JP2013199838A - Injection rate waveform generation method and control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable generation of an injection rate waveform without a sensor even if an injection area of a fuel injection valve is changed.SOLUTION: A plurality of injection rate waveforms are measured while a fuel pressure and an injection amount are changed, each measured injection rate waveform is modeled, and a reference injection rate tilt and a reference reaching injection rate of the injection rate waveform are sampled. A mathematical expression indicative of the relationship between the reference injection rate tilt and the reference reaching rate, and the fuel pressure is obtained based on a sampled data group. Using the mathematical expression, the reference injection rate tilt and the reference reaching injection rate are calculated from the fuel pressure. Moreover, the injection rate tilt and the reaching injection rate are calculated from the reference injection rate tilt, the reference reaching injection rate and an area ratio. Furthermore, the injection rate waveform is generated based on the injection rate amount corresponding to the injection rate tilt, the reaching injection rate and an area of the injection rate waveform.

Description

  The present invention relates to an injection rate waveform creation method for creating an injection rate waveform of fuel injected from a fuel injection valve toward a cylinder in a compression self-ignition internal combustion engine represented by a diesel engine. The present invention also relates to an internal combustion engine control device having a function of creating such a fuel injection rate waveform.

  In an engine that performs lean combustion, such as a diesel engine, the operating region that burns a mixture with a high air-fuel ratio (lean atmosphere) occupies most of the entire operating region, so nitrogen oxide (hereinafter referred to as NOx) There is a concern that a relatively large amount will be discharged. In addition, when incomplete combustion of the air-fuel mixture occurs during combustion in the combustion chamber, smoke is generated in the exhaust gas, leading to deterioration of exhaust emission.

  For this reason, it is required to suppress both the amount of NOx generated and the amount of smoke generated to improve exhaust emission. An exhaust gas recirculation (EGR) device that recirculates part of exhaust gas to the intake passage is known as a means for suppressing the amount of NOx generated (for example, Patent Document 1 and Patent Document 2 below). reference).

  Until now, it has been proposed to control the heat generation rate in the combustion chamber for the purpose of suppressing both the generation amount of NOx and the generation amount of smoke. However, in the operating state of the engine, the actual heat generation in the combustion chamber is intended as described above (to suppress both NOx generation amount and smoke generation amount) (heat generation rate waveform: combustion period) It is necessary to evaluate (verify) whether or not it is carried out by changing the heat generation rate in the inside. In order to evaluate the heat generation rate (evaluate the diffusion combustion state), a fuel injection rate waveform is required.

  In order to obtain such an injection rate waveform, it is necessary to detect an actual fuel injection start timing, an injection end timing, and a fuel injection rate (a fuel injection amount per unit time). For this reason, in order to detect these, for example, a pressure sensor (injector injection pressure sensor) may be built in the injector, but such a pressure sensor is expensive and it is difficult to ensure detection accuracy.

  Therefore, conventionally, the injection rate gradient and the arrival injection rate are calculated from the fuel pressure by using an injection rate inclination (injection rate gradient), which is a parameter of the injection rate waveform, and a mathematical expression showing the correlation between the arrival injection rate and the fuel pressure (fuel pressure). There has been proposed an injection rate waveform creation method that calculates and creates an injection rate waveform based on the calculated injection rate slope, the reached injection rate, and the fuel injection amount (see, for example, Patent Document 3 below). Thereby, it was possible to create an injection rate waveform without using a pressure sensor that detects the injection start timing, the injection end timing, and the injection rate. In addition, the mathematical expression indicating the correlation between the injection rate inclination and the ultimate injection rate and the fuel pressure is derived in advance from a plurality of injection rate waveforms actually measured using the injection rate measuring device.

  Here, the “arrival injection rate” means the arrival injection rate when the injector reaches full lift from the start of injection, and when the injection rate reaches a constant state (saturating state) after the injector reaches full lift. Is the ultimate injection rate.

JP 2004-003415 A JP 2002-188487A Japanese Patent Application Laid-Open No. 2011-16312

  However, in the injection rate waveform creation method disclosed in Patent Document 3, when the injection hole area (total area of the plurality of injection holes) of the injector is changed, the injection rate waveform depends on the injection hole area of the injector. Therefore, it becomes difficult to create an injection rate waveform. That is, when the nozzle hole area of the injector is changed, there is a problem in that it is necessary to derive a mathematical formula for calculating the injection rate inclination and the ultimate injection rate.

  The present invention has been made in consideration of such circumstances, and the object of the present invention is to create an injection rate waveform sensorlessly even when the nozzle hole area of the fuel injection valve is changed. It is an object of the present invention to provide an injection rate waveform generation method and an internal combustion engine control apparatus that can perform the above-described operation.

  The method of the present invention is an injection rate waveform creation method for creating an injection rate waveform of fuel injected from a fuel injection valve into a cylinder of a compression self-ignition internal combustion engine, and is a reference injection having a correlation with fuel pressure The rate gradient and the standard injection rate are calculated from the fuel pressure, and the injection rate gradient is calculated from the standard injection rate gradient and the area ratio that is the ratio of the nozzle hole area to the standard area of the fuel injection valve. The technical feature is to calculate the ultimate injection rate from the ultimate injection rate and the area ratio, and create an injection rate waveform based on the injection rate gradient, the ultimate injection rate, and the fuel injection amount.

  Specifically, in the injection rate waveform creation method of the present invention, preferably, the reference injection rate gradient and the reference pressure are calculated from a fuel pressure based on a mathematical formula derived from a plurality of injection rate waveforms measured using an injection rate measuring device. A reference reaching injection rate is calculated, and the reference area is a technical feature that is a nozzle hole area of the fuel injection valve measured by the injection rate measuring device.

  By configuring in this way, the reference injection rate inclination and the reference reaching injection rate are calculated from the fuel pressure, and the injection rate inclination and the reaching injection rate are calculated using the area ratio from the reference injection rate inclination and the reference reaching injection rate. Thus, even when the nozzle hole area of the fuel injection valve is changed, the injection rate waveform can be created without a sensor. That is, by correcting the reference injection rate inclination and the reference reaching injection rate by the area ratio, the injection rate waveform can be appropriately created even when the nozzle hole area of the fuel injection valve is changed.

  The apparatus of the present invention is a control device for a compression ignition type internal combustion engine in which fuel is injected from a fuel injection valve into a cylinder, and is a ratio of the injection hole area of the fuel injection valve to a reference area. A storage unit that stores an area ratio, a reference injection rate slope and a reference arrival injection rate that correlate with fuel pressure are calculated from fuel pressure, an injection rate slope is calculated from the reference injection rate slope and the area ratio, and the reference An injection rate waveform creating unit that calculates an ultimate injection rate from the ultimate injection rate and the area ratio, and creates an injection rate waveform based on the injection rate inclination, the ultimate injection rate, and the fuel injection amount; Is a technical feature.

  Specifically, in the control device for an internal combustion engine according to the present invention, preferably, the storage unit stores mathematical formulas derived from a plurality of injection rate waveforms actually measured using an injection rate measuring device, and the injection rate waveform The preparation unit is configured to calculate the reference injection rate inclination and the reference reaching injection rate from a fuel pressure based on the mathematical formula, and the reference area is measured by the injection rate measuring device when the fuel injection valve is actually measured. The technical feature is the area of the nozzle hole.

  By comprising in this way, even if it is a case where the nozzle hole area of a fuel injection valve is changed, an injection rate waveform can be created sensorlessly.

