GB2161215A

GB2161215A - Exhaust systems for internal combustion engines

Info

Publication number: GB2161215A
Application number: GB08516446A
Authority: GB
Inventors: David Vizard
Original assignee: Shelburne Inc
Current assignee: Shelburne Inc
Priority date: 1984-07-05
Filing date: 1985-06-28
Publication date: 1986-01-08
Also published as: GB8516446D0

Abstract

An exhaust system for an internal combustion engine comprises two exhaust pipes 10, 11, a balance tube assembly 16 which connects the two exhaust pipes and places them in communication with one another intermediate their inlets and outlets, and noise attenuation means 19 incorporated in the balance tube assembly. The noise attenuation means 19 assists in reducing the noise level of the exhaust system as a whole and may comprise any device which would act as a silencer if exhaust gases were passed through it in the normal manner of operation of a silencer. Examples of such devices are described. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Exhaust Systems for Internal Combustion Engines The invention relates to exhaust systems for internal combustion engines and particularly to systems where the engine has two exhaust manifolds connected to separate exhaust pipes. For example, in a V8 engine each bank of four cylinders will normally be connected to a separate exhaust pipe through an appropriate manifold.

In such systems, each exhaust pipe will normally include one or more conventional silencers.

However, it is also known in such systems to connect one bank of cylinders to the other bank by means of a simple balance pipe, and this may have the effect of helping to reduce the noise level from the exhaust system. The present invention provides an improvement in this known arrangement whereby the silencing of the exhaust system is enhanced.

According to the invention there is provided an exhaust system for an internal combustion engine, comprising two exhaust pipes each of which has at one end an inlet for connection to an engine exhaust manifold and at the other end an outlet, a balance tube assembly which connects the two exhaust pipes and places them in communication with one another intermediate the respective inlets and outlets, and noise attenuation means incorporated in the balance tube assembly.

When the engine is running, exhaust gases flowing along the exhaust pipes do not simply flow through the balance tube assembly but resonate backwards and forwards along the tube. It has been found, unexpectedly, that in spite of there being no continuous flow along the balance tube assembly, the incorporation of noise attenuation means in the assembly will assist in reducing the noise level of the exhaust system as a whole.

It has been found that the noise attenuation means may comprise any device which would act as a silencer if exhaust gases were passed completely through it in the normal manner of operation of a silencer, and the invention therefore includes within its scope systems of the kind referred to which incorporate in the balance tube assembly any conventional form of silencer or other noise attenuation means.

However, tests have shown that certain forms of silencer give better results than others.

According to one particular preferred embodiment of the invention, therefore, the noise attenuation means comprise at least one silencer comprising a closed chamber, a first pipe extending into the chamber and communicating with one of said exhaust pipes, and a second pipe extending into the chamber and communicating with the other of said exhaust pipes.

The chamber may have opposed end walls, the first pipe passing through one end wall and having an open end spaced from the opposite end wall and the second pipe passing through the opposite end wall and having an open end spaced from said one end wall, the two pipes being substantially parallel and overlapping within the chamber.

Alternatively, the silencer may comprise a casing having opposed end walls and defining a closed chamber, the first pipe passing through one end wall and extending into the interior of the chamber and the second pipe also passing through the same end wall and extending into the interior of the chamber, the first and second pipes extending into the closed chamber to different extents and overlapping.

In the last-mentioned arrangement, the silencer casing and the first and second pipes are preferably disposed to extend generally parallel to the exhaust pipes the first and second pipes leading from generally right-angled extensions thereof which lead to the exhaust pipes respectively.

In any of the above arrangements two or more silencers may be disposed in series in the balance tube assembly.

In any arrangement according to the invention a noise reflector may be located opposite and spaced from the open end of at least one of the pipes within the chamber in such manner as to reflect down the pipe length a proportion of the noise passing along the pipe length. For example, said noise reflector may be a parabolic reflector located on the central axis of the pipe.

