JPH07309257A - Vehicle under floor structure - Google Patents

Abstract

PURPOSE:To efficiently cool the heat generating section of a differential gear, etc. CONSTITUTION:A center undercover 25 having a guide duct 25A for guiding air flowing from the front of a vehicle to the rear side thereof upward is provided on a floor back surface side behind an engine 1. The center undercover 25A is arranged about directly below a floor tunnel 21 for housing the propeller shaft 3, etc., of a driving force transmission system so as to allow air guided upward to flow into the floor tunnel 21. Meanwhile, an engine undercover 20 is provided below the engine 1 and a constriction section 20B for compressing air flowing backward from the vehicle front and discharging it backward is formed in this engine undercover 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an underfloor of a vehicle, and more particularly to an apparatus for efficiently cooling a device, such as a differential gear or a fuel tank, which is desired to be cooled.

[0002]

2. Description of the Related Art As a conventional vehicle underfloor structure, there is one disclosed in Japanese Patent Application Laid-Open No. 5-330457 previously proposed by the present applicant. In this conventional technique, a floor member closes a lower side of a high pressure portion such as an engine room usually formed in a front portion of a vehicle, and the floor member is communicated with the high pressure portion at a substantially target position with respect to a vehicle center line. A pair of hot air exhaust portions that direct the air in the high-pressure portion to the rear wheels to flow out are formed, and an air flow that flows along the lower side of the floor member from the front of the vehicle is contracted between the pair of hot air exhaust portions. The throttle portion is formed so as to direct the heat to a heat generating portion such as a transmission or a differential gear on the lower side of the floor behind the floor member.

With such a structure, an air flow having a sufficiently low flow velocity and a high pressure flows out from the hot air exhaust portion communicating with the engine room toward the rear wheels, but the air flow advances to the rear of the vehicle. Gradually spreads in the left and right direction of the vehicle,
Since the rear wheels are almost entirely covered, the aerodynamic force received by the rear wheels is reduced, and the air resistance acting on the vehicle is reduced. On the other hand, since the airflow that is relatively high speed due to the contraction is supplied to the transmission, the differential gear, etc. from the throttle part, an effective cooling action can be obtained and the high-speed airflow The action also has the effect of reducing the lift.

[0004]

Although the above-described conventional underfloor structure for a vehicle can certainly achieve the above-mentioned remarkable effects, it still has some points to be improved. I understood. That is, according to the above-mentioned conventional technique, as shown in FIG. 20, which is a side view conceptually showing the configuration of the lower part of the floor of the vehicle, the center undercover 20
By creating a relatively fast air flow u ₁ on the back side of the floor by the transmission 2, the transmission 2 arranged behind the engine 1 and the differential gear to which the driving force is transmitted from the transmission 2 via the propeller shaft 3 The heat is taken from the lower surface of the heat generating portion such as 4 to obtain a cooling effect. However, in a vehicle in which the engine 1 is mounted on the front part of the vehicle body, hot air in the engine room flows into the groove type floor tunnel 21 formed on the back surface side of the floor to accommodate the propeller shaft 3 and the like, and this A very slow-moving air flow u ₅ is created, which flows backward through the floor tunnel 21 to cover the upper surface of the differential gear 4 and create a stagnation s of hot air.

In other words, the high-temperature and low-speed air flow u ₅ existing in the floor tunnel 21 reduces the heat radiation effect on the upper surfaces of the transmission 2 and the differential gear 4. Therefore, the transmission 2 and the differential 2 are processed by the conventional technique. There is an unsolved problem that it cannot be dealt with only by cooling the lower surface side of the gear 4.

The present invention has been made by paying attention to the unsolved problems of the prior art, and particularly, an expensive member or the like is used for the influence of hot air flowing into the floor tunnel from the engine room. It is an object of the present invention to provide a vehicle underfloor structure that can be effectively solved without any problems.

[0007]

In order to achieve the above object, the invention according to claim 1 is an underfloor structure for a vehicle having a groove type floor tunnel extending in the vehicle front-rear direction on the back side of the floor. A center under cover having an introduction duct for guiding the air flowing backward from the front side of the vehicle to the rear side of the floor is provided on the rear side of the floor behind the engine.

