JP7005974B2 - Combustion chamber structure of direct injection internal combustion engine - Google Patents

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

Japanese Unexamined Patent Publication No. 2-149719 Japanese Unexamined Patent Publication No. 3-279617 Japanese Unexamined Patent Publication No. 2006-125388

In many cases, the outer circumference of the piston top surface located radially outside the cavity is a simple flat or flat surface. However, according to the results of diligent research by the present inventor, it has been found that the air in the space above the plane cannot be used efficiently, which is disadvantageous for smoke suppression.

Therefore, the present invention was conceived in view of such circumstances, and an object thereof is to provide a combustion chamber structure of a direct injection type internal combustion engine capable of effectively suppressing smoke.

According to one aspect of the invention
A cavity recessed in the center of the top of the piston,
The outer peripheral portion of the top surface of the piston located on the outer side in the radial direction of the cavity, and
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 on the outer side in the radial direction thereof.
A second tapered surface portion connected to the first tapered surface portion and located outside the radial direction thereof and having an inclination angle larger than that of the first tapered surface portion with respect to a virtual plane perpendicular to the piston center axis.
Equipped with
When the rich region moves radially outward along the first tapered surface portion and the second tapered surface portion during the descent of the piston, the first is to move the vortex in the vertical direction in accordance with the movement of the rich region. Provided is a combustion chamber structure of a direct injection type internal combustion engine, characterized in that one tapered surface portion and the second tapered surface portion are formed.

Preferably, the outer peripheral portion of the piston top surface is connected to the second tapered surface portion and is located radially outside the piston top surface portion, and further includes a flat surface 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 located on the outer side in the radial direction and formed in an arc shape in a cross section having a center of the first radius of curvature above the bottom wall portion.
A second curved surface portion connected to the first curved surface portion and located inward in the radial direction thereof and formed in an arc shape in cross section having a center of the second radius of curvature below the bottom wall portion.
To prepare for.

Preferably, the second radius of curvature is larger 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 vertical sectional view which shows the piston of embodiment of this invention. It is a vertical sectional view which shows the state of the inside of the combustion chamber at the 1st specific timing. It is a vertical sectional view which shows the state of the inside of the combustion chamber at the 2nd specific timing. It is a vertical sectional view which shows the state of the inside of the combustion chamber at the 3rd specific timing.

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

The combustion chamber structure according to the present embodiment is applied to a diesel engine which is a typical example of a direct injection type internal combustion engine. The engine is for a vehicle and is particularly used as a vehicle power source for a large vehicle such as a truck. However, the types and uses of internal combustion engines and vehicles 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 raised and lowered and is housed coaxially, a cylinder head 4 that closes the upper end opening of the cylinder 3, and a piston 2. It is provided with a plurality of piston rings 5 (three, only one is shown in the present embodiment) mounted on the outer peripheral surface of the above, 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 a cylinder head 4 and injecting fuel into the combustion chamber 6.

As shown in FIG. 1, the piston 2 is configured to be axisymmetric with respect to the piston central axis C. Unless otherwise specified, the axial direction, the radial direction, and the circumferential direction with respect to the piston central axis C are simply referred to as the axial direction, the radial direction, and the circumferential direction. The piston 2 has a top surface (piston top surface) 8 and an outer peripheral surface 9. A plurality of (three in this 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 in 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 with respect to the lower bottom side. The cavity 11 is defined by the cavity inner wall 30. The cavity inner wall 30 defines the inlet portion of the cavity 11 and is continuously connected to the top surface 8, and is continuously connected to the lip portion 12 protruding inward in the radial direction and the lip portion 12, and is connected to the lip portion 12. A side wall portion 13 whose diameter is expanded in an undercut shape at the bottom and a bottom wall portion 14 continuously connected to the side wall portion 13 are provided. The connection position (or boundary position) between the top surface 8 and the lip portion 12 is indicated by a, the connection position between the lip portion 12 and the side wall portion 13 is indicated by b, and the connection position between 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 radius of curvature R1, and the cross-sectional shape of the side wall portion 13 is also an arc shape having a radius of curvature R2. R1 <R2. The cross-sectional shape of the lip portion 12 may be a shape in which a straight line is sandwiched between the arcs. The cross-sectional shape of the bottom wall portion 14 is a chevron shape. The bottom wall portion 14 has a slope portion 16 that gradually rises as it approaches the piston central axis C. The slope portion 16 extends from the connection position c between the side wall portion 13 and the bottom wall portion 14 to the apex position d of the bottom wall portion 14 located on the piston central axis C.

