is preferably at least one selected from the group consisting of carbon fiber, aramid fiber, glass fiber, polyester fiber, nylon fiber, polypropylene fiber, and polyethylene fiber, and more preferably carbon fiber or glass fiber.

[0072] 1. Reinforcing Fiber: Carbon Fiber 1.1. Carbon Fibers in General When using carbon fibers, polyacrylonitrile (PAN)-based carbon fibers, petroleum / coal pitch-based carbon fibers, rayon-based carbon fibers, cellulose-based carbon fibers, lignin-based carbon fibers, phenol-based carbon fibers, and the like are generally known, but any of these carbon fibers can be suitably used in the present disclosure. Among these, polyacrylonitrile (PAN)-based carbon fibers are preferred in the present disclosure because of their excellent tensile strength. As a PAN-based carbon fiber, for example, Teijin Limited's "Tenax" (registered trademark) carbon fiber STS40-24KS (average fiber diameter 7 μm) can be used.

[0073] 1.2 Carbon Fiber Sizing Agent The carbon fibers used in the present disclosure may have a sizing agent attached to their surfaces. When using carbon fibers with a sizing agent attached, the type of sizing agent can be appropriately selected depending on the type of carbon fiber and the type of resin used in the X material or Y material, and is not particularly limited.

[0074] 2. Reinforcing Fiber: Glass Fiber The case where the reinforcing fiber used in the present disclosure is glass fiber will be described. 2.1. General Glass Fiber The glass fiber used in the present disclosure may be any glass fiber that is generally called glass fiber. There is no particular limitation on the glass composition such as A-glass, C-glass, E-glass, etc., and in some cases TiO ２ , S.O. ３ , P ２ O ５ The glass fiber may contain components such as E-glass RS240QR-483 (count: 2400 g / 1000 m) manufactured by Nitto Boseki Co., Ltd., for example.

[0075] 2.2. Glass Fiber Sizing Agent The glass fibers used in the present disclosure may have a sizing agent attached to their surfaces. When using glass fibers with a sizing agent attached, the type of sizing agent can be appropriately selected depending on the type of glass fiber and the type of resin, and is not particularly limited. Glass fibers that have been pre-treated with a conventionally known coupling agent, such as an organosilane compound, an organotitanium compound, an organoborane compound, or an epoxy compound, can be preferably used.

[0076] [Method for Manufacturing Battery Undercover: Press Molding] 1. Hot Press Molding and Cold Press Molding When manufacturing the battery undercover of the present disclosure, a composite material containing reinforcing fibers and resin can be produced by press molding (sometimes called compression molding). Molding methods such as hot press molding and cold press molding can be used as press molding. By press molding the composite material, fiber-reinforced plastic battery undercovers with various shapes can be manufactured.

[0077] 2. Cold Press Molding When the resin contained in the composite material (which becomes fiber-reinforced plastic after molding) is a thermoplastic resin, press molding using cold press is preferred. In cold press molding, for example, a composite material heated to a first predetermined temperature is placed in a mold set to a second predetermined temperature, and then pressurized and cooled.

[0078] Specifically, if the thermoplastic resin contained in the composite material is crystalline, the first predetermined temperature is equal to or higher than the melting point, and the second predetermined temperature is lower than the melting point. If the thermoplastic resin is amorphous, the first predetermined temperature is equal to or higher than the glass transition temperature, and the second predetermined temperature is lower than the glass transition temperature. That is, the cold pressing method includes at least the following steps A-1) to A-2).

[0079] Step A-1) A step of heating the thermoplastic resin to a temperature above the melting point but below the decomposition temperature if the thermoplastic resin is crystalline, or above the glass transition temperature but below the decomposition temperature if the thermoplastic resin is amorphous. Step A-2) A step of placing the composite material heated in step A-1) in a mold whose temperature is adjusted to below the melting point if the thermoplastic resin is crystalline, or below the glass transition temperature if the thermoplastic resin is amorphous, and applying pressure. By performing these steps, the molding of the composite material can be completed (a battery undercover, which is a press-molded product, can be produced).

[0080] The above steps must be performed in the order described above, but other steps may be included between the steps. For example, the other steps include a shaping step, prior to step A-2), in which a shaping mold different from the mold used in step A-2) is used to pre-shape the mixture into the shape of the cavity of the mold.

