JP6015563B2 - Heat generation rate waveform creation device and combustion state diagnostic device for internal combustion engine - Google Patents

Description

  The present invention relates to a heat generation rate waveform generation device that generates a heat generation rate waveform of an internal combustion engine such as a diesel engine, and a combustion state diagnosis device that diagnoses the combustion state of the internal combustion engine.

  Conventionally, the combustion state of a diesel engine (hereinafter, simply referred to as “engine”) used as an automobile engine or the like is evaluated. Specifically, this combustion state evaluation method uses a heat generation rate waveform that is a change in the heat generation rate (heat generation amount per unit rotation angle of the crankshaft) in the combustion chamber, and the waveform is an ideal waveform. The combustion state in the combustion chamber is evaluated by judging whether or not (see, for example, Patent Document 1). In addition, as the reaction form (combustion form) constituting the heat release rate waveform, there are a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, a high temperature oxidation reaction, etc., and a heat release rate waveform is obtained for each of the reactions, The combustion state of each reaction form is diagnosed using the heat release rate waveform.

JP 2011-106334 A JP 2010-138712 A

  In a diesel engine, the atomized fuel injected into the cylinder is vaporized (vaporization reaction), and when the in-cylinder temperature (in-cylinder gas temperature) reaches 750 K (low temperature oxidation reaction start temperature), the low temperature of the atomized fuel. Oxidation of an oxidation reaction component (n-cetane or the like) is started (low temperature oxidation reaction is started). In such a low temperature oxidation reaction, the floating period in which the fuel floats in the cylinder changes depending on the fuel injection timing. When the fuel floating period changes, the temperature at which the low-temperature oxidation reaction can start (reaction start time) changes. Therefore, it is important to accurately determine the reaction start time in order to accurately generate the heat release rate waveform. It becomes.

  The present invention has been made in consideration of such circumstances, and provides a heat generation rate waveform creation device for an internal combustion engine capable of creating a heat generation rate waveform of a low-temperature oxidation reaction with high accuracy, and An object of the present invention is to provide a combustion state diagnostic device for diagnosing the combustion state of an internal combustion engine.

  The present invention is directed to an apparatus for creating a heat generation rate waveform of a fuel reaction in an internal combustion engine that burns fuel injected into a cylinder from a fuel injection valve. In such a heat generation rate waveform creation device, when creating the ideal heat generation rate waveform of the low temperature oxidation reaction among the reactions of the fuel injected from the fuel injection valve, the in-cylinder gas temperature is the reference reaction of the low temperature oxidation reaction. In the case of fuel injection in a temperature region below the start temperature, the reaction start time is set to an advance side as the floating period is longer according to the floating period in which the fuel floats in the cylinder, and the ideal heat of the low temperature oxidation reaction The technical feature is to create an incidence waveform.

  In this invention, the floating period is a period from the start of vaporization of the fuel injected into the cylinder until the in-cylinder gas temperature reaches the reference reaction start temperature (750 K) of the low temperature oxidation reaction.

  In the present invention, when the in-cylinder gas temperature at the time of fuel injection is the reference reaction start temperature (750 K), when the floating period necessary for starting the low temperature oxidation reaction is used as a reference, the actual floating period is more than the reference floating period. Pay attention to the fact that the longer the floating period (activation energy acquisition period), the lower the temperature at which the reaction start of the low-temperature oxidation reaction starts, the lower the temperature from 750 K (the reaction start time of the low-temperature oxidation reaction changes to the advance side). When the fuel is injected into the cylinder in the above-described configuration, that is, the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature of the low-temperature oxidation reaction (750 K or less), the fuel (vaporized fuel) floats in the cylinder. A configuration is adopted in which the reaction start time is set to the advance side as the floating period is longer depending on the period. With such a configuration, it is possible to accurately define the reaction start timing of the low-temperature oxidation reaction, and an ideal heat generation rate waveform of the low-temperature oxidation reaction can be created with high accuracy.

  Here, the “ideal heat generation rate waveform” in the present invention means that the fuel injection amount according to the command injection amount, the fuel injection pressure according to the command injection pressure, and the fuel injection period according to the command injection period are secured. This is the state of the heat release rate waveform that should be obtained theoretically assuming that the combustion efficiency is sufficiently high.

  Further, 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.

  Further, the “vaporization start timing” will be described. When the temperature field (in-cylinder gas temperature) at which the fuel is injected is equal to or higher than 623 K (the boiling point (maximum value) of light oil), vaporization starts simultaneously with the start of fuel injection. Therefore, the vaporization start timing is the same as the fuel injection start timing (vaporization start timing = fuel injection start timing). When fuel is injected in a temperature range lower than 623K, the vaporization start timing shifts to the retard side with respect to the fuel injection start timing, so that the temperature range lower than 623K is also targeted. May determine the vaporization start time in consideration of the delay.

  In the heat generation rate waveform creation device of the present invention, in addition to creating an ideal heat generation rate waveform for a low temperature oxidation reaction, an ideal heat generation rate waveform for each reaction such as a vaporization reaction, a thermal decomposition reaction, and a high temperature oxidation reaction is created. You may make it do. Thus, by obtaining the ideal heat generation rate waveform for each of the vaporization reaction, the low temperature oxidation reaction, the thermal decomposition reaction, and the high temperature oxidation reaction, it is possible to individually define each reaction form. For example, when used for diagnosis of a combustion state to be described later, it is possible to determine in which reaction an abnormality has occurred by comparing the ideal heat generation rate waveform and the actual heat generation rate waveform. Become. In particular, the vaporization reaction and the thermal decomposition reaction are endothermic reactions (the thermal decomposition reaction may be an exothermic reaction), but there are abnormalities in the reaction rate, reaction amount, and reaction period for this endothermic reaction. It is possible to diagnose whether or not there is any, and it is possible to improve the diagnostic accuracy.

