JP2012092748A - Apparatus for estimating generation amount of nox in internal combustion engine, and control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for estimating a generation amount of NOin an internal combustion engine, and a control apparatus that can highly accurately estimate the amount NOrelated to fuel consumption and facilitate improving exhaust emission as an example.SOLUTION: A maximum value of an increase degree in a heat generation rate from changes of the heat generation rate in a combustion process is extracted as a maximum inclination of the heat generation rate. A total amount of the NOgeneration is calculated by multiplying the maximum inclination of the heat generation rate by a function "f" defining a correction value as a variable according to a combustion field temperature, an oxygen concentration, a filling gas amount and ignition timing at the time of combustion ignition relative to the maximum inclination of the heat generation rate. An oxygen concentration in a combustion chamber is controlled so that the total amount of the NOgeneration reaches a NOacceptable amount or smaller.

Description

  The present invention relates to a NOx generation amount estimation device for a compression ignition type internal combustion engine represented by a diesel engine, and an internal combustion engine that controls the combustion state of fuel in a combustion chamber based on the estimated NOx generation amount. Related to the control device. In particular, the present invention relates to measures for improving the estimation accuracy of the NOx generation amount and for improving exhaust emission.

  In an engine that performs lean combustion, such as a diesel engine, an operation region in which an air-fuel mixture with a high air-fuel ratio (lean atmosphere) is burned occupies most of the entire operation region. For this reason, there is a concern that a relatively large amount of nitrogen oxides (hereinafter referred to as NOx) is discharged.

  Further, as disclosed in Patent Document 1 and Patent Document 2, it is generally known that the amount of NOx generated has a correlation with the combustion temperature in the cylinder (hereinafter sometimes referred to as flame temperature). ing. Therefore, in order to reduce the amount of NOx generated, it is effective to appropriately control the flame temperature in the cylinder.

  As a measure for reducing the amount of NOx generated, it is known to provide an exhaust gas recirculation (EGR) device that recirculates a part of the exhaust gas to the intake passage. In other words, the exhaust gas is recirculated toward the cylinder to reduce the oxygen concentration and oxygen density in the cylinder. As a result, the combustion temperature (flame temperature) during the combustion stroke is lowered to suppress the generation of NOx, thereby improving exhaust emission.

JP 2003-293817 A JP-A-2005-180220 JP 2008-184908 A

  However, in the above diesel engine, the combustion state in the combustion chamber cannot be obtained properly due to various variations (manufacturing variation, variation in fuel properties, variation in fuel injection amount, etc.) that affect combustion, and NOx is generated. The amount may increase. For example, when a fuel with a cetane number higher than the specified cetane number is used, or when the fuel injection amount exceeds the appropriate amount, the heat generation rate (heat generation amount per unit rotation angle of the crankshaft) There is a possibility that the amount of NOx generated increases with a rapid increase in the amount of NOx.

  Until now, it has been known that a NOx sensor is provided in the exhaust system as means for detecting the amount of NOx generated (for example, Patent Document 3).

  However, when the NOx sensor is provided, the cost increases and sensor mounting work is required, so that practicality is lacking.

  In addition, no technology has yet been proposed that makes it possible to estimate the amount of NOx generated with high accuracy without using a NOx sensor. That is, it has not yet been realized to estimate the NOx generation amount with high accuracy without using the NOx sensor and obtain control amounts (correction amounts) for various control parameters suitable for the estimated NOx generation amount. is the current situation.

  For this reason, at present, even if the above-described various variations occur, the control amount with respect to the control parameter has a margin so that the NOx generation amount does not exceed the allowable range. That is, the actual condition is that the control amount value with respect to the control parameter is largely biased toward the side of suppressing the NOx generation amount. Specifically, the EGR amount is set larger than the appropriate amount, or the fuel injection amount is set larger so that the excess oxygen ratio in the cylinder does not become higher than necessary.

  However, if the EGR amount is set too large, the engine may not be able to obtain sufficient torque (torque required by the driver during a transition), and if the fuel injection amount is set too large Will lead to an increase in fuel consumption. This leads to a decrease in merchantability in terms of engine performance and fuel consumption rate.

  The present invention has been made in view of such a point, and an object of the present invention is to estimate the amount of NOx generated accompanying the combustion of fuel with high accuracy and to make use of it for improving exhaust emission and the like. An object of the present invention is to provide an engine NOx generation amount estimation device and an internal combustion engine control device.

-Principle of solving the problem-
The solution principle of the present invention taken in order to achieve the above object is that the change in the heat generation rate accompanying the combustion of fuel in the combustion chamber (the slope of the heat generation rate: for example, the differential value of the heat generation rate (the amount of heat generation) Based on the second derivative value of the above and the like)), the amount of NOx generated by the combustion is estimated.

-Solution-
Specifically, the present invention is premised on an apparatus that estimates the amount of NOx generated when fuel injected from a fuel injection valve burns into a combustion chamber of a compression ignition type internal combustion engine. A NOx generation amount estimating means for estimating the NOx generation amount by performing correction according to the state quantity in the combustion chamber with respect to the degree of increase in the heat generation rate due to the combustion of the fuel. I am preparing.

  The present invention finds that there is a correlation between the degree of increase in the heat generation rate due to the combustion of fuel and the amount of NOx generated due to the combustion, and estimates the amount of NOx generation with high accuracy based on the degree of increase in the heat generation rate. It is possible. That is, the NOx generation amount can be estimated with high accuracy without using a NOx sensor. Also, even if the rate of increase in the heat generation rate is the same, the amount of NOx generated may vary depending on the state quantity in the combustion chamber. The amount of NOx generated is estimated by performing correction according to the state quantity in the room. As a result, even when various variations (manufacturing variation, fuel property variation, injection amount variation, etc.) occur, the control parameters of the internal combustion engine are controlled based on the NOx generation amount estimated with high accuracy. , NOx generation amount can be suppressed within an allowable range. For this reason, taking into account the occurrence of the above-mentioned various variations, there is a margin in the control amount for the control parameter (the value of the control amount for the control parameter is largely biased toward the side that suppresses the NOx generation amount). This eliminates the need to improve the exhaust gas emission and improve the performance and fuel consumption rate of the internal combustion engine.

  Specific examples of the degree of increase in the heat generation rate that are corrected according to the state quantity in the combustion chamber include the maximum value of the degree of increase in the heat generation rate during the combustion stroke. That is, the NOx generation amount estimation means estimates the NOx generation amount by performing correction according to the state quantity in the combustion chamber with respect to the maximum value of the degree of increase in the heat generation rate during the combustion stroke. Is.

  This solution finds that the NOx generation amount has a particularly high correlation with the maximum value of the degree of increase in the heat generation rate during the combustion stroke, uses the maximum value of the degree of increase in the heat generation rate, The NOx generation amount is estimated by performing correction according to the state quantity. In this case, as the information processing operation after obtaining the maximum value of the degree of increase in the heat generation rate during the combustion stroke, it is not necessary to deal with the degree of increase in the heat generation rate throughout the combustion stroke, and the degree of increase in the heat generation rate It is only necessary to handle only the maximum value of the above-mentioned rise degree as information regarding. For this reason, compared with the case where the increase rate of the heat release rate in the whole combustion stroke is handled, the amount of information can be greatly reduced, and the processing capacity of the arithmetic unit (CPU) can be reduced. Become.

