Muffler for internal combustion engine

Abstract

The muffler (7) comprises an exhaust gas intake pipe (21) which is divided into a main pipe (27) and a secondary pipe (29). The muffler (7) further comprises a muffler body (31). The muffler body (31) defines an expansion volume (33) and at least partially accommodates the main pipe (27) and the secondary pipe (29). A throttle valve (41) is provided in the main pipe (27). A catalytic device (45) is provided in the exhaust gas intake pipe (21). The main pipe (27) comprises a wall (27A) between the catalytic device (45) and the throttle valve (41), and the wall (27A) is provided with a plurality of inlet holes (51) arranged around the axis of the wall. The wall portion (27A) is surrounded by an outer sleeve (53), and the outer sleeve (53) and the wall portion (27) define an annular chamber (57) surrounding the wall portion (27A), the annular chamber (57) being in fluid communication with the primary pipe (27) via the inlet hole (51) and in fluid communication with the secondary pipe (29) via at least one passage provided in the outer sleeve (53).

Description

Technical Field

[0001] The present invention relates to an improvement of a muffler for an internal combustion engine, particularly a muffler used in a vehicle with a prime mover. More specifically, the embodiments disclosed herein relate to a muffler provided with a catalytic device.

Background Art

[0002] The use of a muffler (silencer) is known to reduce the emission of sound, i.e., the noise caused by an internal combustion engine and the exhaust gas it generates. Here, the exhaust gas passes through a pipe by reflection, i.e., by appropriately lengthening the path through which the exhaust gas passes, and / or absorption, i.e., by bringing the exhaust gas flowing through the muffler into contact with a sound-absorbing material such as glass wool, before being discharged into the atmosphere.

[0003] As is well known, in the field of vehicles with a prime mover, regulations regarding the emission of sound, i.e., the noise caused by the vehicle, are established. These regulations are particularly aimed at reducing noise pollution in urban areas, and usually, the engine is operated at a low speed and limited output. The values defined by the regulations simulate the daily usage situation when the internal combustion engine is not used at maximum output.

[0004] For this reason, a muffler provided with a throttle valve that operates based on the rotational speed of the engine is known to allow the gas to pass through a pipe with an appropriate cross-sectional area before discharging it into the atmosphere.

[0005] WO 2018 / 083650 describes a muffler having an intake pipe for exhaust gas. The intake pipe is separated into a main pipe and a secondary pipe at a branch portion. The main pipe is completely or partially closed by an on-off valve as a function of the engine speed. At low speeds, the exhaust gas is forced to pass through the secondary pipe. The main pipe and the secondary pipe are at least partially accommodated in a muffler body that defines an expansion volume. The main pipe has a distal end that defines an outlet for discharging the exhaust gas into the atmosphere. At high speeds, the valve is open and the exhaust gas mainly flows through the main pipe and only slightly through the secondary pipe.

[0006] The secondary pipe is configured such that the exhaust gas flowing through it cannot directly exit into the atmosphere forward from the secondary pipe and must pass through a tortuous path connecting the secondary pipe and the main pipe within the expansion volume partitioned by the muffler body that houses the main pipe and the secondary pipe.

[0007] The purpose of this arrangement is that when the engine is operating at low speed, the low flow rate of the exhaust gas flows through the secondary pipe and the main pipe downstream thereof, and the emission of noise is further reduced. In this way, the muffler can more efficiently reduce noise in the low-speed state of the engine, that is, under conditions where the regulation regarding the emission of noise is more severely restricted. Conversely, in the high-speed state and high-output state of the engine, the valve is open and the exhaust gas flows out mainly through the main pipe with low resistance and low pressure loss. In this case, the effect of noise reduction is small, but this is not a drawback because a higher level of noise emission is permitted by regulation in the high-speed state and high-output state.

[0008] The muffler described in WO 2018 / 083650 is very efficient, but there are also points that can be further improved.

[0009] In particular, the branch portion that divides the intake pipe into a main pipe and a sub-pipe is arranged close to the catalytic device for spatial reasons. Therefore, when the throttle valve is closed and the exhaust gas stops flowing through the main pipe, the flow rate of the exhaust gas becomes non-uniform within the catalytic device. In particular, the exhaust gas mainly flows through the catalytic device in the inner volume disposed opposite the mouth of the sub-pipe where the pressure loss of the gas flow is lower.

[0010] This involves non-uniform and inefficient use of the catalytic device.

