JP2010112350A - Piston of direct injection type diesel internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston of a direct injection type diesel internal combustion engine for enhancing combustion efficiency in a squish area with a simple structure, while maximally maintaining the volume of a combustion chamber. <P>SOLUTION: This piston 1 is provided for the direct injection type diesel internal combustion engine corresponding to a fuel injection nozzle N for atomizing fuel by force injected from nozzle ports H, and has the combustion chamber 10 and a recess 20. The combustion chamber 10 is arranged in a top part 1a. The recess 20 is independently arranged on the outer periphery of the combustion chamber 10 individually in response to a diffusion range of a fuel spray M injected from a plurality of nozzle ports H of the fuel injection nozzle N. A cross-sectional shape of the recess 20 in the radial direction of the piston 1 is arranged in response to the distribution of the fuel concentration of the fuel spray M different by a peripheral directional position to the center line C of the piston 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piston in which the outer periphery of a combustion chamber provided at the top is improved in order to reduce the generation of smoke and NOx in a direct injection diesel internal combustion engine.

  In the case of a piston corresponding to a fuel injection nozzle structured to atomize fuel into the combustion chamber with the injected momentum, about 90% of the injected fuel burns in the combustion chamber and the remaining about 10% burns in the squish area I know you will. Soot generated from the fuel burned in the squish area penetrates into the top land, causing seizure of the piston and piston ring, and deterioration of the lubricating oil. Therefore, it is necessary to increase the combustion efficiency in the squish area and promote soot oxidation.

  Rich lean burn is a method for reducing the amount of NOx discharged from a diesel internal combustion engine. In this method, rich combustion is performed from ignition to the initial stage, and then lean combustion is performed in the middle and later stages. In this way, while suppressing the amount of NOx generated, flammable intermediate organisms (CO, HC, cyan, etc.) and smoke components (C) produced by the early rich combustion can be removed by the later lean combustion. As a result, the amount of NOx and smoke generated is reduced.

The structure of a combustion chamber capable of performing rich lean burn is disclosed in the prior art of Patent Document 1. According to this, the annular groove is formed on the outer periphery of the combustion chamber provided on the top surface of the piston. In order to maintain the same compression ratio, the volume of the combustion chamber is reduced by the amount provided with the annular groove. In the vicinity of the top dead center, rich combustion is performed in the combustion chamber, and in the subsequent expansion stroke, lean combustion is performed in which combustible intermediate products and smoke are burned using air in the annular groove.
Japanese Patent Laid-Open No. 10-238350

  However, the piston structure described in the prior art of Patent Document 1 creates a fuel spray in the combustion chamber by collision diffusion, and agitates and mixes the fuel spray and air by a swirl of air entering from the intake port. Therefore, if a part of the air entering from the intake port is led to the annular groove provided around the combustion chamber, the stirring force of the combustion chamber due to swirl is insufficient, and a separate device is required to compensate for this. .

  Further, in the case of the piston structure described in the prior art of Patent Document 1, since the fuel is collided and diffused, even if an annular groove is provided on the outer periphery of the combustion chamber, the fuel spray is difficult to reach. On the other hand, in the case of a piston structure corresponding to a fuel injection nozzle having a structure in which fuel is atomized by the injected momentum, there is a possibility that fuel spray injected in the compression stroke enters the annular groove beyond the combustion chamber. is there. The fuel spray that has entered consumes oxygen in the annular groove at the beginning of combustion. As a result, oxygen is insufficient in the later stage of combustion, and the combustion efficiency in the squish area cannot be improved.

  It is conceivable to increase the volume of the annular groove in order to supply sufficient oxygen. However, it is not preferable because the volume of the combustion chamber must be reduced in order to maintain the compression ratio of the combustion chamber.

  Therefore, the present invention provides a piston for a direct injection type diesel internal combustion engine having a simple structure and improving the combustion efficiency in the squish area while maintaining the volume of the combustion chamber as much as possible.

