FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION REACTIVE EXHAUST MUFFLER
2. APPLICANT(S)
MAHINDRA & MAHINDRA LIMITED
1, GATEWAY BUILDING, APOLLO BUNDER, MUMBAI - 400001,
MAHARASHTRA, INDIAN.
The following specification describes the invention.

FIELD OF THE INVENTION
The present invention generally relates to a restrictive type of sound attenuation device incorporated with engine exhaust system for attenuating frequencies of exhaust gas sound waves by way of expansion of exhaust gas through a plurality of holes provided on straight through pipe along with a restrictive wall disposed therein without increase in back pressure in the engine exhaust system.
BACKGROUND OF THE INVENTION
Essentially, an exhaust muffler consists of a housing having provided with an inlet port at the upstream end for entry of exhaust gas into it and an outlet port at the downstream end for exiting the exhaust gas out of the muffler. Compared with other applications of muffler, design of (an engine) exhaust muffler is very complex and critical due to the design parameter, backpressure. Thus, while designing an exhaust muffler, besides the key purpose of attenuating noise, care should be taken to avoid creation of undesirable backpressure in the exhaust system, since disposing of any device along the flow path of exhaust gas tends to pose as obstacle or resistance to the gas-flow and thus tends to increase backpressure, which causes negative effect on engine performance and in turn would lead to higher specific fuel consumption. To take care of the above said points, there have been mufflers developed previously with a straight through pipe provided with perforations for entry and exit of the exhaust gas and enclosed with a shell with sound-absorbing materials therein for attenuating desired sound frequencies/level. However, in

this type of configuration of muffler, plates/ baffles shall be provided around the straight through pipe radially or longitudinally for disposing the absorbing material. And also care should be taken to avoid mixing of the absorbing material particles with the exhaust gas which might lead to increased pollution. In straight through pipe muffler construction, it is also very important to ensure sufficient torturous flow path of exhaust gas for effective sound attenuation of sound waves without compromising much on the backpressure in the engine exhaust system.
Hence, in the kind of applications where backpressure is not considered as a paramount design parameter, the shell is partitioned into different chambers which may be completely closed or partially closed by providing openings in separating baffle plates, and provided with an inlet pipe for communicating exhaust gas with desired chambers within the muffler and an outlet pipe for exiting the exhaust gas out of the muffler. Also, desired number of perforated tubes may be provided in the muffler for communicating the exhaust gas between different chambers as required. This particular configuration of the muffler would be more efficient in attenuating the sound level but would cause creation of increased backpressure in the exhaust system of the engine due to resistance in flow path of the gas.
In general, mufflers are distinguished as restrictive, reactive (reflective), absorptive (dissipative) and hybrid/ compound (combination of two or more types) mufflers. A restrictive muffler incorporates perforated tubes and tortuous gas flow paths. A reactive muffler incorporates plurality of expansion and resonator chambers. Restrictive and reactive mufflers are more effective in attenuating lower and medium ranges of frequencies of exhaust sound. An

absorptive muffler incorporates plurality of expansion chambers filled with sound absorbing material and perforated tube with straight through gas flow path. It is more effective in attenuating medium and higher ranges of frequencies of exhaust sound.
As is known from the prior arts, there have been many inventions in the field of sound attenuation devices using perforated tubes and absorbing materials depending upon desired requirements of noise level attenuation. According to the present invention, a hybrid muffler having combination of restrictive and reactive effects is being developed to meet the desired performance. Some of the related prior arts are being described hereunder as reference.
US Patent 1173583 discloses a muffler that includes an outer imperforate shell provided with end headers which are connected by an inner shell passing through both of the headers. In the annular space between the shells are diaphragms which reinforce the muffler and also form resonating chambers. A plurality of small and closely spaced perforations in the inner shell effects communication of gas between the resonating chamber and the inner shell. Since the invention is having a straight through pipe and provided with small perforation, possibility of effective communication of gas between the various resonating chambers and the inner shell will be less which may cause deficiency in attenuating the sound waves.
US Patent 1173583 discloses a muffler having a centre tube which is disposed with a first pair of apertures at opposite sides of the periphery of the tube and second pair of apertures having diameter perpendicular to said first pair of apertures at the periphery of the tube forward to said first pair of apertures. A

wall is disposed in between said first pair of apertures and second pair of apertures thereby to restrict the gas flow and cause for torturous flow path of exhaust gas. Said tube is enclosed with a cylindrical casing and set of each first & second pair of apertures is separated by disks so as to form different chambers. In this configuration of the muffler, tendency of creation of backpressure in the engine exhaust system is high due to the continuous restriction of the gas flow by the walls. And valve arrangements in the walls and closing and opening arrangements thereof make the system and manufacturing and assembling the muffler very complex.
US Patent 1051130 discloses an exhaust muffler comprising an outer shell member having inlet and exhaust ports, and also provided with water inlet and exhaust ports, a chambered inner cylindrical casing having charge receiving and charge exhausting chambers, pipe extensions projecting into said chambered casing from the inlet and exhaust ports of the outer shell member and a cap member adapted to be separably attached to the outer shell member. This invention has the disadvantages of necessity of means for supplying water into the muffler which will make the exhaust system very complex and expensive. The water may enter into the charge receiving chamber and charge exhausting chamber thereby it affect the reliability of the muffler. Importantly, less number of openings in the cylindrical casing for exit and entry of the exhaust gas may cause high backpressure in the engine exhaust system.
US Patent 2039800 discloses a silencer which, in combination with a duct, comprises a shell having flanges attached thereto surrounding at least a portion of said duct and enclosing an annular chamber, an annular disk spaced a uniform distance from and adjacent interiorly of one of said flanges and

