JP3269197B2 - Car underfloor structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle underfloor structure.

[0002]

2. Description of the Related Art Conventionally, as an underfloor structure of an automobile, an underfloor structure in which the underfloor is flattened to improve aerodynamic characteristics is known. Referring to FIG. 20, reference numeral 1 denotes a vehicle body, reference numeral 3 denotes a center floor, and a floor tunnel 5 is formed at a central portion thereof in the front-rear direction of the vehicle. A drive transmission system such as a shaft 11 and a rear differential 13 is provided. Reference numeral 15 denotes a front wheel house.
7 are arranged. Reference numeral 19 denotes a rear wheel house in which a rear wheel 21 is arranged. The lower opening portion of the engine room 25 separated by the front wheel house 15 and the dash lower panel 23 is closed by a flat undercover 27, and the lower portion of the engine room 25 is made as flat as possible. The air flow velocity is improved to reduce the lift of the air resistance.

On the other hand, when the lower opening of the engine room 25 is closed by the under cover 27, the high-temperature air that has passed through a radiator (not shown) becomes
5 becomes difficult to be discharged from the lower side, and the engine room 2
The high-temperature air stays in the inside 5 and the ambient temperature in the engine room 25 rises, and the inside of the room 25 becomes high pressure, so that it becomes difficult to introduce cooling air from the radiator opening, and the radiator performance deteriorates. For this reason, the under cover 27 has a large number of louvers 27a over substantially the entire area between the left and right front wheel housings 15, 15.
And the engine room 25 from these louvers 27a.
I try to discharge the hot air inside. This analogous structure
For example, it is disclosed in Japanese Utility Model Laid-Open Publication No. Sho 60-105526.

[0004] Japanese Patent Laid-Open Publication No. 2-61792 discloses a technique for improving the running stability by reducing the yawing moment due to the crosswind.

That is, the side air dam of an automobile is formed so that the front part and the rear part have different ground heights at the lower ends and the rear part is low.

[0006] As a result of lowering the lower end of the rear part lower than the lower end of the front part, the lateral wind pressure receiving area of the rear part is widened and the lateral force is increased, thereby causing the yawing to act in the opposite direction to the moment. An anti-yaw moment is generated strongly.

[0007]

In the conventional example shown in FIG. 20, a large number of louvers 27
a, a low-velocity airflow from the engine room 25 flows out of the engine room 25, so that a high-speed underfloor flow from the front of the vehicle below the undercover 27 is decelerated. U ₁ , U ₂ , U ₃ ,
Becomes the flow velocity distribution as shown by U _4, the flow rate of the floor center part is lowered.

For example, according to a wind tunnel experiment corresponding to a vehicle speed of 120 km / h, in the transmission 9 portion and the rear differential 13 portion which are the heat generating portions below the floor, the cooling air speed becomes relatively low at all.
While a sufficient cooling effect of the rear differential 13 cannot be obtained, the airflow having a high flow velocity on the side floor directly hits the rear wheel 21, thereby increasing the drag at the rear wheel 21.

Further, the lift of the rear wheel is increased with respect to the lift of the front wheel, which affects the steering stability.

Further, in a traffic jam or the like, the hot air in the engine room 25 discharged from the louver 27a provided on substantially the entire surface of the under cover 27 is not sufficiently ventilated to the rear of the under cover 27, and the lower portion of the under cover 27 Since the air stays in the vicinity, there is a possibility that the high-temperature air may circulate again from a radiator (not shown).

In the conventional example disclosed in Japanese Utility Model Laid-Open Publication No. 2-61792, the rear part and the lower end of the lower side of the side air dam are low in front of the rear wheel, so that they easily interfere with curbs and the like. On the leeward side, the lifting of the underfloor flow on the body side surface is impeded by the side air dam, so the negative pressure on the body side becomes small behind the vehicle center of gravity on the leeward side, and as a result, it is difficult to generate a sufficient anti-yaw moment. there were.

Accordingly, the present invention can optimize the flow under the floor with the air flowing out of the high-pressure section at the front of the vehicle, improve the effect of reducing the lift and the drag, and improve the heating section at the lower side of the floor. It is an object of the present invention to provide an underfloor structure of an automobile capable of enhancing a cooling effect and further improving the steering stability by reducing the vehicle's rotation due to a crosswind.

