JP2011202629A - Method of determining center of gravity of combustion of internal combustion engine and combustion control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of accurately determining whether an appropriate heat production coefficient is obtained or not according to the operating conditions of an internal combustion engine, and a combustion control device of an internal combustion engine capable of providing an appropriate heat production coefficient utilizing the results of the determination.SOLUTION: The pressure of the fuel jetted from an injector is proportionally distributed according to an output requested by the engine. According to the injected fuel amount, the appropriate value of the time of the center of gravity of combustion of the heat production coefficient produced by the combustion in a combustion chamber is calculated, and it is determined whether or not the actual time of the center of gravity of combustion generally matches the calculated time of the center of gravity of combustion. When these times are different from each other, the actual time of the center of gravity of combustion is roughly aligned with the calculated time of the center of gravity of combustion by correcting a fuel injection timing or an in-cylinder oxygen concentration.

Description

  The present invention relates to a method for determining a combustion center of gravity in a combustion chamber in a combustion stroke of a compression ignition type internal combustion engine represented by a diesel engine. The present invention also relates to a combustion control device that controls the combustion mode in the combustion chamber based on the determination result. The combustion center of gravity is defined as a complete combustion state in which combustion of all the fuel is completed when fuel injected into the combustion chamber (for example, fuel injected by main injection) is combusted in the combustion chamber. “100%” means that the degree of combustion has reached “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.

  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, conventionally, it has been required to suppress both NOx generation and smoke generation 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). 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, thereby eliminating oxygen shortage in the combustion field. It is known (see, for example, Patent Document 3 below).

Japanese Patent Laid-Open No. 2004-3415 JP 2002-188487A JP 2001-193526 A

  Up to now, it has been proposed to control the heat generation rate in the combustion chamber (conventional heat generation amount per unit rotation angle of the crankshaft) for the purpose of suppressing both the NOx generation amount and the smoke generation amount. ing.

  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 difficult to verify whether or not this is done by changing the heat generation rate in the interior. When the combustion actually performed in the combustion chamber is performed at a heat generation rate different from an appropriate heat generation rate, an effect of suppressing both the NOx generation amount and the smoke generation amount can be obtained. Disappear.

  Also, fuel injection mode (fuel injection start timing, etc.) to obtain an appropriate heat generation rate, in-cylinder environment (in-cylinder oxygen concentration when the intake valve is closed) ) Is adjusted according to a fuel injection map or EGR map created in advance. When these maps are created, parameters for each operating state (engine speed and required torque, such as engine speed and engine required torque) are prepared. The fuel injection mode and the EGR amount (exhaust gas recirculation amount) are adapted to each grid point of the operation state map. In other words, for each engine operating state, experimental values of fuel injection form and EGR amount are obtained individually by trial and error, and fuel injection is performed by mapping the corresponding values corresponding to each of these many engine operating states. Created maps and EGR maps. Then, according to the fuel injection map, the fuel injection mode 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 the EGR valve. I was controlling.

  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 certain operating conditions (transient operation or environmental changes for which the above-mentioned conformity values are not required) or fuel property changes (such as when low cetane number fuel is supplied), both the amount of NOx generated and the amount of smoke generated are There is a possibility that the operation of the engine may be continued without obtaining the heat generation rate to be suppressed.

  In addition, since the adaptation values for a plurality of operating states are determined by trial and error, the adaptation becomes complicated, and it is impossible to construct a systematic combustion control method common to various engines.

  The present invention has been made in view of the above points, and an object of the present invention is to determine with high accuracy whether or not an appropriate heat generation rate according to the operating state of the internal combustion engine is obtained. Another object of the present invention is to provide a combustion control device for an internal combustion engine capable of obtaining an appropriate heat generation rate using the determination result.

-Principle of solving the problem-
The solution principle of the present invention taken to achieve the above object is to manage the heat generation rate accompanying combustion in the combustion chamber on the time axis, in other words, by treating combustion as a function of time. The combustion center-of-gravity time is uniformly defined according to the fuel injection amount regardless of the rotational speed of the internal combustion engine. Then, based on the defined combustion gravity center time, it is determined whether or not an appropriate heat generation rate is obtained.

