JPH11351055A - Engine piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce oil consumption, and return excess oil depositing on the internal surface of a cylinder into an oil pan smoothly. SOLUTION: A piston body 12 having a plurality of annular grooves 12b and 12c is formed with a connecting-rod receiving recess in its lower face counter to the crown. Within the lower groove 12c most distant from the piston body crown out of those grooves, an oil ring 13 is fitted with its outside surface butting against the internal surface of a cylinder 14. The piston body 12 is further formed with a first oil return hole 31 that extends slantly downwardly from the lower groove 12c into the connecting-rod receiving recess and has a first oil return hole inlet 31a situated at the depth surface of the lower groove 12c. The piston body 12 is furthermore formed in its outside surface with an oil sump groove 12f that is spaced with specified interval downward from the lower groove 12c, as well as formed with a second oil return hole 32 that extends slantly downwardly from the oil sump groove 12f into the connecting-rod receiving recess.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston of an engine having a groove formed on an outer peripheral surface for receiving an oil ring. More specifically, the present invention relates to an engine piston having an oil return hole for returning excess oil on the inner peripheral surface of the cylinder scraped off by the oil ring to an oil pan.

[0002]

2. Description of the Related Art Conventionally, as this type of piston, as shown in FIGS. 8 and 9, three ring-shaped concave grooves 2a, 2b, 2c are formed on the outer peripheral surface of a piston body 2. A connecting rod housing concave portion 2e is formed on the lower surface opposite to the top surface of the piston 2 and a lower concave groove 2c formed at a position farthest from the top surface of the piston body 2 among these concave grooves 2a, 2b, 2c. An oil ring 3 is housed, and a configuration is known in which the outer peripheral surface of the oil ring 3 is in contact with the inner peripheral surface of the cylinder 6. This piston 1
In the embodiment, the piston body 2 is provided with an oil return hole 4 for communicating the outer peripheral surface of the piston body 2 with the connecting rod housing recess 2e. The inlet 4a of the oil return hole 4 is formed relatively large over the inner surface of the lower groove 2c, the lower surface of the lower groove 2c, and the outer peripheral surface of the piston body 2 below the lower groove 2c. The oil return hole 4 extends from the outer peripheral surface of the piston body 2 toward the connecting rod housing recess 2e.
Is formed to be inclined away from the top surface of the. 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 ring 3 and the elastic force of the coil spring 3a. Reference numeral 3c in FIG. 8 is a long hole.

In the engine piston constructed as described above, first, as shown in FIGS. 8 (a-1) and 8 (b-1), when the piston body 2 descends from the top dead center to a predetermined position, the piston A downward acceleration acts on the main body 2, that is, the descending speed of the piston main body 2 gradually increases.
At this time, the excess oil 5 scraped off by the oil ring 3 passes through a gap between the lower surface of the oil ring 3 and the lower surface of the lower groove 2c and accumulates on the rear surface of the oil ring 3 as shown by a broken arrow.

Next, when the piston body 2 passes the predetermined position, the acceleration acting on the piston body 2 changes upward, and the lowering speed of the piston body 2 gradually decreases.
When the direction of the acceleration changes, the oil ring 3 that has been in close contact with the upper surface of the lower groove 2c moves relatively downward with respect to the lower groove 2c due to its inertial force, and adheres to the lower surface of the lower groove 2c. (FIGS. 8 (a-2) and (b-2)). At this time, a part of the oil 5 accumulated on the back surface of the oil ring 3 rises as shown by a dashed line arrow through a gap between the upper surface of the oil ring 3 and the upper surface of the lower groove 2c.

On the other hand, the remainder of the oil 5 accumulated on the back of the oil ring 3 falls into an oil pan (not shown) through the oil return hole 4 as indicated by a two-dot chain line arrow due to its inertia. At this time, the oil 5 scraped off by the oil ring 3 is pushed back by the falling oil 5, and falls into the oil pan through the oil return hole 4 as shown by a broken arrow.

[0006]

However, in the above-described conventional engine piston, the oil accumulated on the back surface of the oil ring rises (backflows) through a gap between the upper surface of the oil ring and the upper surface of the lower groove. The amount of oil is relatively large (indicated by dashed-dotted arrows in FIGS. 8 (a-2) and (b-2)), and this oil is exposed to extremely high temperature combustion gas and burns, and the oil consumption is reduced There was an increasing problem. An object of the present invention is to provide an engine piston capable of reducing oil consumption and smoothly returning excess oil adhering to an inner peripheral surface of a cylinder to an oil pan.

