JP2018150850A - diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine capable of promoting mixing with air by improving fluidity in a cavity even when a spray has low penetration.SOLUTION: A diesel engine includes: a cylinder 12a; a cylinder head 14; a piston 13 having a cavity 30; and a fuel injection valve 17 having nozzle holes 17a each oriented to inside of the cavity 30 located at a top dead center. The piston 13 further includes notch portions 40 each recessed radially from a cavity inner peripheral wall surface 30a over a crown surface side. The notch portion 40 includes: a first recess 60 provided in a cavity opening 31 and recessed to the outer diameter side of the cavity inner peripheral wall surface 30a; and a second recess 70 extending to the outer diameter side while continuing to an outer end of the first recess and recessed from a crown surface 13a to the piston bottom surface side. A rounded chamfered portion 43 is formed in a joining portion between the first recess 60 and the second recess 70.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a diesel engine, and more particularly to a direct injection diesel engine in which a cavity is recessed in a crown surface of a piston and fuel is directly injected into the cavity from a fuel injection valve.

  There is known a diesel engine in which a cavity is formed in a crown surface of a piston. In this engine, the fuel injected from the fuel injection valve reaches the vicinity of the peripheral edge of the cavity, and then is guided along the inner peripheral wall surface toward the center of the cavity to promote mixing with air. ing. In particular, in a medium load range or a high load range where a relatively large amount of fuel is injected, the penetration of the spray injected from the fuel injection valve is strong, and the spray speed is even at a position sufficiently away from the fuel injection valve. Is maintained at high speed and mixing with air is promoted.

  On the other hand, in the low load region where the fuel injection amount is small, the spray tends to stay in the vicinity of the peripheral edge of the cavity, and the miscibility with air is reduced. In order to improve the mixing with air, it is effective to increase the penetration of the spray, but if the penetration of the spray is unnecessarily strong, the amount of heat radiated from the wall near the peripheral edge of the cavity increases. As a result, the cooling loss increases.

  On the other hand, in Patent Document 1, in order to suppress cooling loss in a low load region, the shape of the cavity and the shape (length, length) of the injection hole of the fuel injection valve are prevented so that the penetration of the spray does not become unnecessarily strong. It is disclosed that the aperture is set so as to satisfy a predetermined relationship.

Japanese Patent Laying-Open No. 2015-232288

However, according to Patent Document 1, although an increase in cooling loss in a low load region can be suppressed, the fluidity of the spray is low and mixing with air in the cavity cannot be promoted. For this reason, local combustion tends to occur in the vicinity of the peripheral edge of the cavity, and NO _X and soot may increase due to the high temperature and oxygen shortage due to the local combustion.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a diesel engine that can improve the fluidity in the cavity and promote the mixing with air even in the case of a spray having a low penetration. To do.

  In order to solve the above problems, the present invention is configured as follows.

  The present invention according to claim 1 of the present application is a cylinder and a cylinder head that covers an end face of the cylinder, wherein the intake port for generating a swirl flow is formed in a combustion chamber, and the cylinder head A diesel engine comprising: a piston having a cavity recessed to the opposite side; and a fuel injection valve having an injection hole directed in the cavity of the piston located at a top dead center, Further includes a notch that is radially recessed from the inner peripheral wall surface of the cavity to the crown side, and the notch is provided at the peripheral edge of the cavity, and the inner peripheral wall surface of the cavity. A first recess recessed toward the outer diameter side, and extending to the outer diameter side continuously from the outer end of the first recess, recessed from the crown surface of the piston to the piston bottom surface side, Second It includes a part, characterized in that the chamfer R shape is formed at the junction between the first recess and the second recess.

  The invention according to claim 2 is the diesel engine according to claim 1, wherein the chamfered diameter of the chamfered portion is 2 mm or more.

  The invention according to claim 3 is the diesel engine according to claim 1 or 2, wherein the second recess has a vertical wall portion on the downstream side of the swirl flow on the downstream side of the swirl flow in plan view. The chamfered diameter of the chamfered portion is less than or equal to half of the radius of the peripheral portion of the second recess in plan view.

  According to a fourth aspect of the present invention, in the diesel engine according to any one of the first to third aspects, a plurality of the first concave portions and the second concave portions are formed at intervals in the circumferential direction. It is characterized by being.

  According to a fifth aspect of the present invention, in the diesel engine according to the fourth aspect, the fuel injection valve is located at the center in the radial direction when viewed in the central axis direction of the cylinder, and is radially It has a plurality of injection holes capable of injecting fuel.

  The invention according to claim 6 is the diesel engine according to claim 5, wherein each of the plurality of injection holes is positioned between the first recesses adjacent in the circumferential direction. It arrange | positions so that it may face the inner peripheral wall surface of the said cavity.

  According to the invention of each claim of the present application, the following effects can be obtained by the above configuration.

  First, according to the first aspect of the present invention, the horizontal flow (for example, swirl flow or squish flow) generated in the squish portion of the piston in the vicinity of the top dead center is transferred to the cavity through the first recess. It can be introduced so as to go to the center side. As a result, the spray injected from the fuel injection valve and positioned in the vicinity of the inner peripheral wall surface of the cavity is promoted to flow toward the center of the cavity by the air flow introduced by the first recess. That is, even if the spray is likely to stay on the inner peripheral wall surface of the cavity because of low penetration, the flow is promoted and the mixing with the air in the cavity can be improved.

  Moreover, an R-shaped chamfered portion (fillet) is formed at the joint portion (ridge line) between the first concave portion and the second concave portion. As a result, the air flow introduced from the squish portion into the second recess can be smoothly introduced into the first recess through the chamfered portion. If an R-shaped chamfer is not formed at the joint between the first recess and the second recess, the direction of air flow changes abruptly from the second recess to the first recess. The air flow introduced is reduced.