Each exhaust pipe may incorporate a main silencer intermediate its respective exhaust manifold and outlet, said balance tube assembly being connected to each exhaust pipe intermediate the respective exhaust manifold and main silencer.

As previously mentioned, each exhaust manifold may have four branches for communication with a different four cylinders of an eight cylinder engine.

However, the invention includes within its scope arrangements in which each exhaust manifold has three branches for communication with a different three cylinders of a six cylinder engines well as all other arrangements where two exhaust manifolds are connected to two separate exhaust pipes.

The invention includes within its scope an exhaust system for an internal combustion engine comprising two engine exhaust manifolds, two exhaust pipes each of which has at one end an inlet connected to an engine exhaust manifold and at the other end an outlet, a balance tube assembly which connects the two exhaust pipes and places them in communication with one another intermediate the respective inlets and outlets, and noise attenuation means incorporated in the balance tube assembly.

The noise attenuation means may be of any of the forms referred to above.

The invention also provides a balance tube assembly for use in an exhaust system of an internal combustion engine of the kind comprising two exhaust pipes, the balance tube assembly comprising connection ports at opposite ends thereof with T-junction means for connecting opposite ends of the assembly in transverse communication with respective ones of said exhaust pipes, and noise attenuation means incorporated in the balance tube assembly. Again, the noise attenuation means may be in any of the forms referred to above.

The invention further provides a method of reducing the noise level from the exhaust system of an internal combustion engine, of the kind comprising two exhaust pipes, the method comprising interconnecting the two exhaust pipes by a balance tube assembly incorporating noise attenuation means, such noise attenuation means being of any of the kinds referred to above.

In the accompanying drawings: Figure 1 is a diagrammatic representation of an engine exhaust system according to the invention, Figure 2 is a similarview of an alternative form of exhaust system, Figure 3 is a longitudinal section through an example of a silencer suitable for use in the system of Figure 1, Figure 4 is a longitudinal section through an example of a silencer suitable for use in the system of Figure 2, Figure 5 is a section along the line V-V of Figure 4, Figures 6 to 16 are diagrammatic longitudinal sections through other forms of silencer which may be used in exhaust systems according to the invention.

Referring to Figure 1,there is shown diagrammatically an exhaust system for a V8 engine. The conventional part of the exhaust system comprises two exhaust pipes 10 and 11 which extend from exhaust manifolds 12 and 13 respectively, each manifold being connected to one of the two banks of four cylinders of the engine. The exhaust pipes incorporate main silencers 14 and 15 respectively which may be of any conventional type.

According to the invention, the noise level of such an exhaust system is reduced by connecting between the exhaust pipes 10 and 11 a balance tube assembly indicated generally at 16. The assembly comprises pipes 17 and 18 which are connected by means of any suitable T-junction connections to the exhaust pipes 10 and 11 respectively.

The pipes 17 and 18 lead into opposite ends of a silencer 19.

The silencer 19 may comprise any form of silencer which, when used in the normal manner with exhaust gases flowing completely through it, would serve to reduce the noise of the exhaust. For example, the silencer may be of the kind comprising a casing defining a closed chamber, the pipes 17 and 18 forming the inlet and outlet portions of a single continuous pipe which passes straight through the chamber and is formed within the chamber with perforations whereby gases flowing along the pipe may escape through the perforations into the interior of the chamber which may be packed, around the pipe, with sound absorbing means such as conventional glass fibre packing.

Alternatively, the silencer might be of the kind wherein the casing is divided internally by two spaced bulkheads to divide the casing into first and second buffer compartments separated by an intermediate compartment, the inlet and outlet pipes 17 and 18 extending through the bulkheads and across the intermediate compartment, a pass tube being provided which extends through the buikhead and across the intermediate compartment and opens, at opposite ends thereof, into first and second buffer compartments, at least one of the inlet pipe, outlet pipe and pass tube having perforated walls whereby gases flowing therealong may escape through the perforations into the intermediate chamber, which may be packed with gas permeable material such as glass fibre packing.

