KR20000013233A - Piston of engine - Google Patents

Abstract

PURPOSE: A piston of an engine is provided to prevent the back current of oil, and to reduce the oil consumption by securing a seal function of the bottom of an oiling at rising a piston body. CONSTITUTION: The engine comprises:many ring-shaped recessed parts(12a, 12b, 12c) formed in an outer circumference; a piston body(12) formed a cone rod accepting recessed unit(12e) in the bottom of the opposite side on the top; an oiling(13) contacted in the inner circumference of a cylinder(16) by accepting in the lower recessed groove(12c) located far from the top of the piston body(12); first oil return holes(31)(51) equipped by inclining to be withdrawn from the top of the piston body(12); entrances(31a, 51a) of the first oil return holes(31, 51) formed in the position not to be reached in the corner of the lower girth of the lower recessed groove(12c).

Description

Piston of engine

The present invention relates to a piston of an engine having a recess groove for receiving an oil ring on its outer circumferential surface. In more detail, it is related with the piston of the engine which has the oil return hole for returning the excess oil of the cylinder inner peripheral surface scraped off by this oil ring to an oil pan.

As a piston of this type in the prior art, as shown in Figs. 7 and 8, a cone is formed on the bottom surface opposite to the top surface of the piston body 2 having three ring-shaped recessed grooves 2a, 2b, and 2c formed on the outer circumferential surface thereof. The rod receiving recess 2e is formed, and the oil ring 3 is accommodated in the lower inlet groove 2c located farthest from the top surface of the piston body 2 among these recessed grooves 2a, 2b and 2c. It is also known that the outer circumferential surface of the oil ring 3 is configured to contact the inner circumferential surface of the cylinder 6. In this piston (1), an oil return hole (4) communicating with the piston body (2) outer circumferential surface and the cone rod receiving recess (2e) is provided in the piston body (2). The inlet 4a of the oil return hole 4 is relatively over the inner surface of the lower mouth groove 2c, the bottom of the lower mouth groove 2c and the outer peripheral surface of the piston body 2 below the lower mouth groove 2c. It is largely formed. In addition, the oil return hole 4 is formed to be inclined away from the top surface of the piston body 2 as it faces the cone rod receiving recess 2e from the outer peripheral surface of the piston body 2. The oil ring 3 is configured to be in close contact with the inner peripheral surface of the cylinder 6 by the elastic force of the oil ring 3 and the elastic force of the coil spring 3a. The code | symbol 3c of FIG. 7 is a long hole.

In the piston of the engine configured as described above, the piston body 2 descends relative to the cylinder 6 in the expansion stroke shown in Figs. 7A and 7A, and the oil ring 3 is lowered by this lowering. The excess oil adhering to the inner circumferential surface of the cylinder 6 is scraped off to form a lubricating oil film having a minimum thickness required on the inner circumferential surface of the cylinder 6. The surplus oil shaved by the oil ring 3 falls into the oil pan (not shown) through the oil return hole 4 as indicated by the dashed arrow marks and the dashed-dotted arrows.

Next, in the intake stroke shown in Figs. 7 (b-1) and (b-2) after the piston main body 2 rises in the exhaust stroke, the piston body 2 descends relative to the cylinder 6, so that the oil ring ( 3) operates in the same manner as the expansion stroke.

In the expansion stroke and the intake stroke of the engine, first, as shown in Figs. 7A and 7B, when the piston body 2 descends from the dead point above to a predetermined position, the piston body Acceleration acts downward on (2). That is, the descending speed of the piston body 2 gradually increases. Next, as shown in Figs. 7A and 7B-2, when the piston body 2 descends from a predetermined position to a lower dead point, acceleration acts on the piston body 2 upwards. That is, the descending speed of the piston body 2 gradually decreases. At this time, the oil ring 3 accommodated in the lower inlet groove 2c of the piston body 2 descends while contacting the bottom of the lower inlet groove 2c by the inertia force. The oil passes through the inlet 4a of the oil return hole 4 through the inlet 4a of the oil return hole 4 as shown by the dashed-dotted arrows in Figs. 7 (a-2) and (b-2) and the lower groove 2c. There was a case of reverse flow upward from the gap between the upper surfaces. As a result, since this countercurrent oil is diluted with extremely high temperature combustion gas and burns, there is a problem that the oil consumption increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piston of an engine that can prevent backflow of oil and reduce oil consumption by securing the seal function of the bottom surface of the oil ring when the piston body rises with respect to the cylinder.