  Further, according to the invention described in claim 2, it is easy to guide the air flow from the second recess to the first recess along the chamfered portion. When the chamfered diameter of the chamfered portion is less than 2 mm, the effect of gently changing the direction of air flow from the second recessed portion to the first recessed portion is reduced.

  Moreover, according to invention of Claim 3, it can prevent that a 2nd recessed part lose | disappears by a chamfering part.

  According to the invention described in claim 4, since air flow is introduced into the cavity through the second recess and the first recess at a plurality of locations in the circumferential direction, the flow of the spray toward the cavity central portion side Is further strengthened.

  According to the fifth aspect of the present invention, the spray sprayed from the plurality of nozzle holes can be made to flow toward the cavity center by the air flow introduced from the plurality of notches. As a result, the spray whose mixing with air is promoted can be diffused substantially uniformly into the cavity.

  According to the invention of claim 6, since the spray is injected between the first recesses adjacent in the circumferential direction, the spray is introduced from the notch after being guided by the inner peripheral wall surface of the cavity. The flow of air to the center portion side is further promoted by the air flow.

  That is, the diesel engine according to the present invention can improve the fluidity in the cavity and promote the mixing with the air even when the spray has a low penetration.

1 is a cross-sectional view schematically showing a combustion chamber of an engine according to an embodiment of the present invention. Sectional drawing of the cavity which comprises a combustion chamber. The top view of the piston provided with the cavity. It is a figure which shows the structure of a fuel injection valve, (a) is a side view, (b) is sectional drawing. The perspective view which looked at the piston from the crown side. The front view of a notch part by A arrow view of FIG. The top view which expands and shows a notch part. The perspective view which expands and shows a notch part. Explanatory drawing which shows the spray and air flow in a cavity. Explanatory drawing which shows the combustion state in the first half of combustion. Explanatory drawing which shows the combustion state in the second half of combustion. The top view which shows the piston which concerns on a modification. Explanatory drawing which shows the spraying and air flow in the piston of FIG. Sectional drawing which shows the cavity at the time of changing the inclination-angle of a circumferential direction wall part. Explanatory drawing which shows the spray and air flow in the cavity of FIG.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In addition, the following description is only illustrations essentially and does not intend restrict | limiting this invention, its application thing, or its use. Further, the drawings are schematic, and the ratio of each distance is different from the actual one.

  FIG. 1 shows a combustion chamber structure of a diesel engine according to an embodiment of the present invention. A combustion chamber 11 of the engine 10 reciprocates within a cylinder 12a formed in a cylinder block 12 and the cylinder 12a. The piston crown surface 13a of the piston 13 to be opened, the lower surfaces of the intake valve 15 and the exhaust valve 16 that open and close the intake port 14a and the exhaust port 14b, respectively, and the piston of the cylinder head 14 in which the intake valve 15 and the exhaust valve 16 are disposed. The lower surface 14c is opposed to the crown surface 13a.

  Further, a cavity 30 that is recessed in a direction away from the lower surface 14 c of the cylinder head 14 is formed in the piston crown surface 13 a, and this inner space also constitutes the combustion chamber 11. The cavity 30 has a substantially circular basic shape in plan view. A fuel injection valve 17 is attached to the cylinder head 14. The fuel injection valve 17 is located in the center of the cylinder 12a in plan view, and is arranged so that the tip portion faces the combustion chamber.

  2 is a cross-sectional view of the combustion chamber 11 on a cross section passing through the central axis XX of the cylinder 12a, and FIG. 3 is a plan view of the combustion chamber 11. As shown in FIG. 2 and 3 both show a state in which the piston 13 is located at the compression top dead center, and the fuel spray injected from the fuel injection valve 17 is also indicated by the symbol F. FIG. The cavity 30 is set to a shape and size that can receive the fuel (spray F) injected from the fuel injection valve 17 when at least the piston 13 is located at or near the compression top dead center.

  As shown in FIG. 2, the cavity 30 is configured as a so-called reentrant type, is located in the cavity opening 31, and has a lip portion 32 that is reduced in diameter compared to the inside of the cavity 30, and the lip portion 32. A peripheral portion 33 that extends from the peripheral portion 33 toward the bottom of the cavity 30 and a central portion 34 that extends from the peripheral portion 33 toward the central portion of the cavity. The peripheral portion 33 is recessed outward in the radial direction so as to have a larger diameter than the lip portion 32. The central portion 34 is formed in a mountain shape that protrudes toward the fuel injection valve 17 located above the central portion.

  That is, in the cavity 30, the inner peripheral wall surface 30a constituting the radially outer wall portion of the cavity is constituted by the lip portion 32 and the radially outer portion of the peripheral portion 33, and the bottom wall portion 30b is formed in the central portion. 34 and the bottom portion of the peripheral portion 33.

  As shown in FIG. 3, a plurality of notches 40 are formed in the cavity opening 31. The notch 40 is formed to be radially recessed from the inner peripheral wall surface 30a of the cavity 30 to the piston crown surface 13a, and the air flow on the piston crown surface 13a is cavityd through the plurality of notches 40. The fluidity of the spray F in the cavity 30 is increased by being introduced into the inside of the cavity 30.

  A plurality of injection holes 17 a... 17 a are formed around the tip of the fuel injection valve 17. The fuel injection valve 17 is configured to inject fuel radially as shown in FIG. 3 when the injection hole 17a is located at or near the compression top dead center. 2, the spray F is configured to be directed near the boundary between the lip portion 32 and the peripheral portion 33 of the cavity 30.

