JP6471851B2 - Engine exhaust system - Google Patents

Description

  The present invention relates to an engine exhaust device that can improve the volumetric efficiency of an engine.

  Generally, in an engine mounted on a vehicle, when exhaust from an exhaust port reaches a muffler via an exhaust pipe, a pressure wave is reflected at the boundary between the exhaust pipe and the muffler, and a negative pressure wave is generated. It is known that when this negative pressure wave reaches the exhaust port at the time of valve overlap, residual gas in the cylinder is sucked to the exhaust port side, so that volume efficiency in the cylinder is improved and engine output torque is increased. .

  On the other hand, a high compression ratio is being promoted as a means for improving the fuel consumption of the engine. However, particularly at the time of low rotation, the flame propagation speed becomes slow, so that torque reduction is a problem. As a means for avoiding such a decrease in torque, as described above, an exhaust device including an exhaust pipe having a length that improves volumetric efficiency by a negative pressure wave and a muffler connected to the exhaust pipe has been proposed ( For example, see Patent Document 1).

  However, even if the length of the exhaust pipe and the arrangement of the muffler are designed so that the volume efficiency is improved by the negative pressure wave, it may not be actually adopted. For example, there may be a case where the length of the calculated exhaust pipe must be longer than the calculated length of the exhaust pipe due to the structure of the vehicle and the positional relationship with a device other than the exhaust device. Thus, when the exhaust device is matched to the actual vehicle structure, the structure is different from the originally designed structure, so that the volume efficiency cannot be sufficiently improved.

JP 2013-113224 A

  The present invention has been made in view of the above situation, and an object of the present invention is to provide an engine exhaust device that can adapt to an actual vehicle structure, improve volumetric efficiency, and increase torque.

  A first aspect of the present invention that solves the above problems includes a first exhaust passage that communicates with an exhaust port of an engine, a first muffler that communicates with the first exhaust passage, a second exhaust passage that communicates with the first muffler, An exhaust system for an engine having a second muffler communicating with the second exhaust passage and a third exhaust passage communicating with the second muffler, from the exhaust port to the first boundary of the first exhaust passage and the first muffler The exhaust path length from the exhaust port to the second boundary of the second exhaust passage and the second muffler, and the exhaust path length from the exhaust port to the third exhaust path and the third boundary outside are different from each other. The exhaust pressure wave discharged from the engine operating at the first engine speed, the second engine speed, or the third engine speed is reflected at each of the first boundary, the second boundary, and the third boundary. The negative pressure wave generated is a length that reaches the exhaust port during the valve overlap period, the volume of the second muffler is larger than the volume of the first muffler, and the cross-sectional area of the second exhaust passage is An exhaust system for an engine, wherein the cross-sectional area of the third exhaust passage is smaller than the cross-sectional area of the first exhaust passage, and the cross-sectional area of the first exhaust passage and the cross-sectional area of the second exhaust passage are larger. It is in.

  In the first aspect, the exhaust path length is adapted to the actual vehicle structure, while the volumetric efficiency is reduced by the relative cross-sectional areas of the first exhaust passage, the second exhaust passage, and the third exhaust passage. In addition, it can be compensated by making it medium, small and large. In other words, the exhaust device of the present invention is more suitable than the case where the exhaust passage length is adapted to the actual vehicle structure and the cross-sectional areas of the first exhaust passage, the second exhaust passage, and the third exhaust passage are the same. The volumetric efficiency due to can be greatly improved.

  According to a second aspect of the present invention, in the engine exhaust system described in the first aspect, the ratio of the volume of the second muffler to the volume of the first muffler is 1: 4 to 1: 6. It is in the exhaust system of the engine.

  In the second aspect, the average volume efficiency can be further improved.

According to a third aspect of the present invention, in the engine exhaust device described in the first or second aspect, the third engine speed is lower than the first engine speed and the second engine speed, The engine exhaust speed is lower than the first engine speed.

  The third aspect is useful for improving the volume efficiency in the low and medium rotation range and increasing the torque output.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust apparatus of the engine which adapts to the actual vehicle structure, can improve volumetric efficiency, and can increase a torque is provided.

