JP4240083B2 - In-cylinder injection spark ignition internal combustion engine control device - Google Patents

Description

  The present invention relates to a control device for an in-cylinder injection spark ignition internal combustion engine.

  A tumble flow is generated in the cylinder of an in-cylinder injection spark ignition internal combustion engine, and this tumble flow is further strengthened with fuel injected near the bottom dead center of the intake stroke during homogeneous combustion, so that the tumble flow is maintained until the ignition timing. Can be maintained. As a result, the turbulence of the air-fuel mixture can be increased at the ignition timing, so that the combustion speed of the air-fuel mixture can be improved moderately and good homogeneous combustion can be obtained. As a technique relating to such fuel injection, for example, Patent Document 1 proposes a fuel injection control device that reinforces a circulating airflow in a cylinder with fuel injected from a fuel injection valve. As a technique for enhancing the in-cylinder intake flow at the time of homogeneous combustion, for example, in Patent Document 2, intake control of a direct injection type internal combustion engine that controls the intake flow control valve provided in the intake passage to strengthen the intake flow A device has been proposed.

Japanese Patent Laid-Open No. 2003-332022 JP 2005-180247 A

  By the way, in the above-described in-cylinder spark ignition internal combustion engine, when the air-fuel ratio is lean, the amount of in-cylinder air is larger than in the case of stoichiometric, so the mass of the tumble flow is increased, and as a result, fuel is injected similarly. Even so, the tumble flow cannot be sufficiently enhanced. In this case, since the tumble flow having a sufficiently strong ignition timing cannot be secured due to the attenuation of the tumble flow T, the turbulence of the air-fuel mixture cannot be sufficiently increased at the ignition timing. Furthermore, if the turbulence of the air-fuel mixture cannot be sufficiently increased at the ignition timing as described above, the combustion speed becomes insufficient, and therefore, there is a possibility that good combustion cannot be obtained such that knocking is likely to occur. there were.

  Therefore, the present invention has been made in view of the above problems, and in enhancing the tumble flow with the injected fuel, by changing the fuel injection according to the lean degree of the required air-fuel ratio, good combustion is achieved. It is an object of the present invention to provide a control device for an in-cylinder injection spark ignition internal combustion engine that can be obtained.

In order to solve the above-described problems, the present invention controls a cylinder injection spark ignition internal combustion engine that generates a tumble flow in a cylinder and enhances the tumble flow with fuel injected near the bottom dead center of the intake stroke. A control device for an in-cylinder injection spark ignition internal combustion engine, wherein the lean degree of the required air-fuel ratio is larger, the injection timing changing means for retarding the fuel injection timing, and the lean degree of the required air-fuel ratio is a predetermined lean And a split injection unit that splits and injects the fuel when the boundary value is exceeded, and homogenizes the mixture by sandwiching air between the split and injected fuels . According to the present invention, since the fuel injection timing is retarded, the period from the fuel injection timing to the ignition timing can be shortened. Therefore, the ignition timing is set before the tumble flow reinforced with the injected fuel is greatly attenuated. Can be greeted. Thereby, the disturbance of the air-fuel mixture at the ignition timing can be increased, so that good combustion can be obtained according to the present invention. However, if the fuel injection timing is retarded, the period from the fuel injection timing to the ignition timing is shortened, and the homogeneity of the air-fuel mixture tends to gradually deteriorate. In particular, if the fuel is injected at a retarded angle commensurate with the required lean degree exceeding the predetermined lean boundary value, the period from the fuel injection timing to the ignition timing is considerably shortened, so that the energy efficiency greatly decreases. The homogeneity of the mixture will deteriorate. On the other hand, according to the present invention, air can be sandwiched between the injected fuels by dividing and injecting the fuel. Thereby, vaporization of the fuel can be promoted and the homogeneity can be improved, so that good combustion can be obtained.