  Note that the fuel pressure used to create the injection rate waveform is detected by, for example, a rail pressure sensor, but such a sensor is a sensor that is equipped for fuel injection control, and is not a sensor provided for creating the injection rate waveform. . Therefore, it can be said that “the injection rate waveform can be created without a sensor” from the fuel pressure and the fuel injection amount.

  In the control device of the present invention, it may be determined whether or not the combustion in the combustion chamber of the internal combustion engine is properly performed using the injection rate waveform created by the injection rate waveform creation unit. Specifically, with reference to the injection rate waveform created from the fuel pressure and the fuel injection amount, the injection end timing (specifically, the period T1 in FIG. 4) of the reference injection rate waveform, the actual combustion gravity center position, and Are compared, and when the actual combustion center of gravity position is deviated from the injection end timing of the reference injection rate waveform, it is determined that the combustion is not properly performed.

  In the control device of the present invention, the presence / absence of abnormality of the pressure sensor built in the fuel injection valve may be determined using the injection rate waveform created by the injection rate waveform creating unit. Specifically, based on the injection rate waveform created from the fuel pressure and the fuel injection amount, the pressure waveform (injector injection pressure) obtained from the injection start timing and injection end timing of the reference injection rate waveform and the output signal of the pressure sensor For example, if the injection start timing / injection end timing of the pressure waveform deviates by a predetermined amount or more with respect to the injection start timing / injection end timing of the injection rate waveform, it is determined that the pressure sensor is abnormal To do.

  According to the present invention, even if the injection hole area of the fuel injection valve is changed, it is possible to create an injection rate waveform without a sensor, and using the created fuel injection rate waveform, for example, heat The incidence can be evaluated.

1 is a schematic configuration diagram of an engine to which the present invention is applied and a control system thereof. 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 a 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), respectively. It is a figure which shows the relationship between an engine request output and the target fuel pressure set according to the request output. It is a figure which shows the fuel pressure setting map referred when determining target fuel pressure. It is a figure which shows the measured injection rate waveform and the injection rate waveform model. It is a figure which shows the measured injection rate waveform and the injection rate waveform model. It is a figure which shows the measured injection rate waveform and the injection rate waveform model. It is a figure which shows the measured injection rate waveform and the injection rate waveform model. It is a figure which shows the reference | standard characteristic value of an injection rate waveform. It is a table | surface which shows each numerical value of the reference injection rate inclination G1a which was extract | collected for every fuel pressure, the reference | standard reached injection rate Q1a, the reference | standard injection rate inclination G2a, the reference | standard reached injection rate Q2a, and the reference | standard injection rate inclination G3a. It is a figure which shows together the graph (a) which plotted the reference | standard reached | attained injection rate Q1a by making √ (fuel pressure) into a parameter, and the data table (b) used for preparation of the graph. It is a figure which shows together the graph (a) which plotted the reference | standard reached | attained injection rate Q2a by making √ (fuel pressure) into a parameter, and the data table (b) used for preparation of the graph. It is a figure which shows together the graph (a) which plotted the reference | standard injection rate inclination G1a by using (root) (fuel pressure) as a parameter, and the data table (b) used for preparation of the graph. It is a figure which shows together the graph (a) which plotted the reference | standard injection rate inclination G2a by using (square) (fuel pressure) as a parameter, and the data table (b) used for preparation of the graph. It is a figure which shows together the graph (a) which plotted the reference | standard injection rate inclination G3a by using (square) (fuel pressure) as a parameter, and the data table (b) used for preparation of the graph. It is a figure which shows an example of the creation process of an injection rate waveform. It is a flowchart for demonstrating the creation process of the injection rate waveform which ECU performs. It is a figure which writes together and shows an injector injection pressure waveform and a piezo drive signal waveform. It is a figure which compares an injector injection pressure waveform and an injection rate waveform.

  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, an example of a diesel engine (hereinafter simply referred to as an engine) to which the present invention is applied will be described. FIG. 1 is a schematic configuration diagram of the engine 1 and its control system. FIG. 2 is a cross-sectional view showing the combustion chamber 3 of the diesel engine and its periphery.

  As shown in FIG. 1, the engine 1 of this example 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 needle valve and a piezoelectric element (piezo element) therein, and is configured by a piezo injector that is appropriately opened to inject 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.

  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 that makes the exhaust A / F become the target A / F) by an addition control operation by the ECU 100 described later. In addition, it is constituted by an electronically controlled on-off valve whose 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 that constitutes an intake passage is connected to the intake manifold 63. In addition, an air cleaner 65, an air flow meter 43, and a throttle valve (intake throttle valve) 62 are arranged in this intake passage sequentially 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.

  The exhaust system 7 includes an exhaust manifold 72 connected to an 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. . Further, 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. Yes. 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 carrier, and an alkali such as potassium (K), sodium (Na), or lithium (Li) is formed on the carrier. Metal, alkaline earth such as barium (Ba) and calcium (Ca), rare earth such as lanthanum (La) and yttrium (Y), and a noble metal such as platinum (Pt) are supported. Yes.

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 NOx occlusion reduction catalyst supported on a porous ceramic structure, 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 with a relatively small volume in the central portion, and on the outer peripheral side. The structure is such that the space is gradually expanded toward the expansion 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 an intake port 15a for introducing air into the combustion chamber 3 and an exhaust port 71 for discharging exhaust gas from the combustion chamber 3, and an intake valve for opening and closing the intake port 15a. 16 and an exhaust valve 17 for opening and closing the exhaust port 71 are 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 of this example 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.

  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 impeller 53 that are connected via a turbine shaft 51. The compressor impeller 53 is arranged facing the inside of the intake pipe 64, and the turbine wheel 52 is arranged facing the inside of the exhaust pipe 73. Therefore, the turbocharger 5 performs a so-called supercharging operation in which the compressor impeller 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 is provided further downstream than the intercooler 61. The throttle valve 62 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner. The throttle air flow area of the intake air is reduced under a predetermined condition, and the supply amount of the intake air is adjusted (reduced). ) Function.

  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 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 (hereinafter also referred to as fuel pressure). 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 CPU 101 and the ROM 102 correspond to the “injection rate waveform creation unit” and the “storage unit” of the present invention, respectively.

  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 injector injection pressure sensor (built in the injector 23) 23a, and the like are connected.

  The injector injection pressure sensor 23a is a pressure sensor that directly detects the upstream pressure of the nozzle sheet of the injector 23. Since it is difficult to ensure the detection accuracy of the injector injection pressure sensor 23a, it may be required to determine whether the operation is normal or abnormal. The determination process will be described later.

  On the other hand, the injector 23, the fuel addition valve 26, the throttle valve 62, the EGR valve 81, and the like are connected to the output interface 106.

  The ECU 100 executes various controls of the engine 1 based on the outputs of the various sensors described above. For example, the ECU 100 executes pilot injection and main injection (main injection) described later as fuel injection control of the injector 23. Further, the ECU 100 executes [injection rate waveform creation processing], [combustion state determination processing], [combustion gravity center movement control], and [injector injection pressure sensor abnormality determination processing], which will be described later.

-Fuel injection mode-
Hereinafter, an outline of each operation of the pilot injection and the main injection in the present embodiment will be described.

[Pilot injection]
The pilot injection is an injection operation for injecting a small amount of fuel in advance prior to the main injection from the injector 23. That is, after the execution of this pilot injection, the fuel injection is temporarily interrupted and the compressed gas temperature (in-cylinder temperature) is sufficiently increased to reach the self-ignition temperature of the fuel until the main injection is started. This ensures good ignitability of the fuel injected in the main injection. That is, the function of pilot injection in this embodiment is specialized for preheating in the cylinder. In other words, the pilot injection in this embodiment is an injection operation (preheating fuel supply operation) for preheating the gas in the combustion chamber 3. If the injection amount is 2 mm ³ and the injection is started before the compression top dead center (BTDC) 15 ° CA of the piston 13, the preheating function can be sufficiently secured.

