JP4840213B2 - 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 a direct injection spark ignition internal combustion engine, injected fuel tends to adhere to the cylinder bore or piston top surface. If the injected fuel adheres to the cylinder bore and does not vaporize, the engine oil is diluted. Further, the fuel that is attached to the top surface of the piston and does not vaporize until the ignition timing is discharged as unburned fuel or particulates, thereby deteriorating exhaust emission. Accordingly, it has been proposed to suppress the adhesion to the cylinder bore or the piston top surface by dividing and injecting the required amount of fuel to reduce the mass of each injected fuel and to facilitate vaporization of each (for example, , See Patent Document 1).

JP 2002-161790 A JP 2001-173499 A

  However, in order to perform such divided injection, the fuel injector must be repeatedly opened and closed, which not only increases power consumption but also reduces the life of the fuel injector.

  Accordingly, an object of the present invention is to suppress a decrease in the life of the fuel injection valve in a direct injection spark ignition internal combustion engine, and also to suppress the occurrence of problems caused by the fuel adhering to the cylinder bore or the piston top surface. .

Injection spark ignition internal combustion engine according to claim 1 according to the present invention, necessary fuel amount for comprising a fuel injection valve for directly injecting fuel into the cylinder, carrying out homogeneous combustion is increased The fuel amount after increase is divided by the fuel injection valve only until the cylinder inner wall surface temperature at the position where the injected fuel is attached reaches the set temperature set for the fuel amount after increase. It is characterized by spraying.

A direct injection spark ignition internal combustion engine according to claim 2 according to the present invention is an amount of fuel required for performing homogeneous combustion at low engine load in the direct injection spark ignition internal combustion engine according to claim 1. From the time when the fuel is increased until the cylinder inner wall surface temperature at the fuel adhering position reaches the set temperature set with respect to the required fuel amount after the increase. Is divided and injected.

According to the in-cylinder injection spark ignition internal combustion engine according to claim 1 of the present invention, the cylinder inner wall surface temperature at the position where the injected fuel is attached is increased after the amount of fuel required for carrying out homogeneous combustion is increased. The increased required fuel amount injected by the fuel injection valve is divided and injected only until the set temperature set for the required fuel amount is reached. During steady operation, the smaller the amount of fuel required to perform homogeneous combustion, the lower the temperature of the cylinder inner wall, such as the cylinder bore and the top surface of the piston, and the attached fuel is less likely to vaporize. The smaller the amount, the smaller the amount of fuel adhering to the cylinder inner wall surface. Therefore, during steady operation, the amount of fuel adhering to the cylinder inner wall surface can be easily increased regardless of whether the amount of fuel required for homogeneous combustion is large or small. Vaporization causes little dilution of engine oil and deterioration of exhaust emissions. Accordingly, the split injection is not performed at this time.

However, the cylinder wall surface temperature when the amount of fuel required to perform homogeneous combustion is increased is the first wall surface temperature at the steady state corresponding to the amount of fuel before increase, and the increased amount of fuel required Each time this operation is repeated, the temperature is gradually raised to the second wall surface temperature at the steady state corresponding to the required fuel amount after the increase. If the second wall surface temperature is reached, as described above, split injection is not necessary, but during the period from the first wall surface temperature to the second wall surface temperature, the wall surface temperature is low relative to the amount of attached fuel and The fuel adhering to the wall surface does not evaporate easily and may cause dilution of engine oil or deterioration of exhaust emission. Therefore, the cylinder inner wall surface temperature at the injection fuel adhesion position increases from the time when the required fuel amount is increased. Split injection is performed only until the set temperature set for the required amount of fuel later is reached, so that each split injected fuel can be easily vaporized in flight as a small lump. The fuel adhesion to the wall surface is suppressed. Thus, even if the opportunity for performing the split fuel injection is reduced as compared with the case where the split fuel injection for reducing the life of the fuel injection valve is always performed, the problem caused by the fuel adhering to the cylinder bore or the piston top surface is generated. Can be suppressed.