  According to the present invention, in order to enhance the tumble flow with the injected fuel, in-cylinder injection spark ignition that can obtain good combustion by changing the fuel injection according to the lean degree of the required air-fuel ratio A control device for an internal combustion engine can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing a control device for a direct injection spark ignition internal combustion engine according to the present embodiment realized by an ECU (Electronic Control Unit) 1A together with an internal combustion engine system 100. . The internal combustion engine system 100 includes an intake system 10, a fuel injection system 20, an exhaust system 30, and an internal combustion engine 50. The intake system 10 is configured to introduce air into the internal combustion engine 50, and includes an air cleaner 11 for filtering intake air, an air flow meter 12 for measuring the amount of air, a throttle valve 13 for adjusting the flow rate of intake air, For temporarily storing the intake tank 15, the intake manifold 15 for distributing the intake air to the cylinders of the internal combustion engine 50, the intake pipe appropriately disposed therebetween, and the like.

  The fuel injection system 20 is configured to supply and inject fuel, and includes a fuel injection valve 21, a fuel injection pump 22, a fuel tank 23, and the like. The fuel injection valve 21 is a structure for injecting fuel, and is opened at an appropriate injection timing to inject fuel under the control of the ECU 1A. The fuel injection amount is adjusted by the length of the valve opening period until the fuel injection valve 21 is closed under the control of the ECU 1A. The fuel injection pump 22 is configured to pressurize the fuel and generate an injection pressure, and adjusts the injection pressure to an appropriate injection pressure under the control of the ECU 1A.

  The exhaust system 30 includes an exhaust manifold 31, a three-way catalyst 32, a silencer (not shown), and an intake pipe appropriately disposed between these components. The exhaust manifold 31 is configured to merge the exhaust from the cylinders, and the exhaust passages branched in correspondence with the cylinders are gathered into one exhaust passage on the downstream side. The three-way catalyst 32 is a structure for purifying exhaust gas, and performs oxidation of hydrocarbons HC and carbon monoxide CO and reduction of nitrogen oxides NOx. In the exhaust system 30, an A / F sensor 33 for linearly detecting the air-fuel ratio based on the oxygen concentration in the exhaust is upstream of the three-way catalyst 32, and the air-fuel ratio is based on the oxygen concentration in the exhaust from the stoichiometric air-fuel ratio. Also, oxygen sensors 34 for detecting whether the gas is rich or lean are respectively disposed downstream of the three-way catalyst 32.

  FIG. 2 is a diagram schematically showing a main part of the internal combustion engine 50. The internal combustion engine 50 includes a cylinder block 51, a cylinder head 52, a piston 53, a spark plug 54, an intake valve 55, and an exhaust valve 56. The internal combustion engine 50 shown in this embodiment is an in-line four-cylinder in-cylinder spark ignition internal combustion engine. However, the internal combustion engine 50 may have other appropriate cylinder arrangement structure and the number of cylinders. In FIG. 2, the main part of the internal combustion engine 50 is shown with respect to the cylinder 51a as a representative of each cylinder, but in this embodiment, the other cylinders have the same structure. The cylinder block 51 is formed with a substantially cylindrical cylinder 51a. A piston 53 is accommodated in the cylinder 51a. A cavity 53 a for guiding the tumble flow T is formed on the top surface of the piston 53. A cylinder head 52 is fixed to the upper surface of the cylinder block 51. The combustion chamber 57 is formed as a space surrounded by the cylinder block 51, the cylinder head 52, and the piston 53. In addition to an intake port 52a for guiding intake air to the combustion chamber 57, the cylinder head 52 is formed with an exhaust port 52b for exhausting the combusted gas from the combustion chamber 57, and opens and closes the intake and exhaust ports 52a and 52b. For this purpose, intake and exhaust valves 55 and 56 are provided. The internal combustion engine 50 may have an intake / exhaust valve structure including an appropriate number of intake / exhaust valves 55 and 56 per cylinder.

  The spark plug 54 is disposed in the cylinder head 52 with an electrode protruding substantially in the center above the combustion chamber 57. The fuel injection valve 21 is also disposed in the cylinder head 52 with the fuel injection hole protruding into the combustion chamber 57 from a position adjacent to the spark plug 54 above the combustion chamber 57. The arrangement of the fuel injection valve 21 is not limited to this. For example, the cylinder head with the fuel injection hole projecting into the combustion chamber 57 from the intake port 52a side (portion A shown in FIG. 2) above the combustion chamber 57. 52 may be provided. A plurality of fuel injection valves 21 may be provided per cylinder.

