JP5070854B2 - Direct injection internal combustion engine - Google Patents

Description

  The present invention relates to a spark ignition direct injection internal combustion engine.

  2. Description of the Related Art Conventionally, a direct injection internal combustion engine that performs lean air-fuel ratio operation by stratified combustion is known (see Patent Document 1).

  This consists of a fuel injection valve and a spark plug at the approximate center of the upper surface of the combustion chamber, a bowl in which a deep pan portion is arranged at the center of the piston crown surface and a circular shallow pan portion around which a valve recess is arranged. By injecting the hollow spray from the injection valve toward the bowl, the air-fuel mixture is held in the combustion chamber to form a stratified state and perform a lean air-fuel ratio operation.

And, in the middle and low speed range, fuel spray is applied to the piston deep dish part, and in the high speed range, it is injected toward the shallow dish part to form a strong stratified mixture in the deep dish part and above, and the shallow dish part In addition, the stratified state of the injected fuel is changed according to the operation region by switching the case where the weakly stratified air-fuel mixture is formed in the deep dish portion and the sky.
JP 2000-265841 A

  However, in the above-described conventional example, the circular shallow dish portion constituting the bowl is arranged to be a valve recess around the central deep dish portion, and is not formed in a circular shape centering on the injection valve. For this reason, there is a possibility that the injected fuel spray spills out from between the shallow plate parts and is not sufficiently received by the shallow plate part, and there is a concern that fuel consumption deteriorates and unburned HC increases.

  Further, in the above conventional example, since the boundary between the central deep dish part and the outer shallow dish part is uniformly formed, in order to obtain a weak stratification state, injection is performed at a low position of the piston in the compression stroke. The spray cone spreads out and hits the shallow plate part toward the outside in the radial direction, and the air-fuel mixture formed via this shallow plate part is a non-ignitable lean mixture near the spark plug in the center. In order to form a strong stratified state, when the piston is injected at a high position, the injection cone is completely received by the central basin, and an air-fuel mixture is formed, near the spark plug. There is a possibility that the concentration of the air-fuel mixture formed will be excessive.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a direct injection internal combustion engine suitable for forming an appropriate stratified air-fuel mixture corresponding to changes in engine load.

The present invention includes a cavity constituted by an inner cavity provided near the center of the piston crown surface and an outer cavity provided so as to surround the outer periphery of the inner cavity, and fuel is set in advance toward the cavity of the piston crown surface. A fuel injection valve provided close to the spark plug at the upper part of the combustion chamber so as to supply the fuel radially along the conical surface, and in the entire peripheral region on the outer peripheral side of the inner cavity so as to form the outer peripheral region of the inner cavity The height of the bottom surface of the outer cavity with respect to the bottom surface of the inner cavity is made different in each region in the radial direction along the conical surface where the fuel is injected.

Therefore, in the present invention, the cavity provided on the piston crown surface is constituted by an inner cavity provided near the center of the piston crown surface and an outer cavity provided so as to surround the outer periphery of the inner cavity, and the outer peripheral region of the inner cavity. The height of the bottom surface of the outer cavity with respect to the bottom surface of the inner cavity is made different in each radial region along the conical surface where the fuel is injected. . Therefore, if the fuel injection amount is increased by advancing the fuel injection start timing in the compression stroke according to the engine load state in the stratified operation region, the supply range of fuel injected from the fuel injection valve is reduced. In the load state, the piston cavity and the fuel injection valve at the end of the compression stroke are performed at a close distance, and only the inner cavity can be formed, and the distance increases corresponding to the advance angle of the injection start timing as the load increases. The divided side walls are expanded to a part of the outer cavities having a low height, and the distance is gradually increased as the load is further increased, so that the side walls are sequentially increased to a high height. For this reason, it is possible to form a stratified air-fuel mixture having an appropriate size corresponding to changes in the engine load, stably realizing stratified combustion under a wide range of operating conditions, and improving fuel efficiency.

  Hereinafter, it demonstrates based on one Embodiment of the direct injection type internal combustion engine of this invention. 1 to 5 show a first embodiment of a direct injection internal combustion engine to which the present invention is applied, FIG. 1 is a schematic configuration diagram including a combustion chamber of a direct injection internal combustion engine to which the present invention is applied, and FIG. FIG. 3 is a developed view of the inner and outer bowls of the piston crown surface, FIG. 4 is a side view and a plan view showing a spray state from the fuel injection valve, and FIG. 5 is a spray view from the fuel injection valve. It is a top view which shows the relationship with the inner and outer bowl of a piston crown surface.

