DESC:

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

EXHAUST PIPE STRUCTURE FOR AN INTERNAL COMBUSTION ENGINE

HERO MOTOCORP LIMITED, an Indian Company at: The Grand Plaza, Plot No.2, Nelson Mandela Road, Vasant Kunj- Phase -II, New Delhi, India, 110 070

THEFOLLOWINGSPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION:
[001] The present invention relates to an exhaust muffler for an internal combustion engine used in a vehicle.

BACKGROUND OF THE INVENTION:
[002] An exhaust muffler is a device for reducing the exhaust noise of the exhaust gas emitted by the vehicle and lowers the exhaust noise by lowering the temperature and pressure of the exhaust gas. Typically, an exhaust muffler defines an interior space which is partitioned into a plurality of chambers by one or more separators in order to increase the attenuation effect.

[003] However, in certain cases, it is desired to provide an exhaust muffler for controlling a quality of the exhaust noise (which is dependent upon factors of the engine such as the capacity of the engine, engine rotational speed, etc.). In particular, it is desired to control the quality of the exhaust noise without substantially affecting the performance of engine and the size of the exhaust muffler.

[004] Additionally, in certain instances, it is desired to provide an exhaust muffler that increases the exhaust noise to provide a distinctive sound effect (producing a booming effect). In particular, it is desired to increase the intensity of distinctive sound without substantially affecting the performance of engine and the size of the exhaust muffler.

SUMMARY OF THE INVENTION:
[005] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features.

[006] In one aspect of the invention, there is provided an exhaust muffler of a vehicle, the exhaust muffler comprising: an outer wall, a first end wall, and a second end wall defining an internal space; at least a first separator located between the first end wall and the second end wall thereby dividing the internal space into at least a first chamber, and a second chamber; an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for releasing exhaust gas from the second chamber into the atmosphere; at least a first inter-chamber communication pipe communicating a first part of the exhaust gas from the first chamber to the second chamber; and an aperture provided in the first separator for communicating a second part of the exhaust gas from the first chamber to the second chamber.

[007] In an embodiment of the invention, the exhaust muffler being a two-chamber exhaust muffler. In another embodiment of the invention, the first part of the exhaust gas as coming from the first inter-chamber communication pipe mixes with the second part of the exhaust gas as coming from the aperture provided in the first separator in a mixing zone.

[008] In yet another embodiment of the invention, at least one characteristic of a sound waves generated by the exhaust gas selected from a group comprising wavelength, loudness, and velocity is modified in the mixing zone. In a furthermore embodiment of the invention, the mixing zone being located between the inlet pipe and an entry portion of the outlet pipe.

[009] In a further embodiment of the invention, the mixing zone being located within the second chamber and defined between the aperture and an entry portion of the outlet pipe. In a furthermore embodiment of the invention, the mixing zone being located within the second chamber and within a predetermined distance (L) from an entry portion of the outlet pipe.

[0010] In an embodiment of the invention, the mixing zone being located within the second chamber and within a predetermined radial distance (R) from an axis of the outlet pipe.

[0011] In another embodiment of the invention, the entry portion of the outlet pipe is positioned with respect to an exit portion of the first inter-chamber communication pipe such that the first part of the exhaust gas takes a tortuous path there-between.

[0012] In yet another embodiment of the invention, the tortuous path comprises at least one bend.

[0013] In still another embodiment of the invention, the exhaust gas undergoes an expansion in the first chamber before reaching an entry portion of the first inter-chamber communicating pipe and/or the aperture in the first separator; and the exhaust gas undergoes an expansion and a compression in the second chamber before reaching an entry portion of the outlet pipe.

[0014] In a further embodiment of the invention, the outlet pipe comprises perforations such that the first part of the exhaust gas gets bifurcated into a third part of the exhaust gas and a fourth part of the exhaust gas; the second part of the exhaust gas mixes with the third part of the exhaust gas in the mixing zone and enters the outlet pipe via the entry portion and the fourth part of the exhaust gas enters the outlet pipe via the perforations.

[0015] In another aspect of the invention, there is provided a saddle type vehicle, comprising: a single cylinder engine unit emitting exhaust gas; and an exhaust muffler attached to the engine and being adapted to reduce the exhaust noise of the exhaust gas. In an embodiment of the invention, the exhaust muffler comprising: an outer wall, a first end wall, and a second end wall defining an internal space; at least a first separator located between the first end wall and the second end wall thereby dividing the internal space into at least a first chamber, and a second chamber; an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for releasing exhaust gas from the second chamber into the atmosphere; at least a first inter-chamber communication pipe communicating a first part of the exhaust gas from the first chamber to the second chamber; and an aperture provided in the first separator for communicating a second part of the exhaust gas from the first chamber to the second chamber.

[0016] In yet another aspect of the invention, there is provided an exhaust muffler of a vehicle, the exhaust muffler being a three chamber muffler pipe and comprising: an outer wall, a first end wall, and a second end wall defining an internal space; a first separator and a second separator located between the first end wall and the second end wall so as to divide the internal space into a first chamber, a second chamber and a third chamber; an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for releasing exhaust gas from the second chamber into the atmosphere; a first inter-chamber communication pipe communicating a first part of the exhaust gas from the first chamber to the third chamber; a second inter-chamber communication pipe communicating the first part of the exhaust gas from the third chamber to the second chamber; and an aperture provided in the first separator for communicating a second part of the exhaust gas from the first chamber to the second chamber.

[0017] In an embodiment of the invention, the first part of the exhaust gas as coming from the second inter-chamber communication pipe mixes with the second part of the exhaust gas as coming from the aperture in a mixing zone; and at least one characteristic of a sound waves generated by the exhaust gas selected from a group comprising wavelength, loudness, and velocity is modified in the mixing zone.

[0018] In another embodiment of the invention, the mixing zone being located within the second chamber and defined between the aperture and an entry portion of the outlet pipe.

