JP7622700B2 - Vehicle underfloor structure - Google Patents

Description

The present invention relates to a vehicle underfloor structure.

Conventionally, a technology related to vehicle underfloor structures is known in which an automobile airflow straightening structure is formed in which a slit for separating the running wind and a connecting part for reinforcing the cover are formed adjacent to the rear end edge of a cover having a substantially flat airflow straightening surface extending in the fore-and-aft direction of the vehicle (see, for example, Patent Document 1).

Patent No. 6315038

In the technical field of vehicle dynamics, if a driver feels something is wrong with the vehicle's straight-line running or feels that there is a lack of consistency in the response and reaction force to the driver's steering operation, the driver tends to find it difficult to perceive the vehicle's dynamics as excellent. Thus, there is room for improvement in the vehicle dynamics that the driver perceives from the vehicle response.

The present invention aims to provide a vehicle underfloor structure that can improve the vehicle dynamics that the driver perceives from the vehicle response.

In order to solve the above problem, the inventors have conducted extensive research into vibrations that occur in the body of a vehicle while it is moving, and as a result have discovered new facts about the impact on vehicle dynamics performance caused by the air flowing around the vehicle as the vehicle moves. When a vehicle moves, pressure fluctuations occur on the surface of the vehicle and at the rear of the vehicle due to the air flowing around the vehicle. An external force is generated on the vehicle body as a reaction force, causing the vehicle body to periodically vibrate with six degrees of freedom at extremely low frequencies (1 Hz or less). This vibration of the vehicle body is difficult for the driver to directly feel, but it appears as an adverse effect on the vehicle response to the driver's operation. Previously, no attention had been paid to the impact on vehicle response caused by such extremely low-frequency vibrations of 1 Hz or less.

In other words, the vehicle underfloor structure according to one aspect of the present invention comprises a high-frequency vortex generating section that is provided under the floor of the vehicle forward of the center line of the front wheels and includes at least one of a plurality of protrusions and a plurality of holes arranged along the vehicle width direction, and a vortex straightening section that is provided under the floor rearward of the vehicle's center of gravity position and includes a plurality of fins arranged along the vehicle width direction, and the high-frequency vortex generating sections are arranged more densely in the center of the vehicle width direction than in other parts of the vehicle width direction.

In the vehicle underfloor structure according to one aspect of the present invention, the frequency band of the pressure fluctuation of the airflow flowing rearward of the vehicle near the front wheels under the vehicle floor is changed to the high frequency side by intentionally generating vortices in a predetermined range in the vehicle width direction by the high frequency vortex generating unit. The vortex generated by the high frequency vortex generating unit strengthens the turbulence near the front wheels under the vehicle floor in a short time, and makes the turbulence spread toward the end of the vehicle width direction under the vehicle floor as it moves toward the rear of the vehicle. As a result, for example, when the high frequency vortex generating unit is not provided, the pressure fluctuations on the vehicle surface and rear of the vehicle vary periodically (for example, 4 second period, 0.25 Hz, etc.) with a large amount of fluctuation. In contrast, in the vehicle underfloor structure according to one aspect of the present invention, the turbulence of the airflow generated by the high frequency vortex generating unit is used to alleviate the periodicity of the pressure fluctuations at the rear of the vehicle, and the variation in the amount of fluctuation can be suppressed. In addition, the airflow is rectified by the vortex rectifying unit behind the center of gravity under the vehicle floor, so the decrease in the flow speed of the airflow is suppressed. This makes it possible to effectively suppress the generation of external forces that act as moments around the center of gravity due to the airflow in the center of the vehicle's width direction under the vehicle floor, while utilizing the turbulence of the airflow described above to suppress periodic pressure fluctuations at both ends in the vehicle width direction. As a result, when averaged over time, the pressure fluctuations that occur on the vehicle surface and at the rear of the vehicle are suppressed from becoming extremely low-frequency vibrations, and the external force acting as a reaction force at extremely low frequencies (1 Hz or less) is suppressed from acting periodically on the vehicle body. Therefore, the vehicle underfloor structure according to one aspect of the present invention makes it possible to improve the vehicle dynamics performance that the driver feels from the vehicle response.

Specifically, as a configuration that optimally achieves the above-mentioned effects, the high-frequency vortex generating section and the vortex straightening section are arranged on both sides of the vehicle center line in the vehicle width direction, and each side includes eight or more protrusions, holes, or fins, and the dimension of the protrusions, holes, or fins along the vehicle width direction may be 8 mm or less.

Specifically, the fins may be arranged at intervals of 10 mm or less to best achieve the above-mentioned effects.

The vehicle underfloor structure according to one aspect of the present invention makes it possible to improve the vehicle dynamics that the driver perceives from the vehicle response.

