JP6648442B2 - Piston for internal combustion engine, internal combustion engine, and method for designing piston for internal combustion engine - Google Patents

Description

  The present invention promotes mixing of fuel spray and intake air in a cavity (combustion chamber) in an internal combustion engine such as a diesel engine, and suppresses generation of a fuel rich region due to interference between adjacent fuel sprays. The present invention relates to a piston for an internal combustion engine, an internal combustion engine, and a method for designing a piston for an internal combustion engine that can avoid generation of soot, HC, CO, and the like due to incomplete combustion.

  2. Description of the Related Art In a piston for an internal combustion engine such as a diesel engine, a concave portion called a cavity is provided at a top portion (crown surface: piston top) of the piston, and fuel is injected from a fuel injection nozzle provided opposite to a central portion of the cavity. The injected fuel spray is mixed with intake air inside the cavity to burn fuel. In this combustion, there is generation of soot, HC, CO, and the like due to incomplete combustion. The phenomenon is as follows. As shown in FIG. 8, in the cavity 10X provided at the top 2 of the piston 1X, as shown in FIG. 9, the fuel spray F is caused to flow to the swirl S after colliding with the outer peripheral wall 11 of the cavity 10X. The fuel spray Fs flowing through the swirl S exists on the downstream side of the swirl, and as shown in FIG. 10, the fuel sprays F1 and F2 injected from the adjacent injection holes 31 overlap in the cavity 10X, and interference occurs. Occurs.

  When the fuel sprays F1 and F2 interfere with each other, there is a possibility that an oxygen-enriched region Ro where the fuel becomes insufficient will be formed, and soot, HC, CO, and the like may be generated. This is a finding obtained from observation results of combustion in an internal combustion engine. Therefore, in order to avoid these phenomena and improve the combustion efficiency, various ideas have been devised for the shape of the cavity.

  For example, in order to suppress the formation of a fuel rich region due to the fuel spray injected from the injector toward the cavity spreading in the circumferential direction along the wall surface of the cavity and interfering with adjacent sprays, A combustion chamber structure of an internal combustion engine having a cavity in which a plurality of fuel sprays, which are injected at intervals in a circumferential direction from an injector arranged above, collide with a top of the cavity, and the spray collides with a wall surface of the cavity. The combustion chamber structure of the internal combustion engine is provided with a plurality of guide projections along the inner and outer directions of the cavity, which suppress the interference between adjacent sprays due to the spray spreading in the circumferential direction of the cavity along the wall surface. It has been proposed (for example, see Patent Document 1).

  However, it has been found that when the soot is deposited in the concave portions, the effect of the guide projection is weakened, or the guide projection may be broken by thermal stress.

  In other words, the structure for preventing spray diffusion is a structure that is easily damaged by thermal stress, so there is room for improvement that it is not suitable for use in areas where the load is high, and the cross-sectional shape of the piston cavity is There is no significant change in the circumferential direction, and there is no structure that promotes the mixing of spray and intake by making use of the swirl (lateral vortex: swirl) flow. Obtained.

In this connection, the direct injection corresponding to the fuel injection nozzle, which atomizes the fuel with the momentum injected from the injection hole, has been used to increase the combustion efficiency of the squish area with a simple structure while maintaining the volume of the combustion chamber as much as possible. A piston of a diesel internal combustion engine, wherein the piston is independent of the outer periphery of the combustion chamber by individually corresponding to the combustion chamber recessed at the top and the diffusion range of the fuel spray injected from the plurality of injection holes of the fuel injection nozzle. A piston provided in accordance with the distribution of the fuel concentration of the fuel spray depending on the cross-sectional shape of the recess along the radial direction of the piston depending on the circumferential position with respect to the center of the piston. For example, see Patent Document 1).

  However, in this configuration, since the depression is provided at the top of the piston independently of the space of the combustion chamber, it is effective in improving the combustion of the fuel spray in the squish area beyond the outer peripheral edge of the combustion chamber. However, there is a problem that it is not directly useful for improving the combustion in the center of the combustion chamber.

