JP2019019676A - Combustion chamber structure of direct injection type internal combustion engine - Google Patents

Abstract

To effectively suppress smoke.SOLUTION: A combustion chamber structure of a direct injection type internal combustion engine comprises a cavity 11 which is recessed at center part of a piston apex face 8, and an external peripheral part 20 of the piston apex face which is located outside the cavity in a radial direction. The external peripheral part of the piston apex face comprises: a first tapered face part 21 which is connected to an inner wall 30 of the cavity defining the cavity, and located outside the radial direction; and a second tapered face part 22 which is connected to the first tapered face part, located outside the radial direction indicator, and has an inclination angle θ2 which is larger than the first tapered face part with respect to a virtual plane face f which is vertical to a piston center axis C. The first tapered face part and the second tapered face part are formed so as to move a vortex flow in a vertical direction conforming to the movement of a rich region when the rich region moves to the outside of the radial direction sequentially along the first tapered face part and the second tapered face part.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a combustion chamber structure of a direct injection internal combustion engine, and more particularly to a combustion chamber structure suitable for a diesel engine.

  For example, a combustion chamber structure of a direct-injection internal combustion engine, which is a diesel engine, generally includes a cavity recessed in the center of a piston top surface. The fuel is self-ignited in the cylinder by injecting the fuel near the compression top dead center toward the cavity.

JP-A-2-149719 JP-A-3-279617 JP 2006-125388 A

  In many cases, the outer periphery of the top surface of the piston located radially outside the cavity is a simple flat or flat surface. However, according to the result of earnest research by the present inventor, it was found that such a flat surface cannot efficiently use the air in the space above it, which is disadvantageous for smoke suppression.

  Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide a combustion chamber structure of a direct injection internal combustion engine that can effectively suppress smoke.

According to one aspect of the invention,
A cavity recessed in the center of the piston top surface;
An outer periphery of the piston top surface located radially outward of the cavity;
With
The outer periphery of the piston top surface is
A first tapered surface portion connected to an inner wall of the cavity defining the cavity and positioned radially outward thereof;
A second taper surface portion connected to the first taper surface portion and located radially outside thereof, and having an inclination angle larger than the first taper surface portion with respect to a virtual plane perpendicular to the piston central axis;
With
When the rich region moves radially outward along the first tapered surface portion and the second tapered surface portion while the piston is descending, the vortex flow in the vertical direction is moved in accordance with the movement of the rich region. There is provided a combustion chamber structure for a direct injection internal combustion engine, wherein a first tapered surface portion and the second tapered surface portion are formed.

  Preferably, the outer peripheral portion of the piston top surface is further connected to the second taper surface portion and is positioned on the radially outer side, and further includes a flat portion perpendicular to the piston central axis.

Preferably, the cavity inner wall has a bottom wall portion, and the bottom wall portion has a slope portion that gradually increases as it approaches the piston central axis,
The slope portion is
A first curved surface portion that is located on the radially outer side and is formed in a cross-sectional arc shape having a center of a first curvature radius above the bottom wall portion;
A second curved surface portion connected to the first curved surface portion and positioned radially inwardly, and formed in a cross-sectional arc shape having a center of a second radius of curvature below the bottom wall portion;
Is provided.

  Preferably, the second radius of curvature is greater than the first radius of curvature.

  Preferably, the cavity is a reentrant type cavity.

  According to the present invention, smoke can be effectively suppressed.

It is a longitudinal cross-sectional view which shows the piston of embodiment of this invention. It is a longitudinal cross-sectional view which shows the mode inside the combustion chamber in a 1st specific timing. It is a longitudinal cross-sectional view which shows the mode of the inside of a combustion chamber in a 2nd specific timing. It is a longitudinal cross-sectional view which shows the mode of the inside of a combustion chamber in a 3rd specific timing.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following embodiment.

  The combustion chamber structure according to this embodiment is applied to a diesel engine that is a typical example of a direct injection internal combustion engine. The engine is for vehicles, and is used as a vehicle power source for large vehicles such as trucks. However, the types and applications of the internal combustion engine and the vehicle are not limited to these. For example, the vehicle may be a small vehicle such as a passenger car, and the engine may be a gasoline engine.

  As shown in FIG. 2, the combustion chamber structure 1 of the present embodiment includes a piston 2, a cylinder 3 in which the piston 2 can be moved up and down and accommodated coaxially, a cylinder head 4 that closes an upper end opening of the cylinder 3, and a piston 2. Are provided with a plurality of piston rings 5 (only three are shown in the present embodiment, only one is shown) and a combustion chamber 6 which is a closed space defined by these piston rings 5. As shown in FIG. 1, the combustion chamber structure 1 includes an injector 7 that is attached to the cylinder head 4 and injects fuel into the combustion chamber 6.