1 is a schematic bottom view of a vehicle equipped with a vehicle underfloor structure of one embodiment. 1 is a schematic bottom view of a front part of a vehicle showing an example of a high-frequency vortex generating portion. FIG. 13 is a schematic bottom view of the front part of the vehicle showing another example of a high-frequency vortex generating portion. FIG. 4A is a plan view of the high frequency vortex generating portion of Fig. 3, and Fig. 4B is a cross-sectional view of the high frequency vortex generating portion of Fig. 3 taken along line IVb-IVb. 1A is a plan view of an example of a vortex straightening portion, FIG. 1B is a side view of an example of a vortex straightening portion, and FIG. 1C is a cross-sectional view of the vortex straightening portion of FIG. 1A taken along line Vc-Vc. 6A is a bottom perspective view of another example of a vortex straightening portion, and FIG. 6B is a cross-sectional view taken along a virtual plane VIb of the vortex straightening portion of FIG. FIG. 11 is a schematic rear view of another example of a vortex straightening portion. 1A is a bottom view showing the flow of air under the floor of a vehicle equipped with a vehicle under-floor structure according to a comparative example, and FIG. 1B is a bottom view showing the flow of air under the floor of a vehicle equipped with a vehicle under-floor structure according to an embodiment. 1A is a side view showing the flow of airflow on a side surface of a vehicle equipped with a vehicle underfloor structure according to a comparative example, and FIG. 1B is a side view showing the flow of airflow on a side surface of a vehicle equipped with a vehicle underfloor structure according to an embodiment. 1A is a plan view showing an eddy viscosity coefficient distribution at the rear of a vehicle equipped with a vehicle underfloor structure according to a comparative example, and FIG. 1B is a longitudinal sectional view taken along line Xb-Xb showing an eddy viscosity coefficient distribution at a predetermined distance from the rear end of the vehicle in the pressure distribution of FIG. 1A is a plan view showing an eddy viscosity coefficient distribution at the rear of a vehicle equipped with a vehicle underfloor structure according to an embodiment, and FIG. 1B is a longitudinal cross-sectional view taken along line XIb-XIb showing an eddy viscosity coefficient distribution at a predetermined distance from the rear end of the vehicle in the pressure distribution shown in FIG. 4 is a diagram illustrating an example of a change over time in yaw rate when a vehicle travels straight; FIG. 1 is a diagram illustrating an example of a variation level of yaw rate when a vehicle travels straight.

Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, the front-rear direction and the up-down direction refer to the front-rear direction of the vehicle and the up-down direction of the vehicle, respectively. Note that the vehicle width direction is a direction perpendicular to the front-rear direction of the vehicle and the up-down direction of the vehicle.

Figure 1 is a schematic bottom view of a vehicle equipped with a vehicle underfloor structure of one embodiment. Figure 1 is a schematic bottom view of the underfloor F of the vehicle 1 as viewed from below. As shown in Figure 1, the vehicle 1 equipped with the vehicle underfloor structure 10 of this embodiment is a box-shaped vehicle such as a passenger car.

As shown in FIG. 1, the vehicle 1 includes a vehicle body 2, front wheels 3, rear wheels 4, a front bumper 5, and a rear bumper 6. The vehicle body 2 has a floor panel 7 extending in the front-rear direction. A floor tunnel through which an exhaust pipe and a propeller shaft pass in the front-rear direction is formed in the center of the vehicle of the floor panel 7, and is covered by a cover member C1. The cover member C1 is an aerodynamic cover that covers the center of the underfloor F of the vehicle 1 and includes a flat portion C1a extending in the front-rear direction as its longitudinal direction. The vehicle body 2 supports a front suspension 8 in front of the floor panel 7, and supports a rear suspension 9 in the rear of the floor panel 7.

The front suspension 8 includes a lower arm 8a that supports the front wheels 3, and a cross member 8b that supports the lower arm 8a. The cross member 8b is covered with a cover member C2. The cover member C2 is an aerodynamic cover that covers the central portion of the underfloor F of the vehicle 1 between the front wheels 3 in the vehicle width direction and includes a flat portion that extends approximately horizontally.

The rear suspension 9 includes a lower arm 9a that supports the rear wheel 4, and a cross member 9b that supports the lower arm 9a. In front of the lower arm 9a, a pair of left and right cover members C3 are arranged to fill the gap between the cover member C1 and the lower arm 9a, for example. In front of the cross member 9b, for example, a fuel tank is arranged covered by a cover member C4. The cover member C4 is an aerodynamic cover that covers the underfloor F of the vehicle 1 between the rear end of the cover member C1 and the center in the vehicle width direction between the rear wheels 4.

The front bumper 5 is provided at the front end of the vehicle body 2. The front bumper 5 has a bottom portion 5a that is formed so as to wrap around the underfloor F of the vehicle 1. The bottom portion 5a includes a flat portion that extends in a substantially arc shape connecting the left and right front wheels 3 when viewed from below. The front bumper 5 may be provided with a lip spoiler along the front edge of the bottom portion 5a.

The area between the rear end of the bottom 5a of the front bumper 5 and the cover member C2 is covered with the cover member C5. The cover member C5 is an aerodynamic cover with a flat surface that continues from the bottom 5a of the front bumper 5 and extends between the left and right front wheels 3. The cover member C5 is provided under the floor F of the vehicle 1, forward of the center line 3X of the front wheels 3.

The rear bumper 6 is provided at the rear end of the vehicle body 2. The rear bumper 6 has a bottom 6a formed to wrap around the underfloor F of the vehicle 1. The bottom 6a extends in a generally arc shape connecting the left and right rear wheels 4 when viewed from below. As an example, the bottom 6a includes a flat portion 6b (see FIG. 7) that extends along a horizontal plane in the center in the vehicle width direction, and the rest of the bottom 6a is inclined upward from the front to the rear. The area between the front end of the bottom 6a of the rear bumper 6 and the rear end of the cross member 9b may be covered with a cover member.