[0007]

The invention according to claim 1 is
As shown in FIGS. 1 and 2, a plurality of ring-shaped concave grooves 12 a, 12 b, and 12 c are formed on an outer peripheral surface, and a connecting rod housing concave portion 12 e is formed on a lower surface opposite to a top surface. An oil ring 13 which is housed in a lower groove 12c formed at a position farthest from the top surface of the piston body 12 among the grooves 12a, 12b, 12c, and whose outer peripheral surface is in contact with the inner peripheral surface of the cylinder 14. It is an improvement of the engine piston. The characteristic configuration is that the piston body 12 is provided with a first oil return hole 31 which is inclined downward from the lower groove 12c and communicates with the connecting rod accommodating recess 12e, and the inlet 31a of the first oil return hole 31 is provided with the lower groove. The lower groove is formed only on the inner surface of the lower groove 12c or from the inner surface of the lower groove 12c to the lower surface of the lower groove 12c so as not to reach the lower edge corner of the lower groove 12c. An oil sump groove 12f is formed downward at a predetermined distance from the oil sump groove 12c in parallel with the lower groove 12c, and the piston body 12 is inclined downward from the oil sump groove 12f and communicates with the connecting rod housing recess 12e.
This is where the oil return hole 32 is provided.

The piston of the engine according to the first aspect is provided between the lower groove 12c and the oil reservoir groove 12f when the piston body 12 is lowered, such as during the expansion stroke and the intake stroke of the engine. The ridge 12h scrapes off most of the oil adhering to the inner peripheral surface of the cylinder 14, and further removes excess oil from the oil that has passed between the outer peripheral surface of the ridge 12h and the inner peripheral surface of the cylinder 14.
As a result, the lubricating oil film having a required minimum thickness is formed on the inner peripheral surface of the cylinder 14. Excess oil scraped off by the ridge 12h falls into the oil pan through the oil sump groove 12f and the second oil return hole 32. Excess oil scraped off by the oil ring 13 passes through the gap between the lower surface of the oil ring 13 and the lower surface of the lower concave groove 12c and goes around the back surface of the oil ring 13, but the amount of the oil is extremely small.

Next, when the piston main body 12 passes the predetermined position, the acceleration acting on the piston main body 12 changes upward, and the lowering speed of the piston main body 12 gradually decreases. When the direction of the acceleration changes, the oil ring 13 that has been in close contact with the upper surface of the lower groove 12c moves relatively downward with respect to the lower groove 12c due to its inertial force, and adheres to the lower surface of the lower groove 12c. I do. At this time, oil ring 1
Part of the oil accumulated on the back surface of the oil ring 13 flows upward through the gap between the upper surface of the oil ring 13 and the upper surface of the lower groove 12c, and the remaining oil accumulated on the back surface of the oil ring 13 is caused by its inertia. It falls into the oil pan through the first oil return hole 31. As a result, the amount of oil flowing backward is extremely small, so that the amount of oil consumed by combustion can be reduced.

According to a second aspect of the present invention, as shown in FIGS. 3 and 4, the piston body 42 is inclined downward from the lower groove 42c to communicate with the connecting rod accommodating recess 42e.
An oil return hole 51 is provided, and a ring-shaped oil sump groove 42f is formed at a position on the upper surface of the lower groove 42c that does not reach the upper edge corner of the lower groove 42c. In the piston of the engine according to the second aspect, when the piston body 42 descends with respect to the cylinder 14, first, a downward acceleration acts on the piston body 42 from the top dead center to a predetermined position. Ring 1
3 descends by its inertia force in a state of being in close contact with the upper surface of the lower concave groove 42c. As a result, the oil 15 scraped off by the oil ring 13 passes through the gap between the lower surface of the oil ring 13 and the lower surface of the lower concave groove 42c, and the oil accumulation groove 42
accumulate in f. Next, when the piston main body 42 passes the predetermined position, the acceleration acting on the piston main body 42 changes upward, so that the oil ring 13 moves downward relative to the lower concave groove 42c due to its inertia force. It is in close contact with the lower surface of the lower concave groove 42c. As a result, the oil sump groove 4
Although the oil 15 overflowing from 2f flows upward through the gap between the upper surface of the oil ring 13 and the upper surface of the lower concave groove 42c, the amount thereof is small, so that the consumption of the oil 15 due to combustion can be reduced.