[0019] In yet embodiment of the invention, the second inter-chamber communication pipe comprises an entry portion positioned with respect to an exit portion of the first inter-chamber communication pipe such that the first part of the exhaust gas takes a first tortuous path there-between. In still embodiment of the invention, an entry portion of the outlet pipe is positioned with respect to an exit portion of the second inter-chamber communication pipe such that the first part of the exhaust gas takes a second tortuous path there-between.

[0020] In a further embodiment of the invention, the first tortuous path comprises at least one bend. In a furthermore embodiment of the invention, the second tortuous path comprises at least one bend.

[0021] In an embodiment of the invention, the exhaust gas undergoes an expansion in the first chamber before reaching an entry portion of the first inter-chamber communicating pipe and/or the aperture in the first separator; and the exhaust gas undergoes an expansion and a compression in the third chamber before reaching an entry portion of the second inter-chamber communicating pipe; and the exhaust gas undergoes an expansion and a compression in the second chamber before reaching an entry portion of the outlet pipe.

[0022] In another embodiment of the invention, the outlet pipe for removing exhaust gas from the second chamber comprises perforations. In yet another embodiment of the invention, the outlet pipe located in the third chamber comprises perforations.

[0023] In still another embodiment of the invention, the outlet pipe located in the second chamber comprises perforations. In a further embodiment of the invention, the aperture and an entry portion of the outlet pipe overlap each other with respect to the axis of the outlet pipe. In another embodiment of the invention, the aperture and an entry portion of the outlet pipe overlap by at least 20% with respect to the axis of the outlet pipe.

[0024] In still another aspect of the invention, there is provided a saddle type vehicle, comprising: a single cylinder engine unit emitting exhaust gas; and an exhaust muffler attached to the engine and being adapted to reduce the exhaust noise of the exhaust gas. In an embodiment of the invention, the exhaust muffler comprising: an outer wall, a first end wall, and a second end wall defining an internal space; a first separator and a second separator located between the first end wall and the second end wall so as to divide the internal space into a first chamber, a second chamber and a third chamber ;an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for releasing exhaust gas from the second chamber into the atmosphere; a first inter-chamber communication pipe communicating a first part of the exhaust gas from the first chamber to the third chamber; a second inter-chamber communication pipe communicating the first part of the exhaust gas from the third chamber to the second chamber; and an aperture provided in the first separator for communicating a second part of the exhaust gas from the first chamber to the second chamber.

[0025] In a further aspect of the invention, there is provided an exhaust muffler of a vehicle, the exhaust muffler comprising: an outer wall, a first end wall, and a second end wall defining an internal space; at least a first separator located between the first end wall and the second end wall thereby dividing the internal space into at least a first chamber, and a second chamber; an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for releasing exhaust gas from the second chamber into the atmosphere, the outlet pipe comprising an entry port and perforations for allowing the exhaust gas to enter into the outlet pipe from the second chamber; and at least a first inter-chamber communication pipe communicating the exhaust gas from the first chamber to the second chamber, the first inter-chamber communication pipe comprising a first exit portion allowing exit of the exhaust gas along a direction parallel to an axis of the first inter-chamber communication pipe.

[0026] In an embodiment of the invention, the exhaust muffler being at least one of a two-chamber exhaust muffler and a three chamber exhaust muffler.

[0027] In another embodiment of the invention, the three chamber exhaust muffler comprises: a first separator and a second separator located between the first end wall and the second end wall so as to divide the internal space into a first chamber, a second chamber and a third chamber; a first inter-chamber communication pipe communicating the exhaust gas from the first chamber to the third chamber; a second inter-chamber communication pipe communicating the exhaust gas from the third chamber to the second chamber.

[0028] In one more embodiment of the invention, the first inter-chamber communication pipe comprises a first exit portion allowing exit of the exhaust gas along a direction parallel to the axis of the first inter-chamber communication pipe.

[0029] In yet another embodiment of the invention, the second inter-chamber communication pipe comprises a second exit portion allowing exit of the exhaust gas along a direction parallel to the axis of the second inter-chamber communication pipe.

[0030] In a furthermore aspect of the invention, there is provided a saddled type vehicle comprising: a single cylinder engine unit emitting exhaust gas; and an exhaust muffler attached to the engine and being adapted to reduce the exhaust noise of the exhaust gas; the exhaust muffler comprising: an outer wall, a first end wall, and a second end wall defining an internal space; at least a first separator located between the first end wall and the second end wall thereby dividing the internal space into at least a first chamber, and a second chamber; an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for releasing exhaust gas from the second chamber into the atmosphere, the outlet pipe comprising an entry port and perforations for allowing the exhaust gas to enter into the outlet pipe from the second chamber; and at least a first inter-chamber communication pipe communicating the exhaust gas from the first chamber to the second chamber, the first inter-chamber communication pipe comprising a first exit portion allowing exit of the exhaust gas along a direction parallel to an axis of the first inter-chamber communication pipe.

[0031] An advantage of the invention is that the exhaust muffler increases the exhaust noise to provide a distinctive sound effect. In particular, the exhaust muffler produces a booming sound effect. Another advantage of the invention is that the exhaust muffler does not substantially affect the performance of engine. Still another advantage of the invention is that the size of the exhaust muffler is not increased to produce the booming sound effect. A further advantage of the invention is that the no additional components are used for constructing the exhaust muffler. Another advantage of the invention is that a time period required for making the exhaust muffler is substantially low. A furthermore advantage of the invention is that the cost of the exhaust muffler is substantially low.

