FIELD OF INVENTION

The invention relate to the design of muffler, which are used to control noise level in the exhaust gas in an exhaust system. The invention particularly relates to the designs of elliptical vertical hybrid muffler, which negates the need of additional after treatment devices.

BACKGROUND OF THE INVENTION

Commercial vehicles are the major contributors for 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 and also the after treatment devices. 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 the muffler should give the best noise reduction and offer optimum back pressure 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 iterations 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 defined as the difference in 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 drawback of conventional muffler is that it consumes larger packaging space leading to a shorter tail pipe & sharp bends of the tail pipes in some vehicles. As the muffler has a higher length, it is very difficult to package the muffler in the already limited space available. Also, the existing conventional muffler requires more number of brackets as it is longer in length and requires additional length tail pipes to bring the tailpipe outlet to the side of the vehicle. Another problem with the conventional muffler is, because of the elongated tail pipe, there is an increased back pressure which hampers the proper running of the engine. This also means that there is lesser scope for noise attenuation as the muffler back pressure is forced to be lower.

In addition to these, there is a need for exhaust systems to meet stricter emission norms.

In such cases, there is a need to have additional after-treatment devices. The common ones used are SCR (selective catalytic reduction) and DOC/POC (oxidation catalysts in tandem with EGR-exhaust gas re-circulation). When these are brought in to effect, we need to have additional space to package these in separate enclosures. All this results in addition of more brackets, lesser space for packaging, higher costs and need for more maintenance. Also there is always the risk of pilferage of the after treatment device.

In case of petroleum tanker application, conventionally a front exhaust system was made use. A muffler with outlet on the side of the vehicle is very dangerous as the hot exhaust gases flow close to the tanker body. This could lead to severe consequences. This is the reason for the incorporation of a front-exhaust system. It comprised of an additional spark arrestor, which helps filter the larger particles of unborn fuel which would otherwise come out of the tail pipe. This was a precaution to prevent the production of any spark.

For vehicles which comply with higher emission norms, there is a need for after treatment devices. But for a front exhaust system where packaging is already a constraint, further addition of components is not manageable. Also, the new safety standards for smaller vehicles on road calls for additional under-protection devices, like FUPD (front under protection device), RUPD (rear under protection device) and SUPD (side under protection device). This calls for additional space requirements. Currently the muffler being made use of in all commercial vehicles has a conventional circular or elliptical cross section with a high length to diameter ratio.

OBJECT OF THE INVENTION

The object of the present invention is to design the muffler in such a way so that it occupies minimum space but at the same time does not compromise the emission and noise performance of machines comprising an exhaust system such as automobile engines and power generators.

It is also an objective of the invention, to provide a single new muffler that would blend the performance characteristics of two different varieties of twin combinations, which negates the need of an additional spark-arrester and after treatment devises.
Yet another objective of the present invention is the reduction of back pressure, which improves the engine performance as well as an increased transmission loss of the exhaust gas.

SUMMARY OF THE INVENTION

In order to achieve the above objective, the present invention provides a novel advanced integrated muffler for an inline pump engine, which incorporates the noise reduction principle of reflection and absorption and there by reduces the exhaust noise.

Accordingly, the present invention provides a hybrid muffler mounted vertically for automotive vehicles comprising a hollow jacket having a first and second end: a first end cover with a hole on the first end of the jacket; a second end cover with a hole on the second end of the jacket; three perforated baffles with four, seven and one holes respectively in such a manner that the jacket is divided into four chambers by the three baffles, an inlet pipe extending from the first end of the jacket up to the third chamber of the jacket through the holes in the first end cover and the first and second perorated baffles. One end of the inlet pipe is connected to a flange on one end and a connector is mounted on the other end.

An outlet pipe extending from second end of the jacket up to 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 predetermined size, the outlet pipe extending in the second third and fourth chambers has different set of perforations with predetermined sizes and the outlet pipe located in the fourth chamber is wrapped with glass wool material.

The packaging is done in such a way that the piping required for the exhaust system is as low as possible. This results in lower back pressure which improves the engine performance. The vertical elliptical muffler directs the exhaust gases in such a way that it is nowhere near any critical components like fuel tank and also away from the lower part of the side of the vehicle which otherwise would pose a problem to pedestrians and other smaller vehicles. The design of the hybrid muffler is done in such a manner, that the size of the particulate matter coming out is negligible. This negates the need for using an additional spark attestor which otherwise would be necessary in petroleum tanker applications.