-Solution-
Specifically, the present invention is directed to a method of determining a combustion center of gravity when fuel injected from a fuel injection valve burns into a cylinder of a compression ignition type internal combustion engine. And after setting the pressure of the fuel injected from the fuel injection valve by proportionally distributing according to the magnitude of the output required for the internal combustion engine,
The following formula (1),
Combustion center of gravity time = reference combustion center of gravity time x (fuel injection amount / reference fuel injection amount) ^1/2 (1)
(Reference combustion center-of-gravity time: time of combustion center of gravity given with reference fuel injection amount and ignition start time set in advance as reference points, reference fuel injection amount: fuel used as a reference specified in advance for setting reference combustion center-of-gravity time Injection amount)
Thus, the combustion center-of-gravity time is obtained.

Then, the combustion center-of-gravity time is replaced with a combustion center-of-gravity angle corresponding to the crankshaft rotation angle corresponding thereto (2)
Combustion center-of-gravity angle = reference combustion center-of-gravity angle x (fuel injection amount / reference fuel injection amount) ^1/2
× (Internal combustion engine speed / reference internal combustion engine speed) (2)
(Reference combustion center-of-gravity angle: crankshaft rotation angle of combustion center of gravity given with reference fuel injection amount and ignition start angle set in advance)
The combustion center-of-gravity angle is obtained from the above, and based on the amount of deviation between the obtained combustion center-of-gravity angle and the actual combustion center-of-gravity angle, it is determined that combustion is not properly performed when the amount of deviation is a predetermined amount or more. Judgment operation is performed.

  With this specific matter, when the fuel injected from the fuel injection valve burns in the combustion chamber, the heat generation rate is treated as “a heat generation amount per unit time”. As a result, a heat release rate waveform that is approximately approximated for each fuel injection amount is obtained, and the respective combustion centroids substantially coincide. This combustion center of gravity is obtained as a substantially coincident time if the fuel injection amount is the same even if the rotational speed of the internal combustion engine is different. For this reason, when the time of the actual combustion center of gravity is equal to or longer than a predetermined deviation time with respect to the time of the appropriate combustion center of gravity (the combustion center of gravity obtained by the above equation (1)) according to the fuel injection amount (or It can be determined that combustion is not properly performed when the combustion centroid angle obtained by the above equation (2) is equal to or greater than a predetermined deviation angle. That is, by using the above formula, it is possible to calculate the combustion center-of-gravity time for substantially the entire operating range of the internal combustion engine, and to compare the calculated combustion center-of-gravity time with the actual combustion center-of-gravity time. Thus, it is possible to determine whether or not an appropriate combustion center of gravity is obtained over substantially the entire operation range of the internal combustion engine, in other words, whether or not combustion is being performed at an appropriate heat generation rate.

  In the combustion center-of-gravity determination method, examples of means for performing combustion control when it is determined that combustion is not properly performed include the following. That is, when it is determined that the combustion performed in the combustion chamber is not properly performed by the combustion center-of-gravity determination method of the internal combustion engine, the deviation time between the calculated combustion center-of-gravity time and the actual combustion center-of-gravity time Combustion center-of-gravity time changing means for controlling combustion in the combustion chamber so as to shorten the combustion time is provided.

  Specific operations for changing the combustion center-of-gravity time by the combustion center-of-gravity time changing means include the following. First, the fuel injection timing from the fuel injection valve that injects fuel into the combustion chamber is corrected. The longer the delay time of the actual combustion center-of-gravity time relative to the calculated combustion center-of-gravity time, the longer the fuel injection timing is advanced. The correction is made to the side.

  Further, the oxygen concentration in the combustion chamber is corrected, and the oxygen concentration in the combustion chamber is set higher as the delay time of the actual combustion gravity center time with respect to the calculated combustion gravity center time is longer.

