US3888332A

US3888332A - Exhaust silencers

Info

Publication number: US3888332A
Application number: US410409A
Authority: US
Inventors: Geoffrey Ernest Roe; John Edward Favill
Original assignee: Norton Villiers Ltd
Current assignee: Norton Villiers Ltd
Priority date: 1973-04-18
Filing date: 1973-10-29
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

An exhaust silencer comprises a body which includes inner, intermediate and outer coaxial tubes. The outlet is formed as a slot and immediately upstream of the outlet in the direction of gas flow is a passage between the intermediate and outer tubes, the height of the passage being such as to attenuate the sound of the gas flowing through the passage. Between the inner and intermediate tubes is one or more resonator chambers and the exhaust gas flows through the inner tube and the passage in one direction and through the chambers in the opposite direction.

Description

United States Patent [191 Roe et al.

[ EXHAUST SILENCERS [75] Inventors: Geoffrey Ernest Roe, Bramhall;

John Edward Favill, Dudley, both of England [73] Assignee: Norton ViIIiers Limited,

Staffordshire, England [22] Filed: Oct. 29, 1973 [21] App]. No.: 410,409

[30] Foreign Application Priority Data Apr. 18. 1973 United Kingdom l. 18675/73 [52] US. Cl. 181/53 [5i] Int. Cl. F0ln 1/08 [58] Field of Search 181/53-57 [56] References Cited UNITED STATES PATENTS 674,2IO 5/1901 Loomis I8l/57 X 1,598,578 Maxim l8l/S3 June 10, 1975 3073.684 l/l963 Williams l8l/55 UX FOREIGN PATENTS OR APPLICATIONS 781,087 5/[935 France l8I/53 Primary ExaminerRichard B. Wilkinson Assistant Examiner-John F. Gonzales Attorney, Agent, or FirmSpencer & Kaye [57] ABSTRACT An exhaust silencer comprises a body which includes inner, intermediate and outer coaxial tubes. The outlet is formed as a slot and immediately upstream of the outlet in the direction of gas flow is a passage between the intermediate and outer tubes, the height of the passage being such as to attenuate the sound of the gas flowing through the passage. Between the inner and intermediate tubes is one or more resonator chambers and the exhaust gas flows through the inner tube and the passage in one direction and through the chambers in the opposite direction.

4 Claims, 5 Drawing Figures SHEET PATENTEDJUH I 0 I975 FIGS EXHAUST SILENCERS This invention relates to exhaust silencers for use in association with internal combustion engines to reduce the noise level of the exhaust without effecting the power output of the engine to an unacceptable extent.

The exhaust noise from an internal combustion engine encompasses a band of frequencies and the noise level normally peaks over a compact range of frequencies within the band. Silencers are designed to attenuate the noise within the range of frequences where the noise peaks, thus to reduce the overall level of the noise.

It is known to employ for this purpose a number of resonators or acoustic filters which are tuned to respond to different frequences in the range. Standing waves are thus formed and the supply of energy required to keep these standing waves in existence attenuates the noise level within said range and thus the peak noise level of the exhaust.

The object of the invention is to provide an improved silencer using resonating chambers.

According to the invention we provide an exhaust silencer comprising: a body which includes inner, intermediate and outer co-axial tubes; an exhaust gas inlet at one end ofthe body and in one end of the inner tube; an exit opening at the other end of the inner tube; an outlet at the other end of the body in the form ofa slot; a passage between the intermediate and outer tubes immediately upstream of said slot in the direction of flow of the exhaust gas, the passage having an inlet and ter minating in the slot; the walls of the passage being imperforate and spaced apart by a distance such that the height of the passage between the walls is such as to cause attenuation of the noise of gas flowing through the passage while the area of the slot and of the cross section of the passage transverse to the direction of .low of gas therethrough is at least as great as the crosssectional area of the inlet transverse to the general direction of flow of exhaust gases through the inlet; the passage having a length equal to at least times the height of the slot; there being no part of the flow path of the gas between the inlet and the outletwhich has a cross-sectional area perpendicular to the general direction of gas flow which is less than said cross-sectional area of the inlet; and there being one or more chambers between the exit opening of the inner tube and the inlet to the passage and arranged so that the direction of flow of exhaust gases through the chamber or chambers is in a direction generally opposite to the direction of flow of exhaust gases through the inner tube and the passage.

