FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rulel3)
1. TITLE OF THE INVENTION:
"HYBRID SOUND ATTENUATINGDEVICE FOR INTERNAL COMBUSTION ENGINE'"
2. APPLICANT:
(a) NAME: MAHINDRA & MAHINDRA LIMITED
(b)NATIONALITY: Indian Company incorporated under the Companies Act, 1956
(c) ADDRESS: Gateway Building, Apollo Bunder, Mumbai - 400001, Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION:
The following specification describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
The present invention relates to a hybrid sound attenuating device, and particularly, for attenuating the sound waves entrained in the exhaust gas which comes out from internal combustion engines, and more particularly, to a sound attenuating device having combined configuration of resonator chambers, expansion chambers and absorption materials provided with multi torturous flow path for achieving attenuation of different ranges/bands of frequencies of sound waves.
BACKGROUND OF THE INVENTION:
Conventionally, there have been lots of inventions in the field of sound attenuating devices depending upon intended applications, specific objectives and required performance by having different configurations and combinations of the essential parts of the device. Presently, a sound attenuating device in use with automobile applications comprises a closed chamber or shell having provided with passage ways for inlet and outlet for the medium from which entrained sound waves need to be attenuated, different compartments within the shell separated by baffles for attenuating particular frequencies, and tubes with openings of required diameter on circumferential surface thereof for communicating the medium from one compartment to another compartment as well as for attenuating desired ranges of frequencies of sound waves. Depending upon frequency of sound waves to be attenuated, aforesaid components are designed and constructed in different configuration and combinations for desired acoustic impedance mismatch to achieve maximum sound attenuation.
According to the present invention, sound attenuating device being described herein is mainly applicable for dampening frequencies of sound waves contained in exhaust gases coming out from internal combustion engines. It is also understandable that a person skilled in the art can also modify the present invention without departing from the scope of the invention in accordance with the requirement of other applications. Generally, present sound attenuating devices are designed with an intention to dampened particular range of frequencies with respect to the noise generated by different applications. Also limitations such as developing an effective sound attenuating device of shell size that can be accommodated within the space available also need to be considered while defining an efficient configuration or combination of components of sound attenuating devices.

Another prime criteria that requires to be considered is-ensuring least restriction to the flow of exhaust gases passing through the device without compromising effectiveness of attenuation of the sound waves which would otherwise create backpressure in the exhaust system of internal combustion engine, which if not controlled effectively may adversely affect engine performance. Hence, configuration of sound attenuating device needs be designed in such a way that it should suitably design the flow path so as to achieve ultimate objective of getting efficient sound attenuation with less backpressure.
Hence, there remains necessity in the field of sound attenuating devices to develop a device having a combination of resonator chambers, expansion chambers, plurality of tubes and absorption materials with innovative configuration so as to dampen most frequency bands of sound waves without increasing backpressure in the exhaust system of internal combustion engines, also to have such a device of shell size to be possible to accommodate within limited space available for disposition thereof.
Some known sound attenuating devices are described here below, which may perform according to the intention with which it is developed for different application. However, to meet specific requirement like ours, we needed to develop a device which would overcome the limitations and shortcomings possessed by the prior arts, some of which are described here below.
US Patent 20070238272 discloses a discharge muffler provided with Helmholtz Resonator and torturous flow path, wherein the resonator which communicates with torturous path has two distinct Helmholtz throats and Helmholtz resonator volumes in series with each other for dampening two distinct frequencies. This invention is not capable of eliminating noises generating throughout entire operation of engine in both high and low speed operation zones.
US Patent 4911262 discloses a muffler which includes first expansion chamber, second expansion chamber, a resonator chamber, a resonator pipe and a return pipe. The configuration of the inlet pipe, return pipe and outlet pipe indicates high chances of backpressure getting increased as the kind of arrangement done here makes the flow path highly twisted and may boost development of backpressure.