  As shown in FIG. 1, the piston 2 is configured to be substantially symmetric with respect to the piston central axis C. Unless otherwise specified, the axial direction, radial direction, and circumferential direction with respect to the piston central axis C are simply referred to as axial direction, radial direction, and circumferential direction. The piston 2 has a top surface (piston top surface) 8 and an outer peripheral surface 9. A plurality of (three in the present embodiment) ring grooves 10 for fitting the piston ring 5 are formed on the outer peripheral surface 9.

  The piston 2 has a cavity 11 that is recessed in the center of the top surface 8. The cavity 11 of this embodiment is a reentrant type cavity, and has a shape in which the upper inlet side is narrowed with respect to the lower bottom side. The cavity 11 is defined by the cavity inner wall 30. The cavity inner wall 30 defines an inlet portion of the cavity 11 and is continuously connected to the top surface 8. The lip portion 12 protrudes radially inward and is continuously connected to the lip portion 12. The side wall part 13 which expands in undercut shape below is provided, and the bottom wall part 14 connected to the side wall part 13 continuously is provided. The connection position (or boundary position) between the top surface 8 and the lip part 12 is indicated by a, the connection position between the lip part 12 and the side wall part 13 is indicated by b, and the connection position between the side wall part 13 and the bottom wall part 14 is indicated by c. .

  The cross-sectional shape of the lip portion 12 is an arc shape having a curvature radius R1, and the cross-sectional shape of the side wall portion 13 is also an arc shape having a curvature radius R2. R1 <R2. The cross-sectional shape of the lip portion 12 may be a shape in which a straight line is sandwiched between arcs. The cross-sectional shape of the bottom wall portion 14 is a mountain shape. The bottom wall portion 14 has a slope portion 16 that gradually increases as the piston central axis C is approached. The slope portion 16 extends from the connection position c between the side wall portion 13 and the bottom wall portion 14 to the vertex position d of the bottom wall portion 14 located on the piston central axis C.

  The slope portion 16 is connected to the first curved surface portion 31 that is located radially outside and the second curved surface portion that is continuously connected to the first curved surface portion 31 and located radially inside the first curved surface portion 31. 32. The connection position of the 1st curved surface part 31 and the 2nd curved surface part 32 is shown by e. The first curved surface portion 31 is formed in a cross-sectional arc shape having the center of the first curvature radius R3 or the base point S3 above the bottom wall portion 14 or the slope portion 16. On the other hand, the second curved surface portion 32 is formed in a cross-sectional arc shape having the center of the second curvature radius R4 or the base point S4 below the bottom wall portion 14 or the slope portion 16. Accordingly, the first curved surface portion 31 and the second curved surface portion 32 have an S-shaped cross-sectional shape as a whole when viewed macroscopically. In short, a cross-section in which Rs in opposite directions are connected at the connection position e. It has a shape.

  It should be noted that the length and direction of the radius of curvature shown and the position of the center of the radius of curvature are schematically shown and are not accurate.

  In the present embodiment, the second radius of curvature R4 is larger than the first radius of curvature R3. The first curved surface portion 31 is located on the outermost side in the radial direction of the slope portion 16 and is directly and continuously connected to the side wall portion 13 at the connection position c. The second curved surface portion 32 extends from the connection position e with the first curved surface portion 31 to the apex position d of the bottom wall portion 14, that is, the slope portion 16 or the bottom wall portion 14 excluding the portion of the first curved surface portion 31. The entirety is a second curved surface portion 32.

  Note that “continuously connected” refers to a smooth connection mode in which steps and unevenness are not generated as much as possible at the connection position. By performing such a smooth connection, it is possible to suppress the stay of the combustion chamber gas at the connection position, to activate the flow, and to perform the combustion well.

  A cooling passage 17 through which oil for cooling the piston 2 flows is formed in the piston 2 located on the radially outer side of the side wall portion 13. The cooling passage 17 has a ring shape surrounding the cavity 11. Oil that is blown upward by an oil jet (not shown) from the lower side of the piston 2 toward the piston 2 is introduced into the cooling passage 17, and an oil outlet hole 18 that discharges the introduced oil has a cooling function. It is formed to penetrate between the passage 17 and the lower surface 19 of the piston 2.

