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:
"LOW BACKPRESSURE MULTI CHAMBER SILENCER"
2. APPLICANT:
(a) NAME: MAHINDRA & MAHINDRA LIMITED
(b) NATIONALITY: Indian Company incorporated under the Indian
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 silencer for attenuating sound waves entrained in exhaust gas
that comes out from internal combustion engines and, more particularly, to a silencer with configuration having provided multi resonating chambers for attenuating different ranges of frequencies of sound waves, advantageously with very low backpressure.
BACKGROUND OF THE INVENTION:
There have been a lot of inventions in the field of silencers depending upon intended
applications, specific objectives and desired performance by having different configurations and combinations of essential parts of the sijencer. Conventionally, a silencer in use with automobile applications comprises a closed chamber or shell having provided with inlet and outlet, for the medium from which the entrained sound waves need to be attenuated to pass through and a plurality of compartments within the shell separated by baffles for nullifying different ranges of frequencies of sound waves.
Generally, there are two prime parameters which have to be appropriately taken into consideration while designing any kind of configuration of silencers for use with internal combustion engines for eliminating sound waves contained in the exhaust gas with minimum backpressure. The first parameter is effectiveness in dampening/attenuating definite ranges of frequencies of sound waves whichever are dominantly seen in frequency spectrum of particular application, and secondary parameter is maintaining minimum backpressure in the exhaust system of internal combustion engines. Since both the parameters are inversely proportional to each other in designing a silencer, it is of paramount importance to have a silencer which should be able to effectively dampen any or most or definite ranges of frequencies of sound waves with minimum backpressure in the exhaust system of engine.
US Patent 5839405 discloses an exhaust muffler provided with maximum three Resonators placed in parallel and torturous flow path, wherein the resonator which communicates with torturous path has several perforations instead of using set of multi-tubes. This US patent invention can be used to average dampening of broad range exhaust sound waves, but will not be capable for effective elimination of lower exhaust frequencies and some harmonics of sound

waves which is dominant in automotive application, and also unable to effectively control high frequency noise contents due to absence of dissipative chamber.
US Patent 5365025 discloses a muffler which includes first and end dissipative chambers with sound absorbing material and middle expansion chamber with wire screen to reduce sound pressure pulsation. The configuration of the said US patent is not able to attenuate lower frequency exhaust sound waves which are dominant.
US Patent 2003754619 discloses a muffler which includes four expansion chambers to average dampening of broad range medium to high frequency noise contents and three dissipative chambers separated by transverse perforated plates to dampen high frequency exhaust noise contents. This, however, is unable to effectively dampen lower frequency exhaust noise which is one of the prime sources of noise in internal combustion engines.
Considering aforementioned limitations of prior arts and configuration of existing silencers, and with the objective of developing a sound dampening device for effectively attenuating lower dominant frequencies along with their harmonics and medium to higher frequencies of sound waves entrained in the exhaust gases with minimum backpressure encouraging best engine performance along with maximum noise reduction, the present invention is being designed.
In general, two types of muffling devices are used, reactive1 and dissipative. Both these types of configuration have their own advantages and purposes/ applications. Reactive types of muffling devices are mainly for dampening broad frequency ranges with lower attenuation at lower frequencies whereas higher attenuation at comparatively medium and higher frequencies of sound waves by providing plurality of expansion chambers, multiple tubes with perforation and torturous flow path. This leads to restriction to the flow of fluid medium which further causes backpressure in the exhaust system of internal combustion engines. Dissipative types of muffling devices are more useful for dampening high and medium frequencies of sound waves by having a combination of plurality of chambers filled with absorbing materials and straight through, uniform cross section pipe with perforation. This kind of configuration is more useful in application where engine performance is mandatory or of primary importance and low