According to a third aspect of the present invention, as shown in FIGS. 5 to 7, a first oil return hole 71 is provided in the piston main body 62 so as to be inclined downward from the lower concave groove 62c and communicate with the connecting rod housing concave portion. The inlet 71 of the first oil return hole 71
a is only on the inner surface of the lower groove 62c or the lower groove 62c
From the inner surface of the lower groove 62c to the lower surface of the lower groove 62c.
The oil sump groove 62 is formed at a position not reaching the lower edge corner portion of the piston main body 62 and at a predetermined interval from the lower groove 62c on the outer peripheral surface of the piston body 62 and in parallel with the lower groove 62c.
f is formed, and the oil sump groove 62 f is
2 It is characterized in that it is formed so as to communicate with the oil escape recess 62g formed on the outer peripheral surface.

In the piston of the engine according to the third aspect, when the piston body 62 is lowered, the lower groove 62 is formed.
ridge 62 provided between c and oil sump groove 62f
m scrapes off most of the oil adhering to the inner peripheral surface of the cylinder 14, and the scraped excess oil passes through the oil sump groove 62f and accumulates in the oil escape recess 62g. The oil collected in the oil escape recess 62g falls into the oil pan when the lower portion of the oil escape recess 62g projects downward from the lower end of the cylinder 14. The operation other than the above is the same as that of the first aspect.

The invention according to a fourth aspect is the invention according to the third aspect. As shown in FIGS. 6 and 7, the oil escape recess 62g has a piston pin hole 62j of the piston main body 62 and a piston pin hole 62j. 62h formed by the end face of the piston pin 66 inserted into the piston body 66 or the piston body 6
2 It is characterized by being one or both of the meat stealing portions 62i formed on the outer peripheral surface. In the engine piston according to the fourth aspect, since it is not necessary to newly machine the oil escape recess 62g, the number of machining steps can be reduced.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. As shown in FIGS. 1 and 2, a piston 11 of a diesel engine includes a piston body 12 having a plurality of ring-shaped concave grooves 12a, 12b, 12c formed on an outer peripheral surface thereof. And an oil ring 13 housed in a lower groove 12c formed at a position farthest from the top surface of the piston body 12. A combustion chamber 12d is formed on the top surface of the piston body 12, and a connecting rod housing recess 12e is formed on the lower surface (FIG. 2). Although not shown, the upper end of the connecting rod is inserted into the connecting rod accommodating recess 12e, and the upper end of the connecting rod is pivotally attached to the piston body 12 via a piston pin (not shown).

In this embodiment, the number of the grooves 12a, 12b, and 12c is three. In addition to the lower groove 12c, the upper groove 12a formed at a position closest to the top surface of the piston body 12. And a middle groove 12b formed between the upper groove 12a and the lower groove 12c (FIGS. 1 and 2). The first and second compression rings 21, 21 are provided in the upper groove 12a and the middle groove 12b.
22 are accommodated, and these compression rings 21 and 22 are connected to the expansion stroke of the engine (FIG. 1 (a-1)).
And (a-2)) and a function of keeping the gas tightness in the combustion chamber 12d in the compression stroke (not shown).

A coil spring 13a is mounted on the inner peripheral surface of the oil ring 13, and two lip portions 13b and 13c are provided on the outer peripheral surface to contact the inner peripheral surface of the cylinder 14 (FIG. 1). A plurality of long holes 13d extending in the longitudinal direction of the oil ring 13 are formed between these lip portions 13b and 13c. The oil ring 13 is configured to be brought into close contact with the inner peripheral surface of the cylinder 14 with a predetermined tension by the elastic force of the 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 peripheral surface of the cylinder 14 from entering the combustion chamber 12d and burning, and forming a minimum necessary oil film on the inner peripheral surface of the cylinder 14.

The piston body 12 has a first oil return hole 31 communicating the lower groove 12c and the connecting rod accommodating recess 12e (FIG. 2), and a predetermined distance from the lower groove 12c on the outer peripheral surface of the piston body 12. And an oil sump groove 12f formed parallel to the lower concave groove 12c, and a second oil return hole 32 communicating the oil sump groove 12f and the connecting rod accommodating recess 12e. The first oil return hole 31 is inclined downward from the lower groove 12c and communicates with the connecting rod accommodating recess 12e (FIG. 2).
As shown in FIG. 3C, it is formed so as to be inclined away from the top surface of the piston main body 12 toward the connecting rod accommodating recess 12e. The inlet 31a (FIG. 1) of the first oil return hole 31 is formed only on the inner surface of the lower groove 12c.