It is a schematic block diagram of an engine exhaust device. It is a figure which shows the relationship between the installation location of a 1st muffler, and average volumetric efficiency, and the rotation speed of an engine, and volumetric efficiency. It is a figure which shows the relationship between the installation location of a 2nd muffler, and average volumetric efficiency, and the rotation speed of an engine, and volumetric efficiency. It is a figure showing the relationship between the internal diameter and average volume efficiency of a 2nd exhaust passage and a 3rd exhaust passage. It is a figure which shows the relationship between the volume of a 1st muffler and a 2nd muffler, and average volume efficiency.

  Hereinafter, modes for carrying out the present invention will be described. In addition, description of embodiment is an illustration and this invention is not limited to the following description.

  FIG. 1 is a schematic configuration diagram of an engine exhaust device according to the present embodiment. Although not particularly shown, the engine 1 is, for example, an in-line three-cylinder engine and has three cylinders. Each cylinder is provided with an ignition plug, and is provided with an intake port and an exhaust port. The engine 1 includes an intake manifold connected to the intake port and an exhaust manifold connected to the exhaust port.

The exhaust device 10 according to the present embodiment includes a first exhaust passage 11, a second exhaust passage 12, a third exhaust passage 13, a first muffler 21, and a second muffler 22.
The first exhaust passage 11 is a pipe that communicates with an exhaust port via an exhaust manifold of the engine and guides exhaust from the exhaust port to the first muffler 21. The second exhaust passage 12 is a pipe that is connected to the first muffler 21 and guides the exhaust gas that has passed through the first muffler 21 to the second muffler 22. The third exhaust passage 13 is a pipe that is connected to the second muffler 22 and guides the exhaust gas that has passed through the second muffler 22 to the outside.

  The cross-sectional area of the first exhaust passage 11 is S1, the cross-sectional area of the second exhaust passage 12 is S2, and the cross-sectional area of the third exhaust passage 13 is S3. The sectional area S2 is smaller than the sectional area S1, and the sectional area S3 is larger than the sectional areas S1 and S2. That is, the cross-sectional areas S1, S2, and S3 are relatively medium, small, and large. In the present embodiment, since the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are all circular in cross section, their inner diameters φ1, φ2, and φ3 are relatively medium and small. The size is large.

The first muffler 21 and the second muffler 22 are pipes that reduce the noise of the inflowing exhaust gas, and the volume of the second muffler 22 is configured to be larger than the volume of the first muffler. By setting it as such a volume, the sound reduction effect by a muffler can be heightened.
The boundary between the first exhaust passage 11 and the first muffler 21 is defined as a first boundary A, the boundary between the second exhaust passage 12 and the second muffler 22 is defined as a second boundary B, and the third exhaust passage 13 and the outside (third A boundary between the exhaust passage 13 and the opening from which the exhaust gas is discharged to the outside is defined as a third boundary C.

The first exhaust passage L from the exhaust port to the first boundary A refers to an exhaust passage including the exhaust port, the exhaust manifold, and the first exhaust passage 11. The second exhaust path M from the exhaust port to the second boundary B is an exhaust path including the first exhaust path L, the first muffler 21, and the second exhaust path 12. Further, the third exhaust path N from the exhaust port to the third boundary C refers to an exhaust path including the second exhaust path M, the second muffler 22, and the third exhaust path 13. The lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N are referred to as the exhaust path length.
The position of the exhaust port that is the starting point of the exhaust path length of the first exhaust path L, the second exhaust path M, and the third exhaust path N is the seating position of the exhaust valve in the engine exhaust port (the opening at which the exhaust port faces the cylinder). ).

  Here, the exhaust pressure wave generated with the operation of the engine 1 propagates from the exhaust port to each part of the exhaust device 10. The propagated exhaust pressure wave is reflected to the exhaust port side as a negative pressure wave whose phase is inverted at each of the first boundary A, the second boundary B, and the third boundary C. Thereafter, the negative pressure wave reaches the exhaust port and is reflected in the same phase, and further, the negative pressure wave is repeatedly reflected at the first boundary A, the second boundary B, and the third boundary C.

