JP5953067B2 - Direct injection diesel engine and piston for direct injection diesel engine - Google Patents

Description

  The present invention relates to a direct injection diesel engine and a piston applied to the direct injection diesel engine.

  Conventionally, in diesel engines, exhaust gas recirculation (EGR) is performed to reduce NOx contained in exhaust gas by recirculating a part of the exhaust gas to the intake side. In such exhaust gas recirculation, NOx can be reduced as the EGR rate, which is the ratio of exhaust gas to the intake air in the cylinder, increases.

  On the other hand, if the exhaust gas recirculation amount is increased to increase the EGR rate, the amount of air in the intake air is reduced. Therefore, black smoke containing particulate matter (PM) due to incomplete combustion of the fuel Is likely to occur. In addition, the pumping loss in the compression stroke is increased by increasing the pressure of the intake air in the cylinder, and the fuel consumption may be deteriorated by the increased pumping loss.

  Therefore, in order to increase the EGR rate while suppressing the generation of black smoke and pumping loss, the utilization efficiency of the air sucked into the cylinder is increased so that the generation of black smoke can be suppressed even if the exhaust gas recirculation amount is increased. That is, it is required to use the air in the cylinder without any problem.

  In order to satisfy these requirements, Patent Document 1 discloses the following diesel engine. FIG. 18 is a diagram for explaining the configuration of the diesel engine disclosed in Patent Document 1, and is a sectional view showing a sectional structure of the diesel engine around the piston.

  As shown in FIG. 18, the diesel engine disclosed in Patent Document 1 is a direct injection diesel engine, and a piston 55 is accommodated in a cylinder 53 formed by a cylinder block 51 and a cylinder head 52. . The piston 55 includes a first cavity 56 having a circular opening on the top surface 58 of the piston 55 and a second cavity 60 having a second opening 60 having a circular opening on the bottom surface 57 of the first cavity 56. A cavity is formed. The opening edge of the first cavity 56 and the opening edge of the second cavity 60 are concentrically formed with respect to the outer peripheral edge of the piston 55 in a plan view facing the top surface 58 of the piston 55.

  The first cavity 56 is formed such that a bottom surface 57 substantially parallel to the top surface 58 of the piston 55 rises so as to draw a gentle curved surface from the outer peripheral end toward the top surface 58 of the piston 55. The second cavity 60 has a lip portion 61 that is an opening edge on the bottom surface 57 of the first cavity 56, and a wall surface that descends from the lip portion 61 so as to draw a gentle S-curve and projects outward from the lip portion 61. It is formed by the part 62 and the conical center cone 63 which protrudes from the lower end of the wall surface part 62 toward the center. In the period before and after the piston 55 reaches the compression top dead center, fuel is injected radially from the plurality of injection ports formed in the fuel injection valve 65 toward the lip portion 61.

  During low-speed operation, the fuel injected from the fuel injection valve 65 is distributed into a flow toward the first cavity 56 and a flow toward the second cavity 60 by colliding with the lip portion 61. A part of the fuel distributed to the first cavity 56 flows into a squish area 67 that is a space between the lower surface 52 a of the cylinder head 52 and the top surface 58 of the piston 55. That is, in the diesel engine disclosed in Patent Document 1, the first cavity 56 and the second cavity 60 described above form a cavity, and the fuel is directed toward the lip portion 61 that is the opening edge of the second cavity 60. By being injected, fuel is distributed in the cavity and to the squish area 67. That is, the air utilization efficiency in the cylinder 53 is increased by increasing the air utilization efficiency in the squish area 67.

JP 2007-21644 A

  On the other hand, in the process of earnestly researching the diesel engine disclosed in Patent Document 1, the present inventor conducted an investigation on the piston 55 after the test operation. FIG. 19 is a diagram schematically showing the state of the piston top after the test operation for further improving the performance of the diesel engine disclosed in Patent Document 1. In FIG. 19, the flow direction of the swirl flow generated in the cylinder 53 is indicated by an arrow 68, and the axial direction of the injection port, which is the fuel injection direction in a plan view facing the top surface 58 of the piston 55. Is indicated by a virtual line 69.

  As shown in FIG. 19, when the present inventor investigated the piston 55 after the test operation, the fuel injection direction of the top surface 58 of the piston 55 near the opening edge of the first cavity 56 was determined. It was recognized that the wrinkles 70 were attached to portions corresponding to the virtual lines 69 shown. From this, in the squish area 67, even if a swirl flow is generated in the cylinder 53, a high fuel concentration region in which the equivalence ratio exceeds 1 so as to correspond to the fuel injection direction. Is considered to be locally formed.

  That is, although the diesel engine disclosed in Patent Document 1 can obtain a high EGR rate while suppressing the pumping loss by increasing the utilization efficiency of the air in the cylinder, it can be expected to further reduce black smoke. It was.

  The technique of this indication aims at providing the piston for direct injection type diesel engines and direct injection type diesel engines which can use the air in a cylinder efficiently.

In one aspect of the direct injection diesel engine according to the present disclosure, a cavity is configured by a first cavity having an opening on a top surface facing the cylinder head and a second cavity having an opening on the bottom surface of the first cavity. A direct injection type diesel engine including a piston, wherein the piston is integrally formed at a corner formed by a bottom surface of the first cavity and a side surface of the first cavity, and is opposed to a top surface of the piston. A tapered protrusion extending from a side surface of the first cavity in a plan view, and a recess formed on a side surface of the first cavity with respect to a top surface of the piston. Has a pair of side surfaces that connect a facing surface that faces the cylinder head and a bottom surface of the first cavity, and is formed in the cylinder among the pair of side surfaces. The downstream side surface disposed downstream with respect to the flow direction of the swirl flow is a portion disposed upstream with respect to the flow direction of the swirl flow in a plan view facing the top surface of the piston. The inclined surface is arranged so as to be closer to the tip end side of the protrusion, and the recess is a surface continuous with the downstream side surface in a plan view facing the top surface of the piston. It has a continuous surface extending downstream in the flow direction of the swirl flow, the amount of depression with respect to the side surface of the first cavity is smaller than the width of the top surface of the piston, and the width becomes farther away from the side surface of the first cavity. It has a narrow shape.

