JP2008038740A - In-cylinder injection spark ignition internal combustion engine - Google Patents

Abstract

In a cylinder injection spark ignition internal combustion engine in which a tumble flow is strengthened by fuel injected toward a cylinder bore, dilution of engine oil when the temperature of a cylinder bore wall surface is low is suppressed.
In a cylinder injection spark ignition internal combustion engine in which a tumble flow T is intensified by fuel F injected toward a cylinder bore in the vicinity of intake bottom dead center at the time of homogeneous combustion, the measured or estimated temperature of the cylinder bore wall surface is lower than the set temperature. Sometimes, the lower the measured or estimated temperature of the injected fuel, the weaker the penetration of the injected fuel.
[Selection] Figure 1

Description

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

  In homogeneous combustion in which a homogeneous mixture is formed in the cylinder and this homogeneous mixture is ignited and combusted at the ignition timing at the end of the compression stroke, a tumble flow is formed in the cylinder by the intake air supplied into the cylinder, and this tumble flow is By maintaining the ignition timing at the end of the compression stroke until the ignition timing causes turbulence in the cylinder due to the tumble flow, and the turbulence increases the combustion speed of the homogeneous mixture, good homogeneous combustion can be realized.

  In order to maintain the tumble flow until the ignition timing at the end of the compression stroke, an intake flow control valve is arranged in the intake port, and by this intake flow control valve, intake air is supplied into the cylinder along the upper wall of the intake port. An in-cylinder injection spark ignition internal combustion engine that forms a strong tumble flow in a cylinder has been proposed (see, for example, Patent Document 1).

JP 2005-180247 A

  In the above-described in-cylinder spark ignition internal combustion engine, when intake air is supplied into the cylinder along the upper wall of the intake port by the intake flow control valve, the intake port is throttled by the intake flow control valve. As a result, when the required intake air amount is relatively small, a strong tumble flow can be formed in the cylinder without any problem. However, when the required intake air amount is relatively large, the intake port is controlled by the intake air flow control valve. Since a shortage of intake may occur if the throttle valve is throttled, a strong tumble flow cannot be formed in the cylinder by the intake flow control valve.

  Even if such an intake flow control valve is not provided, in a direct injection spark ignition internal combustion engine, if the fuel injection direction is appropriately selected and fuel with a strong penetration force is injected at the end of the intake stroke, a tumble flow is generated. Can strengthen. However, at this time, a part of the injected fuel having a strong penetrating force reaches the cylinder bore and may be taken into the engine oil and adhere to the cylinder bore wall surface. When the wall surface temperature of the cylinder bore is high, it evaporates from the engine oil. However, when the wall surface temperature of the cylinder bore is low, the engine oil is diluted while remaining in the engine oil.

  Accordingly, an object of the present invention is to suppress dilution of engine oil when the temperature of the cylinder bore wall surface is low in a direct injection spark ignition internal combustion engine in which a tumble flow is strengthened by fuel injected toward the cylinder bore.

  According to a first aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine in which a tumble flow is strengthened by fuel injected toward a cylinder bore in the vicinity of intake bottom dead center at the time of homogeneous combustion. When the measured or estimated temperature of the cylinder bore wall surface is lower than the set temperature, the penetration force of the injected fuel is weakened as the measured or estimated temperature of the injected fuel is lower.

  According to the in-cylinder injection spark ignition internal combustion engine of the first aspect of the present invention, when the tumble flow is strengthened by the fuel injected toward the cylinder bore in the vicinity of the intake bottom dead center at the time of homogeneous combustion, the cylinder bore wall surface is measured. Alternatively, when the estimated temperature is lower than the set temperature and the fuel adhering to the cylinder bore wall is less likely to evaporate, the lower the measured or estimated temperature of the injected fuel, the more difficult it is to vaporize during flight in the cylinder. Since the amount of adhered fuel further increases, the penetrating force of the injected fuel is further weakened to make it difficult for the injected fuel to reach the cylinder bore wall surface. Thereby, dilution of the engine oil when the temperature of the cylinder bore wall surface is low can be suppressed. In addition, since the lower the measured or estimated temperature of the injected fuel, the more difficult it is to vaporize during flight in the cylinder, the tumble flow can be sufficiently increased even if the penetration force of the injected fuel is weakened.