On the other hand, in order to achieve the above object, the invention according to claim 2 is an underfloor of a vehicle having an engine mounted on the front part of the vehicle body and having a groove type floor tunnel extending in the vehicle front-rear direction on the back side of the floor. A pair of structures in which the lower side of the engine room is closed by an engine undercover, and the air in the engine room is directed toward the rear wheels and flows out to a substantially target position across the vehicle centerline of the engine undercover. In addition to forming the hot air discharge part of, between the pair of hot air discharge parts, a throttle part that contracts the air flowing from the vehicle front side to the rear side on the back side of the floor and flows out rearward is formed
Then, behind the narrowed portion, a center under cover having an introduction duct for guiding the air flowing backward from the vehicle front side to the rear side on the floor rear surface side is arranged.

The invention according to claim 3 is the underfloor structure for a vehicle according to claim 2, wherein:
The width of the introduction duct is narrower than the width of the narrowed portion on the outflow side. The invention according to claim 4 is the underfloor structure for a vehicle according to any one of claims 1 to 3, wherein the height of the vehicle front side end portion of the center undercover is arranged at the engine rear portion. The height is the same as or higher than the bottom surface of the transmission to be installed.

Further, the invention according to claim 5 is the underfloor structure for a vehicle according to any one of claims 1 to 4, wherein the lower surface of the transmission and the center undercover arranged at the rear portion of the engine. The bottom surface was continuous. The invention according to claim 6 is the above-mentioned claim 1.
In the vehicle underfloor structure of the invention according to claim 5, the shape of the introduction duct is changed to NACA (National
Advisory Committee for Aeronautics) Duct shape.

The invention according to claim 7 is the underfloor structure for a vehicle according to any one of claims 1 to 6, wherein the floor tunnel is a tunnel for accommodating a rotary shaft of a driving force transmission system. An air guide is provided to surround a portion of the rotary shaft on which air guided by the center under cover hits. Further, the invention according to claim 8 is the underfloor structure for a vehicle according to any one of claims 1 to 7, wherein a communication pipe is provided for communicating the inside of the engine room with the space near the side surface of the transmission.

Furthermore, the invention according to claim 9 is the underfloor structure for a vehicle according to any one of claims 1 to 8 above, characterized in that at the vehicle rear side end portion of the introduction duct,
An air guide was provided to control the direction of air flow.

[0013]

In the invention according to claim 1, for example, the air flow on the lower surface side of the floor generated while the vehicle is traveling is guided upward by the introduction duct of the center under cover. Then,
It flows toward the rear of the vehicle along the floor tunnel, the rear surface of the floor, and the like, and reaches the space near the heat generating portion such as the differential gear located in the rear. Since the air flow on the lower surface side of the floor is a traveling wind, the temperature is sufficiently lower than that of the hot air generated in the engine room and the like, so that the heat generating portion such as the differential gear is cooled by the air flow.

Next, according to the second aspect of the present invention, the hot air exhaust portion formed in the engine undercover flows out a high-velocity air stream having a sufficiently low flow velocity toward the rear wheels. The airflow gradually spreads in the left-right direction of the vehicle as it goes rearward of the vehicle, and covers almost the entire rear wheel. On the other hand, from the throttle part, the air flow that is relatively high speed due to the contraction flows out toward the rear,
The high-speed airflow is guided upward by the introduction duct of the center undercover and reaches a heat generating portion such as a differential gear which is present in the rear, similarly to the invention according to claim 1, and the heat generating portion such as the differential gear is generated. Is cooled. That is, according to the invention of claim 2, a high-speed air flow is positively created on the lower surface side of the floor by the engine undercover, and the high-speed air flow is guided upward by the center undercover. Cooling is performed more efficiently than the invention according to item 1.

According to the third aspect of the invention, the entire width of the introduction duct of the center under cover exists in the air flow flowing out from the throttle portion of the engine under cover. Therefore, all of the air flow guided upward by the introduction duct is the air flow that has flowed out from the throttle portion, so that the action of the invention according to claim 2 is more reliably exhibited. Further, in the invention according to claim 4, since the vehicle front side end portion of the center under cover is located at the same level as or above the lower surface of the transmission, the vehicle front side end portion of the center under cover is Do not disturb the air flow from the front of the vehicle to the rear along the back of the floor.

