JP4715687B2 - In-cylinder injection spark ignition internal combustion engine - Google Patents

Description

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

  In order to perform homogeneous combustion in an in-cylinder injection spark ignition internal combustion engine, it is preferable to disperse the injected fuel throughout the cylinder using a tumble flow generated in the cylinder during the intake stroke. For this purpose, it is preferable to inject fuel into the tumble flow along the traveling direction of the tumble flow, and even if the fuel injection valve is arranged on the intake valve side around the cylinder upper portion, it is arranged at the approximate center of the cylinder upper portion. However, the fuel injection valve injects fuel toward the exhaust valve side of the cylinder bore.

  However, when fuel is injected into the cylinder bore in this way, a large amount of fuel swirls in the cylinder along with the tumble flow and is dispersed throughout the cylinder as intended, but some fuel penetrates the tumble flow and reaches the cylinder bore. Then, it may adhere to the cylinder bore and dilute the engine oil. In order to solve this problem, the required amount of fuel is divided into a plurality of parts and injected, and the amount of fuel injected is reduced to reduce the penetration force of each injected fuel so that the injected fuel does not reach the cylinder bore. Has been proposed (see, for example, Patent Document 1).

JP 2002-161790 A

  Thus, the problem of engine oil dilution can be solved by split injection. However, in the split injection, since the interval (no injection period) for each fuel injection is included, the fuel injection time becomes longer, and when the engine speed increases, the time from the end of fuel injection to ignition becomes shorter as it is. As a result, the fuel does not vaporize sufficiently and the combustion deteriorates. Even if split injection is stopped and the fuel injection time is shortened as a single continuous injection, when the engine speed is considerably high, sufficient vaporization time of the injected fuel cannot still be secured, and good homogeneous combustion is achieved. It cannot be realized.

  Accordingly, an object of the present invention is to suppress dilution of engine oil accompanying fuel adhesion to a cylinder bore in a direct injection spark ignition internal combustion engine that includes a fuel injection valve that injects fuel toward the cylinder bore and performs homogeneous combustion. At the same time, it is an object of the present invention to provide a fuel injection control device capable of sufficiently vaporizing the injected fuel and realizing good homogeneous combustion even when the engine speed becomes considerably high.

  A fuel injection control device for an in-cylinder injection spark ignition internal combustion engine according to claim 1 of the present invention includes a fuel injection valve that injects fuel toward a cylinder bore and performs in-cylinder combustion spark ignition. A fuel injection control device for an internal combustion engine, wherein the fuel injection valve is capable of performing fuel injection at a first injection pressure and fuel injection at a second injection pressure higher than the first injection pressure, When the first engine speed and the second engine speed higher than the first engine speed are set and the engine speed is equal to or lower than the first engine speed, the fuel injection valve causes the first injection pressure to The fuel injection is divided and performed, and when the engine speed is equal to or higher than the second engine speed, the fuel injection at the second injection pressure is performed without being divided by the fuel injection valve. To do.

  The fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 2 according to the present invention is the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1, wherein the engine speed is When the speed is between the first engine speed and the second engine speed, fuel injection at the second injection pressure is divided and performed by the fuel injection valve.

  According to a third aspect of the present invention, there is provided a fuel injection control device for a direct injection spark ignition internal combustion engine according to the first or second aspect, wherein the fuel injection control device is a fuel injection control device for a direct injection spark ignition internal combustion engine. The valve can also perform fuel injection at a third injection pressure lower than the first injection pressure, a third engine speed lower than the first engine speed is set, and the engine speed is the third engine When the engine load is lower than the rotation speed and lower than the first engine load, fuel injection at the third injection pressure is divided and performed by the fuel injection valve.

  According to a fourth aspect of the present invention, there is provided a fuel injection control device for a direct injection spark ignition internal combustion engine according to the first aspect of the present invention. The engine speed is set for each engine load so as to increase as the engine load decreases.

  A fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 5 according to the present invention is the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1, wherein the engine speed is When the engine speed is equal to or lower than the first engine speed, the fuel injection valve performs fuel injection at the first injection pressure divided into a larger number as the engine load is higher.

  A fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 6 of the present invention is the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 1 or 5, wherein the engine speed is When the engine load is lower than the first engine speed when the engine load is lower than the first engine speed, the fuel injection at the first injection pressure is performed without being divided by the fuel injection valve.