  With these specific matters, it is possible to quickly eliminate the situation in which the operation with the combustion center of gravity time deviating from the appropriate time is continued, and combustion at an appropriate heat generation rate becomes possible. Both the generation amount and the generation amount of smoke can be suppressed, and exhaust emission can be improved.

  In the present invention, the heat generation rate associated with the combustion in the combustion chamber is managed on the time axis so that the combustion center-of-gravity time is uniformly defined according to the fuel injection amount regardless of the rotational speed of the internal combustion engine. To do. This makes it possible to accurately determine whether or not an appropriate heat generation rate is obtained.

It is a schematic block diagram of the engine which concerns on embodiment, and its control system. It is sectional drawing which shows the combustion chamber of a diesel engine, and its peripheral part. It is a block diagram which shows the structure of control systems, such as ECU. It is a wave form diagram which shows the change of the heat release rate (heat generation amount per unit rotation angle of a crankshaft) and the change of a fuel injection rate (fuel injection amount per unit rotation angle of a crankshaft) at the time of an expansion stroke, 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 wave form diagram which shows the change of the heat release rate (The amount of heat generation per unit rotation angle of a crankshaft and the amount of heat generation per unit time) when the engine speed differs in each of a plurality of fuel injection amounts. It is a wave form diagram which shows the change of the heat release rate (heat generation amount per unit time) and the change of a fuel injection rate (fuel injection amount per unit time) for every fuel injection amount, respectively.

  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.

  Furthermore, as shown in FIG. 1, the engine 1 is provided with a supercharger (turbocharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor wheel 53 that are connected via a turbine shaft 51. The compressor wheel 53 is disposed facing the 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 executes pilot injection, pre-injection, main injection (main injection), after-injection, and post-injection described later as fuel injection control of the injector 23.

-Fuel injection mode-
Hereinafter, an outline of each operation of the pilot injection, pre-injection, main injection, after-injection, and post-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 pilot injection is performed, the fuel injection is temporarily interrupted, and the compressed gas temperature (in-cylinder temperature) is sufficiently increased until the main injection is started to reach the fuel self-ignition temperature. This ensures good ignitability of the fuel injected in the main injection. That is, the pilot injection function 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.

Specifically, in order to optimize spray distribution and local concentration, the injection amount per pilot injection is set to the minimum limit injection amount (for example, 1.5 mm ³ ) of the injector 23, and the number of injections is set. This ensures the necessary total pilot injection amount. Thus, the interval of pilot injection that is dividedly injected is determined by the responsiveness of the injector 23 (speed of opening and closing operation). This interval is set to 200 μs, for example. In addition, the injection start timing of the pilot injection is set, for example, at a crank angle and after 80 ° before compression top dead center (BTDC) of the piston 13. Note that the injection amount, interval, and injection start timing per pilot injection are not limited to the above values.

(Pre-injection)
Pre-injection is an injection operation in which a small amount of fuel is injected in advance prior to main injection from the injector 23. The pre-injection is an injection operation for suppressing the ignition delay of the fuel due to the main injection and leading to stable diffusion combustion, and is also called sub-injection. Further, the pre-injection in the present embodiment has not only a function of suppressing the initial combustion speed by the main injection described above but also a preheating function of increasing the in-cylinder temperature.

  Specifically, in the present embodiment, the total fuel injection amount (the injection amount in the pre-injection) for obtaining the required torque determined according to the operating state such as the engine speed, the accelerator operation amount, the cooling water temperature, the intake air temperature, etc. And the injection amount in the main injection), for example, the pre-injection amount is set as 10%. The ratio of the pre-injection amount to the total fuel injection amount is set according to the amount of heat required for preheating the inside of the cylinder.

When the total fuel injection amount is less than 15 mm ³ , the pre-injection is not executed because the injection amount in the pre-injection is less than the minimum limit injection amount (1.5 mm ³ ) of the injector 23. . In this case, the fuel injection in the pre-injection may be performed by the minimum limit injection amount (1.5 mm ³ ) of the injector 23. On the other hand, when the total injection amount of the pre-injection is required to be at least twice the minimum limit injection amount of the injector 23 (for example, 3 mm ³ or more), it is necessary for this pre-injection by executing a plurality of pre-injections. The total injection amount is secured. Thereby, the ignition delay of the pre-injection can be suppressed, the initial combustion speed by the main injection can be surely suppressed, and the stable diffusion combustion can be led.