Although, as mentioned, any form of silencer may be used, Figure 3 shows in section one form of silencer which has been found to give particularly good results in an arrangement such as is shown in Figure 1.

Referring to Figure 3, the silencer comprises a hollow casing 20 which is generally elliiptical in section and is closed by end walls 21 and 22.

Passing through the end wall 21 of the casing is a first pipe 23 which extends into the casing and has a flared open end 24 which is spaced from the opposite end wall 22. The portion of the pipe 23 outside the casing 20 is of enlarged diameter as indicated at 25 for connection to the pipe 17.

Similarly, a second pipe 26 extends through the opposite end wall 22 of the casing and has a flared end 27 spaced from the end wall 21. The portion 28 of the pipe 26 outside the casing is of enlarged diameter for connection to the pipe 18 of the arrangement of Figure 1. Opposite the flared open end 24 of the pipe 23, the end wall 22 of the casing is deformed to provide a parabolic reflector 29 which is coaxial with the pipe 23. A similar parabolic reflector 30 is formed in the end wall 21 opposite tht flared open end of the pipe 26. The flared open end of each pipe is formed by rolling outwardly and backwardly the end periphery of each pipe.

The two pipes 23 and 26 extend into the casing 20 to approximately the same length and overlap as shown in Figure 3. The rolled back portion forming the flared end of each pipe is spot welded to the outer surface of the adjacent pipe and also to the peripheral wall of the casing where it touches said peripheral wall.

It is believed that the silencing effect provided by the silencer shown in Figure 3, when incorporated ii the balance tube assembly 16 between the two exhaust pipes, occurs as a result of the following phenomena: 1. Volume damping: It is believed that the volum added to the exhaust system by the chamber tends to buffer the exhaust pulse. This leads to reduction in the noise that the conventional silencers 14 and 15 downstream of the balance tube assembly have to contend with.

2. Resonance: The chamber defined by the casino 20 and end walls 21 and 22 acts as a resonator box and the gases within the box will vibrate at a certair frequency which will have the tendency to cancel out certain noise frequencies at certain points in th( rpm range. This will occur in spite of the fact that th gases do not actually pass completely through the silencer in the balance tube assembly, but simply travel back and forth.

3. Noise reflection: The parabolic reflectors 29 ar 30 reflect down their associated pipes shock waves or sound waves travelling along the pipes. The noise reflected back down the pipe by each parabolic reflector will tend to cancel out the noise passing along the pipe.

In the alternative arrangement shown in Figure 2, the balance tube assembly 31 comprises two silencers 32 and 33 arranged in series and extending generally parallel to the exhaust pipes 10 and 11.

The two silencers 32 and 33, which are preferably similar in construction, may, as in the arrangement of Figure 1, comprise any form of silencer which would produce silencing in an engine exhaust system if exhaust gases were caused to flow continuously through the silencer. However, a preferred form of silencer is shown in greater detail in Figures 4 and 5.

Referring to Figures 4 and 5, the silencer comprises an outer casing 34 of generally elliptical cross-section formed with end walls 35 and 36. The end wall 35 is formed with two circular apertures through which pass pipes 37 and 38. The pipe 37 extends into the casing 34 to a greater extent than the pipe 38 and the open ends of both pipes are spaced from the opposite end wall 36. The inner open end of the pipe 38 is flared outwardly as indicated at 39 in similar fashion to the pipes in the arrangement of Figure 3. The flared portion of the pipe 38 is spot welded to the outer surface of the pipe 37 and to the inner surface of the casing 34 where it contacts these.Externally of the casing 34 the two pipes are turned in opposite directions through 90O and have connecting portions of enlarged diameter, only the connecting portion 40 of the pipe 37 being shown in Figure 4.