  The exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N correspond to the first boundary A and the second boundary during the valve overlap period of the intake valve and the exhaust valve of the engine. The negative pressure wave reflected by each of B and the third boundary C reaches the exhaust port.

  When the negative pressure wave reaches the exhaust port during the valve overlap period, the residual gas in the cylinder is sucked to the exhaust port side, so that the volumetric efficiency in the cylinder is improved and the torque is also increased. By improving the volume efficiency by the negative pressure wave in the low to medium rotation range of the engine, the output torque of the engine in the low to medium rotation range can be increased.

  In this embodiment, the engine output torque is increased for each of extremely low rotation (1300 rpm or less), low rotation (1300 to 2000 rpm), and medium rotation (2000 to 3000 rpm). The specific rotation speed included in the medium rotation is the first engine rotation speed, the specific rotation speed included in the low rotation is the second engine rotation speed, and the specific rotation speed included in the extremely low rotation is the third engine rotation speed. And

  The exhaust path length of the first exhaust path L is such that the negative pressure wave reflected from the first boundary A at the first engine speed and the exhaust pressure wave propagated from the exhaust port is exhausted during the valve overlap period at the first engine speed. The length to reach the port is set. In other words, the exhaust path length of the first exhaust path L is determined by the time until the valve overlaps from the start of engine exhaust at the first engine speed, and the exhaust pressure wave is reflected at the first boundary A. The time until the negative pressure wave reaches the exhaust port is set to coincide.

  The exhaust path length of the second exhaust path M is such that the negative pressure wave reflected by the second boundary B of the exhaust pressure wave propagated from the exhaust port at the second engine speed is exhausted during the valve overlap period at the second engine speed. The length to reach the port is set. In other words, the length of the exhaust path M of the second exhaust path M is the time from when the engine starts exhausting at the second engine speed to the time when the valve overlaps, and the exhaust pressure wave is reflected at the second boundary B. The time until the negative pressure wave reaches the exhaust port is set to coincide.

  The exhaust path length of the third exhaust path N is such that the negative pressure wave reflected from the third boundary C at the third engine speed is reflected from the exhaust port during the valve overlap period at the third engine speed. The length to reach the port is set. In other words, the exhaust path length of the third exhaust path N is determined by the time until the valve overlaps from the start of engine exhaust at the third engine speed, and the exhaust pressure wave is reflected at the third boundary C. The time until the negative pressure wave reaches the exhaust port is set to coincide.

  Here, if the actual vehicle structure is ignored, the exhaust path length and the arrangement and volume of the first muffler 21 and the second muffler 22 that maximize the volumetric efficiency improvement effect by the negative pressure wave can be adopted. However, the exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N, and the arrangement and volume of the first muffler 21 and the second muffler 22 must be adjusted according to the actual vehicle structure. I must. Matching the actual vehicle structure is, for example, when the length of the exhaust path must be increased due to the vehicle structure or the positional relationship with a device other than the exhaust device, or to increase the noise reduction effect. This is the case where the arrangement and volume of the first muffler 21 and the second muffler 22 are changed.

  As a result of adjusting the exhaust path length etc. according to the actual vehicle structure, when focusing only on the exhaust path length, the arrangement and volume of each muffler, the volume efficiency is reduced compared to the configuration where volume efficiency by negative pressure wave is most desired It becomes the composition which ends.

  However, in the exhaust device 10 of the present embodiment, the inner diameters φ1 to φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are relatively medium, small, and large. As a result, while the lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N are matched to the actual vehicle structure, as described above, during the valve overlap period. The length is such that the negative pressure wave reaches the exhaust port, and the volumetric efficiency can be improved.

  Hereinafter, the exhaust path length and the inner diameters φ1 to φ3 will be described in detail.

FIG. 2 is a diagram showing the relationship between the installation location of the first muffler 21 and the average volume efficiency, and the relationship between the engine speed and the volume efficiency. FIG. 3 shows the installation location of the second muffler 22 and the average volume efficiency. It is a figure which shows the relationship between these, and the relationship between the rotation speed of an engine, and volumetric efficiency.
The horizontal axis in FIG. 2A represents the distance from the exhaust port to the inlet of the first muffler 21, that is, the exhaust path length of the first exhaust path L, and the vertical axis represents the average volume efficiency.

