JPWO2011118028A1 - Combustion control device for internal combustion engine - Google Patents

Abstract

For an engine in which premixed combustion and diffusion combustion are performed in the combustion chamber, the ratio of the injection amount of the fuel injection for premixed combustion to the total fuel injection amount increases as the engine load decreases, and the fuel for diffusion combustion The ratio of the injection amount is set low. Thereby, the ratio of the heat generation amount of diffusion combustion to the total heat generation amount during the combustion period in which premixed combustion and diffusion combustion coexist is gradually reduced. Combustion stability can be ensured during high load operation, and exhaust emission can be improved and combustion noise can be reduced during low load operation.

Description

  The present invention relates to a combustion control device for a compression ignition type internal combustion engine represented by a diesel engine. In particular, the present invention relates to an improvement in the combustion mode of premixed combustion and diffusion combustion in a combustion chamber.

  As is well known in the art, in a diesel engine used as an automobile engine or the like, a fuel injection valve (hereinafter referred to as an injector) may be used depending on the engine speed, accelerator operation amount, cooling water temperature, intake air temperature, and the like. The combustion mode in the combustion chamber is controlled by adjusting the fuel injection timing and the fuel injection amount from.

  The combustion of the diesel engine is mainly composed of premixed combustion and diffusion combustion as disclosed in Patent Document 1 below. When fuel injection from the injector into the combustion chamber is started, first, a combustible mixture is generated by vaporization and diffusion of fuel (ignition delay period). Next, this combustible air-fuel mixture self-ignites almost simultaneously in several places in the combustion chamber, and the combustion proceeds rapidly (premixed combustion). Further, fuel injection into the combustion chamber is continued, and combustion is continuously performed (diffusion combustion). Thereafter, since unburned fuel exists even after the fuel injection is completed, heat generation is continued for a while (afterburn period).

  By the way, in a diesel engine, it is important to meet various requirements such as improving exhaust emissions by reducing both NOx generation and smoke generation, reducing combustion noise during the combustion stroke, and ensuring sufficient engine torque. It is. An exhaust gas recirculation (EGR) device that recirculates part of exhaust gas to an intake passage is known as a means for suppressing the amount of NOx generated (see, for example, Patent Document 2 below). In addition, as a measure for suppressing the amount of smoke generated, sub-injection is executed during the compression stroke of the engine, and combustion in this sub-injection is premixed combustion to eliminate oxygen shortage in the combustion field. Is known (see, for example, Patent Document 3 below).

JP 2004-156519 A Japanese Patent Laid-Open No. 2004-3415 JP 2001-193526 A

  Until now, it has been proposed to control the combustion mode in the combustion chamber for the purpose of suppressing both the generation amount of NOx and the generation amount of smoke (Patent Document 1, etc.).

  Conventionally, in order to achieve various requirements such as improvement of exhaust emission, reduction of combustion noise during combustion stroke, and sufficient engine torque, engine rotation speed is a method for realizing proper combustion in the combustion chamber. Appropriate fuel injection mode (fuel injection pattern) and in-cylinder environment (in-cylinder gas) for each operation state (for each grid point of the operation state map with engine speed and required torque as parameters) Status).

  For example, experimental values for fuel injection timing, EGR amount, etc. are individually determined by trial and error for each engine operating state, and the corresponding values corresponding to each of the many engine operating states are mapped. An injection map and an EGR map were created. Then, according to the fuel injection map, the fuel injection timing suitable for the current engine operating state is set to control the injector, or according to the EGR map, the EGR amount suitable for the current engine operating state is set to set EGR. The valve was controlled.

  In this way, since the optimum values are experimentally obtained individually for a plurality of operating states of the engine, there is no guarantee that an appropriate fuel injection form and in-cylinder environment are set over the entire engine operating region. It was. In other words, in a certain operating state (an operating state for which the above-mentioned conformity value is not required), the amount of NOx generation is significantly increased due to the excessive diffusion combustion ratio in the combustion in the combustion chamber. In the state, if the ratio of the premixed combustion in the combustion in the combustion chamber becomes too high, the combustion becomes unstable and the combustion noise may be remarkably increased. In order to suppress the amount of NOx generated, the fuel injection timing is also largely shifted to the retarded side. However, this causes deterioration in combustion efficiency and makes it impossible to secure sufficient engine torque. Or lead to a deterioration of the fuel consumption rate.

  This invention is made | formed in view of this point, The place made into the objective is implement | achieving the suitable combustion form (combustion form of premixed combustion and diffusion combustion) according to the driving | running state of an internal combustion engine. An object of the present invention is to provide a combustion control device for an internal combustion engine.

-Principle of solving the problem-
The solution principle of the present invention taken to achieve the above object is to adjust the degree of independence of these combustions so that the advantages of premixed combustion and diffusion combustion can be used effectively as combustion forms in the combustion chamber. (By adjusting the ratio of heat generation when each combustion is performed in parallel, the degree of independence of each combustion is adjusted), thereby coordinating these combustions, and improving the stability of combustion and exhaust emissions. Improvements and suppression of combustion noise are made possible.

-Solution-
Specifically, the present invention relates to compression auto-ignition in which fuel injected from a fuel injection valve burns in a combustion chamber by at least “premixed combustion” and “diffusion combustion” started after the start of this “premixed combustion”. The premise is a combustion control device for an internal combustion engine. With respect to the combustion control device of the internal combustion engine, as the load on the internal combustion engine becomes lower or the required output of the internal combustion engine becomes smaller, the premixed combustion and the diffusion combustion are in a combustion period. Diffusion that adjusts at least one of the fuel injection form of the fuel injection valve and the gas state before fuel injection in the combustion chamber so that the ratio of the heat generation amount of diffusion combustion to the total heat generation amount gradually decreases Combustion execution rate adjusting means is provided.

  Due to this specific matter, in a situation where the load of the internal combustion engine is relatively high (or a situation where the required output of the internal combustion engine is relatively large), the total heat generation amount during the combustion period in which the premixed combustion and the diffusion combustion coexist. The ratio of heat generation amount of diffusion combustion (hereinafter referred to as diffusion combustion execution rate) is set high. As described above, when the diffusion combustion execution rate is set high, the independence between the premixed combustion and the diffusion combustion during the same combustion stroke is set high. As a result, even if the combustion state in the premixed combustion deteriorates (unstabilizes), the degree of influence on the diffusion combustion is small, the stabilization of the diffusion combustion is maintained, and the combustion in the combustion chamber is stable. Can be done. For this reason, a sufficient output can be obtained particularly during high-load operation that requires stabilization of combustion.

