EP0077148A1

EP0077148A1 - Improved exhaust system for automotive vehicle or the like

Info

Publication number: EP0077148A1
Application number: EP82305162A
Authority: EP
Inventors: Motohiro Inaba; Hirofumi Takei
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1981-09-29
Filing date: 1982-09-29
Publication date: 1983-04-20
Also published as: JPS5857017A

Abstract

The resonance energy normally produced with an internal combustion engine exhaust tail pipe (10) is attenuated by providing auxiliary pipes (14, 16) which branch off from the tail pipe (10) and which have lengths selected to produce resonances which offset and attenuate the noise produced by the resonance occuring in the tail pipe (10) per se.

Description

The present invention relates generally to an exhaust arrangement for an automotive vehicle or the like and more . specifically to an exhaust arrangement which reduces the resonance noise produced in the exhaust arrangement without increasing the flow resistance thereof.
As is well known, present exhaust systems function to not only reduce the noise of the exhaust gases being emitted from the engine but also to purify same. Thus, an exhust system frequently includes an emission control device ( e.g. catalytic converter) a diffuser, a silencer heat insulation, conduiting interconnection the various elements and brackets for suspending the conduiting, muffler, converter etc, beneath the vehicle.
Fig. 1 of the drawings shows a previously proposed exhaust arrangement (publically disclosed in Nissan Periodical Bulletin No. 346 issued March 1981) wherein a center tube 1 leads from either the engine or a catalytic converter (or the like) to a main silencer 2. Leading from the silencer 2 is a tail pipe 3. In this arrangement the center tube 1 is curved so as to pass over the rear axle of the vehicle (not shown).
However, this arrangement has suffered from the drawback of emitting unwanted noise due to the resonance which tends to occur within the tail pipe at frequencies which may be identified using the equation:
wherein C denotes the acoustic velocity within the pipe, L the length of the pipe and n a whole number integer.
An object of the present invention is to provide an exhaust arrangement which can attenuate resonance noise without incurring any back pressure inducing flow restriction.
The present invention accordingly features an arrangement wherein the resonance energy normally produced within the tail pipe of an exhaust system is attenuated by providing auxiliary pipes which branch-off from the main tail pipe and which have lengths selected to produce resonances which offset and thus attenuate the noise producing resonances in the main pipe.
More specifically, the present invention takes the form of an exhaust arrangement for an internal combustion engine comprising a tail pipe having an upstream end and a downstream end, a plurality of branch pipes each fluidly communicating with the tail pipe at a location intermediate of said upstream and downstream ends, and wherein the plurality of branch pipes each have a length half that of the preceding one.

Fig. 1 is an elevation showing the prior art arrangement briefly discussed in the opening paragraphs of the present disclosures;
Fig. 2 is an elevation of an exhaust arrangement according to a first embodiment of the present invention;
Fig. 3 is a plan view of the arrangement shown in Fig. 2;
Fig. 4 is an plan view showing in detail the manner in which the main tail pipe and the auxiliary branch pipes interconnect;
Fig. 5 is an elevation of the arrangement shown in Fig 4;
Fig. 6 is a graph showing in terms of noise (dB) and frequency (KHz) the difference in noise emitted from the prior art arrangement and the present invention;
Fig. 7 is a plan view of a second embodiment of the present invention formed by press working;
Fig. 8 is a front elevation of the arrangement shown in Fig. 7;
Figs. 9 to 12 are sectional elevations taken along section lines IX - IX, X -X, XI - XI, and XII - XII respectively; and
Fig. 13 is a schematic diagram of the second embodiment showing the lengths of the tail pipe and the first and second branch pipes operatively connected therewith.