(Sequential combustion)
As described above, in the present embodiment, the cylinder is sufficiently preheated by the pilot injection and the pre-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. As a result, controlling the fuel injection timing is substantially equivalent to controlling the combustion timing as it is, and the controllability of combustion can be greatly improved. That is, until now, the premixed combustion of the diesel engine has occupied a considerable proportion. In the present embodiment, the fuel injection timing and the fuel injection are reduced by minimizing the premixed combustion rate. Control of the heat generation rate waveform (ignition timing and heat generation amount) by controlling the amount (controlling the injection rate waveform) can greatly improve the controllability of combustion. In the present embodiment, this new type of combustion mode is referred to as “sequential combustion (combustion started immediately after fuel is injected)” or “controlled combustion (combustion actively controlled by fuel injection timing and fuel injection amount)”. ".

(Main injection)
The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. In the present embodiment, the injection amount in the pre-injection is subtracted from the total fuel injection amount to obtain the required torque determined according to the operating state such as the engine speed, the accelerator operation amount, the coolant temperature, the intake air temperature, etc. Is set as the injection amount.

  Here, the control process of the above-described pre-injection and main injection will be briefly described.

  First, a total fuel injection amount that is the sum of the injection amount in the pre-injection and the injection amount in the main injection is calculated with respect to the torque request value of the engine 1. That is, the total fuel injection amount is calculated as an amount for generating the torque required for the engine 1.

  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.

  After the total fuel injection amount is calculated in this way, the ratio (split rate) of the injection amount in the pre-injection with respect to the total fuel injection amount is set. That is, the pre-injection amount is set as an amount divided by the above-described division ratio with respect to the total fuel injection amount. This division ratio (pre-injection amount) is obtained as a value that achieves both “suppression of fuel ignition delay by main injection” and “suppression of the peak value of the heat generation rate of combustion by main injection”. By suppressing these, it is possible to reduce the combustion noise and the amount of NOx generated while securing a high engine torque. In the present embodiment, the division ratio is set to 10%.

(After spray)
After injection is an injection operation for increasing the exhaust gas temperature. Specifically, in this embodiment, after-injection is performed at a timing at which most of the combustion energy of the fuel supplied by this after-injection is obtained as exhaust heat energy without being converted into engine torque. I have to. Also in this after injection, as in the case of the pilot injection described above, this after injection is performed by performing a plurality of after injections with a minimum injection rate (for example, an injection amount of 1.5 mm ³ per injection). Therefore, the necessary total after injection amount is secured.

(Post injection)
The post-injection is an injection operation for directly introducing fuel into the exhaust system 7 to increase the temperature of the manipulator 77. For example, when the accumulated amount of PM trapped in the DPNR catalyst 76 exceeds a predetermined amount (for example, detected by detecting a differential pressure before and after the manipulator 77), post injection is performed. .

-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. 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 rotation speed based on the detection value of the crank position sensor 40, obtains the amount of depression of the accelerator pedal (accelerator opening) based on the detection value of the accelerator opening sensor 47, Based on the engine speed and the accelerator opening, the total fuel injection amount (the sum of the injection amount in the pre-injection and the injection amount in the main injection) is determined.

-Setting of target fuel pressure-
Next, a method for setting the target fuel pressure and a fuel pressure setting map will be described. First, a technical idea when setting the target fuel pressure in the present 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. The verification as to whether or not the change state of the heat generation rate is appropriately controlled is performed by a “combustion center of gravity determination operation” described later.

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

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

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

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

  As described above, in the present embodiment, the cylinder is sufficiently preheated by the pilot injection and the pre-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.