According to one aspect of the direct injection diesel engine in the present disclosure, the fuel injected toward the opening edge of the second cavity collides with the opening edge, thereby causing the flow toward the second cavity and the first. Distributed to the flow towards the cavity. A part of the fuel distributed to the first cavity is further distributed in a flow that sandwiches the protrusion by colliding with the tip of the protrusion. Therefore, the formation of the protrusions reduces the amount of fuel distributed to a region of the squish area corresponding to the fuel injection direction and having a high fuel concentration. Is distributed to the area around the area where the fuel concentration is low. As a result, the fuel is more easily dispersed in the squish area than in the case where the protrusions are not formed, so that air in the squish area can be used efficiently. Therefore, it is possible to efficiently use the air in the cylinder. The protrusion is preferably provided corresponding to each of the injection ports through which the fuel is injected, and the specifications of the direct injection diesel engine, for example, the flow of intake air in the cylinder, the fuel injection pressure, It is preferable to be formed at a position corresponding to the injection mode or the like.
Further, in a direct injection type diesel engine, a swirl flow is usually generated in a cylinder in order to promote mixing of fuel and air. According to one aspect of the direct injection type diesel engine in the present disclosure, even if a part of the fuel injected from the fuel injection valve is caused to flow by the swirl flow, most of the fuel distributed to the first cavity is It will collide with the inclined surface of the projection. And the fuel which collided with the inclined surface of the projection part is guided to the inclined surface without going against the flow direction of the swirl flow. As a result, the fuel is more easily dispersed in the circumferential direction of the squish area than in the case where the side surface disposed on the downstream side of the swirl flow is a surface along the imaginary line.
Further, according to one aspect of the direct injection diesel engine in the present disclosure, the recess is open to the top surface of the piston and is a surface that is continuous with the side surface of the protrusion and has a swirl flow. It has a continuous surface extending downstream with respect to the flow direction. Therefore, a part of the fuel that collided with the protrusion is guided to the side surface of the protrusion, and then enters the recess. A part of the fuel that has entered the recess is distributed to the squish area from the opening of the recess on the top surface of the piston.
That is, the fuel is distributed from a position closer to the outer peripheral end of the piston than in the case where the depression is not formed in a part of the squish area. As a result, the fuel is easily distributed to the outer region in the squish area, so that it is possible to improve the efficiency of air use in the squish area.

  One aspect of the direct injection type diesel engine according to the present disclosure is that the top surface of the piston is a flat surface, and the protrusion has a facing surface facing the cylinder head on the same plane as the top surface of the piston. Or it has in the bottom face side of the 1st cavity rather than the top face of the piston.

  When the protruding part protrudes from the top surface of the piston, the protruding part may become an obstacle, and the fuel distributed to the area where the fuel concentration is high in the squish area may be excessively reduced. There is. According to one of the aspects of the direct injection diesel engine in the present disclosure described above, the projecting portion has a facing surface facing the cylinder head on the same plane as the top surface of the piston, or the first cavity than the top surface of the piston. On the bottom side. That is, the protrusion does not protrude from the top surface of the piston. As a result, it is possible to suppress excessive reduction of the fuel distributed to the region where the fuel concentration is high as compared with the case where the protrusion protrudes from the top surface of the piston.

In one aspect of the direct injection diesel engine according to the present disclosure, the protrusion has a tip portion on a side surface side of the first cavity with respect to an opening edge of the second cavity.
When the protrusion extends to the opening edge of the second cavity, the fuel that collides with the periphery of the tip of the protrusion in the opening edge is the same as in the case where the first cavity is not provided. A part becomes an obstacle and becomes difficult to be distributed to a squish area. In this regard, according to one aspect of the direct injection diesel engine in the present disclosure described above, the protrusion has a tip portion on the side surface side of the first cavity with respect to the opening edge of the second cavity. Therefore, compared with the case where the protrusion extends to the opening edge of the second cavity, the fuel that collides with the opening edge of the second cavity is easily distributed to the squish area. As a result, it is possible to suppress a decrease in the fuel distribution amount with respect to the squish area as compared with the case where no protrusion is formed.

  One of the aspects of the direct injection diesel engine in the present disclosure is that the protrusion has a base end portion on an imaginary line extending radially from the center of the second cavity in a plan view facing the top surface of the piston. And a tip.

  In a direct injection type diesel engine, a swirl flow is usually generated in a cylinder in order to promote mixing of fuel and air. For this reason, the fuel in the cavity is caused to flow in the circumferential direction by the swirl flow, and a centrifugal force acts. The center of the cavity is usually coincident with the center of the cylinder. For this reason, according to one aspect of the direct injection diesel engine of the present disclosure, the centrifugal force acts radially on the fuel injected into the cavity from the center of the second cavity. By colliding with the edge, the flow is divided into a flow toward the second cavity and a flow toward the first cavity. A part of the fuel distributed to the first cavity is further distributed in a flow that sandwiches the protrusion by colliding with the tip of the protrusion. For this reason, the formation of the protrusions reduces the amount of fuel distributed to the region of the squish area corresponding to the fuel injection direction and having a high fuel concentration. It is possible to distribute the fuel to the area around the area where the fuel concentration is low. As a result, the fuel is more easily dispersed in the squish area than in the case where the protrusions are not formed, so that air in the squish area can be used efficiently. Therefore, it is possible to efficiently use the air in the cylinder.

One of the aspects of the direct injection diesel engine in the present disclosure is that the continuous surface is a surface obtained by extending the downstream side surface.

According to one aspect of the direct injection diesel engine in the present disclosure, the fuel guided to the side surface can smoothly enter the recess portion.
One of the aspects of the direct injection diesel engine in the present disclosure is a direct injection diesel engine in which fuel is injected on the phantom line in a plan view facing the top surface of the piston.

  In a direct injection diesel engine, fuel is usually injected radially from the center of the cavity. For this reason, according to one aspect of the direct injection type diesel engine in the present disclosure, the fuel injected into the cavity has a force that causes the fuel injection device to advance radially from the center of the combustion chamber by applying the injection pressure. Since it works, it collides with the flow toward the second cavity and the flow toward the first cavity by colliding with the opening edge of the second cavity. A part of the fuel distributed to the first cavity is further distributed in a flow that sandwiches the protrusion by colliding with the tip of the protrusion. Therefore, the formation of the protrusions reduces the amount of fuel distributed to a region of the squish area corresponding to the fuel injection direction and having a high fuel concentration. Is distributed to the area around the area where the fuel concentration is low. As a result, the fuel is more easily dispersed in the squish area than in the case where the protrusions are not formed, so that air in the squish area can be used efficiently. Therefore, it is possible to efficiently use the air in the cylinder.

In one aspect of the piston for a direct injection type diesel engine according to the present disclosure, a cavity is constituted by a first cavity having an opening on a top surface facing a cylinder head and a second cavity having an opening on the bottom surface of the first cavity. A piston for a direct injection diesel engine that is integrally formed at a corner formed by a bottom surface of the first cavity and a side surface of the first cavity and is opposed to the top surface of the piston. And a tapered projection extending from the side surface of the first cavity, and a recess formed on the side surface of the first cavity with respect to the top surface of the piston. A pair of side surfaces that connect a facing surface facing the cylinder head and a bottom surface of the first cavity, and a swath generated in the cylinder among the pair of side surfaces. The downstream side surface disposed on the downstream side with respect to the flow direction of the flow of the fluid is closer to the portion disposed on the upstream side with respect to the flow direction of the swirl flow in a plan view facing the top surface of the piston. It is an inclined surface disposed so as to be closer to the tip end side of the protrusion, and the recess is a surface continuous with the downstream side surface in a plan view facing the top surface of the piston, and the swirl A continuous surface extending downstream in the flow direction of the flow, the amount of depression with respect to the side surface of the first cavity is smaller than the width of the top surface of the piston, and narrower as it goes away from the side surface of the first cavity. The shape is as follows.

