Vehicle lower part structure

Abstract

This vehicle lower part structure comprises a battery unit (3) having a cooling water channel (4) on the lower surface thereof, and an undercover (5) disposed on the vehicle-lower side of the battery unit (3) so as to cover the lower surface of the battery unit (3). The upper surface of the undercover (5) is provided with protrusions (9, 10) that protrude toward the vehicle-upper side and suppress the flow of air in a gap (11) between the lower surface of the battery unit (3) and the upper surface of the undercover (5).

Description

Vehicle undercarriage

[0001] The present invention relates to a vehicle undercarriage.

[0002] The following Patent Document 1 describes a vehicle undercarriage structure that includes a battery unit that is arranged under the floor of the vehicle and has a cooling water channel on its underside, and an undercover that is arranged on the vehicle below the battery unit so as to cover the underside of the battery unit.

[0003] International Publication No. 2021 / 220027

[0004] However, there is a gap between the underside of the battery unit where the cooling water passage is located and the upper surface of the undercover, and air flow, specifically air flow accompanied by the inflow of outside air, occurs in this gap during driving. When air flow accompanied by the inflow of outside air occurs in this gap between the underside of the battery unit and the upper surface of the undercover, the cooling water passage is affected by the outside temperature, resulting in a problem that the temperature regulation performance of the battery unit cannot be fully demonstrated. An object of the present invention is to provide a vehicle undercarriage structure that is less likely to produce air flow accompanied by the inflow of outside air in the gap between the underside of the battery unit where the cooling water passage is located and the upper surface of the undercover.

[0005] One aspect of the present invention is a vehicle undercarriage structure that includes a battery unit that is arranged under the floor of the vehicle and has a cooling water channel on its underside, and an undercover that is arranged on the vehicle below the battery unit so as to cover the underside of the battery unit, wherein the undercover protrudes toward the upper side of the vehicle and has a protrusion on its upper surface that suppresses air flow in the gap between the underside of the battery unit and the upper surface of the undercover.

[0006] According to one aspect of the present invention, a protrusion is provided on the upper surface of the undercover, which prevents airflow accompanied by the inflow of outside air from occurring in the gap between the lower surface of the battery unit, where the cooling water channel is provided, and the upper surface of the undercover. The objects and advantages of the present invention are realized and attained by using the elements and combinations thereof set forth in the claims. It should be understood that both the foregoing general description and the following detailed description are merely exemplary and explanatory and are not intended to limit the invention as defined by the claims.

[0007] 1 is a perspective view showing an undercover used in one embodiment of a vehicle undercarriage structure; FIG. 2 is a bottom view of a battery unit disposed on the vehicle upper side of the undercover of FIG. 1; FIG. 3 is a bottom view of a beam member attached to the underside of the battery unit of FIG. 2; FIG. 4 is a left side cross-sectional view showing a rear protrusion provided on the upper surface of the undercover of FIG. 1; FIG. 5 is an explanatory diagram of air flow occurring in a gap between the upper surface of the undercover of FIG. 1 and the lower surface of the battery unit of FIG. 2; FIG. 6 is a front cross-sectional view showing a side protrusion provided on the upper surface of the undercover of FIG. 1; FIG. 7 is a perspective view of side protrusions, protrusions, and ribs on the upper surface of the undercover of FIG. 1;

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic and may differ from the actual product. The vehicle undercarriage structure of the embodiment shown in FIG. 1 is applied to an electric vehicle (BEV: Battery Electric Vehicle) as an example. As shown in FIG. 5, a motor room 1 housing a motor (not shown) serving as a vehicle drive source is provided in the front of the vehicle. A battery unit 3 for driving the motor is disposed under the floor of a passenger compartment 2. The battery unit 3 has a generally thick plate shape that is somewhat thick in the vertical direction of the vehicle. As shown in the bottom view of FIG. 2, the battery unit 3 is large enough to cover most of the floor of the passenger compartment 2. The bottom of the battery unit 3 is generally rectangular, but both sides of the rear end of the vehicle in the vehicle width direction form inclined portions 3a that gradually narrow toward the rear of the vehicle (conversely, gradually widen toward the front of the vehicle). Briefly, the internal structure of the battery unit 3 includes a frame member surrounding the outer periphery of the bottom surface of the battery unit 3 (see FIG. 2 ), and a cross-shaped framework member arranged inside the frame member. Numerous battery modules, each containing a plurality of battery cells, are mounted within the space between the frame member and the frame member. The frame member on which the battery modules are mounted is covered by a top cover member on the upper side of the vehicle and a bottom plate member on the lower side of the vehicle, and the bottom plate member has a cooling water channel 4 (see FIG. 2 ) formed on the lower side of the vehicle. Cooling water (coolant) flows into the cooling water channel 4, for example, from the upper left of FIG. 2 , and flows out from the lower left of FIG. 2 through the complex layout of the cooling water channel 4. As shown in FIG. 6 , the cooling water channel 4 has a base at the upper side of the vehicle and a small, isosceles trapezoidal cross section. As shown in FIG. 5 , the motor compartment 1 and the passenger compartment 2 are separated by a bulkhead (dash panel) 21.