  Note that the utilization form of the ideal heat release rate waveform obtained for each of the reactions includes not only the diagnosis of the combustion state but also the design of the internal combustion engine and the acquisition of the appropriate value of the control parameter.

  In addition, as a procedure for creating an ideal heat release rate waveform of each reaction including the low-temperature oxidation reaction, the reaction rate is the slope of the reaction, the reaction amount is the area, and the reaction period is the base length, starting from the reaction start time. It is created by creating an ideal heat release rate waveform model consisting of triangles, 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.

  More specifically, 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 is determined. When there is a reaction that is more than a fixed amount, it is configured to diagnose that an abnormality has occurred in the reaction.

  The “reaction abnormality” here 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, exhaust gas). This includes the case where there is a deviation in the heat generation rate waveform to the extent that it is possible to correct emissions and combustion noise within the limits of regulation.

  With 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 a plurality of fuel reactions (reaction forms), it is diagnosed that the reaction is abnormal. It will be. In other words, each reaction of the fuel has different characteristics (reaction start temperature, reaction rate, etc.), so that each ideal characteristic and the actually obtained (actually measured) actual heat generation rate waveform By comparing with the characteristics, 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 the control parameter when the control parameter of the internal combustion engine is corrected so that the deviation is less than the abnormality determination deviation amount, an oxygen 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 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, when a lower limit value is set in advance for each of the in-cylinder gas temperature, oxygen density, and fuel density, and any of these in-cylinder gas temperature, oxygen density, or fuel density is lower than the lower limit value. If the control parameter correction amount of the internal combustion engine exceeds a predetermined guard value, it is diagnosed that the internal combustion engine has failed.

  Here, the usage pattern of the heat generation rate waveform generating device for the internal combustion engine specifically includes mounting on a vehicle or mounting on an experimental device.

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

  According to the present invention, in the case of fuel injection in a temperature range where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature of the low-temperature oxidation reaction, the reaction starts as the floating period increases according to the floating period in which the fuel floats in the cylinder. Since the timing is set to the advance side, the reaction start timing of the low temperature oxidation reaction can be accurately defined. As a result, an ideal heat generation rate waveform of the low-temperature oxidation reaction can be created with high accuracy. Further, when the combustion state is diagnosed using this ideal heat generation rate waveform, the accuracy of the diagnosis can be increased.

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. FIG. 6 is a waveform diagram showing an example of a relationship between a fuel injection rate (fuel injection amount per unit rotation angle of crankshaft) waveform and a heat generation rate (heat generation amount per unit rotation angle of crankshaft) waveform. It is a figure which shows an example of the map which calculates | requires the reaction start possible temperature of a low-temperature oxidation reaction. 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 a rotational speed correction coefficient map. 9A shows an ideal heat generation rate waveform model, FIG. 9A shows a case where the ideal heat generation rate waveform model is an isosceles triangle, and FIG. 9B shows a case where the ideal heat generation rate waveform model is an unequal triangle. FIG. FIG. 10A shows the relationship between the elapsed time when the fuel is injected from the injector and the amount of fuel supplied into the cylinder, and FIG. 10B 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. 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. 11 by a filter process. It is a figure which shows an example of the ideal heat release rate waveform (solid line) at the time of one fuel injection, and an actual heat release rate waveform (a broken line and a dashed-dotted line).

  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 of 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 a vehicle will be described. To do.

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

  As shown in FIG. 1, the engine 1 according to the present 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 increases the pressure of the fuel pumped from the fuel tank 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 accumulating chamber that holds (accumulates) high-pressure fuel at a predetermined pressure, and distributes the accumulated fuel to the injectors 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 storage 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. .

  The 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 energization of the glow plug 19 is controlled by the ECU 100.

  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.

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 43 outputs a detection signal corresponding to the flow rate (intake air amount) of the intake air upstream of the intake throttle valve 62 in the intake system 6. The rail pressure sensor 41 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22. The throttle opening sensor 42 detects the opening of the intake throttle valve 62. The intake pressure sensor 48 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The intake air temperature sensor 49 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the temperature of the intake air. The A / F (air-fuel ratio) sensors 44a and 44b are arranged on the upstream side and the downstream side of the NSR catalyst 75, respectively, and output detection signals that change continuously according to the oxygen concentration in the exhaust gas.

-ECU-
The ECU 100 includes a microcomputer (not shown) such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and an input circuit and an output circuit.

  As shown in FIG. 3, the input circuit of the ECU 100 includes the rail pressure sensor 41, the throttle opening sensor 42, the air flow meter 43, the A / F sensors 44a and 44b, the exhaust temperature sensors 45a and 45b, the intake pressure sensor 48, An intake air temperature sensor 49 is connected. Further, the input circuit includes a water temperature sensor 46 that outputs a detection signal corresponding to the cooling water temperature of the engine 1, an accelerator opening sensor 47 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, and an output shaft (crank) of the engine 1. A crank position sensor 40 that outputs a detection signal (pulse) every time the shaft rotates a certain angle, an in-cylinder pressure sensor (CPS (Combustion Pressure Sensor)) 4A that detects the pressure in the cylinder (combustion chamber 3), etc. Is connected.