We have found that by having an outlet in the form of a slot and a passage upstream of the slot and having imperforate walls, the noise level of the exhaust is attenuated to a greater extent than in exhaust silencers using resonators or acoustic filters as heretofore provided. We do not wish to be bound by an explanation as to why this attenuation is obtained but we believe that it is obtained because of interference and damping which takes place between the pressure waves in the gas as the waves travel along the passage to the outlet slot.

The exit opening of the inner tube may lead to a diffuser from which the gas passes to the chamber or chambers between the inner and intermediate tubes.

The slot can be continuous, for example. circular, oval, rectangular or of sinuous shape. Alternatively, the slot can be finite and may be straight or arcuate. In any event, the slot is preferably of a constant width along its length. The cross-sectional shape (and hence the height) of the passage is preferably the same as that of the slot and the passage is preferably of a length greater than fifty times the height of the slot.

The silencer may include, between the inner and intermediate tubes, a number of resonator chambers arranged in series and tuned to different frequencies within the frequency band of the exhaust noise to be silenced. The chambers may be placed in communication by a number of tuned pipes and spaced apart around the inner tube.

In designing the silencer we have found that it is desirable that the height of the slot and of the passage shall not be greater than one-tenth of the shortest wave length of the sound to be attenuated and shall not be less than one-tenth of a quarter of such shortest wave length. The height of the passage is the dimension thereof corresponding to the height of the slot.

It is preferred that the slot be in the form of a sharpedged orifice but this is not essential.

Two embodiments of the invention will now be described in detail by way of example with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal section through a silencer constituting a first embodiment of the invention;

FIG. 2 is a section on the line 22 of FIG. 1;

FIG. 3 is a section on the line 3-3 of FIG. 1;

FIG. 4 is a section on the line 44 of FIG. I and FIG. 5 is a diagrammatic cross section through a second embodiment of the invention.

Referring now to FIGS. 1 to 4 of the drawings, the silencer there shown comprises an inner tube 10 which at the inlet end, the left hand end in FIG. I, is surrounded by a front tube 11 which is adapted to be connected to the exhaust pipe of an engine. At its right hand end the inner tube 10 has an exit opening which leads to a diffuser indicated generally at 12 and connected to the tube 10. The diffuser has a cylindrical part 13 which fits over the right hand end of the inner tube 10, a frusto-conical part I4, a cylindrical part 15 of greater cross-sectional area than the part 13 and an end plate 16. The end plate 16 is imperforate but the cylindrical portion 15 is provided with a plurality of slots some of which are shown at 17. The inner tube 10 and the diffuser 12 are so dimensioned that the distance between the end plate 16 and the exhaust ports of the engine is the optimum distance for the generation of engine power.

Surrounding the inner tube 10 is an intermediate tube 18 and surrounding the tube 18 is an outer tube 19. The tubes l0, l8 and 19 are coaxial and are cylindrical as will be clear from FIG. 2. Two support rings 20 are interposed between the

tubes

18 and 19 and are spaced apart longitudinally of the tubes. As shown in FIG. 2, each support ring has three outer portions 21 which engage the outer tube 19 and three inner portions 22 which engage the intermediate tube 18. It will be seen that the support rings locate the intermediate tube within the outer tube without substantially obstructing the cross-sectional area of an annular outlet passage 23 between the

tubes

18 and 19 and which has an entrance at the left hand end of the intermediate tube 18.

The right hand end of the tube 18 is closed by an end plate indicated generally at 24. This end plate has a circular portion 25 opposite to the end plate 16, a diverging wall portion 26 and a cylindrical portion 27 which flts within, and is secured to, the tube 18. The outlet from the outlet passage 23 is a slot indicated at 28 and it will be seen that it is formed between the opposed rear ends of the outer tube 19 and the intermediate tube 18. The length of the outlet passage 23 is thus from the entrance at the left hand end of the tube 18 to the slot 28.

The left hand end of the outer tube 19 is connected to the larger diameter end 29 of a front cone 30, the smaller diameter end 31 thereof being connected to the front tube 11.

An annular front plate 32 surrounds the tube and is secured thereto by a flange 33. The front plate 32 is located adjacent the left hand end of the outer tube 19 and is provided with a number of equi-angularly spaced apertures 34, some of which are seen in FIG. 4.

