FORM 2
THE PATENT ACT 1970 (as amended)
[39 OF 1970]
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
[See Section 10 and Rule 13]
TITLE: “AN EXHAUST MUFFLER AND METHOD OF ASSEMBLING THEREOF”
NAME AND ADDRESS OF THE APPLICANT: TATA MOTORS LIMITED, an Indian company having its registered office at Bombay house, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001, Maharashtra, INDIA.
Nationality: INDIAN
The following specification particularly describes the nature of the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The disclosure is related to an exhaust system of an automobile, more particularly related to exhaust muffler used in medium and heavy commercial vehicles.
BACKGROUND AND PRIOR ARTS
Exhaust muffler is a device used to attenuate the noise of exhaust gas, coming out from engine to the desired decibel as per automotive norms/regulations for all type of vehicles. Desired noise attenuation is the primary functional requirement of all categories of exhaust muffler. The existing mufflers occupy more space and affect the packaging or fitment of all other aggregates of vehicles. Hence, it would be difficult to handle as they are heavy in weight. For an example in the Exhaust muffler of NTA series is not meeting all required parameters of exhaust muffler except sound attenuating function. Further, the mufflers performance is satisfactory.
In this context a new low cost, low weight, low volume, environment friendly and easily manufacture-able exhaust Muffler has been developed for 5.9 lt engine swept volume vehicles (M & HCV).
OBJECTS OF THE DISCLSOURE
One object of the present invention is to develop an exhaust muffler having lower volume (25-26%) without changing cross sectional area (i.e. - reduction of length is approx 25-26%) than existing muffler without compromising its performance (i.e.-noise attenuation level) for medium and heavy range of commercial vehicles.
Another object of this invention is to design a new muffler of approx 40 % lesser weight than existing muffler to improve handling and packaging of it.
Yet other object of this current invention is to design a new exhaust muffler which is robust and simple in design wise, can be manufacture easily and required lesser time for development for Medium and Heavy Commercial Vehicles.
Yet other object of present invention is to develop a cost-effective exhaust muffler for medium and Heavy Commercial Vehicles.

Yet other object of present invention is to develop an environment friendly exhaust muffler for Medium and Heavy Commercial Vehicles.
Yet other object of this invention is to design an exhaust muffler which can perform consistently in its recommended life span.
STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure provides for an exhaust muffler, comprising a muffler body; a front end cover enclosing an inlet of the muffler body; an inlet pipe connected to the front end cover; one or more intermediate pipes offset to the inlet pipe is connected to a non-perforated front baffle positioned adjacent to the inlet pipe, wherein said intermediate pipe comprises perforations on its circumference; a perforated middle baffle comprising a through hole at its center and is positioned adjacent to the one or more intermediate pipes; and an outlet pipe, wherein one end of the outlet pipe is extended through the through hole of the middle baffle for a predetermined distance towards the one or more intermediate pipes, other end of the outlet pipe is passed through a through hole of a perforated rear baffle, before connecting to a rear end cover, and also provides for a method of assembling an exhaust muffler comprising enclosing a front end cover at an inlet of the muffler body; connecting an inlet pipe to the front end cover; connecting one or more intermediate pipes offset to the inlet pipe to a non-perforated front baffle positioned adjacent to the inlet pipe; connecting a perforated middle baffle comprising a through hole at its center and positioning it adjacent to the one or more intermediate pipes; and connecting an outlet pipe to the rear end cover, wherein one end of the outlet pipe is extended through the through hole of the middle baffle for a predetermined distance towards the one or more intermediate pipes, other end of the outlet pipe is passed through a through hole of a perforated rear baffle.
SUMMARY OF THE DISCLOSURE
In one embodiment, an exhaust muffler, comprising a muffler body; a front end cover enclosing an inlet of the muffler body; an inlet pipe connected to the front end cover; one or more intermediate pipes offset to the inlet pipe is connected to a non-perforated front baffle positioned adjacent to the inlet pipe, wherein said intermediate pipe comprises

