JP2017008897A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device which can optimize an injection control amount of pilot injection.SOLUTION: A control device of an internal combustion engine calculates an ignition index value Ib which correlates with a temperature of an ignition determination position F on a virtual extension line L1 in which a distance between the virtual extension line L1 of a center line of an injection hole of an injector 23 and an exhaust valve 17 becomes shortest from a state amount of an exhaust gas at a previous cycle, a state amount of a current suction gas, specifications of the exhaust valve 17, and specifications of the injection hole. The control device determines whether or not pilot injection fuel is ignited at the ignition determination position F on the basis of a reference injection control amount which is acquired according to the ignition index value Ib and a current engine operation state. When it is determined that the pilot injection fuel is not ignited, the control device calculates a correction amount of the injection control amount of the pilot injection for making a fuel spray of the pilot injection arrive at the ignition determination position F. The control device corrects the reference injection control amount of the pilot injection by the correction amount, and performs the pilot injection at the corrected injection control amount.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to improved pilot injection control.

  Conventionally, in a diesel engine mounted on a vehicle or the like, pilot injection is executed prior to main injection that contributes to torque generation. Combustion of fuel injected by this pilot injection (hereinafter referred to as pilot injection fuel) is mainly premixed combustion. That is, when the temperature of the space where the spray of the pilot injected fuel exists (compressed gas temperature) reaches the ignition temperature of the fuel (premixed combustion temperature), the pilot injected fuel self-ignites.

  Japanese Patent Application Laid-Open No. H10-260260 discloses that the compressed gas temperature at the target ignition timing is estimated and the pilot injection is executed when the compressed gas temperature is lower than the fuel ignition temperature (diffusion combustion temperature).

JP 2009-167821 A

  However, in an actual cylinder, the compressed gas temperature is not uniform and has a temperature distribution. For example, the temperature around the exhaust valve is higher than the temperature around the intake valve. So far, no proposal has been made for adjusting the injection control amount of pilot injection in consideration of this temperature distribution.

  The inventor of the present invention pays attention to the occurrence of temperature distribution in the cylinder, obtains a value correlated with the compressed gas temperature at a specific position in the cylinder, and based on this value, the injection control amount of pilot injection It was considered that the injection control amount can be optimized by correcting the above.

  The present invention has been made in view of the above points, and an object thereof is to provide a control device capable of optimizing the injection control amount of pilot injection.

  In order to achieve the above object, a solution means of the present invention comprises a fuel injection valve that injects fuel into a cylinder and a compression valve that opens and closes an exhaust port that discharges exhaust gas generated in the cylinder. A control device that is applied to a self-ignition internal combustion engine and that executes pilot injection prior to main injection as fuel injection from the fuel injection valve is assumed. The control device includes an ignition index value calculation unit, a reference injection control amount acquisition unit, an ignition determination unit, a correction amount calculation unit, and a pilot injection command unit. The ignition index value calculation unit is correlated with the temperature at the ignition determination position on the virtual extension line where the distance between the virtual extension line of the center line of the injection hole of the fuel injection valve and the exhaust valve is the shortest. The ignition index value is calculated from the exhaust gas state quantity in the previous cycle of the internal combustion engine, the current intake gas state quantity introduced into the cylinder, the exhaust valve specifications, and the injection hole specifications. To do. The reference injection control amount acquisition unit is a current engine operation state among the reference injection control amount of the pilot injection, the reference injection amount, and the reference injection timing that are defined in advance according to the engine operation state. At least one reference injection control amount corresponding to is acquired. Based on the ignition index value and a reference injection control amount acquired according to the current engine operating state, the ignition determination unit determines whether the fuel injected in the pilot injection is the ignition determination when the pilot injection is executed. It is determined whether or not to ignite at the position. The correction amount calculation unit is configured to perform injection control of the pilot injection for causing the fuel spray of the pilot injection to reach the ignition determination position when the ignition determination unit determines that the fuel injected by the pilot injection does not ignite. A correction amount of the amount is calculated. The pilot injection command unit corrects the reference injection control amount of the pilot injection with the correction amount, and causes the pilot injection to be executed with the corrected injection control amount.

  With this specific matter, the reference injection control amount for pilot injection is corrected in accordance with whether or not the pilot injection fuel is ignited at the ignition determination position that is the highest temperature in the cylinder. That is, even if a temperature distribution occurs in the cylinder, the presence or absence of pilot injection fuel is determined based on the gas state at the ignition determination position at which the temperature is highest, and the pilot injection The reference injection control amount is corrected. For this reason, it can be avoided that the pilot injection fuel is misfired or the injection amount of the pilot injection fuel becomes larger than necessary.