  Thus, in this embodiment, the preheating in the cylinder is sufficiently performed by the pilot injection. When main injection, which will be described later, is started by this preheating, the fuel injected by the main injection is immediately exposed to a temperature environment equal to or higher than the self-ignition temperature, and thermal decomposition proceeds. After the injection, combustion starts immediately. Will be.

  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.

[Main injection]
The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. The fuel injection amount of the main injection is a target fuel injection amount for generating the torque based on the required torque determined according to the operating state such as the engine speed, accelerator operation amount, cooling water temperature, intake air temperature, etc. Is set.

  The torque request value of the engine 1 is determined according to the engine speed, the accelerator operation amount, the operating state such as the cooling water temperature, the intake air temperature, etc., and the usage status of the auxiliary machinery. 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). The higher the required accelerator torque of the engine 1, the higher the accelerator opening.

-Fuel injection pressure-
The fuel injection pressure for executing the main 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 as the engine speed (engine speed) increases. It is supposed to be expensive. That is, when the engine load is high, the amount of air sucked into the combustion chamber 3 is large, so that a large amount of fuel must be injected from the injector 23 into the combustion chamber 3, and therefore the injection pressure from the injector 23 Need 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. A specific method for setting the target value of the fuel pressure will be described later.

  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 speed based on the detected value of the crank position sensor 40, obtains the amount of depression of the accelerator pedal (accelerator opening) based on the detected value of the accelerator opening sensor 47, The fuel injection amount in the 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 and a fuel pressure setting map will be described. First, the technical idea when setting the target fuel pressure in this embodiment will be described.

  In the diesel engine 1, it is important to simultaneously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque. The inventor of the present invention can 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) as a method for simultaneously satisfying these requirements. Focusing on the effectiveness, we found a target fuel pressure setting method as described below as a method for controlling the change state of the heat generation rate.

  First, FIG. 4 shows an ideal heat generation rate waveform related to the combustion of fuel injected by main injection and an injection rate waveform of fuel injected from the injector 23. 4 indicates the crank angle position corresponding to the compression top dead center of the piston 13.

  In the heat release rate waveform shown in FIG. 4, for example, combustion of fuel injected by the main injection is started from 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 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 is combusted at 10 degrees after compression top dead center (ATDC 10 °). The situation is completed. 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 amount reduction starts to the injector 23 until fuel injection is completely stopped (see FIG. 4 is located in the period T1).

  In the heat generation rate waveform shown in FIG. 4, the heat generation rate is, for example, 10 [J / ° CA] at the compression top dead center (TDC) of the piston 13, and thus the fuel injected in the main injection. Thus, stable diffusion combustion can be realized. This value is not limited to this, and is appropriately set according to the total fuel injection amount, for example. Pilot injection is also performed prior to main injection, thereby sufficiently increasing the temperature in the cylinder and ensuring good ignitability of fuel injected by main injection.

  As described above, in the present embodiment, the cylinder is sufficiently preheated by the pilot injection. When the main injection is started by this preheating, the fuel injected by the main injection is immediately exposed to a temperature environment equal to or higher than the self-ignition temperature, and the thermal decomposition proceeds, and the combustion starts immediately after the injection. become.

  As described above, the target fuel pressure setting method according to the present embodiment is a technical idea that the combustion efficiency is improved by optimizing the change state of the heat generation rate (optimization of the heat generation rate waveform). It is based on. In order to realize this, the target fuel pressure is set as described later. This point will be described with reference to FIG.

  The solid line in FIG. 5 indicates the relationship between the required output (required power) in the engine 1 according to this embodiment and the target fuel pressure set according to the required output. Thus, the required output and the target fuel pressure are in a proportional relationship, and the target fuel pressure is uniquely determined with respect to the required output. In other words, the target fuel pressure is assigned in advance to each required output.

  Hereinafter, a method for setting the target fuel pressure with respect to the required output will be specifically described with reference to FIG.

  First, a temporary fuel pressure line indicated by a broken line in FIG. 5 is set. This temporary fuel pressure line is set so that the target fuel pressure is also “0” when the required output is “0”, passes through the origin of the graph shown in FIG. 5 and has a predetermined slope. As given.

  The inclination of the temporary fuel pressure line is determined by the displacement of the engine 1 or the like. That is, for example, the inclination of the temporary fuel pressure line is set smaller for the engine 1 having a larger displacement. The target fuel pressure on the temporary fuel pressure line is determined in a proportional relationship with a predetermined proportional constant (corresponding to the inclination of the temporary fuel pressure line) with respect to the required output. That is, the target fuel pressure is obtained by multiplying the required output by a predetermined proportionality constant, and the set of the target fuel pressure is the temporary fuel pressure line.

  Then, the temporary fuel pressure line is moved parallel to the high fuel pressure side (upper side in FIG. 5) by a predetermined pressure offset amount with respect to the power center of gravity point (the point of the required output of 40 kW in the case shown in FIG. 5) on the temporary fuel pressure line. Thus, a fuel pressure line indicated by a solid line in the figure is set. The power centroid point is not limited to the above value.

  Here, the power center-of-gravity point is set as a value corresponding to the most frequently used output in the output range of the engine 1.

  Further, as the pressure offset amount, when the fuel of the main injection injected from the injector 23 starts combustion at the compression top dead center (TDC) of the piston 13, a predetermined piston position (after the compression top dead center) It is set so that the heat generation rate in the cylinder reaches a maximum value (peak value) at 10 degrees after compression top dead center (ATDC 10 °). That is, the pressure offset amount is set so that the ideal heat release rate waveform shown in FIG. 4 can be obtained at the power center of gravity.

  This pressure offset amount is individually set for each type of engine 1 through experiments and simulations in advance according to the displacement of the engine 1 and the number of cylinders. In the fuel supply system 2 of the engine 1 according to this embodiment, the upper limit value (upper limit rail pressure) of the target fuel pressure is set to 200 MPa.

  FIG. 6 is a fuel pressure setting map that is referred to when the target fuel pressure is determined. This fuel pressure setting map is created according to the fuel pressure line shown by the solid line in FIG. 5 and is stored in the ROM 102, for example. In this fuel pressure setting map, the horizontal axis is the engine speed, and the vertical axis is the engine torque. Further, Tmax in FIG. 6 indicates a maximum torque line.

  As a feature of this fuel pressure setting map, an equal fuel injection pressure line (equal fuel injection pressure region) indicated by A to I in the figure is a required output (required power) to the engine 1 that is obtained based on the depression amount of the accelerator pedal. Are allocated to the equal power line (equal output region). That is, in this fuel pressure setting map, the equal power line and the equal fuel injection pressure line are set to substantially coincide.

  Specifically, a curve A in FIG. 6 is a line having a required engine output of 10 kW, and a line of 66 MPa is allocated as the fuel injection pressure. Hereinafter, similarly, the curve B is a line with a required engine output of 20 kW, and a line with 83 MPa is allocated as the fuel injection pressure. A curve C is a line having a required engine output of 30 kW, and a line of 100 MPa is allocated to this as a fuel injection pressure. A curve D is a line having a required engine output of 40 kW, and a line of 116 MPa is allocated to the line as a fuel injection pressure. Curve E is a line with a required engine output of 50 kW, and a line with 133 MPa is allocated as the fuel injection pressure. A curve F is a line having a required engine output of 60 kW, and a line of 150 MPa is allocated as the fuel injection pressure. Curve G is a line with a required engine output of 70 kW, and a line of 166 MPa is allocated to this as the fuel injection pressure. A curve H is a line having an engine output demand of 80 kW, and a line of 183 MPa is allocated as the fuel injection pressure. Curve I is a line with a required engine output of 90 kW, and a line with 200 MPa is allocated as the fuel injection pressure. These values are not limited to this, and are set as appropriate according to the performance characteristics of the engine 1 and the like.