The various features incorporated in the elliptical hybrid muffler to prevent the production of spark are

1. Muffler design is such that two 180-degree flow reversal elements have been incorporated. Providing such flow reversal elements forces the gases to flow in a longer path thereby reducing risk of spark.

2. Muffler design is such that several sets of perforations have been provided which help in more complex 3-dimensional flow and better circulation / centrifugal action thereby minimizing the chances of spark. A total of 4 sets of perforations have been used at different locations.

In addition to this, special purpose absorptive material has been added at critical positions in the flow path which will inhibit the passage of any spark through the flow chambers.

3. Care has been taken to use the same material for the muffler as that used in spark arrestors to give the muffler elements the same material properties. MS has been replaced with Aluminized steel.

4. Special acoustic elements like exponential connector and plug connectors have been added which, in addition to providing noise benefits, also help in increasing the flow path through flow reversal, thereby reducing the spark propagation.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIGURE 1: shows a perspective view of the present invention FIGURE 2: shows a front view of the muffler of the. present invention FIGURE 3: shows a cross section view of the muffler of the present invention

DETAILED DESCRIPTION:

It is good practice to design a muffler to work best in the frequency range where the engine has the highest sound energy. In practice the sound spectrum of an engine exhaust is continually changing, as it is dependent on the engine speed that is continually varying when the car is being driven. It is impossible to design a muffler that achieves complete destructive interference, however some will always occur.

Noise spectrum variation makes muffler design quite difficult and testing is the only sure way to determine whether the muffler performs well at all engine speeds. However, as a general rule of thumb, exhaust noise is generally limited to the fundamental frequency and the first few harmonics, which can be calculated; therefore these frequencies should be used as a starting point for preliminary muffler design.

A practical way of determining the frequency range to be controlled is to measure the unmuffled engine noise. This measured spectrum can then be used to identify the frequencies, at which the higher noise levels occur. The high noise level frequencies should be treated with appropriate noise control to achieve an overall noise reduction.

There are numerous functional requirements that should be considered when designing a muffler for a specific application. Such functional requirements may include adequate insertion loss, backpressure, size, durability, desired sound, cost, shape and style.

A mufflers performance or attenuating capability is generally defined in terms of insertion loss or transmission loss. Insertion loss is defined as the difference between the acoustic powers radiated without and with a muffler fitted. The transmission loss is defined as the difference (in decibels) between the sound power incidents at the entry to the muffler to that transmitted by the muffler. The muffler designer must determine the required insertion loss so that a suitable style of muffler can be designed for the specific purpose

Backpressure represents the extra static pressure exerted by the muffler on the engine through the restriction in flow of exhaust gasses. Generally the better a muffler is at attenuating sound the more backpressure is generated. Backpressure should be kept to a minimum to avoid power losses especially for performance vehicles where performance is paramount. Every time the exhaust gasses are forced to change direction additional backpressure is created. Therefore to limit backpressure geometric changes are to be kept to a minimum.

The available space has a great influence on the size and therefore type of muffler that may be used A muffler may have its geometry designed for optimum attenuation however if it does not meet the space constraints, it is useless. Generally the larger a muffler is, the more it weighs and the more it costs to manufacture. For a performance vehicle every gram saved is crucial to its performance/acceleration, especially when dealing with light open wheeled race vehicles. Therefore a small lightweight muffler is desirable.

Effectively supporting a muffler is always a design issue and the larger a muffler is the more difficult it is to support. A muffler's mounting system not only needs to support the mufflers weight but it also needs to provide vibration isolation so that the vibration of the exhaust system is not transferred to the chassis and then to the passenger cabin. This vibration isolation is usually achieved with the use of hard rubber inserts and brackets that isolate or dampen vibration from the muffler to the chassis.

The life expectancy of a muffler is another important functional requirement especially when dealing with hot exhaust gasses and absorptive silencers that are found in performance vehicles. Overtime, hot exhaust gasses tend to clog the absorptive material with unburnt carbon particles or burn the absorptive material in the muffler. This causes the insertion loss to deteriorate. There are however, good products such as mineral wool, fiberglass, sintered metal composites and white wool that resist such unwanted effects.

