JP4248727B2 - Piston for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piston for an internal combustion engine, and more particularly to a piston for an internal combustion engine in which sliding resistance in a cylinder is reduced as much as possible.
[0002]
[Prior art]
Generally, a piston for an internal combustion engine has been proposed in Japanese Patent Application Laid-Open No. 1-1131847. This piston 7 is a skirt that serves as a sliding portion of the piston 7 with respect to the cylinder 2 as shown in FIGS. A plurality of grooves 18 along the circumferential direction of the piston 7 are formed on the surface of the portion 17, and oil is retained in the grooves 18 to secure an oil film formed on the inner surface of the cylinder 2. .
[0003]
[Problems to be solved by the invention]
However, such a conventional piston structure still has the following problems to be improved.
[0004]
That is, the outer diameter of the piston 7 is usually smaller than the inner diameter of the cylinder 2, and the gap is sealed with a pressure ring or an oil ring attached to the piston 7.
For this reason, when the piston 7 is slid, a phenomenon occurs in which the piston 7 falls down slightly or is displaced to the inner surface of the cylinder 2.
When such a phenomenon occurs, as shown in FIG. 8, a part of the circumferential surface of the piston 7 approaches the inner surface of the cylinder 2, and the piston 7 and the cylinder 2 are moved from the closest position to the circumferential direction. And the oil retained in the groove 18 is pushed out toward both sides of the groove 18, and the amount of oil retained by the groove 18 is reduced.
[0005]
As described above, if the amount of oil retained in the groove 18 is reduced, the above-described oil film forming action on the inner surface of the cylinder 2 is assumed to be reduced, so there is room for improvement.
[0006]
The present invention has been made in view of such conventional problems, and provides a piston for an internal combustion engine that can sufficiently secure an oil film forming function on the inner surface of the cylinder and can reduce the sliding resistance of the piston as much as possible. The purpose is to do.
[0007]
In order to achieve the above-mentioned object, a piston for an internal combustion engine according to claim 1 of the present invention is a piston slidably mounted in a cylinder of the internal combustion engine, and a sliding contact portion with the cylinder. A plurality of dimples are formed in the skirt portion, and the plurality of dimples are formed in a staggered manner in the axial direction and the circumferential direction of the piston, and the skirt portion of the piston is processed along the circumferential direction. A gap is formed, and an interval between opposing edges of adjacent dimples in the axial direction of the piston is set larger than the width of the machining trace and smaller than the diameter of the dimple, and is adjacent in the circumferential direction of the piston. The dimple edge is formed so as to overlap in the circumferential direction of the piston .
By adopting such a configuration, when the piston slides, it is possible to suppress the movement of oil between the dimples positioned in the axial direction thereof, and it is possible to suppress a decrease in the oil holding action in each dimple. In addition , oil can be gently moved between the dimples adjacent in the circumferential direction via the processing marks. Further, in the piston for an internal combustion engine according to claim 2 , the cylinder according to claim 1 is arranged along a substantially horizontal direction, and the skirt portion of the piston is positioned vertically. The dimples are formed in the skirt portion located above. In such an internal combustion engine, a phenomenon occurs in which the oil supplied into the cylinder falls downward along the inner wall of the cylinder, and as a result, the amount of oil in the upper part is lower than that in the lower part of the cylinder. It is possible that there will be less. In consideration of such a phenomenon, the above-described configuration can ensure the film thickness of the oil film above the cylinder.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 5 and 6, the internal combustion engine includes a crankcase 1, a cylinder block 3 that is attached to the crankcase 1 and forms a cylinder 2, and a cylinder head 4 that is attached to cover the cylinder block 3. A crankshaft 5 rotatably provided in the crankcase 1 and a piston 20 slidably mounted in the cylinder 2 and connected to the crankshaft 5 via a connecting rod 6; Is schematically configured.
[0009]
The cylinder block 3 is provided with an air supply port 9 for supplying a combustion mixture to a combustion chamber 8 formed by the cylinder 2, the piston 20 and the cylinder block 3, and for exhausting exhaust gas after combustion. An exhaust port 10 is provided, and an air supply valve 11 and an exhaust valve 12 for opening and closing the air supply port 9 and the exhaust port 10 are provided.
[0010]
The air supply valve 11 and the exhaust valve 12 are driven to open and close by a valve mechanism 13 attached to the cylinder head 4.
