JP2014238039A - Heat release rate waveform preparation device and combustion state diagnostic device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat release rate waveform preparation device and a combustion state diagnostic device for an internal combustion engine that can highly accurately define a combustion state of fuel within a cylinder of the internal combustion engine.SOLUTION: In a diesel engine, when an ideal heat release rate waveform model is prepared relative to each reaction form of fuel injected into a cylinder, as carbon dioxide density that increases along with rise in an EGR rate is higher, reaction speed of the fuel is made lower, so as to prepare the ideal heat release rate waveform model relative to each reaction form. By smoothening and synthesizing the ideal heat release rate waveform model through filter processing, an ideal heat release rate waveform of each reaction form is prepared. By comparing the ideal heat release rate waveform of each reaction with an actual heat release rate waveform that is determined from detected cylinder pressure, whether or not an abnormality occurs is diagnosed.

Description

  The present invention relates to an apparatus for creating a heat release rate waveform of an internal combustion engine such as a diesel engine, and an apparatus for diagnosing an actual combustion state using the created heat release rate waveform.

  As is well known in the art, in a diesel engine (hereinafter sometimes simply referred to as an engine) used as an automobile engine or the like, each control parameter such as a fuel injection amount is corrected according to the engine operating state. In this case, it is desirable to recognize the reaction state of the fuel in the cylinder (hereinafter sometimes referred to as a combustion state) and correct each control parameter accordingly so as to obtain a desired reaction state.

  Thus, as one of the means for correcting each control parameter according to the reaction state of the fuel in the cylinder, the heat generation rate waveform at the time of combustion is obtained, and each heat generation rate waveform is set to an ideal waveform. It is known to correct control parameters (Patent Document 1).

JP 2011-106334 A JP2011-89445A JP 2006-52676 A

  In general, the heat generation rate (heat generation amount per unit rotation angle of the crankshaft) when the fuel reacts depends on whether or not EGR (Exhaust Gas Recirculation) is performed, the EGR rate when EGR is performed, and the like. Change. This is because the heat generation rate is greatly affected by the amount of oxygen in the cylinder.

  In view of this point, the inventors of the present invention have focused on the fact that the ideal heat generation rate waveform can be optimized by defining the heat generation rate based on the oxygen density in the cylinder. By optimizing the ideal heat generation rate waveform in this way, the reliability in diagnosing the combustion state is increased by comparing the ideal heat generation rate waveform with the actual heat generation rate waveform. .

  Furthermore, the inventor of the present invention pays attention to the fact that the ideal heat generation rate waveform cannot be made appropriate by defining the heat generation rate only according to this oxygen density, particularly in a situation where the oxygen density is relatively low. . Then, it has been found that the amount of carbon dioxide in the cylinder greatly affects the heat generation rate. This is presumed to be due to the fact that the presence of carbon dioxide reduces the percentage of oxygen molecules and fuel particles, and this carbon dioxide is a combustion inhibitor.

  Patent Document 2 and Patent Document 3 disclose that the amount of carbon dioxide in a cylinder affects the ignition timing of fuel.

  However, the degree of influence of carbon dioxide on the heat generation rate actually differs depending on the oxygen density in the cylinder, and when considering the influence of the amount of carbon dioxide on the heat generation rate, It is necessary that the incidence is specified. In each of the above-mentioned patent documents, there is no description about that, and only the technical idea of these patent documents cannot properly define the relationship between the amount of carbon dioxide in the cylinder and the heat generation rate. There is a limit to the optimization of the ideal heat generation rate waveform.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a heat release rate waveform of an internal combustion engine capable of defining the combustion state of fuel in a cylinder of the internal combustion engine with high accuracy. An object of the present invention is to provide a creation device and a combustion state diagnosis device.

-Solution principle of the invention-
The solution principle of the present invention taken in order to achieve the above object is to apply the amount of carbon dioxide in addition to the oxygen density as a parameter for defining the heat generation rate waveform, and the heat generation rate according to the amount of carbon dioxide. By defining this, the ideal heat generation rate waveform can be optimized.

-Solution-
Specifically, the present invention is directed to an apparatus that creates a heat release rate waveform of a fuel reaction in an internal combustion engine that burns fuel injected into a cylinder from a fuel injection valve. When creating the ideal heat generation rate waveform of the reaction of the fuel injected from the fuel injection valve to the heat generation rate waveform generating device, the reference heat generation rate defined based on the oxygen density in the cylinder is It is set as the structure which calculates an ideal heat release rate by correct | amending according to the amount of carbon dioxide in the inside.

  The “ideal heat generation rate waveform” here refers to a state in which a fuel injection amount corresponding to the command injection amount, a fuel injection pressure corresponding to the command injection pressure, and a fuel injection period corresponding to the command injection period are secured. It is a heat generation rate waveform that should be theoretically obtained assuming that the combustion efficiency is sufficiently high.

  Based on the specific matter, the ideal heat generation rate is calculated by correcting the reference heat generation rate defined based on the oxygen density in the cylinder according to the amount of carbon dioxide in the cylinder, and based on this ideal heat generation rate. To create an ideal heat release rate waveform. That is, in the present solution, the accuracy is improved by correcting the ideal heat generation rate, which could not be obtained with sufficient accuracy only by the oxygen density, according to the amount of carbon dioxide in the cylinder, which becomes a reaction inhibiting factor, An ideal heat generation rate waveform is created based on the corrected ideal heat generation rate. Thereby, an appropriate ideal heat release rate waveform can be created.

  The “creation of the ideal heat generation rate waveform” in the present invention is not limited to the one that actually draws the ideal heat generation rate waveform. It is a concept that includes a state in which the heat generation amount for each unit rotation angle is defined.

  Specifically, the reaction gradient of the ideal heat release rate waveform defined based on the oxygen density in the cylinder is corrected according to the carbon dioxide density obtained from the amount of carbon dioxide in the cylinder and the cylinder volume. Thus, an ideal heat generation rate waveform is created.

  In this case, the ideal heat generation rate waveform is created by decreasing the reaction gradient of the ideal heat generation rate waveform as the carbon dioxide density increases.

  The higher the carbon dioxide density, the lower the percentage of oxygen molecules and fuel particles. That is, the degree of progress of the reaction in the cylinder is reduced. Therefore, the higher the carbon dioxide density is, the smaller the reaction gradient of the ideal heat generation rate waveform is made to create the ideal heat generation rate waveform. For this reason, the reaction gradient, which is a waveform component specifying the ideal heat generation rate waveform, can be defined with high accuracy, and an appropriate ideal heat generation rate waveform can be created.

  In addition, the degree of influence of the carbon dioxide density on the fuel reaction rate varies depending on the oxygen density. Specifically, the higher the carbon dioxide density, the lower the reaction rate of the fuel, and the lower the oxygen density in the cylinder, the greater the degree of influence of the carbon dioxide density on the reaction rate of the fuel. A waveform is created.

  If the carbon dioxide density in the cylinder increases as the EGR rate rises, etc., part of the oxygen amount in the cylinder will be replaced by the amount of carbon dioxide, and the amount of carbon dioxide will increase by the amount of decrease in the oxygen amount. Will do. That is, the ratio of the amount of carbon dioxide to the amount of oxygen increases while the ratio of the combined amount of oxygen and carbon dioxide to the total amount of gas is maintained constant. For this reason, the carbon dioxide density increases as the oxygen density in the cylinder decreases. In this case, the lower the oxygen density in the cylinder, the more the decrease in the soot rate (the soot rate between oxygen molecules and fuel particles) due to the presence of carbon dioxide, so the influence of the carbon dioxide density on the fuel reaction rate. The rate increases and the rate of decrease in reaction rate with increasing carbon dioxide density increases. Thus, by defining the fuel reaction rate according to the oxygen density and the carbon dioxide density, it is possible to create an appropriate ideal heat generation rate waveform.

  The parameter for calculating the ideal heat generation rate is made different between when the state of the air-fuel mixture in the cylinder is uniform and when the state of the air-fuel mixture in the cylinder is non-uniform. Specifically, when the state of the air-fuel mixture in the cylinder is uniform, the ideal heat generation rate is calculated based on the oxygen density, oxygen excess rate, and carbon dioxide density in the cylinder. On the other hand, when the state of the air-fuel mixture in the cylinder is not uniform, the ideal heat generation rate is calculated based on the oxygen density, oxygen excess rate, carbon dioxide density, and fuel density in the cylinder.

  When the air-fuel mixture in the cylinder is uniform, the fuel density is substantially uniform throughout the cylinder. Therefore, without considering this fuel density, the ideal heat according to the oxygen excess rate throughout the cylinder. It is possible to calculate the incidence. On the other hand, when the state of the air-fuel mixture in the cylinder is not uniform, the fuel density in each combustion field in the cylinder may be different, so that each combustion field (region in the cylinder) is different. It is necessary to calculate the ideal heat generation rate for each combustion field in consideration of the fuel density. Thus, the ideal heat generation rate corresponding to the state of the air-fuel mixture can be appropriately obtained by varying the parameter for calculating the ideal heat generation rate depending on whether the state of the air-fuel mixture in the cylinder is uniform or not. Is possible.

  Specifically, the timing for obtaining the carbon dioxide density is set to the timing at which the piston reaches compression top dead center.

  In this case, since the volume (compression end volume) in the cylinder (particularly in the case of a piston having a cavity on the top surface) is determined in advance, the calculation of the carbon dioxide density can be simplified. The reliability will be increased. As a result, the carbon dioxide density can be calculated with high accuracy, and the ideal heat generation rate waveform can be optimized.

  As a specific method for creating the ideal heat generation rate waveform, the inside of the cylinder is divided into an internal region of a cavity provided in the piston and an external region of the cavity, and the internal region of the cavity and the external region of the cavity are respectively divided. The ideal heat generation rate waveform of the fuel reaction is created, and the ideal heat generation rate waveform for each of these regions is synthesized to create an ideal heat generation rate waveform for the entire cylinder.

  As a result, high reliability can be obtained in the ideal heat generation rate waveform for the entire created cylinder.

  In addition, the ideal heat release rate waveform is created by using an ideal triangle consisting of a starting point of each reaction of the fuel, a reaction rate as a slope, a reaction amount as an area, and a reaction period as a base length. It is created by creating a heat release rate waveform model and smoothing the ideal heat release rate waveform model of each reaction by filtering.

  By creating a heat release rate waveform model that approximates a triangle in this way and creating an ideal heat release rate waveform using this heat release rate waveform model, the calculation process for the creation is simplified. It is possible to reduce the load on the calculation means such as the ECU.

  Specific examples of the apparatus for diagnosing the combustion state using the ideal heat generation rate waveform obtained by the above-described heat generation rate waveform generating apparatus for an internal combustion engine include the following configuration. That is, the ideal heat generation rate waveform is compared with the actual heat generation rate waveform when the fuel actually reacts in the cylinder, and the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform becomes a predetermined amount or more. In this case, it is configured to diagnose that an abnormality has occurred in the fuel reaction.

  The “reaction abnormality” herein is not limited to a reaction abnormality (such as equipment failure) that hinders the operation of the internal combustion engine, but can correct (or learn) the control parameters of the internal combustion engine (for example, This includes the case where there is a deviation in the heat generation rate waveform to such an extent that correction can be made to keep exhaust emission and combustion noise within the limits of regulation.

  By this specific matter, when the actual heat generation rate waveform deviates from the ideal heat generation rate waveform by a predetermined amount or more in the fuel reaction (reaction form), it is diagnosed that the reaction is abnormal. Become. For example, when diagnosis is performed for each of a plurality of reactions, the characteristics (reaction start temperature, reaction rate, etc.) of each fuel reaction are different from each other. By comparing the characteristics of the actual heat release rate waveform (measured), it is possible to identify the reaction in which an abnormality has occurred with high accuracy. For this reason, improvement of diagnostic accuracy can be aimed at. Then, by taking improvement measures (for example, correction of control parameters of the internal combustion engine) for the reaction form diagnosed as abnormal, a control parameter suitable for the reaction form diagnosed as abnormal is selected, The control parameter can be corrected. For this reason, the controllability of the internal combustion engine can be greatly improved.

  Specific operations when it is diagnosed that an abnormality has occurred in the reaction include the following. That is, when there is a reaction in which the deviation of the actual heat generation rate waveform with respect to the ideal heat generation rate waveform is equal to or greater than a predetermined abnormality determination deviation amount, and when it is diagnosed that the reaction is abnormal, When the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform is equal to or less than a predetermined correctable deviation amount, the control parameter of the internal combustion engine is corrected so that the deviation is less than the abnormality determination deviation amount. On the other hand, when the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform exceeds the correctable deviation amount, the internal combustion engine is diagnosed as having a failure.

  In this way, when it is diagnosed that an abnormality has occurred in the reaction, whether or not the abnormality can be resolved is determined based on the deviation amount of the actual heat generation rate waveform from the ideal heat generation rate waveform. I am doing so. For this reason, it is possible to accurately discriminate between a state in which a normal reaction state is obtained by correcting the control parameter and a state in which maintenance such as component replacement is required.

  In addition, as a control parameter when correcting the control parameter of the internal combustion engine so that the deviation is less than the abnormality determination deviation amount, an oxygen amount, a carbon dioxide amount, and a fuel amount in the cylinder are exemplified. The amount of oxygen in the cylinder is determined by the oxygen density and can be adjusted by the EGR rate, the intake air supercharging rate, and the like. The amount of carbon dioxide in the cylinder is determined by the carbon dioxide density and can be adjusted by the EGR rate or the like. Further, the amount of fuel in the cylinder is determined by the fuel density, and can be adjusted by the fuel injection timing, the fuel injection pressure, and the fuel injection amount. On the other hand, an example of diagnosing that a failure has occurred in the internal combustion engine is a case where the deviation of the actual heat generation rate waveform exceeds the correctable deviation amount. In this case, the control parameter of the internal combustion engine Since the correction amount exceeds a predetermined guard value, it is possible to diagnose that a failure has occurred in the internal combustion engine. Specifically, lower limit values are set in advance for the in-cylinder temperature, oxygen density, and fuel density, respectively, and when any of these in-cylinder temperature, oxygen density, or fuel density is below the lower limit value, If the upper limit value of the carbon density is set in advance, and the carbon dioxide density exceeds the upper limit value, it is determined that the correction amount of the control parameter of the internal combustion engine exceeds a predetermined guard value, and the internal combustion engine has failed. It will be diagnosed as occurring.

  Specifically, the usage state of the combustion state diagnosis device for the internal combustion engine includes mounting on a vehicle or mounting on an experimental device.

  In the present invention, the ideal heat generation rate is calculated by correcting the reference heat generation rate defined based on the oxygen density in the cylinder according to the amount of carbon dioxide in the cylinder. It becomes possible to obtain high reliability in the rate waveform. Further, when the abnormality diagnosis of the combustion state is performed using the ideal heat generation rate waveform, the diagnosis accuracy can be improved.