  As described above, a more specific configuration for estimating the NOx generation amount by correcting the maximum value of the degree of increase in the heat generation rate during the combustion stroke according to the state quantity in the combustion chamber is as follows. Is mentioned. That is, the predetermined period at the time of the combustion stroke is divided into a plurality of divided combustion stroke periods, and among the average values of the plurality of heat generation rate increases obtained in each divided combustion stroke period, the highest heat generation rate increase degree is obtained. The average value is the maximum value of the degree of increase in the heat release rate. That is, the NOx generation amount estimation means divides the predetermined period during the combustion stroke into a plurality of divided combustion stroke periods, and the highest heat generation among the average values of the plurality of heat generation rates obtained in each divided combustion stroke period. The average value of the rate of increase in the rate of heat is extracted as the maximum value of the rate of increase in the rate of heat release, and the maximum value of the rate of increase in the rate of heat release is corrected according to the state quantity in the combustion chamber. The generation amount is estimated.

  According to this configuration, even if the degree of increase in the heat generation rate suddenly changes due to a temporary disturbance, the maximum value of the degree of increase in the heat generation rate to be extracted is the plurality of heats obtained in the divided combustion stroke period. Since this is the average value of the rate of increase in the rate of occurrence, the influence of this disturbance can be mitigated, and the maximum value of the rate of increase in the rate of heat generation can be obtained as an accurate reflection of the combustion state. As a result, the NOx generation amount can be estimated with high accuracy, and the control parameters of the internal combustion engine can be controlled based on the estimated NOx generation amount, so that the exhaust emission can be improved.

  The degree of increase in the heat generation rate that is corrected according to the state quantity in the combustion chamber may be an average value of the degree of increase in the heat generation rate during a predetermined period during the combustion stroke. That is, the NOx generation amount estimation means estimates the NOx generation amount by correcting the average value of the degree of increase in the heat generation rate during a predetermined period during the combustion stroke according to the state quantity in the combustion chamber. It is to be configured.

  Also in this case, the influence of temporary disturbance can be mitigated and the maximum value of the degree of increase in the heat generation rate can be acquired as accurately reflecting the combustion state. For this reason, the amount of NOx generated can be estimated with high accuracy, and the control parameters of the internal combustion engine can be controlled based on the estimated amount of NOx generated, so that exhaust emission can be improved.

  The state quantity in the combustion chamber that corrects the degree of increase in the heat generation rate due to the combustion of the fuel includes the combustion field temperature at the time of fuel ignition, the oxygen concentration in the combustion chamber, the amount of charged gas in the combustion chamber, and the ignition of the fuel. Includes at least the time.

  Specific examples of the device that controls the combustion of fuel based on the NOx generation amount estimated by the NOx generation amount estimation device described above include the following. That is, an oxygen concentration control means for controlling the oxygen concentration in the combustion chamber is provided so that the estimated NOx generation amount is equal to or less than a preset NOx allowable amount.

  Specifically, the oxygen concentration control means is configured to execute control for reducing the oxygen concentration in the combustion chamber when the estimated NOx generation amount exceeds the NOx allowable amount.

  For example, the exhaust gas recirculation amount may be increased by an exhaust gas recirculation device that recirculates a part of the exhaust gas discharged to the exhaust system to the intake system. Thus, by reducing the oxygen concentration in the combustion chamber, the combustion temperature in the combustion chamber can be reduced, and the amount of NOx generated can be suppressed. The exhaust emission can be improved by continuing this operation until the estimated NOx generation amount reaches the NOx allowable amount or less.

  In the present invention, the amount of NOx generated by the combustion is estimated based on the change in the heat generation rate accompanying the combustion of the fuel in the combustion chamber. For this reason, even if various variations (manufacturing variation, variation in fuel properties, variation in injection amount, etc.) occur, the NOx generation amount estimated with high accuracy without using a NOx sensor is used. It becomes possible to control the control parameters of the internal combustion engine and suppress the NOx generation amount within an allowable range.

It is a figure which shows schematic structure of the 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 wave form diagram which shows the change of the heat release rate (heat generation amount per unit rotation angle of a crankshaft) and the change of a fuel injection rate (fuel injection amount per unit rotation angle of a crankshaft) at the time of a combustion stroke, respectively. It is a schematic diagram of the intake / exhaust system and the combustion chamber for explaining the outline of the combustion mode in the combustion chamber. It is sectional drawing which shows a combustion chamber at the time of fuel injection and its peripheral part. It is a top view of the combustion chamber at the time of fuel injection. It is a figure which shows a part of heat release rate waveform for demonstrating the heat release rate maximum inclination calculation operation | movement. FIG. 9A is a diagram showing the correlation between various state quantities in the combustion chamber and the NOx generation amount. FIG. 9A shows the correlation between the combustion field temperature and the NOx generation amount at the time of fuel ignition, and FIG. FIG. 9 (c) shows the correlation between the oxygen concentration in the room and the NOx generation amount, FIG. 9 (c) shows the correlation between the charge gas amount in the combustion chamber and the NOx generation amount, and FIG. 9 (d) shows the relationship between the fuel ignition timing and the NOx generation amount. It is a figure which shows a correlation, respectively. It is a figure for demonstrating the relationship of the heat release rate maximum inclination and NOx generation | occurrence | production total amount accompanying the state quantity change in a combustion chamber. It is a flowchart figure which shows the procedure of the control action of the control parameter based on the estimated NOx generation amount. O ₂ is a graph showing the concentration reduction amount map. It is a figure which shows a fuel ignition timing retard amount map.

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

-Engine configuration-
First, a schematic configuration of a diesel engine (hereinafter simply referred to as an engine) according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and its control system according to the present embodiment. Moreover, FIG. 2 is sectional drawing which shows the combustion chamber 3 of a diesel engine, and its peripheral part.

  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, a shutoff valve 24, a fuel addition valve 26, an engine fuel passage 27, an addition fuel passage 28, and the like.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and supplies it to the common rail 22 via the engine fuel passage 27. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to the injectors 23. The injector 23 includes a piezoelectric element (piezo element) therein, and is configured by a piezo injector that is appropriately opened to supply fuel into the combustion chamber 3. Details of the fuel injection control from the injector 23 will be described later.

  The supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 26 via the addition fuel passage 28. The added fuel passage 28 is provided with the shutoff valve 24 for shutting off the added fuel passage 28 and stopping fuel addition in an emergency.

  Further, the fuel addition valve 26 is configured so that the fuel addition amount to the exhaust system 7 becomes a target addition amount (addition amount at which the exhaust A / F becomes the target A / F) by the addition control operation by the ECU 100. The valve opening timing is controlled so that the fuel addition timing becomes a predetermined timing. That is, a desired fuel is injected and supplied from the fuel addition valve 26 to the exhaust system 7 (from the exhaust port 71 to the exhaust manifold 72) at an appropriate timing.

