Internal-combustion engines – Particular piston and enclosing cylinder construction – Piston
Reexamination Certificate
2002-02-28
2004-01-13
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
Piston
Reexamination Certificate
active
06675762
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a piston in an internal combustion engine for use with an diesel engine, and more particularly, to a piston assembly for use in an internal combustion engine, having a counter-flow thwarting construction therewith, whereby an unwanted combustion of an engine oil together with a fuel, which may occur when the engine oil is introduced into a combustion chamber by an inner pressure being instantaneously generated in the piston moving down during its ordinary reciprocating movements, can be prevented, resulting that an excessive consumption of the lubricant, smoke caused by incomplete combustion and reduction of power can be avoided.
(b) Description of the Related Art
In general, a piston in an internal combustion engine reciprocates within a cylinder, wherein a suction stroke, a compression stroke, an explosion stroke and an exhaust stroke occur generating a power. In order to increase the power, various efforts such as an endeavor to remove the factors that would reduce the power have been attempted.
The power-reducing factors are, e.g., an incomplete combustion occurring when an engine oil is introduced into a combustion chamber to be burnt together with the fuel, an inferiority of an injection nozzle tip, a shortage of the amount of the suction air and a poor air-tight property of the piston ring.
Studies have found that the incomplete combustion caused by the engine oil results in a mass of carbon or soot adhering to a crown of the piston or an external surface of the piston, especially, that a reverse flow of the engine oil or air into the combustion chamber of the cylinder or an introduction of the fuel into an inside of the piston is caused by an internal pressure generated within the chamber near a crank during the reciprocating movement of the piston.
Hereunder, this phenomenon will be described in detail with reference to the accompanying drawings.
FIG. 1
a
presents a suction stroke of a cylinder where a piston
20
moves down from a top dead point to a bottom dead point and a suction valve V
1
is opened simultaneously, introducing air and fuel into a combustion chamber
10
a.
FIG. 1
b
represents a compression stroke of the cylinder where the piston moves up from the bottom dead point and the suction valve V
1
is closed simultaneously, thereby compressing the air and fuel in high temperature and high pressure.
FIG. 1
c
represents an explosion stroke where the fuel compressed in the high temperature and pressure condition is exploded to be burnt when the piston
20
reaches the top dead point; and
FIG. 1
d
represents an exhaust stroke where an exhaust valve V
2
is opened and the piston moves up to the top dead point, resulting that the combustion gas is exhausted out of the combustion chamber
10
a.
As shown in
FIGS. 1
a
to
1
d
, the piston reciprocating within the cylinder
10
has a plurality of ring grooves
22
a
,
23
, wherein a compression ring
22
and an oil ring
24
are mounted in the ring groove
22
a.
Accordingly, during the reciprocating movements of the piston, the compression ring
22
presses against the internal surface of the cylinder to generate a surface pressure therebetween, providing a pressing pressure in the combustion chamber
10
a
. The oil ring
24
functions to scratch the engine oil off the cylinder.
In the suction stroke (shown in
FIG. 1
a
) where the piston
20
moves down from a top dead point to a bottom dead point and a suction valve V
1
is opened simultaneously, generating a vacuum state in the combustion chamber
10
a
, a pressure within the piston
20
is sharply increased. For this reason, a reversed flow of air is introduced in a direction indicated with an arrow A in an oil passageway, thereby allowing oil sticking to or remaining on the oil ring
24
and the ring groove
23
to be introduced into the combustion chamber along an internal surface of the cylinder liner.
The oil conversely flown into the combustion chamber sticks to the internal wall of the cylinder liner in a large amount and is further introduced into the combustion chamber in the compression stroke, in a direction indicated with an arrow B, during which the piston
20
moving up scratches up the oil sticking to the internal wall of the cylinder liner. The engine oil introduced into the combustion chamber having a higher level of flash point would hinder the combustion in the explosion stroke (see
FIG. 1
c
), causing the incomplete combustion and would emit smoke in the exhaust stroke (see
FIG. 1
d
).
In the operation of the four cycle engine, since the internal pressure of the piston becomes lower sharply during the exhaust stroke (see
FIG. 1
d
) where the exhaust valve V
2
is opened and the piston moves up toward the top dead point, the combustion gas in the combustion chamber
10
a
is introduced into the cylinder
20
and the inside of the piston
20
through a gap between the internal wall of the cylinder
10
and the external surface of the piston
20
, a gap between the compression ring
22
and the cylinder liner, and the ring groove
23
and a hole
26
, in a direction indicated with an arrow of D. This phenomenon also occurs during the explosion stroke (see
FIG. 1
c
), in which the air flows in a direction indicated with an arrow C. The cause of this problem mainly resides on the oil ring and the space between the ring grooves through which the exhaust and the suction occur.
More detailed description of this will be made with reference to
FIGS. 2
a
and
2
b.
FIG. 2
a
shows the kinds of the oil rings which may be mounted around the piston; and
FIG. 2
b
represents a sectional view of a state of the oil ring mounted on a one piece piston, while
FIG. 2
c
being an enlarged sectional view of the oil ring shown in
FIG. 2
b.
As shown in
FIG. 2
a
, the oil ring has through-holes
24
c
formed through a center of the oil ring
24
and a pair of protrusions
24
a
and
24
b
protruding along a circumferential direction on an external surface of the oil ring
24
and being separated from each other. The protrusions serve to scratch the engine oil adhering to the internal wall of the cylinder liner during the reciprocating movements of the piston. The lower protrusion
24
b
firstly scratches down the oil adhering to the internal wall of the cylinder liner, while the upper protrusion
24
a
further scratches down the oil remaining thereon, providing a dual performance in scratching the oil.
As shown in
FIG. 2
b
, the oil scratched down by the oil ring
24
is introduced into the through-hole
24
c
to flow into the inside
20
b
of the piston via the hole
26
communicating with the inside
20
b
of the piston.
As shown in
FIGS. 2
a
through
2
c
, the oil ring
24
may have a ring-shaped spring
29
mounted therein. However, the ring-shaped spring
29
equipped in the oil ring makes a space between the oil ring and the ring groove
23
. Accordingly, a certain amount of oil will be kept within the ring groove
23
.
That is, during the reciprocating movements of the piston as shown in
FIGS. 1
a
through
1
d
, especially, when the piston moves down from the top dead point to the bottom dead point, the internal pressure is instantaneously generated in the piston due to the inertia of the air within the piston and then the oil remaining in the ring groove and the oil sticking to the internal wall of the cylinder liner are drawn to flow conversely into the combustion chamber
10
a
, going against the oil ring
24
along the internal wall of the piston liner.
In this regard, developments for an oil ring capable of providing a strong air-tight condition between the oil ring
24
and the ring groove
23
, thereby reducing the communication between both sides of the oil ring and efficiently removing the oil adhering to the internal wall of the cylinder liner has been requested. Particularly, in case of the one-piece piston, since it is made by using casting, being accompanied by a lot of limitations, the development of the oil ring capable of providing t
Edell Shapiro & Finnan LLC
McMahon Marguerite
Samyung Machinery Co., Ltd.
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