frequencies of sound is allowable, such as in race cars. Resonator chambers are primarily provided to dampen particular single frequency of sound waves with very less backpressure due to no direct gas flow obstacle or restriction.
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 silencer having very low back pressure with maximum possible sound attenuation capability.
Another object of the present invention is to dampen different low frequencies of sound waves and associated harmonics by providing multi-resonator chambers and plurality of resonator tubes therein.
Yet another object of the present invention is to provide an expansion chamber with highly dense absorbing materials thereby for attenuating medium and high range frequencies of sound waves.
Yet another object of the present invention is to provide straight through pipe with radial multi-resonator chambers and expansion chamber so as to enable smooth flow of exhaust gas without any direct restriction to the exhaust gas flow path thereby to avoid creation of backpressure in the exhaust system of internal combustion engines.
Yet another object of the present invention is to reduce backpressure to maximum extent (i.e. as good as negligible backpressure like in simple pipe) in the exhaust system of internal combustion engine by avoiding direct restriction to flow, providing multiple flow passes and area discontinuities.
Yet another object of the present invention is to provide a silencer of robust construction by extending inlet pipe from inlet end to the exit end in continuity and supported by multiple baffles

comprising different resonating chambers to outer shell so as to avoid breakout noise and also to have structurally robust construction.
Yet another object of the present invention is to provide an effective silencer of compact / limited shell size having innovative configuration of components thereby to accommodate the silencer in limited available space for assembly without compromising performance of the device.
In accordance with the present invention one aspect of the silencer comprises an outer shell having both ends closed with plates; Wherein, Outer shell is partitioned by baffles for plurality of resonator chambers and provided therein a plurality of resonator tubes disposed in such way to communicate exhaust gas with plurality of corresponding resonator chamber for dampening different low frequencies and associated harmonics of engine exhaust sound waves, a straight through pipe having first end for receiving exhaust gas that comes out from internal combustion engine, and second end for exiting the exhaust gas to atmosphere, an expansion chamber filled with highly dense absorbing material for attenuating medium and high.frequencies of sound waves(high frequencies in more effective way).
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 said 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 preferred embodiment according to present invention.

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 silencer according to present invention is designated as numeral 1. The silencerl is a substantially long hollow body of circular in shape, which is not limited to the scope of the present invention, comprises an outer shell 20 made preferably of steel having a first end 31 covered with a circular plate/baffle30 and a second end 32covered with a circular plate/baffle21, a straight through pipe 2having firstend53 for receiving exhaust gases coming out from exhaust system of internal combustion engine and second end36 for exiting the exhaust gas to atmosphere.
According to the preferred embodiment of the present invention, said straight through' pipe 2 passes through parallely positioned, unevenly spaced consecutive baffles 30,29,28,27,26,25, 24, 23, 22 and 21.. Uneven placement of chambers 3, 4, 5, 6, 7, 8, 9, and lOis done purposefully for creating different acoustic volumes separated by said parallel baffles 30, 29, 28, 27, 26, 25, 24, 23, 22 and 21. The pipe 2 is having perforations 34 near to second end thereof for acoustical communicating with a chamber 11 separated by baffles 22 and 21 and filled with suitable absorbing materials 33 like glass wool.
One set of two coplanar radially equi-spaced tubes 12is provided within the chamber 3, one set of four coplanar radially equi-spaced tubes 13 is provided within the chamber 4, one set of six coplanar radially equi-spaced tubes 14 is provided within the chamber 5, one set of two coplanar radially equi-spaced tubes 15 is provided within the chamber 6, one set of four coplanar radially equi-spaced tubes 16 is provided within the chamber 7, one set of six coplanar radially equi-spaced tubes 17 is provided within the chamber 8, one set of two coplanar radially equi-spaced tubes 18 is provided within the chamber 9 and one set of four coplanar radially equi-spaced tubes 19 is provided within the chamber 10 for reducing different ranges of frequencies of sound waves as well as for having a silencer of optimized (compact) size over the prior arts without degrading the performance of silencer