  An air flow control valve 58 for generating a tumble flow T in the combustion chamber 57 is disposed in the intake port 52a. The airflow control valve 58 is configured to generate a tumble flow T in the combustion chamber 57 by causing the intake air to drift in the intake port 52a under the control of the ECU 1A. However, the tumble flow generating means for generating the tumble flow T in the combustion chamber 57 is not limited to the air flow control valve 58, and for example, the shape of the intake port 52a formed so that the tumble flow T can be generated in the cylinder. There may be other appropriate means capable of generating the tumble flow T in the cylinder. The tumble flow T is a forward tumble flow that turns in the cylinder so as to rise on the intake valve 55 side in the combustion chamber 57. In this embodiment, the fuel injection valve 21 injects fuel near the bottom dead center of the intake stroke under the control of the ECU 1A during homogeneous combustion. The injected fuel moderately strengthens the tumble flow T, and the strengthened tumble flow T is maintained until the ignition timing. As a result, the turbulence of the air-fuel mixture increases at the ignition timing and the combustion speed is improved moderately, so that good homogeneous combustion can be obtained.

  The airflow control valve 58 is opened at an opening degree such as half-opened or fully-opened to increase intake during homogeneous combustion, and it is difficult to obtain a sufficiently strong tumble flow T only by the shape of the intake port 52a. However, there is generally room for improvement in the mixing characteristics of the air-fuel mixture and the flame propagation characteristics during homogeneous combustion. In addition, the internal combustion engine 50 is provided with various sensors such as a crank angle sensor 71 that generates an output pulse proportional to the rotational speed NE and a water temperature sensor 72 for detecting the water temperature of the internal combustion engine 50.

  The ECU 1A includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output circuit, and the like (not shown). The ECU 1A is mainly configured to control the internal combustion engine 50. In this embodiment, in addition to the fuel injection valve 21 and the fuel injection pump 22, an ignition plug 54 (more specifically, an igniter not shown) and an airflow control valve 58 are provided. (More specifically, an actuator for the airflow control valve 58 (not shown)) is also controlled. In addition to the fuel injection valve 21 and the like, various control objects are connected to the ECU 1A via a drive circuit (not shown). Further, the ECU 1A detects the amount of depression (accelerator opening) of the air flow meter 12, the A / F sensor 33, the oxygen sensor 34, the crank angle sensor 71, the water temperature sensor 72, and the accelerator pedal (not shown). Various sensors such as an accelerator sensor 73 are connected.

  The ROM is configured to store a program in which various processes executed by the CPU are described. In this embodiment, the ROM is used for controlling the fuel injection valve 21 for controlling the fuel injection valve 21 in addition to the program for controlling the internal combustion engine 50. Also stores programs. The fuel injection valve program may be configured as a part of the internal combustion engine 50 control program. The fuel injection valve control program includes an injection amount control program for controlling the fuel injection amount, an injection pressure control program for controlling the fuel injection pressure, and an injection for controlling the fuel injection timing. And a timing control program. The present embodiment is characterized in that the injection timing control program is configured to have an injection timing specifying control program for retarding the fuel injection timing as the degree of leanness of the required air-fuel ratio increases. is doing.

  In this embodiment, the injection timing specifying control program specifically refers to map data (hereinafter simply referred to as an injection timing map) indicating the relationship between the lean degree of the required air-fuel ratio and the injection timing. The injection timing corresponding to the lean degree of the fuel ratio is read, and the injection timing is changed to the injection timing read from the injection timing map. FIG. 3 is a diagram schematically showing ignition timing map data showing the relationship between the lean degree of the required air-fuel ratio and the injection timing. In this embodiment, this injection timing map is also stored in the ROM. When the air-fuel ratio is stoichiometric in the injection timing map, it indicates that the injection timing is the normal injection timing, and the tumble flow T moderately strengthened by the fuel injected near the bottom dead center of the intake stroke at the time of homogeneous combustion Basically, good homogeneous combustion can be obtained at the injection timing at this time.