  A piston according to the present invention is a piston of a direct injection type diesel internal combustion engine corresponding to a fuel injection nozzle that atomizes fuel with the momentum injected from an injection hole, and includes a combustion chamber and a depression. The combustion chamber is provided at the top. The depressions are independently provided on the outer periphery of the combustion chamber so as to individually correspond to the diffusion range of the fuel spray injected from the plurality of injection holes of the fuel injection nozzle. And the cross-sectional shape of the hollow along the radial direction of the piston is provided according to the distribution of the fuel concentration of the fuel spray that varies depending on the circumferential position with respect to the center of the piston.

  In this case, the fuel spray is provided so that the area of the cross-sectional shape of the depression is maximized at the circumferential position where the fuel concentration distribution of the fuel spray is maximized. Further, the range in which the depressions are provided in the circumferential direction of the piston is matched with the range in which the fuel spray is diffused in the circumferential direction.

  When a swirl is set in the combustion chamber, the recess is provided by being offset in the downstream direction of the swirl. Alternatively, the recess has a side wall closer to the fuel injection nozzle at an acute angle with respect to the top surface and a side wall far from the fuel injection nozzle at an obtuse angle with respect to the top surface. Or the depth of a hollow is provided in the dimension according to distribution of the fuel concentration of a fuel spray which changes with circumferential positions. Alternatively, the opening width of the recess in the radial direction centering on the fuel injection nozzle is set to a size corresponding to the distribution of the fuel concentration of the fuel spray that varies depending on the circumferential position. Or a hollow is provided inside half of the distance from the outer periphery of a top part to the outer periphery of a combustion chamber. Or a hollow makes the opening width of the radial direction centering on a fuel-injection nozzle into 1/3 or less of the distance from the outer periphery of a top part to the outer periphery of a combustion chamber. Alternatively, the recess has an arc shape centered on the fuel injection nozzle.

  According to the piston of the present invention, the air accumulated in the depression during the compression stroke can be supplied to the squish area during the expansion stroke, so that the combustion efficiency of the squish area is improved. As a result, the amount of smoke generated is reduced. In addition, depressions are provided individually corresponding to the diffusion ranges of the fuel sprays ejected from the respective nozzle holes. In order to maintain the same compression ratio as compared to the volume of the combustion chamber of the piston without the depression, it is necessary to reduce the volume of the combustion chamber by the amount of the depression. However, providing the depression does not significantly reduce the compression ratio of the combustion chamber. In other words, the volume of the combustion chamber can be maintained substantially the same as that of the conventional one, so that the influence on the characteristics of the diesel internal combustion engine equipped with this piston is small.

  And the cross-sectional shape of the hollow in alignment with the radial direction of a piston is provided according to distribution of the fuel concentration of fuel spray. Therefore, the mixing ratio of fuel spray and air in the cylinder is easily homogenized, and combustion is stabilized.

  Further, according to the piston of the invention in which the cross-sectional shape of the depression is matched to the fuel concentration distribution of the fuel spray, or the range in which the depression is provided in the diffusion range of the fuel spray is matched, the mixing ratio of the fuel spray and air is further uniform. Therefore, combustion is stabilized and combustion efficiency is improved.

  According to the piston of the invention in which the position of the depression is offset by the amount of the swirl, the depression is arranged just at the position where the atomized fuel injected from the fuel injection nozzle is caused to flow downstream by the swirl. Therefore, since the air accumulated in the depression can be efficiently provided for the fuel spray diffused to the squish area, the combustion efficiency can be improved.

  According to the piston of the invention in which the angle formed by the inner peripheral side wall of the recess with respect to the top surface is an acute angle, even when the fuel spray injected from the fuel injection nozzle is diffused into the squish area during the compression stroke, The fuel spray is difficult to enter. Since air can be reliably held inside the recess, sufficient oxygen can be supplied to the squish area in the expansion stroke. As a result, the combustion efficiency in the squish area is improved and the amount of smoke generated is reduced.

  According to the piston of the invention in which the depth of the recess is set to a depth corresponding to the fuel concentration distribution of the fuel spray, an amount of air corresponding to the amount of fuel can be supplied from the recess. Therefore, the combustion efficiency in the squish area is improved and the amount of smoke generated is reduced. In addition, the volume of the recess can be kept to the minimum necessary by combining with the distribution of the fuel concentration, so that the amount of reducing the volume of the combustion chamber can be reduced. That is, there is little influence on the characteristics of the diesel internal combustion engine equipped with this piston.

