JPH0151898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a piston of a reciprocating piston type internal combustion engine, and more particularly to a structure for preventing gas leakage from between the piston and the cylinder.

[Prior art]

The combustion section of a marine diesel engine, etc. has a cylindrical cylinder whose head is closed by a cylinder head, and the combustion gas pressure in the combustion chamber of the cylinder head and the intake/exhaust force reciprocate within the cylinder and drive the crankshaft via a connecting rod. It is made up of a rotating piston. Each of the plurality of ring grooves provided on the outer circumferential surface of the piston is fitted with a piston ring that has a slightly larger diameter than the piston diameter, has an expansion force, and is tightly fitted to the inner wall surface of the cylinder. The piston is configured to transmit high-temperature heat received by the cylinder to the cylinder to prevent the piston from overheating, and to reduce gas leakage outside the combustion chamber and maintain compression pressure to achieve good combustion.

However, in the conventional combustion section, the piston ring cannot necessarily be expected to have a satisfactory effect in preventing gas leakage. In other words, between the piston ring and the ring groove, there is a gap in the thickness direction and a gap in the circumferential direction due to expansion, and there is also a gap in the piston ring by cutting one point in the circumferential direction. If these gaps are too small, the piston ring will break due to thermal expansion and the cylinder wall will wear out, so appropriate gaps must be provided.
Therefore, it has been impossible to completely prevent gas leakage. Therefore, in the past, it was unavoidable to increase the number of piston rings to minimize gas leakage, which resulted in easy wear of the cylinder wall and increased mechanical loss due to the frictional force between the piston ring and the cylinder wall. There was a drawback.

[Summary of the invention]

The present invention was made in view of the above points, and includes a plurality of annular grooves and a plurality of piston rings on the outer circumferential surface, and directs combustion gas into the annular groove during approximately half a stroke on the top dead center side. By configuring the piston to diffuse into the combustion chamber, it works together with the action of the piston ring to block gas leakage from the combustion chamber, making it possible to reduce the number of piston rings and prevent wear on the cylinder. This is what we provide. Embodiments of the present invention will be described in detail below with reference to the drawings.

〔Example〕

Figures 1 to 6 show an embodiment of a piston for an internal combustion engine according to the present invention, and Figure 1 is a longitudinal cross-section of the piston cut away with the right half and left half shifted in phase by 90° in the circumferential direction. Figure 2 is a sectional view along AA of Figure 1, Figure 3 is a top view of Figure 1 viewed from the direction of arrow B, Figure 4 is a partially cutaway front view of the spherical head of the connecting rod, and Figure 5 is a partially cutaway front view of the spherical head of the connecting rod. The figure is a CC sectional view of FIG. 4, and FIG. 6 is an enlarged sectional view of the annular groove. In the figure, cylinder 1
has a cylindrical liner 2 fitted on its inner circumferential surface, and a piston, generally designated by reference numeral 3, is slidably fitted on the inner circumferential surface of the liner 2. The piston 3 is made up of a piston crown 4, a skirt 5, and a connecting rod support metal fitting 6. Of these, the piston crown 4 is made of ceramic material in the shape of a disk, and its outer periphery is made of heat-resistant steel. A plurality of formed screw fittings 7 are enclosed during molding. Further, a concave portion 8 is provided on the upper end surface of the piston crown 4 in order to avoid interference with an intake/exhaust valve (not shown) and to improve combustion. Stopper 7
It is fixed to the skirt 5 by a bolt 9 that is inserted into the screw hole of the skirt 5 and screwed into the screw hole of the skirt 5. The piston crown 4 may be made of heat-resistant cast iron and coated with ceramic coating. The skirt 5 has the same diameter as the piston crown 4, and has a hemispherical surface 5a formed on approximately 1/2 of its inner circumference, and the remaining 1/2
A cylindrical surface 5b is formed on the cylindrical surface 5b. Reference numeral 10 denotes a positioning pin for centering the piston crown 4 and skirt 5 when they are fixed with bolts 9.
It is screwed in from the side, and the pin-shaped portion at the tip is tightly fitted into the pin hole of the piston crown 4.
The connecting rod support metal fitting 6 is fitted into the cylindrical surface 5b of the skirt 5, and is fixed to the skirt 5 by a plurality of bolts 11 screwed into end face screw holes of the skirt 5 from the flange thereof. Connecting rod support hardware 6
is fixed to the skirt 5 and its hemispherical surface 5
It is provided with a truncated hemispherical surface 6a forming a spherical surface together with a, and below the truncated hemispherical surface 6a are a pair of opposing sliding surfaces 6b, half of which are shown surrounded by diagonal lines in FIG. Holes 6c are continuously formed.
What is generally designated by the reference numeral 12 is a connecting rod consisting of a spherical head 15 and a rod-shaped portion 16 whose flange portions are connected by a bolt 13 and a double nut 14.
A pair of sliding surfaces 17 that are parallel to each other are formed on the joining flange portion. and connecting rod 12
is connected to the piston 3 by rotatably fitting the spherical head 15 into the spherical surface composed of the hemispherical surfaces 5a and 6a, and by bringing the sliding surface 17 into sliding contact with the sliding surface 6b. The other end of the rod-shaped portion 16 is fitted into an eccentric portion of a crankshaft (not shown).
With this configuration, the piston 3 that compresses air and is at the top dead center shown in FIG.
When fuel is injected into compressed air and ignited, the gas pressure that combusts and expands moves down inside the cylinder 1 and rotates the crankshaft via a connecting rod. The rotation of the crankshaft causes the piston 3 to move up and down into the exhaust and intake air, and as the piston rises, the air is compressed, and the above-mentioned stroke is then repeated. Note that the chain line 12A in FIG. 1 indicates the connecting rod that is tilted due to the crank action while the piston 3 is moving up and down.