The inner diameters φ1, φ2, and φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are all the same size, and the capacities of the first muffler 21 and the second muffler 22 are V ₀ , W, respectively. Under the condition of ₀ , the installation location of the first muffler 21 is changed by changing the length of the first exhaust passage 11 constituting the first exhaust passage L, and the average volume efficiency is obtained for each installation location. The graph showing the relationship between the installation location and the average volumetric efficiency is shown. In addition, average volume efficiency takes the average of volume efficiency in the rotation speed of the engine shown in FIG.2 (b) at 1000-4000 rpm.

For example, when the exhaust path length of the first exhaust path L is L ₀ (mm), the average volume efficiency is about 86%, which is a peak. On the other hand, when the exhaust path length of the first exhaust path L is L _ref (mm), the average volume efficiency is about 82%.

The horizontal axis in FIG. 2B represents the engine speed, and the vertical axis represents volumetric efficiency. The solid line G1 is an exhaust path length of the first exhaust passage L is fixed at L _0, to change the rotational speed to obtain the volumetric efficiency for each rotation speed, a graph showing the relationship between the rotational speed and the volumetric efficiency. A solid line G2 is a graph showing the relationship between the rotational speed and the volume efficiency by fixing the exhaust path length of the first exhaust path L to L _ref and changing the rotational speed to obtain the volume efficiency for each rotational speed.

As indicated by the solid line G1, when the exhaust path length of the first exhaust path L is fixed at L ₀ and the rotation speed is changed, the volume efficiency is relatively high in the low to medium rotation range. Here, the first engine speed was set to 2500 rpm at which the volumetric efficiency is about 90%, which is relatively high.

Therefore, under the condition that the inner diameters φ1, φ2, and φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are all the same size, the exhaust passage length of the first exhaust passage L is set to L _0. By doing so, it is possible to further increase the volumetric efficiency due to the negative pressure wave in the vicinity of 2500 rpm that is the first engine speed.

For reference, when the exhaust path length of the first exhaust path L is L _ref , as indicated by the solid line G2, the volumetric efficiency is about 65% in the vicinity of 2500 rpm that is the first engine speed. Yes. That is, at the first engine speed (2500 rpm), which is one of the engine speeds for which the torque is to be improved, by setting the exhaust path length to L ₀ , higher volume efficiency can be obtained as shown by the solid line G1. You can see that

On the other hand, the exhaust path length of the second exhaust path M is determined as follows.
The horizontal axis in FIG. 3A represents the distance from the exhaust port to the inlet of the second muffler 22, that is, the exhaust path length of the second exhaust path M, and the vertical axis represents the average volume efficiency.

  The length of the second exhaust passage 12 constituting the second exhaust passage M under the condition that the inner diameters φ1, φ2, and φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are all the same size. By changing the height, the installation location of the second muffler 22 is changed, the average volume efficiency is obtained for each installation location, and a graph showing the relationship between the installation location and the average volume efficiency is shown. In addition, average volume efficiency takes the average of volume efficiency in the rotation speed of the engine shown in FIG.3 (b) at 1000-4000 rpm.

For example, when the exhaust path length of the second exhaust path M is M _ref (mm), the average volumetric efficiency is about 84% that reaches a peak. On the other hand, when the exhaust path length of the second exhaust path M is M ₀ (mm), the average volumetric efficiency is about 79%, which is the next largest peak.

The horizontal axis in FIG. 3B represents the engine speed, and the vertical axis represents volumetric efficiency. The solid line G3 is an exhaust path length of the second exhaust passage M was fixed at M _0, by varying the rotation speed, determine the volumetric efficiency of each rotation speed, a graph showing the relationship between the rotational speed and the volumetric efficiency. A solid line G4 is a graph representing the relationship between the rotational speed and the volumetric efficiency by fixing the exhaust path length of the second exhaust path M at _Mref , changing the rotational speed, obtaining the volumetric efficiency for each rotational speed.

