Title:
AIR RUSH SILENCER
United States Patent 3752260


Abstract:
A silencer for the end of an internal combustion engine exhaust system comprises a perforated open end gas flow tube inside of an imperforate open end shell, the tube having restrictive means in it to force gas to flow through the perforations.



Inventors:
HEATH R
Application Number:
05/162959
Publication Date:
08/14/1973
Filing Date:
07/15/1971
Assignee:
TENNECO INC,US
Primary Class:
Other Classes:
181/249
International Classes:
F01N1/08; F01N13/02; (IPC1-7): F01N1/00
Field of Search:
181/36R,36B,35C,47,57,72,61-63,46,44
View Patent Images:
US Patent References:
3429397LAMINATED CONDUIT AND ACOUSTIC SILENCER1969-02-25Case
3404750Combination tailpipe spout and silencer1968-10-08Powers et al.
3209861Muffler with two longitudinally separated chambers1965-10-05Whitney
2047443Muffler1936-07-14Starkweather et al.



Foreign References:
FR1157254A1958-05-28
GB387113A1933-02-02
GB751881A1956-07-04
Primary Examiner:
Wilkinson, Richard B.
Assistant Examiner:
Gonzales, John F.
Claims:
I claim

1. A muffler for attenuating air rush noise in an exhaust gas system for an internal combustion engine, said system including an outlet, comprising a housing having a reduced size inlet for attachment to said outlet, a straight through gas flow tube supported in the housing to receive all gas from said inlet, said tube and housing defining an annular passage surrounding the tube, said tube and said annular passage having transversely separated outlets inside said housing with the annular passage outlet surrounding the tube outlet and both outlets spaced axially upstream from the downstream end of the housing, said tube having a reduced cross section portion therein providing a restriction to gas flow through the tube, said tube having a perforated wall upstream of the restriction and the restriction forcing some gas to flow through the perforations in said wall into the annular passage whereby the gas flows in two separate parallel streams in said housing, said housing having an open downstream end extending across substantially the full and largest cross section of the housing and a curved wall portion axially aligned with and spaced downstream from the outlet of the tube whereby gas in said separate streams impinges upon said curved wall portion prior to passing out of said open downstream end.

2. A muffler as set forth in claim 1 wherein said restriction is centrally located in said tube, said tube having a perforated wall portion located downstream of the restriction with the perforations opening into the annular passage.

3. In an exhaust gas system for an internal combustion engine, said system including an outlet, a muffler for attenuating air rush noise out of said outlet comprising a housing having a reduced size inlet attached to said outlet, a straight through gas flow tube supported in the housing to receive all gas from said inlet, said tube and housing defining an annular passage surrounding the tube and defining two separate gas flow streams in the housing, said tube and said annular passage having a common outlet chamber for said separate gas streams inside said housing, said chamber being substantially the full and largest cross sectional area of the housing and extending to the downstream end of the housing and said downstream end being open to atmosphere across substantially the full and largest cross sectional area of the housing, said tube having a centrally located reduced cross section therein providing a restriction to gas flow through the tube, the wall of said tube both upstream and downstream of the restriction being perforated and the perforations opening into said annular passage to provide for flow of some of the gas from the tube into the annular passage.

4. A muffler as set forth in claim 3 wherein said perforations are provided by louvers in the tube.

Description:
BRIEF SUMMARY OF THE INVENTION

It is the purpose of this invention to provide a means to attenuate "air rush" noise in an internal combustion engine exhaust system.

The invention accomplishes this purpose by means of a combination silencer and tailpipe spout wherein the flowing gas is forced by restriction means into two flow streams that impinge upon a curved wall prior to reaching the silencer outlet.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation of an internal combustion engine exhaust system having a silencer in accordance with the invention;

FIG. 2 is an enlarged longitudinal cross section through a silencer as used in the system of FIG. 1 that embodies the invention;

FIG. 3 is a cross section along the line 3--3 of FIG. 2; and

FIG. 4 is a cross section along the line 4--4 of FIG. 2.

DESCRIPTION OF THE INVENTION

The automobile 1 has an internal combustion engine 3 with an exhaust manifold 5 that discharges exhaust gas into an exhaust system 7 that comprises an exhaust pipe 9 to carry gas to a muffler 11 from which, after silencing of engine generated sound, the gas flows through tailpipe 13 to a silencer 15 and then to atmosphere. The silencer 15 embodies the present invention and is intended to attenuate "air rush" noise, that is the sound generated by the high velocity exhaust gases which would otherwise enter the atmosphere at the end of the tailpipe 13.

The silencer 15 comprises a housing or imperforate outer shell 17, of circular cross section, which is reduced in diameter at its upstream end to form an inlet bushing 19 which receives the end of the tailpipe 13 and may be clamped to it. Supported in and spotwelded to the bushing 19 is a straight through gas flow tube 21 that is preferably the same size as the tailpipe 13, the downstream end of the tube being supported by dimples 22 in the shell 17. The tube 21 is fully open at its inlet and outlet ends 23 and 25 but is reduced in diameter between its ends at cross section 27 to form a restriction means located along the length of tube 21. The restriction may be formed by means of four U-shaped pinch sections 29 as indicated in FIG. 3. The portion of the wall of tube 21 that is upstream of restrictor section 27 is perforated, preferably by means of a louver patch 31 of sufficient area to prevent excessive back pressure; and the portion of the wall of tube 21 that is downstream of restrictor section 27 is perforated, preferably by means of a louver patch 33.

The downstream end of the housing 17 is fully open as seen at 35. However, the end portion extends a substantial distance beyond the end of tube 21 and the housing is curved or bent downward to the axis of tube 21 as seen at 37. This provides an interior wall section 39 that is in alignment with a substantial portion of the cross sectional area of tube 21 and the annular passage 41 between the tube 21 and the inner surface of housing 17. It also defines, in part, a common empty outlet chamber 43 in housing 17 for gas leaving annular passage 41 and the end 25 of tube 21.

In operation, gas reaching the tailpipe 13 has had much of the engine generated sound removed. If permitted to discharge directly into atmosphere at the outlet end of tailpipe 13 (i.e., the normal outlet for the system 7), there is often an audible high frequency sound due to the velocity of the gas entering the atmosphere. The source of this sound is considered to be somewhat beyond the end of the tailpipe. By the addition of the silencer 15 the source is located within the tube 21. The restriction 27 forces some of the gas to flow through the resistive louver patch into the compliant annular passage 41. Pressure differentials also cause some of the gas to flow out of louver patch 33 into passage 41. The gas in passage 41 is colder and slower than the gas leaving outlet 25 of tube 21 so that there is a moving cold stream of gas around a moving hot stream. This relationship plus the effect of chamber 43 and reflection off wall 39 create a turbulence between the outer and inner gas streams to slow down the jet stream in tube 21 and attenuate the air rush noise. This is done without any harmful increase in back pressure.

Modifications may be made in the specific structure shown without departing from the spirit and scope of the invention.