Another object of the present invention is to provide a piston of an engine capable of smoothly returning excess oil accumulated on the bottom of an oil ring to an oil pan.

1 and 2, a plurality of ring-shaped recessed grooves 12a, 12b, 12c are formed on the outer circumferential surface, and the cone rod receiving recess 12e is provided on the bottom surface opposite to the top surface. Is formed in the piston body 12 and the lower inlet groove 12c farthest from the top surface of the piston body 12 among the plurality of recessed grooves 12a, 12b and 12c, and the outer circumferential surface of the cylinder 16 is It relates to an improvement of an engine having an oil ring (13) in contact with.

The configuration having such a feature communicates with the piston body 12 in the lower inlet groove 12c and the cone rod receiving recess 12e and also toward the cone rod receiving recess 12e in the lower mouth groove 12c. The first oil return hole 31 is provided to be inclined away from the top surface of the piston body 12, and the inlet 31a of the first oil return hole 31 is only on the inner surface of the lower inlet groove 12c or the lower It exists in the position which does not reach the bottom edge corner part of the lower mouth groove | channel 12c from the inner surface of the recessed part 12c to the lower surface of the lower mouth groove | channel 12c.

In the piston of the engine according to claim 1, when the piston body 12 descends with respect to the cylinder 16, such as the expansion stroke or the intake stroke of the engine, the piston body 12 accelerates downward from the upper dead point to a predetermined position. Since the oil ring 13 is lowered in contact with the upper surface of the lower mouth groove 12c by the inertia force. As a result, the excess oil accumulated on the bottom of the oil ring 13 is shaved by the oil ring 13, and the gap between the bottom of the lower inlet groove 12c and the bottom of the oil ring 13 and the first oil return hole 31 are closed. Through the oil pan.

Next, since the acceleration acting on the piston body 12 changes upward when the piston body 12 passes the predetermined position, the oil ring 13 contacts the bottom surface of the lower mouth groove 12c by its inertia force. Descend from the state. As a result, excess oil at the bottom of the oil ring 13 accumulates on the bottom of the oil ring 13, but the bottom of the oil ring 13 is in close contact with the bottom of the lower groove 12c, and the oil at the bottom of the oil ring 13 Since there are no holes or gaps flowing into the lower mouth groove 12c, oil does not flow back through the lower mouth groove 12c.

The invention according to claim 2 is an invention according to claim 1, wherein the outer circumferential surface of the piston body 12 and the cone rod accommodation recess below the lower inlet groove 12c in the piston body 12 are shown in FIGS. 1 and 2. A second oil return hole 32 communicating with the mouth 12e is provided, and the second oil return hole 32 is provided on the outer rod surface of the piston body 12 below the lower inlet groove 12c. It is characterized in that it is formed inclined away from the top surface of the piston body 12 toward the mouth (12e).

In the piston of the engine according to claim 2, when the piston body 12 is lowered and the acceleration acting on the piston body 12 is directed downward, the oil ring 13 is scraped off and surpluses accumulated on the bottom of the oil ring 13. The oil is smoothly returned to the oil pan via the first oil return hole 31 and the second oil return hole 32. When the piston body 12 descends, when the acceleration acting on the piston body 12 faces upward, the oil ring 13 is scraped off and excess oil accumulated on the bottom of the oil ring 13 is returned to the second oil return hole ( 32) back to the oil pan smoothly.

The invention according to claim 3 is the invention according to claim 1, and the piston main body 12 extends from the bottom edge of the piston main body 12 to the outer circumferential surface of the piston main body 12 as shown in FIG. At the same time as extending in the moving direction of the oil inlet portion 77 formed shallower than the depth of the lower inlet groove (12c) or the same as the depth of the lower inlet groove (12c) is provided on the outer peripheral surface of the piston body (12) do.

In the piston of the engine according to claim 3, when the piston body 12 is lowered and the acceleration acting on the piston body 12 is downward, the oil ring is scraped off and excess oil accumulated on the bottom of the oil ring is returned to the first oil. It smoothly returns to the oil pan via the hole 31 and the oil escape inlet 77. When the piston body 12 is lowered, when the acceleration acting on the piston body 12 is upward, the oil ring is scraped off and excess oil accumulated on the bottom of the oil ring is smoothly passed through the oil escape inlet 77. Return to the fan.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged cross-sectional view of portion A of Fig. 2 showing an expansion stroke and an intake stroke of a four cycle engine according to a first embodiment of the present invention;

2 is a longitudinal sectional view of main parts of an engine including the piston;

Fig. 3 is a cross-sectional view corresponding to Figs. 1 (a-2) and (b-2) showing a second embodiment of the present invention.

