JP5359581B2 - Piston structure of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston structure designed to reduce apparent viscosity of lubricating oil, and to lower sliding resistance as well as to enhance durability of an engine and fuel economy. <P>SOLUTION: Air introduction grooves 31, 32 for guiding air 9 between the piston 1 and the cylinder bore 8 to an oil film formation range (A) where the lubricating oil film 6 is formed, are provided on the surface of the skirt portion 3, when the piston 1 ascends and descends within the cylinder bore 8, in a piston structure of an internal combustion engine, which ascends and descends within cylinder bore 8, in the state where lubricating oil film 6 is formed in the middle part of a skirt portion 3 of a piston 1 accommodated in the cylinder bore 8. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a piston structure for an internal combustion engine.

  Generally, a piston of an internal combustion engine is composed of a cylindrical head portion 2 in which an oil ring groove or the like is formed as shown in FIG. 6 and a skirt portion 3 extending downward from the head portion 2. The cylinder bore (not shown) reciprocates in the vertical direction while being lubricated with lubricating oil.

  The piston 1 has a clearance with the cylinder bore inner wall surface in consideration of expansion and distortion caused by combustion, and lubricating oil (engine oil) is interposed in the clearance.

  However, the entire area between the cylinder bore inner wall surface and the surface of the skirt portion 3 (outer peripheral surface) is not filled with the lubricating oil. Normally, the oval filled in FIG. 6 is filled with the lubricating oil and lubricated. An oil film 6 is formed (oil film formation range A). And parts other than the oil film formation range A are filled with air.

  During the reciprocating motion of the piston 1, the outer peripheral surface of the skirt portion 3 slides through a lubricating oil film 6 formed between the inner wall surface of the cylinder bore. Resistance will occur.

  If sliding resistance is generated in the piston 1, the fuel consumption of the engine is deteriorated, and it is desirable that the sliding resistance of the piston 1 is low. As a method for reducing this sliding resistance, a slit is conventionally formed in the skirt portion 3. In some cases, the rigidity of the skirt part 3 is lowered (Patent Document 1) or a part of the skirt part 3 is cut.

JP 2005-188303 A

  By the way, it is known that the sliding resistance of the lubricating oil film 6 is proportional to the viscosity of the oil and the thickness of the lubricating oil film 6 apart from lowering the rigidity of the skirt portion 3. Therefore, the present applicant pays attention to reducing the sliding resistance by reducing the apparent viscosity of the lubricating oil, and reducing the apparent viscosity of the lubricating oil, thereby reducing the sliding resistance of the piston 1. The engine piston structure has been developed.

  The present invention has been made in view of the above points, and an object of the present invention is to reduce the apparent viscosity of the lubricating oil and to improve the fuel consumption by reducing the sliding resistance. To provide a structure.

In order to solve the above-described problems, the present invention provides a piston structure for an internal combustion engine that moves up and down in a cylinder bore in a state where a lubricating oil film is formed in a central portion of a skirt portion of the piston accommodated in the cylinder bore. when lifting a between the piston and the cylinder bore of the air, the air introducing groove for guiding the lubricating oil film formed range oil film is formed, the piston in the coating layer which is applied to the surface of said skirt portion A plurality of coating layers are provided from the upper end and the lower end of the coating layer toward the center of the oil film formation range along the ascending / descending direction or obliquely with respect to the ascending / descending direction, and at least the groove width and the groove depth of the air introduction groove One of the two is formed so as to widen from the inside to the outside of the oil film forming range .

  According to the above configuration, as the piston moves up and down with respect to the cylinder bore, the air between the piston and the cylinder bore is distributed in the form of bubbles in the lubricating oil film in the oil film forming range formed in the central portion of the skirt portion. As a result, the apparent viscosity of the lubricating oil film is lowered, so that the sliding resistance of the piston can be lowered.

Moreover, according to the said structure, it becomes easier to introduce air by forming at least one of the groove width and the groove depth of the air introduction groove from the inner side toward the outer side of the oil film forming range .

