FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules  2005

COMPLETE SPECIFICATION
(SEE MEMBER 10 AND RULE 13)

TITLE OF THE INVENTION

“A HYBRID SOUND ATTENUATING DEVICE”

APPLICANT:

Name : Mahindra & Mahindra Ltd.

Nationality : Indian

Address :Mahindra Research Valley  Mahindra World
City Plot No. 41/1  Anjur P.O. Chengalpattu Kancheepuram Dist  Tamilnadu.- 603204

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:-

FIELD OF THE INVENTION

[001] The present invention generally relates to a sound attenuating device used with work vehicles such as tractors and alike  and particularly related to a hybrid sound attenuating device for muffling various frequencies.

BACKGROUND OF THE INVENTION

[002] In automotive vehicle  a typical sound attenuating device is incorporated with the exhaust system of the internal combustion engine to attenuate the noise associated with the exhaust gas produced by the internal combustion engine to a desired level. The construction of the sound attenuating device does vary with respect to the type of vehicle such as on road passenger vehicle  race cars  construction vehicles and agricultural vehicles. A sound attenuating device is generally classified into two categories  namely; reactive and dissipative. The reactive type muffler has multiple resonating chambers of different volume acoustically communicated with each other through plurality of tubes having different diameter and some of them could be with perforated with numerous holes. In such cases  the sound waves associated with the exhaust gas gets reflected with various chambers and then come out of such attenuating device. The paramount factor to be considered while designing such silencer is noise level reduction & backpressure. Where a straight through pipe is used in a sound attenuating device to receive and exit the exhaust gas  and provided with perforations to acoustically communicate with different chambers  there the sound attenuating device will generate least back pressure  but the level of noise reduction shall not be satisfied. To overcome this issue  the sound attenuating device shall be adapted to go for a torturous flow path of the exhaust gas  but this may lead to high back pressure which ultimately affects engine performance. Hence  any sound attenuating device needs to be designed in such a way to have satisfactory noise level reduction without affecting engine performance.

[003] To have an agreeable trade of between back pressure and noise reduction  a dissipative type of sound attenuating device shall be constructed in which heat resistance and noise attenuating fibrous materials such as glass wool or ceramic wools is disposed in a chamber or chambers either longitudinally or transversely to absorb the sound waves.

[004] Nowadays the diverse applications of automotive vehicle demand for sound attenuating device of various sound quality and sound level. All the passenger car segment demand for a sound attenuating device that should reduce the noise level of engine exhaust gas at its maximum extent without affecting engine performance. Whereas  race car segment demand for a high performance silencer wherein the loudness and sharpness of the sound is given utmost priority rather than noise reduction without affecting the engine performance. The other segment such as construction vehicle and agricultural vehicle does not mandatorily demand for least noise reduction like passenger car segment and power full and loud noise like race car segment  in fact  the noise level reduction  loudness of sound  sharpness of sound and roughness of sound shall be customized with respect to the customers need. However  in all these segments  the construction of the sound attenuating device should be designed in such a way to limit the noise level within the statutory requirement.

[005] In agricultural vehicles such as tractors  the sound attenuating device is disposed at the front of the vehicle nearby engine compartment  and in most of the vehicle the device is disposed outside of the hood or bonnet in a vertical plane at a particular height to dispose the exhaust gas to the atmosphere thereby to provide a better visibility to the operator or driver of the vehicle from the smoke of the exhaust gas. In this particular configuration of the vehicle construction  the silencer could be designed in any desired shape such as elliptical  cylindrical  oval  etc as desired and the length of the silencer shall also be varied as per the requirement of the inside chamber volume. In the same segment  some customers or manufacture will go for an under-hood silencer to give better visibility to the operator or driver from the bulky design of the silencer and also to give better aesthetic look to the vehicle. In this configuration of the vehicle  the silencer would be disposed under the hood so as not to get exposed outside of the vehicle and a tail pipe would be coming out of the silencer through the hood which will be positioned in vertical plane at certain height to exit the exhaust gas to the atmosphere. Below are some of the constraints within which an under-hood silencer need to be developed to meet the intended objective: the overall volume of the silencer has to be limited to the given space under the hood so as not to get disturbed with other surrounding parts under the hood  the cross section of the silencer body should be to accommodated under the hood  the overall length of the silencer should be within the allowable space under the hood and should be easily and comfortably accessible for better serviceability.

