Silencer

Abstract

A muffler or silencer, preferably for motor vehicles, adapted to be mounted to the exhaust pipe of an exhaust gas system. The silencer comprises a casing having arranged therein a number of means arranged to impede the passage of a major part of the gas flow and to re-direct said part gas flow rearwardly. Gas through-flow openings are provided at alternate ends of the gas flow re-directing means, between said ends and the casing walls. The arrangement of the through-flow openings is such as to force the gas flow to follow a zig-zag path, and baffle means may be arranged, if desired. The whole device may be made from a heat resistant plastics material.

Description

The present invention relates to a silencer or muffler, especially for use in motor vehicles, comprising a casing provided with an inlet and an outlet and being capable of being coupled to an exhaust system, said casing having mounted therein partition walls arranged to influence the flow of exhaust gases through the casing, there being arranged at opposite side walls of the casing alternatingly located through-flow openings for the gas and at least one of said partition walls having a curved portion which together with the casing defines a slot-like through-flow opening for the gas.

The object of the present invention is to provide a novel silencer of the type described which combines an extremely high degree of sound damping with a very low resistance to the flow of exhaust gases. Another object is to provide a novel silencer of the type described which is of simple and durable construction. These objects are achieved by means of the inventive silencer or muffler which is mainly characterized in that it is made of a heat resistant plastics material, preferably polyester resins, and in that the partition wall presents a curved portion and that the concave side of which is directed generally towards the inlet end of the casing, thus causing the gas stream to be re-directed towards the inlet end of the casing before passing through the slot-like through-flow opening.

One explanation -- borne out by practical tests -- as to why the silencer of the present invention has a substantially lower resistance to the flow of exhaust gases than silencers of conventional construction is that the curved walls, which because of their curvature catch the flow of gas passing through the casing, eliminate or substantially reduce the occurrence of turbulence in the gas stream and impart a generally laminar flow to the gases. Associated with the laminar character of the gas stream is the surprisingly low level of sound obtained.

The invention will now be described in more detail with reference to a number of embodiments thereof illustrated in the accompnaying drawing, in which

FIGS. 1 and 2 illustrate in longitudinal section two alternative embodiments of the silencer according to the invention,

FIG. 3 is a cross-sectional view of the silencer shown in FIG. 2, and

FIGS. 4 and 5 illustrate in longitudinal section two further variations of a silencer constructed in accordance with the invention.

In FIGS. 1-5 the reference numeral 1 indicates a cylinder or casing 1 in which are arranged or mounted one or more intermediate walls adapted to influence the flow path of the exhaust gases and therewith to reduce the level of the sound caused thereby. The casing 1 can be coupled to the exhaust pipe of a motor vehicle for example by means of connectors 2a and 2b.

In accordance with the basic concept of the invention, the silencer illustrated in FIG. 1 comprises an intermediate wall 4 which is curved in a manner such that the gases flowing through the silencer are caught by the wall and passed generally rearwardly. The end of the wall 4 terminates short of the inner surface of the casing 1 to form an opening 5 through which gases can pass to beyond the wall.

With the embodiment illustrated in FIG. 1, the wall 4 is of planar construction and has a portion 6 which is inclined relative to the longitudinal direction of the silencer and a curved portion 7, the portion 7 to advantage being of arcuate or circular configuration. It should be noted that the area of the planar, inclined portion 6 is much greater than the area of the curved portion 7.

The curved portion 7 should be smoothly rounded and have a curvature radius of the order of one fifth to four fifths, preferably one third to two thirds, and suitably about one half the inner cross-width or diameter of the casing 1.

In accordance with one special feature of the invention, one or more further partition walls acting as baffle means are arranged in front of and/or behind the curved wall 4 and are adapted to direct the gas stream away from the opening 5 and to extend the path of the gases through the casing 1. With the illustrated embodiment, arranged in front of and behind the wall 4, as seen in the general direction of flow of the gas through the silencer, is a baffle means 8 and a baffle means 9, respectively. With this embodiment, each of the baffle means 8, 9 comprises a simple partition wall structure having arranged therein gas through-flow openings 10 and 11, respectively. In accordance with the invention, the opening 10 in the baffle wall 8 located in front of the wall 4 and the openings 11 in the baffle wall 9 behind said wall are located close to or adjacent the side wall 12 of the casing 1 or the portion of the casing opposite the side wall 13, or the portion of the casing adjacent to which the gas through-flow opening 5 defined by the end of the wall 4 and the inner surface of the casing is located. In this way, the gas stream is imparted a substantially zig-zag pattern of movement, as indicated by the flow arrows in the Figure. With the illustrated embodiment, the through-flow openings 10 and 11 of the baffles 8, 9 comprise a number of small holes disposed in tightly packed relationship so that the total area presented thereby provides a suitable through-flow opening for the gas.