JP 2011-174388 A JP 2010-112350 A

  The present invention has been made in view of the above, and an object of the present invention is to use a swirl in an internal combustion engine such as a diesel engine to promote mixing of fuel spray and intake air in a cavity, and to improve the adjacency of the fuel. Design of a piston for an internal combustion engine, an internal combustion engine, and a piston for an internal combustion engine capable of suppressing generation of a soot, HC, CO, etc. due to incomplete combustion by suppressing generation of a fuel rich region due to interference between fuel sprays It is to provide a method.

  In order to achieve the above object, a piston for an internal combustion engine of the present invention includes a cavity provided in a concave shape at the top of the piston, and a fuel injection nozzle provided in a cylinder head opposed to a center of the cavity. A piston for an internal combustion engine for an internal combustion engine for swirling intake air, wherein the region of the cavity is divided into divided regions for each injection hole of the fuel injection nozzle, and a peripheral wall surface of the cavity is provided inside the divided region. The outer peripheral upper portion is provided with a ledge having a depression, and at the boundary portion with the partitioned region adjacent to the partitioned region, the ledge is formed in a shape without the shelf, and with respect to the swirl direction, the swirl most upstream side of the partitioned region Then, a first transition portion that transitions from a shape without the shelf portion to a shape in which the shelf portion is hollowed out to the outer peripheral side, and an outer peripheral side of the depression gradually to the center of the partitioned area A first recessed portion for increasing the amount of gouging, a maximum recessed portion for maximizing the amount of gouging to the outer peripheral side of the recess at the center of the partitioned region, and the recessed portion gradually from the center of the partitioned region to the swirl downstream side. And a second transition portion that transitions from a shape with the shelf portion to a shape without the shelf portion on the most downstream side of the swirl in the partition area. , Formed so as to be continuous with the shape of the swirl most upstream side of the adjacent partitioned area, and further, in the order of the first transition portion, the second transition portion, the second depression portion, and the first depression portion, The amount of change in the circumferential direction in the amount of gouging to the outer peripheral side is made small.

  According to this configuration, the structure is such that the cross-sectional area of the cavity changes in the circumferential direction of the cavity of the piston for each fuel spray, and the intake and the fuel spray in the partitioned area are devised to be mixed. It is possible to sufficiently mix the intake air and fuel spray in the interior, and it is possible to suppress the generation of soot, HC, CO, and the like. This partitioned area is set corresponding to the injection hole, that is, it changes according to the number of injection holes.

  In addition, since interference between adjacent fuel sprays is eliminated to prevent interference, it is possible to suppress the occurrence of a fuel-rich region due to interference between adjacent fuel sprays. , HC and CO can be avoided. In addition, since the mixing of the intake air and the fuel spray is favorably promoted, it is possible to reduce Soot and CO in this aspect as well.

  Therefore, in an internal combustion engine such as a diesel engine, the swirl is used to promote the mixing of the fuel spray and the intake air in the cavity, and to suppress the generation of the fuel rich region due to the interference between the adjacent fuel sprays. Generation of soot, HC, CO, and the like due to incomplete combustion can be avoided.

  In the piston for an internal combustion engine described above, at a portion of the second recess where the shelf is located, a mouth portion of a corner of the piston and a top of the piston protrudes toward the piston center axis. In other words, after the injected fuel spray collides with the outer peripheral wall of the cavity and is swirled, the mouth of the cavity is protruded so as to be mixed with the intake air at the center of the cavity. This makes it easier for the fuel spray to mix with the intake air at the center of the cavity in accordance with the swirl flow.

  In addition, due to the structure of the mouth, the flow that flows from the cavity to the cylinder when the piston enters the expansion stroke beyond the compression top dead center is called the reverse squish flow. And the intake of air can be promoted.

  An internal combustion engine according to the present invention for achieving the above object is provided with the above-mentioned piston for an internal combustion engine, and has the same operational effects as the above-described fuel injection device.

