Exhaust system for an internal combustion engine

Abstract

Exhaust device for an internal combustion engine for releasing exhaust gas from the internal combustion engine through a multi-stage expansion silencer (1) which has a plurality of expansion chambers (31, 33, 35) which include at least one upstream expansion chamber (33) and one downstream expansion chamber (35) to dampen the sound of the exhaust gas during its passage;wherein the multi-stage expansion silencer (1) comprises a first end pipe (41) not connected to the upstream expansion chamber (33) for establishing the connection between the downstream expansion chamber (35) and the outside of the silencer (1), and a second end pipe (42) for establishing the connection between the upstream expansion chamber (33) and the outside of the silencer (1), wherein the downstream ends of the first and second end pipes (41, 42) extend freely to the outside, characterized in that the opening area of ​​the second end pipe (42) is larger than the opening area of ​​the first end pipe (41).

Description

[0001] The invention relates to an exhaust device for an internal combustion engine for discharging exhaust gas of the internal combustion engine through a multi-stage expansion muffler having a plurality of expansion chambers to dampen the sound of the exhaust gas as it passes through.

[0002] Conventionally known is a multi-stage expansion muffler comprising a plurality of expansion chambers, a pipe for connecting between the expansion chambers, and a tail pipe, wherein the pressure of exhaust gas from an internal combustion engine is reduced in each expansion chamber to thereby attenuate the sound of the exhaust gas, and the pressure-reduced exhaust gas is discharged from the tail pipe to the outside of the muffler, see, for example, JP H01-285615A.

[0003] In the above-mentioned conventional exhaust muffler, the exhaust sound of the exhaust gas can be reduced by reducing the diameter of each pipe. However, if the diameter of each pipe is too small, sufficient engine power cannot be achieved at high engine speeds. Furthermore, since the exhaust sound in this case is small at low engine speeds, it is difficult to adjust the timbre of the exhaust sound. On the other hand, if the diameter of each pipe is larger, sufficient engine power can be achieved easily and sufficiently at high engine speeds. However, the sound pressure of the exhaust sound becomes high at low engine speeds.

[0004] One proposed solution to this problem is to provide an exhaust valve that switches according to engine speed, thereby making the exhaust note and engine power compatible. However, this system is structurally complex and expensive.

[0005] The older, but subsequently published, DE 10 2009 054 074 A1 shows an exhaust system with two tailpipes, the downstream ends of which flow into a common rear muffler via a common flap valve. This flap valve selectively opens one of the two tailpipes to the rear muffler.

[0006] DE 20 2006 004 006 U1 shows an exhaust device according to the preamble of claim 1.

[0007] DE 10 2005 041 692 A1 shows a three-chamber muffler with two tailpipes. One of the tailpipes connects both the upstream and downstream expansion chambers to the outside via a flap valve.

[0008] In DE 698 32 764 T2 only a single tailpipe is shown.

[0009] The object of the invention is therefore to provide an exhaust muffler with a simple structure which can improve the timbre of the exhaust sound in the low engine speed range and also increase the engine power in the high engine speed range.

[0010] According to the invention, an exhaust device for an internal combustion engine according to claim 1 is provided.

[0011] According to the invention, the timbre of the exhaust sound in the low engine speed range can be improved and the engine power in the high engine speed range can also be increased.

[0012] Furthermore, the opening area of ​​the second tailpipe is larger than the opening area of ​​the first tailpipe.

[0013] With this configuration, sufficient engine power can be achieved in the low to medium engine speed range.

[0014] Preferably, the expansion chambers include first, second, and third expansion chambers arranged in the order of exhaust gas passage; wherein the downstreammost expansion chamber is the third expansion chamber; the upstream expansion chamber is the second expansion chamber; and the volume of the second expansion chamber is greater than the volume of the third expansion chamber.

[0015] With this configuration, a damping effect can be increased in the low to medium engine speed range.

[0016] Preferably, the third expansion chamber is provided between the first expansion chamber and the second expansion chamber, and a small hole for adjusting the back pressure penetrates a partition wall between the first expansion chamber and the third expansion chamber.

[0017] With this configuration the back pressure can be finely adjusted.

[0018] Preferably, the sum of the opening area of ​​the first tail pipe and the opening area of ​​the second tail pipe is substantially equal to the opening area of ​​an inlet pipe of the silencer.

[0019] With this configuration, the timbre of the exhaust note can be improved in the low engine speed range and the engine power can also be increased in the high engine speed range.

