JP4840515B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine represented by a diesel engine. In particular, the present invention relates to an improvement in the injection mode of fuel injected from a fuel injection valve in order to raise an exhaust purification catalyst provided in an exhaust system of an internal combustion engine to an activation temperature.

  2. Description of the Related Art As is well known, in a diesel engine used as an automobile engine or the like, a fuel injection valve (hereinafter referred to as an injector) is selected in accordance with operating conditions such as engine speed, accelerator operation amount, cooling water temperature, and intake air temperature. In some cases, fuel injection control is performed to adjust the fuel injection timing and fuel injection amount.

  The combustion of the diesel engine is composed of premixed combustion and diffusion combustion. When fuel injection from the fuel injection valve is started, a combustible air-fuel mixture is first generated by fuel vaporization and diffusion (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).

  Incidentally, an exhaust system of this type of diesel engine is provided with a catalyst for exhaust purification. As the exhaust purification catalyst, for example, an oxidation catalyst, a three-way catalyst, a lean NOx catalyst, and the like are known. In any case, in order to obtain a high purification rate, the temperature is raised to a predetermined activation temperature or higher. It needs to be warm. That is, in a situation where the temperature is lower than the activation temperature, the catalyst purification rate becomes extremely low, and the exhaust purification function is not exhibited.

  Therefore, there is a possibility that a sufficient exhaust purification cannot be performed in an operation state in which the exhaust gas temperature is relatively low, such as when the engine is cold started or during a light load operation. In particular, in the case of a diesel engine, the air-fuel ratio in the cylinder is lean (for example, about A / F = 30), and lean combustion is performed in the expansion stroke, so the exhaust temperature is lower than that in a gasoline engine. Yes. For this reason, the rate of temperature increase of the catalyst is slow, and a situation in which activation of the catalyst is not performed quickly tends to occur.

In view of this point, for example, as disclosed in Patent Document 1 below, a reducing agent addition valve is provided upstream of the catalyst in the exhaust system, and fuel is supplied from the reducing agent addition valve toward the catalyst ( A technique is known in which the fuel is burned on or around the catalyst to increase the catalyst temperature (catalyst bed temperature) to the activation temperature. Further, as disclosed in Patent Document 2 below, after the expansion stroke of the engine, fuel injection (generally called post injection) is performed from the injector, and this fuel is supplied to the exhaust system in a sprayed state. As in the case of the fuel addition described above, it is also known that the fuel is burned on or around the catalyst to raise the catalyst temperature to the activation temperature.
JP 2001-327838 A JP 2004-308509 A JP 2004-68606 A

  In order to raise the catalyst temperature by the above-described fuel addition or post-injection, it is necessary for the exhaust system to have a quantity of heat sufficient to ignite the supplied fuel. However, immediately after the cold start of the engine or the like, the heat energy existing in the exhaust system is very small. Even if fuel (spray) is supplied to the exhaust system by the fuel addition or post injection in this state, This fuel does not ignite. As a result, not only the catalyst temperature cannot be raised to the activation temperature, but also wasteful fuel supply causes a deterioration in the fuel consumption rate, or this fuel is released into the atmosphere as it is and exhaust emissions are reduced. There is also concern that this will lead to deterioration.

  As a measure for ensuring good ignitability of the fuel supplied to the exhaust system by such fuel addition or post injection, the temperature of the exhaust gas (combustion gas) exhausted from the combustion chamber is made high. It is possible. For example, a large amount of fuel injection in the main injection is set.

  However, when the fuel injection amount in the main injection is increased, the kinetic energy generated by the combustion of the fuel increases the engine torque more than necessary, that is, the engine torque is increased by the fuel increase amount. As a result, the engine torque cannot be obtained. As a result, problems such as deterioration of drivability occur. In addition, as the fuel injection amount increases, the penetration force (penetration) of the injected fuel increases and may reach the inner wall surface of the cylinder. In this case, the lubricating oil is diluted by the fuel that has reached the inner wall surface of the cylinder. In addition, the occurrence of smoke due to deterioration of the ignitability of fuel is a concern.

  The present invention has been made in view of such a point, and the object of the present invention is to rapidly increase the catalyst temperature to the activation temperature in a situation where the catalyst temperature is relatively low, with almost no increase in torque of the internal combustion engine. An object of the present invention is to provide a fuel injection control device for an internal combustion engine that can be heated up to a high temperature.

-Principle of solving the problem-
The solution principle of the present invention taken in order to achieve the above object is that a fuel specializing in raising the temperature of a catalyst as a fuel ignited by thermal energy in a cylinder after main injection from a fuel injection valve is performed. Injection (catalyst temperature rising injection) is performed. Then, most of the energy generated by the combustion of the fuel injected by the catalyst temperature rising injection is supplied as heat energy to the exhaust system, so that the temperature of the catalyst can be raised quickly.

-Solution-
Specifically, the present invention relates to a compression ignition type internal combustion engine capable of performing multiple fuel injections including a main injection that is a fuel injection for generating torque from a fuel injection valve during one cycle of the internal combustion engine. A fuel injection control device is assumed. For this fuel injection control device, after executing the main injection, by performing the catalyst temperature rising injection that ignites using the thermal energy in the cylinder generated by the combustion of the fuel injected in the main injection, There is provided a catalyst temperature rise injection executing means for sending most of the energy of the combustion gas of the fuel injected in the catalyst temperature rise injection to the exhaust system as heat energy for raising the catalyst temperature of the exhaust system. The fuel injection execution means is within a catalyst temperature increase injection possible period in which the cylinder internal temperature is equal to or higher than the fuel self-ignition temperature and the fuel combustion speed is equal to or lower than a predetermined speed when the catalyst temperature increase injection is executed. The catalyst temperature raising injection is executed .

Due to this specific matter, the catalyst temperature increase injection is executed at a predetermined timing after the main injection is executed from the fuel injection valve . Catalyst Atsushi Nobori for injection This is ignited by the heat energy due to combustion of fuel injected in the main injection. And most of the combustion gas of the fuel injected by this catalyst temperature rising injection is sent to the exhaust system as thermal energy. That is, the combustion gas of the fuel injected by the catalyst temperature rising injection hardly acts as an increase in the torque of the internal combustion engine, and the energy of the combustion gas is consumed as heat energy for raising the temperature of the catalyst. It is. For this reason, for example, even when the catalyst bed temperature is relatively low, such as during cold start of an internal combustion engine or during light load operation, high temperature combustion gas is generated in the exhaust system, particularly around the catalyst. It can be present and the catalyst temperature can be rapidly raised to the activation temperature. Moreover, since the situation in which the torque of the internal combustion engine greatly increases due to the execution of the catalyst temperature rise injection is performed, an appropriate torque can be obtained from the internal combustion engine, and drivability does not deteriorate.
Further, by performing the catalyst temperature increase injection during the catalyst temperature increase injection possible period, the injected fuel can be reliably ignited, and the combustion speed at that time becomes relatively low. In addition, a situation in which the torque of the internal combustion engine greatly increases is not caused. That is, it is possible to rapidly increase the catalyst temperature to the activation temperature while preventing deterioration of drivability.