  Further, in each of the lines A to I, the ratio of the change amount of the fuel injection pressure to the change amount of the engine required output is set to be approximately equal.

  In accordance with the fuel pressure setting map created in this way, a target fuel pressure suitable for a required output to the engine 1 is set, and the supply pump 21 is controlled.

  Also, when both the engine speed and the engine torque increase (see arrow I in FIG. 6), when the engine speed is constant and the engine torque increases (see arrow II in FIG. 6), and In any case where the engine torque is constant and the engine speed increases (see arrow III in FIG. 6), the fuel injection pressure is increased. This ensures a fuel injection amount suitable for the intake air amount when the engine torque (engine load) is high, and increases the fuel injection amount per unit time when the engine speed is high, which is required in a short period of time. A fuel injection amount can be secured.

  On the other hand, even if the engine speed and the engine torque change, if the engine output after the change does not change (see arrow IV in FIG. 6), the fuel injection pressure is not changed so far. Maintain the appropriate value of the set fuel injection pressure. In other words, the fuel injection pressure is not changed when the engine operating state changes along the equal fuel injection pressure line (corresponding to the equal power line), and the combustion mode with the ideal heat release rate waveform described above is used. To continue. In this case, it is possible to continuously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque.

  As described above, in the present embodiment, there is a unique correlation between the required output (required power) for the engine 1 and the fuel injection pressure (common rail pressure), and at least one of the engine speed and the engine torque. When the engine output changes as a result of the change, fuel injection can be performed at an appropriate fuel pressure accordingly, and conversely, the engine output does not change even if the engine speed or engine torque changes. The fuel pressure is not changed from the appropriate value that has been set. This makes it possible to bring the heat generation rate change state closer to the ideal state over substantially the entire engine operation region.

-Injection rate waveform creation process-
Next, an example of an injection rate waveform creation process will be described below. In the present embodiment, an injection rate waveform is created using characteristic values (reachable injection rates Q1, Q2 and injection rate gradients G1 to G3 described later) that are parameters of the injection rate waveform and the target fuel injection amount. Further, the characteristic value is calculated using a reference characteristic value (reference reaching injection rates Q1a and Q2a and reference injection rate gradients G1a to G3a described later) and an area ratio described later.

<About standard characteristic values>
First, the derivation of the reference characteristic value calculation formula will be described. In addition, as will be described in detail below, the calculation formula for the reference characteristic value is obtained by actually measuring a plurality of injection rate waveforms with different fuel pressure and injection amount conditions, and modeling each measured injection rate waveform. The injection rate gradient and the reference reaching injection rate are sampled, and the collected data group of the reference injection rate gradient and the reference reaching injection rate is derived by organizing the square root of fuel pressure [√ (fuel pressure)].

[Measurement of injection rate waveform]
The fuel pressure and the fuel injection amount were set to the following values (i) to (iv), and a plurality of injection rate waveforms were measured using an injection rate measuring device based on the long tube method.

(I) Fuel pressure: 40 MPa, pilot injection: 2.4 mm ³ / st, main injection: 28.3 mm ³ / st],
(Ii) Fuel pressure: 80 MPa, pilot injection: 2.4 mm ³ / st, main injection: 61.6 mm ³ / st
(Iii) Fuel pressure: 140 MPa, pilot injection: 1.8 mm ³ / st, main injection: 89.4 mm ³ / st
(Iv) Fuel pressure: 200 MPa, pilot injection: 1.6 mm ³ / st, main injection: 79.3 mm ³ / st
The actual measurement result of the injection rate waveform thus measured is shown by the solid line in FIGS.

  Here, the injection rate waveform indicated by the solid line in FIGS. 7 to 10 is a reference waveform (nominal value) at each fuel pressure (40 MPa, 80 MPa, 140 MPa, 200 MPa), and is an ideal heat release rate waveform (for example, FIG. 4). The injection start timing / injection end timing (time with respect to TDC) and the fuel injection rate of pilot injection and main injection are set so that the heat generation rate waveform shown in FIG.

  The long tube method applied to the actual measurement of the injection rate waveform is a general method for measuring the fuel injection rate, and in a state where a long tube having a constant cross-sectional area is filled with fuel, an injector is inserted in the tube. This is a method of measuring the injection rate by injecting fuel from the fuel and detecting the pressure wave generated in the pipe by the fuel injection. Moreover, the nozzle hole area (total area of a plurality of nozzle holes) Aa of the injector when actually measured by the injection rate measuring device is the reference area.

[Modeling and quantification of injection rate waveform]
As shown in FIGS. 7 to 10, the actually measured injection rate waveform is approximated by a straight line (broken line) and modeled. Next, from each modeled injection rate waveform (broken line: main injection), a parameter (reference characteristic value) of the injection rate waveform shown in FIG. 11, that is, a reference injection rate gradient G1a on the rising side (injection start side), respectively. The reference reaching injection rate Q1a, the rising-side reference injection rate gradient G2a, the reference reaching injection rate Q2a, and the falling-side (injection end-side) reference injection rate gradient G3a were read and digitized. However, the reference injection rate gradients G1a, G2a, and G3a were calculated by [G1a = Q1a / xl1], [G2a = (Q2a−Q1a) / xl2], and [G3a = Q2a / xl4], respectively. FIG. 11 shows only the reference characteristic value of the injection rate waveform of the main injection.

  Of the parameters (reference characteristic values) of the injection rate waveform, the reference injection rate gradient G1a is the rate of change over time of the injection rate until the needle valve of the injector 23 reaches full lift, and the reference injection rate gradient G2a is the injector. It is a time change rate of the injection rate after 23 needle valves reach full lift.

  Further, the reference reaching injection rate Q1a is the reaching injection rate when the needle valve of the injector 23 reaches the full lift, and the reference reaching injection rate Q2a is that the injection rate is constant after the needle valve of the injector 23 reaches the full lift. This is the ultimate injection rate when reaching the state (saturating state).

  FIG. 12 shows data (read values) of the reference injection rate gradient G1a, the reference reaching injection rate Q1a, the reference injection rate gradient G2a, the reference reaching injection rate Q2a, and the reference injection rate gradient G3a collected as described above. FIG. 12 shows only data of main injection.

[Derivation of reference characteristic value calculation formula]
First, when fuel is injected from an injector, [Qa = Ca · Aa · √ (ΔP)] if the injection amount Qa, injection pressure (fuel pressure) ΔP, nozzle hole area (reference area) Aa, and flow coefficient Ca There is a relationship.

Here, the reference characteristic values G1a [mm ³ / ms ² ], Q1a [mm ³ / ms], G2a [mm ³ / ms ² ], Q2a [mm ³ / ms], and G3a [mm ³ / ms ^{2] described above.} ], Since the main component is [mm ³ / ms], each reference characteristic value correlates with the square root of the injection pressure, that is, the square root of the fuel pressure [√ (fuel pressure)]. Focusing on these points, each reference characteristic value (actually measured value) of the injection rate waveform is arranged by the square root of fuel pressure [√ (fuel pressure)], and the results shown in FIGS. 13 (a) to 17 (a). was gotten.