[0032] To further clarify the advantages and features of the invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES:
[0033] In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying drawings, where like reference numerals refer to identical or functionally similar elements throughout the separate views. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention where:

[0034] Figure 1 illustrates a side view of an exemplary two wheeled vehicle, in accordance with an embodiment of the present invention;

[0035] Figure 2 illustrates a schematic view of a two-chamber exhaust muffler constructed in accordance with a first embodiment of the invention;

[0036] Figure 3 illustrates a schematic view of a two-chamber exhaust muffler constructed in accordance with a second embodiment of the invention;

[0037] Figure 4 illustrates a schematic view of a three-chamber exhaust muffler constructed in accordance with a third embodiment of the invention;

[0038] Figure 5 illustrates a schematic view of a three-chamber exhaust muffler constructed in accordance with a fourth embodiment of the invention;

[0039] Figure 6 illustrates a schematic view of a two-chamber exhaust muffler constructed in accordance with a fifth embodiment of the invention;

[0040] Figure 7 illustrates a schematic view of a three-chamber exhaust muffler constructed in accordance with a sixth embodiment of the invention; and

[0041] Figure 8 illustrates a graph showing a variation in exhaust gas pressure with time coming out of the exhaust muffler constructed in accordance with the first embodiment of the invention.

[0042] It may be noted that to the extent possible, like reference numerals have been used to represent like elements in the drawings. Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of aspects of the present invention. Furthermore, one or more elements may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION:
[0043] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0044] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof. As used in the description herein and throughout the claims that follow, the meaning of “a,”“an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0045] Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0046] The terms "comprises", "comprising", or any other variations thereof, are intended to cover anon-exclusive inclusion, such that one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0047] As used herein, and unless the context dictates otherwise, the terms "coupled to", “connected to”, “operably connected to”, and “operatively connected to” are intended to include both direct connection / coupling (in which two elements that are coupled / connected to each other contact each other) and indirect coupling / connection (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Similarly, the terms “connected to” and “connected with” are used synonymously.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one ordinary skilled in the art to which this invention belongs. The device, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0049] The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention. No language in the specification should be construed as indicating any non-mentioned element as being essential to the practice of the invention.

[0050] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used.

[0051] While the present invention is illustrated in the context of a vehicle, however, cover and aspects and features thereof can be used with other types of vehicles as well. The terms “vehicle”, “two wheeled vehicle” and “motorcycle” have been interchangeably used throughout the description. The term “vehicle” comprises vehicles such as motorcycles, scooters, bicycles, mopeds, scooter type vehicles, All-Terrain Vehicles (ATV) and the like.

[0052] The terms “front / forward”, “rear / rearward / back / backward”, “up / upper / top”, “down / lower / lower ward / downward, bottom”, “left / leftward”, “right / rightward” used therein represents the directions as seen from a vehicle driver sitting astride and these directions are referred by arrows Fr, Rr, U, Lr, L, R in the Figures.

[0053] Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0054] Referring to Figure 1, there is illustrated a side view of a two-wheeled vehicle (10) according to an embodiment of the present invention. The vehicle (10) comprises, inter-alia, a front fork (12), a head pipe (14), a front fender (16), a front wheel (18), a headlight (20), a steering handle bar (22), a fuel tank (24), an engine unit (26), a rear wheel (28), a rear fender (30), a tail light (32), a seat (34), a tool box (36), a frame (38), and exhaust-muffler(100). It may be noted that the vehicle (10) is shown to have included above stated parts, however, those skilled in the art would appreciate that the vehicle (10) includes other parts which may not be relevant for explaining the present invention and hence are not shown and described.

[0055] Referring to Figure 2, there is illustrated a schematic view of a two-chamber exhaust muffler (100) constructed in accordance with a first embodiment of the invention. The two chamber exhaust-muffler (100) comprises an outer wall (102), a first end wall (104), and a second end wall (106). The outer wall (102), the first end wall (104), and the second end wall (106) define an internal space of the two-chamber exhaust muffler (100). Further, at least a first separator (108) is located between the first end wall (104) and the second end wall (106) thereby dividing the internal space into at least a first chamber (110), and a second chamber (112).

[0056] The two-chamber exhaust-muffler (100) comprises an inlet pipe (114) for introducing exhaust gas coming from the engine unit (26) of the vehicle (10) into the first chamber (110). Further, an outlet pipe (116) is provided in the two-chamber exhaust-muffler (100)for releasing exhaust gas from the second chamber (112) into the atmosphere. Further, the two-chamber exhaust-muffler (100) comprises at least a first inter-chamber communication pipe (118) communicating a first part of the exhaust gas from the first chamber (110) to the second chamber (112). In an embodiment of the invention, an aperture (120) is provided in the first separator (108) for communicating a second part of the exhaust gas from the first chamber (110) to the second chamber (112).

[0057] In another embodiment of the invention, the first part of the exhaust gas as coming from the first inter-chamber communication pipe (118) mixes with the second part of the exhaust gas as coming from the aperture (120) provided in the first separator (108) in a mixing zone (122).In an embodiment of the invention, the location of the mixing zone (122) varies within the internal space of the two chamber exhaust muffler (100). By way of a non-limiting example, the mixing zone (122) being located between the inlet pipe (114) and an entry portion (124) of the outlet pipe (116). By way of another non-limiting example, the mixing zone (122) being located within the second chamber (112) and defined between the aperture (120) and an entry portion (124) of the outlet pipe (116).

[0058] Now coming to the aspect of location of the outlet pipe (116), by way of a non-limiting example, the entry portion (124) of the outlet pipe (116) is positioned with respect to an exit portion (128) of the first inter-chamber communication pipe (118) such that the first part of the exhaust gas takes a tortuous path (130) there-between. In other embodiment of the invention, the tortuous path (130) comprises at least one bend.

[0059] Now coming to the aspect of construction of the first inter-chamber communication pipe (118), in an embodiment of the invention, the first inter-chamber communication pipe (118) comprises an entry portion (132) at a proximal portion and an exit portion (128) at about a distal portion. By way of a non-limiting example, the exit portion (128) allows exit of the exhaust gas along a direction parallel to an axis of the first inter-chamber communication pipe (118). For instance, the distal portion of the first inter-chamber communication pipe (118) may be open and function as the exit portion (128).