In order to achieve the above object, a method for designing a piston for an internal combustion engine according to the present invention includes a cavity provided in a concave shape at the top of the piston, and a cavity provided in a cylinder head opposed to a central portion of the cavity. In a method of designing a piston for an internal combustion engine for an internal combustion engine for swirling intake air, the fuel spray injected from each injection hole of the fuel injection nozzle is caused to flow by a preset swirl. A first step of measuring or calculating a range to be mixed, and measuring a mixed distribution of the injected fuel spray and the intake air, and an equivalent ratio of less than 1 in which the amount of oxygen in the intake air mixed with the amount of the fuel spray becomes excessive. A second step of measuring or calculating an area, and dividing the area of the cavity such that a division area for each injection hole of the fuel injection nozzle includes the area having an equivalence ratio of less than 1. 3 and step, and a fourth step of determining the shape of the cavity for each of the divided area, the at fourth step, in the direction in which fuel is injected from the injection hole, an outer peripheral fuel spray of the cavity In order to increase the mixing distance before colliding with the wall, the outer peripheral wall of the cavity is arranged far from the central axis of the piston, and on the downstream side of the swirl, the fuel spray is swirled after colliding with the outer peripheral wall of the cavity. In order to mix with the intake air inside the cavity, the mouth portion of the cavity is formed to protrude so as to push fuel spray, and on the swirl upstream side, after the fuel spray collides with the outer peripheral wall of the cavity, it is adjacent The outer peripheral wall of the cavity is arranged closer to the piston center axis side so as not to interfere with fuel spray, and the piston center axis is When the cross-sectional shape of the cavity in the plane is rotated along the circumferential direction around the center axis of the piston along the flow of swirl, after the cavity is spread outward with this rotation, the original shape is obtained. The method is characterized in that the shape of the cavity is continuously formed so as to return to the above .

According to this method of designing a piston for an internal combustion engine, the same operation and effect as those of the piston for an internal combustion engine can be obtained.

  According to the piston for an internal combustion engine, the internal combustion engine and the method for designing a piston for an internal combustion engine of the present invention, in an internal combustion engine such as a diesel engine, swirl is used to promote mixing of fuel spray and intake air in a cavity. In addition, the generation of a fuel-rich region due to interference between adjacent fuel sprays can be suppressed, and generation of soot, HC, CO, and the like due to incomplete combustion can be avoided.

It is a side sectional view of a piston which shows typically the structure of the cavity of the piston for internal-combustion engines of an embodiment concerning the present invention. It is a figure for explaining the 1st step in the design method of the piston for internal-combustion engines of an embodiment concerning the present invention, and is a figure showing typically a flow of fuel spray by a swirl in a cavity. FIG. 4 is a diagram for explaining a second step and a third step in the method for designing a piston for an internal combustion engine according to the embodiment of the present invention, and is a diagram schematically illustrating a region in the cavity having an equivalent ratio of less than 1; It is a figure for explaining the 4th step in a piston design method for an internal-combustion engine of an embodiment concerning the present invention, and is a figure showing typically the division area in a cavity, and the position of each section. It is a figure showing typically section shape in a piston for internal-combustion engines of an embodiment concerning the present invention. It is a perspective view which shows the sectional shape in the piston for internal-combustion engines of an embodiment concerning the present invention three-dimensionally. It is a figure which shows typically the state of the adjacent fuel spray in the piston for internal combustion engines of embodiment concerning this invention. It is a side sectional view of a piston which shows typically the structure of the cavity of the piston for internal combustion engines of the prior art. FIG. 4 is a view schematically showing a flow of fuel spray by swirl in a cavity of a piston for a conventional internal combustion engine. FIG. 4 is a view schematically showing an overlapping state of adjacent fuel sprays in a cavity of a piston for a conventional internal combustion engine.

  Hereinafter, a piston for an internal combustion engine, an internal combustion engine, and a method for designing a piston for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. The internal combustion engine according to the embodiment of the present invention is configured to include the piston for the internal combustion engine according to the embodiment of the present invention, and has the same operation and effects as those of the piston for the internal combustion engine described later. Can play.

  First, a method of designing a piston for an internal combustion engine according to an embodiment of the present invention will be described. As shown in FIG. 1, a method of designing a piston for an internal combustion engine includes, as shown in FIG. 1, a cavity 10 provided in a concave shape on a top 2 of a piston 1, and a cylinder head (not shown) opposed to a center of the cavity 10. This is a method for designing a piston for an internal combustion engine that has a fuel injection nozzle 30 provided in the internal combustion engine and swirls intake air.

