Combustion chamber for internal combustion engine

A combustion chamber for an internal combustion engine is provided which includes a cylinder head body having at least one generally dome-shaped combustion chamber defined by a lower surface of the body and having an intake side and an exhaust side, and a spark plug bore disposed in the combustion chamber so that when a spark plug is engaged in the bore, the dome-shaped portion is provided with an upper surface configured to shelter the electrode from direct impingement of a fresh charge introduced into the combustion chamber through the intake side.

BACKGROUND OF THE INVENTION 
The present invention relates generally to internal combustion engines, and 
specifically to a specialized configuration for a combustion chamber used 
on such an engine which is designed to minimize spark plug fouling. 
Spark plug fouling can be caused when oil, gasoline, or mixtures of the two 
directly contact the spark plug electrodes to the extent that firing of 
the electrodes are interrupted or prevented entirely. The problem of 
fouling is a major design consideration in two-cycle engines, wherein the 
combustion charge is composed of a fuel-oil mixture, and where the 
electrodes are located in the cylinder in a position which is exposed to 
the flow of fresh charge or incompletely combusted fuel, oil and air. 
The fouling problem is even more troublesome in small displacement 
two-cycle outboard marine engines of the type often used to power small 
boats. This latter class of engines is popular with recreational 
fishermen, who run their engines for prolonged periods of time at slow or 
idle speeds, during which the spark plug temperature does not reach the 
level where excess deposits of excess fuel/oil mixture can be burned off. 
This type of use exacerbates the spark plug fouling problem. 
Small displacement two-cycle engines are often manufactured in the 
cross-flow format, wherein the fresh charge of gasoline, oil and air 
enters the cylinder through an intake port virtually simultaneously with 
the discharge of spent exhaust gases from an exhaust port. In these 
engines, the intake and exhaust ports are disposed in diametrically 
opposed locations of the cylinder. To prevent the mixing of fresh charge 
with the exhaust gases, and to reduce the passage of noncombusted fresh 
charge out the exhaust port prior to combustion, cross-flow engines are 
provided with a piston having a top-mounted deflector formation in the 
shape of a vane or baffle. This vane directs the fresh charge toward the 
spark plug electrodes, and prevents the fresh charge from passing through 
the exhaust port prior to combustion. 
Cross-flow engines are quite suitable for outboard engines, in that the 
cross-flow design is particularly effective at "scavenging" the fresh 
charge gases at low rpm or at idle, when the volume of fresh charge in the 
combustion chamber is relatively small. This is because the movement of 
the piston in a two-cycle engine draws the fresh charge into the 
combustion chamber from the crankcase. 
Another operational by-product of a two-cycle engine at idle is that the 
fresh fuel charge is not fully atomized by the action of the piston, 
connecting rod and crank shaft on the gas volume in the crankcase. Thus, 
when these relatively larger droplets of a fresh fuel charge are 
introduced into the combustion chamber, the potential for fouling 
increases. 
It can be seen that the two-pronged problems of low spark plug temperature 
and incomplete atomization of the fresh charge in an idling two-cycle 
engine are significant contributors to the fouling problem. This problem 
is an especially acute one for sport fisherman, who depend on such small 
engines for transportation to and from the fishing grounds, and who are 
inconvenienced in a major way from engine fouling, especially when fouling 
occurs in remote locations or in foul weather. 
One attempt at minimizing the spark plug fouling problem in two-cycle 
cross-flow engines is disclosed in commonly-assigned U.S. Pat. No. 
4,146,004, wherein the cylinder head is provided with a generally V-shaped 
deflector extending towards the combustion chamber from the internal 
surface of the head. The deflector is intended to divert the incoming flow 
of fresh charge away from the spark plug electrodes, and to shield the 
electrodes from deposits of oil and/or gasoline, or from the impact of the 
combustion gas flow. Although this design reduced fouling over prior 
designs, the problem of engine fouling has not been eliminated. 