  In the present invention, the presence or absence of ignition of pilot injected fuel is determined based on the ignition index value correlated with the temperature of the ignition determination position that is the highest temperature in the cylinder and the reference injection control amount, and the determination result is Accordingly, the reference injection control amount for pilot injection is corrected. For this reason, it is possible to optimize the injection control amount of the pilot injection, and it is possible to avoid the occurrence of misfiring of the pilot injection fuel or the excessive increase of the injection amount of the pilot injection fuel.

It is a schematic block diagram of the diesel engine which concerns on embodiment, and its control system. It is sectional drawing which shows the combustion chamber of a diesel engine, and its peripheral part. It is a block diagram which shows the structure of control systems, such as ECU. It is a figure for demonstrating the ignition determination position, the specification of an exhaust valve, and the specification of the injection hole of an injector. It is a flowchart figure which shows the procedure of pilot injection control. It is a figure which shows an example of a pilot injection pressure correction amount map. It is a figure which shows an example of a pilot injection amount correction amount map. It is a figure which shows an example of a pilot injection time correction amount map.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this 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-
FIG. 1 is a schematic configuration diagram of a diesel engine 1 (hereinafter simply referred to as an engine) and its control system according to the present embodiment.

  As shown in FIG. 1, the engine 1 according to this embodiment includes a fuel supply system 2, a combustion chamber 3, an intake system 6, and an exhaust system 7.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, an engine fuel passage 24, and the like.

  The supply pump 21 supplies the fuel pumped up from the fuel tank to the common rail 22 through the engine fuel passage 24 after making the pressure high. The common rail 22 distributes high-pressure fuel to the injectors 23. The injector 23 is a piezo injector.

  The intake system 6 includes an intake manifold 61 connected to an intake port 15 a formed in a cylinder head 15 (see FIG. 2), and an intake pipe 62 is connected to the intake manifold 61. In this intake pipe 62, an air cleaner 63, an air flow meter 43, an intercooler 65, and an intake throttle valve (diesel throttle) 64 are arranged in this order from the upstream side.

  The exhaust system 7 includes an exhaust manifold 71 connected to an exhaust port 15 b formed in the cylinder head 15, and an exhaust pipe 72 is connected to the exhaust manifold 71. The exhaust pipe 72 is provided with an NSR (NOx Storage Reduction) catalyst 74 and a DPF (Diesel Particulate Filter) 75.

  As shown in FIG. 2, the cylinder block 11 is formed with a cylinder bore 12 for each cylinder (four cylinders). A piston 13 is accommodated in each cylinder bore 12. A cavity 13 b is recessed in the center of the top surface 13 a of the piston 13, and this cavity 13 b constitutes the combustion chamber 3. The fuel injected from the central portion of the combustion chamber 3 by the injector 23 burns by self-ignition, and the combustion pressure acts on the piston 13. The piston 13 is connected to a crankshaft (not shown) by a connecting rod 18, and engine power is taken out from the crankshaft.

  The cylinder head 15 is provided with an intake valve 16 that opens and closes an intake port 15a and an exhaust valve 17 that opens and closes an exhaust port 15b.

  Further, as shown in FIG. 1, the engine 1 is provided with a turbocharger (supercharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor wheel 53 that are connected via a turbine shaft 51.

  Further, the engine 1 is provided with an EGR (Exhaust Gas Recirculation) passage 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is provided with an EGR valve 81 and an EGR cooler 82.

-ECU-
The ECU (Electronic Control Unit) 100 includes a microcomputer (not shown) such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output circuit. As shown in FIG. 3, the input circuit of the ECU 100 includes a crank position sensor 40, a rail pressure sensor 41, a throttle opening sensor 42, an air flow meter 43, exhaust temperature sensors 45a and 45b, a water temperature sensor 46, and an accelerator opening sensor 47. An intake pressure sensor 48, an intake air temperature sensor 49, an in-cylinder pressure sensor 4A, an air-fuel ratio sensor 4B, and the like are connected. Since the functions of these sensors are well known, description thereof is omitted here.

  On the other hand, the supply pump 21, the injector 23, the intake throttle valve 64, the EGR valve 81, and the like are connected to the output circuit of the ECU 100.

  The ECU 100 executes various controls of the engine 1 based on outputs from the respective sensors, calculated values obtained by calculation formulas using the output values, or various maps stored in the ROM. For example, the ECU 100 executes fuel injection control such as pilot injection and main injection as fuel injection control of the injector 23.

  Pilot injection is an operation for injecting a small amount of fuel prior to main injection. This pilot injection has a preheating function for increasing the in-cylinder temperature. That is, the temperature in the cylinder is sufficiently increased until the main injection is started, thereby suppressing the ignition delay of the main injected fuel and ensuring the ignitability of the main injected fuel.