  As shown in FIG. 1, the cavity 10 includes an outer peripheral wall 11, a bottom portion 12, an outer edge portion 13, a mouth portion (projection portion) 13 a, a shelf 14, a depression 15, and a mouth portion (projection portion) 16 of the shelf portion 16. And so on.

  This method of designing a piston for an internal combustion engine has first to fourth steps. In the first step, as shown in FIG. 2, each of the fuel injection nozzles 30 is set by a preset swirl S. The range Rs in which the fuel spray F injected from the injection hole 31 collides with the virtual outer peripheral wall 11X and flows is measured or calculated. Since this virtual outer peripheral wall 11X is for obtaining the range Rs in which the fuel spray F flows, the virtual outer peripheral wall 11X may have an appropriate shape. For example, it is possible to use the shape of a cavity having an annular outer peripheral wall of the prior art. it can.

  In the second step, as shown in FIG. 3, the mixture distribution of the injected fuel spray F and the intake air is measured, and the amount of oxygen in the intake air mixed with the amount of the fuel spray F becomes excessive. The region R1 having an equivalence ratio of less than 1 is measured or calculated.

  In the third step, as shown in FIG. 3, the area of the cavity 10 is divided by the straight line Li and the straight line Li + 1 extending from the center of the cavity 10 into the equivalence ratio Di in the divided area Di for each injection hole 31 of the fuel injection nozzle 30. The area is divided so as to include the area R <1. In the next fourth step, as shown in FIGS. 4 to 6, the shape of the cavity 10 is determined for each partitioned area Di. The division area Di changes according to the number of the injection holes 31, in other words, the number of the injection holes 31. That is, the number of the divided areas Di is equal to the number of the injection holes 31.

  That is, for the purpose of setting the shape of the cavity (combustion chamber) 10 so as to reduce the interference between the adjacent fuel sprays F, the range in which the fuel sprays F flow through the preset swirl S is measured or fluid analysis is performed. Calculate by using a program, etc., and measure the equivalent ratio (reciprocal of excess air ratio = weight of oxygen required for complete combustion / weight of oxygen contained in actual air-fuel mixture) by LAS method (laser absorption scattering method) etc. , The region R1 where the equivalence ratio is less than 1, in other words, the region R1 in which oxygen is excessive is a range divided in the circumferential direction of the cavity 10 so as to be arranged for each divided region Di injected from each injection hole 31. The sectional area Di is determined, and the cross-sectional shape (S1 to S7) of the cavity 10 for each of the sectional areas Di determined by the area where the fuel spray F injected from each injection hole 31 is generated is determined.

  Then, based on the swirl S set in advance, the partition area Di is set so that the equivalent ratio in the circumferential direction of the cavity 10 when viewed from above is less than 1, and the sectional shape (S1) of the cavity 10 is set for each of the partition areas Di. To S7) are set. In setting the cross-sectional shape (S1 to S7) of the cavity 10, the location S4 where the injected fuel spray F directly collides is set as far as possible from the injection hole 31 and the sprays overlap on the virtual outer peripheral wall 11X. When the equivalence ratio exceeds 1 and oxygen deficiency occurs or is measured or calculated, walls (S1, S7) are set in a wall shape so that adjacent injected fuel sprays F1, F2 are formed. Avoid overlapping. Therefore, the cross-sectional shapes (S1, S7) of both ends of each partitioned area Di reduce the distance of the cavity 10 from the piston center axis C in the radial direction so as not to interfere with the fuel sprays F1, F2 of the adjacent areas.