Therefore, a structure for preventing gas leakage during combustion will be explained. Approximately 1/1 of the stroke 7 of the piston 3 is located on the top dead center side of the inner peripheral surface of the liner 2 of the cylinder 1.
Ceramic coding 18 having a length of 2 and a thickness of about 0.4 mm is applied by thermal spraying, while a plurality of annular grooves 1 facing the ceramic coding 18 are formed on the outer peripheral surface of the skirt 5 of the piston 3.
9 are provided in parallel in the axial direction. This annular groove 19 prevents gas from flowing downward in FIG. 1 through the gap between the cylinder 1 and the piston 3.
The part 9 generates and diffuses a vortex to reduce its pressure, and its position is at the top so that it faces the ceramic coding 18 while the piston 3 moves about half a stroke toward the top dead center. It is set on the dead center side. Further, as shown in an enlarged view in FIG. 6, the cross-sectional shape of the annular groove 19 is formed by an upper inclined surface, a lower horizontal surface, and a vertical surface. The clearance is set to approximately twice the clearance with the cylinder 1. On the other hand, on the lower outer peripheral surface of the skirt 5,
A plurality of ring grooves 20 (three in this example) are provided, and one part of the circumference is cut in the ring groove 20 and the inner peripheral surface of the liner 2 is formed and fitted by the expansion force. A conventionally known piston ring 21 is fitted therein. This piston ring 21
is opposite to the inner circumferential surface of the liner 2 which is not provided with the ceramic coding 18 at the top dead center shown in FIG. The length of the ring 18 is set so that it slides along the inner circumferential surface of the liner 2 as the piston 3 rises and falls, and blocks the passage of gas whose pressure has decreased due to diffusion in the annular groove 19. It is configured.

Next, the circulation path of lubricating oil will be explained. The connecting rod 12 is provided with an oil hole 22 that passes through the shaft core and allows the lubricating oil pumped from the crankshaft side to rise by the lubricating oil pump, and its upper end is connected to the space between the positioning pin 10 and the locating pin 10. It is opened in the middle.

Further, from the upper part of the oil hole 22, a plurality of oil holes 24 connected by an annular groove 23 on the circumferential surface of the spherical part 15 are branched, and a part of the oil rising inside the oil hole 22 is spouted out. It is configured to lubricate the circumferential surface of the spherical portion 15. Further, the positioning pin 10 is provided with a hole 25 that also serves as a spanner insertion hole and a plurality of oil holes 26 branching from the hole 25.
A plurality of oil grooves 27 are provided radially from an annular groove 28 connecting the openings of the oil holes 26 on the upper end surface of the oil hole 26 . Reference numeral 29 denotes an annular oil groove that connects the ends of the oil groove 27, and vertical holes 30 that penetrate the skirt 5 in the axial direction are bored at multiple locations in the circumferential direction of the annular oil groove. It opens into an annular oil passage 31 which is a space surrounding the center of the spherical part 15 .
Numeral 32 is an oil groove provided on the hemispherical surface 5a of the skirt 5 to improve oil lubrication, and 33 is a spherical oil groove provided at two locations in the circumferential direction of the connecting culm support metal fitting 6, as shown in FIG. This is an oil groove along the section 15 and is open below the spherical section. With this configuration, the oil that has lubricated the fitting surfaces of the hemispherical surfaces 5a and 6a and the spherical portion 15 is transferred from the annular oil passage 31 to the oil groove 3.
2 and is emitted downward toward the crankshaft.