The pipe 37 externally of the casing is connected at right angles to the exhaust pipe 10 by any suitable form of T-connection and the pipe 38 is connected to the corresponding pipe of the silencer 33. The two pipes 38 of the two silencers may be connected by a straight connecting tube the length of which will vary according to the physical spacing apart of the exhaust pipes 10 and 11. Alternatively, the pipes 38 and the connecting tube may form portions of a single integral U-shaped pipe.

The end wall 36 of the casing opposite the open ends of the pipes 37 and 38 is outwardly curved as shown in Figure 4 and serves to reflect noise waves back along the casing. The disposition of the curved end wall 36 is such that noise passing axially along the pipe 37 tends to be reflected back along the pipe 38 and vice versa, and this leads to damping of the noise. Noise reduction will also occur due to volume damping and resonance as previously described in relation to the arrangement of Figure 3.

Although Figures 1 and 2 show the invention in a twin pipe exhaust system for a V8 engine, it will be appreciated that it may be employed in any exhaust system incorporating two or more exhaust pipes and is suitable for V6 engines, straight-8 and straight-6 engines as well as four cylinder engines.

Although in the arrangement Figure 1 only one silencer 19 is shown in the balance tube assembly, such assembly may include two or more silencers arranged in series and such silencers may be of any suitable type. Similarly in the arrangement of Figure 2 there may be provided any number of silencers in the balance tube assembly and transverse silencers of the kind shown in the Figure 1 arrangement may be combined with in line silencers of the kind shown in Figure 2 in a single balance tube assembly. Also, more than one balance tube assembly incorporating silencers may be connected in parallel between the exhaust pipes 10 and 11.

Figures 6 to 16 show diagrammatically, in longitudinal section, other forms of silencer which might be used in the balance tube assemblies 16 and 31 of Figures 1 and 2. Figures 6 to 14 show forms of silencer which might be used for the transverse silencer 19 of Figure 1 and Figures 15 and 16 show silencers which might be used as the in-line silencers 32 and 33 of Figure 2.

In Figure 6 the silencer comprises a hollow casing 40 closed by end walls 41 and 42. Passing through the end walls and the interior of the casing is a continuous pipe 43, the portion of the pipe within the casing being perforated, as indicated at 44, so that exhaust gases may expand outwardly through the perforations and into the casing 40.

Figure 7 shows a similar arrangement in which the casing 40 is filled around the perforated portion of the tube 44 with a sound absorbing material 45 such as glass fibre or any conventional silencer sound absorbing material.

Figure 8 shows a silencer which is somewhat similar to that shown in Figure 3, except that the pipes 46 and 47 extending into the casing 48 from opposite ends thereof do not overlap. Figure 9 shows overlapping pipes 49 and 50 in a casing 51, but in this case the portion of each pipe within the casing is perforated so that exhaust gases can expand outwardly through the perforations into the casing as well as passing axially through the open ends of the pipes 49 and 50. The arrangement of Figure 10 is similar to that of Figure 9 except that the perforated pipes 49 and 50 have closed ends, as indicated at 52 and 53 respectively. Figure 11 is a further development of the Figure 10 arrangement in which the pipes 49 and 50 are surrounded by sound-absorbing packing as indicated at 54.

Figure 12 shows a known form of silencer in which the casing 55 is divided internally by two spaced bulkheads 56 and 57 which divide the casing into a first buffer compartment 58, an intermediate compartment 59 and a second buffer compartment 60. Pipes 61 and 62 extend from opposite ends of the casing 55 and through the bulkheads 56 and 57.

A pass tube 63 also extends through the bulkheads 56 and 57 and opens, at opposite ends thereof, into the first and second buffer compartments. All of the pipes 61,62 and 63 have open ends. Figure 13 shows a modified arrangement in which the portions of the pipes 61,62 and 63 within the casing 55 are perforated. In the alternative arrangement shown in Figure 14, only the pipe 62 is perforated and the second buffer compartment 60 is partly filled with sound absorbing material as indicated at 64.