  On the other hand, in a situation where the load on the internal combustion engine is relatively low (or a situation where the required output of the internal combustion engine is relatively small), the diffusion combustion execution rate is set low. At a high load of the internal combustion engine, the combustion period is long and there is no room for retarding the combustion center of gravity. On the other hand, at a light load of the internal combustion engine, there is a margin to retard the combustion center of gravity, and the diffusion execution rate can be reduced. Therefore, in such a situation where the load of the internal combustion engine is relatively low, the diffusion combustion execution rate is set low, the ratio of premixed combustion during the combustion period in which each combustion coexists is increased, and the amount of smoke generated and NOx is increased. We will improve exhaust emissions as a combustion mode that can suppress both generations.

  As described above, in the present solution, the diffusion combustion execution rate is continuously adjusted (including the case where it is adjusted in stages) in accordance with the load of the internal combustion engine (or the required output of the internal combustion engine). The advantages of mixed combustion and diffusion combustion can be used effectively, and various requirements such as improvement of exhaust emission, reduction of combustion noise during combustion stroke, and sufficient securing of engine torque can be achieved.

  Specific examples of the configuration for adjusting the diffusion combustion execution rate according to the fuel injection mode of the fuel injection valve include the following. First, the fuel injection valve performs premixed combustion fuel injection mainly for performing “premixed combustion” as combustion in the combustion chamber, and mainly performs “diffusion combustion” as combustion in the combustion chamber. It is assumed that the fuel injection for diffusion combustion is performed separately. Then, the diffusion combustion execution rate adjusting means adjusts the fuel injection for premixed combustion in the total fuel injection amount as the load on the internal combustion engine becomes lower or the required output of the internal combustion engine becomes smaller. In addition, the ratio of the injection amount in the above is gradually increased, and the ratio of the injection amount in the diffusion combustion fuel injection in the total fuel injection amount is gradually decreased.

  Further, in this case, the diffusion combustion execution rate adjusting means injects at least by the premixed combustion fuel injection as the load of the internal combustion engine decreases or as the required output of the internal combustion engine decreases. The combustion period in which the premixed combustion and diffusion combustion coexist (the period in which each combustion overlaps) is lengthened by shifting the combustion center of gravity of the “premixed combustion” of the generated fuel to the retard side. It is configured. In this case, it is also possible to shift the combustion center of gravity of the “diffusion combustion” of the fuel injected by the fuel injection for diffusion combustion to the retarded angle side. There is a limit to the amount of transition to owing to problems with the output of the internal combustion engine and exhaust emissions. Further, the center of combustion of this “diffusion combustion” is also influenced by the amount of in-cylinder preheating caused by “premixed combustion”. The combustion center of gravity is a complete combustion that completes the combustion of all fuel when the fuel injected into the combustion chamber (for example, the fuel injected by the fuel injection for premixed combustion) burns in the combustion chamber. When the state is the combustion degree “100%”, the combustion degree reaches “50%”. In other words, the cumulative heat generation amount in the combustion chamber reaches “50%” with respect to the heat generation amount when the entire injected fuel burns.

  Further, specific configurations for adjusting the diffusion combustion execution rate according to the gas state before fuel injection in the combustion chamber include the following. Examples of the gas state before fuel injection in the combustion chamber include the oxygen concentration in the combustion chamber and the pressure in the combustion chamber before the fuel injection of the fuel injection valve.

  First, as a specific configuration for adjusting the diffusion combustion execution rate based on the oxygen concentration in the combustion chamber before the fuel injection of the fuel injector, the oxygen concentration in the combustion chamber before the fuel injection of the fuel injector can be adjusted. An oxygen concentration adjusting means is provided. Then, as the load on the internal combustion engine decreases or the required output of the internal combustion engine decreases, the diffusion combustion execution rate adjusting means adjusts the oxygen in the combustion chamber adjusted by the oxygen concentration adjusting means. The density is gradually lowered.

  Specifically, the oxygen concentration adjusting means in this case is an exhaust gas recirculation device that recirculates part of the exhaust gas discharged to the exhaust system to the intake system. The oxygen concentration in the combustion chamber is gradually lowered by increasing the amount of exhaust gas recirculated to the intake system by the exhaust gas recirculation device.

  On the other hand, as a specific configuration for adjusting the diffusion combustion execution rate according to the pressure in the combustion chamber before the fuel injection of the fuel injector, the pressure adjustment capable of adjusting the pressure in the combustion chamber before the fuel injection of the fuel injector is performed. Provide means. Then, as the load on the internal combustion engine decreases or the required output of the internal combustion engine decreases, the diffusion combustion execution rate adjusting means adjusts the pressure in the combustion chamber adjusted by the pressure adjusting means. The structure is gradually lowered.

  Specifically, the pressure adjusting means in this case is a supercharging device that supercharges intake air in the intake system. The pressure in the combustion chamber is gradually lowered by decreasing the amount of supercharging of the intake air by the supercharging device.

  An example of the pressure adjusting means is an intake throttle valve that can limit the amount of intake air in the intake system. And the pressure in the combustion chamber is gradually lowered by increasing the restriction of the intake air by the intake throttle valve.

  These specific matters make it possible to easily and continuously adjust the diffusion combustion execution rate, and to set an appropriate fuel injection form and in-cylinder environment over the entire operation region of the internal combustion engine. Therefore, the advantages of premixed combustion and diffusion combustion can be used effectively.

  In the present invention, the degree of independence of these combustions is adjusted so that the advantages of premixed combustion and diffusion combustion can be used effectively as combustion modes in the combustion chamber. Thereby, these combustion can be coordinated and combustion stability, improvement of exhaust emission, and suppression of combustion noise can be achieved.

FIG. 1 is a schematic configuration diagram of an engine and its control system according to the embodiment. FIG. 2 is a cross-sectional view showing a combustion chamber of a diesel engine and its peripheral part. FIG. 3 is a block diagram showing a configuration of a control system such as an ECU. FIG. 4 is a diagram illustrating a heat generation rate waveform at each diffusion combustion execution rate and a fuel injection pattern for obtaining the heat generation rate waveform. FIG. 5 is a view showing an injection rate setting map for diffusion combustion fuel injection. FIG. 6 is a diagram showing a setting map for the diffusion combustion execution rate. FIG. 7 is a diagram showing a map for setting the injection ratio of the premixed combustion fuel according to the diffusion combustion execution rate.

  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.

  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. 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.

  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. 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 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 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 wheel 53 that are connected via a turbine shaft 51. The compressor wheel 53 is disposed facing the inside of the intake pipe 64, and the turbine wheel 52 is disposed facing the inside of 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 the engine 1. A crank position sensor 40 that outputs a detection signal (pulse) each time the output shaft (crankshaft) rotates by a certain angle is connected. 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 performs fuel injection control of the injector 23. As fuel injection control of the injector 23, in this embodiment, sub-injection such as pilot injection and pre-injection, which is executed in a conventional general diesel engine, is not executed, and only main injection for obtaining engine torque is performed. It is supposed to be executed. That is, by not performing pilot injection or pre-injection, the preheating operation in the cylinder until the main injection is started is not performed.