  In the direct injection internal combustion engine of this embodiment, a combustion chamber 4 defined by a cylinder block 1, a cylinder head 2 and a piston 3 is formed, and an intake valve 5 is provided on the cylinder head 2 side constituting the combustion chamber 4. The intake port 6 is communicated with the exhaust port 8 and the exhaust port 8 is communicated with the exhaust valve 7. The intake valve 5 and the exhaust valve 7 are driven to open and close by an intake valve cam and an exhaust valve cam (not shown), respectively. A fuel injection valve 9 and a spark plug 10 are arranged near the center of the upper surface of the combustion chamber 4 formed by the cylinder head 2, and fuel injection and ignition are performed based on a drive signal from the engine control unit 11, respectively. Is executed. 12 is an intake air amount sensor, 13 is an accelerator opening sensor, 14 is a crank angle sensor, 15 is a coolant temperature sensor, and 16 is an exhaust oxygen sensor.

  The cylinder head 2 that forms the upper surface of the combustion chamber 4 has valve seats 5A and 7A on which the intake and exhaust valves 5 and 7 are seated, with the central portion where the fuel injection valve 9 and the spark plug 10 are disposed at the top. Constitutes a pent roof type combustion chamber 4 that constitutes an inclined slope. The piston crown surface 3A is also a convex shape having an inclined slope 3B that forms a squish area along the inclined slope on the left and right in the cylinder row direction, and a flat top 3C that continues to the top of the left and right slopes. Is formed. Therefore, when the piston 3 rises to the top dead center position, the flat top portion 3C of the piston 3 and the cylinder head 2 form a pent roof type combustion chamber 4 having a substantially triangular cross section.

  As shown in FIG. 2, the piston crown surface 3 </ b> A surrounds an inner cavity 18 made of a circular deep dish formed relatively deeply in the vicinity of the center thereof, and surrounds the inner cavity 18 substantially concentrically. An annular outer cavity 20 formed shallower than the inner cavity 18 is provided on the outer periphery. The inner cavity 18 has an outer peripheral side wall 19 (hereinafter referred to as “side wall”) whose upper edge is connected to the bottom 21 of the outer cavity 20 that surrounds the outer peripheral side wall 22. In the following, the upper edge of the outer wall is formed so as to be connected to the flat top 3C and the left and right inclined surfaces 3B of the piston crown surface 3A. The upper edge of the outer wall 22 of the outer cavity 20 is located higher in a range connected to the flat top portion 3C of the piston crown surface 3A, and is in a range connected to the left and right slopes 3B of the piston crown surface 3A. The position of the central part is low.

  The outer cavity 20 is divided into a plurality of regions in the circumferential direction, and the respective regions are arranged with different depths (height of the side walls 19 constituting the inner cavity 18). In the example of illustration, it divides | segments into 6 area | regions, 2 area | region A which faces the left-right slope 3B, and 4 area | regions B and C which face a flat top part. And the height dimension of the bottom part 21 (height dimension of the side wall 19 which comprises the inner side cavity 18) of the two area | regions A which faces the right-and-left slope 3B is set to the smallest, and the height of the outer wall 22 which comprises the outer side cavity 20 The dimensions are ensured to some extent. Further, the height dimension of the bottom portion 21 of each of the four regions B and C facing the flat top 3C (the height dimension of the side wall 19 constituting the inner cavity 18) is larger than the region A and is stepped with respect to the region A. Two types of height dimensions are set so as to form a shape.

  The number of divisions of the region of the outer cavity 20 is preferably set so as to correspond to the number of fuel sprays injected from the fuel injection valve 9. That is, as shown in FIG. 4, as the fuel injection valve 9, a multi-hole injection valve that has a small change in the spray shape even when the in-cylinder pressure rises in the latter half of the compression stroke, is hollow, and has a strong directivity is used. Injected in an obliquely downward direction while expanding along a conical surface having an axis that is parallel to the cylinder axis and coincides with the central axes of the inner cavity 18 and the outer cavity 20 formed on the piston crown surface 3A. Then, as shown in FIG. 5, the plurality of sprays injected are directed to the respective central positions of the divided regions of the outer cavity 20, and the divided regions of the outer cavity 20 and the multiple fuel injection valves 9. The direction of the hole is set to match.

