JP6992350B2 - Internal combustion engine piston - Google Patents

Description

The present invention relates to a piston of an internal combustion engine mounted on a vehicle.

In an internal combustion engine mounted on a vehicle, a piston structure having a groove (ring groove) provided in the circumferential direction and a hole (oil drain hole) formed in the radial direction is known (see Patent Document 1). For example, three ring grooves are formed in the piston, and three piston rings (two compression rings and one oil ring) are mounted on each ring groove, one for each. The oil drain hole has openings at both ends. The opening on one end side opens to the back surface side (internal space) of the piston, and the opening on the other end side includes the bottom of the oil ring groove in which the oil ring is mounted, or the bottom and wall of the oil ring groove. Open.

For example, in the intake process in which the piston descends, the engine oil adhering to the inner surface (liner) of the cylinder (hereinafter referred to as liner adhering oil) is scraped from above to below by the oil ring. The scraped liner-adhered oil is guided from the oil drain hole to the back surface side (internal space) of the piston and returned to the oil pan. As a result, the oil adhering to the liner is suppressed from flowing into the combustion chamber, and the oil consumption is reduced. The piston also descends in the combustion (expansion) process. In this case, since the combustion gas spreads downward, the scraped liner-adhered oil is pushed downward and is difficult to flow into the combustion chamber.

Also, the unburned fuel that was not burned in the combustion chamber has a lower viscosity than the liner-adhered oil. Therefore, when unburned fuel is mixed with the liner-adhered oil, the viscosity of the mixed oil is lowered, which tends to cause deterioration of the friction of the piston. Therefore, in each of the compression, combustion (expansion), and exhaust steps other than the intake step, it is preferable to positively induce the unburned fuel into the oil drain hole.

Japanese Unexamined Patent Publication No. 11-236853

As described above, by providing the oil drain hole, the liner-adhered oil can be guided from the oil drain hole to the back surface side (internal space) of the piston in the intake step. In particular, when the oil drain hole is configured to include the bottom portion and the wall portion of the oil ring groove, the opening on the oil ring groove side of the oil drain hole is always greatly opened regardless of the position of the oil ring in the oil ring groove. It will be in the state of being done. Therefore, it is possible to more reliably guide the liner-adhered oil to the back surface side of the piston in the intake step. However, on the other hand, in each process of compression, combustion (expansion), and exhaust, the opening of the oil drain hole on the oil ring groove side between the skirt portion of the piston and the inner surface of the cylinder (hereinafter referred to as a sliding gap). There is a problem of promoting the infiltration of unburned fuel into the engine.

The present invention has been made based on this, and an object thereof is to guide the liner-adhered oil to the back surface side (internal space) of the piston in the intake process, and in each process of compression, combustion (expansion), and exhaust. It is an object of the present invention to provide a piston of an internal combustion engine capable of guiding unburned fuel to the back surface side of the piston and guiding oil adhering to a liner to a sliding gap.

The piston of the internal combustion engine of the present invention has a ring groove that is continuous in an annular shape along the circumferential direction, an oil ring that is mounted on the ring groove and scrapes off oil adhering to the inner surface of the cylinder of the internal combustion engine, and a scraping on the oil ring. It has a drain structure that guides the oil and unburned fuel. In such a piston of an internal combustion engine, the drain structure has openings at both ends, and the first one penetrates the piston in the radial direction so that one end opens on the back surface side of the piston and the other end opens on the groove bottom of the ring groove. A second drain that is adjacent to the drain portion and the groove wall near the bottom dead center of the piston in the ring groove, is recessed along the radial direction from the outer peripheral portion of the piston, and opens to the outer peripheral portion and the groove wall of the piston, respectively. It has a part. The opening at the other end of the first drain portion is arranged within the range of the groove bottom. The radial depth of the piston of the second drain portion is set to be shallower than the radial depth of the piston of the ring groove.

The oil ring has an oil film control member that scrapes off the oil adhering to the inner surface of the cylinder to keep the oil film on the inner surface of the cylinder in an appropriate state, and a contact pressure adjusting member that adjusts the contact pressure of the oil film control member with respect to the inner surface of the cylinder. Be prepared. In the radial direction of the piston, the position of the deepest portion of the second drain portion coincides with the inner peripheral position of the oil film control member mounted in the ring groove concentrically with the piston.