It is a figure which shows schematic structure of the diesel engine which concerns on embodiment, and its control system. It is sectional drawing which shows the combustion chamber of a diesel engine, and its peripheral part. It is a block diagram which shows the structure of control systems, such as ECU. It is a schematic diagram of the intake / exhaust system and the combustion chamber for explaining the outline of the combustion mode in the combustion chamber. It is sectional drawing which shows a combustion chamber at the time of main injection execution, and its peripheral part. It is a top view of a combustion chamber at the time of main injection execution. FIG. 7A is a schematic diagram around the combustion chamber showing a state in which substantially the entire amount of injected fuel is injected toward the cavity inner region, and FIG. 7A shows the fuel in the compression stroke in which the piston moves toward the compression top dead center. FIG. 7B is a diagram showing the time of fuel injection during the expansion stroke in which the piston moves toward the bottom dead center. FIG. 8A is a schematic diagram of the vicinity of the combustion chamber showing a state in which substantially the entire amount of injected fuel is injected toward the region outside the cavity, and FIG. 8A shows the fuel in the compression stroke in which the piston moves toward the compression top dead center. FIG. 8B is a diagram showing the time of fuel injection during the expansion stroke in which the piston moves toward the bottom dead center. FIG. 9A is a schematic diagram of the periphery of the combustion chamber showing a state in which a part of the injected fuel is injected toward the area inside the cavity and the other is injected toward the area outside the cavity. FIG. FIG. 9B is a view showing the time of fuel injection in the expansion stroke in which the piston moves toward the bottom dead center, respectively, during the fuel injection in the compression stroke that moves toward the point. It is a figure which shows the relationship between a crank angle position and the fuel distribution rate in a cavity. It is a figure for demonstrating the calculation method of the fuel distribution rate in a cavity. It is a diagram showing an example of change in each amount of cylinder N ₂ in the gas, O _2, CO ₂ with respect to the change in the EGR rate. It is a figure which shows the example of the heat release rate waveform from which the carbon dioxide density in a cylinder differs mutually. It is a flowchart figure which shows the procedure of a combustion state diagnosis and control parameter correction | amendment. It is a figure which shows an example of a rotational speed correction coefficient map. It is a figure which shows an example of the gradient correction coefficient map for extracting the gradient correction coefficient according to a carbon dioxide density. 17A shows an ideal heat generation rate waveform model. FIG. 17A shows a case where the ideal heat generation rate waveform model is an isosceles triangle, and FIG. 17B shows a case where the ideal heat generation rate waveform model is an unequal triangle. FIG. 18A shows the relationship between the elapsed time and the amount of fuel supplied into the cylinder when fuel is injected from the injector, and FIG. 18B shows the reaction of the fuel injected in each injection period. It is a figure which shows quantity. It is a figure which shows an example of the ideal heat release rate waveform model in each reaction form when one fuel injection is performed to the area | region outside a cavity. It is a figure which shows the ideal heat release rate waveform produced by synthesize | combining each waveform obtained by smoothing the ideal heat release rate waveform model of FIG. 19 by a filter process. It is a figure which shows an example of the ideal heat release rate waveform model in each reaction form when one fuel injection is performed to the area | region in a cavity. It is a figure which shows the ideal heat release rate waveform produced by synthesize | combining each waveform obtained by smoothing the ideal heat release rate waveform model of FIG. 21 by a filter process. This figure shows the ideal heat release rate waveform for the entire cylinder created by combining the ideal heat release rate waveform for the region outside the cavity and the ideal heat release rate waveform for the region inside the cavity. is there. It is a figure which shows an example of an ideal heat release rate waveform (solid line) and an actual heat release rate waveform (a broken line and a dashed-dotted line). FIG. 25A shows the relationship between the oxygen excess rate and the amount of smoke generated when the engine speed changes, and FIG. 25B shows the relationship between the oxygen excess rate and the amount of smoke generated when the carbon dioxide density changes. It is a figure which shows a relationship.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the combustion state diagnosis device according to the present invention is mounted on a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on an automobile. explain.

-Engine configuration-
FIG. 1 is a schematic configuration diagram of a diesel engine 1 (hereinafter simply referred to as an engine) and its control system according to the present embodiment.

  As shown in FIG. 1, the engine 1 according to this embodiment is configured as a diesel engine system having a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7 and the like as main parts.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, an engine fuel passage 27, and the like.

  The supply pump 21 raises the fuel pumped from the fuel tank to a high pressure and then supplies the fuel to the common rail 22 via the engine fuel passage 27. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) high pressure fuel at a predetermined pressure, and distributes the accumulated fuel to the injectors 23, 23,. The injector 23 is a piezo injector provided with a piezoelectric element (piezo element) inside.

  The intake system 6 includes an intake manifold 63 connected to an intake port 15 a formed in the cylinder head 15 (see FIG. 2), and an intake pipe 64 is connected to the intake manifold 63. The intake system 6 is provided with an air cleaner 65, an air flow meter 43, and an intake throttle valve (diesel throttle) 62 in order from the upstream side.

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head 15, and an exhaust pipe 73 is connected to the exhaust manifold 72. The exhaust system 7 is provided with an exhaust purification unit 77. The exhaust purification unit 77 is provided with an NSR (NOx Storage Reduction) catalyst 75 and a DPF (Diesel Particle Filter) 76 as NOx occlusion reduction type catalysts.

  As shown in FIG. 2, the cylinder block 11 is formed with a cylinder bore 12 for each cylinder (four cylinders), and a piston 13 is accommodated in each cylinder bore 12 so as to be slidable in the vertical direction. .

  A combustion chamber 3 is formed above the top surface 13 a of the piston 13. That is, the combustion chamber 3 is defined by the lower surface of the cylinder head 15 attached to the upper portion of the cylinder block 11, the inner wall surface of the cylinder bore 12, and the top surface 13 a of the piston 13. A cavity (concave portion) 13 b is formed in a substantially central portion of the top surface 13 a of the piston 13, and this cavity 13 b also constitutes a part of the combustion chamber 3.

  As the shape of the cavity 13b, the concave dimension is small in the central portion (on the cylinder center line P), and the concave dimension is increased toward the outer peripheral side.

  The piston 13 is connected to a crankshaft that is an engine output shaft by a connecting rod 18. Further, a glow plug 19 is disposed toward the combustion chamber 3.

  The cylinder head 15 is provided with an intake valve 16 for opening and closing an intake port 15a and an exhaust valve 17 for opening and closing an exhaust port 71.

  Further, as shown in FIG. 1, the engine 1 is provided with a supercharger (turbocharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor wheel 53 that are connected via a turbine shaft 51. The turbocharger 5 in the present embodiment is a variable nozzle type turbocharger, and a variable nozzle vane mechanism (not shown) is provided on the turbine wheel 52 side.

  The intake pipe 64 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5.

  Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 8 for appropriately returning a part of the exhaust gas to the intake system 6. The EGR passage 8 is provided with an EGR valve 81 and an EGR cooler 82.

-ECU-
The ECU 100 includes a microcomputer including a CPU, a ROM, a RAM, and the like (not shown) and an input / output circuit. As shown in FIG. 3, the input circuit of the ECU 100 includes a crank position sensor 40, a rail pressure sensor 41, a throttle opening sensor 42, an air flow meter 43, A / F sensors 44a and 44b, exhaust temperature sensors 45a and 45b, a water temperature. A sensor 46, an accelerator opening sensor 47, an intake pressure sensor 48, an intake air temperature sensor 49, an in-cylinder pressure sensor 4A, an outside air temperature sensor 4B, an outside air pressure sensor 4C, and the like are connected. Since the function of each sensor is well known, description thereof is omitted here.

  On the other hand, the output circuit of the ECU 100 is connected to the supply pump 21, the injector 23, the intake throttle valve 62, the EGR valve 81, the variable nozzle vane mechanism 54 of the turbocharger 5, and the like.

  Then, the ECU 100 executes various controls of the engine 1 based on outputs from the various sensors described above, calculated values obtained by arithmetic expressions using the output values, or various maps stored in the ROM. .

  For example, the ECU 100 executes pilot injection (sub-injection) and main injection (main injection) as fuel injection control of the injector 23. Since the functions of the pilot injection and the main injection are well known, description thereof is omitted here.

  The fuel injection pressure when executing the fuel injection is determined by the internal pressure of the common rail 22. As the common rail internal pressure, generally, the target value of the fuel pressure supplied from the common rail 22 to the injector 23, that is, the target rail pressure, increases as the engine load (engine load) increases and the engine speed (engine speed) increases. It will be expensive.

  In addition to the pilot injection and main injection described above, after injection and post injection are performed as necessary. Since the function of these injections is also well-known, explanation here is omitted.

  Further, the ECU 100 controls the opening degree of the EGR valve 81 according to the operating state of the engine 1 to adjust the exhaust gas recirculation amount (EGR amount) toward the intake manifold 63.

-Outline of combustion mode-
Next, the outline of the combustion mode in the combustion chamber 3 in the engine 1 according to the present embodiment will be described.

  As shown in FIG. 4, the gas sucked into the cylinder includes fresh air sucked from the intake pipe 64 and EGR gas sucked from the EGR passage 8.

  The fresh air and EGR gas sucked into the cylinder in this way are sucked into the cylinder as the piston 13 (not shown in FIG. 4) is lowered through the intake valve 16 which is opened in the intake stroke. It becomes in-cylinder gas. This in-cylinder gas is sealed in the cylinder (inside the combustion chamber 3) by closing the intake valve 16 when the valve is closed according to the operating state of the engine 1 (in-cylinder gas confinement state). In the subsequent compression stroke, the piston 13 is compressed as it rises. When the piston 13 reaches the vicinity of the compression top dead center, the injector 23 is opened for a predetermined time by the injection amount control by the ECU 100 described above, so that fuel is directly injected into the combustion chamber 3 (pilot injection or main injection). Run).

  FIG. 5 is a cross-sectional view showing the combustion chamber 3 and its periphery when the main injection is performed, and FIG. 6 is a plan view of the combustion chamber 3 when the fuel is injected (a view showing the upper surface of the piston 13).

  The energy generated by the combustion of the fuel injected in the main injection includes kinetic energy for pushing down the piston 13 toward the bottom dead center, thermal energy for raising the temperature in the combustion chamber 3, the cylinder block 11 and the cylinder head 15. The heat energy is radiated to the outside (for example, cooling water).

  The in-cylinder gas after combustion is discharged to the exhaust port 71 and the exhaust manifold 72 as the piston 13 rises through the exhaust valve 17 that opens in the exhaust stroke, and becomes exhaust gas.

-Fuel injection mode-
Next, the form in the cylinder of the fuel injected from the injector 23 will be described.

  The fuel sprays A, A,... Injected from the injection holes of the injector 23 diffuse in a substantially conical shape. In general, the pilot injection is performed at a crank angle position that is more advanced than the crank angle position at which the piston 13 reaches the compression top dead center, and almost all of the injected fuel is in the region outside the cavity 13b (the top surface of the piston 13). 13a and the lower surface of the cylinder head 15; hereinafter, this space is injected toward the “outside cavity region”). This contributes to preheating of the area outside the cavity.

  Further, depending on the injection period of this pilot injection, fuel is injected toward the region outside the cavity in the first half of the injection period, and in the second half of the injection period, the internal space of the cavity 13b (hereinafter, this space is referred to as “intracavity region”). In some cases, fuel is injected toward the At this time, the area outside the cavity and the area inside the cavity are each preheated.

  Further, the main injection is executed at a crank angle position where the piston 13 reaches the vicinity of the compression top dead center. For example, FIG. 7 (FIG. 7A) is a compression stroke in which the piston 13 moves toward the compression top dead center. In general, as shown in FIG. 7B, the fuel is injected during the expansion stroke in which the piston 13 moves toward the bottom dead center. The whole amount will be injected toward the cavity area.

  Note that the fuel injected by the main injection is not necessarily injected entirely into the cavity region. If early injection is performed or the injection period is long, the injection of the main injection is performed. Depending on the start timing and the injection end timing, some fuel may be injected into the region outside the cavity. This will be specifically described below.

  For example, as shown in FIG. 8A (when fuel is injected during the compression stroke in which the piston 13 moves toward the compression top dead center), the piston 13 advances by a predetermined amount from the crank angle position at which the compression top dead center is reached. When main injection is started in a state where the crank angle position is on the corner side, the fuel injected at the beginning of the injection period of the main injection is injected toward the region outside the cavity. Further, for example, as shown in FIG. 8B (when fuel is injected during the expansion stroke in which the piston 13 moves toward the bottom dead center), a predetermined amount is obtained from the crank angle position at which the piston 13 has reached the compression top dead center. When the main injection is continued until the crank angle position is on the retard side, the fuel injected at the end of the injection period of the main injection is injected toward the outside of the cavity. .

  In addition, at the piston position shown in FIG. 7A, when fuel injection is performed on the advance side of the piston position, a part of the injected fuel is injected toward the region outside the cavity. Therefore, the piston position shown in FIG. 7A can be called an intra-cavity injection advance limit. Further, at the piston position shown in FIG. 7 (b), when fuel injection is performed on the retard side from the piston position, a part of the injected fuel is injected toward the region outside the cavity. Therefore, the piston position shown in FIG. 7B can be called an intra-cavity injection retardation limit.

  Further, at the piston position shown in FIG. 8A, when fuel injection is performed on the retard side from the piston position, a part of the injected fuel is injected toward the cavity inner region. Therefore, the piston position shown in FIG. 8A can be called an out-cavity injection retardation limit. Further, at the piston position shown in FIG. 8 (b), when fuel injection is performed on the advance side of the piston position, a part of the injected fuel is injected toward the cavity inner region. Therefore, the piston position shown in FIG. 8B can be referred to as an outside-cavity injection advance limit.

  The crank angle position corresponding to each limit described above can be defined in advance by the engine specifications, the spray angle of fuel injected from the injector 23, and the like. As an example, the outside-cavity injection retardation limit (FIG. 8A) is the crank angle at a position of 28 ° CA before compression top dead center, and the in-cavity injection advance limit (FIG. 7A) is the crank angle. The position is 18 ° CA before compression top dead center. Further, the injection delay limit in the cavity (FIG. 7B) is a position at 18 ° CA after compression top dead center in the crank angle, and the injection advance limit in the cavity (FIG. 8B) is compressed at the crank angle. The position is 28 ° CA after top dead center. These values are not limited to this.

  When fuel injection is performed only during the period between the intra-cavity injection advance limit (FIG. 7A) and the intra-cavity injection retard limit (FIG. 7B), Substantially the entire amount is injected toward the cavity region. Further, when the fuel injection is performed in a period on the advance side of the outside-cavity injection delay limit (FIG. 8A), or more retarded than the outside-cavity injection advance limit (FIG. 8B). When fuel injection is performed during this period, the fuel injected during that period is injected toward the region outside the cavity.