  According to one aspect of the piston for a direct injection type diesel engine according to the present disclosure, the fuel injected toward the opening edge of the second cavity collides with the opening edge to thereby flow toward the second cavity. Distributed to the flow toward the first cavity. Then, a part of the fuel distributed to the first cavity is further distributed into a flow that sandwiches the protrusion in a plan view facing the top surface of the piston by colliding with the tip of the protrusion. Is done. Therefore, the formation of the protrusions reduces the amount of fuel distributed to a region of the squish area corresponding to the fuel injection direction and having a high fuel concentration. Is distributed to the area around the area where the fuel concentration is low. As a result, the fuel is more easily dispersed in the squish area than in the case where the protrusions are not formed, so that air in the squish area can be used efficiently. Therefore, it is possible to efficiently use the air in the cylinder.

FIG. 3 is a perspective cross-sectional view of a first embodiment that embodies a piston that is applied to a direct injection diesel engine according to the present disclosure, and is an enlarged view of a portion where a protrusion is formed. The top view which shows the planar structure of the top surface of the piston in 1st Embodiment. It is a top view which shows the planar structure of the top surface of the piston in 1st Embodiment, Comprising: The figure for demonstrating the shape of a projection part. It is a figure for demonstrating the shape of the projection part in 1st Embodiment, Comprising: The figure which overlapped and showed the outline in the 1b-1b line of FIG. 3 with respect to sectional drawing in the 1a-1a line of FIG. The figure for demonstrating the flow of the fuel near the projection part in 1st Embodiment. The graph which shows an example of the result of the simulation performed about protrusion amount W1 of a protrusion part in 1st Embodiment. In 1st Embodiment, the graph which shows an example of the result of the simulation performed about angle (theta) 2 of a projection part. The graph which shows an example of the result of the simulation performed about angle (theta) 1 of a projection part in 1st Embodiment. It is a perspective sectional view of a 2nd embodiment of the piston applied to the direct injection type diesel engine in this indication, and is a figure expanding and showing the portion in which the projection part was formed. It is a top view which shows the planar structure of the top surface of the piston in 2nd Embodiment, Comprising: The figure for demonstrating the shape of a hollow part. It is a figure for demonstrating the shape of the piston in 2nd Embodiment, Comprising: The figure which overlapped and showed the outline in the 2b-2b line of FIG. 3 with respect to sectional drawing in the 2a-2a line of FIG. The figure for demonstrating the flow of the fuel near the projection part in 2nd Embodiment. The figure for demonstrating the flow of the fuel in the hollow part vicinity in 2nd Embodiment. In 2nd Embodiment, the graph which shows an example of the result of the simulation performed about angle (theta) 2 of a projection part. The graph which shows an example of the result of the simulation performed about angle (theta) 1 of a projection part in 2nd Embodiment. In 2nd Embodiment, the graph which shows an example of the result of the simulation performed about angle (theta) 3 of a hollow part. In 2nd Embodiment, the graph which shows an example of the result of the simulation performed about hollow amount W2 of the hollow part. The figure for demonstrating the structure of the diesel engine disclosed by patent document 1. FIG. The figure which showed typically the mode of the piston top part after the test driving | running | working of the diesel engine disclosed by patent document 1. FIG.

(First embodiment)
Hereinafter, a direct injection type diesel engine (hereinafter simply referred to as a diesel engine) and a first embodiment that embodies a piston applied to the direct injection type diesel engine in the technology of the present disclosure will be described with reference to FIGS. To explain.

As shown in FIG. 1, in the first embodiment, the piston 10 of the diesel engine has the same basic structure as the piston 55 described in FIG. 18. That is, the cavity formed in the piston 10 includes a first cavity 12 having an opening on the top surface 11 of the piston 10 that is a flat surface, and a second cavity 15 having an opening on the bottom surface 13 of the first cavity 12. The The first cavity 12 has a bottom surface 13 that is substantially parallel to the top surface 11 of the piston 10 and a side surface 14 that extends from the outer peripheral end of the bottom surface 13 toward the top surface 11 of the piston 10. The connecting portion between the bottom surface 13 and the side surface 14 is formed in a curved surface shape that gradually rises toward the top surface 11 as the side surface 14 is approached. The second cavity 15 has a lip portion 16 having a tip at the opening edge of the bottom surface 13 of the first cavity 12, and descends from the lip portion 16 so as to draw a gentle S-shaped curve, and is outside the lip portion 16. It is formed by a wall surface portion 17 that projects and a conical center cone 18 that protrudes from the lower end of the wall surface portion 17 toward the center. The opening edge of the first cavity 12 by the side surface 14 and the opening edge of the second cavity 15 are concentrically formed with respect to the outer peripheral edge of the piston 10 in a plan view facing the top surface 11 of the piston 10. In the period before and after the piston 10 reaches compression top dead center, fuel is injected radially from the fuel injection valve toward the tip of the lip portion 16.

  The piston 10 is integrally formed with a protrusion 20 at a corner formed by the bottom surface 13 of the first cavity 12 and the side surface 14 of the first cavity 12. The protrusion 20 extends from the side surface 14 of the first cavity 12 toward the tip of the lip portion 16. The protrusion 20 is formed in a tapered shape having a tip 21 on the side surface 14 side of the first cavity 12 relative to the tip of the lip 16. As for the projection part 20, the opposing surface 22 which is a surface which opposes a cylinder head is arrange | positioned on the same plane as the top surface 11 of the piston 10. The connecting portion between the bottom surface 13 of the first cavity 12 and the protruding portion 20 is formed in a curved surface that gradually rises toward the facing surface 22 of the protruding portion 20 as the protruding portion 20 is approached. The connecting portion between the side surface 14 of the first cavity 12 and the protrusion 20 is formed in a gently curved shape that approaches the tip 21 of the protrusion 20 as the protrusion 20 is approached.