[0013]

According to a first aspect of the present invention, a lower portion of a high-pressure portion such as an engine room separated from a front portion of a vehicle is closed with a flat floor member. A pair of hot air discharge units having an outlet communicating with the high-pressure unit and directing the air having a low flow velocity in the high-pressure unit to the rear wheel at substantially symmetric positions with respect to the vehicle center line of the floor member. While forming, the air flow flowing along the lower side of the floor member from the front of the vehicle is reduced between the pair of hot air discharge portions to reduce the flow velocity.
As soon as possible, a narrowed portion is formed to flow out toward the heat generating portion on the lower side of the floor behind the floor member , and the vehicle is at least extended from the wheel house extension line on the lower surface of the floor located between the front wheel house and the rear wheel house. A flat surface is formed in a region outside in the width direction and in front of the vehicle center of gravity, and the other regions are non-flat surfaces.

According to a second aspect of the present invention, the lower side of a high-pressure portion such as an engine room separated at the front of the vehicle is closed by a flat floor member, and the floor member is positioned substantially symmetrically with respect to the vehicle center line. To
Forming a pair of hot air discharge portions having an air outlet communicating with the high pressure portion and directing air with a low flow velocity in the high pressure portion through the rear wheel to flow out, and between the pair of hot air discharge portions,
The front wheel house and the rear are formed with a constricted portion that reduces the flow of air flowing along the lower side of the floor member from the front of the vehicle to increase the flow velocity, and directs and flows out the heat generation part on the lower side of the floor behind the floor member. A flat surface is formed in the area of the lower surface of the floor located between the wheel house and at least the vehicle center line side from the extended line of the wheel house, and in the area behind the vehicle center of gravity, and the other areas are non-flat surfaces. It is characterized by having done.

According to a third aspect of the present invention, a lower side of a high-pressure portion such as an engine room separated at a front portion of a vehicle is closed by a flat floor member, and the floor member is positioned substantially symmetrically with respect to a vehicle center line. To
A pair of hot air discharge portions having an air outlet communicating with the high pressure portion and allowing air having a low flow velocity in the high pressure portion to flow toward the rear wheel is formed, and between the pair of hot air discharge portions, from the front of the vehicle. A narrowed portion is formed to contract the air flow flowing along the lower side of the floor member to increase the flow velocity and to direct the heat generation portion on the lower side of the floor behind the floor member to flow out, and the front wheel house and the rear wheel house and On the lower surface of the floor located between, outside the wheel house extension line in the vehicle width direction,
In addition, a flat surface is formed in a region in front of the vehicle center of gravity, and a flat surface is formed in a region on the vehicle center line side from the extended line of the wheel house and in a region behind the vehicle center of gravity. Is characterized by having a non-flat surface.

According to a fourth aspect of the present invention, in the underfloor structure for an automobile according to the first, second or third aspect, the cross-sectional shape of the side sill in the vehicle width direction at a portion forward of the vehicle center of gravity is changed to the vehicle width of the side sill at another portion. It is characterized by being formed smaller than the cross-sectional shape in the direction.

[0017]

According to the first aspect of the present invention, the flow rate of the high-pressure air flows out of the hot air discharge section toward the rear wheel, which is sufficiently lower than the high-speed flow under the floor from the front of the vehicle. . Since this air flow gradually expands in the vehicle width direction as it advances toward the rear of the vehicle, it expands to cover it at the rear wheel position, and the flow near the vehicle center line is relatively contracted. And the throttle section reduces the under-floor flow from the front of the vehicle and supplies a high-speed airflow to the rear heating section, so that the heating section can be effectively cooled. In addition to this, the underfloor flow can be made high speed, so that the lift can be reduced.

Further, the air flow contracted when passing through the front wheel house outside the high-pressure air flow flowing toward the rear wheel from the hot air discharge portion is located outside the extended line of the wheel house in the vehicle width direction. In addition, since the flat surface is formed in a region in front of the center of gravity of the vehicle, the flow velocity further increases, and the flow under the floor can be increased.

According to the second aspect of the present invention, similarly to the first aspect of the invention, the flow velocity from the hot air discharge portion toward the rear wheel is low,
And a high-pressure air flow flows out. In addition, a high-speed air flow is supplied from the throttle section toward the heat-generating section, so that the heat-generating section can be effectively cooled and the under-floor flow can be performed at high speed.