Generally a muffler is used to reduce the sound of a combustion engine to a desired level that provides comfort for the driver and passengers of the vehicle as well as minimizing sound pollution to the environment. Muffler designs generally aim to reduce any annoying characteristics of the untreated exhaust noise such as low frequency rumble. Breakout noise from the muffler shell may be a problem and should be minimized together with flow-generated noise, especially when designing a muffler for a high insertion loss.

The elliptical muffler has the following features incorporated in it by virtue of design calculations and trying out of new ideas which help it in attaining a significant contribution to reducing noise levels:

The elliptical muffler incorporates five different sets of perforations holes. These sets of holes are made based on design calculations. Each perforation diameter has been calculated such that it will assist in eliminating certain frequencies. The frequencies are a direct function of the engine and cylinder firing rates. When the exhaust gases pass through the pipes and over the perforations frequencies corresponding to a particular perforation diameter are eliminated. This results in a significant reduction in noise levels.
The elliptical muffler incorporates a novel technique of using two different diameters for the inlet and the outlet pipes. The advantage of having this kind of an arrangement is to help in reducing a set of frequencies which enter the larger pipe diameter but get cancelled off when they pass through the smaller diameter pipe. This help in giving the benefit of additional transmission losses.

Once the perforation diameters are calculated, the number of perforations to be punched in the pipes is determined by a parameter called the open area ratio. The open area ratio is a factor which is the ratio of the total area of all the perforations of a particular diameter punched on the perforation pipe to the cross section are of the pipe opening. The higher the open area ratio the better it is for back pressure but lower the noise attenuation. The converse results in better sound attenuation but leads to an increased back pressure for the engine. By means of proper calculation and testing the optimum number of holes is punched in the pipes which correspond to an optimum open area ratio. This gives the benefit of increased transmission losses.

The exhaust gases, as they exit the inlet pipe are forced to flow through the exponential connector. The exponential connector is designed such that it helps the gases corning out of the inlet pipe assembly to get compressed through the connector. The gases lose energy further resulting in loss of sound energy.

The outlet pipe is surrounded by glasswool which is packed. The construction of the glasswool is in the form of a continuous fiber. When the sound waves pass through the outlet tube, they pass through the perforations in the tube and into the chamber which is packed with glasswool. The glasswool absorbs the energy and vibrations of the sound waves. This helps in reducing sound intensity and gives better acoustic performance.

Referring to Figure 1, the perspective view of the elliptical muffler, the arrangement of the elliptical muffler along with the other components in the exhaust system is illustrated. The inlet pipe (3) and outlet pipe (10) which facilitate the inflow and outflow of the exhaust gas of the elliptical muffler. The inlet pipe (3) is attached to the first end cover (4) and connected through the flange (2) and the out let pipe (10) is connected to the second end cover (8) of the hollow jacket (1). The external surface of the hollow jacket (1) wherein the different components of the muffler assembly is arranged and the compatibility of the same with the adjacent part of the exhaust system are shown.

As illustrated in figure 2, the muffler of the present invention comprises a hollow jacket (1) which is covered at both ends by end covers (04 & 08) having a hole. The jacket (1) is divided into four chambers (A,B,C & D) with a help of two perforated baffles (05 & 06) has two and five holes respectively. An inlet pipe (03) is inserted from the first end cover (04) and extends up to third chamber of the jacket through the holes in the end cover (08) and the perforated bafflers (07). One end of the inlet pipe (03) is connected to a flange (02) of the engine and the other end of the inlet pipe (03) is fitted with a connector (09).