  In the present embodiment, ten nozzle holes 17a are provided at equal intervals in the circumferential direction, and are formed in the same size. 4 is an enlarged view of the tip of the fuel injection valve 17, FIG. 4 (a) shows a side view, and FIG. 4 (b) shows a cross-sectional view taken along line BB in FIG. 4 (a). Show.

  As shown in FIG. 4B, the nozzle hole 17a is formed to have a predetermined nozzle hole diameter D and nozzle hole length L. The nozzle hole diameter D and the nozzle hole length L of the nozzle hole 17a are configured so as to satisfy a predetermined relationship with the cylinder diameter B (see FIG. 1), thereby reducing the spray F in the low load region. It is possible to realize penetration and reduce cooling loss, and to reduce soot in the medium and high load range.

2, the peripheral portion 33 of the cavity 30 includes a first portion 33a farthest from the fuel injection valve 17, a second portion 33b located on the lip portion 32 side of the first portion 33a, and a first portion 33a. And a third portion 33c located on the central portion 34 side. The first portion 33 a, the second portion 33 b, and the third portion 33 c are all configured by arcs having centers O ₁ , O ₂ , and O ₃ on the center side of the cavity 30.

In the present embodiment, the radius R ₂ of the arc of the second portion 33b is equal to the radius R ₃ of the arc of the third portion, and the radius R ₁ of the arc of the first portion 33a is equal to the radius R _2. It is smaller than and R _3. Accordingly, the peripheral portion 33 has the straight line YY connecting the injection hole 17a of the fuel injection valve 17 and the center position of the first portion 33a farthest from the injection hole 17a as an axis, and the second portion 33b side on both sides thereof. And the third portion 33c side are symmetrical.

Lip 32 following the second portion 33b of the peripheral portion 33, on the cross section including the central axis X-X of the cylinder 12a, and is formed by an arc having a center O ₄ in the counter-cavity center side.

  As shown by a two-dot chain line in FIG. 3, two intake ports 14 a and two exhaust ports 14 b are opened at four corners of the combustion chamber 11. The two intake ports 14a are composed of a helical port and / or a tangential port, and a portion opened to the combustion chamber 11 of at least one intake port 14a (port located in the lower right in FIG. 3 in this embodiment). Is configured to point in the clockwise direction in FIG.

  Accordingly, fresh air introduced into the combustion chamber 11 from the intake port 14a located at the lower right in FIG. 3 is easily introduced in the clockwise direction toward the combustion chamber 11, and the swirl flowing in the clockwise direction into the combustion chamber 11 A stream S is generated. The swirl flow S is generated not only on the piston crown surface 13 a but also inside the cavity 30.

  Further, in the combustion chamber 11, the air located in the squish portion between the piston crown surface 13 a and the lower surface 14 c of the cylinder head 14 flows into the cavity 30 as the piston 13 moves toward the compression top dead center. A squish flow V flowing from the outside to the inside is generated. That is, in this embodiment, the swirl flow S and the squish flow V are generated in the combustion chamber 11.

  Hereinafter, the notch 40 formed in the cavity opening 31 of the piston 13 will be described in detail with reference to FIGS. FIG. 5 is a perspective sectional view of the piston 13 and shows the cavity 30. FIG. 6 is a front view of the notch 40 as viewed in the direction of arrow A in FIG. FIG. 7 is an enlarged plan view showing the notch 40. FIG. 8 is an enlarged perspective view showing the notch 40. As shown in FIG. 5, a plurality of notches 40 are provided at equal intervals in the circumferential direction, and are formed to have the same size.

  The notch 40 includes a first recess 60 provided in the cavity opening 31 of the cavity 30 and a second recess 70 provided in the piston crown surface 13a continuously to the outer end in the piston radial direction. It is demarcated by a bottom wall portion 41 constituting a concave bottom surface and a pair of vertical wall portions 42 erected from both ends in the circumferential direction. The pair of vertical wall portions 42 includes an upstream vertical wall portion 42a located on the upstream side (swirl upstream side) of the swirl flow and a downstream vertical wall portion 42b located on the downstream side (swirl downstream side) of the swirl flow. Contains.

Referring also to FIG. 3, the notch 40 is provided at a position that avoids the spray F injected from the fuel injection valve 17. In other words, the nozzle hole 17a of the fuel injection valve 17 faces the non-notched portion 50 that is located between the adjacent notched portions 40 and is a basic shape portion of the cavity 30 (that is, the inner peripheral wall surface 30a). It is like that. Here, in this embodiment, the number N _C of the cutout portion 40, the number of the injection holes 17a of the fuel injection valve 17 (hereinafter, referred to as the injection hole number N _H) in relation to the following formula (1) It is set to satisfy the relationship.

N _H / 2 ≦ N _C ≦ N _H (1)

That is, the notch 40 is formed with a number that is not less than half of the number of nozzle holes _NH and not more than the number of nozzle holes _NH . In other words, the notch 40 is configured to be adjacent to at least one side in the circumferential direction of the spray F that has reached the inner peripheral wall surface 30 a of the cavity 30.

In the present embodiment, the same number of notches 40 as the number of injection holes _NH of the fuel injection valve 17 are provided. That is, the notches 40 are formed at equal intervals in the circumferential direction at 10 locations of the cavity opening 31, and the notches are formed on both sides in the circumferential direction of the sprays F injected to the non-notched portions 50. 40 are located adjacent to each other.

  The first recess 60 is recessed toward the piston outer diameter side from the cavity inner peripheral wall surface 30a, and is formed in a groove shape having a predetermined width in the circumferential direction. The first recess 60 has a first bottom wall 61 that extends in the circumferential direction opposite to the radial direction and forms a groove bottom surface, and a pair of first vertical walls in the circumferential direction that are erected at both ends of the circumferential direction. Part 62.

