FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, rule 13]
“A SYSTEM WITH A METHOD FOR MEASURING EFFICIENCY OF NOISE REDUCTION OF AN EXHAUST SYSTEM”
NAME AND ADDRESS OF THE APPLICANT:
TATA MOTORS LIMITED, an Indian company having its registered office at Bombay house, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001, Maharashtra, INDIA.
Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The present invention generally relates to exhaust systems of vehicles, and more particularly it relates to a system and method for measuring efficiency of silencer of an exhaust system.
BACKGROUND OF THE INVENTION
The exhaust system of a vehicle consists of an element known as Silencer / Muffler. The silencer is inserted intermediately or at the end on the exhaust system, to suppress the noise. The effectiveness of the silencer is determined by the Insertion Loss and Noise Reduction (NR). As would be apparent to those skilled in the art, the Insertion Loss of a silencer is measured as a difference in the tail-pipe noise level with the baseline silencer replaced by a straight pipe. Typically, it is measured by running the vehicle on a highspeed test track. Sound pressure level (SPL) is measured near orifice (at a distance of 0.5m @ 45 deg from the exhaust pipe); thus it is likely to be dominated by tyre/road & wind-noise or power-train/ driveline, if they are in close proximity. Moreover, certain tests are carried out using a speaker as a source to excite the medium at the inlet. The difference in the inlet & outlet dB-levels of SPL of the silencer determines the Noise Reduction. However, the test results often prove to be inconclusive as they fail to take into account the effect of a high speed fluctuating hot gas-flow. The work happened in the past by various researchers highlight the importance of this new study of NR of a silencer in the presence of such gas-flow.
OBJECTS OF THE INVENTION
The objective of invention is to provide a reliable, simple and cost effective, mechanism for measuring the efficiency of a silencer in terms of the Noise Reduction [NR].
Another objective of the invention is to provide a method and system for measuring the NR-efficiency of a silencer in an accurate and / or a realistic way suiting to road-load conditions of a vehicle, whose silencer is under study.

Further objects and features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.
SUMMARY OF THE INVENTION
The various embodiments of the present invention disclose a silencer testing system comprising an automobile having a set of wheels driven by an internal combustion engine through a transmission system; a dynamometer supporting the wheels of the automobile, the dynamometer being adapted to keep the automobile stationary even during the rotation of the wheels; an exhaust pipe connected to the internal combustion engine, the exhaust pipe adapted to carry exhaust gases from the internal combustion engine; a silencer having an inlet and an outlet, the inlet of the silencer being connected to a distal end portion of the exhaust pipe; a tail pipe having a first end portion connected to the outlet of the silencer; and, a sound proof box enclosing the distal end portion of the exhaust pipe, the first end portion of the tail pipe and the silencer; and, a pair of sound measuring devices, high temperature micro-phones, positioned within the distal end portion of the exhaust pipe and the first end portion of the tail pipe respectively, to measure the sound pressure level at inlet and outlet of the silencer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic view of the silencer efficiency measuring system, according to an embodiment of the invention,
FIG. 2 illustrates graph showing sample results for different vehicle silencers, and
FIG. 3 illustrates a flow diagram for a method of determining the efficiency [NR] of a silencer.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same.

FIG. 1 illustrates a perspective view of a view of the silencer NR-efficiency measuring system 100, according to an embodiment of the invention. The silencer efficiency measuring system 100 (also referred to as “silencer (Noise Reduction, NR) efficiency measuring system 100, or “silencer testing system 100”) is adapted to determine efficiency of the silence by measuring noise level at before entry into the silencer and exit from the silencer. The silencer NR efficiency measuring system 100, includes an automobile 10. Preferably, the automobile 10 may be similar, with regard to the noise generation and exhaust output, to the automobiles in which a given silencer may find its application. The automobile 10 includes a set of wheels 12 driven by an internal combustion engine 14 through a transmission system (not illustrated). The operation of the internal combustion engine to drive the wheels, is known to those skilled in the art and therefore the description of the same has been omitted from herein.
The silencer NR-efficiency measuring system 100 further includes a dynamometer 16 supporting the wheels of the automobile 10. In one embodiment of the present invention, the dynamometer 16 is a chassis-dynamometer. The dynamometer supports the wheels of the automobile 10 in such as manner that when the internal combustion powers the wheel to cause rotation thereof, automobile remains stationary, i.e. positioned on the dynamometer 16. This arrangement of the dynamometer 16 and the automobile 100 enables the automobile 100 (and thus the internal combustion engine 14), to be operated at any desired speed & road-load, to get the exhaust noise.
An exhaust pipe 18 is connected to the internal combustion engine 14, so the exhaust pipe is adapted to carry exhaust gases from the internal combustion engine 14. As would be apparent to those skilled in the art, that the exhaust flow coming from the internal combustion engine will be a pulsating flow of high speed hot gases, which hereinafter be refereed to as exhaust flow. In an embodiment of the present invention, the exhaust pipe 18 is made up of three pipes joined with each other, a first end of which is connected to the internal while the second end is positioned distant form the automobile 10. In one preferred embodiment of the invention the exhaust pipe 18 has a uniform cross section.