  Furthermore, the fact that the depth of the depression is set according to the fuel concentration distribution of the fuel spray means that both ends of the depression are shallow in the circumferential direction. If the swirl is set, the airflow from the swirl enters the recess and stirs. Even if the operating condition deteriorates and driving soot accumulates in the depression, the retired soot is scraped out by the swirl airflow when the operating condition is recovered.

  According to the piston of the invention in which the opening width of the recess along the radial direction of the piston is provided with a recess having a shape that differs in the circumferential position in accordance with the fuel concentration distribution of the fuel spray, the amount of air corresponding to the amount of fuel Can be provided from the recess. As a result, the combustion efficiency in the squish area is improved and the amount of smoke generated is reduced.

  According to the piston of the invention in which the center of the opening width of the hollow in the radial direction of the piston is closer to the combustion chamber than the half of the distance from the outer peripheral edge of the combustion chamber to the outer periphery of the top, the piston is sucked into the squish area during the expansion stroke. Air can be supplied to the combustion gas in the combustion chamber that has been discharged from the recess at an early stage. Therefore, the combustible intermediate product (CO, HC, cyan) and smoke component (C) can be combusted before the combustion gas spreads to the squish area. Therefore, the generation amount of soot can be suppressed.

  The opening width of the dent in the radial direction of the piston is made smaller than the width of the bottom wall of the dent, or less than 1/3 of the distance from the outer periphery of the combustion chamber to the outer periphery of the top, that is, the width of the squish area. According to the piston of the invention, it is easy to hold air inside the recess.

  A piston 1 according to a first embodiment of the present invention will be described with reference to FIGS. The piston 1 is a piston for a direct injection type diesel internal combustion engine, and has a combustion chamber 10 having a shape corresponding to a fuel injection nozzle N that atomizes fuel with the momentum injected from the injection hole H. As shown in FIGS. 1 and 2, the fuel injection nozzle N is disposed on the center line C of the piston 1 and has injection holes H for injecting fuel radially in six directions. The combustion chamber 10 is provided at the top 1 a of the piston 1 with the fuel injection nozzle N as the center. In the state where the piston 1 is located at the top dead center shown in FIG. 3, there is almost no gap between the lower surface 2 a of the cylinder head 2 and the top surface T of the piston 1.

  The peripheral wall 11 of the combustion chamber 10 is provided at a point where the fuel ejected from the fuel injection nozzle N has changed from a liquid column to a spray. Further, the bottom wall 12 of the combustion chamber 10 projects in a conical shape toward the fuel injection nozzle N at the center. The outer peripheral edge 13 formed by the peripheral wall 11 and the top surface T of the piston 1 has an acute reentrant angle. That is, the combustion chamber 10 is a so-called reentrant combustion chamber.

  In the squish area 14 that extends from the combustion chamber 10 to the outer periphery, recesses 20 are provided at positions that individually correspond to the diffusion ranges of the fuel sprays M ejected from the six nozzle holes H, respectively. Each recess 20 is independent of the combustion chamber 10 and the adjacent recess 20 and is provided in an arc shape along the outer periphery of the combustion chamber 10 with the fuel injection nozzle N as the center, as shown in FIG. In the present embodiment, “independently” means that the portions (combustion chamber 10 and depression 20) that are recessed from the top surface T of the piston 1 are not connected to each other.

  At this time, the center position K of the depression 20 in the radial direction of the piston 1 is provided so as to be inside the position L that is half of the distance from the outer periphery of the top 1 a of the piston 1 to the outer peripheral edge 13 of the combustion chamber 10. The opening width W of the recess 20 in one radial direction centering on the fuel injection nozzle N is 1/3 or less of the distance from the outer periphery of the top portion 1a to the outer peripheral edge 13 of the combustion chamber 10, that is, the radial direction of the piston 1. The width of the squish area 14 is 1/3 or less.