[006] The FIG.1 shows internal construction of an under-hood silencer 10 that is currently used in the agricultural vehicle. This internal construction is being enclosed in a shell that is not shown in the figure. The silencer has three chambers A  B & C separated by two baffle plates 12 & 14 and are being acoustically communicated with plurality of tubes. The chamber A has a perforated tube 16 to receive the exhaust gas coming out from the internal combustion engine and to communicate the gas with the chamber A and Chamber B. Chamber C has another perforated tube 18 to communicate the exhaust gas with an exit tube 20 and the chamber B. Both inlet 22 and outlet 24 are opened at one end 26 of the silencer 10. The chamber B has two perforated tubes (not shown) to communicate the exhaust gas among chambers A  B & C. The cross section of the silencer is elliptical in shape. This silencer is reactive in nature and being constructed in such a way to attenuate engine noise below 500Hz. The noise reduction of this muffler is showing higher noise reduction in low frequency upto 500 Hz and low noise reduction in high frequency. i.e. more than 500Hz

[007] In view of aforesaid shortcomings of existing silencers  there was a need to develop a sound attenuating device which will ensure very loud noise at the low frequency range that means below 500Hz and drastically reduced noise level at medium and high range frequencies. .

SUMMARY OF THE INVENTION

[008] The main object of the present invention is to have power full and loud noise with very less volume due to serviceability and packaging requirements. According to one aspect of the present invention  the hybrid sound attenuating device for muffling various frequencies comprising a housing defined by an outer shell that is extended longitudinally between a first end plate and a second end plate  which are aligned at spaced apart relationship with each other; an inner shell disposed inside of the housing at a spaced apart relation from inner surface of the outer shell and extended between the first end plate and the second end plate; a first perforated baffle disposed inside of the inner shell at a spaced apart relation from the first end plate to define a first chamber with the first end plate; a second perforated baffle disposed inside of the inner shell at a spaced apart relation from the first perforated baffle to define a second chamber with the first baffle plate  and to define a third chamber with the second end plate; an inlet pipe adapted to acoustically communicate exhaust gas coming out from internal combustion engine with the second chamber and the third chamber; and an outlet pipe adapted to communicate with the third chamber to exit the exhaust gas to the atmosphere. A space is defined by inner circumferential area of the outer shell and the outer circumferential area of the inner shell to fill with fibrous materials such as glass wools. The inner shell is secured from inside surface of the first and second end plates and provided with a plurality of holes throughout surface area thereof  through which the fibrous material absorbs sound waves associated with the exhaust gas. The inlet pipe is having a trialing end inserted through the first end plate and extended up to the second perforated baffle to communicate the exhaust gas with the third chamber  wherein surface area of the inlet pipe extended between the first perforated baffle and the second perforated baffle is provided with a plurality of holes to acoustically communicate the exhaust gas with the second chamber. The first perforated baffle is provided with plurality of holes to acoustically communicate the exhaust gas with the first chamber. The second perforated baffle is provided with plurality of holes to acoustically communicate the exhaust gas with the third chamber.

[009] 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

[010] Further features and advantages of the present invention  as well as the structure and operation of various embodiments of the present invention  are described in detail below with reference to the accompanying drawings.

[011] FIG.1 is a perspective view of an under-hood sound attenuating device being currently used in the agricultural vehicle.
[012] FIG.2 is a perspective view of an under-hood sound attenuating device according to one embodiment of the present invention.
[013] FIG.3 is a perspective exploded view of the sound attenuating device of FIG.1.
[014] FIG.4 is a sectional view of the sound attenuating device taken along line A-A of FIG.1
[015] FIG.5 is a sectional view of the sound attenuating device taken along line B-B of FIG.1

DETAILED DESCRIPTION OF THE INVENTION

[016] While this invention is susceptible of embodiments in many different forms  the detailed description of the preferred embodiment and the corresponding drawings shown herein below are to be understood that the present disclosure shall be deemed as an example of the principles of the invention and not intended to limit the invention to the specific embodiment shown and described. In the description below  like reference numerals are used to describe the same  similar or corresponding parts in the several views of FIG 2- 5