Further, in the invention according to claim 5,
Since the lower surface of the transmission and the lower surface of the center under cover are continuous, the end portion of the center under cover on the vehicle front side can be more reliably moved from the vehicle front side to the rear side along the back surface of the floor as compared with the invention according to claim 4. It does not disturb the air flow flowing through. Further, in the invention according to claim 6, since the shape of the introduction duct is the NACA duct shape, the airflow flowing from the vehicle front side to the vehicle rear side on the floor back surface side is efficiently guided upward.

Since there is usually a rotating shaft that constitutes a driving force transmission system such as a propeller shaft in a state of being housed in a floor tunnel on the rear side of the vehicle, it is guided upward by a center under cover. Since the air hits the rotating shaft of the propeller shaft or the like, the rotation of the rotating shaft disturbs the air flow and may not reach the heat generating portion such as the differential gear.

Therefore, according to the invention of claim 7, since the air guide is provided at the portion where the air guided by the center undercover hits, the turbulence of the air flow guided upward can be avoided. There is a high possibility that the airflow will reach the heat generating portion such as the differential gear.
On the other hand, according to the invention of claim 8, since the communication pipe that connects the inside of the engine room and the space near the side surface of the transmission is provided, a part of the hot air in the engine room is near the side surface of the transmission through the communication pipe. Since it flows out into the space, the amount of hot air reaching the differential gear or the like via the floor tunnel or the like is reduced.

In the invention according to claim 9, the direction of the air flow guided upward from the center under cover is finely adjusted by the air guide provided on the air outflow side of the introduction duct. For example, when it is desired to efficiently cool the differential gear, the airflow can be brought into contact with the upper surface and both side surfaces of the differential gear by adjusting the air guide.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 are diagrams showing a configuration of a first embodiment of the present invention, FIG. 1 is a bottom view conceptually showing a configuration of a vehicle floor back side, and FIG. 2 is a diagram showing a floor back side configuration. FIG.

First, the structure will be described. In FIG.
10FL and 10FR are front wheels as steered wheels, 10RL and 10RR
Is a rear wheel as a drive wheel, and the rear wheels 10FL and 10FR are composed of an engine 1 mounted on the front part of the vehicle, a transmission 2, a propeller shaft 3, a differential gear 4, drive shafts 5, 5 and the like. The driving force is transmitted via the driving force transmission system. That is, the vehicle shown in FIG. 1 is a so-called FR (front engine-rear drive) vehicle. An exhaust pipe 11 connects the exhaust side of the engine 1 and the muffler 7.

On the lower surface side of the engine 1, the engine 1
An engine undercover 20 is arranged so as to close an engine room that accommodates the engine. The engine undercover 20 is made of, for example, a resin material or a steel plate material, has a substantially flat plate shape as shown in FIG. 3, which is a perspective view thereof, and is fixed substantially horizontally to the vehicle body. The engine undercover 20 is formed with a pair of hot air discharge parts 20A and one throttle part 20B.

Of these, a pair of hot air discharge parts 20A
Is a substantially groove consisting of a bottom portion 20a formed by bending a part of both sides of the engine undercover 20 sandwiching the vehicle center line so that the vehicle rear side becomes lower, and side portions 20b guiding both sides of the bottom portion 20a. Type duct, the upper surface of which opens in the engine room, and the rear end side opening is slightly outward in the vehicle width direction so as to direct the rear wheels 10FL and 10FR on the same side across the vehicle center line. Leaning on.

Further, the throttle portion 20B is provided with the hot air exhaust portion 20.
It is a groove-shaped duct that is formed in a portion sandwiched by the side portions 20b on the inner side in the vehicle width direction of A, and has front and rear surfaces and a lower surface side that are open, and that faces the vehicle front and rear direction substantially coaxially with the vehicle center line.
However, the widthwise dimension thereof is the same as the widthwise dimension of the transmission 2. In this embodiment, the opening 20c is formed in the rear end portion of the throttle portion 20B so that the lower surface of the engine 1 is exposed. The opening 20c is formed so that the oil can be changed through the oil pan 1a of the engine 1 without removing the engine undercover 20.

