HYBRID MUFFLER
The present invention relates to a novel hybrid muffler which reduces the noise level of the exhaust gas. Particularly, the present invention relates to a muffler which employs the principles of both reflective and absorptive techniques to reduce the noise level of exhaust gas of automotive vehicles to a pre-determined range.
Commercial vehicles are the major contributors for the noise pollution by automobiles. The main contributor of noise in a commercial vehicle, per se, is the exhaust system. The control of noise from the exhaust system depends on the design of the muffler, the layout of the exhaust system, the piping etc. However, the specific focus is towards the design of the muffler. Design of mufflers is a complex function that affects the noise characteristics and the fuel efficiency of the vehicle. So, a good design of muffler should give the best noise reduction and offer optimum backpressure for the engine. Moreover, for a given internal configuration, mufflers have to work for a broad range of engine speed. Mufflers can have a number of elements inside which need to be chosen as per the level of attenuation required and recommended Engine back pressure, this involves a lot of iteration of physical testing for each of the prototypes. Any muffler is qualified by the amount of Insertion Loss (IL) that takes place within the muffler. Insertion Loss can be defied as the difference in the Sound Pressure Levels (SPL) at the exhaust outlet, with and without the muffler. Based on the required Insertion Loss, mufflers with different internal configurations can be designed and tested for muffled noise spectrum and vehicle noise.
The conventional muffler consists of two mufflers, namely a main muffler and an auxiliary muffler, as shown in fig. 1.

Main muffler is a reactive muffler wherein the exhaust gases interact with various acoustic elements inside the muffler & thereby causing transmission loss leading to reduced noise of exhaust gas that comes out of the outlet. Auxiliary muffler is an absorptive type wherein the exhaust gases react with the filaments of glasswool, thereby resulting in frictional loss of energy, leading to further noise reduction of the exhaust gas that comes out of the outlet. The combination of main muffler & auxiliary muffler leads to attenuation of broad range of frequencies. This attenuation for a broad range of frequencies is required to meet the target of exhaust noise requirement in line with the vehicle noise target as per MOEF notification GSR849 (E) ie. 78dB(A). Further, flanges are used at each end of main & auxiliary muffler respectively to avoid leakage, which is also a concern for overall exhaust noise. There are two varieties of combination of of main muffler & auxiliary muffler to suit different engines on different vehicles, supplied by different vendor.
The drawback of the conventional muffler is that it consumes larger packaging space leading to shorter tail pipe & sharp bends of the tail pipes in some vehicles. As each of the muffler i.e. main & auxiliary has flanges on either side, it results in three flanged joints viz at main muffler inlet, auxiliary muffler outlet & in between main & auxiliary muffler. This results in use of more bolts & more time to assemble the muffler on the vehicle. Also the cost is more owing to usage of flange & gaskets. The combined weight of main muffler & auxiliary muffler is around 20 kg, thereby resulting in more load on clamps/brackets & more material cost. Further, the conventional mufflers occupy more storage space & also more inventory owing to variety of such combinations of main muffler & auxiliary muffler. The glasswool material used in auxiliary muffler is lose bonded. This results in escape of the same in tiny quantities along with exhaust gas, which is hazardous to environment. The slow escape of glass wool as mentioned above would result in less quantity of glass wool in auxiliary muffler in comparison with the required amount. This results in deterioration of muffler performance & hence leading to vehicle noise deterioration.

Hence, there is a need for a muffler which can overcome the drawbacks of the conventional muffler.
An object of the present invention is to provide a novel hybrid muffler which can overcome the above drawbacks. Another object of the present invention is to provide a new single muffler, that would blend the performance characteristics of two different varieties of twin muffler combinations with following benefits.
a) Consistent performance
b) Reduced weight
c) Reduced cost
d) Decreased variety
e) Ease in vehicle assembly
f) Reduced component assembly time
The muffler of the present invention employs the principles of both reflective & absorptive mufflers, hence the name Hybrid Muffler.
Accordingly, the present invention provides a hybrid muffler for automotive vehicles comprising a hollow jacket having a first and a second end; a first end cover with a hole mounted on the first end of the jacket; a second end cover with a hole mounted on the second end of the jacket; two perforated baffles with at least four holes and one plain baffle with one hole fixed inside the jacket in such a manner that the jacket is divided into four chambers, an inlet pipe extending from the first end of the jacket upto the third chamber of the jacket through the holes in the first end cover and the perforated baffles; one end of the inlet pipe is connected to a flared tube of the engine and a connector is mounted on the other end of the inlet pipe; an outlet pipe extending from the second end of the jacket upto the first chamber of the jacket through the holes in the said end cover and the baffles; the inlet pipe extending in the second chamber has a set of perforations with a pre-determined size, the outlet pipe extending in the second, third and fourth chambers has different set of perforations

with pre-determined sizes and the outlet pipe (4) located in the fourth chamber (D) is wrapped with glass wool material.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS :

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS :
The muffler of the present invention comprises a hollow jacket (8) which is covered at both ends by end covers (6, 7) having a hole. The jacket (8) is divided into four chambers (A,B,C,D) with a help of two perforated baffles (5) and one plain baffle (9). Each of the perforated baffles (5) has at least four holes. An inlet pipe (2) is inserted from the first end cover (7) and extend upto third chamber of the jacket through the holes in the end cover (7) and the perforated baffles (5). One end of the inlet pipe (2) is connected to a flared tube of the engine and the other end of the inlet pipe (2) is fitted with a connector (3).
An outlet pipe is inserted from the second end cover (6) and extends upto the first chamber of the jacket (8) through the hole in the second end cover (6) and the baffles (5, 9). The fourth chamber (D) is filled with glass wool material with thickness of filament in microns called silentex. A portion of the inlet pipe (2) which is placed in the second chamber (B) comprises one set of perforation of predetermined size to kill certain frequencies. Each row of perforation is staggered compared to adjacent row of perforation. In a preferred embodiment, the diameter of the perforation can be

from 5.5mm to 6.5mm and the pitch i.e. distance between corresponding points of consecutive rows can be about 18mm. The inlet pipe could have about 12 rows of perforation with 16 perforations per row. The inlet pipe could extend into the third chamber (C) for 70mm to 90mm , preferably 80mm. The connector (3) which is fixed to the free end of the inlet pipe (2) converges from about 73mm outer diameter at one end to about 50mm inner diameter at the other end with a width of about 10mm.
The outlet pipe (4) comprises three set of perforations to kill certain frequencies. Each row of perforation is staggered compared to adjacent row of perforations for a given set. The first set of perforations are made in the outlet pipe (4) which is placed in the fourth chamber (D). Preferably, the diameter of the first set of perforations can be from 3.5mm to 4.5mm and the pitch can be about 12 mm. The first set could contain about 17 rows of perforations with about 20 perforations per row. The second set of perforations are made in the outlet pipe (4) which runs through the third chamber (C). Preferably, the diameter of the second set of perforations can be from 2.0mm to 2.8mm and the pitch can be about 8 mm. The second set could contain about 9 rows of perforations with about 20 perforations per row. The third set of perforations are provided in the outlet pipe (4) which runs through second chamber (B). Preferably, the diameter of the third set of perforations can be from 2.4mm to 3.2mm and the pitch can be about 19 mm. The third set could contain about 19 rows of perforations with about 13 perforations per row. The outlet pipe (4) runs through all four chambers and extends in the first chamber (A) for 70mm to 90mm, preferably 70mm.
In a preferred embodiment, the four chambers (A,B,C,D) of the jacket (8) could be having specific dimensions of 218mm 249mm, 137mm and 200mm respectively. The free holes of the perforated baffles (5) could be preferably of the 60mm in the diameter. These holes act as an acoustic elements.
The shape of the jacket (8) could be of two semi circles joined by a rectangle at their ends.

The length of the jacket preferably range from 740mm to 940mm. The jacket is preferably constructed from a plane sheet with ends overlapped and welded across the whole length or crimped across the whole length of the jacket (8).
The working of the muffler of the present invention are explained in detail herein below :
The muffler according to the present invention uses both the principles of reflective and absorptive principles and hence named as hybrid muffler.
Reflective Principle:
The first 3 chambers (A,B,C) of the jacket (8) form the reflective muffler. As the exhaust gas enters the inlet pipe, it goes straight to second chamber because there is no other path to escape into first chamber. On entering the second chamber (B) it comes across the 1st set of perforation of the Inlet pipe & some gas (gl) thus escapes from the inlet pipe into the shell around the inlet pipe, this phenomenon can be explained by following two points
i) Expansion: The exhaust gas is initially present in the pipe, which is of smaller diameter compared to the shell/jacket diameter. There is difference between the volume of the pipe & the volume of the shell giving rise to expansion of the gas into the larger volume space. This gives the benefit of transmission loss.
ii) Pipe perforation: The perforations are the specific designs to kill certain frequencies during the passage of the gas from inside of the pipe to outside of the pipe. The thickness of the pipe also plays a role. This gives the benefit of transmission loss.
Some of the exhaust gas (g21) of the inlet pipe goes straight & hits the connectors at the end & gets reflected resulting in reflected waves that cancel some of