[017] Referring to FIG. 2  perspective view of a hybrid sound attenuating device according to the present invention is being designated as numeral 100. The hybrid sound attenuating device 100 has a housing 102 defined by an outer shell 104  which is extended longitudinally between a first end plate 106 and a second end plate 108. The outer shell 104 according to the preferred embodiment of the present invention has a cross section circular in shape. However  the cross section of the outer shell 104 shall be modified to an elliptical or oval shape or a shape that is satisfactory to a person skilled in the art without departing from the scope of the present invention. Hence this feature should not be deemed to limit the scope of the present invention. The first end plate 106 and the second end plate 108 are secured with the outer shell 104 through seem welding. The hybrid sound attenuating device 100 is disposed under hood of vehicle such as tractor in a horizontal plane adapted to be accommodated in the space available in the engine compartment. The surface area of the outer shell 104 that comes on top in the mounted position of the sound attenuating device and exposed to operator of the vehicle is provided with a cover plate 110. The profile of the cover plate 110 is adapted to cover the entire top surface area of the sound attenuating device 100 and bolted with the outer shell 104 via two mounting means 112 (shown in FIG.4). The cover plate 110 restricts the operator hand from being touched on to the surface of the outer shell 104 during the maintenance or service of the vehicle thereby to avoid human injury due to the high temperature exposed from the sound attenuating device for some time immediately after the operation thereof.

[018] Referring to FIG.3  the cover plate mounting means 112 has a pair of bracket 114 provided with a threaded hole adapted to receive a bolt 116 and welded over the surface of the outer shell 104. The cover plate 110 has a through hole 118 with which the cover plate 110 is bolted with the outer shell 104. The surface of the outer shell 104 facing downward during the mounted position of the sound attenuating device is welded with a pair of bracket 120 which is having a hole aligned with a threaded nut as shown in FIG. 3 adapted to be mounted on to engine cylinder cover (not shown). The housing 102 encloses an inner shell 122 which is extended between the first end plate 106 and the second end plate 108  wherein the inner shell 122 has plurality of holes 124 throughout the length thereof and supported over a circular projection 126 from inside surface of the first and second end plates 106 & 108 and secured with seem welding.

[019] The housing 102 further comprises an inlet pipe 128 and an outlet pipe 130  wherein leading end 132 of the inlet pipe 128 has a flange 134 provided with a pair of mounting holes adapted to be mounted with an exhaust pipe (not shown) comes out from exhaust manifold of an internal combustion engine and trialing end 136 of the outlet pipe 130 has a flange 138 provided with a pair of mounting holes adapted to be mounted with a tail pipe (not shown) that comes out through a hole provided in hood of the vehicle and disposed in vertical plane in such a way to give better visibility to the operator or driver. The outlet pipe 130 is being adapted to bring the trailing end 136 thereof in a same plane of the leading end 132 of the inlet pipe 128 so as to facilitate mounting position of the sound attenuating device 100 within the space available in the engine compartment. Leading end 140 of the outlet pipe 130 is mounted with a hole 142 provided on the outer shell 104 via seem welding.

[020] Referring to FIG.3 & 4  the housing 102 further comprises a plurality of chambers defined between the inner shell 122 and the first end second end plates 106 & 108  wherein the plurality of chambers includes a first chamber 144  a second chamber 146 and a third chamber 148. The first chamber 144 is defined between the first end plate 106 and a first perforated baffle150 which laterally extend up to inner circumference of the inner shell 122; the second chamber 146 is defined between the first perforated baffle 150 and a second perforated baffle 152 which laterally extend up to inner circumference of the inner shell 122; and the third chamber 148 is defined between the second perforated baffle 152 and the second end plate 108. Both the first perforated baffle 150 and the second perforated baffle 152 have plurality of holes 154 (shown in FIG.5) to acoustically communicate among the chambers 144  146 & 148  and a hole centrally having diameter adapted to receive the inlet pipe 128. Trialing end 156 of the inlet pipe 128 is inserted through the first end plate 106 and extended up to the second perforated baffle 152  wherein the surface area of the inlet pipe 128 extended between the first perforated baffle 150 and the second perforated baffle 152 is provided with a plurality of holes 158. The leading end 140 of the outlet pipe 130 is welded on to the hole 142 to acoustically communicate with the third chamber 148. The inner shell 122 is disposed inside the outer shell in such a way to define a space 160 between the inner circumferential area of the outer shell 104 and outer circumferential area of the inner shell 122  wherein said space 160 is fully filled with fibrous materials such as glass wool.