The opening at the other end of the first drain portion and the opening located at the outer peripheral portion of the piston of the second drain portion are arranged so that their positions in the circumferential direction of the piston are offset. Alternatively, the opening at the other end of the first drain portion and the opening located at the outer peripheral portion of the piston of the second drain portion are arranged so as to coincide with each other in the circumferential direction of the piston.

Further, the opening located on the outer peripheral portion of the piston of the second drain portion may have a larger opening area than the opening at the other end of the first drain portion.

According to the present invention, the liner-adhered oil is guided to the back surface side (internal space) of the piston in the intake process, and the unburned fuel is guided to the back surface side of the piston in each of the compression, combustion (expansion), and exhaust processes. At the same time, it is possible to realize a piston of an internal combustion engine capable of guiding the liner-adhered oil to the sliding gap.

The schematic diagram which shows the whole structure of the piston of the internal combustion engine which concerns on embodiment of this invention. The schematic diagram (intake step) for demonstrating the drain structure in the piston of the internal combustion engine which concerns on embodiment of this invention. The schematic diagram (compression step, combustion (expansion) step, and exhaust step) for explaining the drain structure in the piston of the internal combustion engine which concerns on embodiment of this invention. FIG. 2 is a partially enlarged view. FIG. 3 is a partially enlarged view. The schematic diagram which shows the 1st example of the arrangement of the 1st drain part and the 2nd drain part in the ring groove (third ring groove) of the piston of the internal combustion engine which concerns on embodiment of this invention. The schematic diagram which shows the 2nd example of the arrangement of the 1st drain part and the 2nd drain part in the ring groove (third ring groove) of the piston of the internal combustion engine which concerns on embodiment of this invention. The schematic diagram which shows the 3rd example of the arrangement of the 1st drain part and the 2nd drain part in the ring groove (third ring groove) of the piston of the internal combustion engine which concerns on embodiment of this invention. FIG. 6 is a schematic diagram showing a fourth example of arrangement of a first drain portion and a second drain portion in a ring groove (third ring groove) of a piston of an internal combustion engine according to an embodiment of the present invention.

Hereinafter, the piston of the internal combustion engine according to the embodiment of the present invention (hereinafter, simply referred to as a piston) will be described with reference to FIGS. 1 to 9.

FIG. 1 schematically shows the overall configuration of the piston 1. The piston 1 reciprocates between the top dead center and the bottom dead center in the cylindrical cylinder 2. In the following description, the reciprocating direction of the piston 1 is the vertical direction, the top dead center is the top, and the bottom dead center is the bottom. One end of a connecting rod 3 is connected to the piston 1 via a piston pin 4. The other end of the connecting rod 3 is connected to a crank shaft (not shown). When the piston 1 reciprocates, the crank shaft rotates via the connecting rod 3. The cylinder 2 has a combustion chamber 21 between the top portion 1a of the piston 1 and the lower surface portion of the cylinder head (not shown).

As shown in FIG. 1, a ring groove 5 continuously formed in an annular shape along the circumferential direction is formed in the outer peripheral portion 1b of the piston 1. A piston ring 6 is mounted in the ring groove 5. The piston ring 6 has a heat exhausting function of releasing the heat of the piston 1 to the cylinder 2. In this embodiment, the piston 1 has three ring grooves 5. These ring grooves 5 are arranged in the order of the first ring groove 5a, the second ring groove 5b, and the third ring groove 5c from the top (closer to the top dead center of the piston 1).

As shown in FIGS. 2 and 3, a top ring 6a is mounted on the first ring groove 5a, and a second ring 6b is mounted on the second ring groove 5b. Both the top ring 6a and the second ring 6b are compression rings that keep the combustion chamber 21 airtight (acting as a gas seal function). The material of the top ring 6a and the second ring 6b, the presence or absence of a joint, and the like are not particularly limited. For example, the top ring 6a can be a metal annular member having a joint, and the second ring 6b can be a resin annular member having no joint.