According to the in-cylinder injection spark-ignition internal combustion engine according to claim 2 of the present invention, in the in-cylinder injection spark-ignition internal combustion engine according to claim 1, there is a need for performing homogeneous combustion at low engine load. Increased required fuel that is injected by the fuel injection valve only from when the fuel amount is increased until the cylinder inner wall surface temperature at the injected fuel attachment position reaches the set temperature set for the increased required fuel amount The quantity is divided and injected. At the time of high engine load, the amount of increase is not so great because the amount of fuel required to perform homogeneous combustion is relatively large. Thereby, at the time of high engine load, the difference between the steady-state first wall surface temperature corresponding to the required fuel amount before the increase and the steady-state second wall temperature corresponding to the required fuel amount after the increase is small, Moreover, since the first wall surface temperature is relatively high, it is possible to easily vaporize a larger amount of fuel adhering than the amount of fuel required before the increase, and the amount of fuel required after the increase is not so large. It can be easily vaporized even with the corresponding amount of attached fuel. Thus, even when the amount of fuel required to perform homogeneous combustion is increased, if the engine is under high load, split fuel injection is not necessary, and the injection fuel attachment position from when the required amount of fuel is increased at low engine load. The split injection is performed only until the cylinder inner wall surface temperature reaches the set temperature set for the required fuel amount after the increase . Thus, even if the opportunity for performing split fuel injection, which reduces the life of the fuel injection valve, is further reduced, it is possible to suppress the occurrence of problems due to fuel adhesion to the cylinder bore or piston top surface.

  FIG. 1 is a schematic longitudinal sectional view showing an embodiment of an in-cylinder injection spark ignition internal combustion engine according to the present invention, and shows a fuel injection timing in an intake stroke for homogeneous combustion. In the figure, reference numeral 1 denotes a fuel injection valve that is disposed substantially at the center of the cylinder and directly injects fuel into the cylinder, and 2 is an ignition plug that is disposed near the intake port side of the fuel injection valve 1. is there. Reference numeral 3 denotes a piston, 4 denotes a pair of intake ports, and 5 denotes a pair of exhaust ports.

This in-cylinder injection spark ignition internal combustion engine forms a homogeneous air-fuel mixture that is leaner than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the cylinder, and performs homogeneous combustion in which this homogeneous air-fuel mixture is ignited and burned by the spark plug 2. is there. When the homogeneous combustion that is leaner than the stoichiometric air-fuel ratio is performed, the lean air-fuel ratio is set so that the amount of NO _x generated is relatively small (for example, 20). For example, when the engine speed is high and the load is high, homogeneous combustion at the stoichiometric air-fuel ratio or rich air-fuel ratio may be performed. Further, when the NO _X storing catalyst apparatus for storing the NO _X when the air-fuel ratio of the exhaust gas in the engine exhaust system is lean is located, to release the occluded NO _X from the NO _X storing catalyst apparatus reducing and purifying When performing, homogeneous combustion is performed with the combustion air-fuel ratio set to the set rich air-fuel ratio.

  In particular, in homogeneous combustion at a lean air-fuel ratio, a desired engine output cannot be obtained unless the combustion speed is increased by causing turbulence in the cylinder at the ignition timing. As a result, a tumble flow T that descends along the exhaust port side of the cylinder bore and rises along the intake port side by the intake air supplied into the cylinder during the intake stroke is formed in the cylinder. The tumble flow T is preferably maintained until the latter half of the compression stroke and is crushed by the piston 3 so that turbulence exists in the cylinder at the ignition timing.

  However, unless the cylinder head is thickened to devise the shape and arrangement of the intake port, or an intake flow control valve is provided in the intake port, the tumble flow formed in the cylinder is not so strong, and due to attenuation It disappears easily in the first half of the compression stroke, and turbulence due to the tumble flow cannot exist in the cylinder at the ignition timing. Thus, in the in-cylinder injection spark ignition internal combustion engine, the tumble flow T formed in the cylinder during the intake stroke is exhausted from the cylinder bore by the fuel injection valve 1 in the vicinity of the intake bottom dead center, preferably at the end of the intake stroke. The penetration force of the fuel F injected diagonally downward toward the exhaust port side periphery of the port side lower part or the piston top surface is strengthened by using the penetration force. Since the spark plug 2 is disposed on the intake port side of the fuel injection valve 1, the spark plug 2 is not wet by the injected fuel and does not hinder the generation of arc.

  In order to surely strengthen the tumble flow T, it is preferable to increase the penetration force of the injected fuel F1 so that, for example, the fuel tip after 1 ms from the start of injection reaches 60 mm or more. In the in-cylinder injection spark ignition internal combustion engine, the fuel injection valve 1 is arranged in a semicircular arc shape, for example, as shown in FIG. 2 when the injection hole center C is viewed from the fuel injection direction P shown in FIG. In order to strengthen the tumble flow T in the vicinity of the intake bottom dead center, the columnar fuel injected from each round nozzle hole has a lower part on the exhaust port side of the cylinder bore (substantially semicircular cross section). Of the piston) and at least one of the exhaust port side peripheral portion (substantially semicircular belt-like portion) on the top surface of the piston.