Thus, a primary object of the present invention is to provide a combustion 
chamber shape for an internal combustion engine in which spark plug 
fouling is reduced significantly from conventional levels. 
Another object of the present invention is to provide a cylinder head for a 
two-cycle cross-flow type engine having a combustion chamber shape in 
which the spark plug electrodes are protected from exposure to the direct 
flow of the fresh charge, but which still provides adequate power to the 
engine. 
SUMMARY OF THE INVENTION 
Accordingly, the above-identified objects are met or exceeded by the 
present internal combustion chamber, which is specially configured to 
shelter the spark plug electrode, and to deflect the fresh charge away 
from the electrode to prevent the impingement of fuel or oil upon the 
electrode and thus minimize fouling. The electrode is located in a 
specially designed cylinder head recess which places it out of the flow of 
the incoming fresh charge. 
More specifically, the present invention includes a combustion chamber for 
an internal combustion engine, including a cylinder head having at least 
one generally dome-shaped combustion chamber portion defined by the lower 
surface of the cylinder head and having an intake side and an exhaust 
side. The cylinder head also includes a spark plug bore disposed in the 
dome-shaped portion so that when a spark plug having an electrode is 
engaged in the bore, the dome-shaped portion is provided with an upper 
surface configured to shelter the electrode from direct impingement of a 
fresh charge introduced into the combustion chamber through the intake 
side. 
In the preferred embodiment, the present cylinder head is mounted upon a 
two-cycle cross-flow type engine, wherein the piston has a top surface 
with a deflector formation for directing the fresh charge into the 
cylinder and minimizing the flow of fresh charge out to the exhaust. The 
present cylinder head combustion chamber portion is configured such that, 
in conjunction with the deflector formation on the top of the piston, it 
properly directs the flow of incoming charge to concentrate the fresh 
charge near the spark plug electrodes. 
In another embodiment, the present invention provides a combustion chamber 
for combusting a fuel/air mixture for a cross flow two-cycle spark-ignited 
engine, the chamber including a side wall having an intake port through 
which an incoming charge of the fuel/air mixture enters the chamber, a 
reciprocating bottom wall opening and closing the intake port and having a 
fresh charge deflecting baffle for directing the charge from the intake 
port in a first direction, and a top wall having a fresh charge deflecting 
lip extending in a direction generally normal to the first direction 
located above the intake port, as well as a recess located substantially 
adjacent said lip and adapted to retain a spark plug having an electrode. 
The chamber is configured so that the spark plug electrode disposed in the 
recess is not in the direct path of the incoming fresh charge after 
deflection of the fresh charge in the first direction by the deflecting 
baffle and in the second direction by the top wall deflecting lip. 
Instead, the fresh charge flows past the electrode to prevent fouling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, an internal combustion engine is generally 
designated 10 and is depicted in fragmentary form in FIGS. 1 and 3. The 
engine 10 is preferably of the two-cycle cross-flow type, but it is 
contemplated that the concepts embodied in the present combustion chamber 
may also be employed in other types of internal combustion engines. An 
engine block 12 includes at least one, and preferably two or more 
cylinders 14. 
Each cylinder 14 has an intake side 16 and an exhaust side 18, and a 
sidewall 20 provided with at least one intake port 22 on the intake side, 
and at least one exhaust port 24 on the exhaust side. A transfer passage 
26 places the intake port 22 in fluid communication with the engine 
crankcase (not shown) from which the fresh charge of fuel/oil/air mixture 
is drawn. 
Mounted for reciprocating vertical movement inside each of the cylinders 14 
is a piston 28 (shown fragmentarily), which is connected in conventional 
fashion to a crankshaft (not shown) by a connecting rod 30 (best seen in 
FIG. 3) for movement between an intake/exhaust position (best seen in FIG. 
1) and a compression/ignition position (best seen in FIG. 3). 