As shown in FIGS. 2 to 5, an oil ring 6c is attached to the third ring groove (oil ring groove) 5c. The oil ring 6c scrapes off the engine oil (hereinafter referred to as liner-adhered oil) adhering to the inner surface (liner) 2a of the cylinder 2 and keeps the state of the oil film properly. The groove height (dimension in the vertical direction) of the third ring groove 5c is slightly larger than the height (dimension in the axis direction) of the oil ring 6c. With the oil ring 6c mounted concentrically with the piston 1, the inner diameter of the oil ring 6c is larger than the diameter of the groove bottom 51c of the third ring groove 5c. That is, in such a mounted state, between the inner peripheral portion of the oil ring 6c (specifically, the inner peripheral portion 63d of the spacer expander 63c described later) and the groove bottom 51c of the third ring groove 5c. Has a void. Further, the outer diameter dimension of the oil ring 6c is substantially the same as the inner diameter dimension of the cylinder 2.

In the present embodiment, the oil ring 6c is configured by assembling three members. The oil ring 6c includes a pair of side rails 61c and 62c, and a spacer expander 63c interposed between them. The pair of side rails 61c and 62c are members (oil film control members) that scrape off the oil adhering to the liner and keep the oil film on the inner surface 2a of the cylinder 2 in an appropriate state. The pair of side rails 61c and 62c are formed in the shape of a thin metal plate and are also formed in an annular shape having a joint. The spacer expander 63c is a member (contact pressure adjusting member) that adjusts the contact pressure of the side rails 61c and 62c with respect to the inner surface 2a of the cylinder 2. The spacer expander 63c has a structure in which a thin metal plate is wavy up and down when viewed in the radial direction of the piston 1 and is continuous in an annular shape without having a joint. The inner peripheral portion 63d of the spacer expander 63c is provided with protrusions (hereinafter, referred to as selvage portions) 64c alternately up and down along the circumferential direction.

The pair of side rails 61c and 62c are assembled one above and one below the wavy portion 65c of the spacer expander 63c with the inner peripheral portions 61d and 62d in contact with the selvage portion 64c. The selvage portion 64c presses the inner peripheral portions 61d and 62d of the side rails 61c and 62c so that the outer peripheral portions 61e and 62e are brought into contact with the inner surface 2a of the cylinder 2 at a desired contact pressure.

The oil ring 6c is not limited to the above-mentioned configuration (3-piece type). For example, it may be a configuration (two-piece type) in which two members are assembled. In this case, as an example, an oil ring is configured by including a rail body (oil film control member) and a coil expander (contact pressure adjusting member) that presses the rail body against the inner surface 2a of the cylinder 2. The rail body has a cross-sectional shape along the axis direction in which the M-shape is turned sideways (rotated by 90 ° toward the inner diameter side). The coil expander is configured by winding a metal wire in a coil shape so that the cross-sectional shape along the axis direction is annular. The rail body and the coil expander are assembled by positioning the rail body on the outside and the coil expander on the inside and bringing them into contact with each other. The coil expander presses the inner peripheral portion of the rail body to bring the outer peripheral portion of the rail body into contact with the inner surface 2a of the cylinder 2 at a desired contact pressure.

The piston 1 includes a drain structure 10 that guides the liner-adhered oil scraped off by the oil ring 6c and the unburned fuel. The unburned fuel is a fuel that has not been burned in the combustion chamber 21. 2 to 9 show a drain structure 10 according to the present embodiment. In the drain structure 10, the scraped liner-adhered oil is applied to the back surface side of the piston 1 (internal space S1) and between the skirt portion 1c of the piston 1 and the inner surface 2a of the cylinder 2 (hereinafter referred to as sliding gap S2). Induce. Further, the drain structure 10 does not guide the unburned fuel to the sliding gap S2, but guides it to the back surface side (internal space S1) of the piston 1.

The drain structure 10 includes a first drain portion 7 and a second drain portion 8. In the present embodiment, the drain structure 10 includes a plurality of first drain portions 7 and a plurality of second drain portions 8, respectively. The first drain portion 7 and the second drain portion 8 are arranged side by side at predetermined intervals along the circumferential direction of the piston 1, respectively. The number of the first drain portion 7 and the number of the second drain portions 8 may be the same or different.