The vehicle underfloor structure 10 of this embodiment equipped with such a vehicle 1 is a structure for improving pressure fluctuations on the vehicle surface and rear of the vehicle caused by air flowing around the vehicle 1 as the vehicle 1 moves, so as to prevent them from adversely affecting the vehicle dynamics performance of the vehicle 1. In the present invention, pressure fluctuations that adversely affect the vehicle dynamics performance of the vehicle 1 refer to pressure fluctuations that cause the vehicle 1 to vibrate in six degrees of freedom at extremely low frequencies of 1 Hz or less (e.g., 0.2 Hz, 0.3 Hz, etc.). Note that since the effects are particularly noticeable with steering, the following explanation will be representative of the six degrees of freedom, yaw rate.

The vehicle underfloor structure 10 includes a high-frequency vortex generating section 20 provided in front of the center line 3X of the front wheels 3 in the underfloor F of the vehicle 1 (for example, the area of dashed line A1 in FIG. 1). The high-frequency vortex generating section 20 has the function of intentionally turbulenting the airflow that has entered the underfloor F from the front of the vehicle 1, and converting the vibration energy of the airflow into higher frequency energy. Specifically, the high-frequency vortex generating section 20 can be configured like the high-frequency vortex generating sections 20A and 20B shown in FIGS. 2 to 4.

Figure 2 is a schematic bottom view of the front of a vehicle showing an example of a high-frequency vortex generating section. Figure 2 shows the cover member C5 between the rear end of the bottom 5a of the front bumper 5 and the cover member C2 when the underfloor F of the vehicle 1 is viewed from below. As shown in Figure 2, the high-frequency vortex generating section 20A is, as an example, a plurality of holes 21 arranged in the cover member C5 along the vehicle width direction of the vehicle 1 (for example, the area of the dashed line A2 in Figure 1). The plurality of holes 21 are arranged on both sides of the vehicle center line Y in the vehicle width direction. The plurality of holes 21 are provided on each side of the vehicle center line Y, with eight or more holes (11 in the example of Figure 2) provided.

The high-frequency vortex generating portion 20A is arranged more densely in the center M in the vehicle width direction than in other parts of the center M in the vehicle width direction. The multiple holes 21 have a pair of holes 21a arranged at the center M in the vehicle width direction from the vehicle center line Y by a first distance d1, and multiple holes 21b arranged at the center M in the vehicle width direction from the vehicle center line Y by a second distance d2 larger than the first distance d1. The first distance d1 is, for example, 10 mm or more and 20 mm or less. The second distance d2 is, for example, 20 mm or more and 50 mm or less. The hole 21a may be arranged rearward of the frontmost hole 21b by a third distance d3. The third distance d3 is, for example, 5 mm or more and 35 mm or less. The multiple holes 21b may be spaced apart from each other by a fourth distance d4 in the front-rear direction. The fourth distance d4 is, for example, 15 mm or more and 25 mm or less. The holes 21 include holes 21c and holes 21d arranged along the vehicle width direction, except at the center part M in the vehicle width direction. The holes 21c and holes 21d may be spaced apart from each other by a fifth distance d5 along the vehicle width direction. The fifth distance d5 is at least greater than the third distance d3, and more preferably greater than the fourth distance d4, and is, for example, 40 mm or more and 80 mm or less. Therefore, the holes 21a and holes 21b arranged at the center part M in the vehicle width direction are arranged more densely than the holes 21c and holes 21d arranged in the parts other than the center part M in the vehicle width direction. The holes 21c and holes 21d may be offset from each other in the front-rear direction.

The diameter of the multiple holes 21 is, for example, 3 mm or more and 8 mm or less. In other words, the dimension of the multiple holes 21 along the vehicle width direction is 8 mm or less. In the example of FIG. 2, the diameter of holes 21a and 21b is 3 mm or more and 6 mm or less. The diameter of holes 21c and 21d is 4 mm or more and 8 mm or less. The diameter of holes 21a and 21b may be smaller than the diameter of holes 21c and 21d.

Figure 3 is a schematic bottom view of the front of the vehicle showing another example of a high-frequency vortex generating section. Figure 3 shows a high-frequency vortex generating section 20B provided on the same cover member C5 as in Figure 2. As shown in Figure 3, the high-frequency vortex generating section 20B is, as an example, a plurality of protrusions 22 arranged on the cover member C5 along the vehicle width direction of the vehicle 1. The protrusions 22 extend linearly along the cover member C5 and protrude from the cover member C5 at a predetermined height. The protrusions 22 may be molded integrally with the cover member C5, or may be separate resin members attached to the flat surface of the cover member C5. The multiple protrusions 22 constituting the high-frequency vortex generating section 20B are, for example, each of the same shape.

The multiple protrusions 22 are arranged on both sides of the vehicle center line Y in the vehicle width direction. The multiple protrusions 22 are provided on each side, with two sets of four protrusions. The multiple protrusions 22 have a pair of protrusions 22A arranged close to the vehicle center line Y, and a pair of protrusions 22B arranged farther away from the vehicle center line Y in the vehicle width direction than the protrusions 22A. The distance between the center of the protrusions 22A and the vehicle center line Y is smaller than the distance between the center of the protrusions 22A and the center of the protrusions 22B. Therefore, the high-frequency vortex generating parts 20B are arranged more densely in the center part M in the vehicle width direction than in other parts of the vehicle width direction.