4 is a B view of FIG. 5 showing a third embodiment of the present invention;

5 is a cross-sectional view taken along the line C-C of FIG.

FIG. 6 is a view D of FIG. 5; FIG.

7 is a cross-sectional view corresponding to FIG. 1 showing a conventional example.

8 is a longitudinal sectional view of a main portion of an engine including the piston;

※ Explanation of symbols about main part of drawing ※

11: piston 12: piston body

12a: upper indentation groove 12b: middle indentation groove

12c: Lower groove 12e: Cone rod receiving hole

13: oil ring 16: cylinder

31, 51: 1st oil return hole 31a, 51a: entrance of 1st oil return hole

32, 52: 2nd oil return hole 77: oil escape part

The following describes an embodiment of the present invention with reference to the drawings.

As shown in Figs. 1 and 2, the piston 11 of the diesel engine has a piston body 12 having a plurality of ring-shaped recessed grooves 12a, 12b, and 12c formed on an outer circumferential surface thereof, and these recessed grooves 12a. (12b) (12c) has an oil ring (13) accommodated in the lower inlet groove (12c) located the furthest from the top surface of the piston body (12). The combustion chamber 12d is formed in the top surface of the piston body 12, and the cone rod accommodation recessed part 12e is formed in the bottom surface (FIG. 2). Although not shown, the upper end of the cone rod is inserted into the cone rod receiving recess 12e, and the upper end of the cone rod is fixed to the piston body 12 through a piston pin (not shown).

In addition, there are three recessed grooves 12a, 12b, and 12c in this embodiment, and the upper recessed grooves 12a positioned closest to the top surface of the piston body 12 in addition to the lower grooved grooves 12c. , The middle inlet groove 12b is formed between the upper inlet groove 12a and the lower inlet groove 12c (FIGS. 1 and 2). The first and second compression rings 21 and 22 are accommodated in the upper inlet groove 12a and the middle inlet groove 12b, respectively, and these compression rings 21 and 22 are used for the expansion stroke of the engine (Fig. 1 (a-1) and (a-2)) or in a compression stroke (not shown), the airtightness of the gas in the combustion chamber 12d is maintained.

A coil spring 13a is mounted on the inner circumferential surface of the oil ring 13, and two lip portions 13b and 13b are provided on the outer circumferential surface to contact the inner circumferential surface of the cylinder 16 (FIG. 1). Between these ribs 13b and 13b, a plurality of long holes 13c extending in the oil ring 13 are formed. The oil ring 13 is configured to be in close contact with the inner circumferential surface of the cylinder 16 by a predetermined tension by the elastic force of the oil ring 13 and the elastic force of the coil spring 13a. The oil ring 13 has a function of preventing oil adhering to the inner circumferential surface of the cylinder 16 to enter and combust the combustion chamber 23d and forming a minimum required oil film on the inner circumferential surface of the cylinder 16.

In addition, the piston main body 12 has a first oil return hole 31 communicating with the lower groove 12c and the cone rod receiving recess 12e, and an outer circumferential surface of the lower piston main body 12 below the lower groove 12c. And a second oil return hole 32 communicating with the cone rod receiving recess 12e (Figs. 1 and 2). The first oil return hole 31 is inclined away from the top surface of the piston main body 12 toward the cone rod receiving recess 12e from inside the lower mouth groove 12c, and the first oil return hole 31 The inlet 31a of) is formed only on the inner side of the lower mouth groove 12c. The second oil return hole 32 faces the cone rod receiving recess 12e from the outer circumferential surface of the piston body 12 below the lower oil return groove 12c, that is, below the first oil return hole 31. It is inclined away from the top surface of the piston body 12. The inlet 32a of the second oil return hole 32 is formed just below the lower inlet groove 12c of the outer circumferential surface of the piston body 12. Four first and second oil return holes 31 and 32 are provided in the piston body 12 in this embodiment. In addition, the outer circumferential surface of the lower piston groove 12 of the lower inlet groove 12c is smoother than the lower inlet groove 12c in order to smoothly draw oil accumulated in the bottom of the oil ring 13 into the second oil return hole 32. A ring-shaped recess is formed.