The first drain portion 7 is a hole portion (through hole) having openings 7a and 7b at both ends. One end of the first drain portion 7 is open to the back surface side (internal space S1) of the piston 1. The other end of the first drain portion 7 is open to the groove bottom 51c of the third ring groove 5c. That is, the first drain portion 7 penetrates the piston 1 in the radial direction so as to communicate the back surface side (internal space S1) of the piston 1 and the third ring groove 5c.

The opening 7b of the first drain portion 7 is arranged within the range of the groove bottom 51c. That is, the opening 7b does not reach (do not cover) the edge of the piston 1 near the top dead center or the bottom dead center at the groove bottom 51c.

The second drain portion 8 has an open portion 8a at one end, and the other end is a hole portion closed (dead end) by the bottom 8b. The second drain portion 8 functions as a pool for temporarily storing the scraped liner-adhered oil. The second drain portion 8 is arranged adjacent to the groove wall 52c on the lower side (closer to the bottom dead center) of the piston 1 in the third ring groove 5c. Further, the second drain portion 8 is configured to be recessed along the radial direction from the outer peripheral portion 1b of the piston 1. The opening portion 8a has an opening 81a located in the outer peripheral portion 1b of the piston 1 and an opening 82a located in the groove wall 52c.

That is, the second drain portion 8 opens in the outer peripheral portion 1b of the piston 1 and the groove wall 52c, respectively. As a result, the second drain portion 8 communicates with the sliding gap S2 through the opening 81a and communicates with the third ring groove 5c through the opening 82a (that is, in a part of the groove wall 52c). In other words, the second drain portion 8 does not communicate directly with the first drain portion 7 (in short, its opening 7b), but communicates with the third ring groove 5c.

The radial depth of the piston 1 of the second drain portion 8 (hereinafter, simply referred to as the depth of the second drain portion 8) is the radial depth of the piston 1 of the third ring groove 5c (hereinafter, simply referred to as the depth). , The depth of the third ring groove 5c) is set shallower. That is, the bottom 8b of the second drain portion 8 is located outside the groove bottom 51c of the third ring groove 5c in the radial direction of the piston 1.

In the present embodiment, as an example, the position of the bottom 8b (the deepest part in the radial direction of the piston 1) of the second drain portion 8 in the radial direction of the piston 1 is concentrically with the piston 1 in the third ring groove 5c. It coincides with the inner peripheral position of the side rail 62c (oil film control member) on the lower side (closer to the bottom dead center) of the mounted oil ring 6c. That is, in the present embodiment, the diameter dimension of the bottom 8b of the second drain portion 8 is set to be the same as the inner diameter dimension of the lower side rail 62c.

Since the depth of the second drain portion 8 may be shallower than the depth of the third ring groove 5c, the position of the bottom 8b of the second drain portion 8 is the lower side rail concentric with the piston 1. It may be outside the radial position of the piston 1 from the inner peripheral position of 62c. In short, the diameter dimension of the bottom 8b may be equal to or larger than the inner diameter dimension of the lower side rail 62c. However, the position of the bottom 8b of the second drain portion 8 is set to be inside the radial direction of the piston 1 with respect to the radial position of the bottom 9a of the recess 9 described later.

In order to maximize the function of the scraped liner-adhered oil as a pool, it is desirable that the position of the bottom 8b of the second drain portion 8 coincides with the position of the inner circumference of the lower side rail 62c. Further, in the intake process described later, this becomes a bottleneck when the liner-adhered oil scraped off by the lower side rail 62c and stored in the second drain portion 8 is guided to the third ring groove 5c. The part can be kept to a minimum.

If the oil ring 6c is a two-piece type, the position of the bottom 8b of the second drain portion 8 coincides with the inner peripheral position of the rail body mounted in the third ring groove 5c concentrically with the piston 1. It may be set to the outside of the piston 1 in the radial direction.