  The total fuel injection amount in the main injection is a fuel injection amount necessary for obtaining a required torque that is determined according to an operating state such as engine speed, accelerator operation amount, cooling water temperature, intake air temperature, and environmental conditions. Is set. 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 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.

  The optimum value of the fuel injection parameter in the main injection varies 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 (engine speed) based on the detection value of the crank position sensor 40 and also determines the amount of depression of the accelerator pedal (accelerator opening) based on the detection value of the accelerator opening sensor 47. Degree) and the total main injection amount (injection amount in the main injection) is determined based on the engine speed, the accelerator opening, and the like.

-Split main injection-
In the diesel engine 1, it is important to meet various requirements such as improvement of exhaust emission by reducing the NOx generation amount and smoke generation amount, 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, the present inventors have found a fuel injection method using divided main injection (divided main injection) as described below as a method for appropriately controlling the change state of the heat generation rate. This will be specifically described below.

  In the present embodiment, the injection mode of the main injection is continuously changed according to changes in engine load. Specifically, in the fuel injection control in the present embodiment, by executing two or three divided main injections as the injection mode of the main injection, the total main injection amount (required torque) required for the main injection is performed. The total fuel injection amount) is secured.

  The divided main injection, which is a feature of the present embodiment, is a premixed combustion fuel injection that is a fuel injection mainly for performing premixed combustion as combustion in the combustion chamber 3, and mainly diffusion combustion. The diffusion combustion fuel injection, which is a fuel injection to be performed, is executed individually once or twice, and the injection timing and injection amount of these divided main injections are changed according to the engine load. Like to do.

  A predetermined interval is provided between the end timing of the premixed combustion fuel injection and the start timing of the diffusion combustion fuel injection. That is, after the fuel injection for premixed combustion is executed, the fuel injection is temporarily stopped (the injector 23 is shut off), and after a predetermined interval, the fuel injection for diffusion combustion is started. This interval is set, for example, as the shortest valve closing period determined by the performance of the injector 23 (the shortest period from when the injector 23 is closed until the valve opening is started: 200 μs, for example). The interval of this divided main injection is not limited to the above value, and is appropriately set as an interval for realizing a “diffusion combustion execution rate” described later. The details of the fuel injection mode (fuel injection pattern) in the divided main injection according to the load will be described later.

  The outline of the combustion mode during the combustion stroke in the combustion chamber 3 in the present embodiment is as follows.

  In this combustion mode, premixed combustion and diffusion combustion are sequentially performed during the same combustion stroke. In other words, during the same combustion stroke, first, the fuel injection for premix combustion is executed once or twice, and the injected fuel generates heat in the combustion chamber 3 by premix combustion. At the beginning of the premixed combustion, since the fuel injection for diffusion combustion has not been executed yet, the combustion in the combustion chamber 3 is only the premixed combustion. Hereinafter, this combustion period is referred to as a “premixed single combustion period”.

  Thereafter, the fuel injection for diffusion combustion is executed once or twice at a predetermined timing, and the injected fuel is combusted in the combustion chamber 3 by diffusion combustion. At the initial start of diffusion combustion, combustion of fuel injected by the premixed combustion fuel injection (premixed combustion) is still continued. That is, at the beginning of the diffusion combustion, superimposed combustion (overlap combustion) in which premixed combustion and diffusion combustion coexist (concurrently) is performed. Hereinafter, the combustion period in which the premixed combustion and the diffusion combustion coexist is referred to as an “overlap combustion period”.

  In this overlap combustion period, the heat generation rate in the premixed combustion (heat generation amount per unit rotation angle of the crankshaft) gradually decreases with time, and conversely, the heat generation rate in diffusion combustion decreases. Gradually grows.

  After the overlap combustion period has elapsed, the heat generation rate in the premixed combustion becomes “0”, and the combustion in the combustion chamber 3 is only diffusion combustion. Hereinafter, the combustion period only by diffusion combustion after the overlap combustion period ends will be referred to as “diffusion single combustion period”.

  As described above, during one combustion process, the combustion mode in the combustion chamber 3 sequentially changes in the order of “premixed single combustion period”, “overlap combustion period”, and “diffusion single combustion period”. Will go.

  The premixed combustion in the “premixed single combustion period” is a fuel existing in the combustion chamber 3 in a state where the temperature in the cylinder is lower than a predetermined diffusion combustion start temperature (for example, 900 K) leading to diffusion combustion. Is done by igniting. Specifically, when the combustion field temperature in the combustion chamber 3 is in the range of 800K or higher and lower than 900K as the compression stroke progresses, the fuel injected by the premixed combustion fuel injection is ignited. Thus, the “premixed single combustion period” is started.

  Further, the diffusion combustion in the “overlap combustion period” is performed after the start of the premix combustion in the state where the temperature in the combustion chamber 3 is equal to or higher than the diffusion combustion start temperature by the premix combustion. This is done by executing. Specifically, the “overlap combustion period” is started by performing fuel injection for diffusion combustion immediately after the combustion field temperature of the premixed combustion reaches 900K.

  Hereinafter, when the fuel injection for premixed combustion is executed twice, the first fuel injection for premixed combustion is referred to as “first fuel injection for premixed combustion”, and the second premixed combustion fuel injection is called. The fuel injection for mixed combustion will be referred to as “second premixed combustion fuel injection”. When the diffusion combustion fuel injection is executed twice, the first diffusion combustion fuel injection is referred to as “first diffusion combustion fuel injection” and the second diffusion combustion fuel injection is performed. Is referred to as “second fuel injection for diffusion combustion”.

−Diffusion combustion execution rate−
The feature of this embodiment is the heat in diffusion combustion with respect to the total heat generation amount during the overlap combustion period (the sum of the heat generation amount by premixed combustion and the heat generation amount by diffusion combustion in the overlap combustion period). This is to adjust the ratio of the amount of generation (heat generation amount in diffusion combustion during overlap combustion period / total heat generation amount during overlap combustion period). Hereinafter, the ratio of the heat generation amount in diffusion combustion to the total heat generation amount during the overlap combustion period is referred to as “diffusion combustion execution rate”.

  Hereinafter, the technical idea for setting the diffusion combustion execution rate will be described. This diffusion combustion execution rate correlates with the degree of independence between premixed combustion and diffusion combustion during the same combustion stroke. That is, when this diffusion combustion execution rate is high, premix combustion and diffusion combustion in the same combustion stroke are highly independent. In other words, most of the heat generation amount in the premixed combustion during the same combustion stroke is generated during the premixed single combustion period, and most of the heat generation amount in the diffusion combustion in the combustion stroke is the above. It occurs during the diffusion combustion single combustion period. In this case, the heat generation rate waveform has a relatively long interval between the timing at which the heat generation rate in premixed combustion peaks (maximum value) and the timing at which the heat generation rate in diffusion combustion peaks. Will do.