perforations on its circumference; a perforated middle baffle comprising a through hole at its center and is positioned adjacent to the one or more intermediate pipes; and an outlet pipe, wherein one end of the outlet pipe is extended through the through hole of the middle baffle for a predetermined distance towards the one or more intermediate pipes, other end of the outlet pipe is passed through a through hole of a perforated rear baffle, before connecting to a rear end cover.
In one embodiment, a partially or semi open perforated plate is mounted at outlet of the intermediate pipe.
In one embodiment, glass wool or ceramic wool is provided in a space formed between the rear baffle and the rear end cover to absorb noise of exhaust gases.
In one embodiment, the through hole of the rear baffle is provided at its center.
In one embodiment, cross section or diameter of hole of the perforations of the middle baffle is larger than that of the rear baffle.
In one embodiment, flange thicknesses of the front baffle, the middle baffle and the rear baffle are in the range of about 10 mm -20 mm.
In one embodiment, number of perforations in the rear baffle is more than that of the middle baffle.
In one embodiment, a method of assembling an exhaust muffler comprising enclosing a front end cover at an inlet of the muffler body; connecting an inlet pipe to the front end cover; connecting one or more intermediate pipes offset to the inlet pipe to a non-perforated front baffle positioned adjacent to the inlet pipe; connecting a perforated middle baffle comprising a through hole at its center and positioning it adjacent to the one or more intermediate pipes; and connecting an outlet pipe to the rear end cover, wherein one end of the outlet pipe is extended through the through hole of the middle baffle for a predetermined distance towards the one or more intermediate pipes, other end of the outlet pipe is passed through a through hole of a perforated rear baffle.

In one embodiment, the inlet pipe and the outlet pipe are mounted axially and are connected to the muffler body by gas welding process.
In one embodiment, the front baffle and the middle baffle are welded to the muffler body by gas welding process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:
FIG. 1 shows front view of muffler assembly according to the disclosure,
FIG. 2 shows top view of muffler assembly according to the disclosure,
FIG. 3 shows cross sectional view of the muffler assembly according to the disclosure,
FIG. 4 shows details of front end cover of the muffler assembly according to the
disclosure,
FIG. 5 shows details of rear end cover of the muffler assembly according to the
disclosure,
FIG. 6 shows details of front baffle of the muffler assembly according to the disclosure,
FIG. 7 shows details of middle baffle of the muffler assembly according to the disclosure,
FIG. 8 shows details of rear baffle of the muffler assembly according to the disclosure,
FIG. 9 shows details of inlet pipe assembly of the muffler assembly according to the
disclosure,
FIG. 10 shows details of intermediate pipe of the muffler assembly according to the
disclosure,
FIG. 11 shows details of outlet pipe of the muffler according to the disclosure,
FIG.12 shows details of third chamber of muffler assembly according to the disclosure,

FIG.13 shows the schematic flow pattern through muffler assembly according to the
disclosure,
FIG.14 shows the isometric view of muffler assembly in both complete assembly and
sectional view according to the disclosure.
The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, and figures are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.
Referral numerals

Description Referral numeral
1 Muffler
1a Muffler body
2 Front end cover
2a Through hole in front end cover
3 Rear end cover
3a Through hole in the Rear end cover
3b Perforations on rear end cover
4 Front baffle

4a Front baffle hole
5 Middle baffle
5a Through hole in the Middle baffle
5b Perforations on the middle baffle
6 Rear baffle
6a Through hole in the Rear baffle
6b Perforations on the rear baffle
7 Inlet pipe
7a Pipe portion of the inlet pipe
7b Perforated pipe portion of the inlet pipe
7c Pipe baffle of the inlet pipe
7d Holes on the pipe baffle of the inlet pipe
8 Intermediate baffle
8a Perforations on the intermediate pipe
8b Partial open perforated baffle of the intermediate pipe
9 Outlet pipe
10 Glass wool or ceramic wool
C1 First compartment
C2 Second compartment
C3 Third compartment
L1 Length of first compartment
L2 Length of second compartment
L3 Length of third compartment
The disclosure is relating to exhaust gas muffler for automobiles, more particularly related to sound attenuating device of exhaust gases for medium and heavy commercial vehicles having engine swept volume of 5.9 Lt but not limited to the 5.9 lt. it can also be used and is effective for vehicles having engine swept volume in range of 5.5 to 6 lt
FIGS. 1 and 2 illustrate front and top views of muffler (1) according to the disclosure. A shell sheet of predetermined thickness is crimped/welded (as shown in FIG. 14) into a