The exhaust gas passing through said straight through pipe 2, which extends from the baffle 30 is acoustically communicating with the first expansion chamber 3 by means of said both side open ended one set of two tubes 12 having geometrical as well as dimensional exactness' in the preferred embodiment of the present invention. Further extension of the pipe 2 passing from baffle 29 is acoustically communicating with the second expansion chamber 4 by means of said both side open ended set of four tubes 13 having geometrical as well as dimensional exactness. Further extension of the pipe 2 passing from the baffle 28 is acoustically communicating with the third expansion chamber 5 by means of said both side open ended set of six tubes 14 having geometrical as well as dimensional exactness. Further extension of the pipe 2 passing from baffle 27 is acoustically communicating with the fourth expansion chamber 6 by means of said both side open ended set of two tubes 15 having geometrical as well as dimensional exactness. Further extension of the pipe 2 passing from baffle 26 is acoustically communicating with the fifth expansion chamber 7 by means of said both side open ended set of four tubes 16 having gedmetrical as well as dimensional exactness. Further extension of the pipe 2 passing from baffle 25 is acoustically communicating with the sixth expansion chamber 8 by means of said both side open ended set of six tubes 17 having geometrical as well as dimensional exactness. Further extension of the pipe 2 passing from baffle 24 is acoustically communicating with the seventh expansion chamber 9 by means of said both side open ended set of two tubes 18 having geometrical as well as dimensional exactness. Further extension of the pipe 2 passing from baffle 23 is acoustically communicating with the eighth expansion chamber 10 by means of said both side open ended set of four tubes denoted by 14 having geometrical as well as dimensional exactness. Further extension of the said pipe 2 passing from baffle 22 is acoustically communicating with the expansion chamber 11 filled with highly dense sound absorbing material by means of circular perforations having geometrical as well as dimensional exactness provided on the portion of the pipe 2 between the baffles 22 and 21, thereby to acoustically attenuate particular firing frequencies and associated harmonics of sound energies entrained in the exhaust gas coming from internal combustion engine.
The preferred embodiment according to present invention shown in FIG. 1 is mainly designed for attenuating frequencies of sound energies entrained in the exhaust gas which comes out from a


three-cylinder, four-stroke engines. Every two revolutions of the crank shaft generates single firing pulse which varies proportionally to the engine rpm. Generally, vehicle-level silencer performance test is being carried out at maximum engine rpm in running under partial and maximum loading conditions. Engine rpm will be different, at different loading conditions so 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, chamber 3 is designed for dampening frequencies in the range of 51.5Hz to 53,5Hz at 2100 engine rpm, targeting fundamental firing frequency i.e. 52.5Hz at 2100rpm. Subsequently, chamber 4 and chamber 5 are designed for dampening frequencies in the range of 102Hz to 108Hz and 153Hz to 162Hz targeting first and second harmonic frequencies i.e. 105 Hz and 157.5Hz of said fundamental frequency at 2100rpm.
Also, chamber 6 is designed for dampening frequencies in the range of 50.5Hz to 52.5Hz at 2050 engine rpm, targeting fundamental firing frequency i.e. 51.25Hz at 2050rpm. Subsequently, chamber 7 and chamber 8 are designed for dampening frequencies in the range of 99.5Hz to 105.5Hz and 149Hz to 162.5Hz targeting first and second harmonic frequencies i.e. 102.5 Hz and 153.75 Hz of said fundamental frequency at 2050rpm.
Also, chamber 9 is designed for dampening frequencies in the range of 53.4Hz to 56.7Hz at 2200 engine rpm, targeting fundamental firing frequency i.e. 55Hz at 2200rpm. Subsequently, chamber 10 is designed for dampening frequencies in the range of 107Hz to 113Hz targeting first harmonic frequencies i.e. 110 Hz of said fundamental frequency at 2200rpm which is high idle or maximum engine rpm according to the present invention. Chamber 11 is designed for dampening medium to high frequencies in the range of 250Hz to 5000Hz but is more effective for.high range of frequencies i.e. over 1 KHz.
With this configuration of multiple resonator chambers, expansion chamber and straight through pipe, the backpressure is reduced to 20milibar whereas allowable (permissible as per regulatory norms) is 180milibar for the considered application thereby the power loss due to backpressure is also minimized. The noise level achieved by the vehicle at maximum engine rpm in running