[0020] According to the invention, the muffler includes the first tailpipe connecting the downstream expansion chamber to the outside of the muffler, and the second tailpipe connecting the upstream expansion chamber on the upstream side of the downstream expansion chamber to the outside of the muffler. Accordingly, the timbre of the exhaust note can be improved at low engine speeds and the engine power can be increased at high engine speeds.

[0021] In the configuration where the opening area of ​​the second tailpipe is larger than the opening area of ​​the first tailpipe, the engine power can be sufficiently achieved in the low to medium engine speed range.

[0022] In the configuration where the expansion chambers include the first, second, and third expansion chambers, the downstream expansion chamber is the third expansion chamber, the upstream expansion chamber is the second expansion chamber, and the volume of the second expansion chamber is larger than the volume of the third expansion chamber, the silencing effect in the low to medium engine speed range can be improved.

[0023] In the configuration where the third expansion chamber is provided between the first expansion chamber and the second expansion chamber, and the small hole for adjusting back pressure penetrates the partition wall between the first expansion chamber and the third expansion chamber, the back pressure can be finely adjusted.

[0024] In the configuration where the sum of the opening area of ​​the first tail pipe and the opening area of ​​the second tail pipe is substantially equal to the opening area of ​​the inlet pipe of the muffler, the timbre of the exhaust sound in the low engine speed range can be improved and the engine power in the high engine speed range can also be increased.

[0025] The invention is described below using exemplary embodiments and reference to the accompanying drawings. Fig. 1 is a plan view of an exhaust silencer according to the invention; Fig. 2 is a partially sectioned view of the exhaust silencer; Fig. 3 is a cross section along the line III-III in Fig. 2 Fig. 4 is a cross section along the line IV-IV in Fig. 2 Fig. 5 is a cross section along the line VV in Fig. 2 Fig. 6 is a schematic perspective view of the exhaust gas flow in the exhaust muffler of the low engine speed; Fig. Figure 7 is a schematic perspective view of the exhaust gas flow in the exhaust muffler at high engine speeds; Fig. 8 is a graph showing the relationship between engine speed and engine power; and Fig. Figure 9 is a graph showing the exhaust sound pressure and its frequency distribution.

[0026] Now, as a preferred embodiment of the exhaust device for an internal combustion engine of the invention, an exhaust muffler or silencer for attachment to a motorcycle will be described.

[0027] Fig. Figure 1 is a plan view of an exhaust muffler according to the invention. The exhaust muffler 1 is connected to the rear end of the exhaust pipe (not shown) extending from an engine (not shown) of a motorcycle. Exhaust gas at high temperatures and high pressures flows through the exhaust pipe, and its pressure is reduced by the exhaust muffler 1. This reduced-pressure exhaust gas is discharged from the exhaust muffler 1.

[0028] The exhaust muffler 1 is composed of a connecting pipe 3 connected to the rear end portion of the exhaust pipe and a muffler body 5 connected to the rear end portion of the connecting pipe 3. As shown in Fig. 2, the muffler body 5 includes a cylindrical portion 7 having front and rear openings, a front cap 9 for closing the front opening of the cylindrical portion 7, and an end cap 11 for closing the rear opening of the cylindrical portion 7. A mounting flange 13 is provided at the longitudinal center portion of the outer surface of the cylindrical portion 7. The exhaust muffler 1 is mounted to the rear end portion of a main frame (not shown) of a motorcycle by this mounting flange 13.

[0029] The cylindrical portion 7 of the muffler body 5 has a dual structure composed of an outer member 7A and an inner member 7B. The front end of the outer member 7A is connected to the rear end of the front cap 9, and the rear end of the outer member 7A is connected to the front end of the end cap 11.

[0030] The inner element 7B is supported within the outer element 7A by front and rear support elements 15 and 17. A sound and heat insulation element 19, formed, for example, from glass wool, is provided between the outer element 7A and the inner element 7B.

[0031] A first partition wall 21 and a second partition wall 23 are provided in the inner member 7B, spaced apart from each other in the axial direction of the cylindrical portion 7, and a third partition wall 25 is provided at the rear end of the inner member 7B. The interior of the muffler body 5 is divided by these partition walls 21, 23, and 25 into a first expansion chamber 31, a second expansion chamber 33, and a third expansion chamber 35. Thus, the exhaust muffler 1 is a multi-stage expansion muffler with three expansion chambers.