The flow near the vehicle center line, which has flowed out of the hot air discharge portion and is relatively contracted, is gentle in a region on the vehicle center line side from the wheel house extension line and behind the vehicle center of gravity. Trying to slow down and spread,
By making this region a flat surface, diffusion can be reduced.

According to the third aspect of the invention, similarly to the first and second aspects of the invention, a high-pressure airflow having a low flow velocity flows out from the hot air discharge portion toward the rear wheel. In addition, a high-speed air flow is supplied from the throttle section toward the heat-generating section, so that the heat-generating section can be effectively cooled and the under-floor flow can be performed at high speed.

The air flow contracted when passing through the front wheel house outside the high-pressure air flow flowing toward the rear wheel from the hot air discharge portion is located outside the wheel house extension line in the vehicle width direction. In addition, since the flat surface is formed in a region in front of the center of gravity of the vehicle, the flow velocity further increases, and the flow under the floor can be increased.

Further, the flow near the vehicle center line, which has flowed out of the hot air discharge portion and is relatively contracted, is gentle in a region on the vehicle center line side from the extended line of the wheel house and behind the vehicle center of gravity. However, by making this area a flat surface, diffusion can be reduced.

According to the fourth aspect of the present invention, in combination with the functions of the first, second and third aspects, the upward flow of the under-floor flow to the leeward side of the vehicle is suppressed ahead of the vehicle center of gravity in the crosswind, and the center of gravity of the vehicle is maintained. Behind the point, the winding to the body side increases, so the negative pressure generated on the body side increases, and the turning moment (yawing moment) acting on the vehicle can be reduced.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a bottom view of a vehicle according to an embodiment of the present invention, in which the same components as those of the prior art are denoted by the same reference numerals.

In FIG. 1, a floor tunnel 5 is formed in the center of the center floor 3 of the vehicle body 1 in the front-rear direction of the vehicle body, and the transmission 9, the propeller shaft 11,
A drive transmission system such as a rear differential 13 is provided. And
A flat undercover made of a floor member, for example, a resin material or a steel plate material, is provided between the left and right front wheel houses 15 of the vehicle body 1 and a lower open portion of the engine room 25 which is a high-pressure portion of the vehicle separated by the dash floor panel 23. 27
And the basic structure such as the closed point is the same as that of the conventional example.

Here, the undercover 27 is positioned substantially symmetrically with respect to the vehicle center line Y (the longitudinal axis of the vehicle passing through the vehicle center of gravity COG) in the region between the left and right front wheel houses 15. A pair of hot air discharge portions 35 are formed to communicate with the engine room 25 and allow the air in the engine room 25 to flow out to the rear wheel 21 and flow out between the pair of hot air discharge portions 35. The airflow flowing along the lower side of the undercover 27 from the front of the vehicle is contracted and directed toward the generating section below the center floor 3 and the rear floor 7 behind the undercover 27, that is, toward the transmission 9 and the rear differential 13. An aperture portion 37 is formed.

In this embodiment, the hot air discharging section 35
As shown in FIG. 2, the under cover 27 is formed as a duct 39 which is inclined downward toward the rear of the vehicle and is recessed from the floor surface. The outlet 39a is set at the rear end edge of the under cover 27, and a narrowed portion 37 is formed between opposing side walls of the ducts 39, 39 on the vehicle center line Y side. The throttle section 37 is located on the left and right front wheel house 1
It is set to approximately 1/3 of the dimension between 5 and 15 so as to be substantially equivalent to the left and right of the transmission 9 which is the lower heating portion of the floor immediately after the throttle portion 37.

Further, in this embodiment, the left and right front wheel houses are separated from each other by the left and right front wheel houses 15 and the left and right rear wheel houses 19 by the floor tunnel 7 of the center floor 3. 15 and the rear wheel house 19, the longitudinal axes LH and RH passing through the left and right side members 41 disposed on the innermost extension lines in the vehicle width direction, and the vehicle width direction passing through the center of gravity COG of the vehicle. The first area, the second area, the third area, and the fourth area shown in FIG. 3 are divided into four areas by the axis X, and the first area and the fourth area are made of a resin material, a steel plate, or the like. Undercovers 43 and 45
Are provided to form a flat surface.