[0011] In particular, when a vehicle with an engine equipped with a muffler travels at a low speed for a long time (typically a long-distance travel in an urban area), the materials inside the catalytic device essentially wear unevenly. Therefore, even if only a part of the internal material volume is utilized, it is necessary to replace the catalytic device.

[0012] As is well known, the function of the catalytic device is to reduce the harmful emissions of exhaust gas by promoting the complete oxidation and reduction of the exhaust gas. Therefore, the catalytic device has a main body, and hundreds of small channels are provided inside it, and precious metals such as palladium, platinum, and rhodium are applied to its walls to catalyze oxidation and reduction. Since these metals are very expensive, it is important to utilize the internal volume of the catalytic device efficiently and uniformly in order to avoid early replacement of the catalytic device.

Summary of the Invention

Problems to be Solved by the Invention

[0013] Therefore, there is a need to improve the muffler by at least partially overcoming the drawbacks of the prior art muffler.

Means for Solving the Problems

[0014] According to one aspect, a muffler for an internal combustion engine is provided. The muffler includes an intake pipe for exhaust gas that separates into a main pipe and a sub-pipe at a branch portion. The muffler also includes a muffler body that defines an expansion volume and at least partially houses the main pipe and the sub-pipe. The sub-pipe is disposed on the opposite side of the branch portion and has a distal end that ends within the expansion volume. The main pipe is disposed on the opposite side of the branch portion and has a distal end that forms an exhaust gas outlet that ends outside the expansion volume for discharging exhaust gas. A throttle valve is provided within the main pipe. The throttle valve is preferably disposed downstream of the branch portion with respect to the flow direction of the exhaust gas. The throttle valve is selectively adapted to allow or block the entry of exhaust gas into the main pipe based on the engine speed. The muffler also includes a catalytic device provided within the intake pipe for exhaust gas between the intake port and the branch portion.

[0015] To reduce the drawbacks of prior art mufflers, the main pipe includes a wall portion disposed between the catalytic device and the throttle valve. The wall portion is provided with a plurality of inlet holes disposed around the axis of the wall portion. The wall portion is also surrounded by an outer sleeve. The wall portion and the outer sleeve define an annular chamber surrounding the wall portion. The annular chamber is in fluid communication with the main pipe through the inlet holes and is in fluid communication with the sub-pipe through at least one path provided in the outer sleeve. In some embodiments, the annular chamber is in fluid communication with the sub-pipe through a plurality of paths provided in the outer sleeve.

[0016] With this arrangement, when the throttle valve is closed during use, the exhaust gas flows from the catalytic device into the sub-pipe through the annular chamber. The presence of the annular chamber and the plurality of inlet holes provided in the wall of the main pipe enables optimization of the flow of exhaust gas within the catalytic device even if the main pipe is closed or partially closed. Due to the plurality of inlet holes disposed around the axis of the main pipe, even if the main pipe is closed or partially closed, the exhaust gas can flow across the entire cross-section of the catalytic device rather than passing through only a portion of it.

[0017] Essentially, even when the catalytic device is arranged near the branch portion, a plurality of inlet holes and an annular chamber that receives the exhaust gas from the inlet holes and conveys it toward the sub-pipe optimize the flow of the exhaust gas in the catalytic device at low speeds. Typically, the presence of the inlet holes and the annular chamber connecting the inlet holes and the sub-pipe enables a sufficiently uniform flow distribution of the exhaust gas in the catalytic device at low speeds even when the exhaust opening of the catalytic device is separated from the branch portion by a distance shorter than four times the maximum lateral dimension of the useful passage of the catalytic device. In particular, it has been found that the flow of the exhaust gas flows sufficiently uniformly throughout the cross-section of the catalytic device even when the outlet of the exhaust gas from the catalytic device is at a very short distance from the branch portion, typically equal to or shorter than twice the maximum lateral dimension of the path portion of the catalytic device. By arranging the inlet holes circularly around the axis of the main pipe on the downstream side of the exhaust opening of the catalytic device, the flow of the exhaust gas can be made sufficiently uniform throughout the cross-section of the catalytic device even if the outlet is separated from the path leading to the sub-pipe by a distance equal to or shorter than, for example, the maximum dimension of the cross-section of the catalytic device, particularly the exhaust opening of the catalytic device.