Between the inner tube 10 and the intermediate tube 18 are mounted front and rear baffles. The front baffle is indicated generally at 35 and is a ring of substantially Z cross section having an inner flange 36 welded to the tube 10 and an outer flange 36a welded to the tube 18. The baffle carries six pipes 37 which, as shown in FIG. 2, are equi-angularly spaced around the tube 10. The left hand ends of the tubes 37 are supported by a flanged ring 38 welded to the tube 10.

in a similar manner, the rear baffle 39 is an annular ring of Z cross-section having an inner flange 41 welded to the tube 10 and an outer flange 41a welded to the tube 18. The baffle 40 carries twelve pipes 40 which are equiangularly spaced as shown in FIG. 3. It will be noted that the pipes 40 are shorter and smaller in diameter than the pipes 37.

The

baffles

35 and 39 divide the space between the

tubes

10 and 18 into two

chambers

42 and 43. A fur ther chamber 44 is provided within the outer tube 19 to the left or forwardly of the front baffle 45 and a dead air space 45 is provided within the front cone 30 around the tube 10.

Pommels 46 are welded to the outer tube 19 to provide means for mounting the silencer on a support bracket.

In operation, exhaust gas flows from left to right along the inner tube 10. When the gas reaches the diffuser 12 the gas expands and its velocity decreases and it passes through the slots 17 into the chamber 42. The gas then passes through the pipes 40 into the chamber 43 and through the pipes 37 into the chamber 44. The volumes of the

chambers

42, 43 and 44 and the lengths and diameter of the

pipes

37 and 40 are arranged to provide the desired attenuation characteristics for the silencer. The gas then flows from the chamber 44 along the outlet passage 23 and through the outlet 28. The gas flow is in contact with the dead air space 45 through the apertures 34 and this gives further attenuation. It will be noted that the chamber 44 has a greater volume than the chamber 43 which has a greater volume than the chamber 42.

The cross-sectional area of the flow path of the gas is not restricted between the entry to the inner tube 10 and the exit from the outlet 28. Preferably the crosssectional area of the outlet is greater than that of the inlet and may be 40 percent greater. The outlet 28 is in the form of a slot which is at the downstream end of the passage 23 whose concentric walls, provided by the

tubes

18 and 19, are imperforate and are a constant distance apart. The cross-sectional area of the outlet 28 can be considered to be defined by the inner surface of the outer tube 19 and the outer surface of the inner tube 18 as it has been found that the exhaust gases emerging from the outlet do not follow the angle of the diverging wall portion 26 unless this angle is less than 8. The height of the passage 23 and slot 28 is the radial distance between the outer surface of the intermediate tube 18 and the inner surface of the outer tube 19. The height of the passage is such as to cause attenuation of the noise of the exhaust gas flowing through the passage. The passage has a length equal to approximately times the height of the slot (and also the height of the passage itself) although for this embodiment it could be between 50 and 60 times the height of the slot.

Referring now to FIG. 5 this shows another embodiment of the invention in which the silencer comprises an elongated body 50 comprising an outer tube 51 and an intermediate tube 52. The outer tube 51 is longer than the inner tube 52 and there is an annular passage 53 between the tubes which leads to an annular exit slot 54 similar to the slot 28 in FIG. 1. The passage 53 corresponds to the passage 23 in the first embodiment and is similarly dimensioned to attenuate the noise of the exhaust gas flowing through it. The tube 52 has a closure 55 at the outlet end of the silencer and has a perforated plate 56 at its other end.

The inlet end of the silencer is indicated at 57 and comprises a cone 58 welded to the outer tube 51 and also to an inner tube 59 which extends into the cham ber 60 provided within the tube 52 and is connected at its end to an apertured diffuser 61 which has a number of apertures 62 therein. The length of the passage 53 is at least 15 times the height of the outlet slot 54 and there is no restriction to flow between the inlet to the tube 59 and the slot 54.

The operation of the silencer of FIG. 5 is as follows. Exhaust gas enters through the tube 59 and flows into the diffuser 61 and from thence through the apertures 62 into the chamber 60 which acts as a resonator and absorbs sound energy. The gas then flows through apertures 63 in the plate 56 into the chamber 64 provided in the outer tube 51 and this chamber 64 also acts as a resonator absorbing further sound energy. It will be understood that the

chambers

60 and 64 are tuned to resonate at different frequencies within the range of frequencies required to be attenuated by the silencer. The gas then flows from the chamber 64 along the passage 53 to the outlet slot 54 which is in the form of a sharp edged orifice. The passage 53 which has imperforate walls formed by the

tubes

51 and 52 acts in the same manner as the passage 23 of FIGS. 1 to 4 and we have found that the inclusion of such a passage improves the performance of the silencer as compared with those known heretofore.