  ADVANTAGE OF THE INVENTION According to this invention, the piston structure of the internal combustion engine which reduced the apparent viscosity of lubricating oil, reduced sliding resistance, and improved the durability and fuel consumption of the engine can be provided.

1A and 1B are views showing a piston of an internal combustion engine according to an embodiment of the present invention, in which FIG. 1A is a front view and FIG. 1B is an enlarged view of a skirt portion viewed from an arrow X in FIG. . FIG. 2 is a perspective view of a piston of the internal combustion engine shown in FIG. 3A shows the left half of the piston as viewed from the arrow X in FIG. 1, and FIG. 3B shows the skirt portion and the inner wall surface of the cylinder bore when sectioned along line AA in FIG. It is a figure which shows a relationship and is the figure which expanded the shape of the skirt part to the horizontal direction. FIGS. 4A and 4B are explanatory views showing a state where air enters the lubricating oil film between the skirt portion and the cylinder bore inner wall surface, where FIG. 4A shows when the piston is raised, and FIG. 4B shows when the piston is lowered. . FIGS. 5A and 5B are explanatory views showing a state in which air is discharged from the lubricating oil film between the skirt portion and the inner wall surface of the cylinder bore. FIG. 5A shows when the piston is raised, and FIG. is there. FIG. 6 is a perspective view of a piston of a conventional internal combustion engine.

  A preferred embodiment of the present invention will be described with reference to the accompanying drawings.

  1 to 5, members having the same functions as the members shown in the conventional example of FIG. 6 are described with the same reference numerals.

  As shown in FIGS. 1 and 2, the piston 1 includes a cylindrical head portion 2 that forms a combustion chamber in a cylinder (not shown), and a pair of skirt portions that extend downward from the head portion 2. 3 (hereinafter referred to as a skirt portion 3) and a thick pin boss portion 4 in which a piston pin hole 5 is formed.

  Two piston ring grooves 20 and 21 and one oil ring groove 22 are formed on the outer peripheral surface of the head portion 2 in order from the upper side. A piston ring (not shown) is fitted in each piston ring groove 20, 21, and an oil ring (not shown) is fitted in the oil ring groove 22.

  A piston pin (not shown) for connecting the piston 1 and a connecting rod (not shown) is inserted into the piston pin hole 5 formed at the center of the pin boss 4.

  The skirt portion 3 slides up and down on the cylinder bore inner wall surface 8a (FIG. 3) to guide the raising and lowering of the piston 1, and to release the heat generated by the combustion to the cylinder block 7. The skirt portion 3 is disposed on the lower side of the head portion 2 so as to face each other with the pin boss portion 4 interposed therebetween. The skirt portion 3 is a direction in which the skirt portion 3 abuts against the cylinder bore inner wall surface 8a. The coating layer 30 is coated with carbon or molybdenum disulfide by a general-purpose screen printing method (see FIG. 2).

  Such a piston 1 is inserted into the cylinder bore 8, and its side surface faces the cylinder bore inner wall surface 8a. Of the side surface of the piston 1, a piston ring (not shown) mounted in the ring grooves 20 and 21 of the head portion 2 is slidably contacted with the cylinder bore inner wall surface 8a to keep airtight. The piston 1 rises on the cylinder bore inner wall surface 8a in the compression stroke, and is lowered by the pressure of the combustion gas in the explosion stroke.

  By the way, in the gap (clearance) between the skirt portion 3 and the cylinder bore inner wall surface 8a, lubricating oil such as engine oil is interposed in order to reduce sliding resistance. This lubricating oil is shown in FIG. ) And an elliptical lubricating oil film 6 as shown in FIG. 2 is formed. The lubricating oil film 6 is formed in the range indicated by A in FIGS. 1B and 2 (oil film forming range A), and outside the oil film forming range A, air 9 is interposed between the cylinder bore inner wall surface 8a. ing.

  The sliding resistance of the lubricating oil film 6 is proportional to the viscosity of the lubricating oil, and the viscosity decreases when air is mixed. Therefore, if the air interposed between the side surface of the piston 1 and the cylinder bore inner wall surface 8a is introduced into the lubricating oil film 6 on the surface of the skirt portion 3, the apparent viscosity of the lubricating oil film 6 is lowered.

