JP2008031895A - Control device of in-cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an in-cylinder injection type spark ignition internal combustion engine capable of obtaining favorable homogeneous combustion by changing a combustion state based on characteristics of fuel when enhancing a tumble flux using fuel injected in a homogeneous combustion time. <P>SOLUTION: An ECU (Electronic Control Unit) 1A generating a tumble flux T inside a cylinder, and controlling an internal combustion engine 50 enhancing the tumble flux T with fuel injected near a bottom dead-center in an air intake stroke in a homogeneous combustion time, comprises: a determining means for characteristics of fuel determining the characteristics of the fuel; and a means for changing a combustion state changing the combustion state based on the determined characteristics of the fuel. When the fuel has a characteristic with an air-fuel ratio of a stoichi smaller than that of gasoline, the means for changing the combustion state changes the combustion state by delaying ignition timing, for example. Thereby, a combustion speed is suppressed to get excessively high since the combustion state can be changed to slow combustion. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 the tumble flow is moderately strengthened with fuel injected near the bottom dead center of the intake stroke during homogeneous combustion. 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 related 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 recent years, there is a vehicle called FFV (Flexible Fuel Vehicle) capable of traveling with a mixed fuel of alcohol and gasoline (hereinafter also simply referred to as alcohol mixed fuel) in addition to gasoline. The alcohol-mixed fuel has a carbon atom content different from that of ordinary gasoline, so that the stoichiometric air-fuel ratio is smaller than that of gasoline. Specifically, for example, when the fuel is gasoline, the stoichiometric air-fuel ratio is about 14.5, whereas when the fuel is alcohol-mixed fuel, the stoichiometric air-fuel ratio is about 9 depending on the alcohol concentration. There is also. In the case of using the above-described in-cylinder injection spark ignition internal combustion engine, the air flowing into the cylinder at the time of homogeneous combustion is not limited to the alcohol-mixed fuel. As a result, the mass of the fuel with respect to the quantity becomes larger than that in the case of gasoline, so that the air flow assist effect by the injected fuel is enhanced and the combustion speed is further improved. If the ignition timing remains the same at this time, the combustion state becomes a state corresponding to the combustion state when the ignition timing is over-advanced, and the thermal efficiency may be deteriorated. On the other hand, when fuel with a property that makes the stoichiometric air-fuel ratio larger than that of gasoline is used, the fuel mass with respect to the amount of air flowing into the cylinder becomes smaller than in the case of gasoline as a result of injecting as a result of homogeneous combustion. There is a possibility that the airflow assist effect by the fuel is weakened and the tumble flow cannot be sufficiently enhanced.

  Accordingly, the present invention has been made in view of the above-described problems, and in enhancing the tumble flow with the fuel injected during homogeneous combustion, good homogeneous combustion is obtained by changing the combustion state based on the properties of the fuel. It is an object of the present invention to provide a control device for an in-cylinder injection spark ignition internal combustion engine.

  In order to solve the above-described problems, the present invention provides 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 the intake stroke during homogeneous combustion. A control device for an in-cylinder spark-ignition internal combustion engine that controls the fuel, a fuel property determining unit that determines the property of the fuel, and a combustion state changing unit that changes the combustion state based on the determined property of the fuel It is characterized by providing. According to the present invention, it is possible to change the combustion speed by changing the fuel state based on the properties of the fuel, and as a result, it is possible to suppress the combustion speed from being improved or lowered more than necessary. Therefore, according to the present invention, good homogeneous combustion can be realized even when fuels having different properties are used.

  Further, according to the present invention, when the fuel is a fuel having a stoichiometric air-fuel ratio smaller than that of gasoline, the combustion state changing means may retard the ignition timing. Here, when the fuel is a fuel having the above-described properties, since the disturbance of the air-fuel mixture at the ignition timing is further increased, the combustion speed is improved more than necessary. On the other hand, according to the present invention, the ignition speed can be retarded so that the combustion state can be changed so that the slow combustion is performed. Therefore, according to the present invention, it is possible to suppress the deterioration of the thermal efficiency, thereby obtaining a good homogeneous combustion.