Here, the first area is the left and right side members 4
1 between the longitudinal axes LH and RH passing through the vehicle body 1 and the left and right side sills 47 which are the outermost in the vehicle width direction.
The second region is formed by an area LH, RH in the vehicle longitudinal direction passing through the left and right side members 41 and a floor tunnel 7 on the inside in the vehicle width direction. It is formed in a region which is forward of the vehicle width direction axis X passing through the vehicle center of gravity COG in the vehicle longitudinal direction. Further, the third region is a single unit from the axis X in the vehicle width direction passing through the vehicle center of gravity COG between the longitudinal axes LH and RH passing through the left and right side members 41 and the left and right side sills 47 at the outermost sides in the vehicle width direction. The fourth region is formed by a region extending in the front-rear direction, and the fourth region is a vehicle width direction passing through the vehicle center of gravity COG between the vehicle body front-rear direction axis lines LH and RH passing through the left and right side members 41 and the floor tunnel 7 inside the vehicle width direction. Axis X of
It is formed in a region that is more in the vehicle longitudinal direction.

The undercover 43 disposed below the center floor 3 in the first region is shown in FIG. 4 between the rear end of the front wheel house 15 and the axis X in the vehicle width direction passing through the vehicle center of gravity COG. So, side sill 47
Are attached to the stay 49 and the side member 41 provided with the bolts and the like.

The under cover 45 disposed below the center floor 3 in the fourth area is located at the vehicle center of gravity COG.
As shown in FIG. 5, between the axis X in the vehicle width direction passing through the vehicle and the front end of the rear wheel house 19,
And a stay 51 provided in the floor tunnel 5 with bolts or the like.

Next, the operation of the first embodiment will be described with reference to FIGS.

FIG. 6 shows, for example, a vehicle speed of 120 km / h (3
FIG. 7 is a view showing the appearance of air flow on the center floor at the time of straight traveling obtained by a wind tunnel experiment corresponding to 3.3 m / sec), and FIG. 7 shows a side wind (swing angle of 20 °) obtained by a similar experiment. It is a figure which shows the aspect of the flow of the air in the center floor of FIG.

First, the flow of air on the center floor when traveling straight is roughly divided into three flows, a first flow A, a second flow B, and a third flow C, as shown in FIG. be able to.

Here, the first flow A is the engine room 2
5, the flow on the vehicle center line Y passing through the throttle portion 31 between the ducts 33, 33 of the under cover 27 whose lower opening portion is closed, the throttle action by the throttle portion 31 and the ducts 33, 3
Engine room 2 flowing out of the exits 33a, 33a of the engine 3
5 is a flow having a flow velocity of 30 m / sec or more, which is contracted and accelerated by a high-pressure and slow-flowing air flow.

The second flow B is formed at the outlets 3 of the ducts 33, 33.
This is a flow of air in the engine lum 25 flowing out of 3a and 33a, and the flow is directed toward the rear wheels 21 at a slow flow of 20 m / sec or less, and expands toward the rear of the vehicle.

The third flow C is a flow located further outside the vehicle than the second flow B. When the third flow C passes through the front wheel house 15, the flow is contracted by the front wheels 17 and the second flow C is further reduced.
Flow velocity 30 m / sec, which is reduced and accelerated by the flow B
It is a flow of c or more.

Hereinafter, the flow and action of air in each area of the center floor 3 divided as shown in FIG. 3 will be described.

First, the flow and action of air when traveling straight will be described with reference to FIG.

The underfloor flow in the first area is the third flow C having a high flow velocity. In this area, since the lower surface of the center floor 3 is flattened by the undercover 37, the air resistance at the lower surface of the floor is small. The flow rate is increased. Therefore, in this region, the air resistance on the center floor 3 can be reduced, and the lift acting on the vehicle can be reduced.

The underfloor flows in the second area are the first flow A having a high flow velocity and the second flow B having a low flow velocity. In this area, the underfloor space is not formed because the lower surface of the center floor 3 is not flattened. Duct 3
The second flow B of the air in the engine room 25 flowing out of the outlets 33a, 33a of the engine 33, 33 can be made a smoother flow. Performance can be improved.