  Specifically, the injection form of the catalyst temperature increase injection is set as follows. That is, a total catalyst temperature increase injection amount calculating means for obtaining a total catalyst temperature increase injection amount required for the catalyst temperature increase injection is provided, and the catalyst temperature increase injection execution means is provided for the total catalyst temperature increase injection means. The total catalyst temperature increase injection amount obtained by the injection amount calculation means is divided by a plurality of divided catalyst temperature increase injections so as to be intermittently injected from the fuel injection valve. The catalyst temperature increase divided injection amount per time of the catalyst temperature increase divided injection is set to the minimum limit injection amount of the fuel injection valve. In addition, the opening period of the fuel injection valve per one of the catalyst temperature increase divided injection may be set to the shortest opening period of the fuel injection valve.

  In this way, the injection amount of the catalyst temperature increase divided injection per time is set to the minimum limit injection amount of the fuel injection valve, or the fuel injection valve opening in the catalyst temperature increase divided injection per time When the period is set to the shortest valve opening period of the fuel injection valve, the injection amount of the catalyst temperature rising divided injection per one time is extremely small, and the endothermic reaction of the fuel during the catalyst temperature rising divided injection is The endothermic amount due to is small. Therefore, there is no ignition delay of the catalyst temperature division split injection, and the catalyst is quickly ignited and sent to the exhaust system. The thermal energy obtained by the combustion of the fuel injected by the first catalyst temperature-raising split injection shows the ignitability of the fuel injected by the second catalyst temperature-raising split injection. It is used as heat energy to make it good. In this way, by performing split injection for raising the catalyst temperature in a plurality of stages, a chain fuel combustion operation can be obtained. For this reason, it is possible to sufficiently ensure the effect of performing the catalyst temperature increase injection (rapidly raising the catalyst temperature to the activation temperature).

  Specifically, as the total catalyst temperature increase injection amount obtained by the total catalyst temperature increase injection amount calculation means, the total catalyst temperature increase injection amount is set to be larger as the catalyst temperature is lower than the activation temperature. I am doing so.

  In other words, the larger the amount of heat required to reach the catalyst temperature to the activation temperature, the more the total catalyst temperature increase injection amount is set so that more heat energy is given to the exhaust system for catalyst temperature increase. Yes. Also in this case, since it is preferable that the injection amount of the catalyst temperature increase divided injection per one time is small, the larger the total catalyst temperature increase injection amount is set, the more the total catalyst temperature increase injection amount is set. The number of divisions (the number of divided injections for raising the catalyst temperature) increases.

  As described above, the catalyst temperature increase divided injection amount per one of the catalyst temperature increase divided injection is set to the minimum limit injection amount of the fuel injection valve, or the fuel injection valve per time of the catalyst temperature increase divided injection is set. When the valve opening period is set to the shortest valve opening period of the fuel injection valve, there is a possibility that the required number of times of catalyst temperature division split injection cannot be executed within the catalyst temperature increase injection possible period. This is particularly the case when the above-mentioned catalyst temperature raising injection possible period is short. As a countermeasure in this case, the catalyst temperature increase divided injection amount per time of the catalyst temperature increase divided injection is set to be larger than the minimum limit injection amount of the fuel injection valve, or the catalyst temperature increase divided injection per time In this case, the opening period of the fuel injection valve is set longer than the shortest opening period of the fuel injection valve. Specific control operations in this case include the following.

  First, the temperature of the catalyst is increased when the fuel injected into the combustion chamber is provided with a glow plug for assisting ignition and when a plurality of divided injections for increasing the temperature of the catalyst are executed within the above-described period of possible injection of the temperature of the catalyst. The fuel heating operation by the glow plug is executed when the divided temperature injection amount for raising the catalyst per divided fuel injection is set larger than the minimum limit injection amount of the fuel injection valve. It is.

  In addition, when the catalyst temperature rising split injection is executed a plurality of times within the catalyst temperature rising injection possible period, the opening period of the fuel injection valve per one catalyst temperature rising divided injection is When it is set longer than the shortest valve opening period, the fuel heating operation by the glow plug is executed.

  According to these, it is possible to reliably ignite the fuel injected by the catalyst temperature increase divided injection while executing the required number of times of catalyst temperature increase divided injection within the catalyst temperature increase injection possible period. Become. In other words, it is necessary to reliably ignite the fuel injected by the catalyst temperature rising injection, to avoid a situation in which the torque of the internal combustion engine greatly increases, and to generate heat necessary for raising the catalyst temperature to the activation temperature. It is possible to simultaneously supply energy to the exhaust system.

  In addition, it is ideal that the above-mentioned catalyst temperature raising injection does not increase the torque of the internal combustion engine. However, a part of the injection is converted into torque depending on the load region of the internal combustion engine and the temperature environment. There is a possibility that. The following can be cited as countermeasures in this case.

  That is, when a surplus torque resulting from the catalyst temperature raising injection occurs as the generated torque of the internal combustion engine, a torque substantially equal to the surplus torque resulting from the catalyst temperature raising injection is subtracted from the torque resulting from the main injection. In this way, there is provided an injection amount correction means for correcting the decrease in the injection amount of the main injection.

  According to this, it is possible to cancel the torque increase caused by the catalyst temperature increase injection and the torque decrease due to the main fuel reduction correction, and the torque step at the start of the catalyst temperature increase injection is It will hardly occur. That is, a torque obtained by adding the torque generated due to the catalyst temperature increase injection and the torque generated due to the main injection after the reduction is obtained as a torque substantially equal to the target torque. As a result, the torque of the internal combustion engine can be appropriately obtained and good drivability can be obtained while the catalyst temperature can be rapidly raised to the activation temperature as described above.

  Further, the injection amount correction means corrects the injection amount of the main injection by a predetermined reduction correction amount in accordance with the execution of the catalyst temperature increase injection, and even if this reduction correction is performed, the catalyst temperature increase When the surplus torque resulting from the injection for the engine remains, the additional reduction correction amount corresponding to the remaining surplus torque is obtained, and the injection amount of the main injection is further reduced by this additional reduction correction amount. Has been. Further, when the injection amount correction means corrects the injection amount of the main injection by the preset reduction correction amount, and the torque shortage occurs due to the reduction correction, the torque shortage amount An increase correction amount corresponding to the above is obtained, and the injection amount of the main injection is increased and corrected by this increase correction amount.

  According to this, it is possible to appropriately obtain a reduction correction amount with respect to the injection amount of the main injection, it is possible to eliminate a torque step at the start of the catalyst temperature increase injection, and further improve drivability. be able to.

  In this case, the injection amount correcting means determines whether or not surplus torque resulting from the catalyst temperature increase injection is generated for each cylinder of the internal combustion engine, and only for the cylinder in which the surplus torque is generated. It is configured to perform main fuel reduction correction. Further, when a torque shortage occurs due to this reduction correction, an increase correction amount corresponding to the torque shortage is obtained, and the main injection amount is increased and corrected by this increase correction amount. ing.