  A fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 7 according to the present invention is the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 2, wherein the engine speed is When the engine speed is between the first engine speed and the second engine speed, the fuel injection valve performs fuel injection at the second injection pressure divided into a larger number as the engine load increases. To do.

  The fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 8 according to the present invention is the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 2 or 7, wherein the engine speed is If the engine load is lower than the third engine load when the engine speed is between the first engine speed and the second engine speed, the fuel injection valve does not divide the fuel injection at the second injection pressure. It is made to carry out.

  A fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 9 according to the present invention is the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 3, wherein the engine speed is When the engine load is lower than the third engine speed and lower than the first engine load, the fuel injection valve performs fuel injection at the third injection pressure divided into a larger number as the engine load is higher. To do.

  A fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 10 of the present invention is the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 3 or 9, wherein the engine speed is If the engine load is lower than the fourth engine load lower than the first engine load when the engine load is lower than the first engine load when the engine load is lower than the third engine speed, the fuel injection valve causes the third injection pressure to The fuel injection is performed without being divided.

  The fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 11 according to the present invention is the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to any one of claims 1 to 10. The fuel injection valve is arranged on the intake valve side around the upper part of the cylinder, and injects fuel toward the upper part of the cylinder bore toward the exhaust valve side.

  According to the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 1 of the present invention, when the engine speed is equal to or lower than the first engine speed, the fuel injection valve reduces the first injection pressure. In order to divide and execute the fuel injection at, the penetration force of each of the divided injected fuels is weakened, and it is suppressed that each injected fuel reaches the cylinder bore and dilutes the engine oil. Further, when the engine speed is considerably higher than the second engine speed, fuel injection at a high second injection pressure is performed without being divided by the fuel injection valve. As a result, the fuel injection time becomes sufficiently short, and even at this time, a sufficient fuel vaporization time can be secured from the end of fuel injection to ignition, and good homogeneous combustion can be realized. In addition, when the engine speed is considerably high, the tumble flow generated in the cylinder becomes strong, so even the fuel continuously injected at high pressure is taken into the tumble flow, and almost all of it is with the tumble flow. Moving and reaching the cylinder bore and diluting the engine oil are suppressed.

  According to the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 2 of the present invention, in the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1, the engine speed Is between the first engine speed and the second engine speed, the same as when the engine speed is equal to or less than the first engine speed, when divided injection is performed at a low first injection pressure, the interval is Therefore, it is difficult to secure the fuel vaporization time with respect to the fuel injection time that becomes longer, so that the fuel injection at the high second injection pressure is divided and executed by the fuel injection valve. However, the fuel injection time is shortened, and the injected fuel can be sufficiently vaporized to achieve good homogeneous combustion.

  According to the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 3 of the present invention, in the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1 or 2, When a third engine speed lower than one engine speed is set and the engine speed is lower than the third engine speed and the engine load is lower than the first engine load, the required fuel amount is small and the engine speed is the first engine speed. Even if it is attempted to perform split injection at the first injection pressure when the rotational speed is less than the rotational speed, the split becomes difficult due to the presence of the minimum injection amount associated with the minimum valve opening time of the fuel injection valve. The minimum injection amount is reduced as the third injection pressure, and the fuel injection is surely divided and executed by the fuel injection valve. As a result, it is possible to prevent the injected fuel from reaching the cylinder bore and dilute the engine oil, and to increase the number of divisions. As the number of divisions increases, the amount of injection decreases, and each injected fuel decreases. Since it becomes easy to vaporize, favorable homogeneous combustion is realizable.

  According to a fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 4 of the present invention, in the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1 or 2, The two engine speed is set for each engine load so as to increase as the engine load decreases. As a result, when the engine speed is equal to or higher than the second engine speed at any engine load, the amount of intake air supplied into the cylinder increases and the tumble flow generated in the cylinder becomes stronger. Even if fuel injection is performed without splitting at the high second injection pressure so as to ensure sufficient fuel vaporization time by shortening the injection time, almost all of the injected fuel can be moved with the tumble flow. The injection fuel is prevented from reaching the cylinder bore and diluting the engine oil.