cylindrical shaped body to form a muffler body (1a). The muffler body (1a) is made of single layer of shell having higher thickness than individual shell having inner and outer layers as in case of existing mufflers. The thickness of the shell is ranging from about 1.25 mm to 1.6 mm and having good corrosive, heat resistant properties. Further, this helps to make the design simple so that improve its manufacturability. The shell consists of three numbers of holes at bottom side for venting purpose and it is represented as “H”. These holes are made at predetermined interval and off-set distance among the holes for this typical case. The muffler body (1a) is configured into three numbers of chambers (C1, C2 and C2) starting from inlet of the muffler (1) to the outlet of the muffler (1). The chambers (C1, C2 and C3) are separated using plurality of baffles. The baffles are front baffle (4), middle baffle (5) and rear baffle (6). The muffler (1) is provided with an end cover (2 and 3) on its either ends, wherein inlet end is covered using a front end cover (2) and outlet end is covered using a rear end cover (3). The inlet of the muffler (1) is provided with two chambers i.e. the first chamber (C1) and the second chamber (C2). The chambers (C1 and C2) are reactive type and are suitable for low frequency noise reduction. The chambers (C1 and C2) are interconnected through an intermediate pipe (8) and a front baffle (4). An inlet pipe (7) is inserted centrally in the first chamber (C1) and welded with the front end cover (2) of the muffler body (1a). The inlet pipe (7) comprises a pipe portion (7a) extended with a perforated portion (7b) with a pipe baffle (7c) at its exit end. The baffle end of the inlet pipe (7) has plurality of holes of same diameter except central hole of the pipe baffle (7c) of the inlet pipe (7). For interconnection of the chambers (C1 and C2), two numbers of the intermediate pipes (8) are used. The intermediate pipes (8) are inserted in second chamber (C2) and welded with the front baffle (4) at equal distance and are offset from centre/axis of the muffler (1). The intermediate pipe (8) (as shown in FIG. 10) comprises perforations (8a) on its surface and a baffle (8b) at its exit end. The baffle (8a) of the intermediate pipe (8) comprises a central hole having larger diameter than perforations in the baffle (8a). There are 12 perforations/holes in the baffle (8b) and are located near to the periphery. Outer diameter of the baffle (8b) is less than or equal to inner diameter of intermediate Pipe (8a). Diameters of all perforations except the central hole in baffle (8a) are same. The sheet thickness of both intermediate Pipe (8a) and the baffle (8b) is within range of about 1.25

mm to about 2 mm. The interconnecting porosity ratio between the first chambers (C1) and the second chamber (C2) is ranging from about 0.9 to about 1.1.
The total muffler volume is 25-26% lesser than existing and one of the primary reason for this reduction is due to reduction in length wise. The total length of this muffler is L. The length of first chamber (C1), the second chamber (C2) and the third chamber (C3) (as shown in FIG. 12) are L1, L2 and L3 respectively (as shown in FIG. 1). The value of L1, L2 and L3 are within 0.4-0.45 L, 0.37-0.4L, 0.17- 0.2L respectively. Material properties and thickness of all baffles and end covers are same and the thickness is ranging from about 1.5 mm to about 2 mm. The through holes (2a and 3a) in the front end cover (2) and the rear end cover (3) is at central position (shown in FIG.S 4 and 5). The diameter of the front and rear end covers (2 and 3) is represented as ØD. The three baffles (4, 5 and 6) and two end covers (2 and 3) are welded with muffler body (1a) of the muffler (1). All these baffles (4, 5 and 6) and the end covers (2 and 3) have same outer perimeter as cross sectional area is uniform throughout the muffler (1) and are modified in opening areas. The front end cover (2), the rear end cover (3), and the middle baffle (5) are not having same flange thickness and thus help to reduce cost and weight of muffler (1) to restrict to use over design baffles. The flange thickness of the front end cover (2), the rear end cover (3) and the front baffle (4) is same and is about 20 mm. Further, bend radius (R0) of the front end cover (2) and the front baffle (4) and machining tolerance are same as shown in FIGS. 4 and 5. R1 indicates the radius of the front end cover (2) profile as shown in FIG. 4 and is applicable for all end covers (2, 3) and the baffles (4, 5 and 6). The middle baffle (5) and the rear baffle (6) are perforated. Both the middle baffle (5) and rear baffle (6) (FIG. 8) consist of central through hole (5a and 6a) bigger than the through hole (4a) provided in the front baffle (4). The front baffle (4) has two numbers of openings/holes (4a) of same diameter at equal offset distance from center/axis of the muffler (1) (as shown in FIG. 6). The diameter of hole on perforation for middle baffle (5) is approximately twice than diameters of the perforations on inlet pipe (7) and intermediate pipe (8) and rear baffle (6). The diameter of perforations on middle baffle (5) is ranging from about 14 mm to about 16 mm. Further, central opening/through hole (6a) of the rear baffle (6) is not flanged as provided in the middle baffle (5) (as shown in FIG. 8).