  When fuel is injected in the compression stroke as shown in FIG. 1 with respect to the piston 1 configured as described above, the fuel is atomized and hits the peripheral wall 11 in the state of the fuel spray M, and a part thereof is a combustion chamber. 10 is spread to the squish area 14 beyond the outer peripheral edge 13. At this time, most of the fuel spray M diffused in the squish area 14 is pushed back from the squish area 14 toward the combustion chamber 10 as the piston 1 approaches the top dead center. Since the opening width W of the depression 20 is 1/3 or less of the width of the squish area 14, the amount of the fuel spray M that is replaced with air and enters the depression 20 is small, and the air accumulates in the depression 20.

  As shown in FIG. 3, when combustion is started at the top dead center, the combustion region B expands into the combustion chamber 10 and expands to the squish area 14 as shown in FIG. 4 as the piston 1 is lowered in the expansion stroke. At this time, since the pressure in the combustion chamber 10 is lowered as the piston 1 is lowered, the air secured in the depression 20 is released to the squish area 14. As a result, the fuel spray M that has entered the squish area 14 in the compression stroke and the oxygen in the air that has entered the dent 20 are supplied to the combustion region B that has spread to the squish area 14. Promoted.

  Thus, this piston 1 is provided with the recess 20 in the squish area 14 on the outer periphery of the combustion chamber 10 so as to correspond to the diffusion range of the fuel spray M. The combustion of the fuel that has entered the squish area 14 in the compression stroke and the smoke component in the combustion region B that expands in the squish area 14 in the expansion stroke can be promoted, so that the amount of soot is reduced and the combustion efficiency is improved.

  The recess 20 is provided so that the center of the opening width W is located inside the half of the squish area 14 in the radial direction of the piston 1. Therefore, air can be supplied from the depression 20 at an early stage to the combustion region B that expands to the squish area 14 in the expansion stroke.

  Further, the piston 1 supplies the air secured in the depression 20, that is, oxygen therein, to the combustion region B that expands to the squish area 14 in the expansion stroke in the later stage of combustion, and smoke in the combustion region B To burn. Therefore, the piston 1 can reduce the amount of smoke generated under the operating conditions where the fuel consumption is good but the amount of smoke generated is large.

  Further, the piston 1 is provided with a recess 20 corresponding to the diffusion range of the fuel spray M. Therefore, as shown in FIGS. 1 and 2, oxygen can be efficiently supplied to the region where the fuel spray M has entered. Further, since the depression 20 is provided only in the portion corresponding to the diffusion range of the fuel spray M, the amount of reducing the volume of the combustion chamber 10 can be minimized in order to maintain the compression ratio of the combustion chamber 10.

  The piston 1 of 2nd Embodiment which concerns on this invention is demonstrated with reference to FIG. A counterclockwise swirl S is set in the combustion chamber 10 of the piston 1 as shown in FIG. Therefore, when the fuel injected from the nozzle hole H of the fuel injection nozzle N is atomized and becomes the fuel spray M, it flows into the swirl S. Therefore, the recess 20 of the piston 1 in the present embodiment is provided to be offset in the downstream direction of the swirl S with respect to the nozzle hole H as shown in FIG. In other words, the nozzle hole H of the fuel injection nozzle N is provided toward the upstream side with respect to the recess 20 by the amount that the swirl S is set.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawings and the description thereof is omitted. Moreover, the cross-sectional shape of the top part 1a of the piston 1 shall refer to FIG. 1, FIG. 2, and FIG. 3 of the first embodiment.

  A piston 1 according to a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. As shown in FIG. 6, the depth of the recess 20 of the piston 1 changes along the circumferential direction. That is, both end portions 21 of the recess 20 are shallow in the circumferential direction of the piston 1 and the central portion 22 is deep. As shown in FIG. 7, the distribution of the fuel concentration (fuel density) of the fuel spray M is thick at the center of the fuel spray M and thin at the periphery.