Considering aforementioned limitations of prior arts and configuration of existing sound attenuating devices, and with the objective of developing a sound dampening device for effectively attenuating any ranges of frequencies of sound waves entrained in exhaust gases, the present invention is designed, in which two resonator chambers and two resonator tubes therein are provided to dampen two low frequencies of sound waves, plurality of expansion chambers and plurality of intermediate pipes therein are provided to dampen medium frequencies of sound waves and circumferential walls of the expansion chambers are covered with selective absorbing materials to dampen high frequency sound waves more effectively.
OBJECTIVE OF THE INVENTION:
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
The main object of the present invention is to provide a sound attenuating device having plurality of resonator chambers, plurality of expansion chambers, plurality of resonator tubes, plurality of intermediate pipes and absorbing material for dampening different ranges of frequencies of sound waves entrained in exhaust gases coming out from internal combustion engines while operating at high or low speed zones.
Another object of the present invention is to dampen two low frequencies by providing two resonator chambers and corresponding two resonator tubes in parallel with inlet pipe for communicating with each resonator chambers from first expansion chamber.
Yet another object of the present invention is to cover the internal circumferential surface of the expansion chambers with suitable absorbing materials thereby attenuating high range frequencies of sound waves more effectively.
Yet another object of the present invention is to provide a novel and innovative design of intermediate pipes and positioning thereof in the expansion chamber so as to enable smooth flow of exhaust gases with minimal restriction thereby avoiding creation of backpressure in the exhaust system of internal combustion engines.

Yet another object of the present- invention is to reduce backpressure in the exhaust system of internal combustion engine by limiting the number of intermediate pipes and at the same time by providing absorbing material over the internal circumferential surface of the expansion chambers for achieving affective attenuation of the desired sound waves.
Yet another object of the present invention is to avoid mixing of loose particles of absorbing materials with exhaust gas that comes out from the outlet pipe, by suitably covering both internal circumferential surface and external circumferential surface of the absorbing material sheet.
Yet another object of the present invention is to provide a sound attenuating device of robust construction by extending inlet pipe upto the middle of the shell through the central axis of the shell and having parallel placement of baffles to have different chambers so as to avoid breakout noise.
Yet another object of the present invention is to provide an effective sound attenuating device of shell size/shape having innovative configuration of components thereby to accommodate in the available limited space for assembly without compromising on performance of the device.
In accordance with the present invention, one aspect of the sound attenuating device comprises an outer shell having both ends closed with plates, an inner shell also having both ends closed with plates, plurality of resonator chambers, plurality of expansion chambers, an inlet pipe for receiving exhaust gas that comes out from internal combustion engine, an outlet pipe for exiting the exhaust gas to atmosphere, plurality of intermediate pipes, plurality of resonator tubes in parallel with inlet pipe and absorbing materials;
Wherein,
Outer shell is partitioned by baffles for plurality of resonator chambers, expansion chamber(s) for disposition of said inner shell; Wherein, Said inner shell is partitioned by baffles for plurality of expansion chambers; Wherein, Inlet pipe is provided with perforations for acoustically communicating with expansion chamber partitioned in outer

shell and for acoustically communicating with inner shell; Wherein, plurality of intermediate pipes are positioned at expansion chambers of inner shell for having a zigzag flow path thereby to ensure dampening of medium frequencies of sound waves with minimum back pressure; Wherein, Plurality of resonator tubes dispositioned in-a way so as to communicate exhaust gas with plurality of corresponding resonator chambers for dampening two low frequencies of sound waves;
Wherein,
Absorbing material is positioned between outer periphery of said inner shell throughout the length thereof and inner periphery of said outer shell for acoustically communicating with exhaust gas present in the expansion chambers of inner shell for dampening high frequencies of sound waves more effectively.
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 embodiments 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 view of preferred embodiment of the sound attenuating device
according to present invention; and FIG. 2 is cross sectional view along the line A-A with reference to FIG.l.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
The preferred embodiment of the present invention will now be described in detail with reference to accompanying drawings and which is merely exemplary in nature and is in no way intended to limit the invention, its applications or uses.