  Further, the spray injected from the fuel injection valve 9 (here, described as spraying in the entire range from the middle of the upward stroke of the piston 3 to the vicinity of the top dead center) has a large distance from the piston 3. In the case (piston position in the compression stroke), it collides with each region of the outer cavity 20. Since the spray sprayed has a conical shape as a whole, the height dimension of the bottom 21 of the outer cavity 20 (the height dimension of the side wall 19 constituting the inner cavity 18) is first increased as the piston position rises. The edge of the side wall 19 in the largest area crosses the spray, and then the edge of the side wall 19 in the area where the height dimension of the bottom 21 of the outer cavity 20 (the height dimension of the side wall 19 constituting the inner cavity 18) is the next. The edge of the side wall 19 in the region where the height dimension of the bottom 21 of the outer cavity 20 (the height dimension of the side wall 19 constituting the inner cavity 18) is the next largest will cross the spray.

  Therefore, until the spray crosses the edge of the side wall 19 of the region, the spray collides with the outer cavity 20 of the region and is vaporized between the outer wall 22 of the outer cavity 20 and crosses the edge of the side wall 19 of the region. When the piston 3 is lifted up, the spray does not collide with the outer cavity 20 in that region, but the spray collides with the side wall 19 that continues downward through the edge and flows into the inner cavity 18 to vaporize the spray. It will be. Since the height of the side wall 19 has a stepwise difference in each region, each spray sequentially has a collision position from the outer outer cavity 20 to the inner inner cavity 18 according to the rising position of the piston 3. This will result in a transition.

  In the present embodiment, when the engine load and the rotation speed calculated by the engine control unit 11 are equal to or higher than a predetermined value (high load high rotation region), the fuel injection start timing is started and ended during the intake stroke. In this way, so-called homogeneous combustion is performed. The fuel injection start timing and end timing are controlled based on a signal from the crank angle sensor 14. In addition, when the engine load state and / or rotation state is lower than the high load high rotation region, the fuel injection start timing of the fuel injection valve 9 depends on the engine load state and / or rotation state. And control so as to form a stratified air-fuel mixture corresponding to the load state and / or rotational state of the engine.

  FIGS. 6 to 9 schematically illustrate the relationship between the fuel spray and the piston position for each engine load and the mixture distribution in the vicinity of the ignition timing when stratified combustion is performed in the present embodiment.

  First, when the engine load is high, as shown in FIG. 6A, the fuel injection start timing is set to a relatively early timing (piston lift position A1) in the latter half of the compression stroke. When the injection start timing is advanced, the piston 3 collides with the fuel spray at a position away from the fuel injection valve 9, so that the fuel injected in a conical shape travels while spreading, and all outside the entire region in the outer wall 22. It can be received in the areas A to C of the cavity 20. When the engine load is high, the injection period is longer than when the engine load is low, and the piston 3 rises during that period, so that the fuel injected in the latter half of the injection period can be received by the inner cavity 18, and the piston rising position A2 Then, the fuel injection is finished.

  The injected fuel spreads substantially uniformly throughout the inner cavity 18 and the outer cavity 20, as shown in FIGS. 6B and 6C. And the density of the injected fuel becomes thin as it moves to the center part as it becomes thinner at the peripheral part by decreasing the circle that collides with the piston 3 as the piston 3 rises. Thereby, even when the load is high, it becomes possible to form a homogeneous stratified air-fuel mixture, and stratified combustion can be performed without deteriorating the exhaust performance.

  When the engine load becomes low, the injection start timing A1 is retarded as shown in FIG. Since the piston 3 approaches the fuel injection valve 9 due to the delay of the injection start timing A1, the position at which the injected fuel starts to collide with the piston 3 moves relatively closer to the piston center.

  At this time, the height of the side wall 19 of the inner cavity 18 is set to be stepped so as to vary depending on the region of the outer cavity 20. For this reason, when the fuel spray collides with the vicinity of the boundary between the upper end of the side wall 19 of the piston 3 and the bottom 21 of the outer cavity 20, the outer cavity 20 is injected into the outer cavity 20 in the region A where the side wall 19 is low at the beginning of injection. The fuel is received. For the outer cavity 20 in the region C where the side wall 19 is high, the fuel spray does not reach the outer cavity 20 and is received by the side wall 19 even in the initial stage of injection.