  On the other hand, the output circuit of the ECU 100 includes the supply pump 21, the injector 23, the intake throttle valve 62, the EGR valve 81, the variable nozzle vane mechanism (actuator for adjusting the opening degree of the variable nozzle vane) 54 of the turbocharger 5 and the like. It is connected.

  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 the 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. Further, the ECU 100 performs energization control of the glow plug 19.

-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) descends via 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).

-Separation of reaction form of fuel-
Each reaction form (combustion form) of the fuel injected into the cylinder (combustion chamber 3) of the engine 1 is separated into a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, and a high temperature oxidation reaction, as shown in FIG. be able to. These combustion forms occur in the order of a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, and a high temperature oxidation reaction. In addition, FIG. 5 is a figure which shows the heat release rate waveform in each reaction form when one fuel injection (pilot injection) is performed. Details of each reaction mode will be described later.

-Reaction start time of low-temperature oxidation reaction-
Next, the reaction start timing of the low temperature oxidation reaction will be described.

  First, in an engine mounted on a vehicle or the like, when fuel injection is performed in a temperature range where the in-cylinder gas temperature is 750 K or less, a floating period (activation energy acquisition period) in which the fuel floats in the cylinder depending on the fuel injection timing Changes. When the sprayed fuel floating period changes, the temperature at which the low-temperature oxidation reaction can start (the low-temperature oxidation reaction start time) changes. Therefore, it is possible to accurately grasp the reaction start time and accurately calculate the heat release rate waveform. It is important in creating.

  In consideration of such points, in the present embodiment, the fuel is injected into the cylinder (inside the combustion chamber 3) in the temperature range where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature (750K) of the low temperature oxidation reaction. By setting the reaction start time variably according to the floating period of fuel floating in the cylinder and creating the heat release rate waveform of the low temperature oxidation reaction, the ideal heat release rate waveform of the low temperature oxidation reaction can be obtained with high accuracy. Allow creation.

  Here, the reference reaction start temperature of the low-temperature oxidation reaction is 750 K. For example, when early injection (for example, fuel injection at BTDC 70 to 40 [° CA]) is performed, the floating period becomes longer and the activation energy is increased. Therefore, the low-temperature oxidation reaction can be started on the low-temperature side before reaching 750K. Moreover, depending on the floating period, the longer the floating period, the lower the reaction start temperature (the reaction start time becomes the advance value). In view of these points, in the present embodiment, when fuel is injected into the cylinder in a temperature region where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature of the low-temperature oxidation reaction, the floating period is determined according to the floating period. The longer the is, the longer the reaction start time is set (regulated), and the ideal heat release rate waveform of the low-temperature oxidation reaction is created using the reaction start time. The process of creating the ideal heat generation rate waveform will be described later.

(Processing for setting the reaction start time of the low-temperature oxidation reaction)
Next, an example of the process for setting the reaction start time of the low-temperature oxidation reaction will be described.

  First, in this processing example, when the in-cylinder gas temperature at the time of fuel injection is 750 K (reference reaction start temperature), the floating period necessary for starting the low temperature oxidation reaction is used as a reference, and the actual floating period is longer than the reference floating period. The longer the period (activation energy acquisition period), the more the temperature at which the reaction start of the low temperature oxidation reaction can be changed to a lower temperature than 750K (the reaction start time of the low temperature oxidation reaction changes to the advance side). Set (specify) the reaction start time of the low-temperature oxidation reaction.

Further, in this treatment example, the minimum value on the low temperature side of the reaction start possible temperature of the low temperature oxidation reaction is 650 K ([boiling point of light oil 623 K (maximum value)] + margin). When fuel is injected into the cylinder in such a temperature field (temperature field of 650 K or more), vaporization starts at the same time as fuel injection starts. That is, the vaporization start timing is the same as the fuel injection start timing (vaporization start timing = fuel injection start timing).
Specific Example of Reaction Start Time Setting Process Next, a specific example of the reaction start time setting process will be described below. However, the following processing is targeted for the case of fuel injection in a temperature region (the minimum value is 650 K) where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature 750 K. The process for setting the reaction start time of the low-temperature oxidation reaction is executed in the ECU 100, for example.

  [ST11] A cylinder angle at which the in-cylinder gas temperature reaches the reference reaction start temperature 750K using the estimated in-cylinder gas temperature and the reference reaction start temperature 750K of the low temperature oxidation reaction [°] CA] is calculated, and the calculated crank angle (absolute value) is set as the reference temperature arrival time [° CA].

  The in-cylinder gas temperature is estimated based on, for example, the intake air temperature detected by the intake air temperature sensor 49 and the air compression rate that changes as the piston 13 moves (from a calculation formula based on polytropic change). calculate. Further, when estimating the in-cylinder gas temperature, the temperature corresponding to the reaction heat amount of the vaporization reaction (endothermic reaction) may be subtracted.

  [ST12] Using the reference temperature arrival time [° CA] calculated in [ST11] and the vaporization start time (actual fuel injection start time) [° CA], the fuel spray is calculated from the following equation (1). The floating period FTx [sec] (absolute value) is calculated.

Floating period FTx = | (Vaporization start time−reference temperature arrival time) × {60 [sec] / (NE [rpm] × 360 [° CA])} | (1)
The engine speed (rotation speed) NE [rpm] is calculated from the output signal of the crank position sensor 40.

  [ST13] With reference to the map shown in FIG. 6 using the fuel spray floating period FTx [sec] calculated in [ST12] above, the reaction start possible temperature αx [K] (reference reaction start temperature 750 K) of the low temperature oxidation reaction Temperature on the lower temperature side). And the crank angle at which the in-cylinder gas temperature reaches the reaction startable temperature αx [K] of the low temperature oxidation reaction is calculated using the calculated low temperature oxidation reaction startable temperature αx [K], and the calculated Let the crank angle be the reaction start time [° CA] of the low-temperature oxidation reaction. The reaction start time of the low-temperature oxidation reaction calculated in this way is used for the process of creating an ideal heat generation rate waveform to be described later.