  Further, for example, as shown in FIG. 9A (when the fuel is injected in the compression stroke in which the piston 13 moves toward the compression top dead center), from the outside-cavity injection delay limit (FIG. 8A), When fuel injection is performed over the injection advance limit (FIG. 7 (a)), for example, in FIG. 9 (b) (at the time of fuel injection in the expansion stroke in which the piston 13 moves toward the bottom dead center). As shown, when fuel injection is performed from the intra-cavity injection retardation limit (FIG. 7B) to the outside-cavity injection advance limit (FIG. 8B), a part of the injected fuel is It will be injected toward the area inside the cavity, and the other will be injected toward the area outside the cavity. That is, fuel is injected separately into the cavity inner region and the cavity outer region.

  In this way, when the fuel is sprayed into the area outside the cavity and the area inside the cavity, in the situation where the amount of fuel existing in each area does not exceed the predetermined amount, the spray of each area and the amount of burned gas are large. The part stays in the jetted area and has little amount to flow into the other area. For this reason, each combustion of the area | region outside a cavity and the area | region in a cavity can be handled separately.

−Calculation of in-cylinder environmental parameters−
When creating an ideal heat release rate waveform used for the combustion state diagnosis described later, it is necessary to define the fuel reaction start timing, reaction rate, and reaction amount. And in order to prescribe | regulate these waveform components (reaction start time, reaction rate, reaction amount), it is necessary to obtain | require the fuel density and oxygen density in a cylinder. In this embodiment, in addition to the fuel density and oxygen density, the carbon dioxide density in the cylinder is obtained, and the ideal heat release rate waveform is created by correcting the heat release rate based on the carbon dioxide density. I am doing so. In other words, the ideal heat generation rate is calculated by correcting the reference heat generation rate defined based on the oxygen density in the cylinder according to the carbon dioxide density in the cylinder (a value correlated with the amount of carbon dioxide). An ideal heat generation rate waveform is created based on the corrected ideal heat generation rate.

  In addition, when the fuel density in each of the in-cavity region and the out-of-cavity region is different from each other, the fuel density in each of the in-cavity region and the out-cavity region is individually obtained. An ideal heat generation rate waveform in each region is created based on the density and the carbon dioxide density. In addition, when the oxygen excess rate in a cylinder is required, it is possible to obtain the oxygen excess rate from the fuel density and the oxygen density. This oxygen excess rate is a parameter used particularly when predicting the amount of smoke generated. Details will be described later.

  Hereinafter, a method of calculating these in-cylinder environmental parameters (fuel density, oxygen density, carbon dioxide density, oxygen excess rate) will be described. In the following, the region where the fuel injection is performed out of the region inside the cavity and the region outside the cavity will be referred to as a “target region” (if the fuel injection is performed in one region, this one region) Corresponds to the target area, and both areas correspond to the target area when fuel injection is performed in both areas).

(Fuel density)
First, a method for obtaining the fuel density in the cylinder will be described.

  Here, when the state of the air-fuel mixture in the cylinder is uniform, that is, when the fuel density in each of the in-cavity region and the outer-cavity region is substantially the same, the state of the air-fuel mixture in the cylinder is not uniform. The case, that is, the case where the fuel density of the in-cavity region and the out-cavity region is different from each other will be described. The determination of whether or not the state of the air-fuel mixture in the cylinder is uniform is made based on the fuel density obtained from the fuel amount in each region calculated based on the total fuel distribution ratio in the cavity and the stroke volume in each region. Based on.

<When the state of the air-fuel mixture is uniform>
When the state of the air-fuel mixture in the cylinder is uniform, the fuel density ρfuel is calculated by the following equation (1) or equation (2).

Fuel density ρfuel = fuel injection amount / stroke volume at start of reaction (1)
Fuel density ρfuel = fuel injection amount / stroke volume at the start of fuel injection (2)
Here, the fuel injection amount is a fuel amount injected from the injector 23 (for example, a fuel amount in main injection). This fuel injection amount can be calculated from the fuel injection pressure detected by the rail pressure sensor 41 and the valve opening period (command injection period) of the injector 23. The stroke volume at the start of the reaction is the in-cylinder volume (the sum of the volume in the cavity area and the volume in the outside cavity area) when the in-cylinder temperature reaches the reaction temperature described later. The relationship between the in-cylinder temperature and the in-cylinder volume is based on the outside air temperature detected by the outside air temperature sensor 4B, the compression ratio, the amount of preheating in the cylinder (the amount of preheating by pilot injection, etc.), etc. as parameters. It is prescribed. The reaction start time, reaction rate, and reaction amount for each fuel reaction (vaporization reaction, low-temperature oxidation reaction, thermal decomposition reaction, high-temperature oxidation reaction by premixed combustion, and high-temperature oxidation reaction by diffusion combustion) are the fuel density at the time of the reaction. It changes according to. For this reason, in order to obtain the reaction start time, reaction rate, and reaction amount in each reaction, it is necessary to individually specify the fuel density at the time of the reaction. In the present embodiment, the calculation timing of the fuel density ρfuel corresponding to each reaction of fuel is set, and the fuel density ρfuel corresponding to each reaction can be individually specified using the stroke volume at this timing. I have to. The stroke volume at the start of fuel injection is the in-cylinder volume at the time when fuel injection from the injector 23 is started (when the fuel injection command signal is transmitted from the ECU 100). Since the in-cylinder volume is determined according to the crank angle position, the in-cylinder volume can be obtained based on the crank angle position at the time when fuel injection from the injector 23 is started.

<When the air-fuel mixture is uneven>
If the air-fuel mixture in the cylinder is not uniform, the amount of fuel present in each of the cavity region and the cavity region is calculated, and the fuel amount is calculated as the volume of the target region (stroke volume) or The fuel density in each region is calculated by dividing by the volume of the target region at the start of fuel injection.

  Hereinafter, a method for calculating the amount of fuel existing in each of the cavity inner region and the outer cavity region will be described.

  FIG. 10 shows the relationship between the crank angle position and the ratio of the injection amount to the in-cavity region with respect to the fuel amount injected from the injector 23 at each crank angle position (hereinafter referred to as “in-cavity fuel distribution ratio”). FIG. In FIG. 10, the horizontal axis is the crank angle, and the vertical axis is the intra-cavity fuel distribution rate.

  The crank angle position α in FIG. 10 corresponds to the piston position of the outside-cavity injection delay limit (FIG. 8A). The crank angle position β in FIG. 10 corresponds to the piston position of the in-cavity injection advance limit (FIG. 7A). Further, the crank angle position γ in FIG. 10 corresponds to the piston position of the intra-cavity injection retardation limit (FIG. 7B). Further, the crank angle position δ in FIG. 10 corresponds to the piston position of the outside-cavity injection advance limit (FIG. 8B).

  As shown in FIG. 10, when the fuel injection timing from the injector 23 is on the advance side with respect to the crank angle position α in the figure, or on the retard side with respect to the crank angle position δ in the figure. Since almost all of the injected fuel is injected toward the region outside the cavity, the fuel distribution rate in the cavity becomes “0”.

  Further, when the fuel injection timing from the injector 23 is between the crank angle positions β and γ in the figure, almost the entire amount of the injected fuel is injected toward the in-cavity region. The internal fuel distribution rate is “1”.

  Further, when the fuel injection timing from the injector 23 is between the crank angle positions α and β in the drawing, or between the crank angle positions γ and δ in the drawing, the injection from the injector 23 is performed. The fuel thus injected is divided into an area outside the cavity and an area inside the cavity, so that the fuel distribution ratio in the cavity becomes a value between “0” and “1” according to the fuel injection timing.

  In the following description, a period on the more advanced side than the crank angle position α is a first period, a period between the crank angle positions α and β is a second period, and a period between the crank angle positions β and γ. A period is referred to as a third period, a period between the crank angle positions γ and δ is referred to as a fourth period, and a period retarded from the crank angle position δ is referred to as a fifth period.

  In order to obtain the amount of fuel in each of the in-cavity region and the out-cavity region, it is necessary to obtain the fuel distribution ratio in each region with respect to the total fuel amount injected from the injector 23. Hereinafter, the ratio of the fuel amount in the in-cavity region to the total fuel amount injected from the injector 23 is referred to as “in-cavity region total fuel distribution ratio”, and the ratio of the fuel amount in the region outside the cavity to the total fuel amount injected from the injector 23 is The ratio is referred to as “outside cavity region total fuel distribution ratio”.

  As described above, when the fuel injection period from the injector 23 is the third period, the fuel distribution ratio in the cavity is “1”. Therefore, the ratio of the fuel injection period in the third period to the total fuel injection period Can be calculated as the third period (the ratio of the fuel injection period in the third period to the total fuel injection period × “1”) of the total fuel distribution ratio in the cavity.

  On the other hand, since the fuel distribution rate in the cavity changes during the second period, a representative value of the fuel distribution ratio in the cavity during this period is obtained, and the fuel in the second period with respect to the total fuel injection period is obtained. The ratio of the injection period is multiplied by a representative value of the fuel distribution ratio in the cavity, and the second period of the total fuel distribution ratio in the cavity (the fuel injection period in the second period with respect to the total fuel injection period). It is necessary to calculate (ratio × representative value of intra-cavity fuel distribution ratio in the second period). The same applies to the fourth period.

  Hereinafter, a method for obtaining the representative value of the fuel distribution ratio in the cavity will be specifically described with reference to FIG. FIG. 11 shows the relationship between the crank angle position and the fuel distribution ratio in the cavity when fuel is injected during the predetermined period in the second period.

  The waveform shown in FIG. 11 is obtained by simplifying the change in the fuel distribution ratio in the cavity with respect to the change in the crank angle position by the Wiebe function, and the ACO at the beginning of the second period is set to “0 (X = 0)”. The fuel distribution rate in the cavity at the timing of “ACO = 0” is set to “0”, and the ACI at the end of the second period is set to “1 (X = 1)”. The terms a and m, which are the shape parameters of the Wiebe function, are set so that the fuel distribution rate in the cavity at the timing “1” is “1”. For example, a = 8.06 and m = 2.54 are set.

  Consider a case where fuel injection is started at the timing Ais in the drawing during the second period and the fuel injection is ended at the timing Aie.

  In this case, the length Xis of the period from the time when the crank angle reaches the angular position α (ACO = 0) to the time when the fuel injection starts, and the fuel injection ends from the time when the crank angle reaches the angular position α. The length Xie of the period up to this point is given by the following equations (3) and (4).

Xis = (Ais-ACO) / (ACI-ACO) (3)
Xie = (Aie-ACO) / (ACI-ACO) (4)
In this case, the representative value f (X) of the fuel distribution ratio in the cavity is calculated by the following equation (5).

f (X) = {f (Xis) + f (Xie)} / 2 (5)
Here, f (Xis) is the fuel distribution rate in the cavity at the timing Ais and corresponds to Yis in the figure. Further, f (Xie) is the fuel distribution rate in the cavity at the timing Aie and corresponds to Yie in the drawing.

  In this way, it is possible to calculate the representative value f (X) of the intra-cavity fuel distribution ratio when the fuel is separately injected into the outer cavity region and the inner cavity region.

  Actually, fuel injection may be performed not only in the second period but also in each of the first, third, fourth, and fifth periods. Therefore, the fuel injection in these periods is also taken into consideration. Therefore, it is necessary to calculate the total fuel distribution ratio (the total fuel distribution ratio in the cavity) for the entire fuel injection period.

  For this reason, first, the fuel injection rate ΔAinj (i) in each period i (i = 1 to 5) is obtained by the following equation (6).

ΔAinj (i) = period X (i) / total fuel injection period (6)
“I” in the formula (6) is a value corresponding to the target periods 1 to 5.

  That is, the ratio of the injection period in each of the first to fifth periods to the total fuel injection period from the injector 23 is calculated as the fuel injection rate (ΔAinj (1) to ΔAinj (5)) in each period.

  Further, the intra-cavity fuel distribution ratio in the first period and the fifth period is “0”, and the intra-cavity fuel distribution ratio in the third period is “1” (see FIG. 10). For this reason, the fuel injection rates (ΔAinj (1), ΔAinj (5)) in the first period and the fifth period do not contribute to the total intra-cavity region fuel distribution ratio, and the fuel injection rates (ΔAinj ( In 3)), the total amount of injected fuel contributes to the total fuel distribution ratio in the cavity region (which affects the total fuel distribution ratio in the cavity region). Further, the intra-cavity fuel distribution ratios (ΔAinj (2), ΔAinj (4)) in the second period and the fourth period vary depending on the fuel injection period (length of the fuel injection period) in each period.

For this reason, the in-cavity area total fuel distribution ratio for the entire period of fuel injection can be obtained by the following equation (7).
Total fuel distribution ratio in the cavity = ΔAinj (2) × f (X (2)) + ΔAinj (3)
+ ΔAinj (4) × f (X (4)) (7)
As a result, the total fuel distribution ratio in the cavity region for the entire fuel injection period is calculated.

  Then, by multiplying the total fuel injection amount from the injector 23 by this total intra-cavity region fuel distribution rate, the amount of fuel existing in the intra-cavity region can be calculated. Further, if the total fuel distribution ratio outside the cavity is obtained from the total fuel distribution ratio within the cavity (1−total fuel distribution ratio within the cavity), the total fuel injection rate is multiplied by the total fuel injection ratio outside the cavity. The amount of fuel existing in the area outside the cavity can be calculated. The amount of fuel existing in the region outside the cavity can also be calculated by subtracting the amount of fuel present in the region inside the cavity from the total fuel injection amount.

  After calculating the fuel amount existing in the cavity inner region and the fuel amount existing in the outer cavity region in this way, the fuel density ρfuel is calculated by the following equation (8) or equation (9).

Fuel density ρfuel = fuel amount in target area / volume of target area at start of reaction (8)
Fuel density ρfuel = fuel amount in the target area / volume of the target area at the start of fuel injection (9)
Here, when the target region is the intracavity region, the volume of the target region is constant regardless of the position of the piston 13. On the other hand, when the target area is set as the area outside the cavity, the volume of the target area changes according to the position of the piston 13. In this case, since the volume of the area outside the cavity is determined according to the crank angle position, the volume of the area outside the cavity (volume of the target area) can be obtained based on the crank angle position.

  Further, the corrected final fuel density may be obtained by performing the following correction on the fuel density ρfuel calculated by any of the formulas (1), (2), (8), and (9). . Specifically, parameters for varying the fuel density ρfuel include fuel injection pressure PCR (variation in fuel dispersion due to fuel injection pressure), fuel injection amount Fq (variation in fuel flight distance due to fuel injection amount), fuel injection timing. Ainj and in-cylinder pressure Pcyl are listed. Therefore, a correction coefficient is obtained by an arithmetic expression F (PCR, Fq, Ainj, Pcyl) using the fuel injection pressure PCR, the fuel injection amount Fq, the fuel injection timing Ainj, and the in-cylinder pressure Pcyl as variables. The final fuel density is obtained by multiplying the fuel density ρfuel (see the following formula (10)).