As shown by the solid line G3, an exhaust path length of the second exhaust passage M was fixed at M _0, when changing the rotational speed, and has a relatively high volumetric efficiency at low and medium speed range. Here, 1500 rpm at which the volumetric efficiency is relatively high, which is about 95%, is set as the second engine speed.

Therefore, under the condition that the inner diameters φ1, φ2, and φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are all the same size, the exhaust passage length of the second exhaust passage M is set to M _0. By doing so, the improvement in volumetric efficiency due to the negative pressure wave can be further increased in the vicinity of 1500 rpm that is the second engine speed.

For reference, when the exhaust path length of the second exhaust path M is M _ref , as indicated by the solid line G4, the volumetric efficiency is about 70% around 1500 rpm that is the second engine speed. Yes. In other words, at the second engine speed (1500 rpm), which is one of the engine speeds for which torque is to be improved, by setting the exhaust path length to M ₀ , higher volume efficiency can be obtained as shown by the solid line G3. You can see that

As shown in FIG. 3A, the average volume efficiency is higher in the case where the exhaust path length is M _ref than in M ₀ . However, if the exhaust path length is M _ref , the second muffler 22 is closer to the exhaust port than the first muffler 21 (see FIG. 2A). In order to obtain a sound reduction effect, the second muffler 22 having a large capacity must be arranged on the downstream side of the first muffler 21 having a small capacity, so that the exhaust path length of the second exhaust path M is set to M _ref. It cannot be.

Although not particularly illustrated, the exhaust path length of the third exhaust path N is also determined in the same manner as the first exhaust path L and the second exhaust path M. Let the exhaust path length of the third exhaust path N at which the volume efficiency reaches a peak at the third engine speed (for example, 1200 rpm) be N ₀ .

  As described above, at the first engine speed, the volumetric efficiency is about 90% due to the negative pressure wave reflected at the first boundary A, and at the second engine speed, the volume is increased by the negative pressure wave reflected at the second boundary B. The efficiency is about 95%, and at the third engine speed, the first exhaust path L, the second exhaust path M, and the third exhaust path N are set so as to have a high volumetric efficiency due to the negative pressure wave reflected at the third boundary C. Is determined.

  These exhaust path lengths can be adopted when the actual vehicle structure is ignored. Actually, the exhaust path length is adjusted according to the actual vehicle structure, or the first muffler 21 and the second muffler. The arrangement and capacity of 22 must be adjusted.

For example, as shown in FIGS. 2A and 3A, the exhaust path length of the first exhaust path L is set to L ₁ longer than L _0, and the exhaust path length of the second exhaust path M is set to M ₀ . in some cases also the long M _1, shall not particularly illustrated exhaust path length of the third exhaust passage N and long N ₁ than N _0. In this case, the average volume efficiency also decreases, and the volume efficiency at the first engine speed, the second engine speed, and the third engine speed also decreases.

  However, volume efficiency can be improved by making the inner diameters φ1 to φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 relatively medium, small, and large.

  FIG. 4 is a graph showing the relationship between the inner diameters of the second exhaust passage and the third exhaust passage and the average volume efficiency. 4A and 4B, the vertical axis represents the average volume efficiency, the horizontal axis in FIG. 4A represents the inner diameter (mm) of the second exhaust passage, and the horizontal axis in FIG. 3 represents the inner diameter of the exhaust passage.

First, it is stated that the exhaust path length, average volume efficiency, etc. were calculated under the condition that the inner diameters φ1, φ2, and φ3 of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are all the same size. It was. The inner diameter at this time is, for example, D ₁ (about 31.6 mm).

In FIG. 4A, the exhaust path lengths of the first exhaust path L and the second exhaust path M are L ₁ and M ₁ adjusted to match the actual vehicle structure, and the inner diameter φ1 of the first exhaust path 11 is shown. in the conditions with D _1, to change the inner diameter .phi.2 of the second exhaust passage 12, there is shown a graph of the mean was calculated volumetric efficiency for each inner diameter .phi.2.
According to this graph, it can be seen that there is a characteristic that the average volume efficiency peaks upward at D ₂ (about 29.0 mm) smaller than D ₁ .