  On the other hand, when the air-fuel ratio becomes lean, the amount of air in the cylinder increases and the mass of the tumble flow T increases, so that the tumble flow T is sufficiently strengthened when fuel is injected at the same injection timing as in the case of stoichiometry. I can't. In this case, since the strength of the tumble flow T at the ignition timing cannot be secured at a sufficient magnitude due to the attenuation of the tumble flow T, the turbulence of the air-fuel mixture at the ignition timing is reduced. As a result, the combustion rate cannot be sufficiently improved, so that good combustion cannot be obtained. For this reason, the injection timing map is set so that the injection timing is retarded as the lean degree of the required air-fuel ratio increases. As a result, the greater the degree of leanness of the required air-fuel ratio, the shorter the period from the injection timing to the ignition timing, and as a result, the tumble flow T is suppressed from being greatly attenuated by the ignition timing. . Note that the relationship between the lean degree of the required air-fuel ratio and the injection timing does not necessarily have to be set to a linear relationship in the injection timing map. In the present embodiment, various detection means, determination means, control means, and the like are realized by a CPU, a ROM, a RAM (hereinafter simply referred to as a CPU, etc.), and a program for controlling the internal combustion engine 50. The injection timing changing means is realized by the injection timing specifying control program.

  Next, the processing performed by the ECU 1A when changing the injection timing in accordance with the lean degree of the required air-fuel ratio will be described in detail with reference to the flowchart shown in FIG. The ECU 1A controls the internal combustion engine 50 by repeatedly executing the processing shown in the flowchart based on various programs such as the above-described internal combustion engine 50 control program stored in the ROM and the fuel injection valve control program. To do. The CPU executes a process for determining the mode of combustion performed in the internal combustion engine 50 (step 11). In this embodiment, the combustion speed is defined by the rotational speed Ne detected based on the output signal of the crank angle sensor 71, the load factor KL detected based on the output signal of the accelerator sensor 73, and the rotational speed Ne and the load factor KL. A mode of combustion performed in the internal combustion engine 50 is determined based on the map data.

  FIG. 5 is a diagram schematically showing map data of the combustion mode. In this embodiment, the combustion mode is divided into three areas of stoichiometric, homogeneous lean burn and super lean burn according to the rotational speed Ne and load factor KL in this map data. However, the present invention is not limited to this, and the combustion mode may be set by dividing it into appropriate regions, for example, by subdividing it into a plurality of regions. Further, in the present embodiment, the required lean degree of the air-fuel ratio is roughly set according to these regions, the lean degree of the required air-fuel ratio is “None” in the case of stoichiometric, and the lean degree of the required air-fuel ratio in the case of homogeneous lean burn. The degree of leanness of the required air-fuel ratio is set to “large” when the degree is “medium” and in the case of super lean burn. However, the present invention is not limited to this, and the required lean degree of the air-fuel ratio may be appropriately set according to the rotational speed Ne and the load factor KL. Note that the combustion mode and the lean degree of the required air-fuel ratio are not limited to the rotational speed Ne and the load factor KL, and may be set according to an appropriate operating state of the internal combustion engine 50.

  Subsequent to step 11, the CPU executes a process of determining whether or not the required air-fuel ratio corresponding to the rotational speed Ne and the load factor KL detected from the combustion mode map data is lean (step 12). If the determination is negative, the process returns to step 11 because no special processing is required in this flowchart. On the other hand, if the determination is affirmative, the CPU reads the lean degree of the required air-fuel ratio from the combustion mode map data, reads the injection timing corresponding to this lean degree with reference to the injection timing map, and determines the injection timing from the injection timing map. A process of changing to the read injection timing is executed (step 13A). As a result, the injection timing is retarded as the lean degree of the required air-fuel ratio increases. FIG. 6 is a diagram schematically showing the state of fuel injection before and after changing the injection timing. Before the injection timing is changed, as shown in FIG. 6 (a), the fuel injected near the bottom dead center of the intake process and close to the intake process is retarded in this step, so that FIG. ), The fuel is injected so that it is injected near the bottom dead center of the intake process and closer to the compression process.

  Subsequently, the CPU executes a process for controlling the fuel injection valve 21 to inject fuel at the injection timing read in step 13A (step 14A). As a result, since the period from the injection timing to the ignition timing is shortened, the strength of the tumble flow T is ensured to be sufficiently large for the ignition timing, and as a result, the turbulence of the air-fuel mixture can be sufficiently increased. Can do. And since a combustion rate can be improved moderately by this, favorable combustion can be obtained. As described above, when the tumble flow T is enhanced with the injected fuel, the ECU 1A that can obtain good combustion can be realized by changing the fuel injection according to the lean degree of the required air-fuel ratio.