The opening 7b (opening at the other end) of the first drain portion 7 and the opening 81a located on the outer peripheral portion of the piston 1 of the second drain portion 8 are the first to third examples shown in FIGS. 6 to 8. As in the example, the positions of the piston 1 in the circumferential direction are offset. By offsetting in this way, the following effects can be obtained. That is, when the liner-adhered oil scraped off by the side rails 61c and 62c and the unburned fuel are mixed and exposed to a high temperature in the vicinity of the oil ring 6c, the carbon contained therein tends to become sludge. Therefore, from the viewpoint of washing away the carbon with the liner-adhered oil scraped off, it is preferable to use an offset arrangement in which the oil can be easily actively guided along the circumferential direction of the third ring groove 5c. However, the openings 7b and 81a can be arranged so that the positions of the piston 1 in the circumferential direction are aligned as in the fourth example shown in FIG. 9 without offsetting.

The shapes of the opening 7b (the opening at the other end) of the first drain portion 7 and the opening 81a located on the outer peripheral portion of the piston 1 of the second drain portion 8 are not particularly limited. For example, the shapes as shown in the first to fourth examples shown in FIGS. 6 to 9 can be arbitrarily adopted. In the first to fourth examples, the opening 81a has a larger opening area than the opening 7b (see FIGS. 6 to 9).

Further, in the present embodiment, the outer peripheral portion 1b of the piston 1 is provided with a recess 9 that is continuous along the circumferential direction. The recess 9 is configured by recessing the outer peripheral portion 1b of the piston 1 in the radial direction over the entire circumference. The recess 9 is arranged adjacent to the lower edge of the third ring groove 5c (the edge of the lower groove wall 52c). The recess 9 functions as an oil passage for temporarily retracting the scraped liner-adhered oil. The second drain portion 8 is recessed from the bottom 9a of the recess 9 along the radial direction of the piston 1. The bottom 9a of the recess 9 is the inner end of the recess 9 in the radial direction of the piston 1. The depth of the recess 9 in the radial direction of the piston 1 is set to be shallower than the depth of the second drain portion 8. The recess 9 may be omitted.

Next, the operation of the drain structure 10 in the present embodiment will be described with reference to FIGS. 2 to 5. FIG. 2 shows the operation of the drain structure 10 in the intake process of the internal combustion engine. FIG. 3 shows the operation of the drain structure 10 in the compression step, the combustion (expansion) step, and the exhaust step of the internal combustion engine. FIG. 4 is an enlarged view showing the drain structure 10 shown in FIG. 2, and FIG. 5 is an enlarged view showing the drain structure 10 shown in FIG.

The intake process shown in FIGS. 2 and 4 will be described. In the intake step, the lower side rail 61c of the oil ring 6c comes into contact with the upper groove wall 53c of the third ring groove 5c due to the lowering of the piston 1. On the other hand, the lower side rail 62c of the oil ring 6c is separated from the lower groove wall 52c of the third ring groove 5c.

As the piston 1 descends, the liner-adhered oil is scraped from above to below by the side rails 61c and 62c of the oil ring 6c. The oil scraped off by the upper side rail 61c of the oil ring 6c is blocked by the lower side rail 62c. The dammed oil is guided from the wavy portion 65c of the spacer expander 63c to the first drain portion 7 in the third ring groove 5c, and flows into the back surface side (internal space S1) of the piston 1 (FIG. 2). Arrow A1) shown in.

Further, the oil scraped off by the lower side rail 62c is stored in the second drain portion 8 (arrow A2 shown in FIG. 2). At this time, the hydraulic pressure due to the liner-adhered oil stored in the second drain portion 8 acts upward on the lower side rail 62c. Therefore, the moment load acting on the lower side rail 62c due to the lowering of the piston 1 is reduced by the amount of the applied hydraulic pressure as compared with the case where the second drain portion 8 is not provided. Therefore, the lower side rail 62c maintains a constant posture along the radial direction of the piston 1 without tilting. When the second drain portion 8 is not provided, a moment load such that the inner peripheral portion 62d is lowered and the outer peripheral portion 62e is raised on the lower side rail 62c when the piston 1 is lowered (during the intake process). Works.

In the present embodiment, the lower side rail 62c is separated from the lower groove wall 52c of the third ring groove 5c, and the oil stored in the second drain portion 8 is from the second drain portion 8 to the third. It is guided to the ring groove 5c of. The oil guided to the third ring groove 5c is further guided to the first drain portion 7 and flows into the back surface side (internal space S1) of the piston 1 (arrow A3 shown in FIG. 2).