  Conversely, when the diffusion combustion execution rate is low, the premixed combustion and the diffusion combustion in the same combustion stroke are less independent. In other words, the heat generation amount of the premixed combustion during the premixed single combustion period during the same combustion stroke is small, and the heat generation amount of the diffusion combustion during the diffusion single combustion period during the combustion stroke is also small. It has become. In this case, as the heat generation rate waveform, the interval between the timing at which the heat generation rate in the premixed combustion reaches a peak (maximum value) and the timing at which the heat generation rate in the diffusion combustion reaches a peak becomes short.

  As described above, the diffusion combustion execution rate has a correlation with the degree of independence between the premixed combustion and the diffusion combustion in the same combustion stroke. That is, the degree of independence between the premixed combustion and the diffusion combustion can be controlled by adjusting the diffusion combustion execution rate.

  In this embodiment, the diffusion combustion execution rate is gradually set higher as the engine load increases, that is, as the output required for the engine 1 increases. That is, the independence of the premixed combustion and the diffusion combustion during the same combustion stroke is enhanced (the operation for adjusting the diffusion combustion execution rate by the diffusion combustion execution rate adjusting means). In other words, the diffusion combustion execution rate is gradually set lower as the engine load becomes lower, that is, as the output required for the engine 1 becomes smaller. That is, the independence of premixed combustion and diffusion combustion during the same combustion stroke is reduced.

  Each heat generation rate waveform shown in FIGS. 4A to 4E shows the heat generation rates of the premixed combustion and the diffusion combustion when the diffusion combustion execution rate is changed (per unit rotation angle of the crankshaft). An example of a change in heat generation amount) is shown. In each heat generation rate waveform shown in FIG. 4, the horizontal axis represents the crank angle and the vertical axis represents the heat generation rate. Further, in FIG. 4, the heat generation part in the premixed combustion is indicated by a dashed oblique line, and the heat generation part in the diffusion combustion is indicated by a solid oblique line. Further, the overlap combustion period is indicated by T.

  As can be seen from FIG. 4, the higher the diffusion combustion execution rate (as it goes from FIG. 4 (e) to FIG. 4 (a)), the premixed combustion and the diffusion combustion in the same combustion stroke are more independent. It is expensive. Thus, it is possible to stabilize the combustion in the combustion chamber 3 by setting the independence of the premixed combustion and the diffusion combustion high. This is because if the independence of these combustion is set high, even if the combustion state in premixed combustion deteriorates (stabilizes), the degree of influence on diffusion combustion is small, and diffusion combustion is stabilized. This is because it is maintained. In this embodiment, since the diffusion combustion execution rate is set high during the high load operation of the engine 1 that particularly requires stabilization of combustion, a sufficient engine output can be obtained during the high load operation, It is possible to respond quickly to torque demands.

  On the other hand, when the engine 1 is in a low load operation, the degree of demand for stabilization (high output) of combustion in the combustion chamber 3 is relatively low, but improvement of exhaust emission is required. For this reason, the diffusion combustion execution rate is set low, and a large proportion of premixed combustion is ensured during the overlap combustion period. However, the exhaust emission is improved by adopting a combustion mode that can suppress both the smoke generation amount and the NOx generation amount.

-Fuel injection pattern for setting the diffusion combustion execution rate-
The fuel injection pattern for setting the diffusion combustion execution rate as described above will be specifically described below. The fuel injection pattern described below is an example for obtaining a desired diffusion combustion execution rate, and the present invention is not limited to this fuel injection pattern.

  As the fuel injection pattern for adjusting the diffusion combustion execution rate, the fuel injection amount in the fuel injection for premixed combustion as the engine load decreases or the required output of the engine 1 decreases. The ratio of the fuel injection amount in the fuel injection for diffusion combustion with respect to is gradually reduced. In other words, as the engine load decreases or the required output of the engine 1 decreases, the ratio of the injection amount in the premixed combustion fuel injection in the total fuel injection amount gradually increases. At the same time, the ratio of the injection amount in the diffusion combustion fuel injection out of the total fuel injection amount is gradually reduced. As a result, the diffusion combustion execution rate is gradually set lower.

  Conversely, as the engine load increases or the required output of the engine 1 increases, the ratio of the fuel injection amount in the diffusion combustion fuel injection to the fuel injection amount in the premixed combustion fuel injection Will gradually increase. In other words, as the engine load increases or the required output of the engine 1 increases, the ratio of the injection amount in the premixed combustion fuel injection in the total fuel injection amount gradually decreases. At the same time, the ratio of the injection amount in the diffusion combustion fuel injection out of the total fuel injection amount is gradually increased. Thereby, the diffusion combustion execution rate is gradually set higher.

  Each fuel injection rate waveform shown in FIGS. 4A to 4E shows a fuel injection pattern for obtaining a corresponding heat generation rate waveform. Each waveform shown in FIG. 4 is a relationship between the fuel injection pattern and the heat release rate waveform obtained by the fuel injection pattern when the oxygen concentration in the cylinder is the same (relatively low oxygen concentration). Is shown.

  4A shows the fuel injection pattern when the diffusion combustion execution rate is 99% and the heat release rate waveform obtained by the fuel injection pattern, and FIG. 4B shows the case where the diffusion combustion execution rate is 90%. FIG. 4C shows a fuel injection pattern obtained when the diffusion combustion execution rate is set to 60%, and a heat generation rate waveform obtained by the fuel injection pattern. 4 (d) shows the fuel injection pattern when the diffusion combustion execution rate is 40% and the heat release rate waveform obtained by the fuel injection pattern, and FIG. 4 (e) shows the diffusion combustion execution rate as 20%. The fuel injection pattern and the heat release rate waveform obtained by the fuel injection pattern are shown respectively.

  Explaining each, in the case of FIG. 4A in which the diffusion combustion execution rate is set to 99%, the premixed combustion fuel injection is executed on the advance side from the compression top dead center (TDC) of the piston 13, and thereafter Then, the two diffusion combustion fuel injections, the first diffusion combustion fuel injection and the second diffusion combustion fuel injection, are executed. The first diffusion combustion fuel injection is executed on the advance side of the compression top dead center (TDC) of the piston 13. Further, the second diffusion combustion fuel injection is started on the advance side with respect to the compression top dead center (TDC) of the piston 13 and is ended on the retard side with respect to the compression top dead center (TDC) of the piston 13. Further, the fuel injection amount is set to be larger in the order of premixed combustion fuel injection, first diffusion combustion fuel injection, and second diffusion combustion fuel injection. Thereby, the premixed combustion of the fuel injected by the fuel injection for premixed combustion and the diffusion combustion of the fuel injected by each fuel injection for diffusion combustion become highly independent. That is, as described above, combustion in the combustion chamber 3 is stably performed.