The operation of the piston of the engine thus constructed will be described.

In the expansion stroke shown in Fig. 1 (a-1), since the fuel in the combustion chamber 12d takes place and the pressure in the combustion chamber 12d rapidly increases, the piston body 12 is pushed down by this gas pressure. Acceleration acts downward on the piston body 12 from a dead point above it to a predetermined position, and the descending speed of the piston body 12 gradually increases. At this time, the first and second compression rings 21 and 22 are kept in contact with the bottom surfaces of the upper inlet groove 12a and the middle inlet groove 12b by the gas pressure, and the oil ring 13 Since the gas pressure hardly acts on the oil ring 13, the oil ring 13 is fixed in contact with the upper surface of the lower inlet groove 12c by the inertia force.

As a result of the lowering of the piston body 12, the oil ring 13 scrapes off excess oil attached to the inner circumferential surface of the cylinder 16 to form a lubricant film having a minimum thickness required on the inner circumferential surface of the cylinder 16. The surplus oil, which is shaved by the oil ring 13 and accumulated on the bottom of the oil ring 13, has a gap between the bottom of the oil ring 13 and the bottom of the lower groove 12c and the first oil return hole as indicated by the broken arrow marks. After passing through (31), or through a second oil return hole 32, as shown by the dashed-dotted arrow, it falls to an oil pan (not shown). In addition, the oil penetrating between the two lip portions 13b and 13b of the oil ring 13 falls into the oil pan via the long hole 13c and the first oil return hole 31 as indicated by the dashed-dotted arrow. .

Next, when the piston body 12 passes the predetermined position, the acceleration acting on the piston body 12 changes upward, and the descending speed of the piston body 12 gradually decreases. At this time, the first and second compression rings 21 and 22 are fixed to the lower surfaces of the upper inlet groove 12a and the middle inlet groove 12b, respectively, and the oil ring 13 is fixed by the elastic force. Contact the bottom of the lower mouth groove (12c) (Fig. 1 (a-2)). The oil ring 13 is lowered while scraping off excess oil attached to the inner circumferential surface of the cylinder 16, and a lubricating oil film having a minimum thickness required is formed on the inner circumferential surface of the cylinder 16. As shown in FIG.

The surplus oil that is shaved by the oil ring 13 and accumulated on the bottom of the oil ring 13 passes through the second oil return hole 32 as shown by the dashed-dotted arrow, The oil penetrating the first oil return hole 31 and penetrating between the two lip portions 13b and 13b of the oil ring 13 by the inertia force is shown by the dashed line arrow. Likewise, it passes through the long hole 13c and the first oil return hole 31 to fall into the oil pan. As a result, since the surplus oil which burns with the combustion gas by reaching the 2nd compression ring 22 or the 1st compression ring 21 is eliminated, oil consumption can be reduced.

Next, when moving to the exhaust stroke (not shown), the piston body 12 rises with respect to the cylinder 16. At this time, the oil ring is formed on the inner circumferential surface of the cylinder 16 because only a lubricating oil film having the minimum thickness required is formed. The oil shaved to (13) is a little.

When the piston moves to the intake stroke, the piston body 12 descends relative to the cylinder 16. Since the gas pressure is not applied to the upper surface of the piston body 12 in the expansion stroke shown in FIG. 1 (b-1), the first and second compression rings 21 and 22 have an upper recessed groove 12a and a middle. Except for being fixed in contact with the upper surface of the concave groove 12b, respectively, the operation in the intake stroke (Figs. 1 (b-1) and (b-2)) is the expansion stroke (Fig. 1 (a-1)). And (a-2)), the repeated description is omitted.

In this embodiment, three recessed grooves are formed on the outer circumferential surface of the piston, but may be two or four or more.

In this embodiment, four first and second oil return holes are provided in the piston body, but two, three or five or more oil return holes may be provided in the piston body.

In this embodiment, the second oil return hole is provided below the return hole together with the first oil return hole, but only the first oil return hole may be formed in the piston body. In this case, if the acceleration acting on the piston body is changed upward when the piston body descends, the oil accumulated on the bottom of the oil ring acts to push up the oil ring by the inertia force, but the oil ring has a tension in close contact with the inner surface of the cylinder. Since it is working, the oil ring is never pushed up by the pushing force.