  According to the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 5 of the present invention, in the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1, the engine speed When the engine speed is less than or equal to the first engine speed, the fuel injection valve performs fuel injection at the first injection pressure divided into a larger number as the engine load is higher. The amount of injection can be reduced sufficiently, making it difficult for the injected fuel to reliably reach the cylinder bore to suppress dilution of engine oil, and each injected fuel is easy to vaporize. Homogeneous combustion can be realized.

  According to the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 6 of the present invention, in the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 1 or 5, If the engine load is lower than the second engine load when the engine speed is equal to or less than the first engine engine speed, the required fuel amount is small, and the injected fuel may not be divided due to the presence of the minimum injection amount of the fuel injection valve. Then, the fuel injection at the first injection pressure is performed without being divided by the fuel injection valve. However, if the fuel injection amount is small in this manner, it is sufficiently suppressed that the injected fuel reaches the cylinder bore and dilutes the engine oil.

  According to the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 7 of the present invention, in the fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 2, the engine speed Is between the first engine speed and the second engine speed, the fuel injection valve performs fuel injection at the second injection pressure divided into a larger number as the engine load is higher, Thereby, the injection amount of each divided fuel injection can be sufficiently reduced, and it is difficult to reliably reach the cylinder bore of the injected fuel, thereby suppressing dilution of the engine oil. Since it becomes easy to vaporize, favorable homogeneous combustion is realizable.

  According to the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 8 of the present invention, in the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 2 or 7, If the engine speed is between the first engine speed and the second engine speed and the engine load is lower than the third engine load, the amount of fuel required is small and the injected fuel is reduced due to the presence of the minimum injection amount of the fuel injection valve. The fuel injection valve may cause the fuel injection at the second injection pressure to be performed without being divided. However, if the fuel injection amount is small in this manner, it is sufficiently suppressed that the injected fuel reaches the cylinder bore and dilutes the engine oil.

  According to the fuel injection control device of a cylinder injection type spark ignition internal combustion engine according to claim 9 of the present invention, in the fuel injection control device of the cylinder injection type spark ignition internal combustion engine according to claim 3, the engine speed When the engine load is lower than the third engine speed and lower than the first engine load, the fuel injection valve performs fuel injection at the third injection pressure divided into a larger number as the engine load is higher, Thereby, the injection amount of each divided fuel injection can be sufficiently reduced, and it is difficult to reliably reach the cylinder bore of the injected fuel, thereby suppressing dilution of the engine oil. Since it becomes easy to vaporize, favorable homogeneous combustion is realizable.

  According to the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 10 of the present invention, the fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 3 or 9, wherein the engine When the engine speed is lower than the third engine speed and the engine load is lower than the first engine load, if the engine load is lower than the fourth engine load lower than the first engine load, the required fuel amount is small and the minimum injection amount of the fuel injection valve Therefore, the injected fuel cannot be divided, and the fuel injection at the third injection pressure is performed without being divided by the fuel injection valve. However, if the fuel injection amount is small in this manner, it is sufficiently suppressed that the injected fuel reaches the cylinder bore and dilutes the engine oil.

  According to the fuel injection control device of a cylinder injection type spark ignition internal combustion engine according to claim 11 of the present invention, the fuel injection of the cylinder injection type spark ignition internal combustion engine according to any one of claims 1 to 10. In the control device, the fuel injection valve is disposed on the intake valve side around the upper part of the cylinder, and injects fuel toward the upper part of the cylinder bore toward the exhaust valve side. Thus, the fuel injection valve can inject fuel into the tumble flow along the traveling direction of the tumble flow that descends along the exhaust valve side of the cylinder bore and rises along the intake valve side. It is possible to widely disperse the injected fuel in the cylinder by utilizing it, and the tumble flow can be strengthened by the penetration force of the injected fuel, and if the turbulence due to the tumble flow exists in the cylinder at the ignition timing, the combustion of homogeneous combustion You can speed up.

  FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine controlled by a fuel injection control device according to the present invention, showing the latter half of an intake stroke which is a fuel injection start timing for homogeneous combustion. ing. In the figure, reference numeral 1 denotes an ignition plug disposed substantially at the center of the cylinder upper portion, and reference numeral 2 denotes a fuel injection valve disposed on the intake valve side around the cylinder upper portion for directly injecting fuel into the cylinder. Although not shown, a pair of intake ports 5 are connected to the right side of the upper part of the cylinder via a pair of intake valves, and a pair of exhaust ports 6 are connected to the left side via a pair of exhaust valves. . In this case, the fuel injection valve 2 is disposed between the two intake valves. 3 is a piston.