In FIG. 4B, the exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N are set to L ₁ , M _1, and N ₁ adjusted to match the actual vehicle structure. the inside diameter φ1 of the first exhaust passage 11 D _1, under conditions in which the inner diameter φ2 of the second exhaust passage 12 and the D _2, by changing the inner diameter φ3 of the third exhaust passage 13, the average volumetric efficiency for each inner diameter φ3 The calculated graph is shown.
According to this graph, it can be seen that there is a characteristic that the average volume efficiency peaks upward at D ₃ (about 32.5 mm) larger than D ₁ .

Accordingly, the inner diameter φ2 of the second exhaust passage 12 and smaller D ₂ from D _1, the inner diameter φ3 of the third exhaust passage 13 by a larger D ₃ than D _1, it is possible to improve the average volumetric efficiency. Since the average volumetric efficiency is improved, the volumetric efficiency at the first engine speed, the second engine speed, and the third engine speed is also improved.

Thus, the actual vehicle structure is obtained by setting the exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N from L ₀ , M ₀ , N ₀ to L ₁ , M ₁ , N _1. However, the decrease in volumetric efficiency, which is reduced by this, can be compensated by making the inner diameters of the first exhaust passage 11, the second exhaust passage 12 and the third exhaust passage 13 relatively medium, small and large. it can.

Such a relationship between the exhaust path length and the inner diameter is based on the Helmholtz principle. Helmholtz's principle is that, in a structure including a hollow box and a cylindrical member attached so as to communicate with the inside of the box, the speed of sound is c, the volume inside the box is V, and the length of the cylindrical member is Where l is the cross-sectional area of the cylindrical member, S is the resonance frequency, and f ₀ is the resonance frequency.

  The volume V inside the box corresponds to the volume of the first muffler 21 or the second muffler 22, l corresponds to the length of the exhaust path of the first exhaust path L, the second exhaust path M or the third exhaust path N, S corresponds to the cross-sectional area (inner diameter) of the first exhaust passage 11, the second exhaust passage 12, or the third exhaust passage 13. The resonance frequency f0 corresponds to the first engine speed, the second engine speed, or the third engine speed.

For example, the length l of the cylindrical member, that is, the exhaust path length of the second exhaust path M or the third exhaust path N extends from M ₀ to M ₁ , N ₀ to N ₁ , and the desired resonance frequency, If the second engine speed or the second engine speed is used, the cross-sectional areas (inner diameters) of the second exhaust passage 12 and the third exhaust passage 13 corresponding to V or S of other parameters may be changed. In the example shown in FIG. 4, the inner diameters of the second exhaust passage 12 and the third exhaust passage 13 at which the average volume efficiency reaches a peak are specified based on the Helmholtz principle.

Moreover, the volume of the 1st muffler 21 and the 2nd muffler 22 influences the improvement of the volume efficiency by a negative pressure wave.
FIG. 5 is a diagram illustrating the relationship between the volume of the first muffler 21 and the second muffler 22 and the average volume efficiency. The horizontal axis represents the capacity of the first muffler 21, and the vertical axis represents the capacity of the second muffler 22.

The exhaust path lengths of the first exhaust path L, the second exhaust path M and the third exhaust path N are L ₁ , M ₁ and N _1, and the inner diameters of the first exhaust path 11, the second exhaust path 12 and the third exhaust path. Under the conditions where φ1, φ2, and φ3 were D ₁ , D ₂ , and D ₃ , the capacities of the first muffler 21 and the second muffler 22 were changed, and the average volume efficiency for each capacity was calculated. The average volume efficiency is displayed by dividing the range from 82.5 to 87.5 in 0.5 increments and arranging the same color for each division.