The slope portion 16 is continuously connected to the first curved surface portion 31 located on the outer side in the radial direction and the second curved surface portion 31 located on the inner side in the radial direction of the first curved surface portion 31. 32 and. The connection position between 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 cross-sectional arc shape having a center or a base point S3 of the first radius of curvature 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 cross-sectional arc shape having a center or a base point S4 of the second radius of curvature R4 below the bottom wall portion 14 or the slope portion 16. Therefore, 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, and in short, a cross-section in which rounds 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 shown schematically and are 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 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 whole is the second curved surface portion 32.

The term "continuous connection" refers to a smooth connection mode in which steps and irregularities are not generated as much as possible at the connection position. By performing such a smooth connection, it is possible to suppress the retention of the gas in the combustion chamber at the connection position, activate the flow, and perform good combustion.

Inside the piston 2 located on the outer side in the radial direction of the side wall portion 13, a cooling passage 17 through which oil for cooling the piston 2 flows is formed. The cooling passage 17 has a ring shape surrounding the cavity 11. Oil 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 for discharging the introduced oil is cooled. It is formed so as to penetrate between the passage 17 and the lower surface 19 of the piston 2.

The top surface 8 located on the outer side in the radial direction of the cavity 11 forms the outer peripheral portion 20 of the top surface 8. Specifically, the outer peripheral portion 20 of the top surface is a portion of the top surface 8 located radially outside the boundary position a between the top surface 8 and the lip portion 12.

The top surface outer peripheral portion 20 is continuously connected to the lip portion 12, is connected to the first tapered surface portion 21 located radially outside the lip portion 12, and is connected to the first tapered surface portion 21 and is radially outside thereof. It is provided with a second tapered surface portion 22 located at. Further, the outer peripheral portion 20 of the top surface of the present embodiment further includes a flat surface portion 23 connected to the second tapered surface portion 22 and located on the outer side in the radial direction 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 inclined by a second inclination angle θ2 with respect to the virtual plane f perpendicular to the piston central axis C. The second tilt angle θ2 is larger than the first tilt angle θ1, and therefore the second tapered surface portion 22 has a tilt angle θ2 larger than that of the first tapered surface portion 21. The first tapered surface portion 21 and the second tapered surface portion 22 are tapered surfaces whose height increases toward the outside in the radial direction. Therefore, the inclination angle of the tapered surface portion gradually becomes tighter toward the outer side in the radial direction, and the first tapered surface portion 21 and the second tapered surface portion 22 form a two-step taper.

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

On the other hand, the flat surface portion 23 is formed by a flat surface or a flat surface perpendicular to the piston central axis C. The flat surface 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 set to be about 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 arranged so as to be coaxial with the piston center axis C, that is, the cylinder center axis. Further, as shown by the arrow g, the injector 7 injects fuel toward the top of the lip portion 12, that is, the portion located most radially inside when the piston 2 is located at or near the compression top dead center. Arranged and oriented. The fuel may be injected slightly downward from the top of the lip portion 12.

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

FIG. 2 shows the inside of the combustion chamber 6 after the fuel injection from the injector 7 and at the first specific timing (for example, after the compression top dead center (ATDC) 15 ° CA) when the piston 2 is descending. .. The line h indicates the outer edge of the first region A in which the gas equivalent ratio in the combustion chamber 6 is the first value or more, and the line i is the second line in which the gas equivalent ratio is the second value or more. The outer edge of the region B is shown. Here, gas is a general term that refers to a mixture of air and fuel, or air. The equivalent ratio refers to the mixing ratio or mixing ratio of fuel and air. When the mixing ratio is the stoichiometric air-fuel ratio, the equivalent ratio is 1, and the value of the equivalent ratio increases as the mixing ratio becomes the fuel increasing 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. Further, the second region B is the richest region in the entire combustion chamber 6. Therefore, here, the second region B is referred to as a rich region.

