Acoustics – Sound-modifying means – Muffler – fluid conducting type
Reexamination Certificate
2000-12-08
2002-09-03
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Muffler, fluid conducting type
C181S255000, C181S265000, C181S269000
Reexamination Certificate
active
06443255
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to a sound attenuating muffler or exhaust silencer for use as part of an exhaust system for inboard marine engines, and in particular to a marine muffler to be used in the exhaust system of high-performance powerboats to reduce exhaust sound levels to acceptable decibel levels without significantly reducing performance.
(2) Description of the Prior Art
The majority of states have now set maximum levels for motorboat noise, and similar regulations are likely in additional states. State regulations are not uniform. Tennessee and Colorado, for example, require a maximum noise level of 86 decibels at 50 feet or more. Ohio limits noise levels to 90 decibels when subjected to a stationary, on-site sound level test, or 75 decibels when subjected to a shoreline test. Vermont requires a noise level to not more than 82 decibels at 50 feet in a normal operating environment. Georgia requires a noise level that does not exceed 84 decibels measured at a distance of 50 feet. The National Marine Manufacturers Association recommends a maximum of 75 and 90 decibels, depending on whether the boat is moving or stationary, while The National Association of State Boating Law Administrators recommends an 88-decibel maximum.
Reduction of exhaust noise levels to 90 decibels or less has heretofore required a significant reduction in horsepower and performance, particularly when muffling the exhaust noise of high horsepower, high-performance powerboats, which can reach top speeds in excess of 80 mph. Since these boats are designed for speed, a significant reduction in horsepower, and resultant top speed, is highly undesirable.
Therefore, an exhaust silencer or muffler that could reduce the exhaust sound levels of high performance inboard powerboats to 90 decibels or less without significantly sacrificing horsepower and speed would be of considerable value in meeting noise regulations without sacrificing the enjoyment of boaters.
SUMMARY OF THE INVENTION
The present invention relates to a muffler meeting these requirements. These mufflers are adapted to be attached to the end of the exhaust pipe that extends rearwardly from the boat engine. Normally, the muffler will be attached at the exterior of the boat transom beneath the swim platform. In the following description, the muffler and its components will be described as having an intake or inner end, meaning the end that is toward the boat engine and exhaust pipe when the muffler is mounted on the boat, and the discharge or outer end, meaning the end opposite the intake or inner end, and away from the engine and exhaust pipe. While the invention will be described in terms of one muffler, it will be appreciated that a boat may also have two or more exhaust pipes with a muffler mounted at the end of each pipe.
Generally, the present muffler is comprised of a cylindrical outer housing that has an intake end adapted to be attached directly or indirectly to the discharge end of an exhaust pipe and a discharge end on the opposite end of the cylindrical housing. The housing encloses a pair of adjacent parallel interior cylinders, i.e., a first or intake cylinder that has an inlet end that communicates through the intake end of the outer housing with the exhaust pipe, and a second or discharge cylinder that communicates through the discharge end of the outer housing to the exterior of the muffler.
The outer housing and the intake and discharge cylinders are sized such that the inner diameter of the outer housing is substantially equal to the combined external diameters of the interior cylinders. Therefore, when the two interior cylinders are positioned in an abutting and parallel relationship, the interior cylinders will snugly fit into the interior of the outer housing, with the interior cylinders abutting the interior wall of the outer housing. As a result, the two interior cylinders effectively divide the interior of the outer housing into first and second interior chambers that are on opposite sides of the interior cylinders.
Exhaust gas entering the intake cylinder is discharged into the first and second interior chambers through openings or perforations in the wall of the intake cylinder and through the cylinder discharge end. Continuing discharge of exhaust gas forces the exhaust gas from the interior chambers and into the second or discharge interior cylinder through openings in the wall of the discharge cylinder, and then from the muffler through the discharge end of the discharge cylinder.
In a preferred embodiment, the cylindrical outer housing is capped at its intake end with a transverse annular end plate that extends across the end of the cylinder. A connector pipe is joined to the intake plate around the periphery of the central opening, and extends away from the muffler in the intake direction for connection directly or indirectly to the exhaust pipe of the boat's exhaust system.
The longitudinal axis of the connector pipe can be parallel to the longitudinal axis of the muffler, or all or a part of the pipe can be at an angle, depending upon the configuration of the boat's exhaust system and the placement of the muffler. Preferably, at least part of the muffler will be mounted in a generally horizontal alignment on the outer side of the transom with the connector pipe being angled upwardly. As a result, any water entering the muffler will not enter the exhaust system.
The discharge end of the outer housing is preferably covered with a perforated screen, which may be in the form of a perforated plate or a woven screen, which will not interfere with the discharge of exhaust gas, but which will largely prevent debris and other objects from entering the muffler. The screen may be held in place with an annular ring secured to the end of the housing.
The muffler also includes first and second interior baffle plates that extend transversely across the interior of the housing. The first or intake end baffle plate is spaced from the discharge side of the intake end plate to form an entrance chamber. This entrance chamber provides some sound attenuation, and also serves as an adapter to join the connector pipe, which will normally be of the same diameter as the exhaust pipe, and equal to or slightly less in diameter than the outer housing, to the smaller diameter intake cylinder. The intake end of the intake cylinder communicates with the entrance chamber through a hole or opening in the first baffle plate. The first baffle plate also caps the inner end of the discharge cylinder.
Similarly, a second or exhaust end baffle plate extends across the interior of the housing, and is spaced toward the intake end of the muffler from the discharge screen to form an exhaust chamber. The exhaust cylinder discharge end communicates through an opening in the second baffle plate, permitting exhaust gases to be discharged into the exhaust chamber, and from there through the screen to the atmosphere.
In a preferred embodiment of the invention, the discharge end of the intake cylinder is spaced from the interior side of the second baffle plate, so that exhaust gases can be discharged from the intake cylinder openings and from the discharge end of the intake cylinder. As exhaust gases are discharged from the discharge end of the intake cylinder, the exhaust gases impinge upon the inner face of the second baffle plate, and are redirected into the first and second interior chambers for subsequent removal through the discharge cylinder.
Sound attenuation is a function of the number and shape of surfaces contacted by the exhaust gas in the muffler and the pathways followed by the exhaust gases between the intake and discharge ends of the muffler. The configuration of the openings in the walls of the intake and discharge cylinders is believed to be particularly suited to achieving maximum sound attenuation or deadening, bringing the exhaust sound into the desired decibel range, without significantly diminishing horsepower and resultant speed.
In the preferred embodiment, ea
,MacCord Mason PLLC
Dang Khanh
Fountain Powerboats, Inc.
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