  The intake system 6 includes an intake manifold 63 connected to an intake port 15a formed in the cylinder head 15 (see FIG. 2), and an intake pipe 64 constituting an intake passage is connected to the intake manifold 63. Further, an air cleaner 65, an air flow meter 43, and a throttle valve (intake throttle valve) 62 are arranged in this intake passage in order from the upstream side. The air flow meter 43 outputs an electrical signal corresponding to the amount of air flowing into the intake passage via the air cleaner 65.

  Further, the intake system 6 is provided with a swirl control valve (swirl speed variable mechanism) 66 for making the swirl flow (horizontal swirl flow) in the combustion chamber 3 variable (see FIG. 2). . Specifically, as the intake port 15a, two systems, a normal port and a swirl port, are provided for each cylinder. Of these, a normal valve 15a shown in FIG. A swirl control valve 66 is disposed. An actuator (not shown) is connected to the swirl control valve 66, and the flow rate of air passing through the normal port 15a can be changed according to the opening of the swirl control valve 66 adjusted by driving the actuator. Yes. The larger the opening of the swirl control valve 66, the greater the amount of air taken into the cylinder from the normal port 15a. For this reason, the swirl generated by the swirl port (not shown in FIG. 2) becomes relatively weak, and the inside of the cylinder becomes low swirl (a state where the swirl speed is low). Conversely, the smaller the opening of the swirl control valve 66, the smaller the amount of air drawn into the cylinder from the normal port 15a. For this reason, the swirl generated by the swirl port is relatively strengthened, and the inside of the cylinder becomes a high swirl (a state where the swirl speed is high).

  The exhaust system 7 includes an exhaust manifold 72 connected to the exhaust port 71 formed in the cylinder head 15, and exhaust pipes 73 and 74 constituting an exhaust passage are connected to the exhaust manifold 72. In addition, a maniverter (exhaust gas purification device) 77 including a NOx storage catalyst (NSR catalyst: NOx Storage Reduction catalyst) 75 and a DPNR catalyst (Diesel Particle-NOx Reduction catalyst) 76 is disposed in the exhaust passage. Hereinafter, the NSR catalyst 75 and the DPNR catalyst 76 will be described.

The NSR catalyst 75 is an NOx storage reduction catalyst. For example, alumina (Al ₂ O ₃ ) is used as a support, and potassium (K), sodium (Na), lithium (Li), cesium (Cs), for example, is supported on this support. Alkali metal such as barium (Ba), alkaline earth such as calcium (Ca), rare earth such as lanthanum (La) and yttrium (Y), and noble metal such as platinum (Pt) were supported. It has a configuration.

The NSR catalyst 75 occludes NOx in a state where a large amount of oxygen is present in the exhaust gas, has a low oxygen concentration in the exhaust gas, and a large amount of reducing component (for example, an unburned component (HC) of the fuel). In the existing state, NOx is reduced to NO ₂ or NO and released. NO NOx released as NO ₂ or NO, the N ₂ is further reduced due to quickly reacting with HC or CO in the exhaust. Further, HC and CO are oxidized to H ₂ O and CO ₂ by reducing NO ₂ and NO. That is, by appropriately adjusting the oxygen concentration and HC component in the exhaust gas introduced into the NSR catalyst 75, HC, CO, and NOx in the exhaust gas can be purified. In the present embodiment, the oxygen concentration and HC component in the exhaust gas can be adjusted by the fuel addition operation from the fuel addition valve 26.

  On the other hand, the DPNR catalyst 76 is, for example, a porous ceramic structure carrying a NOx storage reduction catalyst, and PM in the exhaust gas is collected when passing through the porous wall. Further, when the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage reduction catalyst, and when the air-fuel ratio becomes rich, the stored NOx is reduced and released. Further, the DPNR catalyst 76 carries a catalyst that oxidizes and burns the collected PM (for example, an oxidation catalyst mainly composed of a noble metal such as platinum).

  Here, the structure of the combustion chamber 3 of a diesel engine and its peripheral part is demonstrated using FIG. As shown in FIG. 2, a cylinder block 11 constituting a part of the engine body is formed with a cylindrical cylinder bore 12 for each cylinder (four cylinders), and a piston 13 is formed inside each cylinder bore 12. Is accommodated 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 part of the cylinder block 11 via the gasket 14, 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 for 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. That is, as shown in FIG. 2, when the piston 13 is in the vicinity of the compression top dead center, the combustion chamber 3 formed by the cavity 13b is a narrow space having a relatively small volume at the center portion, and is directed toward the outer peripheral side. Thus, the space is gradually enlarged (expanded space).

  The piston 13 has a small end portion 18a of a connecting rod 18 connected by a piston pin 13c, and a large end portion of the connecting rod 18 is connected to a crankshaft which is an engine output shaft. As a result, the reciprocating movement of the piston 13 in the cylinder bore 12 is transmitted to the crankshaft via the connecting rod 18, and the engine output is obtained by rotating the crankshaft. Further, a glow plug 19 is disposed toward the combustion chamber 3. The glow plug 19 functions as a start-up assisting device that is heated red when an electric current is applied immediately before the engine 1 is started and a part of the fuel spray is blown onto the glow plug 19 to promote ignition and combustion.

  The cylinder head 15 is formed with the intake port 15a for introducing air into the combustion chamber 3 and the exhaust port 71 for exhausting exhaust gas from the combustion chamber 3, and intake air for opening and closing the intake port 15a. An exhaust valve 17 that opens and closes the valve 16 and the exhaust port 71 is provided. The intake valve 16 and the exhaust valve 17 are disposed to face each other with the cylinder center line P interposed therebetween. That is, the engine 1 is configured as a cross flow type. The cylinder head 15 is provided with the injector 23 that directly injects fuel into the combustion chamber 3. The injector 23 is disposed at a substantially upper center of the combustion chamber 3 in a standing posture along the cylinder center line P, and injects fuel introduced from the common rail 22 toward the combustion chamber 3 at a predetermined timing. It has become.

  Furthermore, 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 compressor wheel 53 is disposed facing the intake pipe 64, and the turbine wheel 52 is disposed facing the exhaust pipe 73. For this reason, the turbocharger 5 performs a so-called supercharging operation in which the compressor wheel 53 is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 52 to increase the intake pressure. 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. By adjusting the opening of the variable nozzle vane mechanism, the engine 1 supercharging pressure can be adjusted.

  An intake pipe 64 of the intake system 6 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5.

  The throttle valve 62 provided further downstream than the intercooler 61 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly. It has a function of narrowing down the area and adjusting (reducing) the supply amount of the intake air.

  Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it again to the combustion chamber 3, thereby reducing the amount of NOx generated. In addition, the EGR passage 8 is opened and closed steplessly by electronic control, and the exhaust gas passing through the EGR passage 8 (recirculating) is cooled by an EGR valve 81 that can freely adjust the exhaust flow rate flowing through the passage. An EGR cooler 82 is provided. The EGR passage 8, the EGR valve 81, the EGR cooler 82, and the like constitute an EGR device (exhaust gas recirculation device).

-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 of intake air (intake air amount) upstream of the throttle valve 62 in the intake system 6. 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 intake pressure sensor 48 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The A / F (air-fuel ratio) sensor 44 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas downstream of the manipulator 77 of the exhaust system 7. Similarly, the exhaust temperature sensor 45 outputs a detection signal corresponding to the temperature of the exhaust gas (exhaust temperature) downstream of the manipulator 77 of the exhaust system 7. 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 throttle valve 62.

