JP2009293526A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder injection type spark ignition internal combustion engine can form an air-fuel mixture appropriate for homogenous combustion. <P>SOLUTION: The cylinder ignition type spark ignition internal combustion engine includes a fuel injection valve 18 for injecting fuel in a fuel chamber 5. After starting a compression stroke, an intake valve 6 is closed after gas in the combustion chamber 5 starts to reversely flow into an intake passage 7. The fuel injection timing is set during a compression stroke and when the intake valve 6 is opened, and injected fuel spray 30 is made to flow into the intake passage 7 along with the gas reversely flowing toward the intake passage 7 from the combustion chamber 5. The fuel spray 30 that flows into the intake passage 7 is introduced into the combustion chamber 5 along with intake air during the next intake stroke. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In a cylinder-injection spark-ignition internal combustion engine that performs homogeneous combustion with a fuel injection valve that injects fuel into the combustion chamber, the fuel to be injected is divided into early injection fuel and late injection fuel and injected during the intake stroke An in-cylinder injection spark ignition internal combustion engine is known (see Patent Document 1). In this internal combustion engine, the flow of the intake air accompanying the lowering of the piston promotes the vaporization of the early injection fuel, and further prevents the late injection fuel from adhering to the cylinder wall surface to obstruct the homogenization of the fuel and There is an effect that fuel vaporization is promoted by ensuring a long time until the fuel is vaporized.

Japanese Patent Laid-Open No. 11-218051

  However, even in a cylinder-injection spark ignition internal combustion engine that injects fuel into the combustion chamber in the intake stroke as described above, compared to an internal combustion engine of a type that injects fuel into the intake passage, the time until ignition after fuel injection is reached. Due to the short time, the fuel may not vaporize sufficiently and may not mix with the intake air. For this reason, a uniform air-fuel mixture cannot be obtained in the combustion chamber that is optimal for homogeneous combustion, and satisfactory combustion cannot be obtained. This problem also occurs in a cylinder injection spark ignition internal combustion engine that closes the intake valve after the gas in the combustion chamber starts flowing back into the intake passage via the intake valve after the compression stroke starts. .

  Therefore, the present invention is suitable for homogeneous combustion in a direct injection spark ignition internal combustion engine that closes the intake valve after the gas in the combustion chamber starts to flow back into the intake passage via the intake valve after the compression stroke starts. The object is to form a mixture.

  In order to solve the above-described problem, according to the invention described in claim 1, the fuel injection valve for injecting fuel into the combustion chamber is provided, and after the compression stroke starts, the gas in the combustion chamber starts to flow backward into the intake passage. In a direct injection spark ignition internal combustion engine that closes the intake valve later, the fuel injection timing is set during the compression stroke and the intake valve is opened, and the injected fuel is directed from the combustion chamber into the intake passage. A direct injection spark ignition internal combustion engine is provided in which fuel flows into the intake passage along with a reverse gas flow, and the fuel that flows into the intake passage is introduced into the combustion chamber along with the intake air in the next intake stroke.

  That is, according to the first aspect of the present invention, the fuel is once injected into the combustion chamber and starts to vaporize at the same time. Further, the vaporization progresses after flowing into the intake passage and mixing with the intake air existing in the intake passage. Therefore, there is an effect that a good air-fuel mixture is formed in the combustion chamber in the intake stroke in the next cycle.

  According to a second aspect of the present invention, there is provided a direct injection spark ignition internal combustion engine according to the first aspect, wherein the fuel injection is performed a plurality of times by dividing the fuel to be injected. Provided.

  That is, in the invention described in claim 2, the fuel to be injected is divided and injected a plurality of times to reduce the penetration force of the injected fuel spray, and the injected fuel spray is There is an effect that the gas flow from the combustion chamber toward the intake valve is more likely to flow into the intake passage.

  According to the invention described in each claim, there is a common effect that an air-fuel mixture suitable for homogeneous combustion can be formed.