  Even if the same amount of catalyst temperature increase injection is performed for each cylinder at the same timing, the work amount in each cylinder may vary. According to this means for solving the problem, it is possible to eliminate the surplus torque even when such a variation in the work amount between the cylinders occurs.

  In the present invention, in the compression ignition type internal combustion engine, after the main injection is performed, the catalyst temperature increase injection specialized for the catalyst temperature increase is performed, and the fuel injected by the catalyst temperature increase injection is Most of the energy generated upon combustion is supplied as heat energy to the exhaust system. As a result, even when the catalyst bed temperature is relatively low, such as during cold start of an internal combustion engine or during light load operation, high temperature combustion gas should be present in the exhaust system, especially around the catalyst. And the catalyst temperature can be rapidly raised to the activation temperature. In addition, since the situation where the torque of the internal combustion engine greatly increases due to the execution of the catalyst temperature raising injection is not caused, an appropriate torque of the internal combustion engine can be obtained, and the drivability is not deteriorated.

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 portion. FIG. 3 is a block diagram showing a configuration of a control system such as an ECU. FIG. 4 is a diagram showing each injection pattern of pilot injection, main injection, and exhaust heat injection, and changes in in-cylinder pressure and in-cylinder temperature in the case where three exhaust heat split injections are executed. . FIG. 5 is a diagram showing each injection pattern of pilot injection, main injection, and exhaust heat split injection in Modification 1. FIG. 6 is a diagram showing each injection pattern of pilot injection, main injection, and exhaust heat split injection in Modification 2. FIG. 7 is a diagram showing each injection pattern of pilot injection, main injection, and exhaust heat injection in Modification 4. FIG. 8 is a timing chart showing the execution timing of the temperature increase control and the change in the engine work amount in Modification 4. FIG. 9 is a diagram showing each injection pattern of pilot injection, main injection, and exhaust heat injection in Modification 5. FIG. 10 is a view showing a main injection additional reduction correction map. FIG. 11 is a timing chart showing an execution timing of temperature increase control and a change in engine work amount in Modification 5.

Explanation of symbols

1 engine (internal combustion engine)
12 Cylinder bore 19 Glow plug 23 Injector (fuel injection valve)
77 Maniverter (catalyst)

  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. FIG. 2 is a cross-sectional view showing the combustion chamber 3 of the diesel engine and its periphery.

  As shown in FIG. 1, the engine 1 according to the present embodiment is a diesel engine system that includes 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 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, which will be described later, is disposed in the exhaust passage. Yes. Hereinafter, the NSR catalyst 75 and the DPNR catalyst 76 will be described.

The NSR catalyst 75 is an NOx storage reduction catalyst. For example, alumina (Al ₂ O ₃ ) is used as a 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 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.

  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 that 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, this engine 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 5B and a compressor wheel 5C that are connected via a turbine shaft 5A. The compressor wheel 5C is disposed facing the inside of the intake pipe 64, and the turbine wheel 5B is disposed facing the inside of the exhaust pipe 73. Therefore, the turbocharger 5 performs a so-called supercharging operation in which the compressor wheel 5C is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 5B 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 5B 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.

-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 of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  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. Further, the ECU 100 also executes fuel injection control of an injector 23 described later.

  The fuel injection pressure at the time of executing the fuel injection of the injector 23 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, the higher the engine load (engine load), and the engine speed (engine speed). The higher the value, the higher. That is, when the engine load is high, the amount of air sucked into the combustion chamber 3 is large, so that the pressure in the combustion chamber 3 in the injector 23 must be high and a large amount of fuel must be injected. It is necessary to increase the injection pressure. Further, since the injection time is short when the engine speed is high, the amount of fuel injected per unit time must be increased, and therefore the injection pressure from the injector 23 must be increased. Thus, the target rail pressure is generally set based on the engine load and the engine speed.

  As for fuel injection parameters in fuel injection such as main injection, which will be described later, the optimum values vary depending on the temperature conditions of the engine, intake air, and the like.

  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 and obtains the depression amount (accelerator opening) to the accelerator pedal based on the detection value of the accelerator opening sensor 47. The fuel injection amount is determined based on the engine speed and the accelerator opening.

  Further, the ECU 100 sets the fuel injection mode (pilot injection, main injection, etc.) from the injector 23 based on the engine speed and the fuel injection amount. Hereinafter, the outline of each injection form in the present embodiment will be described.

(Pilot injection)
Pilot injection (sub-injection) is an injection operation that injects a small amount of fuel in advance prior to main injection (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 is an injection operation (preheating fuel supply operation) for ensuring good ignitability of the fuel injected in the main injection. That is, the function of pilot injection in the present embodiment is specialized for preheating in the cylinder.

Specifically, in the pilot injection in the present embodiment, in order to optimize the distribution of the spray and the local concentration, the injection rate is set to the minimum injection rate (for example, the injection amount per injection 1.5 mm ³ ), and a plurality of injection rates are used. By executing the number of pilot injections, the total pilot injection amount necessary for this pilot injection is ensured. More specifically, the number of pilot injections is determined by the following equation (1).

N = {(Ca · ΔT) · Kc · Kv} / (J · η) (1)
(N: number of pilot injections, Ca: heat capacity of air introduced into the cylinder, ΔT: temperature of unsatisfied auto-ignition temperature, Kc: heat capacity correction coefficient based on EGR rate, Kv: target space for combustion contribution, J: theoretical calorific value of 1.5 mm ³ , η: fuel efficiency)
Here, the temperature ΔT that does not reach the self-ignition temperature is the target gas fuel ignition timing at the time of main injection (for example, the time when the piston 13 reaches compression top dead center) and the fuel self-ignition. This is a difference from the temperature, and corresponds to the amount of heat necessary to make the compressed gas temperature at the target ignition timing reach the self-ignition temperature of the fuel. Note that the above formula (1) sets the pilot injection amount per time to a fixed value (for example, 1.5 mm ³ ), and secures the necessary total pilot injection amount by setting the number of injections. . The fixed value of the pilot injection amount is not limited to the above value.

  In addition, the interval of the pilot injection that is divided and injected in this way is determined by the responsiveness of the injector 23 (speed of opening and closing operation). In the present embodiment, it is set to 200 μs, for example. The pilot injection interval is not limited to the above value.

  Further, the injection start timing of this pilot injection is set by the following equation (2), for example, at a crank angle and before 80 ° of compression top dead center (BTDC) of the piston 13. In addition, the angle said below means the value converted into the rotation angle of the crankshaft.

Pilot injection start angle = Pilot combustion end angle + Pilot injection period working angle + (Crank angle converted value of required combustion time in one pilot injection × N + Crank angle converted value of ignition delay time−Crank angle converted value of overlap time) (2)
Here, the pilot combustion end angle is an angle set in order to complete combustion by pilot injection before the start of pre-injection. The ignition delay time is a time delay from when the pilot injection is executed until the fuel is ignited. Further, the overlap time is the overlap time between the fuel combustion period by the pilot injection executed in advance and the fuel combustion period by the pilot injection executed subsequently (two combustions are performed simultaneously). Time) and the combustion period of the fuel from the final pilot injection and the combustion period of the fuel from the subsequent pre-injection.