  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 the vicinity of an intake bottom dead center which is a fuel injection timing 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 injects fuel directly into the cylinder, and 20 is an ignition plug that is disposed near the intake valve side of the fuel injection valve 1. is there. Although not shown, a pair of intake valves are disposed on the right side of the upper part of the cylinder, and a pair of exhaust valves are disposed on the left side. 30 is a piston.

  The in-cylinder injection spark ignition internal combustion engine of the present embodiment uses the fuel injection valve 1 to inject fuel in the vicinity of the intake bottom dead center (for example, in accordance with the fuel injection amount so that the fuel injection end crank angle is in the vicinity of the intake bottom dead center). By setting the start crank angle or setting the fuel injection start crank angle in the latter half of the intake stroke regardless of the fuel injection amount), the fuel is directly injected into the cylinder, thereby achieving the ignition timing at the end of the compression stroke. Forms a homogenous mixture in the cylinder, and sparks the homogeneous mixture to perform homogeneous combustion.

  As shown in FIG. 1, the fuel injection valve 1 injects the fuel F in an obliquely downward direction toward the exhaust valve side of the cylinder bore (preferably, the lower portion of the cylinder bore near the intake bottom dead center). The penetration force of the fuel F injected from the fuel injection valve 1 is set so that the fuel tip 1 ms after the start of fuel injection reaches 60 mm or more.

  When the fuel F having such a strong penetrating force is injected obliquely downward from the approximate center of the cylinder upper part toward the exhaust valve side of the cylinder bore, the exhaust valve side in the cylinder is lowered and the intake valve side is raised. The tumble flow T formed in the cylinder can be strengthened by the penetration force of the fuel. The strengthened tumble flow T is reliably maintained in the cylinder until the latter half of the compression stroke, and turbulence is generated in the cylinder at the end of the compression stroke, thereby realizing good homogeneous combustion with a high combustion speed. be able to.

  The shape of the injected fuel F injected from the fuel injection valve 1 can be arbitrarily set, and may be, for example, a solid or hollow conical shape injected from a single injection hole. Moreover, it is good also as an approximately fan shape with comparatively thin thickness injected from a slit-shaped nozzle hole. Moreover, it is good also as a comparatively thin arc-shaped cross-section shape or convex line-shaped cross-section shape which makes the upper side and the exhaust valve side convex, by combining arc-shaped slit nozzle holes or a plurality of linear slit nozzle holes. In any case, it is sufficient that the injected fuel has a strong penetration force as described above to accelerate the tumble flow T in the cylinder.

  In the present embodiment, since the spark plug 2 is disposed on the intake valve side from the fuel injection valve 1, it is not wetted by the fuel injected from the fuel injection valve 1 toward the exhaust valve side of the cylinder bore. An arc can be reliably generated at the ignition timing.

In the present embodiment, the air-fuel ratio of homogeneous combustion is made leaner than the stoichiometric air-fuel ratio (preferably, the lean air-fuel ratio in which the amount of NO _x produced is suppressed), so that fuel consumption is suppressed. In addition, the combustion tends to be slow, and it is particularly effective to increase the combustion speed as described above. Of course, the air-fuel ratio of homogeneous combustion may be a stoichiometric air-fuel ratio or a rich air-fuel ratio. In this case as well, it is effective to increase the combustion speed.

  By the way, when fuel with such a strong penetration force is injected toward the exhaust valve side of the cylinder bore in the vicinity of the intake bottom dead center, a part of the injected fuel reaches the cylinder bore wall surface in the liquid state and is taken into the engine oil. May adhere to the cylinder bore wall. If the temperature of the cylinder bore wall surface is equal to or higher than the set temperature, there is no particular problem because the fuel easily evaporates even if it is taken into the engine oil. However, if the temperature of the cylinder bore wall surface is lower than the set temperature, such as when the engine is cold, the fuel taken into the engine oil remains as it is and the engine oil is diluted.