  Note that the reaction start time [° CA] of the low-temperature oxidation reaction calculated as described above may be corrected using a reference engine rotation speed (for example, 1000 rpm). Specifically, the low temperature oxidation reaction is obtained by multiplying the reaction start timing [° CA] of the low temperature oxidation reaction obtained in the above calculation process by the engine speed ratio (reference engine speed / actual engine speed NE). The rotational speed of the reaction start time [° CA] is corrected.

Here, the map shown in FIG. 6 shows that the floating period FT ₇₅₀ (for example, FT ₇₅₀ = 833 [necessary] for starting the low-temperature oxidation reaction when the in-cylinder gas temperature at the time of fuel injection is 750 K (reference reaction start temperature). μsec]) as a reference, and the longer the actual floating period FTx (activation energy acquisition period) than the reference floating period FT _{750, the} temperature at which the low-temperature oxidation reaction can be started changes to a lower temperature than 750K. In consideration, the relationship between the floating period FTx and the reaction start possible temperature αx [K] of the low-temperature oxidation reaction is defined in advance through experiments and simulations, and is stored in the ROM of the ECU 100.

  In the map shown in FIG. 6, the longer the floating period FTx [sec], the lower the temperature startable temperature αx [K] of the low-temperature oxidation reaction is set to a lower value. That is, the reaction start timing [° CA] of the low temperature oxidation reaction calculated from the reaction start possible temperature αx [K] of the low temperature oxidation reaction calculated from the map of FIG. 6 is advanced as the floating period FTx [sec] becomes longer. It becomes the value of the side.

  As described above, according to the present embodiment, when fuel is injected into the cylinder in a temperature range where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature of the low-temperature oxidation reaction, during the floating period in which the fuel floats in the cylinder. Accordingly, since the reaction start time is set to the advance side as the floating period is longer, the reaction start time of the low-temperature oxidation reaction can be accurately obtained. Thereby, the ideal heat release rate waveform mentioned later can be created with high accuracy.

-Judgment of necessity of glow plug energization
Next, when the in-cylinder gas temperature at the time of fuel injection is in a temperature range of 750 K (reference reaction start temperature) or less, the glow plug 19 is energized using the floating period necessary for the start of the low temperature oxidation reaction. Processing for determining necessity is described.

  In this example, it is determined whether or not the glow plug 19 needs to be energized when returning from a fuel cut state during traveling on a downhill road at an extremely low temperature, that is, when restarting in a high rotation / low temperature state. An example of the specific processing will be described below. This glow plug energization necessity determination process is executed by the ECU 100, for example.

  [ST21] The in-cylinder gas temperature at the time of fuel injection is estimated, and the estimated in-cylinder gas temperature is used as the temperature parameter (reaction startable temperature) on the horizontal axis in FIG. Thus, the floating period FTx [sec] necessary for starting the low-temperature oxidation reaction is calculated. The in-cylinder gas temperature is estimated based on, for example, the intake air temperature detected by the intake air temperature sensor 49 and the air compression rate that changes as the piston 13 moves (from a calculation formula based on polytropic change). calculate.

  [ST22] A crank angle period Cint [° CA] (absolute value) from the actual fuel injection start timing (vaporization start timing) to the compression TDC is obtained. The crank angle period Cint [° CA] is converted into a determination time interval Tcint [sec]. Specifically, the crank angle period Cint [° CA] is set to the determination time interval Tcint [sec] by an arithmetic expression [Tcint = Cint × {60 [sec] / (NE [rpm] × 360 [° CA])}]. Convert.

  [ST23] The floating period FTx [sec] calculated in [ST21] is compared with the determination time interval Tcint [sec] calculated in [ST22], and the floating period FTx is shorter than the determination time interval Tcint ( Even if the in-cylinder gas temperature does not reach 750K, the floating period FTx, which is a temporal condition (condition for starting a low-temperature oxidation reaction), is established before the compression TDC (the floating period FTx is Since it falls within the compression stroke), it is determined that a low-temperature oxidation reaction occurs, and it is determined that energization to the glow plug 19 is unnecessary.

  On the other hand, when the floating period FTx is longer than the determination time interval Tcint (when the floating period FTx is not established before reaching the TDC), it is determined that the low-temperature oxidation reaction does not occur and it is determined that ignition is impossible. When ignition is impossible, the glow plug 19 is energized. If ignition is impossible, exhaust air circulation may be performed to prohibit fresh air intake (intake air cooling is prohibited), or fresh air may be generated by energizing the glow plug 19 and exhaust gas circulation. An inhalation prohibition process may be performed. Note that the fresh air inhalation prohibition process by exhaust gas circulation may be executed during fuel cut.

  Since the process of determining whether or not the glow plug 19 needs to be energized is executed in this way, the energization of the glow plug 19 can be optimized. Frequency) and deterioration of the glow plug 19 can be suppressed.

  In the above example, the crank angle period Cint used for determining whether or not the glow plug is energized is the period from the fuel injection start timing (vaporization start timing) to the compression TDC, but the compression is started from the fuel injection start timing (vaporization start timing). The crank angle period Cint may be a predetermined crank angle before TDC, or the crank angle period Cint may be from a fuel injection start timing (vaporization start timing) to a predetermined crank angle after compression TDC.

