JP2006077609A - Muffler structure of automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a muffler structure of an automobile capable of reducing adhesion of exhaust gas components onto a rear bumper due to turbulence generated in the vicinity of the vehicle body rear end of an automobile. <P>SOLUTION: In a muffler 10 for an automobile provided toward a rear lower position of a vehicle body 11, a main muffler 12 is equipped with a vortex generator having a plurality of recessed dimples in its lower surface 12a. The dimple is preferable to be selected between 5.15 and 7.20 mm in diameter, 0.49 and 1.32 mm in depth, and 0.53 and 1.33 mm in space. The main muffler is also allowed to include a plurality of recessed dimples in a side surface and/or an upper surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a muffler structure for an automobile in which the adhesion of exhaust gas components to a rear bumper due to turbulent airflow generated near the rear end of the automobile body is reduced.

  Conventionally, when the automobile 1 travels, as shown in FIG. 8, the airflow X flowing along the vehicle body surface from the front of the automobile causes boundary layer separation at the vehicle body rear end 2, and turbulence 3 due to negative pressure. Is known to occur. As the turbulent air flow 3 is generated, the exhaust gas 5 discharged from the muffler 4 opened below the rear end of the vehicle body is attracted to the turbulent air flow 3 as shown in FIG. The exhaust gas component particles 5 a contained therein adhere to the rear bumper 6.

  When the exhaust gas component particles 5a adhere to the rear bumper 6 in this way, in the case of a resin bumper, the carbon particles in the exhaust gas component cause dullness on the bumper surface, and in the case of a metal bumper. Since rust water adheres to the surface, it is not preferable for rust prevention of the bumper. Therefore, even if it is a resin bumper or a metal bumper, it looks bad.

  On the other hand, it is known to finish the entire rear bumper or at least the exhaust gas component particle adhesion region in order to make the dirt due to the exhaust gas component particles adhering to the rear bumper inconspicuous. Thereby, even if particles of exhaust gas components adhere to the base finish portion of the rear bumper, the dirt is not so noticeable and the appearance is maintained.

  It is also known to increase the back pressure (exhaust gas pressure applied to the exhaust gas) by reducing the diameter of the diffuser part of the muffler of the automobile muffler. As a result, the exhaust gas exhaust flow is not affected by the turbulence generated in the vicinity of the rear end of the vehicle body, and the exhaust gas components are exhausted rearward, so that the exhaust gas component particles do not adhere to the rear bumper.

  Further, a large number of protrusions, so-called vortex generators 7 are formed on the lower surface of the main muffler 4a of the automobile muffler 4 as shown in FIG. 10, or spirally formed on the main muffler 4a as shown in FIG. A method of winding the tripping wire 8 is also known.

In addition to the automobile muffler structure described above, conventional examples of ducts and antennas with airflow countermeasures are shown.
JP 2001-280311 A JP 04-124901 A

  Patent Document 1 discloses a duct having dimples provided on an inner surface inside a bent portion. According to the duct having such a configuration, since the dimple is provided, the separation of the airflow and the pressure loss at the bent portion are suppressed, and the airflow noise is reduced.

  Patent Document 2 discloses an automobile antenna in which the antenna surface is roughened or a small depression or protrusion is provided on the surface. According to the automobile antenna having such a configuration, since the airflow flowing on the antenna surface during driving of the automobile generates a small turbulent flow due to the rough surface, the depression or the protrusion on the antenna surface, the turbulent airflow generated at the rear end of the antenna is generated. As a result, the air resistance, vibration and noise generation of the antenna are reduced.

However, when at least a partial region of the rear bumper as described above is finished, since the adhesion of particles of exhaust gas components is not suppressed, it is difficult to see the adhesion of dirt. Since the component particles are attached, the adhesion of rusted water cannot be avoided particularly with a metal bumper.
On the other hand, when the diameter of the muffler diffuser portion is reduced, the reduction in the exhaust diameter of the engine due to the reduction in the diameter, the engine output also decreases, vibration and noise may occur, and fuel consumption may deteriorate. Therefore, it is difficult to actually adopt it.

Moreover, the method of using the vortex generator 7 or the tripping wire 8 is that the minimum ground clearance of the automobile is lowered because the vortex generator 7 and the tripping wire 8 protrude downward from the lower surface of the main muffler 4a. become.
Therefore, for example, when traveling on a rough road surface or steep slope, as shown in FIG. 12, there is a high possibility that these vortex generators 7 and tripping wires 8 interfere with the road surface, and these vortex generators 7 and 7 Since the tripping wire 8 is visible from the outside, it looks bad.