[0060] Although not shown, by way of another non-limiting example, the exit portion (128) allows exit of the exhaust gas along a direction perpendicular to an axis of the first inter-chamber communication pipe (118). For instance, a circumferential wall of the first inter-chamber communication pipe (118) proximate to the distal portion may comprise at least one perforation which functions as the exit portion (128).

[0061] As to the functioning of the exhaust muffler (100) shown in Figure 2, in an embodiment of the invention, the exhaust gas undergoes an expansion in the first chamber (110) before reaching an entry portion (132) of the first inter-chamber communicating pipe (118) and the aperture (120) in the first separator (108). In an embodiment of the invention, since the exhaust gas undergoes an expansion in the first chamber (110) and only a first part of the exhaust gas is transported by the inter-chamber communicating pipe (118), a first level noise dampening effect is obtained in the first chamber (110). The first part of the exhaust gas upon reaching the second chamber (112) undergoes an expansion and a compression before reaching an entry portion (124) of the outlet pipe (116). Thus, a second level noise dampening effect is obtained in the second chamber (112).

[0062] Now after attaining the noise dampening effect to the second level, at least one characteristic of the sound waves generated by exhaust gas selected from a group comprising wavelength, loudness, and velocity is modified. It is believed that the modification in the at least one characteristic of the sound wave generated by exhaust gas is due to mixing of the first part of the exhaust gas with the second part of the exhaust gas in the mixing zone (122). Thus, the characteristic of the sound waves generated by exhaust gas exiting from the exhaust muffler can be controlled by the nature of mixing of the first part of the exhaust gas with the second part of the exhaust gas in the mixing zone (122) and a location of the mixing zone (122).

[0063] The nature of mixing of the first part of the exhaust gas with the second part of the exhaust gas can be controlled by controlling a size and shape of the aperture (120) provided in the first separator (108). By way of non limiting example, the aperture (120) and an entry portion (124) of the outlet pipe (116) overlap each other with respect to an axis (126) of the outlet pipe (116). More particularly, the aperture (120) provided in the first separator (108) has a dimension in a range of 25 to 47% of a dimension of an entry port (124) of the outlet pipe (116). By way of another non-limiting example, the aperture (120) provided in the first separator (108) may have a shape selected from circular shape, elliptical shape, square share, pentagonal shape, hexagonal shape, heptagonal shape, octagonal shape, nonadecagonal shape, decagonal shape, etc.

[0064] Now coming to the aspect of the location of the mixing zone (122), by way of a non-limiting example, the mixing zone (122) may be located within a predetermined distance (L) from an entry portion (124) of the outlet pipe (116). By way of a further non-limiting example, the mixing zone (122) may be located within a predetermined radial distance (R) from an axis (126) of the outlet pipe (116). By way of a furthermore non-limiting example, the location of the mixing zone (122) can be easily controlled by controlling the location of the aperture (120) formed in the first separator (108). By way of a non-limiting example, the aperture (120) and an entry portion (124) of the outlet pipe (116) overlap by at least 20% with respect to the axis (126) of the outlet pipe (116).

[0065] Referring now to Figure 8, there is illustrated a graph showing variation in exhaust gas pressure with time coming out of the exhaust muffler constructed in accordance with the first embodiment of the invention and variation in exhaust gas pressure with time coming out of the exhaust muffler not having the aperture in the first separator. In particular, it can be seen that the exhaust gas exiting out of the exhaust muffler not having the aperture in the first separator has pressure variation as shown by the first curve (202) while the exhaust gas exiting out of the exhaust muffler constructed in accordance with the first embodiment of the invention has pressure variation as shown by the second curve (204). The peaks in the second curve (204) are higher than the peaks in the first curve (202) and hence, an amplitude of the exhaust gas exiting out of the exhaust muffler constructed in accordance with the first embodiment of the invention is higher than an amplitude of the exhaust gas exiting out of the exhaust muffler not having the aperture in the separator. Additionally, a frequency of the exhaust gas exiting out of the exhaust muffler constructed in accordance with the first embodiment of the invention is different than a frequency of the exhaust gas exiting out of the exhaust muffler not having the aperture in the separator. Thus, exhaust gas exiting out of the exhaust muffler constructed in accordance with the first embodiment of the invention ha a booming effect as compared to the exhaust gas exiting out of the exhaust muffler not having the aperture in the separator.

[0066] Referring to Figure 3, there is illustrated a schematic view of a two chamber exhaust muffler (100) constructed in accordance with a second embodiment of the invention. The construction of the two chamber exhaust muffler (100) as per the second embodiment is substantially similar to the construction of the two chamber exhaust muffler (100) as per the first embodiment, with the difference being in terms of the construction of the outlet pipe (116) for removing exhaust gas from the second chamber (112). Therefore, the difference between the construction of the two chamber exhaust muffler as per the first embodiment (shown in Figure 2 and described above) and the construction of the two chamber exhaust muffler as per the second embodiment (shown in Figure 3) will be described hereinafter in detail.

[0067] While the outlet pipe (116) for removing exhaust gas from the second chamber (112) in the two chamber exhaust muffler (100) as per the first embodiment is solid, the outlet pipe (116) for removing exhaust gas from the second chamber (112) as per the second embodiment is partially perforated. In particular, a part of the outlet pipe (116) located in the second chamber (112) includes perforations (134).