Figure 4(a) is a plan view of the high-frequency vortex generating section of Figure 3. Figure 4(b) is a cross-sectional view of the high-frequency vortex generating section of Figure 3 taken along line IVb-IVb. As shown in Figure 4(a), the pair of protrusions 22 are arranged in a V-shape with the other end 22f spaced apart from the one end 22r so as to open forward. The ends 22r of the protrusions 22 are spaced apart by a sixth distance d6. The sixth distance d6 is, for example, 5 mm or more and 20 mm or less. The other ends 22f of the protrusions 22 are spaced apart by a seventh distance d7 that is greater than the sixth distance d6. The seventh distance d7 is, for example, 50 mm or more and 75 mm or less. The length L1 from the one end 22r to the other end 22f of the protrusion 22 is, for example, 30 mm or more and 50 mm or less. Each of the multiple protrusions 22 constituting the high-frequency vortex generating section 20B has a similar shape. The cross-sectional shape of the protrusions 22 is substantially rectangular as shown in FIG. 4(b). The width L2 of the protrusions 22 is, for example, 2 mm or more and 6 mm or less. In other words, the dimension of the multiple protrusions 22 along the vehicle width direction is 8 mm or less. The height H1 of the protrusions 22 is, for example, 2 mm or more and 5 mm or less. The corners of the protrusions 22 may be rounded. Note that a set of protrusions 22 may be V-shaped (V-shaped) that opens toward the rear.

In addition, the high-frequency vortex generating portion 20 may have multiple protrusions (not shown) along the front edge of the bottom portion 5a of the front bumper 5 (for example, along the lip spoiler). In this case, the protrusions may have a cross section similar to that shown in FIG. 4(b) and an extension length in the front-rear direction of 5 mm to 20 mm. In this case, the protrusions are arranged on both sides of the vehicle center line Y in the vehicle width direction. In this case, eight or more protrusions (for example, 19 protrusions) may be provided on each side of the vehicle center line Y.

The vehicle underfloor structure 10 includes a vortex straightening section 30 provided behind the center of gravity G of the vehicle 1 in the underfloor F. The vortex straightening section 30 straightens the airflow turbulent in the high-frequency vortex generating section 20 behind the center of gravity G of the vehicle 1, thereby preventing a decrease in the flow speed of the airflow toward the rear of the vehicle compared to when the vortex straightening section 30 is not provided, and has the function of increasing the boundary layer height while suppressing the effect on the CD value. Specifically, the vortex straightening section 30 can be configured as shown in Figures 5 to 7.

5A is a plan view of an example of a vortex straightening section. In FIG. 5, a protruding fin 30A is shown as an example of a vortex straightening section arranged under the floor F (for example, the area of the dashed line A3 in FIG. 1) rearward of the center of gravity G of the vehicle 1 and toward the center of the vehicle 1. As shown in FIG. 5A, the protruding fin 30A has a plurality of fins 31 arranged in parallel along the vehicle width direction of the vehicle 1. Each of the plurality of fins 31 has a similar shape with the airflow direction being the front-rear direction. The protruding fins 30A are arranged, for example, on a pair of cover members C3 (for example, the area of the dashed line A5 in FIG. 1) installed in front of the lower arm 9a. In this arrangement, the plurality of fins 31 are provided on each side of the vehicle center line Y, with 8 or more (for example, 16) fins on each side, and are arranged on both sides of the vehicle center line Y in the vehicle width direction. The protruding fin 30A may be molded integrally with the cover member C3, or may be a separate resin member that is attached to the flat surface of the cover member C3.

Figure 5(b) is a side view of an example of the vortex straightening portion. Figure 5(c) is a cross-sectional view along the line Vc-Vc of the vortex straightening portion of Figure 5(a). As shown in Figure 5(b), the length L3 of the fin 31 in the front-rear direction is, for example, 15 mm or more and 50 mm or less. The height H2 of the fin 31 is, for example, 5 mm or more and 20 mm or less. The corners of the fin 31 may be rounded. As shown in Figure 5(c), the cross-sectional shape of the fin 31 is a flat plate. The cross-sectional shape of the fin 31 may be a tapered shape due to molding. The width (thickness) L4 of the fin 31 is, for example, 1 mm or more and 5 mm or less. In other words, the dimension of the fin 31 along the vehicle width direction is 8 mm or less. The parallel arrangement interval L5 of the fins 31 is, for example, 5 mm or more and 15 mm or less.

Figure 6(a) is a bottom perspective view of another example of a vortex straightening section. Figure 6 shows a recessed fin 30B as another example of a vortex straightening section that is disposed under the floor F (e.g., the area of dashed line A4 in Figure 1) rearward of the center of gravity G of the vehicle 1 and toward the center of the vehicle 1. The recessed fin 30B is disposed, for example, on the flat portion C1a of the cover member C1 (e.g., the area of dashed line A4 in Figure 1). The recessed fin 30B may be molded integrally with the cover member C1.

6(a), the recessed fin 30B has, for example, a recess 32 provided in the flat portion C1a of the cover member C1 and a plurality of fins 33 provided inside the recess 32. The recess 32 is recessed higher than the portion of the flat portion C1a of the cover member C1 other than the recessed fin 30B when the cover member C1 is viewed from the underfloor F side. The recess 32 may be formed, for example, by flat plate portions 32a and 32b that are provided to form an inverted V shape when viewed from the vehicle width direction. The length of the flat plate portion 32a along the front-rear direction is, for example, 50 mm or more and 125 mm or less. The length of the flat plate portion 32b along the front-rear direction is, for example, 125 mm or more and 200 mm or less. The depth of the recess 32 is, for example, 5 mm or more and 15 mm or less.