Figures 15 and 16 show silencers which may be used in the exhaust system illustrated in Figure 2.

The arrangement of Figure 15 is somewhat similar to that of Figure 4 except that the overlapping pipes 65 and 66 within the casing 67 are perforated. In the arrangement of Figure 15 the casing 57 is empty. In the arrangement of Figure 16 the casing 67 partly filled with sound absorbing material 68. In this arrangement also the pipes 65 and 66 are of substantially the same length within the casing 67.

It will be appreciated that Figures 6 to 16 merely.

illustrate byway of example several known forms of silencer which may be used in an exhaust system according to the invention, and the invention is not limited to the use of the silencers illustrated. As previously mentioned, anyform of noise attenuation means, such as a conventional silencer, may be used in the balance tube assembly in an exhaust system according to the invention.

Claims

1.An exhaust system for an internal combustion engine, comprising two exhaust pipes each of which has at one end an inlet for connection to an engine exhaust manifold and at the other end an outlet, a balance tube assembly which connects the two exhaust pipes and places them in communication with one another intermediate the respective inlets and outlets, and noise attenuation means incorporated in the balance tube assembly.

2. An exhaust system according to Claim 1, wherein the noise attenuation means comprise at least one silencer comprising a closed chamber, a first pipe extending into the chamber and communicating with one of said exhaust pipes, and a second pipe extending into the chamber and communicating with the other of said exhaust pipes.

3. An exhaust system according to Claim 2, wherein the chamber has opposed end walls, the first pipe passing through one end wall and having an open end spaced from the opposite end wall and the second pipe passing through the opposite end wall and having an open end spaced from said one end wall, the two pipes being substantially parallel and overlapping within the chamber.

4. An exhaust system according to Claim 2, wherein the silencer comprises a casing having opposed end walls and defining a closed chamber, the first pipe passing through one end wall and extending into the interior of the chamber and the second pipe also passing through the same end wall and extending into the interior of the chamber, the first and second pipes extending into the closed chamber to different extents and overlapping.

5. An exhaust system according to Claim 4, wherein the silencer casing and the first and second pipes are disposed to extend generally parallel to the exhaust pipes, the first and second pipes leading from generally right-angled extensions thereof which lead to the exhaust pipes respectively.

6. An exhaust system according to any of Claims 1 to 5, wherein the noise attenuation means comprise at least two silencers connected in series in the balance tube assembly.

7. An exhaust system according to any of Claims 1 to 6, wherein a noise reflector is located opposite and spaced from the open end of at least one of the pipes within the chamber in such manner as to reflect down the pipe length a proportion of the noise passing along the pipe length.

8. An exhaust system according to Claim 7, wherein said noise reflector is a parabolic reflector located on the central axis of the pipe.

9. An exhaust system according to any of Claims 1 to 8 wherein each exhaust pipe incorporates a main silencer intermediate its respective inlet and outlet, said balance tube assembly being connected to each exhaust pipe intermediate the respective inlet and main silencer.

10. An exhaust system for an internal combustion engine according to any of the preceding claims and further comprising two engine exhaust manifolds to which the inlets of the two exhaust pipes are connected respectively.

11. A balance tube assembly for use in an exhaust system of an internal combustion engine of the kind comprising two exhaust pipes, the balance tube assembly comprising connection ports at opposite ends thereof with T-junction means for connecting opposite ends of the assembly in transverse communication with respective ones of said exhaust pipes, and noise attenuation means incorporated in the balance tube assembly.

12. A method of reducing the noise level from the exhaust system of an internal combustion engine, o the kind comprising two exhaust pipes, the method comprising interconnecting the two exhaust pipes by a balance tube assembly incorporating noise attenuation means.

13. An exhaust system for an internal combustion engine substantially as hereinbefore described with reference to Figure 1 or Figure 2, together with any of Figures 3 to 16 of the accompanying drawings.