[0032] The connecting pipe 3 has a rear end portion 36 extending into the muffler body 5. The rear end portion 36 extends through the front cap 5 and opens into the first expansion chamber 31. A first connecting pipe 37 extends in the muffler body 5 through the first partition wall 21 and the second partition wall 23, thereby establishing communication between the first expansion chamber 31 and the second expansion chamber 33. A second connecting pipe 38 extends in the muffler body 5 through the second partition wall 23, thereby establishing communication between the second expansion chamber 33 and the third expansion chamber 35.

[0033] In this preferred embodiment, two tailpipes 41 and 42 are provided.

[0034] The first tailpipe 41 is a general tailpipe that extends through the second partition wall 23, the third partition wall 25, and the end cap 11, thereby establishing communication between the third expansion chamber 35 and the outside of the exhaust muffler 1. The second tailpipe 42 is an additional tailpipe that extends through the third partition wall 25 and the end cap 11, thereby establishing communication between the second expansion chamber 33 and the outside of the exhaust muffler 1.

[0035] Fig. 3 is a cross section along the line III-III in Fig. 2, Fig. 4 is a cross section along the line IV-IV in Fig. 2 and Fig. 5 is a cross section along the line VV in Fig. 2.

[0036] As in the Fig. 2 to 4, the front end of the first connecting pipe 37 opens into the first expansion chamber 31. The first connecting pipe 37 extends through the first partition wall 21 and the second partition wall 23 in the muffler body 5 at a vertically middle position on the left side (see Fig. 3). The rear end of the first connecting pipe 37 opens into the second expansion chamber 33.

[0037] As in the Fig. 2 and Fig. 4, the rear end of the second connecting pipe 38 opens into the second expansion chamber 33. The second connecting pipe 38 extends through the second partition wall 23 in the muffler body 5 at a vertically middle position on the right side (see Fig. 4). The front end of the second connecting pipe 38 opens into the third expansion chamber 35.

[0038] As in the Fig. 2, Fig. 4 and Fig. 5, the front end of the first tail pipe 41 opens into the third expansion chamber 35. The first tail pipe 41 extends through the second partition wall 23 and the third partition wall 25 in the muffler body 5 at a laterally middle position on the upper side (see Fig. 4 and Fig. 5) and extends further through the end cap 11, bending downward at its rear end. The rear end of the first tail pipe 41 opens toward the outside of the end cap 11.

[0039] As in the Fig. 2 and Fig. 5, the front end of the second tail pipe 42 opens into the second expansion chamber 33. The second tail pipe 42 extends through the third partition wall 25 in the muffler body 5 at the lateral middle position on the bottom (see Fig. 5) and extends further through the end cap 11. The rear end of the second tailpipe 42 opens to the outside of the end cap 11.

[0040] The rear end portion 36 of the connecting pipe 3, the first connecting pipe 37, and the second connecting pipe 38 are formed of pipe elements having substantially the same inner diameter. The inner diameter of the first end pipe 41 is smaller than that of the second end pipe 42, and the inner diameter of each of the pipes 41 and 42 is smaller than that of the second connecting pipe 38. In other words, the end pipe 41 has the smallest inner diameter, and the second end pipe 42 has the second smallest inner diameter. The sum of the opening areas or cross-sections of the first end pipe 41 and the second end pipe 42 is substantially equal to the opening area of ​​the second connecting pipe 38.

[0041] Comparing the sizes of the expansion chambers 31, 33 and 35, the first expansion chamber 31 has the largest volume, the second expansion chamber 33 has the second largest volume and the third expansion chamber 35 has the smallest volume.

[0042] Now the operation of the exhaust silencer 1 with respect to Fig. 2 described.

[0043] The exhaust gas flowing through the connecting pipe 3 into the muffler body 5 first enters the first expansion chamber 31 and then flows through the first connecting pipe 37 into the second expansion chamber 33.

[0044] A portion of the exhaust gas flowing into the second expansion chamber 33 is reversed in flow direction to flow into the third expansion chamber 35 through the second connecting pipe 38 and then discharged to the outside of the exhaust muffler 1 through the tail pipe 31. On the other hand, another portion of the exhaust gas flowing into the second expansion chamber 33 is directly discharged to the outside of the exhaust muffler 1 through the second tail pipe 42.

[0045] The Fig. 6 and Fig. 7 schematically show the exhaust gas flow in the silencer body 5. Fig. 6 shows the flow at low engine speeds (the flow is shown with thin arrows because the amount of exhaust gas flowing into the muffler body 5 is small), and Fig. 7 shows the flow at high engine speeds (the flow is shown with thick arrows because the amount of exhaust gas flowing into the muffler body 5 is large).

