EP0340326A1

EP0340326A1 - Exhaust silencer

Info

Publication number: EP0340326A1
Application number: EP88107200A
Authority: EP
Inventors: Jan Stanislaw Kula
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-11-06
Filing date: 1988-05-05
Publication date: 1989-11-08

Abstract

An exhaust silencer suitable for an internal combustion engine. The silencer comprises an outer cylinder, (1) a concentric inner cylinder (2) and an annulus (3) therebetween. The outer cylinder communicates with an inlet pipe (7) at one end of the silencer and the inner cylinder communicates with an outlet pipe (8) at the opposite end. The inner cylinder is provided with a plurality of tubes (11) which extend diametrically across the inner cylinder and they are open at each end so that they communicate with the annulus (3). Each tube is provided intermediate its length with an opening (12) and each tube forms part of a pair of passage ways of equal length arranged to direct the gases from the inlet (7) to a meeting place at the intermediate openings of the tube (11) where the gases from each of the pair of passageways are directed at one another. The gases then pass to the end of the inner cylinder (2) to the outlet (8).

Description

This invention relates to an exhaust silencer and has been devised particularly though not solely as a silencer for an internal combustion engine.
In the past internal combustion engines have been provided with exhaust silencers of many different types, most of which are provided with a series of internal baffles designed to break up the sound waves in the exhaust gases so as to muffle the effect of the sound waves. Some silencers are also provided with absorbent materials intended to absorb different spectrums of the sound waves issuing from the internal combustion engine. The baffles and/or sound deadening material in an exhaust silencer generally restrict the flow of gases through the silencer causing back pressure on the engine and reducing the power of the engine. In designing an exhaust silencer it is therefore desirable to provide a free flow of gases through the silencer while yet dampening or destroying the sound wave patterns present in those gases. This invention achieves this aim without resorting to the use of multiple baffles or sound absorbing material which are expensive to manufacture and have provided excessive back pressures in previous silencers.
The present invention therefore provides an exhaust silencer comprising an inlet for exhaust gases, one or more pairs of passageways communicating with the inlet, the or each pair comprising two equal length passageways arranged to direct the gases from the inlet to a meeting place where the gases from each of the pair of passageways are directed at one another, and ducting directing the gases from the or each meeting place to an outlet.
Preferably the passageways in each pair have the same configuration as one another.
Preferably the passageways are defined by tubes within the silencer.
Preferably the silencer is formed from concentrically located inner and outer cylinders having an annulus therebetween, the inner cylinder having a closed end adjacent to the inlet, the inlet being directed into the annulus, the tubes communicating with the annulus and extending inwardly from the inner cylinder to meeting places located on the axis of the cylinders.
Preferably the tubes extend continuously diametrically across the inner cylinder being open to the annulus at each end, and have an opening to exhaust the gases therefrom at the mid-point of the tube.
Preferably the tubes are spaced from one another along the axis of the cylinders and the opening from each tube impinges on the back of the next tube.
Preferably each tube is displaced through approximately 90° about the axis of the cylinder from the next axially preceding tube in the cylinder.
Preferably the annulus is closed toward the end remote from the inlet, and the corresponding end of the inner cylinder communicates with the outlet from the silencer.
Preferably the annulus is provided with a transverse pressure plate adjacent the inlet, the pressure plate being provided with a plurality of holes therein having a total area greater than or equal to the cross sectional area of the inlet.
Preferably each hole in the pressure plate has edges burst or otherwise deformed from the pressure plate in the direction of travel of gases therethrough.
Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings, in which:-

Fig. 1 is a longitudinal cross section through an exhaust silencer according to the invention;
Fig. 2 is a transverse cross section on the line II-II of Fig. 1; and
Fig. 3 is a transverse cross section on the line III-III of Fig. 1.