The multiple fins 33 extend in the front-rear direction and are arranged side by side inside the recess 32 along the vehicle width direction of the vehicle 1. Each of the multiple fins 33 has a similar shape with the airflow direction being in the front-rear direction. When the multiple fins 33 are arranged in the area of the dashed line A4 in FIG. 1, eight or more (e.g., 16) are provided on each side of the vehicle center line Y, and are arranged on both sides of the vehicle center line Y in the vehicle width direction. The recessed fins 30B can be molded, for example, integrally with the cover member C1.

Figure 6 (b) is a cross-sectional view along the imaginary plane VIb of the vortex straightening portion of Figure 6 (a). As shown in Figures 5 (a) and (b), the multiple fins 33 have a triangular shape similar to the shape of the internal space of the recess 32 when viewed from the vehicle width direction. The multiple fins 33 have a lower end 33a that is flush with the flat portion C1a of the cover member C1 and an upper end 33b that perpendicularly intersects with the flat plate portions 32a and 32b. The length of the lower end 33a of the fin 33 in the front-rear direction is, for example, 175 mm or more and 300 mm or less. The height H3 of the fin 33 is, for example, equal to the depth of the recess 32 and is, for example, 5 mm or more and 15 mm or less. The cross-sectional shape of the fin 33 is, for example, an Ω shape due to integral molding with the cover member C1. The cross-sectional shape of the fin 33 may be a tapered shape due to molding. The width L6 of the fin 33 is, for example, 3 mm or more and 8 mm or less. In other words, the dimension of the fins 33 along the vehicle width direction is 8 mm or less. The spacing L7 between the fins 33 is, for example, 5 mm or more and 15 mm or less.

With such recessed fins 30B, in cases where it is difficult to provide protruding fins that would narrow the minimum ground clearance of the vehicle 1, it is possible to provide a vortex straightening section 30 while preventing the minimum ground clearance from being narrowed.

Figure 7 is a schematic diagram of another example of a vortex straightening section as seen from the rear. Figure 7 shows a rear fin 30C as another example of a vortex straightening section. The rear fin 30C is disposed, for example, at the bottom 6a of the rear bumper 6 (for example, the area of dashed line A6 in Figure 1) and has multiple fins 34. The rear fin 30C is disposed under the floor F rearward of the center of gravity G of the vehicle 1 and toward the rear end of the vehicle 1.

As shown in FIG. 7, the multiple fins 34 are arranged side by side along the vehicle width direction of the vehicle 1 on the flat portion 6b at the bottom 6a of the rear bumper 6. The fins 34 extend linearly along the flat portion 6b and protrude from the flat portion 6b at a predetermined height. The fins 34 may be, for example, integrally molded with the rear bumper 6, or may be separate resin members attached to the flat portion 6b. The multiple fins 34 each have, for example, the same shape.

The cross-sectional shape of the fin 34 is, for example, substantially rectangular, as in FIG. 4(b). The width L8 of the fin 34 is, for example, 2 mm or more and 5 mm or less. In other words, the dimension of the multiple fins 34 along the vehicle width direction is 8 mm or less. Adjacent fins 34 may be spaced apart from each other by an eighth distance d8 in the vehicle width direction. The eighth distance d8 is, for example, 5 mm or more and 10 mm or less. The height H4 of the fin 34 is, for example, 1.5 mm or more and 5 mm or less. The corners of the fin 34 may be rounded.

The dimensions of the holes 21, the protrusions 22, the fins 31, the fins 33, and the fins 34 are not particularly limited. They may also be changed as appropriate depending on the specifications of the vehicle 1.

Next, the operation and effects of the vehicle underfloor structure 10 according to this embodiment will be described with reference to Figures 8 to 13.

First, referring to FIG. 8 and FIG. 9, the change in the way the air flows under the floor F and on the sides of the vehicle 1 will be described. FIG. 8(a) is a bottom view showing the airflow under the floor of a vehicle 100 having a vehicle underfloor structure according to a comparative example. FIG. 8(b) is a bottom view showing the airflow under the floor of a vehicle having a vehicle underfloor structure according to an embodiment. FIG. 9(a) is a side view showing the airflow on the side of a vehicle 100 having a vehicle underfloor structure according to a comparative example. FIG. 9(b) is a side view showing the airflow on the side of a vehicle having a vehicle underfloor structure according to an embodiment. In FIG. 8(a), FIG. 8(b), FIG. 9(a), and FIG. 9(b), streamline vectors having lengths corresponding to the time-averaged flow velocity are shown, rather than turbulent or laminar flows over a small time period.

8(a) and 9(a) show the streamline vectors when a vehicle underfloor structure according to a comparative example in which the high-frequency vortex generating unit 20 and the vortex straightening unit 30 are not provided is adopted. The vehicle speed in the simulation was set to 30 km/h. As shown in FIG. 8(a), in front of the center line 3X of the front wheel 3 in the underfloor F of the vehicle 1, the air flows to avoid the front wheel 3, so the flow around the front wheel 3 is more disturbed than in the center in the vehicle width direction. As shown in FIG. 9(a), a part of the air that avoided the front wheel 3 passes through the wheel house of the front wheel 3 above the front wheel 3 and flows out to the side of the vehicle 1. As shown in FIG. 8(a), the remaining air that avoided the front wheel 3 flows in a curved manner from the center in the vehicle width direction to both ends so as to go around the underfloor F of the vehicle 1 behind the front wheel 3, and flows out to the side of the vehicle 1 through between the front wheel 3 and the rear wheel 4 (the side sill part below the door). That is, part of the air flowing under the floor F of the vehicle 1 is blown up toward the side of the vehicle 1.