  In the above example, the determination is performed by converting the crank angle period Cint [° Ca] to the determination time interval Tcint [sec]. Instead of this, the floating period FTx [sec] is used as the engine speed. The crank angle period [° CA] may be converted using NE, and the determination may be made by comparing the floating crank angle period [° CA] with the crank angle period Cint [° CA].

  In the above example, it is determined whether or not the glow plug needs to be energized when returning from the fuel cut state during downhill travel at extremely low temperatures. For example, it may be determined whether or not glow plug energization is necessary in other operating states.

  In addition to mounting on a vehicle, mounting on an experimental device can be cited as a usage pattern of the combustion state diagnostic device for an internal combustion engine that determines whether or not glow plug energization is necessary.

-Creation of heat release rate waveform, combustion state diagnosis, and control parameter correction-
Next, creation of a heat release rate waveform (creation of an ideal heat release rate waveform), which is a feature of this embodiment, combustion state diagnosis (diagnosis of each reaction mode of fuel in a cylinder), and the diagnosis result The control parameter correction executed in this way will be described.

  In the generation of the heat generation rate waveform, the combustion state diagnosis, and the control parameter correction, as shown in FIG. 7, (1) generation of an ideal heat generation rate waveform and (2) generation of an actual heat generation rate waveform are performed. (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. The operations (processes) (1) to (4) or the operations (processes) (2) to (4) may be executed every cycle, or may be executed every predetermined multiple cycles. Also good.

  Further, in the creation of the (1) ideal heat release rate waveform, (1-A) separation of fuel reaction forms, (1-B) ideal heat release rate waveform models for the separated reaction forms, respectively. Creation of an ideal heat release rate waveform by filtering (filter processing) of (1-C) ideal heat release rate waveform model is 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.

  As the rate-limiting conditions for the reaction (chemical reaction, etc.) of the fuel injected into the cylinder from the injector 23, the in-cylinder gas temperature, the oxygen amount in the cylinder (a value correlated with the oxygen density in the cylinder), Examples include the amount of fuel (a value that correlates with the fuel density in the cylinder) and the distribution of fuel in the cylinder. Among these, the order of low control freedom is the order of in-cylinder gas temperature, the amount of oxygen in the cylinder, the amount of fuel in the cylinder, and the distribution of fuel in the cylinder.

  That is, the in-cylinder gas temperature is substantially determined by the intake air temperature and the compression ratio of the engine 1 before the fuel reacts, and the degree of freedom of control is the lowest. The in-cylinder gas temperature also varies depending on the amount of preheating caused by combustion of the fuel when fuel injection is performed in advance (for example, when fuel injection for preheating is performed). Further, since the amount of oxygen in the cylinder can be adjusted by the opening of the intake throttle valve 62 and the opening of the EGR valve 81, the degree of freedom of control is higher than the in-cylinder gas temperature. Further, the oxygen amount in the cylinder also varies depending on the supercharging rate by the turbocharger 5. Further, the amount of oxygen in the cylinder also varies depending on the amount of oxygen consumed by combustion of the fuel when fuel injection (fuel injection for preheating or the like) is performed in advance. Further, the amount of fuel in the cylinder 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 degree of freedom of control is higher than that. In addition, since the fuel distribution in the cylinder 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.

  And in this embodiment, the priority of the conditions which determine the reaction state of a fuel is set high in order with the said low degree of freedom of control. Here, the quantitative conditions of the in-cylinder gas temperature, the oxygen amount in the cylinder, and the fuel amount in the cylinder have higher priority than the fuel distribution in the cylinder. That is, the start timing (reaction start timing) of each reaction of the fuel is determined using the in-cylinder gas temperature 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 in-cylinder gas temperature (compressed gas temperature).

  Based on this reaction start time (reaction start time according to the floating period in the case of low-temperature oxidation reaction), the reaction rate, reaction amount, and reaction period are obtained, and an ideal heat release rate waveform model is obtained for each reaction form. I try to create it. That is, the reaction speed, the reaction amount, and the reaction period of each of the plurality of reaction forms of the fuel injected into the cylinder are defined as the in-cylinder environment (cylinder gas temperature that determines the reaction start timing) and the fuel composition (the fuel that contributes to the reaction). The ideal heat release rate waveform model for each reaction is created.

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 in-cylinder gas temperature (reference temperature), the fuel composition, and the like at the reaction start time and The reference reaction amount efficiency [J / mm ³ ] is 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 efficiency and the fuel amount. Further, the reaction speed is corrected according to the engine speed described later. The “reaction rate efficiency” is also referred to as “reaction rate gradient coefficient”, and the “reaction amount efficiency” is also referred to as “combustion efficiency”.

  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 determined by the following equation (2).

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

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

  When fuel is injected from the injector 23, a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, and a high temperature oxidation reaction are performed in the cylinder according to the in-cylinder environment. Hereinafter, each reaction mode will be described.

(A) Vaporization reaction The vaporization reaction is a reaction in which the fuel injected from the injector 23 receives the heat in the cylinder and vaporizes, and is a reaction independent of other reactions. The boiling point of light oil used in the diesel engine 1 is generally 453 K (180 ° C.) to 623 K (350 ° C.). The reaction amount efficiency in the vaporization reaction is, for example, 1.14 [J / mm ³ ].

  The effective injection amount in the vaporization reaction (the amount of fuel contributing to the vaporization reaction) is an amount obtained by subtracting the wall surface adhesion amount (the fuel amount adhering to the wall surface of the cylinder bore 12) from the fuel injection amount. This wall surface adhesion amount can be experimentally determined according to the injection amount (which has a correlation with fuel penetration force) and the injection timing (which has a correlation with cylinder pressure). For this reason, the reaction amount in this vaporization reaction is obtained by an arithmetic expression [reaction amount in vaporization reaction = −1.14 × effective injection amount].