[0046] As in Fig. As shown in Figure 6, the amount of exhaust gas flowing into the first expansion chamber 31 of the muffler body 5 is small at low engine speeds. Accordingly, the amount of exhaust gas flowing into the second expansion chamber 33 is also small, and the back pressure in the second expansion chamber 33 is therefore low. When the back pressure in the second expansion chamber 33 is low, most of the exhaust gas is discharged to the outside of the exhaust muffler 1 through the second tail pipe 42.

[0047] However, as in Fig. 7, the amount of exhaust gas flowing into the second expansion chamber 33 is large at high engine speeds, and the back pressure in the second expansion chamber 33 is therefore high. When the back pressure in the second expansion chamber 33 is high, flow resistance acts on the exhaust gas flowing through the second tail pipe 42 due to its small diameter, so that the exhaust gas is difficult to discharge through the second tail pipe 42 to the outside of the exhaust muffler 1. Accordingly, part of the exhaust gas flowing into the second expansion chamber 33 is discharged through the second tail pipe 42 to the outside of the exhaust muffler 1, and another part of the exhaust gas flowing into the second expansion chamber 33 is reversed in flow direction to flow into the third expansion chamber 35 through the second connecting pipe 38 and then discharged through the first tail pipe 41 to the outside of the exhaust muffler 1.

[0048] The inventors measured the engine power in the case where the exhaust muffler 1 (having the two tailpipes 41 and 42) according to this preferred embodiment is mounted on a motorcycle, as well as in the case where a conventional exhaust muffler (having a single tailpipe) is mounted on the motorcycle.

[0049] Fig. Figure 8 is a graph showing the relationship between engine speed and engine power in the above cases. In Fig. 8, the characteristic curve shown by a solid line corresponds to the case where the exhaust silencer 1 according to this preferred embodiment is mounted on the motorcycle, and the characteristic curve shown by a broken line corresponds to the case where the conventional exhaust silencer without a second tail pipe 42 is mounted on the motorcycle.

[0050] When the engine speed is in the low speed range (2000 to 7000 rpm), the engine power in the case where the exhaust muffler 1 according to this preferred embodiment is mounted is substantially the same as in the case where the conventional exhaust muffler is mounted.

[0051] However, when the engine speed is in the high speed range (7000 to 9500 rpm), the engine performance in the case where the exhaust muffler 1 according to this preferred embodiment is mounted becomes better than the engine performance in the case where the conventional exhaust muffler is mounted.

[0052] Fig. Figure 9 is a graph showing the sound pressure of an exhaust tone and its frequency distribution (shown in the lower part of the graph with a histogram). In Fig. 9, the vertical axis represents the sound pressure, the upper horizontal axis represents the frequency, and the lower horizontal axis represents the motor speed.

[0053] In Fig. 9, the solid lines show experimental data for the case where the exhaust muffler 1 according to this preferred embodiment is mounted, and the broken lines show experimental data for the case where a conventional exhaust muffler is mounted.

[0054] The two upper continuous lines (the solid line and the broken line) show changes in the sound pressure of the exhaust tone.

[0055] When the engine speed is in the high-speed range (4000 to 9500 rpm), the sound pressure in the case where the exhaust muffler 1 according to this preferred embodiment is mounted is substantially the same as in the case where the conventional exhaust muffler is mounted. However, when the engine speed is in the low-speed range (1500 to 4000 rpm), the sound pressure in the case where the exhaust muffler 1 according to this preferred embodiment is mounted is slightly higher than in the case where the conventional exhaust muffler is mounted. Regarding the frequency distribution (shown in the lower part of the histogram graph), the sound pressure at frequencies close to 250 Hz is higher in the case where the exhaust muffler 1 according to this preferred embodiment is mounted (solid line) than in the case where the conventional exhaust muffler is mounted (broken line), so the timbre of the exhaust sound is improved.

[0056] If, as in Fig. 7, the back pressure in the second expansion chamber 33 becomes high at high engine speeds, the exhaust gas in the second expansion chamber 33 is difficult to discharge to the outside of the exhaust muffler 1 through the second tail pipe 42 because the flow resistance in the second tail pipe 42 is smaller than that in the second connecting pipe 38. Accordingly, a part of the exhaust gas is reversed in flow direction to flow into the third expansion chamber 35 through the second connecting pipe 38 and is then discharged to the outside of the exhaust muffler 1 through the first tail pipe 41.