  In the fourth step, in the direction in which the fuel spray F is injected from the injection hole 31 (cross section S4), in order to increase the mixing distance until the fuel spray F collides with the outer peripheral wall 11 of the cavity 10, The outer peripheral wall 11 of the cavity 10 is disposed far from the center axis C of the piston, and on the downstream side of the swirl (sections S5 and S6), the fuel spray F impinges on the outer peripheral wall 11 of the cavity 10 and then flows while being swirled. The mouth 13a of the cavity 10 is shaped so that the fuel spray F is pushed in so as to be mixed with the intake air inside the fuel injection F. On the swirl upstream side (sections S2 and S3), the fuel spray F is applied to the outer peripheral wall 11 of the cavity 10. After the collision, the outer peripheral wall 11 of the cavity 10 is arranged close to the piston center axis C side so as not to interfere with the adjacent fuel spray F, as shown in FIG. When the cross-sectional shape (S1 to S7) of the cavity 10 in a plane including the piston center axis C is rotated along the circumferential direction around the piston center axis C along the flow of the swirl S, this rotation Accordingly, the shape of the cavity 10 is continuously formed so that the cavity 10 spreads outward and then returns to the original state. That is, the cross-sectional shape (S1 to S7) of the cavity 10 in a plane including the piston center axis C is continuously extended in the circumferential direction around the piston center axis C to form the shape of the cavity 10.

  That is, the cross-sectional shape (S1 to S7) of the cavity 10 cut along a plane including the piston center axis C changes in the radial direction according to the direction of the swirl S in accordance with the swirl S which is the flow of the intake air in the cavity 10. With regard to the change in the cross-sectional shape (S1 to S7) of the cavity 10, the mouth 13a of the portion (S4) where the fuel spray F directly collides with the portion farthest from the injection hole 31 and the first step and the As a result obtained in two steps, a wall-like shape is set at a portion (S1, S7) where it overlaps with the adjacent fuel spray F and the equivalent ratio exceeds 1. Further, as the fuel spray F flows through the swirl S, the mouth 13 a is pushed out toward the center C so as to push the fuel F so that the fuel spray F mixes with the intake air at the center C of the cavity 10. .

  Next, a piston (hereinafter, piston) 1 for an internal combustion engine according to an embodiment of the present invention will be described. As shown in FIGS. 1 to 6, the piston 1 is provided with a cavity 10 provided in a concave shape on the top 2 of the piston 1 and a cylinder head (not shown) opposed to the center of the cavity 10. The internal combustion engine has a fuel injection nozzle 30 and swirls intake air.

  In the piston 1, the area of the cavity 10 is divided into divided areas Di for each injection hole 31 of the fuel injection nozzle 30, and a shelf 15 having a recess 15 at the outer peripheral upper part of the outer peripheral wall 11 of the cavity 10 inside the divided area Di. A part 14 is provided.

  At the same time, at the boundary portion with the partition area Di + 1 adjacent to the partition area Di, the shelf section 14 having the depression 15 is formed in a shape without the shelves 14, and with respect to the direction of the swirl S, on the swirl most upstream side (S1) of the partition area Di. A first transition portion (S1 to S2) is provided which is provided with a depression 15 which is provided with a gouge on the outer peripheral side from a shape having no shelf portion 14 and shifts to a shape in which the shelf portion 14 is formed.

  Further, a first recessed portion (S2 to S4) in which the depth of the recess 15 is gradually increased toward the center (S4) of the partitioned area Di, and an outer circumferential side of the recess 15 at the center (S4) of the partitioned area Di. A maximum recessed portion (S4) that maximizes the depth of the hollow is provided.

  Further, a second dent portion (S4 to S6) for gradually reducing the amount of depression from the center (S4) of the partitioned area Di to the outer peripheral side of the dent 15 toward the swirl downstream side, and a swirl most downstream side (S7) of the partitioned area Di. ), A second transition portion (S6 to S7) that transitions from the shape with the shelf 14 having the depression 15 to the shape without the shelf 14 having the depression 15 is formed in the swirl uppermost stream of the adjacent partitioned area Di + 1. It is formed so as to be continuous with the side shape.

  In addition, the outer peripheral side of the depression 15 in the order of the first transition part (S1 to S2), the second transition part (S2 to S4), the second depression part (S4 to S6), and the first depression part (S6 to S7). The amount of change in the circumferential direction in the amount of gouge is reduced.