The silencer efficiency measuring system 100 furthermore includes a silencer 20, a tail pipe 22 and a sound proof box 24. The silencer 20 includes an inlet and an outlet portion opposite to the inlet portion. As best shown in FIG. 1, the second end portion of the exhaust pipe 18 is removably connected to the inlet of the silencer 20. It may herein be noted that it is the silencer 20 which is to be tested. It shall be apparent to those skilled in the art that, different silencers (one at a time) may be engaged therein, for testing and the silencer NR efficiency measuring system 100 is not restricted to silencer 20.
The tail pipe 22 has a first end portion connected to the outlet of the silence 20. The second end portion (partially shown) of the tail pipe 22 is adapted to release the exhaust gases to the outside environment. The sound proof box 24 encloses the silencer 20. Particularly, the sound proof box 24 encloses the distal end portion of the exhaust pipe 18, silencer 20, and the first end portion of tail pipe 22. The sound proof box 24 is adapted to preclude any sound, other than the sound through the exhaust pipe 18 for example sound from power-train, drive-line, tires, wind etc, from entering therein.
In accordance with a preferred embodiment, the sound proof box 24 is an anechoic chamber. In such an embodiment, to prepare an anechoic chamber Plywood of 15mm thick (Length 1600 X Width 1000 X Height 1000 mm) may be used. Further, PU Foam of 40mm thick may be applied as noise absorbent on the inner side of the chamber. Complete sealing was ensured for better noise isolation. Fixing arrangement may be provided for proper locating the silencers of different sizes.
Referring now to FIG. 1, the silencer NR-efficiency measuring system 100 further includes a pair of sound measuring devices 26, 27. In an embodiment of the present invention, the pair of sound measuring devices 26, 27 may be two high temperature microphones. The pair of sound measuring devices 26, 27 may be positioned within the sound proof box 24 and is thermally coupled therewith. More specifically, the sound measuring device 26 is positioned within the distal end portion of the exhaust pipe and the sound measuring device 26 is positioned within the first end portion of the tail pipe 22, such that each of the sound measuring devices are within the sound proof box 24. The sound measuring device 26 positioned within the distal end portion of the exhaust pipe 18, measures sound therein, i.e. at the inlet of the silencer 20. Likewise, the sound

measuring device 27, positioned within the first end portion of the tail pipe 22, measures sound therein, i.e. at the outlet of the silencer 20. Being within the sound proof box 24, the pair of sound measuring deices measures sound only from within the exhaust pipes and not from outside environment. The difference in sound dB (Decibels)-levels at the inlet and outlet, i.e. sound measured by sound measuring device 26, and 27, is NR and indicative of the noise attenuation in various frequency bands achieved during flow of the exhaust gases through the silencer 20. Therefore the sound at the inlet and the outlet may be utilized to calculate the NR efficiency of the silencer which is under study.
Referring now to FIG. 2, which illustrates a graph showing the results for different vehicle silencers, measured NR using the hot pulsating gas flow. It was observed that NR of the silencers reduced by 50 to 75% when subjected to the hot high speed gas-flows in comparison with those with only the sound-waves of the speaker used in traditional tests.
During utilization of this silencer Noise Reduction efficiency measuring system 100 of FIG. 1, the following steps/method may be applied. As best shown in FIG. 3, the flow chart illustrates a method 400 to determine the NR efficiency of a silencer, such as a silencer 20 of an automobile, such as an automobile 10, having a set of wheels driven by an internal combustion engine through a transmission system. The method includes running the automobile at a desired engine speed & load, at step 402. The speed of the engine, the duration of running of the engine etc, will determine the extent and state of the exhaust gases coming therefrom. However, the automobile is run and positioned, in such a manner that the wheels rotate on a stationary dynamometer and the automobile remains stationary.
At step 404, the exhaust gases from the internal combustion engine are communicated to the silencer 20 of FIG.1 through an exhaust pipe, such as the exhaust pipe 18. The silencer is positioned distant from the exhaust pipe 18. A sound proof box encloses the silencer along with inlet and outlet portion of it.
At step 406, sound pressure levels of the exhaust gases at the inlet silence 20 is measured. Thereafter, at step 408 the sound pressure levels of the exhaust gases at the outlet of the silence 20 is measured. The measurement of the sound but here steps 406 and 408 are