  In the present invention, when the fuel is a fuel having a stoichiometric air-fuel ratio smaller than that of gasoline, the combustion state changing means may increase the EGR amount. Further, when the fuel has the above properties, for example, the combustion state can be changed so that the combustion temperature is lowered by increasing the EGR amount as in the present invention, so that the combustion speed is higher than necessary. Can be suppressed. Therefore, according to the present invention, it is possible to suppress the deterioration of the thermal efficiency, thereby obtaining a good homogeneous combustion.

  According to the present invention, in order to enhance a tumble flow with fuel injected during homogeneous combustion, a cylinder injection type spark ignition internal combustion engine capable of obtaining good homogeneous combustion by changing the combustion state based on the properties of the fuel. An engine control device 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 gas recirculation 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.

  An alcohol concentration sensor 24 is disposed in the fuel passage communicating with the fuel tank 23. The alcohol concentration sensor 24 is configured to detect the alcohol concentration of the fuel. The alcohol concentration sensor 24 is composed of a pair of electrodes and the like, and detects the alcohol concentration by detecting a current change based on electrical conductivity that varies with the alcohol concentration. However, the present invention is not limited to this, and the alcohol concentration sensor 24 may be a resistance detection type, capacitance type, optical type sensor or the like capable of detecting the alcohol concentration. Further, in detecting the alcohol concentration, instead of using the alcohol concentration sensor 24, the estimation may be performed by using an exhaust air-fuel ratio based on an output signal from an oxygen sensor or an air-fuel ratio sensor (not shown), for example. The exhaust gas recirculation system 30 includes an EGR (Exhaust Gas Recirculation) cooler 31, an EGR valve 32, and a connection pipe appropriately disposed therebetween. The EGR cooler 31 is configured to cool the exhaust gas recirculated. The EGR valve 32 is configured to perform exhaust gas recirculation, and communicates or shields the flow path to an appropriate degree under the control of the ECU 1A.

  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 air flow control valve 58 is opened at an opening degree such as half-open or full-open 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 includes an air flow meter 12, an alcohol concentration sensor 24, a crank angle sensor 71, a water temperature sensor 72, an accelerator sensor 73 for detecting the amount of depression (accelerator opening) of an accelerator pedal (not shown), and the like. Various sensors are connected.

  The ROM is configured to store a program in which various processes executed by the CPU are described. In this embodiment, in addition to the internal combustion engine 50 control program, a fuel property determination program for determining the fuel property, Also stored is a combustion state changing program for changing the combustion state based on the determined fuel properties. The fuel property determination program and the combustion state change program may be configured as a part of the internal combustion engine 50 control program. Specifically, the fuel property determination program is created to detect the alcohol concentration based on the output signal of the alcohol concentration sensor 24 and to determine whether the fuel is gasoline or alcohol mixed fuel. The fuel property determination program may be created so as to estimate the alcohol concentration and determine whether the fuel is gasoline or alcohol mixed fuel.

  In this embodiment, the combustion state changing program includes an ignition timing specifying control program for retarding the ignition timing when the fuel is a fuel having a characteristic that the stoichiometric air-fuel ratio is smaller than that of gasoline. Configured. Specifically, the ignition timing specifying control program refers to map data (hereinafter simply referred to as an ignition timing map) indicating the relationship between the alcohol concentration and the ignition timing during homogeneous combustion, and outputs the output signal of the alcohol concentration sensor 24 to the output signal. The ignition timing corresponding to the detected alcohol concentration is read, and the ignition timing is changed to the ignition timing read from the ignition timing map. FIG. 3 is a diagram schematically showing ignition timing map data showing the relationship between the alcohol concentration and the ignition timing. In this embodiment, this ignition timing map is also stored in the ROM. When the alcohol concentration is 0% in the ignition timing map, it indicates that the fuel is ordinary gasoline. Based on the tumble flow moderately enhanced by the fuel injected near the bottom dead center of the intake stroke during homogeneous combustion. In addition, good homogeneous combustion can be obtained at this ignition timing.