[0011]
Further, the crankcase 1 is provided with an oil pump 14 for supplying oil for lubricating the movable parts of the internal combustion engine to the movable parts as shown in FIG. The pump 14 is driven by the rotation of the crankshaft 5.
[0012]
The oil pump 14 passes through an oil passage 15 formed in the crankcase 1, the cylinder block 3, and the cylinder head 4, or a sliding portion of the air supply valve 11 and the exhaust valve 12, or a valve mechanism 13. As shown in FIG. 6, oil is supplied to the connecting portion with the connecting rod 6 through an oil passage 16 formed in the crankshaft 5, and further, the oil is supplied from the connecting portion to the movable portion. By scattering oil and adhering it to the inner surface of the cylinder 2 and the piston 20, the cylinder 2 and the piston 20 are cooled and lubrication is performed at the sliding portion between the cylinder 2 and the piston 20. Yes.
[0013]
By the way, in the internal combustion engine configured as described above, an oil film is formed on the inner surface of the cylinder 2 by the oil supplied to the sliding portion between the piston 20 and the cylinder 2. Although sliding resistance is reduced, as described above, there is a demand for more effective formation of this oil film.
[0014]
Therefore, as shown in FIG. 1, the internal combustion engine piston 20 according to the present embodiment is provided continuously with a piston head 21 and a lower portion of the piston head 21, and a pressure ring and an oil ring (both not shown). ) And a pair of piston boss portions 23 provided below the ring mounting portion 22 and provided at positions retracted from the peripheral surface of the ring mounting portion 22 to the inside of the piston 20. And a pair of skirt portions 24 formed in portions other than the piston boss portions 23 and serving as sliding portions with the cylinder 2.
The piston boss portion 23 and the skirt portion 24 are provided at positions shifted by 90 degrees around the axis of the piston 20.
[0015]
The skirt portion 24 is formed with a large number of dimples 25 which are characteristic portions of the present invention.
These dimples 25 are formed in a substantially spherical shell shape, and the dimensions thereof are, for example, a diameter: 3.8 mm and a maximum depth: 0.15 mm, and are formed over almost the entire surface of the skirt portion 24. ing.
Preferably, the surface area ratio per unit area of the dimple 25 is about 30% or more.
[0016]
As shown in FIG. 5, the piston 20 according to the present embodiment configured as described above is mounted in the internal combustion engine by being connected to the small end portion of the connecting rod 6 by a piston pin.
[0017]
As the internal combustion engine is started, the cylinder 2 is reciprocated in the axial direction. At this time, oil is sprayed from the crankshaft 5 to the inner surface of the cylinder 2, and this oil is applied to the piston 20. The oil film is stretched by an oil ring or the like to form an oil film on the inner surface of the cylinder 2.
[0018]
At the same time, the oil adhering to the inner surface of the cylinder 2 is captured by the dimples 25 of the piston 20 and held in these dimples 25, and the oil film formed on the inner surface of the cylinder 2 becomes thin. The oil held in the dimple 25 is supplied, and the film thickness of the oil film is maintained.
[0019]
Since each of the dimples 25 is independent, even if the piston 20 falls down or is displaced with respect to the cylinder 2, the movement of oil between the dimples 25 is minimized.
Therefore, the above-described oil film maintenance action is maintained over a long period of time.
[0020]
Here, since the function of holding the oil by the piston 20 is high, the amount of oil supplied to the inside of the cylinder 2 can be reduced. As a result, the load on the oil ring for extending the oil is reduced. Also, the sliding resistance of the piston 20 is suppressed.
[0021]
On the other hand, by providing the dimples 25 in a staggered manner as shown in FIG. 1, the number of the dimples 25 can be increased, and as a result, the unevenness of the oil film to be formed can be reduced.
[0022]
Further, as shown in FIGS. 2 and 3, there may be a circumferential machining mark 26 on the surface of the skirt portion 24 of the piston 20 at the time of manufacture.
In such a case, it is desirable to form the dimples 25 formed on the skirt portion 24 in the following positional relationship.
[0023]
That is, each dimple 25 is formed so that the interval between the opposing edge portions of the adjacent dimples 25 in the axial direction of the piston 20 (vertical direction in FIGS. 2 and 3) is larger than the width of the machining mark 26. .
By adopting such a positional relationship, when the piston 20 slides, the movement of oil between the dimples 25 positioned in the axial direction thereof is suppressed, and the decrease in the oil holding action in each dimple 25 can be suppressed. it can.
