Noise Attenuating Apparatus

This invention pertains generally to the field of noise attenuating apparatus, and particularly to mufflers for internal combustion engines for power implements such as lawn mowers, snowblowers, generators or any other implement where noise generation has deleterious consequences on the operator or the environment.

In general, noise abatement systems, silencers, or mufflers, of the type to which the instant invention is directed include a plurality of chambers for expansion or resonance. In the prior art, such as U.S. Pat. No. 4,415,059, issued to Yoshimasa Hayashi, partitions are arranged in a longitudinal direction while the interiors of the chambers are interconnected by tubes or perforations which allow combustion gasses to flow through the chambers in a predetermined order. The combustion gasses blow out of the final chamber into the ambient air via an outlet pipe. Another approach to sound attenuation is that suggested in U.S. Pat. No. 4,109,750, issued to Leslie Spencer, whereby an acoustically lined chamber of varying cross-sectional shape is employed to simultaneously maintain an essentially constant acoustic resistance while obtaining a scaled acoustic reactance, thereby attenuating specific frequencies of interest.

The instant invention relates to a noise attenuation apparatus for an internal combustion engine, but is not limited to such engines. The invention can be applied to any source of sound. To name a few, this would include: an air compressor intake module, a vacuum cleaner intake module, such large scale systems as steam turbines or generators, pumps used on air conditioners, fans associated with grain driers or the like, motors powering jack-hammers as well as mechanical systems such as the jackhammer tool head that strikes a pavement or concrete surface as well as tires moving across such a surface.

The noise attenuation apparatus is simple in structure and thereby produced by streamlined manufacturing steps. The instant invention requires no acoustical lining as in the aforementioned prior art and has a shape conducive to the simple manufacturing steps to be detailed in this disclosure.

The instant invention includes a plurality of expansion or resonance chambers divided by partitions which are arranged concentrically, or where non-circular, for example pyramidal, align the chambers in a nested fashion. Each chamber is connected to a subsequent chamber by a plurality of sound attenuators which conduct incoming gasses to said subsequent chambers through a larger opening from the innermost concentric body to a smaller opening toward the outermost concentric body. The gasses are vented from a final chamber via a plurality of open holes or sound attenuators. These sound attenuators allow prescribed restriction for the exhaust gasses as they exit from each chamber to the succeeding chamber. Each chamber is further described to include an inlet tube which passes through each intermediate chamber wall and terminates where the inlet tube inputs gasses into the innermost chamber.

In accordance with the invention, the exhaust gasses are intended to exit from each chamber to the succeeding chamber through a prescribed plurality of sound attenuators and finally into the ambient environment. The sound attenuators have a total cumulative volumetric dimension whereby their cumulative exit volume corresponds to an exhaust gas flow rate prescribed by the specifications of the noise source so that the instant noise attenuation apparatus shall be utilized to conduct he exhaust gases to the ambient environment while reatly attenuating the noise.

In the drawings:

FIG. 1 is a front perspective view, partially broken away, of a sound attenuating apparatus in accordance with the invention.

FIG. 2a is a front perspective view of an innermost chamber which may be utilized in the invention.

FIG. 2b is a top view of the innermost chamber which may be utilized in the invention.

FIG. 2c is a bottom view of the innermost chamber which may be utilized in the invention.

FIG. 2d is a side perspective view of the innermost chamber which may be utilized in the invention.

FIG. 3a is a top perspective view of an intermediate chamber which may be utilized in the invention.

FIG. 3b is a bottom perspective view of the intermediate chamber which may be utilized in the invention.

FIG. 3c is a side perspective view of the intermediate chamber which may be utilized in the invention.

FIG. 3d shows flat sheets that can be used to prepare a shroud of the sound attenuating apparatus.

FIG. 4a is an exploded composite side view showing an outermost chamber which is defined by the front of the shroud for the invention. A phantom side view of the intermediate and innermost chambers which may be utilized in the invention is also depicted in FIG. 4a.

FIG. 4b is a side view of the outermost chamber being formed by the shroud for the invention.

With reference to the drawings, an apparatus for carrying out the attenuation of noise from a source of noise such as an internal combustion engine, a fan, pump, hammer, etc., is shown generally at 20 in FIG. 1, with the apparatus being partially cut away to illustrate the interior. The apparatus 20 includes an enclosure having walls defining a shroud 21 through which an exhaust port 30 from an internal combustion engine passes. More particularly, the walls of the shroud 21 define the exterior portions of the chamber walls of an intermediate chamber 22 and an outermost chamber 24 which chambers are separated one from the other by a further chamber or partition wall 25 extending across the hollow interior of the shroud 21. The further chamber or partition wall 25 preferably serves as a portion of the chamber walls of both the intermediate chamber 22 and the outermost chamber 24 and is formed from a downwardly extending section of a metal sheet 38 (FIG. 3a) as will be described hereinafter. The port 30 is the inlet to the noise attenuating apparatus and it directs gasses into the innermost chamber 23 which is disposed within the intermediate chamber 22 in communication therewith. Shown also in FIGS. 2a, 2b, 2c and 2d, the innermost chamber 23 is constructed of a plurality of substantially flat sheets of conventional materials, e.g., steel, copper, aluminum, stainless steel or ceramics, etc. which are fastened together to form the chamber wall thereof, preferably by welding, but not limited to this type of fastening, and perforated by a sound attenuator 31 having a passage therethrough. The shape of the sound attenuator is conical or pyramidal such that the diameter of the orifice 36 at the inlet end is greater than the diameter of the orifice 34 of the outlet end to provide a true conical horn without flare affecting the attenuation of sound. Thus, each sound attenuator 31 narrows or tapers from the orifice 36 to the orifice 34. As used herein, the inlet end of a sound attenuator is the end closest to a preceding chamber and the outlet end is the end closest to a succeeding chamber. The compression of the sound wave will cause an inverted resonance and if the terminating impedance is not totally restricted, as in a closed tube, wave components of a substantially homogeneously reflected sound wave approaching the point of resonance are blurred and canceled by superposition with any oncoming sound waves. Interference is the physical effect of this superposition. Recall the case of two waves, y.sub.1 and y.sub.2, having the same frequency, .omega., but different amplitudes, A, and a phase difference, .phi.. If:

and

then the resultant wave is y=y.sub.1 +Y.sub.2. This is expressed as:

Expanding, the resultant amplitude is given by:

The resulting amplitude of the combined waves is at a maximum when .phi.=0 or .phi. is any even multiple of .pi.. Conversely, the waves interfere destructively when .phi.=.pi. or any odd multiple of .pi.. Since there is no other reason for a phase difference to be introduced to the sound waves propagating from a single source as is the case for this invention, the source of the phase difference comes from the different paths lengths followed by the waves. Thus, the geometry of the sound attenuators forces a destructive interference pattern on the sound waves moving through the noise attenuating apparatus of the instant invention.

The mathematical equations used to define the diminution of sound in conical forms would lead us into the far reaches of differential geometry, requiring a complete knowledge of the properties of the sound wave equation in three dimensions. Nevertheless, the approach taken to design the preferred embodiment 20 of this noise attenuating apparatus uses these sound attenuators 31 to their greatest advantage to both attenuate noise and to control backpressure. The noise attenuating apparatus of the instant invention is capable of operating over a wide range of internal combustion engine backpressure requirements by gauging the size of the orifice 34 of the outlet end of each sound attenuator 31 and an outlet port 33 to provide the backpressure.

The innermost chamber 23 is further constructed to include an outlet port 33 of a size dictated by available outlet for gas flow through the inverted megaphone-like orifices 34 combined with the outlet port 33 and dictated by the backpressure needs prescribed by the specification of an internal combustion engine or other sound source that the instant noise attenuation apparatus shall be used in combination with. The range of backpressure requirements to be accommodated can be broadened by enlarging or restricting the outlet port 33 by adjusting the cut made along a line 35 as depicted in FIG. 2c and FIG. 2d.

The outlet port 33 is a means to connect the innermost chamber 23 to the intermediate chamber 22. The chamber walls defining the intermediate chamber 22 are constructed of a plurality of substantially flat sheets of conventional malleable materials, e.g., steel, copper, aluminum or stainless steel, etc, as shown in FIGS. 3a, 3b and 3c. Using substantially flat sheets 38 and 39 (FIG. 3d) of conventional malleable materials and wrapping these shapes into the configuration of the intermediate chamber 22 and then fastening, for example welding or riveting, etc., is one useful way to form the intermediate chamber 22. Once constructed, a forward portion of the sheet 38 defines the chamber or partition wall 25 between the intermediate chamber 22 and the outermost chamber 24 while the remaining portions of the sheets 38 and 39 define a rearward portion of the shroud 21. The exhaust port 30 can be fastened to and protrude through an opening 37 in one flat sheet 38 of malleable material while the sound attenuators 31 can be fastened to the outer surface of the intermediate chamber 22 fixed at the openings 36 prepared in one flat sheet 38 or malleable material.

FIG. 4a shows one way that the innermost chamber 23 shown in phantom is encased inside the intermediate chamber 22 with the outermost chamber 24 of the shroud 21 being formed on the forward end of the intermediate chamber 22 by additional sheets 40 and 41 one of which contains a plurality of port holes 32 defining passages to exhaust the gasses into the ambient environment. In the apparatus shown in FIG. 4a, the exhaust gas enters at the end of the inlet tube 30, it passes through the shroud 21 into the innermost chamber 23 and passes through the sound attenuators 31 and into intermediate chamber 22. The gasses then pass through the second set of sound attenuators 31 into the outermost chamber 24 of the shroud 21 and exit from the shroud 21 through the holes 32 into the ambient air. Using the substantially flat sheets 40 and 41 of a conventional malleable material and wrapping these shapes into the configuration of the forward portion of the shroud 21 and then also wrapping this portion of the shroud around the front end of the intermediate chamber 22 as shown in FIG. 4b and then fastening, for example welding or riveting, etc., the sheets 40 and 41 to the intermediate chamber 22 is one exemplary way of forming the sound attenuating apparatus 20. The relative shaping of the shroud 21 is depicted in FIG. 4b.

While one intermediate chamber 22 is illustrated, any number of additional intermediate chambers can be formed in the shroud 21 with each additional chamber being connected to an adjacent chamber by a plurality of the conical sound attenuators. In such instance, the larger orifice 36 of the sound attenuator is connected to the adjacent chamber on the side nearest the exhaust port 30 and the smallest orifice 34 is connected to the next adjacent chamber on the side nearest the port holes 32.

This device is also useful for sound attenuation in any situation where volumes of gasses or liquid fluids are drawn or expelled across a surface or where contact produces an audible resonation in a free or held gas or liquid fluid medium such as gas and water discharge from outboard motors or jet skis.

It is understood that the invention is not confined to the illustrative embodiment described herein, but embraces all such modified forms thereof as come within the scope of the following claims.