  Therefore, if an appropriate fuel injection timing A1 is set, as shown in FIGS. 7B and 7C, the fuel is diffused and received only in the outer cavity 20 having a low side wall 19 or an intermediate height. Therefore, excessive leaning of fuel in the outer cavity 20 can be suppressed. And the density of the injected fuel is in a stratified state where the circle that collides with the piston 3 becomes smaller as the piston 3 rises, so that it becomes thinner at the peripheral part and becomes thicker as it moves to the central part. . That is, combustion is not deteriorated by a load in the middle of high load operation and low load operation. Also in this case, the fuel injection end timing A2 is set at the same timing as that shown in FIG. In FIG. 7C, in the region B including the side wall 19 having an intermediate height, the fuel spray is diffused on one side and the fuel spray is not diffused on the other side. This can be realized by setting the height of the lower than the other.

  When the engine load is lower and when the engine speed is low, the fuel injection start timing A1 is delayed so that the fuel spreads only in a part of the region A of the outer cavity 20, as shown in FIG. Also in this case, the fuel injection end timing A2 is set at the same timing as that shown in FIG. Also in this case, as shown in FIGS. 8B and 8C, the concentration of the peripheral portion due to the spraying to the outer cavity 20 in one region A is thin, and in the central region due to the spraying to the inner cavity 18. A dense stratified air-fuel mixture can be obtained, and combustion is not deteriorated.

  Further, when the engine load is the lowest as in the idling operation, as shown in FIG. 9A, the injection timing A1 is retarded so that the fuel can be received only in the inner cavity 18 as shown in FIG. As shown in FIG. 9B and FIG. 9C, formation of a compact air-fuel mixture can be realized.

  If the side wall 19 at the boundary between the inner cavity 18 and the outer cavity 20 is set low, the fuel received by the inner cavity 18 may exceed the side wall 19 toward the outer cavity 20 and the fuel may be excessively diffused. However, by installing the spark plug 10 on the side of the fuel injection valve 9, spark ignition is performed near the end of fuel spraying during idle operation or low load operation with a small total fuel injection amount and a large lean operation. It is possible to adopt a method (spray guide type stratified combustion) in which fuel is burned before it diffuses. Even in this case, combustion proceeds while the fuel diffuses and mixes. Therefore, a fuel receiving guide corresponding to the inner cavity 18 is necessary so that the fuel does not diffuse excessively. There is no harmful effect of lowering.

  FIG. 10 shows the shape of the piston crown surface 3A of the second example of the present embodiment. In the present embodiment, only the height of the side wall 19 of the inner cavity 18 that is the boundary between the inner cavity 18 and the outer cavity 20 is set to be different from each other in the same manner as in the first embodiment, and the bottom of the outer cavity 20 is set. For example, the height of 21 is the same as the height of the bottom 21 of the outer cavity 20 in the lowest region A.

  The present embodiment is the same as the first embodiment in that it is possible to vary the timing at which each of the plurality of fuel sprays is received by the outer cavity 20. However, since the height of the bottom 21 of the outer cavity 20 is constant, the height of the bottom 21 of the outer cavity 20 can be set arbitrarily and optimally regardless of the side wall 19 of the inner cavity 18.

  That is, when the height of the bottom 21 of the outer cavity 20 is made different, there is a concern that fuel spills from the outer outer wall 22 to the outside (squish area) at the highest portion of the bottom 21 of the outer cavity 20. In the configuration shown in the second embodiment, the outer cavities 20 are each formed with a high outer wall 22, and there is no spillage to the external squish area 3 </ b> B, the flat top 3 </ b> C of the piston 3, etc. An increase in the surface area through which the fuel diffuses can be suppressed, and an increase in cooling loss and unburned HC can be prevented.

  However, in this configuration, since only the height of the side wall 19 of the inner cavity 18 is different, there is no action of suppressing the fuel received in the outer cavity 20 from diffusing in the circumferential direction beyond each region. For this reason, the height of the side wall 19 on the outer periphery of the inner cavity 18 and the bottom of the outer cavity 20 depend on the setting of the diameter of the inner cavity 18 and the outer wall 22 of the outer cavity 20, the nozzle angle (spray umbrella angle) of the fuel injection valve 9, and the number of nozzles. It is desirable to optimize the height of 21.

  FIG. 11 shows the shape of the piston crown surface 3A of the third example of the present embodiment. In the present embodiment, the height of the side wall 19 that is the boundary between the inner cavity 18 and the outer cavity 20 is set so as to change continuously in the circumferential direction, not in a staircase pattern. In this embodiment, the height of the side wall 19 of the inner cavity 18 (the height of the bottom 21 of the outer cavity 20) is set to continuously change in the circumferential direction.