The operation of the piston configured as above will be explained. When the piston 3 rises to the top dead center position shown in the figure and fuel is injected into the compressed high temperature and high pressure air, the combustion gas expands and the piston 3 descends, causing the hemispherical surface of the skirt 5 to 5a, 6a
The connecting rod 12 into which the spherical portion 15 is fitted is lowered. In this case, since the lower end of the connecting rod 12 is connected to the eccentric portion of the crankshaft, rotation of the connecting rod 12 is restricted by bringing its sliding surface 17 into sliding contact with the sliding surface 6b of the connecting rod support fitting 6. The first
The crankshaft is rotated while rocking as shown by the chain line 12A in the figure. Also, the lubricating oil is pumped from the crankshaft side to the oil hole 22 of the connecting rod 12.
The oil that has risen through the opening of the oil hole 22 and the oil hole 2
A part of the oil flows out from the opening of No. 4, lubricates the spherical surface 5a, and flows down into the annular oil passage 31. Further, the remaining oil passes through the oil hole 26 and the oil groove 27 to reach the annular oil groove 29, and flows down inside the vertical hole 30 toward the annular oil passage 31. This oil cools the back surface of the piston crown 4 as it passes through the oil groove 27 and the annular oil groove 29, and also cools the back surface of the piston crown 4.
When flowing down, the sliding surface between the annular groove 19, which is the outer peripheral part of the skirt 5, and the ceramic coding 18 is cooled. The oil collected in the annular oil passage 31 flows into the oil groove 3.
2 and is emitted toward the crankshaft. In this way, the piston 3, which has descended due to the expansion of the combustion gas, moves up and down due to the rotation due to the inertia of the crankshaft, during which air is exhausted and taken in. When the piston 3 rises again, the air is compressed, and one cycle is completed. The cycle repeats.

The piston 3 that moves up and down during the above cycle
During the approximately half stroke on the top dead center side, the annular groove 19 and the ceramic coding 18 face each other, and the piston ring 21 faces the inner circumferential surface of the liner 2 without the ceramic coding. 3 goes up and down. Further, during approximately half a stroke toward the bottom dead center, the piston 3 moves up and down while the annular groove 19 and the piston ring 21 both face the inner circumferential surface of the liner 2. Therefore, during approximately half a stroke on the top dead center side where the gas pressure is high, the combustion gas in the combustion chamber attempts to leak toward the piston ring 21 through the gap between the piston 3 and the cylinder 1, but in the middle of this, the annular Because of the groove 19, the gas is diffused while generating excess flow within the annular groove 19, and the pressure can be lowered to 1/3 or less of that without the annular groove 19. Even if the number is reduced, gas leakage can be minimized. Also, cylinder 1
Ceramic coding 1 on the inner wall surface on the top dead center side.
8, it has excellent heat resistance and can suppress heat dissipation from the cylinder 1 and reduce heat loss. Moreover, since it is not in contact with the piston 3, there is no wear. Furthermore, by forming the piston crown 4 from a ceramic material, it is possible to provide a heat insulating effect against combustion gas.

In addition, in this example, an example in which the present invention was implemented in a 4-stroke diesel engine was shown, but
The same can be applied to two-stroke diesel engines, four-stroke and two-stroke gasoline engines.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, in a piston of an internal combustion engine, a plurality of annular grooves are provided on the outer peripheral surface on the top dead center side, and the annular grooves are inserted between approximately half a stroke on the top dead center side. A plurality of piston rings are fitted in ring grooves on the outer circumferential surface of the cylinder facing the ceramic coding inner wall surface on the bottom dead center side, and are inserted into the inner wall surface of the cylinder that is not ceramic coding during the entire stroke of the piston. By configuring them to face each other,
The pressure of gas attempting to leak from the combustion chamber is lowered by diffusion in the annular groove, reducing leakage from the piston rings. This allows the number of piston rings to be reduced compared to conventional methods, and mechanical Losses are reduced and engine efficiency is increased, while cylinder wear is reduced and service life is increased. Furthermore, since the inner wall surface on the top dead center side of the cylinder is coated with ceramic coating, it is possible to suppress heat dissipation from the cylinder, thereby reducing heat loss.

[Brief explanation of drawings]

Figures 1 to 6 show an embodiment of a piston for an internal combustion engine according to the present invention, and Figure 1 is a longitudinal cross-section of the piston cut away with the right half and left half shifted in phase by 90° in the circumferential direction. Figure 2 is a sectional view along AA of Figure 1, Figure 3 is a top view of Figure 1 viewed from the direction of arrow B, Figure 4 is a partially cutaway front view of the spherical head of the connecting rod, and Figure 5 is a partially cutaway front view of the spherical head of the connecting rod. The figure is a CC sectional view of FIG. 4, and FIG. 6 is an enlarged sectional view of the annular groove. 1... Cylinder, 2... Liner, 3... Piston, 12... Connecting rod, 18... Ceramic coding, 19... Annular groove, 20... Ring groove, 2
1... Piston ring.

Claims (1)

[Claims] 1. A plurality of annular grooves for combustion gas diffusion are provided on the circumferential surface of the cylinder facing the ceramic coating inner wall surface on the cylinder top dead center side during approximately half a stroke on the top dead center side. A piston for an internal combustion engine, characterized in that a plurality of piston rings are fitted into an outer ring groove so as to be in sliding contact with an inner wall surface that is not coated with ceramic.