(Pre-injection)
The pre-injection is an injection operation (torque generating fuel supply operation) for suppressing the initial combustion speed by the main injection and leading to stable diffusion combustion. Specifically, in the present embodiment, the total injection amount (the injection amount in the pre-injection and the total injection amount for obtaining 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. The pre-injection amount is set to 10% with respect to the injection amount in the main injection).

In this case, when the total injection amount is less than 15 mm ³ , the injection amount in the pre-injection is less than the minimum limit injection amount (1.5 mm ³ ) of the injector 23, so the pre-injection is not executed. become. 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.

  Further, the injection start angle of this pre-injection is set by the following equation (3).

Pre-injection start angle = Pre-combustion end angle + Pre-injection period working angle + (Crank angle conversion value of combustion required time in pre-injection + Crank angle conversion value of ignition delay time−Crank angle conversion value of overlap time) (3) )
Here, the ignition delay time is a time delay from when the pre-injection is executed until the fuel is ignited. Further, the overlap time is an overlap between the fuel combustion period by the pre-injection executed in advance and the fuel combustion period by the pre-injection executed subsequently in the case where a plurality of pre-injections are performed. Time (time during which two combustions are performed simultaneously), and the overlap time between the combustion period of the fuel by the final pre-injection and the combustion period of the fuel by the subsequent main injection, and the final This is the overlap time between the fuel combustion period by pilot injection and the fuel combustion period by pre-injection.

(Main injection)
The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. Specifically, in the present embodiment, the injection in the pre-injection is performed from the total injection amount for obtaining the required torque that is determined according to the operating state such as the engine speed, the accelerator operation amount, the cooling water temperature, the intake air temperature, and the like. It is set as the injection amount obtained by subtracting the amount.

  Further, the injection start angle of the main injection is set by the following equation (4).

Main injection start angle = Main ignition timing + Main injection period working angle + (Crank angle conversion value of combustion required time in main injection + Crank angle conversion value of ignition delay time−Crank angle conversion value of overlap time) (4)
Here, the ignition delay time is a time delay from when the main injection is executed until the fuel is ignited. The overlap time is defined as the overlap time between the fuel combustion period by the pre-injection and the fuel combustion period by the main injection, and the overlap between the fuel combustion period by the main injection and the fuel combustion period by the after injection. Lap time.

(Exhaust heat injection)
In the present embodiment, the catalyst temperature raising injection (hereinafter referred to as exhaust heat injection) is executed as an injection mode different from the conventional injection mode (pilot injection, pre-injection, main injection, after-injection, post-injection). It is a feature. This exhaust heat injection is an injection operation for increasing the temperature of the maniverter 77 provided in the exhaust system. A specific injection control operation of the exhaust heat injection will be described later.

(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. .

  In the description of the fuel injection mode described above, conventionally well-known after-injection has not been described, but after-injection may be executed after the main injection, if necessary. In this case, the exhaust heat injection is performed after the after injection is executed.

-Control operation of exhaust heat injection-
The exhaust heat injection control operation, which is an injection operation characteristic of the present embodiment, will be specifically described below.

As described above, the exhaust heat injection is an injection operation for increasing the temperature of the maniverter 77 provided in the exhaust system. Specifically, in the present embodiment, the exhaust heat injection is performed at a timing at which most of the combustion energy of the fuel supplied by the exhaust heat injection is obtained as the heat energy of the exhaust gas without being almost converted into the engine torque. I am trying to do it. Also in this exhaust heat injection, as in the case of the pilot injection and the pre-injection described above, basically, the minimum injection rate (for example, the injection amount per injection is 1.5 mm ³ ), and the exhaust heat is repeated a plurality of times. By executing injection (hereinafter, this divided exhaust heat injection is referred to as “exhaust heat split injection”), a total exhaust heat injection amount necessary for this exhaust heat injection is ensured.

  Hereinafter, the control operation for executing the exhaust heat injection will be specifically described.

(Injection rate)
In the present embodiment, in order to optimize spray distribution and local concentration, the injection rate of the exhaust heat split injection is set to a minimum injection rate (for example, an injection amount of 1.5 mm ³ per time), and a plurality of times By executing the exhaust heat division injection, the total exhaust heat injection amount necessary for the exhaust heat injection is ensured.

For example, when the total exhaust heat injection amount is 3 mm ³ , 1.5 mm ³ exhaust heat division injection that is the minimum limit injection amount of the injector 23 is performed twice. When the total exhaust heat injection amount is 4.5 mm ³ , 1.5 mm ³ exhaust heat split injection, which is the minimum limit injection amount of the injector 23, is performed three times. Further, when the total exhaust heat injection amount is 5 mm ³ , 1.5 mm ³ exhaust heat split injection that is the minimum limit injection amount of the injector 23 is performed twice, and then 2.0 mm ³ exhaust heat is performed. Split injection is performed once. Further, when the total exhaust heat injection amount was 2.0 mm ^3, the exhaust heat split injection of 1.5 mm ³ which is the minimum limit injection amount of the injectors 23 is performed twice, required injection amount or the exhaust heat The injection amount is ensured.

FIG. 4 shows each injection pattern of pilot injection, main injection, and exhaust heat injection when exhaust heat split injection is executed three times (for example, when the total exhaust heat injection amount is 4.5 mm ³ ), and The changes in the in-cylinder pressure and the in-cylinder temperature are shown. The pre-injection or after-injection may be performed as necessary.

  As shown in this figure, in each exhaust heat split injection constituting the exhaust heat injection, the lift amount of the needle valve provided in the injector 23 is limited and the injection at the minimum injection rate is performed.

  In this way, the exhaust heat split injection at the minimum limit injection amount is executed a plurality of times to ensure the total exhaust heat injection amount.

In addition, it replaces with what makes the injection form at the time of exhaust heat division | segmentation injection the minimum limit injection amount (1.5mm < ³ >) of the injector 23, and the injection form at once of exhaust heat division | segmentation injection is the injector 23 The shortest valve opening period (for example, 200 μs) may be set.

(Total exhaust heat injection amount)
Further, the total exhaust heat injection amount is calculated based on the temperature of the manipulator 77 and its activation temperature. That is, the total exhaust heat injection amount is set to be larger as the temperature of the manipulator 77 is lower than the activation temperature (calculation of the total catalyst temperature increase injection amount by the total catalyst temperature increase injection amount calculation means). Operation). Specifically, the total exhaust heat injection amount is calculated by comparing the sensing value from the temperature sensor for detecting the temperature of the manipulator 77 with the catalyst activation temperature stored in advance.

  The total exhaust heat injection amount may be calculated by estimating the temperature of the manipulator 77 and comparing the estimated temperature with a pre-stored catalyst activation temperature. In this case, as a temperature estimation operation of the manipulator 77, a catalyst temperature estimation map for estimating the temperature of the maniverter 77 from the engine speed and the engine load (throttle valve opening etc.) is stored in the ROM 102, and this catalyst temperature is stored. The temperature of the manipulator 77 is estimated by fitting the current engine speed and engine load to the estimation map. Further, the temperature of the manipulator 77 may be estimated from the exhaust gas temperature. For example, an exhaust temperature sensor is also provided on the upstream side of the manipulator 77, and the temperature of the maniverter 77 is estimated based on the exhaust gas temperature detected by the exhaust temperature sensor 45 upstream and downstream of the manipulator 77.