The first flow A is generated by the second flow B.
Is further reduced and the flow velocity is increased, so that the surface cooling wind speed of the heat generating portion such as the transmission 9 and the rear differential 13 is improved, so that the cooling effect of the transmission 9 and the rear differential 13 can be enhanced. 13, the heat resistance can be improved by increasing the oil temperature, and at the same time, the lift acting on the vehicle can be reduced by increasing the underfloor flow rate.

The under-floor flow in the third area is the second flow B having a low flow velocity. In this area, the lower surface of the center floor 3 is not flattened. Since the third flow C, which flows in the direction of the wheel 21 and flows through the first region and has a high flow velocity, can be prevented from hitting the rear wheel 21, the drag at the rear wheel 21 is reduced, and the fairing effect of the rear wheel 21 is reduced. Is more remarkable, and the air resistance received by the vehicle can be reduced.

The under-floor flow in the fourth area is an area where the first flow A having a high flow velocity slowly diffuses and decelerates.
As a result, the air resistance on the lower surface of the floor is small, so that the flow velocity of the first flow A is prevented from decreasing and diffusing, and the cooling effect of the transmission 9 and the rear differential 13 can be increased, and at the same time, the downforce is improved. Can be done.

Next, the flow and action of air during a cross wind will be described with reference to FIG.

Since the first region is located ahead of the vehicle center of gravity COG, the floor resistance against the underfloor flow in this region is defined as a turning moment (a yawing moment around the vehicle center of gravity COG) that turns the head of the vehicle toward the leeward side. In this region, the underfloor of the center floor 3 is flattened by the undercover 37 in this region, so that the yawing moment is reduced without receiving the floor resistance. Further, the flattening of this region increases the flow velocity at the lower side of the side sill 41 on the leeward side. Further, if the cross-sectional shape of the side sill 41 in the vehicle width direction is reduced, separation occurs with the increase in the flow velocity, so that the body side Is suppressed. As a result, the negative pressure on the leeward body side surface is reduced, and the yawing moment is further reduced.

Since the second area is also located forward of the vehicle center of gravity COG, the floor resistance against the downstream of the floor in this area also acts as a turning moment for turning the head of the vehicle toward the leeward side. Since the flow velocity is lower than the air flow in other areas, the floor resistance due to non-flattening is small, and the increase in turning moment is very small, and the increase in turning moment here can be ignored.

The third area is located behind the vehicle center of gravity COG, and is not flat with respect to the center floor 3, so that the floor resistance against the under-floor flow is large and the lateral force increases due to the floor resistance. I do. As a result, an anti-yaw moment acting in the opposite direction to the yaw moment is generated, and the yaw moment is reduced.

Further, in this region, the flow velocity of the underfloor flow is reduced by the floor resistance, so that the flow is prevented from being separated at the side sill 41 continuous to this region, and the underfloor flow is wound up on the side surface of the body. Negative pressure is efficiently generated on the side surface, thereby reducing the yawing moment. Further, if the X section R of the side sill 41 that continues to this area is increased, the underfloor flow can be further rolled up to the body side, the negative pressure generated on the body side can be further increased, and the yawing moment can be further reduced. Can be reduced.

The fourth area is located behind the vehicle center of gravity COG, and the underfloor flow in this area is a flow that collides with the rear wheel 21. Since this area is flattened with respect to the center floor 3 by the under cover 39, the flow velocity is increased, and the under-floor flow having a high flow velocity hits the rear wheel 21, thereby increasing the drag at the rear wheel 21. As a result, an anti-yaw moment is generated, and the yaw moment is reduced.

Accordingly, the effect of reducing the lift and the drag of the vehicle can be enhanced, and the effect of cooling the lower heating portion on the floor near the vehicle center line can be enhanced.

FIGS. 8 and 9 show a second embodiment of the present invention. FIG. 8 shows a cross section similar to FIG.
Shows a cross section similar to FIG.

In this embodiment, as in the first embodiment, an under cover 27 is attached to the lower side of the engine room 25, and the first area and the fourth area of the center floor 3 are provided.
Area covers 43 and 45 are attached to the area.

Further, in this embodiment, the side sill 47 is provided.
Is different between the front and rear of the vehicle center of gravity COG. That is, the vehicle center of gravity C
The other party than OG, form rather represented a cross-section R ₁ of the side sill 47 as shown in FIG. 8, the behind the vehicle center of gravity COG, as shown in FIG. 9, the cross section R ₂ sites sill 47 sectional R ₁ It is formed sufficiently large as compared with.