The second oil return hole 32 is inclined downward from the oil sump groove 12f so as to be inclined downward.
e (FIG. 2), that is, it is formed to be inclined away from the top surface of the piston body 12 as it goes from the oil reservoir groove 12f to the connecting rod housing recess 12e. The inlet 32a (FIG. 1) of the second oil return hole 32 is provided with an oil sump groove 12f and the piston body 12 below the groove 12f.
It is formed over the outer peripheral surface. In this embodiment, ten and six first and second oil return holes 31 and 32 are provided in the piston body 12, respectively. Further, the lower groove 12c and the oil sump groove 1 are formed by forming the oil sump groove 12f.
Skirt land 12g of piston body 12 between 2f
Of the piston main body 12 between the upper groove 12a (FIG. 2) and the middle groove 12b, and the middle groove 12b. The outer peripheral surface of the ridge 12h is formed very close to the inner peripheral surface of the cylinder 14.

The operation of the piston 11 of the engine configured as described above will be described. In the expansion stroke shown in FIG. 1 (a-1), fuel burns in the combustion chamber 12d and the pressure in the combustion chamber 12d sharply increases, so that the gas pressure pushes down the piston body 12. At this time, the piston body 12 slightly expands due to the gas pressure, and a side pressure acts on the oil attached to the inner peripheral surface of the cylinder 14. A downward acceleration acts on the piston body 12 from its top dead center 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 close contact with the lower surfaces of the upper groove 12a and the middle groove 12b by the gas pressure, and the gas pressure hardly acts on the oil ring 13. The oil ring 13 is kept in close contact with the upper surface of the lower groove 12c by its inertia.

When the piston body 12 is lowered, the protruding ridges 12h approaching the inner peripheral surface of the cylinder 14 immediately below the lower groove 12c.
Scrapes most of the oil adhering to the inner peripheral surface of the cylinder 14, and the oil ring 13 scrapes excess oil out of the oil that has passed between the outer peripheral surface of the ridge 12 h and the inner peripheral surface of the cylinder 14. Thereby, a lubricating oil film having a minimum necessary thickness is formed on the inner peripheral surface of the cylinder 14. Ridge 12h
The excess oil scraped off by the oil storage groove 12f and the second oil accumulation groove 12f as shown by the two-dot chain line arrow in FIG.
It falls into the oil pan through the oil return hole 32. The excess oil scraped off by the oil ring 13 passes through the gap between the lower surface of the oil ring 13 and the lower surface of the lower groove 12c as shown by the dashed arrow, and goes around to the back of the oil ring 13. Very few.

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. When the direction of this acceleration changes, the upper groove 12
The first and second compression rings 21 and 22 which have been in close contact with the lower surfaces of the lower groove 12a and the middle groove 12b, respectively, are kept in close contact with the lower surfaces of the upper groove 12a and the middle groove 12b, respectively. Groove 12
The oil ring 13 that has been in close contact with the upper surface of c moves downward relative to the lower groove 12c due to its inertia force,
It is in close contact with the lower surface of the lower concave groove 12c (FIG. 1 (a-2)).
At this time, a part of the oil accumulated on the back surface of the oil ring 13 passes through a gap between the upper surface of the oil ring 13 and the upper surface of the lower groove 12c as shown by a dashed line, and rises toward the second compression ring 22, The remaining oil remaining on the back surface of the oil ring 13 falls into the oil pan through the first oil return hole 31 as indicated by the dashed arrow due to its inertial force. As a result, the second compression ring 2
Since the amount of oil rising toward 2 is very small,
Oil consumption can be reduced.

Next, when the process proceeds to the exhaust stroke (not shown),
The piston body 12 rises with respect to the cylinder 14,
At this time, since only the necessary minimum thickness of the lubricating oil film is formed on the inner peripheral surface of the cylinder 14, the excess oil scraped off by the oil ring 13 is small. When the process further shifts to the intake stroke, the piston body 12 moves down with respect to the cylinder 14. Since no gas pressure is applied to the upper surface of the piston body 12 in the expansion stroke shown in FIG.
The second compression rings 21 and 22 are kept in close contact with the upper surfaces of the upper concave groove 12a and the middle concave groove 12b, respectively, except that the side pressure due to the swelling of the piston body 12 does not act on the oil. The operations in FIGS. 1 (b-1) and (b-2) are the same as those in the above-described expansion stroke (FIGS. 1 (a-1) and (a-2)), and therefore, repeated description will be omitted.

