WO2019013221A1

WO2019013221A1 - Combustion chamber structure for direct injection internal combustion engine

Info

Publication number: WO2019013221A1
Application number: PCT/JP2018/026087
Authority: WO
Inventors: 祐多清水; 大輔小澤; 仁建石; 拓也荒井
Original assignee: いすゞ自動車株式会社
Priority date: 2017-07-11
Filing date: 2018-07-10
Publication date: 2019-01-17
Also published as: PH12020500006A1; JP2019019676A; JP7005974B2; CN110869592B; CN110869592A

Abstract

This combustion chamber structure for a direct injection internal combustion engine is provided with: a cavity 11 formed at the center of a piston top surface 8; and the outer peripheral section 20 of the piston top surface, which is located radially outside the cavity. The outer peripheral section of the piston top surface comprises: a first tapered surface 21 which is connected to a cavity inner wall 30 defining the cavity, is located radially outside the cavity inner wall, and has a first tilt angle θ1 relative to an imaginary plane perpendicular to a piston center axis; and a second tapered surface 22 which is connected to the first tapered surface, is located radially outside the first tapered surface, and has a second tilt angle θ2 relative to the imaginary plane f perpendicular to the piston center axis C. The second tilt angle θ2 of the second tapered surface 22 is greater than the first tilt angle θ1 of the first tapered surface 21.

Description

Combustion chamber structure of direct injection type internal combustion engine

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

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

Japanese Patent Application Laid-Open No. 2-149719 Japanese Patent Application Laid-Open No. 3-279617 Japanese Patent Laid-Open Publication No. 2006-125388

In many cases, the outer periphery of the piston top surface located radially outward of the cavity is a simple flat or flat surface. However, according to the results of the inventors' intensive studies, it has been found that such a flat surface can not efficiently use the air in the space above it, which is disadvantageous for smoke suppression.

Therefore, the present disclosure is devised in view of the above circumstances, and provides a combustion chamber structure of a direct injection type internal combustion engine capable of effectively suppressing smoke.

According to one aspect of the present disclosure,
The combustion chamber structure of a direct injection type internal combustion engine is
A cavity recessed in the center of the piston top surface;
An outer circumferential portion of the piston top surface located radially outward of the cavity;
Equipped with
The outer peripheral portion of the piston top surface is
A first tapered surface portion connected to the inner wall of the cavity defining the cavity and located radially outward thereof and having a first inclination angle with respect to a virtual plane perpendicular to the central axis of the piston;
A second tapered surface portion connected to the first tapered surface portion and located radially outward thereof and having a second inclination angle with respect to a virtual plane perpendicular to the piston central axis;
Equipped with
The second inclination angle of the second tapered surface portion is larger than the first inclination angle of the first tapered surface portion.

In the combustion chamber structure of the direct injection type internal combustion engine described above, the first inclination angle may be larger than 0 degree.

In the combustion chamber structure of the direct injection type internal combustion engine described above, when the rich region moves radially outward along the first tapered surface portion and the second tapered surface portion during descent of the piston, the movement of the rich region is matched to the movement of the rich region. The first tapered surface portion and the second tapered surface portion may be formed to move the vortex in the longitudinal direction.

In the above-described combustion chamber structure of a direct injection type internal combustion engine, the outer peripheral portion of the piston top surface is connected to the second tapered surface portion and located radially outside thereof and further including a flat portion perpendicular to the central axis of the piston May be

In the combustion chamber structure of the direct injection type internal combustion engine described above, the inner wall of the cavity may have a bottom wall portion, and the bottom wall portion may have a slope portion which gradually becomes higher as approaching the central axis of the piston.
The slope section is
A first curved surface portion formed in an arc shape in cross section which is located radially outward and has 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 located radially inward of the first curved surface portion and formed in a circular arc shape having a center of a second curvature radius below the bottom wall portion;
May be provided.

In the combustion chamber structure of the direct injection type internal combustion engine described above, the second radius of curvature may be larger than the first radius of curvature.

Preferably, the cavity is a reentrant cavity.