[0081] The shape of the composite material may be a shape developed by computer through inverse molding analysis from the three-dimensional shape of the battery undercover to be manufactured.

[0082] 3. Hot Press Molding In the hot press molding method, for example, a composite material is placed in a mold, pressure is applied while the temperature of the mold is raised to a first predetermined temperature, and the mold is cooled to a second predetermined temperature. Specifically, if the thermoplastic resin constituting the composite material is crystalline, the first predetermined temperature is equal to or higher than the melting point, and the second predetermined temperature is lower than the melting point. If the thermoplastic resin contained in the composite material is amorphous, the first predetermined temperature is equal to or higher than the glass transition temperature, and the second predetermined temperature is lower than the glass transition temperature. Hot press molding preferably includes at least the following steps B-1) to B-4).

[0083] B-1) A step of placing the composite material in a mold (second mold, lower mold). B-2) A step of applying pressure while heating the mold (first pressing step) to a temperature above the melting point and below the thermal decomposition temperature of the thermoplastic resin if the thermoplastic resin is crystalline, or to a temperature above the glass transition temperature and below the thermal decomposition temperature of the thermoplastic resin if the thermoplastic resin is amorphous. B-3) A step of applying pressure in one or more stages, with the pressure in the final stage being 1.2 to 100 times the pressure in the first pressing step (second pressing step). B-4) A step of adjusting the mold temperature to below the melting point if the thermoplastic resin is crystalline, or below the glass transition temperature if the thermoplastic resin is amorphous. By performing these steps, an integrally molded structure can be created.

[0084] 4. Commonalities between Cold Press Molding and Hot Press Molding Steps A-2) and B-3) are steps in which pressure is applied to a composite material to obtain a fiber-reinforced plastic (molded product) of the desired shape. The molding pressure at this time is not particularly limited, but it is preferable that it is as low as possible within a range that allows the desired battery undercover shape to be obtained. Specifically, it is preferable that the molding pressure is less than 30 MPa relative to the mold cavity projected area, more preferably 20 MPa or less, and even more preferably 10 MPa or less. A molding pressure of less than 30 MPa is preferable because it does not require capital investment or maintenance costs for a press machine. Naturally, various processes may be inserted between the above steps during compression molding. For example, vacuum compression molding, in which compression molding is performed while in a vacuum, may be used.

[0085] (1) Preparation of Composite Material: E-glass RS240QR-483 (manufactured by Nitto Boseki Co., Ltd.) cut to a fiber length of 20 mm was used as the glass fiber. Polypropylene resin (Novatec PP BC03C manufactured by Japan Polypropylene Corporation) was used as the resin, and a composite composition of glass fiber and polypropylene resin in which the glass fibers were two-dimensionally randomly oriented was prepared based on the method described in U.S. Patent No. 10,006,677. The resulting composite composition was heated at 2.0 MPa for 5 minutes in a press heated to 250°C to prepare a flat composite material with an average thickness of 3 mm.

[0086] (2) Preparation of Battery Undercovers (Examples 1 to 12) The flat composite material obtained in (1) was heated to above the softening point of the resin to soften it, placed in a mold, and press-molded at a pressure of 20 MPa to produce battery undercovers having a repeating structure of circular protrusions in plan view, as shown in FIGS. 2 and 5 . The height h of the protrusions and the pitch p of the connection portions were varied to 7 mm, 14 mm, 21 mm, and 28 mm, and Examples 1 to 12 were produced as shown in Tables 1 and 2. As shown in FIG. 16 , a battery undercover 60A was fixed on a base 70 having support portions 71 shaped to correspond to the non-battery mounting area of ​​the battery tray 20, so that the connection portions 61A were in contact with the support portions 71 and the protrusions 62A protruded upward. A load of 10,000 N was applied to one of the protrusions 62A from above the cavity 72 corresponding to the battery mounting area, and the maximum change in height h was defined as the deformation (mm). The pitch of the connecting portions 61A (7 mm, 14 mm, 21 mm, 28 mm) was matched with the pitch of the supporting portions 71 (7 mm, 14 mm, 21 mm, 28 mm).