  Therefore, the cross-sectional shape of the recess 20 along the radial direction of the piston 1 is provided in accordance with the distribution of the fuel concentration of the fuel spray M that varies depending on the circumferential position with respect to the center of the piston 1. Specifically, as shown in FIG. 7, the depth of the recess 20 is set to a dimension according to the distribution of the fuel concentration of the fuel spray M that varies depending on the circumferential position. In the present embodiment, the recess 20 is provided so that the cross-sectional area of the recess 20 is maximum at the position where the fuel concentration of the fuel spray M is maximum, and in this case, the depth is maximum.

  The piston 1 configured as described above can supply oxygen from the recess 20 in an amount suitable for the density distribution of the fuel spray M that has entered the squish area 14. As a result, the combustion temperature and combustion speed in the combustion region B can be homogenized, and soot generation can be reduced.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawings and the description thereof is omitted. When the swirl S is set, for example, a deviation such that the downstream side is shallow and the upstream side is deep along the direction of the swirl S is included so as to match the distribution of the fuel density of the fuel spray M. A recess 20 that is asymmetric in the direction may be provided.

  A piston 1 according to a fourth embodiment of the present invention will be described with reference to FIG. The depression 20 of the piston 1 is different from the previous embodiment in the opening width W in the radial direction centered on the center line C of the piston 1 and the fuel injection nozzle N. The opening width W of the recess 20 of the piston 1 according to the present embodiment is set to a size according to the distribution of the fuel concentration of the fuel spray M that varies depending on the circumferential position. That is, the cross-sectional shape of the depression 20 along the radial direction of the piston 1 is provided according to the distribution of the fuel concentration of the fuel spray that varies depending on the circumferential position with respect to the center line C of the piston 1. The opening width W is made to correspond to the fuel concentration distribution.

  As shown in FIG. 8, the recess 20 has an opening shape in which the base of an isosceles triangle faces the fuel injection nozzle, and the center of the fuel spray M that is the injection direction of the fuel injected from the injection hole H is the widest opening width. W is large, and the opening width W decreases as the distance from the center increases.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawings and the description thereof is omitted. In addition, regarding the cross-sectional shape of the combustion chamber 10 and the arrangement of the depressions 20, the first embodiment and FIGS. 1 to 4 are referred to. When the swirl S is set, the arrangement of the recesses 20 may be offset as shown in FIG. 5 and the triangle may be a triangle whose apex is biased to the upstream side of the swirl S. Further, the depth of the recess 20 may be changed according to the circumferential position in accordance with the fuel density distribution of the fuel spray M.

  A piston 1 according to a fifth embodiment of the present invention will be described with reference to FIG. As for the hollow 20 of this piston 1, the opening width W of the radial direction centering on the fuel-injection nozzle N is changing similarly to 4th Embodiment. As shown in FIG. 9, the recess 20 of the piston 1 of the present embodiment has a rhombus opening shape that is long in the circumferential direction. Similar to the depression 20 of the fourth embodiment, the opening width W corresponds to the distribution of the fuel density of the fuel spray M, and the center of the fuel spray M is the largest and becomes smaller as the distance from the center increases.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawing and the description thereof is omitted. In addition, regarding the cross-sectional shape of the combustion chamber 10 and the arrangement of the depressions 20, the first embodiment and FIGS. 1 to 4 are referred to. Further, when the swirl S is set, the arrangement of the depressions 20 is offset as shown in FIG. 5, and a long rhombus is formed downstream of the swirl S with respect to the diagonal passing through the center line C of the piston 1. Make an opening shape. In the present embodiment, only the opening width W is changed with respect to the distribution of the fuel density of the fuel spray M, but a change in the depth direction may be further added to the recess 20 as in the third embodiment.

  A piston 1 according to a sixth embodiment of the present invention will be described with reference to FIG. The recess 20 of the piston 1 has an opening width W in the radial direction centered on the fuel injection nozzle N as in the fourth and fifth embodiments, and has an opening along the shape of the fuel spray M. It has a shape. That is, as shown in FIG. 10, the opening shape of the dent 20 is a crescent shape. Since the opening shape along the fuel spray M is provided, oxygen can be supplied in a more suitable range with respect to the recess 20 of the fourth and fifth embodiments.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawing and the description thereof is omitted. In addition, regarding the cross-sectional shape of the combustion chamber 10 and the arrangement of the depressions 20, the first embodiment and FIGS. 1 to 4 are referred to. When the swirl S is set, a teardrop-shaped opening shape having a tail extending downstream is provided along the shape of the fuel spray M formed by the swirl S shown in FIG. In the present embodiment, only the opening width W is changed with respect to the fuel density distribution of the fuel spray M, but a change in the depth direction may be added to the recess 20 as in the third embodiment.