Figure 10(a) is a plan view showing the eddy viscosity coefficient distribution at the rear of a vehicle 100 equipped with a vehicle underfloor structure according to a comparative example. Figure 10(b) is a vertical cross-sectional view along line Xb-Xb showing the eddy viscosity coefficient distribution at a predetermined distance from the rear end of the vehicle in the pressure distribution of Figure 10(a). Note that in Figures 10(a), 10(b), 11(a) and 11(b), the region V1 with sparse hatching slanting downward to the right is a part with a larger eddy viscosity coefficient than the white region surrounded by a contour extending from the periphery of the vehicle 1, and the region V2 with dense hatching slanting upward to the right is a part with a larger eddy viscosity coefficient than the region V1 with sparse hatching slanting downward to the right. The left side of the figure is the front of the vehicle 1, the top of the figure is the right side of the vehicle 1, the bottom of the figure is the left side of the vehicle 1, and the right side of the figure is the rear of the vehicle 1.

As shown in FIG. 10(a), the eddy viscosity coefficient distribution in the rear of the vehicle 1 when the vehicle underfloor structure according to the comparative example is adopted varies greatly between the left and right sides of the rear of the vehicle 1. The left and right sides of the rear of the vehicle 1 mean the left and right sides in the vehicle width direction, sandwiched between the vehicle 1 and directly behind it. In the example of FIG. 10(a), a region V2 of dense hatching that slopes upward to the right has developed on the right side of the rear of the vehicle 1, and occurs alternately on the left and right sides, for example, at a period of 4 seconds (0.25 Hz, etc.). The eddy viscosity coefficient of this region V2 is larger than that of the left side of the rear of the vehicle 1, as shown in FIG. 10(b). Thus, in the rear of the vehicle 1 when the vehicle underfloor structure according to the comparative example is adopted, vortices in which the eddy viscosity coefficient is significantly biased between the left and right are generated alternately on the left and right sides periodically (for example, at a period of 4 seconds, 0.25 Hz, etc.). That is, when the vehicle 1 runs, pressure fluctuations occur on the surface of the vehicle 1 and behind the vehicle 1 due to the air flowing around the vehicle 1. An external force is generated in the vehicle body 2 as a reaction force, causing the vehicle body 2 to periodically vibrate with six degrees of freedom at an extremely low frequency (1 Hz or less). This vibration of the vehicle body 2 is unlikely to be directly felt by the driver, but it appears as an adverse effect on the response of the vehicle 1 to the driver's operation (e.g., yaw rate YR). The effect of such extremely low-frequency vibrations of 1 Hz or less on the response of the vehicle 1 has not been noticed in the past.

In contrast, in the vehicle underfloor structure 10 according to the present embodiment, the high-frequency vortex generating unit 20 intentionally generates vortices in a predetermined range in the vehicle width direction, so that the frequency band of the pressure fluctuation of the airflow flowing toward the rear of the vehicle near the front wheels 3 of the underfloor F of the vehicle 1 is changed to the high-frequency side. The vortex generated by the high-frequency vortex generating unit 20 strengthens the turbulence near the front wheels 3 of the underfloor F of the vehicle 1 for a short period of time, and makes the turbulence more likely to spread toward the end (side sill) of the underfloor F of the vehicle 1 in the vehicle width direction as it moves toward the rear of the vehicle. As a result, for example, when the high-frequency vortex generating unit 20 is not provided, as described in the above comparative example, the pressure fluctuation varies with a large amount of periodic (for example, 4-second period, 0.25 Hz, etc.) fluctuation on the surface of the vehicle 1 and at the rear of the vehicle 1. In contrast, in the vehicle underfloor structure 10 according to the present embodiment, the turbulence of the airflow generated by the high-frequency vortex generating unit 20 is utilized to reduce the periodicity of the pressure fluctuation at the rear of the vehicle 1, and the variation in the amount of fluctuation can be suppressed. In addition, behind the center of gravity G of the underfloor F of the vehicle 1, the airflow is straightened by the vortex straightening unit 30, so that the decrease in the flow rate of the airflow is suppressed. As a result, while periodic pressure fluctuations are suppressed at both ends in the vehicle width direction by utilizing the above-mentioned turbulence of the airflow, the generation of an external force in a direction that becomes a moment around the center of gravity due to the airflow in the center of the vehicle width direction of the underfloor F of the vehicle 1 can be effectively suppressed. As a result, when averaged over time, the pressure fluctuations generated on the surface of the vehicle 1 and at the rear of the vehicle 1 are suppressed from becoming extremely low frequency vibrations, and the external force acting as a reaction force at extremely low frequencies (1 Hz or less) is suppressed from acting periodically on the vehicle body 2. Therefore, according to the vehicle underfloor structure 10 of this embodiment, it is possible to improve the vehicle dynamics performance that the driver feels from the response of the vehicle 1.