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

FIG. 1 is a longitudinal cross-sectional view showing a piston of an embodiment of the present disclosure. FIG. 2 is a longitudinal sectional view showing the inside of the combustion chamber at the first specific timing. FIG. 3 is a longitudinal sectional view showing the inside of the combustion chamber at a second specific timing. FIG. 4 is a longitudinal sectional view showing the inside of the combustion chamber at the third specific timing.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

The combustion chamber structure according to the present embodiment is applied to a diesel engine that is a typical example of a direct injection type internal combustion engine. An engine is for vehicles, and is used as a vehicle power source of a large vehicle such as a truck in particular. 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 coaxially housed, a cylinder head 4 that closes the upper end opening of the cylinder 3, and the piston 2. A plurality of (three in this embodiment, only one is shown) piston rings 5 mounted on the outer peripheral surface of the combustion chamber 6 and a combustion chamber 6 which is a closed space defined by these. Further, as shown in FIG. 1, the combustion chamber structure 1 includes an injector 7 attached to the cylinder head 4 and injecting fuel into the combustion chamber 6.

As shown in FIG. 1, the piston 2 is configured to be substantially axially symmetrical with respect to a piston central axis C. Unless otherwise stated, the axial, radial and circumferential directions with respect to the piston center axis C are simply referred to as axial, radial and circumferential directions. 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 recessed at the center of the top surface 8. The cavity 11 of the present embodiment is a reentrant type cavity, and has a shape in which the upper inlet side is narrowed relative to the lower bottom side. The cavity 11 is defined by the inner cavity wall 30. The inner cavity wall 30 defines the inlet of the cavity 11 and is continuously connected to the top surface 8 and is continuously connected to the radially inward projecting lip 12 and the lip 12. It has a side wall portion 13 which expands downward in the shape of an undercut at the lower side, and a bottom wall portion 14 continuously connected to the side wall portion 13. The connection position (or boundary position) of the top surface 8 and the lip portion 12 is indicated by a, the connection position of the lip portion 12 and the side wall portion 13 is indicated by b, and the connection position of the side wall portion 13 and the bottom wall portion 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 is smaller than 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 mountain-shaped. The bottom wall portion 14 has a sloped portion 16 which gradually becomes higher as it approaches the piston central axis C. The inclined surface portion 16 extends from a connection position c of the side wall portion 13 and the bottom wall portion 14 to an apex position d of the bottom wall portion 14 located on the piston central axis C.

The sloped portion 16 is connected to the first curved surface portion 31 located radially outward and the first curved surface portion 31 and a second curved surface portion located radially inward of the first curved surface portion 31. And 32. The connection position of the first curved surface portion 31 and the second curved surface portion 32 is indicated by e. The first curved surface portion 31 is formed in a circular arc shape having a center or base point S3 of the first curvature radius R3 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 circular arc shape having a center or base point S4 of the second curvature radius R4 below the bottom wall portion 14 or the slope portion 16. Therefore, when viewed macroscopically, the first curved surface portion 31 and the second curved surface portion 32 have an S-shaped cross-sectional shape as a whole. It has a shape.

It should be noted that the length and orientation of the illustrated radius of curvature, and the location of the center of radius of curvature, are schematically illustrated and not accurate.

In the case of 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 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 a vertex position d of the bottom wall portion 14, that is, except for the portion of the first curved surface portion 31 The whole is a second curved surface portion 32.

"Continuously connected" refers to a smooth connection mode in which no level difference or unevenness occurs at the connection position. With such a smooth connection, it is possible to suppress the retention of the gas in the combustion chamber 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 inside the piston 2 located radially outward of the side wall portion 13. The cooling passage 17 is in the form of a ring surrounding the cavity 11. The oil discharged from the lower side of the piston 2 toward the piston 2 upward by an oil jet (not shown) is introduced into the cooling passage 17, and the oil outlet hole 18 for discharging the introduced oil is cooled It is formed penetrating between the passage 17 and the lower surface 19 of the piston 2.

The top surface 8 located radially outward 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 located radially outward of the boundary position a of the top surface 8 and the lip portion 12.

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

The first tapered surface portion 21 is formed by a tapered surface inclined by a first inclination angle θ1 with respect to a virtual plane f perpendicular to the piston central axis C. Similarly, the second tapered surface portion 22 is formed by a tapered surface which is inclined by a second inclination angle θ2 with respect to a virtual plane f perpendicular to the piston central axis C. The second inclination angle θ 2 is larger than the first inclination angle θ 1, so that the second taper surface 22 has an inclination angle θ 2 larger than that of the first taper surface 21. The first tapered surface portion 21 and the second tapered surface portion 22 are tapered surfaces whose heights increase in the radially outward direction. Therefore, as it goes radially outward, the inclination angle of the tapered surface portion becomes stepwise stepwise, and the first tapered surface portion 21 and the second tapered surface portion 22 form a two-stage tapered shape.

The first tilt angle θ1 has a value slightly larger than zero, for example, about 10 °. The second tilt angle θ2 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 circumferential surface 9. The width of the flat 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.