As is clear from the results of FIG. 13A, the reference injection rate Q1a is correlated with √ (fuel pressure), and the relationship can be approximated by a quadratic curve. Deriving the approximate expression, that is, the calculation formula for the reference reaching injection rate Q1a,
Q1a = 0.0253 [√ (fuel pressure)] ² +3.2189 [√ (fuel pressure)] − 0.2033 (1)
It becomes. In addition, the graph of Fig.13 (a) plots the data shown in the table | surface of the same figure (b).

As is clear from the results of FIG. 14A, the reference reaching injection rate Q2a is also correlated with [√ (fuel pressure)], and the relationship can be approximated by a quadratic curve. Deriving the approximate expression, that is, the calculation formula for the reference reaching injection rate Q2a,
Q2a = 0.018 [√ (fuel pressure)] ² +4.7593 [√ (fuel pressure)] − 0.1076 (2)
It becomes. In addition, the graph of Fig.14 (a) plots the data shown in the table | surface of the same figure (b).

As is clear from the results of FIG. 15A, the reference injection rate gradient G1a is also correlated with [√ (fuel pressure)], and the relationship can be approximated by a quadratic curve. Deriving the approximate expression, that is, the calculation formula of the reference injection rate gradient G1a,
G1a = 0.7636 [√ (fuel pressure)] ² +9.0974 [√ (fuel pressure)] − 0.488 (3)
It becomes. In addition, the graph of Fig.15 (a) plots the data shown in the table | surface of the same figure (b).

As is apparent from the results of FIG. 16A, the reference injection rate gradient G2a is also correlated with [√ (fuel pressure)], and the relationship can be approximated by a quadratic curve. Deriving the approximate expression, that is, the calculation formula for the reference injection rate gradient G2a,
G2a = 0.3111 [√ (fuel pressure)] ² +1.6959 [√ (fuel pressure)] − 0.6092 (4)
It becomes. In addition, the graph of Fig.16 (a) plots the data shown in the table | surface of the same figure (b).

As is clear from the result of FIG. 17A, the reference injection rate gradient G3a is also correlated with [√ (fuel pressure)], and the relationship can be approximated by a quadratic curve. Deriving the approximate expression, that is, the calculation formula of the reference injection rate gradient G3a,
G3a = 0.2107 [√ (fuel pressure)] ² +20.304 [√ (fuel pressure)] − 0.0207 (5)
It becomes. In addition, the graph of Fig.17 (a) plots the data shown in the table | surface of the same figure (b).

  Expressions (1) to (5) for calculating the reference characteristic values Q1a, Q2a, G1a, G2a, and G3a of the injection rate waveform are stored in the ROM 102 of the ECU 100, for example.

<About characteristic values>
Next, characteristic value calculation formulas will be described. In the present embodiment, in order to cope with the change of the injector (increase / decrease in the number of injection holes, increase / decrease in the area of each injection hole, etc.), the reference characteristic value is corrected according to the area ratio and is a parameter of the injection rate waveform. Calculate the characteristic value.

  When the fuel is injected from the injector, if the injection amount Q, the injection pressure (fuel pressure) ΔP, the nozzle hole area A, and the flow coefficient C, there is a relationship of [Q = C · A · √ (ΔP)]. Further, when [Ca · √ (ΔP)] of the above [Qa = Ca · Aa · √ (ΔP)] is treated as a constant, the relationship [Q = Qa · (A / Aa)] is established. That is, the relationship of “characteristic value = reference characteristic value × area ratio” is established.

  In addition, the area ratio is the injection hole area (the plurality of injection holes when the injection rate waveform is created) with respect to the injection hole area (total area of the plurality of injection holes) Aa of the injector when actually measured by the injection rate measuring device. It is the ratio of the total area A) of the nozzle holes. For this reason, when the nozzle hole area Aa of the injector when actually measured by the injection rate measuring device is the same as the nozzle hole area A of the injector when the injection rate waveform is created, the characteristic values Q1, Q2, and G1 , G2, and G3 are the same as the reference characteristic values Q1a, Q2a, G1a, G2a, and G3a, respectively.

  Therefore, the ultimate injection rate Q1, the ultimate injection rate Q2, the injection rate gradient G1, the injection rate gradient G2, and the injection rate gradient G3 are derived from the following equations.

Q1 = Q1a × (A / Aa) (6)
Q2 = Q2a × (A / Aa) (7)
G1 = G1a × (A / Aa) (8)
G2 = G2a × (A / Aa) (9)
G3 = G3a × (A / Aa) (10)
In addition, Formula (6)-Formula (10) which calculates area ratio (A / Aa) and characteristic value Q1, Q2, G1, G2, G3 are memorize | stored in ROM102 of ECU100, for example.

  Here, the injection rate waveform of pilot injection will be described. Since the injection rate gradient PG1 on the rising side (injection start side) of the pilot injection can be regarded as the same as the injection rate gradient G1 of the main injection, in this example, the calculation formula of the injection rate gradient G1 obtained by the main injection (above Equation (8) is also used for calculating the injection rate gradient PG1 of pilot injection. Similarly, for the injection rate gradient PG3 on the falling side (injection end side) of pilot injection, the calculation formula (the above formula (10)) of the injection rate gradient G3 obtained in the main injection is used.

  As shown in FIGS. 7 to 10, the actual injection rate waveform of pilot injection is approximated by a straight line (broken line) and modeled, and the pilot injection rising side (injection start side) is performed in the same manner as described above. An equation for calculating the injection rate inclination PG1 and an equation for calculating the injection rate inclination PG3 on the falling side (injection end side) of the pilot injection are obtained, and the injection rate inclination PG1 of the pilot injection is calculated using the equation. PG3 may be calculated.

<Injection rate waveform creation process>
A specific example of the injection rate waveform creation process will be described.

  First, the fuel pressure is acquired from the output signal of the rail pressure sensor 41, and using the acquired fuel pressure, from the above formulas (1) to (10), the final injection rate Q1, which is each parameter of the injection rate waveform, the final injection The values of the rate Q2, the rising-side injection rate gradient G1, the rising-side injection rate gradient G2, and the falling-side injection rate gradient G3 are calculated. 18A to 18C using the calculated Q1, Q2, G1, G2, G3 and the target fuel injection amount (main fuel injection amount) corresponding to the torque request of the engine 1. The horizontal axes xl1, xl2, xl3, and xl4 are determined, and an injection rate waveform is created. Specific examples of the waveform creation processing will be described for each example of FIGS. 18A, 18B, and 18C.

[Waveform creation process 1]
In the example of FIG. 18A, the fuel injection amount (target fuel injection amount) of the main injection is such an injection amount that the height h1 of the injection rate waveform is less than the ultimate injection rate Q1 (h1 <Q1). Indicates. In the example of FIG. 18A, when the area of the injection rate waveform is S, the area S [S = h1 * (xl1 + xl2) / 2] corresponds to the fuel injection amount.

Here, since xl1 = h1 / G1 and Xl2 = h1 / G3, the height h1 of the injection rate waveform shown in FIG.
h1 = √ ((2 * S * G1 * G3) / (G1 + G3)) (11)
It becomes.

  When the fuel injection amount is an injection amount at which the height h1 of the injection rate waveform does not reach the ultimate injection rate Q1, the height h1, the rising-side injection rate gradient G1, and the falling-side injection Using the rate gradient G3, xl1 and xl2 shown in FIG. 18A are determined, and an injection rate waveform of the main injection is created. The injection start timing (time with respect to TDC) of the injection rate waveform of the main injection is a reference value (fixed value). That is, the injection start timing of the reference injection rate waveform (solid line) shown in FIGS.