  The fuel injection valve 2 injects the fuel F slightly obliquely downward with respect to the horizontal direction toward the upper part of the cylinder bore on the exhaust valve side. The fuel injection start timing of the fuel injection valve 2 is, for example, the latter half of the intake stroke, whereby the fuel F is generated in the cylinder in the intake stroke by the intake air supplied into the cylinder via the intake port 5. It is injected into the tumble flow TB along the traveling direction of the tumble flow TB. Here, the tumble flow TB is an air flow swirling vertically in the cylinder so as to descend along the exhaust valve side of the cylinder bore and ascend along the intake valve side of the cylinder bore.

  In this way, the fuel F injected into the tumble flow TB swirls in the cylinder together with the tumble flow TB and is dispersed throughout the cylinder, so that a good homogeneous mixture is easily formed. 2 is a cross-sectional view taken along the line PP in FIG. In the figure, reference numeral 4 denotes a pair of intake valves being opened, and the fuel injection valve 2 has, for example, a slit-like injection hole and injects a relatively thin flat, substantially fan-shaped fuel spray F. To do. The substantially fan-shaped fuel spray F has a width direction substantially parallel to a horizontal plane (a plane perpendicular to the cylinder axis) and a traveling direction obliquely downward with respect to the horizontal plane. It is made not to collide.

  Of course, the fuel spray shape injected from the fuel injection valve 2 is not limited to a substantially fan shape, and may be, for example, a hollow or solid conical shape or a solid column shape. Further, as shown in FIG. 3 corresponding to FIG. 2, a plurality of solid circular cross-section sprays may be used. In this case, the center fuel spray F1 passes between the two intake valves 4 and is injected toward the upper part on the exhaust valve side of the cylinder bore slightly obliquely downward with respect to the horizontal direction. F2 is injected at a slight angle with respect to the central fuel spray F1, and neither fuel spray F1 nor F2 collides with the intake valve 4 being opened.

  In any fuel spray, since the fuel spray has a penetrating force, when it is injected into the tumble flow TB along the traveling direction of the tumble flow TB, it acts to strengthen the tumble flow TB. As a result, if the tumble flow TB is sustained until the latter half of the compression stroke and turbulence can be generated in the cylinder at the ignition timing at the end of the compression stroke, the combustion speed can be increased to achieve good homogeneous combustion. it can.

  However, when the penetrating force of the injected fuel is strong, even if the tumble flow TB can be enhanced satisfactorily, some fuel may penetrate the tumble flow TB and reach the cylinder bore and adhere. This adhered fuel not only contributes to combustion, but also dilutes engine oil. As a result, the required fuel amount for each engine operating state is divided and injected, and the divided force is made small to reduce the penetration force and make it difficult to reach the cylinder bore.

  Preferably, as shown in the time chart of FIG. 4, the valve opening time T from the fuel injection start timing t1 to the fuel injection end timing t2 for injecting the required fuel amount for each engine operating state is equally divided (for example, , Quadrant T / 4), and divided injection is performed with an interval I (for example, 2 to 2.5 ms) provided therebetween.

  FIG. 5 shows the fuel that generates the maximum engine output when the required fuel amount is injected at the first injection pressure (for example, 12 MPa) at the low rotation medium load (triangle mark) and the low rotation high load (circle mark). The relationship between the injection end timing (crank angle before compression top dead center) and the amount of fuel adhering to the cylinder bore is shown for each number of divisions (the number shown in the figure is the number of divisions).

  As shown in FIG. 5, as a whole, the penetration force of the injected fuel is stronger at low rotation and high load with a large amount of required fuel even at the same injection pressure than at low load and low load with a small amount of required fuel. Thus, the amount of fuel adhering to the cylinder bore increases. Also, in any engine operating state, if divided, compared to fuel injection that is not divided (number of divisions 1), each injection amount is reduced and the penetration force is reduced. Further, as the number of divisions increases, the amount of fuel injected becomes smaller and the penetration force becomes smaller, so that the amount of fuel adhesion can be further reduced.