the incoming waves. This gives the benefit of transmission loss. Some of the gas (g22) passes through the centre of the pipe & bangs with the baffle (9) that is positioned in front of the inlet pipe. This results in reflected waves that cancel some of the incoming waves. Here the expansion principle as explained above also holds true, the only difference is that the some gas (g23) expands directly through the connector into the shell.
Some of the exhaust gas (gl + g23 + g22) of the inlet pipe tries to enter the perforation of the outlet pipe in 2nd chamber (B) & 3rd chamber (C). This results in interaction of the gases that are trying to come out of the outlet pipe & the gases that are trying to enter the outlet pipe through the perforation, giving rise to molecular interaction & the acoustic energy loss. The gas that has occupied the shell (gs = gl + g23 + g22) passes through the connectors of the baffles (5) & tries to enter the outlet pipe in the first chamber. This gas further comes across the perforation in the 2nd chamber resulting in an phenomenon as explained for inlet pipe above. The same phenomenon gets further repeated when it comes across the perforation of the outlet pipe in 3 rd chamber. It is to be noted that the exhaust gas that is entering the muffler has high pressure & there is heavy interaction of the gas molecules by virtue of reflection caused by various elements including the impingement of the gases on the inner surface of the jacket. This also adds to the transmission loss
Absorptive Principle:
The exhaust gas that passes away through the outlet pipe of 3rd chamber (C) gets further carried away to 4 chamber (D). This gas comes across the outlet pipe perforation in the 4th chamber. Part of this gas escapes into the shell through the perforations by blasting the glass wool bag that is wrapped around the perforation, resulting in attenuation of certain frequencies & spread of the glass wool across the whole chamber. The remaining exhaust gases escape the muffler. As the 4 chamber (D) is filled with glass wool having filament thickness in microns, there is more surface contact between the exhaust gas escaped from the perforations & the filaments

of glass wool. This results in friction & conversion of acoustic energy into heat energy, thus helping in further transmission loss.
Thus the noise level of the exhaust gas of the vehicle is reduced to the required level before leaving the muffler. The exhaust frequency mapping for conventional twin muffler and the hybrid muffler of the present invention is shown in figure 5. The noise level near exhaust pipe for conventional muffler is 97.21 dB(A) and for the hybrid muffler of the present invention is 94.87dB(A).
Thus it is clearly evident that the hybrid muffler of the present invention has a potential to reduce the noise level of exhaust gas. It should be noted that the muffler of the present invention can also be used to reduce the noise level of the exhaust gas of power generator and the like.
The above explanation merely illustrates the principle of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.

WE CLAIM :
1. A hybrid muffler for automotive vehicles comprising a hollow jacket (8) having a first and a second end; a first end cover (7) with a hole mounted on the first end of the jacket; a second end cover (6) with a hole mounted on the second end of the jacket; two perforated baffles (5) with at least four holes and one plain baffle (9) with one hole fixed inside the jacket (8) in such a manner that the jacket is divided into four chambers (A,B5C,D) an inlet pipe (2) extending from the first end of the jacket upto the third chamber (C) of the jacket through the holes in the first end cover (7) and the perforated baffles (5); one end of the inlet pipe is connected to a flared tube (1) of the engine and a connector (3) is mounted on the other end of the inlet pipe; an outlet pipe (4) extending from the second end of the jacket (8) upto the first chamber (A) of the jacket through the holes in the said end cover (6) and the baffles (5,9); the inlet pipe extending in the second chamber (B) has a set of perforations with a pre-determined size, the outlet pipe extending in the second, third and fourth chambers (B,D) has different set of perforations with pre-determined sizes; the outlet pipe (4) located in the fourth chamber (D) is wrapped with glass wool material.
2. The muffler as claimed in claim 1, wherein the inlet pipe (2) in the second chamber (B) has about 12 rows of perforations with about 16 perforations in each row and the perforations are preferably of 5.5mm to 6.5mm in diameter.
3. The muffler as claimed in. claim 1, wherein the inlet pipe (2) extends into the third chamber (C) preferably for 70mm to 90mm.
4. The muffler as claimed in claim 1, wherein the outlet pipe (4) in the fourth chamber (D) has about has about 17 rows of perforations with about 20 perforations in each row and the perforations are preferably of 3.5mm to 4.5mm in diameter.

5. The muffler as claimed in claim 1, wherein the outlet pipe (4) in the third
chamber (C) has about 9 rows of perforations with about 20 perforations in
each row and the perforations are preferably of 2.0mm to 2.8mm in diameter.
6. The muffler as claimed in claim 1, wherein the outlet pipe (4) in the second chamber (B) has about 19 rows of perforations with about 13 perforations in each row and the perforations are preferably of 2.4mm to 3.2mm in diameter.
7. The muffler as claimed in claim 1, wherein the jacket (8) has a shape of two semicircles joined by a rectangle at their ends.
8. The muffler as claimed in claim 1, wherein the dimension of the first, second,
third and fourth chambers (A,B,C,D) are preferably 218mm. 249mm, 137mm
and 200mm respectively.
dated this 13 day of December 2006