  As shown by a broken line in FIG. 2, the first bottom wall portion 61 extends in the circumferential direction and is inclined radially inward from the piston crown surface toward the peripheral portion 33 of the cavity 30. More specifically, on the cross-sectional view shown in FIG. 2, the lower end portion 61 a of the first bottom wall portion 61 is connected to the peripheral portion 33 of the cavity 30 in a tangential continuous manner. Therefore, the path from the first bottom wall portion 61 to the peripheral portion 33 is smoothly connected without being bent or stepped.

  In the present embodiment, the first bottom wall portion 61 is inclined radially inward from the piston crown surface side toward the peripheral portion 33 at an inclination angle α of about 30 ° with respect to the central axis XX of the cylinder 12a. Yes. The first bottom wall portion 61 does not have to be inclined radially outward toward the peripheral portion 33, and the inclination angle α is configured to be 0 ° (the circumferential wall portion 41 is parallel to the central axis XX). Alternatively, the inclination angle α may be increased from 30 ° or conversely decreased. Preferably, the inclination angle α is configured to be 0 ° or more and 50 ° or less.

  When the inclination angle α is less than 0 °, the path from the piston crown surface side to the first recess 60 is greatly bent radially outward in the cross section shown in FIG. 2, and the air flow on the piston crown surface 13a Is difficult to smoothly introduce into the cavity 30. On the other hand, the larger the inclination angle α, the smoother the path from the piston crown side to the first recess 60 can be configured in the cross section shown in FIG. Can be increased.

  However, when the inclination angle α exceeds 50 °, it is necessary to excessively reduce the volume of the cavity 30 in order to maintain the compression ratio of the combustion chamber 11. In this case, as shown by a dotted line in FIG. 14, when the cavity 30 is formed so that the inclination angle α of the first bottom wall portion 610 is larger than 50 ° and the central portion 340 is shallow, as shown in FIG. The spray F0 injected from the fuel injection valve 17 and the spray F1 whose direction is changed by the inner peripheral wall surface 30a and guided along the central portion 340 are likely to interfere with each other as indicated by F2 in the figure. The flow of F is hindered, and the effect of improving the mixing with air is reduced. On the other hand, if the cavity opening 31 is made small, the penetration of the spray F when it reaches the inner peripheral wall surface 30a becomes relatively strong, so that the cooling loss increases.

  In the present embodiment, the first bottom wall portion 61 has an inclination angle α set to 30 °, and is positioned so that the upper end portion 61b opens toward the piston crown surface in the radial direction. When the inclination angle α is small (for example, 0 °), the upper end portion 61b of the first bottom wall portion 61 is positioned so as to open toward the lip portion 32 side.

  As shown in FIG. 7, the pair of first vertical wall portions 62 in the circumferential direction includes an upstream first vertical wall portion 621 located on the upstream side of the swirl and a downstream first vertical wall portion located on the downstream side of the swirl. 622. The upstream first vertical wall portion 621 extends radially with respect to the center of the cylinder 12a. The downstream-side first vertical wall portion 622 is curved and extends in an arc toward the swirl upstream side radially outward. Moreover, as FIG. 6 shows, a pair of 1st vertical wall part 62 is extended in parallel with the central axis XX of the cylinder 12a, and is orthogonally crossed with respect to the piston crown surface 13a.

  As shown in FIG. 6, the second recess 70 is configured as a surface portion that is one step down from the piston crown surface 13 a so as to incline toward the piston bottom surface toward the swirl downstream side in the piston circumferential direction. It is recessed from the surface 13a to the piston bottom surface side. The second concave portion 70 includes a second bottom wall portion 71 that extends from the piston crown surface 13a so as to incline toward the piston bottom surface, and a second vertical wall portion 72 that stands up from the peripheral edge portion.

  The second bottom wall portion 71 extends so as to incline toward the piston bottom surface toward the swirl downstream side in a front view in the circumferential direction, and extends parallel to the radial direction in the radial direction. Specifically, referring to FIG. 8, among the points located on the peripheral edge of the downstream first vertical wall portion 622 on the cavity inner peripheral wall surface 30 a side, it is located on the innermost diameter side (that is, the lip portion 32 of the lip portion 32. The tip side) is a plane passing through the reference point P0 with the reference point P0 being orthogonal to a straight line extending radially from the central axis XX of the cylinder 12a (that is, orthogonal to the radial direction). Is assumed to be a virtual plane Q (indicated by a two-dot chain line).

  On the virtual plane Q, a straight line passing through the reference point P0 and extending in parallel with the central axis XX of the cylinder 12a is defined as a first line L1, along the second bottom wall portion 71 projected on the virtual plane Q. The extending straight line is defined as a second line L2, and the straight line extending along the piston crown surface 13a projected on the virtual plane Q is defined as a third line L3. Furthermore, the intersection of the first line L1 and the third line L3 is the first point P1, the intersection of the first line and the second line is the second point P2, and the intersection of the second line L2 and the third line L3 Is a third point P3.

  In this case, the position of the second point P2 is such that the distance H to the first point P1 is 2 mm or more in the direction parallel to the first line L1, and the third point in the direction parallel to the third line L3. The distance W from P3 is set to be 2 mm or more. Further, the second point P2 is located on the piston crown surface side with respect to the lower end portion 61a of the first bottom wall portion 61 (that is, the joint portion between the first bottom wall portion 61 and the inner peripheral wall surface 30a).

  As for the 2nd bottom wall part 71, the upstream edge part 73 located in the swirl upstream is located on the piston crown surface 13. The upstream edge 73 extends radially from the outer end of the upstream first vertical wall 621. That is, the second bottom wall portion 71 is configured to be inclined toward the piston bottom surface toward the swirl downstream side with the upstream edge portion 73 as a base axis.