  The injection rate waveform of pilot injection is the same as [Waveform creation processing 1] using the fuel injection amount of pilot injection (corresponding to the area of the injection rate waveform) and the injection rate gradients G1 and G3 of the main injection. A method is used to determine xl1 and xl2 shown in FIG. The injection start timing (time with respect to TDC) of the injection rate waveform of this pilot injection is also set to the reference value (fixed value). That is, the injection start timing of the reference injection rate waveform (solid line) shown in FIGS.

[Waveform creation process 2]
In the example of FIG. 18B, the fuel injection amount (target fuel injection amount) of the main injection is such that the height h1 of the injection rate waveform reaches the ultimate injection rate Q1, but the height h2 reaches the ultimate injection rate Q2. A case where the injection amount is not performed (injection amount such that h1 = Q1 and h2 <Q2) is shown. In the example of FIG. 18B, the area S (corresponding to the fuel injection amount) of the injection rate waveform is [S = xl1 * Q1 / 2 + xl2 * (Q1 + h2) / 2 + xl3 * h2 / 2].

Here, since xl1 = Q1 / G1, xl2 = (h2-Q1) / G2, and xl3 = h2 / G3, the height h2 of the injection rate waveform shown in FIG.
h2 = √ ((2 * S-Q1 * Q1 * (1 / G1-1 / G2)) / (1 / G2 + 1 / G3)) (12)
It becomes.

  In this way, when the fuel injection amount is an injection amount in which the height h1 of the injection rate waveform reaches the ultimate injection rate Q1, but the height h2 does not reach the ultimate injection rate Q2, the height h2, The ultimate injection rate Q1, the rising injection rate gradients G1 and G2, and the falling injection rate gradient G3 are used to determine xl1, xl2, and xl3 shown in FIG. create. The injection start timing (time with respect to TDC) of the injection rate waveform created in this way is also set as a reference value (fixed value). That is, the injection start timing of the reference injection rate waveform (solid line) shown in FIGS.

[Waveform creation process 3]
The example of FIG. 18C shows a case where the fuel injection amount (target fuel injection amount) of the main injection is an injection amount that reaches the height h2 of the injection rate waveform. In the example of FIG. 18C, the area S (corresponding to the fuel injection amount) of the injection rate waveform is [S = xl1 * Q1 / 2 + xl2 * (Q1 + Q2) / 2 + L * Q2 + xl4 * Q2 / 2].

Here, since xl1 = Q1 / G1, xl2 = (Q2-Q1) / G2, and xl4 = Q2 / G3, L (injection rate constant period) shown in FIG.
L = (1 / Q2) * (S- (Q1 * Q2) / (2 * G1)-(Q2 * Q2-Q1 * Q1) / (2 * G2)-(Q2 * Q2) / (2 * G3) (13)
It becomes.

  When the fuel injection amount reaches the height h2, the injection rate is constant L, the arrival injection rates Q1 and Q2, the rising injection rate gradients G1 and G2, and the falling injection. Using the rate gradient G3, xl1, xl2, and xl4 shown in FIG. 18C are determined, and the injection rate waveform of the main injection is created. The injection start timing (time with respect to TDC) of the injection rate waveform created in this way is also set as a reference value (fixed value). That is, the injection start timing of the reference injection rate waveform (solid line) shown in FIGS.

  Next, an injection rate waveform creation process executed by the ECU 100 will be described with reference to FIG.

Step S1:
First, the fuel pressure is acquired from the output signal of the rail pressure sensor 41, and the target fuel injection amount (main injection amount) is calculated from the required torque value of the engine 1.

Step S2:
Using the acquired fuel pressure, characteristic values (reachable injection rates Q1, Q2 and injection rate gradients G1-G3) are calculated. Specifically, using the fuel pressure, reference characteristic values (reference reaching injection rates Q1a and Q2a and reference injection rate gradients G1a to G3a) are calculated from the above-described equations (1) to (5). Then, using the calculated reference characteristic value and the area ratio, the characteristic value is calculated from the above formulas (6) to (10).

Step S3:
Using the calculated injection rate gradient G1, injection rate gradient G3, and area S of the injection rate waveform corresponding to the target fuel injection amount, the injection rate waveform shown in FIG. The length h1 is calculated.

Step S4:
The calculated height h1 is compared with the ultimate injection rate Q1, and when the height h1 is smaller than the ultimate injection rate Q1 (when h1 <Q1), the process proceeds to step S5. On the other hand, when the height h1 has reached the ultimate injection rate Q1 (when h1 = Q1), the process proceeds to step S6.

Step S5:
Using the height h1 and the injection rate gradients G1 and G2 of the injection rate waveform, the horizontal axis xl1 and xl2 in FIG. To do.

  Here, as for the injection rate waveform of the pilot injection, as described above, the injection rate gradient PG1 on the rising side and the injection rate gradient PG3 on the falling side of the pilot injection are the injection rate gradients G1 and G3 of the main injection, respectively. In this example, the injection rate gradient G1 on the rising side and the injection rate gradient G3 on the falling side calculated when creating the injection rate waveform of the main injection, and the fuel injection amount of pilot injection are used in this example. The horizontal axis xl1 and xl2 in FIG. 18A is obtained by the above-described [Waveform creation process 1] using the area S of the injection rate waveform corresponding to, and the pilot rate injection rate waveform is created.

Step S6:
As shown in FIG. 18 (b), when the target fuel injection amount (main injection amount) is an injection amount at which the height h1 of the injection rate waveform reaches the ultimate injection rate Q1, the ultimate injection rate Q1, Using the injection rate gradients G1, G2, and G3 and the area S of the injection rate waveform corresponding to the target fuel injection amount, the height h2 of the injection rate waveform shown in FIG. calculate.

Step S7:
The calculated height h2 is compared with the ultimate injection rate Q2, and when the height h2 is smaller than the ultimate injection rate Q2 (when h2 <Q2), the process proceeds to step S8. On the other hand, when the height h2 has reached the ultimate injection rate Q2 (when h2 = Q2), the process proceeds to step S9.

Step S8:
Using the injection rate height h2, the ultimate injection rate Q1, and the injection rate gradients G1, G2, and G3, the horizontal axis xl1, xl2, and xl3 in FIG. Obtain the injection rate waveform.

  In the process of FIG. 18B, when the height h1 of the injection rate waveform reaches the ultimate injection rate Q1 (when h1 = Q1), the dot area area Sb shown in FIG. When the fuel injection amount corresponding to is equal to the target fuel injection amount, xl1 (xl1 = Q1 / G1) and xl2 ′ (xl2 ′ = Q1 / G3) are obtained to create an injection rate waveform.

Step S9:
As shown in FIG. 18C, when the target fuel injection amount is an injection amount at which the height h2 of the injection rate waveform reaches the ultimate injection rate Q2, the ultimate injection rates Q1, Q2 and the injection rate gradient Using the area S of the injection rate waveform corresponding to G1, G2, G3 and the target fuel injection amount, the horizontal axis xl1, xl2, L in FIG. , Xl4 is obtained to create an injection rate waveform.

  In the process of FIG. 18C, when the height h2 of the injection rate waveform reaches the ultimate injection rate Q2 (when h2 = Q2), the area Sc of the dot region shown in FIG. Is equal to the target fuel injection amount, xl1 (xl1 = Q1 / G1), xl2 = (Q2-Q1) / G2, and xl3 ′ = Q2 / G3 are obtained to obtain the injection rate waveform. create.