  Since this vaporization reaction is an endothermic reaction, the reaction amount (generated heat amount) is a negative value.

(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 diesel oil as a diesel engine fuel burns. It is a reaction. The low-temperature oxidation reaction is a reaction that occurs by hydrogen abstraction and oxygen addition at the end of a linear hydrocarbon, and is not a carbon chain decomposition, and is therefore a reaction that is independent of the thermal decomposition reaction.

  The low-temperature oxidation reaction component is a component that can be ignited even when the in-cylinder gas temperature is relatively low, and as the amount of n-cetane or the like increases (the higher the cetane fuel), The low temperature oxidation reaction easily proceeds, and the ignition delay is suppressed. Specifically, the low temperature oxidation reaction component such as n-cetane starts combustion (low temperature oxidation reaction) when the in-cylinder gas temperature 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 in-cylinder gas temperature reaches about 900K.

The standard reaction rate efficiency in this low-temperature oxidation reaction is, for example, 0.294 [J / CA ² / mm ³ ]. The standard reaction amount efficiency is, for example, 5.0 [J / mm ³ ].

The reaction rate and reaction amount of the low-temperature oxidation reaction are calculated based on the reference reaction rate efficiency and the reference reaction amount efficiency (for example, calculated by multiplying the effective injection amount). Further, in calculating the reaction rate of the low temperature oxidation reaction, a coefficient (rotational speed correction coefficient = (rotational speed correction coefficient) = (reference reaction speed) obtained by multiplying the reference reaction speed efficiency by the effective injection amount (reference reaction speed). The reference rotation speed / actual rotation 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. 8 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, and its reaction temperature is about 800K. The standard reaction rate efficiency in this thermal decomposition reaction is, for example, 0.384 [J / CA ² / mm ³ ]. The reaction amount efficiency is, for example, 5.0 [J / mm ³ ]. The reaction rate and reaction amount of the thermal decomposition reaction are also calculated based on the reference reaction rate efficiency and reaction amount efficiency (for example, calculated by multiplying the effective injection amount).

  In this 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 (premixed combustion)
The reaction temperature of the high temperature oxidation reaction by premixed combustion is about 900K. That is, the reaction that starts combustion when the in-cylinder gas temperature reaches 900 K is a high-temperature oxidation reaction by this premixed combustion. Since this high temperature oxidation reaction is an oxidation reaction of a thermally decomposed carbon chain, the thermal decomposition reaction occurs in pairs.

  When fuel is injected into the cylinder where the in-cylinder gas temperature is 1000 K or more (main injection), the injected fuel starts to burn immediately after injection. This reaction is a high temperature oxidation reaction by diffusion combustion.

The standard reaction rate efficiency in the high-temperature oxidation reaction by premixed combustion is, for example, 4.3 [J / CA ² / mm ³ ]. The reaction amount efficiency is, for example, 30.0 [J / mm ³ ]. The reaction rate and reaction amount of the high-temperature oxidation reaction by this premixed combustion are also calculated based on the above-mentioned standard reaction rate efficiency and reaction amount efficiency (for example, the wall injection amount is determined from the effective injection amount (fuel injection amount (command value)). Calculated by multiplying the subtracted amount)).

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

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

(1-B) Creation of Ideal Heat Release Rate Waveform Model for Each Separated Reaction Form Next, creation of ideal heat release rate waveform models for each separated reaction form 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 the vaporization reaction, the low temperature oxidation reaction, the thermal decomposition reaction, and the high temperature oxidation reaction.

  In this embodiment, the ideal heat release rate waveform model is approximated to an isosceles triangle for each reaction. That is, with the reaction start temperature (reaction start time) as a base point, the reaction rate is the slope of the hypotenuse of the isosceles triangle, the reaction amount is the area of the isosceles triangle, and the reaction period is the length of the base of the isosceles triangle. Create an ideal heat release rate waveform model.

(A) Reaction start timing-Vaporization reaction As described above, when the temperature field (in-cylinder gas temperature) at which fuel is injected is 623 K or more, the reaction start timing of the vaporization reaction is the same as the fuel injection start timing. (Evaporation reaction start time = fuel injection start time) Note that when fuel is injected in a temperature region lower than 623K, the vaporization start timing is shifted to the retard side with respect to the fuel injection start timing, so that the temperature region lower than 623K is also targeted. May determine the reaction start time of the vaporization reaction in consideration of the delay.

-Low-temperature oxidation reaction The reaction start time of the low-temperature oxidation reaction is set by the processes of [ST11] to [ST13] described above. When fuel is injected into the cylinder in a temperature field (temperature region) where the in-cylinder gas temperature is higher than 750K, the crank angle [° CA] at the start of the fuel injection is set as the reaction start timing of the low-temperature oxidation reaction. To do.

・ Thermal decomposition reaction As described above, since the reaction temperature is about 800K, the crank angle [° CA] when the in-cylinder gas temperature reaches about 800K is determined as the reaction start time of the thermal decomposition reaction. And In addition, regarding the in-cylinder gas temperature when obtaining the reaction start timing of the thermal decomposition reaction, the temperature corresponding to the reaction heat amount of the vaporization reaction and the low-temperature oxidation reaction may be adjusted.