Final fuel density = ρfuel × F (PCR, Fq, Ainj, Pcyl) (10)
The arithmetic expression F (PCR, Fq, Ainj, Pcyl) is based on experiments and simulations in advance, and the degree of influence of the fuel injection pressure PCR, fuel injection amount Fq, fuel injection timing Ainj, and in-cylinder pressure Pcyl on the fuel density ρfuel. It is prescribed in consideration of

  Further, the correction coefficient is not limited to one that reflects all of the fuel injection pressure PCR, the fuel injection amount Fq, the fuel injection timing Ainj, and the in-cylinder pressure Pcyl. For example, the final fuel density may be obtained by obtaining a correction coefficient reflecting two or three parameters selected from these four parameters. Note that the following formula (11) may be used as the calculation formula F (PCR) using the fuel injection pressure PCR as a variable.

F (PCR) = A × (PCR / reference PCR) + B (11)
Here, the reference PCR is a pressure serving as a reference for the common rail internal pressure, and is appropriately set. A and B are constants set in advance based on experiments and simulations.

  Which of the formulas (1), (2), (8), (9), and (10) to use the fuel density ρfuel calculated depends on the simplification of the calculation process and the reliability of the fuel density ρfuel. It is appropriately selected in consideration of the high nature.

(Oxygen density)
Next, a method for obtaining the oxygen density in the cylinder will be described.

  The oxygen density is an index representing the oxygen supply capacity (temporal oxygen supply capacity) for the fuel, whether or not EGR is performed, the EGR amount (including the residual gas amount in the cylinder (so-called internal EGR amount)), It fluctuates according to the altitude of the road that is running. And if this oxygen density changes, it will affect the reaction start time, reaction rate, and reaction amount in each reaction of fuel. That is, the lower the oxygen density, the more the reaction start timing shifts to the retarded side, the reaction rate becomes lower (the reaction becomes slower), and the reaction amount decreases. In particular, the effects of low-temperature oxidation reaction, thermal decomposition reaction, and high-temperature oxidation reaction among fuel reactions appear.

  Here, even if fuel multistage injection (for example, pilot injection and main injection) is performed, the amount of oxygen consumed by combustion of fuel injected by pilot injection or the like is very small compared to the amount of oxygen in the entire cylinder. (Even if oxygen is consumed only in one region (for example, the region outside the cavity), the consumption amount is very small), so it is assumed that the oxygen density in the cavity region and the region outside the cavity are the same. A case where the oxygen density is obtained for the entire cylinder will be described.

The oxygen density ρo ₂ for the entire cylinder is obtained by the following formula (12) or formula (13).

Oxygen density ρo ₂ = Oxygen amount in intake air / clearance volume (12)
Oxygen density ρo ₂ = Oxygen amount in intake / stroke volume at start of reaction (13)
Here, the oxygen amount (mass) in the intake air can be calculated from the intake air amount detected by the air flow meter 43, the outside air temperature detected by the outside air temperature sensor 4B, the outside air pressure detected by the outside air pressure sensor 4C, and the like. An example of the clearance volume is a stroke volume (compression end volume) when the piston 13 reaches the compression top dead center. According to this, since the gap volume can be handled as a fixed value, the calculation of the oxygen density ρo ₂ can be simplified, and the reliability thereof is increased. The gap volume used in Expression (12) is not limited to this.

When the oxygen density ρo ₂ is calculated by the equation (13), the reaction start timing, reaction rate, and reaction amount in each reaction of the fuel change according to the oxygen density at the time of the reaction. For this reason, in order to obtain the reaction start time, reaction rate, and reaction amount in each reaction, it is necessary to individually specify the oxygen density during the reaction. In this embodiment, the calculation timing of the oxygen density ρo ₂ corresponding to each reaction of the fuel is set, and the oxygen density ρo ₂ corresponding to each reaction is specified individually using the stroke volume at this timing. I can do it.

Which of the formulas (12) and (13) is used as the oxygen density ρo ₂ is appropriately determined in consideration of the simplification of the arithmetic processing and the high reliability of the oxygen density ρo _2. Will be selected.

When EGR is not performed, the oxygen amount is determined in accordance with the total gas amount, so that the oxygen density ρo ₂ can be substituted with the total gas amount.

By calculating the oxygen density .rho.o ₂ In this way, it is possible to calculate the oxygen excess ratio .lamda.o ₂ in the cylinder by utilizing this oxygen density .rho.o ₂ and the fuel density Rofuel. This oxygen excess rate λo ₂ is an index representing the oxygen supply capacity (quantitative oxygen supply capacity), and is calculated by the following equation (14).

Oxygen excess rate λo ₂ = oxygen density ρo ₂ / fuel density ρfuel (14)
(Carbon dioxide density)
Next, a method for obtaining the carbon dioxide density in the cylinder will be described.

  Carbon dioxide is a reaction obstacle (combustion inhibitor). Further, the carbon dioxide density is an index representing the oxygen supply capacity for fuel, and fluctuates depending on whether or not EGR is performed and the amount of EGR (including the amount of residual gas in the cylinder (so-called internal EGR amount)). It is. And if this carbon dioxide density changes, it will affect the reaction rate in each reaction of fuel. That is, the higher the carbon dioxide density, the lower the reaction rate (the reaction becomes slower). In particular, when the oxygen density is low, the influence of the carbon dioxide density on the reaction rate becomes large. Although this reduction in reaction rate leads to a reduction in the amount of NOx in the exhaust gas, there is a possibility of promoting the production of smoke and CO.

  Carbon dioxide density may affect the reaction start time and reaction amount in each reaction of the fuel, but since it has a large effect on the reaction rate, the effect on the reaction rate is described below. Will be described.

FIG. 12 is a diagram illustrating an example of changes in the amounts of N ₂ , O ₂ , and CO _{2 in} the in-cylinder gas with respect to changes in the EGR rate. As shown in FIG. 12, the gas amount in the cylinder decreases as the EGR rate increases, but the ratio of the N ₂ amount to the total gas amount does not change (for example, is maintained at 77%). Only the ratio of the amount of O _{2 and the} amount of CO _2, which are the components, changes. That is, when the EGR rate is “0”, since the exhaust gas does not recirculate, the ratio of the O ₂ amount to the total gas amount is about 23%, whereas the EGR rate increases. Then, a part of the O ₂ amount is replaced with the CO ₂ amount (replaced with the refluxed CO ₂ amount), and the CO ₂ amount ratio is increased by the decrease in the O ₂ amount ratio. . That is, the ratio of the CO ₂ amount to the O ₂ amount increases while the ratio of the combined amount of the O ₂ amount and the CO ₂ amount to the total gas amount is maintained at about 23%.

  Here, even if fuel multi-stage injection (for example, pilot injection and main injection) is performed, the amount of carbon dioxide generated due to combustion of fuel injected by pilot injection or the like is very small (assuming one Even if carbon dioxide is generated only in the region (for example, the region outside the cavity), the generated amount is very small), and it is assumed that the carbon dioxide density in the cavity region and the region outside the cavity are the same. The case where the carbon dioxide density is determined for the whole will be described.

The carbon dioxide density ρco ₂ for the entire cylinder is obtained by the following equation (15) or equation (16).

Carbon dioxide density ρco ₂ = carbon dioxide amount in cylinder / gap volume (15)
Carbon dioxide density ρco ₂ = carbon dioxide amount in cylinder / stroke volume at start of reaction (16)
Here, the amount (mass) of carbon dioxide in the cylinder can be calculated from the engine rotation speed, the EGR rate, and the like calculated based on the output from the crank position sensor 40. An example of the clearance volume is a stroke volume (compression end volume) when the piston 13 reaches the compression top dead center. According to this, since the gap volume can be handled as a fixed value, the calculation of the carbon dioxide density ρco ₂ can be simplified, and the reliability thereof can be improved. The gap volume used in Equation (15) is not limited to this.

When the carbon dioxide density ρco ₂ is calculated by the above equation (16), the reaction rate in each reaction of the fuel changes according to the carbon dioxide density at the time of the reaction. For this reason, in order to obtain | require the reaction rate in each reaction, it is necessary to specify the carbon dioxide density at the time of the reaction separately. In this embodiment, the calculation timing of the carbon dioxide density ρco ₂ corresponding to each reaction of the fuel is set, and the stroke volume at this timing is used to individually calculate the carbon dioxide density ρco ₂ corresponding to each reaction. Can be specified.

Formula (15), (16) or to employ a carbon dioxide density Roco ₂ calculated in any expression of, in consideration of the reliability of the height of the simplification of the processing and carbon dioxide density Roco ₂ Will be selected accordingly.

  FIG. 13 shows an example of the shape change of the heat release rate waveform having the same fuel injection mode (injection timing, injection pressure, and injection amount) and different carbon dioxide densities. The density of carbon dioxide increases in the order of FIGS. 13 (a), (b), (c), and (d).

  As is clear from these figures, as the carbon dioxide density increases, the reaction rate of the fuel decreases (the reaction slows down), its maximum value (peak value) decreases, and the reaction period becomes longer. . As described above, the carbon dioxide density in the cylinder has a great influence on the reaction rate of the fuel, and as a result, it is a factor that greatly changes the heat release rate waveform.

In the case where the EGR rate is relatively low and the influence of the carbon dioxide distribution is relatively small, the carbon dioxide density ρco ₂ can be substituted by the EGR rate.

(About nitrogen)
Nitrogen is present in the intake air. This nitrogen accounts for about 77% of the atmosphere. And the relationship of the gas composition in a cylinder in the case where EGR is not implemented and the case where it is implemented can be prescribed | regulated like the following formula | equation (17) from FIG.

N ₂ : O ₂ = N ₂ : (O ₂ + CO ₂ ) (17)
The left side of the equation (17) represents the gas composition in the cylinder when EGR is not performed, and the right side represents the gas composition in the cylinder when EGR is performed.

  Nitrogen also becomes a reaction obstacle to fuel, like carbon dioxide, and inhibits the oxidation reaction of carbon in fuel, but the degree of inhibition is the amount of nitrogen in the total gas amount even if the EGR rate increases. Since the ratio is constant, it does not change. In other words, even if the total gas amount in the cylinder changes, the ratio of nitrogen in the total gas amount is constant, so the degree of inhibition of the fuel reaction remains unchanged even if the EGR rate changes. For this reason, unlike the carbon dioxide density in which the ratio in the total gas amount changes according to the change in the EGR rate, the nitrogen density can be excluded from the combustion evaluation index.

  For this reason, in this embodiment, the ideal heat generation rate waveform is created by treating the fuel density, oxygen density, oxygen excess rate, and carbon dioxide density as combustion evaluation indices.

  More specifically, when the state of the air-fuel mixture in the cylinder is uniform, the fuel density is substantially uniform throughout the cylinder, so that the oxygen in the entire cylinder can be considered without considering this fuel density. It is possible to calculate the ideal heat generation rate according to the excess rate. For this reason, when the state of the air-fuel mixture in the cylinder is uniform, the ideal heat generation rate is calculated based on the oxygen density, oxygen excess rate, and carbon dioxide density in the cylinder. On the other hand, if the air-fuel mixture in the cylinder is not uniform, the fuel density in the cavity area and the area outside the cavity may be different from each other. In addition, it is necessary to calculate an ideal heat generation rate for each of these regions. For this reason, when the state of the air-fuel mixture in the cylinder is not uniform, the ideal heat generation rate is calculated based on the oxygen density, oxygen excess rate, carbon dioxide density, and fuel density in the cylinder.

−Creation of heat release rate waveform, combustion state diagnosis, and control parameter correction−
Next, according to the creation of the heat release rate waveform (creation of the ideal heat release rate waveform), the combustion state diagnosis (diagnosis of each reaction mode of the fuel in the cylinder), and the diagnosis result, which are the features of this embodiment The control parameter correction executed in this way will be described. In the following description, the case where the state of the air-fuel mixture in the cylinder is non-uniform, that is, the case where the fuel density in the in-cavity region and the out-cavity region is different from each other will be described as an example.

  In the generation of the heat generation rate waveform, the combustion state diagnosis, and the correction of the control parameter, as shown in FIG. 14, (1) generation of an ideal heat generation rate waveform and (2) generation of an actual heat generation rate waveform (3) The combustion state diagnosis is performed by comparing the ideal heat generation rate waveform and the actual heat generation rate waveform. (4) The control parameters of the engine 1 are corrected according to the result of the combustion state diagnosis. All of the configurations for performing the operations (1) to (4) may be mounted (implemented) on the vehicle, or only the operation (1) is performed by a laboratory or the like, and the result (creation) The ideal heat generation rate waveform) is stored in the ROM, and the configuration for performing the operations (2) to (4) may be mounted on the vehicle.

  In the present embodiment, the inside of the cylinder is divided into the cavity inner region and the cavity outer region, and the combustion state in each is individually defined. For this reason, in the creation of the ideal heat generation rate waveform (1), the creation of the ideal heat generation rate waveform for the region inside the cavity and the creation of the ideal heat generation rate waveform for the region outside the cavity are individually performed. The ideal heat generation rate waveform (synthesized ideal heat generation rate waveform) for the entire cylinder is created by synthesizing these ideal heat generation rate waveforms.

  The feature of this embodiment is that, when the ideal heat release rate waveform is created for each of the in-cavity region and the out-cavity region, as described above, in addition to the oxygen density, fuel density, and oxygen excess rate in the cylinder, The carbon density is used.

  In the combustion state diagnosis (3), the combustion state diagnosis is performed by comparing the ideal heat generation rate waveform and the actual heat generation rate waveform for the entire cylinder.

  More specifically, in the creation of the ideal heat generation rate waveform, (1-A) division of reaction region, (1-B) separation of fuel reaction form, (1-C) each separated reaction Creation of ideal heat generation rate waveform model for each form, (1-D) generation of ideal heat generation rate waveform by filtering (filtering) of ideal heat generation rate waveform model, and synthesis of ideal heat generation rate waveform are sequentially performed. .

  Each operation will be specifically described below.

(1) Creation of ideal heat release rate waveform The creation of the ideal heat release rate waveform will be described. First, an outline of creating an ideal heat generation rate waveform will be described.

  The rate-limiting conditions for the reaction (chemical reaction, etc.) of the fuel injected from the injector 23 into the target region include the temperature in the target region, the oxygen amount in the target region (a value correlated with the oxygen density in the target region), the target region The amount of internal fuel (a value that has a correlation with the fuel density in the target region) and the fuel distribution in the target region are listed. Among these, the order of low degree of freedom of control is the order of the temperature in the target region, the oxygen amount in the target region, the fuel amount in the target region, and the fuel distribution in the target region.