[0009] The underside of the battery unit 3, in which the cooling water passage 4 is provided, is covered with an undercover 5 shown in FIG. 1 . Needless to say, the undercover 5 is located at the lowest position under the floor of the vehicle and may interfere with the road surface in some cases. In this embodiment, to prevent the undercover 5 from contacting the underside of the battery unit 3, i.e., the cooling water passage 4, etc., multiple beam members 6 extending in the vehicle width direction are arranged in the front-rear direction of the vehicle and attached to the underside of the battery unit 3, as shown in FIG. 3 . That is, the undercover 5 is connected to the underside of the battery unit 3 via the beam members 6. The beam members 6 have through holes formed at both ends in the vehicle width direction and at the center in the vehicle width direction. Fasteners such as bolts inserted into the through holes are screwed into threaded holes provided in the frame members and framework members of the battery unit 3, thereby attaching each beam member 6 to the underside of the battery unit 3. Meanwhile, the beam members 6 and the undercover 5 are connected at multiple (numerous) locations. The beam member 6 is formed, for example, by press-molding a metal plate member. A circular bulge 6a (in plan view) that bulges downward from the vehicle is formed by embossing or the like at the joint with the undercover 5 (see FIG. 6 ). In contrast, the undercover 5 is formed as a plate by injection molding of resin. A circular (or rectangular) protrusion 7 (in plan view) that bulges upward from the joint with the beam member 6 is formed. Through holes are formed in the centers of the bulge 6a and the protrusion 7. The bulge 6a is overlapped with the upper side of the protrusion 7, and a fastener such as a clip is inserted into the through holes from the lower side of the vehicle to fasten the undercover 5 and the beam member 6. The undercover 5 extends downward from the motor room 1 to cover the entire underside of the battery unit 3.

[0010] As shown in FIG. 1 , a number of ribs 8 are formed between adjacent protrusions 7 of the undercover 5, protruding upward from the vehicle so as to connect those protrusions 7. These ribs 8 are each a relatively thin, elongated plate with a small height, and are formed by injection molding of the resin that constitutes the undercover 5 together with the protrusions 7. A rib 8 connecting two adjacent protrusions 7 and two ribs 8 connecting two protrusions 7 adjacent to those protrusions 7 are laid out to form a triangle in plan view, and these ribs 8 form a truss. The truss has a simple structure and provides the undercover 5 with high rigidity and strength.

[0011] In this embodiment, the undercover 5 includes ribs 8 that connect the projections 7 and protrude upward, as well as ridges 9 and 10 that protrude upward. These ridges 9 and 10 restrict airflow in a gap 11 between the underside of the battery unit 3 (cooling water channel 4) and the upper surface of the undercover 5 (including the beam member 6), as shown in FIG. 4 . Analysis of the wind and airflow during vehicle travel reveals that wind entering the motor compartment 1 at the front of the vehicle from the front of the vehicle flows out through the wheelhouses of the front wheels. This air pocket generates negative pressure, which draws air from other locations. This negative pressure draws air from the rear of the undercover 5 toward the front of the vehicle, and some of the air flows into the gap 11 between the underside of the battery unit 3 and the lower surface of the upper surface of the undercover 5. This air flow eventually reaches the motor room 1, but because it is originally an air flow that draws in outside air, if the cooling water passage 4 is exposed to this air flow, it may be affected by the outside air temperature and not perform its intended cooling function. In order to suppress the air flow in the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5 and to suppress exposure of the cooling water passage 4 to the outside air, protrusions 9, 10 are provided protruding from the upper surface of the undercover 5 toward the upper side of the vehicle.