[0018] In this way, a muffler having a silencer and a catalytic device can be provided. Here, the exhaust opening of the catalytic device is arranged at a distance shorter than three times the maximum dimension of the cross-section of the catalytic device from the throttle valve, preferably shorter than twice the maximum dimension of the cross-section of the catalytic device, more preferably equal to or shorter than the maximum dimension of the cross-section of the catalytic device.

[0019] Also, in the embodiments described herein, the distance between the exhaust opening of the catalytic device and the branch portion, i.e., the intake port of the sub-pipe, is equal to or shorter than three times the maximum dimension of the cross-section of the catalytic device, preferably equal to or shorter than twice the maximum dimension of the cross-section of the catalytic device, more preferably equal to or shorter than once the maximum dimension of the cross-section of the catalytic device.

[0020] When the catalytic device has a circular cross-section, the maximum dimension of the cross-section described above corresponds to the diameter. However, this cross-section can be non-circular, for example, elliptical. In this case, the maximum lateral dimension corresponds to the major axis of the ellipse.

[0021] In the embodiments described in this specification, a connection path for connecting the sub-pipe and the main pipe is provided inside the muffler body. Through the connection path, the exhaust gas can flow from the sub-pipe into the main pipe.

[0022] In an advantageous embodiment, in order to achieve a particularly effective distribution of the exhaust gas flow across the entire cross-section of the catalytic device, the inlet holes are arranged around the axis of the wall portion at a substantially constant distance from each other or at a substantially constant angular pitch.

[0023] In order to achieve a uniform distribution of the exhaust gas flow, i.e., a highly efficient and uniform utilization of the materials within the catalytic device, the inlet holes are configured and arranged such that, for example, when the throttle valve is at least partially closed during use, the exhaust gas flows through the entire cross-section of the catalytic device, preferably with a substantially constant volumetric flow rate at each point of the cross-section of the catalytic device. The inlet holes are configured and arranged such that, for example, when the throttle valve is closed during use, the exhaust gas flow is substantially constant across the entire useful cross-section of the catalytic device.

[0024] In some embodiments, each inlet hole is configured to define a respective path between the exhaust opening of the catalytic device and the sub-pipe. Here, during use, the exhaust gas has a substantially equal pressure drop in each path.

[0025] In some embodiments, each inlet hole preferably has a cross-sectional area that varies according to the distance between the inlet hole and the path formed in the outer sleeve that forms the connection between the annular chamber and the sub-pipe. More specifically, the cross-sectional area of the inlet hole increases as the distance between the inlet hole and the path increases. In this way, for example, the inlet holes closer to the path connecting the annular chamber and the sub-pipe have a smaller cross-sectional area than the adjacent inlet holes. The inlet holes closer to the sub-pipe and farther from the path have the largest cross-sectional area.

[0026] In this way, the increase in the pressure drop that occurs between a specific inlet hole and the path from the annular chamber to the auxiliary pipe due to the increase in distance is balanced by the decrease in the pressure drop concentrated on the cross-section of the inlet hole.

[0027] The effect of making the velocity and flow rate of the exhaust gas uniform in the cross-section of the path of the catalytic device increases as the number of inlet holes increases. Therefore, at least 4, preferably 6, more preferably 8 inlet holes can be provided. However, in order to make the flow of the exhaust gas in the catalytic device even more uniform, it is also possible to provide a larger number of inlet holes. The number of inlet holes can be varied based on the cross-sectional area of the inlet holes. In particular, the smaller the inlet hole, the larger the number. Considering that the larger the number of inlet holes (i.e., the smaller their dimensions) the higher the pressure drop when the total area of the inlet holes is the same, in some embodiments, a limited number of inlet holes having a non-circular cross-section with a large tangential dimension may be used to make the flow of the exhaust gas in the cross-section of the catalytic device more uniform.

[0028] According to a further aspect, a unit is provided that has an internal combustion engine and a muffler as described above. The unit can in particular be a propulsion unit of a motor vehicle with a prime mover.

[0029] A further object of the present invention is to provide an inclined saddle-riding motor vehicle with a prime mover having two, three, or four wheels, such as a scooter or a motorcycle, in particular equipped with an internal combustion engine and a muffler as described above, but not limited thereto.

Brief Description of the Drawings

[0030] The present invention will become clear from the following detailed description and the drawings related to non-limiting embodiments of the present invention.