[021] The exhaust gas comes out from the internal combustion engine is received to the hybrid sound attenuating device 100 through the leading end 132 of the inlet pipe 128 and communicate with the second chamber 146 via the plurality of holes 158 provided in the inlet pipe 128 and communicate with the third chamber 148 via the trialing end 156 of the inlet pipe. In second chamber 146  the sound waves of high frequency range associated with the exhaust gas is absorbed by the fibrous material through the plurality of holes 124 provided in the inner shell 122 wherein the sound waves of medium frequency range is reflected back and communicate with the first chamber 144 through the plurality of holes 154 provided in the first perforated baffle 150 and communicate with the third chamber 148 through the plurality of holes 154 provided in the second perforated baffle 152. Further  in the first chamber 144  sound waves of high frequency range is absorbed by the fibrous material through the plurality of holes 124 provided in the inner shell 122 and sound waves of medium frequency range got expanded and attenuated thereinside. Still further  in the third chamber 148  remaining sound waves of high frequency range is absorbed by the fibrous material through the plurality of holes 124 provided in the inner shell 122 and sound waves of medium frequency range get reflected at 126 and got attenuated inside of third chamber 148 and sound waves of low frequency get reflected and exit through the outlet pipe 130 along with exhaust gas.

[022] It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly  the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention  which is to be given the full breadth of the appended claims and any all equivalents thereof.

CLAIMS

We claim 
1) A hybrid sound attenuating device for muffling various frequencies comprising:
a housing defined by an outer shell 104  said outer shell 104 is extended longitudinally between a first end plate 106 and a second end plate 108  which are aligned at spaced apart relationship with each other;

an inner shell 122 disposed inside of the housing 102 at a spaced apart relationship from inner surface of the outer shell 104 and extended between the first end plate 106 and the second end plate 108;

a first perforated baffle 150 disposed inside of the inner shell 122 at a spaced apart relationship from the first end plate to define a first chamber 144 with the first end plate 106;

a second perforated baffle152 disposed inside of the inner shell 122 at a spaced apart relation from the first perforated baffle150 to define a second chamber 146 with the first perforated baffle150  and to define a third chamber 148 with the second end plate 108;

an inlet pipe 128 adapted to acoustically communicate exhaust gas coming out from internal combustion engine with the second chamber 146 and the third chamber 148; and
an outlet pipe 130 adapted to communicate with the third chamber 148 to exit the exhaust gas to the atmosphere.
2) The hybrid sound attenuating device according to claim 1  wherein a space 160 is defined by inner circumferential area of the outer shell 104 and the outer circumferential area of the inner shell 122  said space 160 is filled with fibrous materials.
3) The hybrid sound attenuating device according to claim 2  said fibrous material is glass wool or ceramic wool.
4) The hybrid sound attenuating device according to claim 1 has said inner shell 122 secured from inside surface of the first and second end plates 106 & 108 and provided with a plurality of holes 124 throughout surface area thereof  through which the fibrous material absorbs sound waves associated with the exhaust gas.

5) The hybrid sound attenuating device (100) according to claim 1 has said inlet pipe 128 having provided with a plurality of holes 158 in a spaced apart relationship with each other.
6) The hybrid sound attenuating device according to claim 1 has said inlet pipe 128 having a trialing end 156 inserted through the first end plate 106 and the second perforated baffle152 and then opened in the third chamber 148 to communicate the exhaust gas with the third chamber 148  wherein surface area of the inlet pipe 128 extended between the first perforated baffle150 and the second perforated baffle152 is provided with a plurality of holes 158 to acoustically communicate the exhaust gas with the second chamber 146.
7) The hybrid sound attenuating device according to claim 1 has said first perforated baffle150 provided with plurality of holes 154 to acoustically communicate the exhaust gas with the first chamber 144.
8) The hybrid sound attenuating device according to claim 1 has said second perforated baffle152 provided with plurality of holes 154 to acoustically communicate the exhaust gas with the third chamber 148

Date 11th December  2012 Signature:

Dr. Kalyan Chakravarthy
Patent Agent

ABSTRACT

A hybrid sound attenuating device comprising a housing defined by an outer shell and an inner shell disposed inside of the housing. The outer shell and the inner shell extend longitudinally between a first end plate and a second end plate. A first perforated baffle is disposed inside of the inner shell at a spaced apart relationship from the first end plate to define a first chamber. A second perforated baffle disposed inside of the inner shell at a spaced apart relation from the first perforated baffle to define a second chamber with the first perforated baffle  and to define a third chamber with the second end plate. An inlet pipe adapted to acoustically communicate exhaust gas from internal combustion engine with the second chamber and the third chamber and an outlet pipe adapted to communicate with the third chamber to exit the exhaust gas to the atmosphere. FIG.2