FIGS. 3 and 4 show a second embodiment of the present invention. 3 and 4, the same reference numerals as those in FIGS. 1 and 2 indicate the same parts. In this embodiment, the piston body 42 is provided with a first oil return hole 51 communicating the lower concave groove 42c and the connecting rod housing concave portion 42e, and an oil reservoir groove 42f formed on the upper surface of the lower concave groove 42c.
The first oil return hole 51 is inclined downward from the lower groove 42c and communicates with the connecting rod accommodating recess 42e. That is, the first oil return hole 51 is inclined away from the top surface of the piston main body 42 as going from the lower groove 42c to the connecting rod accommodating concave 42e. Provided. The inlet 51a of the first oil return hole 51 is formed relatively large over the inner surface, the bottom surface of the lower groove 42c, and the outer peripheral surface of the piston body 42 below the lower groove 42c. A chamfer 42 g is formed in the lower edge corner of the lower groove 42 c to smoothly guide the oil 15 accumulated on the lower surface of the oil ring 13 to the first oil return hole 51. Here, the lower edge corner portion of the lower concave groove 42c refers to the lower corner portion of the upper and lower corner portions at the mouth of the lower concave groove 42c. In this embodiment, the oil sump groove 42f is formed in a ring shape along the upper surface of the lower concave groove 42c deep inside the upper surface of the lower concave groove 42c. Here, the upper edge corner portion of the lower concave groove 42c refers to the upper corner portion of the upper and lower corner portions at the mouth of the lower concave groove 42c. In this embodiment, four first oil return holes 51 are provided in the piston body 42.

The operation of the piston 41 of the engine configured as described above will be described. In the expansion stroke shown in FIG. 3 (a-1), fuel burns in the combustion chamber 42d and the pressure in the combustion chamber 42d sharply increases, so that the gas pressure pushes down the piston body 42. A downward acceleration acts on the piston main body 42 from the top dead center to a predetermined position, and the descending speed of the piston main body 42 gradually increases. At this time, the first and second compression rings 2
1 and 22 are kept in close contact with the lower surfaces of the upper groove 42a and the middle groove 42b, respectively.
Since the above gas pressure hardly acts on the oil ring 1
3 is kept in close contact with the upper surface of the lower concave groove 42c due to its inertial force. The lowering of the piston body 42 causes the oil ring 13 to scrape off excess oil 15 adhering to the inner peripheral surface of the cylinder 14, thereby forming a lubricating oil film having a required minimum thickness on the inner peripheral surface of the cylinder 14. The excess oil 15 scraped off by the oil ring 13 passes through the gap between the lower surface of the oil ring 13 and the lower surface of the lower concave groove 42c and wraps around the rear surface of the oil ring 13 as shown by a broken arrow, and the oil accumulation groove It accumulates at 42f and its pressure rises.

Next, when the piston main body 42 passes the predetermined position, the acceleration acting on the piston main body 42 changes upward, and the descending speed of the piston main body 42 gradually decreases. When the direction of the acceleration changes, the upper groove 42
The first and second compression rings 21 and 22 that have been in close contact with the lower surfaces of the upper and lower grooves 42a and 42b, respectively, are maintained in close contact with the lower surfaces of the upper and middle grooves 42b, respectively. Groove 42
The oil ring 13 which has been in close contact with the upper surface of c moves downward relative to the lower groove 42c due to its inertia force,
It is in close contact with the lower surface of the lower concave groove 42c (FIG. 3A-2).
At this time, the oil 15 overflowing from the oil sump groove 42f passes through a gap between the upper surface of the oil ring 13 and the upper surface of the lower concave groove 42c, and rises toward the second compression ring 22 as indicated by an alternate long and short dash line arrow. However, since the amount of the oil 15 is small, the consumption of the oil 15 by combustion can be reduced. On the other hand, the oil 15 accumulated in the oil sump groove 42f falls into the oil pan through the first oil return hole 51 as indicated by the two-dot chain line arrow due to its inertia force. At this time, the oil 15 scraped off by the oil ring 13 is pushed back by the oil 15 falling from the oil reservoir groove 42f, and falls into the oil pan through the first oil return hole 51 as shown by a broken arrow.

Next, when the process proceeds to the exhaust stroke (not shown),
The piston body 42 rises with respect to the cylinder 14,
At this time, since only the necessary minimum thickness of the lubricating oil film is formed on the inner peripheral surface of the cylinder 14, the extra oil 15 scraped off by the oil ring 13 is small. When the process further shifts to the intake stroke, the piston body 42 descends with respect to the cylinder 14. Since gas pressure is not applied to the upper surface of the piston main body 42 in the expansion stroke shown in FIG.
Except that the first and second compression rings 21 and 22 are kept in close contact with the upper surfaces of the upper groove 42a and the middle groove 42b, respectively, this intake stroke (FIGS. 3 (b-1) and 3 (b)). The operation in -2)) is the same as the expansion stroke (FIGS. 3 (a-1) and (a-2)), and a repeated description will be omitted.