  The protrusion 20 has a pair of side surfaces that connect the facing surface 22 of the protrusion 20 and the bottom surface 13 of the first cavity 12. The pair of side surfaces are configured by an upstream side surface 24 disposed on the upstream side and a downstream side surface 25 disposed on the downstream side with reference to the flow direction 23 of the swirl flow generated in the cylinder. The upstream side surface 24 is disposed on the downstream side of the swirl flow as the site on the tip portion 21 side, and the downstream side surface 25 is disposed on the upstream side in the swirl flow on the site on the tip portion 21 side. The upstream side surface 24 and the downstream side surface 25 are connected to each other through a curved surface that is formed at the distal end portion 21 of the projection portion 20 and projects toward the distal end portion of the lip portion 16. The connecting portion between the upstream side surface 24 and the facing surface 22 is formed in a gently curved shape that descends toward the bottom surface 13 of the first cavity 12 as the upstream side surface 24 is approached. Similarly, the connecting portion between the downstream side surface 25 and the facing surface 22 is formed in a gently curved shape that descends toward the bottom surface 13 of the first cavity 12 as it approaches the downstream side surface 25. The base end portion of the protrusion 20 is configured such that the connecting portion of the upstream side surface 24 with respect to the side surface 14 of the first cavity 12 and the connecting portion of the downstream side surface 25 with respect to the side surface 14 of the first cavity 12 are side surfaces of the first cavity 12. 14 is a part to be tied along the line 14.

  As shown in FIG. 2, the projecting portion 20 is an imaginary line that indicates the axial direction of the injection port formed in the fuel injection valve in the fuel injection direction in a plan view facing the top surface 11 of the piston 10. 29 extends from the side surface 14 of the first cavity 12 toward a portion where the tip of the lip portion 16 intersects. The protrusion 20 is provided so as to correspond to each of the virtual lines 29, that is, each of the injection ports through which the fuel is injected, and has a base end portion and a distal end portion 21 on each virtual line 29. .

  That is, as shown in FIG. 3, the protrusion 20 has an upstream side surface 24 that is inclined with respect to the imaginary line 29 by an angle θ <b> 1 in a plan view facing the top surface 11 of the piston 10. Is formed, and the downstream side surface 25 is formed so as to be inclined with respect to the virtual line 29 by an angle θ2. Further, as shown in FIG. 4, the protrusion 20 has a height h from the bottom surface 13 of the first cavity 12 to the facing surface 22 of the protrusion 20, and the height of the piston 10 from the bottom surface 13 of the first cavity 12. It is formed at the same height as the height H up to the surface 11. Further, the protrusion 20 is formed such that the protrusion amount W1 from the side surface 14 of the first cavity 12 is smaller than the protrusion amount L1 of the lip portion 16. The protrusion amount W1 and the angles θ1 and θ2 are set to values at which the upstream side surface 24 of the projection 20 and the downstream side surface 25 of the projection 20 adjacent to the projection 20 do not interfere with each other.

Next, the operation of the above-described piston 10 and the diesel engine to which the piston 10 is applied will be described with reference to FIG.
As shown in FIG. 5, a part of the fuel injected toward the tip of the lip 16 collides with the tip of the lip 16 and then flows toward the first cavity 12 and the second cavity 15. Is distributed to the flow toward. Part of the fuel distributed to the first cavity 12 subsequently collides with the tip portion 21 of the protrusion 20. Part of the fuel that has collided with the tip 21 of the protrusion 20 is further divided into a flow guided to the upstream side 24 of the protrusion 20 and a flow guided to the downstream side 25 of the protrusion 20. .

  That is, a part of the fuel distributed to the squish area becomes the fuel distributed so as to sandwich the protrusion 20 at the tip 21 of the protrusion 20. Therefore, the fuel distribution amount for the region where the fuel concentration is high when the protrusion 20 is not formed is reduced, and a part of the reduced fuel has a low fuel concentration when the protrusion 20 is not formed. Will be distributed to other areas. That is, since the fuel is dispersed in the squish area as compared with the case where the protrusion 20 is not formed, the air in the squish area can be used efficiently.

  Here, if the opposing surface 22 of the protrusion 20 is arranged at a position higher than the top surface 11 of the piston 10, the region protruding from the top surface 11 becomes an obstacle, and the region where the fuel concentration is high There is a risk that the amount of fuel distributed to the fuel will be excessively reduced. In this regard, the protrusion 20 has a facing surface 22 on the same plane as the top surface 11 of the piston 10. Therefore, it is possible to prevent the fuel distribution amount from being excessively reduced with respect to the region where the fuel concentration is high, as compared with the case where such a protrusion 20 protrudes from the top surface 11 of the piston 10. In addition, for example, even if the existing piston is replaced with the piston 10 having the protrusion 20, the clearance between the piston 10 and the cylinder head can be ensured.

  When the protrusion 20 extends to the tip of the lip 16, the fuel that collides with the vicinity of the tip 21 of the protrusion 20 in the lip 16 becomes an obstacle at the tip 21 of the protrusion 20. This makes it difficult to flow toward the first cavity 12. In this regard, the protrusion 20 has a tip 21 on the side surface 14 side of the first cavity 12 relative to the tip of the lip 16. Therefore, when the fuel that has collided with the tip of the lip portion 16 generates a flow toward the first cavity 12, the protrusion 20 is less likely to become an obstacle. As a result, even when the protrusion 20 is provided, it is possible to obtain the fuel distribution amount for the squish area in the same manner as when the protrusion 20 is not provided.

  Further, the downstream side surface 25 of the protrusion 20 is inclined by an angle θ2 with respect to the virtual line 29 in a plan view facing the top surface 11 of the piston 10. Therefore, even if a part of the fuel is affected by the swirl flow and flows to the downstream side of the swirl flow, most of the fuel distributed to the first cavity 12 collides with the downstream side surface 25 of the protrusion 20. It becomes possible to make it. As a result, for example, compared with the case where the downstream side surface 25 of the protrusion 20 is a surface along the imaginary line 29, the fuel that collides with the protrusion 20 is increased among the fuel distributed to the first cavity 12. And since the fuel which collided with the projection part 20 is guided to the downstream side surface 25 without countering the flow direction of a swirl flow, a fuel becomes easy to disperse | distribute in the circumferential direction of a squish area.

  Next, an example of the results of various simulations performed on the protrusion amount W1 of the protrusion 20, the angle θ2 of the downstream side surface 25, and the angle θ1 of the upstream side surface 24 will be described with reference to FIGS.

  First, an example of the result of the simulation performed on the protrusion amount W1 of the protrusion 20 will be described with reference to FIG. In this simulation, the inventor analyzed the fuel distribution amount Q with respect to the squish area by changing the protrusion amount W1 of the protrusion 20 under the following conditions. The analysis result is shown in FIG. In FIG. 6, the horizontal axis indicates the ratio of the protruding amount W1 of the protruding portion 20 to the protruding amount L1 of the lip portion 16.