(Injection interval)
Furthermore, when performing multiple times of exhaust heat division | segmentation injection, the injection interval which is a time interval between each exhaust heat division | segmentation injection is calculated | required as follows. That is, the interval of each exhaust heat split injection is determined by the responsiveness of the injector 23 (speed of opening / closing operation). For example, the shortest opening / closing period determined by the performance of the injector 23 is set to 200 μs, for example. The interval of this exhaust heat division injection is not limited to the above value.

(Injection period)
The injection period of the exhaust heat injection is set to a period in which the following two conditions are both satisfied.
(1) The in-cylinder temperature is equal to or higher than the fuel self-ignition temperature.
(2) The combustion speed of the fuel when exhaust heat injection is executed is not more than a predetermined speed.

  Here, the self-ignition temperature of the fuel changes according to the pressure in the combustion chamber 3. That is, the higher the pressure in the combustion chamber 3, the lower the fuel self-ignition temperature. For this reason, for example, a map for obtaining the self-ignition temperature corresponding to the pressure in the combustion chamber 3 is stored in the ROM 102, and the self-ignition temperature of the fuel is obtained by referring to this map.

  Further, the combustion speed of the fuel when exhaust heat injection is performed has a correlation with the amount by which the combustion energy is extracted as torque (kinetic energy) of the engine 1. That is, the higher the combustion speed, the larger the ratio of the conversion amount to kinetic energy with respect to the total amount of combustion energy. Conversely, the ratio of the amount of conversion to heat energy given to the exhaust system becomes small. For this reason, in order to ensure a large amount of heat energy given to the exhaust system, it is necessary to suppress the combustion speed of the fuel to a predetermined speed or less.

  By executing the exhaust heat injection during the period when both of the above two conditions are satisfied, it is possible to convert most of the energy generated by the combustion of the fuel injected by the exhaust heat injection as heat energy given to the exhaust system. It becomes. In the graph showing the change in the in-cylinder temperature in FIG. 4, as shown by the broken line, the in-cylinder temperature is equal to or higher than the self-ignition temperature of the fuel (the lower limit value of the self-ignition temperature), and the combustion speed is a predetermined speed. Exhaust heat split injection is executed three times in a period (hereinafter referred to as “catalyst temperature increase injection possible period”) that is equal to or less than the upper limit value of the in-cylinder temperature.

  Further, in the graph showing the change in the in-cylinder pressure in FIG. 4, the combustion of the fuel injected during the injection period of the exhaust heat injection affects the torque of the engine 1 (results in an increase in torque). Values are shown with dashed lines. That is, if the in-cylinder pressure is equal to or less than this broken line, the fuel injected by the exhaust heat injection does not affect the torque of the engine 1. In the case shown in FIG. 4, since the combustion speed is suppressed to a predetermined speed or less, the in-cylinder pressure during the injection period of the exhaust heat injection is suppressed low, and the fuel injected by the exhaust heat injection is It can be seen that the torque is not affected.

As described above, after the injection rate of the exhaust heat split injection, the total exhaust heat injection amount, the injection interval of the exhaust heat split injection, and the injection period of the exhaust heat injection are obtained, the exhaust heat injection is executed according to these values. Thus, the fuel injection control of the injector 23 is performed. That is, as described above, the exhaust heat split injection is executed a plurality of times at the minimum injection rate (for example, the injection amount per injection 1.5 mm ³ ) (intermittent fuel by the catalyst temperature increase injection execution means). Injecting operation), the injector 23 is controlled so as to secure the total exhaust heat injection amount (Qp) necessary for this exhaust heat injection.

  By executing the exhaust heat split injection as described above, the fuel injection amount per one time of the exhaust heat split injection is small. For this reason, the amount of heat absorbed by the endothermic reaction of the fuel at the time of exhaust heat split injection is small, there is no ignition delay of exhaust heat injection, and the ignitability of the fuel injected by exhaust heat injection is ensured well. ing. Thereby, the thermal energy obtained by burning the fuel injected by the first exhaust heat split injection improves the ignitability of the fuel injected by the second exhaust heat split injection thereafter. It is used as heat energy for Further, the thermal energy obtained by burning the fuel injected by the second exhaust heat split injection improves the ignitability of the fuel injected by the third exhaust heat split injection thereafter. It is used as heat energy for In this way, by performing exhaust heat split injection in a plurality of stages, a chained fuel combustion operation can be obtained.

  As described above, in the present embodiment, the exhaust gas split injection is executed a plurality of times at the minimum injection rate, so that most of the combustion gas of the fuel injected by the exhaust heat injection is converted into thermal energy. It will be sent to the exhaust system. In other words, the combustion gas of the fuel injected by the exhaust heat injection hardly acts as an increase in the torque of the engine 1, and the energy of the combustion gas is consumed as the heat energy for raising the temperature of the manipulator 77. It is. For this reason, for example, even when the catalyst bed temperature is relatively low, such as during cold start of the engine 1 or during light load operation, high temperature combustion gas is generated in the exhaust system, particularly around the catalyst. It can be present and the catalyst temperature can be rapidly raised to the activation temperature. Moreover, since the situation where the torque of the engine 1 increases significantly due to the execution of the exhaust heat injection does not occur, an appropriate torque can be obtained for the engine 1, and the drivability does not deteriorate.

  The fuel injected by the exhaust heat injection does not need to be completely combusted in the cylinder, and the combustion proceeds while flowing through the exhaust passage, and when the fuel reaches the manipulator 77, a predetermined temperature rise (for example, 100 deg) It is only necessary that the effect of temperature increase) can be exhibited.

  Also, by dividing the total exhaust heat injection amount required for exhaust heat injection by multiple exhaust heat split injections, the penetration force of fuel injected by this exhaust heat split injection can be kept low, thereby This fuel can be prevented from adhering to the inner wall surface of the cylinder. Thereby, the dilution of the lubricating oil with the fuel and the occurrence of the bore flushing can be prevented. Further, the amount of HC and CO generated in the exhaust gas caused by the fuel adhering to the inner wall surface of the cylinder can be greatly reduced, and the generation of smoke can be suppressed, so that exhaust emission can be improved.

-Modification 1-
Next, a modified example of the injection period of the exhaust heat injection will be described. In the embodiment described above, the injection period of the exhaust heat injection includes (1) that the in-cylinder temperature is equal to or higher than the fuel self-ignition temperature, and (2) the fuel combustion speed when the exhaust heat injection is executed. Is set to a period in which both of the two conditions are satisfied. In this modification, instead of that, the injection period of the exhaust heat injection is set as described below.

  That is, as shown in FIG. 5, after the main injection is performed, the fuel can be burned when the fuel is injected (the region below the one-dot chain line in FIG. A region where combustion of fuel injected by exhaust heat injection is not converted into torque of the engine 1 (region below the broken line in FIG. 5 is not converted into torque of the engine 1) The exhaust heat split injection is executed within the range (within the range where the two regions overlap). In FIG. 5, as in the case of the above-described embodiment, the injection amount of each exhaust heat division injection is set to the minimum limit injection amount of the injector 23.