  That is, the temperature in the target region is substantially determined by the intake air temperature and the compression ratio of the engine 1 in the stage before the fuel reacts, and the degree of freedom of control is the lowest. In addition, the temperature in the target region also varies depending on the amount of preheating due to the combustion of the fuel when fuel injection is performed in advance (for example, when fuel injection for preheating is performed). Further, since the oxygen amount (oxygen density) in the target area can be adjusted by the opening degree of the intake throttle valve 62 and the opening degree of the EGR valve 81, the degree of freedom of control is higher than the temperature in the target area. Further, the oxygen amount in the target region also varies depending on the supercharging rate by the turbocharger 5. In addition, since the fuel amount (fuel density) in the target region can be adjusted by controlling the fuel injection pressure (common rail pressure) by the supply pump 21 and controlling the injection period of each of the multistage injections of fuel from the injector 23, the target region The degree of freedom of control is high compared to the amount of oxygen inside. Further, since the fuel distribution in the target region can be adjusted by controlling the fuel injection pressure and the injection period of each of the multistage fuel injections, the degree of freedom in control is high.

  In the present embodiment, on the condition that the warm-up operation of the engine 1 is completed and the outside air temperature is equal to or higher than a predetermined temperature (for example, 0 ° C.), the reaction state of the fuel in ascending order of the degree of freedom of control. The priority of the condition for determining the is set high. Here, the quantitative conditions of the target region temperature, the target region oxygen amount, and the target region fuel amount are set to have a higher priority than the target region fuel distribution. That is, the start timing (reaction start timing) of each reaction of the fuel is determined using the temperature in the target region as an axis. That is, the reference temperature arrival angle (crank angle position at the reaction start timing of each reaction mode) is determined from the temperature in the target region (compressed gas temperature in the target region). In the present embodiment, when determining the start time of each reaction, the start time is corrected according to the oxygen density.

  Then, based on this reaction start time (reaction start time corrected by the oxygen density) as a base point, a reference value for the reaction rate and the reaction amount is obtained, respectively, and based on the oxygen density, a reference value for the reaction rate and the reaction amount is obtained. Find the correction amount. Further, a correction amount for the reaction rate is obtained based on the carbon dioxide density. Corrections based on these correction amounts are performed to determine the reaction rate, reaction amount, and reaction period, and an ideal heat release rate waveform model is created for the target region for each reaction mode.

  Specifically, as the oxygen density decreases, the reaction start timing shifts to the retard side, the reaction rate decreases (the reaction becomes slow), and the reaction amount decreases. In addition, the degree of influence of the oxygen density on the reaction start timing, reaction rate, and reaction amount is different. Furthermore, fuel reactions include vaporization, low-temperature oxidation, thermal decomposition, high-temperature oxidation by premixed combustion, and high-temperature oxidation by diffusion combustion, but the degree of influence of oxygen density on these reactions is also different. .

  Also, the higher the carbon dioxide density, the lower the reaction rate (the reaction becomes slower). Further, the degree of influence on the reaction rate by the carbon dioxide density varies depending on the oxygen density. Specifically, the lower the oxygen density, the greater the degree of influence of the carbon dioxide density on the reaction rate. That is, the lower the oxygen density, the greater the degree of decrease in the reaction rate associated with the higher carbon dioxide density. Details will be described later.

  As described above, the reaction rate, reaction amount, and reaction period of each of the plurality of reaction forms of the fuel injected into the target region are set as the temperature in the target region (the gas temperature in the target region that determines the reaction start timing), the fuel composition ( The ideal heat release rate waveform model for each reaction is created by calculation according to the oxygen density and carbon dioxide density in the target region. That is, when fuel injection is performed in one of the cavity inner region and the outer cavity region, an ideal heat release rate waveform model is created for this one region (target region), and the fuel is generated in both regions. When the injection is performed, ideal heat generation rate waveform models are individually created for these two regions (both target regions).

  As described above, the generation of the ideal heat generation rate waveform model is performed only in the region where the spray exists in the region inside the cavity and the region outside the cavity. This is because when no spray is present, no fuel reaction occurs, and therefore an ideal heat release rate waveform model cannot be created. The determination of in which region the spray is present (or whether the spray is present in both regions) can be performed based on the fuel injection period as described above.

As an operation for creating the ideal heat release rate waveform model, specifically, the reference reaction rate efficiency [J / CA ² / mm ³ ] corresponding to the gas temperature (reference temperature) in the target region and the fuel composition at the reaction start time. And the reference reaction amount efficiency [J / mm ³ ] are determined for each reaction form, and the reference reaction rate efficiency and the reference reaction amount efficiency are corrected based on the oxygen supply capacity (oxygen density) to the combustion field. The reaction rate and reaction amount are determined from the reaction rate efficiency and reaction amount efficiency.

  For the reaction rate, a correction coefficient (gradient correction coefficient) for the reaction rate efficiency is obtained based on the carbon dioxide density, and the reaction rate efficiency (reaction rate corrected based on the oxygen density) is calculated by the gradient correction coefficient. Efficiency: By correcting the reaction rate efficiency correlated with the reference heat generation rate, the corrected reaction rate efficiency (reaction rate efficiency correlated with the ideal heat generation rate) is obtained (referred to as “in-cylinder in the present invention”). Corresponding to the operation of calculating the ideal heat generation rate by correcting the reference heat generation rate defined based on the oxygen density according to the amount of carbon dioxide in the cylinder. Furthermore, the final reaction rate efficiency is obtained by correcting the reaction rate according to the engine rotation speed described later. The “reaction rate efficiency” is also referred to as “reaction rate gradient”, and the “reaction amount efficiency” is also referred to as “combustion efficiency”. Hereinafter, “reaction rate efficiency” will be described as “reaction rate gradient”.

  Then, an ideal heat release rate waveform model (triangle model) described later is created from the reaction start timing, reaction rate, and reaction amount, thereby determining the reaction period. This reaction period is obtained by the following equation (18).

Reaction period = 2 × (reaction amount / reaction rate) ^1/2 (18)
Details of creation of the ideal heat release rate waveform model (triangle model) will be described later.

(1-A) Reaction Region Division Next, the reaction region division, which is the first procedure for creating the ideal heat release rate waveform, will be described in detail.

  As described above, the region where the fuel injected from the injector 23 into the cylinder exists includes the outside-cavity region and the inside-cavity region. In each of these regions, there is a possibility that the amount of fuel and the temperature that exist are different from each other, and it is necessary to obtain these for each region. This will be specifically described below.

(A) Amount of fuel existing in the region When fuel injection is performed on the advance side with respect to the outside-cavity injection delay limit (FIG. 8 (a)), or the outside-cavity injection advance limit (FIG. 8 (b) When fuel injection is performed at a more retarded angle than)), substantially the entire amount of injected fuel is injected toward the region outside the cavity, and substantially all this fuel exists in the region outside the cavity. There will be almost no spray in the area within the cavity. For this reason, the fuel amount injected into the cylinder from the injector 23 becomes the fuel amount existing in the region outside the cavity as it is.

  In addition, when fuel injection is performed only during the period between the intra-cavity injection advance limit (FIG. 7A) and the intra-cavity injection retard limit (FIG. 7B), Substantially the entire amount will be injected toward the region inside the cavity, and the substantially whole amount of this fuel will be present in the region inside the cavity, and there will be almost no spray in the region outside the cavity. For this reason, the fuel amount injected into the cylinder from the injector 23 becomes the fuel amount existing in the cavity region as it is.

  Further, when fuel injection is performed from the outside-cavity injection delay limit (FIG. 8A) to the in-cavity injection advance limit (FIG. 7A), or within the injection delay limit (FIG. 8). 7 (b)) to the outside-cavity injection advance limit (FIG. 8 (b)), a part of the injected fuel is injected toward the outside of the cavity, and the other is the cavity. Injected toward the inner region, a part of the injected fuel exists in the region outside the cavity, and the other exists in the region inside the cavity. In this case, the ratio of the spray amount (fuel amount) existing in the region outside the cavity and the spray amount existing in the region in the cavity is, as described above, the total fuel distribution ratio in the cavity region calculated by the equation (7), etc. Can be calculated based on

  That is, the amount of fuel injected toward the in-cavity region (spray amount existing in the in-cavity region) can be calculated by multiplying the total fuel injection amount from the injector 23 by the in-cavity region total fuel distribution ratio. it can. Also, the amount of fuel injected toward the area outside the cavity (the amount of spray existing in the area outside the cavity) is calculated by subtracting the amount of fuel injected toward the area inside the cavity from the total fuel injection amount. can do.

  As described above, in this embodiment, the inside of the cylinder is divided (divided) into the area outside the cavity and the area inside the cavity, and the amount of fuel for each is obtained individually using the total fuel distribution ratio in the area inside the cavity.

  As described above, when the state of the air-fuel mixture in the cylinder is uniform, or when it is assumed to be uniform, the fuel density is substantially uniform throughout the cylinder. In addition, it is possible to calculate the ideal heat generation rate according to the oxygen excess rate in the entire cylinder without separately obtaining the amount of fuel in each cavity region.

(B) Intra-region temperature As a method for determining the temperature of each of the region outside the cavity and the region in the cavity (the temperature of each region during execution of fuel injection), the intake air temperature, the piston position (compression degree of intake gas), The preheating state of the target area by pilot injection etc. is used as a parameter, and the relationship between these parameters and the temperature of the outside area of the cavity and the inside area of the cavity is obtained by experiments and simulations in advance, and this map is stored in the ROM. ing. That is, by fitting parameters such as the intake air temperature, the piston position, and the preheating state of each region to the map, the temperatures of the outside region and the inside region of the cavity can be individually obtained. In addition, when determining the temperature in the cavity region, the total fuel distribution ratio in the cavity region may be used. Specifically, the temperature rise obtained by the product of the compressed gas temperature calculated based on the compression ratio, the amount of fuel obtained from the total fuel distribution ratio in the cavity region, and the amount of heat generated per unit mass of fuel, Is obtained as the temperature in the cavity region. The temperature in the region outside the cavity can be obtained in the same manner.

  The method for obtaining these temperatures is not limited to this, and a value obtained by subtracting the predetermined temperature from the in-cylinder average temperature is set as the temperature of the outside region of the cavity, and the value obtained by adding the predetermined temperature to the in-cylinder average temperature is set as the method. The temperature may be set as the temperature of the inner region. The predetermined temperature to be subtracted and added in this case is obtained as a map value corresponding to the operating state of the engine 1 by experiment or simulation, and is made variable according to this map value. Further, the temperature may be calculated from the thermal energy equation Q = mcT. Here, Q is the heat energy input to the target area (outer cavity area or inner cavity area), m is the mass of the gas in the target area, c is the specific heat of the gas, and T is the temperature of the target area.

  As described above, in the present embodiment, it is assumed that the oxygen density and the carbon dioxide density in the cavity area and the cavity outside area are the same, so there is no need to obtain the oxygen density and the carbon dioxide density for each area. As described above, the oxygen density and the carbon dioxide density are determined for the entire cylinder.

(1-B) Separation of Fuel Reaction Form Next, separation of fuel reaction form, which is the second procedure for creating the ideal heat release rate waveform, will be described.

  When fuel injection is performed from the injector 23, a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, a high temperature oxidation reaction by premixed combustion, and a high temperature oxidation reaction by diffusion combustion depend on the environment in the target region. Done. That is, when fuel is injected into each of the outer region and the inner region, these reactions are performed in each of these regions in accordance with the environment. Hereinafter, each reaction mode will be described.

(A) Vaporization reaction In the vaporization reaction, the fuel injected from the injector 23 is vaporized by receiving heat in the target region. This reaction is generally a spray-controlled reaction that starts when the fuel spray spreads to some extent in a state where the fuel is exposed to an environment where the gas temperature in the target region is 500K or higher. Yes.

  The boiling point of light oil used in the diesel engine 1 is generally 453K to 623K, and a practical region where fuel injection is performed in the target region (for example, the timing when the pilot injection is performed) is BTDC (compression top dead center). Previous) 40 ° CA. Since the gas temperature in the target region at this timing generally rises to about 550K to 600K (other than in cold regions), it is not necessary to consider the temperature-limiting condition in this vaporization reaction.

The reference reaction amount efficiency in this vaporization reaction is, for example, −1.14 [J / mm ³ ].

  The effective injection amount in this vaporization reaction (the amount of fuel that contributes to the vaporization reaction) is determined from the fuel injection amount to the wall surface adhesion amount (the wall surface of the cylinder bore 12 (when injected into the region outside the cavity) or the inner wall surface of the cavity 13b ( This is the amount obtained by subtracting the amount of fuel adhering to the region in the cavity) and the amount of unburned floating fuel (fuel that exists outside the spray mass and does not contribute to the reaction). Hereinafter, these fuel amounts are referred to as unburned fuel amounts. These unburned fuel amounts can be obtained experimentally according to the injection amount (which has a correlation with fuel penetration force) and the injection timing (which has a correlation with cylinder pressure).

  Specifically, since the spray is more easily diffused when the fuel is injected into the region outside the cavity than when the fuel is injected into the region within the cavity, the ratio of the unburned fuel amount to the total injected fuel amount is Get higher. For example, the ratio of the unburned fuel amount when the fuel is injected into the area inside the cavity is about 15%, whereas the ratio of the unburned fuel amount when the fuel is injected into the area outside the cavity is about 20%. It is. These values are not limited to this, and vary depending on the temperature and pressure of each region, the fuel injection pressure, and the like, and thus are obtained in advance through experiments and simulations.

  And as reaction amount in the said vaporization reaction, it calculates | requires by the following formula | equation (19).

Reaction amount in vaporization reaction = −1.14 × effective injection amount (19)
Since this vaporization reaction is an endothermic reaction, the reaction amount (generated heat amount) is a negative value. This vaporization reaction is hardly affected by the oxygen density because the amount of oxygen required for the reaction is small.

(B) Low-temperature oxidation reaction In the low-temperature oxidation reaction, a low-temperature oxidation reaction component (such as a fuel having a linear single bond composition such as n-cetane (C ₁₆ H ₃₄ )) contained in the diesel oil that is the fuel of the diesel engine 1 is burned. It is a reaction to. This low-temperature oxidation reaction component is a component that can be ignited even when the temperature in the target region is relatively low, and the higher the amount of n-cetane or the like (the higher the cetane fuel), the higher the target region. Thus, the low temperature oxidation reaction is easy to proceed, and the ignition delay is suppressed. Specifically, a low-temperature oxidation reaction component such as n-cetane generally starts combustion (low-temperature oxidation reaction) when the temperature in the target region reaches about 750K. In addition, fuel components (high temperature oxidation reaction components) other than n-cetane do not start combustion (high temperature oxidation reaction) until the temperature in the target region reaches about 900K.

The reference reaction rate gradient (reference reaction rate efficiency) in this low-temperature oxidation reaction is, for example, 4.0 [J / CA ² / mm ³ ]. The standard reaction amount efficiency is, for example, 5.0 [J / mm ³ ].