On the other hand, immediately after the transmission 2,
The center of the floor tunnel 21 (see FIG. 2) is formed so as to cover a part of the lower surface opening side of a floor tunnel 21 (see FIG. 2) formed of a groove formed in the rear surface of the floor and extending in the vehicle front-rear direction so as to accommodate a driving force transmission system such as the propeller shaft 3. An under cover 25 is provided. The center under cover 25 is also made of, for example, a resin material or a steel plate material, has a substantially flat plate shape as shown in FIG. 4 which is a perspective view thereof, and is fixed horizontally to the vehicle body. At the center of the center under cover 25 in the vehicle width direction, a part of the flat plate-shaped main body is pressed upward, for example, to be bent, so that an introduction duct 25A oriented in the horizontal plane along the vehicle center line is formed. Has been formed.

That is, the introduction duct 25A has an upper portion 25a bent so that the rear end portion of the vehicle becomes higher, and a pair of substantially triangular side portions 25 for guiding both sides of the upper portion 25a.
It is a substantially groove type duct consisting of b and b, and its lower surface side is open. Further, in the present embodiment, the dimension in the width direction of the introduction duct 25A is gradually increased from the vehicle front side that is the inflow side toward the vehicle rear side that is the outflow side, thereby forming a so-called NACA duct shape.

Further, as shown in FIG. 2 in particular, the center under cover 25 is arranged at the same level as or above the straight line L representing the same height as the lower surface of the transmission 2 arranged immediately before. In addition, as shown in FIG. 1, the maximum width W ₁ of the introduction duct 25A is the narrowed portion 20B.
Is smaller than the width W ₂ . Next, the operation of this embodiment will be described.

That is, as shown in FIG. 5 in which the flow of air generated by the engine undercover 20 during traveling is represented by arrows, the hot air in the engine room flows from the hot air exhaust portions 20A on both sides to the bottom of the floor while the vehicle is traveling. Is discharged to the side,
An air flow u ₂ having a high temperature and a relatively slow flow is created with the hot air exhaust portion 20A as a base point. Then, this air flow u ₂ is directed toward the rear of the vehicle, but that the hot air exhaust portion 20A is directed to the rear wheels 10RL and 10RR, and that the throttle portion 20B formed between the hot air exhaust portions 20A is formed. Since the width is substantially the same as that of the transmission 2, the air flows u ₂ pass through a locus that spreads in the vehicle width direction while passing a position slightly apart from the side surface of the transmission 2 as shown in FIG. The rear wheels 10RL and 10RR are reached, and the rear wheels 10RL and 10RR are covered.

Therefore, the aerodynamic force received by the rear wheels 10RL, 10RR is reduced, and the air resistance acting on the vehicle is reduced, so that the fuel consumption is improved. On the other hand, while the vehicle is traveling, an airflow is generated from the front side of the vehicle toward the rear side on the rear surface side of the floor. The airflow is, as shown in FIG. , The air flow u ₁ having a relatively high velocity is contracted by the slow air flow u ₂ formed on both sides in the vehicle width direction. The air flow u ₁ is at a relatively low temperature because the air flow u ₁ is a flow of external air, and as shown in FIG. 6, the air flow u ₁ flows rearward along the substantially vehicle center line on the floor rear surface side. Since the lower surfaces of the transmission 2 and the differential gear 4 pass by touching, the heat can be effectively taken from the lower surfaces of the transmission 2 and the differential gear 4. In other words, by creating the air flow u ₁ by the engine undercover 20, it is possible to improve the cooling effect on the lower surface side of the transmission 2 or the differential gear 4 as the heat generating portion.

Further, the interaction of the air flows u ₁ and u ₂ also has the effect of significantly reducing the rear wheel lift.
The reason is that the lift is reduced because the air flow u ₁ flows substantially straight in the vicinity of the center line of the vehicle from the front to the rear, while the air flow u ₂ is directed toward the rear wheels 10RL and 10RR. As a result of the flow, it is considered that the vicinity of the drive shaft 5 becomes a depletion region and a negative pressure is generated there.

Further, the air flow u ₁ also passes through the lower surface side of the center under cover 25 arranged immediately after the transmission 2, but the air flowing around the object flows along the surface of the object. In addition, since the introduction duct 25A has a NACA duct shape in which the air drawing action is remarkable, the center undercover 25
Part of the air flow u ₁ passing through the lower surface of the inlet duct 25
A is pulled up to the vehicle body side to create an air flow u ₃ as shown in FIG.