  Further, the waveform indicated by a two-dot chain line α in FIG. 4 is a heat generation rate waveform when the fuel injection pressure is set higher than the appropriate value, and both the combustion speed and the peak value are too high, and the combustion This is a state in which there is a concern about an increase in sound and an increase in the amount of NOx generated. On the other hand, the waveform indicated by the two-dot chain line β in FIG. 4 is a heat release rate waveform when the fuel injection pressure is set lower than the appropriate value, and the timing at which the combustion speed is low and the peak appears is greatly retarded. There is a concern that sufficient engine torque cannot be ensured by shifting to.

  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.

  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”, and is given as a straight line passing through the origin of the graph shown in FIG. 5 and having a predetermined inclination. It has been.

  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 an ideal heat generation rate waveform indicated by a solid line in FIG. 4 can be obtained at the power barycentric point. The 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. 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.

-Combustion center of gravity judgment-
Next, the operation for determining the combustion center of gravity, which is a feature of the present invention, will be described. This combustion center of gravity is determined when the fuel injected in the main injection burns (mostly diffusion combustion), and the combustion center of gravity is at an appropriate timing (for example, 10 degrees after compression top dead center (ATDC 10 °)). This is an operation for determining whether or not it is at the time. That is, if the combustion center of gravity is at an appropriate timing, the combustion in the combustion chamber 3 is performed well, and the exhaust emission is improved by reducing the NOx generation amount and the smoke generation amount, the combustion noise is reduced, the engine It is determined that each request such as sufficient securing of torque can be achieved simultaneously. On the other hand, if the combustion center of gravity is not at an appropriate timing, it is determined that the above requests cannot be made simultaneously, and combustion control for shifting the combustion center of gravity to an appropriate timing is performed. This will be specifically described below.

(Combustion center of gravity judgment operation)
First, the combustion gravity center determination operation for determining whether or not the combustion gravity center is at an appropriate timing will be described.

  The basic technical idea of determining the combustion center of gravity is, as described above, first, a state in which the target fuel pressure (target common rail internal pressure) is assigned to each required output (a state of proportional distribution). In this state, when the fuel injected by the main injection burns in the combustion chamber 3, the heat generation rate is treated as “a heat generation amount per unit time”. That is, the horizontal axis of the heat release rate waveform shown in FIG. 4 is replaced with time from the crank angle. As a result, a heat generation rate waveform approximately approximated for each fuel injection amount is obtained, and the respective combustion centroids (accumulation of the heat generation amount in the combustion chamber 3 is the case where the entire amount of fuel injected in the main injection is burned) The point of time (at which “50%” is reached) for the amount of heat generated is substantially the same.

7A to 7D are waveform diagrams showing changes in the heat generation rate when the engine speed is different for each of a plurality of fuel injection amounts. For example, FIG. 7A shows the case where the fuel injection amount in the main injection is 10 mm ³ , FIG. 7B shows the case where the fuel injection amount in the main injection is 30 mm ³ , and FIG. When the fuel injection amount is 50 mm ³ , FIG. 7D is a heat release rate waveform for each of the cases where the fuel injection amount in the main injection is 70 mm ³ . In each figure, the upper row is the one with the horizontal axis as the crank angle, that is, the heat generation rate per unit rotation angle of the crankshaft is the heat generation rate, and the lower row is the one with the horizontal axis as the time, that is, the unit The amount of heat generated per hour is the heat generation rate. In each figure, the solid line indicates the case where the engine speed is 2000 rpm, the broken line indicates the case where the engine speed is 3600 rpm, and the alternate long and short dash line indicates the case where the engine speed is 4800 rpm.

  As described above, when the heat generation rate per unit rotation angle of the crankshaft is defined as the heat generation rate, the combustion center-of-gravity angle varies with the engine speed. Specifically, as the engine speed increases, the combustion gravity center angle shifts to the retard side. On the other hand, when the heat generation rate per unit time is defined as the heat generation rate, the heat generation rate waveform is approximately approximated even if the engine speed is different, and the combustion gravity center angle is approximately the same.