forming an end wall of said chamber, the space between said flange and said disk opening into said duct, said annular disk having one or more acoustic-resistance openings therein. This invention is generally designed for diverse applications and because of which, it cannot be simply adapted for effective attenuation of noise associated with exhaust gas coming out from engine.
Hence the present invention is designed with the objective of effectively attenuating dominant lower range of sound frequencies along with their harmonics and some of the medium range of sound frequencies of engine exhaust gas with minimum backpressure on engine. Exhaust gas sound pressure level and exhaust gas back pressure on engine are inversely proportional to each other. Hence it is of paramount importance to design an exhaust muffler, which will effectively dampen broader spectrum of sound frequencies with minimum backpressure on engine.
OBJECTIVES OF THE INVENTION
The present invention overcomes the shortcomings associated with the prior arts and achieves other advantages not realized by the prior arts.
The main objective of the present invention is to provide an exhaust muffler to attenuate sound level associated with exhaust gas arising from engine in application used with off-road vehicle such as tractors and alike.
Another objective of the present invention is to provide an exhaust muffler for attenuating dominant lower frequencies along with their harmonics of engine exhaust and some medium frequencies of sound waves, by a straight through

tube with flow divider plate at center to achieve tortuous exhaust gas flow path with plurality of holes for converting sound energy into heat energy.
Yet another objective of the present invention is to provide an exhaust muffler, which has least gas flow resistance thereby to achieve least exhaust backpressure on engine, which in turn results in reduced engine specific fuel consumption and improvement in overall engine performance.
Yet another objective of the invention is to provide a simple, cost effective, structurally rigid exhaust muffler, which generates least self induced vibrations, hence which is very durable.
Yet another objective of the present invention is to design an exhaust muffler having size constrained with respect to the given space for disposing the same in the exhaust system of the vehicle without getting disturbed with surrounding parts and without compromising on performance of muffler.
In accordance with one aspect of the present invention, the exhaust muffler comprises an outer shell which is of cylindrical hollow member in structure and having upstream end closed with an inlet end cap and downstream end closed with an outlet end cap, an inlet pipe for communicating exhaust gas coming out from the exhaust system of the engine with the muffler, an outlet pipe for exiting the exhaust gas out of the muffler, a straight through perforated tube with an exhaust gas flow divider plate and one side branch resonator chamber each at inlet and outlet end of shell for attenuating specific dominant notes in low frequency spectrum of exhaust gas sound.
Wherein the first side-branch resonator chamber is formed between the inlet end cap and first baffle plate which is partially closed chamber and communicates with exhaust gas sound waves through perforations provided on periphery of inlet pipe between inlet end cap and first baffle plate. This

chamber is being designed to attenuate dominant note of first harmonic of fundamental engine firing frequency present in exhaust gas sound.
Wherein the second side-branch resonator chamber is formed between outlet end cap and second baffle plate which is partially closed chamber and communicates with exhaust gas sound waves through perforations provided on periphery of outlet pipe between second baffle plate and outlet end cap. This chamber is being designed to attenuate dominant note of fundamental engine firing frequency present in exhaust gas sound.
Wherein, inlet and outlet pipes are partitioned by a flow divider plate. Both inlet and outlet pipes have number of holes over entire length, and hole diameter designed sufficient enough and also larger with respect to inlet pipe diameter so as to maintain least resistance to exhaust gas flow for minimum exhaust backpressure on engine.
Wherein the expansion chamber is formed between first and second baffle plates and communicates with two side-branch resonator chambers.
This particular combination and configuration of the exhaust muffler ensures effective attenuation of engine exhaust sound pressure level with minimum backpressure in the engine exhaust system.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiment of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
FIG. 1 is longitudinal sectional view of the exhaust muffler according to the present invention. Cross sectional views drawn on line A-A, B-B and C-C in longitudinal sectional view are also shown herewith.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
While this invention is susceptible of embodiments in many different forms, it should be understood that the present disclosure is to be considered as an example of the principle of the invention and not intended to limit the invention to the preferred embodiment shown and described,
Referring to FIG.1, preferred embodiment of exhaust muffler according to the present invention for using on off road vehicles such as tractors or alike is being described in detail herein below. The exhaust muffler is mounted on exhaust stub pipe (not shown) of the exhaust system of the vehicle by inserting outer diameter of the stub pipe inside inlet pipe 1 of the muffler. Specifications of the engine for which the proposed muffler is being designed are naturally aspirated direct injection diesel engine developing 45 BHP at 1900 rotational speed and at 2090 fly-up (high idle, no-load) speed. This particular engine is used in off-road vehicle such as tractors or alike. However, without having any substantial change in the preferred configuration of the exhaust muffler in accordance with the present invention and by changing diameter of perforations provided on inlet pipe 1 and outlet pipe 8, volumes of different chambers and additionally by providing sound absorbing material, the