  A cylinder injection spark ignition internal combustion engine according to the present invention will be described with reference to FIG. In FIG. 1, 1 is an engine body having four cylinders, for example, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an intake valve, 7 is an intake passage, 8 is an exhaust valve, Reference numeral 9 denotes an exhaust passage, and 10 denotes a spark plug. The intake passage 7 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air cleaner 14 via an intake duct 13. An air flow meter 15 for detecting the intake air flow rate and a throttle valve 17 driven by a step motor 16 are arranged in the intake duct 13. Further, an electrically controlled fuel injection valve 18 for injecting fuel into the combustion chamber 5 is disposed in the combustion chamber 5.

  Furthermore, the intake valve 6 and the exhaust valve 8 are respectively provided with variable valve mechanisms 19 and 20 that change their valve opening operations. Here, the valve opening operation is determined, for example, by one or more of the lift amount, the valve opening period (working angle), and the valve opening start timing, and any known mechanism can be used as the mechanism of this embodiment. It will not be described in detail.

  On the other hand, the exhaust passage 9 is connected to a small capacity three-way catalyst 22 via an exhaust branch pipe 21, and an air-fuel ratio sensor 23 for detecting the air-fuel ratio is attached to the exhaust passage upstream of the three-way catalyst 22. A water temperature sensor 24 for detecting the engine cooling water temperature is attached to the engine body 1.

  The electronic control unit (ECU) 40 is a digital computer and includes a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, An output port 46 is provided. The accelerator pedal 49 is connected to a load sensor 50 for detecting the depression amount of the accelerator pedal 49. Here, the depression amount of the accelerator pedal 49 represents a required load.

  Output signals from the air flow meter 15, the air-fuel ratio sensor 23, the water temperature sensor 24, and the load sensor 50 are input to the input port 45 via the corresponding AD converters 47. Further, the input port 45 is connected to a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 30 °. The CPU 44 calculates the engine speed based on the output pulse of the crank angle sensor 51.

  On the other hand, the output port 46 is connected to the spark plug 10, the step motor 16, the fuel injection valve 18, and the variable valve mechanisms 19 and 20 through corresponding drive circuits 48, which are output signals from the electronic control unit 40. Controlled based on

  The three-way catalyst 22 has an oxygen storage capacity, so that when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 22 is lean, it stores oxygen in the exhaust gas and flows into the three-way catalyst 22. When the air-fuel ratio of the exhaust gas is rich, the stored oxygen is released to oxidize and purify HC and CO contained in the exhaust gas.

  The in-cylinder spark-ignition internal combustion engine according to the present invention is in an operating state in which after the compression stroke starts, the gas in the combustion chamber 5 starts to flow backward into the intake passage 7 via the intake valve 6 and then closes the intake valve 6. Have This operating state is performed, for example, during cold start, (homogeneous) lean combustion, mirror cycle, and the like.

  Next, the movement of the fuel spray 30 injected at the fuel injection timing according to the present invention will be described with reference to FIG. FIG. 2 is a schematic longitudinal sectional view of a direct injection spark ignition internal combustion engine showing fuel injection during the compression stroke and when the intake valve 6 is open. The fuel spray 30 ′ indicates fuel injected during the compression stroke in which the intake valve 6 is closed. In this fuel injection, no backflow gas flow is generated in the intake passage 7, so that the fuel travels straight due to penetration force (penetration).

  First, during the compression stroke and when the intake valve 6 is open, the piston 4 rises from the compression bottom dead center and pushes up the gas in the combustion chamber 5, so that the gas passes through the intake valve 6 and the intake passage 7. It is in a state of flowing backward. Therefore, when fuel is injected at this timing, the injected fuel spray 30 flows into the intake passage 7 together with the backflowing gas flow.

  More precisely, immediately after the start of the compression stroke, even if the intake valve 6 is open, a backflow does not occur immediately because of the inertial force of the gas, and a backflow occurs after a predetermined time. Therefore, in order to flow more fuel spray 30 into the intake passage 7 more reliably, it is desirable to perform fuel injection after the backflow has occurred.