[0012] First, in order to prevent air from entering the cooling water passage 4 through the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5, a rear protrusion 9 is provided at the vehicle rear end of the upper surface of the undercover 5, as shown in FIG. 1 . This rear protrusion 9 is taller than the rib 8, as described below, but like the rib 8, it is a relatively thin plate, and like the rib 8, it is formed by injection molding of the resin that constitutes the undercover 5. This rear protrusion 9 is provided rearward of the cooling water passage 4, as shown in FIG. 4 , in order to prevent the cooling water passage 4 from being exposed to the flow of outside air. Furthermore, because the vehicle rear end of the undercover 5 also serves as an inlet for outside air, the rear protrusion 9 protrudes high from the lower surface of the undercover 5 in order to minimize the inflow of outside air into the gap 11 between the lower surface of the battery unit 3 and the upper surface of the undercover 5, and its upper end is located slightly below the vehicle below the lower surface of the battery unit 3. The main portion of this rear protrusion 9 extends in the vehicle width direction across the center of the undercover 5 in the vehicle width direction along the rear end of the underside of the battery unit 3, but on both sides in the vehicle width direction, it extends gradually outward in the vehicle width direction from the rear side to the front side of the vehicle, following the sloped portion 3a of the bottom surface shape of the battery unit 3. Here, the rear protrusion 9 that matches the sloped portion 3a of the battery unit 3 is defined as part of the rear protrusion 9 that has an element extending in the vehicle width direction.

[0013] In this embodiment, as shown in FIG. 1 , protrusions are also provided on both sides of the underside of the undercover 5 in the vehicle width direction. These protrusions are defined as side protrusions 10. These side protrusions 10 protrude upward from the vehicle between adjacent protrusions 7 at both ends in the vehicle width direction, connecting two protrusions 7. These side protrusions 10 resemble ribs 8 but are taller than the ribs 8. Like the ribs 8 and the rear protrusions 9, these side protrusions 10 are also formed by injection molding of the resin constituting the undercover 5. FIG. 6 is a front cross-sectional view showing the outer portion of the battery unit 3 in the vehicle width direction. The battery unit 3 is disposed inside a side sill inner 23 constituting a side sill 22 and is attached to the underside of the side sill inner 23 via a side rail 12 attached to the outer side in the vehicle width direction at the bottom of the frame member. Meanwhile, the undercover 5 extends to a position below the side sill outer 24 on the vehicle width direction outer side of the side sill inner 23 and is attached to the underside of the side sill outer 24. Therefore, a relatively large space exists between the side sill 22 and the undercover 5 on the outer side of the battery unit 3 in the vehicle width direction. As a result of the air flow analysis described above, it was found that the air flow toward the front of the vehicle in this space is faster than the air flow in the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5, and that this causes the air in the gap 11 to flow out into the space on the outer side in the vehicle width direction.

[0014] Therefore, by providing lateral protrusions 10 extending in the vehicle longitudinal direction at positions outside the cooling water channels 4 in the vehicle width direction, air is prevented from leaking from a gap 11 between the lower surface of the battery unit 3 and the upper surface of the undercover 5 into the space outside the vehicle width direction, thereby suppressing the air flow within the gap 11. In this embodiment, as shown in the perspective view of FIG. 7 , the lateral protrusions 10 are provided between adjacent protrusions 7 at the vehicle width direction ends so as to connect two of the protrusions 7. This allows the amount of resin required for the lateral protrusions 10 to be reduced compared to, for example, forming a continuous lateral protrusion 10 extending in the vehicle longitudinal direction at positions outside the cooling water channels 4 in the vehicle width direction, thereby reducing costs. Furthermore, in this embodiment, the rear protrusion 9 reduces the inflow of outside air into the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5. Therefore, it is considered that the outflow of air from the gap 11 into the space outside the vehicle width direction is not significant. Therefore, the upper end of the side protrusion 10 is positioned lower than the upper end of the rear protrusion 9. In other words, the height of the side protrusion 10 is smaller than the height of the rear protrusion 9, which also reduces the amount of resin required for the side protrusion 10 and reduces costs. Furthermore, as can be seen from FIG. 7 , the side protrusion 10 also serves as a rib 8 connecting two adjacent protrusions 7 at the vehicle width direction ends. Therefore, as shown in FIG. 8 , the side protrusion 10 forms a truss together with the rib 8 connecting the two adjacent protrusions 7 between them. This reduces the amount of resin required for the rib 8 and the side protrusion 10, which also reduces costs.

[0015] Although the vehicle undercarriage structure according to the embodiment has been described above, the present invention is not limited to the configuration described in the above embodiment and various modifications are possible within the scope of the present invention. For example, the above embodiment describes a battery unit 3 in which cooling water channels 4 with an isosceles trapezoidal cross section, with the upper side of the vehicle as its base, are arranged in a tangled manner on the underside of the battery unit 3. However, the vehicle undercarriage structure according to the present invention can be applied to any vehicle, regardless of the cross-sectional shape or arrangement of the cooling water channels 4, as long as the battery unit 3 has cooling water channels 4 on its underside and a gap 11 exists between the underside of the battery unit 3 and the upper surface of the undercover 5. Furthermore, the above embodiment describes a single (single) plate-shaped resin undercover 5. However, the configuration and material of the undercover 5 are not limited to those described above. Furthermore, the connection structure of the undercover 5 to the battery unit 3 is not limited to those described above.