In FIG. 9, views (a), (b) and (c) represents the front, side and isometric views of inlet pipe (7) respectively. Expansion ratio is more in first chamber (C1), due to which higher noise attenuation performance is achieved in the first chamber (C1). There are holes (7d) on the rear end of the inlet pipe (7) and are made with certain pitch at alternate rows. To avoid chocking of holes/perforations (7d) in series, all the perforations/holes (7d) are made in alternative rows. One through hole is located at centre and rest 36 holes are at 3 different Pitch Circle Diameter (PCD) of the pipe baffle (7c). The pipe baffle (7c) outer diameter is less than or equal to inner diameter of the inlet pipe (7). The sheet thickness of both the inlet pipe (7) and the pipe baffle (7c) are ranging from about 1.6 mm to about 2 mm. The porosity ratio is defined as the ratio of total area of the perforations to the cross sectional area of the perforated portion (7a) of the inlet pipe (7) and is maintained in between 1.9 to 2.1. The inlet pipe (7) is provided with plurality of small diameter holes rather to use a big diameter of hole of less numbers and thus helps to improve the performance of the reactive chamber of the exhaust muffler (1) (as shown in FIG. 7).
FIG. 12 illustrates third chamber (C3) of the muffler (1). The third chamber (C3) of the muffler (1) is a resonative cum absorptive type chamber. In third chamber (C3), small amount of glass wool or ceramic wool (10) is used. The glass wool or ceramic wool (10) is placed in between the rear baffle (3) and the rear end cover (3) in a sandwich pattern. The chamber (C3) with glass wool or ceramic wool (10) acts as an absorptive chamber. In addition, the muffler uses less quantity of glass wool or ceramic wool and the density of glass wool or ceramic wool is 115-135 kg/m3, wherein it is approximately about 7.5% to about 8% in volume and weight wise and 125 grams to about 150 grams in weight than existing mufflers. Further, these ensures the cost effectiveness and easily manufacturability and to reduce weight reduction from existing. Also, indirectly these help to improve handling and packaging. The function of Glass wool or ceramic wool bag is to absorption of high frequency sound but it is temperature sensitive and it has lost its sound absorption property in long run in high temperature application. Hence, it is placed in such a pattern that it will experienced lowest temperature in the muffler. Also, there is a very little chance to come out of burnt glass wool or ceramic wool which is a hazardous material through outlet pipe to environment because of placement position of it

in inside the muffler. Both quantity and placement feature of glass wool or ceramic wool are the indication of environment friendly nature of the muffler.
Outlet pipe (9) is passed across and welded with the rear end cover (3), the middle baffle (5) and the rear baffle (6). The fitment of the outlet pipe (9) is concentric with the rear end cover (3), the middle baffle (5) and the rear baffle (6). The second and third chambers (C2 and C3) are interconnected through the middle baffle (5). Hence, the third chamber (C3) acts as a resonator chamber. For better resonative effect inline to absorptive effect, diameter of the perforations on the middle baffle (5) is made larger than the diameter of the perforations made on the rear baffle (3). Also, the diameter of the perforations on the middle baffle (5) is larger than the diameter of the perforations made on the inlet pipe (7) and the intermediate pipe (8). The diameter of hole in the middle baffle (5) is twice than diameter of the holes of the rear baffle (6), the inlet pipe (7) and the intermediate pipe (8). The diameter of the perforations provided on the inlet pipe (7), the intermediate pipe (8), the front baffle (4) and the rear baffle (6) are ranging from about 6 mm to 8 mm. The diameter of perforations provided in the middle baffle (5) is ranging from about 14 mm to about 16 mm. The inlet pipe (7), the outlet pipe (9) (as shown in FIG. 11) and the intermediate pipes (8) (as shown in FIG. 10) are straight and cylindrical in nature and have no critical joining between any pipes. As the outside extension length (for tail pipe fitment) and diameter of outlet pipe (9) is same as the existing muffler, the tail pipes can be fitted easily with any angle of rotation and in both left hand drive and right hand drive vehicles without any modification of existing tail pipes.
FIG.13 illustrates the schematic flow pattern through muffler assembly according to the disclosure. The working principle of third chamber (C3) along with other two chambers (C1 and C2) is illustrated.
Further, it can be observed from the illustrations that length, perforations, size of perforations, number of perforations, and size (diameter) of the intermediate pipes (8) can be varied. Also, the middle baffle (5) and the rear baffle (6) could provide with varying number of perforations with various sizes and patterns of the perforations. Furthermore,