As can be seen from the figure, the fuel injected radially outward and diagonally downward from the injector 7 collides with the lip portion 12 and branches or splits upward and downward. The fuel branched downward flows to the side wall portion 13, and in the process, forms an air-fuel mixture while mixing with the surrounding air. On the other hand, the fuel branched upward flows outward in the radial direction along the outer peripheral portion 20 of the top surface, and forms an air-fuel mixture while mixing with the surrounding air in the process. At the timing shown, 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 branching above the lip portion 12, a gas flow toward the outer side in the radial direction is generated on the outer peripheral portion 20 of the top surface. This gas separates when moving from the lip portion 12 to the first tapered surface portion 21, and generates a vertical (or vertical) vortex flow j. Since the positions of the rich region B and the vortex flow j are aligned, the rich air-fuel mixture in the rich region B is positively agitated and mixed with the thin air-fuel mixture or air located above the rich air-fuel mixture by the vortex flow j. This promotes agitation and mixing of fuel and air, and can increase the utilization rate of air in the gap between the outer peripheral portion 20 of the top surface and the cylinder head 4, that is, the space above the outer peripheral portion 20 of the top surface.

Then, 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 the second specific timing (for example, ATDC 25 ° CA) after the first specific timing. The rich region B around the lip portion 12 is further expanded, and above the lip portion 12, it reaches the second tapered surface portion 22.

On the other hand, the previous vortex flow 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 in the same manner as 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 vortex flow j can be moved according to 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 vortex flow j is used during the movement. , The rich air-fuel mixture in the rich region B and the thin air-fuel mixture or air above it can be positively stirred and mixed.

Therefore, it is possible to increase the utilization rate of air in the gap between the outer peripheral portion 20 of the top surface and the cylinder head 4, that is, the space above the outer peripheral portion 20 of the top surface, and it is possible to effectively suppress smoke.

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, it is vertically aligned with the movement of the rich region B. The first tapered surface portion 21 and the second tapered surface portion 22 are formed so as to move the vortex flow j in the direction. Therefore, the utilization rate of air in the space above the outer peripheral portion 20 of the top surface can be increased, and smoke can be effectively suppressed. At the same time, combustion can be improved and fuel efficiency can be improved.

When the rich region B and the vortex flow j reach the second tapered surface portion 22, the inclination of the second tapered surface portion 22 is so steep that the movement of the rich region B and the vortex flow j to the outside in the radial direction is not a little hindered, and they tend to be stagnant. Will be. Therefore, it is possible to prevent them from reaching the inner wall of the cylinder 3 and staying 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. However, if they stay near the second tapered surface portion 22, the vicinity of the radial center portion of the outer peripheral portion 20 of the top surface 20 Since it can be stirred and mixed with, the air around it can be effectively used 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 can be separated from the inner wall of the cylinder 3 by a certain distance, the stirring and mixing in the vicinity of the central portion can be promoted, the air utilization rate can be improved, and smoke can be suppressed.

Then, 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 the third specific timing (for example, ATDC 45 ° CA) after the second specific timing.

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

The fuel branched downward from the lip portion 12 flows to the slope portion 16 via the side wall portion 13 and mixes with the surrounding air in the process to form an air-fuel mixture. The air-fuel mixture gradually mixes with the surrounding air and dilutes, and flows inward in the radial direction on the slope portion 16. This flow is generally a flow along the slope portion 16 as indicated by the reference numeral 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-sectional shape as a whole, when the air-fuel mixture moves or transfers from the first curved surface portion 31 to the second curved surface portion 32, a separation flow as shown by the reference numeral 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 air-fuel mixture can partially follow the second curved surface portion 32. It peels off. As a result, an upward separation flow k is generated on the downstream side immediately after the connection position e.

The separation flow k of this 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 effectively used and the air utilization rate can be increased. The peeling flow k also has the effect of peeling off the fuel adhering to the slope portion 16 and mixing it with air. Therefore, it is possible to promote the mixing of fuel and air and suppress smoke.

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 is tighter than the curvature of the second curved surface portion 32. Therefore, it is possible to promote the peeling at these connection positions e, effectively generate the peeling flow k, and increase the air utilization rate.

