JPH07165126A - Underfloor structure for rear part of automobile - Google Patents

Abstract

PURPOSE:To provide an underfloor structure of a rear part of an automobile capable of improving the air flow without providing any exclusive aerodynamic parts. CONSTITUTION:A muffier 11 of almost flat section is horizontally arranged under the underfloor surface S2 in the vicinity of a rear overhang part 3 which is located higher than the underfloor surface S1 of a wheel base part 2, and the lowest surface 11a of the muffler 11 is located higher than the underfloor surface S1 of the wheel base part 2 and lower than the lower end 10a of a rear bumper 10. The muffier 11 functions as an aerodynamic parts, and prevents the reduction in the flow speed and the separation of the air A, and the aerodynamic performance of an automobile can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underfloor structure at the rear of an automobile.

[0002]

2. Description of the Related Art An automobile is placed in a flow of air as it travels, so that air resistance acting in the direction of blocking the forward movement of the automobile and lift force acting in the direction of raising the automobile are generated. To do. If the air resistance increases, the fuel efficiency of the vehicle deteriorates, and if the lift increases, the ground contact force of the tires weakens and the running stability is adversely affected.Therefore, research has been conducted to suppress the generation of such air resistance and lift. There is.
The air flow to the automobile can be roughly classified into a flow along the outer surface of the body of the vehicle body and a flow along the underfloor of the vehicle body. When the two studies on the air flow are compared, until now, most studies have been on the air acting on the outer surface of the body (for example, Japanese Patent Laid-Open No. 63-170177). Attention has also been paid to research on the flow of air under the floor. For example, a structure has been proposed in which the flow velocity of the air flowing under the floor is improved by flattening the entire floor lower surface to suppress the generation of the air resistance and the lift force.

[0003]

However, the structure for completely flattening the underfloor of an automobile can be implemented in a special automobile such as a racing car, but in the case of an ordinary passenger car, it is structurally and costly. It is difficult to implement.
Particularly in the case of general passenger cars, the floor underside at the rear overhang portion at the rear of the vehicle body is located higher than the floor underside of the wheelbase portion at the center of the vehicle body, and the air passage under the floor of the vehicle suddenly expanded. It is in a state. Therefore, the air flow cannot follow such shape change under the floor in the rear overhang portion, and the air flow velocity suddenly decreases there, or the air flow separates from the vehicle body and swirls, As described above, the air resistance and lift of the vehicle are increased. Such an inconvenient flow of air under the floor at the rear of an automobile can be improved by providing a dedicated aerodynamic component such as a flap at that portion. However, providing such a dedicated aerodynamic component is equivalent to the weight of the vehicle body and It is disadvantageous in terms of cost.

The present invention has been made by paying attention to such a conventional technique, and provides an underfloor structure of a rear portion of an automobile capable of improving the flow of air without providing a dedicated aerodynamic component.

[0005]

In order to achieve the above object, an underfloor structure for a rear portion of an automobile according to the present invention is to improve the air flow by using a muffler arranged at the rear portion of the automobile. is there. Specifically, a muffler with a substantially flat cross-section is placed horizontally under the floor underneath near the rear overhang, which is located above the floor underside of the wheel base, and the muffler The lower surface is located above the floor lower surface of the wheel base and below the lower end of the rear bumper. Further, the muffler may be not only horizontal but also tilted forward.

[0006]

Since the lowermost surface of the muffler is located above the floor lower surface of the wheel base portion and below the lower end of the rear bumper, the sudden enlargement portion of the air passage near the rear overhang portion is located inside the sudden enlargement portion. It will be covered by the muffler located at. Therefore, this muffler functions as an aerodynamic component that improves the air flow in the sudden expansion portion, and prevents the flow velocity of air under the floor near the rear overhang portion from decreasing and separating, so that the air resistance coefficient ( _CD value of the vehicle is reduced. ) And lift coefficient ( _CL value) can be reduced. In addition, the muffler is tilted forward and the tilt angle is adjusted to adjust the air resistance coefficient (C _D
It is possible to obtain an optimum compatible state of the value) and the lift coefficient ( _CL value).

[0007]

1 and 2 show a preferred embodiment of the present invention. Reference numeral 1 denotes a rear wheel, a front side of the rear wheel 1 is a wheel base portion 2 of the automobile, and a rear side thereof is a rear overhang portion 3. A vehicle compartment R is formed in the wheel base portion 2, and a rear portion 4a of the floor 4, which is a bottom surface of the vehicle compartment R, is provided on the upper side so that the rear seat 5 is installed on the upper side and the fuel tank 6 is held on the lower side. It is formed by launching. The lower surface 6a of the fuel tank 6 is flat and
It is at the same height as this floor 4 and fuel tank 6
The lower surface 6 a of the wheel base portion 2 forms a flattened floor lower surface S ₁ of the wheel base portion 2.

On the other hand, a trunk room T is formed in the rear overhang portion 3, and a spare tire house 9 for accommodating a spare tire 8 is recessed at a substantially center of a trunk floor 7 which is a bottom surface of the trunk room T. There is. A floor lower surface S ₂ centering on the rear overhang portion 3 is formed behind the floor lower surface S ₁ . The underfloor surface S ₂ is at a position higher than the floor surface S ₁ of the front, rapid expansion portion K of the air passage is formed in the lower the floor surface S _2. A rear bumper 10, which is the rearmost part of the automobile, is provided behind the floor lower surface S ₂ in the rear overhang portion 3. Lower end 1 of this rear bumper 10
0a is located above the floor lower surface S ₁ of the wheel base portion 2 and below the floor lower surface S ₂ of the rear overhang portion 3.