FIGS. 5 to 7 show a third embodiment of the present invention. 5 to 7, the same reference numerals as those in FIGS. 1 and 2 indicate the same parts. In this embodiment, the piston body 61
Has a lower groove 62c and a connecting rod receiving recess (not shown).
A first oil return hole 71 that communicates with the piston body 6
An oil sump groove 62f formed in parallel with the lower groove 62c at a predetermined distance from the lower groove 62c is provided on the outer peripheral surface of the lower groove 2c. The first oil return hole 71 is downwardly inclined from the lower groove 62c and communicates with the connecting rod accommodating recess. That is, the first oil return hole 71 is formed so as to be inclined away from the top surface of the piston body 62 as going from the lower groove 62c to the connecting rod accommodating concave. Is done. The inlet 71a (FIG. 5) of the first oil return hole 71 is formed at a position extending from the inner surface to the lower surface of the lower groove 62c so as not to reach the lower edge corner of the lower groove 62c. Here, the lower edge corner portion of the lower groove 62c refers to the upper corner portion of the upper and lower corner portions at the mouth of the lower groove 62c. In this embodiment, ten first oil return holes 71 are provided in the piston main body 62.

The oil sump groove 62f is provided with an oil escape recess 62g (FIG. 6) formed on the outer peripheral surface of the piston body 62.
And FIG. 7). In this embodiment, the oil relief recess 62g is provided with the piston body 6.
A depression 62 formed by the piston pin hole 62j and the end face of the piston pin 66 inserted into the hole 62j.
h (FIG. 7), and a meat robbing portion 62i (FIGS. 6 and 7) formed on the outer peripheral surface of the piston main body 62.

Further, by the formation of the oil sump groove 62f, a ring-shaped ridge 62m (FIGS. 5 and 6) forming a part of the skirt land 62k of the piston body 62 is provided between the lower concave groove 62c and the oil sump groove 62f. This ridge 6 is provided
The outer diameter of 2 m corresponds to the outer diameter of the piston body 62 between the upper groove 62a (FIG. 6) and the middle groove 62b (FIGS. 5 and 6) and the outer diameter of the piston body 62 between the middle groove 62b and the lower groove 62c. It is formed larger than the outer diameter.
The outer peripheral surface of 2 m is formed very close to the inner peripheral surface of the cylinder 14.

In the piston 61 of the engine configured as described above, when the piston body 62 descends, the lower concave groove 62
The ridge 62m adjacent to the inner peripheral surface of the cylinder 14 immediately below c scrapes off most of the oil adhering to the inner peripheral surface of the cylinder 14, and the excess oil that has been scraped off is indicated by a two-dot chain line arrow in FIG. After the oil accumulates in the oil sump groove 62f, the oil escape recess 62g as shown by the two-dot chain line arrow in FIG.
Is accumulated in the recess 62h and the meat steal part 62i. Depression 6
2h and the oil accumulated in the meat stealing part 62i
In addition, the lower part of the meat steal part 62i protrudes downward from the lower end of the cylinder 14, and falls into the oil pan. Operations other than those described above are substantially the same as those in the first embodiment, and thus, repeated description will be omitted.

In the first to third embodiments,
Although three concave grooves are formed on the outer peripheral surface of the piston body, two or four or more concave grooves may be provided. In the first embodiment, the first
And ten and six oil return holes are provided in the piston body, respectively. In the second embodiment, four first oil return holes are provided in the piston body, and in the third embodiment, the first oil return hole is provided in the piston body.
Although ten return holes are provided in the piston main body, these oil return holes are not limited to the above number. Also,
In the first embodiment, the inlet of the first oil return hole is formed only on the inner surface of the lower groove, but the lower oil groove is formed by connecting the inlet of the first oil return hole from the inner surface of the lower groove to the lower surface of the lower groove. The groove may be formed at a position that does not reach the lower edge corner portion of the groove.

In the second embodiment, the oil sump groove is formed deep inside the upper surface of the lower groove. However, the position is not limited to the above position as long as it does not reach the upper edge corner of the upper surface of the lower groove. Further, in the third embodiment, the inlet of the first oil return hole is formed from the inner surface of the lower groove to the lower surface of the lower groove, but the inlet of the first oil return hole is formed only on the inner surface of the lower groove. May be formed. Further, in the third embodiment,
The oil escape recess is formed as both a dent formed by the piston pin hole of the piston body and the end face of the piston pin inserted into this hole, and a meat pit formed on the outer peripheral surface of the piston body. Any one of the meat stealing portions may be used.