  As shown in FIG. 7, the second vertical wall portion 72 is connected to the outer end portion of the downstream first vertical wall portion 622 and extends radially outward toward the upstream side of the swirl, It is connected to the outer end 73 a of the side edge 73. More specifically, the second vertical wall portion 72 is located on the circumference of the virtual circle C0 indicated by a two-dot chain line. A downstream first vertical wall 622 is also located on the circumference of the virtual circle C0. That is, the downstream vertical wall 42b of the notch 40 is configured as a curved surface continuously connected without a step by the downstream first vertical wall 622 and the second vertical wall 72.

  When a straight line extending in the radial direction through the first point P1 is a fourth line L4, and a concentric circle offset from the outer diameter side end of the piston 13 to the inner diameter side by a predetermined amount d is a circle C1, the virtual circle C0 is It is set as a circle in contact with the fourth line L4 and the circle C1. More specifically, the virtual circle C0 is set as a circle passing through the first point P1.

  That is, in the plan view shown in FIG. 7, the downstream vertical wall 42 of the notch 40 extends from the outer end 73a of the upstream edge 73 toward the downstream side of the swirl on the virtual circle C0 to the reference point. It reaches P0 and faces the central axis XX of the cylinder 12a at the reference point P0. The predetermined amount d is appropriately set so that a predetermined amount of the wall thickness between the second recess 70 and the outer peripheral surface of the piston 13 is ensured.

  An R-shaped chamfered portion 43 is formed at a joint portion between the first bottom wall portion 61 and the second bottom wall portion 71. Therefore, the bottom wall portion 41 of the cutout portion 40 is configured to gradually go from the circumferential direction toward the cavity 30 by the first bottom wall portion 61, the chamfered portion 43, and the second bottom wall portion 71. . The chamfered portion 43 extends while inclining radially inward toward the swirl downstream side. As shown in FIG. 2, the chamfered diameter r1 of the chamfered portion 43 is 2 mm or more, and is set to a size of half or less of the radius r0 (see FIG. 7) of the virtual circle C0.

  Further, since the second recess 70 is inclined toward the piston bottom surface toward the swirl downstream side, the second vertical wall portion 72 extends in an arc shape toward the radially inner diameter side toward the swirl downstream side. The height in the central axis XX direction of the cylinder 12a is gradually increased.

  Returning to FIG. 3, each notch 40 is formed in a predetermined angle range β around the central axis XX of the cylinder 12a. The notch 40 is open to the cavity inner peripheral wall surface 30a within the angle range β at the tip position of the lip portion 32, but toward the upstream side of the swirl as the downstream vertical wall portion 42b advances radially outward. Therefore, the circumferential width gradually decreases.

  The angle range β is set in consideration of the spray angle θ (spread in a plan view of FIG. 3) of the spray F so that the non-notched portion 50 that receives the spray F is secured in a predetermined angle range (at least 15 °). ing. The angle range β of the notch 40 is set so that the non-notch 50 has a wider angle range than the spray angle θ of the spray F, and the expected number of nozzle holes (for example, at most 16 nozzle holes). Is set to 7.5 ° or more and 30 ° or less.

  That is, in consideration of the spray angle θ of the spray F, the non-notched portion requires an angle range of at least 15 °. However, when the angle range β of each of the plurality of notched portions 40 is set to 7.5 °, the maximum The non-notched portion 50 can be secured in an angle range of 15 ° up to the fuel injection valve 17 having 16 injection holes. In addition, when the angle range β of each of the plurality of notches 40 is set to 30 °, the non-notch 50 can be secured in the angle range of 15 ° up to the fuel injection valve 17 having the maximum 8 injection holes.

  In the present embodiment, the angle range β of the notch 40 is set to 14 °, and in this case, the non-notch 50 is secured in an angle range of 22 ° and is wider than 15 °.

  Next, the function and effect of this embodiment will be described.

  FIG. 9 is a perspective view schematically showing the spray F and the air flow Z in the combustion chamber 11 when the piston 13 is positioned near the compression top dead center. In the present embodiment, as described above with reference to FIG. 3, a swirl flow S and a squish flow V are generated in the combustion chamber 11, and a piston crown located near the compression top dead center. These horizontal flows S and V generated on the surface 13a are introduced from the inner peripheral wall surface 30a of the cavity 30 toward the central portion 34 through the plurality of notches 40.

  The air flow Z generated in this case is composed of the swirl flow S that flows clockwise in a plan view and the squish flow V that flows from the radially outer side to the radially inner side, and from the notch 40 to the inside of the cavity 30. Will be introduced. For this reason, as shown in FIG. 9, the air flow Z introduced into the cavity flows in the clockwise direction along the swirl flow S and moves inward in the radial direction along the squish flow V. It will flow in a spiral toward the center.

  At this time, the notch 40 is configured by the first recess 60 and the second recess 70 continuous to the outer diameter side, and the downstream vertical wall portion 42a is radially inward toward the swirl downstream side. It is formed in an extending arc shape. As a result, the swirl flow S flowing in the circumferential direction on the piston crown surface 13a is gradually changed radially inward along the arc-shaped second vertical wall portion 72 of the second recess 70, and the first recess 60 Be guided to. That is, since the flow in the horizontal direction on the piston crown surface 13a can be introduced into the first recess 60 while suppressing loss, the air flow Z can be generated more effectively.

  Moreover, the 2nd recessed part 70 inclines in the piston bottom face side toward a swirl downstream. Accordingly, the swirl flow S flowing in the horizontal direction on the piston crown surface 13 a is guided to the first recess 60 while being changed in direction toward the piston bottom surface along the second bottom wall portion 71 of the second recess 70. That is, since the direction of the air flow in the horizontal direction on the piston crown surface 13a can be changed stepwise toward the piston bottom surface, the air flow Z is compared with the case where it is introduced directly from the piston crown surface 13a to the first recess 60. Can be gradually changed from the horizontal direction to the bottom surface of the piston. Therefore, the air flow Z from the piston crown surface 13a can be introduced into the cavity while suppressing loss.