・ Engine speed: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Angle θ1: 45 ° of upstream side surface 24
-Angle θ2 of the downstream side surface 25: 60 °
As a result, as shown in FIG. 6, the fuel distribution amount Q with respect to the squish area does not provide the protrusion 20 in the range where the protrusion amount W1 of the protrusion 20 is “0 × L1 <W1 ≦ 0.8 × L1”. It was confirmed that it would be almost equivalent to or more than the case. On the other hand, it was confirmed that the fuel distribution amount Q with respect to the squish area decreases as the protrusion amount W1 increases in the range where the protrusion amount W1 of the protrusion 20 is “0.8 × L1 <W1 ≦ L1”. That is, by disposing the tip portion 21 of the protrusion 20 closer to the side surface 14 of the first cavity 12 than the tip portion of the lip portion 16, the range of “0.8 × L1 <W1 ≦ L1” is satisfied with respect to the squish area. Although the fuel distribution amount Q decreases, it has been confirmed that the decrease in the fuel distribution amount Q is suppressed as the protrusion amount W1 decreases. Similar results were obtained in a simulation performed by appropriately changing the above conditions within a range in which the upstream side surface 24 and the downstream side surface 25 of the adjacent protrusions 20 do not interfere with each other. That is, it is considered that the protrusion amount W1 of the protrusion 20 is preferably in the range of “0 × L1 <W1 ≦ 0.8 × L1”.

  Next, an example of the result of the simulation performed on the angle θ2 of the downstream side surface 25 in the protrusion 20 will be described with reference to FIG. In this simulation, the inventor analyzed the equivalence ratio distribution in the squish area by changing the angle θ2 of the downstream side surface 25 under the following conditions. Then, the present inventor pays attention to the following equation for the soot production rate, and since the soot production rate can be expressed by the fourth power of the equivalence ratio, the distribution of (Φ−Φ∞) ^ 4 The range corresponding to the angle θ2 was examined with the value corresponding to the center of gravity of the distribution as the evaluation value E. This evaluation value E indicates that the higher the value, the higher the fuel concentration region is formed in the squish area, and black smoke is more likely to be generated. This time, the reference value of the evaluation value E is E0.

なお、Ａは係数、Ｐは燃焼室内の圧力（雰囲気圧力）、Φは当量比、Φ∞はすす生成臨界当量比、Ｋは係数、ｔは時間を表している。

A is a coefficient, P is a pressure in the combustion chamber (atmospheric pressure), Φ is an equivalence ratio, Φ∞ is a soot production critical equivalent ratio, K is a coefficient, and t is time.

・ Engine speed: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Protrusion 20 protrusion amount W1: 0.5 × L1
-Angle θ1: 45 ° of upstream side surface 24
As shown in FIG. 7, when the angle θ2 of the downstream side surface 25 is in the range of “40 ° ≦ θ2 ≦ 75 °”, the evaluation value E is smaller than the reference value E0, and “0 ≦ θ2 <40 °” and “ It was confirmed that the evaluation value E is larger than the reference value E0 in the range of 75 ° <θ2 ”.

  This is considered because the fuel guided to the downstream side surface 25 cannot be dispersed in the circumferential direction of the squish area when the angle θ2 of the downstream side surface 25 becomes small. Further, when the angle θ2 of the downstream side surface 25 increases, the fuel distributed to the first cavity 12 is easily blocked by the downstream side surface 25, and is distributed to the squish area without being guided by the downstream side surface 25. It is thought to be done.

  Similar results were obtained in a simulation performed after changing the above conditions within a range in which the upstream side surface 24 and the downstream side surface 25 of the adjacent protrusions 20 do not interfere with each other. That is, it is considered that the angle θ2 of the downstream side surface 25 is preferably in the range of “40 ° ≦ θ2 ≦ 75 °”.

  Next, an example of the result of the simulation performed on the angle θ1 of the upstream side surface 24 in the protrusion 20 will be described with reference to FIG. In this simulation, the inventor changes the angle θ1 of the upstream side surface 24 under the following conditions, analyzes the equivalence ratio distribution in the squish area, and examines the range of the angle θ1 based on the evaluation value E described above. did.

-Engine speed of diesel engine: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Protrusion 20 protrusion amount W1: 0.5 × L1
-Angle θ2 of the downstream side surface 25: 60 °
As shown in FIG. 8, the evaluation value E is smaller than the reference value E0 when the angle θ1 of the upstream side surface 24 is in the range of “0 ≦ θ1 ≦ 55 °”, and the evaluation value is within the range of “55 ° <θ1”. It was confirmed that E becomes larger than the reference value E0. This is because the fuel distributed to the first cavity 12 is easily blocked by the upstream side surface 24 when the angle θ1 of the upstream side surface 24 is in the range of “55 ° <θ1”. This is considered to be distributed to the squish area without being guided.

  Similar results were obtained in a simulation performed by changing the above conditions within a range in which the upstream side surface 24 and the downstream side surface 25 of the adjacent protrusions 20 do not interfere with each other. That is, it is considered that the angle θ1 of the upstream side surface 24 is preferably “0 ≦ θ1 ≦ 55 °”.

As described above, according to the diesel engine and the piston 10 in the first embodiment, the effects listed below can be obtained.
(1) A part of the fuel distributed to the first cavity 12 subsequently collides with the protrusion 20, whereby a flow guided to the upstream side surface 24 of the protrusion 20 and a downstream side surface 25 of the protrusion 20. And is further distributed to the flow guided. As a result, the fuel is more easily dispersed in the squish area than in the case where the protrusions 20 are not formed, so that air in the squish area can be used efficiently.

  (2) The facing surface 22 of the protrusion 20 is disposed on the same plane as the top surface 11 of the piston 10. Therefore, compared with the case where the protrusion 20 protrudes from the top surface 11 of the piston 10, it is possible to suppress an excessive reduction in the fuel distribution amount for the region where the fuel concentration is high when the protrusion 20 is not formed. It is possible.

  (3) The protrusion 20 has a tip 21 on the side surface 14 side of the first cavity 12 relative to the tip of the lip 16. Therefore, compared with the case where the front-end | tip part 21 of the projection part 20 is extended to the front-end | tip part of the lip | rip part 16, fuel becomes easy to be distributed with respect to a squish area.

  (4) In a plan view facing the top surface 11 of the piston 10, the downstream side surface 25 of the projection 20 is inclined by an angle θ2 with respect to a virtual line 29 indicating the fuel injection direction. Therefore, even if the fuel injected toward the cavity flows under the influence of the swirl flow, compared with the case where the downstream side surface 25 is a surface along the imaginary line 29, Most of them can collide with the protrusions 20 and the fuel is easily dispersed in the circumferential direction of the squish area.

(Second Embodiment)
Hereinafter, a second embodiment in which a diesel engine according to the technology of the present disclosure and a piston applied to the diesel engine are embodied will be described with reference to FIGS. 9 to 17.

  In addition, the piston 30 of the diesel engine in 2nd Embodiment has the same main structure as the piston 10 of the diesel engine of 1st Embodiment. Therefore, in 2nd Embodiment, a different part from 1st Embodiment is demonstrated in detail, and the detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol about the part similar to 1st Embodiment.