In a preferred form of the invention the exhaust silencer is formed from an outer cylinder (1) and a concentric inner cylinder (2) forming an annulus (3) therebetween and being located relative to one another by transverse annular plates (4) and (5). The transverse plates may be dished as shown in Fig. 1. The outer cylinder is provided with tapered truncated cone portions (6) at either end terminating in an inlet pipe (7) at one end of the silencer, and an outlet pipe (8) at the opposite end. The inlet and outlet are designed to be connected into the exhaust pipe from an engine in the normal manner.
The end of the inner cylinder (2) adjacent the inlet (7) is closed, preferably by way of a tapered cone (9) having walls parallel to the tapered walls of the truncated cone portion (6). The transverse plate (4) is provided with a plurality of holes (10) (Fig. 2) having a total cross sectional area which is preferably greater than the cross sectional area of the inlet (7).
The inner cylinder (2) is provided with a plurality of tubes (11) which extend diametrically across the inner cylinder and which are open at each end communicating with the annulus (3) between the inner and outer cylinders. The tubes are spaced from one another down the length of the inner cylinder and are orientated so that each tube is displaced through approximately 90° about the axis (12) of the cylinder from the next preceding tube in the cylinder. This orientation can clearly be seen in Figs. 1 and 3. Each tube is provided at mid-length with an opening (12), typically in the form of a semi-circular cut away portion as shown in Fig. 1, such that exhaust gases entering the tube from the annulus (3) are exhausted into the inner cylinder through the opening in each tube.
In this manner each tube forms part of a pair of passageways from the inlet (7) to the annulus (3) between the inner and outer cylinders and from there into each end of the tube (11) until the gases are directed at each other at a meeting place at the mid-length of the tube, which is located on the axis (12) of the cylinder. Because each passageway (in each pair of passageways formed by each tube) is of the same length and configuration as the other passageway in that pair, the pressure waves in exhaust gases arriving at the meeting place at the mid-point of the tube from one end of the tube are exactly out of phase with the pressure waves in the exhaust gases arriving from the other end of the tube, so that the pressure waves cancel each other out and effectively reduce or destroy the sound pressure waves in the exhaust gases.
The exhaust gases then issue from the opening (12) in each tube (11) and impinge on the back of the neighbouring tube (11) further breaking up any sound waves which may remain in the exhaust gases. The exhaust gases then pass down the length of the inner cylinder (2) to the end of the tube (13) which is open and from there pass to the outlet (8).
The tubes (11) have been described as being continuous from one side of the inner cylinder (12) to the other, and being provided with openings at mid-length, as this configuration is easy and inexpensive to manufacture. The tubes could however comprise shorter lengths of tube protruding inwardly from the inner cylinder (2) to a point adjacent the axis (12), in diametrically opposed pairs on opposite sides of the cylinder. In this manner the gases issuing from a tube on one side of the cylinder are opposed by gases issuing from an equal length tube on the opposite side of the cylinder at a meeting place on the axis of the cylinder causing the same cancelling effect of pressure sound waves from each tube in the pair. The principle remains the same however of providing pairs of passageways which have an equal length from the inlet (7) so that the pressure waves in the gases are cancelled out by equal pressure waves in gases meeting in opposite directions at the meeting place.
Because there are no restrictive baffles within the silencer, there is very low back pressure, but this can be reduced even further by the formation of the transverse plate (4) into a "pressure plate" by the size and configuration of the holes (10) therein. The holes have a total cross sectional area which is greater than or equal to the cross sectional area of the inlet pipe (7) and furthermore have side portions which are burst or otherwise deformed from the baffle plate in the direction of travel of exhaust gases through the holes forming chamfered edges (14). The chamfered edges of the holes act like tuned pipes, assisting the flow of exhaust gases through the holes and reducing the back pressure within the silencer.
In this manner an exhaust silencer is provided which by utilising the principle of cancellation of pressure waves from oppositely orientated passageways of equal length and configuration significantly reduce the pressure waves and hence the sound level in the exhaust gases from an engine. The silencer has particular application to internal combustion engines but can be utilised on the exhaust gases from any type of engine for reduction of the sound pressure waves therein.
The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims

1. An exhaust silencer comprising an inlet for exhaust gases, one or more pairs of passageways communicating with the inlet, the or each pair comprising two equal length passageways arranged to direct the gases from the inlet to a meeting place where the gases from each of the pair of passageways are directed at one another, and ducting directing the gases from the or each meeting place to an outlet.

2. An exhaust silencer as claimed in claim 1, wherein the passageways in each pair have the same configuration as one another.

3. An exhaust silencer as claimed in either claim 1 or claim 2, wherein the passageways are defined by tubes within the silencer.

4. An exhaust silencer as claimed in claim 3, wherein the silencer is formed from concentrically located inner and outer cylinders having an annulus therebetween, the inner cylinder having a closed end adjacent the inlet, the inlet being directed into the annulus, the tubes communicating with the annulus and extending inwardly from the inner cylinder to meeting places located on the axis of the cylinders.

5. An exhaust silencer as claimed in claim 4, wherein the tubes extend continuously diametrically across the inner cylinder being open to the annulus at each end, and have an opening to exhaust the gases therefrom at the mid-point of the tube.

6. An exhaust silencer as claimed in claim 5, wherein the tubes are spaced from one another along the axis of the cylinders and the opening from each tube impinges on the back of the next tube.

7. An exhaust silencer as claimed in either claim 4 or claim 5, wherein each tube is displaced through approximately 90° about the axis of the cylinder from the next axially preceding tube in the cylinder.

8. An exhaust silencer as claimed in any one of claims 4 to 7, wherein the annulus is provided with a transverse pressure plate adjacent the inlet, the pressure plate being provided with a plurality of holes therein having a total area greater than or equal to the cross sectional area of the inlet.

9. An exhaust silencer as claimed in claim 8, wherein each hole in the pressure plate has edges burst or otherwise deformed from the pressure plate in the direction of travel of gases therethrough.