  With the above processing, an injection rate waveform can be created from the fuel pressure and the fuel injection amount without using a pressure sensor that detects the fuel injection start timing, the injection end timing, and the injection rate. In the present embodiment, the reference characteristic values (reference reaching injection rates Q1a and Q2a and reference injection rate gradients G1a to G3a) are calculated from the fuel pressure, and the characteristic value (reaching injection rate Q1 is calculated from the reference characteristic values using the area ratio. , Q2 and injection rate gradients G1 to G3), the injection rate waveform can be created sensorlessly even when the injection hole area of the injector is changed. That is, by correcting the reference characteristic value by the area ratio, the injection rate waveform can be appropriately created even when the injection hole area of the injector is changed. In other words, in the present embodiment, it is not necessary to remeasure the characteristic value every time the injector is changed, so that an increase in man-hours, an increase in cost, and a decrease in quality can be suppressed.

  The injection rate waveform obtained in this way is a waveform based on the actually measured injection rate waveforms of FIGS. 7 to 10, and the injection start timing / injection end timing (time with respect to TDC) and fuel of pilot injection and main injection The injection rate is a target injection rate waveform that is set so as to be in an optimal heat generation rate change state (a state in which most of the fuel injected in the main injection diffuses and burns). Therefore, the actual combustion state (diffusion combustion state) can be evaluated using this injection rate waveform. An example of the process (fuel state determination process) will be described.

[Combustion state judgment processing]
First, in the case of combustion of fuel injected by main injection (mostly diffusion combustion), if the combustion center of gravity (see FIG. 4) is at an appropriate timing, the fuel in the combustion chamber 3 of the engine 1 is good. Therefore, it can be determined that various requests such as improvement of exhaust emission by reducing the NOx generation amount and smoke generation amount, reduction of combustion noise, and sufficient engine torque can be achieved.

  Therefore, in this example, an injection rate waveform is created by the above-described processing using the fuel pressure obtained from the output signal of the rail pressure sensor 41 and the target fuel injection amount, and the created injection rate waveform (reference waveform) The injection end timing (period T1 in FIG. 4) is compared with the actually detected (actually measured) combustion centroid position, and it is determined whether or not the actual combustion centroid position is within the period T1 shown in FIG. To do.

Here, time [ms] is a parameter for the injection rate waveform as a reference for comparison, and the measured combustion center of gravity position is an angle (crank angle from TDC), and thus is calculated based on the detected value of the crank position sensor 40. the engine speed NE [rpm] which is the required time per unit angle ^{((60 * 10 3/360} ) / NE [ms / ° CA]) to seek, "TDC the actual combustion center position (angle) The above-mentioned comparison is performed by converting to "time from". The required angle per unit time is obtained from the engine speed NE, the period T1 (time) of the reference injection rate waveform is converted into a crank angle (crank angle from TDC), and the comparison is performed. Also good.

  Further, as a method for actually measuring the combustion gravity center position (crank angle), it is performed based on a change in engine speed (a change in engine speed calculated based on a detected value of the crank position sensor 40). Further, an in-cylinder pressure sensor may be provided, and the combustion gravity center position may be actually measured based on the in-cylinder pressure change. Furthermore, the combustion gravity center position may be measured based on a signal (vibration signal) from a knocking sensor attached to the cylinder block. Furthermore, the combustion gravity center position may be measured by a combination thereof.

  Based on the comparison result, it is determined that the heat generation rate is properly obtained when the actual combustion gravity center position is within the period T1 of the reference injection rate waveform. On the other hand, when the actual combustion gravity center position deviates from the period T1 of the reference injection rate waveform, it is determined that the heat generation rate is not properly obtained. That is, it is determined that the requests such as improvement of exhaust emission by reducing the NOx generation amount and the smoke generation amount, the reduction of combustion noise, and sufficient securing of the engine torque cannot be achieved simultaneously. When such a determination is made, the following combustion gravity center movement control is executed. Hereinafter, this combustion center-of-gravity movement control will be described.

[Combustion center of gravity movement control]
In this example, the combustion center-of-gravity movement control is performed for the period T1 of the reference injection rate waveform created by the above-described processing. This is control when it is determined that the combustion center of gravity is deviated when is deviated to the retarded angle side or the advanced angle side. That is, when it is determined that the heat generation rate is not properly obtained, this control is for obtaining this heat generation rate appropriately (obtaining the combustion center of gravity appropriately). This will be specifically described below.

  Specifically, as the combustion center-of-gravity movement control, correction of the injection timing of fuel injected from the injector 23 and correction of the oxygen concentration in the combustion chamber 3 are performed.

  As the correction of the fuel injection timing, the actually detected combustion gravity center position (combustion gravity center position after being converted to the time from TDC) with respect to the period T1 of the reference injection rate waveform created by the above-described processing is used. When it is shifted to the retard side, the fuel injection timing is corrected to the advance side so that the combustion gravity center position is moved to the advance side. Conversely, when the actually detected combustion gravity center position (combustion gravity center position after being converted to time from TDC) is shifted to the advance side with respect to the period T1 of the reference injection rate waveform, combustion is performed. The fuel injection timing is corrected to the retard side so that the position of the center of gravity is moved to the retard side. This makes it possible to optimize the heat generation rate by setting the combustion center of gravity to an appropriate position, improve exhaust emissions by reducing the amount of NOx generated and smoke generated, reduce combustion noise, and provide sufficient engine torque. Each request such as securing can be combined.

  On the other hand, as the correction of the oxygen concentration in the combustion chamber 3, the combustion center of gravity position (after conversion to the time from the TDC) is actually detected for the period T1 of the reference injection rate waveform created by the above-described processing. When the combustion center of gravity position is shifted to the retarded angle side, an operation for increasing the oxygen concentration in the combustion chamber 3 is performed so as to move the combustion center of gravity position to the advanced angle side. Specifically, the opening degree of the EGR valve 81 is reduced or fully closed. Alternatively, the opening degree of the nozzle vane provided in the variable nozzle vane mechanism of the turbocharger 5 is decreased, and the supercharging pressure of the engine 1 is increased. Alternatively, the opening degree of the throttle valve 62 is increased. Of these EGR valve 81 control, nozzle vane control, and throttle valve 62 control, only one control may be executed, or a plurality may be executed simultaneously.

  By these operations, the oxygen concentration in the combustion chamber 3 is increased, and the combustion center of gravity moves to the advance side as the combustion speed increases, so that the combustion center of gravity can be set to an appropriate position. As a result, the heat generation rate can be optimized, and it is possible to meet various requirements such as improving exhaust emissions, reducing combustion noise, and ensuring sufficient engine torque by reducing NOx generation and smoke generation. Become. It should be noted that the combustion gravity center position actually detected (combustion gravity center position after being converted to the time from TDC) is shifted to the advance side with respect to the period T1 of the reference injection rate waveform created by the above-described processing. If so, an operation of lowering the oxygen concentration in the combustion chamber 3 is performed so as to move the combustion gravity center position to the retard side. This operation is performed by an operation opposite to the operation for increasing the oxygen concentration in the combustion chamber 3 described above.

  As described above, in the present embodiment, it is determined in the combustion chamber 3 by determining whether or not the combustion center of gravity is deviated from the appropriate timing and performing the combustion center of gravity movement control according to the determination result. It is possible to quickly resolve the situation where the operation with the combustion center of gravity deviating from the appropriate timing is continued. As a result, combustion can be performed at an appropriate heat generation rate, and both the amount of NOx generated and the amount of smoke generated can be suppressed, and exhaust emission can be improved.