  On the other hand, if the alcohol concentration is high, the stoichiometric air-fuel ratio becomes smaller than that of gasoline, so if ignition is performed at the same ignition timing as gasoline fuel during homogeneous combustion, the combustion state becomes the combustion state when the ignition timing is over-advanced. It will be in an equivalent state. In this case, since the combustion rate is improved more than necessary, the thermal efficiency is reduced. For this reason, the ignition timing map is set so that the ignition timing is retarded as the alcohol concentration increases. As a result, the ignition timing is retarded as the alcohol concentration increases, so that the combustion state can be changed so that slow combustion is performed, and as a result, the combustion speed is prevented from being increased more than necessary. Note that the relationship between the alcohol concentration and the ignition timing is not necessarily set to a linear relationship in the ignition 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 fuel property determining means is realized by the fuel property determining program, and the combustion state changing means is realized by the CPU and the ignition timing specifying control program.

  Next, the processing performed by the ECU 1A when changing the combustion state based on the properties of the fuel will be described in detail with reference to the flowchart shown in FIG. In the ECU 1A, the CPU repeatedly executes 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, the fuel property determination program, and the fuel state change program. The internal combustion engine 50 is controlled. The CPU executes processing for determining whether or not the combustion mode performed in the internal combustion engine 50 is homogeneous combustion (step 11). Whether the combustion is homogeneous or not is determined by, for example, the rotational speed Ne detected based on the output signal of the crank angle sensor 71, the load detected based on the output signal of the accelerator sensor 73, and the combustion mode defined by the rotational speed Ne and the load. It can be determined by determining whether or not the combustion mode performed in the internal combustion engine 50 is homogeneous combustion based on the map data. In this embodiment, map data of this combustion mode is also stored in the ROM. If the determination is negative, the CPU repeatedly executes the process shown in step 11 until the determination in step 11 is positive.

  On the other hand, if an affirmative determination is made in step 11, the CPU executes a process of determining whether or not the fuel is alcohol-mixed fuel based on the output signal of the alcohol concentration sensor 24, that is, the property of the fuel (step 12). In this step, the alcohol concentration is detected, and it is determined whether the fuel is gasoline or alcohol mixed fuel. If it is determined that the fuel is gasoline, a negative determination is made in step 12, and the process returns to step 11. On the other hand, if it is determined that the fuel is an alcohol mixed fuel, an affirmative determination is made in step 12, and the CPU reads the ignition timing corresponding to the alcohol concentration detected in step 12 with reference to the ignition timing map and A process of changing the timing to the ignition timing read from the ignition timing map is executed (step 13A). As a result, the ignition timing is changed based on the properties of the fuel and the combustion state is changed.

  Subsequently, the CPU executes a process for controlling the fuel injection valve 21 to inject fuel near the bottom dead center of the intake stroke (step 14). Since the ignition timing is changed in step 13A based on the properties of the fuel, the fuel injected in this step then burns slowly at the changed ignition timing. As a result, since the combustion speed is suppressed from being increased more than necessary, the thermal efficiency is improved and good homogeneous combustion can be obtained. As described above, when the tumble flow T is reinforced with the fuel injected during the homogeneous combustion, the ECU 1A that can obtain a good homogeneous combustion can be realized by changing the combustion state based on the properties of the fuel.

  The ECU 1B according to the present embodiment has a point that the combustion state change program does not have the ignition timing specific control program shown in the first embodiment, and the combustion state change program has the following EGR specific control program. The ECU 1A is the same as the ECU 1A according to the first embodiment, except for the points configured as described above. However, the ECU 1B may have the ignition timing specifying control program shown in the first embodiment. 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 EGR specific control program refers to map data (hereinafter simply referred to as an EGR map) indicating the relationship between the alcohol concentration and the EGR rate (formula: EGR amount / (cylinder air amount + EGR amount)) during homogeneous combustion. The corresponding EGR rate is read from the detected alcohol concentration, and the EGR valve 42 is controlled so that the EGR rate becomes the EGR rate read from the EGR map.

  For example, when the internal combustion engine 50 is provided with a variable valve mechanism, the EGR specifying control program controls the variable valve mechanism instead of controlling the EGR valve 42 to control the intake and exhaust valves 54 and 55. By changing the valve overlap amount, the EGR rate may be created to be the EGR rate read from the EGR map. The EGR specific control program is not limited to either the EGR valve 42 or the variable valve mechanism, and may be created so as to control both of them. Further, the combustion state changing program may have a program for increasing the ratio of the in-cylinder gas amount to the fuel injection amount instead of the EGR specific control program.