FIG. 2 illustrates an embodiment in which two intermediate partition walls 14 and 15 are attached in zig-zag fashion to opposing portions or walls 12 and 13 of the casing 1, wherewith gas through-flow openings 16 and 17 are formed alternately between the walls 14, 15 and opposing sides or portions 12 and 13 of the casing. It should be observed that the openings 11 in the baffle 9 located behind the walls 14 and 15, as seen in the gas through-flow direction, are located in the proximity of the casing portion 13, and that the gas outlet, comprising a connection means 2b, is located in the proximity of the opposite portion 12 of said casing so that the gas stream is guided in a zig-zag pattern as illustrated by the flow arrows.

The wall 15 mounted downstream of the gas flow path through the silencer is arranged to capture the gas passing the wall 14, located upstream of said gas path, and to pass the gas generally rearwardly. It will readily be perceived that the casing can be provided with more than two intermediate walls. The position and angle of inclination of the baffle wall 9 and also the position of the connecting means 2b in relation to the end wall of the casing depends on the number of intermediate walls arranged in said casing. It is also possible to make the straight portions of the walls 14 and 15 in FIG. 2 substantially parallel to each other.

Reference is now made to FIG. 3 which illustrates one of several possible cross-sectional shapes of the casing 1, namely a rectangular cross-sectional shape. In addition to the aforementioned sides 12 and 13, the casing may also comprise two sides 18 and 19 of shorter length than sides 12 and 13 to form the illustrated rectangular cross-sectional shape. In accordance with the invention, the intermediate wall 14, similarly to the remaining intermediate walls, may suitably be sealingly connected to the three sides or walls 12, 18 and 19 of the casing while leaving the through-flow opening 16 between the intermediate wall and the wall 13 of said casing.

Although FIG. 3 illustrates a casing of rectangular cross-section, it is obvious that other cross-sectional shapes are conceivable, such as for example a square cross-section, circular, oval or even polygonal cross-section. Irrespective of the cross-sectional shape of the casing, it is desirable that the sides of the intermediate walls arranged in the casing are firmly connected to or at least touch the inner surface of the casing, with the exception of the side defining part of the through-flow opening.

A generatris of the curved portion 7 of the intermediate wall 6 in FIG. 1 or the corresponding curved portions of the intermediate walls 14 and 15 of FIG. 2 is constantly parallel with itself and preferably also with one or two of the walls of the casing, in the illustrated cases the walls 12 and 13.

Reference is now made to FIG. 4 which illustrates an embodiment with which the silencer includes two baffle means 25 and 26, each of which includes at least two baffle walls 27 and 28 having through-flow openings disposed therein, said walls forming together with portions of the casing a container-like chamber 29 within the casing 1. As illustrated in the Figure, the chamber 29 may be of triangular configuration, or may be constructed to present some other configuration. Thus, it is not necessary that the walls 27 and 28 join at a common point, but can be separated from each other, although attached to the inner surface of the casing.

In accordance with one feature of the invention, the spaces formed between the baffle walls and portions of the casing can be either completely or partially filled with sound absorbing material such as mineral wool or steel wool.

In accordance with the basic concept of the invention, an inlet opening 30 leading to a chamber 29 formed between the intermediate walls 27 and 28 and a casing portion 25 is located close to or adjacent the portion 13 of the casing opposite the portion 12 adjacent to which an outlet opening 31 of the chamber is located. In turn, the outlet 31 is located opposite that portion of the casing adjacent to which a gas through-flow opening 32 is located between said casing and an intermediate wall 33.

The positioning of the upper baffle means 26 and its inlet and outlet openings depends on the number of intermediate walls arranged in the casing. With the embodiment illustrated in FIG. 4, the intermediate wall 33 is curved along the whole of its length.

FIG. 5 illustrates an embodiment where the casing is provided with three intermediate walls 34, 35 and 36, each of which is curved along the whole of its length. Arranged upstream of the intermediate walls is a baffle means 37, while a baffle means 38 is located downstream of said walls. With this embodiment, only the baffle means 38 located downstream of the intermediate walls is filled with sound absorbing material, while the baffle means located upstream of said walls is empty. It should be observed that the first baffle means 37 is inverted with respect to the first baffle means 25 illustrated in FIG. 4, and with respect to the direction in which the point of the triangle extends relative to the adjacent intermediate wall. Thus, the narrowing portion of the space formed by the baffle means is directed towards the casing portion 13 which together with the end of the intermediate wall 34 constitutes the gas through-flow opening. The baffle means 38 is also inverted relative the baffle means 26 in FIG. 4, and an odd number of intermediate walls is arranged in the embodiment of FIG. 6, as also in the embodiment of FIG. 4. The inlet opening 39 of the baffle means 37 is located in the proximity of the narrowing portion of the space formed by said baffle means, while the outlet opening 40 of said baffle means is located on the opposite side of the arrangement and remote from the opening 39.