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0031] In FIG. 1, as an exemplary embodiment of a motor vehicle using the muffler according to the present invention, a motorcycle 1 is schematically shown. The motorcycle 1 has a frame 3 on which an internal combustion engine 5 is mounted. Its exhaust port is connected to the muffler 7 via a manifold 9. The saddle of the motorcycle is indicated by reference numeral 11, the handlebar by reference numeral 13, the front wheel by reference numeral 15, and the rear wheel by reference numeral 16. Note that it should be noted that the motor vehicle illustrated here is only one of the motor vehicles having an internal combustion engine to which the muffler 7 of the present invention can be connected.

[0032] FIG. 2 is a side view and partial cross-sectional view of the muffler 7 according to one embodiment. The muffler 7 includes an intake pipe 21 for exhaust gas having an intake port 23 for exhaust gas adapted to be in fluid communication with the internal combustion engine 5. In the embodiment shown in the figure, the intake port 23 for exhaust gas is connected to the manifold 9. The intake pipe 21 for exhaust gas separates into a main pipe 27 and a sub-pipe 29 at a branch portion 25.

[0033] The main pipe 27 and the sub-pipe 29 extend within the muffler body 31. The muffler body 31 defines an expansion volume 33 for exhaust gas and at least partially houses the main pipe 27 and the sub-pipe 29.

[0034] In the embodiment shown in FIG. 2, the auxiliary pipe 29 has a proximal end 29.1 provided at the branch portion 25 and a distal end 29.2 disposed on the opposite side of the branch portion 25 and ending at an expansion volume 33 formed within the muffler body 31. In a practical embodiment, the distal end 29.1 of the auxiliary pipe 29 is provided within the expansion volume 33, i.e., within the muffler body 31. Therefore, the auxiliary pipe 29 is not in direct fluid communication with the environment outside the muffler body 31. This can increase the effect of reducing the emission of noise from the engine to which the muffler is applied when the exhaust gas is passed through the auxiliary pipe 29 and the passage of the main pipe 27 is blocked.

[0035] Therefore, in the embodiment shown in the figure, at the distal end 29.2, the auxiliary pipe 29 is closed at the front portion 29.3. At least a part of the tubular wall defining the auxiliary pipe 29 has an exhaust gas outlet port 29.4 so that the exhaust gas can flow from the auxiliary pipe 29 into the expansion volume 33. The outlet port 29.4 puts the interior of the auxiliary pipe 29 and the expansion volume 33 in fluid communication. In the embodiment shown in the figure, the outlet port 29.4 is provided at a portion close to the distal end 29.2 of the auxiliary pipe 29.

[0036] The main pipe 27 has a proximal end 27.1 provided at the branch portion 25 and a distal end 27.2 on the opposite side of the branch portion. The distal end 27.2 forms an exhaust gas outlet 27.3 that ends outside the expansion volume 33 and the muffler body 31, and discharges the exhaust gas to the atmosphere.

[0037] The main pipe 27 has a plurality of ports 27.4 and 27.5 in at least a part of it that extends within the muffler body 31. These ports put the interior of the main pipe 27 and the expansion volume 33 in fluid communication.

[0038] In the embodiment shown in the figure, the expansion volume 33 is divided into two sub-volumes by the intermediate partition 35. Port 27.4 fluidly communicates the inside of the main pipe 27 with the sub-volume further upstream, and port 27.5 fluidly communicates the inside of the main pipe 27 with the sub-volume further downstream in the flow direction of the exhaust gas indicated by arrows F, F1, and F2.

[0039] Inside the muffler body 31, additional components such as, for example, a substantially cylindrical wall 37 extending around the substantially cylindrical main pipe 27 and auxiliary pipe 29, and a further cylindrical wall 39 extending around the auxiliary pipe 29 may be provided. Reference numerals 37.1 and 39.1 respectively indicate communication ports provided through the cylindrical walls 37 and 39.

[0040] The various ports and walls inside the muffler body 31 define a path for the exhaust gas from the inside of the auxiliary pipe 29 to the inside of the main pipe 27. Note that it should be noted that the specific structure included inside the muffler body 31 can vary significantly more than those described above. In the embodiment shown in the figure, a path is provided for the exhaust gas from the inside of the auxiliary pipe 29 through port 29.4, port 39.1, and port 27.5.

[0041] However, the internal structure of the muffler body 31 shown in the accompanying drawings is shown merely as a non-limiting example. That is, the muffler body 31 and its internal components can have different shapes while always maintaining the functions of the main pipe 27 and the auxiliary pipe 29 detailed below.