Since the rear end portion of the introduction duct 25A on the discharge side is directed obliquely upward, the air flow u ₃ guided upward flows into the floor tunnel 21 as shown in FIG. It flows backward in the floor tunnel 21 and reaches the upper surface of the differential gear 4, and its velocity is as high as that of the air flow u ₁ , so that it overcomes the differential gear 4 without creating a stagnation in the space above the differential gear 4. Is discharged to the outside of the floor tunnel 21. At this time, the stagnation of hot air that has conventionally reached the upper surface of the differential gear 4 from the inside of the engine room through the floor tunnel 21 is also eliminated.

That is, the air flow u ₃ generated by the introduction duct 25A flows so as to come into contact with the upper surface of the differential gear 4 as a heat generating portion, and the temperature of the air flow u ₃ is relatively low as well as the air flow u _1. Therefore, heat can be effectively taken from the upper surface side of the differential gear 4, and the cooling effect on the upper surface side of the differential gear 4 can be improved.

As described above, according to the structure of this embodiment, the cooling effect on both the upper surface side and the lower surface side of the differential gear 4 can be improved, so that the atmospheric temperature of the differential gear 4 decreases and The oil temperature of the differential gear 4 is drastically reduced.
9 to 11 show the oil temperature of the differential gear 4 (FIG. 9) and the ambient temperature of the differential gear 4 (FIG. 10) in the present embodiment and the conventional example (the structure of the present embodiment with the center under cover 25 removed). ) And the wind speed around the differential gear 4 (FIG. 11) are shown by comparing the results confirmed in an actual running experiment. Particularly, as apparent from FIG. 9, the structure of the present embodiment allows Compared with the past, the differential oil temperature is 100 km /
A reduction effect of about 5 to 10 ° C. can be obtained in the high speed region of h or more. And the reason is as shown in FIGS.
As can be seen from the above, the ambient temperature of the differential gear 4 is lowered and the ambient wind speed is increased. In other words, the center under cover 25 is provided to positively create the air flow u ₃ in the floor tunnel 21, and as a result, the cooling effect of the differential gear 4 can be dramatically improved.

Further, in this embodiment, since the width W ₁ of the introduction duct 25A is smaller than the width W ₂ of the narrowed portion 20B, the entire introduction duct 25A can be placed in the air flow u ₁ . it can. Therefore, the air flow u ₃ can be reliably generated, so that the above-described cooling effect on the upper surface side of the differential gear 4 can be reliably obtained. Furthermore, in the present embodiment, as shown in FIG. 2, in particular, the height direction position of the lower surface of the center under cover 25 which is horizontally arranged is set to be lower than the lower surface (straight line L) of the transmission 2 which is arranged immediately before. Also, since the vehicle front side end portion of the center under cover 25 does not protrude below the lower surface of the transmission 2. Therefore, by providing the center under cover 25, the air flow u ₁
Therefore, the cooling effect described above will not be adversely affected. Although the height of the lower surface of the center under cover 25 is above the straight line L in this embodiment, it may be the same as the straight line L.

In this embodiment, the hot air in the engine room is discharged from the hot air discharge portion 20A formed in the engine undercover 20 as an air flow u ₂ to the diagonally rear side. Even at times such as when the air flow u ₂ flows toward the rear wheels 10RL and 10RR and does not remain directly below the engine undercover 1, the hot air once discharged heats a radiator (not shown). You can avoid such a situation.

Further, since the center under cover 25 is not a particularly expensive member, it does not cause a significant increase in cost in spite of the above-mentioned excellent effects.
FIG. 12 and FIG. 13 are views showing a second embodiment of the present invention, both of which are side views conceptually showing the structure of the floor rear surface side of the vehicle as in FIG. 2 of the first embodiment. In addition,
The same components as those in the first embodiment are designated by the same reference numerals, and the duplicated description will be omitted. Further, other configurations not shown are the same as those in the first embodiment.

That is, the present embodiment is characterized in that the vehicle front side end of the center under cover 25 is arranged at the same height as the lower surface of the transmission 2 and the space between them is continuous. With such a configuration, as shown in FIG. 12 or 13, for example, when the center under cover 25 is mistakenly attached obliquely, or when the center under cover 25 is initially fixed horizontally, a collision of a rocking stone or the like occurs. Even if it is tilted due to, the center under cover 2
5 does not disturb the air flow on the rear surface side of the floor, the air flow u ₃ can be reliably introduced into the floor tunnel 21, and the cooling effect described in the first embodiment can be reliably obtained. It is possible.