8(b) and 9(b) show streamline vectors when the vehicle underfloor structure 10 according to this embodiment is adopted. As shown in FIG. 8(b), in front of the center line 3X of the front wheel 3 in the underfloor F of the vehicle 1, the airflow that has entered the underfloor F from the front of the vehicle 1 is intentionally disturbed by the high-frequency vortex generating unit 20, and the vibration energy of the airflow is converted into higher frequency energy. Since the high-frequency vortex generating unit 20 is arranged more densely in the center part M in the vehicle width direction than in other parts of the center part M in the vehicle width direction, it is possible to convert the vibration energy into sufficient high frequency energy in the center part in the vehicle width direction forward of the center line 3X of the front wheel 3 in the underfloor F of the vehicle 1. By providing the high-frequency vortex generating unit 20 on the end side in the vehicle width direction, the airflow from the front of the front wheel 3 is disturbed in advance. As a result, the airflow from the front of the front wheel 3 is more likely to be drawn into the airflow in the center part in the vehicle width direction than to flow into the wheel house of the front wheel 3. As shown in FIG. 8(b), the airflow toward the front wheels 3 is drawn toward the center of the underfloor F in the vehicle width direction, and is contracted so that the airflow is gathered in the underfloor F sandwiched between the front wheels 3. In the example of FIG. 8(a), the airflow around the front wheels 3 is more turbulent than in the center in the vehicle width direction, whereas in the example of FIG. 8(b), the time-average flow velocity in the center in the vehicle width direction is greater than the time-average flow velocity around the front wheels 3. As a result, as shown in FIG. 9(b), the airflow that passes from the wheelhouse of the front wheels 3 above the front wheels 3 and flows out to the side of the vehicle 1 is reduced compared to FIG. 9(a).

In addition, the vibration energy of the airflow collected in the underfloor F between the front wheels 3 is high-frequency energy, so that the airflow can be reduced from being rolled up (wound up) on the side of the vehicle 1 (near the quarter pillar on the side). In other words, in the comparative example of FIG. 8(a), the airflow that flows out to the side of the vehicle 1 through between the front wheels 3 and the rear wheels 4 (the side sill part below the door) is repeatedly generated stably at a constant cycle, but in the example of FIG. 8(b), the turbulence strengthened by the high-frequency vortex generating unit 20 causes the airflow to curve from the center in the vehicle width direction to both ends so as to wrap around the underfloor F of the vehicle 1 behind the front wheels 3, becoming irregular (non-periodic). Therefore, the airflow that flows out to the side of the vehicle 1 is also irregular. On the other hand, the airflow flowing through the center in the vehicle width direction increases the number of high-frequency vortices on the upstream side (front) in a very short time, so it can be said that the degree of turbulence tends to spread toward the end side in the vehicle width direction, but the time-averaged flow velocity has a streamline vector that makes it seem as if the airflow is contracted as if it flows through the area between the front wheels 3 directly to the center in the vehicle width direction at the rear (see the opposing thick black arrows in FIG. 8(b)). The airflow turbulent by the high-frequency vortex generating unit 20 is rectified by the vortex rectifying unit 30 behind the center of gravity G of the vehicle 1 under the floor F. This makes it possible to prevent the flow velocity of the airflow toward the rear of the vehicle from decreasing compared to when the vortex rectifying unit 30 is not provided, and it is possible to suppress a reduction in the boundary layer height under the floor F while suppressing the effect on the CD value of the vehicle 1. In addition, it is possible to suppress the generation of external forces that act as moments around the center of gravity G of the vehicle 1 at the center of the vehicle width direction behind the center of gravity G, due to the airflow disturbed by the high-frequency vortex generating unit 20.

In this way, by reducing entrainment (rolling up) on the side of the vehicle 1 (near the quarter pillar on the side), the eddy viscosity coefficient distribution at the rear of the vehicle 1 is improved. Figure 11(a) is a plan view showing the eddy viscosity coefficient distribution at the rear of a vehicle equipped with a vehicle underfloor structure according to an embodiment. Figure 11(b) is a longitudinal cross-sectional view taken along line XIb-XIb showing the eddy viscosity coefficient distribution at a specified distance from the rear end of the vehicle in the pressure distribution in (a).

11(a), the eddy viscosity coefficient distribution in the rear of the vehicle 1 when the vehicle underfloor structure 10 according to the present embodiment is adopted is such that the densely hatched area V2 slanting upward to the right is hardly developed on both the right and left sides of the rear of the vehicle 1, and the sparsely hatched area V1 slanting downward to the right is scattered. In the example of FIG. 11(a), the sparsely hatched area V1 slanting downward to the right occurs irregularly (non-periodically), unlike the densely hatched area V2 slanting upward to the right in FIG. 10(a). As shown in FIG. 11(b), the variation in the eddy viscosity coefficient on the left and right sides of the rear of the vehicle 1 is smaller than that in the case of adopting the vehicle underfloor structure according to the comparative example shown in FIG. 11(b). According to the vehicle underfloor structure 10 of this embodiment, fluctuations in the eddy viscosity coefficient distribution occur irregularly (non-periodically), so it is possible to suppress large periodic (e.g., 4 seconds, 0.25 Hz, etc.) variations in the eddy viscosity coefficient on the left and right sides of the rear of the vehicle 1. As a result, periodic external forces acting on the vehicle body 2 as a reaction force to pressure fluctuations on the surface of the vehicle 1 and at the rear of the vehicle 1 that occur as the vehicle 1 travels are suppressed.