  A piston 1 according to a seventh embodiment of the present invention will be described with reference to FIG. As shown in FIG. 11, the recess 20 of the piston 1 has a constant opening width W in the radial direction centered on the fuel injection nozzle N, and is an oval extending straight in a direction perpendicular to the radial direction. The opening shape is as follows. Easy to process due to its simple shape.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawing and the description thereof is omitted. In addition, regarding the cross-sectional shape of the combustion chamber 10 and the arrangement of the depressions 20, the first embodiment and FIGS. 1 to 4 are referred to. Further, when the swirl S is set, the recess 20 is provided by being offset by the amount of the swirl S as in the second embodiment. Further, as in the third embodiment, the depth of the recess 20 may be changed in the circumferential position according to the fuel density distribution of the fuel spray M.

  A piston 1 according to an eighth embodiment of the present invention will be described with reference to FIG. In the recess 20 of the piston 1 shown in FIG. 12, an inner peripheral side wall 23 near the fuel injection nozzle N is provided at an acute angle with respect to the top surface T. Further, the outer peripheral side wall 24 far from the fuel injection nozzle N is provided at an obtuse angle with respect to the top surface T, and faces the inner peripheral side wall 23 substantially in parallel. The bottom wall 25 of the recess 20 is provided in parallel to the top surface T, and has a constant depth in the circumferential direction of the piston 1.

  The opening shape of the recess 20 may be an arc shape parallel to the outer peripheral edge 13 of the combustion chamber 10 or a rectangle extending perpendicular to the radial direction of the piston 1. The recess 20 is disposed on the top 1a of the piston 1 corresponding to the fuel spray M that is injected and diffused from the fuel injection nozzle N.

  Since the configuration of the piston 1 other than the above is the same as that of the piston 1 of the first embodiment, the same reference numerals are given in the drawing and the description thereof is omitted. For the arrangement of the combustion chamber 10 and the recess 20 and the like, the first embodiment and FIG. 2 are referred to. In addition, when the swirl S is set, the depression 20 is arranged with an offset by the amount of the swirl S as in the second embodiment. As in the third embodiment, the depth of the depression 20 may be changed at the circumferential position according to the fuel density distribution of the fuel spray M. Further, as in the piston 1 of the fourth to sixth embodiments, the opening width W of the recess 20 may be changed in accordance with the fuel density distribution of the fuel spray M.

  In the piston 1 configured as described above, fuel is injected from each injection hole H in the range of −30 ° to 0 ° ATDC during the compression stroke. As shown in FIG. 12, since there is a gap between the squish area 14 and the cylinder head 2, a part of the fuel spray M beyond the outer peripheral edge 13 of the combustion chamber 10 is diffused to the squish area 14 side. At this time, since the side wall 23 on the inner peripheral side of the depression 20 is provided at an acute angle with respect to the top surface T, the inside of the depression 20 is not easily replaced by the fuel spray M. Therefore, a lot of air is stored in the recess 20. When shifting to the expansion stroke beyond the top dead center, it is possible to supply the air secured in the depression 20, that is, oxygen in the air. As a result, the fuel that has not been completely combusted in the combustion chamber 10 and the fuel that has entered the squish area 14 are burned, so that the amount of smoke discharged is reduced.

  A piston 1 according to a ninth embodiment of the present invention will be described with reference to FIG. The piston 1 shown in FIG. 13 is different from that of the previous embodiment in the cross-sectional shape of the recess 20. The side wall 23 on the inner peripheral side of the recess 20 is provided at an acute angle with respect to the top surface T. The side wall 24 on the outer peripheral side of the recess 20 is provided at an obtuse angle with respect to the top surface T such that the lower end is connected to the lower end of the side wall 23 on the inner peripheral side. Therefore, the recess 20 is formed so that the inner side is deep in the radial direction of the piston 1 and becomes shallower toward the outside. The configuration of the piston 1 other than the above is the same as that of the eighth embodiment.