  Further, the reaction amount of the low-temperature oxidation reaction is calculated based on the reaction amount efficiency obtained by correcting the reference reaction amount efficiency by the oxygen density (for example, by multiplying the effective injection amount). )

The reaction rate of the low-temperature oxidation reaction is calculated based on the reaction rate gradient obtained by correcting the reference reaction rate gradient with the oxygen density and the carbon dioxide density (for example, multiplying by the effective injection amount). Is calculated). Further, in calculating the reaction rate of the low-temperature oxidation reaction, a coefficient corresponding to the engine rotation speed (rotation speed correction coefficient = (reference rotation speed / actual rotation) is obtained by multiplying the reaction speed gradient by the effective injection amount. Speed) ² ) is multiplied. An arbitrary rotation speed (for example, 2000 rpm) can be set as the reference rotation speed for obtaining the rotation speed correction coefficient. Thereby, even if a gas composition etc. change, reaction rate can be calculated | required as a value depending on time.

The rotational speed correction coefficient may be obtained from the rotational speed correction coefficient map shown in FIG. The rotation speed correction coefficient map shown in FIG. 15 is obtained by setting the reference rotation speed to 2000 rpm. In a region where the actual rotational speed of the engine 1 is equal to or higher than the reference rotational speed (2000 rpm), a value corresponding to “(reference rotational speed / actual rotational speed) ² ” (a value corresponding to the engine rotational speed indicated by a one-dot chain line in the figure). ) As the rotation speed correction coefficient. On the other hand, in a region where the actual rotational speed of the engine 1 is less than the reference rotational speed (2000 rpm), the value corresponding to “(reference rotational speed / actual rotational speed) ² ” is corrected by a predetermined ratio (to the lower side). The corrected value is obtained as the rotation speed correction coefficient (see the solid line in the region below the reference rotation speed). In this case, the correction ratio is obtained by experiment or simulation.

  The reference rotation speed is not limited to the above-described value, and is preferably set to a rotation speed range where the engine 1 is used most frequently.

  Since this low-temperature oxidation reaction is an exothermic reaction, the reaction amount (generated heat amount) is a positive value.

(C) Thermal decomposition reaction The thermal decomposition reaction is a reaction that performs thermal decomposition of a fuel component. In general, the reaction temperature is about 800K.

The reference reaction rate gradient in this thermal decomposition reaction is, for example, −0.2 [J / CA ² / mm ³ ]. The standard reaction amount efficiency is, for example, 5.0 [J / mm ³ ].

  The reaction amount of the thermal decomposition reaction is also calculated based on the reaction amount efficiency obtained by correcting the reference reaction amount efficiency with the oxygen density (for example, by multiplying the effective injection amount). )

  The reaction rate of the thermal decomposition reaction is also calculated based on the reaction rate gradient obtained by correcting the reference reaction rate gradient with the oxygen density and the carbon dioxide density (for example, multiplying the effective injection amount). Is calculated). Further, when calculating the reaction rate of the thermal decomposition reaction, the value obtained by multiplying the reaction rate gradient by the effective injection amount is multiplied by the rotation speed correction coefficient corresponding to the engine rotation speed.

  In the present embodiment, this thermal decomposition reaction is treated as an endothermic reaction. That is, the reaction amount (generated heat amount) is a negative value.

(D) High-temperature oxidation reaction by premixed combustion The reaction temperature of the high-temperature oxidation reaction by premixed combustion is generally about 900K. That is, the reaction that starts combustion when the temperature in the target region reaches 900K is a high-temperature oxidation reaction by this premixed combustion.

Further, the reference reaction rate gradient in the high temperature oxidation reaction by this premixed combustion is, for example, 4.3 [J / CA ² / mm ³ ]. The standard reaction amount efficiency is, for example, 30.0 [J / mm ³ ].

  Further, the reaction amount of the high temperature oxidation reaction by the premixed combustion is also calculated based on the reaction amount efficiency obtained by correcting the reference reaction amount efficiency by the oxygen density (for example, multiplying the effective injection amount). Is calculated).

  The reaction rate of the high-temperature oxidation reaction by the premixed combustion is also calculated based on the reaction rate gradient obtained by correcting the reference reaction rate gradient with the oxygen density and the carbon dioxide density (for example, the effective injection Calculated by multiplying the amount). Further, when calculating the reaction rate of the high temperature oxidation reaction by the premixed combustion, the value obtained by multiplying the reaction rate gradient by the effective injection amount is multiplied by the rotation speed correction coefficient corresponding to the engine rotation speed.

  Since the high temperature oxidation reaction by this premixed combustion is an exothermic reaction, the reaction amount (generated heat amount) is a positive value.

(E) High temperature oxidation reaction by diffusion combustion The reaction temperature of the high temperature oxidation reaction by diffusion combustion is generally about 1000K. That is, the reaction in which the fuel injected toward the target region having a temperature of 1000 K or more immediately starts combustion after the injection is a high temperature oxidation reaction by this diffusion combustion.

  Moreover, the reaction rate in the high temperature oxidation reaction by this diffusion combustion changes according to the common rail pressure, and is obtained from the following equations (20) and (21).

GrdB = A × common rail pressure + B (20)
Grd = GrdB × (reference engine speed / actual engine speed) ²
X (d / reference d) x (N / reference N) (21)
GrdB: reference reaction rate, Grd: reaction rate, d: nozzle hole diameter of the injector 23, N: number of nozzle holes of the injector 23, A, B: constants obtained by experiments, etc. Multiplying the ratio of the actual nozzle hole diameter to the reference nozzle hole diameter and the ratio of the actual nozzle hole number to the reference nozzle hole number of the injector 23 is a generalized equation. In addition, the equation (21) is obtained by multiplying the rotation speed correction coefficient so that the reaction speed corrected in accordance with the engine rotation speed is obtained.

The standard reaction amount efficiency of the high temperature oxidation reaction by diffusion combustion is, for example, 30.0 [J / mm ³ ]. The reaction amount of the high temperature oxidation reaction by diffusion combustion is also the above standard reaction amount efficiency. It is calculated based on the reaction amount efficiency obtained by correcting by the oxygen density (for example, it is calculated by multiplying the effective injection amount).

  Since the high temperature oxidation reaction by diffusion combustion is also an exothermic reaction, the reaction amount (generated heat amount) is a positive value.

  As described above, the reaction form of the fuel can be separated.

(F) Effect of Oxygen Density on Each Reaction As described above, the oxygen density affects the reaction start timing, reaction rate, and reaction amount in each reaction of fuel. That is, the lower the oxygen density, the more the reaction start timing shifts to the retarded side, the reaction rate becomes lower (the reaction becomes slower), and the reaction amount decreases.

  Hereinafter, the influence of the oxygen density on the reaction start timing, reaction rate, and reaction amount of each reaction will be specifically described.

<Reaction start time>
As described above, the reaction start timing shifts to the retard side as the oxygen density decreases. The reaction start time in this case is calculated by the following equation (22).

Reaction start time = reference temperature arrival time + oxygen density decrease correction retardation amount (22)
Here, the temperature reaching the reference temperature generally reaches about 750K for the low temperature oxidation reaction, about 800K for the thermal decomposition reaction, about 900K for the high temperature oxidation reaction by premixed combustion, and about 1000K for the high temperature oxidation reaction by diffusion combustion. It is time to perform (crank angle position).

  The oxygen density decrease correction retardation amount is a correction amount for the reaction start time due to the influence of the oxygen density. The relationship between the oxygen density and the corrected oxygen amount reduction retardation amount is stored in the ROM as a correction retardation amount map obtained in advance by experiments and simulations. A decrease correction retardation amount is extracted.

<Reaction rate gradient>
As described above, the reaction rate decreases as the oxygen density decreases. That is, the reaction rate gradient is reduced. The reaction rate gradient in this case is calculated by the following equation (23).

Reaction rate gradient = (reference reaction rate gradient × gradient correction factor) × (2000 / NE) ² (23)
Here, the reference reaction rate gradient is about 40 [J / CA ² / mm ³ ] in the low-temperature oxidation reaction and about −0.2 [J / CA ² / mm ³ ] in the thermal decomposition reaction. NE is the engine speed at the calculation timing of the oxygen density. In this equation (23), the reference rotational speed is set to 2000 rpm, and the reaction speed gradient at the calculation timing of the oxygen density is obtained.

  The gradient correction coefficient is a correction amount of the reaction rate gradient due to the influence of the oxygen density. The relationship between the oxygen density and the gradient correction coefficient is stored in the ROM in a gradient correction coefficient map that is obtained in advance by experiments and simulations, and the gradient correction coefficient is extracted from the gradient correction coefficient map.

<Reaction amount>
As described above, the amount of reaction decreases as the oxygen density decreases. The reaction amount efficiency in this case is calculated by the following equation (24).

Reaction amount efficiency = reference reaction amount efficiency × oxygen density correction coefficient (24)
Here, the oxygen density correction coefficient is a correction amount of the reaction amount efficiency due to the influence of the oxygen density. The relationship between the oxygen density and the oxygen density correction coefficient is stored in the ROM as an oxygen density correction coefficient map that has been obtained in advance by experiments and simulations. From this oxygen density correction coefficient map, the oxygen density correction coefficient can be calculated. Extracted.

  Although the oxygen density can affect all reactions, it is preferable to consider the influence of this oxygen density only on reactions and waveform components that are particularly sensitive to oxygen density. Specifically, examples of the reaction that is greatly affected by the reaction start time depending on the oxygen density include a low-temperature oxidation reaction and a thermal decomposition reaction. Examples of the reaction that is greatly affected by the reaction rate depending on the oxygen density include a low temperature oxidation reaction, a thermal decomposition reaction, and a high temperature oxidation reaction by premixed combustion. Furthermore, examples of the reaction that is greatly affected by the reaction amount depending on the oxygen density include a high temperature oxidation reaction by premixed combustion and a high temperature oxidation reaction by diffusion combustion. In addition, the reaction and waveform component which consider the influence of oxygen density are not limited to these.

(G) Effect of carbon dioxide density on each reaction As described above, the carbon dioxide density affects the reaction rate in each reaction of fuel. That is, the higher the carbon dioxide density, the lower the reaction rate (the reaction becomes slower). As described above, the carbon dioxide density may affect the reaction start timing and the reaction amount in each reaction of the fuel. However, since the influence on the reaction rate is particularly great, this reaction is described here. The effect on speed will be described.

  The reaction rate gradient due to the influence of the carbon dioxide density is calculated by the following equation (25).

Reaction rate gradient due to carbon dioxide density = (reaction rate gradient × gradient correction coefficient) × (1600 / NE) ² (25)
Here, the reaction rate gradient is a reaction rate gradient (reaction rate gradient correlated with the reference heat generation rate) obtained in consideration of the influence of the oxygen density or the like (see the above equation (23)). NE is an engine speed at the calculation timing of the carbon dioxide density. In this equation (25), the reference rotational speed is set to 1600 rpm, and the reaction speed gradient at the calculation timing of the carbon dioxide density is obtained.

  The gradient correction coefficient is a correction amount of the reaction rate gradient due to the influence of the carbon dioxide density. The relationship between the carbon dioxide density and the gradient correction coefficient is stored in the ROM in a gradient correction coefficient map that is obtained in advance by experiments and simulations, and the gradient correction coefficient is extracted from the gradient correction coefficient map. .

  FIG. 16 shows an example of the gradient correction coefficient map (for example, a gradient correction coefficient map for high temperature oxidation reaction by premixed combustion). The gradient correction coefficient map is obtained by simplifying the change of the gradient correction coefficient with respect to the change of the carbon dioxide density by using the Wiebe function.

  In this gradient correction coefficient map, when the carbon dioxide density changes from 0 to ρ1, the gradient correction coefficient when the carbon dioxide density is “0” is set to “1”, and the carbon dioxide density is ρ1. The terms a and m, which are the shape parameters of the Wiebe function, are set so that the gradient correction coefficient in this case is “A (for example, 0.2)”. These values are not limited to this.

(1-C) Creation of ideal heat release rate waveform model for each separated reaction form Next, creation of ideal heat release rate waveform model for each reaction form separated in each of the in-cavity region and the outside-cavity region. Will be described.

  By separating the reaction forms as described above, it is possible to create an ideal heat release rate waveform model in each reaction form. That is, an ideal heat release rate waveform model can be created for each of a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, a high temperature oxidation reaction by premixed combustion, and a high temperature oxidation reaction by diffusion combustion.

  In this embodiment, the ideal heat release rate waveform model is approximated to an isosceles triangle for each reaction. That is, the reaction rate (reaction rate corrected according to the oxygen density and carbon dioxide density) is set to the slope of the hypotenuse of the isosceles triangle, and the reaction amount (corrected according to the oxygen density) is based on the reaction start temperature described above. An ideal heat release rate waveform model is created for each of the in-cavity region and the outside-cavity region, where the reaction amount is an isosceles triangle area and the reaction period is the length of the base of the isosceles triangle. As described above, the reaction start time is a value obtained by correcting the reference temperature arrival time by the oxygen density decrease correction delay amount. The creation of the ideal heat release rate waveform model below is applied to each of the reaction modes described above. This will be specifically described below.

(A) Reaction rate (reaction rate gradient)
The reaction rate is set based on the reaction rate gradient, and when the ideal heat generation rate waveform model is approximated to an isosceles triangle, the reaction rate during the period in which the heat generation rate increases and the period in which the heat generation rate decreases Their absolute values are consistent with the reaction rate at.

  In addition, when the reaction rate in the period in which the heat generation rate decreases is lower than the reaction rate in the period in which the heat generation rate increases (when the ideal heat generation rate waveform model is an inequilateral triangle), The descending gradient is obtained by multiplying the ascending gradient by a predetermined value α (<1).

  In the ideal heat release rate waveform model in the high temperature oxidation reaction by diffusion combustion, the reaction rate is proportional to the injection rate waveform gradient, and the reaction rate is constant if the fuel injection pressure (common rail internal pressure) is constant. In the ideal heat release rate waveform model in other reactions (for example, high temperature oxidation reaction by premixed combustion), the reaction speed is proportional to the fuel injection amount.

  As described above, in the present embodiment, the inside of the cylinder is divided into an outer cavity region and an inner cavity region, and ideal heat generation rate waveform models are created for each. In each reaction, the reaction rate gradient changes according to physical quantities such as oxygen density, fuel density, and carbon dioxide density in the combustion field. For this reason, in this embodiment, the reaction rate is obtained individually for each region, and an ideal heat release rate waveform model is created based on the obtained reaction rate. Specifically, after obtaining the reference reaction rate based on the oxygen density and fuel density in the combustion field, the reaction rate is calculated by correcting the reference reaction rate based on the carbon dioxide density. I have to.

(B) Generated heat (area)
The reaction amount efficiency [J / mm ³ ] in each reaction can be regarded as a constant (for example, 30 J / mm ^{3 in} the case of a high temperature oxidation reaction) if the combustion period is optimized. For this reason, the generated heat amount is obtained by multiplying the reaction amount efficiency by the fuel injection amount (the effective injection amount).

  However, the low-temperature oxidation reaction is completed together with the high-temperature oxidation reaction, and the high-temperature oxidation reaction by diffusion combustion is completed alone.

  The amount of heat generated in this way corresponds to the area of a triangle that is an ideal heat generation rate waveform model.

(C) Combustion period (base)
The combustion period corresponding to the length of the base of the triangle is obtained from the gradient of the triangle (reaction rate) and the area of the triangle (amount of generated heat).