  Even when the injection period of the exhaust heat injection is set in this way, as in the above-described embodiment, most of the energy from the combustion of the fuel injected by the exhaust heat injection is converted as heat energy given to the exhaust system. For example, even when the catalyst bed temperature is relatively low, such as during cold start of the engine 1 or during light load operation, the exhaust system, particularly around the catalyst, has a high temperature. Combustion gas can be present and the catalyst temperature can be rapidly raised to the activation temperature. Moreover, since the situation where the torque of the engine 1 increases significantly due to the execution of the exhaust heat injection does not occur, an appropriate torque can be obtained for the engine 1, and the drivability does not deteriorate.

-Modification 2-
FIG. 6A to FIG. 6C show an exhaust heat injection pattern in a further modification of the above-described exhaust heat injection period. In any injection pattern, as in the case described above, after the main injection is performed, the fuel can be burned when the fuel is injected (the region below the one-dot chain line in the figure). And the exhaust heat split injection is executed within a range where the combustion of the fuel injected by the exhaust heat injection is not converted into the torque of the engine 1 (a region below the broken line in the figure). ing.

  In FIG. 6A, the injection timing of each exhaust heat divided injection is the same as that described above, but the injection amount of the second exhaust heat divided injection (lift amount of the injector 23) is other exhaust heat. It is set more than that of split injection. In the injection pattern shown in FIG. 6B, the injection timing of each exhaust heat division injection is shifted to the advance side, and the injection amount is set to be larger as the exhaust heat division injection on the retard side. Further, in the injection pattern shown in FIG. 6C, the injection timing of each exhaust heat division injection is shifted to the retard side, and the injection amount is set to be larger for the advance side exhaust heat division injection. Regardless of the injection pattern, each exhaust heat split injection is executed in a region where the fuel can be burned and the fuel injected by the exhaust heat injection is not converted into the torque of the engine 1. Therefore, most of the energy generated by combustion of the fuel injected by the exhaust heat injection is converted as heat energy given to the exhaust system, and the catalyst temperature can be rapidly raised to the activation temperature. . Moreover, since the situation where the torque of the engine 1 increases significantly due to the execution of the exhaust heat injection does not occur, an appropriate torque can be obtained for the engine 1, and the drivability does not deteriorate.

-Modification 3-
Next, Modification 3 will be described. As in the embodiment and the modification described above, the exhaust heat split injection amount per exhaust heat split injection is set to the minimum limit injection amount of the injector 23, or the injector 23 is opened per exhaust heat split injection. When the period is set to the shortest valve opening period, there is a possibility that the required number of exhaust heat split injections cannot be executed within the above-described catalyst temperature increase injection possible period. In particular, this is a case where the catalyst temperature rising injection possible period is short. As countermeasures in this case, the exhaust heat injection amount per exhaust heat split injection is set to be larger than the minimum limit injection amount of the injector 23, or the valve opening period of the injector 23 per exhaust heat split injection is set. It is necessary to set longer than the shortest valve opening period.

  In this case, with the increase in the amount of exhaust heat injection, there is a possibility that the ignitability may not be ensured, so in this modification, in such a situation, the heating operation by the glow plug 19 is performed, The ignitability of the fuel injected by the exhaust heat split injection is ensured. That is, in conjunction with the start of the exhaust heat injection or prior to the start of the exhaust heat injection, the glow plug 19 is energized so that the glow plug 19 is heated red.

  The heating operation by the glow plug 19 may be performed only when the first exhaust heat split injection is performed, or may be performed when all the exhaust heat split injections are performed.

  This makes it possible to reliably ignite the fuel injected by the exhaust heat split injection while executing the required number of exhaust heat split injections within the above-described catalyst temperature increase injection possible period. That is, the fuel injected by the exhaust heat injection is surely ignited, the situation in which the torque of the engine 1 is greatly increased, and the thermal energy required to raise the catalyst temperature to the activation temperature are obtained. It is possible to simultaneously supply the exhaust system.

-Modification 4-
Next, Modification 4 will be described. In this modification, when the exhaust heat injection is executed, an engine torque resulting from the exhaust heat injection is generated, and the total engine torque is obtained by the required torque (as described above, originally the pre-injection and the main injection). The present invention relates to a countermeasure for the case where the torque increases more than the power torque.

  In this modification, when the torque is increased due to the exhaust heat injection (when surplus torque is generated), the injection amount of the main injection is corrected to be reduced and substantially equal to the surplus torque. Is reduced from the torque resulting from the main injection (injection amount reduction correction operation by the injection amount correction means). This will be specifically described below.

  FIG. 7 shows each injection pattern of pilot injection, main injection, and exhaust heat injection when torque due to exhaust heat injection is generated in the engine 1 and the main injection reduction correction is performed. The pre-injection or after-injection may be performed as necessary.

  The broken lines shown in FIG. 7 indicate the injection pattern of the main injection before the injection amount of the main injection is corrected for reduction. In addition, the injection pattern of the main injection indicated by the solid line in FIG. 7 is an injection pattern after the injection amount of the main injection is corrected for reduction. In this way, the injection amount of the main injection is corrected to decrease by advancing the injection end timing of the main injection (correcting to the advance side). In the example shown in FIG. 7, only one injection is performed as the exhaust heat injection, but as described above, the exhaust heat division is divided into a plurality of parts in order to secure the necessary total exhaust heat injection amount. You may make it perform injection.

  A specific control procedure for correcting the amount of main injection to be reduced will be described below.

  First, before the exhaust heat injection is performed (before the temperature increase control is performed), so-called inter-cylinder correction control is performed, and work equalization (combustion torque generation) by combustion of the air-fuel mixture in each cylinder is performed. The fuel injection amount is corrected so as to achieve equalization. That is, the fuel injection control is performed so that the work amount of the engine 1 substantially matches the requested target work amount.

  Then, for example, when the temperature of the manipulator 77 is lowered due to the continued light load operation or the like and the temperature needs to be raised, the exhaust heat injection is started. It is ideal that the exhaust heat injection should not increase the torque of the engine 1. However, depending on the load region of the engine 1, the temperature environment, and the like, the fuel injected by the exhaust heat injection There is a possibility that a part of energy generated by combustion is converted into torque. When the torque increases due to the exhaust heat injection and the surplus torque is generated, the injection amount of the main injection is corrected to decrease according to the injection amount in the exhaust heat injection (FIG. 7). (Refer to the injection pattern of the main injection shown by the solid line).

  In this case, the operation of determining whether torque due to exhaust heat injection has occurred (whether a torque step has occurred with the start of exhaust heat injection) or not is performed in each cylinder before the exhaust heat injection is performed. Detects the difference between the total value of the work generated by the combustion of the air (corresponding to the amount converted to torque) and the total value of the work generated by the combustion of the air-fuel mixture in each cylinder after execution of exhaust heat injection Is done. This calculation of the amount of work is based on the difference in rotation fluctuation of each cylinder in each cycle (for example, the engine rotation speed before the compression top dead center of the piston and the maximum engine rotation speed after the expansion stroke starts (for example, compression of the piston). It is calculated on the basis of the difference between the engine speed at a position of 20 ° CA after top dead center.