According to this embodiment, in the case of a crosswind, the flow of the underfloor flow to the leeward side of the vehicle is suppressed before the vehicle center of gravity COG, and the flow of the underfloor flow to the body side behind the vehicle center of gravity COG is large. Become. Thereby, the negative pressure generated on the body side can be increased, and the yawing moment acting on the vehicle can be reduced.

Accordingly, the effect of reducing the lift and the drag of the vehicle can be enhanced, and the effect of cooling the lower heating portion on the floor near the vehicle center line can be enhanced.
At the time of crosswind, the effect of reducing the yawing moment can be similarly enhanced in addition to the above effect.

Further, in order to prove the superiority of the effect of the present invention, other underfloor structures will be exemplified and described in comparison with these.

FIGS. 10 and 11 show the state of air flow in the underfloor structure as the first example.

In this underfloor structure, a flat surface is formed by mounting an undercover 27 similar to that of the first embodiment under the engine room 25, and the center floor 3 does not have a flat surface, The bead and the like remain exposed. In such an underfloor structure, an air flow (flow direction and flow velocity) as shown in FIG. 10 is exhibited during straight traveling, and an air flow as shown in FIG. 11 is displayed during cross wind.

FIG. 12 shows an underfloor structure according to a second embodiment, in which an undercover 27 similar to that of the first embodiment is provided below the engine room 25 to form a flat surface. An under cover 53 is attached to the entire lower surface of the first to fourth regions (see FIG. 3) of the center floor 3 to form a flat surface.
The undercover 53 is made of a flat resin material or a steel material, and is provided on the side sill 47 between the rear end of the front wheel house 15 and the front end of the rear wheel house 19, as shown in FIGS. Stay 49
And a stay 51 and a side member 41 provided in the floor tunnel 5 are respectively attached by bolts or the like.
In such an underfloor structure, an air flow as shown in FIG. 5 is obtained when the vehicle is traveling straight, and an air flow as shown in FIG. 16 is obtained during a crosswind.

Here, the reference car without the undercover is a, the car of the first example with the undercover only on the lower side of the engine room is b, and the undercover is on the entire lower side of the engine room and the lower part of the center floor. the second example car equipped with a c, and the first embodiment vehicle of the present invention d, a second embodiment vehicle of the present invention as e, the experimental results by the resulting C _D reduction, Cym reduction effect and cooling The effect will be described in comparison.

[0064] Figure 17 is a chart showing a comparison of C _D reduction effect, a is the reference vehicle, b car of the first example, c is the car of the second example, d
Shows the characteristics of the first embodiment vehicle of the present invention, respectively.
The car B of the first example in which the lower part of the engine room is flat has a smaller _CD reduction effect as compared with the reference car a, but the car c of the second example in which the entire center floor is flat has a C lower than that of the reference car a. _D a can be reduced by a large margin, further according to the first embodiment car d of the present invention, it is possible to further reduce the C _D than car c of the second embodiment. Therefore, it is possible to increase Silurian properly the C _D reduction effect.

FIG. 18 is a diagram showing a comparison of the Cym reduction effect, in which the change in Cym is compared with the yaw angle characteristic of the reference wheel a. The car b of the first example has a Cy compared to the standard car a.
m becomes worse and further worse in car b of the second example,
In the example vehicle d, the standard vehicle a is substantially equivalent, and in the second example vehicle e, Cym can be improved. Therefore, the effect of reducing the yawing moment can be enhanced.

FIG. 19 is a table showing a comparison of the cooling wind speeds of the heat generating portions of the transmission system. The vehicle b of the first example and the vehicle c of the second example can increase the wind speed to 150 compared to the standard vehicle a. In the vehicle d according to the first embodiment of the present invention, the wind speed can be further increased (about 170), and the cooling effect of the lower heat generating portion on the floor can be further enhanced.

[0067]

As is apparent from the above description, according to the first aspect of the present invention, the under-floor flow to the rear wheels is caused by the air flow flowing out through the hot air discharge portion at the front portion of the vehicle and the contraction action of the throttle portion. For this purpose, a low-velocity flow and a high-velocity flow near the vehicle center line can be exhibited, which can enhance the effect of reducing the lift and drag of the vehicle and generate heat below the floor near the vehicle center line. The cooling effect of the part can be enhanced.