For this reason, in order to ensure the minimum ground clearance, it is necessary to change the shape of the main muffler 4a. However, the volume of the main muffler 4a changes, and the exhaust noise may increase in some cases. .
Further, when the protrusion-type vortex generator 7 is attached to the lower surface of the existing main muffler 4a later, the number of parts increases and the assembly process increases, so that the production cost increases, and the protrusions from the rear or side. Since it can be visually recognized, the appearance is degraded.

On the other hand, the duct according to Patent Document 1 reduces airflow noise by suppressing airflow separation and pressure loss at the bent portion with respect to the airflow flowing in the duct. Are different.
Further, the automobile antenna according to Patent Document 2 suppresses the generation of turbulent airflow behind the antenna and suppresses the generation of air resistance, noise, and vibration, and is different in configuration and purpose from the present invention. .

  In view of the above, an object of the present invention is to provide an automobile muffler structure that reduces the adhesion of exhaust gas components to a rear bumper due to turbulence generated near the rear end of the automobile body.

  According to the present invention, the above object is achieved by providing a main muffler having a vortex generator having a large number of concave dimples on the lower surface thereof in an automobile muffler attached to the lower rear portion of the automobile body.

  In the automobile muffler structure according to the present invention, preferably, the dimples are selected to have a diameter of 5.15 to 7.20 mm, a depth of 0.49 to 1.32 mm, and a distance of 0.53 to 1.33 mm.

  In the muffler structure for automobiles according to the present invention, preferably, the main muffler has a large number of concave dimples on its side surface.

  In the muffler structure for an automobile according to the present invention, preferably, the main muffler has a large number of concave dimples on its upper surface.

  According to the above configuration, since the vortex generator composed of a number of concave dimples is provided on the lower surface of the main muffler, the airflow flowing along the lower surface of the main muffler of the automobile muffler is Based on the shape of the vortex generator, a small eddy current is intentionally generated. As a result, the frictional resistance is reduced by forming a turbulent boundary layer in the vicinity of the rear end of the lower surface of the main muffler, so that a decrease in flow velocity is reduced at the rear end of the lower surface of the main muffler. Generation of turbulent flow due to separation is suppressed.

Therefore, the exhaust gas exhausted rearward from the muffler exhaust port is exhausted backward without being attracted by the turbulent airflow generated at the rear end of the automobile body. There is no such thing as sticking to the rear bumper.
In this way, the exhaust gas discharged from the opening at the rear end of the automobile muffler is entrained in the turbulent air flow due to boundary layer separation at the rear end of the automobile body, and the particles of the components do not adhere to the rear bumper. The occurrence of dullness and corrosion is suppressed and the appearance of the rear bumper is improved.

  When the main muffler has a large number of concave dimples on its side surface or top surface, the main muffler has an intentional small swirl of airflow that flows along the side surface or top surface of the main muffler. The reverberation characteristics and exhaust sound of the entire muffler and automobile muffler will change, and it is possible to tune to the desired exhaust sound by appropriately adjusting the size of the dimples provided on the side or top surface of the main muffler It is.

  Thus, according to the present invention, by forming a large number of concave dimples on the lower surface of the main muffler, a decrease in the flow velocity of the airflow flowing along the lower surface of the main muffler is suppressed, and the vehicle body is located near the rear end of the vehicle body. Adhesion of exhaust gas components to the rear bumper due to the generated turbulence can be reduced.

The present invention will be described in detail below based on the embodiments shown in the drawings.
FIG. 1 shows an embodiment of an automobile muffler structure according to the present invention. In FIG. 1, an automobile muffler 10 is provided below a rear end of a vehicle body 11 of an automobile and includes a main muffler 12.

  The main muffler 12 has a known configuration and has, for example, an elliptical cross section, and its lower surface 12a is formed so as to satisfy a predetermined minimum ground clearance, and is attached to the vehicle body 11.

  The above-described configuration is the same as that of the conventional automobile muffler 4 shown in FIG. 8, but in the automobile muffler 10 according to the present invention, as shown in FIG. This is different in that a vortex generator 13 composed of a concave dimple 13a is formed.