  In the piston 1 configured as described above, the fuel spray M injected in the compression stroke is unlikely to enter the inside of the recess 20 as in the eighth embodiment. Therefore, the air supplied to the squish area 14 in the expansion stroke Can be stored in the depression 20.

Sectional drawing which shows the piston of 1st Embodiment which concerns on this invention, and its periphery. The top view which shows the top surface of the piston shown in FIG. Sectional drawing which shows the piston periphery when the piston shown in FIG. 1 exists in a top dead center. Sectional drawing which shows the piston periphery when the piston shown in FIG. 1 exists in an expansion stroke. The top view which shows the top part of the piston of 2nd Embodiment which concerns on this invention. The perspective view which shows the hollow of the piston of 3rd Embodiment which concerns on this invention. The figure which shows the relationship between the hollow of a piston shown in FIG. 6, and a fuel density. The top view which shows the hollow of the piston of 4th Embodiment which concerns on this invention. The top view which shows the hollow of the piston of 5th Embodiment which concerns on this invention. The top view which shows the hollow of the piston of 6th Embodiment which concerns on this invention. The top view which shows the hollow of the piston of 7th Embodiment which concerns on this invention. Sectional drawing which shows the hollow of the piston of 8th Embodiment which concerns on this invention. Sectional drawing which shows the hollow of the piston of 9th Embodiment which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piston, 1a ... Top part, 10 ... Combustion chamber, 11 ... Perimeter wall, 12 ... Bottom wall, 13 ... Outer periphery, 14 ... Squish area, 20 ... Depression, 23 ... (Inner periphery side) Side wall, 24 ... (Outer periphery) Side wall, C ... center line, H ... injection hole, M ... fuel spray, N ... fuel injection nozzle, S ... swirl, T ... top surface.

Claims (9)

A direct-injection type diesel internal combustion engine piston corresponding to a fuel injection nozzle that atomizes fuel by the momentum injected from the injection hole,
A combustion chamber recessed at the top,
A depression provided independently on the outer periphery of the combustion chamber in correspondence with the diffusion range of the fuel spray injected from the plurality of nozzle holes of the fuel injection nozzle, and the depression along the radial direction of the piston. The piston is characterized in that the cross-sectional shape is provided in accordance with the distribution of the fuel concentration of the fuel spray that varies depending on the circumferential position with respect to the center of the piston. The piston according to claim 1,
The area of the cross-sectional shape of the depression is maximized at the circumferential position where the fuel concentration distribution of the fuel spray is maximized. The piston according to claim 1 or claim 2,
The range in which the depression is provided in the circumferential direction of the piston is the same as the range in which the fuel spray is diffused in the circumferential direction. The piston according to claim 1 or claim 2,
When the swirl is set in the combustion chamber, the recess is provided by being offset in the downstream direction of the swirl. The piston according to claim 1 or claim 2,
The recess is characterized in that a side wall close to the fuel injection nozzle is provided at an acute angle with respect to the top surface, and a side wall far from the fuel injection nozzle is provided at an obtuse angle with respect to the top surface. The piston according to claim 1 or claim 2,
The recess is provided at a depth corresponding to a fuel concentration distribution of the fuel spray, which varies depending on a circumferential position. The piston according to claim 1 or claim 2,
The depression is provided with a size corresponding to a distribution of fuel concentration of the fuel spray, the opening width in the radial direction centering on the fuel injection nozzle being different depending on the circumferential position. The piston according to claim 1 or claim 2,
The recess is provided on the inner side of half of the distance from the outer periphery of the top to the outer peripheral edge of the combustion chamber. The piston according to claim 1 or claim 2,
The depression has a radial opening width centered on the fuel injection nozzle, which is 1/3 or less of a distance from an outer periphery of the top portion to an outer peripheral edge of the combustion chamber.

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