length of compartmentalization provided in disclosure may also be varied with respect to other variations in the muffler so as to enhance the performance. The disclosed dimensions or ratios amongst the compartments are for illustrative purpose only and should not be construed to limit the scope of the invention.
Advantages:
The muffler disclosed in the disclosure occupies lesser volume and hence weigh less is cost effective. The muffler is easy to manufacture, easy to pack and handle. The muffler comprises thicker shell in place two shells (outer and inner) and ceramic blanket as per the prior art designs. Hence, the design of the muffler improves effectiveness in cost and manufacturability, and also reduction of lead time of product development. Further, unnecessary usage of larger flange is controlled on design of bafflers unless the system demands to limit both weight and cost of muffler.
Baffles used in third chamber have smaller flange and rear baffle has no flange for central big through hole. For manufacturing convenience, perforation hole-size is kept same in rear baffle with inlet and intermediate pipes of the muffler. Further, diameter for perforation is kept same as existing baffle of existing muffler to avoid additional tooling cost though this size (i.e-diameter) is bigger than all other perforation on any parts of present muffler. However, this will help to reduction of cost in line with weight. In totality, it will indirectly help to improve handling due to lesser weight in addition to lesser length and volume.
To reduce further cost and lead time of product development existing end covers with minor modifications are used in this muffler in line with straight type pipes and same diameter hole for perforation. There is no critical joining between any pipes as existing muffler.
The function of Glass wool or ceramic wool bag is to absorb high frequency sound, but it is temperature sensitive and it would lose its sound absorption property in long run in high temperature application. Hence, it is placed in such a pattern that it will experience lowest temperature in the muffler. The glass wool or ceramic wool bag is placed in the

muffler body using the perforated rear baffle. Also, there is a very little chance to come out of burnt glass wool or ceramic wool which is a hazardous material through outlet pipe to environment because of placement position of it in inside the muffler. Both quantity and placement feature of glass wool or ceramic wool are the indication of environment friendly nature of the muffler.
Equivalents
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least

two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

We claim:
1. An exhaust muffler (1), comprising:
a muffler body (1a);
a front end cover (2) enclosing an inlet of the muffler body (1a);
an inlet pipe (7) connected to the front end cover (2);
one or more intermediate pipes (8) offset to the inlet pipe (7) is connected to a non-perforated front baffle (4) positioned adjacent to the inlet pipe (7), wherein said intermediate pipe (8) comprises perforations (8a) on its circumference;
a perforated middle baffle (5) comprising a through hole (5a) at its center and is positioned adjacent to the one or more intermediate pipes (8); and
an outlet pipe (9), wherein one end of the outlet pipe (9) is extended through the through hole (5a) of the middle baffle (5) for a predetermined distance towards the one or more intermediate pipes (8), other end of the outlet pipe (9) is passed through a through hole (6a) of a perforated rear baffle (6), before connecting to a rear end cover (3).
2. The muffler (1) as claimed in claim 1, wherein a partial open perforated plate (8b) is mounted at outlet of the intermediate pipe (8).
3. The muffler (1) as claimed in claim 1, wherein glass wool or ceramic wool (10) is provided in a space formed between the rear baffle (6) and the rear end cover (3) to absorb noise of exhaust gases.
4. The muffler (1) as claimed in claim 1, wherein the through hole (6a) of the rear baffle (6) is provided at its center.
5. The muffler (1) as claimed in claim 1, wherein cross section area or diameter of hole of the perforations (5b) of the middle baffle (5) is larger than that of the rear baffle (6).
6. The muffler (1) as claimed in claim 1, wherein flange thicknesses of front baffle (4), the middle baffle (5) and the rear baffle (6) are in the range of about 10 mm -20 mm.

7. The muffler (1) as claimed in claim 1, wherein number of perforations (6b) in the rear baffle (6) is more than that of the middle baffle (5).
8. A method of assembling an exhaust muffler (1) comprising:
enclosing a front end cover (2) at an inlet of the muffler body (1a);
connecting an inlet pipe (7) to the front end cover (2);
connecting one or more intermediate pipes (8) offset to the inlet pipe (7) to a non-perforated front baffle (4) positioned adjacent to the inlet pipe (7);
connecting a perforated middle baffle (5) comprising a through hole (5a) at its center and positioning it adjacent to the one or more intermediate pipes (8); and
connecting an outlet pipe (9) to the rear end cover (3), wherein one end of the outlet pipe (9) is extended through the through hole (5a) of the middle baffle (5) for a predetermined distance towards the one or more intermediate pipes (8), other end of the outlet pipe (9) is passed through a through hole (6a) of a perforated rear baffle (6).
9. The method as claimed in claim 8, wherein the inlet pipe (7) and the outlet pipe (9) are mounted axially and are connected to the muffler body (1a) by gas welding process.
10. The method as claimed in claim 8, wherein the front baffle (4) and the middle baffle (5) are welded to the muffler body (1a) by gas welding process.
11. An exhaust muffler and a method of assembling substantially as herein above described and as illustrated in accompanying drawings.