In accordance with the invention, the casing, the intermediate walls and the baffle means may be made from heat resistant plastics material which may be reinforced to advantage with glass fibres or any other suitable reinforcing material. When such heat resistance plastics material is used, the intermediate walls and the baffle means, when embodied, should be fusion welded to the inner surface of the casing. When other material is used such as conventional sheet metals, for example, the intermediate walls and the baffle means may be secured by conventional welding techniques or by other appropriate methods.

In accordance with a special feature of the invention, the connecting means mounted on the casing 1 may comprise two or more concentrically arranged, although longitudinally displaced pipe portions of mutually different width or diameter. An embodiment of such connecting means is illustrated in FIG. 1. Thus, the connecting means 2a comprises a first pipe portion 41 located nearest the housing 1 and having the smallest width or diameter, a second pipe portion 42 of slightly larger diameter, and a third pipe portion 43 or larger diameter than the pipe portions 41 and 42, respectively. The advantage of such a connecting means is that the silencer in question can be connected to exhaust pipes of different dimensions in a simple and convenient manner. The exhaust pipe in question can be inserted in the outermost pipe portion 43 and, if too narrow to be sealingly accommodated by said pipe portion, can be moved through the connecting means until it is sealingly held by a pipe portion of the proper diameter or width. The pipe portions located externally of the appropriate pipe portion can then be removed as by sawing and the pipe connected to the silencer. Thus, the disadvantages encountered with the many different dimensions of conventional exhaust pipes, particularly motor vehicles exhaust pipes, is eliminated.

Instead of a connecting device whose diameter progressively increases in a direction outwardly from the casing 1, it is naturally also possible to construct a connecting means whose diameter is progressively smaller in a direction outwardly from said casing. It is also possible to construct the connecting means with more than three or four pipe portions illustrated in FIG. 1.

The amount of heat absorbed in a silencer from the throughflowing gases is dependent upon the type of flow in the silencer. If, as in the inventive silencer, the flow is generally laminar, the heat absorption is reduced, which is advantageous for the durability of the silencer.

Tests have indicated that by using plastics material, especially polyester plastics, in the silencer it is possible to simplify the manufacturing process to an extent not possible with conventionally used metallic materials. Equally important, however, is that by changing from conventional materials to plastics material an improvement in noise reduction is obtained, the explanation of which probably lies in the specific properties characteristic for the plastics material.

Although the invention has been described with reference to a number of embodiments thereof, the invention is not restricted to such embodiments but can be modified within the scope of the claims. Thus, the geometric shape of the intermediate walls and the baffle means can be modified without detracting from the desired efficiency of the device.

Claims

1. A silencer for motor vehicles, comprising a casing of glass fiber reinforced, heat resistant polyester plastics and having rectangular cross section, said casing forming a tubular body having end walls at its ends and an inlet at one end and an outlet at the other end of said casing, a first and a second acoustic chamber being located between a pair of axially spaced baffle walls of plastics material, each of said baffle walls being perforated in a predetermined area to admit through-flow of gases, said baffle walls being integral with the casing and mounted in spaced relationship to the respective end wall to define an inlet chamber and an outlet chamber respectively, at least one of the acoustic chambers containing sound absorbing material, a number of rigid partition walls of plastics material being integral with the walls of the casing and guiding the gas flow in a predetermined path between the two acoustic chambers, each partition wall extending between and being connected to two opposite walls of the casing and being connected at one end to one of the other two opposite casing walls and being disposed outside said sound absorbing material, whereas the opposite end of the partition wall forms a straight edge located in spaced relationship to the adjacent casing wall to form a through-flow opening, said through-flow openings being located alternately at opposite sides of the longitudinal axis of the casing to provide a zigzag flow of gases through the casing, each partition wall having a generally curved cross section with its concave side facing the inlet end of the casing and comprising a leg portion connected at its one end to the casing and merging at its other end into a reversing partition wall portion directed generally towards the inlet end of the casing to provide a pocket for locally redirecting the flow before it passes the free edge of the partition wall and thereafter again is redirected to enter into the adjacent through-flow opening, said perforated areas of said baffle walls being offset relative to the lengthwise axis of the casing to provide in each acoustic chamber an oblique flow path smoothly connected to the said zigzag flow path.