BACKGROUND OF THE INVENTION
The field of the present disclosure generally relates to vehicle exhaust systems. More particularly, the field of the invention relates to an apparatus and a method for an anti-resonance muffler to attenuate vehicle exhaust system resonance in a narrow frequency range.
A vehicle exhaust system that has been designed for minimal back pressure commonly exhibits a substantial resonance. The resonance can be excited at certain engine speeds, thereby amplifying the resonance and causing a potentially objectionable sound or noise. Said resonance is also known as drone and is a natural phenomenon of a vehicle exhaust system without some apparatus and method for attenuating or eliminating it.
A high-flow type of muffler that is commonly used in vehicle exhaust systems is a wide-band attenuation device and has minimal effect on a strong resonance in a lower frequency range. A more effective means of attenuating a strong resonance is to employ the use of a Helmholtz resonator. A Helmholtz resonator that is tuned to substantially the same frequency as the exhaust system resonance acts to phase-cancel said resonance.
Some commercially available exhaust systems employ the use of a Helmholtz resonator that is comprised of a chamber and a perpendicularly mounted port tube. Said perpendicularly mounted port tube is a conventional implementation of a Helmholtz resonator and does not maximize the attenuation of vehicle exhaust system resonance. What is needed, therefore, is a device and method for attenuating vehicle exhaust system resonance that maximizes the attenuation effect of a Helmholtz resonator.
BRIEF SUMMARY OF THE INVENTION
An apparatus and method are provided for an anti-resonance muffler to attenuate vehicle exhaust system resonance. The anti-resonance muffler comprises a chamber having a specific volume, a port having a specific volume, an exhaust tube, an outlet and an inlet which is connected to a vehicle exhaust system. The combination of the chamber and port create a Helmholtz resonator that phase-cancels a narrow range of frequencies that are generated by the vehicle exhaust system. The chamber and port are mounted radially relative to the exhaust tube. The radially mounted Helmholtz resonator port exhibits improved resonance attenuating performance compared to a Helmholtz resonator port that is perpendicularly attached to an exhaust tube.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings refer to embodiments of the present disclosure in which:
FIG. 1A illustrates a cross section view of an exemplary embodiment of an anti-resonance muffler, according to the present disclosure.
FIG. 1B illustrates a perspective cut-away view of an exemplary embodiment of an anti-resonance muffler, according to the present disclosure.
FIG. 2 illustrates a perspective view of a conventional Helmholtz resonator, according to the present disclosure.
FIG. 3 illustrates frequency response plots of an exemplary embodiment of an anti-resonance muffler as compared to a conventional Helmholtz resonator, according to the present disclosure.
FIG. 4 illustrates frequency response plots of an exemplary embodiment of an anti-resonance muffler as compared to no muffler, according to the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
In general, the present disclosure describes an apparatus and method for an anti-resonance muffler to reduce vehicle exhaust system resonance. The anti-resonance muffler comprises a chamber having a specific volume, a port having a specific volume, an exhaust tube, an outlet and an inlet which is connected to a vehicle exhaust system. The combination of the chamber and port create a Helmholtz resonator that phase-cancels a narrow range of frequencies that are generated by the vehicle exhaust system. Said chamber and port are mounted radially relative to the exhaust tube.
FIG. 1A illustrates a cross section view of an exemplary embodiment of an anti-resonance muffler, according to the present disclosure. The anti-resonance muffler comprises an outer case 5, comprising a length and a diameter, which creates a chamber 3, which is mounted radially relative to an exhaust tube 1, comprising a length and a diameter, and a port tube 2, comprising a length and a diameter, which is mounted to the outer case 5. The port tube 2 further is mounted radially relative to the exhaust tube 1 and creates a port area 4 between the exhaust tube 1 and the port tube 2. The anti-resonance muffler further comprises an inlet 6, which comprises a length and two diameters, which is connected to the exhaust system at the smaller diameter end and the port tube 2 at the larger diameter end, and an outlet 7, which comprises a length and a diameter, which is connected to the exhaust tube 1 at a first end and the exhaust system at a second end.
FIG. 1B illustrates a perspective cut-away view of an exemplary embodiment of an anti-resonance muffler, according to the present disclosure.
In an exemplary embodiment of an anti-resonance muffler, the embodiment comprises components manufactured from 16 gauge stainless steel tube and sheet. Further, the outer case is substantially 12 inches in length and 6 inches in diameter.
It will be appreciated by those skilled in the art that the exemplary embodiment illustrated in FIGS. 1A and 1B is similar to a Helmholtz resonator which generally comprises a chamber connected to the system of interest through one or more port tubes. The Helmholtz resonator generally operates to reflect sound waves back to the source, thereby cancelling out certain frequencies generated by said source. It will be further appreciated that the tuning parameters of chamber volume, port area and port length predictably affect the natural frequency of the anti-resonance muffler.
As will be appreciated, the anti-resonance muffler effectively attenuates vehicle exhaust system resonance. It will be further appreciated that the anti-resonance muffler exhibits improved attenuation performance compared to that of a conventional Helmholtz resonator which comprises a port tube 8 that is perpendicularly attached to an exhaust tube.