-High-temperature oxidation reaction As described above, the high-temperature oxidation reaction (premixed combustion) is about 900K, so the crank angle [° CA] when the in-cylinder gas temperature reaches about 900K is oxidized at high temperature. This is the reaction start time of the reaction. In addition, regarding the in-cylinder gas temperature at the time of obtaining the reaction start timing of the reaction start timing of the high temperature oxidation reaction, a temperature corresponding to the reaction heat amount of the vaporization reaction and the low temperature oxidation reaction may be adjusted.

  The in-cylinder gas temperature used for each process is estimated based on, for example, the intake air temperature detected by the intake air temperature sensor 49 and the air compression ratio that changes as the piston 13 moves (polytropic change). (Calculated from a calculation formula based on).

  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.

(B) Reaction rate (gradient)
The reaction rate is set based on the reference reaction rate efficiency. When the ideal heat generation rate waveform model is approximated to an isosceles triangle, the rising rate during the period in which the heat generation rate increases and the heat generation rate decrease. Their absolute values are consistent with the descending slope of the period.

  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.

(C) Generated heat (area)
The thermal 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 thermal 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.

(D) 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 (heat generation amount).

  As shown in FIG. 9, the area of the triangle (corresponding to the amount of generated heat) is S, the length of the base (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. 9A shows a case where the ideal heat generation rate waveform model is an isosceles triangle, and FIG. 9B shows a 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. 10A 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. 10A, the fuel injection period in which the fuel supply amount is obtained is divided into ten periods. That is, the fuel injection period is divided into ten periods with the same fuel supply amount, and the period numbers from the first period to the tenth period are assigned to each period. 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 not interrupted. The fuel injection is continued until the end of the tenth period in the injection mode in which the fuel injection in the three periods is started.

  FIG. 10B shows the reaction amount of the fuel injected in each period (the one shown in FIG. 10B is the exothermic amount in the exothermic reaction). As shown in FIG. 10B, the fuel injection in the first period is started and the fuel injection in the second period is started (period t1 in FIG. 10B). Only the reaction of the fuel injected in the period takes place. Then, during 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. 10B), the reaction of the fuel injected in the first period and The reaction of the fuel injected in the second period is 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. 10B), the reaction of the fuel injected in the second period and thereafter is not completed, and the reaction of the fuel injected in the second period to the tenth period continues. Yes. Then, when the reaction of the fuel injected in the second period is completed (timing T2 in FIG. 10B), the reaction of the fuel injected in the third period and thereafter is not completed. The reaction of the fuel injected in the 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. 10B) is a negative gradient period (a period retarded from the peak position of the reaction) of the ideal heat release rate waveform model. 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. 11 shows an ideal heat generation rate waveform model (an isosceles triangle corresponding to each reaction) when one fuel injection is performed. In FIG. 11, in order to facilitate the understanding of the present invention, an ideal heat release rate waveform model in the case where a vaporization reaction, a low temperature oxidation reaction, a thermal decomposition reaction, and a high temperature oxidation reaction are sequentially performed by one fuel injection ( An isosceles triangle corresponding to each reaction is shown. Specifically, I in the figure is an ideal heat release rate waveform model of a vaporization reaction, II is an ideal heat release rate waveform model of a low-temperature oxidation reaction, and III is an ideal heat release rate of a thermal decomposition reaction (a thermal decomposition reaction that is endothermic). A waveform model IV is an ideal heat generation rate waveform model of a high temperature oxidation reaction (premixed combustion).

  FIG. 12 shows an ideal heat generation rate waveform obtained by smoothing the ideal heat generation rate waveform model by filtering. In this way, the ideal heat release rate waveform model (isosceles triangle) corresponding to each reaction (vaporization reaction, low temperature oxidation reaction, thermal decomposition reaction, high temperature oxidation reaction) is smoothed by filtering, and the ideal heat release rate waveform Will be created.

  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 is created in the cylinder in the same way as described above, and this is smoothed by filtering to create an ideal heat release rate waveform. Is done.

  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, in order to synthesize each ideal heat generation rate waveform, in-cylinder gas temperature at the timing of fuel injection at the preceding stage (advance side), and thereafter It is necessary to consider that the in-cylinder gas temperature 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. Considering this, the ideal heat generation rate waveform due to the reaction of fuel injected on the advance side and the ideal heat generation 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 actual heat generation rate waveform to the crank angle side (advance side or When there is a reaction form in which the delay angle deviation is 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. 12 is created will be described as an example. Like the actual heat generation rate waveform shown by the broken line in FIG. When the actual heat generation rate waveform in the high-temperature oxidation reaction (premixed combustion) is shifted to the retard side with respect to the waveform shown in FIG. 12, and the deviation exceeds the threshold, the high-temperature oxidation reaction is abnormal. That is, it is diagnosed that an abnormality has occurred at the reaction start time of the high-temperature oxidation reaction.

  In addition, the peak value of the heat generation rate waveform in the high-temperature oxidation reaction is higher than the ideal heat generation rate waveform shown by the solid line as shown by the dashed line in FIG. If so, it is diagnosed that an abnormality has occurred in the high temperature oxidation reaction, that is, an abnormality has occurred in the reaction amount in the high temperature oxidation reaction. Such a diagnosis is not limited to the high temperature oxidation reaction, but is similarly performed for the above-described vaporization reaction, low temperature oxidation reaction, and 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 as shown by a broken line in FIG. 13, 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. 13, 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 other corrective action, when the reaction start time in the actual heat generation rate waveform is on the retard side with respect to the ideal heat generation rate waveform, the intake supercharging rate is increased or the pilot in the cylinder is piloted. 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 cylinder is excessive or insufficient, learning is performed so as to correct the EGR gas or the intake supercharging rate as the learning value. Further, when the fuel density in the cylinder is excessive or insufficient, learning is performed such that the fuel injection timing, the fuel injection pressure, and the fuel injection amount are corrected as the learning value.