-ECU-
As shown in FIG. 3, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results in the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a non-volatile memory that stores data to be saved when the engine 1 is stopped, for example.

  The CPU 101, the ROM 102, the RAM 103, and the backup RAM 104 are connected to each other via the bus 107, and are connected to the input interface 105 and the output interface 106.

  The input interface 105 is connected with the rail pressure sensor 41, the throttle opening sensor 42, the air flow meter 43, the A / F sensor 44, the exhaust temperature sensor 45, the intake pressure sensor 48, and the intake temperature sensor 49. Further, the input interface 105 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 of the engine 1. A crank position sensor 40 that outputs a detection signal (pulse) every time the (crankshaft) rotates by a certain angle, an in-cylinder pressure sensor 4A that detects in-cylinder pressure, and the like are connected.

  On the other hand, the output interface 106 is connected to the supply pump 21, the injector 23, the fuel addition valve 26, the throttle valve 62, the swirl control valve 66, the EGR valve 81, and the like. In addition, an actuator (not shown) provided in the variable nozzle vane mechanism of the turbocharger 5 is also connected to the output interface 106.

  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 102. .

  For example, the ECU 100 executes pilot injection (sub-injection) and main injection (main injection) as fuel injection control of the injector 23.

  The pilot injection is an operation for injecting a small amount of fuel in advance prior to the main injection from the injector 23. The pilot injection is an injection operation for suppressing the ignition delay of fuel due to the main injection and leading to stable diffusion combustion, and is also referred to as sub-injection. Further, the pilot injection in the present embodiment has not only a function of suppressing the initial combustion speed by the main injection described above but also a preheating function of increasing the in-cylinder temperature. That is, after the pilot injection is performed, the fuel injection is temporarily interrupted, and the compressed gas temperature (in-cylinder temperature) is sufficiently increased until the main injection is started to reach the fuel self-ignition temperature (for example, 1000 K). In this way, the ignitability of the fuel injected by the main injection is ensured satisfactorily.

  The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. The injection amount in the main injection is basically determined so as to obtain the required torque according to the operation state such as the engine speed, the accelerator operation amount, the coolant temperature, the intake air temperature, and the like. For example, the higher the engine speed (the engine speed calculated based on the detection value of the crank position sensor 40), the larger the accelerator operation amount (the accelerator pedal depression amount detected by the accelerator opening sensor 47). As the accelerator opening becomes larger, the required torque value of the engine 1 is higher, and accordingly, the fuel injection amount in the main injection is also set higher. In addition, when the pre-injection in the cylinder is sufficiently performed by the pilot injection, the fuel injected by the main injection is immediately exposed to a temperature environment equal to or higher than the auto-ignition temperature, and the thermal decomposition proceeds. Will start burning immediately.

  Specifically, the fuel ignition delay in a diesel engine includes a physical delay and a chemical delay. The physical delay is the time required for evaporation / mixing of the fuel droplets and depends on the gas temperature of the combustion field. On the other hand, the chemical delay is the time required for chemical bonding / decomposition of fuel vapor and oxidation heat generation. As described above, in the situation where the cylinder is sufficiently preheated, the physical delay can be minimized, and as a result, the ignition delay can be minimized. Therefore, as a combustion mode of the fuel injected by the main injection, premixed combustion is hardly performed, and most of it is diffusion combustion. As a result, controlling the injection timing of the main injection is substantially equivalent to controlling the start timing of diffusion combustion as it is, and the controllability of combustion can be greatly improved. That is, the rate of heat generation by controlling the fuel injection timing and the fuel injection amount in the main injection (controlling the injection rate waveform) by minimizing the ratio of the premixed combustion of the fuel injected in the main injection. Control of the waveform (ignition timing and heat generation amount) can greatly improve the controllability of combustion.

  In addition to the pilot injection and main injection described above, after injection and post injection are performed as necessary. After injection is an injection operation for increasing the exhaust gas temperature. Specifically, after injection is performed at a timing at which most of the combustion energy of the supplied fuel is obtained as thermal energy of the exhaust gas without being converted into torque of the engine 1. The post-injection is an injection operation for directly introducing fuel into the exhaust system 7 to increase the temperature of the manipulator 77. For example, when the accumulated amount of PM trapped in the DPNR catalyst 76 exceeds a predetermined amount (for example, detected by detecting a differential pressure before and after the manipulator 77), post injection is performed. .

  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. The EGR amount is set according to an EGR map stored in advance in the ROM 102. Specifically, this EGR map is a map for determining the EGR amount (EGR rate) using the engine speed and the engine load as parameters. This EGR map is created in advance by experiments, simulations, or the like. That is, by applying the engine speed calculated based on the detection value of the crank position sensor 40 and the opening of the throttle valve 62 (corresponding to the engine load) detected by the throttle opening sensor 42 to the EGR map. An EGR amount (opening degree of the EGR valve 81) is obtained.

  Further, the ECU 100 executes the opening degree control of the swirl control valve 66. In order to control the opening degree of the swirl control valve 66, the amount of movement of the fuel spray injected into the combustion chamber 3 per unit time (or per unit crank rotation angle) in the circumferential direction in the cylinder is changed. Is called.

-Fuel injection pressure-
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. That is, when the engine load is high, the amount of air sucked into the combustion chamber 3 is large. Therefore, a large amount of fuel must be injected from the injector 23 into the combustion chamber 3, and therefore the injection from the injector 23 is performed. The pressure needs to be high. Further, when the engine speed is high, the injection period is short, so the amount of fuel injected per unit time must be increased, and therefore the injection pressure from the injector 23 needs to be increased. . Thus, the target rail pressure is generally set based on the engine load and the engine speed. The target rail pressure is set according to a fuel pressure setting map stored in the ROM 102, for example. That is, by determining the fuel pressure according to this fuel pressure setting map, the valve opening period (injection rate waveform) of the injector 23 is controlled, and the fuel injection amount during the valve opening period can be defined.

  In the present embodiment, the fuel pressure is adjusted between 30 MPa and 200 MPa according to the engine load and the like.

  Regarding the fuel injection parameters such as the pilot injection and the main injection, the optimum values differ depending on the temperature conditions of the engine 1 and the intake air.

  For example, the ECU 100 adjusts the fuel discharge amount of the supply pump 21 so that the common rail pressure becomes equal to the target rail pressure set based on the engine operating state, that is, the fuel injection pressure matches the target injection pressure. To measure. Further, the ECU 100 determines the fuel injection amount and the fuel injection form based on the engine operating state. Specifically, the ECU 100 calculates the engine rotation speed based on the detection value of the crank position sensor 40, obtains the amount of depression of the accelerator pedal (accelerator opening) based on the detection value of the accelerator opening sensor 47, The total fuel injection amount (the sum of the injection amount in pilot injection and the injection amount in main injection) is determined based on the engine speed and the accelerator opening.

-Setting of target fuel pressure-
Next, a method for setting the target fuel pressure will be described. In the diesel engine 1, it is important to meet various requirements such as improvement of exhaust emission by reducing NOx generation amount and smoke generation amount, reduction of combustion noise during combustion stroke, and sufficient securing of engine torque. As a method for simultaneously satisfying these requirements, it is effective to appropriately control the change state of the heat generation rate in the cylinder during the combustion stroke (change state represented by the heat generation rate waveform).