[0033]

Next, examples of the present invention will be described in detail together with comparative examples. <Example 1> 11 liters of oil was stored in an oil pan of a diesel engine with a 6-cylinder turbocharger having a displacement of about 8 liters. As shown in FIGS. 1 and 2, each of the piston bodies 12 of the engine is provided with ten first oil return holes 31 that communicate the lower concave groove 12c and the connecting rod housing concave part 12e, and a predetermined oil return hole 31 is provided below the lower concave groove 12c. An oil sump groove 12f was formed at intervals, and six second oil return holes 32 communicating the oil sump groove 12f and the connecting rod housing recess 12e were provided. The hole diameters of the first and second oil return holes 31 and 32 are 3 mm and 5 mm, respectively.
The depth and width of the oil reservoir groove 12f were 1 mm and 3.5 mm, respectively. This engine was designated as Example 1.

Comparative Example 1 As shown in FIGS. 8 and 9,
Each piston body 2 was provided with four oil return holes 4 each having a hole diameter of 4 mm communicating the lower concave groove 2c and the connecting rod receiving concave portion 2e, but the oil sump groove and the second oil return hole of the first embodiment were not formed. Except for the above, the configuration was the same as that of the first embodiment. This engine was designated as Comparative Example 1.

<Comparative Tests and Evaluations> After the engines of Example 1 and Comparative Example 1 were operated for 14 hours with the load kept constant at 100% of the full load and the engine speed kept constant at 2700 rpm, Then, the engine was stopped, and the reduced oil amount in each oil pan of Example 1 and Comparative Example 1 was measured. As a result, the reduced oil amount of Example 1 was 750 cc, whereas the reduced oil amount of Comparative Example 1 was 950 cc, and the oil consumption of Example 1 was about 20% less than that of Comparative Example 1. % Reduction.

[0036]

As described above, according to the present invention, the piston body is provided with the first oil return hole communicating from the lower groove to the connecting rod receiving recess, and the inlet of the first oil return hole is formed by the lower groove. A second oil return hole formed at a position not reaching the lower edge corner portion, an oil reservoir groove formed below the lower concave groove on the outer peripheral surface of the piston main body, and further connected to the piston main body from the oil reservoir groove to the connecting rod receiving concave portion. Is provided, the projection between the lower concave groove and the oil reservoir groove scrapes off most of the oil attached to the inner peripheral surface of the cylinder when the piston body is lowered. As a result, the surplus oil scraped off by the oil ring is extremely small, and passes through the gap between the lower surface of the oil ring and the lower surface of the lower groove to reach the back surface of the oil ring. Next, when the piston body passes the predetermined position, the acceleration acting on the piston body changes upward, and the oil ring that has been in close contact with the upper surface of the lower groove closely adheres to the lower surface of the lower groove by its inertia. . At this time, part of the oil accumulated on the back of the oil ring flows back upward through the gap between the upper surface of the oil ring and the upper surface of the lower groove, and the rest of the oil accumulated on the back of the oil ring is due to its inertia. It falls into the oil pan through the first oil return hole. As a result, the amount of oil flowing backward is extremely small, so that the amount of oil consumed by combustion can be reduced.

Further, if a first oil return hole is provided in the piston body to communicate from the lower groove to the connecting rod accommodating recess, and an oil sump groove is formed on the upper surface of the lower groove so as not to reach the upper edge corner portion of the lower groove. During the downward movement of the piston body, a downward acceleration acts on the piston body from the top dead center to a predetermined position, and the oil ring descends in a state of being in close contact with the upper surface of the lower groove by its inertial force. As a result, the oil scraped by the oil ring passes through a gap between the lower surface of the oil ring and the lower surface of the lower groove, and accumulates in the oil accumulation groove. Next, when the piston body passes the predetermined position,
Since the acceleration acting on the piston body changes upward,
The oil ring moves relatively downward with respect to the lower groove due to its inertia force and comes into close contact with the lower surface of the lower groove. As a result, the oil that overflows from the oil reservoir groove flows upward through the gap between the upper surface of the oil ring and the upper surface of the lower concave groove, but the amount is small, so that the amount of oil consumed by combustion can be reduced. .

The inlet of the first oil return hole is formed at a position which does not reach the lower edge corner of the lower groove, and the oil reservoir groove formed below the lower groove is formed on the outer peripheral surface of the piston body. If formed so as to communicate with the escape recess, the oil accumulated in the oil escape recess through the oil sump groove falls into the oil pan by projecting the lower portion of the oil escape recess downward from the lower end of the cylinder.
The same effects as above can be obtained. Further, if the oil escape recess is any one or both of a recess formed by the piston pin hole and the end face of the piston pin inserted into this hole, and / or a hollow portion formed on the outer peripheral surface of the piston body, Since the oil relief recess does not need to be machined, the number of working steps can be reduced.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a part A in FIG. 2 showing an expansion stroke and an intake stroke of a four-stroke engine according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a main part of an engine including the piston.