  The top surface 8 located on the radially outer side of the cavity 11 forms an outer peripheral portion 20 of the top surface 8. Specifically, the top surface outer peripheral portion 20 is a portion of the top surface 8 that is located radially outward from the boundary position a between the top surface 8 and the lip portion 12.

  The outer peripheral portion 20 of the top surface is continuously connected to the lip portion 12, and is connected to the first tapered surface portion 21 located on the radially outer side of the lip portion 12, and to the first tapered surface portion 21 and radially outward thereof. And a second taper surface portion 22 positioned at the center. Moreover, the top surface outer peripheral portion 20 of the present embodiment further includes a flat portion 23 that is connected to the second tapered surface portion 22 and is positioned on the outer side in the radial direction.

  The first tapered surface portion 21 is formed by a tapered surface that is inclined by a first inclination angle θ1 with respect to a virtual plane f perpendicular to the piston center axis C. Similarly, the second tapered surface portion 22 is formed by a tapered surface that is inclined by a second inclination angle θ2 with respect to a virtual plane f perpendicular to the piston center axis C. The second inclination angle θ <b> 2 is larger than the first inclination angle θ <b> 1, so that the second taper surface portion 22 has an inclination angle θ <b> 2 larger than the first taper surface portion 21. The 1st taper surface part 21 and the 2nd taper surface part 22 are made into the taper surface where height becomes high as it goes to a radial direction outer side. Therefore, as it goes outward in the radial direction, the inclination angle of the taper surface portion becomes tighter in steps, and the first taper surface portion 21 and the second taper surface portion 22 form a two-step taper.

  The first inclination angle θ1 has a value slightly larger than zero, and is about 10 °, for example. The second inclination angle θ1 has a value smaller than 90 °, for example, about 30 °.

  On the other hand, the flat portion 23 is formed by a flat surface or a flat surface perpendicular to the piston central axis C. The flat portion 23 extends radially outward to the position of the outer peripheral surface 9. The width of the flat surface portion 23 in the radial direction is approximately the same as the total width of the first tapered surface portion 21 and the second tapered surface portion 22.

  As shown in FIG. 1, the injector 7 is disposed so as to be coaxial with the piston central axis C, that is, the cylinder central axis. Further, as shown by an arrow g, the injector 7 injects fuel toward the top portion of the lip portion 12, that is, the portion located on the innermost side in the radial direction when the piston 2 is located at or near the compression top dead center. So arranged and oriented. The fuel may be injected slightly below the top of the lip portion 12.

  Next, the effect of this embodiment is demonstrated.

  FIG. 2 shows the inside of the combustion chamber 6 at a first specific timing (for example, after compression top dead center (ATDC) 15 ° CA) after fuel injection from the injector 7 and when the piston 2 is descending. . Line h indicates the outer edge of the first region A where the gas equivalent ratio in the combustion chamber 6 is equal to or greater than the first value, and line i is the second where the gas equivalent ratio is equal to or greater than the second value. The outer edge of region B is shown. Here, the gas is a generic term indicating an air-fuel mixture or air. The equivalence ratio is the mixing ratio or mixing ratio of fuel and air. When the mixing ratio is the stoichiometric air-fuel ratio, the equivalence ratio is 1, and the equivalence ratio becomes larger as the mixing ratio becomes the fuel increasing side (rich side). Become. In the illustrated example, the first value is about 1, the second value is about 2, and the second region B is a relatively rich region than the first region A. Further, the second region B is the richest region as viewed in the entire combustion chamber 6. Therefore, here, the second region B is referred to as a rich region.

  As understood from the figure, the fuel injected from the injector 7 radially outward and diagonally downward collides with the lip portion 12 and branches or splits upward and downward. The fuel branched downward flows into the side wall portion 13 and forms an air-fuel mixture while mixing with the surrounding air in the process. On the other hand, the fuel branched upward flows radially outward along the top surface outer peripheral portion 20, and forms an air-fuel mixture while mixing with the surrounding air in the process. At the timing shown in the drawing, the rich region B covers the lip portion 12, the first tapered surface portion 21 and the side wall portion 13 located near the lip portion 12, and exists around them. Although ignition may occur at the timing shown in the figure, it is assumed here that ignition has not occurred for convenience of explanation.