Referring to FIG. 1, the preferred embodiment of a sound attenuating device according to present invention is designated as numeral 1. The sound attenuating device 1 is a substantially long hollow body of oval in shape, not limited to the scope of the present invention, comprises an outer shell 14 made preferably of steel having a first end 20 covered with a plate 8 and a second end 21 with a plate 4, an inlet pipe 10 inserted through said plate 8 for receiving exhaust gases coming out from exhaust system of internal combustion engine, an outlet pipe 18 inserted through said plate 4 & 42 for exiting the exhaust gas to atmosphere via an exit end 32.
According to the preferred embodiment of the present invention, said inner shell 13 is extended from second end 21 of the outer shell 14 up to middle of the outer shell 14. It will be appreciated that a person having sufficient knowledge in the art can vary length of the inner shell 13 and the same may be positioned at any location along the length of the outer shell 14 as per the requirement. Said inner shell 13 is also having a first end 38 closed with a plate 33 and a second end 43closed with a plate 42 and partitioned by baffles 2 and 3 to form first expansion chamber 23 defined by said plate 33 and said baffle 3, and third expansion chamber 25 defined by said baffle 2 and said plate 42. Sufficient space is made available between the outer periphery of said inner shell 13 and inner periphery of said outer shell 14 to fill up with suitable absorbing materials 19 such as ceramic, throughout the length of said inner shell 13. Said inner shell 13 is provided with perforations for acoustically communicating exhaust gases with said absorbing materials. Said outer shell 14 is also partitioned into fourth expansion chamber 20 defined by said plate 8 and a baffle 7, a first resonator chamber 21 defined by baffles 6 and 7 and a second resonator chamber defined by said baffles 6 and 5.
The inlet pipe 10 of said attenuating device 1 passes through said baffles 7, 6, 5 and 33, leading to a downstream end 26, which is acoustically communicated with the first expansion chamber 23. Portion of the inlet pipe 10 extended from the plate 8 to the first expansion chamber 23 and passing through the fourth expansion chamber 20 is provided with perforations 39 &44 respectively for acoustically communicating with respective expansion chambers 23 and 20. Said attenuating device also incorporates a first intermediate pipes 15 and a second intermediate pipes 16 within the inner shell 13,

wherein first end 27 of the second intermediate pipe 16 is acoustically communicated with first expansion chamber 23 and second end 28 there of is closely connected with the baffle 2 and second end 30 of first intermediate pipe 15 is acoustically communicated with third expansion chamber 25 and first end 29 thereof is connected with baffle 3 and partially communicated with first expansion chamber 53 through a hole 40 provided on the baffle 3 along the axis of the first intermediate pipe 15 as shown in FIG. 2. The outlet pipe 18 having a first end 31, thereof is closely connected to baffle 2 and provided with perforations 17 throughout the length of the third expansion chamber 25 acoustically communicating with exhaust gas. Said baffle 3 is also provided with holes 41 around the central axis of the outer shell 14 for directly communicating the first expansion chamber 23 and second expansion chamber 24.
The sound attenuating device 1 also comprises a first resonator tube 11 and a second resonator tube 12, which are inserted through baffles 7 and disposed in parallel with said inlet pipe 10, wherein an inlet and 34 of said resonator tube 11 and an another inlet end 36 of said resonator tube 12 is acoustically communicated with said expansion chamber 20. The resonator tube 11 leading to a downstream end 35 is communicated with said resonator chamber 21 and a downstream end 37 0f said resonator tube 12 is communicated with said resonator chamber 22.
The preferred embodiment according to present invention shown in FIG.l is mainly designed for attenuating frequencies of sound energies Entrained in the exhaust gas which comes out from three-cylinder, four-stroke engines. Every two revolutions of the crank shaft generate single firing pulse which varies proportionally to the engine speed. Generally, vehicle-level silencer performance test is carried out at maximum engine rpm in running under partial and maximum loading condition Engine rpm will be different at different loading conditions, so the sound waves possess different ranges of frequencies, correspondingly, the noise level and back pressure of silencer is measured for efficiently dampening different ranges low frequencies of sound waves without compromising on back pressure.
Referring to FIG.l, combination of said resonator charter 21 and resonator tube 11 is designed for dampening 54Hz to 55Hz frequencies (i.e targeting fundamental firing