FIG. 3 is an enlarged sectional view of a portion B in FIG. 4 showing a second embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of a main part of an engine including the piston.

FIG. 5 is an enlarged sectional view of a part C in FIG. 6 showing a third embodiment of the present invention.

FIG. 6 is a side view of a main part of the piston.

FIG. 7 is a sectional view taken along line DD of FIG. 6;

FIG. 8 is an enlarged sectional view of a portion E of FIG. 9 showing a conventional example.

FIG. 9 is a longitudinal sectional view of a main part of an engine including the piston.

[Description of Signs] 11, 41, 61 Piston 12, 42, 62 Piston body 12a, 42a, 62a Upper concave groove 12b, 42b, 62b Middle concave groove 12c, 42c, 62c Lower concave groove 12e, 42e Connecting rod housing concave part 12f, 42f, 62f Oil reservoir groove 13 Oil ring 14 Cylinder 31, 51, 71 First oil return hole 31a, 71a Inlet of first oil return hole 32 Second oil return hole 62g Oil escape recess 62h Recess 62i Meat steal portion 62j Piston pin Hole 66 Piston pin

Claims (4)

[Claims] 1. A plurality of ring-shaped concave grooves (12a, 12a)
(b, 12c) is formed and a connecting rod housing recess (12e) is formed on the lower surface opposite to the top surface, and the piston body (12a, 12b, 12c) of the plurality of grooves (12a, 12b, 12c). In an engine piston provided with an oil ring (13) which is housed in a lower concave groove (12c) formed at a position farthest from the top surface of the cylinder (12) and whose outer peripheral surface is in contact with the inner peripheral surface of the cylinder (14), The piston body (12) is provided with a first oil return hole (31) inclined downward from the lower groove (12c) and communicating with the connecting rod housing recess (12e), wherein the first oil return hole (31) is provided. ) Entrance (31a) is the lower groove
(12c) only, or formed at a position that does not reach the lower edge corner of the lower groove (12c) from the inner surface of the lower groove (12c) to the lower surface of the lower groove (12c). An oil sump groove (12f) is formed on an outer peripheral surface of the piston body (12) at a predetermined distance from the lower groove (12c) and parallel to the lower groove (12c), and the piston body An engine piston, wherein a second oil return hole (32) is provided in (12), which is inclined downward from the oil sump groove (12f) and communicates with the connecting rod housing recess (12e). 2. A plurality of ring-shaped concave grooves (42a, 42a)
(b, 42c) is formed and a connecting rod housing recess (42e) is formed on the lower surface opposite to the top surface, and the piston body (42) of the plurality of grooves (42a, 42b, 42c). An oil piston (13) housed in a lower concave groove (42c) formed at a position farthest from the top surface of (42) and having an oil ring (13) whose outer peripheral surface is in contact with the inner peripheral surface of the cylinder (14). The piston body (42) is provided with a first oil return hole (51) which is inclined downward from the lower groove (42c) and communicates with the connecting rod housing recess (42e), and an upper surface of the lower groove (42c). A ring-shaped oil sump groove (42f) at a position not reaching the upper edge corner of the lower concave groove (42c).
A piston for an engine, wherein a piston is formed. 3. A plurality of ring-shaped grooves (62a, 62
b, 62c) is formed and a piston body (62) in which a connecting rod receiving recess is formed on the lower surface opposite to the top surface, and the plurality of concave grooves
Of the (62a, 62b, 62c), the oil which is accommodated in the lower groove (62c) formed at the position farthest from the top surface of the piston body (62) and whose outer peripheral surface abuts the inner peripheral surface of the cylinder (14) Ring (1
3), the piston body (62) is provided with a first oil return hole (71) inclined downward from the lower groove (62c) and communicating with the connecting rod housing recess, The inlet (71a) of the first oil return hole (71) is connected to the lower groove.
(62c) only, or from the inner surface of the lower groove (62c) to the lower surface of the lower groove (62c), at a position not reaching the lower edge corner of the lower groove (62c). An oil sump groove (62f) is formed on an outer peripheral surface of the piston body (62) at a predetermined interval from the lower groove (62c) and in parallel with the lower groove (62c), and the oil sump is formed. An engine piston characterized in that a groove (62f) is formed so as to communicate with an oil relief recess (62g) formed on the outer peripheral surface of the piston body (62). 4. The piston body has an oil escape recess (62 g).
The recess (62) formed by the piston pin hole (62j) of (62) and the end face of the piston pin (66) inserted into this hole (62j).
The engine piston according to claim 3, wherein the piston is one or both of h) and a steal part (62i) formed on an outer peripheral surface of the piston body (62).