  Driven by the flow of fuel that diverges above the lip portion 12, a gas flow is generated radially outward on the top outer peripheral portion 20. The gas is separated when moving from the lip portion 12 to the first tapered surface portion 21, and generates a vertical (or vertical) vortex j. Since the positions of the rich region B and the vortex j are aligned, the rich air-fuel mixture in the rich region B is actively stirred and mixed by the vortex j with the thin air-fuel mixture or air positioned above the rich air-fuel mixture. Thereby, stirring and mixing of fuel and air can be promoted, and the utilization rate of air in the space between the top surface outer peripheral portion 20 and the cylinder head 4, that is, the space above the top surface outer peripheral portion 20 can be increased.

  Next, when the piston 2 is further lowered, the state shown in FIG. 3 is obtained. FIG. 3 shows the inside of the combustion chamber 6 at a second specific timing (for example, ATDC 25 ° CA) after the first specific timing. The rich region B around the previous lip portion 12 further expands and reaches the second tapered surface portion 22 above the lip portion 12.

  On the other hand, the previous eddy current j also moves outward in the radial direction in accordance with the movement of the rich region B, and reaches the second tapered surface portion 22 as in the rich region B. During the movement of the rich region B, at least a part of the vortex j is located in the rich region B. Therefore, the eddy current j can be moved in accordance with or in conjunction with the movement of the rich region B from the first tapered surface portion 21 to the second tapered surface portion 22, and the eddy current j is utilized during the movement. The rich air-fuel mixture in the rich region B and the thin air-fuel mixture or air above the air-fuel mixture can be actively stirred and mixed.

  Therefore, the air utilization factor in the gap between the top surface outer peripheral portion 20 and the cylinder head 4, that is, the space above the top surface outer peripheral portion 20 can be increased, and smoke can be effectively suppressed.

  As described above, in the present embodiment, when the rich region B moves radially outward along the first tapered surface portion 21 and the second tapered surface portion 22 while the piston 2 is descending, the rich region B is vertically aligned with the movement of the rich region B. A first tapered surface portion 21 and a second tapered surface portion 22 are formed so as to move the eddy current j in the direction. For this reason, the utilization factor of the air in the space above the outer peripheral part 20 of the top surface can be increased, and smoke can be effectively suppressed. In addition, combustion can be improved and fuel consumption can be improved.

  When the rich region B and the eddy current j reach the second tapered surface portion 22, the inclination of the second tapered surface portion 22 is so tight that the movement of the rich region B and the eddy current j to the outside in the radial direction is not a little inhibited and they are stagnant. It becomes. Therefore, it can suppress that they reach the inner wall of the cylinder 3 and stay in the vicinity thereof. That is, if they stay near the inner wall of the cylinder, it becomes difficult to stir and mix, and the available air is limited, but if they stay near the second tapered surface portion 22, the vicinity of the central portion in the radial direction of the top outer peripheral portion 20 Therefore, the air around it can be used effectively and the air utilization rate can be increased. Therefore, it is advantageous for smoke suppression.

  By providing the flat surface portion 23, the second tapered surface portion 22 is separated from the inner wall of the cylinder 3 by a certain distance, and stirring and mixing in the vicinity of the center portion is promoted, and the air utilization rate is improved and smoke can be suppressed.

  Next, when the piston 2 is further lowered, the state shown in FIG. 4 is obtained. FIG. 4 shows the inside of the combustion chamber 6 at a third specific timing (for example, ATDC 45 ° CA) after the second specific timing.

  At this stage, the air-fuel mixture is further diluted in the combustion chamber 6, the rich region B disappears, and only the first region A having a smaller equivalence ratio (lean) exists.

  The fuel branched downward from the lip portion 12 flows to the slope portion 16 through the side wall portion 13 and mixes with ambient air in the process to form an air-fuel mixture. The air-fuel mixture flows radially inward on the slope 16 while gradually diluting by mixing with the surrounding air. This flow is generally a flow along the sloped portion 16 as indicated by the symbol m.

  The air-fuel mixture sequentially passes through the first curved surface portion 31 and the second curved surface portion 32. However, since they have an S-shaped cross section as a whole, when the air-fuel mixture moves from the first curved surface portion 31 to the second curved surface portion 32 or transfers, an exfoliation flow as indicated by a symbol k is generated. That is, when the air-fuel mixture flowing along the first curved surface portion 31 is transferred to the second curved surface portion 32, the curved shape of the second curved surface portion 32 is reversed, so that it can partially follow the second curved surface portion 32. Without peeling off. As a result, an upward separated flow k is generated on the downstream side immediately after the connection position e.