  As shown in FIG. 17, the triangular area (corresponding to the amount of generated heat) is S, the base length (corresponding to the combustion period) is L, and the height (corresponding to the heat generation rate at the peak of the heat generation rate) is H. , A is the period from the start of combustion to the peak of the heat generation rate, and B is the period from the peak of the heat generation rate to the end of combustion (B = A when the ideal heat generation rate waveform model is an isosceles triangle), G is the ascending gradient (corresponding to the reaction rate during the period when the heat generation rate increases), and α (≦ 1) is the ratio of the descending gradient (corresponding to the reaction rate during the period when the heat generation rate decreases) to this ascending gradient. In this case, the following relationship holds. FIG. 17A shows the case where the ideal heat generation rate waveform model is an isosceles triangle, and FIG. 17B shows the case where the ideal heat generation rate waveform model is an unequal triangle.

H = A × G = B × α × G
From this, B = A / α.

S = A ² × G / 2 + A × G × B / 2 = (1 + 1 / α) × A ² × G / 2
Therefore, A = SQRT [2S / {(1 + 1 / α) G}].

Therefore, the base length L is
L = A + B = A (1 + 1 / α)
= (1 + 1 / α) × SQRT [2S / {(1 + 1 / α) G}]
When the ideal heat release rate waveform model is an isosceles triangle, α = 1.
L = 2 × SQRT (S / G) = 2 × SQRT (30 × Fq / G).

(Fq is the fuel injection amount (effective injection amount). As described above, when the heat generation amount per 1 mm ^{3 of} fuel is 30 J, “30 × Fq” is the triangular area S)
In this way, the combustion period is determined when the injection amount (injection amount command value: a value correlated with the generated heat amount) and the gradient (reaction rate) are given.

  Hereinafter, the reason why the ideal heat generation rate waveform model can be approximated to a triangle (especially an isosceles triangle) will be described. FIG. 18A shows the relationship between the elapsed time when fuel is injected from the injector 23 and the amount of fuel supplied into the cylinder in one reaction mode (the amount of fuel used in that reaction mode). ing. In FIG. 18A, the fuel injection period in which the fuel supply amount is obtained is divided into 10 periods. That is, the fuel injection period is divided into ten periods in which the fuel supply amounts are equal to each other, and the period numbers from the first period to the tenth period are assigned to each. That is, after the fuel injection in the first period is completed, the fuel injection in the second period is started without interruption, and after the fuel injection in the second period is completed, the fuel injection is interrupted. The fuel injection is continued until the end of the tenth period in such an injection form that the fuel injection in the third period is started without any change.

  FIG. 18B shows the reaction amount of the fuel injected in each period (the one shown in FIG. 18B is the exothermic amount in the exothermic reaction). As shown in FIG. 18 (b), fuel injection in the first period is started and fuel injection in the second period is started (period t1 in FIG. 18 (b)). Only the reaction of the fuel injected in the first period is performed. The fuel injected in the first period is the period from the start of fuel injection in the second period to the start of fuel injection in the third period (period t2 in FIG. 18B). And the reaction of the fuel injected in the second period are performed together. In this way, every time a new injection period is reached, the total reaction amount of fuel gradually increases (the total reaction amount increases by the amount of fuel in the period during which new injection is started). This increase period corresponds to the positive gradient period (advanced period relative to the peak position of the reaction) of the ideal heat release rate waveform model.

  Thereafter, the reaction of the fuel injected in the first period ends. At this time (timing T1 in FIG. 18B), the reaction of the fuel injected in the second period and thereafter is not completed, and the reaction of the fuel injected in the tenth period from the second period is completed. continuing. When the reaction of the fuel injected in the second period is completed (timing T2 in FIG. 18B), the reaction of the fuel injected in the third period and thereafter is not completed, so the third period The reaction of the fuel injected in the tenth period will continue. In this way, the reaction of the fuel injected in each period ends in sequence, so that the total reaction amount of the fuel gradually decreases (the total reaction amount decreases by the amount of fuel for which the reaction has ended). Go). This decrease period (a period in which the reaction amount is indicated by a broken line in FIG. 18B) is a period of a negative slope of the ideal heat generation rate waveform model (a period on the retard side from the peak position of the reaction). Equivalent to.

  Since the fuel reaction is performed in the above-described manner, the ideal heat generation rate waveform model can be approximated as a triangle (isosceles triangle).

  The above is the procedure for creating the ideal heat release rate waveform model for each reaction mode of fuel.

(1-D) Creation of ideal heat release rate waveform by filtering of ideal heat release rate waveform model After creating an ideal heat release rate waveform model as described above, this ideal heat release rate waveform model is subjected to well-known filter processing ( For example, an ideal heat generation rate waveform is created by performing smoothing by processing using a Wiebe filter. This will be specifically described below.

  FIG. 19 shows an example of an ideal heat release rate waveform model (isosceles triangle corresponding to each reaction) in each reaction mode when fuel injection is performed once in the region outside the cavity. In FIG. 19, an ideal heat generation rate waveform model (isosceles triangle corresponding to each reaction) in which a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, and each high temperature oxidation reaction are sequentially performed by one fuel injection is obtained. Yes. Specifically, in the figure, I is the ideal heat release rate waveform model of the vaporization reaction, II is the ideal heat release rate waveform model of the low-temperature oxidation reaction, and III is the ideal heat release rate of the thermal decomposition reaction (pyrolysis reaction that is endothermic). A waveform model, IV is an ideal heat generation rate waveform model of a high temperature oxidation reaction by premixed combustion, and V is an ideal heat generation rate waveform model of a high temperature oxidation reaction by diffusion combustion.

  In addition, FIG. 20 was created by synthesizing each waveform obtained by smoothing the ideal heat generation rate waveform model when the fuel was injected once in the region outside the cavity by filtering. An ideal heat generation rate waveform (outside cavity injection ideal heat generation rate waveform) is shown. In this way, ideal heat release rate waveform models (isosceles triangles) corresponding to each reaction (vaporization reaction, low-temperature oxidation reaction, thermal decomposition reaction, each high-temperature oxidation reaction) are smoothed and synthesized by filtering. Thus, an ideal heat generation rate waveform only for the region outside the cavity is created.

  On the other hand, FIG. 21 shows an example of an ideal heat generation rate waveform model (isosceles triangle corresponding to each reaction) in each reaction mode when fuel injection is performed once in the cavity region. In FIG. 21, due to the rapid rise in the temperature in the cavity region, after a vaporization reaction and a thermal decomposition reaction are sequentially performed by one fuel injection, a low temperature oxidation reaction and a high temperature oxidation reaction by premixed combustion are performed. In parallel with this, after the start of these reactions, an ideal heat generation rate waveform model (isosceles triangle corresponding to each reaction) in which a high-temperature oxidation reaction by diffusion combustion is performed is obtained. Specifically, I 'in the figure is the ideal heat release rate waveform model for the vaporization reaction, II' is the ideal heat release rate waveform model for the low-temperature oxidation reaction, and III 'is the ideal for the thermal decomposition reaction (the thermal decomposition reaction that is endothermic). A heat generation rate waveform model, IV ′ is an ideal heat generation rate waveform model of a high temperature oxidation reaction by premixed combustion, and V ′ is an ideal heat generation rate waveform model of a high temperature oxidation reaction by diffusion combustion.

  In addition, FIG. 22 was created by synthesizing each waveform obtained by smoothing the ideal heat release rate waveform model by filtering the fuel injection once in this cavity region. The ideal heat release rate waveform (injection ideal heat release rate waveform in the cavity) is shown. In this way, ideal heat release rate waveform models (isosceles triangles) corresponding to each reaction (vaporization reaction, low-temperature oxidation reaction, thermal decomposition reaction, each high-temperature oxidation reaction) are smoothed and synthesized by filtering. Thus, an ideal heat generation rate waveform for only the region in the cavity is created.

  Furthermore, in one fuel injection, when a part of the fuel is injected into the area outside the cavity and another fuel is injected into the area inside the cavity, that is, the fuel is injected separately into the area outside the cavity and the area inside the cavity. In this case, an ideal heat generation rate waveform that targets these areas outside the cavity and an ideal heat generation rate waveform that covers the areas inside the cavity are created respectively. The ideal heat release rate waveform is created. For example, when the ideal heat generation rate waveform for the region outside the cavity is as shown in FIG. 20 and the ideal heat generation rate waveform for the region within the cavity is as shown in FIG. An ideal heat generation rate waveform (in-cylinder ideal heat generation rate waveform) as shown in FIG. 23 is created as an ideal heat generation rate waveform for the whole.

  As described above, the oxygen density affects the reaction start timing, reaction rate, and reaction amount in each reaction of fuel. That is, the lower the oxygen density, the more the reaction start timing shifts to the retarded side, the reaction rate becomes lower (the reaction becomes slower), and the reaction amount decreases. Carbon dioxide density also affects the reaction rate in each reaction of fuel. That is, the higher the carbon dioxide density, the lower the reaction rate (the reaction becomes slower). For this reason, the ideal heat release rate waveform created by the above-described method has a different shape depending on the oxygen density and the carbon dioxide density, and is a waveform reflecting the influence of the oxygen density and the carbon dioxide density.

  In the actual engine 1, pilot injection, after injection, and the like are performed in addition to the main injection. Therefore, for these pilot injections and after-injections, an ideal heat release rate waveform model in the target area is created in the same manner as described above, and the ideal heat release rate waveform is created by smoothing this model by filtering. Is done. Generally, pilot injection is performed at a crank angle position that is advanced by a predetermined angle or more from the compression top dead center of the piston 13, and after injection is performed at a crank angle position that is retarded by a predetermined angle or more from the compression top dead center of the piston 13. In order to be executed, these injections are directed towards the out-cavity region. For this reason, the ideal heat generation rate waveform targeting these injections is obtained as the ideal heat generation rate waveform outside the cavity.

  Then, an ideal heat generation rate waveform for the entire cylinder in the main injection and these ideal heat generation rate waveforms (ideal heat generation rate waveforms for pilot injection and after injection) are combined for one cycle. An ideal heat generation rate waveform for the target is created.

  Even when the main injection is divided into a plurality of times and executed (divided main injection), the ideal heat generation rate for one cycle is obtained by synthesizing the ideal heat generation rate waveforms in each main injection. A waveform will be created.

  When multiple injections are performed in this way, the respective ideal heat generation rate waveforms are synthesized, the temperature within the target region at the timing of fuel injection at the preceding stage (advance side), and thereafter It is necessary to consider that the temperature in the target region at the timing of fuel injection (on the retard side) is different from each other. Specifically, in the steady operation state of the engine, when the preheating or the like is not performed at the timing of fuel injection on the advance side, fresh air sucked from the outside, residual gas in the cylinder, and EGR The reaction is started based on the compressed gas temperature resulting from the temperature rise of the gas such as gas as the piston 13 moves. When starting the engine or returning the fuel injection from the fuel cut, the reaction starts based on the compressed gas temperature due to the rise in temperature of the fresh air drawn from the outside as the piston 13 moves. Will be. On the other hand, when the fuel is injected at the retarded angle side, the temperature rises by adding the temperature of burned gas (combustion gas of fuel injected at the advanced angle side) to the compressed gas temperature. Since the fuel is injected with respect to the temperature field, the reaction start timing shifts to the advance side as compared with the case where there is no temperature increase due to the burned gas. Taking this into account, the ideal heat release rate waveform due to the reaction of fuel injected on the advance side and the ideal heat release rate waveform due to the reaction of fuel injected on the retard side are considered the temperature changes described above. Ask. That is, the start time of each reaction in each injection is defined by temperature management. Thereby, it is possible to appropriately obtain the start time of each reaction in each injection. As a result, it is possible to properly define the reaction start order, the period in which the reactions are paralleled, etc., and the ideal heat generation rate waveform by synthesizing the ideal heat generation rate waveform created for each injection Can be created with high accuracy.

(2) Creation of actual heat generation rate waveform The actual heat generation rate waveform to be compared with the ideal heat generation rate waveform is generated according to a change in the in-cylinder pressure detected by the in-cylinder pressure sensor 4A. In other words, there is a correlation between the heat generation rate in the cylinder and the in-cylinder pressure (the higher the heat generation rate, the higher the in-cylinder pressure). Therefore, from the in-cylinder pressure detected by the in-cylinder pressure sensor 4A. An actual heat generation rate waveform can be created. Since the process of creating the actual heat generation rate waveform from the detected in-cylinder pressure is known, the description thereof is omitted here.

(3) Diagnosis of combustion state by comparing ideal heat generation rate waveform and actual heat generation rate waveform As a diagnosis of combustion state (diagnosis of reaction mode), the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform Done based on size. For example, when there is a reaction form in which the divergence is equal to or greater than a preset threshold value (abnormality judgment divergence amount in the present invention), it is diagnosed that the reaction form is abnormal. Become. For example, when there is a reaction form in which the deviation of the heat generation rate is 10 [J / ° CA] or more, or the deviation of the crank angle of the actual heat generation rate waveform from the ideal heat generation rate waveform (advanced side or retardation) If there is a reaction form having a deviation of 3 ° CA or more, it is diagnosed that the reaction form is abnormal. These values are not limited to this, and are set as appropriate through experiments and simulations.

  For example, the case where the ideal heat generation rate waveform shown in FIG. 23 is created will be described as an example. Like the actual heat generation rate waveform shown by a broken line in FIG. The waveform of the actual heat generation rate in each high-temperature oxidation reaction (high-temperature oxidation reaction by premixed combustion and high-temperature oxidation reaction by diffusion combustion) is shifted to the retard side with respect to the high-temperature oxidation reaction (the waveform shown in FIG. 23). If it exceeds, it is diagnosed that an abnormality has occurred in each high-temperature oxidation reaction, that is, an abnormality has occurred in the reaction start timing of each high-temperature oxidation reaction.

  In addition, as shown in the actual heat generation rate waveform indicated by the one-dot chain line in FIG. If it exceeds, it is diagnosed that an abnormality has occurred in each high-temperature oxidation reaction, that is, an abnormality has occurred in the reaction amount in each high-temperature oxidation reaction. Such diagnosis is not limited to the high temperature oxidation reaction, but is similarly performed for the vaporization reaction, the low temperature oxidation reaction, and the thermal decomposition reaction.

  The parameters for diagnosing whether or not an abnormality has occurred in the reaction form are not limited to the above-described reaction time deviation (ignition delay, etc.) or the peak value deviation of the heat release rate waveform, but the reaction rate. Deviation, reaction period deviation, peak phase, and the like.

(4) Correction of control parameter of engine 1 according to diagnosis result In the diagnosis of the combustion state by comparing the ideal heat generation rate waveform and the actual heat generation rate waveform, the actual heat generation rate with respect to the ideal heat generation rate waveform as described above. When there is a reaction form in which the waveform deviation exceeds a preset threshold, it is diagnosed that an abnormality has occurred in the reaction form, and the control parameter of the engine 1 is corrected so as to reduce this deviation. .