FIG. 8 is a waveform diagram showing changes in the heat generation rate (heat generation amount per unit time) and changes in the fuel injection rate (fuel injection amount per unit time) for each fuel injection amount. The solid line in FIG. 8 indicates the case where the fuel injection amount is 70 mm ³ , the broken line indicates the case where the fuel injection amount is 50 mm ³ , the one-dot chain line indicates the case where the fuel injection amount is 30 mm ³ , and the two-dot chain line indicates the case where the fuel injection amount is 10 mm ³ Respectively. Even if the engine speed is different, the heat generation rate waveform approximates each waveform shown in FIG. 8 for each fuel injection amount. In other words, one heat release rate waveform can be drawn for each fuel injection amount, which means that the combustion gravity center time (elapsed time from TDC) does not change even if the engine speed changes. Yes. Specifically, in FIG. 8, the time t1 is the combustion center of gravity when the fuel injection amount is 10 mm ³ , the time t2 is the combustion center of gravity when the fuel injection amount is 30 mm ³ , and the time t3 is the fuel injection amount 50 mm ³ . The combustion center of gravity when the fuel injection amount is 70 mm ³ at time t4.

  The combustion center of gravity (on the time axis) when the combustion is actually performed with respect to the combustion center of gravity (time at which the combustion center of gravity on the time axis) is obtained for each fuel injection amount thus obtained. It is determined whether or not the combustion center of gravity is at an appropriate position, in other words, whether or not the heat generation rate is properly obtained. ing. The above is the basic technical idea of determining the combustion center of gravity.

  Next, this combustion center-of-gravity determination method will be specifically described.

  The combustion barycenter time is calculated by the following equation (1).

Combustion center of gravity time = reference combustion center of gravity time x (fuel injection amount / reference fuel injection amount) ^1/2 (1)
Here, the “reference combustion gravity center time” is the time of the combustion gravity center given by a preset reference fuel injection amount. Further, the “reference fuel injection amount” is a fuel injection amount that is a reference that is defined in advance in order to set the “reference combustion gravity center time”. These “reference combustion center of gravity time” and “reference fuel injection amount” are obtained in advance by experiments and simulations. For example, when the engine speed is 2000 rpm, the “reference fuel injection amount” is set to 30 mm ³ , and when the “reference combustion gravity center time” in this case is 700 μsec elapsed time from TDC, these The values of “reference fuel injection amount” and “reference combustion centroid time” are given as “reference fuel injection amount” and “reference combustion centroid time” in the above equation (1). These values are not limited to this, and can be arbitrarily set.

  The “fuel injection amount” corresponds to the fuel injection amount actually injected from the injector 23, and is a target fuel injection amount set according to the required output (required power) or the like. Alternatively, a flow rate sensor may be provided in the middle of the pipe connecting the common rail 22 and the injector 23, and the “fuel injection amount” may be obtained based on the fuel flow rate detected by the flow rate sensor.

  Then, as an actual operation for determining whether or not the combustion center of gravity is at an appropriate position, the combustion center of gravity angle is calculated by the following equation (2), and the calculated combustion center of gravity angle is actually detected. The combustion center-of-gravity angle is compared. This is done by determining whether the combustion center of gravity is appropriate or not by comparing the combustion center of gravity on the ideal crankshaft rotation angle in the calculation with the crankshaft rotation angle that is easy to measure. This is to simplify the operation. That is, the combustion centroid time is calculated by the following equation (2) using the fact that the combustion centroid time is replaced with the combustion centroid angle by multiplication of the rotation speed ratio. That is, the following formula (2) is a calculation formula having the same meaning as the above formula (1).

Combustion center-of-gravity angle = reference combustion center-of-gravity angle x (fuel injection amount / reference fuel injection amount) ^1/2
X (engine speed / reference engine speed) (2)
Here, the “reference combustion gravity center angle” is a crank rotation angle at the combustion center of gravity given by a preset reference fuel injection amount. In addition, the “reference fuel injection amount” is a fuel injection amount that is a reference that is defined in advance in order to set the “reference combustion gravity center angle”. This equation (2) assumes that the time required for each rotation of the crankshaft by 1 ° is constant during the period in which the fuel injected by the main injection is burned (main combustion period). Is an approximate expression.