3 shows a second embodiment of the present invention. In FIG. 3, the same reference numerals as used in FIG. 1 denote the same components.

In this embodiment, the first and second oil return holes 51 and 52 are parallelly moved downwards by a predetermined distance from the first and second oil return holes of the first embodiment, respectively. It is comprised similarly to an Example. The inlet 51a of the first oil return hole 51 is located at a position where oil accumulated in the bottom of the oil ring 13 is not introduced by the seal surface formed by the oil ring 13 contacting the bottom of the lower inlet groove 12c. That is, formed from the inner surface of the lower mouth groove 12c is formed over the lower surface of the lower mouth groove 12c and is formed at a position that does not reach the bottom edge corner of the entrance portion of the lower mouth groove 12c. The inlet 52a of the 2nd oil return hole 52 is formed so that it may be located below the lower opening groove 12c by a predetermined distance. In addition, in order to smoothly draw oil accumulated in the bottom of the oil ring 13 to the second oil return hole 52 on the outer circumferential surface of the piston body 12 immediately below the lower inlet groove 12c, as in the first embodiment. A ring-shaped recess is formed that is shallower than the lower mouth groove 12c.

Since the operation of the piston of the engine configured as described above is substantially the same as in the first embodiment, the repeated description is omitted.

4 to 6 show a third embodiment of the present invention. 4 and 6, the same reference numerals as those in Figs. 1 and 2 denote the same components.

In this embodiment, two oil escape concavities 77 and 77 are provided on the outer peripheral surface of the piston body 12 instead of the second oil return hole of the first embodiment. The oil escape inlet 77 extends in the movement direction of the piston body 12 from the bottom edge of the lower body groove 12c on the outer circumferential surface of the piston body 12 over the lower end of the piston body 12 and also the lower mouth groove. It is formed shallower than the depth of 12c. In addition, in this embodiment, the oil escape inlet 77 is formed wider than the pin insertion hole 12f, and is formed on the outer circumferential surface of the piston body 12, centering on the hole wick of the pin insertion hole 12f, respectively. This is to allow the oil escape portion 77 to be removed from the mold because the piston body 12 is a cast of aluminum alloy or the like.

In the piston of the engine configured as described above, surplus oil accumulated in the bottom of the oil ring (not shown) when the piston body 12 in the expansion stroke or the intake stroke descends is the first oil return hole 31 and the oil escape inlet 77. The operation is substantially the same as that of the first embodiment except for falling through the oil escape portion 77 or only through the oil escape portion 77, and thus repeated description is omitted. In this embodiment, there is no second oil return hole in the second embodiment, and machining is unnecessary.

In this embodiment, the oil-embedded inlet is made shallower than the depth of the lower inlet groove, but the oil-covered indentation may be formed equal to the depth of the lower inlet groove.

In addition, in this embodiment, two oil-derived concave portions are formed, but three or more may be used.

In this embodiment, the oil bleeding concave portions are formed on the outer circumferential surface of the piston body centered on the hole wick of the pin insertion hole, respectively, but are not limited to these positions.

Next, the Example of this invention is described in detail with a comparative example.

(Example)

As shown in Figs. 1 and 2, 11000 cc of oil is stored in an oil pan of a diesel engine having a displacement of 7961 cc (about 8 liters) of a six-cylinder turbocharger, and the first and second oils are stored in each piston body 12. Four oil return holes 31 and 32 were provided. The hole diameters of the first and second oil return holes 31 and 32 were 3 mm and 4 mm, respectively.

(Comparative Example)

As shown in FIG.7 and FIG.8, the engine comprised similarly to the said Example was made into the comparative example except having provided four oil return holes 4 with a hole diameter of 4 mm in each piston main body 2. As shown in FIG.

Comparative test and evaluation

The engines of Examples and Comparative Examples were operated for 8 hours while the load was kept constant at 100% of the total load and the engine rotation speed was kept constant at 2700 rpm. The amount of oil remaining in each oil pan of Examples and Comparative Examples at this time was measured.

As a result, the oil amounts of Examples and Comparative Examples were 10689cc and 10476cc, respectively, and it was found that the Example consumed 41% less oil than the Comparative Example.