  In order to realize this, the present invention guides the air 9 between the side surface of the piston 1 and the inner surface of the cylinder bore 8 to the oil film formation range A in which the lubricating oil film 6 is formed when the piston 1 moves up and down in the cylinder bore 8. The air introduction grooves 31 and 32 are provided on the surface of the skirt portion 3.

  That is, as shown in FIGS. 1 and 2, the air introduction grooves 31 and 32 are formed so as to cross the oil film formation range A on the surfaces of the skirt portions 3 and 3 from the outside toward the inside. Specifically, three air introduction grooves 31 are formed from the upper end toward the approximate center of the oil film formation range A, and similarly three air introduction grooves 32 are provided from the lower end toward the approximate center of the oil film formation range A. doing. The groove width of the air introduction grooves 31 and 32 is, for example, 1 to 2 mm, and the groove depth is about 10 μm.

  The air introduction grooves 31 and 32 may be formed by scraping off part of the coating layer 30 applied to the surface of the skirt portion 3. Alternatively, the air introduction grooves 31 and 32 may be formed by masking from the beginning and providing a coating missing portion that is not coated.

  Moreover, since the piston 1 is normally a printing type (screen printing) coating as described above, it can be coated with a grooved shape from the beginning.

  The air introduction groove 31 is formed with an inlet 31 a for air 9 on the upper end side of the coating layer 30 on the surface of the skirt portion 3, and the air introduction groove 32 is formed on the lower end side of the coating layer 30 on the surface of the skirt portion 3. Nine inlets 32a are formed (see FIG. 3B). The air introduction grooves 31 and 32 are formed so that at least one of the groove width and the groove depth is widened from the inside to the outside of the oil film forming range A. That is, the air 9 is easily introduced by forming the inlets 31a and 32a of the air 9 so as to widen toward the end.

  The air 9 introduced into the lubricating oil film 6 through the air introducing grooves 31 and 32 is distributed in the form of bubbles, and as a result, the apparent viscosity of the lubricating oil decreases, so that the sliding resistance of the piston 1 can be lowered.

  Further, the air introduction grooves 31 and 32 are bifurcated, for example, in the middle so that the air 9 introduced from the inlets 31a and 32a is uniformly distributed in the form of bubbles in the oil film formation range A.

  The air introduction grooves 31 and 32 can be easily introduced into the oil film formation range A, and if the air 9 is evenly distributed in the oil film formation range A in the form of bubbles, the air introduction grooves 31 and 32 can be used. The number may be other than three, and the shape is not limited to the one bifurcated in the figure.

  The lubricating oil film 6 and air 9 formed between the surface of the skirt portion 3 and the cylinder bore inner wall surface 8a will be described with reference to FIG.

  In FIG. 3B, for easy understanding, the gap between the cylinder bore inner wall surface 8a and the surface of the skirt portion 3 and the shape of the skirt portion 3 are greatly enlarged in the horizontal direction.

  The lubricating oil interposed in the gap between the surface of the skirt portion 3 and the cylinder bore inner wall surface 8a forms the lubricating oil film 6 over the oil film forming range A on the surface of the skirt portion 3 when the piston 1 is raised or lowered. Locations other than the formation range A are filled with air 9. That is, the portion of the B portion that is the gap between the upper portion of the skirt portion 3 and the cylinder bore inner wall surface 8a and the portion of the C portion that is the gap between the lower portion of the skirt portion 3 and the inner wall surface 8a of the cylinder bore shown in FIG. Filled with.

  Accordingly, the air introduction grooves 31 and 32 of the present invention are formed on the surface of the skirt portion 3, and the inlets 31a and 32a of the air introduction grooves 31 and 32 are formed at locations corresponding to the B portion and the C portion, respectively. As the air travels up and down, the air 9 in the B part or C part is introduced into the lubricating oil film 6 from the inlets 31a and 32a through the air introduction grooves 31 and 32.

  Hereinafter, based on FIG.4 and FIG.5, the effect | action of the piston structure of the internal combustion engine by this embodiment is demonstrated.