done by pair of sound measuring devices, such as the pair of sound measuring devices 26, 27.
At step 410, the NR efficiency of the silencer is calculated based on the measurements obtained at step 406 and 408, i.e. at the inlet and outlet of the silencer. In the preferred embodiment of the present invention, this is done in all 1/3rd octave bands of frequency of interest to sound-quality perceived by people passing by the vehicle –exhaust.
The foregoing description provides specific embodiments of the present invention. It should be appreciated that these embodiment are described for purpose of illustration only, and that numerous other alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Referral Numerals Description
100 Silencer efficiency measuring system, Silencer testing system
10 Automobile
12 Set of wheels
14 Internal combustion engine
16 Dynamometer
18 Exhaust pipe
20 Silencer
22 Tail pipe
24 Sound Proof Box

26, 27
Sound measuring devices
400 Method to determine the efficiency of a silencer
402 Step
404 Step
406 Step
408 Step
410 Step

We claim:
1. A silencer testing arrangement comprising:
an automobile having a set of wheels driven by an internal combustion engine through a transmission system;
a dynamometer supporting the wheels of the automobile, the dynamometer being adapted to keep the automobile stationary even during the rotation of the wheels;
an exhaust pipe connected to the internal combustion engine, the exhaust pipe adapted to carry exhaust gases from the internal combustion engine;
a silencer having an inlet and an outlet, the inlet of the silencer being connected to a distal end portion of the exhaust pipe;
a tail pipe having a first end portion connected to the outlet of the silencer; and,
a sound proof box enclosing the distal end portion of the exhaust pipe, the first end portion of the tail pipe and the silencer; and,
a pair of sound measuring devices positioned within the distal end portion of the exhaust pipe and the first end portion of the tail pipe respectively, to measure the sound pressure level at inlet and outlet of the silencer.
2. The silencer testing system as claimed in claim 1, wherein the pair of sound measuring devices positioned within the distal end portion of the exhaust pipe and the first end portion of the tail pipe respectively measure the sound pressure level at inlet and outlet of the silencer in all 1/3rd octave frequency bands of interest to sound quality of the vehicle.
3. The silencer testing system as claimed in claim 1, wherein the sound measuring devices are high temperature microphones.

4. The silencer testing system as claimed in claim 1, wherein the sound proof box is an anechoic chamber.
5. The silencer testing system as claimed in claim 1, wherein the dynamometer is a chassis-dynamometer.
6. The silencer testing system as claimed in claim 1, wherein an exhaust pipe has a uniform cross section to give minimum losses of gas-pressure.
7. A method of determining the Noise Reduction efficiency of a silencer of an automobile having a set of wheels driven by an internal combustion engine through a transmission system, the method comprising;
running the automobile, such that the wheels rotate on a stationary dynamometer and the automobile remains stationary;
communicating exhaust gases coming from the internal combustion engine, through an exhaust pipe, to a silencer positioned distantly from the automobile; a sound proof box enclosing the silencer;
measuring sound pressure levels from the exhaust pipe at inlet of the silencer within the sound proof box;
measuring sound pressure levels at outlet of the silencer and within the sound proof box; and,
calculating the Noise Reduction efficiency of the silencer based on the sound pressure levels measured at the inlet and outlet of the silencer.