[0042] Regardless of the specific internal shape of the muffler body 31, the exhaust gas flowing in the auxiliary pipe 29 can exit through the distal end 27.2 by the paths provided inside the auxiliary pipe 29 and the main pipe 27.

[0043] At least a part of the expansion volume 33 defined inside the muffler body 31 is filled with rock wool or other sound-absorbing materials. This reduces the noise emission of the muffler 7 during use.

[0044] Furthermore, the muffler 7 includes a throttle valve 41 provided in the main pipe 27. The throttle valve 41 is selectively adapted to allow or block the exhaust gas from entering the main pipe 27. In the illustrated embodiment, the throttle valve 41 is controlled to rotate about a rotation axis 41A perpendicular to the plane of FIG. 2, and by performing a rotational movement in the direction indicated by the bidirectional arrow f41, the main pipe 27 is opened and closed.

[0045] The throttle valve 41 is appropriately provided in the main pipe 27 at or downstream of the branch portion 25.

[0046] For example, as described in International Publication No. 2018 / 083650, the throttle valve 41 is controlled in a known manner according to the operating conditions of the engine 5. Generally, as a non-limiting example, in order to change the exhaust gas path as described later, when the engine 5 exceeds a given rotational speed, the throttle valve 41 is opened, and when the engine 5 is below the given rotational speed, the throttle valve 41 is closed.

[0047] The muffler 1 includes a catalyst device 45 provided in the intake pipe 21 for exhaust gas between the intake port 23 and the branch portion 25. Generally, the catalyst device may preferably have a cylindrical shape with a circular cross-section, and has an intake opening 45.1 facing the intake port 23 of the intake pipe 21 and an exhaust opening 45.2 facing the branch portion 25 and the throttle valve 41.

[0048] In order to make the muffler 7 compact, the catalytic device 45 is provided in the vicinity of the branch portion 25 and the throttle valve 41. Preferably, the distance between the exhaust opening 45.2 of the catalytic device and the branch portion 25 is equal to or shorter than three times the diameter of the cross-section 45 of the useful catalytic device. The useful cross-section 45 of the catalytic device is the cross-section through which the exhaust gas can pass. When the useful cross-section 45 of the catalytic device does not have a circular shape, the distance between the exhaust opening 45.2 of the catalytic device 45 and the branch portion 25 is equal to or shorter than three times the maximum dimension of the cross-section. For example, when the cross-section is elliptical, the maximum dimension corresponds to the major axis of the ellipse. Preferably, the distance between the exhaust opening 45.2 of the catalytic device 45 and the branch portion 25 is equal to or shorter than twice the maximum dimension of the cross-section. In the embodiment shown in the figure, this distance is shorter than the maximum lateral dimension (i.e., diameter) of the catalytic device 45.

[0049] In the region of the branch portion 25 between the catalytic device 45 and the throttle valve 41, the main pipe 27 includes a wall portion 27A provided with a plurality of inlet holes 51 arranged around the axis of the wall portion 27A. In the embodiment shown in the figure, the wall portion 27A has a substantially conical shape with a top portion having a tapered shape from the intake end facing the catalytic device 45 to the outlet end facing the throttle valve 41 and the top being cut flat.

[0050] The wall portion 27A of the main pipe 27 is surrounded by an outer sleeve 53. The wall portion 27A of the main pipe 27 and the outer sleeve 53 form an annular chamber 57 surrounding the wall portion 27A of the main pipe 27.

[0051] The annular chamber 57 is in fluid communication with the main pipe 27 via the inlet holes 51 and is in fluid communication with the auxiliary pipe 29 via at least one path 59 provided in the outer sleeve 53. In the embodiment shown in the figure, only the path 59 is provided to put the annular chamber 57 and the auxiliary pipe 29 in fluid communication, but more paths 59 can be provided to put the annular chamber 57 and the auxiliary pipe 29 in fluid communication.

[0052] As shown in FIG. 2, the path 59 has a point of the shortest distance from the exhaust opening 45.2 of the catalytic device 45. The line P-P is orthogonal to the axis of the main pipe 27 and indicates the locus of a plane passing through a point close to the exhaust opening 45.2 of the catalytic device 45 in the path 59. DI indicates the distance between the plane P-P and the center of the exhaust opening 45.2 of the catalytic device 45. In fact, the distance DI is the distance between the exhaust opening 45.2 of the catalytic device 45 and the branch portion 25.