  The ECU 1B according to the present embodiment is the same as the ECU 1A according to the first embodiment, except that the fuel injection valve control program further includes a divided injection program described below. In this embodiment, each configuration of the internal combustion engine system 100 to which the ECU 1B is applied is the same as each configuration shown in FIG. The split injection program is created so that fuel injection is split when the lean degree of the required air-fuel ratio exceeds a predetermined lean boundary value. Specifically, in this embodiment, when the combustion mode shown in FIG. 5 changes from homogeneous lean burn to super lean burn, the lean degree of the required air-fuel ratio exceeds a predetermined lean boundary value. In the present embodiment, the split injection means is realized by the CPU and the like and the split injection program, and the control device for the cylinder injection spark ignition internal combustion engine is realized by the ECU 1B.

  Next, processing performed by the ECU 1B when performing divided injection according to the lean degree of the required air-fuel ratio will be described in detail with reference to the flowchart shown in FIG. Since this flowchart is the same as the flowchart shown in FIG. 4 except that steps 13B and 14B are added, steps 13B and 14B will be specifically described in this embodiment. Subsequent to step 13A, the CPU executes a process of determining whether or not the lean degree of the required air-fuel ratio read in step 13A exceeds the lean boundary value (step 13B). If the determination is negative, it is not necessary to perform divided injection, and therefore the CPU executes processing for controlling the fuel injection valve 21 to inject fuel at the injection timing read in step 13A (step 14A).

  On the other hand, if the determination is affirmative, the CPU executes processing for controlling the fuel injection valve 21 so as to perform fuel split injection at the injection timing read in step 13A (step 14B). FIG. 8 is a diagram schematically showing the state of fuel injection before and after split injection. As shown in FIG. 8 (a), the fuel injected before the split injection near the bottom dead center of the intake stroke and close to the intake stroke is further retarded in accordance with the required lean degree exceeding the lean boundary value. Thus, in this step, as shown in FIG. 8 (b), the divided fuel is injected so that the total amount of fuel injection becomes substantially the same before and after the divided injection. As a result, air can be sandwiched between the injected fuels, so that vaporization of the fuel can be promoted and the homogeneity of the air-fuel mixture can be improved. As a result, even if fuel is injected at a retarded angle commensurate with the required lean degree exceeding the lean boundary value, the deterioration of the homogeneity of the air-fuel mixture can be suppressed. Combustion can be obtained. As described above, when the tumble flow T is enhanced with the injected fuel, the ECU 1B that can obtain good combustion can be realized by changing the fuel injection according to the required lean degree of the air-fuel ratio.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a diagram schematically showing an ECU 1A together with an internal combustion engine system 100. FIG. FIG. 2 is a diagram schematically showing a main part of an internal combustion engine 50. It is a figure which shows an injection timing map typically. It is a figure which shows the process performed by ECU1A with a flowchart. It is a figure which shows typically the map data of a combustion mode. It is a figure which shows typically the mode of the fuel injection before and behind injection timing change. It is a figure which shows the process performed by ECU1B with a flowchart. It is a figure which shows typically the mode of the fuel injection before and behind split injection.

Explanation of symbols

1 ECU
DESCRIPTION OF SYMBOLS 10 Intake system 20 Fuel injection system 21 Fuel injection valve 30 Exhaust system 50 Internal combustion engine 100 Internal combustion engine system

Claims (1)

A control device for a cylinder injection spark ignition internal combustion engine that controls a cylinder injection spark ignition internal combustion engine that generates a tumble flow in a cylinder and that reinforces the tumble flow with fuel injected near the bottom dead center of an intake stroke. There,
Injection timing changing means for retarding the fuel injection timing as the lean degree of the required air-fuel ratio increases ,
Split injection means for splitting and injecting the fuel when the lean degree of the required air-fuel ratio exceeds a predetermined lean boundary value, and homogenizing the mixture by sandwiching air between the split and injected fuel;
A control apparatus for an in-cylinder injection spark ignition internal combustion engine.

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