Internal-combustion engines – Particular piston and enclosing cylinder construction – Piston
Reexamination Certificate
2002-03-04
2003-09-09
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
Piston
Reexamination Certificate
active
06615788
ABSTRACT:
CLAIMING FOREIGN PRIORITY
The applicant claims and requests a foreign priority, through the Paris Convention for the Protection of Industry Property, based on a patent application filed in the Republic of Korea (South Korea) with the filing date of Jul. 30, 2001, with the application number 2001-0046024, by the applicant. (See the Attached
BACKGROUND OF THE INVENTION
The present invention relates to a piston assembly for an internal combustion engine. More particularly, the invention relates to a piston assembly for an internal combustion engine which prevents air from an air source for an internal combustion engine like an air cleaner or a turbo charger from leaking into the inside of the piston assembly and prevents lubrication oil leak from a crankcase into a combustion chamber of the engine thereby reducing lubrication oil loss and incomplete combustion.
An internal combustion engine comprises one or more cylinders and pistons, which move reciprocally in the cylinders. For example, as shown in.
FIG. 1
, a two-cycle internal combustion engine includes a piston assembly
10
, and a cylinder liner
12
, which surround the piston assembly
10
, and fits into a cylinder (not shown). In the middle part of the cylinder and between the cylinder liner
12
, is formed an air intake port
14
.
The piston assembly
10
includes a piston
16
, a plurality of grooves
18
formed at the outer periphery of the upper part of the piston
16
, compression rings
17
inserted into the grooves
18
to keep sealing between the piston
16
and the cylinder liner
12
. The Piston assembly
10
has also two grooves
20
,
22
formed at the outer periphery of the lower part of the piston
16
, an oil ring
24
inserted into the groove
22
and another oil ring, or an oil scraper ring
26
inserted into the groove
20
, which is positioned above the groove
22
.
The oil ring
24
collects lubrication oil and returns it to the crankcase of the engine. The oil-scraping ring
26
scrapes down lubrication oil spread on the cylinder liner
12
. The entire outer periphery or a portion of the periphery of the oil scraping ring
26
contacts the cylinder liner
12
, and adjusts the thickness of the lubrication oil film by scraping down excess oil. An oil passage
28
is formed between the grooves
20
,
22
to communicate the inside of the piston
16
and the gap between the outer cylindrical wall of the piston
16
and the inner wall of the cylinder liner
12
.
FIGS. 2 through 4
show the oil scraper ring
26
. The oil scraper ring
26
has an upper rail
30
and a lower rail
32
. Diameters of the rails are the same. A plurality of evenly spaced scallops
34
is formed on the lower rail
32
. The scallops
34
pass the oil collected by the upper rail
30
to the crankcase via the oil passage
28
.
At down stroke of the piston's reciprocal movement, air pressure builds up within the space confined by the inside of the piston, the cylinder, and the crankcase. The pressure forces some oil from the inside of the piston
16
to be leaked into the gap between the cylinder liner
12
or the inner wall of the cylinder and the piston
16
. The leaked oil eventually reaches the air intake port
14
and flows into the combustion chamber causing incomplete combustion.
The cause of this phenomenon is explained referring to FIG.
5
. While a semi-vacuum state is formed in the space below the piston at upstroke of the piston's reciprocal movement, at down stroke, a portion of air flowing in via the air intake port
14
passes through a gap between the cylinder liner
12
and the oil scraper ring
26
, or through a gap between the oil scraper ring
26
and the groove
20
. The leaked air flows into the inside of the piston
16
via the scallops
34
and the oil passage
28
. As the piston
16
moves down further, the air in the space below the piston
16
is compressed to increase the air pressure within the space. The increased pressure causes a reverse air flow via the path explained above. This reverse flow forces oil spread on the cylinder liner
12
or on the outer wall of the piston
16
to be sprayed onto the portion of the cylinder liner
12
near the air intake port
14
. The sprayed oil is flowed into the combustion chamber together with the intake air and burned together with the fuel.
Since the ignition point of oil is higher than that of fuel, such combustion of the mixture of oil and fuel causes incomplete combustion, reduction of combustion efficiency, excessive consumption of fuel, and exhausting smoke. Another problem is that the pressure buildup hinders down stroke movement of the piston, and causes engine efficiency drop or noise. Still another problem is excessive consumption of lubrication oil due to the combustion of the leaked oil.
Such problems are inherent to the construction of an oil ring, a cylinder, and a cylinder liner of prior art. The portion of the cylinder around the air intake port is machined to have an increasing size considering thermal expansion. However, since the diameters of the rails of the oil-scraping ring are the same, when the piston is at the top dead point or at down stroke, the lower rail
32
contacts the cylinder liner but the upper rail
30
does not contact the cylinder liner. Therefore, a gap is formed between the cylinder liner and the oil-scraping ring, providing a leakage path.
Accordingly, there has been a demand for an improved sealing mechanism between an oil ring of a piston assembly and a cylinder liner of an internal combustion engine.
SUMMARY OF THE INVENTION
The present invention is contrived to overcome the conventional disadvantages. Therefore, an object of the invention is to provide an enhanced sealing mechanism for a piston assembly for an internal combustion engine.
Another object of the invention is to prevent air leak into the inside of the piston assembly.
Still another object of the invention is to prevent oil leak into a combustion chamber of the engine.
Still another object of the invention is to prevent excessive pressure buildup in a crankcase of the engine.
Still another object of the invention is to prevent formation of gaps around the oil ring in its assembled state.
To achieve the above-described objects, in accordance with an embodiment thereof, the invention provides a piston assembly for an internal combustion engine comprising a piston that has a shape of a cylinder and has an outer cylindrical wall and a top portion on one end of the cylinder; an oil ring that is pressed against a cylinder liner of the internal combustion engine; and a circular groove that is formed in the outer cylindrical wall of the piston and holds the oil ring. The groove has an upper wall, a sidewalk, and a lower wall and the upper wall is positioned toward the too portion of the piston. The piston assembly further includes a circular recess that is formed in the upper wall of the groove and a sealing member that is inserted into the recess and contacts the oil ring.
The sealing member may be an elastic member and in the assembled state within the circular groove, the sealing member is compressed to provide sealing between the groove and the oil ring. Preferably, the sealing member is an O-ring.
In accordance with another embodiment thereof, the invention provides a piston assembly for an internal combustion engine comprising a piston that has a shape of a cylinder and has an outer cylindrical wall and a top portion on one end of the cylinder, an oil ring that has an upper projection and a lower projection that are formed on an outer periphery of the oil ring, a circular groove that is formed in the outer cylindrical wall of the piston and holds the oil ring.
The upper projection of the oil ring is positioned toward the top portion of the piston. Both of the projections of the oil ring have tapered edges, and the outer diameter of the upper projection is greater than the outer diameter of the lower projection.
The groove has an upper wall, a sidewall, and a lower wall and the upper wall is positioned toward the top portion of the piston. The piston
McMahon Marguerite
Park John K.
Park & Sutton LLP
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