Abstract:
A muffler for an internal combustion engine for effectively damping noise over a wide frequency range, from low frequency noise to high frequency noise. An absorber packed type muffler adapted to absorb noise by a sound absorbing material is inserted in and fixed to a housing which has a bore or bores thereinside, thereby forming one of a pipe inserted type muffler, a resonance type muffler and an interference type muffler to attain combined characteristics of both the types of mufflers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a muffler for damping noise entailed by the emission of exhaust gases from an exhaust system of an internal combustion engine and, more particularly, to a high performance muffler and for an internal combustion engine which effectively dampens noise over a wide frequency range, including low frequency noises to high frequency noise. 
     2. Description of the Prior Art 
     Mufflers of the kind described may generally be classified into two types, i.e., a type having a sound absorbing material or absorbent packed therein and a type having pipes inserted therein. The first-mentioned type of muffler, generally referred to as an absorbent type muffler, shows a satisfactory degree of damping performance against high frequency noise but not against low or medium frequency noise. The second-mentioned type of muffler, referred to as a pipe insertion type muffler hereinafter, is effective to damp noise over an acceptable frequency range due to damping by combined expansion and resonance. Nevertheless, prior art mufflers of the absorbent type or the pipe insertion type are not fully acceptable. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved muffler for use with an exhaust system of an internal combustion engine. 
     It is another object of the present invention to provide a muffler which effectively damps noise over a considerable frequency range, from low frequency noise to high frequency noise. 
     It is another object of the present invention to provide a muffler for an internal combustion engine which is simple in construction and, therefore, producible at low costs. 
     According to the present invention, a muffler assembly for admitting gases accompanied by noise thereinto to dampen the noise comprises an absorbent type muffler for admitting the gases thereinto to absorb the noise by means of a sound absorbing member, and a housing member formed with at least one bore. The absorbent type muffler is disposed in and fixed to the housing member. 
     In accordance with the present invention, a muffler for an internal combustion engine effectively damps noise over a wide frequency range, from low frequency noise to high frequency noise. An absorbent type muffler adapted to absorb noise by a sound absorbing material is inserted in and fixed to a housing which has a bore or bores thereinside, thereby forming one of a pipe insertion type muffler, a resonance type muffler, and an interference type muffler to attain combined characteristics of both types of mufflers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the present invention will become more apparent from a consideration of the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a vertical section of a basic construction of an absorbent type muffler embodying the present invention; 
     FIGS. 2-6 are vertical sections each showing a possible arrangement in accordance with the present invention in which an absorbent type muffler with the basic construction shown in FIG. 1 is combined with a pipe insertion type muffler; 
     FIG. 7 is a vertical section of a second embodiment of the basic construction of the absorbent type muffler in accordance with the present invention; and 
     FIG. 8 is a vertical section of a third embodiment of the basic construction of the absorbent type muffler in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, a basic construction of an absorbent type muffler embodying the present invention is shown. The muffler, generally 10, includes a perforated pipe 12 which is perforated with a number of holes 12a through its wall and an inlet 12b and an outlet 12c at its opposite ends. A heat resisting, sound absorbing member, or absorbent, 14 is wound around the perforated pipe 12 over a length of the latter where the holes 12a are formed. The absorbent 14 may be made of glass wool, rock wool, slag wool, asbestos fibers, etc. The outer periphery of the absorbent 14 is covered with a retainer tube, or outer tube, 16 which is locally provided with an open, communication section 18 constituted by a number of holes (no numeral). In short, the muffler 10 in accordance with the present invention comprises an absorbent type muffler 10a made up of the perforated pipe 12, absorbent 14, and retainer tube 16. 
     The absorbent type muffler 10a is disposed in a bore 20c of a tubular housing 20 which is closed by end plates 20a and 20b at opposite ends, respectively, the bore 20c serving as an expansion chamber. The perforated pipe 12 of the muffler 10a is supported by the end plates 20a and 20b, constituting, as a whole, a pipe insertion type muffler 10b. That is, in the illustrated construction, a non-communication section 16a of the retainer tube 16 at the inlet side of the retainer tube 16 and adjacent to the end plate 20a functions as an inserted inlet pipe, while at the outlet side of the tube 16 a non-communication section 16b adjacent to the end plate 20b functions as an inserted outlet pipe. 
     As described above, the muffler shown in FIG. 1 is comprised of the combination of the absorbent type muffler 10a and the pipe insertion type muffler 10b and, therefore, attains their characteristics at the same time. 
     In the illustrative embodiment, assuming that the overall length of the tubular housing 20 is L and the lengths of the non-communication sections 16a and 16b of the retainer tube 16 are La and Lb, respectively, they may be suitably selected to effectively damp noise in conformity to particular characteristics of an intended internal combustion engine. This in turn allows the communication section 18 of the retainer tube 16 to be positioned and dimensioned in a desired manner. For specific numerical values, a reference may be made to Japanese Utility Model Publication Nos. 57-30401/1982 and 57-52372/1982, for example. 
     The communication section 18 of the retainer tube 16 may comprise a meshing instead of the numerous holes shown and described. Concerning the absorbent 14 wound around the perforated pipe 12, its thickness has little influence on the resulting sound absorbing effect if the volume of the expansion chamber 20c is constant; typically, the thickness may be 5, 8, 15 or 30 millimeters. For noise in the medium frequency range, however, a thicker absorbent would achieve greater performance in sound absorption. In the illustrative embodiment, the absorbent 14 is 8 millimeters thick by way of example. 