  This configuration is the same as the first and second embodiments in that each of the plurality of fuel sprays can be received by the outer cavity 20 at different times, but the side wall 19 and the outer cavity 20 are the same. By not providing a clear step in the height of the bottom portion 21, deterioration (increase) of the combustion chamber S / V ratio (ratio of the surface area S of the combustion chamber 4 to the volume V of the combustion chamber) is suppressed. As a result, stratified combustion can be achieved without increasing unburned HC due to cooling loss and extinguishing of flame near the combustion chamber wall surface.

  However, in the present embodiment, since the height of the bottom 21 of the outer cavity 20 continuously changes, the fuel received at the bottom 21 of the outer cavity 20 is similar to the second embodiment described above. There is no effect of suppressing diffusion in the circumferential direction. For this reason, the continuity of the height of the side wall 19 and the height of the bottom 21 of the outer cavity 20 depends on the setting of the diameter of the inner cavity 18 and the outer wall 20 of the outer cavity 20, the nozzle angle (spray umbrella angle) of the fuel injection valve 9, and the number of nozzles. It is desirable to optimize the smoothness of the boundary.

  In the above-described embodiment, the fuel injection valve 9 using a multi-hole injection valve has been described. However, although not illustrated, the fuel is set in a conical surface set in advance toward the cavities 18 and 20 of the piston crown surface 3A. It may be one that is jetted and fed radially.

  In the first embodiment, the outer cavity 20 has been described as having a stepped shape. However, although not illustrated, the outer cavity 20 may have a stepped shape while alternately repeating the height.

  In the second embodiment, the side wall 19 whose height changes stepwise in a stepwise manner has been described. However, although not shown, the side wall 19 may change in height continuously.

  In the above embodiment, four stages of high load, medium load, low load, and extremely low load have been described as the load state in the stratified combustion of the engine. It may correspond to a load state of five or more stages.

  In the present embodiment, the following effects can be achieved.

  (A) A cavity comprising an inner cavity 18 provided near the approximate center of the piston crown surface 3A and an outer cavity 20 provided so as to surround the outer periphery of the inner cavity 18 is provided, and fuel is directed toward the cavity of the piston crown surface 3A. Is provided with a fuel injection valve 9 provided in the vicinity of the spark plug 10 at the upper part of the combustion chamber 4 so as to be injected radially along a predetermined conical surface, forming the inner cavity 18 and the inner cavity 18 and the outer side. The height of the side wall 19 separating the cavity 20 is made different in each region in the circumferential direction. Therefore, if the fuel injection amount is increased by advancing the fuel injection start timing in the compression stroke according to the engine load state in the stratified operation region, the amount of fuel injected from the fuel injection valve 9 in a conical surface shape is increased. When the supply range is low, the piston cavities 18 and 20 and the fuel injection valve 9 are close to each other at the end of the compression stroke, and only the inner cavity 18 responds to the advance of the injection start timing as the load increases. Then, the distance is expanded and divided into a part of the outer cavities 20 having a low height of the side wall 19, and the distance is gradually increased as the load is further increased, and the side wall 19 is successively increased in height. The supply range is gradually expanded to 20. For this reason, it is possible to form a stratified air-fuel mixture having an appropriate size corresponding to changes in the engine load, stably realizing stratified combustion under a wide range of operating conditions, and improving fuel efficiency.

  (A) As in the first embodiment, the outer cavity 20 is divided into a plurality of regions in the circumferential direction, and the height of the side wall 19 that forms the inner cavity 18 by making the height of the bottom 21 of each region different. When the heights are different from each other, the intended stratified air-fuel mixture can be formed by suppressing the diffusion of the fuel received in the outer cavity 20 in the circumferential direction.

  (C) As in the second embodiment, when the side wall 19 is divided into a plurality of regions in the circumferential direction and the heights in the respective regions are different, the height of the bottom 21 of the outer cavity 20 and the outer wall 22 The height can be set to an arbitrary height, and scattering of the fuel received by the outer cavity 20 to the outside of the cavity can be suppressed.

  (D) The height of the bottom 21 of the outer cavity 20 or the height of the side wall 19 in each of the regions divided in the circumferential direction is low in the regions facing each other in the circumferential direction, and the regions facing each other in the region sandwiched between the regions. By being formed higher than the region to be formed, the degree of stratification of the stratified air-fuel mixture formed can be increased.