  Thus, in the map shown in FIG. 8, the fuel injection control device of the present embodiment is configured such that when the engine speed is equal to or lower than the first engine speed N1 (regions A, A ′, and D), the fuel injection valve 2 Thus, the fuel injection at the first injection pressure (12 MPa) is divided and executed to reduce the amount of fuel adhering to the cylinder bore and suppress the engine oil dilution. At this time, as described above, increasing the number of divisions is advantageous for reducing the fuel adhesion amount. However, the fuel injection valve 2 generally has a minimum valve opening time due to the responsiveness of the actuator, and there is a minimum injection amount corresponding to the minimum valve opening time, so that the fuel injection valve 2 is smaller than the minimum injection amount. It is not possible to divide the required fuel amount.

  As a result, the higher the engine load, that is, the greater the required amount of fuel, the more fuel injection is divided and injected, and the divided injection amount does not fall below the minimum injection amount as much as possible. If the fuel injection is divided and injected, the amount of fuel adhering to the cylinder bore can be minimized and engine oil dilution can be satisfactorily suppressed. In addition, the more the fuel injection is divided, the easier it is to vaporize because the amount of fuel for each injected fuel decreases, so dividing the fuel injection into as many as possible forms a good homogeneous mixture Also effective.

  When the engine load is low and the required fuel amount is less than twice the minimum injection amount of the fuel injection valve 2, the fuel injection cannot be divided and continuous injection is performed. Further, even when the engine load is low and the required fuel amount is slightly larger than twice the minimum injection amount of the fuel injection valve 2, the amount of fuel adhering to the cylinder bore is small even if split injection is not performed with this amount of injection. Yes, continuous injection may be performed.

  However, when the divided injection is performed in this way, as shown in FIG. 4, since the interval I is included as compared with the continuous injection, the fuel injection end timing t2 becomes t2 'and the fuel injection time becomes longer. When the engine speed is equal to or lower than the first engine speed N1 and the engine speed is not so high, there is a relatively long time from the fuel injection end timing t2 ′ to the ignition timing, and the injected fuel may be sufficiently vaporized during this time. it can. However, when the engine speed is quite high, dividing the fuel injection at the first injection pressure results in a very short time from the fuel injection end timing t2 ′ to the ignition timing. Combustion worsens without being able to vaporize.

  FIG. 6 shows the relationship between the injection pressure and the generated torque at the time of high rotation and high load for each number of divisions (the number shown in the figure is the number of divisions). As the number of divisions decreases, the number of included intervals I decreases, so the fuel injection time decreases. As the injection pressure increases, the fuel injection time decreases, and the time from the end of fuel injection to ignition increases. The generated torque increases because the fuel is easily vaporized.

  As a result, the fuel injection control device of the present embodiment is configured so that when the engine speed is equal to or higher than the second engine speed N2 (regions B and B ′) in the map shown in FIG. The fuel injection at the second injection pressure (20 MPa) higher than the one injection pressure is performed without being divided. Thus, the fuel injection time is shortened to ensure the fuel vaporization time until ignition. By the way, when the engine speed is high as described above, the intake amount increases and the tumble flow TB generated in the cylinder in the intake stroke becomes strong. However, even such injection fuel swirls in the cylinder together with the tumble flow TB and hardly penetrates the tumble flow TB, thereby reducing the amount of fuel adhering to the cylinder bore and reducing engine oil dilution. Can be suppressed.

  FIG. 7 shows the relationship between the fuel injection start timing (crank angle before compression top dead center) and the amount of smoke generated for each injection pressure in continuous injection at high rotation and high load. After the fuel injection start timing (second half of the intake stroke) of the present embodiment after 270 degrees (the side with a smaller value), the smoke generation amount increases as the injection pressure decreases significantly. This is because as the injection pressure is lower, the penetration force of the injected fuel becomes smaller, and immediately after being injected from the fuel injection valve 2, it is pushed to the cylinder head side by the strong tumble flow TB and easily adheres to the cylinder head. (See FIG. 1). Thus, if the injection pressure is set to a high pressure (second injection pressure) when the engine speed is high as described above, it is effective to suppress the generation of smoke. Further, when the penetration force of the injected fuel is increased, the frictional force with the intake air during the flight is increased and the injected fuel is easily vaporized, which is advantageous for the formation of a good homogeneous mixture.