As shown in FIG. 9, in the piston 30 of the second embodiment, on the side surface 14 of the first cavity 12, the outer peripheral edge of the piston 30 on the downstream side of the protrusion 20 with respect to the flow direction 23 of the swirl flow. A recess 40 that is recessed toward is formed. The recess 40 has a bottom surface 41 continuous with the bottom surface 13 of the first cavity 12 and is open to the top surface 11 of the piston 30. The recessed portion 40 is a surface that connects the bottom surface 41 and the top surface 11 of the piston 30, and is disposed on the upstream side surface 42 and the downstream side with respect to the flow direction 23 of the swirl flow. And a downstream side surface 43. The connecting portion between each side surface 42, 43 and the bottom surface 41 is formed in a gently curved shape that rises toward the top surface 11 of the piston 30 as it approaches each side surface 42, 43. Further, the connecting portion between the upstream side surface 42 and the top surface 11 of the piston 30 is formed in a gently curved shape that descends toward the bottom surface 41 of the recessed portion 40 as it approaches the upstream side surface 42. Similarly, the connecting portion between the downstream side surface 43 and the top surface 11 of the piston 30 is formed in a gently curved surface that descends toward the bottom surface 41 of the recessed portion 40 as the downstream side surface 43 is approached.

  As shown in FIG. 10, the upstream side surface 42 and the downstream side surface 43 are curved surfaces that project toward the opposite side of the tip of the lip portion 16 in a plan view facing the top surface 11 of the piston 30. They are connected via a certain connection surface 44. The upstream side surface 42 of the recessed portion 40 is a continuous surface that is continuous with the downstream side surface 25 of the protrusion 20 and is a surface obtained by extending the downstream side surface 25. That is, the upstream side surface 42 of the recess 40 is a surface that is inclined with respect to the imaginary line 29 by an angle θ 2, similarly to the downstream side surface 25 of the protrusion 20. The downstream side surface 43 of the recess 40 is a surface that is inclined with respect to the upstream side surface 42 of the recess 40 by an angle θ3.

  In addition, as shown in FIG. 11, the recess 40 is recessed by a recess amount W <b> 2 with respect to the side surface 14 of the first cavity 12. Further, the bottom surface 41 of the recessed portion 40 is formed in a curved shape that is disposed closer to the top surface 11 side of the piston 30 as the portion is closer to the connection surface 44. The protruding amount W1, the recessed amount W2, and the angles θ1, θ2, and θ3 are the downstream side surface 43 of the recessed portion 40 that is continuous with the protruding portion 20, and the protruding portion 20 that is adjacent to the protruding portion 20 on the downstream side of the swirl flow. Are set to values that do not interfere with each other.

Next, the operation of the above-described piston 30 and the diesel engine to which the piston 30 is applied will be described with reference to FIGS.
A part of the fuel that collides with the tip portion of the lip portion 16 and is distributed to the first cavity 12 is guided to the downstream side surface 25 of the projection portion 20 by colliding with the tip portion 21 of the projection portion 20.

  Here, when only the protrusion 20 is formed on the piston 30, the fuel guided to the downstream side surface 25 of the protrusion 20 includes the fuel that remains in the first cavity 12 without being distributed to the squish area. To do.

  On the other hand, in addition to the projection part 20, the hollow part 40 is formed in the piston 30 of 2nd Embodiment. The fuel guided to the downstream side surface 25 of the protrusion 20 continues to enter the recess 40 as shown in FIG. The fuel that has entered the recess 40 is guided to the bottom surface 41 and the upstream side surface 42 of the recess 40. As shown in FIG. 13, the fuel guided to the bottom surface 41 generates a flow toward the opening of the recess 40 in the top surface 11 of the piston 30. Further, part of the fuel that has collided with the connection surface 44 and the downstream side surface 43 of the recess 40 also generates a flow toward the opening of the recess 40 in the top surface 11 of the piston 30. These fuels are distributed from the opening to the squish area as the piston 30 moves downward.

  That is, by forming the recess 40 in addition to the protrusion 20 like the piston 30, the fuel remaining in the first cavity 12 when only the protrusion 20 is formed is easily distributed to the squish area. . Moreover, the fuel is distributed to the squish area from a position near the outer peripheral end of the piston 30. As a result, the fuel is easily distributed to a region outside the squish area where there is a relatively large amount of air that is not used for combustion, so that it is possible to increase the efficiency of air utilization in the squish area.

  Further, the bottom surface 41 of the recessed portion 40 is formed in a curved surface that is disposed closer to the top surface 11 side of the piston 30 as the portion is closer to the connection surface 44. Therefore, the fuel that has entered the recess 40 is guided to the bottom surface 41, so that the flat surface is formed by the bottom surface 13 of the first cavity 12 and the bottom surface 41 of the recess 40. A fuel flow toward the opening is also easily generated.

  Next, an example of the results of various simulations performed on the depression amount W2 of the depression 40, the angles θ1 and θ2 at the protrusion 20, and the angle θ3 at the depression 40 will be described with reference to FIGS.

  First, an example of the result of the simulation performed on the angle θ2 in the protrusion 20 will be described with reference to FIG. In this simulation, the inventor analyzed the equivalence ratio distribution in the squish area by changing the angle θ2 of the protrusion 20 under the following conditions, and examined the angle θ2 based on the evaluation value E.

-Engine speed of diesel engine: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Protrusion 20 protrusion amount W1: 0.5 × L1
-Angle θ1: 45 ° at the protrusion 20
-The hollow amount W2 of the hollow part 40: 0.2 * L2
-Angle θ3 at the depression 40: 90 °
As shown in FIG. 14, in the range where the angle θ2 of the downstream side surface 25 of the protrusion 20 is “40 ° ≦ θ2 ≦ 80 °”, the evaluation value E is smaller than the reference value E0, and “0 ≦ θ2 <40”. In the range of “°” and “80 ° <θ2”, it was confirmed that the evaluation value E is smaller than the reference value E0. Similar results were obtained in a simulation performed by changing the above conditions within a range in which the upstream side surface 24 of the protrusion 20 and the downstream side surface 43 of the recess 40 do not interfere with each other. That is, it is considered that the angle θ2 of the downstream side surface 25 of the protrusion 20 is preferably in the range of “40 ° ≦ θ2 ≦ 80 °”.

  Here, the upper limit value of the angle θ2 is higher than that of the piston 10 of the first embodiment in which only the protrusion 20 is formed. This is because a part of the fuel distributed to the first cavity 12 is blocked by the downstream side surface 25 of the projection 20, but the fuel is guided by the downstream side surface 25 to the recess 40. It is thought to enter.

  Next, an example of the result of the simulation performed on the angle θ1 in the protrusion 20 will be described with reference to FIG. In this simulation, the inventor analyzes the equivalence ratio distribution in the squish area by changing the angle θ1 of the upstream side surface 24 of the protrusion 20 under the following conditions, and based on the evaluation value E, the range of the angle θ1 Was examined.