  The solid line of the waveforms shown in the upper part of FIG. 4 shows an ideal heat generation rate waveform related to the combustion of fuel injected in pilot injection and main injection, with the horizontal axis representing the crank angle and the vertical axis representing the heat generation rate. ing. TDC in the figure indicates the crank angle position corresponding to the compression top dead center of the piston 13. The waveform shown in the lower part of FIG. 4 shows the waveform of the injection rate of fuel injected from the injector 23 (fuel injection amount per unit rotation angle of the crankshaft).

  As the heat release rate waveform, for example, combustion of fuel injected by main injection is started from the vicinity of the compression top dead center (TDC) of the piston 13, and a predetermined piston position after the compression top dead center of the piston 13 (for example, The heat generation rate reaches a maximum value (peak value) at 10 degrees after compression top dead center (ATDC 10 °), and a predetermined piston position after compression top dead center (for example, 25 degrees after compression top dead center ( At the time of ATDC 25 °), the combustion of the fuel injected in the main injection ends. If combustion of the air-fuel mixture is performed in such a state where the heat generation rate changes, for example, 50% of the air-fuel mixture in the cylinder burns at 10 degrees after compression top dead center (ATDC 10 °). Completed status. That is, the combustion center of gravity is 10 degrees after compression top dead center (ATDC 10 °), and about 50% of the total heat generation amount in the expansion stroke is generated by ATDC 10 °, and the engine 1 is operated with high thermal efficiency. Is possible.

  The relationship between the crank angle and the fuel injection rate waveform when the combustion center of gravity is reached is the period from when the fuel injection stop signal is transmitted to the injector 23 until the fuel injection is completely stopped (see FIG. 4 is located in the period T1).

  In such a situation in which combustion with an ideal heat generation rate waveform is performed, the cylinder is sufficiently preheated by pilot injection, and the fuel injected in the main injection is immediately self-ignited by this preheating. The thermal decomposition proceeds due to exposure to a temperature environment higher than the temperature, and combustion starts immediately after injection.

  The waveform indicated by the two-dot chain line α in FIG. 4 is a heat generation rate waveform when the fuel injection pressure is set higher than the appropriate value, and both the combustion rate and the peak value of the heat generation rate are too high. Therefore, there is a concern about an increase in combustion noise and an increase in the amount of NOx generated. On the other hand, a waveform indicated by a two-dot chain line β in FIG. 4 is a heat generation rate waveform when the fuel injection pressure is set lower than an appropriate value, and the timing at which the combustion rate is low and the peak of the heat generation rate appears. There is a concern that sufficient engine torque cannot be secured due to the large shift to the retard side.

-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.

  In FIG. 5, gas (air) is sucked into one cylinder of the engine 1 through the intake manifold 63 and the intake port 15 a, and combustion is performed by fuel injection from the injector 23 into the combustion chamber 3. FIG. 6 is a diagram schematically showing how the subsequent gas is discharged to the exhaust manifold 72 through the exhaust port 71.

  As shown in FIG. 5, the gas sucked into the cylinder includes fresh air sucked from the intake pipe 64 through the throttle valve 62, and from the EGR passage 8 when the EGR valve 81 is opened. Inhaled EGR gas is included. The ratio of the amount of EGR gas to the sum of the amount of fresh air (mass) to be sucked and the amount of mass of EGR (mass) to be sucked (that is, the EGR rate) is appropriately controlled by the ECU 100 according to the operating state. It changes according to the opening degree of 81.

  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. 5) is lowered through the intake valve 16 which is opened in the intake stroke. It becomes in-cylinder gas. This in-cylinder gas is sealed in the cylinder by closing the intake valve 16 when the valve is determined according to the operating state of the engine 1 (in-cylinder gas confinement state), and in the subsequent compression stroke The piston 13 is compressed as the piston 13 moves up. When the piston 13 reaches the vicinity of the 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 the fuel is directly injected into the combustion chamber 3. Specifically, the pilot injection is performed before the piston 13 reaches the top dead center, and after the fuel injection is temporarily stopped, the piston 13 reaches the vicinity of the top dead center after a predetermined interval. Main injection will be executed.

  FIG. 6 is a cross-sectional view showing the combustion chamber 3 and its peripheral part at the time of fuel injection, and FIG. 7 is a plan view of the combustion chamber 3 at the time of fuel injection (a view showing the upper surface of the piston 13). As shown in FIG. 7, the injector 23 of the engine 1 according to the present embodiment is provided with eight injection holes at equal intervals in the circumferential direction, and fuel is injected equally from these injection holes. It has become so. The number of nozzle holes is not limited to eight.

  The fuel sprays A, A,... Injected from the nozzle holes diffuse in a substantially conical shape. Further, since fuel injection from each nozzle hole (the pilot injection and the main injection) is performed when the piston 13 reaches the vicinity of the compression top dead center, as shown in FIG. ,... Diffuses in the cavity 13b.

  As described above, the fuel sprays A, A,... Injected from the respective injection holes formed in the injector 23 are mixed with the in-cylinder gas with the passage of time and become air-fuel mixtures in the cylinder. It diffuses in a conical shape and burns by self-ignition. That is, each of the fuel sprays A, A,... Forms a substantially conical combustion field together with the in-cylinder gas, and combustion is started in each of the combustion fields (eight combustion fields in this embodiment). It will be.

  The energy generated by this combustion is kinetic energy for pushing down the piston 13 toward the bottom dead center (energy serving as engine output), thermal energy for raising the temperature in the combustion chamber 3, cylinder block 11 and cylinder head 15 It becomes the heat energy radiated to the outside (for example, cooling water) through.

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

-NOx generation amount estimation operation-
The feature of this embodiment is the operation of estimating the amount of NOx generated by the combustion of fuel in the combustion chamber 3 (mainly the combustion of fuel injected by main injection). The NOx generation amount estimated by this NOx generation amount estimation operation (NOx generation amount generated in one combustion stroke: hereinafter sometimes referred to as “NOx generation total amount”) is set in advance as the NOx generation amount. This is used for control of control parameters (EGR amount, fuel injection timing, etc.) for suppressing the amount to an allowable amount (NOx restriction amount) or less. Hereinafter, the NOx generation amount estimation operation will be specifically described.

  As the NOx generation amount estimation operation, a “heat generation rate maximum slope” calculation operation and a “NOx generation total amount” calculation operation are sequentially performed.

<Calculation of maximum slope of heat release rate>
First, the calculation operation of the maximum heat release rate gradient will be described.

  In this calculation operation, the heat generation rate during a predetermined period of the combustion stroke is calculated at predetermined intervals (each time the crankshaft rotates by a predetermined angle), and the degree of increase (slope) of the heat generation rate during that period is calculated. Extract the maximum value.