frequency:55Hz at engine rpm of 2200, which is high idle or maximum engine rpm according to the present invention). Subsequently, combination of resonator chamber 22 and resonator tube 12 is designed for dampening 107Hz to 113Hz frequencies (i.e. targeting first harmonic of said fundamental firing frequency: 110Hz at engine rpm of 2200, which is high idle or maximum engine rpm according to the present invention). Said inner shell 13, which is partitioned with baffles 2 and 3 to form first expansion chamber 23, second expansion chamber 24 and third expansion chamber 25 is provided with intermediate pipes 15 and 16 along with said absorbing material sheet 19 between inner shell 13 and outer shell 14 for dampening medium to high frequencies in the range of250Hz to 5000Hz.
With this combination and configuration of plurality resonator chambers and corresponding resonator tubes therein, expansion chambers, intermediate pipes, inlet & outlet pipe and absorbing material, the backpressure is reduced to 140 milibar whereas allowable (permissible as per regulator)' norms) limit for the considered application is 180milibar. The noise level of the vehicle in running Condition with maximum loading condition is achieved at 89.3dB as compared with 106.6dB for vehicle having no silencer with same load and same running condition. Thus, the total noise level reduction achieved with the present invention is 17.3dB (A) at Operator's Ear (OEL) Level.
The method of performance of the preferred embodiment according to the present invention, described in detail construction above will now be described herein below with referring to FIG. 1 & FIG. 2. The sound attenuating device 1 is removably connected to exhaust system of internal combustion engine to receive exhaust gas via inlet end 9 of said inlet pipe 10. Some amount of the exhaust gas(es) passing along the length of the inlet pipe 10 gets diverted and communicates with expansion chamber 20 through perforations 44, and remaining exhaust gas acoustically communicates with inner shell 13 specifically with first expansion chamber 23 through perforations 39. Exhaust gas that communicates with the expansion chamber 20 is passing through inlet end 34 of first resonator tube 11 and inlet end 36 of second resonator tube 12 and communicates with resonator chamber 21 and resonator chamber 22 respectively. Since the resonator chambers are completely closed chambers the exhaust gas entering inside is getting reflected and molecules of sound energy collide with each other and get nullified. By this

way of providing two resonator chambers and correspondingly two resonator tubes, two low frequencies of sound waves can be dampened.
The exhaust gas communicating with first expansion chamber 23 via downstream end 26 of inlet pipe 10 and the perforations 39 is passing through first end 27 of second intermediate pipe 16 and communicates with second expansion chamber 24 through perforation provided therein and communicates with first intermediate pipe 15 through said hole 40. Also the exhaust gas present in the first expansion chamber 23 directly communicates with holes 41 mainly to minimize back pressure in the system. The exhaust gas present in the second expansion chamber 24 communicates with first intermediate pipe 15 via perforation provided therein, then with third expansion chamber 25 and then with outlet pipe 18 through the perforations and exits to atmosphere via exit end 32. The specific configuration of the intermediate pipes 15 & 16 with perforations provided therewith, position of outlet pipe 18 and holes 41 makes the exhaust gas to pass/flow with optimum back pressure with dampening of medium Frequencies of sound waves more effectively.
The exhaust gas communicated to inner shell 13 and with expansion chambers 23, 24 & 25 is acoustically communicated with absorbing materials 19 for dampening high frequencies of sound waves efficiently through perforations provided on the inner shell 13, Outer circumferential area and inner circumferential area of said absorbing material 19 is covered with suitable filtering material like paper sheet to avoid mixing with exhaust gas, loose particles coming out from the outlet pipe 18. Description of the invention described herein is illustrative only, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings.