-Engine speed of diesel engine: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Protrusion 20 protrusion amount W1: 0.5 × L1
-Angle θ2 at the protrusion 20: 60 °
-The hollow amount W2 of the hollow part 40: 0.2 * L2
-Angle θ3 at the depression 40: 90 °
As shown in FIG. 15, as in the first embodiment, the evaluation value E is smaller than the reference value E0 when the angle θ1 of the upstream side surface 24 of the protrusion 20 is in the range of “0 ≦ θ1 ≦ 55 °”. In the range of “55 ° <θ1”, it was confirmed that the evaluation value E is larger than the reference value E0. Similar results were obtained in a simulation performed by changing the above conditions within a range where the upstream side surface 24 of the protrusion 20 and the downstream side surface 43 of the recess 40 do not interfere with each other. That is, it is considered that the angle θ1 of the upstream side surface 24 is preferably “0 ≦ θ1 ≦ 55 °”.

  Next, an example of the result of the simulation performed on the angle θ3 in the depression 40 will be described with reference to FIG. In this simulation, the present inventor analyzed the equivalence ratio distribution in the squish area by changing the angle θ3 in the depression 40 under the following conditions, and examined the range of the angle θ3 based on the evaluation value E.

-Engine speed of diesel engine: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Protrusion 20 protrusion amount W1: 0.5 × L1
-Angle θ1: 45 ° at the protrusion 20
-Angle θ2 at the protrusion 20: 60 °
-The amount of depressions in the depression 40: 0.2 x L2
As shown in FIG. 16, the evaluation value E is smaller than the reference value E0 when the angle θ3 of the depression 40 is in the range of “80 ° ≦ θ3”, and the evaluation value E is the reference in the range of “θ3 <80 °”. It was confirmed that the value becomes larger than the value E0. This is considered because the fuel guided to the depression 40 cannot be distributed in the circumferential direction of the squish area in the range of θ3 <80 °. Similar results were obtained in a simulation performed by changing the above conditions within a range in which the upstream side surface 24 of the protrusion 20 and the downstream side surface 43 of the recess 40 do not interfere with each other. That is, it is considered that the angle θ3 of the recess 40 is preferably in the range of “80 ° ≦ θ3”.

  Next, an example of the simulation performed for the depression amount W2 of the depression 40 will be described with reference to FIG. In this simulation, the present inventor analyzed the equivalence ratio distribution in the squish area by changing the depression amount W2 of the depression 40 under the following conditions, and examined the range of the depression amount W2 based on the evaluation value E. . In FIG. 17, the horizontal axis indicates the ratio of the depression amount W <b> 2 of the depression 40 to the width L <b> 2 of the top surface 11 of the piston 30.

・ Engine speed: 1000rpm
・ Engine load: 100%
-Height h of the protrusion 20: height H
-Protrusion 20 protrusion amount W1: 0.5 × L1
-Angle θ1: 45 ° at the protrusion 20
-Angle θ2 at the protrusion 20: 60 °
-Angle θ3 at the depression 40: 90 °
As shown in FIG. 17, the evaluation value E is smaller than the reference value E0 when the dent amount W2 of the dent portion 40 is in the range of “0 × L2 <W2 ≦ 0.5 × L2”, and “0.5 × L2 It was confirmed that the evaluation value E is larger than the reference value E0 within the range of <W2. Similar results were obtained in a simulation performed by changing the above conditions within a range in which the upstream side surface 24 of the protrusion 20 and the downstream side surface 43 of the recess 40 do not interfere with each other. That is, it is considered that the depression amount W2 is preferably in the range of “0 × L2 <W2 ≦ 0.5 × L2” .

  As described above, according to the diesel engine and the piston 30 in the second embodiment, in addition to the effects (1) to (4) described in the first embodiment, the effects listed below can be obtained. .

  (5) In addition to the protrusion 20, a recess 40 is formed in the piston 30. Therefore, a part of the fuel remaining in the first cavity 12 when only the protrusions 20 are formed is easily distributed to the squish area from a position near the outer peripheral end of the piston 30. As a result, the fuel is easily distributed to a region outside the squish area where there is a relatively large amount of air that is not used for combustion, so that it is possible to increase the efficiency of air utilization in the squish area.

  (6) Since the upstream side surface 42 of the recessed portion 40 is a surface obtained by extending the downstream side surface 25 of the protruding portion 20, the fuel guided to the downstream side surface 25 of the protruding portion 20 smoothly flows into the recessed portion 40. Will enter.

  (7) The bottom surface 41 is formed in a curved surface that is disposed closer to the top surface 11 of the piston 30 as the portion is closer to the connection surface 44. Therefore, for example, compared to the case where the bottom surface 41 is disposed on the same plane as the bottom surface 13 of the first cavity 12, a flow toward the top surface 11 of the piston 30 is easily generated in the recessed portion 40. As a result, in the fuel distributed from the opening of the recess 40 to the squish area, the outward force in the squish area is easily maintained, so that the fuel is easily distributed to the outer region in the squish area.

The first and second embodiments can be implemented with appropriate modifications as follows.
-In 2nd Embodiment, the upstream side 42 of the hollow part 40 should just be a surface which continues to the downstream side 25 of the projection part 20, and is extended to the downstream in the flow direction 23 of a swirl flow. The downstream side surface 25 of 20 may not be the surface extended. That is, the upstream side surface 42 of the recess 40 may be bent by a predetermined angle with respect to the downstream side surface 25 of the protrusion 20.

-In 2nd Embodiment, the surface arrange | positioned on the same plane as the bottom face 13 of the 1st cavity 12 may be sufficient as the bottom face 41 of the hollow part 40. FIG.
In the second embodiment, the bottom surface 41 of the recess 40 may be a surface that connects the bottom surface 13 of the first cavity 12 and the top surface 11 of the piston 30.

  In the second embodiment, at least one of the upstream side surface 42 and the downstream side surface 43 of the recessed portion 40 may be a surface that is inclined so that the recessed portion 40 becomes narrower as it approaches the bottom surface 41. .

  In the second embodiment, the protrusion amount W1, the recess amount W2, the angle θ1, the angle θ2, and the angle θ3 are the values of the downstream side surface 43 of the recess portion 40 connected to the protrusion portion 20 and the protrusion portion 20 adjacent to the protrusion portion 20. It is sufficient that the upstream side surface 24 is set to a value that does not interfere with each other. Therefore, the protrusion amount W1, the depression amount W2, the angle θ1, the angle θ2, and the angle θ3 may be set to values that make the downstream side surface 43 and the upstream side surface 24 continuous.

  In the first and second embodiments, the projecting portion 20 has one of the upstream side surface 24 and the downstream side surface 25 along the imaginary line 29 in a plan view facing the top surface 11 of the pistons 10 and 30. The surface may extend.