  Specifically, during the period from the predetermined crankshaft rotation angle position after the main injection is executed until the crankshaft rotation angle reaches the predetermined rotation angle position, the in-cylinder pressure sensor 4A is set for each predetermined crank angle. Thus, the cylinder pressure (pressure in the combustion chamber 3) is detected. That is, the heat generation rate for each predetermined crank angle (a heat generation amount per unit rotation angle of the crankshaft) is calculated based on the change in the cylinder pressure during the predetermined period. That is, since there is a correlation between the in-cylinder pressure and the heat generation rate, the heat generation rate for each crank angle is obtained based on the in-cylinder pressure.

  For example, when the main injection is started and the in-cylinder pressure sensor 4A starts detecting the in-cylinder pressure from the time when the crankshaft rotation angle advances by 5 ° CA, each time the rotation angle of the crankshaft advances by 0.5 ° CA, The in-cylinder pressure detected by the in-cylinder pressure sensor 4A is monitored. Thereby, the heat generation rate is calculated every time the rotation angle of the crankshaft advances by 0.5 ° CA.

  The end point of the period during which the in-cylinder pressure is detected by the in-cylinder pressure sensor 4A is the point at which the heat generation rate reaches the maximum value (peak value) (in the case of the heat generation rate waveform shown in FIG. 10 ° after the top dead center (ATDC 10 °), or when the crankshaft rotation angle has advanced 15 ° CA after the start of main injection. These values are not limited to this and are set as appropriate.

  FIG. 8 shows a heat generation rate waveform obtained based on the in-cylinder pressure detected by the in-cylinder pressure sensor 4A (from the start of combustion of the fuel injected in the main injection until the heat generation rate reaches a peak value. It is a figure which shows an example of the heat release rate waveform of a period. In this case, after the main injection is executed, the detection of the in-cylinder pressure by the in-cylinder pressure sensor 4A is started from the time when the rotation angle of the crankshaft advances by 5 ° CA (timing t1 in FIG. 8). In the waveform shown in FIG. 8, this timing t1 is the time when the rotation angle of the crankshaft reaches 2.5 ° (ATDC 2.5 °) after compression top dead center.

  During the period from this timing t1 until the time when the heat generation rate reaches the maximum value (peak value) (timing t6 in FIG. 8), the in-cylinder pressure is detected by the in-cylinder pressure sensor 4A and the crank angle is 0.5 °. This is executed every time the CA advances, and the heat generation rate is calculated from the in-cylinder pressure every 0.5 ° CA. Specifically, as the operation for obtaining the time point at which the heat generation rate reaches the maximum value (peak value), the time point when the change rate of the in-cylinder pressure detected by the in-cylinder pressure sensor 4A changes from positive to negative. The heat generation rate is determined to be the time when the maximum value (peak value) is reached.

  Then, the above-described in-cylinder pressure detection period (period from timing t1 to t6 in FIG. 8) is divided into a plurality of heat generation rate inclination calculation periods (divided combustion stroke period in the present invention), and each heat generation rate inclination calculation is performed. The slope of the heat release rate in each period is calculated. Specifically, in the example shown in FIG. 8, the period is divided into five periods s1 to s5. Here, the period from the timing t1 to the timing t2 is the first heat generation rate inclination calculation period s1, the period from the timing t2 to the timing t3 is the second heat generation rate inclination calculation period s2, and the period from the timing t3 to the timing t4. The period is the third heat generation rate inclination calculation period s3, the period from the timing t4 to the timing t5 is the fourth heat generation rate inclination calculation period s4, and the period from the timing t5 to the timing t6 is the fifth heat generation rate inclination calculation. Each is called a period s5. Further, as described above, the in-cylinder pressure detection period by the in-cylinder pressure sensor 4A is a period from 2.5 ° after compression top dead center (ATDC 2.5 °) to 10 ° after compression top dead center (ATDC 10 °). Therefore, each of the first to fifth heat generation rate inclination calculation periods s1 to s5 is a period of 1.5 ° CA in terms of the rotation angle of the crankshaft. Further, as described above, each time the crank angle advances by 0.5 ° CA, the in-cylinder pressure is detected by the in-cylinder pressure sensor 4A. Therefore, in each of the first to fifth heat generation rate inclination calculation periods s1 to s5, respectively. The in-cylinder pressure is detected three times, and the average value of the heat generation rate gradient obtained from these in-cylinder pressures is set as the average value of the heat generation rate gradient in the heat generation rate inclination calculation periods s1 to s5. Thereby, the average value of the heat release rate gradient is calculated in each of the periods s1 to s5. In addition, as a specific calculation method of the heat generation rate gradient, the heat generation rate gradient is obtained by performing differentiation twice on the acquired heat generation amount. Alternatively, the heat generation rate gradient is obtained by performing differentiation once on the obtained heat generation rate. This calculation method is not limited to this.

  In this embodiment, the average value of the plurality of heat release rate slopes calculated as described above (the heat release rates obtained in each of the first heat release rate slope calculation period s1 to the fifth heat release rate slope calculation period s5). The average value of the slope of the heat generation rate is extracted as the “maximum slope of heat generation rate”, and the following operation for calculating the total NOx generation amount is performed. In the example shown in FIG. 8, the average value of the heat generation rate gradient in the fourth heat generation rate inclination calculation period s4 is the average value of the heat generation rate inclination in the other heat generation rate inclination calculation periods s1, s2, s3, and s5. Therefore, the average value of the heat generation rate gradient in the fourth heat generation rate inclination calculation period s4 is obtained as the maximum heat generation rate inclination (the heat generation rate indicated by the broken line in FIG. 8). See Tilt).

  Note that each of the values described with reference to FIG. 8 is not limited to this value, and is set as appropriate.

  As described above, by setting the average value of the slopes of the plurality of heat generation rates as the average value of the heat generation rate slopes in the heat generation rate slope calculation periods s1 to s5, the degree of increase in the heat generation rate due to temporary disturbance can be increased. Even if there is a sudden change, the influence of this disturbance can be mitigated, and the maximum slope of heat generation rate can be obtained accurately.

<Operation for calculating the total amount of NOx generated>
After the maximum heat release rate slope is calculated as described above, the total NOx generation amount is calculated by the following equation (1) (NOx generation amount estimation operation by the NOx generation amount estimation means). This total NOx generation amount is the total amount of NOx generation contained in the exhaust gas due to fuel combustion in the target combustion stroke. According to regulations according to automobile exhaust emission regulations (Euro 6 and the like), it is necessary to suppress this total NOx generation amount to a predetermined allowable amount or less.

As shown in this equation (1), “Tig (combustion field temperature at the time of fuel ignition) correction value”, “O ₂ concentration correction value (correction value based on oxygen concentration)”, “charging gas amount (charging air amount)” The NOx generation total amount is calculated by multiplying the maximum slope of the heat generation rate by a function “f” having “correction value” and “ignition timing correction value” as variables. In other words, there is a correlation between the maximum slope of heat generation rate and the total amount of NOx generation. Even if the maximum slope of heat generation rate is the same, NOx is generated according to the Tig, O ₂ concentration, amount of charged gas, and ignition timing. Since the total amount changes, the above “Tig correction value”, “O ₂ correction value”, “filling gas amount correction value”, “ignition timing” which are correction values based on these Tig, O ₂ concentration, charging gas amount, and ignition timing. By multiplying the function “f” having the “correction value” as a variable by the maximum slope of the heat generation rate, the total NOx generation amount is calculated with high accuracy.