  FIG. 5 is a diagram schematically showing an EGR map showing the relationship between the alcohol concentration and the EGR rate. In this embodiment, this EGR map is also stored in the ROM. In this EGR map, when the alcohol concentration is 0%, it indicates that the fuel is ordinary gasoline, and the tumble flow T moderately strengthened by the fuel injected near the bottom dead center of the intake stroke during homogeneous combustion is also obtained. In addition, good homogeneous combustion can be obtained at the EGR rate at this time. On the other hand, when the alcohol concentration is high, the stoichiometric air-fuel ratio becomes smaller than that of gasoline, so that the combustion speed is improved more than necessary during homogeneous combustion, and conversely, the thermal efficiency is lowered. For this reason, the EGR map is set so that the EGR rate increases as the alcohol concentration increases. Thereby, since a combustion state can be changed so that combustion temperature becomes low, it is suppressed that a combustion rate improves more than necessary. In the EGR map, the relationship between the alcohol concentration and the EGR rate may not necessarily be set to a linear relationship. In this embodiment, the enhancement degree changing means is realized by the CPU or the like and the EGR specific control program, and the control device for the in-cylinder injection spark ignition internal combustion engine is realized by the ECU 1B.

  Next, the processing performed by the ECU 1B when changing the combustion state based on the properties of the fuel 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 step 13A is changed to step 13B, step 13B will be specifically described in this embodiment. If the determination in step 12 is affirmative, the CPU refers to the EGR map, reads the EGR rate corresponding to the alcohol concentration detected in step 12, and sets the EGR valve so that the EGR rate becomes the EGR rate read from the EGR map. Processing for controlling 42 is executed (step 13B). As a result, the combustion state is changed based on the properties of the fuel, and the EGR amount is increased in the case of an alcohol-mixed fuel having a stoichiometric air-fuel ratio smaller than that of gasoline. Subsequently, the CPU executes a process for controlling the fuel injection valve 21 to inject fuel near the bottom dead center of the intake stroke (step 14). Since the EGR amount is increased based on the property of the fuel in step 13B, the combustion temperature of the fuel injected in this step is suppressed low. As a result, since the combustion speed is suppressed from being increased more than necessary, the thermal efficiency is improved and good homogeneous combustion can be obtained. As described above, in strengthening the tumble flow T with the fuel injected during the homogeneous combustion, the ECU 1B that can obtain a good homogeneous combustion can be realized by changing the combustion state based on the properties of the fuel.

  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. In particular, in the above-described embodiments, the case where the fuel used is an alcohol mixed fuel has been described in detail. However, the present invention is not limited to the alcohol mixed fuel, and can be applied to other properties of fuel different from normal gasoline. It is.

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 ignition timing map data typically. It is a figure which shows the process performed by ECU1A with a flowchart. It is a figure which shows an EGR map typically. It is a figure which shows the process performed by ECU1B with a flowchart.

Explanation of symbols

1 ECU
DESCRIPTION OF SYMBOLS 10 Intake system 20 Fuel injection system 24 Alcohol concentration sensor 30 Exhaust gas recirculation system 32 EGR valve 50 Internal combustion engine 100 Internal combustion engine system

Claims (3)

An in-cylinder injection spark ignition internal combustion engine that controls an in-cylinder injection spark ignition internal combustion engine that generates a tumble flow in a cylinder and reinforces the tumble flow with fuel injected near the bottom dead center of the intake stroke during homogeneous combustion. A control device,
Control of a direct injection spark ignition internal combustion engine comprising: fuel property determining means for determining the property of the fuel; and combustion state changing means for changing a combustion state based on the determined property of the fuel. apparatus. 2. The in-cylinder injection according to claim 1, wherein when the fuel is a fuel having a characteristic such that the stoichiometric air-fuel ratio is smaller than that of gasoline, the combustion state changing means retards the ignition timing. -Type spark ignition internal combustion engine control device. 2. The in-cylinder injection system according to claim 1, wherein when the fuel is a fuel having a characteristic such that the stoichiometric air-fuel ratio is smaller than that of gasoline, the combustion state changing means increases the EGR amount. Control device for a spark ignition internal combustion engine.

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