  Further, as shown in FIG. 3 similar to FIG. 2, the fuel injection valve 1 has a semi-arc shaped slit injection hole connecting the plurality of round injection holes of FIG. In order to increase the tumble flow, the cylinder bore is substantially hollow toward the exhaust port side lower part of the cylinder bore (a belt-like part of a substantially semicircular cross section) and the exhaust port side peripheral part (a belt-like part of a substantially semicircular arc) of the piston top surface. A semi-conical fuel may be injected.

  Further, as shown in FIG. 4 similar to FIG. 2, the fuel injection valve 1 has a linear slit injection hole, and in order to strengthen the tumble flow in the vicinity of the intake bottom dead center, the exhaust port side of the cylinder bore The fan-shaped fuel may be injected so as to go to at least one of the lower portion (a belt-like portion having a substantially semicircular cross section) and the peripheral portion of the piston top surface on the exhaust port side (a belt-like portion having a substantially semicircular arc).

  Further, as shown in FIG. 5 similar to FIG. 2, the fuel injection valve 1 has a plurality of linear injection holes arranged in a straight line, and in order to strengthen the tumble flow in the vicinity of the intake bottom dead center, A plurality of columnar fuels are injected so as to be directed to at least one of a lower part of the cylinder bore on the exhaust port side (a belt-like portion having a substantially semicircular cross section) and a peripheral portion of the piston port on the exhaust port side (a belt-like portion having a substantially semicircular arc). Also good.

  In addition, the fuel injection valve 1 is arranged so as to be in the range of the lower part on the exhaust port side of the cylinder bore (a belt-like portion having a substantially semicircular cross section) and the periphery of the piston port on the exhaust port side (a belt-like portion having a substantially semicircular arc). It may be one that injects a real or hollow conical fuel. Since the tumble flow T thus strengthened is reliably maintained even in the latter half of the compression stroke, when the piston 3 is crushed, the turbulence in the cylinder maintained even at the ignition timing can be generated.

  In this way, it is not limited to the in-cylinder spark-ignition internal combustion engine that intensifies the tumble flow with the injected fuel. However, when the fuel is directly injected into the cylinder, a part of the injected fuel is in the cylinder bore or piston top surface, etc. It collides with and adheres to the cylinder inner wall surface. When the penetration force of the injected fuel is increased as in the present embodiment, the injected fuel particularly easily collides with the cylinder inner wall surface. In the present embodiment, the fuel injection valve 1 is disposed substantially at the center of the upper part of the cylinder, the fuel injection timing is set to the vicinity of the intake bottom dead center, the exhaust port side lower part of the cylinder bore (a belt-like part having a substantially semicircular cross section) and the exhaust of the piston top surface. Since the fuel is injected within the range of the port-side peripheral portion (substantially semicircular belt-like portion), the flight distance of the injected fuel to the cylinder inner wall surface is relatively long, and thereby, to the cylinder inner wall surface. The collision of the injected fuel is suppressed. However, this fuel collision cannot be completely prevented, and a part of the fuel adheres to the inner wall surface of the cylinder.

  If the fuel adhering to the cylinder bore does not vaporize before the rising piston 3 passes, it does not contribute to combustion and is mixed with the engine oil to dilute the engine oil. Further, if the fuel adhering to the piston top surface does not vaporize before ignition, it does not contribute to combustion, but is discharged as unburned fuel or particulates, thereby deteriorating exhaust emission.

  During steady operation, the smaller the required amount of fuel, the lower the temperature of the cylinder inner wall, such as the cylinder bore and the piston top surface, and the more difficult the fuel adhering to vaporize. Because the amount of fuel is reduced, the fuel adhering to the inner wall of the cylinder easily vaporizes during steady operation, even if the amount of fuel required is large or small, and almost no deterioration of engine oil dilution and exhaust emission occurs. do not do.

  However, the cylinder inner wall surface temperature when the required fuel amount is increased is the first wall surface temperature in the steady state corresponding to the required fuel amount before the increase (the temperature for each required fuel amount before the increase) and increased. Each time the operation with the required fuel amount is repeated, the temperature is gradually raised to the second wall surface temperature at the steady state (the temperature for each required fuel amount after the increase) corresponding to the required fuel amount after the increase. As described above, when the second wall surface temperature is reached, the fuel adhering to the cylinder inner wall surface is easily vaporized, but during the period from the first wall surface temperature to the second wall surface temperature, the wall surface temperature with respect to the amount of adhered fuel. However, the fuel adhering to the inner wall surface of the cylinder is not easily vaporized, and may cause dilution of engine oil or deterioration of exhaust emission.