In V ₀ and W ₀ which are the capacities of the first muffler 21 and the second muffler 22 which are assumed when the exhaust path length and the inner diameter are determined, the average volume efficiency is between 86.5 and 87.0. On the other hand, when the capacity of the first muffler 21 is in the range of 1.5 to 2.0 and the capacity of the second muffler 22 is in the range of 8 to 10, for example, V ₁ and W ₁ included in the range Thus, the average volume efficiency is in the range of 87.0 to 87.5. The ratio of the volume of the second muffler 22 to the volume of the first muffler 21 that provides such an average volumetric efficiency is 1: 4 to 1: 6.

  Under conditions where the exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N and the inner diameters of the first exhaust path 11, the second exhaust path 12, and the third exhaust path are fixed. By setting the ratio of the volume of the second muffler 22 to the volume of the first muffler 21 to 1: 4 to 1: 6, the average volume efficiency can be further improved.

  As described above, the first engine speed, the second engine speed, and the third engine under the condition that the inner diameters of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are the same. The exhaust path length can also be set so that the improvement in volumetric efficiency due to the negative pressure wave is optimal at each rotation speed. However, such an exhaust path length ignores the actual vehicle structure, and is not always applicable.

According to the exhaust system of the present invention, the exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N are set to L ₁ , M ₁ , and N ₁ adapted to an actual vehicle structure. Thus, the decrease in volumetric efficiency that is reduced can be compensated by making the inner diameters of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 relatively medium, small, and large.

In other words, the exhaust system of the present invention is simply L ₁ , M ₁ , N _{1 in} which the exhaust path lengths of the first exhaust path L, the second exhaust path M, and the third exhaust path N are adapted to the actual vehicle structure. As compared with the case where the inner diameters of the first exhaust passage 11, the second exhaust passage 12 and the third exhaust passage 13 are the same, the volumetric efficiency due to the negative pressure wave can be greatly improved.

  In particular, since the first engine speed to the third engine speed are set to be in the low / medium speed range, the volume efficiency in the low / mid speed range can be improved and the torque output can be increased.

  The first engine speed to the third engine speed are not limited to the case where the engine speed is selected from the low / medium speed range, and may be set to any engine speed at which torque is desired to be improved. In the present embodiment, the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 are circular in cross section having an inner diameter φ1 to φ3, but the cross section is limited to such a shape. It can be made into arbitrary shapes. In this case, the cross-sectional areas of the first exhaust passage 11, the second exhaust passage 12, and the third exhaust passage 13 may be relatively medium, small, and large.

  The present invention can be used in the industrial field of automobiles.

A First boundary B Second boundary C Third boundary L First exhaust passage M Second exhaust passage N Third exhaust passage 1 Engine 10 Exhaust device 11 First exhaust passage 12 Second exhaust passage 13 Third exhaust passage 21 First Muffler 22 Second muffler

Claims (3)

A first exhaust passage communicating with the exhaust port of the engine, a first muffler communicating with the first exhaust passage, a second exhaust passage communicating with the first muffler, a second muffler communicating with the second exhaust passage, and the An engine exhaust system comprising a third exhaust passage communicating with a second muffler,
The exhaust path length from the exhaust port to the first exhaust path and the first boundary of the first muffler, the exhaust path length from the exhaust port to the second exhaust path and the second boundary of the second muffler, and the exhaust port to the third exhaust path And the exhaust path length to the external third boundary is such that the exhaust pressure wave discharged from the engine operating at different predetermined first engine speed, second engine speed, or third engine speed is first. The length of the negative pressure wave generated by reflection at each of the boundary, the second boundary, and the third boundary reaches the exhaust port during the valve overlap period,
The volume of the second muffler is larger than the volume of the first muffler,
A cross-sectional area of the second exhaust passage is smaller than a cross-sectional area of the first exhaust passage;
An engine exhaust system, wherein a cross-sectional area of the third exhaust passage is larger than a cross-sectional area of the first exhaust passage and a cross-sectional area of the second exhaust passage. The engine exhaust device according to claim 1,
An exhaust system for an engine, wherein a ratio of a volume of the second muffler to a volume of the first muffler is 1: 4 to 1: 6. The engine exhaust system according to claim 1 or 2,
The third engine speed is lower than the first engine speed and the second engine speed,
The exhaust system for an engine, wherein the second engine speed is lower than the first engine speed.