below described muffler can be adopted to any naturally aspirated engine used on off-road vehicle such as tractors or alike
FIG.1 shows schematic longitudinal section of preferred embodiment of the exhaust muffler according to the present invention, made from sheets of structural steel. Shell 3 of the muffler is a round hollow member. At inlet end, inside diameter of inlet end cap 2 is joined to outside diameter of inlet pipe 1 and outside diameter of inlet end cap 2 is joined to inside diameter of shell 3. Inside diameter of first baffle plate 4 is joined to outside diameter of the inlet pipe 1 and outside diameter of first baffle plate 4 is joined to inside diameter of shell 3. The inlet pipe 1 is provided with perforations on its periphery between inlet end cap 2 and first baffle plate 4. Outside diameter of second baffle plate 6 is joined to inside diameter of shell 3. Downstream end of inlet pipe 1 and upstream end of outlet pipe 8 are joined a plate 5. Inlet pipe 1 is provided with perforations on its periphery between first baffle plate 4 and plate 5. Outlet pipe 8 is also provided with perforations on its periphery between plate 5 and outlet end cap 7. Space between the first baffle plate 4 and the second baffle plate 6 in the longitudinal direction of the muffler forms an expansion chamber 12. Space between the inlet end cap 2 and the first baffle plate 4 in the longitudinal direction of the muffler forms a first resonator chamber 10. Space between the second baffle plate 6 and the outlet end cap 7 in the longitudinal direction of the muffler forms a second resonator chamber 15.
The aforementioned constructional details, according to present invention, describe attenuation of different frequency ranges of exhaust gas sound with minimum backpressure on engine as below.
Engine exhaust gas enters into said exhaust muffler through the inlet pipe 1 from its inlet opening. Inside diameter of inlet pipe 1 is derived from exhaust gas flow rate of applicable engine, ensuring minimum back-pressure on engine.

Sound waves passing through inlet pipe 1 communicate with first resonator chamber 10 through perforations 9 provided on the inlet pipe 1.
From inlet pipe 1, exhaust gas enters into the expansion chamber 12 through perforations 11 on inlet pipe 1 between first baffle plate 4 and plate 5. Size, number and spacing of perforations on inlet pipe 1 are designed in such a way that area of all the holes put together is substantially larger than cross sectional area of inlet pipe 1 without affecting structural rigidity of inlet pipe 1. This ensures minimum exhaust backpressure on engine as exhaust gas passes through said perforations on inlet tube 1 with least resistance and substantial sound energy is getting converted into heat energy. Although perforations of round-shaped holes are preferred from standpoint of ease of manufacturing, holes of shape other than circular/round may also be preferred for desired performance result.
From expansion chamber 12, exhaust gas enters into outlet pipe 8 through perforations 13 provided on outlet pipe 8 between the plate 5 and second baffle plate 6. Size, number and spacing of holes on outlet pipe 8 between plate 5 and second baffle plate 6 are designed in such a way that area of all holes is substantially larger than cross sectional area of the inlet pipe 1 without affecting structural rigidity of the outlet pipe 8. This ensures minimum exhaust backpressure on engine as exhaust gas passes through said perforations on outlet pipe 8 with least resistance and substantial sound energy is getting converted into heat energy. Although perforations of round hole are preferred from viewpoint of ease of manufacturing, holes of shape other than circular may also be preferred for desired performance result. Inside diameter of outlet pipe 8 is equal to or bigger than inside diameter of inlet pipe 1 to ensure minimum back-pressure on engine, Sound waves in outlet pipe 8 communicate with second resonator chamber 15 through perforations 14 provided on outlet pipe 8. From outlet pipe 8, exhaust gas is released to atmosphere.

The plate 5 between inlet pipe 1 and outlet pipe 8 plays two functions. Firstly, it forces exhaust gas through a two-stage expansion. In first stage, from inlet tube 1 through perforation 11 into expansion chamber 12 and in second stage, from expansion chamber 12 through perforations 13 into outlet pipe 8. The second function is that it provides structural rigidity to inlet pipe 1 and outlet pipe 8, which reduces self induced vibrations of the inlet pipe 1 and the outlet pipe 8 and increases durability of muffler.
The first baffle plate 4 and the second baffle plate 6 also provide structural rigidity to exhaust muffler by acting as gussets. The first baffle plate 4 acts as gusset between inlet pipe 1 and shell 3 and the second baffle plate 6 acts as gusset between outlet pipe 8 and shell 3.
With this configuration of exhaust muffler, according to the present invention, a test has been carried out on a 4 cylinder, naturally aspirated, 45 BHP diesel engine and found that the engine exhaust sound pressure level at operator ear level is reduced to 87.5 db.