  As described above, the fuel spray 30 flowing into the intake passage 7 is again introduced into the combustion chamber 5 and combusted in the intake stroke in the next engine cycle. Here, the fuel spray 30 is sufficiently vaporized and mixed with the intake air until it is injected into the combustion chamber 5 and again introduced into the combustion chamber 5. That is, the injected fuel spray 30 starts to vaporize in the combustion chamber 5 immediately after injection. According to normal engine operation, the injected fuel spray 30 is directly mixed with intake air in the combustion chamber, compressed, ignited, and burned. However, according to the present invention, the injected fuel spray 30 flows into the intake passage 7, where further vaporization proceeds and mixing with the intake air present in the intake passage 7 is performed.

  Therefore, according to the present invention, it is possible to secure more time for vaporizing and mixing the fuel as compared to the conventional in-cylinder spark ignition internal combustion engine. A better mixture is formed within 5. This is because the fuel mixture is better than the internal combustion engine of the type in which the fuel is first injected into the combustion chamber 5 and vaporized and then injected into the intake passage 7 so as to inject the fuel into the intake passage from the beginning. Can be obtained. As described above, good combustion is performed in the next cycle, and the above-described problems such as combustion fluctuation and increase in PM are solved.

  Next, a method for causing the injected fuel to flow into the intake passage 7 more efficiently will be described. As described above, when fuel is injected, it tends to go straight due to its penetration force. As the penetration force is increased, the influence of the gas flow is less likely to occur, so that the amount of fuel flowing into the intake passage 7 is reduced along with the backflow of gas. On the other hand, when the penetrating force is small, the gas flow is more easily affected, and the amount of fuel flowing into the intake passage 7 can be increased together with the backflow of gas. From the viewpoint of fuel vaporization and mixing, as described above, it is preferable that the fuel once flows into the intake passage 7, and therefore, it is desirable that the penetration force is small.

  By the way, in general, it is considered that the greater the flight speed of the fuel spray 30, the greater the penetration force. However, the initial speed of the fuel injected from the fuel injection valve 18 is usually independent of the amount of fuel to be injected and the operating state. It is almost constant. Therefore, in the embodiment according to the present invention, in order to slow down the flight speed of the fuel spray 30, the fuel to be injected is not injected at a time, but is divided into a plurality of times and injected.

  The injected fuel spray 30 gradually decreases its flight speed by colliding with the gas in the combustion chamber 5. However, if the fuel to be injected is injected at a time as shown in FIG. 2, only the first injected fuel collides with the gas in the combustion chamber 5, and a series of subsequent fuel sprays are caused by the first fuel spray. It follows the space in the combustion chamber 5 from which the gas is removed. Therefore, as a whole fuel spray, the resistance of gas is reduced and the flight speed is difficult to decrease. Therefore, it has a high penetrating force and is difficult to flow into the intake passage 7.

  On the other hand, in the embodiment shown in FIG. 3, when the fuel to be injected is divided and injected, the resistance of the gas to the divided fuel sprays 30 is relatively larger than that in the case where the fuel is injected all at once. . Therefore, the flight speed of the fuel spray 30 is likely to decrease, and therefore the penetration force is reduced. Therefore, in the present embodiment, the fuel to be injected is divided and injected, thereby reducing the penetration force and facilitating the flow into the intake passage 7.

  FIG. 4 is a diagram showing a map of the division number N of fuel injection. In the present embodiment, the division number N is obtained in advance by experiment or calculation as a function of the injected fuel amount Q representing the engine load and the engine speed Ne when the interval between the divided fuel injections is constant. 4 and stored in advance in the ROM 42 in the form of a map as shown in FIG. In this embodiment, the interval of each fuel injection is fixed, but it may not be fixed. For example, if the intervals between fuel injections within a certain engine cycle are constant, the intervals between different engine cycles need not be constant.