As described above, the floor lower surface S ₂ of the rear overhang portion 3 and the rear bumper 10 are located above the floor lower surface S ₁ of the wheel base portion 2, and the sudden expansion portion K of the air passage is located there. Since it is formed, the air A that has originally passed through the floor lower surface S ₁ of the wheel base 2 is
Although the flow velocity is reduced or the separation phenomenon occurs in the sudden expansion portion K, and the air resistance coefficient ( _CD value) and the lift coefficient ( _CL value) are deteriorated. In this embodiment, the aerodynamic force is applied to the sudden expansion portion K. Since the muffler 11 functioning as a component is arranged, such aerodynamic performance does not deteriorate.

That is, the muffler 11 according to this embodiment
As shown in FIG. 2, is disposed horizontally between the left and right rear side members 12 and at a position corresponding to directly below the spare tire house 9. The muffler 11 is of a large size having a length L larger than the diameter of the spare tire house 9 and a width W substantially corresponding to the radius of the spare tire house 9, and has a flat cross section (substantially oval shape). Are doing An exhaust pipe 13 is also connected to the left end of the muffler 11.

Further, the muffler 11 is inclined forward by a predetermined angle (diffuser angle) θ with respect to the horizontal, and the lowermost surface 11a thereof is above the floor lower surface S ₁ of the wheel base 2 and the lower end 10a of the rear bumper 10. It is located below. In this way, since such a large muffler 11 is arranged in the sudden expansion portion K in the rear overhang portion 3, the vertical difference in the sudden expansion portion K is the vertical difference h in the upstream portion d ₁ before the muffler 11. ₁ and the downstream part d
_Since the muffler 11 is divided into the vertical difference h _{2 at 2} and the muffler 11 is tilted forward, the passage of the air A is gradually expanded. As described above, since the intermediate height position of the sudden expansion portion K is covered with the muffler 11 and the flow of the air A can be made smooth, a decrease in the flow velocity of the air A can be suppressed, and the separation of the air A is also eliminated.

That is, such a large muffler 11
Assuming a sudden expansion K where there is no air flow, the flow velocity of the air A flowing from the floor lower surface S ₁ of the wheel base portion 2 decreases in the upstream portion d ₁ , which causes the air resistance coefficient (C _D but is intended to lead to deterioration in value), since the smaller the height difference h ₁ of the upstream portion d ₁ by installing a large muffler 11 as in this embodiment increases the flow rate of the air a, whereby The air resistance coefficient (C _D value) can be reduced. Further, the same applies to the downstream portion d ₂ , and when such a large muffler 11 is not installed, the air A is separated at the downstream portion d ₂ , that is, the air A follows the floor lower surface S ₂ of the rear overhang portion 3. Phenomenon occurs in which a vortex is swirled without flowing due to
Had led to worsening of _L values), in this embodiment, since the height difference h ₂ of the downstream portion d ₂ by the presence of a large muffler 11 is reduced, peeling of the air A as described above is suppressed, Thereby, the lift coefficient ( _CL value) can be reduced.

The air resistance coefficient ( _CD value) and the lift coefficient ( _CL value) are changed by changing the forward tilt angle θ of the muffler 11. Therefore, this muffler 11
The most excellent aerodynamic performance can be exerted by adjusting the forward tilt angle θ of (1) to such a value that the air resistance coefficient ( _CD value) and the lift coefficient ( _CL value) are compatible with each other. As described above, according to this embodiment, since the muffler 11 installed as the silencer can be used to improve the aerodynamic performance of the vehicle, it is not necessary to purposely provide a dedicated aerodynamic component.

In the above embodiments, the muffler 11 having a substantially elliptical cross section is taken as an example, but a rectangular cross section may be used as long as it has a flat shape.

[0015]

The underfloor structure of the rear part of an automobile according to the present invention has the contents as described above, and the lowermost surface of the muffler is above the underfloor surface of the wheel base and below the lower end of the rear bumper. Since it is located at, the sudden expansion portion of the air passage near the rear overhang portion is in a state of being covered by the muffler positioned inside the sudden expansion portion. Therefore, this muffler functions as an aerodynamic component that improves the air flow in the sudden expansion part, and prevents the flow velocity of the air under the floor near the rear overhang part from decreasing and separating, so that the air resistance coefficient ( _CD value) and the lift force are increased. The coefficient ( _CL value) is reduced and the overall aerodynamic performance of the vehicle is improved. Further, the air resistance coefficient ( _CD value) can be obtained by setting the muffler in a forward tilted state and adjusting the tilt angle.
It is possible to obtain the optimum compatible state of the lift coefficient ( _CL value).

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an underfloor structure of a rear portion of an automobile according to an embodiment of the present invention.

FIG. 2 is a plan view seen from a DA direction shown by an arrow in FIG.

[Explanation of symbols]

2 Wheel base part 3 Rear overhang part 10 Rear bumper 10a Lower end of rear bumper 11 Muffler 11a Lowermost surface of muffler A Air K Sudden expansion part S ₁ Floor underside of wheel base part S ₂ Floor underside of rear overhang θ Front of muffler angle

Claims (2)

[Claims] 1. A muffler having a substantially flat cross-section is horizontally arranged below the floor underside near the rear overhang portion located above the floor underside of the wheel base portion, and the muffler is placed at the maximum. An underfloor structure of a rear part of an automobile, characterized in that a lower surface is located above a floor undersurface of a wheel base portion and below a lower end of a rear bumper. 2. The underfloor structure for a rear portion of an automobile according to claim 1, wherein the muffler is tilted forward.