An outlet pipe (10) is inserted from the second end cover (08) and extends up to the first chamber of the jacket (05) through the hole in the second end cover (08) and the baffles (06 & 07). The fourth chamber (D) is filled with glass wool material with thickness of filament in microns called silentex. A portion of the inlet pipe (03) which is placed in the second chamber (B) comprises one set of perforation of pre-determined size to eliminate certain frequencies. Each row of perforation is staggered compared to adjacent row of perforation, ma 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 70 mm to 90mm, preferably 80mm. The connector (3) which is fixed to the free end of the inlet pipe (03) converges from about 73mm outer diameter at the end to abut 50mm inner diameter at the other end with a width of about 10mm. The outlet pipe (10) comprises three set of perforations to eliminate certain frequencies. Each row of perforation is staggered compared to adjacent row of perforations for a given set. The first set of perforations is made in the outlet pipe (10) which is paced in the fourth chamber (D). Preferably, the diameter of the first set of perforations can be from 3.5 mm to 4.5mm and the pitch can be about 12mm. The first set could contain about 17rows of perforations with about 20 perforations per row. The second set of perforations is made in the outlet pipe (10), 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 8mm. The second set could contain about 9 rows of perforations with about 20 perforations per row. The third set of perforations is provided in the outlet pipe (10) 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 19mm. The third set could contain about 19 rows of perforations with about 13 perforations per row. The outlet pipe (10) runs through all four chambers and extends in the first chamber (A) for 70mm to 90mm, preferably 70mm.

In preferred embodiment, the four chambers (A, B. C & D) of the hollow jacket (01) could be having specific dimensions of elliptic shape of 200mm, 300mm. 203 and 208mm. The free holes in the perforated baffler (05) could be preferably of the 60mm diameter and the free holes in the perforated baffle (06) could be preferably of the four numbers of 50mm and one hole of 40mm diameter. The holes act as an acoustic element. The length of the jacket preferably ranges from 900mm to 950mm. The hollow 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 hollow jacket (01).

The working of the muffler of the present invention is explained in detail herein below: The muffler according to the present invention uses both reflective and absorptive principles.

The first 3 chambers (A. B, C) of the jacket (01) 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 in to first chamber. On entering the second chamber (B) it comes across the 1st set of perforation of the Inlet pipe & some gas thus escapes from the inlet pipe in to the shell around the inlet pipe. The refractive phenomenon is based on the destructive Interference. This phenomenon can be explained by following two points 1. 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.

2. Pipe perforation: The perforations are the specific designs to eliminate 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 and 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 (10) 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 some gas (g23) expands directly though the connector in to the shell.

Some of the exhaust gas of the inlet pipe tries to enter the perforation of the outlet pipe in second 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 passes through the connectors of the baffles (05, 06) & tries to enter the outlet pipe in the first chamber. This gas further comes across the perforation in the second chamber resulting in a phenomenon as explained for inlet pipe above. The same phenomenon gets further repeated when it comes across the perforation of the outlet pipe in third 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.

According to the absorptive principle the sound waves are reduced as their energy ids converted into heat in the absorptive material.

The exhaust gas that passes away through the outlet pipe of third chamber (C) gets further carried away to fourth chamber (D). This gas comes across the outlet pipe perforation in the fourth chamber. Part of this gas escapes in to 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 fourth chamber (D) is filled with glass wool having filament thickness in microns which absorbs some of the pressure pulses, 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 in to heat energy, thus helping further transmission loss.

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 the 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 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.

Figure 3 illustrates the cross sectional view of the elliptical vertical muffler. The position and configuration of inlet and outlet pipes and different set of perforations are clearly illustrated.

We Claim:

1. An elliptical muffler comprising; a hollow Jacket (1) having a first end cover (4) and a second end cover (8), an inlet pipe (3)which allows the flow of exhaust gas to the muffler;

an outlet pipe(10), through which the exhaust gas leaves the muffler, and plurality of baffle plates(5,6,7) and the plurality of the said baffle plates (5,6,7) are arranged interior to the hollow jacket to form plurality of chambers (A, B, C & D)

wherein, the arrangement is such a way that the inlet pipe (3) extending from the first cover of the hollow jacket up to the third chamber ( C ) of the hollow jacket (1) though the holes; and the outlet pipe (10) extending from second end cover (8) of the hollow jacket to the first chamber (A) of the hollow jacket (1) through the holes in the said cover and the baffle plates.

2. The elliptical muffler as claimed in claim 1, wherein the inlet pipe (3), the outlet pipe (10) and the baffle plates(5,6,7) are having provision to accommodate set of perforations wherein the dimension and configuration of the said perforations are direct function of an engine and cylinder firing rates.

3. The elliptical muffler as claimed in claim 1, wherein the last chamber (D) may be filled with glasswool.