The engine 10 also includes a cylinder head, generally designated 32 having 
body 34 with an upper surface 36 and a lower surface 38. In the preferred 
embodiment, the lower surface 38 is provided with a relatively planar 
configuration for secure mounting to an upper surface 40 of the engine 
block 12 by threaded fasteners (not shown) as is well known in the art. 
However, it is contemplated that the cylinder head 32 may also be integral 
with the engine block 12. At least one generally dome-shaped portion 42 is 
defined by the lower surface 38 and has an intake side 44 and an exhaust 
side 46. The intake and exhaust sides 44, 46 of the cylinder head 32 
correspond to the intake and exhaust sides 16, 18 of the cylinder 14. An 
upper surface of the piston 28, the sidewall 20 of the cylinder 14, and 
the dome-shaped portion 42 of the cylinder head 32 combine to define a 
combustion chamber 48. 
The intake side 44 of the cylinder head 32 is configured to receive the 
fresh combustion charge flowing in a first, generally vertical direction 
along the sidewall 20 of the cylinder 14 and to deflect the flow of that 
charge to a second, generally horizontal direction which is generally 
normal to the first direction. More specifically, as seen in FIGS. 1 and 
3, the dome-shaped portion 42 on the intake side 44 is provided with a 
generally vertically oriented side wall 50, and a generally 
horizontally-oriented top wall or lip 52 abutting the side wall 50 at an 
approximate right angle. A lower portion 54 of the side wall 50 is 
radiused or flared to provide a smooth flow of charge from the cylinder 
side wall 20 into the dome-shaped portion 42. A spark plug wall 56 abuts 
the top wall 52 and is angled therefrom to define a recess 58 in the 
dome-shaped portion 42. In the preferred embodiment, the spark plug wall 
56 is angled in the approximate range of from 110 degrees to 150 degrees 
from the top wall 52. 
A threaded spark plug bore 60 is located in the spark plug wall 56 and 
places the upper surface 36 and the dome-shaped portion 42 in 
communication. A spark plug 62 having an electrode 64 and a ground bar 66 
disposed in conventional arrangement is threaded into the spark plug bore 
60. The spark plug bore 60 is approximately normal to the plane of the 
spark plug wall 56 and is disposed at an angle relative to the vertical 
axis of the cylinder 14 so that upon the installation of the spark plug 
62, the electrode 64 also projects into the dome-shaped portion 42 at an 
angle. In addition, in the preferred embodiment, the spark plug bore 60 
generally defines the dome-shaped portion 42 into the intake side 44 and 
the exhaust side 46. 
Turning now to the exhaust side 46, in general, the exhaust side has a 
ramped portion 68 (as seen in cross-section) to direct spent gases out of 
the dome-shaped portion 42, and ultimately, from the combustion chamber 
48. The ramped portion 68 of the exhaust side 46 extends from a point 70 
adjacent the spark plug bore 60. A relatively short radiused portion 72 
lies between the bore 60 and the ramped portion 68 of the exhaust side 46. 
A lower portion 74 of the ramped portion 68 is also radiused or flared to 
smoothly direct the flow of exhaust gases from the dome-shaped portion 42 
into the cylinder 14. 
The piston 28 is provided with a top surface, generally designated 76, 
which includes a deflector formation 78. In similar fashion to the 
dome-shaped portion 42, the deflector formation 78 includes an intake 
portion 80 generally shaped in a right angle to nest within the shape of 
said intake side, and an exhaust portion 82 configured with an inclined or 
ramped shape to generally nest within the ramped portion of the exhaust 
side 46. 
Included in the intake portion 80 of the deflector formation 78 is a 
generally vertical wall 84 having a radiused or flared bottom portion 86, 
and a generally horizontal top surface 88 joined at an approximate right 
angle to the vertical wall 84. Exhaust portion 82 gradually slopes from 
the top surface 88. 