These “reference combustion center-of-gravity angle” and “reference fuel injection amount” are obtained in advance by experiments and simulations. For example, when the engine speed is 2000 rpm, the “reference fuel injection amount” is set to 30 mm ³ , and when the “reference combustion gravity center angle” in that case is ATDC 10 ° CA, these “reference fuel injection amounts” are set. The values of “fuel injection amount” and “reference combustion gravity center angle” are given as “reference fuel injection amount” and “reference combustion gravity center angle” in the above equation (2). These values are not limited to this, and can be arbitrarily set.

  Also in this case, the “fuel injection amount” corresponds to the fuel injection amount actually injected from the injector 23, and the target fuel injection amount set in accordance with the required output (required power) or the like. It is. Alternatively, a flow rate sensor may be provided in the middle of the pipe connecting the common rail 22 and the injector 23, and the “fuel injection amount” may be obtained based on the fuel flow rate detected by the flow rate sensor.

  Whether the combustion center of gravity is at an appropriate position is calculated by calculating the combustion center of gravity angle by this equation (2) and comparing the calculated combustion center of gravity angle with the actually detected (actually measured) combustion center of gravity angle. Determine whether. Actually, the data of the combustion gravity center angle calculated by the above equation (2) is stored in the ROM 102, and specific combustion gravity center angle data is read from the ROM 102 in accordance with the fuel injection amount. By comparing the data and the combustion center-of-gravity angle actually detected (actually measured), it is determined whether or not the combustion center-of-gravity is at an appropriate position.

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

  Then, the combustion gravity center angle actually detected deviates from the combustion gravity center angle calculated by the above equation (2) by a predetermined amount (for example, 3 ° CA in crank angle) to the retard side or the advance side. If it is, it is determined that the combustion center of gravity is deviated, that is, 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)
As described above, the combustion center-of-gravity movement control (combustion control by the combustion center-of-gravity time changing means) is such that the actually detected combustion center-of-gravity angle is retarded or advanced with respect to the combustion center-of-gravity angle calculated by the above equation (2). This is control when it is determined that the combustion center of gravity is deviated when the angle is deviated by a predetermined amount or more on the corner side. That is, when it is determined that the heat generation rate is not properly obtained, this control is for obtaining the heat generation rate appropriately (appropriately obtaining the combustion center-of-gravity angle). 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, when the actually detected combustion center of gravity angle deviates more than a predetermined amount on the retard side from the combustion center of gravity angle calculated by the above equation (2), the combustion center of gravity is determined. The fuel injection timing is corrected to the advance side so that the angle is moved to the advance side. Conversely, when the combustion center of gravity angle actually detected deviates from the combustion center of gravity calculated by the above equation (2) by a predetermined amount or more to the advance side, the combustion center of gravity angle is set to the retard side. The fuel injection timing is corrected to the retarded angle side so as to move to. This makes it possible to optimize the heat generation rate by setting the combustion center-of-gravity angle to an appropriate position, improving exhaust emissions by reducing the amount of NOx generated and smoke generated, reducing combustion noise, and sufficient engine torque. It is possible to make simultaneous requests such as secure.

  On the other hand, as the correction of the oxygen concentration in the combustion chamber 3, the actually detected combustion center of gravity angle deviates more than a predetermined amount toward the retard side with respect to the combustion center of gravity angle calculated by the above equation (2). In this case, an operation for increasing the oxygen concentration in the combustion chamber 3 is performed so that the combustion gravity center angle is moved to the advance 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. Note that only one of these EGR valve 81 control, nozzle vane control, and throttle valve 62 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 gravity center angle moves to the advance side as the combustion speed increases, so that the combustion gravity center angle 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. Note that if the combustion center of gravity angle actually detected deviates from the combustion center of gravity calculated by the above equation (2) by a predetermined amount or more to the advance side, the combustion center of gravity angle is set to the retard side. An operation of lowering the oxygen concentration in the combustion chamber 3 is performed so as to be moved. 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 time of combustion deviating from the appropriate time 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.