  The separated flow k of the air-fuel mixture mixes well with the air in the space n above the connection position e. Therefore, the air in the space n can be used effectively and the air utilization rate can be increased. The separation flow k also has an effect of peeling off the fuel adhering to the slope portion 16 and mixing it with air. Therefore, mixing of fuel and air can be promoted and smoke can be suppressed.

  Since the second curvature radius R4 is larger than the first curvature radius R3, the curvature of the first curved surface portion 31 is tighter than the curvature of the second curved surface portion 32. For this reason, the separation at these connection positions e can be promoted, and the separation flow k can be effectively generated to increase the air utilization rate.

  As mentioned above, although embodiment of this invention was described in detail, the following other embodiments are also possible for this invention.

  (1) For example, the cavity may have a shape other than the reentrant type, and may be a shallow dish type, a toroidal type, or the like.

  (2) In the above embodiment, the first curved surface portion 31 is directly connected to the side wall portion 13. However, between the first curved surface portion 31 and the side wall portion 13, a relaxation curve portion that smoothly connects the arcuate cross sections of both may be provided, and the first curved surface portion 31 may be indirectly connected to the side wall portion 13. In the sectional view, the relaxation curve portion has the same radius of curvature R3 as the first curved surface portion 31 at the connection position with the first curved surface portion 31, and the same curvature radius R2 as the side wall portion 13 at the connection position with the side wall portion 13. And has a radius of curvature that continuously changes from R3 to R2 from the connection position with the first curved surface portion 31 to the connection position with the side wall portion 13. In this case, there is a possibility that the air-fuel mixture can move smoothly when moving from the side wall portion 13 to the first curved surface portion 31.

  (3) In the above embodiment, the second curved surface portion 32 extends from the connection position e with the first curved surface portion 31 to the apex position d of the bottom wall portion 14, and the slope portion excluding the portion of the first curved surface portion 31. The entire 16 or the entire bottom wall portion 14 is the second curved surface portion 32. However, the second curved surface portion 32 only needs to be at least in the vicinity of the connection position e with the first curved surface portion 31, and the second curved surface portion 32 is not necessarily provided in a portion relatively distant from the connection position e to the piston central axis C side. There is no need. Accordingly, it is possible to change the shape of the bottom wall portion 14 of the part, that is, the shape of the top portion on the center side of the bottom wall portion 14. For example, the top portion may be formed in a planar shape perpendicular to the piston center axis C.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

DESCRIPTION OF SYMBOLS 1 Combustion chamber structure 2 Piston 8 Top surface 11 Cavity 20 Outer peripheral part 21 1st taper surface part 22 2nd taper surface part 30 Cavity inner wall B Rich area | region C Piston central axis f Virtual plane j Eddy current (theta) 1, (theta) 2 Inclination angle

Claims (5)

A cavity recessed in the center of the piston top surface;
An outer periphery of the piston top surface located radially outward of the cavity;
With
The outer periphery of the piston top surface is
A first tapered surface portion connected to an inner wall of the cavity defining the cavity and positioned radially outward thereof;
A second taper surface portion connected to the first taper surface portion and located radially outside thereof, and having an inclination angle larger than the first taper surface portion with respect to a virtual plane perpendicular to the piston central axis;
With
When the rich region moves radially outward along the first tapered surface portion and the second tapered surface portion while the piston is descending, the vortex flow in the vertical direction is moved in accordance with the movement of the rich region. A combustion chamber structure for a direct injection internal combustion engine, wherein one taper surface portion and the second taper surface portion are formed. 2. The combustion of the direct injection internal combustion engine according to claim 1, further comprising: a flat surface portion that is connected to the second tapered surface portion and is located radially outward of the outer peripheral portion of the piston top surface and perpendicular to the piston central axis. Chamber structure. The cavity inner wall has a bottom wall portion, and the bottom wall portion has a slope portion that gradually increases as it approaches the piston central axis,
The slope portion is
A first curved surface portion that is located on the radially outer side and is formed in a cross-sectional arc shape having a center of a first curvature radius above the bottom wall portion;
A second curved surface portion connected to the first curved surface portion and positioned radially inwardly, and formed in a cross-sectional arc shape having a center of a second radius of curvature below the bottom wall portion;
A combustion chamber structure for a direct injection internal combustion engine according to claim 1 or 2. The combustion chamber structure of a direct injection internal combustion engine according to claim 3, wherein the second radius of curvature is larger than the first radius of curvature. The combustion chamber structure of a direct injection internal combustion engine according to any one of claims 1 to 4, wherein the cavity is a reentrant type cavity.

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