under full load is 91.7dB(A)compared with vehicle having no silencer with same load and same running condition, which is 107.2dB. Thus, the total noise level reduction achieved with the present invention at Operator's Ear (OEL) Level is 15.5 dB(A).
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. The silencer 1 is removably connected to exhaust system of internal combustion engine to receive exhaust gas via first end 53 of said straight through pipe 2. Exhaust gas passing along the length of the pipe 2 gets diverted and acoustically communicated with resonator chamber 3, 4, 5, 6, 7, 8, 9and 10 through corresponding set of tubes for attenuating individual low frequencies and the exhaust gas, which is acoustically communicating with expansion chamber 11 filled with said absorbing material attenuate medium and high frequencies of sound waves.
Accordingly, the specific configuration of resonator chambers 3, 4, 5, 6, 7, 8, 9and lOand radial arrangement of plurality of resonator tubes 38, 40, 42, 44, 46, 48, 50 and 52 therein respectively; and dissipative expansion chamber 11 described in the present invention makes the exhaust gas coming out from internal combustion engine to flow through the straight inlet pipe without any restriction. With this particular type of construction, the silencer becomes very less prone to backpressure and at the same time" gives significant reduction in noise level also. 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 multi resonator chamber silencer comprising:
an outer shell having first end closed with a first plate and second end closed with a second plate;
a straight through pipe having first end for receiving exhaust gas coming out from combustion engine and second end for exiting the exhaust gas to atmosphere;
a plurality of baffle disposed inside the outer shell transversely and spaced longitudinally for defining multiple resonator chambers;
at least one resonator chamber for attenuating fundamental firing frequency of sound waves generated at 2050 - 2200rpm;
at least one resonator chamber for attenuating harmonic of said fundamental firing frequency;
at least one tube connected to said straight through pipe for communicating the exhaust gas with each resonator chamber, and
at least one expansion chamber filled with sound absorbing material.
2) The multi resonator chamber silencer as claimed in claim 1, wherein said expansion chamber communicates the exhaust gas through perforations provided on said straight through pipe.
3) A multi resonator chamber silencer comprising:

an outer shell having first end closed with a first plate and second end closed with a second plate;
a straight through pipe having first end for receiving exhaust gas coming out from combustion engine and second end for exiting the exhaust gas to atmosphere; said straight through pipe is disposed inside the outer shell in parallel to longitudinal axis of the shell and inserted through said first plate and said second plate;
a plurality of baffle disposed inside the outer shell transversely and spaced longitudinally for defining multiple resonator chambers;
a first resonator chamber for attenuating fundamental firing frequency of sound waves generated at 2100-2200 rpm; wherein at least one tube is connected with said straight through pipe for communicating the exhaust gas with said first resonator chamber;
a second resonator chamber for attenuating first harmonic of said fundamental firing

frequency, wherein at least one tube is connected with said straight through pipe for
t
communicating the exhaust gas with said second resonator chamber;
a third resonator chamber for attenuating second harmonic of said fundamental firing frequency, wherein at least one tube is connected with said straight through pipe for communicating the exhaust gas with said third resonator chamber and said tubes are connected to said pipe substantially perpendicularly to longitudinal axis thereof and radially extended with first, second and third resonator chambers respectively, and
at least one expansion chamber filled with sound absorbing material, said expansion chamber communicating the exhaust gas through perforations provided on said straight through pipe.

4) The multi resonator chamber silencer as claimed in claim 3, wherein said first resonator chamber communicates the exhaust gas passing through said straight through pipe through a first set of two tubes.
5) The multi resonator chamber silencer as claimed in claim 4, wherein said two tubes are disposed in single plane at equal distance.
6) The multi resonator chamber silencer as claimed in claim 3, wherein said second resonator chamber communicates the exhaust gas passing through said straight through pipe through a first set of four tubes.
7) The multi resonator chamber silencer as claimed in claim 6, wherein said four tubes are disposed in single plane at equal distance.
8) The multi resonator chamber silencer as claimed in claim 3, wherein said third resonator chamber communicates the exhaust gas passing through said straight through pipe through a first set of six tubes.
9) The multi resonator chamber silencer as claimed in claim 8, wherein said six tubes are disposed in single plane at equal distance.
10) The multi resonator chamber silencer as claimed in claim 3 comprising a fourth resonator chamber, a fifth resonator chamber and a sixth resonator chamber for attenuating fundamental frequency of sound waves generated 2050 rpm and attenuating first and second harmonics of said fundamental frequency, respectively.