  In the map shown in FIG. 8, when the engine speed is between the first engine speed N1 and the second engine speed N2 (regions C and C ′), when the engine speed is equal to or lower than the first engine speed N1. Since the fuel injection at the first injection pressure is divided and carried out in the same manner as in the case of the second engine speed N2, the time from the fuel injection end timing to the ignition timing is shortened. As a result, sufficient fuel vaporization time cannot be secured. Accordingly, the fuel injection at the second injection pressure may be performed without being divided as in the case where the second engine speed N2 or more. However, at this time, since a very strong tumble flow TB is not generated in the cylinder, the amount of fuel adhering to the cylinder bore slightly increases in the continuous injection at the second injection pressure.

  In the fuel injection control device of the present embodiment, when the engine speed is between the first engine speed N1 and the second engine speed N2 (regions C and C ′), the fuel injection valve 2 controls the second engine speed. The fuel injection at the injection pressure (20 MPa) is divided and executed. As a result, the fuel injection time can be shortened as the injection pressure is higher than the split injection at the first injection pressure, and the time from the fuel injection end timing to the ignition timing is increased, so that sufficient fuel The vaporization time can be secured, and the penetration force of each divided fuel injection is smaller than that of continuous injection, so that the amount of fuel adhering to the cylinder bore does not increase and engine oil dilution is suppressed. be able to.

  Further, in the region D of the map of FIG. 8 in which the engine speed is lower than the third engine speed N3 lower than the first engine speed N1 and the engine load is lower than the first engine load L1, the fuel at the first injection pressure is obtained. Although the injection may be divided and performed, since the required fuel amount is reduced, the number of divisions is reduced due to the presence of the minimum injection amount of the fuel injection valve. Thereby, the fuel injection control apparatus of this embodiment sets the minimum injection amount for the same minimum valve opening time of the fuel injection valve 2 by setting the injection pressure to a third injection pressure (for example, 4 MPa) lower than the first injection pressure (12 MPa). The fuel injection valve 2 is used to perform split injection.

  Accordingly, since the number of divisions can be increased, in each divided fuel injection, the injection amount is reduced, so that each injected fuel is easily vaporized and a good homogeneous mixture is formed. Since the force is reduced, the amount of fuel adhering to the cylinder bore is reduced, and engine oil dilution can be suppressed.

  The required amount of fuel for each engine operating state is the amount of fuel that forms a stoichiometric air-fuel ratio homogeneous mixture in the cylinder with respect to the intake air amount. Of course, it may be the amount of fuel that forms a homogeneous mixture of a desired lean air-fuel ratio or a desired rich air-fuel ratio with respect to the intake air amount. Further, regions A ′, B ′, and C ′ in the map of FIG. 8 are maximum load regions, and a high engine output is required. Therefore, the required fuel amount is a rich air-fuel ratio ( For example, it is preferable to set the fuel amount so that a homogeneous mixture of 12.5) is formed. In this case, in the regions A ′, B ′, and C ′, the required fuel amount for the same intake air amount is larger than in the regions A, B, and C.

  FIG. 9 is a map in which the number of fuel injection divisions (the number in the figure is the number of divisions) is set for each engine load in the region divided in the map of FIG. However, in FIG. 9, the second engine speed N2 is not constant with respect to the engine load, and is set to be higher as the engine load is lower. When the current engine speed is equal to or higher than the second engine speed set in this way with respect to the current engine load, fuel injection at the second injection pressure is performed without being divided by the fuel injection valve 2 ( Number of divisions 1).

  In practice, the amount of intake air supplied into the cylinder varies not only with the engine speed but also with the engine load, and the current engine speed is the second engine speed relative to the current engine load (the lower the engine load, the lower the engine load). In this case, the tumble flow TB generated in the cylinder in the intake stroke is surely increased during the intake stroke. Thus, there is also a problem of fuel adhesion to the cylinder head, so that it is preferable to perform fuel injection without dividing it at a high second injection pressure (20 MPa) for good homogeneous combustion, and the tumble flow is strong according to the map of FIG. When this happens, continuous injection at the second injection pressure is reliably performed.

  Further, when the engine speed is equal to or lower than the first engine speed N1, fuel injection at a low first injection pressure (12 MPa) is divided into a larger number as the engine load is higher, and the fuel to the cylinder bore is Reduces engine oil dilution well by minimizing the amount of adhesion. In addition, the more the fuel injection is divided, the easier it is to vaporize because the amount of fuel for each injected fuel decreases, so dividing the fuel injection into as many as possible forms a good homogeneous mixture Also effective.