  In order to solve this problem, in this embodiment, fuel injection is controlled according to the flowchart shown in FIG. First, in step 101, it is determined whether or not the required amount of fuel to be injected determined by the engine load and the engine speed is increased. When this judgment is denied, there is no problem because it is during steady operation or engine deceleration, and the wall surface temperature is high enough to easily vaporize the amount of fuel adhering to the cylinder inner wall surface, In step 105, the fuel injection valve 1 continuously injects the required fuel amount.

  On the other hand, when the determination in step 101 is affirmative, it is during engine acceleration when the required fuel amount is increased. If continuous injection in step 105 is performed at this time, the fuel amount adhering to the cylinder inner wall surface is increased immediately after the increase. The wall temperature of the fuel injection valve 1 is not so high as to easily vaporize it, and the engine oil dilution or exhaust emission deterioration occurs. Divides and injects the increased required fuel amount.

  When the required amount of fuel is divided and divided into two, three, or four parts and injected, each divided fuel will fly in the cylinder as a small lump compared to continuous injection Therefore, vaporization due to friction with intake air during flight is promoted, fuel adhesion to the cylinder inner wall surface can be sufficiently reduced, and engine oil dilution or exhaust emission deterioration can be suppressed. . However, such divided injection has to repeat opening and closing of the valve body of the fuel injection valve 1 and not only increases power consumption but also reduces the life of the fuel injection valve 1. Thereby, it is preferable to minimize the implementation of split fuel injection.

Thus, in step 102, the current wall temperature rise value ΔT at the fuel adhesion position is calculated by the following equation (1).
ΔT = ΔT + (T (Q2) −T (Q1)) / n (1)
Here, the initial value of ΔT is 0, and T (Q2) becomes a constant value by repeating the operation at the wall temperature in the steady state with respect to the required fuel amount Q2 after the current increase, that is, the operation at the required fuel amount Q2. T (Q1) is a wall surface temperature at a steady state with respect to the required fuel amount Q1 before this increase, that is, a wall surface temperature at which the operation with the required fuel amount Q1 is repeated and becomes a constant value, As shown in FIG. 7, it is mapped as T (Q). Of course, Q1 and Q2 are values newly set as the required fuel amount before the increase and the required fuel amount after the increase each time the required fuel amount is increased.

  In step 103, the current wall surface temperature obtained by adding the temperature increase value ΔT to the wall surface temperature T (Q1) in the steady state with respect to the required fuel amount Q1 before the increase is continuously injected at the required fuel amount Q2 after the increase. It is determined whether or not the wall surface temperature T (Q2) ′ necessary for easily vaporizing the amount of fuel adhered to the wall surface has become equal to or higher. Of course, if the current wall surface temperature becomes the steady wall surface temperature T (Q2) with respect to the required fuel amount Q2 after the increase, the fuel amount adhering to the wall surface can be surely vaporized when the required fuel amount Q2 is continuously injected. However, the wall surface attached fuel amount can be easily vaporized even at the wall surface temperature before that. The wall surface temperature T (Q) 'with respect to the required fuel amount Q set in this way is also mapped as shown in FIG.

  Initially, since the determination in step 103 is denied, as described above, the required fuel amount Q2 after the increase in step 104 is divided and injected, but the set period elapses after the required fuel amount is increased. Then, the wall surface temperature gradually increases and the determination in step 103 becomes affirmative. At this time, in step 105, the increased required fuel amount Q2 is continuously injected. In this way, even if the opportunity for performing the split fuel injection is reduced as compared with the case where the split fuel injection is always performed, it is possible to suppress the occurrence of problems due to the fuel adhering to the cylinder bore or the piston top surface.

  In the flowchart of FIG. 6, it is assumed that the cylinder inner wall surface temperature at the fuel adhesion position rises by (T (Q2) −T (Q1)) / n for each unit time passing through step 102. Here, the denominator n may be a constant value. However, since the fuel injection opportunity per unit time increases as the engine speed increases, the denominator n may be reduced.

  In the flowchart of FIG. 6, the wall surface temperature gradually rises by repeating the divided injection of the required fuel amount after the required fuel amount is increased based on the required fuel amount Q1 before the increase and the required fuel amount Q2 after the increase. The time until the wall surface temperature at which the wall surface attached fuel amount evaporates easily when the increased amount of required fuel is continuously injected (may be a function of the engine speed) is set in advance experimentally or by calculation. It is also possible to keep it. Thus, the split fuel injection may be performed for a set period set based on the required fuel amount Q1 before the increase and the required fuel amount Q2 after the increase.