  Accordingly, the temperature of the cylinder bore wall surface is estimated based on the fact that the higher the coolant temperature, the higher the temperature of the cylinder bore wall surface. Alternatively, the higher the engine speed, the greater the fuel injection amount, and the more the ignition timing is advanced. The more the angle is increased, the higher the combustion temperature and the higher the cylinder bore wall temperature, or the cylinder bore wall temperature is estimated (and the lower the engine oil temperature in the engine oil reservoir, It is preferable to consider further cooling the cylinder bore wall surface), or when the estimated or measured temperature of the cinder bore wall surface is lower than the set temperature by actually measuring the temperature of the cylinder bore wall surface, intake air is taken in by the fuel injection valve 1 The penetration force of the fuel F injected near the bottom dead center is weakened so that the injected fuel hardly reaches the cylinder bore wall surface. If, it is possible to solve the problem of the engine oil dilution. However, if the penetration force of the injected fuel F is simply weakened, the tumble flow T cannot be strengthened even if the problem of engine oil dilution is solved.

  FIG. 2 is a cross-sectional view of the tip portion of the fuel injection valve 1. As shown in the figure, the fuel injection valve 1 is provided with a fuel passage 2 extending in the axial direction, and a valve body 3 movable in the axial direction is disposed in the fuel passage 2. A fuel reservoir 5 is formed on the downstream side of the seat portion 4 of the fuel passage 2 that contacts the seal portion at the tip of the valve body 3. The nozzle hole 6 is formed to communicate with the fuel reservoir 5. The fuel passage 2 is filled with high-pressure fuel supplied from a fuel accumulator chamber (not shown).

  In the fuel injection valve 1 configured as described above, when the valve body 3 is lifted to separate the seal portion of the valve body 3 and the seat portion 4 of the fuel passage 2, the high-pressure fuel in the fuel passage 2 is stored in the fuel reservoir 5. When the fuel pressure in the fuel reservoir 5 becomes higher than that in the cylinder, the fuel in the fuel reservoir 5 is injected through the nozzle hole 6. On the other hand, when the seal portion of the valve body 3 is brought into contact with the seat portion 4 of the fuel passage 2, the high pressure fuel in the fuel passage 2 is not supplied into the fuel reservoir 5, and the fuel pressure in the fuel reservoir 5 decreases, If the pressure is lower than that in the cylinder, fuel injection through the nozzle hole 6 is stopped.

  In the present embodiment, such a structure is provided in which the lift amount of the valve body 3 of the fuel injection valve 1 is variable steplessly. FIG. 3 schematically shows this structure. In the structure shown in FIG. 3A, the valve body 3 is urged in the valve closing direction by a valve closing spring 11 disposed between the valve body 3 and the fuel injection valve body 10. Between them, a piezoelectric strain actuator (piezo actuator) 12 is arranged, and the extension of the piezoelectric strain actuator opens the valve body 3. Thereby, the lift amount of the valve body 3 can be controlled steplessly by controlling the voltage applied to the piezoelectric strain actuator to change the extension amount.

  On the other hand, in the structure shown in FIG. 3B, the valve element 3 is urged in the valve closing direction by the valve closing spring 13 disposed between the valve element 3 and the fuel injection valve body 10, and the fuel injection valve body 10. Is provided with an electromagnetic actuator (solenoid actuator) 14 facing the base of the valve body 3 so that the electromagnetic attractive force of the electromagnetic actuator acts in the valve opening direction of the valve body 3. Thereby, the lift applied to the valve body 3 can be controlled steplessly by controlling the voltage applied to the electromagnetic actuator and changing the electromagnetic attractive force acting on the valve body 3.

  In this embodiment, since the lift amount of the valve body 3 can be controlled steplessly by such a structure, the fuel injection valve 1 injects when the estimated or measured temperature of the cinder bore wall surface is lower than the set temperature. The fuel temperature is measured by, for example, a temperature sensor disposed in the fuel passage 2, or estimated based on the fact that the injected fuel temperature increases as the coolant temperature increases, and the estimated or measured temperature of the injected fuel decreases. When the fuel injection valve 1 is opened, the lift amount of the valve body 3 is controlled to be small. The smaller the lift amount of the valve body 3, the smaller the gap between the valve body 3 and the seat portion 4 when the valve body 3 is lifted. Therefore, the pressure loss in this gap increases and the fuel is injected from the fuel reservoir 5. The fuel pressure is low. Thereby, the penetration force of the fuel injected from the nozzle hole 6 is reduced as the lift amount of the valve body 3 is reduced.