As described above, the “Tig correction value”, “O ₂ correction value”, “filling gas amount correction value”, and “ignition timing correction value” affect the NOx generation amount. Is known by. In the following, the calculation formula of the “enlarged Dorzevic mechanism” is presented for reference.

  FIG. 9 is a diagram showing the correlation between various state quantities in the combustion chamber 3 and the NOx generation amount. FIG. 9A shows the correlation between the combustion field temperature (Tig) at the time of fuel ignition and the NOx generation amount. 9 (b) shows the correlation between the oxygen concentration in the combustion chamber 3 and the NOx generation amount, FIG. 9 (c) shows the correlation between the charged gas amount in the combustion chamber 3 and the NOx generation amount, and FIG. d) shows the correlation between the ignition timing of the fuel and the amount of NOx generated.

  As shown in these figures, the combustion field temperature (Tig) at the time of fuel ignition, the oxygen concentration in the combustion chamber 3, the amount of charged gas in the combustion chamber 3, and the fuel ignition timing are correlated with the amount of NOx generated. have. For example, the NOx generation amount increases as the combustion field temperature (Tig) at the time of fuel ignition increases, and the NOx generation amount increases as the oxygen concentration in the combustion chamber 3 increases, and the amount of charged gas in the combustion chamber 3 increases. The NOx generation amount decreases as the fuel ignition timing is advanced, and the NOx generation amount decreases.

It should be noted that the amount of change in the total amount of NOx generated (the degree of influence of each state quantity on the total amount of NOx generated) with respect to changes in the above-described Tig, O ₂ concentration, charge gas amount, and ignition timing differs depending on the engine 1 model. For this reason, the “Tig correction value”, “O ₂ correction value”, “filling gas amount correction value”, and “ignition timing correction value” are also set as different values for each model of the engine 1. For example, in the engine 1 in which the change in the total amount of NOx generated due to the change in the combustion field temperature at the time of fuel ignition becomes large even if the combustion field temperature at the time of fuel ignition is the same, this “Tig correction value” Is set as a large value, and in the engine 1 in which the change in the total amount of NOx generated due to the change in the combustion field temperature at the time of fuel ignition is small, the “Tig correction value” is set as a small value. Become. The same applies to other correction values. The “Tig correction value”, “O ₂ correction value”, “filling gas amount correction value”, and “ignition timing correction value” given for each model of the engine 1 are set in advance through experiments, simulations, or the like.

  FIG. 10 is a diagram for explaining the relationship between the maximum slope of heat generation rate and the total amount of NOx generation that accompanies a change in the state quantity in the combustion chamber 3. For example, in a certain type of engine 1, heat generation in the case where correction (correction of NOx generation amount) according to the above-described state quantities (Tig, oxygen concentration, charge gas amount, ignition timing) in the combustion chamber 3 is not performed. The relationship between the maximum rate gradient and the total NOx generation amount is indicated by a solid line in the figure. On the other hand, by correcting the NOx generation amount according to the state quantity in the combustion chamber 3, the relationship between the maximum slope of the heat generation rate and the total NOx generation amount can be obtained accurately. For example, the broken line X in FIG. 8 shows the characteristic when the increase rate of the total amount of NOx generation increases as the maximum slope of the heat generation rate increases by performing correction according to the state quantity in the combustion chamber 3. The broken line Y shows a change in the case where the increase rate of the total amount of NOx generation accompanying the increase in the maximum slope of the heat generation rate is relatively small by performing correction according to the state quantity in the combustion chamber 3. The characteristic change is shown.

  In this way, the total amount of NOx generated also changes as the state quantity in the combustion chamber 3 changes. As an arithmetic expression that expresses this by the combustion field temperature T of the above formula (3), for example, the following formula (4) can be cited.

-Control parameter control action-
Next, the control operation of the control parameter based on the total NOx generation amount estimated as described above will be described. In the control operation of the control parameters shown below, the control operation for setting the NOx generation amount below the allowable amount based on the estimated total NOx generation amount, and the smoke generation amount based on the estimated smoke generation total amount. A case where the control operation for making the amount less than the allowable amount is performed in parallel will be described.

  FIG. 11 is a flowchart showing the procedure of the control operation of this control parameter. This flowchart is executed every time the combustion stroke is executed after the engine 1 is started (for example, every time the crankshaft rotates 180 ° in the case of a four-cylinder engine).

  First, in step ST1, the total NOx generation amount obtained by the estimation operation described above is acquired, and the total smoke generation amount is acquired. As an operation for obtaining the total amount of smoke generation, a conventionally known method can be employed. For example, based on the amount of intake air detected by the air flow meter 43, the internal pressure of the common rail 22 detected by the rail pressure sensor 41 (corresponding to the fuel injection pressure), the temperature of intake air detected by the intake air temperature sensor 49, and the like. The total amount of smoke generated is obtained from a map of total amount of smoke generated in advance stored in the ROM 102 and a predetermined arithmetic expression.

  After obtaining the total NOx generation amount and the total smoke generation amount, the process proceeds to step ST2, and it is determined whether or not the total NOx generation amount is equal to or less than a preset NOx allowable amount. This allowable NOx amount is set as a value defined by an automobile exhaust emission regulation (Euro 6 or the like) or a value less than that.

  If the NOx generation total amount exceeds the NOx allowable amount and NO is determined in step ST2, the process proceeds to step ST3, and it is determined whether or not the smoke generation total amount is equal to or smaller than a preset smoke allowable amount. This allowable smoke amount is also set as a value defined by an automobile exhaust emission regulation (Euro 6 or the like) or a value less than that.

If the total amount of smoke generated is equal to or less than the allowable amount of smoke and the determination in step ST3 is YES, that is, if the total amount of generated NOx exceeds the allowable amount of NOx and the total amount of generated smoke is equal to or less than the allowable amount of smoke, step ST4 Then, the control of lowering the O ₂ concentration is executed (control operation of the oxygen concentration in the combustion chamber by the oxygen concentration control means). That is, control is performed to reduce the O ₂ concentration during the combustion stroke in the cylinder that will reach the next combustion stroke, and control is performed so that the total amount of NOx generation decreases. Specifically, the O ₂ concentration in the combustion chamber 3 is lowered by correcting the increase in the EGR amount. In this case, the O ₂ concentration decrease amount (EGR increase amount) may be a predetermined constant value, or a deviation between the NOx generation total amount and the NOx allowable amount (NOx allowable amount from the NOx generation total amount). The value may be changed in accordance with the value obtained by subtracting. Figure 12 shows the O ₂ concentration decrease amount map for setting the amount of decrease in O ₂ concentration in accordance with the deviation between the NOx generation amount and the NOx capacity. Based on this O ₂ concentration decrease amount map, the O ₂ concentration decrease amount is set to be larger as the deviation between the total NOx generation amount and the NOx allowable amount is larger. This O ₂ concentration decrease amount map is created in advance by experiments, simulations, and the like, and is stored in the ROM 102.

  If the total NOx generation amount is equal to or less than the NOx allowable amount and YES is determined in step ST2, the process proceeds to step ST5, and the smoke generation total amount is equal to or less than the preset allowable smoke amount as in step ST3. It is determined whether or not there is.