     While in the embodiment of FIG. 1 the pipe insertion type muffler 10b is constructed by combining the muffler 10a made up of the perforated pipe 12, absorbent 14, and retainer tube 16, and the tubular housing 20 having the single expansion chamber 20c, it is naturally permissible to combine such a muffler 10a with a tubular housing having a plurality of expansion chambers. 
     For example, in an alternative construction shown in FIG. 2, a tubular housing 22 is divided by a partition 24 into two compartments, i.e. a first expansion chamber 22c and a second expansion chamber 22d. An absorbent type muffler 10a with the basic construction shown in FIG. 1 is inserted in the first and second expansion chambers 22c and 22d of the housing 22 and securely mounted to the housing 22 by an end plate 22a and the partition 24. Specifically, the perforated pipe 12 is supported by the end plate 22a adjacent to its inlet 12b and the retainer tube 16 is supported by the partition 24 such that its communication section 18 is open to expansion chambers 22c and 22d. The inlet 12b for the entry of engine exhaust is open to the atmosphere and the outlet 12c to the second expansion chamber 22d. Meanwhile, the other end plate 22b in FIG. 2 rigidly carries therewith an outlet pipe 26 having an inlet 26a and an outlet 26b, so that gases admitted into the second expansion chamber 22d are discharged to the atmosphere via the outlet 26b. Again, the muffler in this particular embodiment has both the characteristic of an absorbent type muffler and that of a pipe insertion type muffler. 
     A modification to the construction shown in FIG. 2 is shown in FIG. 3. The difference between the two constructions is that in FIG. 3 the absorbent type muffler 10a is mounted to the housing 22 such that the communication section 18 of the retainer tube 16 is open to the first expansion chamber 22c only. 
     Another modification to the construction shown in FIG. 2 is shown in FIG. 4. In FIG. 4, the perforated pipe 12 is supported by the end plate 22a adjacent to the inlet 12b and by the partition 24 adjacent to the outlet 12c, the inlet 26a of the outlet pipe 26 is open to the first expansion chamber 22c, and instead a pipe 28 for fluid communication between the expansion chambers 22c and 22d is supported by the partition 24. In this particular construction, gaseous streams x emanating from the holes of the communication section 18 and accompanying noise and those y emanating from the pipe 28 interfere with each other, offering further effective noise reduction. 
     Referring to FIG. 5, a modification to the muffler shown in FIG. 4 is shown in which two absorbent type mufflers 10a are installed in the second chamber 22d in the same manner as the muffler 10a in the first expansion chamber 22c. It will be noted that any desired number of such absorbent type mufflers 10a may be disposed in a housing having three or more partitioned compartments, or expansion chambers. 
     In another possible construction shown in FIG. 6, a tubular housing 30 having end plates 30a and 30b has its interior divided by two partitions 32 and 34 into three compartments, i.e. first to third expansion chambers 30c, 30d and 30e. The absorbent type muffler 10a shown in FIG. 1 is installed in the first expansion chamber 30c in exactly the same manner as shown in FIG. 1. That is, the outlet 12c of the perforated pipe 12 is open to the second expansion chamber 30d, and the holes of the communication section 18 to the first expansion chamber 30c. Further, a pipe 32 for fluid communication is installed in the housing 30 which is open at one end to the first expansion chamber 30c and at the other end to the third expansion chamber 30e. The pipe 32 is formed with a plurality of openings 32a in part thereof and rigidly held by the partitions 32 and 34. 
     Referring to FIG. 7, a second embodiment of the basic construction of the absorbent type muffler in accordance with the present invention is shown. 
     In the muffler shown in FIG. 7, the retainer tube 16 associated with the sound absorbing member 14 as shown in FIG. 1 is replaced by suitable covering members 36 which fluid-tightly cover part of the outer periphery of the member 14. The coverings 36 may be adhered by heat resisting binder, for example. Specifically, the member 14 is provided with a communication section 36a open to expansion chamber 20c and non-communication sections 36b and 36c isolated from the chamber 20c. As in the various constructions in accordance with the first embodiment shown in FIGS. 2-6, the absorbent type muffler 10a shown in FIG. 7 is applicable to a housing of the type having a plurality of expansion chambers therein, with a view to attaining the characteristics of both the absorbent type muffler and pipe insertion type muffler. Such may be implemented in essentially the same manner as in FIGS. 2-6 and, therefore, will not be shown or described for simplicity. 
     Referring to FIG. 8, a third embodiment of the basic construction of the absorbent type muffler in accordance with the present invention is shown. In FIG. 8, the perforated pipe 12 shown in the second embodiment of FIG. 7 is omitted and replaced by a heat resisting, sound absorbing member 38 which for itself can hold a tubular shape. As in the embodiment of FIG. 7, the outer periphery of the sound absorbing member or absorbent 38 is partly covered fluid-tight by covering member 36 using heat resisting binder or the like; the member 38 is provided with a communication section 36a open to the expansion chamber 20c and non-communication sections 36b and 36c isolated therefrom. For the member 38, use may be made of porous foamed ceramic, foamed metal or the like. Even the inner periphery of the tubular member 38 may be partly sealed by such a covering member 36. If necessary, the perforated pipe 12 shown in the embodiment of FIG. 1 or that of FIG. 2 may be inserted in the member 38.