-Determination of injector injection pressure sensor abnormality-
The presence or absence of abnormality of the injector injection pressure sensor 23a can be determined using the injection rate waveform of pilot injection and the injection rate waveform of main injection created by the above-described processing. Specific examples thereof will be described below.

  First, the injector injection pressure waveform obtained from the output signal of the injector injection pressure sensor 23a is, for example, a waveform as shown in FIG. 20, and in such an injector injection pressure waveform, a region from the fuel injection start timing to the injection end timing. (A region indicated by dots) is an injection rate contributing region. In FIG. 20, the horizontal axis is the crank angle, and the vertical axis is the injector injection pressure. FIG. 20 also shows the piezo drive signal waveform.

  When the injector injection pressure waveform obtained when the above-described pilot injection and main injection are performed using the injector injection pressure sensor 23a having such characteristics, the waveform changes according to the pilot injection and main injection (see FIG. 21).

  Here, when the injector injection pressure sensor 23a is operating normally, the injector injection pressure waveform obtained from the output signal of the injector injection pressure sensor 23a and the injection rate waveform (reference reference) created by the above-described processing. In this case, it can be determined that the injector injection pressure sensor 23a is normal.

  Specifically, as shown in FIG. 21, an injector injection pressure waveform (an injector injection pressure waveform after [crank angle → time] conversion described later) obtained from an output signal of the injector injection pressure sensor 23a, and a reference injection rate (1) The deviation amount of the injection timing / injection end timing of the injector injection pressure waveform from the injection start timing / injection end timing of the reference injection rate waveform is within the allowable range, and (2) the reference injection When the deviation amount of the area of the injection rate contribution area (dot area) of the injector injection pressure waveform with respect to the area of the rate waveform (area of the dot portion) is within an allowable range (for example, in the case of FIG. 21A), the injector injection It can be determined that the pressure sensor 23a is operating normally.

  On the other hand, when the injection start timing / injection end timing of the injector injection pressure waveform deviates by more than an allowable value with respect to the injection start timing / injection end timing of the reference injection rate waveform (for example, in the case of FIG. 21B), or If the area of the injector injection pressure waveform deviates by more than an allowable value from the area of the reference injection rate waveform, it can be determined that a proper injector injection pressure waveform cannot be obtained. That is, it can be determined that the injector injection pressure sensor 23a is abnormal.

  As described above, it is possible to determine whether or not the injector injection pressure sensor 23a is abnormal by using the injection rate waveform of the pilot injection and the injection rate waveform of the main injection (reference injection rate waveform) created by the above-described processing. become.

  The allowable value for the amount of deviation between the reference injection rate waveform and the injector injection pressure waveform is set to a value that is empirically adapted by experiment / simulation calculation or the like.

Here, when the injector injection pressure waveform and the reference injection rate waveform are compared, the required time per unit angle ((()) is calculated from the engine speed NE [rpm] calculated based on the detected value of the crank position sensor 40. ^{60 * 10 3/360) /} NE [ms / ° CA]) to seek, it performs the comparison by converting the injector injection pressure waveform parameters (horizontal axis) in time.

  The required angle per unit time (crank angle) is obtained from the engine speed NE, and the above-mentioned reference injection rate waveform parameter (horizontal axis) is converted to the crank angle (crank angle from TDC) to compare the above. You may make it perform.

-Other embodiments-
In the above example, the mathematical formulas for calculating the reference reaching injection rates Q1a and Q2a and the reference injection rate gradients G1a, G2a, and G3a are quadratic equations, but FIG. 13 (a), FIG. 14 (a) and FIG. ), The reference reaching injection rates Q1a and Q2a and the reference injection rate inclination G3a can be approximated by straight lines, and the equations for calculating these Q1a, Q2a and G3a may be linear equations. .

  In the above example, the reference injection rate waveform created from the fuel pressure and the fuel injection amount is used to perform the combustion state determination process and the injector injection pressure sensor abnormality determination process, but the present invention is not limited to this. The above-mentioned reference injection rate waveform can also be used for verification / evaluation of the physical quantity (for example, reduction of the fuel injection quantity of the injector itself).

  In the above example, the case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (four-cylinder) diesel engine has been described. The present invention is not limited to this, and can be applied to a diesel engine having any number of cylinders such as a six-cylinder diesel engine. The engine to which the present invention is applicable is not limited to an automobile engine.

  In the above example, the engine 1 to which the piezo injector 23 that changes the fuel injection rate by changing to the fully opened valve state only during the energization period has been described, but the present invention is applied to an engine to which the variable injection rate injector is applied. Is also possible.

  In the above example, the injector injection pressure sensor 23a is incorporated in the injector 23. However, the present invention is not limited thereto, and the injector injection pressure sensor may not be provided.

  The present invention can be used to create a fuel injection rate waveform 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)
23a Injector injection pressure sensor (pressure sensor)
5 Turbocharger 40 Crank position sensor 41 Rail pressure sensor 62 Throttle valve 81 EGR valve 100 ECU (control device for internal combustion engine)
101 CPU (injection rate waveform creation unit)
102 ROM (storage unit)

Claims (6)

An injection rate waveform creation method for creating an injection rate waveform of fuel injected from a fuel injection valve toward a cylinder of a compression ignition type internal combustion engine,
Calculate the reference injection rate slope and the reference injection rate that correlate with the fuel pressure from the fuel pressure,
The injection rate gradient is calculated from the reference injection rate gradient and the area ratio that is the ratio of the nozzle hole area of the fuel injection valve to the reference area, and the ultimate injection rate is calculated from the reference reaching injection rate and the area ratio. Calculate
An injection rate waveform creation method, wherein an injection rate waveform is created based on the injection rate gradient, the ultimate injection rate, and the fuel injection amount. In the injection rate waveform creation method according to claim 1,
Based on a mathematical formula derived from a plurality of injection rate waveforms actually measured using an injection rate measuring device, the reference injection rate slope and the reference reaching injection rate are calculated from fuel pressure,
The reference area is an injection hole area of a fuel injection valve when actually measured by the injection rate measuring device. A control device for a compression self-ignition internal combustion engine in which fuel is injected from a fuel injection valve into a cylinder,
A storage unit that stores an area ratio that is a ratio of a nozzle hole area and a reference area of the fuel injection valve;
A reference injection rate gradient and a reference arrival injection rate that correlate with fuel pressure are calculated from fuel pressure, and an injection rate inclination is calculated from the reference injection rate inclination and the area ratio, and from the reference arrival injection rate and the area ratio. An internal combustion engine comprising: an injection rate waveform creation unit that calculates an ultimate injection rate and creates an injection rate waveform based on the injection rate gradient, the ultimate injection rate, and the fuel injection amount Control device. The control apparatus for an internal combustion engine according to claim 3,
The storage unit stores mathematical formulas derived from a plurality of injection rate waveforms actually measured using an injection rate measuring device,
The injection rate waveform creation unit is configured to calculate the reference injection rate gradient and the reference reaching injection rate from a fuel pressure based on the mathematical formula,
The control apparatus for an internal combustion engine, wherein the reference area is a nozzle hole area of a fuel injection valve when actually measured by the injection rate measuring apparatus. The control apparatus for an internal combustion engine according to claim 3 or 4,
A control apparatus for an internal combustion engine, which determines whether or not combustion in the combustion chamber of the internal combustion engine is properly performed using the injection rate waveform created by the injection rate waveform creation unit. The control apparatus for an internal combustion engine according to claim 3 or 4,
A pressure sensor is built in the fuel injection valve, and the presence or absence of abnormality of the pressure sensor built in the fuel injection valve is determined using the injection rate waveform created by the injection rate waveform creation unit. A control device for an internal combustion engine.

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