  For example, when the actual heat generation rate waveform is shown by a broken line in FIG. 24, it is determined that fuel ignition delay has occurred and oxygen is insufficient, and the cooling capacity of the intake air by the intercooler 61 is determined. The shortage of oxygen is eliminated by reducing the EGR gas amount by decreasing the opening degree of the EGR valve 81 or by increasing the intake supercharging rate.

  Further, when the actual heat generation rate waveform is shown by a one-dot chain line in FIG. 24, it is determined that the reaction amount of the fuel is too large, and the fuel injection amount reduction correction, the EGR gas increase correction, etc. I do.

  As another correction operation, when the reaction start time in the actual heat generation rate waveform is on the retarded side with respect to the ideal heat generation rate waveform, the intake supercharging rate is increased or the pilot for the target region is increased. It is also possible to make corrections such as increasing the amount of preheating by injection.

  Control parameters for bringing the actual heat generation rate waveform closer to the ideal heat generation rate waveform are not limited to those described above, but include fuel injection timing, gas composition in the cylinder, intake air amount (gas amount), and various learning values. (A learned value of the fuel injection amount or fuel injection timing) may be used. For example, when the oxygen density in the target region is excessive or insufficient, the learning value is learned so as to correct the EGR gas or the intake supercharging rate. Further, when the fuel density in the target region is excessive or deficient, the learning value is learned so as to correct the fuel injection timing, the fuel injection pressure, and the fuel injection amount.

  Such correction of the control parameter is executed when the actual heat generation rate waveform can be substantially matched with the ideal heat generation rate waveform by the correction of the control parameter. Specifically, it is executed when the deviation amount of the actual heat generation rate waveform with respect to the ideal heat generation rate waveform is equal to or less than a predetermined correctable deviation amount. This correctable deviation amount is set in advance by experiment or simulation. When the deviation amount of the actual heat generation rate waveform with respect to the ideal heat generation rate waveform exceeds the correctable deviation amount, the correction amount of the control parameter exceeds the predetermined guard value. Diagnose that a failure has occurred in a part of the devices constituting the system 1. Specifically, lower limits for the in-cylinder temperature, oxygen density, and fuel density are set in advance, and when any of the in-cylinder temperature, oxygen density, or fuel density is below the lower limit, If the upper limit value of the carbon density is set in advance and the carbon dioxide density exceeds the upper limit value, it is determined that the correction amount of the control parameter of the engine 1 exceeds a predetermined guard value, and the engine 1 has failed. It will be diagnosed as occurring.

  In this case, without correcting the control parameter, for example, the MIL (warning lamp) on the meter panel in the passenger compartment is lit to urge the driver to warn, and the diagnosis provided in the ECU 100 has abnormality information. Will be written.

-Smoke index-
As described above, the carbon dioxide density affects the amount of smoke produced in the exhaust. For this reason, it is possible to obtain | require beforehand the quantity of the smoke produced | generated by calculating | requiring a carbon dioxide density. When it is estimated that the amount of smoke generated exceeds the allowable range, it is possible to perform control for reducing the carbon dioxide density so as to suppress the amount of smoke generated.

  The following formula (26) is given as a formula for calculating the amount of smoke generated when EGR is not performed. The equation (26) is a smoke index calculation formula representing the smoke amount ratio (%) in the exhaust gas.

Smoke index = 28 × ^λo ₂ ^−12.5 (26)
This equation (26) represents the relationship between the excess oxygen ratio λo ₂ and the smoke index. That is, it represents the relationship between the quantity of oxygen deficiency (degree of oxygen deficiency) in the cylinder and the smoke index. Each constant in the equation (26) is defined by experiment or simulation.

  On the other hand, the following formula (27) can be given as a formula for calculating the amount of smoke generated when EGR is performed. Note that this equation (27) is also a calculation formula for the smoke index representing the ratio (%) of the smoke amount in the exhaust gas.

Smoke index = F (ρco ₂ ) × ^λo ₂ ^{−12.5 × F (PCR, Fq, ρo2, NE)} (27)
F (PCR, Fq, ρo ₂ , NE) in the equation (27) is an arithmetic expression using the fuel injection pressure PCR, the fuel injection amount Fq, the oxygen density ρo ₂ in the cylinder, and the engine speed NE as variables. The constant in equation (27) is also defined by experiment or simulation.

  FIG. 25A shows the relationship between the oxygen excess rate and the amount of smoke generated when the engine speeds are different from each other. In this figure, the relationship between the oxygen excess rate indicated by the broken line and the amount of smoke generated is when the engine speed is higher than that indicated by the solid line, and the relationship between the oxygen excess rate indicated by the alternate long and short dash line and the amount of smoke generated is In this case, the engine speed is lower than that indicated by the solid line.

  When the engine rotation speed is high, the change in the cylinder volume per unit time is large, so that the oxygen density in the combustion field during the expansion stroke tends to decrease locally. Even when the oxygen surplus rate is the same in the entire cylinder, the amount of smoke generated tends to increase compared to when the engine speed is low.

  FIG. 25B is a graph showing the relationship between the oxygen excess rate and the amount of smoke generated when the carbon dioxide density changes. In this figure, the density of carbon dioxide increases in the order of a solid line, a broken line, a one-dot chain line, and a two-dot chain line. That is, it can be seen that as the carbon dioxide density increases, an oxygen deficient state in the combustion field occurs and the amount of smoke generated tends to increase.

  When the smoke generation amount can be estimated in advance in this way, when it is estimated that the smoke generation amount exceeds the allowable range, control for reducing the carbon dioxide density in the cylinder (for example, the EGR rate) The smoke generation amount can be suppressed within an allowable range by executing control for increasing the oxygen density (for example, control for increasing the supercharging rate).

  As described above, in this embodiment, the inside of the cylinder is divided into the cavity inner region and the cavity outer region, and the heat release rate waveform is created for each region. In other words, for each of the cavity inner area and cavity outer area where physical quantities such as temperature and fuel density may be different from each other, the reaction state of the fuel injected into each area is individually determined according to the environment in the area. The ideal heat release rate waveform is created respectively. For this reason, the reaction state of the fuel in each region can be defined more accurately, and high reliability can be obtained in the created ideal heat generation rate waveform.

  In particular, in the present embodiment, when generating the heat generation rate waveform, ideal heat generation is performed by correcting the reference heat generation rate defined based on the oxygen density in the cylinder according to the amount of carbon dioxide in the cylinder. The rate is calculated, and an ideal heat generation rate waveform is created based on this ideal heat generation rate. Specifically, the reaction rate gradient corrected based on the oxygen density is corrected according to the carbon dioxide density to obtain the reaction rate gradient according to the influence of the carbon dioxide density, and based on this, the ideal heat release rate waveform is obtained. I try to create it. For this reason, the accuracy can be improved by correcting the ideal heat generation rate, which could not be obtained with sufficient accuracy only by the oxygen density, according to the amount of carbon dioxide in the cylinder. This makes it possible to obtain high reliability in the ideal heat generation rate waveform.

  In this embodiment, the ideal heat generation rate waveforms are synthesized to create an ideal heat generation rate waveform for the entire cylinder, and the combustion state is diagnosed using the ideal heat generation rate waveform. ing. For this reason, when the actual heat generation rate waveform deviates from the ideal heat generation rate waveform by a predetermined amount or more for each of the plurality of fuel reaction forms, it is possible to diagnose that the reaction form is abnormal. it can. That is, each reaction form can be handled individually and the presence or absence of abnormality can be diagnosed for each. For this reason, it is possible to specify the reaction form in which an abnormality has occurred with high accuracy, and to improve the diagnostic accuracy. And by taking improvement measures (correction of control parameters) for the reaction form diagnosed as abnormal (when the divergence is equal to or less than a predetermined correctable deviation amount), the reaction state of the reaction form is optimized. Therefore, it is possible to correct the optimal control parameter for performing the correction, and an effective correction operation can be performed. As a result, it becomes possible to bring the entire reaction of the fuel closer to the ideal reaction (the actual heat generation rate waveform of each reaction approaches the ideal heat generation rate waveform), and the controllability of the engine 1 is greatly improved. be able to.

  Further, when it is diagnosed that an abnormality has occurred in the reaction, whether or not the abnormality can be resolved is determined based on a deviation amount of the actual heat generation rate waveform from the ideal heat generation rate waveform. Therefore, it is possible to accurately determine a state in which a normal reaction state is obtained by correcting the control parameter and a state in which maintenance such as component replacement is necessary.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to the in-line four-cylinder diesel engine 1 mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited. Further, the present invention is not limited to diesel engines using light oil as fuel, but can also be applied to engines using gasoline or other fuels.

  In the above embodiment, the combustion state diagnosis apparatus according to the present invention is stored in the ROM of the in-vehicle ECU 100 (mounted on the vehicle), and the combustion state is diagnosed in the operating state of the engine 1. The present invention is not limited to this, and the combustion state diagnosis device is provided in an experimental device (engine bench tester), and the combustion state is diagnosed when the engine 1 is tested on the experimental device in the design stage of the engine 1. It is also possible to apply to a usage pattern in which an appropriate value of the control parameter is obtained by performing the above.

  In the above embodiment, ideal heat generation rate waveforms are created for each of the region outside the cavity and the region inside the cavity, and these are combined and used for diagnosis of the combustion state. The present invention is not limited to this, and the diagnosis of the combustion state can be performed by using the ideal heat generation rate waveform created for each region individually, and the engine design and the control parameter can be adjusted. It may be used for seeking.

  Further, in the above-described embodiment, the engine 1 to which the piezo injector 23 that changes the fuel injection rate by being in a fully opened valve state only during the energization period is described. However, the present invention applies a variable injection rate injector. Application to engines is also possible.

  INDUSTRIAL APPLICABILITY The present invention is applicable to creation of a heat release rate waveform for each reaction of fuel and diagnosis of each reaction in a diesel engine mounted on an automobile.

1 engine (internal combustion engine)
12 Cylinder bore 13 Piston 13b Cavity 23 Injector (fuel injection valve)
3 Combustion chamber 4A In-cylinder pressure sensor 100 ECU
I, I 'ideal heat release rate waveform model of vaporization reaction
II, II 'Waveform model of ideal heat release rate for low-temperature oxidation reaction
III, III 'ideal heat release rate waveform model of pyrolysis reaction
IV, IV 'Ideal heat release rate waveform model of high temperature oxidation reaction by premixed combustion V, V' Ideal heat release rate waveform model of high temperature oxidation reaction by diffusion combustion

Claims (11)

An apparatus for creating a heat release rate waveform of a fuel reaction in an internal combustion engine that burns fuel injected into a cylinder from a fuel injection valve,
When creating an ideal heat generation rate waveform of the reaction of the fuel injected from the fuel injection valve, the reference heat generation rate defined based on the oxygen density in the cylinder is corrected according to the amount of carbon dioxide in the cylinder. An apparatus for generating a heat generation rate waveform of an internal combustion engine, characterized in that an ideal heat generation rate is calculated by the above. In the internal combustion engine heat release rate waveform creation device according to claim 1,
Ideal heat generation by correcting the reaction gradient of the ideal heat release rate waveform defined based on the oxygen density in the cylinder according to the carbon dioxide density determined from the amount of carbon dioxide in the cylinder and the volume in the cylinder An apparatus for creating a heat release rate waveform of an internal combustion engine, characterized in that the rate waveform is created. In the internal combustion engine heat release rate waveform creation device according to claim 2,
An apparatus for creating a heat release rate waveform of an internal combustion engine, wherein the ideal heat release rate waveform is created by reducing the reaction gradient of the ideal heat release rate waveform as the carbon dioxide density increases. In the internal combustion engine heat release rate waveform creation device according to claim 3,
The higher the carbon dioxide density, the lower the reaction rate of the fuel, and the lower the oxygen density in the cylinder, the greater the degree of influence of the carbon dioxide density on the reaction rate of the fuel, creating the ideal heat release rate waveform. An apparatus for creating a heat release rate waveform of an internal combustion engine, characterized by being configured. In the internal combustion engine heat release rate waveform creation device according to any one of claims 1 to 4,
When the state of the air-fuel mixture in the cylinder is uniform, the ideal heat release rate is calculated based on the oxygen density, oxygen excess rate, and carbon dioxide density in the cylinder,
When the air-fuel mixture in the cylinder is uneven, the ideal heat release rate is calculated based on the oxygen density, oxygen excess rate, carbon dioxide density, and fuel density in the cylinder. An apparatus for creating a heat release rate waveform of an internal combustion engine. In the heat generation rate waveform creation device for an internal combustion engine according to any one of claims 1 to 5,
When calculating the ideal heat generation rate by correcting the reference heat generation rate by the carbon dioxide density obtained from the amount of carbon dioxide in the cylinder and the volume in the cylinder,
The timing for obtaining the carbon dioxide density is set to the timing at which the piston reaches the compression top dead center. In the internal combustion engine heat release rate waveform creation device according to any one of claims 1 to 6,
The inside of the cylinder is divided into an internal region of a cavity provided in the piston and an external region of the cavity, and an ideal heat generation rate waveform of fuel reaction in each of the internal region of the cavity and the external region of the cavity is created, An apparatus for creating a heat release rate waveform of an internal combustion engine, characterized in that an ideal heat release rate waveform for the entire cylinder is created by synthesizing the ideal heat release rate waveform of each of these regions. In the internal combustion engine heat release rate waveform creation device according to any one of claims 1 to 7,
The ideal heat generation rate waveform is an ideal heat generation rate waveform model composed of triangles with the reaction rate as the base point, the reaction rate as the slope, the reaction amount as the area, and the reaction period as the base length. An apparatus for creating a heat release rate waveform of an internal combustion engine, which is created by smoothing an ideal heat release rate waveform model of each reaction by filtering.   An ideal heat generation rate waveform obtained by the internal combustion engine heat generation rate waveform creation device according to any one of claims 1 to 8, and an actual heat generation rate waveform when the fuel actually reacts in the cylinder And when the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform is equal to or greater than a predetermined amount, it is configured to diagnose that an abnormality has occurred in the fuel reaction. A combustion state diagnostic device for an internal combustion engine. The combustion state diagnosis apparatus for an internal combustion engine according to claim 9,
When there is a reaction in which the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform is greater than or equal to a predetermined abnormality determination deviation amount, and it is diagnosed that the reaction is abnormal, When the deviation of the actual heat generation rate waveform with respect to the generation rate waveform is equal to or less than a predetermined correctable deviation amount, the control parameter of the internal combustion engine is corrected to control the deviation to be less than the abnormality determination deviation amount. A combustion state diagnosis of an internal combustion engine characterized by diagnosing that a failure has occurred in the internal combustion engine when the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform exceeds the correctable deviation amount apparatus. The combustion state diagnosis apparatus for an internal combustion engine according to claim 9 or 10,
A combustion state diagnostic device for an internal combustion engine, which is mounted on a vehicle or mounted on an experimental device.

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