  Further, as described above, when the required fuel amount is less than twice the minimum injection amount of the fuel injection valve 2, the fuel injection cannot be divided, and the required fuel amount is the minimum injection amount of the fuel injection valve 2. Even when the injection amount is slightly more than twice, the amount of fuel adhering to the cylinder bore is small even when the divided injection is not performed at this level. Thus, when the engine load is lower than the second engine load L2, the low pressure The fuel injection at the first injection pressure is performed without being divided (number of divisions 1).

  When the current engine speed is between the first engine speed N1 and the second engine speed relative to the current engine load, the fuel injection time is shortened by setting the injection pressure to a high second injection pressure (20 MPa). The fuel injection is divided into a larger number as the engine load is higher. Thereby, the amount of fuel adhering to the cylinder bore can be minimized, the engine oil dilution can be suppressed well, and the injected fuel can be easily vaporized to form a good homogeneous mixture.

  When the engine load is low and the required fuel amount is less than twice the minimum injection amount at the second injection pressure of the fuel injection valve 2, the fuel injection cannot be divided and continuous injection is performed. Further, even when the engine load is low and the required fuel amount is slightly larger than twice the minimum injection amount of the fuel injection valve 2, the amount of fuel adhering to the cylinder bore is small even if split injection is not performed with this amount of injection. In this way, when the engine load is lower than the third engine load L3, the fuel injection at the high second injection pressure is performed without being divided (number of divisions 1). Since the minimum injection amount of the second injection pressure is larger than the minimum injection amount of the first injection pressure, the third engine load L3 is set higher than the second engine load L2.

  Further, when the engine speed is lower than the third engine speed N3 and the engine load is lower than the first engine load L1, the fuel is set at a third injection pressure (for example, 4 MPa) lower than the first injection pressure (12 MPa). The minimum injection amount for the same minimum valve opening time of the injection valve 2 is reduced, and fuel injection is divided into a larger number as the engine load is higher. Thereby, the number of divisions can be increased as much as possible, and in each divided fuel injection, since the injection amount decreases, each injected fuel is easily vaporized and a good homogeneous mixture is formed, Since the penetrating force is small, the amount of fuel adhering to the cylinder bore is reduced, and engine oil dilution can be suppressed.

  When the engine load is low and the required fuel amount is less than twice the minimum injection amount at the third injection pressure of the fuel injection valve 2, the fuel injection cannot be divided and continuous injection is performed. Further, even when the engine load is low and the required fuel amount is slightly larger than twice the minimum injection amount of the fuel injection valve 2, the amount of fuel adhering to the cylinder bore is small even if split injection is not performed with this amount of injection. In this way, when the engine load is lower than the fourth engine load L4, the fuel injection at the extremely low third injection pressure (4 MPa) is performed without being divided (number of divisions 1). Since the minimum injection amount of the third injection pressure is smaller than the minimum injection amount of the first injection pressure, the fourth engine load L4 can be set lower than the second engine load L2.

  In the present embodiment, the injection pressure has three stages of a low first injection pressure (for example, 12 MPa), a high pressure second injection pressure (for example, 20 MPa), and an extremely low pressure third injection pressure (for example, 4 MPa). Can be switched to. Such switching of the injection pressure is performed by changing the fuel pressure in the pressure accumulating chamber for supplying fuel to the fuel injection valve of each cylinder. The injection pressure is changed by changing the lift amount of the valve body of the fuel injection valve at the time of injection to change the fuel pressure in the fuel reservoir communicating with the injection hole (the smaller the lift amount, This can also be done by lowering the fuel pressure.

  By the way, in the in-cylinder injection spark ignition internal combustion engine, the fuel injection valve 2 is positioned on the intake valve side around the upper part of the cylinder. However, this does not limit the present invention, and the tumble flow or reverse tumble flow ( Depending on the internal combustion engine, a reverse tumble flow that swirls in the cylinder in the opposite direction to the tumble flow that descends along the intake valve side of the cylinder bore and rises along the exhaust valve side may be generated) In order to inject fuel into the tumble flow or reverse tumble flow along the traveling direction, the fuel injection valve can be arranged at any position. For example, the fuel injection valve may be disposed substantially at the center of the upper part of the cylinder. In any case, when fuel is injected in this way, the fuel injection valve is in the intake stroke (from the fuel injection start timing in the latter half of the intake stroke). In this case, fuel is injected toward the cylinder bore.