For example, as shown in FIG. 12, when comparing the change in yaw rate over time when the vehicle is traveling straight (e.g., 30 km/h), when the vehicle underfloor structure according to the comparative example is adopted (dotted line), the vibration crosses the zero point at a period of about 4 seconds (about 0.25 Hz), whereas when the vehicle underfloor structure 10 according to the present embodiment is adopted (solid line), such vibration is hardly observed. As shown in FIG. 13, when comparing the change level of the yaw rate when the vehicle is traveling straight, the fluctuation level of the yaw rate at extremely low frequencies (1 Hz or less) is also reduced when the vehicle underfloor structure 10 according to the present embodiment is adopted (solid line) compared to when the vehicle underfloor structure according to the comparative example is adopted (dotted line), and it can be seen that the vehicle body 2 is suppressed from vibrating periodically with six degrees of freedom at extremely low frequencies. Note that the improvement in the yaw rate at extremely low frequencies (1 Hz or less) as shown in FIG. 12 and FIG. 13 can be obtained in the same way even when the vehicle is traveling at high speed (e.g., 250 km/h). Incidentally, the vehicle underfloor structure 10 according to this embodiment can be said to be effective in that it provides the above-mentioned effects even at low speeds of around 30 km/h.

By suppressing the vibration of the vehicle body 2 in this way, adverse effects on the response of the vehicle 1 to the driver's operation (e.g., yaw rate YR) are suppressed. For example, the vibration of the vehicle body 2 is suppressed from causing the driver to feel that straight-line stability is poor, the response and reaction force differ each time an operation is performed, and the settlement of the response and reaction force varies, making it easier for the driver to recognize that the vehicle's maneuvering performance is good.

[Modification]
Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment. The present invention can be embodied in various forms including the above-mentioned embodiment and various modifications and improvements based on the knowledge of those skilled in the art.

In the above-described embodiment, the high-frequency vortex generating section 20 is disposed forward of the front end of the front wheel 3, but this is not limited thereto. The high-frequency vortex generating section 20 may be disposed in an area other than the dashed line A2 in FIG. 1 (for example, underfloor F within the range of dashed line A1) forward of the center line 3X of the front wheel 3. In short, it is sufficient that the high-frequency vortex generating section 20 is disposed forward of the center line 3X of the front wheel 3.

In the above-described embodiment, the protruding fin 30A is disposed on the cover member C3 (area of dashed line A5 in FIG. 1), but may be disposed on the flat portion C1a of the cover member C1 (area of dashed line A4 in FIG. 1). The recessed fin 30B is disposed on the flat portion C1a of the cover member C1 (area of dashed line A4 in FIG. 1), but may be disposed on the cover member C3 (area of dashed line A5 in FIG. 1). The protruding fin 30A may be disposed on both the cover member C3 and the flat portion C1a of the cover member C1. The recessed fin 30B may be disposed on both the cover member C3 and the flat portion C1a of the cover member C1.

In the above embodiment, the recessed fin 30B is molded integrally with the cover member C1, but it may be a separate resin member that is attached to the flat surface of the cover member C1.

In the above embodiment, the vortex flow straightening unit 30 is disposed behind the center position G of the vehicle 1 in the underfloor F, both in the underfloor F near the center of the vehicle 1 (center portion, areas A3, A4, and A5 in FIG. 1) and in the underfloor F near the rear end of the vehicle 1 (rear portion, area A6 in FIG. 1). However, this is not limited to this. The vortex flow straightening unit 30 may be disposed in either the center portion or the rear portion. In this case, the vortex flow straightening unit 30 may be disposed in the center portion. The vortex flow straightening unit 30 may also be disposed in an area other than the dashed lines A3 to A6 in FIG. 1 (for example, the dashed line A3 area and the dashed line A7 area in FIG. 1) in the underfloor F. In short, the vortex flow straightening unit 30 may be disposed behind the center position G of the vehicle 1 in the underfloor F.

In the above embodiment, multiple holes 21, multiple protrusions 22, multiple fins 31, multiple fins 33, and multiple fins 34 are described, but each configuration is not particularly limited. Various modifications, such as different cross-sectional shapes and different hole opening shapes, are not prohibited.

In the above embodiment, a box-shaped vehicle such as a passenger car is used as an example of the vehicle, but the type of vehicle is not limited to a box-shaped vehicle and may be a truck or other transport vehicle.

1...vehicle, 3...front wheel, 3X...center line, 10...vehicle underfloor structure, 20, 20A, 20B...high frequency vortex generating portion, 21, 21a, 21b, 21c, 21d...hole, 22, 22A, 22B...protrusion, 30...vortex straightening portion, 31, 33, 34...fins, F...underfloor, G...center of gravity position, M...center, Y...vehicle center line.

Claims (3)

a high-frequency vortex generating portion provided under a floor of the vehicle forward of a center line of the front wheels, the high-frequency vortex generating portion including at least one of a plurality of protrusions and a plurality of holes arranged along a vehicle width direction of the vehicle;
a vortex straightening unit that is provided under the floor rearward of a center of gravity of the vehicle and includes a plurality of fins arranged along the vehicle width direction,
A vehicle underfloor structure, wherein the high-frequency vortex generating portions are arranged more densely in a central portion in the vehicle width direction than in portions other than the central portion in the vehicle width direction. the high-frequency vortex generating portion and the vortex rectifying portion are arranged on both sides of a vehicle center line in the vehicle width direction, and each side includes eight or more of the projections, the holes, or the fins,
The vehicle underfloor structure according to claim 1 , wherein a dimension of the projection, the hole, or the fin along the vehicle width direction is 8 mm or less. 3. The vehicle underfloor structure according to claim 1, wherein the fins are arranged at intervals of 10 mm or less.

Images