  Also, when the engine is heavily loaded, the required amount of fuel is relatively large from the beginning, so the increase is not so much. Accordingly, at the time of high engine load, the steady first wall surface temperature T (Q1) corresponding to the required fuel amount before the increase and the steady second wall temperature T (Q1) corresponding to the necessary fuel amount after the increase. The difference from Q2) is small. Further, as the required fuel amount Q increases, as shown in FIG. 7, the difference between the wall surface temperature T (Q) in the steady state and the wall surface temperature T (Q) ′ necessary for easily vaporizing the wall-attached fuel becomes smaller. growing. That is, since the wall surface temperature T (Q1) before the increase is relatively high, it is possible to easily vaporize the amount of attached fuel corresponding to the required fuel amount before the increase, and after the increase is not so large. The amount of attached fuel corresponding to the required amount of fuel can be easily vaporized.

  Thus, even when the required fuel amount is increased, the split fuel injection is not performed if the engine is at a high load, and the split injection is performed only when the required fuel amount is increased at a low engine load. good. Thus, even if the opportunity for performing split fuel injection, which reduces the life of the fuel injection valve, is further reduced, it is possible to suppress the occurrence of problems due to fuel adhesion to the cylinder bore or piston top surface.

  FIG. 8 is a schematic longitudinal sectional view in the vicinity of the intake bottom dead center showing a second embodiment of the direct injection spark ignition internal combustion engine according to the present invention. The difference from the first embodiment is that a fuel injection valve 1 ′ for directly injecting fuel into the cylinder is disposed on the intake port side around the upper part of the cylinder, and the spark plug 2 ′ is substantially at the center of the upper part of the cylinder. It is arranged in. The fuel injection valve 1 ′ injects fuel toward the upper part of the cylinder bore on the exhaust port side (a belt-like portion having a substantially semicircular arc cross section) to strengthen the tumble flow in the cylinder.

  The fuel injection valve 1 ′ may have the linear slit injection holes shown in FIG. 4 or the plurality of injection holes arranged in a straight line in FIG. 5, or may inject fuel into a solid or hollow conical shape. good. Also in this embodiment, if the continuous injection is performed when the required fuel amount is increased, the fuel adhering to the upper part of the exhaust port side of the cylinder bore is not easily vaporized, causing a problem of dilution of the engine oil. Similarly, split fuel injection is performed immediately after the required fuel amount is increased.

  The amount of fuel adhering to the cylinder inner wall surface when the required fuel amount is continuously injected increases as the penetration force of the fuel injected from the fuel injection valve increases, and from the fuel injection valve to the cylinder inner wall surface. The shorter the distance, the more. The greater the amount of adhered fuel, the higher the wall surface temperature T (Q) 'required for easy vaporization. As described above, in the above-described two embodiments in which the position of the fuel injection valve and the fuel injection direction are different, the wall surface attached fuel amount for each required fuel amount is different and the wall surface temperature necessary for easily vaporizing the attached fuel amount. T (Q) ′ is also a different value.

1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention. It is a figure which shows the nozzle hole shape of a fuel injection valve. It is a figure which shows another nozzle hole shape of a fuel injection valve. It is a figure which shows another another nozzle hole shape of a fuel injection valve. It is a figure which shows another another nozzle hole shape of a fuel injection valve. It is a flowchart which shows fuel-injection control. It is a graph which shows the change of the wall surface temperature at the time of steady with respect to required fuel amount, and the wall surface temperature which vaporizes adhering fuel easily. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention.

Explanation of symbols

1, 1 'fuel injection valve 2, 2' spark plug 3 piston 4 intake port 5 exhaust port F injected fuel T tumble flow

Claims (2)

A fuel injection valve for directly injecting fuel into the cylinder is provided, and the cylinder inner wall surface temperature at the position where the injected fuel is attached becomes the required amount of fuel after the increase from the time when the amount of required fuel for performing homogeneous combustion is increased. An in-cylinder injection type spark ignition internal combustion engine that divides and injects the increased amount of fuel that is injected by the fuel injection valve until the set temperature is set . From when the required amount of fuel to perform homogeneous combustion at low engine load is increased until the cylinder inner wall surface temperature at the injected fuel attachment position reaches the set temperature set for the increased required fuel amount The in-cylinder injection spark ignition internal combustion engine according to claim 1, characterized in that the required amount of fuel after the increase injected by the fuel injection valve is divided and injected.

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