  Thus, when the estimated or measured temperature of the cinder bore wall surface is lower than the set temperature, the penetration force of the injected fuel is reduced, and the lower the estimated or measured temperature of the injected fuel, the smaller the penetration force of the injected fuel. The lower the temperature of the injected fuel, the less likely it will vaporize during flight in the cylinder and the easier it will reach the cylinder bore. Therefore, the penetration of the injected fuel is weakened and the injected fuel moves to the cylinder bore wall surface. It is harder to reach. As a result, not only can the engine oil dilution be suppressed when the temperature of the cylinder bore wall surface is low, but the lower the measured or estimated temperature of the injected fuel, the more difficult it is to vaporize during flight in the cylinder. Therefore, the tumble flow can be sufficiently strengthened even if the penetrating force of the injected fuel becomes weaker as the measured or estimated temperature of the injected fuel is lower.

  In this embodiment, in order to control the penetration force of the injected fuel steplessly, the lift amount of the valve body 3 is changed steplessly to control the fuel injection pressure. The fuel injection pressure is set such that a part of the fuel in the fuel passage 2 is returned to the fuel tank or the like and the return fuel amount is controlled steplessly to change the fuel pressure in the fuel passage 2 steplessly. May be controlled.

  Further, since the penetration force of the injected fuel becomes weaker as the fuel injection amount is smaller, the required fuel amount may be divided and injected when the penetration force of the injected fuel is weakened. That is, when the estimated or measured temperature of the Cinder Bore wall surface is lower than the set temperature, the lower the estimated or measured temperature of the injected fuel, the more the required amount of fuel is divided and injected, and the penetrating force of the injected fuel is reduced. good. Here, the required fuel amount is set for each engine operating state, and is set to increase as the engine speed increases and the engine load increases, for example.

  When dividing the injected fuel, the penetration force of the injected fuel is controlled only in multiple stages (corresponding to the maximum possible number of divisions, for example, if it can be divided into eight, the penetration force can be controlled in eight stages). However, if the penetration force is controlled in three stages including the normal penetration force when the estimated or measured temperature of the Cinder Bore wall surface is equal to or higher than the set temperature, the engine oil dilution is suppressed and the temperature of the injected fuel is suppressed. The penetration force can be controlled in two steps so as to strengthen the tumble flow according to the above. Thus, the lift amount of the valve body 3 and the fuel pressure in the fuel passage 2 may be controlled in at least three stages.

  In the present embodiment, homogeneous combustion is performed in this manner. For example, when the engine load is low, which is lower than the set load, fuel is injected by the fuel injection valve 1 in the latter half of the compression stroke to perform stratified combustion. You may make it do. In order to perform stratified combustion, a cavity is formed on the top surface of the piston 30 and fuel injected into the cavity in the latter half of the compression stroke is guided to the vicinity of the spark plug 20 to form a combustible mixture near the spark plug 2. Alternatively, the ignition plug 20 is arranged on the exhaust valve side of the fuel injection valve 1, and a combustible air-fuel mixture is formed directly in the vicinity of the ignition plug 20 by the fuel injected by the fuel injection valve 1. You can do that.

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 schematic sectional drawing of the front-end | tip part of a fuel injection valve. It is the schematic which shows the structure which makes the lift amount of the valve body of a fuel injection valve variable.

Explanation of symbols

1 Fuel Injection Valve 20 Spark Plug 30 Piston T Tumble Flow F Injection Fuel

Claims (1)

  In a cylinder-injection spark ignition internal combustion engine, where the tumble flow is strengthened by fuel injected toward the cylinder bore near the intake bottom dead center during homogeneous combustion, when the cylinder bore wall surface measurement or estimated temperature is lower than the set temperature, measurement of the injected fuel Alternatively, the in-cylinder spark ignition internal combustion engine is characterized in that the lower the estimated temperature, the weaker the penetration of the injected fuel.

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