  (E) The height of the bottom 21 of the outer cavity 20 or the height of the side wall 19 in each of the regions divided in the circumferential direction is made different in all regions, thereby finely stratified mixing with respect to the engine load condition. Air mass can be formed.

  (F) The height of the bottom 21 of the outer cavity 20 or the height of the side wall 19 of each of the regions divided in the circumferential direction is alternately arranged or circumferential with respect to the regions adjacent in the circumferential direction. By being stepwise different in the direction, it is possible to prevent the fuel received by the outer cavity 20 from spreading excessively in the circumferential direction.

  (G) As in the third embodiment, the height of the bottom 21 of the outer cavity 20 or the height of the side wall 19 in each of the regions divided in the circumferential direction is continuously made different in the circumferential direction. The deterioration of the combustion chamber SV ratio can be suppressed.

  (H) The fuel injection valve 9 is provided with a plurality of injection holes, and the direction of the spray injected from each injection hole coincides with the respective divided regions of the outer cavity 20 or the side wall 19 in the circumferential direction angle. Therefore, a change in the spray shape is small even when the in-cylinder pressure rises in the latter half of the compression stroke, and a stratified air-fuel mixture having a high stratification degree can be formed by a hollow and highly directional fuel spray.

  (K) The height of the bottom 21 of the outer cavity 20 in each of the regions divided in the circumferential direction is different from that in the region facing the lowest position of the piston crown surface 3A where the upper end of the outer wall 22 of the outer cavity 20 is continuous. By being set lower than the region, it is possible to prevent the fuel received in the outer cavity 20 from protruding further out of the outer cavity 20 and diffusing.

  (G) The height of the bottom 21 of the outer cavity 20 in each of the regions divided in the circumferential direction is different from that in the region facing the highest point of the piston crown surface 3A where the upper end of the outer wall 22 of the outer cavity 20 is continuous. By setting it higher than the region, the size of the stratified mixture in the high load region can be increased.

  (S) The spark plug gap of the spark plug 10 is arranged offset from the center of the inner cavity 18, and the bottom 21 of the outer cavity 20 in the region located in the offset direction is set higher than the adjacent region, Even with a minimal load such as idle operation where the fuel is received only by the inner cavity 18, the spark plug 10 and the piston crown surface 3A are close to each other, and the vicinity of the spark plug 10 is prevented from becoming too thin, and the fuel is received and mixed sufficiently. Combustion can be performed.

  (B) The size of the stratified air-fuel mixture corresponding to the load condition by controlling the fuel injection amount to be increased by advancing the fuel injection start timing in the compression stroke according to the engine load condition in the stratified operation region Can be changed.

1 is a schematic configuration diagram of a direct injection internal combustion engine showing an embodiment of the present invention. The top view which similarly shows the crown surface of a piston. The development view of the inner and outer bowls on the piston crown surface. The side view (A) and top view (B) which show the spraying state from a fuel injection valve. The top view which shows the relationship between the spray from a fuel injection valve, and the inner and outer bowl of a piston crown surface. Explanatory views (B) and (C) for schematically explaining the relationship (A) between the fuel spray and the piston position at the time of high load subjected to stratified combustion and the air-fuel mixture distribution in the vicinity of the ignition timing. Explanatory views (B) and (C) for schematically explaining the relationship (A) between the fuel spray and the piston position at the middle load during stratified combustion and the air-fuel mixture distribution in the vicinity of the ignition timing. Explanatory views (B) and (C) for schematically explaining the relationship (A) between the fuel spray and the piston position at the time of low load subjected to stratified combustion and the air-fuel mixture distribution in the vicinity of the ignition timing. Explanatory views (B) and (C) for schematically explaining the relationship (A) between the fuel spray and the piston position at the time of extremely low load subjected to stratified combustion and the air-fuel mixture distribution in the vicinity of the ignition timing. The top view which shows the shape of the piston crown surface of 2nd Example of this embodiment, and the circumferential direction expanded view. The top view which shows the shape of the piston crown surface of 3rd Example of this embodiment, and the circumferential direction expanded view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder block 2 Cylinder head 3 Piston 4 Combustion chamber 5 Intake valve 6 Intake valve 7 Exhaust valve 8 Exhaust port 9 Fuel injection valve 10 Spark plug 11 Engine control unit 18 Inner cavity 19 Side wall 20 Outer cavity 21 Bottom 22 Outer wall