  Further, an R-shaped chamfer 43 is formed at the joint between the first recess 60 and the second recess 70. As a result, the air flow Z introduced from the piston crown surface 13 a into the second recess 70 can be smoothly introduced into the first recess 60 through the chamfered portion 43. If an R-shaped chamfered portion is not formed at the joint between the first recess 60 and the second recess 70, the direction of the air flow Z changes rapidly from the second recess 70 to the first recess 60, so that a loss occurs. And air flow introduced into the cavity 30 is reduced.

  Here, FIG. 10 shows the first half of combustion in the low load region. As shown in FIG. 10, in the low load region, the spray F injected from the fuel injection valve 17 reaches the inner peripheral wall surface 30 a, and then most of the spray F travels along the peripheral portion 33 to the bottom side of the cavity 30. You can change the direction. However, the spray F is configured to have low penetration in the low load region, and therefore has low fluidity and stays in the vicinity of the peripheral portion 33.

  At this time, referring also to FIG. 9, the air flow Z introduced from the notch 40 flows spirally toward the central portion 34 while entraining the spray F located downstream in the swirl direction. . As a result, as shown in FIG. 10, the flow of the spray F staying in the peripheral portion 33 toward the central portion 34 is promoted, so that the mixing property between the spray F and the air in the cavity 30 is improved. .

  Moreover, since the air flow Z is directed in substantially the same direction as the direction of the spray F staying in the peripheral portion 33, the air flow Z can be easily assisted to the center portion 34 side without inhibiting the flow of the spray F, and the spray F Easy to improve fluidity. Moreover, since the 1st bottom wall part 61 of the 1st recessed part 60 is connected to the peripheral part 33 tangentially, the air flow Z introduced from the notch part 40 is smoothly introduced into the peripheral part 33. Cheap. This makes it easier to further improve the fluidity of the spray F.

Furthermore, in the present embodiment, since the radius R ₂ of the arc constituting the second portion 33b of the peripheral portion 33 is relatively large, as shown, the tangent line T-T direction at the site spray F collides And the spraying direction of the spray F can be reduced, so that the spray F can be smoothly introduced into the second portion 33b without violently colliding with the inner peripheral wall surface 30a and being scattered around the periphery.

  Further, according to the lip portion 32, the spray F colliding with the lip portion 32 side in the vicinity of the boundary with the second portion 33b is smoothly guided to the second portion 33b side without being scattered so much. The part is smoothly introduced into the cavity 30.

The spray F from the second portion 33b moves to the first portion 33a, the direction of flow from the radially outer side of the piston 3 inwards is changed, this time, the radius R ₁ of the first portion 33a and the second portion because 33b smaller than the radius R ₂ of, along with the diffusion of the spray F is suppressed, coupled with assistance by the air flow Z from the notch 40, its flow is accelerated, so that toward the third portion 33c .

  At this time, combustion of a part of the fuel is already started and combustion gas is generated, and the spray F is in a semi-combustion state in which the combustion gas and unburned fuel are mixed. The flow of this semi-combustion gas is the first part. By acceleration by 33a, the fuel adhering to the inner peripheral wall surface 30a of the cavity peripheral part 33 is blown off, and the generation of soot due to combustion in a local rich region caused by the adhering fuel is suppressed.

  In addition, the peripheral portion 33 has a straight line Y-Y connecting the position farthest from the fuel injection valve 17 and the injection hole 17a of the fuel injection valve 17 at the time of fuel injection in the first portion 33a as an axis of symmetry, and Since the second portion 33b side and the third portion 33c side are formed symmetrically, the flow of the semi-combustion gas that is once accelerated and then decelerated is centered on the farthest position in the first portion 33a. It becomes symmetrical, and the direction of flow from the radially outer side to the inner side of the piston 13 changes smoothly and reliably without being dispersed.

  Next, the second half of the combustion until the semi-combustion gas whose direction is changed radially inward of the piston 13 is mixed with a large amount of air in the central portion 34 of the cavity 30 will be described. As shown in FIG. The gas flow is guided by the third portion 33 c of the peripheral portion 33 toward the central portion 34 at the bottom of the cavity 30 whose central portion is convex from the peripheral portion 33.

At that time, since the radius R ₃ of the third portion 33 c in the peripheral portion 33 is larger than the radius R ₁ of the first portion 33 a, the spray F introduced into the third portion 33 c abruptly becomes closer to the cavity opening 31 side. Therefore, it is possible to avoid interference with the spray F injected from the fuel injection valve 17.

  As a result, the flow of the semi-combustion gas flows toward the central portion 34 side of the cavity 30 without being dispersed while maintaining the momentum, and is excellent in the amount of air present in the central portion of the combustion chamber 11. Mixing produces a uniform and lean combustion gas. And by the combustion progressing in that state, the generation of soot due to combustion in the rich region is suppressed, and the entire combustion gas is relatively lean, so that the soot generated in part is also effective Will be oxidized.

  That is, even if the spray F is likely to stay on the inner peripheral wall surface 30a of the cavity due to the low penetration, the flow is promoted and the miscibility with the air in the cavity 30 can be improved.

  Moreover, the air flow Z is introduced into the cavity 30 from the plurality of notches 40, and the spray F injected from the plurality of injection holes 17a is caused to flow toward the central portion 34 side of the cavity 30 by the air flow Z. Can do. Moreover, since the spray F is injected toward the non-notch part 50, after being changed in direction by being guided by the inner peripheral wall surface 30a of the cavity 30, the notch part 40 introduced in the same direction as this direction. The air flow Z from the air further promotes the flow toward the central portion 34 side.