It is a schematic longitudinal cross-sectional view which shows the cylinder injection type spark ignition internal combustion engine controlled by the fuel-injection control apparatus by this invention. It is PP sectional drawing of FIG. It is another PP sectional drawing of FIG. It is a time chart which shows fuel injection time. It is a figure which shows the relationship between the injection completion timing for every division | segmentation frequency, and the fuel adhesion amount to a cylinder bore. It is a figure which shows the relationship between injection pressure and generated torque. It is a figure which shows the relationship between the injection start time for every injection pressure, and the amount of smoke generation. It is a map which shows the area | region divided | segmented based on the engine speed and engine load for fuel injection control. It is a map which shows the frequency | count of division | segmentation of the fuel injection in the area | region divided | segmented based on the engine speed and engine load for fuel injection control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Fuel injection valve 3 Piston 4 Intake valve TB Tumble flow F Injection fuel

Claims (11)

  A fuel injection control device for an in-cylinder injection spark ignition internal combustion engine having a fuel injection valve for injecting fuel toward a cylinder bore and performing homogeneous combustion, wherein the fuel injection valve is a fuel at a first injection pressure. Injection and fuel injection at a second injection pressure higher than the first injection pressure can be performed, and a first engine speed and a second engine speed higher than the first engine speed are set, When the engine speed is equal to or lower than the first engine speed, the fuel injection valve performs fuel injection at the first injection pressure, and when the engine speed is equal to or higher than the second engine speed. A fuel injection control device for a direct injection spark ignition internal combustion engine, wherein the fuel injection valve performs fuel injection at the second injection pressure without dividing.   The fuel injection at the second injection pressure is divided and performed by the fuel injection valve when the engine speed is between the first engine speed and the second engine speed. Item 2. A fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to Item 1.   The fuel injection valve can also perform fuel injection at a third injection pressure lower than the first injection pressure, a third engine speed lower than the first engine speed is set, and the engine speed is 3. The fuel injection at the third injection pressure is divided and executed by the fuel injection valve when the engine load is lower than the third engine speed and lower than the first engine load. In-cylinder injection spark ignition internal combustion engine fuel injection control device.   3. The fuel injection control for a direct injection spark ignition internal combustion engine according to claim 1, wherein the second engine speed is set for each engine load so as to increase as the engine load decreases. apparatus.   2. The fuel injection at the first injection pressure is divided into a larger number as the engine load is higher by the fuel injection valve when the engine speed is equal to or lower than the first engine speed. A fuel injection control device for an in-cylinder spark-ignition internal combustion engine according to claim 1.   When the engine speed is equal to or lower than the first engine speed and the engine load is lower than the second engine load, the fuel injection at the first injection pressure is performed without being divided by the fuel injection valve. A fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 1 or 5.   When the engine speed is between the first engine speed and the second engine speed, the fuel injection valve performs fuel injection at the second injection pressure divided into a larger number as the engine load increases. The fuel injection control device for an in-cylinder injection spark ignition internal combustion engine according to claim 2, wherein   When the engine speed is between the first engine speed and the second engine speed and the engine load is lower than the third engine load, the fuel injection valve performs fuel injection at the second injection pressure. The fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 2 or 7, wherein the fuel injection control device is implemented without being divided.   When the engine speed is lower than the third engine speed and the engine load is lower than the first engine load, the fuel injection valve performs fuel injection at the third injection pressure divided into a larger number as the engine load increases. The fuel injection control device for a direct injection spark ignition internal combustion engine according to claim 3, wherein   When the engine speed is lower than the third engine speed and the engine load is lower than the first engine load, if the engine load is lower than the fourth engine load lower than the first engine load, the fuel injection valve causes the third engine load to be reduced. The fuel injection control device for a cylinder injection type spark ignition internal combustion engine according to claim 3 or 9, wherein the fuel injection at the injection pressure is performed without being divided.   The in-cylinder according to any one of claims 1 to 10, wherein the fuel injection valve is disposed on an intake valve side around a cylinder upper portion and injects fuel toward an upper portion of an exhaust valve side of a cylinder bore. A fuel injection control device for an injection spark ignition internal combustion engine.

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