  5 and 6 are diagrams showing the relationship between the valve opening period of the intake valve 6 and the fuel injection timing. The abscissa represents the crank angle, and shows the period before the compression bottom dead center (BDC) and after the compression top dead center (TDC). As for the closing timing of the intake valve 6, after the compression stroke started, the piston 4 rose from the compression bottom dead center (BDC), and the gas in the combustion chamber 5 began to flow back into the intake passage 7 via the intake valve 6. Set until later.

  In the embodiment shown in FIG. 5, the fuel injection is started from the compression bottom dead center (BDC), and the fuel to be injected is determined according to the number of divisions determined from FIG. 4 from the injected fuel amount Q and the engine speed Ne. Divided and injected.

  In the embodiment shown in FIG. 6, fuel injection is initiated in time with the onset of backflow. Thereby, as described above, the fuel spray can flow into the intake passage 7 more efficiently.

  FIG. 7 is a flowchart showing a fuel injection control operation according to the present invention. This operation is performed as a routine executed by interruption every predetermined time predetermined by an electronic control unit (ECU) 40.

  First, in step 101, various parameters indicating the engine operating state such as the engine coolant temperature and the air-fuel ratio are detected, and the process proceeds to step 102. Next, in step 102, based on the detected various parameters, the current engine operating state is that after the compression stroke starts, the gas in the combustion chamber 5 starts to flow backward into the intake passage 7 via the intake valve 6. It is determined whether or not the operation state is such that the intake valve 6 is closed, that is, whether or not the operation state is such that backflow of gas into the intake passage 7 occurs. The case where this condition is satisfied includes, for example, a case where the detected engine coolant temperature is equal to or lower than a predetermined temperature, a case where the air-fuel ratio is in a lean region where the air-fuel ratio is equal to or higher than a predetermined air-fuel ratio, and a case where the air-fuel ratio is a mirror cycle region.

  If the reverse flow generation condition is not satisfied, the routine proceeds to step 103, the normal fuel injection condition is set, and the routine proceeds to step. Next, in step 106, fuel injection control according to the present invention is not performed, fuel injection is executed based on the set fuel injection conditions, and the routine is terminated.

  On the other hand, when the backflow generation condition is satisfied in step 102, the process proceeds to step 104. Next, in step 104, the fuel injection start timing, that is, whether the injection starts from the compression bottom dead center (BDC) or the injection starts after the backflow starts is read, and the process proceeds to step 105. Next, at step 105, the number of divisions of the fuel to be injected is read based on the map shown in FIG. Next, at step 106, fuel injection is executed based on the fuel injection start timing read at step 104 and the number of divisions read at step 105, and the routine is terminated.

1 is a schematic longitudinal sectional view of a direct injection spark ignition internal combustion engine according to the present invention. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine which shows the fuel injection in which the intake valve is open. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine which shows the fuel injection in which the intake valve by another embodiment is valve opening. It is a figure which shows the map of the frequency | count of division | segmentation of fuel injection. It is a figure which shows the relationship between the valve opening period of an intake valve, and fuel injection timing. It is a figure which shows the relationship between the valve opening period of an intake valve and fuel injection timing by another embodiment. It is a flowchart which shows fuel-injection control operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 4 Piston 5 Combustion chamber 6 Intake valve 7 Intake passage 10 Spark plug 18 Fuel injection valve 30 Fuel spray

Claims (2)

  In a cylinder injection spark ignition internal combustion engine having a fuel injection valve for injecting fuel into a combustion chamber, and closing the intake valve after gas in the combustion chamber starts to flow backward into the intake passage after the start of the compression stroke, The injection timing is set during the compression stroke and the intake valve is opened, and the injected fuel flows into the intake passage along with the reverse gas flow from the combustion chamber into the intake passage, and then flows into the intake passage. An in-cylinder spark ignition internal combustion engine in which fuel is introduced into a combustion chamber together with intake air in the next intake stroke.   The direct injection spark ignition internal combustion engine according to claim 1, wherein the fuel injection is performed a plurality of times by dividing the fuel to be injected.

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