Further, since a flat surface is formed in the region outside the wheel house extension line in the vehicle width direction and in front of the vehicle center of gravity, the air flow in this region further increases the flow velocity, and the under-floor flow is increased at a high speed. Can be

Further, in the case of a crosswind, the floor resistance acting on the region outside the wheel house extension in the vehicle width direction and in front of the vehicle center of gravity acts as a turning moment (yaw moment) for directing the vehicle to the leeward side. Since this region has a flat surface, the resistance is not received and the yaw moment can be reduced.

According to the second aspect of the present invention, similarly to the first aspect of the present invention, the effect of reducing the lift of the vehicle and the effect of reducing the drag can be enhanced, and the cooling of the heat generating portion below the floor near the vehicle center line can be achieved. The effect can be enhanced.

Further, in the region on the vehicle center line side from the wheel house extension line and behind the vehicle center of gravity,
The flow near the vehicle center line, which has flowed out of the hot air discharge portion and is relatively contracted, diffuses slowly and tries to decelerate. However, by making this area a flat surface, this diffusion can be prevented as much as possible. .

Further, in the case of a cross wind, this area is made a flat surface, so that a rapid flow is applied to the rear wheel to increase the shape resistance of the rear wheel, so that an anti-yaw moment can be generated.

According to the third aspect of the present invention, similarly to the first and second aspects of the present invention, the effect of reducing the lift of the vehicle and the effect of reducing the drag can be enhanced, and the lower heating portion of the floor near the vehicle center line can be provided. The cooling effect can be increased.

Further, since a flat surface is formed outside the wheel house extension line in the vehicle width direction and in a region in front of the vehicle center of gravity, the flow velocity is further increased, and the flow under the floor can be made high. In addition, in the region on the vehicle center line side from the wheel house extension line and behind the vehicle center of gravity, the flow near the vehicle center line, which has flowed out of the hot air discharge portion and is relatively contracted, is gradually diffused and decelerated. However, by making this region a flat surface, this diffusion can be prevented as much as possible.

Further, in the case of a crosswind, the floor resistance acting on the area outside the wheel house extension in the vehicle width direction and forward of the vehicle center of gravity acts as a turning moment (yaw moment) for directing the vehicle to the leeward side. Since this area is a flat surface, the yaw moment can be reduced without receiving this resistance, and the area on the vehicle center line side from the extended line of the wheel house and behind the vehicle center of gravity is located. By making it a flat surface,
An anti-yaw moment can be generated by applying a fast flow to the rear wheel to increase the shape resistance of the rear wheel.

According to the fourth aspect of the invention, in addition to the effects of the first, second and third aspects, the cross-sectional shape of the side sill at the front portion is made smaller than the cross-sectional shape of the side sill at the other portions, so that the vehicle can be driven in a crosswind In front of the center of gravity, the lifting of the underfloor flow to the leeward side of the body is suppressed,
Behind the center of gravity of the vehicle, the winding to the body side increases, so the negative pressure generated on the body side increases, and the yawing moment can be reduced.

[Brief description of the drawings]

FIG. 1 is a bottom view of a vehicle showing a first embodiment of the present invention.

FIG. 2 is a perspective view of an undercover of an engine room portion of the first embodiment.

FIG. 3 is an explanatory diagram of area division of a center floor.

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a sectional view taken along line VV of FIG. 1;

FIG. 6 is a diagram showing an aspect of an air flow on a center floor at the time of straight traveling according to an experimental result of the first embodiment.

FIG. 7 is a diagram showing an aspect of an air flow on a center floor at the time of a cross wind according to an experimental result of the first embodiment.

FIG. 8 is a sectional view similar to FIG. 4, showing a second embodiment of the present invention.

FIG. 9 is a sectional view similar to FIG. 5 of a second embodiment.

FIG. 10 is a diagram showing an aspect of an air flow on the center floor at the time of going straight according to the experimental results of the first example.

FIG. 11 is a diagram showing an aspect of an air flow on the center floor at the time of a cross wind according to the experimental results of the first example.

FIG. 12 is a bottom view of the vehicle showing a second example.

13 is a sectional view taken along line VIII-VIII in FIG.

14 is a sectional view taken along line XIII-VIII in FIG.