Other functions and effects are similar to those of the first embodiment. FIGS. 14 and 15 are views showing a third embodiment of the present invention, and FIG. 14 is a side view conceptually showing the structure of the back side of the floor of the vehicle, similar to FIG. 2 of the first embodiment. 15
[FIG. 3] is a perspective view of a main part of this embodiment. The rest of the configuration not shown is the same as that of the first embodiment.

That is, when there is a rotating shaft such as the propeller shaft 3 of the driving force transmission system in the floor tunnel 21, the air flow u ₃ guided into the floor tunnel 21 by the center undercover 25 rotates the propeller shaft 3. It is conceivable that the cooling effect of the differential gear 4 is deteriorated due to the turbulence. Therefore, in this embodiment, a gutter-shaped air guide 30 having an upper surface opened so as to surround a portion of the propeller shaft 3 which is hit by the air flow u _3.
Was set up.

With such a construction, as shown in FIG. 15, the air flow u ₃ will surely enter the floor tunnel 21 without being disturbed by the rotation of the propeller shaft 3. The cooling effect of the differential gear 4 described in the embodiment can be more reliably obtained. Other functions and effects are similar to those of the first embodiment.

FIGS. 16 and 17 are views showing a fourth embodiment of the present invention, and FIG. 16 is a side view conceptually showing the structure of the back side of the floor of the vehicle as in FIG. 2 of the first embodiment. FIG. 17 and FIG. 17 are plan views showing the main part of this embodiment. The rest of the configuration not shown is the same as that of the first embodiment.
That is, in the present embodiment, the communication pipe 36 that connects the space on the rear side of the engine 1 and the space on the lower side of both sides of the transmission 2 is provided, and the communication pipe 36 straddles the transmission 2 as a whole. A bifurcated shape is formed, and an intake port 36A having a width slightly wider than that of the transmission 2 is formed on the upper end side facing the engine room, and the intake port 36A is formed on the lower end side below both side surfaces of the transmission 2. Has an outlet 36B formed to face obliquely outward.

With such a configuration, hot air above the engine 1 is exhausted to the lower side of the side surface of the transmission 2 through the communication pipe 36, so that the high temperature air flow u ₅ as shown in FIG. 20 is reduced or eliminated. be able to. As a result, the effect of cooling the differential gear 4 can be more efficiently performed, and the heating action of the upper surface of the transmission 2 by the hot air discharged from the engine room can be suppressed.

Moreover, since the discharge port 36B of the communication pipe 36 is positioned so as to face the lower sides of both sides of the transmission 2 and slightly obliquely outward, the hot air discharged from the discharge port 36B is directed toward the center under cover 25. Introduction duct 2
It will not be sucked up by 5A and introduced into the floor tunnel 21. Other actions and effects are the same as the first
It is similar to the embodiment.

18 and 19 are views showing a fifth embodiment of the present invention. FIG. 18 is a perspective view of the center under cover 25, and FIG. 19 is a bottom view of the center under cover 25. The rest of the configuration not shown is the same as that of the first embodiment. That is, the center under cover 2 of this embodiment
5 is basically the same as that of the first embodiment, and a NACA duct-shaped introduction duct 25 is provided at the center of the flat plate-shaped main body.
A is formed. Then, the introduction duct 25 is provided at the vehicle rear mold end (blow-out side) of the introduction duct 25A.
An air duct 37 for controlling the direction of the air flow blown from A
Is provided.

The air duct 37 is the introduction duct 25A.
A pair of flat plates 37 continuous to the upper and lower sides of the blowout side of
A and 37B and four standing plates 37a to 37d vertically interposed between the flat plates 37A and 37B. The flat plates 37A and 37B have a trapezoidal shape in which the front side of the vehicle is an upper bottom, and standing plates 37a and 37d are interposed between both hypotenuses thereof.
Inside the standing plates 37a and 37d, standing plates 37b and 37c are arranged in parallel with them. However, standing plate 37
The distance between a and 37b and the distance between the standing plates 37c and 37d are set to about 1/5 to 1/6 of the width of the flat plates 37A and 37B. Further, at least the upper flat plate 37A is fixed such that the rear side is slightly lifted so as not to prevent the air flow u ₃ from rising.