[0068] While an entirety of the first part of the exhaust gas as coming from the inter-chamber communication pipe (118) reaches the mixing zone (122) in the exhaust muffler shown in Figure 2 and as described above in the first embodiment, an entirety of the first part of the exhaust gas coming from the inter-chamber communication pipe (118) does not reach the mixing zone (122) in the exhaust muffler shown in Figure 3. Instead, only a sub-part thereof, hereinafter referred to as third part of the exhaust gas, reaches the mixing zone (122), and a remaining sub-part, hereinafter referred as fourth part, by-passes the mixing zone (122) and enters directly into the outlet pipe (116) via the perforations (134) provided in the outlet pipe (116). Thus, as per the second embodiment, in the mixing zone (122), the second part of the exhaust gas mixes with the third part of the exhaust gas and enters the outlet pipe (116) via the entry portion (124). The fourth portion of the exhaust gas mixes subsequently (with the second and the third parts of the exhaust gas) within the outlet pipe (116). Due to the above, an increase in the exhaust noise is observed as compared to the first embodiment. Also, the exhaust gas exiting out of the exhaust muffler constructed in accordance with the second embodiment of the invention has a booming effect as compared to the exhaust gas exiting out of the exhaust muffler not having the aperture in the separator.

[0069] Referring to Figure 4, there is illustrated a schematic view of a three chamber exhaust muffler (100) constructed in accordance with a third embodiment of the invention. The three chamber exhaust muffler (100) comprises an outer wall (102), a first end wall (104), and a second end wall (106). The outer wall (102), the first end wall (104), and the second end wall (106) interact with each other to from an internal space. The three chamber exhaust muffler (100) comprises a first separator (108) and a second separator (136) located between the first end wall (104) and the second end wall (106) so as to divide the internal space into a first chamber (110), a second chamber (112) and a third chamber (138).

[0070] Further, the three chamber exhaust muffler (100) comprises an inlet pipe (114) for introducing exhaust gas into the first chamber (110) and an outlet pipe (116) for removing exhaust gas from the second chamber (112).The three chamber exhaust muffler (100) comprises a first inter-chamber communication pipe (118) communicates a first part of the exhaust gas from the first chamber (110) to the third chamber (138). In an embodiment of the invention, the first inter-chamber communication pipe (118) penetrates through the first separator (108) and the second separator (136). The three chamber exhaust muffler (100) comprises a second inter-chamber communication pipe (140) communicates the first part of the exhaust gas from the third chamber (138) to the second chamber (112).

[0071] Additionally, the first separator (108) is provided with an aperture (120) for communicating a second part of the exhaust gas from the first chamber (110) to the second chamber (112).

[0072] In another embodiment of the invention, the first part of the exhaust gas as coming from the second inter-chamber communication pipe (140) mixes with the second part of the exhaust gas as coming from the aperture (120) provided in the first separator (108) in a mixing zone (122).In an embodiment of the invention, the location of the mixing zone (122) varies within the internal space of the three-chamber exhaust muffler (100). By way of a non-limiting example, the mixing zone (122) being located between the inlet pipe (114) and an entry portion (124) of the outlet pipe (116). By way of another non-limiting example, the mixing zone (122) being located within the second chamber (112) and defined between the aperture (120) and an entry portion (124) of the outlet pipe (116).

[0073] Now coming to the aspect of construction of the first inter-chamber communication pipe (118), in an embodiment of the invention, the first inter-chamber communication pipe (118) comprises an entry portion (132) at a proximal portion and an exit portion (128) at about a distal portion. By way of a non-limiting example, the exit portion (128) allows exit of the exhaust gas along a direction parallel to an axis of the first inter-chamber communication pipe (118). For instance, the distal portion of the first inter-chamber communication pipe (118) may be open and function as the exit portion (128). Although not shown, by way of another non-limiting example, the exit portion (128) allows exit of the exhaust gas along a direction perpendicular to an axis of the first inter-chamber communication pipe (118). For instance, a circumferential wall of the first inter-chamber communication pipe (118) proximate to the distal portion may comprise at least one perforation which functions as the exit portion (128).

[0074] Now coming to the aspect of construction of the second inter-chamber communication pipe (140), in an embodiment of the invention, the second inter-chamber communication pipe (140) comprises an entry portion (142) at a distal portion and an exit portion (144) at about a proximal portion. By way of a non-limiting example, the exit portion (144) allows exit of the first part of the exhaust gas along a direction parallel to an axis of the second inter-chamber communication pipe (140). For instance, the distal portion of the second inter-chamber communication pipe (140) may be open and function as the exit portion (144). Although not shown, by way of another non-limiting example, the exit portion (144) of the second inter-chamber communication pipe (140) allows exit of the first part of the exhaust gas along a direction perpendicular to an axis of the second inter-chamber communication pipe (140). For instance, a circumferential wall of the second inter-chamber communication pipe (140) proximate to the proximal portion may comprise at least one perforation which functions as the exit portion (144).

[0075] In an embodiment of the invention, the second inter-chamber communication pipe (140) comprises an entry portion (142) positioned with respect to an exit portion (128) of the first inter-chamber communication pipe (118) such that the first part of the exhaust gas takes a first tortuous path (130) there-between. In an embodiment of the invention, the first tortuous path (130) comprises at least one bend. In an embodiment of the invention, an entry portion (124) of the outlet pipe (116) is positioned with respect to an exit portion (144) of the second inter-chamber communication pipe (140) such that the first part of the exhaust gas takes a second tortuous path (146) there-between. In a further embodiment of the invention, the second tortuous path (146) comprises at least one bend.

[0076] As to the functioning of the exhaust muffler (100) shown in Figure 4, in an embodiment of the invention, the exhaust gas undergoes an expansion in the first chamber (110) before reaching an entry portion (132) of the first inter-chamber communicating pipe (118) and the aperture (120) in the first separator (108). In an embodiment of the invention, since the exhaust gas undergoes an expansion in the first chamber (110) and only a first part of the exhaust gas is transported by the first inter-chamber communicating pipe (118), a first level noise dampening effect is obtained in the first chamber (110). The first part of the exhaust gas upon reaching the third chamber (138) undergoes an expansion and a compression before reaching an entry portion (142) of the second inter-chamber communicating pipe (140). Thus, a second level noise dampening effect is obtained in the third chamber (138). The first part of the exhaust gas upon reaching the second chamber (112) undergoes an expansion and a compression before reaching an entry portion (124) of the outlet pipe (116).Thus, a third level noise dampening effect is obtained in the second chamber (112).