A first embodiment of the present invention is shown in Figs. 2 to 5. In this arrangement a tailpipe 10 leads from a silencer 12 to the ambient atmosphere. A first branch pipe 14 having the same diameter as the tail pipe 10 leads from a point intermediate the two ends of the main tail pipe back toward the silencer 12. The length of this pipe is essentially half that of the main exhaust pipe (Viz., L/2). A second branch pipe 16 also having the same diameter as the tail pipe, leads from a point intermediate the upstream end of the main tail pipe and the point at which the first branch pipe 16 communicates with same, back toward the silencer 12. The length of this branch pipe is essentially 1/4 of the length (L) of the main tail pipe 10. A bracket 18 for supporting the first branch pipe 14 is formed on the connector member 29 via which the second branch pipe 16 is connected to the main tail pipe 10 while a second bracket 22 for supporting the closed ends of the two branch pipes is provided immediately downstream of the silencer 12. It should be noted that the arrangement shown is preferred for reasons of compactness and that the branch pipes may be arranged differently if deemed advantageous.
Figs. 4 and 5 show in detail the manner in which the branch pipes connect with the main tail pipe. As shown the branch pipes interconnect at an angle for the purpose of eliminating whistling or reverberation noise which would be apt to be produced if the pipes intersected at right angles. This generating phenomenon may be further reduced by roughening the inner surfaces of the pipes adjacent the connector members.
A best seen in Fig. 2 both of the branch pipes are adapted to extend parallel with the main tail pipe and thus curve in a manner to pass over the rear axle of the vehicle (not shown).
With the just described arrangement as resonance tends to occur in the main tail pipe 10 at various frequencies which may be identified using the equation (1) Viz.,
Resonance also tends to occur in the first branch tube at frequencies given by
f = C/2L, 3C/2L, etc over the length L/2,
while in the second branch pipe resonance tends to occur at frequencies,
f = 2C/2L, 6C/2L, 10C/2L etc over the length L/4.
Thus as shown in _Fig. 6 (wherein peaks a₁, a₂, a₃₁ etc.'are attributable to exhaust gas pulsations emitted from the engine per se, and peaks bl, b2, b3, etc are produced by resonance in the tail pipe) the resonance which would normally produce peaks b₂, b₃, ^b ₅, ^b ₆ and b₇ is attenuated. According to the first embodiment of the present invention follows the broken line curve while that of the prior art is shown in solid line
It showld be noted that the resonance which tends to produce peak b₄ and corresponding unillustrated peaks b₈ and b₁₂, may be attenuated by providing a branch tube having lengths L/16.
The actual length of the branch pipes in the first embodiment should in actual practice be slightly shorter than the theretical lengths L/2 and L/4, due to a slight tempreature differential which occurs between the gas in the main tail pipe and the branch pipes and according a slight acoustic velocity differential. Alternatively, the branch pipes may be insulated, however this tends to add unnecessarily to the weight of the vehicle.
Figs. 7 to 12, show a second embodiment of the present invention. This arrangement is similar to the first functionally, and differs only in that the branch pipes and the portion of the tail pipe to which they connect, are integrally formed by press-working. As shown, conduits 24 may be inserted into each end of the press formed member 26 so as to complete the arrangement. It will be noted that this arrangement tends to eliminate the previously mentioned temperature differential and thus permit the lenghts of the branch pipes to be formed at the theretical lengths of L.2 and L/4. Moreover, the curvature inherently produced during press working at the sites where the branch passages and the main tail pipe intesect function to reduce the previously mentioned whistling noise phenomenon. Again, roughening may be provided as required.

Claims

1. A exhaust arrangement for an internal combustion engine, comprsing

a tail pipe (10) having an upstream end and a downstream end; charachertised in

a plurality of branch pipes (14,16) each fluidly communicating with said tail pipe (10) at a location intermediate said upstream and downstream ends; said plurality of branch pipes (14, 16) each having a length half that of the preceeding one.

2. An exhaust arrangement as claimed in claim 1, characterised in that the longest of said banch pipes (14) has a length half that of said tail pipe (10).

3. An exhaust arrangement as claimed in claim 1, characterised in that each of said plurality of branch pipes (14, 16) intersects with said tail pipe (10) at an angle inclined in the direction of said downstream end.

4. An exhaust arrangement as claimed in claim 1, characterised in that said plurality of branch pipes (14, 16 and the portion of said tail pipe (10) intersected by said branch pipes (14, 16) are formed integrally by press working.

5. An exhaust arrangement as claimed in claim 1, characterised in that the internal surface of tail pipe (10) and said branch pipes (14, 16) is roughened in the vicinty of the intersection thereof.

6. An exhaust arrangement as claimed in claim 1, characterised in that said branch pipes (14,16) have the same diameter as said tail pipe (10).