[0057] With the configuration of this preferred embodiment, the engine performance in the high-speed range is improved compared to the state of the art, as shown in Fig. 8, and the sound pressure of the exhaust tone in the high engine speed range is substantially the same as in the prior art, as shown in Fig. 9. Thus, in the high engine speed range according to this preferred embodiment, the engine power is increased while maintaining the exhaust sound pressure. Furthermore, the exhaust sound pressure in the low engine speed range is slightly higher than in the prior art, as shown in Fig. 9, thereby improving the timbre of the exhaust sound. The second tail pipe 42 has a larger diameter than the first tail pipe 41, and the difference in inner diameter between the second tail pipe 42 and the second connecting pipe 38 is small. Accordingly, exhaust resistance can be reduced to ensure engine performance.

[0058] Furthermore, the volume of the second expansion chamber 33 is larger than that of the third expansion chamber 35, so that the pressure of the exhaust gas from the second expansion chamber 33 is reduced. Therefore, even if the exhaust gas is directly discharged from the second expansion chamber 33 through the second tail pipe 42 to the outside of the exhaust muffler 1, the exhaust sound can be reduced.

[0059] The sum of the opening area of ​​the first tail pipe 41 and the opening area of ​​the second tail pipe 42 is substantially equal to the opening area of ​​the rear end portion (inlet pipe) 36 of the connecting pipe 33 in the exhaust muffler 1. Accordingly, the timbre of the exhaust sound can be improved in the low engine speed range, and the engine power can also be increased in the high engine speed range.

[0060] Although a particular preferred embodiment of the invention has been described, it is to be understood that the invention is not limited to this preferred embodiment.

[0061] For example, as in Fig. 6 and Fig. 7, the first partition wall 21 may be provided with a small hole 51 to establish communication between the first expansion chamber 31 and the third expansion chamber 35. By forming the small hole 51, the back pressure acting on the second expansion chamber 33 can be finely adjusted.

[0062] Furthermore, while the exhaust muffler 1 has such a structure that the flow direction of the exhaust gas is reversed between the expansion chambers, it is understood that the invention is applicable to a muffler having such a structure where the flow direction of the exhaust gas is not reversed.

[0063] The invention provides an exhaust muffler with a simple structure that can improve the timbre of the exhaust sound in the low engine speed range and can increase the engine power in the high engine speed range.

[0064] In an exhaust device for an internal combustion engine for discharging exhaust gas from the internal combustion engine through a multi-stage expansion muffler (1) having a plurality of expansion chambers (31, 33, 35) for attenuating the sound of the exhaust gas as it passes through, the multi-stage expansion muffler (1) includes a first tail pipe (41) for establishing communication between a downstream side (35) of the expansion chamber (31, 33, 35) and the outside of the muffler (1), and a second tail pipe (42) for establishing communication between an upstream side (33) of the expansion chambers (31, 33, 35) and the upstream side of the downstream side expansion chamber (35) and the outside of the muffler (1).

Claims

[1] An exhaust device for an internal combustion engine for discharging exhaust gas from the internal combustion engine through a multi-stage expansion muffler (1) having a plurality of expansion chambers (31, 33, 35) containing at least one upstream expansion chamber (33) and one downstream expansion chamber (35) for dampening the sound of the exhaust gas during its passage; wherein the multi-stage expansion muffler (1) includes a first tail pipe (41) not connected to the upstream expansion chamber (33) for establishing communication between the downstream expansion chamber (35) and the outside of the muffler (1), and a second tail pipe (42) for establishing communication between the upstream expansion chamber (33) and the outside of the muffler (1), the downstream ends of the first and second tail pipes (41, 42) leading freely to the outside, characterized bythat the opening area of the second tail pipe (42) is larger than the opening area of the first tail pipe (41). [2] An exhaust device for an internal combustion engine according to claim 1, wherein the expansion chambers comprise first, second, and third expansion chambers (31, 33, 35) arranged in the order of exhaust gas passage; the most downstream expansion chamber is the third expansion chamber (35); the most upstream expansion chamber is the second expansion chamber (33); and the volume of the second expansion chamber (33) is larger than the volume of the third expansion chamber (35). [3] An exhaust device for an internal combustion engine according to claim 1 or 2, wherein the third expansion chamber (35) is provided between the first expansion chamber (31) and the second expansion chamber (33), and a small hole (51) for adjusting a back pressure penetrates a partition wall (21) between the first expansion chamber (31) and the third expansion chamber (35). [4] An exhaust device for an internal combustion engine according to any one of claims 1 to 3, wherein the sum of the opening area of the first tail pipe (41) and the opening area of the second tail pipe (42) is substantially equal to the opening area of an inlet pipe (36) of the muffler (1).

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