[0077] Now after attaining the noise dampening effect to the third level, at least one characteristic of the sound waves generated by exhaust gas selected from a group comprising wavelength, loudness, and velocity is modified. It is believed that the modification in the at least one characteristic of the sound wave generated by exhaust gas is due to mixing of the first part of the exhaust gas with the second part of the exhaust gas in the mixing zone (122). Thus, the characteristic of the sound waves generated by exhaust gas exiting from the exhaust muffler can be controlled by the nature of mixing of the first part of the exhaust gas with the second part of the exhaust gas in the mixing zone (122) and a location of the mixing zone (122).

[0078] The nature of mixing of the first part of the exhaust gas with the second part of the exhaust gas can be controlled by controlling a size and shape of the aperture (120) provided in the first separator (108). By way of a non-limiting example, the aperture (120) provided in the first separator (108) has a dimension in a range of 25 to 47% of a dimension of an entry port (124) of the outlet pipe (116). By way of another non-limiting example, the aperture (120) provided in the first separator (108) may have a shape selected from circular shape, elliptical shape, square share, pentagonal shape, hexagonal shape, heptagonal shape, octagonal shape, nonadecagonal shape, decagonal shape, etc.

[0079] Now coming to the aspect of the location of the mixing zone (122), by way of a non-limiting example, the mixing zone (122) may be located within a predetermined distance (L) from an entry portion (124) of the outlet pipe (116). By way of a further non-limiting example, the mixing zone (122) may be located within a predetermined radial distance (R) from an axis (126) of the outlet pipe (116). By way of a furthermore non-limiting example, the location of the mixing zone (122) can be easily controlled by controlling the location of the aperture (120) formed in the first separator (108). By way of a non-limiting example, the aperture (120) and an entry portion (124) of the outlet pipe (116) overlap each other with respect to the axis (126) of the outlet pipe (116). More particularly, the aperture (120) provided in the first separator (108) has a dimension in a range of 25 to 47% of a dimension of an entry port (124) of the outlet pipe (116). By way of a non-limiting example, the aperture (120) and an entry portion (124) of the outlet pipe (116) overlap by at least 20% with respect to the axis (126) of the outlet pipe (116).

[0080] While a graph similar to Figure 8 for the exhaust gas exiting out of the exhaust muffler constructed in accordance with the third embodiment has not been provided, it may be noted that the exhaust gas exiting out of the exhaust muffler constructed in accordance with the third embodiment also has a booming effect as compared to the exhaust gas exiting out of an exhaust muffler not having the aperture in the separator.

[0081] Referring to Figure 5 there is illustrated a schematic view of a three-chamber exhaust muffler (100) constructed in accordance with a fourth embodiment of the invention. The construction of the three-chamber exhaust muffler (100) as per the fourth embodiment is substantially similar to the construction of the three-chamber exhaust muffler (100) as per the third embodiment, with the difference being in terms of the construction of the outlet pipe (116) for removing exhaust gas from the second chamber (112). Therefore, the difference between the construction of the three-chamber exhaust-muffler as per the third embodiment (shown in Figure 4 and described above) and the construction of the three-chamber exhaust-muffler as per the fourth embodiment (shown in Figure 5) will be described hereinafter in detail.

[0082] While the outlet pipe (116) for removing exhaust gas from the second chamber (112) in the three-chamber exhaust-muffler (100) as per the third embodiment is solid, the outlet pipe (116) for removing exhaust gas from the second chamber (112) as per the fourth embodiment is partially perforated. In particular, a part of the outlet pipe (116) located in the third chamber (138) includes perforations (134). While an entirety of the first part of the exhaust gas as coming from the first inter-chamber communication pipe (118) reaches the mixing zone (122) in the exhaust muffler shown in Figure 2 and as described above in the first embodiment, an entirety of the first part of the exhaust gas as coming from the first inter-chamber communication pipe (118) does not reach the mixing zone (122) in the exhaust pipe shown in Figure 5. Instead, only a sub-part thereof, hereinafter referred to as third part of the exhaust gas, reaches the mixing zone (122) and a remaining sub-part, hereinafter referred as fourth part, by-passes the mixing zone (122) and enters directly into the outlet pipe (116) via the perforations (134) provided in the outlet pipe (116). Thus, as per the second embodiment, in the mixing zone (122), the second part of the exhaust gas mixes with the third part of the exhaust gas and enters the outlet pipe (116) via the entry portion (124). The fourth portion of the exhaust gas mixes subsequently (with the second and the third parts of the exhaust gas) within the outlet pipe (116). Due to the above, an increase in the exhaust noise (a booming effect) is observed as compared to the third embodiment. While in Figure 5, the perforations (134) in the outlet pipe (116) are shown to be located in the third chamber (138), in an alternative embodiment (not shown), the perforations (134) in the outlet pipe (116) may be located in the second chamber (112).

[0083] While a graph similar to Figure 8 for the exhaust gas exiting out of the exhaust muffler constructed in accordance with the fourth embodiment has not been provided, it may be noted that the exhaust gas exiting out of the exhaust muffler constructed in accordance with the fourth embodiment also has a booming effect as compared to the exhaust gas exiting out of an exhaust muffler not having the aperture in the separator.

[0084] Thus, keeping in view the embodiments shown in Figures 2 to 5, it can be said that the invention provides an exhaust-pipe structure for an internal combustion engine used in a vehicle, the exhaust-pipe structure comprising an outer wall, a first end wall and a second end wall co-operating to define an internal space; at least one separator located between the first end wall and the second end wall dividing the internal space into at least a first chamber and a second chamber; an inlet pipe for introducing exhaust gas into the first chamber; an outlet pipe for removing exhaust gas from the second chamber; at least one inter-chamber communication pipe penetrating through the at one least separator for communicating a first part of the exhaust gas from the first chamber to the second chamber; and an aperture provided in the separator located between the first and the second chambers for communicating a second part of the exhaust gas from the first chamber to the second chamber. In an embodiment of the invention, the outlet pipe includes perorations.