  That is, with respect to the shape of the cavity (combustion chamber) 10, for each fuel spray F injected from the injection hole 31 of the fuel injection nozzle 30, the cross-sectional shape (S 1 to S 7) extending in the radial direction from the piston center axis C is set in the circumferential direction. A cavity shape is created by overlapping in a fan shape.

  The maximum depression (S4) where the fuel spray F directly collides is made as far as possible to increase the mixing distance until the fuel spray F collides. Further, in the second depressions (S4 to S6), after the fuel spray F collides with the outer peripheral wall 11 of the cavity 10, the fuel spray F is mixed with the intake air at the center C of the cavity 10 while being swirled. The mouth portion 13a is formed to protrude toward the piston center axis C so that the mouth portion 13a pushes the fuel spray F.

  Accordingly, in the part (S4 to S6) where mixing of the fuel spray F and the intake air is desired to be promoted as much as possible, the mixing time is long and the mixing area of the cavity 10 with which the injected fuel spray F collides so that the mixing area becomes large. The outer peripheral wall 11 is formed at a far position.

  On the other hand, on both sides of the partition area Di, the first dents (S2 to S4) on the swirl upstream side in the direction opposite to the direction of the swirl flow are adjacent to each other so as not to interfere with the adjacent fuel spray F. The radial distance of the cavity 10 from the piston center axis C is gradually reduced so as not to interfere with the injected fuel spray F, and a barrier is provided to prevent interference with the adjacent injected fuel spray F without overlapping. Make the shape to be formed.

  In the cavity 10, the outer edge portion 13 which is a line inside the top portion 2 of the piston 1 has a fuel injection through an injection hole 31 when viewed from above the piston center axis C as shown in FIGS. 4 and 6. Is not axisymmetric but non-symmetric with respect to the direction.

  According to this configuration, the structure is such that the cross-sectional area of the cavity 10 changes in the circumferential direction of the cavity 10 of the piston 1 for each fuel spray F, so that the intake air and the fuel spray F in the partitioned area Di are mixed. Therefore, the intake air in the cavity 10 and the fuel spray F can be sufficiently mixed, and the generation of soot, HC, CO, and the like can be suppressed.

  Further, as shown in a region Rx of FIG. 7, the overlap between the injected fuel sprays F1 and F2 is eliminated so that there is no interference, so that the fuel due to the interference between the adjacent fuel sprays F1 and F2 is eliminated. It is possible to suppress the generation of the rich region, and thereby it is possible to avoid the generation of soot, HC, and CO due to incomplete combustion. In addition, since the mixing of the intake air and the fuel spray F is favorably promoted, it is possible to reduce Soot and CO in this aspect as well.

  In addition, at the portion (S4 to S6) of the second recessed portion where the shelf 14 is located, the mouth 13a at the corner with the top 2 of the piston 1 and the mouth 16 of the shelf 14 are moved toward the piston center axis C. It is formed by protruding. In other words, after the injected fuel spray F collides with the outer peripheral wall 11 of the cavity 10 and is swirled by the swirl S, it mixes with the intake air at the center of the cavity 10 so that the mouth 13a of the cavity 10 is mixed. , And a structure in which the lip 16 of the shelf 14 is protruded. Accordingly, the fuel spray F is easily mixed with the intake air at the center of the cavity 10 in accordance with the flow of the swirl S.

  Further, due to the structure of the mouth portions 13a and 16, the reverse squish flow, which flows from the cavity 10 to the cylinder when the piston 1 enters the expansion stroke beyond the compression top dead center, can be utilized, and the fuel spray F and the intake air can be used. Mixing can be promoted.

  Therefore, according to the piston for the internal combustion engine, the internal combustion engine, and the method for designing the piston for the internal combustion engine having the above-described configuration, the fuel spray F in the cavity 10 is utilized in the internal combustion engine such as the diesel engine by using the swirl S. In addition to promoting the mixing of fuel and intake air, the generation of a fuel-rich region due to interference between adjacent fuel sprays F can be suppressed, and generation of soot, HC, CO, and the like due to incomplete combustion can be avoided.