  In the case of FIG. 4B in which the diffusion combustion execution rate is set to 90%, two premixed combustion fuel injections of the first premixed combustion fuel injection and the second premixed combustion fuel injection are executed. The These premixed combustion fuel injections are all performed on the advance side of the compression top dead center (TDC) of the piston 13. Thereafter, fuel injection for diffusion combustion is performed. This diffusion combustion fuel injection is started near the compression top dead center (TDC) of the piston 13, and the injection ends on the retard side of the compression top dead center (TDC) of the piston 13. Further, the injection amount of the first premixed combustion fuel injection is set to be larger than that of the second premixed combustion fuel injection, and the injection amount of the diffusion combustion fuel injection is set to be larger than that of the first premixed combustion fuel injection. Has been. Incidentally, in the case where the diffusion combustion execution rate is set to 90% (FIG. 4 (b)), the total fuel injection amount is compared with the case where the diffusion combustion execution rate is set to 99% (FIG. 4 (a)). Is set to a small value, and the combustion center of gravity of the premixed combustion shifts to the retard side, so that the overlap combustion period T becomes longer.

  In the case of FIG. 4C in which the diffusion combustion execution rate is set to 60%, the premixed combustion fuel injection is executed on the advance side of the compression top dead center (TDC) of the piston 13, and then the diffusion combustion is performed. Fuel injection is performed. This diffusion combustion fuel injection is executed on the retard side from the compression top dead center (TDC) of the piston 13. Further, the injection amount in the diffusion combustion fuel injection is set to be larger than the injection amount in the premixed combustion fuel injection. Incidentally, in the case where the diffusion combustion execution rate is set to 60% (FIG. 4C), the total fuel injection amount is compared to the case where the diffusion combustion execution rate is set to 90% (FIG. 4B). Are set to be small, and the injection start timing of the fuel injection for premixed combustion and the injection start timing of the fuel injection for diffusion combustion are both set to the retard side, and the center of combustion of the premix combustion shifts to the retard side. As a result, the overlap combustion period T becomes longer.

  Further, in the case of FIG. 4D in which the diffusion combustion execution rate is set to 40%, the premixed combustion fuel injection is executed on the advance side of the compression top dead center (TDC) of the piston 13, and then the piston 13 The fuel injection for diffusion combustion is executed on the retard side from the compression top dead center (TDC). The injection amount in the premixed combustion fuel injection is set to be larger than the injection amount in the diffusion combustion fuel injection. Incidentally, in the case where the diffusion combustion execution rate is set to 40% (FIG. 4D), the total fuel injection amount is compared to the case where the diffusion combustion execution rate is set to 60% (FIG. 4C). Are set to be small, and the injection start timing of the fuel injection for premixed combustion and the injection start timing of the fuel injection for diffusion combustion are both set to the retard side, and the center of combustion of the premix combustion shifts to the retard side. As a result, the overlap combustion period T becomes longer.

  In the case of FIG. 4E in which the diffusion combustion execution rate is set to 20%, first, the injection is started on the advance side of the compression top dead center (TDC) of the piston 13 and the compression top dead center (TDC). The premixed combustion fuel injection that terminates the injection on the more retarded angle side is executed. Thereafter, fuel injection for diffusion combustion is executed on the retard side from the compression top dead center (TDC) of the piston 13. The injection amount in the premixed combustion fuel injection is set to be larger than the injection amount in the diffusion combustion fuel injection. Incidentally, in the case where the diffusion combustion execution rate is set to 20% (FIG. 4 (e)), the total fuel injection amount is compared with the case where the diffusion combustion execution rate is set to 40% (FIG. 4 (d)). Are set to be small, and the injection start timing of the fuel injection for premixed combustion and the injection start timing of the fuel injection for diffusion combustion are both set to the retard side, and the center of combustion of the premix combustion shifts to the retard side. As a result, the overlap combustion period T becomes longer. In this case, since the injection amount in the premixed combustion fuel injection is large, a part of the fuel injected in the premixed combustion fuel injection is diffusion combustion.

  In this way, as the diffusion combustion execution rate is set lower, the ratio of the injection amount in the premixed combustion fuel injection to the total fuel injection amount is set higher. In other words, the lower the diffusion combustion execution rate is set, the lower the ratio of the injection amount in the diffusion combustion fuel injection to the total fuel injection amount is set. Further, the fuel injection pattern is adjusted so that the diffusion combustion start timing (start timing of the overlap combustion period) shifts to the retard side as the diffusion combustion execution rate is set lower. This is to suppress the generation amount of NOx by suppressing an excessive increase in the temperature in the combustion chamber 3 due to diffusion combustion. However, the amount of shift of the diffusion combustion fuel injection to the retard side of the injection start timing is limited due to problems with the output of the engine 1 and exhaust emission. Further, as shown by the overlap combustion period T in FIG. 4, the overlap combustion period T becomes longer as the diffusion combustion execution rate is set lower. Specifically, as described above, the premixed combustion and the diffusion combustion are performed by shifting the combustion center of gravity of the “premixed combustion” of the fuel injected by the fuel injection for premixed combustion to the retarded angle side. The combustion period (overlap combustion period) in which the coexists are increased.

-About penetration-
Here, the relationship between the fuel injection amount and the penetration force will be described. In the injector 23, when fuel injection is started in response to the injection command signal, the opening area of the injection hole is gradually increased as the needle closing the injection hole is retracted from the injection hole. When the needle moves to the last retracted position, the opening area of the injection hole becomes maximum. However, if the injection command signal is canceled before the needle reaches the last retracted position (when the valve closing command is received), the needle moves forward in the valve closing direction while moving backward. That is, in this case, the fuel injection is terminated without maximizing the opening area of the injection hole. For this reason, the longer the injection period is set, the larger the opening area of the injection hole is obtained.

  And the opening area of the said injection hole has a correlation with the flight distance of the fuel (spray) injected from the injection hole. In other words, when fuel is injected with a large opening area of the injection hole, the size of the droplet of fuel injected from the injection hole is also large, so that the kinetic energy is also large (the penetration force is large). Yes. For this reason, the flight distance of this fuel droplet becomes long. On the other hand, when fuel is injected in a state where the opening area of the injection hole is small, the size of the droplet of fuel injected from the injection hole is also small, so the kinetic energy is also small (penetration force is small). ing. For this reason, the flight distance of this fuel droplet is also short.

  As described above, when the valve opening period of the injector 23 is set to be relatively long (in other words, when the injection amount per main injection is set to be relatively large), the needle reaches the last retracted position. Since the opening area of the injection hole becomes maximum due to the movement, the flight distance of the fuel droplet in this case becomes long. That is, most of the fuel injected from the injector 23 can fly up to the vicinity of the outer peripheral end of the cavity 13b.

  On the other hand, if the valve opening period of the injector 23 is set to be relatively short (in other words, the injection amount per main injection is set to be relatively small), the needle may move to the last retracted position. Since the opening area of the injection hole is small, the flight distance of the fuel droplet in this case is shortened. That is, most of the fuel injected from the injector 23 can fly only to the vicinity of the center of the cavity 13b.