[0085] Referring to Figure 6, there is illustrated a two chamber exhaust muffler (100) of a vehicle (10) in accordance with fifth embodiment of the invention. The construction of the two chamber exhaust muffler (100) shown in Figure 6 is substantially similar to the construction of the two chamber exhaust muffler (100) as shown in Figure 3 with the following differences. While in the two chamber exhaust muffler (100) as shown in Figure 3 the first separator (108) is provided with the aperture (120), in the two chamber exhaust muffler (100) shown in Figure 6 the first separator (108) does not have the aperture (120). Thus, all of the exhaust gas travels from the first chamber (110) to the second chamber (1120) via the first inter-chamber communication pipe (118). Thus, in the two chamber exhaust muffler (100) shown in Figure 6 a mixing zone (120) is NOT formed.

[0086] Additionally, in the two chamber exhaust muffler (100) shown in Figure 3 the first exit portion (128) forming part of the first inter-chamber communication pipe (118) allows exit of the first part of the exhaust gas along a direction parallel to the axis of the first inter-chamber communication pipe (118) or along a direction perpendicular to the axis of the first inter-chamber communication pipe (118). However, in the two chamber exhaust muffler (100) as shown in Figure 6 the first exit portion (128) forming part of the first inter-chamber communication pipe (118) solely allows exit of the exhaust gas along a direction parallel to the axis of the first inter-chamber communication pipe (118).

[0087] While a graph similar to Figure 8 for the exhaust gas exiting out of the exhaust muffler constructed in accordance with the fifth embodiment has not been provided, it may be noted that the exhaust gas exiting out of the exhaust muffler constructed in accordance with the fifth embodiment also has a booming effect.

[0088] Referring to Figure 7, there is illustrated a three chamber exhaust muffler (100) of a vehicle (10) in accordance with sixth embodiment of the invention. The construction of the three chamber exhaust muffler (100) shown in Figure 7 is substantially similar to the construction of the three chamber exhaust muffler (100) as shown in Figure 5 with the following differences. While in the three chamber exhaust muffler (100) as shown in Figure 5 the first separator (108) is provided with the aperture (120), in the three chamber exhaust muffler (100) shown in Figure 7 the first separator (108) does not have the aperture (120). Thus, all of the exhaust gas travels from the first chamber (110) to the third chamber (138) via the first inter-chamber communication pipe (118). Thus, in the three chamber exhaust muffler (100) shown in Figure 7 a mixing zone (120) is NOT formed in the second chamber (112).

[0089] Additionally, in the three chamber exhaust muffler (100) shown in Figure 5 the first exit portion (128) forming part of the first inter-chamber communication pipe (118) allows exit of the first part of the exhaust gas along a direction parallel to the axis of the first inter-chamber communication pipe (118) or along a direction perpendicular to the axis of the first inter-chamber communication pipe (118). However, in the three chamber exhaust muffler (100) as shown in Figure 7 the first exit portion (128) forming part of the first inter-chamber communication pipe (118) solely allows exit of the exhaust gas along a direction parallel to the axis of the first inter-chamber communication pipe (118). Also, the second exit portion (144) forming part of the second inter-chamber communication pipe (140) shown in Figure 5allows exit of the third part of the exhaust gas along a direction parallel to the axis of the second inter-chamber communication pipe (140) or along a direction perpendicular to the axis of the second inter-chamber communication pipe (140). However, in the three chamber exhaust muffler (100) as shown in Figure 7 the second exit portion (144) forming part of the second inter-chamber communication pipe (140) solely allows exit of the third part of exhaust gas along a direction parallel to the axis of the second inter-chamber communication pipe (140).

[0090] While a graph similar to Figure 8 for the exhaust gas exiting out of the exhaust muffler constructed in accordance with the sixth embodiment has not been provided, it may be noted that the exhaust gas exiting out of the exhaust muffler constructed in accordance with the sixth embodiment also has a booming effect.

[0091] An advantage of the invention is that the exhaust muffler increases the exhaust noise to provide a distinctive sound effect. In particular, the exhaust muffler produces a booming sound effect. Another advantage of the invention is that the exhaust muffler does not substantially affect the performance of engine. Still another advantage of the invention is that the size of the exhaust muffler is not increased to produce the booming sound effect. A further advantage of the invention is that the no additional components are used for constructing the exhaust muffler. Another advantage of the invention is that a time period required for making the exhaust muffler is substantially low. A furthermore advantage of the invention is that the cost of the exhaust muffler is substantially low.

[0092] While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

[0093] The figures and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. The scope of embodiments is by no means limited by these specific examples. Additionally, numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible.
,CLAIMS:WE CLAIM:

1. An exhaust muffler (100) of a vehicle (10), the exhaust muffler (100) comprising:
an outer wall (102), a first end wall (104), and a second end wall (106) defining an internal space;
at least a first separator (108) located between the first end wall (104) and the second end wall (106) thereby dividing the internal space into at least a first chamber (110), and a second chamber (112);
an inlet pipe (114) for introducing exhaust gas into the first chamber (110);
an outlet pipe (116) for releasing exhaust gas from the second chamber (112) into the atmosphere;
at least a first inter-chamber communication pipe (118) communicating a first part of the exhaust gas from the first chamber (110) to the second chamber (112); and
an aperture (120) provided in the first separator (108) for communicating a second part of the exhaust gas from the first chamber (110) to the second chamber (112).

2. The exhaust muffler (100) as claimed in claim 1, wherein the exhaust muffler (100) being a two-chamber exhaust muffler (100).

3. The exhaust muffler (100) as claimed in claim 1, wherein the first part of the exhaust gas as coming from the first inter-chamber communication pipe (118) mixes with the second part of the exhaust gas as coming from the aperture (120) provided in the first separator (108) in a mixing zone (122).