Although the embodiments of the present invention have been described in detail above, the present invention can also have 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, a relaxation curved portion that smoothly connects the arcuate cross sections of both may be provided between the first curved surface portion 31 and the side wall portion 13, and the first curved surface portion 31 may be indirectly connected to the side wall portion 13. 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 radius of curvature R2 as the side wall 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. By doing so, there is a possibility that the air-fuel mixture can smoothly move 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 may be at least near the connection position e with the first curved surface portion 31, and the second curved surface portion 32 is not necessarily provided at a portion relatively distant from the connection position e on the piston central axis C side. No need. Therefore, it is possible to change the shape of the bottom wall portion 14 of the portion, that is, the top portion on the center side of the bottom wall portion 14. For example, the top may be formed into a flat surface perpendicular to the piston central axis C.

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

1 Combustion chamber structure 2 Piston 8 Top surface 11 Cavity 20 Outer peripheral part 21 First tapered surface part 22 Second tapered surface part 30 Cavity inner wall B Rich region C Piston central axis f Virtual plane j Swirl flow θ1, θ2 Tilt angle

Claims (1)

A reentrant type cavity recessed in the center of the top surface of the piston and defined by the inner wall of the cavity.
The outer peripheral portion of the top surface of the piston located on the outer side in the radial direction of the cavity, and
Equipped with
The inner wall of the cavity has a lip portion that defines the entrance portion of the cavity and projects inward in the radial direction, a side wall portion that is connected to the lip portion and has an undercut-like diameter expansion below the lip portion, and the side wall portion. With a bottom wall connected to,
The bottom wall portion has a slope portion that gradually increases as it approaches the central axis of the piston.
The slope portion is
A first curved surface portion located on the outer side in the radial direction and formed in an arc shape in a cross section having a center of the first radius of curvature above the bottom wall portion.
A second arcuate cross-section that is directly connected to the first curved surface portion and is located inside the radial direction thereof and has a center of a second radius of curvature larger than the first radius of curvature below the bottom wall portion. 2 curved surface part and
Equipped with
The outer peripheral portion of the piston top surface is
A flat first tapered surface portion connected to the lip portion and located radially outside the lip portion ,
A flat second tapered surface portion connected to the first tapered surface portion and located outside the radial direction thereof and having an inclination angle larger than that of the first tapered surface portion with respect to a virtual plane perpendicular to the piston center axis.
A flat surface portion connected to the second tapered surface portion and located radially outside the surface portion, perpendicular to the piston central axis, and extending radially outward to the position of the outer peripheral surface of the piston.
Equipped with
When a rich region having a gas equivalent ratio of 2 or more moves radially outward along the first tapered surface portion and the second tapered surface portion while the piston is descending, the vertical direction is matched with the movement of the rich region. The vortex flow is moved from the first tapered surface portion to the second tapered surface portion, and during the movement, the vortex flow is located above the rich region from the rich region, and the equivalent ratio of gas is 1 or more and less than 2. The first tapered surface portion and the second tapered surface portion are formed so as to move to the first region and use the vortex to mix the air-fuel mixture in the rich region and the air-fuel mixture in the first region. And
At the first specific timing after fuel injection and while the piston is descending, the rich region caused by the fuel colliding with the lip portion includes the lip portion, the first tapered surface portion and the side wall portion located in the vicinity of the lip portion. The gas, which is formed around and around them and is driven by the fuel flow branched upward after the collision and heads outward in the radial direction, separates when moving from the lip portion to the first tapered surface portion, and at least. A vertical vortex, partly located in the rich region, is generated on the first tapered surface, and the vortex mixes the air-fuel mixture in the rich region with the air-fuel mixture in the first region.
At the second specific timing thereafter, the rich region further expands and reaches the second tapered surface portion, and the vortex flow also reaches the second tapered surface portion in accordance with the movement of the rich region, and the second tapered surface portion. Above, the vortex causes the air-fuel mixture in the rich region to mix with the air-fuel mixture in the first region.
At the subsequent third specific timing, the rich region disappears, and the air-fuel mixture flowing from the first curved surface portion to the second curved surface portion through the side wall portion due to the fuel branched downward after the collision. When moving to the surface portion, an upward separation flow is generated, and the separation flow mixes the air in the space above the connection position between the first curved surface portion and the second curved surface portion with the air-fuel mixture.
The combustion chamber structure of a direct-injection internal combustion engine is characterized by this.

Images