-In 1st and 2nd embodiment, the projection part 20 may be extended to the front-end | tip part of the lip | rip part 16 which is an opening edge of a 2nd cavity.
In the first and second embodiments, the protrusion 20 may have the facing surface 22 on the bottom surface 13 side of the first cavity 12 with respect to the plane including the top surface 11 of the pistons 10 and 30. That is, the height h of the protrusion 20 may be in the range of 0 <h ≦ H with respect to the height H from the bottom surface 13 of the first cavity 12 to the top surface of the piston 10.

  In the first and second embodiments, the protrusion 20 may have a facing surface 22 on the opposite side of the bottom surface 13 of the first cavity 12 with respect to the plane including the top surface 11 of the pistons 10 and 30. That is, the protrusion 20 may protrude from the top surface 11 of the pistons 10 and 30.

  -In 1st and 2nd embodiment, the front-end | tip part 21 of the projection part 20 is the front-end | tip part side of the lip | rip part 16 rather than the site | part by the side of the bottom face 13 of the 1st cavity 12 at the bottom face 13 side. It may be inclined so that it may be arranged.

  In the first and second embodiments, at least one of the upstream side surface 24 and the downstream side surface 25 of the projecting portion 20 is such that the projecting portion 20 becomes wider toward the bottom surface 13 of the first cavity 12. It may be inclined with respect to the bottom surface 13 of the cavity 12.

  -As for the projection part 20, at least one of a base end part and a front-end | tip part does not need to be arrange | positioned on the virtual line 29. FIG. For example, in the first and second embodiments, the protrusion 20 has a proximal end portion on the virtual line 29 and a distal end portion on the upstream side in the swirl flow direction 23 with respect to the virtual line 29. May be. Further, the shape formed by the side surface 14 of the first cavity 12 and the upstream side surface 24 may be an acute angle in a plan view facing the top surface 11 of the piston 10.

  Further, for example, in the first embodiment, the protrusion 20 may have a proximal end portion on the virtual line 29 and a distal end portion on the downstream side in the swirl flow direction 23 with respect to the virtual line 29. Good. Further, the shape formed by the side surface 14 of the first cavity 12 and the downstream side surface 25 may be an acute angle in a plan view facing the top surface 11 of the piston 10.

  -In 1st and 2nd embodiment, although the projection part 20 is provided corresponding to each of the injection port into which a fuel is injected, the specification of a direct injection type diesel engine, for example, a swirl ratio, the injection pressure of fuel, etc. Depending on the injection mode and the like, the number and arrangement thereof may be changed as appropriate.

  DESCRIPTION OF SYMBOLS 10 ... Piston, 11 ... Top surface, 12 ... 1st cavity, 13 ... Bottom surface, 14 ... Side surface, 15 ... 2nd cavity, 16 ... Lip part, 17 ... Wall surface part, 18 ... Center cone, 20 ... Projection part, 21 DESCRIPTION OF SYMBOLS ... Tip part, 22 ... Opposite surface, 23 ... Flow direction, 24 ... Upstream side surface, 25 ... Downstream side surface, 29 ... Virtual line, 30 ... Piston, 40 ... Depression part, 41 ... Bottom surface, 42 ... Upstream side surface, 43 ... downstream side surface, 44 ... connection surface, 51 ... cylinder block, 52 ... cylinder head, 52a ... lower surface, 53 ... cylinder, 55 ... piston, 56 ... first cavity, 57 ... bottom surface, 58 ... top surface, 60 ... 2nd cavity, 61 ... Lip part, 62 ... Wall surface part, 63 ... Center cone, 65 ... Fuel injection valve, 67 ... Squish area, 69 ... Virtual line, 70 ... Spear.

Claims (7)

A direct injection diesel engine comprising a piston having a cavity formed by a first cavity having an opening on a top surface facing a cylinder head and a second cavity having an opening on a bottom surface of the first cavity,
The piston is integrally formed at a corner formed by the bottom surface of the first cavity and the side surface of the first cavity, and the side surface of the first cavity in a plan view facing the top surface of the piston. A tapered protrusion extending from the first cavity, and a recess formed on the side surface of the first cavity with respect to the top surface of the piston,
The protrusion has a pair of side surfaces that connect a facing surface facing the cylinder head and a bottom surface of the first cavity,
Of the pair of side surfaces, the downstream side surface disposed downstream of the flow direction of the swirl flow generated in the cylinder is a flow of the swirl flow in a plan view facing the top surface of the piston. It is an inclined surface that is disposed so that the portion disposed on the upstream side with respect to the direction is closer to the tip end side of the protrusion,
The concave portion has a continuous surface that is continuous with the downstream side surface and extends downstream in the flow direction of the swirl flow in a plan view facing the top surface of the piston, and the first cavity. A direct injection diesel engine having a shape in which a recess amount with respect to the side surface of the piston is smaller than a width of a top surface of the piston and becomes narrower as the distance from the side surface of the first cavity increases . The direct injection diesel engine according to claim 1 , wherein the continuous surface is a surface obtained by extending the downstream side surface. The top surface of the piston is a flat surface;
3. The direct projection according to claim 1, wherein the protrusion has a facing surface facing the cylinder head on the same plane as the top surface of the piston or on the bottom surface side of the first cavity with respect to the top surface of the piston. Injection type diesel engine. The direct injection diesel engine according to any one of claims 1 to 3 , wherein the protrusion has a tip on a side surface side of the first cavity with respect to an opening edge of the second cavity. The said protrusion part has a base end part and a front-end | tip part on the virtual line extended radially from the center of a said 2nd cavity in planar view which opposes the top surface of the said piston. Direct-injection diesel engine described in 1. The direct injection diesel engine according to claim 5 , wherein fuel is injected onto the imaginary line in a plan view facing the top surface of the piston. A piston for a direct injection diesel engine in which a cavity is constituted by a first cavity having an opening on a top surface facing a cylinder head and a second cavity having an opening on a bottom surface of the first cavity,
A tapered shape integrally formed at a corner formed by the bottom surface of the first cavity and the side surface of the first cavity and extending from the side surface of the first cavity in a plan view facing the top surface of the piston. and the protrusion,
On the side surface of the first cavity, there is a recess that is open to the top surface of the piston,
The protrusion has a pair of side surfaces that connect a facing surface facing the cylinder head and a bottom surface of the first cavity,
Of the pair of side surfaces, the downstream side surface disposed downstream of the flow direction of the swirl flow generated in the cylinder is a flow of the swirl flow in a plan view facing the top surface of the piston. It is an inclined surface that is disposed so that the portion disposed on the upstream side with respect to the direction is closer to the tip end side of the protrusion,
The concave portion has a continuous surface that is continuous with the downstream side surface and extends downstream in the flow direction of the swirl flow in a plan view facing the top surface of the piston, and the first cavity. A piston for a direct injection type diesel engine having a shape in which the amount of depression with respect to the side surface of the piston is smaller than the width of the top surface of the piston and becomes narrower as the distance from the side surface of the first cavity increases .

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