  If the total amount of smoke generated exceeds the allowable amount of smoke and it is determined NO in step ST5, that is, if the total amount of generated NOx is equal to or less than the allowable amount of NOx and the total amount of generated smoke exceeds the allowable amount of smoke, step Moving to ST6, ignition timing retardation control is executed. That is, control is performed to retard the fuel ignition timing during the combustion stroke in the cylinder that will reach the next combustion stroke, and control is performed so that the total amount of smoke generation is reduced. Specifically, the fuel ignition timing is retarded by correcting the injection start timing of the main injection to the retard side. The retardation correction amount in this case may be a predetermined constant value or according to the deviation between the total amount of smoke generated and the allowable amount of smoke (a value obtained by subtracting the allowable amount of smoke from the total amount of generated smoke). It may be changed. FIG. 13 shows a fuel ignition timing retard amount map for setting the retard amount of the fuel ignition timing in accordance with the deviation between the total amount of smoke generated and the allowable smoke. From this fuel ignition timing retard amount map, the larger the deviation between the smoke generation total amount and the smoke allowable amount, the larger the fuel ignition timing retard amount is set. This fuel ignition timing retard amount map is also created in advance by experiments, simulations, etc., and is stored in the ROM 102.

If NO is determined in step ST3, that is, if the total NOx generation amount exceeds the allowable NOx amount and the total smoke generation amount exceeds the allowable smoke amount, the process proceeds to step ST7, and the above-described O _2. The concentration reduction control is executed and the ignition timing retard control is executed. Thereby, control is performed so that both the NOx generation amount and the smoke generation amount are reduced.

When the above control is continued and YES is determined in step ST5, that is, when the total NOx generation amount is less than the NOx allowable amount and the smoke generation total amount is less than the smoke allowable amount, the O ₂ concentration The reduction control and the ignition timing retard control are returned as non-execution.

  As described above, in the present embodiment, even when various variations (manufacturing variation, variation in fuel properties, variation in injection amount, etc.) occur, based on the total NOx generation amount estimated with high accuracy. It is possible to control the control parameters (EGR amount, fuel injection timing, etc.) of the engine 1 and suppress the total NOx generation amount within an allowable range. For this reason, taking into account the occurrence of the above-mentioned various variations, there is a margin in the control amount for the control parameter (the value of the control amount for the control parameter is largely biased toward the side that suppresses the NOx generation amount). Can be eliminated, and the performance of the engine 1 and the fuel consumption rate can be improved.

  In the present embodiment, as the information processing operation after acquiring the maximum heat release rate gradient during the combustion stroke, it is not necessary to handle information on the slope of the heat release rate throughout the combustion stroke, and the heat release rate increases. It is sufficient to handle only the maximum slope of the heat generation rate as information on the degree. For this reason, compared with the case where the information of the increase degree of the heat release rate in the whole combustion stroke is handled, the amount of information can be greatly reduced, and the load on the CPU 101 can be reduced.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to an in-line four-cylinder diesel engine 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-described embodiment, the combustion stroke period is divided into a plurality of heat generation rate inclination calculation periods, and the average value of the heat generation rate inclinations in each heat generation rate inclination calculation period is obtained. The present invention is not limited to this, and a predetermined period during the combustion stroke period (for example, during a period from when the crankshaft rotation angle has advanced by 10 ° CA to when it reaches 15 ° CA after main injection is performed). The average value of the slope of the heat generation rate may be obtained, and this may be treated as the above-described maximum slope of heat generation rate to calculate the total NOx generation amount.

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

  In addition, although the NSR catalyst 75 and the DPNR catalyst 76 are provided as the manipulator 77 in the above embodiment, the NSR catalyst 75 and a DPF (Diesel Particle Filter) may be provided.

  INDUSTRIAL APPLICABILITY The present invention can be applied to control for estimating the NOx generation amount with high accuracy and suppressing the NOx generation amount below an allowable amount in a common rail in-cylinder direct injection multi-cylinder diesel engine mounted on an automobile. .

1 engine (internal combustion engine)
3 Combustion chamber 23 Injector (fuel injection valve)
4A In-cylinder pressure sensor 8 EGR passage 81 EGR valve Tig Combustion field temperature Gcyl at the time of fuel ignition Charge gas amount in combustion chamber

Claims (8)

An apparatus for estimating the amount of NOx generated when fuel injected from a fuel injection valve burns into a combustion chamber of a compression ignition type internal combustion engine,
An internal combustion engine characterized by comprising NOx generation amount estimation means for estimating the NOx generation amount by performing correction according to the state quantity in the combustion chamber with respect to the degree of increase in the heat generation rate due to the combustion of the fuel. Engine NOx generation amount estimation device. In the internal combustion engine NOx generation amount estimation device according to claim 1,
The NOx generation amount estimating means is configured to estimate the NOx generation amount by performing correction according to the state quantity in the combustion chamber with respect to the maximum value of the degree of increase in the heat generation rate during the combustion stroke. An NOx generation amount estimation apparatus for an internal combustion engine characterized by the above. In the internal combustion engine NOx generation amount estimation device according to claim 2,
The NOx generation amount estimation means divides a predetermined period at the time of the combustion stroke into a plurality of divided combustion stroke periods, and the highest heat among the average values of the increase degrees of the plurality of heat generation rates obtained in each divided combustion stroke period. By extracting the average value of the rate of increase in the rate of occurrence as the maximum value of the rate of increase in the rate of heat release, and correcting the maximum value of the rate of increase in the rate of heat release according to the state quantity in the combustion chamber, A NOx generation amount estimation device for an internal combustion engine, characterized in that the NOx generation amount is estimated. In the internal combustion engine NOx generation amount estimation device according to claim 1,
The NOx generation amount estimation means estimates the NOx generation amount by performing correction according to the state quantity in the combustion chamber with respect to the average value of the degree of increase in the heat generation rate during a predetermined period during the combustion stroke. An NOx generation amount estimating apparatus for an internal combustion engine, characterized in that: In the internal combustion engine NOx generation amount estimation device according to any one of claims 1 to 4,
The amount of state in the combustion chamber that is corrected for the degree of increase in the heat release rate due to the combustion of the fuel is the combustion field temperature at the time of fuel ignition, the oxygen concentration in the combustion chamber, the amount of charged gas in the combustion chamber, and the timing of fuel ignition An NOx generation amount estimation device for an internal combustion engine characterized by comprising: An apparatus for controlling the combustion of fuel based on the NOx generation amount estimated by the NOx generation amount estimation device for an internal combustion engine according to any one of claims 1 to 5,
An internal combustion engine control apparatus comprising oxygen concentration control means for controlling the oxygen concentration in the combustion chamber so that the estimated NOx generation amount is equal to or less than a preset NOx allowable amount. The control apparatus for an internal combustion engine according to claim 6,
The oxygen concentration control means is configured to execute control to reduce the oxygen concentration in the combustion chamber when the estimated NOx generation amount exceeds the NOx allowable amount. Control device. The control apparatus for an internal combustion engine according to claim 6 or 7,
The control apparatus for an internal combustion engine, wherein the oxygen concentration adjusting means increases an exhaust gas recirculation amount by an exhaust gas recirculation device that recirculates a part of the exhaust gas discharged to the exhaust system to the intake system.

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