4. The exhaust muffler (100) as claimed in claim 3, wherein at least one characteristic of a sound waves generated by the exhaust gas selected from a group comprising wavelength, loudness, and velocity is modified in the mixing zone (122).

5. The exhaust muffler (100) as claimed in claim 3, wherein the mixing zone (122) being located between the inlet pipe (114) and an entry portion (124) of the outlet pipe (116).

6. The exhaust muffler (100) as claimed in claim 3, wherein the mixing zone (122) being located within the second chamber (112) and defined between the aperture (120) and an entry portion (124) of the outlet pipe (116).

7. The exhaust muffler (100) as claimed in claim 1, wherein an entry portion (124) of the outlet pipe (116) is positioned with respect to an exit portion (128) of the first inter-chamber communication pipe (118) such that the first part of the exhaust gas takes a torturous path (130) there-between, the tortuous path (130) comprises at least one bend.

8. The exhaust muffler (100) as claimed in claim 1, wherein the outlet pipe (116) comprises perforations (134) such that the first part of the exhaust gas gets bifurcated into a third part of the exhaust gas and a fourth part of the exhaust gas; the second part of the exhaust gas mixes with the third part of the exhaust gas in the mixing zone (122) and enters the outlet pipe (116) via the entry portion (124) and the fourth part of the exhaust gas enters the outlet pipe (116) via the perforations (134).

9. The exhaust muffler (100) as claimed in claim 1, wherein the aperture (120) and an entry portion (124) of the outlet pipe (116) overlap each other with respect to an axis (126) of the outlet pipe (116).

10. The exhaust muffler (100) as claimed in claim 1, wherein the aperture (120) and an entry portion (124) of the outlet pipe (116) overlap by at least 20% with respect to the axis (126) of the outlet pipe (116).

11. A saddle type vehicle (10), comprising:
a single cylinder engine unit (26) emitting exhaust gas; and
an exhaust muffler (100) attached to the engine (26); the exhaust muffler (100) comprising:
an outer wall (102), a first end wall (104), and a second end wall (106) defining an internal space;
at least a first separator (108) located between the first end wall (104) and the second end wall (106) thereby dividing the internal space into at least a first chamber (110), and a second chamber (112);
an inlet pipe (114) for introducing exhaust gas into the first chamber (110);
an outlet pipe (116) for releasing exhaust gas from the second chamber (112) into the atmosphere;
at least a first inter-chamber communication pipe (118) communicating a first part of the exhaust gas from the first chamber (110) to the second chamber (112); and
an aperture (120) provided in the first separator (108) for communicating a second part of the exhaust gas from the first chamber (110) to the second chamber (112).

12. An exhaust muffler (100) of a vehicle (10), the exhaust muffler (100) comprising:
an outer wall (102), a first end wall (104), and a second end wall (106) defining an internal space;
at least a first separator (108) located between the first end wall (104) and the second end wall (106) thereby dividing the internal space into at least a first chamber (110), and a second chamber (112);
an inlet pipe (114) for introducing exhaust gas into the first chamber (110);
an outlet pipe (116) for releasing exhaust gas from the second chamber (112) into the atmosphere, the outlet pipe (116) comprising an entry port (124) and perforations (134) for allowing the exhaust gas to enter into the outlet pipe (116) from the second chamber (112); and
at least a first inter-chamber communication pipe (118) communicating the exhaust gas from the first chamber (110) to the second chamber (112), the first inter-chamber communication pipe (118) comprising a first exit portion (128) allowing exit of the exhaust gas along a direction parallel to an axis of the first inter-chamber communication pipe (118).

13. The exhaust muffler (100) as claimed in claim 12, wherein the exhaust muffler (100) being at least one of a two-chamber exhaust muffler (100) and a three chamber exhaust muffler (100).

14. The exhaust muffler (100) as claimed in claim 13, wherein the three chamber exhaust muffler (100)comprises:
a first separator (108) and a second separator (136) located between the first end wall (104) and the second end wall (106) so as to divide the internal space into a first chamber (110), a second chamber (112) and a third chamber (138);
a first inter-chamber communication pipe (118) penetrating through the first separator (108) and the second separator (136) for communicating the exhaust gas from the first chamber (110) to the third chamber (138);
a second inter-chamber communication pipe (140) penetrating through the second separator (136) for communicating the exhaust gas from the third chamber (138) to the second chamber (112).

15. The exhaust muffler (100) as claimed in claim 14, wherein at least one of:
the first inter-chamber communication pipe (118) comprises a first exit portion (128) allowing exit of the exhaust gas along a direction parallel to the axis of the first inter-chamber communication pipe (118); and
the second inter-chamber communication pipe (140) comprises a second exit portion (144) allowing exit of the exhaust gas along a direction parallel to the axis of the second inter-chamber communication pipe (144).

16. A saddle type vehicle (10), comprising:
a single cylinder engine unit (26) emitting exhaust gas; and
an exhaust muffler (100) attached to the engine (26); the exhaust muffler (100) comprising:
an outer wall (102), a first end wall (104), and a second end wall (106) defining an internal space;
at least a first separator (108) located between the first end wall (104) and the second end wall (106) thereby dividing the internal space into at least a first chamber (110), and a second chamber (112);
an inlet pipe (114) for introducing exhaust gas into the first chamber (110);
an outlet pipe (116) for releasing exhaust gas from the second chamber (112) into the atmosphere, the outlet pipe (116) comprising an entry port (124) and perforations (134) for allowing the exhaust gas to enter into the outlet pipe (116) from the second chamber (112); and
at least a first inter-chamber communication pipe (118) communicating the exhaust gas from the first chamber (110) to the second chamber (112), the first inter-chamber communication pipe (118) comprising a first exit portion (128) allowing exit of the exhaust gas along a direction parallel to an axis of the first inter-chamber communication pipe (118).