[0053] Preferably, the distance DI is equal to or shorter than three times the maximum dimension D2 of the useful cross-section 45 of the catalytic device, and preferably equal to or shorter than twice the maximum dimension D2. In the illustrated embodiment, the distance DI is shorter than the maximum dimension D2 of the cross-section 45 of the catalytic device.

[0054] When the catalytic device 45 has a varying cross-section, the above-described size ratio refers to the useful cross-section of the catalytic device.

[0055] The above-described size ratio substantially indicates that the catalytic device 45 is substantially in the vicinity of the branch portion 25. Here, when no specific solution is adopted, the catalytic device 45 is separated from the branch portion 25 such that a specific flow state occurs inside the catalytic device 45 when the main pipe 27 is closed. In this flow state, since there is no pipe of sufficient length to ensure a substantially uniform velocity field across the entire cross-section 45 of the catalytic device, the exhaust gas flows only in a part of the internal volume of the catalytic device.

[0056] In the prior art device, in order to avoid this drawback that results in non-uniform and incomplete utilization of the material inside the catalytic device, the annular chamber 57 is provided with an inlet hole 51 that fluidly connects the annular chamber 57 to the main pipe 27 and the catalytic device 45.

[0057] The operation of the muffler 7 described above is as follows. When the engine 5 rotates at high speed, i.e., at a high rotational speed, the throttle valve 41 opens. The exhaust gas flows directly into the muffler body 31 along the main pipe 27 and exits from the outlet 27.3. The minimum portion of the exhaust gas can pass through the inlet hole 51 and the annular chamber 57, flow into the sub-pipe 29, and then flow into the main pipe 27 through the expansion volume 33. Since the pressure drop along this path is significantly greater than the pressure drop along the main pipe 27, only the minimum portion of the exhaust gas flow passes through the inlet hole 51.

[0058] The velocity field of the exhaust gas passing through the catalytic device 45 is substantially uniform throughout its cross-section.

[0059] When the engine 5 rotates at low speed, i.e., at a low rotational speed, the throttle valve 41 is closed and the exhaust gas cannot flow into the main pipe 27. Therefore, the exhaust gas flows through the inlet hole 51, the annular chamber 57, the path 59, the sub-pipe 29, and the path between the sub-pipe 29 and the main pipe 27 inside the expansion volume 33, and finally exits from the outlet 27.3.

[0060] Between the exhaust opening 45.2 of the catalytic device 45 and the path 59 leading to the sub-pipe 29, the exhaust gas is corrected to flow through a plurality of inlet holes 51. As a result, the velocity field of the exhaust gas becomes substantially uniform throughout the useful cross-section 45 of the catalytic device and does not concentrate in the region before the path 59.

[0061] This result can be further improved by determining the dimensions of the inlet holes 51 such that the pressure drop that occurs when the exhaust gas flows through the inlet holes 51 is not equal for each inlet hole, but decreases as the distance from the path 59 increases. The inlet holes 51 that are far from the opening of the path 59, i.e., the sub-pipe 29, can have a larger cross-section than the inlet holes close to the path 59. This can balance the pressure drops caused by the different lengths of the paths between each inlet hole 51 and the path 59.

[0062] Preferably, the inlet holes 51 are distributed at a constant pitch, i.e., spaced apart from each other by a constant distance on the wall portion 27A, or at a constant angular pitch around the axis of the wall portion 27A of the main pipe 27.

[0063] With only three or four inlet holes 51, the uniformity of the exhaust gas flow through the catalyst device 45 when the throttle valve 41 is closed can be improved. However, by increasing the number of inlet holes 51, the velocity field of the exhaust gas flow in the catalyst device can be made more uniform. By setting the number of inlet holes 51 to six or more, preferably eight or more, for example ten or more, the flow state in the catalyst device can be significantly improved.