As described above, according to the present invention, a first oil return hole is inclined so that the piston body communicates with the lower groove of the piston body and the cone rod receiving recess, and also falls away from the top surface of the piston body toward the cone rod receiving recess in the lower roller groove. And the opening of the return hole of the first oil is formed at a position that does not reach the bottom edge of the lower mouth groove only on the inner surface of the lower mouth groove or on the inner surface of the lower mouth groove. When the piston body descends, when the acceleration acting on the piston body is downward, surplus oil accumulated on the bottom of the oil ring returns to the oil pan through the first oil return hole.

When the piston body descends, when the acceleration acting on the piston body faces upward, the oil accumulated on the bottom of the oil ring tries to move upwards than the oil ring by the inertia force, but the bottom of the oil ring is in close contact with the bottom of the lower groove. Since the oil at the bottom of the oil ring does not have a hole or a gap into the lower inlet groove, the oil does not flow back through the lower inlet groove. As a result, it is possible to reduce the oil consumption by securing the seal function of the bottom of the oil ring to eliminate excess oil that flows back to the top of the oil ring and burns with combustion gas.

In addition, a second oil return hole is provided in the piston body communicating with the piston body outer circumference lower than the lower inlet groove and the cone rod receiving recess, and the second oil return hole is accommodated in the piston body outer circumferential surface lower than the lower inlet groove. If it is formed to be inclined away from the top surface of the piston body toward the concave portion, when the piston body is lowered, the surplus oil accumulated in the oil ring bottom when the acceleration acting on the piston body is downward, the first oil return hole and the second oil The return oil is returned to the oil pan via the return hole, and when the piston body is lowered and the acceleration acting on the piston body is upward, excess oil accumulated on the bottom of the oil ring is returned to the oil pan through the second oil return hole. As a result, oil accumulated in the bottom of the oil ring can be smoothly returned to the oil pan than in the case of only the first oil return hole.

On the outer peripheral surface of the piston main body, the oil bleed indentation extends from the bottom edge of the lower inlet groove to the lower direction of the piston body in the movement direction of the piston body and is formed shallower than the depth of the lower inlet groove or equal to the depth of the lower inlet groove. In this case, when the piston body descends, when the acceleration acting on the piston body faces downward, surplus oil accumulated on the bottom of the oil ring returns to the oil pan through the first oil return hole and the oil escape recess, and the piston body descends. When the acceleration acting on the piston body is upward, excess oil accumulated at the bottom of the oil ring is returned to the oil pan through the oil escape inlet. As a result, oil accumulated in the bottom of the oil ring can be smoothly returned to the oil pan than in the case of only the first oil return hole.

Claims (3)

Piston body 12 having a plurality of ring-shaped recesses 12a, 12b, 12c formed on the outer circumference and a cone rod receiving recess 12e formed on the bottom side opposite to the top surface, and the recesses 12a, In the engine having an oil ring 13 accommodated in the lower inlet groove 12c located farthest from the top surface of the piston body 12 among the 12b, 12c, the outer peripheral surface is in contact with the inner peripheral surface of the cylinder 16, The piston communicates with the piston rod 12 in the lower groove 12c and the cone rod receiving recess 12e and toward the cone rod receiving recess 12e in the lower groove 12c. First oil return holes 31 and 51 are provided to be inclined away from the top surface of the main body 12, Inlets 31a and 51a of the first oil return holes 31 and 51 are formed only on the inner surface of the lower mouth groove 12c or on the inner side of the lower mouth groove 12c. The piston of the engine, characterized in that formed in a position not to reach the bottom edge corner portion of the lower inlet groove (12c) over the bottom surface. The method of claim 1, The piston body 12 is provided with second oil return holes 32 and 52 communicating with the outer circumferential surface of the piston body 12 below the lower inlet groove 12c and the cone rod receiving recess 12e. On the top surface of the piston body 12 as the second oil return holes 32 and 52 face the cone rod receiving recess 12e from the outer peripheral surface of the piston body 12 below the lower groove 12c. Piston of the engine, characterized in that formed to be inclined away. The method of claim 1, Extends in the direction of movement of the piston body 12 over the lower end of the piston body 12 from the bottom edge of the lower body groove 12c on the outer circumferential surface of the piston body 12 and is shallower than the depth of the lower mouth groove 12c; Or the piston of the engine, characterized in that the oil escape concave portion 77 is formed on the outer circumferential surface of the piston body 12 formed to be equal to the depth of the lower groove groove (12c).