Claims (13)

A cavity constituted by an inner cavity provided near the center of the piston crown surface and an outer cavity provided so as to surround the outer periphery of the inner cavity, along a conical surface in which fuel is set in advance toward the cavity of the piston crown surface In a direct injection internal combustion engine provided with a fuel injection valve provided close to the ignition plug at the upper part of the combustion chamber so as to supply the fuel radially,
The height of the bottom surface of the outer cavity with respect to the bottom surface of the inner cavity is set in the radial direction along the conical surface where the fuel is injected in the entire outer peripheral region of the inner cavity so as to form the outer peripheral region of the inner cavity. A direct injection internal combustion engine characterized by being formed differently. The outer cavity is divided into a plurality of regions in the circumferential direction, and the heights of the bottoms of the respective regions are made different so that the side wall forming the outer peripheral region of the inner cavity is formed by the step between the inner cavity and the outer cavity. 2. The direct injection internal combustion engine according to claim 1, wherein the height is different in each region. A side wall formed by an annular projection serving as a boundary separating the inner cavity and the outer cavity is provided, and the side wall is formed with different heights in respective regions divided in the circumferential direction. The direct injection internal combustion engine according to claim 1.   The height of the bottom of the outer cavity or the height of the side wall of each of the regions divided in the circumferential direction is low in the regions facing each other in the circumferential direction, and higher than the regions facing each other in the region sandwiched between the regions. The direct injection internal combustion engine according to claim 2 or 3, wherein the direct injection internal combustion engine is provided.   The height of the bottom of the outer cavity or the height of the side wall of each of the regions divided in the circumferential direction is different in all regions, respectively. The direct injection internal combustion engine described in 1.   The height of the bottom of the outer cavity or the height of the side wall of each of the regions divided in the circumferential direction is alternately arranged with respect to the regions adjacent in the circumferential direction. The direct injection internal combustion engine according to any one of claims 2 to 4.   5. The height of the bottom of the outer cavity or the height of the side wall of each of the regions divided in the circumferential direction is formed to be stepwise different in the circumferential direction. The direct injection internal combustion engine according to any one of the above.   5. The height of the bottom of the outer cavity or the height of the side wall of each of the regions divided in the circumferential direction is formed to be continuously different in the circumferential direction. The direct injection internal combustion engine according to any one of the above.   The fuel injection valve includes a plurality of injection holes, and the direction of spray injected from each injection hole is equal to a circumferential angle of each of the divided areas of the outer cavity or the side wall. The direct injection internal combustion engine according to any one of claims 2 to 8.   The height of the bottom of the outer cavity in each of the circumferentially divided areas is set lower than the other areas in the area where the piston crown surface where the outer wall upper end of the outer cavity continues is the lowest. The direct injection type internal combustion engine according to any one of claims 2 to 8, wherein the direct injection type internal combustion engine is provided.   The height of the bottom of the outer cavity in each of the circumferentially divided regions is set higher than the other regions in the region facing the highest piston crown surface where the outer wall upper end of the outer cavity continues. The direct injection type internal combustion engine according to any one of claims 2 to 8, wherein the direct injection type internal combustion engine is provided.   The spark plug gap of the spark plug is disposed offset from the center of the inner cavity, and the bottom of the outer cavity in the region located in the offset direction is set higher than the adjacent region. The direct injection internal combustion engine according to claim 8. A cavity composed of an inner cavity provided near the center of the piston crown surface and an outer cavity provided to surround the outer periphery of the inner cavity, and a conical surface in which fuel is set in advance toward the cavity of the piston crown surface A fuel injection valve provided close to the ignition plug at the top of the combustion chamber so as to supply the fuel radially, an operating state detecting device for detecting an engine operating state, and fuel injection by the fuel injection valve based on the detected operating state A control device for controlling the timing, fuel injection amount, and ignition timing by the spark plug,
The height of the bottom surface of the outer cavity with respect to the bottom surface of the inner cavity is set in the radial direction along the conical surface where the fuel is injected in the entire outer peripheral region of the inner cavity so as to form the outer peripheral region of the inner cavity. In different forms,
The direct injection type internal combustion engine, wherein the control device controls to increase a fuel injection amount by advancing a fuel injection start timing in a compression stroke according to an engine load state within a predetermined stratified operation region.