Marine engine exhaust muffler assembly

A marine engine exhaust muffler assembly (8) includes inlet and outlet members (10, 11), the axes (13, 14) of which are offset from each other. A muffler housing (12) is disposed between the inlet and outlet members and forms a chamber (15) having disposed therein an annular multi-layered cartridge (23), and with the layers having a multiplicity of perforations (27) therein for passage of exhaust gases and spent engine cooling water therethrough. The water assists in keeping the muffler clean. An imperforate arcuate blocking plate (31) is nested within the lower portion of the cartridge to permit accumulation of the spent engine cooling water within the cartridge to aid in noise reduction at certain engine speeds. The blocking plate is provided with a relief opening means (33) for assisting in water drainage upon engine shutoff.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a marine engine exhaust muffler assembly and more 
particularly to a muffler for use in association with an inboard marine 
engine. 
Over the years, stern drive engines have become more and more powerful, 
with an accompanying increase in noise levels due to exhaust discharge and 
flow noise. Such noise needs to be reduced as much as possible, both for 
the comfort of the user and also to accommodate restrictions on overall 
noise levels imposed by various environmental pollution control agencies. 
It is an object of the present invention to provide a marine engine exhaust 
muffler which effectively reduces related noise levels and which is 
relatively simple in construction and economical to manufacture. It is a 
further object to provide a muffler which can easily be retrofit to most 
stern drive marine engine systems. 
In accordance with the various aspects of the invention, a muffler assembly 
includes inlet and outlet members, the axes of which are offset from each 
other. A muffler housing is disposed between the inlet and outlet members 
and forms a chamber having disposed therein an annular multi-layered 
cartridge, and with the layers having a multiplicity of perforations 
therein for passage of exhaust gases and spent engine cooling water 
therethrough. The water assists in keeping the muffler clean. An 
imperforate arcuate blocking plate is nested within the lower portion of 
the cartridge to permit accumulation of the spent engine cooling water 
within the cartridge to aid in noise reduction at certain engine speeds. 
The blocking plate is provided with a relief opening means for assisting 
in water drainage upon engine shutoff.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings, the various aspects of the invention are to be 
utilized in connection with a stern drive marine internal combustion 
engine 1 mounted within a boat 2 and adjacent the rear transom 3 thereof. 
Engine 1 is adapted to propel boat 2 through the water via the usual stern 
drive unit 4 having a propeller 5 or the like. The engine has the usual 
cooling water system and exhaust manifold (not shown), and is adapted to 
discharge the cooling water and exhaust gases rearwardly through the 
discharge pipe 6 of an exhaust elbow 7 of any suitable well-known type. A 
muffler assembly 8 is connected between exhaust elbow 7 and a tubular 
fitting 9 which extends rearwardly through transom 3 for final gas and 
water discharge outside boat 2. 
Muffler assembly 8 generally includes an inlet pipe 10 adapted to be 
suitably connected to exhaust elbow discharge pipe 6, an outlet pipe 11 
adapted to be suitably connected to fitting 9, and a longitudinally 
extending muffler housing 12 disposed therebetween. Pipes 10 and 11 are 
shown as offset from each other, with the axis 13 of pipe 10 being 
disposed generally parallel to and at a level transversely above the axis 
14 of pipe 11. 
Muffler housing 12 forms an inner muffler chamber 15 defined by a 
transverse upstream end wall 16, a transverse downstream end wall 17 and a 
longitudinally extending intermediate generally rectangular wall 18. These 
walls are contemplated as being formed of heavy gauge metal for purposes 
of rigidity and silencing. Upstream end wall 16 is disposed at the inner 
terminus of inlet pipe 10 and is provided with a suitable opening 19 
providing communication between pipe 10 and chamber 15. Downstream end 
wall 17 is disposed at the inner terminus of outlet pipe 11 and is 
provided with a suitable opening 20 at its lower end for communication 
between pipe 11 and chamber 15. For ease of assembly and access, pipe 11 
and downstream end wall 17 and intermediate wall 18 may be integrally 
formed into a sub-assembly which is attachable to upstream end wall 16 in 
any suitable manner, such as by bolts 21. A suitable sealing member 22 is 
shown as disposed between wall 16 and the edge of wall 18. 
A generally cylindrical muffler cartridge 23 is disposed in the upper 
portion of muffler chamber 15 and is contemplated as being aligned 
coaxially with pipe 10 on common axis 13. The upstream end of cartridge 23 
is received within an annular shoulder 24 formed in the interior face of 
upstream end wall 16. The downstream end of cartridge 23 is received 
within an annular groove 25 formed in the interior face of downstream end 
wall 17. An annular undulating leaf spring washer 26 is confined between 
the downstream edge of cartridge 23 and the base of groove 25 so that 
cartridge 23 is biased upstream against shoulder 24 and against the flow 
of gases and cooling water. 
Muffler cartridge 23 comprises a multilayered cylindrical body, preferably 
of stainless steel, which has a multiplicity of perforations such as holes 
27 scattered throughout in such a manner as to permit fluid communication 
between the inside and outside thereof. A muffler chamber 28 having 
concave internal walls is thereby formed. Chamber 28 is closed at its 
downstream end by end wall 17. In the embodiment shown in FIG. 3A, the 
body of cartridge 23 is formed of a plurality of separate concentrically 
disposed cylinders 29. FIG. 3B illustrates another embodiment wherein the 
body of cartridge 23 is formed of a single spirally wound sheet 30, the 
ends of which are suitably secured to the body, as by tack welding, to 
hold it together. 
During operation of engine 1, spent cooling water and exhaust gases enter 
muffler assembly 8 through inlet pipe 10 and pass into the interior of 
cartridge 23 and thus chamber 28. These fluids are then forced through the 
body of cartridge 23, via holes 27, and pass outwardly into housing 
chamber 15 and downwardly therein by gravity and hence through lower 
downstream opening 20 to fitting 9 for ultimate discharge. The 
construction is such that the flowing water assists in cleaning the 
cartridge, and the water and exhaust gases are thoroughly mixed. 
To aid in the noise reduction provided by cartridge 23, a generally 
imperforate arcuate longitudinal blocking plate 31 is disposed in the 
interior thereof in chamber 28. Plate 31 nests in the bottom of chamber 28 
and causes a buildup of some of the water within the muffler so that the 
water cannot flow through part of the cartridge body. This has been found 
to assist in noise reduction at engine idle. Furthermore, the upper 
longitudinal edges 32 of blocking plate 31 are disposed beneath axis 13 
and form dams for water overflow if needed. 
Means are provided to allow water accumulated above blocking plate 31 to 
drain out when engine 1 is turned off. For this purpose, the bottom of the 
downstream end portion of plate 31 is provided with a relief hole 33 which 
communicates through the area of spring washer 26 within groove 25 at the 
end of cartridge 23 and hence to opening 20, as shown by the arrow in FIG. 
4. 
Various modes of carrying out the invention are contemplated as being 
within the scope of the following claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as to the 
invention.