Claims

1. A muffler (7) for an internal combustion engine, an intake pipe (21) for exhaust gas having an intake port (23) for exhaust gas adapted to be in fluid communication with the internal combustion engine (5), wherein at a branch portion (25), the intake pipe (21) for exhaust gas separates into a main pipe (27) and a sub-pipe (29), a muffler body (31) defining an expansion volume (33) and at least partially accommodating the main pipe (27) and the sub-pipe (29), - the sub-pipe (29) is arranged on the opposite side of the branch portion (25) and has a distal end (29.2) that ends within the expansion volume (33), - the main pipe (27) is arranged on the opposite side of the branch portion (25) and has a distal end (27.2) that forms an exhaust gas outlet (27.3) for discharging exhaust gas outside the expansion volume (33), the muffler body (31); a throttle valve (41) provided in the main pipe (27) and selectively adapted to allow or block the exhaust gas from entering the main pipe (27), a catalytic device (45) provided in the intake pipe (21) for exhaust gas between the intake port (23) and the branch portion (25), comprising the main pipe (27) includes a wall portion (27A) between the catalytic device (45) and the throttle valve (41), the wall portion (27A) is provided with a plurality of inlet holes (51) arranged around the axis of the wall portion, the wall portion (27A) is surrounded by an outer sleeve (53), the outer sleeve (53) and the wall portion (27A) define an annular chamber (57) surrounding the wall portion (27A), the annular chamber (57) is in fluid communication with the main pipe (27) through the inlet holes (51) and is in fluid communication with the sub-pipe (29) through at least one path provided in the outer sleeve (53), muffler (7).

2. The muffler (7) according to claim 1, further comprising a connection path between the sub-pipe (29) and the main pipe (27) within the muffler body (31), the connection path being adapted to allow the exhaust gas to flow from the sub-pipe (29) into the main pipe (27).

3. The muffler (7) according to claim 1, wherein the inlet holes (51) are spaced apart from each other around the axis of the wall portion (27A) at a constant distance or a constant angular pitch.

4. The muffler (7) according to claim 2, wherein the inlet holes (51) are provided at regular intervals or at a regular angular pitch around the axis of the wall portion (27A).

5. The muffler (7) according to claim 1, wherein the wall portion (27A) has a tapered shape from the intake end facing the catalytic device (45) to the outlet end facing the throttle valve (41).

6. The muffler (7) according to any one of claims 2 or 3, wherein the wall portion (27A) has a tapered shape from the intake end facing the catalytic device (45) to the outlet end facing the throttle valve (41).

7. The catalytic device (45) has an intake opening (45.1) and an exhaust opening (45.2) for the exhaust gas, and the exhaust opening (45.2) of the catalytic device is provided at a distance shorter than 4 times the maximum dimension (D2) of the cross-section of the catalytic device, preferably at a distance shorter than 3 times the maximum dimension (D2) of the cross-section of the catalytic device, from the throttle valve (41). The muffler (7) according to any one of claims 1 to 5.

8. The catalytic device (45) has an intake opening (45.1) and an exhaust opening (45.2) for the exhaust gas, and the exhaust opening (45.2) of the catalytic device is provided at a distance shorter than 3 times the maximum dimension (D2) of the cross-section of the catalytic device, preferably at a distance shorter than 2 times the maximum dimension (D2) of the cross-section of the catalytic device, more preferably at a distance equal to or shorter than the maximum dimension (D2) of the cross-section of the catalytic device, from the branch portion (25). The muffler (7) according to any one of claims 1 to 5.

9. The inlet holes (51) are configured and arranged such that when the throttle valve (41) is at least partially closed during use, the exhaust gas flows through the entire cross-section of the catalytic device (45), preferably such that the exhaust gas flows at a substantially constant volumetric flow rate at each point in the cross-section of the catalytic device. The muffler (7) according to any one of claims 1 to 5.

10. The inlet holes (51) are configured and arranged such that when the throttle valve (41) is closed during use, the flow of the exhaust gas becomes substantially constant throughout the useful cross-section of the catalytic device. The muffler (7) according to any one of claims 1 to 5.

11. The inlet holes (51) are each configured to define a respective path between the exhaust opening (45.2) of the catalytic device (45) and the auxiliary pipe (29), and during use, the exhaust gas undergoes a substantially equal pressure drop in each of the paths. The muffler (7) according to any one of claims 1 to 5.

12. Each of the inlet holes (51) has a cross-sectional area that varies as a function of the distance between the inlet hole (51) and the at least one path provided in the outer sleeve adjacent thereto, and the cross-sectional area increases as the distance increases. The muffler (7) according to any one of claims 1 to 5.

13. The muffler (7) according to any one of claims 1 to 5, having at least 4, preferably at least 6, more preferably at least 8 inlet holes (51).

14. A vehicle with a prime mover (1) comprising an internal combustion engine (5) and the muffler (7) according to any one of claims 1 to 5 in fluid communication with the exhaust portion of the internal combustion engine (5).

15. The vehicle with a prime mover (1) according to claim 14, which is a saddle-type vehicle.

Images