[0016] As described above, this embodiment includes a battery unit 3 having cooling water channels 4 on its underside, and an undercover 5 that is arranged on the vehicle lower side of the battery unit 3 so as to cover the underside of the battery unit 3, and the upper surface of the undercover 5 is provided with protrusions 9, 10 that protrude toward the upper side of the vehicle and suppress air flow in a gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5. As a result, air flow accompanied by the inflow of outside air is less likely to occur in the gap 11 between the underside of the battery unit 3, where the cooling water channels 4 are provided, and the upper surface of the undercover 5.

[0017] Furthermore, a rear protrusion 9 extending in the vehicle width direction is provided rearward of the cooling water channel 4 to suppress air from entering the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5 toward the cooling water channel 4. This reduces the inflow of outside air from the rear of the vehicle into the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5, thereby suppressing the air flow in the gap 11. Furthermore, the undercover 5 extends in the front-to-rear direction of the vehicle to a position below the motor room 1 located forward of the battery unit 3, and the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5 communicates with the interior of the motor room 1. As a result, outside air tends to flow into the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5 from the rear of the vehicle, but the rear protrusion 9 provided on the rear side of the vehicle effectively reduces this flow.

[0018] Furthermore, as the protrusions, lateral protrusions 10 extending in the vehicle longitudinal direction are provided outside the cooling water channel 4 in the vehicle width direction to suppress the outflow of air from the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5 to the outside in the vehicle width direction. This reduces the outflow of air from the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5 to the outside in the vehicle width direction, thereby suppressing the air flow in the gap 11. Furthermore, the upper end of the lateral protrusions 10 is located lower than the upper end of the rear protrusions 9, which primarily suppresses the air flow in the gap 11 by reducing the inflow of outside air into the gap 11 between the underside of the battery unit 3 and the upper surface of the undercover 5. This allows the cost required for the lateral protrusions 10 to be reduced.

[0019] Furthermore, a plurality of protrusions 7 that protrude toward the upper side of the vehicle are provided on the upper surface of the undercover 5 to connect to the battery unit 3, and lateral protrusions 10 are provided between adjacent protrusions 7 to connect two of the protrusions 7. This makes it possible to reduce the cost required for the lateral protrusions 10. Furthermore, ribs 8 that protrude toward the upper side of the vehicle are provided on the upper surface of the undercover 5 to connect two of the protrusions 7 between adjacent protrusions 7, and the lateral protrusions 10 together with these ribs 8 form a truss. This makes it possible to reduce the cost required for the ribs 8 and lateral protrusions 10 while ensuring the stiffness and strength required for the undercover 5.

[0020] 1...motor room, 2...vehicle compartment, 3...battery unit, 4...cooling water channel, 5...undercover, 6...beam member, 7...projection, 8...rib, 9...rear protrusion (protrusion), 10...side protrusion (protrusion), 11...gap

Claims

1. A vehicle undercarriage comprising a battery unit arranged under the floor of a vehicle and having a cooling water channel on its underside, and an undercover arranged on the vehicle below the battery unit so as to cover the underside of the battery unit, wherein the undercover has a protrusion on its upper surface that protrudes toward the upper side of the vehicle and suppresses the flow of air in the gap between the underside of the battery unit and the upper surface of the undercover.

2. The vehicle undercarriage structure described in claim 1, characterized in that the protrusion portion is a rear protrusion portion that extends in the vehicle width direction and is located rearward of the vehicle relative to the cooling water channel, and that suppresses air from entering the gap toward the cooling water channel.

3. The vehicle undercarriage structure described in claim 2, characterized in that the undercover extends in the longitudinal direction of the vehicle to a position below the motor room located on the front side of the battery unit, and the gap between the bottom surface of the battery unit and the top surface of the undercover communicates with the interior of the motor room.

4. A vehicle undercarriage structure as described in claim 2, characterized in that the protrusion portion is a lateral protrusion portion that extends in the fore-and-aft direction of the vehicle and is provided outside the cooling water channel in the vehicle width direction, and that suppresses the outflow of air from the gap to the outside in the vehicle width direction.

5. A vehicle undercarriage structure according to claim 4, wherein the upper end of the side protrusions is located lower than the upper end of the rear protrusion.

6. The vehicle undercarriage structure described in claim 4, characterized in that the undercover protrudes toward the upper side of the vehicle and has a plurality of protrusions on its upper surface for connecting to the battery unit, and the side protrusions are arranged between adjacent protrusions so as to connect two of the protrusions.

7. A vehicle undercarriage structure as described in claim 6, characterized in that the lateral protrusions form a truss together with ribs provided on the upper surface of the undercover that protrude toward the upper side of the vehicle and connect two protrusions between adjacent protrusions.

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