  When the piston 1 is lifted, the air 9 in the B part enters the inlet of the air introduction groove 31 on the lubricating oil film 6 formed between the surface of the skirt part 3 and the cylinder bore inner wall surface 8a as shown in FIG. The air 9 enters through the air introduction groove 31 and the air 9 is distributed in the form of bubbles in the lubricating oil film 6. As the piston 1 rises, air 9 is newly introduced as shown in FIG. 5 (A), a lubricating oil film 6a in which the air 9 is distributed in a bubble shape is formed, and the lubricating oil film left behind in the movement of the piston 1 Air 9 is discharged to the lower side of the skirt portion 3 from 6b.

  When the piston 1 is lowered, the air 9 in the portion C is formed in the lubricating oil film 6 formed between the surface of the skirt portion 3 and the cylinder bore inner wall surface 8a as shown in FIG. The air 9 enters from the inlet 32 a and travels through the air introduction groove 32, and the air 9 is distributed in the form of bubbles in the lubricating oil film 6. As the piston 1 descends, air 9 is newly introduced as shown in FIG. 5 (B), a lubricating oil film 6a in which the air 9 is distributed in a bubble shape is formed, and the lubricating oil film left behind in the movement of the piston 1 Air 9 is discharged from 6b above the skirt 3.

  As a result, the air 9 between the surface of the skirt portion 3 and the cylinder bore inner wall surface 8a is introduced into the lubricating oil film 6 along the air introduction grooves 31 and 32 as the piston 1 moves up and down, and the air 9 is foamed. Will be distributed. As a result, the apparent viscosity of the lubricating oil film 6 is reduced, so that the sliding resistance of the piston 1 can be lowered.

  It is said that most of the mechanical loss of the engine is due to the sliding resistance around the piston, and this reduction in sliding resistance leads to improved fuel efficiency. By reducing the apparent viscosity of the oil film 6, the sliding resistance is lowered, and the introduction of the air 9 is performed as the piston 1 moves up and down without using external means, and no special device is required. Can be realized.

  The skirt 3 surface and the cylinder bore inner wall surface 8a are sliding contact surfaces of the piston 1 that moves up and down at a high speed when the engine is operated, and thus are parts that require wear resistance and lubricity (low friction). If air 9 is mixed in the form of foam as described above and an oil film forming portion having a low viscosity is provided, wear of the surface of the skirt portion 3 and the cylinder bore inner wall surface 8a is effectively suppressed due to the presence of the low viscosity lubricating oil. In addition, sufficient lubricity between the surface of the skirt portion 3 and the cylinder bore inner wall surface 8a can be secured by the lubricating oil (engine oil) supplied from the connecting rod or the like.

  As described above, according to the present invention, by suppressing wear and ensuring lubricity (low friction), the sliding resistance of the piston 1 is lowered and the fuel efficiency is improved while maintaining the durability of the engine. Can be achieved.

1 Piston (Piston body)
2 Head portion 3 Skirt portion 4 Pin boss portion 5 Piston pin hole 6 Lubricating oil film 7 Cylinder block 8 Cylinder bore 8a Cylinder bore inner wall surface 9 Air 20, 21 Ring groove 22 Oil ring groove 30 Coating layers 31, 32 Air introduction grooves 31a, 32a Inlet A Oil film formation range

Claims (1)

In the piston structure of the internal combustion engine that moves up and down in the cylinder bore in a state where a lubricating oil film is formed in the central part of the skirt portion of the piston housed in the cylinder bore,
When the piston moves up and down in the cylinder bore, a coating layer is provided on the surface of the skirt portion with an air introduction groove for guiding the air between the piston and the cylinder bore to the oil film forming range where the lubricating oil film is formed. A plurality of the air-introducing grooves are provided along the piston ascending / descending direction or obliquely with respect to the ascending / descending direction from the upper end and the lower end of the coating layer toward the center of the oil film forming range. A piston structure for an internal combustion engine, wherein at least one of the depths is formed so as to widen from the inside to the outside of the oil film forming range .

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