FIG. 15 is a diagram showing an aspect of an air flow on a center floor at the time of going straight according to an experimental result of the second example. ]

FIG. 16 is a diagram showing an aspect of an air flow on a Senfu floor at the time of a cross wind according to an experimental result of the second example.

17 is a chart showing a comparison of C _D reduction effect.

FIG. 18 is a table showing a comparison of Cym reduction effects.

FIG. 19 is a table showing a comparison of cooling air velocities of heat generating parts such as a transmission.

FIG. 20 is a bottom view of a vehicle showing a structure of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Body main body 3 Center floor 5 Floor tunnel 7 Rear floor 9 Transmission (heating part) 13 Rear differential (heating part) 15 Front wheel house 17 Front wheel 19 Rear wheel house 21 Rear wheel 25 Engine room 27 Floor member (under cover) 35 Hot air discharge part 37 Throttle portion 39 Duct 39a Exit 41 Side member 43 Under cover (flat surface) 45 Under cover (flat surface) 47 Side sill COG Vehicle center of gravity Y Axis of vehicle longitudinal direction X Axis of axial direction

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-331670 (JP, A) JP-A-58-152674 (JP, A) JP 1-80581 (JP, U) JP 1-80581 73471 (JP, U) Real opening 58-153175 (JP, U) Real opening Hei 3-120280 (JP, U) Real opening 62-110078 (JP, U) Real opening 60-105526 (JP, U) Hira 2-61792 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 25/20 B62D 35/02

Claims (4)

(57) [Claims] 1. A lower portion of a high-pressure portion such as an engine room separated from a front portion of a vehicle is closed by a flat floor member, and the high-pressure portion is positioned substantially symmetrically with respect to a vehicle center line of the floor member. To form a pair of hot air discharge portions having an air outlet for directing air having a low flow velocity in the high pressure portion to the rear wheel and flowing out to the rear wheel, and between the pair of hot air discharge portions, a floor member from the front of the vehicle. A constricted portion is formed to condense the airflow flowing along the lower side to increase the flow velocity, and to flow out toward the heat generating section on the lower side of the floor behind the floor member , and to form a throttle section, between the front wheel house and the rear wheel house. A flat surface is formed at least on the lower surface of the located floor, at least outside the wheel house extension line in the vehicle width direction, and in a region in front of the vehicle center of gravity,
The other area is a non-flat surface, characterized by an underfloor structure of an automobile. 2. A high pressure portion, such as an engine room, which is separated from a front portion of a vehicle, is closed with a flat floor member, and the high pressure portion is positioned substantially symmetrically with respect to a vehicle center line of the floor member. To form a pair of hot air discharge portions having an air outlet through which the air having a low flow velocity in the high-pressure portion is directed and discharged at the rear wheel, and a floor member is provided between the pair of hot air discharge portions from the front of the vehicle. To reduce the air flow along the lower side of the
A throttle portion is formed to direct and flow out the heat generating portion on the lower side of the floor behind the floor member. An underfloor structure for an automobile, wherein a flat surface is formed on the side and in a region behind the vehicle center of gravity, and the other region is a non-flat surface. 3. A lower part of a high-pressure part such as an engine room separated at a front part of a vehicle is closed with a flat floor member, and the high-pressure part is located substantially symmetrically with respect to a vehicle center line of the floor member. To form a pair of hot air discharge portions having an air outlet for directing air having a low flow velocity in the high pressure portion to the rear wheel and flowing out to the rear wheel, and between the pair of hot air discharge portions, a floor member from the front of the vehicle. A constricted portion is formed to contract the airflow flowing along the lower side to increase the flow velocity and direct the heat generation part on the lower side of the floor behind the floor member to flow out, between the front wheel house and the rear wheel house. A flat surface is formed on the lower surface of the located floor outside the wheel house extension line in the vehicle width direction and in a region in front of the vehicle center of gravity, and on the vehicle center line side from the wheel house extension line, and Behind the center of gravity of the vehicle An underfloor structure for an automobile, wherein a flat surface is formed in a region of the vehicle and a non-flat surface is formed in other regions. 4. The underfloor structure of an automobile according to claim 1, wherein the cross section of the side sill in the vehicle width direction at a portion forward of the center of gravity of the vehicle is different from the cross section of the side sill at the other portion. An underfloor structure of an automobile characterized by being formed small.