The oil that has flowed into the back surface side (internal space S1) of the piston 1 is returned from the crank room (not shown) to the oil pan (not shown).

The compression step, the combustion (expansion) step, and the exhaust step shown in FIGS. 3 and 5 will be described. In these steps, the side rail 61c on the upper side of the oil ring 6c is separated from the groove wall 53c on the upper side of the third ring groove 5c. Further, in these steps, the unburned fuel in the combustion chamber 21 is blocked by the side rail 61c on the upper side of the oil ring 6c. The dammed unburned fuel is guided to the third ring groove 5c from the gap between the upper side rail 61c and the upper groove wall 53c of the third ring groove 5c. The unburned fuel guided to the third ring groove 5c is further guided to the first drain portion 7 and flows into the back surface side (internal space S1) of the piston 1. The unburned fuel that has flowed into the back surface side (internal space S1) of the piston 1 falls from the crankroom into the oil pan (arrow A4 shown in FIG. 3).

In particular, in the compression step, a large moment load acts on the upper side rail 61c as the piston 1 rises. At this time, the upper side rail 61c is in a state of being tilted so that the inner peripheral portion 61d rises due to the moment load and the outer peripheral portion 61e descends (the state shown by the broken line in FIGS. 3 and 5). On the other hand, the lower side rail 62c is sandwiched between the spacer expander 63c and the groove wall 52c of the third ring groove 5c. In this state, the lower side rail 62c does not tilt like the upper side rail 61c, and is in close contact with the groove wall 52c.

Here, in the present embodiment, since the second drain portion 8 is provided, even if the depth of the recess 9 in the radial direction of the piston 1 is made shallow (small), it is scraped off by the lower side rail 62c. The liner-adhered oil can be stored in the second drain portion 8. Therefore, it is possible to move the fulcrum of the moment load acting on the lower side rail 62c to the outside in the radial direction of the piston 1 by the amount that the recess 9 is made shallower. As a result, the posture of the lower side rail 62c can be stabilized along the radial direction of the piston 1.

When the upper side rail 61c is tilted, the unburned fuel passes through the gap between the upper side rail 61c and the inner surface 2a of the cylinder 2. Even when the unburned fuel slips through the gap, the unburned fuel is blocked by the lower side rail 62c. The dammed unburned fuel is guided from the wavy portion 65c of the spacer expander 63c to the first drain portion 7 in the third ring groove 5c, and flows into the back surface side (internal space S1) of the piston 1 (internal space S1). Arrow A4 shown in FIG. 3).

Further, in the compression step, the combustion (expansion) step, and the exhaust step, the side rail 62c on the lower side of the oil ring 6c is pressed by the air-fuel mixture or the combustion gas of the combustion chamber 21 and is under the third ring groove 5c. It contacts the groove wall 52c on the side. Therefore, the liner-adhered oil scraped off by the lower side rail 62c is stored in the second drain portion 8 and is stored in the sliding gap S2 (between the skirt portion 1c of the piston 1 and the inner surface 2a of the cylinder 2). (Arrow A5 shown in FIG. 3). The oil guided to the sliding gap S2 is returned from the crankroom to the oil pan through the inner surface 2a of the cylinder 2 and the skirt portion 1c of the piston 1 (arrow A6 shown in FIG. 3). In the present embodiment, the scraped liner-adhered oil is stored in the recess 9 in addition to the second drain portion 8 and guided to the sliding gap S2.

As described above, according to the present embodiment, in the intake step, the liner-adhered oil scraped off by the oil ring 6c can be guided to the back surface side (internal space S1) of the piston 1. Further, in each process of compression, combustion (expansion), and exhaust, unburned fuel is guided to the back surface side (internal space S1) of the piston 1, and the liner-adhered oil scraped off by the oil ring 6c is slid through the sliding gap. It can be guided to S2.