  Thus, there is a correlation between the opening area of the injection hole determined by the valve opening period of the injector 23 and the flight distance of the fuel (spray) injected from the injection hole. For this reason, as the injection amount in the fuel injection for premixed combustion is set larger, the flight distance of the fuel becomes longer and the fuel flies to the vicinity of the outer peripheral end of the cavity 13b. Oxygen deficiency can be eliminated by ensuring a high percentage of oxygen with the oxygen inside. Thereby, the generation amount of smoke can be suppressed. That is, as the diffusion combustion execution rate is set lower and the injection amount in the premixed combustion fuel injection is set higher, the fuel is injected over a wider area in the combustion chamber 3, thereby reducing oxygen shortage. Combustion is performed without inviting, and the amount of smoke generated can be suppressed.

−Ignition timing of diffusion combustion−
In the present embodiment, the diffusion combustion fuel injection is executed in a state where the preheating in the combustion chamber 3 is sufficiently performed by the premix combustion in the premixed single combustion period, whereby the fuel for diffusion combustion is performed. The fuel injected by the injection is immediately exposed to a temperature environment equal to or higher than the auto-ignition temperature, and the thermal decomposition proceeds. After the injection, combustion starts 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 fuel injection for diffusion combustion, premixed combustion is hardly performed and most of the fuel is diffusion combustion. As a result, controlling the injection timing of the fuel injection for diffusion combustion becomes substantially equal to controlling the start timing of the overlap combustion period as it is, and the controllability of combustion can be greatly improved. More specifically, by adjusting the injection timing and the injection amount of this diffusion combustion fuel injection, the ignition timing in the diffusion combustion, the rate of change in the heat generation rate (the gradient of the heat generation rate waveform), the heat generation rate It is possible to control both the peak and the time to reach the combustion center of gravity.

-Specific control procedure-
Next, a specific control procedure in the case where the diffusion combustion execution rate is set as described above and fuel injection from the injector 23 is executed will be described.

  First, as described above, the total fuel injection amount is determined according to operating conditions such as engine speed, accelerator operation amount, cooling water temperature, intake air temperature, and environmental conditions.

  Then, according to the injection rate setting map shown in FIG. 5, the ratio of the injection amount in the diffusion combustion fuel injection to the total fuel injection amount (injection amount of diffusion combustion fuel injection / total fuel injection amount) is set. This injection rate setting map sets the ratio of the injection amount in the diffusion combustion fuel injection using the engine speed and the engine torque as parameters, and is created in advance by experiments and simulations and stored in the ROM 102. . For example, the higher the engine speed and the higher the engine torque, the higher the ratio of the injection amount in the diffusion combustion fuel injection.

In this way, the ratio between the total fuel injection amount and the injection amount in the diffusion combustion fuel injection (diffusion combustion fuel injection rate) is obtained, so that the total fuel injection amount is injected into the diffusion combustion fuel injection. By multiplying the amount ratio, the injection amount in the diffusion combustion fuel injection is obtained, and by subtracting this injection amount from the total fuel injection amount, the injection amount in the premixed combustion fuel injection is obtained. Become. For example, when the total fuel injection amount is 50 mm ³ and the injection amount ratio in the diffusion combustion fuel injection is set to 60%, the injection amount in the diffusion combustion fuel injection is 30 mm ³ . In this case, the injection amount in the premixed combustion fuel injection is 20 mm ³ .

  Further, the diffusion combustion execution rate is set according to the engine load. FIG. 6 is a diagram showing a setting map for the diffusion combustion execution rate. This map sets the diffusion combustion execution rate using the engine speed and engine torque as parameters, and is stored in the ROM 102 in advance. Then, the higher the engine speed and the higher the engine torque, the higher the diffusion combustion execution rate is set (see the value of the diffusion combustion execution rate indicated by the broken line in FIG. 6). The fuel injection timing in the premixed combustion fuel injection and the fuel injection timing in the diffusion combustion fuel injection performed to execute combustion at the diffusion combustion execution rate set in this way are, for example, predetermined diffusion The combustion execution rate (for example, diffusion combustion execution rate 90%) is used as a reference, and is set according to the amount of divergence of the diffusion combustion execution rate to be executed with respect to the diffusion combustion execution rate used as the reference. That is, when the diffusion combustion execution rate to be performed is lower than the reference diffusion combustion execution rate, the fuel injection timing is shifted to the retard side as the deviation amount is larger. Conversely, when the diffusion combustion execution rate to be performed is higher than the reference diffusion combustion execution rate, the fuel injection timing is shifted to the advance side as the deviation amount increases.

  Whether the injection amount of the required premixed combustion fuel injection is injected by one premixed combustion fuel injection with respect to the injection amount of the premixed combustion fuel injection obtained as described above, 2 Whether the fuel is divided into premixed combustion fuel injections is determined by fitting the diffusion combustion execution rate to the map shown in FIG. That is, when the diffusion combustion execution rate is higher than a predetermined value (60% in the case shown in FIG. 7), the first premixed combustion fuel injection and the second premixed combustion fuel injection are divided into two times. Implement fuel injection for premixed combustion. This corresponds to, for example, the case of the diffusion combustion execution rate of 90% in FIG. 4 (FIG. 4B).

  On the other hand, when the diffusion combustion execution rate is lower than the predetermined value or less, the premixed combustion fuel injection is executed by one injection without being divided. This corresponds to, for example, the case of the diffusion combustion execution rate 60% in FIG. 4 (FIG. 4C) or the case of the diffusion combustion execution rate 40% (FIG. 4D).

  As described above, according to each map, the injection amount in the premixed combustion fuel injection, the injection amount in the diffusion combustion fuel injection, and the like are set, and each injection is executed, so that the desired diffusion combustion execution described above is executed. The rate will be obtained.

  As described above, in the present embodiment, the higher the engine load, that is, the higher the output required for the engine 1, the higher the diffusion combustion execution rate, and the premixed combustion and the diffusion combustion in the same combustion stroke. To increase independence. For this reason, the stability of combustion when the engine load is high can be ensured. That is, it is possible to obtain a sufficient engine output by ensuring a high diffusion combustion execution rate during high load operation.

  On the other hand, the lower the engine load, that is, the lower the output required for the engine 1, the lower the diffusion combustion execution rate, and the lower the independence of premixed combustion and diffusion combustion during the same combustion stroke. ing. That is, premixed combustion and diffusion combustion are executed by combined combustion. For this reason, it is possible to improve the exhaust emission when the engine load is low, and to reduce the combustion noise.

  As described above, in the present embodiment, these combustions are controlled by adjusting the degree of independence of these combustions so that the advantages of premixed combustion and diffusion combustion can be effectively used as combustion forms in the combustion chamber 3. By coordinating, it is possible to improve combustion stability, exhaust emission, and combustion noise.

