DESC:FIELD
The present subject matter relates to the field of mufflers used in vehicular exhaust systems.
BACKGROUND
One of the major part of any vehicle is its exhaust system. A vehicular exhaust system comprises many components, wherein a muffler is the most critical component which is also referred to as a ‘silencer’. As the name suggests, the purpose of the muffler is to reduce the noise generated by high pressure exhaust gases. A design of a typical exhaust muffler is highly complex. There are lots of mufflers available in the market with different internal arrangements of pipes and baffles, to ensure flow of exhaust gases to the atmosphere at reduced sound pressure levels (SPL).
Conventionally, a multiple chambered exhaust muffler includes an outer housing having an upper and lower half shell, an inner shell, and an inner exhaust gas duct through the exhaust gas muffler. The inner exhaust gas duct has at least one curved outlet pipe that has a first curved section and a straight outlet end that runs flush with the outer housing. In such a typical arrangement, manufacturability issues and backpressure values increase with the bends/curves of the pipes. Moreover, flow restrictions on exhaust gases are higher in the conventional mufflers, which result in dominant flow noise for higher frequency ranges. Additionally, back pressure in the mufflers can also lead to poor emission levels.
There is, therefore, felt a need provide a vehicular muffler that limits the aforementioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of conventional vehicular exhaust systems or to at least provide a useful alternative.
Another object of the present disclosure is to provide a vehicular muffler which is tuned for better sound character with reduced sound pressure levels and higher sound transmission losses.
Still another object of the present disclosure is to provide a vehicular muffler that provides for better engine performance parameters like lesser fuel consumption, and reduced mono-nitrogen oxides (NOx) and hydrocarbon emission levels.
Yet another object of the present disclosure is to provide a vehicular muffler which is tuned for different frequency ranges, wherein chamber volumes are optimized for increasing sound transmission loss (STL) in respective frequency ranges.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure envisages a vehicular muffler comprising a shell. The shell includes a plurality of chambers, a semi-perforated connecting pipe, an inlet pipe and an outlet pipe. The plurality of chambers are defined by at least one disc and a plurality of baffles. The connecting pipe is configured to provide a connection between at least two chambers of the plurality of chambers. The inlet pipe is configured to intake exhaust gases produced in a vehicle and the outlet pipe is configured to vent the exhaust gases to the atmosphere. The inlet pipe and the outlet pipe have at least one opening in one of the chamber of the plurality of chambers.
In an embodiment, the shell is elliptical. The at least one disc does not touch the inner walls of the shell and provides a support frame for the connecting pipe, the inlet pipe and the outlet pipe.
In another embodiment, the plurality of chambers include a first chamber, a second chamber, a third chamber and a fourth chamber, such that the disc separates the first and second chamber, a first baffle of the plurality of baffles separates the second and third chamber, and, a second baffle of the plurality of baffles separates the third and fourth chamber. In one embodiment the second baffle is perforated. Further, the first chamber is configured to be tuned for low frequencies, the second chamber is configured to be tuned for mid frequencies and the third chamber is configured to be tuned for high frequencies.
In one embodiment, the first chamber is connected to the third chamber via the connecting pipe, such that perforations on the connecting pipe facilitate the second chamber to be tuned for mid frequencies.
In another embodiment, a perforated glass wool with a pre-determined thickness is wrapped around the first chamber and the second chamber to facilitate high frequency absorption. The third chamber provides an opening for each of the inlet pipe and the outlet pipe. The fourth chamber is filled with glass wool to facilitate sound transmission losses at higher frequencies. Further, the fourth chamber is smaller in size than the first chamber, the first chamber is smaller in size than the second chamber, and the second chamber is smaller in size than the third chamber.
In an embodiment, the second chamber contains a glass wool having a pre-determined density. In another embodiment, the first chamber is a Helmholtz resonator.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A vehicular muffler of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figures 1a, 1b, 1c and 1d illustrate a front view, a side perspective view, a top view and a side view of a muffler, in accordance with an embodiment of the present disclosure;
Figure 2 illustrates a side cross-sectional view of the muffler, in accordance with an embodiment of the present disclosure;
Figure 3 illustrates a top cross-sectional view of the muffler, in accordance with an embodiment of the present disclosure;
Figure 4 illustrates another side cross-sectional view of the muffler, in accordance with an embodiment of the present disclosure;
Figures 5a and 5b illustrate three-dimensional views of the muffler, in accordance with an embodiment of the present disclosure; and
Figure 6 illustrates a chart showing a comparison between a conventional baseline muffler and the muffler of the present disclosure in accordance with one embodiment.
DETAILED DESCRIPTION
The present disclosure envisages a vehicular muffler to limit the issues of conventional mufflers including to manufacturability and poor emission levels.
Referring to the accompanying drawing, Figures 1 to 5 illustrate different views of a muffler 10 in accordance with one embodiment of the present disclosure. The muffler comprises a shell 12 having a plurality of chambers. The plurality of chambers are defined by at least one disc and a plurality of baffles. The muffler 10 also includes a semi-perforated connecting pipe 22, an inlet pipe 28 and an outlet pipe 30. The connecting pipe 22 provides a connection between at least two chambers of the plurality of chambers. The inlet pipe 28 intakes exhaust gases produced in a vehicle and the outlet pipe 30 vents the exhaust gases to the atmosphere. In one embodiment, the shell 12 is elliptical and includes four chambers viz. a first chamber 14, a second chamber 16, a third chamber 18, and a fourth chamber 20, for tuning low, mid and high frequency ranges for higher sound transmission loss as compared to the conventional mufflers.
In an embodiment, the first chamber 14 is used as a Helmholtz resonator for tuning low frequencies. The connecting pipe 22 connects the first chamber 14 and the third chamber 18. The second chamber 16 is used for tuning mid frequencies with the help of perforations 24 provided on the connecting pipe 22. A glass wool wrapping 26 of optimized thickness is wrapped around the first chamber 14 and the second chamber 16 to maximize high frequency absorption. The third chamber 18 defines a space where both the inlet pipe 28 and the outlet pipe 30 of the muffler 10 open. Finally, the fourth chamber 20 is filled with a perforated glass wool. In an embodiment, a packing density of the glass wool inside the fourth chamber 20 is about 200gms/liter. This helps in improving the sound transmission losses in the higher frequency range.
In one embodiment, the glass wool is placed such that, it does not restrict any pipe openings, thereby allowing the third chamber 18, where the inlet pipe 28 and the outlet pipe 30 open, to be tuned for higher frequencies. Also, as there is no obstruction to the flow of the exhaust gases, backpressure created by the muffler 10 is minimal. This helps in overall performance improvement of the associated vehicle.
The elliptical shape of the shell 12 of the muffler 10 helps maximize an expansion ratio (d/D) of the vehicle’s engine. In order to have a sound transmission loss in a lower frequency range, the first chamber 14 and the second chamber 16 are wrapped by perforated glass wool wrapping. On the other hand, the glass wool in the fourth chamber 20 facilitates increase in the absorptive characteristics of the muffler 10 and also prevents heating of an end plate 32 of the muffler 10.
In another embodiment, the first chamber 14 is smaller in size as compared to the second chamber 16. Further, the second chamber 16 is smaller in size than the third chamber 18. The fourth chamber 20 is the smallest chamber as compared to the first chamber 14, the second chamber 16, and the third chamber 18. The connecting pipe 22 acts as a neck that connects the first chamber 14 and the third chamber 18. The connecting pipe 22 allows for a better sound transmission loss in the 300-500hz frequency range, as can be seen in test results provided in Figures 6.
A resonating frequency F in a given chamber can be determined from the following equation:

where, ? is the expansion constant of the exhaust gas;
V is the volume of a chamber;
A is the cross-sectional area of a pipe through which the gases release;
l is the length of the pipe.
Thus larger openings give higher frequency since air can rush in and out faster. Further, a large volume gives a lower frequency since more air must move out to relieve a given pressure excess. Further, a longer neck gives a lower frequency since there is more resistance to the air moving in and out.
If F is the frequency for the first chamber 14, it gets cancelled out in the Helmholtz cavity, i.e., inside the first chamber 14. So, the sound transmission losses are maximum for that frequency. In a Campbell plot, the contribution of F will be the least as compared to overall sound pressure levels (SPL).
Further, a first baffle 34 of the plurality of baffles separates the second chamber 16 from the third chamber 18. The first baffle 34 does not have perforations. This helps in maintaining a single opening for the Helmholtz resonator setup of the first chamber 14. A second baffle 36 of the plurality of baffles separates the third chamber 18 from the fourth chamber 20. The second baffle 36 has perforations.
In an embodiment, the second chamber 16 also contains glass wool of a packing density of about 150gms/liter. This helps in maximizing the sound transmission losses, for a higher frequency range, than for the first chamber 14. The second chamber 16 counts for the absorptive nature of the muffler 10, in which the high frequency wavelengths are absorbed through the perforations on the second baffle 36 and the perforations 24 on the connecting pipe 22. The second baffle 36 helps in improving the absorptive capacity of the muffler 10 by increasing the absorption from the third chamber 18.
Further, as shown in Figure 4, a disc 38 acts as a support frame for the connecting pipe 22, the inlet pipe 28 and the outlet pipe 30. The disc 38 does not touch inner walls of the shell 12, thereby providing a Helmholtz resonator like enclosure between an area encompassed by the first chamber 14 and the second chamber 16.
Furthermore, the third chamber 18 provides an opening for the inlet pipe 28 and the outlet pipe 30. A volume of the third chamber 18 and a length of the outlet pipe 30 are optimized in such a manner so as to have minimum sound transmission losses at around 800Hz. The same can be seen in a Campbell graph of Orifice noise level.
In the muffler 10, a cylindrical air column with both ends open vibrates with a fundamental mode such that an air column length is one-and-a-half of the wavelength of the sound wave. Each end of the air column is an antinode for the air motion, since the ends are open to the atmosphere and cannot produce significant pressure changes. For the fundamental mode, there is one node at the center. The basic wave relationship leads to the frequency of the fundamental mode as follows:

where, L= length of the pipe. The length of pipe is used to optimize the frequency that a human ear perceives in the overall sound contribution of the exhaust system.
With the muffler 10 of the present disclosure, sound pressure levels (SPL) of a vehicle, such as a tractor, was reduced by 3 dB(A) and a backpressure essential for Exhaust Gas Recirculation (EGR) was maintained so as to have a better fuel economy, lesser emission and maximum power output. Table 1 provided below illustrates emission test results of a baseline muffler (Conventional) and the muffler 10 of the present disclosure.
TABLE 1
Emissions- Test Results
Nox+HC (g/kWh) CO (g/kWh) Soot (g/kWh)
Baseline muffler 3.86 1.82 0.008
Muffler of the present disclosure 3.69 0.89 0.005

As compared to the baseline mufflers, nitrogen oxides and hydrocarbon emission levels are lesser in the muffler 10. Also, soot and CO levels have been drastically reduced. So, the muffler 10 as described herein not only reduces noise pollution, but also helps in reducing air pollution by significantly reducing emissions.
Further, Figure 6 illustrates that the dBA levels are considerably reduced at engine LHS and engine RHS after using the muffler 10. It is also observed that the operator ear levels (OEL) is drastically reduced from 89.7 dBA to 88.4 dBA.
Furthermore, from the Table 2 shown below, it is seen that the BSFC (brake specific fuel consumption) levels for the muffler 10 of the present disclosure drastically reduce at higher RPMs at different gear levels.
TABLE 2
Baseline Muffler Muffler of the present disclosure
BSFC BSFC
RPM g/kWh g/kWh
2400
2400 240
246 236
246
2400
2400
1500 276
227
220 275
204
219
1500
1500 220
242 220
240

TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
• a vehicular muffler which is tuned for better sound character with reduced sound pressure levels and higher sound transmission losses;
• a vehicular muffler that provides for better engine performance parameters like lesser fuel consumption, and reduced mono-nitrogen oxides (NOx) and hydrocarbon emission levels;
• a vehicular muffler which is tuned for different frequency ranges, wherein chamber volumes are optimized for increasing sound transmission loss (STL) in respective frequency ranges; and
• a vehicular muffler that is cost efficient and which improves sound transmission losses.
The disclosure is described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. ,CLAIMS:1. A vehicular muffler comprising:
a shell having
a plurality of chambers defined by at least one disc and a plurality of baffles;
a semi-perforated connecting pipe configured to provide a connection between at least two chambers of said plurality of chambers;
an inlet pipe configured to intake exhaust gases produced in a vehicle; and
an outlet pipe configured to vent said exhaust gases to the atmosphere, wherein said inlet pipe and said outlet pipe have at least one opening in one of the chamber of said plurality of chambers.

2. The vehicular muffler as claimed in claim 1, wherein said shell is elliptical.

3. The vehicular muffler as claimed in claim 1, wherein said at least one disc does not touch the inner walls of said shell and provides a support frame for said connecting pipe, said inlet pipe and said outlet pipe.

4. The vehicular muffler as claimed in claim 1, wherein said plurality of chambers include a first chamber, a second chamber, a third chamber and a fourth chamber, such that said disc separates the first and second chamber, a first baffle of said plurality of baffles separates the second and third chamber, and, a second baffle of said plurality of baffles separates the third and fourth chamber.

5. The vehicular muffler as claimed in claim 4, wherein said second baffle is perforated.

6. The vehicular muffler as claimed in claim 4, wherein said first chamber is configured to be tuned for low frequencies, said second chamber is configured to be tuned for mid frequencies and said third chamber is configured to be tuned for high frequencies.

7. The vehicular muffler as claimed in claim 4, wherein said first chamber is connected to said third chamber via said connecting pipe, such that perforations on said connecting pipe facilitate said second chamber to be tuned for mid frequencies.

8. The vehicular muffler as claimed in claim 4, in which a perforated glass wool with a pre-determined thickness is wrapped around said first chamber and said second chamber to facilitate high frequency absorption.

9. The vehicular muffler as claimed in claim 4, wherein said third chamber provides an opening for each of said inlet pipe and said outlet pipe.

10. The vehicular muffler as claimed in claim 4, wherein said fourth chamber is filled with glass wool to facilitate sound transmission losses at higher frequencies.

11. The vehicular muffler as claimed in claim 4, wherein said fourth chamber is smaller in size than said first chamber, said first chamber is smaller in size than said second chamber, and said second chamber is smaller in size than said third chamber.

12. The vehicular muffler as claimed in claim 4, wherein said second chamber contains a glass wool having a pre-determined density.

13. The vehicular muffler as claimed in claim 4, wherein said first chamber is a Helmholtz resonator.