Therefore, the air guide 37 is provided with a duct 38A having a vehicle rear opening extending to both sides in the vehicle width direction at a relatively wide central portion thereof, and is provided on both sides of the passage 38A. This means that the duct 38B facing outward in the vehicle width direction is formed. With such a configuration, as shown in FIG. 19, when the air flow u ₃ generated by the introduction duct 25A reaches the air duct 37, the flow in the central portion thereof passes through the duct 38A and is almost deviated from the vehicle center line. Although the air flow u ₃₁ enters the floor tunnel without passing, the air flows u _{32 on} both sides pass through the duct 38B and thus become an air flow u ₃₂ inclined outward in the vehicle width direction.
Therefore, the airflows entering the floor tunnel from the introduction duct 25A become airflows u ₃₁ and u ₃₂ that radially expand.

Then, since the air flow u ₃₂ comes into contact with both side surfaces of the differential gear 4, all the cooling air on the upper surface, the lower surface and both side surfaces of the differential gear 4 is supplied, and its cooling action is It becomes extremely efficient and the cooling effect is further improved. Other functions and effects are similar to those of the first embodiment.

In each of the above embodiments, the structure suitable for cooling the differential gear 4 as the heat generating portion has been described, but the differential gear 4 is not the only one that can be efficiently cooled by the present invention. .
For example, the opening direction of the introduction duct 25A or the opening direction of the air duct 37 may be appropriately adjusted so that the air flow u ₃ is directed toward the cooling required portion such as the fuel tank.

In each of the above-described embodiments, the case where the engine undercover 20 is provided in addition to the center undercover 25 has been described.
0 may not be provided. In that case, since the airflow that naturally flows on the back side of the floor while the vehicle is traveling is guided upward by the introduction duct of the center undercover 25, the airflow slightly decreases as compared with the case where the engine undercover 20 is provided. The same cooling effect as that of each example can be obtained.

Furthermore, in each of the above embodiments, the case where one center undercover 25 is provided has been described, but the number is not limited to one, and a plurality of them may be arranged in the vehicle front-rear direction, the vehicle width direction, or both directions, for example. You may arrange.

[0052]

As described above, according to the first aspect of the invention, since the center under cover having the introduction duct for guiding the air flowing from the vehicle front side to the rear side on the back side of the floor upward is provided, the inside of the floor tunnel is provided. Since the cooling air can be introduced into the heat generating portion, the heat generating portion such as the differential gear can be efficiently cooled, and there is an effect that the cost is not significantly increased.

According to the second aspect of the invention, since the engine undercover having the hot air exhausting portion and the throttle portion and the center undercover having the introducing duct are provided,
Since the high-speed airflow created by the throttle part of the engine undercover is introduced upward by the introduction duct,
A more effective cooling action can be obtained. And
According to the invention of claim 3, all of the air flow guided upward by the introduction duct is the air flow flowing out from the throttle portion,
The effect of the invention according to claim 2 can be obtained more reliably.

Further, according to the inventions of claims 4 and 5, the air flow flowing on the back side of the floor is not disturbed, so that the cooling effect according to the inventions of claims 1 to 3 is reduced. There is no such thing. Further, according to the invention of claim 6, there is an effect that the airflow on the rear surface side of the floor can be efficiently introduced upward.

In the invention according to claim 7, the airflow introduced upward can be prevented from being disturbed by the rotation of the rotary shaft, so that the airflow can reach the heat generating portion such as the differential gear. As a result, the cooling effect can be obtained more reliably. Further, in the invention according to claim 8, since a part of the hot air in the engine room flows out into the space near the side surface of the transmission through the communication pipe, the hot air reaching the differential gear or the like via the floor tunnel is reduced. The cooling effect can be further improved.

According to the ninth aspect of the invention, since the direction of the air flow guided upward from the center under cover can be adjusted more finely, for example, when it is desired to efficiently cool the differential gear, the air guide thereof is required. The air flow can be brought into contact with the upper surface and both side surfaces of the differential gear by adjusting the, and there is an effect that extremely efficient cooling can be performed.