  When the torque increases due to the exhaust heat injection, the injection amount of the main injection is corrected to decrease in accordance with the injection amount of the exhaust heat injection. In this case, the exhaust heat injection A main injection reduction correction map defining the relationship between the injection amount and the main injection reduction correction amount is stored in advance in the ROM 102, and the main injection reduction correction amount is determined according to the main injection reduction correction map. The main injection reduction correction map is created in advance through experiments, simulations, and the like.

  FIG. 8 is a diagram showing the execution timing of the temperature increase control (exhaust heat injection control) and the change in the work amount of the engine 1 in the present modification.

  First, when the temperature increase control is executed (temperature increase control ON) from the non-execution state of the temperature increase control (temperature increase control OFF) (timing T1), and the torque caused by the exhaust heat injection is generated, Work volume increases. This is detected by the above-described work amount calculation operation, and when the next temperature increase control is executed (temperature increase control ON) (timing T2), the above-described injection amount reduction correction (main By performing the main fuel injection reduction correction amount based on the fuel injection reduction correction map, the torque increase due to the exhaust heat injection is offset from the torque reduction due to the main injection reduction correction. Thus, a torque step at the start of the temperature raising control hardly occurs. In other words, the sum of the torque generated due to the exhaust heat injection and the torque generated due to the main injection after the reduction is obtained as a torque substantially equal to the target torque (torque before the temperature increase control is executed). Therefore, it is possible to avoid an increase in the work amount. As a result, the torque of the engine 1 can be appropriately obtained and good drivability can be obtained while the catalyst temperature can be rapidly raised to the activation temperature as described above.

  In the fourth modification, when the torque caused by the exhaust heat injection is generated and the work amount of the engine 1 is increased, the injection amount reduction correction of the main injection is performed at the next execution of the temperature raising control. . This is to suppress torque fluctuation during the temperature rise control. Instead, when the torque caused by the exhaust heat injection is generated and the work amount of the engine 1 is increased, the main work injection amount is corrected to be reduced in the middle of the temperature increase control to obtain an appropriate work amount. May be obtained early.

  In this modification, when the injection amount of the main injection is reduced and corrected by the preset reduction correction amount (the reduction correction amount obtained from the main injection reduction correction map), the reduction correction is performed. When a torque shortage occurs, an increase correction amount corresponding to the torque shortage amount may be obtained, and the injection amount of the main injection may be increased and corrected by this increase correction amount.

-Modification 5-
Next, Modification 5 will be described. This modified example also relates to a countermeasure when the exhaust heat injection is executed and the engine torque resulting from the exhaust heat injection is generated and the total engine torque is increased from the required torque.

  In this modification, even if the control operation of the modification 4 described above is performed, if the engine torque (surplus torque) due to the exhaust heat injection still remains, the injection amount in the main injection is additionally reduced. Then, a torque substantially equal to this surplus torque is reduced from the torque resulting from the main injection.

  FIG. 9 shows each injection pattern of pilot injection, main injection, and exhaust heat injection when torque resulting from exhaust heat injection is generated in the engine 1 and additional reduction correction of main injection is performed. The pre-injection or after-injection may be performed as necessary.

  The broken lines shown in FIG. 9 indicate the injection pattern of the main injection before the injection amount of the main injection is corrected for reduction. In addition, an alternate long and short dash line in FIG. 9 indicates the injection pattern of the main injection when the amount of main injection is corrected to be reduced by the control operation of the fourth modification. And the continuous line shown in FIG. 9 has shown the injection pattern of the main injection after carrying out the additional amount reduction correction | amendment of the injection quantity of the main injection. As described above, the injection amount of the main injection is corrected to be further reduced by advancing the injection end timing of the main injection (correcting to the advance side). In the case shown in FIG. 9 as well, only one injection is performed as the exhaust heat injection, but as described above, the exhaust divided into a plurality of parts to ensure the required total exhaust heat injection amount. You may make it perform heat division | segmentation injection.

  A specific control procedure for correcting the amount of main injection to be additionally reduced will be described below.

  If engine torque resulting from exhaust heat injection still remains after performing the control operation of the above-described modification 4, the difference in actual work amount with respect to the target work amount is extracted for each cylinder. That is, the increase in the work after the exhaust heat injection is executed is extracted for each cylinder with respect to the work for each cylinder before the exhaust heat injection is executed. As described above, the extraction of the work amount for each cylinder can be calculated based on the rotational fluctuation difference in each cycle of each cylinder.

  In this way, after individually obtaining an increase in the work amount for each cylinder resulting from the execution of the exhaust heat injection, the main injection is performed for each cylinder so as to reduce the increased work amount. Perform weight loss correction. The main injection reduction correction operation for each cylinder is performed in the ROM 102 by adding a main injection additional reduction correction map that defines the relationship between the work amount difference and the main injection reduction correction amount (equivalent to the injection amount) as shown in FIG. The additional reduction correction amount of the main injection is determined according to the main injection additional reduction correction map stored in advance. For example, when the work difference is A on the main injection additional reduction correction map, the main injection reduction correction amount is obtained as B on the main injection additional reduction correction map. The main injection additional reduction correction map is created in advance by experiments, simulations, or the like.

  FIG. 11 is a diagram showing the execution timing of the temperature increase control (exhaust heat injection control) and the change in the work amount of the engine 1 in the present modification.

  First, when the temperature increase control is executed (temperature increase control ON) from the non-execution state of the temperature increase control (temperature increase control OFF) (timing T1), and the torque caused by the exhaust heat injection is generated, Work volume increases. This is detected by the above-described work amount calculation operation, and when the next temperature increase control is executed (temperature increase control ON) (timing T2), the above-described injection amount reduction correction (main Main fuel injection reduction correction by the reduction correction amount obtained from the injection reduction correction map).

  In this case, when the engine torque due to the exhaust heat injection still remains (see the remaining surplus work amount in FIG. 11), the next temperature increase control is executed (temperature increase control ON) (timing T3). ), The main injection reduction correction is performed individually for each cylinder by the additional reduction correction amount obtained from the main injection additional reduction correction map. As a result, the increase in torque caused by the exhaust heat injection and the decrease in torque due to the correction for reducing the amount of main injection cancel each other out, and there is almost no torque step at the start of temperature rise control. become. In other words, the sum of the torque generated due to the exhaust heat injection and the torque generated due to the main injection after the reduction is obtained as a torque substantially equal to the target torque (torque before the temperature increase control is executed). Therefore, it is possible to avoid an increase in the work amount. As a result, the torque of the engine 1 can be appropriately obtained and good drivability can be obtained while the catalyst temperature can be rapidly raised to the activation temperature as described above.