  Each dimple 13a of the vortex generator 13 is preferably selected to have a diameter of 5.15 to 7.20 mm, a depth of 0.49 to 1.32 mm, and an interval of 0.53 to 1.33 mm. Here, the size of the dimple 13a is optimized as follows.

Research on the air resistance of such dimples has been carried out in detail, for example, on the dimples provided on the surface of the golf ball. The air resistance coefficient with respect to the flight speed of the golf ball is shown in FIG. It is known that it varies depending on the difference in dimensions.
In particular, in FIG. 3, when there is no dimple, the air resistance coefficient is substantially constant regardless of the speed as indicated by the symbol M, but when dimples are provided, as indicated by the symbol N, at a higher speed. It can be seen that the air resistance coefficient decreases due to the dimple effect.

  Here, regarding a golf ball having a diameter of 4.26 cm flying at a speed of 160 km / h (45 m / sec), when the air flow state (Reynolds coefficient Re) around the golf ball is calculated by the following formula, the following result is obtained. can get.

Re = speed x diameter ÷ kinematic viscosity coefficient (atmosphere temperature 20 ° C)
= 45 m / sec x 0.0426 m ÷ (15 x 10 ^-6 )
= 1.278 × 10 ⁵
Here, 15 × 10 ⁻⁶ is a kinematic viscosity coefficient value at an ambient temperature of 20 ° C.

  On the other hand, assuming a car traveling at 80 km / h (22.22 m / s), the length χ is calculated by the following formula so that the Reynolds number Re is equivalent to that of a golf ball flying at 160 km / h. To do.

1.278 × 10 ⁵ = 22.22 m / sec × χ ÷ (15 × 10 ⁻⁶ )
Here, 15 × 10 ⁻⁶ is a kinematic viscosity coefficient value at an ambient temperature of 20 ° C.
χ = 0.087m = 8.7cm

That is, the length χ = 8.7 cm is 2.04 times the diameter of the golf ball.
Therefore, the distance, diameter, and depth of the dimples of a golf ball that has low air resistance and is likely to fly are all multiplied by 2.04 to match the driving conditions of the automobile (80 km / h). .
As a result, the dimple effect is verified below for the dimples A to G having the distance b, the diameter c, and the depth k as shown in FIG. Note that no dimples and dimples A to C are already shown in FIG.

  When the vortex generator 13 having the dimples C to F is provided on the lower surface of the main muffler 12, the relationship between the running speed of the automobile and the air resistance coefficient is shown in FIG. That is, in FIG. 5, by setting the dimple interval b to 0.53 to 1.33 mm and the diameter to 5.15 to 7.20 mm, a turbulent boundary layer is generated at a low speed, and a practical range of running speed (about 30 km / h) ) Shows that the dimple effect appears on the high speed side. This is considered to be due to the abrupt transition from laminar flow to turbulent flow when the air flow flowing on the lower surface of the main muffler 12 exceeds the practical range.

  Further, when the vortex generator 13 having the dimples C and G is provided on the lower surface of the main muffler 12, the relationship between the running speed of the automobile and the air resistance coefficient is shown in FIG. That is, in FIG. 6, it is possible to generate turbulence from a lower speed by increasing the depth k of the dimple 13a from 0.69 mm to 1.32 mm. growing. Therefore, the depth k of the dimple 13a is set to about 0.6 to 1.4 mm based on whether the low speed or the high speed is important in accordance with the type of automobile on which the muffler 10 for the automobile is mounted, that is, the vehicle type or destination. You can tune between.

  The automobile muffler 10 according to the embodiment of the present invention is configured as described above, and the lower surface 12a of the main muffler 12 is provided with the vortex generator 13 including a large number of concave dimples 13a. As shown in FIG. 5, the air flow flowing along the lower surface 12 a of the main muffler 12 of the automobile muffler 10 intentionally generates a small eddy current 14 based on the shape of the vortex generator 13 when the automobile is running. Thereby, in the vicinity of the rear end of the lower surface 12a of the main muffler 12, a turbulent boundary layer is formed, whereby the frictional resistance is reduced. Therefore, at the rear end of the lower surface 12a of the main muffler 12, the decrease in flow velocity is reduced, and the occurrence of turbulent flow due to boundary layer separation is suppressed.