The injector 7 is disposed coaxially with the piston central axis C, that is, the cylinder central axis, as shown in FIG. In addition, as indicated by arrow g, injector 7 injects fuel toward the top of lip portion 12, ie, the most radially inner portion, when 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 12.

Next, the operation and effect of the present embodiment will be described.

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 equivalence ratio of gas in the combustion chamber 6 is equal to or greater than the first value, and line i indicates that the equivalence ratio of gas is equal to or greater than the second value The outer edge of region B is shown. Here, gas is a generic term that refers to a mixture of air and fuel, or air. The equivalence ratio means the mixing ratio or mixing ratio of fuel and air, and when the mixing ratio is the theoretical air fuel ratio, the equivalence ratio is 1, and the value of the equivalence ratio is large as the mixing ratio is on the fuel increase side (rich side) Become. In the case of the illustrated example, the first value is about 1, the second value is about 2, and the second region B is a region relatively richer than the first region A. The second region B is the richest region as viewed in the entire combustion chamber 6. Therefore, the second region B is referred to as a rich region here.

As understood from the figure, the fuel injected radially outward and obliquely downward from the injector 7 collides with the lip portion 12 and is branched or branched upward and downward. The downwardly branched fuel flows to the side wall 13 and forms a mixture while mixing with the ambient air in the process. On the other hand, the fuel branched upward flows radially outward along the top outer periphery 20, and forms a mixture while mixing with the surrounding air in the process. At the illustrated timing, the rich region B covers the lip portion 12 and the first tapered surface portion 21 and the side wall portion 13 located in the vicinity of the lip portion 12 and exists around them. Although ignition may occur at the timing shown in the drawing, for convenience of explanation, it is assumed that no ignition occurs.

Driven by the flow of fuel branched to the upper side of the lip portion 12, a flow of gas directed radially outward on the top surface outer peripheral portion 20 is generated. This gas separates when moving from the lip portion 12 to the first tapered surface portion 21 and generates a vortex flow j in the longitudinal direction (or the vertical direction). Since the rich region B and the vortex flow j are aligned, the rich mixture in the rich region B is actively stirred and mixed with the thin mixture or air located thereabove by the vortex flow j. As a result, stirring and mixing of fuel and air can be promoted, and the utilization factor of air in the space between the top outer periphery 20 and the cylinder head 4, that is, the space above the top outer periphery 20 can be increased.

Next, when the piston 2 is further lowered, the state as 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 lip 12 is further expanded, and reaches the second tapered surface 22 above the lip 12.

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

Therefore, the air utilization factor 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, and smoke can be effectively suppressed.

As described above, in the present embodiment, when the rich region B moves radially outward along the order of the first tapered surface portion 21 and the second tapered surface portion 22 during the descent of the piston 2, the longitudinal direction is matched with the movement of the rich region B. The first tapered surface portion 21 and the second tapered surface portion 22 are formed to move the eddy current j in the direction. For this reason, the utilization factor of air in the space above the top surface outer peripheral portion 20 can be increased, and smoke can be effectively suppressed. At the same time, 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 strong that the radially outward movement of the rich region B and the eddy current j is inhibited to some extent and they are stagnant It becomes. Therefore, they can be prevented from reaching the inner wall of the cylinder 3 and staying in the vicinity thereof. That is, when they stay in the vicinity of the cylinder inner wall, it becomes difficult to stir and mix, and the available air becomes limited, but if they stagnate in the vicinity of the second tapered surface portion 22, the central portion in the radial direction of the top surface outer peripheral portion 20 near Because it can be stirred and mixed, the air around it can be used effectively and the air utilization rate can be increased. Therefore, it is advantageous to smoke suppression.

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

Next, when the piston 2 is further lowered, the state as 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 fuel-air mixture leans in the combustion chamber 6, and 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 12 flows through the side wall 13 to the slope 16 and mixes with the surrounding air in the process to form an air-fuel mixture. The air-fuel mixture flows radially inward on the slope portion 16 while gradually mixing with the surrounding air and diluting. This flow is generally a flow along the slope 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 all have an S-shaped cross-sectional shape, when the air-fuel mixture moves from the first curved surface portion 31 to the second curved surface portion 32 or transfers, a separated flow as indicated by a symbol k occurs. That is, when the air-fuel mixture flowing along the first curved surface portion 31 transfers to the second curved surface portion 32, the curved shape of the second curved surface portion 32 is reversed, so that the second curved surface portion 32 can partially follow It peels off. As a result, an upward separating flow k is generated on the downstream side immediately after the connection position e.