  In the fifth modification as well, when torque due to the exhaust heat injection is generated and the work amount of the engine 1 is increased, the injection amount reduction correction of the main injection is performed at the next execution of the temperature raising control. Yes. Instead, when torque due to the exhaust heat injection is generated and the work amount of the engine 1 is increased, the injection amount reduction correction and the additional reduction correction are performed during the temperature increase control. An appropriate amount of work may be obtained early.

  Also in this modified example, when the amount of main injection is reduced by the above operation, if the torque shortage occurs due to the reduction correction, the amount of increase correction corresponding to the amount of torque shortage is performed. The amount may be obtained and the injection amount of the main injection may be increased and corrected by this increase correction amount.

-Other embodiments-
The embodiment and the modification described above have described the case where the present invention is applied to an in-line four-cylinder diesel engine mounted on an automobile. 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.

Further, the number of exhaust heat split injections in the exhaust heat injection is not particularly limited, and the present invention is one time when the calculated value of the total exhaust heat injection amount is relatively low (for example, 1.5 mm ³ ). This also includes the case where exhaust heat injection is completed with the injection.

  In the above-described embodiment and modification, the NSR catalyst 75 and the DPNR catalyst 76 are provided as the manipulator 77. However, the NSR catalyst 75 and a DPF (Diesel Particle Filter) may be provided.

  Moreover, in the said modification 4 and the modification 5, when the engine torque resulting from exhaust heat injection has generate | occur | produced, the injection quantity in the said main injection was reduced correction | amendment. In addition to this, reduction correction may be performed for the injection amount in the exhaust heat injection. According to this, the amount of reduction correction with respect to the main injection can be reduced.

  Moreover, in the said modification 4 and modification 5, although the case where the light load driving | operation continued after the completion of warming-up operation of the engine 1 was demonstrated, the temperature of the manipulator 77 fell, the same thing also at the time of cold start By performing the control, it is possible to rapidly raise the manipulator 77 to the activation temperature.

  INDUSTRIAL APPLICABILITY The present invention can be applied to fuel injection control in a case where a catalyst is rapidly raised in a common rail in-cylinder direct injection multi-cylinder diesel engine mounted on an automobile.

Claims (9)

In a fuel injection control device for a compression ignition type internal combustion engine capable of performing a plurality of fuel injections including a main injection that is a fuel injection for generating torque from a fuel injection valve during one cycle of the internal combustion engine,
After the execution of the main injection, by performing the catalyst temperature increase injection that ignites using the thermal energy in the cylinder generated by the combustion of the fuel injected in the main injection, the catalyst temperature increase injection is performed. And a catalyst temperature raising injection execution means for sending most of the energy of the combustion gas of the generated fuel to the exhaust system as heat energy for raising the temperature of the exhaust system catalyst,
The catalyst temperature rise injection execution means is a catalyst temperature rise injection in which the in-cylinder temperature is equal to or higher than the fuel self-ignition temperature and the fuel combustion speed is equal to or lower than a predetermined speed when the catalyst temperature increase injection is executed. A fuel injection control device for an internal combustion engine, characterized in that the injection for raising the catalyst temperature is executed within a possible period. The fuel injection control device for an internal combustion engine according to claim 1,
A total catalyst temperature increase injection amount calculating means for obtaining a total catalyst temperature increase injection amount required in the catalyst temperature increase injection,
The catalyst temperature increase injection execution means intermittently divides the total catalyst temperature increase injection amount obtained by the total catalyst temperature increase injection amount calculation means by a plurality of catalyst temperature increase injections. It is configured to inject from the fuel injection valve,
The fuel injection control device for an internal combustion engine, wherein the catalyst temperature increase divided injection amount per one of the catalyst temperature increase divided injection is set to a minimum limit injection amount of the fuel injection valve. The fuel injection control device for an internal combustion engine according to claim 1,
A total catalyst temperature increase injection amount calculating means for obtaining a total catalyst temperature increase injection amount required in the catalyst temperature increase injection,
The catalyst temperature increase injection execution means intermittently divides the total catalyst temperature increase injection amount obtained by the total catalyst temperature increase injection amount calculation means by a plurality of catalyst temperature increase injections. It is configured to inject from the fuel injection valve,
The fuel injection control device for an internal combustion engine, wherein a valve opening period of the fuel injection valve per one of the catalyst temperature increase divided injections is set to a shortest valve opening period of the fuel injection valve. The fuel injection control device for an internal combustion engine according to claim 2,
The fuel injection control device for an internal combustion engine, wherein the total catalyst temperature increase injection amount calculating means sets the total catalyst temperature increase injection amount as the catalyst temperature is lower than its activation temperature. The fuel injection control device for an internal combustion engine according to claim 1,
A glow plug is provided to assist the ignition by heating the fuel injected into the combustion chamber,
The divided injection amount for raising the catalyst temperature per one of the divided injections for raising the temperature of the catalyst when the divided injection for raising the temperature of the catalyst is executed a plurality of times within the above-described possible period of time for injecting the catalyst temperature A fuel injection control device for an internal combustion engine, wherein the fuel heating operation by the glow plug is executed when the injection amount is set larger than the injection amount. The fuel injection control device for an internal combustion engine according to claim 1,
A glow plug is provided to assist the ignition by heating the fuel injected into the combustion chamber,
The opening period of the fuel injection valve per one of the catalyst temperature increase divided injections when the catalyst temperature increase divided injection is executed a plurality of times within the catalyst temperature increase injection possible period is the shortest opening of the fuel injection valve. A fuel injection control device for an internal combustion engine, wherein the fuel heating operation by the glow plug is executed when set longer than the valve period. The fuel injection control device for an internal combustion engine according to claim 1,
When a surplus torque resulting from the catalyst temperature rise injection is generated as the generated torque of the internal combustion engine, a torque substantially equal to the surplus torque resulting from the catalyst temperature rise injection is subtracted from the torque resulting from the main injection. A fuel injection control device for an internal combustion engine, comprising an injection amount correction means for correcting a reduction in the injection amount of the main injection. The fuel injection control device for an internal combustion engine according to claim 7,
The injection amount correction means corrects the injection amount of the main injection by a preset reduction correction amount in accordance with the execution of the catalyst temperature increase injection, and also performs the catalyst temperature increase injection even if this reduction correction is performed. When the surplus torque due to the residual torque remains, an additional reduction correction amount corresponding to the remaining surplus torque is obtained, and the main injection amount is further reduced by the additional reduction correction amount. When the amount of main injection is reduced by the set amount of reduction correction, if the torque shortage occurs as a result of this reduction correction, the amount of increase correction corresponding to this amount of torque shortage is obtained and this increase A fuel injection control device for an internal combustion engine, wherein the fuel injection control device is configured to increase and correct the injection amount of the main injection by a correction amount. The fuel injection control device for an internal combustion engine according to claim 8,
The injection amount correcting means determines whether or not surplus torque resulting from the catalyst temperature increase injection is generated for each cylinder of the internal combustion engine, and the main injection is performed only to the cylinder in which the surplus torque is generated. While torque reduction is performed, if torque shortage occurs due to this reduction correction, an increase correction amount corresponding to the torque shortage is obtained, and the main injection amount is increased by this increase correction amount. A fuel injection control device for an internal combustion engine, characterized in that it is configured as described above.

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