-Other control parameters-
In the embodiment described above, the diffusion combustion execution rate is set by the fuel injection pattern of the fuel injected from the injector 23. Instead of this, or in combination with this, it is also possible to set the diffusion combustion execution rate by adjusting the in-cylinder gas state before fuel injection. Examples of the in-cylinder gas state before fuel injection include “in-cylinder oxygen concentration” and “in-cylinder pre-ignition pressure”. Each will be described below.

(Adjustment of diffusion combustion execution rate by oxygen concentration in cylinder)
When adjusting the diffusion combustion execution rate according to the oxygen concentration in the cylinder, the oxygen concentration in the cylinder is set higher as the diffusion combustion execution rate is set higher. Specifically, the oxygen concentration in the cylinder is set high by decreasing the opening degree of the EGR valve 81 and decreasing the EGR amount. Conversely, the lower the diffusion combustion execution rate is set, the lower the oxygen concentration in the cylinder is set. Specifically, the oxygen concentration in the cylinder is set low by increasing the opening degree of the EGR valve 81 and increasing the EGR amount (oxygen concentration adjusting operation in the combustion chamber 3 by the oxygen concentration adjusting means).

(Adjustment of diffusion combustion execution rate by pressure before ignition in cylinder)
Further, when adjusting the diffusion combustion execution rate by the pressure before ignition in the cylinder, the pressure before ignition in the cylinder is set higher as the diffusion combustion execution rate is set higher. Specifically, the opening degree of the nozzle vane provided in the variable nozzle vane mechanism of the turbocharger 5 is reduced, and the supercharging pressure of the engine 1 is increased. Alternatively, the opening degree of the throttle valve 62 is increased. Note that only one of these nozzle vane control and throttle valve 62 control may be executed, or both may be executed simultaneously. Conversely, the lower the diffusion combustion execution rate is set, the lower the pre-ignition pressure in the cylinder is set. Specifically, the opening degree of the nozzle vane is increased and the supercharging pressure of the engine 1 is decreased. Alternatively, the opening degree of the throttle valve 62 is reduced. In this case as well, only one of these nozzle vane control and throttle valve 62 control may be executed or both may be executed simultaneously (pressure adjustment in the combustion chamber 3 by the pressure adjusting means). Operation).

  Even when the diffusion combustion execution rate is adjusted according to the in-cylinder gas state before fuel injection in this way, the same effect as when the diffusion combustion execution rate is adjusted by the fuel injection pattern described above. Can be played. That is, when the engine is operating at a high load, it is possible to obtain a sufficient engine output by ensuring a high diffusion combustion execution rate. Further, when the engine is operating at a low load, exhaust emission can be improved and combustion noise can be reduced.

(Combination of oxygen concentration adjustment in cylinder and pressure adjustment before ignition)
Further, when the adjustment of the diffusion combustion execution rate based on the oxygen concentration in the cylinder described above and the adjustment of the diffusion combustion execution ratio based on the pressure before ignition in the cylinder are used in combination, in the operation region where the engine load is relatively low, Adjust the diffusion combustion execution rate by oxygen concentration. On the other hand, in the operation region where the engine load is relatively high, the diffusion combustion execution rate is adjusted by the pre-ignition pressure in the cylinder. In this way, if the method for adjusting the diffusion combustion execution rate is switched between the oxygen concentration in the cylinder and the pre-ignition pressure in the cylinder according to the engine load, the generation of smoke during the operation transition of the engine 1 is prevented. It becomes possible to suppress.

  For example, when the engine 1 shifts from a high load operation to a low load operation, smoke may be generated due to insufficient oxygen in the combustion chamber 3 when the oxygen concentration in the cylinder is lowered and the diffusion combustion execution rate is set low. There is sex. In order to avoid this, in the present embodiment, the diffusion combustion execution rate can be set low while avoiding the generation of smoke by lowering the pre-ignition pressure in the cylinder and setting the diffusion combustion execution rate low. As a specific control operation, the diffusion combustion execution rate is set low by adjusting the opening degree of the nozzle vane and the opening degree of the throttle valve 62 while the opening degree of the EGR valve 81 is maintained. Thereafter, when the diffusion combustion execution rate is set lower, the diffusion combustion execution rate is set lower by adjusting the opening of the EGR valve 81.

  Further, when the engine 1 shifts from the low load operation to the high load operation, smoke may be generated if the pre-ignition pressure in the cylinder is increased and the diffusion combustion execution rate is set high. In order to avoid this, in the present embodiment, the diffusion combustion execution rate can be set high while avoiding the generation of smoke by increasing the oxygen concentration in the cylinder and setting the diffusion combustion execution rate high. As a specific control operation, the diffusion combustion execution rate is set high by adjusting the opening degree of the EGR valve 81 while maintaining the opening degree of the nozzle vane and the opening degree of the throttle valve 62. Thereafter, when the diffusion combustion execution rate is set higher, the diffusion combustion execution rate is set higher by adjusting the opening degree of the nozzle vane and the opening degree of the throttle valve 62.

-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, etc.) are not particularly limited.

  Moreover, in the said embodiment, although the NSR catalyst 75 and the DPNR catalyst 76 were provided as the manipulator 77, it is good also as a thing provided with the NSR catalyst 75 and DPF (Diesel Particle Filter).

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

  INDUSTRIAL APPLICABILITY The present invention can be used when a combustion mode of premixed combustion and diffusion combustion in a combustion chamber is appropriately controlled according to an engine load 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)
5 Turbocharger (supercharger)
6 Intake system 62 Throttle valve (intake throttle valve)
7 Exhaust system 8 EGR passage 81 EGR valve

-Solution-
Specifically, the present invention relates to compression auto-ignition in which fuel injected from a fuel injection valve burns in a combustion chamber by at least “premixed combustion” and “diffusion combustion” started after the start of this “premixed combustion”. The premise is a combustion control device for an internal combustion engine. For the combustion control device of the internal combustion engine, the fuel injection valve performs fuel injection for premixed combustion for mainly performing “premixed combustion” as combustion in the combustion chamber, and combustion in the combustion chamber. It is assumed that fuel injection for diffusion combustion for mainly performing “diffusion combustion” is performed separately. Further, by performing the premixed combustion fuel injection and the diffusion combustion fuel injection from the fuel injection valve in order, only premixed combustion among premixed combustion and diffusion combustion is performed during the combustion process. The combustion mode changes in the order of “mixed single combustion period”, “overlap combustion period” in which premixed combustion and diffusion combustion coexist, and “diffusion single combustion period” in which only diffusion combustion is performed among premixed combustion and diffusion combustion To go. Then, as the load on the internal combustion engine decreases or the required output of the internal combustion engine decreases , the amount of heat generated in the premixed combustion and the heat in the diffusion combustion during the “overlap combustion period”. The fuel injection form of the fuel injection valve and the combustion so that the ratio of the heat generation amount in the diffusion combustion during the “overlap combustion period” to the total heat generation amount which is the sum of the generation amount gradually decreases Diffusion combustion execution rate adjustment means for adjusting at least one of the gas states before fuel injection in the room is provided.