[Brief description of drawings]

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

FIG. 2 is a side view conceptually showing the structure of the back side of the floor in the first embodiment.

FIG. 3 is a perspective view of an engine undercover.

FIG. 4 is a perspective view of a center under cover.

FIG. 5 is an explanatory diagram of an air flow created by an engine undercover.

FIG. 6 is a bottom view for explaining the airflow on the rear surface side of the floor.

FIG. 7 is an explanatory diagram of an air flow created by the center under cover.

FIG. 8 is a side view for explaining an air flow on the back surface side of the floor.

FIG. 9 is a graph for explaining the effect of the first embodiment.

FIG. 10 is a graph for explaining the effect of the first embodiment.

FIG. 11 is a graph for explaining the effect of the first embodiment.

FIG. 12 is a side view conceptually showing the structure of the back side of the floor in the second embodiment.

FIG. 13 is a side view conceptually showing the structure of the back side of the floor in the second embodiment.

FIG. 14 is a side view conceptually showing the structure of the back side of the floor in the third embodiment.

FIG. 15 is a perspective view conceptually showing the structure of the back side of the floor in the third embodiment.

FIG. 16 is a side view conceptually showing the structure of the back side of the floor in the fourth embodiment.

FIG. 17 is a plan view conceptually showing the structure of the floor back side in the fourth example.

FIG. 18 is a perspective view of a center under cover in the fifth embodiment.

FIG. 19 is a bottom view of the center under cover for explaining the operation of the fifth embodiment.

FIG. 20 is a side view conceptually showing the configuration of the conventional back side of the floor.

[Explanation of symbols]

 1 Engine 2 Transmission 3 Propeller Shaft (Rotary Shaft) 4 Differential Gear 10FL, 10FR Front Wheel 10RL, 10RR Rear Wheel 20 Engine Undercover 20A Hot Air Discharge Section 20B Throttling Section 21 Floor Tunnel 25 Center Undercover 25A Introduction Duct 30 Air Guide 36 Communication Pipe 37 Air guide

Claims (9)

[Claims] 1. An underfloor structure for a vehicle having a groove-type floor tunnel extending in the vehicle front-rear direction on the floor rear surface side, wherein the floor rear surface side is behind the engine, and the floor rear surface side is from the vehicle front side to the rear side. An underfloor structure for a vehicle, characterized in that a center undercover having an introduction duct for guiding flowing air upward is provided. 2. An underfloor structure of a vehicle having an engine mounted on a front portion of a vehicle body and having a groove type floor tunnel extending in a vehicle front-rear direction on a rear surface side of the floor, wherein an underside of an engine room is closed by an engine undercover. Then, at the target position across the vehicle center line of the engine undercover,
While forming a pair of hot air exhaust portions that direct the air in the engine room to the rear wheels and flow out, between the pair of hot air exhaust portions, the air that flows from the vehicle front side to the rear side on the floor back side is contracted to the rear side And a center under cover having an introduction duct for guiding upward air flowing backward from the front side of the vehicle to the rear side of the floor is disposed behind the throttle section. Underfloor structure. 3. The underfloor structure for a vehicle according to claim 2, wherein the width of the introduction duct is narrower than the width of the throttle portion on the outflow side. 4. The height of the vehicle front side end portion of the center under cover is set to be equal to or higher than the height of the lower surface of the transmission disposed in the rear portion of the engine. The underfloor structure of the vehicle described in (1). 5. The underfloor structure for a vehicle according to claim 1, wherein a lower surface of a transmission arranged at a rear portion of the engine and a lower surface of the center undercover are continuous with each other. 6. The underfloor structure for a vehicle according to claim 1, wherein the introduction duct has a NACA duct shape. 7. The floor tunnel is a tunnel for accommodating a rotating shaft of a driving force transmission system, and an air guide is provided to surround a portion of the rotating shaft to which air guided by the center under cover hits. The underfloor structure for a vehicle according to claim 6. 8. A communication pipe for connecting the inside of the engine room and the space near the side surface of the transmission to each other.
An underfloor structure for a vehicle according to claim 7. 9. An air guide for controlling a flow direction of air is provided at a vehicle rear side end portion of the introduction duct.
9. An underfloor structure for a vehicle according to claim 8.