It is also necessary that there be no restriction in the silencer and therefore the cross sectional area of the slot such as 28 or 54 must be at least equal to the cross sectional area of the

tube

10 or 59 respectively. It follows that the cross sectional area transverse to the direction of flow of the gas through the silencer must not, at any position, be less than the cross sectional area of the inlet to the silencer constituted by the tube 10 or the tube 59.

We claim:

1. An exhaust silencer comprising: a body which includes inner, intermediate and outer co-axial tubes; an exhaust gas inlet at one end of the body and in one end of the inner tube; an exit opening at the other end of the inner tube which is imperforate between its one end and the exit opening; an outlet at the other end of the body in the form of a slot; an outlet passage defined between concentric inner and outer walls provided by the intermediate and outer tubes respectively and being located immediately upstream of said slot in the general direction of flow of the exhaust gas, the outlet passage having an entrance at one end and terminating in the slot at the other end and being arranged so that all the exhaust gas flows therethrough; said concentric walls of the passage being imperforate and spaced apart by a constant distance over the whole of the overlapping lengths of the intermediate and outer tubes; said distance being such that the height of the passage between the walls is such as to cause attentuation of the noise of gas flowing through the outlet passage while the area of the slot and of the cross-section of the outlet passage transverse to the general direction of flow of the gas therethrough is at least as great as the cross-sectional area of the inlet transverse to the general direction of flow of exhaust gases through the inlet; the outlet passage having a length between the entrance and the slot equal to at least 50 times the height of the slot and providing a clear path for gas flow in a direction parallel to the longitudinal axis of the passage between the entrance and the slot; there being no part of the flow path of the gas between the inlet and the outlet which has a cross-sectional area transverse to the general direction of gas flow which is less than said cross-sectional area of the inlet; there being one or more chambers through which the gas flows on emerging from the exit opening of the inner tube and arranged so that the direction of flow of exhaust gases through the chamber or chambers is in a direction generally opposite to the direction of flow of exhaust gases through the inner tube and the passage, and there being a further chamber defined between the inner and outer tubes into which the gas flows on emerging from said first mentioned chamber or chambers, the general direction of flow of gas being reversed in said further chamber from the entrance to which the gas passes directly to the entrance to the outlet passage.

2. A silencer according to claim 1 wherein the exit opening of the inner tube leads to a diffuser from which the gas passes to the chamber or chambers between the inner and intermediate tubes.

3. A silencer according to claim 1 wherein there is a number of the first mentioned chambers between the inner tube and the further chamber, all said chambers acting as resonators, being arranged in series and being tuned to different frequencies within the frequency band of the exhaust noise to be silenced.

4. A silencer according to claim 3 wherein adjacent chambers are placed in communication via tuned pipes spaced apart around the inner tube.

Claims

1. An exhaust silencer comprising: a body which includes inner, intermediate and outer co-axial tubes; an exhaust gas inlet at one end of the body and in one end of the inner tube; an exit opening at the other end of the inner tube which is imperforate between its one end and the exit opening; an outlet at the other end of the body in the form of a slot; an outlet passage defined between concentric inner and outer walls provided by the intermediate and outer tubes respectively and being located immediately upstream of said slot in the general direction of flow of the exhaust gas, the outlet passage having an entrance at one end and terminating in the slot at the other end and being arranged so that all the exhaust gas flows therethrough; said concentric walls of the passage being imperforate and spaced apart by a constant distance over the whole of the overlapping lengths of the intermediate and outer tubes, said distance being such that the height of the passage between the walls is such as to cause attentuation of the noise of gas flowing through the outlet passage while the area of the slot and of the croSssection of the outlet passage transverse to the general direction of flow of the gas therethrough is at least as great as the cross-sectional area of the inlet transverse to the general direction of flow of exhaust gases through the inlet; the outlet passage having a length between the entrance and the slot equal to at least 50 times the height of the slot and providing a clear path for gas flow in a direction parallel to the longitudinal axis of the passage between the entrance and the slot; there being no part of the flow path of the gas between the inlet and the outlet which has a cross-sectional area transverse to the general direction of gas flow which is less than said crosssectional area of the inlet; there being one or more chambers through which the gas flows on emerging from the exit opening of the inner tube and arranged so that the direction of flow of exhaust gases through the chamber or chambers is in a direction generally opposite to the direction of flow of exhaust gases through the inner tube and the passage, and there being a further chamber defined between the inner and outer tubes into which the gas flows on emerging from said first mentioned chamber or chambers, the general direction of flow of gas being reversed in said further chamber from the entrance to which the gas passes directly to the entrance to the outlet passage.