[0087] (Comparative Examples 1 to 4) The flat composite material obtained in (1) was press-molded into a flat battery undercover (height of the protrusions h = 0). The obtained flat battery undercover was fixed on a base 70 having support portions 71 shaped to correspond to the non-battery mounting area of ​​the battery tray 20, similar to those used in Examples 1 to 12, and the maximum deformation (mm) in the height direction of the composite material was measured when a load of 10,000 N was applied to the flat composite material from above the cavity 72 corresponding to the battery mounting area. The pitch of the support portions 71 (Comparative Example 1: 7 mm, Comparative Example 2: 14 mm, Comparative Example 3: 21 mm, Comparative Example 4: 28 mm) was regarded as the pitch p of the connection portions.

[0088] Examples 13 to 24 The flat composite material obtained in (1) was heated to above the softening point of the resin to soften it, placed in a mold, and press-molded at a pressure of 20 MPa to create a battery undercover 260A having a structure in which convex portions 262A extending in the Y direction were repeated in the X direction, as shown in Figures 12 and 14. The height h of the convex portions 262A and the pitch p of the connecting portions 261A were varied to create Examples 13 to 24, as shown in Tables 3 and 4. As shown in Figure 17, the battery undercover 260A was fixed on a base 270 having support portions 271 shaped to correspond to the connecting portions 261A extending in the Y direction, so that the connecting portions 261A were in contact with the support portions 271 and the convex portions 262A protruded upward. A load of 10,000 N was applied from above to one of the convex portions 262A, and the maximum change in height h was defined as the deformation (mm). The pitch of the connecting portions 261A (7 mm, 14 mm, 21 mm, 28 mm) was matched with the pitch of the supporting portions 271 (7 mm, 14 mm, 21 mm, 28 mm).

[0089] (Comparative Examples 5 to 8) The flat composite material obtained in (1) was press-molded into a flat battery undercover (height of the protrusions h = 0). The resulting flat battery undercover was fixed on a platform 270 having support portions 271 shaped to correspond to the Y-direction-extending connection portions 261A, similar to those used in Examples 13 to 24. A load of 10,000 N was applied to the flat composite material from above the midpoint between the two support portions 271, and the maximum deformation (mm) in the height direction of the composite material was measured. The pitch of the support portions 271 (Comparative Example 5: 7 mm, Comparative Example 6: 14 mm, Comparative Example 7: 21 mm, Comparative Example 8: 28 mm) was considered to be the pitch p of the connection portions. The deformation and deformation per load measured in Examples 1 to 24 and Comparative Examples 1 to 8 are shown in Tables 1 to 4.

[0090]

[0091] The data in Tables 1 and 2 are plotted in Figure 18, with pitch p (mm) on the horizontal axis and deformation per load (mm / N) on the vertical axis, and the height h of the convex portions varied. The smaller the value on the Y axis in Figure 18, the smaller the deformation per load and the greater the rigidity.

Claims

1. An understructure for an electric vehicle comprising: a battery tray; and a battery undercover provided below the battery tray and covering the bottom surface of the battery tray, wherein the battery tray has a battery mounting area and a battery non-mounting area, and the battery undercover is an integrally molded body made of fiber-reinforced plastic, has a connection part that connects to the battery non-mounting area, and has a convex part facing downward on the vehicle to correspond to the battery mounting area.

2. The lower structure of an electric vehicle according to claim 1, wherein α expressed by the following formula (1) satisfies 0<α<2.

00. In the formula, p is the pitch (mm) of the connecting portions, and h is the height (mm) of the protrusions.

3. The undercarriage of an electric vehicle according to claim 2, wherein the convex portions have a repeating structure, and the pitch is the distance between the centers of adjacent circumscribing circles of the convex portions when the circumscribing circles are drawn.

4. The undercarriage of an electric vehicle according to claim 2 or 3, wherein the pitch p of the connection portions is 3 mm or more and 1500 mm or less, and the height h of the convex portions is greater than 0 mm and less than 20 mm.

5. An undercarriage for an electric vehicle as claimed in any one of claims 1 to 4, wherein the battery provided in the battery tray is a battery in which the single cells are directly arranged.

6. The undercarriage of an electric vehicle according to any one of claims 1 to 5, wherein the rigidity of the connection portion is less than the rigidity of the protruding portion.

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