  Each of the plurality of notches 40 is formed in an angle range of 7.5 ° or more and 30 ° or less around the central axis XX of the cylinder 12a in plan view. As a result, it is possible to secure the non-notched portion 50 in a predetermined angle range and guide the spray F to the inner peripheral wall surface 30a, and more effectively generate the air flow Z by the notched portion 40. it can. That is, when the notch 40 is formed in an angle range β of less than 7.5 °, the volume of the notch 40 becomes relatively small, and therefore the momentum of the air flow introduced by the notch 40 is small, and the spray The effect of promoting the flow of

  Further, when the notch 40 is formed in an angle range β exceeding 30 °, the flow promoting effect of the spray F by the notch 40 tends to converge to a substantially constant value, while the improvement margin is reduced. If the volume becomes excessively large, it is necessary to excessively reduce the volume of the cavity 30 in order to maintain the compression ratio of the combustion chamber 11. In this case, if the combustion chamber 11 is made shallower as described above with reference to FIGS. 14 and 15, the sprays injected from the fuel injection valve 17 easily interfere with each other, and the effect of improving the miscibility with air is reduced. . On the other hand, if the cavity opening 31 is made small, the penetration of the spray F when it reaches the inner peripheral wall surface 30a becomes relatively strong, so that the cooling loss increases.

  Further, as shown in FIG. 8, on the virtual plane Q, the position of the second point is such that the distance H from the first point P1 in the direction parallel to the first line L1 is 2 mm or more, and the third point The distance W from the third point P3 in the direction parallel to the line L3 is set to be 2 mm or more. According to this configuration, it is possible to prevent the shape of the first recess 60 from disappearing while forming the chamfer 43 having a chamfer diameter of at least 2 mm at the joint between the first recess 60 and the second recess 70.

  That is, when the chamfered diameter of the chamfered portion 43 is 2 mm and the distance W between the second point P2 and the third point P3 is less than 2 mm, the first recessed portion 60 disappears by the chamfered portion 43. There is a case. Further, since the distance H between the first point P1 and the second point P2 is 2 mm or more, the second concave portion 70 can be configured to have a predetermined depth range, and thereby, the squish flow caused by the second concave portion 70 is achieved. The guide action to the first recess 60 can be effectively exhibited.

  Further, the second point P <b> 2 is located on the piston crown surface side with respect to the lower end portion 61 a of the first bottom wall portion 61. According to this structure, it can prevent that the 2nd recessed part 70 appears on the cavity inner peripheral wall surface 30a directly. Therefore, the flow in the horizontal direction on the piston crown surface 13a is not directly introduced into the cavity 30 from the second recess 70, but the piston bottom surface side by step through the second recess 70 and the first recess 60 in order. You can change the direction.

  Further, the chamfered diameter r1 of the chamfered portion 43 is set to 2 mm or more. According to this configuration, it is easy to guide the air flow Z from the second recessed portion 70 to the first recessed portion 60 along the chamfered portion 43. When the chamfered diameter of the chamfered portion 43 is less than 2 mm, the effect of gently changing the direction of the air flow Z from the second concave portion 70 to the first concave portion 60 is reduced.

  Further, the chamfered diameter r1 of the chamfered portion 43 is set to a size equal to or less than half of the radius r0 of the virtual circle C0. According to this configuration, the chamfered portion 43 can prevent the second concave portion 70 from disappearing.

In FIGS. 11 to 13, a plan view of the combustion chamber 11, shows a variation of the number N _C was half of the injection hole number N _H of the fuel injection valve 17 of the notch 40. As shown in FIG. 11, the nozzle hole number N _H is 10, the number N _C of the cutout portion 40 is 5, each spray F injected from the fuel injection valve 17, at one side in the circumferential direction It is adjacent to the notch 40 and is adjacent to the spray F on the other side.

In this case, when the swirl flow S is generated in the combustion chamber 11, as shown in FIG. 12, the air flow Z is the spray F ₁ adjacent to the upstream side in the swirl direction S (counterclockwise side in FIG. 12). , The spray F ₂ adjacent to the downstream side in the swirl direction S (clockwise side in FIG. 12) is entrained and flows toward the central portion 34 side of the cavity 30.

Further, the angle range β of the notch 40 may be set as a function of the number of nozzle holes _NH . In this case, the number of injection holes N _H of the fuel injection valve 17 and the angle range β of the notch 40 are set so as to satisfy the relationship of the following expression (2).

(360 ° × 0.1) / N _H ≦ β ≦ (360 ° −N _H × 15 °) / N _H (2)

  That is, according to the lower limit value, at least 10% of the total angular range β of the notch portions 40 in the peripheral portion of the piston crown surface 13 a is secured, and the cavity 30 is interposed via the notch portion 40. The flow rate of the air flow introduced into the can be secured. Further, according to the upper limit value, the non-notched portion 50 can be secured in an angle range of at least 15 °, so that the spray F is received by the non-notched portion 50, and the cavity 30 is formed along the inner peripheral wall surface 30a. I can guide you.

  In the above embodiment, a piston having a reentrant type cavity has been described as an example. However, the present invention may be applied to a piston having various cavities such as a shallow bottom type or a toroidal type.

  Moreover, in the said embodiment, although the notch part 40 was provided with two or more in the cavity opening part 31, it is not restricted to this. That is, you may provide only one place. Also by this, an air flow can be introduced from the notch 40 to the cavity 30.