FIG. 2 illustrates a perspective view of a conventional Helmholtz resonator which comprises a port tube 8 that is perpendicularly attached to an exhaust tube.
FIG. 3 is a graph 9 illustrating acoustic data acquired during bench testing of the anti-resonance muffler illustrated in FIGS. 1A and 1B. Further, the graph 9 illustrates acoustic data acquired during bench testing of a conventional Helmholtz resonator which comprises a port tube 8 that is perpendicularly attached to an exhaust tube. Said bench testing consisted of an acoustic source attached to the inlet of each device under test, a studio microphone placed substantially 12 inches from the outlet of each device under test, connected directly to a personal computer, and spectral analysis software operating on said personal computer. Further, all measurement parameters were identical during bench testing of each device under test. Further, the ambient temperature was substantially 72 degrees Fahrenheit during bench testing.
During said bench testing, the anti-resonance muffler was found to be tuned to an attenuation frequency of substantially 80 Hz. Further, using substantially the same tuning parameters as the anti-resonance muffler of chamber volume, port area, port length, the conventional Helmholtz resonator also was found to be tuned to an attenuation frequency of substantially 80 Hz. When the temperature is raised to a target operating temperature of substantially 400 degrees Fahrenheit, the attenuation frequency will rise to substantially 100 Hz.
It will be appreciated, therefore, that in addition to the dimensions and shapes comprising an anti-resonance muffler, an operating temperature must also be taken into account during designing of an anti-resonance muffler. Further, it will be appreciated that an optimal attenuation of sound pressure generally occurs when a natural frequency of the anti-resonance muffler is substantially equal to an excitation frequency of the vehicle exhaust system of interest.
FIG. 4 is a graph 10 illustrating acoustic data acquired during vehicle testing with the anti-resonance muffler illustrated in FIGS. 1A and 1B. Further, the graph 10 illustrates acoustic data acquired during vehicle testing with no muffler. Said vehicle testing consisted of a test vehicle with a 6 cylinder engine, operated at speeds that resulted in an exhaust excitation frequency range of substantially 75 Hz to 200 Hz, and a studio microphone placed substantially in the center of the vehicle cabin connected directly to a portable recorder. Further, acoustic data recordings from said portable recorder were transferred to a personal computer and analyzed using spectral analysis software. Further, all measurement parameters were identical during vehicle testing of the anti-resonance muffler and no muffler. Further, the test vehicle speed was ramped up from a lower speed to a higher speed.
With reference again to FIG. 3, the graph 9 illustrates a comparison, of relative amplitude (dB) as a function of frequency (Hz), of an anti-resonance muffler and a conventional Helmholtz resonator, based on acoustic data acquired during bench testing. Further, the graph 9 comprises two waveforms. Further, the waveform representing the anti-resonance muffler is depicted by a solid line B and the waveform representing the conventional Helmholtz resonator is depicted by a dashed line A. For the acoustic data shown in the graph 9, the anti-resonance muffler exhibits improved attenuation, substantially 4 dB on average, over the frequency range of 50 Hz to 250 Hz, as compared to the conventional Helmholtz resonator, with a peak attenuation improvement of substantially 12 dB at 80 Hz.
With reference again to FIG. 4, the graph 10 illustrates a comparison, of relative amplitude (dB) as a function of frequency (Hz), of an anti-resonance muffler and no muffler, based on acoustic data acquired during vehicle testing. Further, the graph 10 comprises two waveforms. Further, the waveform representing the anti-resonance muffler is depicted by a solid line D and the waveform representing no muffler is depicted by a dashed line C. For the acoustic data shown in the graph 10, the anti-resonance muffler exhibits effective exhaust system resonance attenuation, substantially 12 dB on average, over the frequency range of 75 Hz to 200 Hz, as compared to no muffler, with a peak attenuation of substantially 20 dB at 105 Hz.
On the basis of the acoustic data illustrated in FIG. 3, one skilled in the art will appreciate that the anti-resonance muffler effectively attenuates the sound level in the frequency range of interest with a peak attenuation improvement of substantially 12 dB as compared to a conventional Helmholtz resonator which comprises a port tube that is perpendicularly attached to an exhaust tube. Further, on the basis of the acoustic data illustrated in FIG. 4, one skilled in the art will appreciate that the anti-resonance muffler effectively attenuates vehicle exhaust system resonance in the frequency range of interest with a peak attenuation of substantially 20 dB as compared to no muffler.
In some embodiments, the anti-resonance muffler may be made of materials that differ from the exemplary embodiment. Further, some embodiments may be constructed to resemble rectangular or oval shapes. Further, some embodiments may be constructed with conical shaped inlets or inlets enclosed within the muffler outer case. It should be understood, therefore, that the anti-resonance muffler may be practiced with a wide variety of shapes, sizes, inlets and materials without deviating from the scope of the present disclosure.
While the invention has been described in terms of a particular variation, those of ordinary skill in the art will recognize that the invention is not limited to the variation described. To the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the invention found in the claims, it is the intent that this patent will cover those variations as well. Therefore, the present disclosure is to be understood as not limited by the specific embodiment described herein, but only by the scope of the appended claims.
Patent Application
20200018204