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

Since the second radius of curvature R4 is larger than the first radius of curvature R3, the curvature of the first curved surface portion 31 becomes stronger than the curvature of the second curved surface portion 32. Therefore, separation at these connection positions e can be promoted, separation flow k can be effectively generated, and the air utilization rate can be increased.

Although the embodiments of the present disclosure have been described in detail above, the present disclosure can be other embodiments as follows.

(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, the first curved surface portion 31 may be indirectly connected to the side wall portion 13 by providing a relaxation curve portion that smoothly connects the two arc-shaped cross sections between the first curved surface portion 31 and the side wall portion 13. The relaxation curve portion has the same curvature radius R3 as the first curved surface portion 31 at the connection position with the first curved surface portion 31 in the cross sectional view, and has the same curvature radius R2 as the sidewall portion 13 at the connection position with the side wall portion 13. It 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 be smoothly moved when moving from the side wall 13 to the first curved surface 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 vertex position d of the bottom wall portion 14 and excludes the portion of the first curved surface portion 31 The entire 16 or the bottom wall 14 is a second curved surface 32. However, the second curved surface portion 32 may 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 necessarily provided in a portion relatively distant from the connection position e toward the piston center axis C side. There is no need. Therefore, it is possible to change the shape of the bottom wall 14 of the portion, that is, the top of the center side of the bottom wall 14. For example, the top may be in the form of a flat surface perpendicular to the piston center axis C.

The embodiment of the present disclosure is not limited to the above-described embodiment, and all variations, applications, and equivalents included in the concept of the present disclosure defined by the claims are included in the present disclosure. Accordingly, the present disclosure should not be construed as limiting, and can be applied to any other technology falling within the scope of the present disclosure.

This application is based on the Japanese Patent Application (Japanese Patent Application No. 2017-135615) filed on July 11, 2017, the contents of which are incorporated herein by reference.

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

DESCRIPTION OF SYMBOLS 1 combustion chamber structure 2 piston 8 top surface 11 cavity 20 outer peripheral part 21 first taper surface 22 second taper surface 30 cavity inner wall B rich region C piston central axis f imaginary plane j eddy current θ1, θ2 inclination angle

Claims

A cavity recessed in the center of the piston top surface;
An outer circumferential portion of the piston top surface located radially outward of the cavity;
Equipped with
The outer peripheral portion of the piston top surface is
A first tapered surface portion connected to the inner wall of the cavity defining the cavity and located radially outward thereof and having a first inclination angle with respect to a virtual plane perpendicular to the central axis of the piston;
A second tapered surface portion connected to the first tapered surface portion and located radially outward thereof and having a second inclination angle with respect to a virtual plane perpendicular to the piston central axis;
Equipped with
The second inclination angle of the second tapered surface portion is larger than the first inclination angle of the first tapered surface portion,
When the rich region moves radially outward along the first tapered surface portion and the second tapered surface portion sequentially during the lowering of the piston, the first vortex surface is moved in accordance with the movement of the rich region. 1. A combustion chamber structure of a direct injection type internal combustion engine in which a tapered surface portion and the second tapered surface portion are formed.
The combustion chamber structure of a direct injection type internal combustion engine according to claim 1, wherein an angle of the first inclination angle is larger than 0 degree.
When the rich region moves radially outward along the first tapered surface portion and the second tapered surface portion sequentially during the lowering of the piston, the first vortex surface is moved in accordance with the movement of the rich region. The combustion chamber structure of a direct injection type internal combustion engine according to claim 1, wherein the first tapered surface portion and the second tapered surface portion are formed.
The combustion of a direct injection type internal combustion engine according to claim 1, wherein the outer peripheral portion of the piston top surface is connected to the second tapered surface portion and is located radially outside thereof and further includes a flat portion perpendicular to the central axis of the piston. Room structure.
The inner wall of the cavity has a bottom wall, and the bottom wall has a slope which gradually rises toward the central axis of the piston,
The slope section is
A first curved surface portion formed in an arc shape in cross section which is located radially outward and has 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 located radially inward of the first curved surface portion and formed in a circular arc shape having a center of a second curvature radius below the bottom wall portion;
A combustion chamber structure of a direct injection type internal combustion engine according to any one of claims 1 to 4, comprising:
The combustion chamber structure of a direct injection type internal combustion engine according to claim 5, wherein the second radius of curvature is larger than the first radius of curvature.
The combustion chamber structure of a direct injection type internal combustion engine according to any one of claims 1 to 4, wherein the cavity is a reentrant type cavity.