[0024]
Further, by forming the dimples 25 so as to partially overlap in the circumferential direction of the piston 20 between adjacent dimples 25 in the circumferential direction of the piston 20 (left and right direction in FIG. 3), the circumferential direction In this case, the oil can be gently moved between the adjacent dimples 25 through the processing marks 26.
As described above, when the oil moves slowly, the oil in the dimple 25 can be replaced without impairing the oil holding action of the dimple 25.
[0025]
Further, depending on the internal combustion engine, as shown in FIG. 5, the cylinder 2 may be mounted so as to be substantially horizontal.
In such an internal combustion engine, a phenomenon occurs in which the oil supplied into the cylinder 2 falls downward along the inner wall of the cylinder 2, and as a result, the oil amount in the lower part of the cylinder 2 is higher than that in the lower part of the cylinder 2. It is conceivable that the amount of oil at
[0026]
In consideration of such a phenomenon, the dimple 25 is formed mainly on the skirt portion 24 positioned above the piston 20 so as to ensure the film thickness of the oil film above the cylinder 2. You can also.
[0027]
Alternatively, the film thickness of the oil film on the upper and lower sides of the cylinder 2 can be made uniform by making the number and density of the dimples 25 above the piston 20 larger than that on the lower side.
[0028]
Note that the shapes, dimensions, and the like of the constituent members shown in the above embodiment are merely examples, and various changes can be made based on design requirements and the like.
For example, as shown in FIG. 4, it is possible to arbitrarily reduce the diameter of each dimple 27 to increase its installation density.
[0029]
【The invention's effect】
As described above, according to the piston for an internal combustion engine according to the present invention, a large number of independent oil sumps are formed in the skirt portion of the piston by a large number of dimples formed in the piston, thereby preventing the piston from falling. Even when misalignment or the like occurs, oil can be reliably held in the skirt portion of the piston, and thereby an oil film can be reliably generated on the inner surface of the cylinder, and the sliding resistance of the piston can be reduced.
In addition, the amount of oil supplied into the cylinder can be reduced by the amount of oil retained by each dimple, and as a result, the load on the oil ring attached to the piston can be reduced. Also, the sliding resistance of the piston can be reduced.
[Brief description of the drawings]
FIG. 1 is a front view of a piston according to an embodiment of the present invention.
FIG. 2 is an enlarged sectional view of a skirt portion of a piston, showing an embodiment of the present invention.
FIG. 3 shows an embodiment of the present invention and is an enlarged front view of a skirt portion of a piston.
FIG. 4 is a front view of a piston, showing a modification of the present invention.
FIG. 5 is a longitudinal sectional side view showing a structural example of an internal combustion engine to which an embodiment of the present invention is applied.
FIG. 6 is a cross-sectional plan view showing a structural example of an internal combustion engine to which an embodiment of the present invention is applied.
FIG. 7 is a front view showing an example of a conventional piston.
FIG. 8 is a schematic view showing the relationship between a conventional piston and cylinder.
[Explanation of symbols]
1 Crankcase 2 Cylinder 3 Cylinder block 4 Cylinder head 5 Crankshaft 6 Connecting rod 7 Piston 8 Combustion chamber 9 Air supply port 10 Exhaust port 11 Air supply valve 12 Exhaust valve 13 Valve mechanism 14 Oil pump 15 Oil passage 16 Oil passage 17 Skirt Part 18 groove 20 piston 21 piston head 22 ring mounting part 23 piston boss part 24 skirt part 25 dimple 26 machining mark 27 dimple

Claims (2)

A piston slidably mounted in a cylinder of an internal combustion engine, wherein a plurality of dimples are formed in a skirt portion that is a sliding contact portion with the cylinder, and the plurality of dimples are in the axial direction of the piston. In addition, it is formed in a zigzag shape in the circumferential direction, a processing mark is formed in the circumferential direction in the skirt portion of the piston, and an interval between opposed edge portions of adjacent dimples in the axial direction of the piston is Set larger than the width of the processing mark and smaller than the diameter of the dimple ,
An internal combustion engine piston , wherein edges of adjacent dimples in the circumferential direction of the piston overlap with each other in the circumferential direction of the piston. The cylinder is disposed along a substantially horizontal direction, the skirt portion of the piston is vertically positioned, and the dimple is formed in the skirt portion positioned above. The piston for an internal combustion engine according to claim 1 .

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