  About the piston 13 of Examples 1-4, the air flow Z in the cavity 30 was evaluated by CAE analysis. As shown in Table 1, Examples 1 to 4 differ only in the chamfered diameter r1 of the R-shaped chamfered portion 43 formed at the joint between the first bottom wall portion 61 and the second bottom wall portion 71, Others are the same. That is, in each notch portion 40, the distance H between the first point P1 and the second point P2 is set to 5 mm, and the inclination angle of the first bottom wall portion 61 is set to 30 °. The angle range β is set to 14 °.

  The cutout portion 40 according to the first embodiment is configured such that the chamfered diameter r1 of the chamfered portion 43 is 0.5 mm, and in the second to fourth embodiments, the chamfered diameter r1 increases in order of 2 mm, 2.5 mm, and 6 mm. Has been. The air flow Z in the low speed region of the piston 13 having the notch portion 40 according to Examples 1 to 4 is evaluated by the maximum flow velocity, and Table 1 shows that the maximum flow velocity of the air flow Z in Example 1 is 100. The maximum flow rate of ˜4 is indicated by an index.

  As is clear from Table 1, the maximum flow velocity of the air flow Z increases as the chamfered diameter r1 of the chamfered portion 43 increases. By setting the chamfered diameter r1 to at least 2 mm, the maximum flow velocity of the air flow Z can be effectively increased, and thereby the fluidity of the spray F in the cavity 30 can be enhanced.

[Reference Example]
About the piston 13 of Examples 5-8, the air flow Z in the cavity 30 was evaluated by CAE analysis. As Table 2 shows, Examples 5-8 differ only in the inclination angle (alpha) of the circumferential direction wall part 41 of the notch part 40, and others are the same. That is, each notch 40, the injection hole number N _H of the fuel injection valve 17 is 10, the number N _C of similarly notch 40 is also 10, the angular range β in the circumferential direction formed at 14 ° Has been. In the reference embodiment, the cutout portion 40 is constituted only by the first recess 60 and does not have the second recess 70.

  The notch portion 40 according to the fifth embodiment has an inclination angle α of 0 °, and in the sixth to eighth embodiments, the inclination angle α of the circumferential wall portion 41 increases in order of 20 °, 30 °, and 45 °. It is configured as follows. The air flow Z in the low speed region of the piston 13 having the notch portion 40 according to Examples 5 to 8 is evaluated based on the maximum flow velocity, and Table 2 shows the maximum air flow velocity in Example 5 as 100. The maximum flow rates of 6 to 8 are indicated by indices.

  As is clear from Table 2, the maximum flow velocity of the air flow Z increases as the inclination angle α of the notch 40 increases from 0 °. In particular, in Example 6, the maximum flow velocity of the air flow Z significantly increases when the inclination angle α is larger than 20 °. On the other hand, as can be seen from Examples 7 and 8, as the inclination angle α increases, the increase in the maximum flow velocity converges.

  Therefore, the maximum flow velocity of the air flow Z can be increased by setting the inclination angle α of the notch 40 to 0 ° or more, and thereby the fluidity of the spray F in the cavity 30 can be increased. On the other hand, by setting the inclination angle α of the notch 40 to 50 ° or less, the fluidity of the spray F can be effectively enhanced while suppressing the notch 40 from being excessively formed.

  As described above, according to the diesel engine according to the present invention, even if the spray is low penetration, the fluidity in the cavity can be improved and the mixing with air can be promoted. There is a possibility that it is preferably used.

DESCRIPTION OF SYMBOLS 10 Engine 11 Combustion chamber 12 Cylinder block 12a Cylinder 13 Piston 13a Piston crown surface 14 Cylinder head 14a Intake port 17 Fuel injection valve 17a Injection hole 30 Cavity 30a Inner peripheral wall surface 31 Cavity opening part 32 Lip part 33 Peripheral part 34 Central part 40 Cutting Notch portion 41 Bottom wall portion 42 Vertical wall portion 43 Chamfered portion 60 First concave portion 61 First bottom wall portion 62 First vertical wall portion 70 Second concave portion 71 Second bottom wall portion 72 Second vertical wall portion 50 Non-notched portion α Inclination angle of the first bottom wall β Angle range of the notch N _H Number of nozzle holes N _C Number of the notch

Claims (6)

A cylinder,
A cylinder head covering an end face of the cylinder, wherein the intake port for generating a swirl flow is formed in the combustion chamber;
A piston having a cavity recessed to the opposite side of the cylinder head;
A fuel injection valve having a nozzle hole directed in the cavity of the piston located at a top dead center;
The piston further includes a notch that is radially recessed from the inner peripheral wall surface of the cavity to the crown surface side,
The notch is
A first recess provided at a peripheral edge of the cavity and recessed toward an outer diameter side than an inner peripheral wall surface of the cavity;
A second recess that extends continuously from the outer end of the first recess to the outer diameter side and is recessed from the crown surface of the piston toward the piston bottom surface;
A diesel engine in which an R-shaped chamfer is formed at a joint between the first recess and the second recess. The chamfered diameter of the chamfered portion is 2 mm or more.
The diesel engine according to claim 1. The vertical recess on the downstream side of the swirl flow is formed in an arc shape extending toward the inner diameter side toward the downstream side of the swirl flow in the plan view,
The chamfered diameter of the chamfered portion is less than or equal to half of the radius of the peripheral portion of the second recess in plan view.
The diesel engine according to claim 1 or 2. A plurality of the notches are formed at intervals in the circumferential direction.
The diesel engine as described in any one of Claims 1-3. The fuel injection valve is located at the center in the radial direction when viewed in the central axis direction of the cylinder, and has a plurality of injection holes that can inject fuel radially.
The diesel engine according to claim 4. The fuel injection valve is arranged such that each of the plurality of injection holes is directed to a non-notched portion located between the notched portions adjacent in the circumferential direction.
The diesel engine according to claim 5.

Images