We Claim,
1. A hybrid sound attenuating device useful in dampening different ranges of frequencies entrained from internal combustion engine comprising a combined configuration of plurality of resonator chambers, plurality of expansion chambers and absorption materials alongwith multi-torturous flow path, wherein said device comprises:
an elongated outer shell (14) closed with plates (8) and (4) on ends (20) and (21), respectively, comprises a substantially elongated inlet pipe (10) at first end (20) for receiving exhaust gas coming out from internal combustion engine and for passing the exhaust gas into said outer shell, an outlet pipe (18) at second end for exiting the exhaust gas to atmosphere from said outer shell; at least one expansion chamber, at least one resonator chamber;
an elongated inner shell (13)having a shorter length than outer shell (13), disposed inside said outer shell (14), wherein, inner shell (13) is closed with plates 33 and 42 on ends 38 and 43 respectively, comprises at least one expansion chamber and at least one intermediate pipe for communicating the exhaust gas passing through inlet pipe (10);
an inlet pipe (10), for receiving exhaust gas from combustion engine and passing the exhaust gas into said outer shell (14) through first end (20);
an outlet pipe (18), for exiting the exhaust gas to atmosphere from outer shell (14) through second end (21);
at least one expansion chamber for communicating the exhaust gas passing through inlet pipe;
at least one resonator chamber for communicating the exhaust gas with said atleast one expansion chamber via atleast one resonator tube, said resonator tube is disposed in the outer shell (14) in a relation parallel with longitudinal axis of outer shell (14);
an absorbing material disposed between inner circumferential surface of outer shell (14) and outer circumferential surface of inner shell (13) and

a plurality of intermediate pipes having perforation throughout the length for creating torturous flow path of exhaust gas.
2. The hybrid sound attenuating device according to claim 1, wherein cross section of outer shell is oval or cylindrical in shape.
3. The hybrid sound attenuating device according to claim 1, wherein the outer shell comprises expansion chamber (20), a first resonator chamber (21) and a second resonator chamber (22).
4. The hybrid sound attenuating device according to claim 1, wherein cross sectional area of inner shell (13) is less than that of outer shell (14).
5. The hybrid sound attenuating device according to claim 1, wherein said inner shell is perforated on circumferential surface.
6. The hybrid sound attenuating device according to claim 5, wherein said inner shell is disposed at second end of said outer shell and very adjacent to said second resonator chamber.
7. The hybrid sound attenuating device according' to claim 5, wherein inner circumferential surface of said inner shell is covered with paper media for avoiding mixing of absorbing material with the exhaust gas.
8. The hybrid sound attenuating device according to claim 5, wherein said inner shell (13) comprises a first expansion chamber (26), a second expansion chamber (24), a third expansion chamber (25), a first intermediate pipe (15) and a second intermediate pipe (16).
9. The hybrid sound attenuating device according to claim 1 and 8, wherein said atleast one expansion chamber is communicating exhaust gas with said first resonator chamber (21) via a first resonator tube (11), said at least one expansion chamber is communicating exhaust gas with said second resonator chamber (22) via a second resonator tube (12).
10. The hybrid sound attenuating device according to claim 9, wherein expansion chamber (20) is on first side of outer shell (14), receives exhaust gas via perforations (44) provided on inlet pipe (10).

11. The hybrid sound attenuating device according to claim 1, wherein first resonator chamber (21) is very adjacent to expansion chamber (20) which communicates with exhaust gas via first resonator tube (11) disposed in parallel relation with said inlet pipe (10).
12. The hybrid sound attenuating device according to claim 1, wherein second resonator chamber (22) is very adjacent to said first resonator chamber (21) which communicates with exhaust gas via second resonator tube (12) disposed in parallel relation with said inlet pipe (10).
13. The hybrid sound attenuating device according to claims 11 and 12, wherein both first resonator chamber (21) and said second resonator chamber (22) parallely communicate exhaust gas with said expansion chamber (20).
14. The hybrid sound attenuating device according to claim 1, wherein downstream end of said inlet pipe (10) is open at first expansion chamber (23) and communicates the exhaust gas therewith, second expansion chamber (24) communicates the exhaust gas with first expansion chamber (23) via said second intermediate pipe(16), hole provided on baffle plate along the central axis of said first intermediate pipe (15)and atleast one hole provided on baffle plate (3) along the central axis of inlet pipe (10), said third expansion chamber (25) communicates the exhaust gas with said second expansion chamber (24) via said first intermediate pipe (15), said third expansion chamber is open with said outlet pipe (18).