1,1X piston for internal combustion engine (piston)
2 Piston top 10, 10X Cavity 11 Cavity outer peripheral wall 11X Virtual outer peripheral wall 12 Cavity bottom 13 Cavity outer edge 13a Cavity mouth (projection)
14 Shelf 15 Depression 16 Shelf mouth (projection)
30 Fuel injection nozzle 31 Injection hole C Central part of cavity (central axis of piston)
Di Sectional area F Fuel spray Li, Li + 1 Straight line Rs extending from the center of the cavity Range R1 where fuel spray collides with the virtual outer peripheral wall and flows below Equivalent ratio 1 Area S Swirl S1 to S7 Cross-sectional shape of cavity

Claims (4)

A piston for an internal combustion engine for an internal combustion engine that has a cavity provided in a concave shape at the top of the piston and a fuel injection nozzle provided in a cylinder head facing the center of the cavity and swirls intake air. ,
Dividing the area of the cavity into partitioned areas for each injection hole of the fuel injection nozzle,
A shelf having a recess is provided on the outer peripheral upper portion of the outer peripheral wall of the cavity inside the partitioned area, and the shelf is formed in a shape without the shelf at a boundary portion with a partitioned area adjacent to the partitioned area,
Regarding the swirl direction,
A first transition portion that transitions from a shape without the shelf portion to a shape formed with the shelf portion which is hollowed out on the outer peripheral side on the most upstream side of the swirl of the partitioned region, and gradually toward the outer peripheral side of the depression to the center of the partitioned region. A first recessed portion for increasing the amount of gouging, a maximum recessed portion for maximizing the amount of gouging to the outer peripheral side of the recess at the center of the partitioned region, and the recessed portion gradually from the center of the partitioned region to the swirl downstream side. And a second transition portion that transitions from the shape with the shelf to the shape without the shelf at the most downstream side of the swirl in the partitioned area. , Formed to be continuous with the shape of the swirl most upstream side of the adjacent partitioned area,
Further, the first transition portion, the second transition portion, the second dent portion, and the first dent portion are sequentially reduced in the amount of change in the amount of gouging toward the outer peripheral side of the dent in the circumferential direction. For internal combustion engines.   2. The piston for an internal combustion engine according to claim 1, wherein at a portion of the second recess where the shelf is located, a mouth portion of a corner of the piston with a top portion is formed to protrude toward a piston center axis side. 3.   An internal combustion engine comprising the internal combustion engine piston according to claim 1. A piston for an internal combustion engine for an internal combustion engine for swirling intake air, having a cavity provided in a concave shape at the top of the piston, and a fuel injection nozzle provided in a cylinder head opposed to the center of the cavity. In the design method,
A first step of measuring or calculating a range in which the fuel spray injected from each injection hole of the fuel injection nozzle flows by a preset swirl,
A second step of measuring a mixture distribution of the injected fuel spray and intake air, and measuring or calculating a region having an equivalence ratio of less than 1 in which the amount of oxygen in the intake air mixed with respect to the amount of fuel spray is excessive;
A third step of dividing the region of the cavity such that the divided region for each injection hole of the fuel injection nozzle includes the region having an equivalence ratio of less than 1;
A fourth step of determining the shape of the cavity for each of the divided areas ,
In the fourth step,
In the direction in which fuel is injected from the injection hole, the outer peripheral wall of the cavity is disposed far from the center axis of the piston in order to increase the mixing distance until the fuel spray collides with the outer peripheral wall of the cavity,
On the downstream side of the swirl, after the fuel spray collides with the outer peripheral wall of the cavity, the mouth of the cavity is pushed out so as to push the fuel spray so as to mix with the intake air inside the cavity while being swirled. age,
On the swirl upstream side, after the fuel spray collides with the outer peripheral wall of the cavity, the outer peripheral wall of the cavity is arranged closer to the piston center axis side so as not to interfere with the adjacent fuel spray,
When the cross-sectional shape of the cavity in a plane including the piston center axis is rotated in a circumferential direction around the piston center axis along a swirl flow, the cavity is moved outward with this rotation. A method for designing a piston for an internal combustion engine, wherein the shape of the cavity is continuously formed so as to return to its original state after being spread .

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