  In addition, when the fuel injection timing is controlled to the retard side in order to suppress the amount of NOx generated, or when the fuel injection timing is controlled to the advance side according to the fuel properties (cetane number, etc.) The combustion center of gravity determination operation described above is performed after correcting that the combustion center of gravity changed to the retard side or the advance side by these controls is an appropriate combustion center of gravity time with respect to the combustion center of gravity obtained by the above calculation formula. Combustion center-of-gravity movement control is performed.

-Other embodiments-
In the embodiment described above, 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.

  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.

  Moreover, in the said embodiment, it was determined whether the combustion gravity center exists in an appropriate position by managing a combustion gravity center on a time-axis. The present invention is not limited to this, and can also be used to verify the optimization of the fuel pressure setting map. That is, when the combustion center of gravity is not at an appropriate position, one reason is that the fuel pressure is not properly obtained. For this reason, when the combustion center of gravity is not at an appropriate position, the set value of the fuel pressure may be changed in order to optimize the fuel pressure setting map.

  INDUSTRIAL APPLICABILITY The present invention can be used to verify whether or not combustion in a combustion chamber is properly performed 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 62 Throttle valve 81 EGR valve

Claims (5)

A method for determining a combustion center of gravity when fuel injected from a fuel injection valve burns into a cylinder of a compression ignition type internal combustion engine,
After setting the pressure of the fuel injected from the fuel injection valve by proportionally distributing according to the magnitude of the output required for the internal combustion engine,
The following formula (1),
Combustion center of gravity time = reference combustion center of gravity time x (fuel injection amount / reference fuel injection amount) ^1/2 (1)
(Reference combustion center-of-gravity time: time of combustion center of gravity given with reference fuel injection amount and ignition start time set in advance as reference points, reference fuel injection amount: fuel used as a reference specified in advance for setting reference combustion center-of-gravity time Injection amount)
A combustion center-of-gravity determination method for an internal combustion engine, characterized in that the combustion center-of-gravity time is obtained by: In the internal combustion engine combustion center-of-gravity determination method according to claim 1,
The following equation (2) that replaces the combustion center-of-gravity time with the corresponding combustion center-of-gravity angle as the crankshaft rotation angle
Combustion center-of-gravity angle = reference combustion center-of-gravity angle x (fuel injection amount / reference fuel injection amount) ^1/2
× (Internal combustion engine speed / reference internal combustion engine speed) (2)
(Reference combustion center-of-gravity angle: crankshaft rotation angle of combustion center of gravity given with reference fuel injection amount and ignition start angle set in advance)
The combustion center-of-gravity angle is obtained from the above, and based on the amount of deviation between the obtained combustion center-of-gravity angle and the actual combustion center-of-gravity angle, it is determined that combustion is not properly performed when the amount of deviation is a predetermined amount or more. A method for determining a combustion center of gravity of an internal combustion engine, wherein a determination operation is performed.   When it is determined by the combustion center-of-gravity determination method of the internal combustion engine according to claim 2 that the combustion performed in the combustion chamber is not properly performed, the calculated combustion center-of-gravity time and the actual combustion center-of-gravity time A combustion control apparatus for an internal combustion engine, comprising combustion center-of-gravity time changing means for controlling combustion in the combustion chamber so as to shorten the deviation time. The combustion control apparatus for an internal combustion engine according to claim 3,
The combustion center-of-gravity time changing means corrects the fuel injection timing from the fuel injection valve that injects fuel into the combustion chamber, and the longer the delay time of the actual combustion center-of-gravity time relative to the calculated combustion center-of-gravity time, A combustion control apparatus for an internal combustion engine, characterized in that the fuel injection timing is corrected to an advance side. The combustion control apparatus for an internal combustion engine according to claim 3,
The combustion center-of-gravity time changing means corrects the oxygen concentration in the combustion chamber, and the oxygen concentration in the combustion chamber is set higher as the delay time of the actual combustion center-of-gravity time with respect to the calculated combustion center-of-gravity time is longer. A combustion control apparatus for an internal combustion engine, characterized in that it is configured.

Images