Referring now to FIG. 2, a plan view of the underside of the cylinder head 
32 is illustrated, and it will be noted how the spark plug wall 56 
generally defines the dome-shaped portion 42 into the intake side 44 and 
the exhaust side 46. It is also evident that the exhaust side 46 is 
generally spherical in shape. The dome-shaped portion 42 is surrounded by 
a water jacket or cooling gallery 90 as is known in the art. Spaced about 
the lower surface 38 of the cylinder head 32 are disposed a plurality of 
throughbores 92 to be used with threaded fasteners (not shown) in mounting 
the cylinder head upon the engine block 12, as is well known in the art. 
Referring now to FIGS. 1 and 3, in operation, in a general sense, the fresh 
charge of fuel/oil and air is introduced from the crankcase, through the 
transfer passage 26, and into the combustion chamber 48 through one or 
more intake ports 22. The fresh charge, indicated by the arrows 94, is 
compressed during the upstroke or compression stroke of the piston 28 in 
the cylinder 14 (best seen in FIG. 1). As the piston 28 progresses 
vertically, the volume of the fresh charge 94 becomes compressed, as 
indicated at 94a. The charge 94 is ignited by the spark plug 62, 
preferably just prior to the piston reaching top dead center. During the 
subsequent downstroke or expansion stroke of the piston 28, the combustion 
products are exhausted from the combustion chamber 48 through one or more 
exhaust ports 24. 
More specifically, a major advantage of the present invention is that, due 
to the configuration of the dome-shaped portion 42 of the cylinder head 
32, the electrode 64 of the spark plug 62 will be sheltered from direct 
impingement of the fresh combustion charge introduced into the chamber 48 
from the intake side 44. Referring to FIG. 3, the fresh charge 94 is 
compressed into the dome-shaped portion 42 during the upstroke of the 
piston 28. 
During this compression, the fresh charge is forced along the generally 
vertical side wall 50 of the intake side 44, until it contacts the top 
wall or lip 52. Due to the compressed nature of the fresh charge, once it 
impacts the top wall 52, it is directed in a generally horizontal 
direction and travels past the spark plug electrode 64 at high velocity. 
The spark plug electrode 64 is located in the recess 58 so that while it 
is not directly exposed to the flow of the fresh charge, the atomized 
fresh charge will fill the recess for successful and complete combustion. 
Due to the generally horizontal flow of the fresh charge, the fuel/oil/air 
mixture passes by the spark plug electrode 64 without becoming impinged 
upon the electrode in a manner which will cause fouling. This is 
especially important when the engine is operated at idle, i.e., low 
operational and spark plug temperatures, and a reduced amount of available 
air. 
Once the electrode 64 ignites the fresh charge, the exhaust gases, 
designated by the arrows 96, are directed down the ramped portion 68 of 
the exhaust side 46. Through the expansion caused by the ignition of the 
fresh charge, the exhaust gases are drawn down the side wall 20 of the 
cylinder 14 during the downstroke of the piston 28, until they reach the 
exhaust port 24 and exit therethrough. 
It has been found that by placing the spark plug 62 in the recess 58, the 
electrode 64 is sheltered from the main flow of fresh charge, and is not 
in the direct path of the fresh charge. When similar displacement engines 
are compared, engines equipped with the present cylinder head 32 operate 
as much as three times longer without fouling than engines in which the 
spark plug is oriented directly in the flow of the fresh charge, as 
disclosed in commonly assigned U.S. Pat. No. 4,146,004, discussed above. 
Another advantage of the present cylinder head 32 is that when the piston 
28 approaches top dead center, the generally horizontally oriented top 
wall 52 of the intake side 44 increases turbulence of the fresh charge 
gases, which also raises the temperature of the gas mixture near the 
electrode 64, thus increasing the propagation of the flame front generated 
by the spark plug. This effect also more completely burns the fuel and 
increases the engine's power and efficiency. 
While a particular embodiment of the cylinder head for internal combustion 
engine of the invention has been shown and described, it will be 
appreciated by those skilled in the art that changes and modifications may 
be made thereto without departing from the invention in its broader 
aspects and as set forth in the following claims.