Due to this specific matter, in a situation where the load of the internal combustion engine is relatively high (or a situation where the required output of the internal combustion engine is relatively large), the ratio of the heat generation amount of diffusion combustion to the total heat generation amount during the overlap combustion period (Hereinafter referred to as the diffusion combustion execution rate) is set high. As described above, when the diffusion combustion execution rate is set high, the independence between the premixed combustion and the diffusion combustion during the same combustion stroke is set high. As a result, even if the combustion state in the premixed combustion deteriorates (unstabilizes), the degree of influence on the diffusion combustion is small, the stabilization of the diffusion combustion is maintained, and the combustion in the combustion chamber is stable. Can be done. For this reason, a sufficient output can be obtained particularly during high-load operation that requires stabilization of combustion.

On the other hand, in a situation where the load on the internal combustion engine is relatively low (or a situation where the required output of the internal combustion engine is relatively small), the diffusion combustion execution rate is set low. At a high load of the internal combustion engine, the combustion period is long and there is no room for retarding the combustion center of gravity. On the other hand, at a light load of the internal combustion engine, there is a margin to retard the combustion center of gravity, and the diffusion execution rate can be reduced. Therefore, in such a situation where the load of the internal combustion engine is relatively low, the diffusion combustion execution rate is set low , the premixed combustion ratio during the overlap combustion period is increased, and the smoke generation amount and NOx generation amount are reduced. The exhaust emission is improved as a combustion form that can be suppressed together.

Specific examples of the configuration for adjusting the diffusion combustion execution rate according to the fuel injection mode of the fuel injection valve include the following . The upper Symbol diffusion combustion execution rate adjusting means in accordance with the load of the internal combustion engine is gradually lowered, or, according to the required output of the internal combustion engine becomes smaller, in the premixed combustion fuel injection of the total fuel injection amount The ratio of the injection amount is gradually increased, and the ratio of the injection amount in the diffusion combustion fuel injection out of the total fuel injection amount is gradually decreased.

Further, in this case, the diffusion combustion execution rate adjusting means injects at least by the premixed combustion fuel injection as the load of the internal combustion engine decreases or as the required output of the internal combustion engine decreases. The “overlap combustion period” is lengthened by shifting the combustion center of gravity of the “premixed combustion” of the fuel to the retarded angle side. In this case, it is also possible to shift the combustion center of gravity of the “diffusion combustion” of the fuel injected by the fuel injection for diffusion combustion to the retarded angle side. There is a limit to the amount of transition to owing to problems with the output of the internal combustion engine and exhaust emissions. Further, the center of combustion of this “diffusion combustion” is also influenced by the amount of preheating in the cylinder by “premixed combustion”. The combustion center of gravity is a complete combustion that completes the combustion of all fuel when the fuel injected into the combustion chamber (for example, the fuel injected by the fuel injection for premixed combustion) burns in the combustion chamber. When the state is the combustion degree “100%”, the combustion degree reaches “50%”. In other words, the cumulative heat generation amount in the combustion chamber reaches “50%” with respect to the heat generation amount when the entire injected fuel burns.

Claims (8)

In a combustion control device for a compression self-ignition internal combustion engine in which fuel injected from a fuel injection valve burns in a combustion chamber by at least “premixed combustion” and “diffusion combustion” started after the start of this “premixed combustion” ,
As the load of the internal combustion engine decreases or the required output of the internal combustion engine decreases, the heat generation of diffusion combustion with respect to the total heat generation amount during the combustion period in which premixed combustion and diffusion combustion coexist. A diffusion combustion execution rate adjusting means for adjusting at least one of a fuel injection form of the fuel injection valve and a gas state before fuel injection in the combustion chamber so that a ratio of the amount gradually decreases; A combustion control apparatus for an internal combustion engine characterized by the above. The combustion control apparatus for an internal combustion engine according to claim 1,
The fuel injection valve performs premixed combustion fuel injection mainly for performing “premixed combustion” as combustion in the combustion chamber, and mainly performs “diffusion combustion” as combustion in the combustion chamber. The fuel injection for diffusion combustion is executed separately,
The diffusion combustion execution rate adjusting means adjusts the premixed combustion fuel injection out of the total fuel injection amount as the load of the internal combustion engine becomes lower or the required output of the internal combustion engine becomes smaller. An internal combustion engine characterized in that the ratio of the injection amount is gradually increased and the ratio of the injection amount in the diffusion combustion fuel injection in the total fuel injection amount is gradually decreased. Combustion control device. The combustion control apparatus for an internal combustion engine according to claim 2,
The diffusion combustion execution rate adjusting means adjusts the “preliminary” of the fuel injected by the fuel injection for premixed combustion at least as the load of the internal combustion engine decreases or the required output of the internal combustion engine decreases. Combustion of an internal combustion engine characterized in that the combustion period in which the premixed combustion and the diffusion combustion coexist is extended by shifting the center of gravity of "mixed combustion" to the retarded angle side. Control device. The combustion control apparatus for an internal combustion engine according to claim 1,
Oxygen concentration adjusting means capable of adjusting the oxygen concentration in the combustion chamber before the fuel injection of the fuel injection valve is performed,
The diffusion combustion execution rate adjusting means adjusts the oxygen concentration in the combustion chamber adjusted by the oxygen concentration adjusting means as the load of the internal combustion engine decreases or as the required output of the internal combustion engine decreases. A combustion control apparatus for an internal combustion engine, characterized by being configured to gradually lower. The combustion control apparatus for an internal combustion engine according to claim 1,
Pressure adjusting means capable of adjusting the pressure in the combustion chamber before the fuel injection of the fuel injection valve is performed,
The diffusion combustion execution rate adjusting means gradually decreases the pressure in the combustion chamber adjusted by the pressure adjusting means as the load of the internal combustion engine becomes lower or as the required output of the internal combustion engine becomes smaller. A combustion control device for an internal combustion engine, characterized by being configured to perform The combustion control device for an internal combustion engine according to claim 4,
The oxygen concentration adjusting means is an exhaust gas recirculation device that recirculates a part of the exhaust gas discharged to the exhaust system to the intake system, and increases the recirculation amount of the exhaust gas to the intake system by the exhaust gas recirculation device. A combustion control device for an internal combustion engine, characterized in that the oxygen concentration in the combustion chamber is gradually lowered. The combustion control device for an internal combustion engine according to claim 5,
The pressure adjusting means is a supercharging device that supercharges intake air in the intake system, and gradually reduces the pressure in the combustion chamber by reducing the supercharging amount of the intake air by the supercharging device. A combustion control device for an internal combustion engine, characterized by being configured to go. The combustion control device for an internal combustion engine according to claim 5,
The pressure adjusting means is an intake throttle valve that can limit the amount of intake air in the intake system, and the pressure in the combustion chamber is gradually reduced by increasing the limit of intake air by the intake throttle valve. A combustion control device for an internal combustion engine, characterized by being configured to go.

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