Accordingly, the exhaust gas discharged from the exhaust port 12b of the automobile muffler 10 toward the rear at a certain flow rate is discharged rearward without being attracted by the turbulence generated at the rear end of the automobile body. The exhaust gas component particles do not adhere to the rear bumper due to turbulent airflow.
In this way, the exhaust gas discharged from the exhaust port 12b at the rear end of the muffler 10 for the automobile is entrained in the turbulent air flow due to boundary layer separation at the rear end of the vehicle body, and the component particles do not adhere to the rear bumper. The occurrence of dullness and corrosion of the rear bumper is suppressed, and the appearance of the rear bumper is improved.

  In this case, since the vortex generator 13 is constituted by the concave dimple 13 a, the vortex generator 13 does not protrude downward from the lower surface 12 a of the main muffler 12. Therefore, there is no influence on the minimum ground clearance of the vehicle body 11 of the automobile. For example, when traveling on a rough road surface or steep slope, the lower surface 12a of the main muffler 12 is less likely to interfere with the road surface, and the dimple 13a itself Because it is difficult to see from the outside, the appearance is not impaired.

  Further, when manufacturing the muffler 10 for an automobile, the muffler manufacturer is provided with a die for dimple processing in the press die of the iron plate that is the material of the main muffler 12, so that the muffler manufacturer is exactly the same as the conventional flat iron plate. Since the main muffler can be manufactured, no additional parts are required, the number of parts, assembly man-hours, and weight are not increased, and an increase in production cost is suppressed.

  Further, since the surface area of the lower surface 12a of the main muffler 12 is slightly increased due to the formation of the dimples 13a, the main muffler 12 is effectively cooled by the air flow flowing along the lower surface 12a when the vehicle is running. As a result, the temperature of the main muffler 12 decreases. Accordingly, the temperature of the exhaust gas also decreases, the occurrence of heat damage such as melting damage to the rear bumper due to the exhaust gas is suppressed, and the degree of freedom in designing the rear bumper is increased.

  In the above-described embodiment, each dimple 13a of the vortex generator 13 is provided only on the lower surface 12a of the main muffler 12. However, the present invention is not limited thereto, and dimples are provided on the side surface and the upper surface of the main muffler 12. Also good. As a result, a small vortex flow is generated in the air flow flowing along the side surface or the upper surface of the main muffler 12, thereby changing the echo characteristics and exhaust sound of the main muffler 12 and the entire vehicle muffler 10. It is also possible to tune to a desired exhaust sound by appropriately adjusting the size (interval, diameter, depth) of the dimples 13a provided on the side surface or the upper surface of the muffler 12.

1 is a schematic side view showing an overall configuration of an automobile provided with an embodiment of an automobile muffler structure according to the present invention. It is a bottom view of the main muffler in the muffler for motor vehicles of FIG. It is a graph which shows the relationship between the speed by a dimple, and an air resistance coefficient. It is a figure which shows the various space | interval, diameter, and depth of a dimple. 5 is a graph showing the relationship between the vehicle speed and the air resistance coefficient in the dimples C to F according to FIG. 4. 5 is a graph showing the relationship between vehicle speed and air resistance coefficient in dimples C and G according to FIG. It is the schematic which shows the airflow at the time of driving | running | working of the motor vehicle by the main muffler of FIG. It is a schematic side view which shows the structural example of the conventional muffler for motor vehicles, and the turbulent flow by boundary layer peeling. It is the schematic which shows the airflow at the time of driving | running | working of the motor vehicle by the main muffler of FIG. It is a schematic side view which shows the structural example of the main muffler provided with the conventional protrusion-type vortex generator. It is a schematic side view which shows the structural example of the main muffler provided with the conventional tripping. It is explanatory drawing which shows interference with the road surface of the main muffler by FIG.

Explanation of symbols

10 Car Muffler 11 Car Body 12 Main Muffler 13 Vortex Generator 13a Dimple

Claims (4)

In the muffler for automobiles attached to the lower rear of the car body,
A muffler structure for an automobile, wherein the main muffler includes a vortex generator having a number of concave dimples on a lower surface.   2. The dimple according to claim 1, wherein the dimple is selected to have a diameter of 5.15 to 7.20 mm, a depth of 0.49 to 1.32 mm, and a distance of 0.53 to 1.33 mm. Muffler structure.   The automobile muffler structure according to claim 1, wherein the main muffler has a large number of concave dimples on a side surface thereof. The automobile muffler structure according to any one of claims 1 to 3, wherein the main muffler has a large number of concave dimples on an upper surface thereof.

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