As a result, the liner-adhered oil scraped off by the oil ring 6c can be reliably suppressed from flowing into the combustion chamber 21, and the oil consumption can be reduced. Further, it is possible to suppress the infiltration of unburned fuel into the sliding gap S2. Therefore, for example, it is possible to effectively prevent unburned fuel from being mixed with the oil adhering to the liner to reduce the viscosity of the oil and causing the friction of the piston 1 to deteriorate. On the other hand, since the liner-adhered oil scraped off by the oil ring 6c can be guided to the sliding gap S2, the lubrication state of the piston 1 can be properly maintained.

The embodiments described above are presented as an example and are not intended to limit the scope of the invention. Such a novel embodiment can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

As an example, the form of the opening 7b of the first drain portion 7 and the opening 81a of the second drain portion 8 (open portion 8a) may be set from the following viewpoints. For example, among the above-mentioned effects, when the induction of unburned fuel to the back surface side (internal space S1) of the piston 1 is emphasized, the second drain is provided with respect to the opening 7b of the first drain portion 7. The opening 81a of the portion 8 (open portion 8a) is opened larger. The first to fourth examples shown in FIGS. 6 to 9 are morphological examples from such a viewpoint. On the other hand, when the induction of the liner-adhered oil to the back surface side (internal space S1) of the piston 1 is emphasized, the first drain portion 7 with respect to the second drain portion 8 (open portion 8a). The opening 7b may be opened larger.

1 ... Piston, 1a ... Top, 1b ... Outer circumference, 1c ... Skirt, 2 ... Cylinder, 2a ... Liner, 5 ... Ring groove, 5a ... First ring groove, 5b ... Second ring groove, 5c ... First 3 ring groove, 6 ... piston ring, 6a ... top ring, 6b ... second ring, 6c ... oil ring, 7 ... first drain part, 7a, 7b ... first drain part opening, 8 ... second Drain portion, 8a ... Open portion of the second drain portion, 8b ... Bottom of the second drain portion, 9 ... Recessed portion, 9a ... Bottom of the recessed portion 10 ... Drain structure, 21 ... Combustion chamber, 51c ... Groove bottom, 52c ... lower groove wall, 53c ... upper groove wall, 61c ... upper side rail, 62c ... lower side rail, 63c ... spacer expander, 64c ... ear, 65c ... wavy, 81a, 81b ... open Opening of the portion, S1 ... Internal space, S2 ... Sliding gap.

Claims (4)

An annular continuous ring groove along the circumferential direction, an oil ring mounted on the ring groove and scraping off oil adhering to the inner surface of the cylinder of the internal combustion engine, and the oil scraped off by the oil ring and unburned. A piston of an internal combustion engine equipped with a drain structure that guides fuel.
The drain structure is
A first drain portion having openings at both ends and penetrating the piston in the radial direction so that one end opens on the back surface side of the piston and the other end opens on the bottom of the ring groove.
A second ring groove adjacent to the groove wall near the bottom dead center of the piston, recessed along the radial direction from the outer peripheral portion of the piston, and opened to the outer peripheral portion of the piston and the groove wall, respectively. With a drain part,
The opening at the other end of the first drain portion is arranged within the range of the groove bottom.
The radial depth of the piston of the second drain portion is set to be shallower than the radial depth of the piston of the ring groove .
The oil ring is a contact between an oil film control member that scrapes off oil adhering to the inner surface of the cylinder and keeps the oil film on the inner surface of the cylinder in an appropriate state, and a contact that adjusts the contact pressure of the oil film control member with respect to the inner surface of the cylinder. With a pressure adjustment member,
In the radial direction of the piston, the position of the deepest portion of the second drain portion coincides with the inner peripheral position of the oil film control member mounted in the ring groove concentrically with the piston.
The piston of an internal combustion engine is characterized by that. The opening at the other end of the first drain portion and the opening located at the outer peripheral portion of the piston of the second drain portion are arranged so that their positions in the circumferential direction of the piston are offset. The piston of an internal combustion engine according to claim 1 . The opening at the other end of the first drain portion and the opening located at the outer peripheral portion of the piston of the second drain portion are arranged so that the positions of the piston in the circumferential direction coincide with each other. The piston of an internal combustion engine according to claim 1 . One of claims 1 to 3 , wherein the opening of the second drain portion located on the outer peripheral portion of the piston has a larger opening area than the opening of the other end of the first drain portion. The piston of the internal combustion engine described in the section.

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