  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, when the in-cylinder gas temperature, the oxygen density, and the fuel density are set in advance as lower limits, and any of the in-cylinder gas temperature, the oxygen density, and the fuel density is lower than the lower limits. If the correction amount of the control parameter of the engine 1 exceeds a predetermined guard value, it is diagnosed that the engine 1 has failed.

  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.

  As described above, according to the present embodiment, when fuel is injected into the cylinder in a temperature range where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature of the low-temperature oxidation reaction, the floating period in which the fuel floats in the cylinder. Accordingly, since the reaction start time is set to the advance side as the floating period is longer, the reaction start time of the low-temperature oxidation reaction can be accurately defined. As a result, an ideal heat generation rate waveform of the low-temperature oxidation reaction can be created with high accuracy.

  In this embodiment, the ideal heat generation rate waveform of such a low temperature oxidation reaction and the ideal heat generation rate waveforms of the vaporization reaction, thermal decomposition reaction, and high temperature oxidation reaction are combined to cover the entire cylinder. An ideal heat generation rate waveform is created, and the combustion state is diagnosed using this ideal heat generation rate waveform. 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.

  In the above example, ideal heat release rate waveforms are created for vaporization, low-temperature oxidation, thermal decomposition, and high-temperature oxidation by premixed combustion. In addition to these reactions, high-temperature by diffusion combustion is used. The combustion state may be diagnosed by creating an ideal heat generation rate waveform such as an oxidation reaction or an afterburning reaction.

-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.

  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 a control parameter is obtained by performing

  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 can be applied to creation of a heat release rate waveform of each reaction of fuel and diagnosis of each reaction in a diesel engine or the like mounted on an automobile.

1 engine (internal combustion engine)
12 Cylinder bore 13 Piston 23 Injector (fuel injection valve)
3 Combustion chamber 40 Crank position sensor 49 Intake air temperature sensor 4A In-cylinder pressure sensor 100 ECU
I Ideal heat release rate waveform model of vaporization reaction II Ideal heat release rate waveform model of low temperature oxidation reaction III Ideal heat release rate waveform model of pyrolysis reaction IV Ideal heat release rate waveform model of high temperature oxidation reaction

Claims (9)

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,
Among the reactions of the fuel injected from the fuel injection valve, when creating an ideal heat release rate waveform of the low-temperature oxidation reaction, the fuel injection in the temperature region where the in-cylinder gas temperature is equal to or lower than the reference reaction start temperature of the low-temperature oxidation reaction. In this case, an ideal heat generation rate waveform of the low-temperature oxidation reaction is created by setting the reaction start timing to an advance side as the floating period is longer according to the floating period in which the fuel floats in the cylinder. An apparatus for creating a heat release rate waveform of an internal combustion engine. In the internal combustion engine heat release rate waveform creation device according to claim 1,
The floating period is a period from the start of vaporization of the fuel injected into the cylinder to the time when the in-cylinder gas temperature reaches the reference reaction start temperature of the low-temperature oxidation reaction. Waveform creation device. In the internal combustion engine heat release rate waveform creation device according to claim 1 or 2,
An apparatus for creating a heat release rate waveform of an internal combustion engine, which creates an ideal heat release rate waveform for each of a vaporization reaction, the low temperature oxidation reaction, a thermal decomposition reaction, and a high temperature oxidation reaction. In the internal combustion engine heat release rate waveform creation device according to any one of claims 1 to 3,
The ideal heat release rate waveform is created by creating an ideal heat release rate waveform model consisting of triangles with the reaction rate as the base point, the reaction rate as the slope of the hypotenuse, 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, wherein the heat release rate waveform model is created by smoothing an ideal heat release rate waveform model by filtering.   An ideal heat generation rate waveform created by the heat generation rate waveform creation device for an internal combustion engine according to any one of claims 1 to 4, and an actual heat generation rate waveform when fuel actually reacts in the cylinder, If the deviation of the actual heat generation rate waveform from the ideal heat generation rate waveform is greater than or equal to a predetermined amount, the fuel reaction is diagnosed as having an abnormality. A combustion state diagnostic device for an internal combustion engine. The combustion state diagnosis apparatus for an internal combustion engine according to claim 5,
The combustion state diagnosis apparatus for an internal combustion engine, wherein the actual heat generation rate waveform is obtained based on an in-cylinder pressure detected by an in-cylinder pressure sensor. The combustion state diagnosis apparatus for an internal combustion engine according to claim 5 or 6,
When the divergence 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 divergence amount, and when it is diagnosed that the reaction is abnormal, the actual heat generation rate waveform with respect to the ideal heat generation rate waveform When the deviation of the heat generation rate waveform is equal to or less than a predetermined correctable deviation, the control parameter of the internal combustion engine is corrected to control the deviation to be less than the abnormality determination deviation, while the ideal heat generation rate A combustion state diagnosis apparatus for an internal combustion engine that diagnoses that a failure has occurred in the internal combustion engine when the deviation of the actual heat generation rate waveform from the waveform exceeds the correctable deviation amount. In the internal combustion engine heat release rate waveform creation device according to any one of claims 1 to 4,
An apparatus for creating a heat release rate waveform of an internal combustion engine, which is mounted on a vehicle or mounted on an experimental device. The combustion state diagnosis apparatus for an internal combustion engine according to any one of claims 5 to 7 ,
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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