  In the pilot injection control in the present embodiment, the fuel injection pressure determined in accordance with the engine rotation speed, the engine load, etc. (reference injection pressure assigned to the operation grid point corresponding to the engine rotation speed and the engine load), Reference injection control amounts such as fuel injection amount (reference injection amount assigned to the operation grid point) and fuel injection timing (reference injection timing assigned to the operation grid point) are set to specific positions (described later) in the cylinder. The final injection control amount (corrected injection control amount) is determined by correcting according to the presence or absence of ignition at the ignition determination position). The pilot injection from the injector 23 is executed with the determined injection control amount. The correction of the injection control amount for pilot injection will be described later.

  The main injection is a fuel injection operation for generating torque of the engine 1. The fuel injection amount and fuel injection timing in the main injection are determined so as to obtain the required torque in accordance with the operation state amount such as the engine speed, the accelerator operation amount (engine load), the coolant temperature, the intake air temperature, and the like. . For example, the fuel injection amount is set to be larger as the engine speed is higher and as the accelerator operation amount (accelerator opening) is larger.

  In addition to the pilot injection and main injection described above, after injection and post injection are performed as necessary. Since these injection functions are well known, description thereof is omitted here.

  The fuel injection pressure at the time of executing each fuel injection described above is determined by the internal pressure of the common rail 22 (common rail internal pressure). As the common rail internal pressure, generally, the target rail pressure, which is the target value of the fuel pressure supplied from the common rail 22 to the injector 23, becomes higher as the engine speed increases and the engine load increases. This target rail pressure is set according to a fuel pressure setting map stored in the ROM, for example.

  Further, the ECU 100 controls the opening degree of the EGR valve 81 according to the operating state of the engine 1 and adjusts the exhaust gas recirculation amount (EGR gas amount) toward the intake manifold 61. The amount of EGR gas is set according to an EGR map that is created in advance by experiments, simulations, etc. and stored in the ROM. This EGR map is a map for determining the EGR rate using the engine speed and the engine load as parameters. The ECU 100 controls the opening degree of the EGR valve 81 so as to obtain an EGR gas amount corresponding to the intake air amount so that the EGR rate determined according to the EGR map is established.

-Pilot injection control-
Next, pilot injection control, which is a feature of this embodiment, will be described. In this pilot injection control, as described above, the injection control amount (after correction) corrected according to the presence or absence of ignition of pilot injected fuel (estimated presence or absence of ignition) at a specific position (ignition determination position) in the cylinder The pilot injection is executed at the injection control amount). That is, when the pilot injection fuel does not ignite at the ignition determination position, the pilot injection fuel can be ignited at the ignition determination position by correcting the reference injection control amount of the pilot injection. I am doing so. Hereinafter, the ignition determination position will be described.

  FIG. 4 is a diagram for explaining the ignition determination position F, the specifications of the exhaust valve 17, and the specifications of the injection holes of the injector 23, and shows the positional relationship between the exhaust valve 17 and the injector 23. A virtual line L1 in FIG. 4 is a virtual extension line of the center line of the injection hole of the injector 23. That is, the fuel injected from the injection hole of the injector 23 diffuses into the cylinder along the virtual extension line L1.

  When the exhaust stroke of the engine 1 is completed and the exhaust valve 17 is closed, the highest temperature point in the cylinder is the lower surface of the umbrella portion of the exhaust valve 17 (the lower surface of the umbrella portion facing the cylinder). ). This is because in the exhaust stroke, high-temperature exhaust gas flows from the cylinder toward the exhaust port 15b, and the umbrella portion of the exhaust valve 17 continues to receive the heat of the exhaust gas during the exhaust stroke. It is.

  For this reason, the location where the temperature is highest on the virtual extension line L1 of the center line of the injection hole of the injector 23 is the location closest to the umbrella portion of the exhaust valve 17. As shown in FIG. 4, the axis L2 of the exhaust valve 17 extends in the vertical direction, and the virtual extension line L1 of the center line of the injection hole of the injector 23 is inclined downward toward the outer peripheral side in the cylinder. ing. That is, the virtual extension line L1 that passes under the umbrella portion of the exhaust valve 17 is separated from the umbrella portion of the exhaust valve 17 toward the outer peripheral side in the cylinder. Therefore, the place where the temperature is highest on the virtual extension line L1 is the innermost position (the position closer to the injector 23) in the cylinder within the range passing under the umbrella of the exhaust valve 17, that is, the position closer to the injector 23. 4 is the position of point F in FIG. 4 (hereinafter referred to as ignition determination position F). The fact that the ignition determination position F is the highest temperature means that the temperature at the ignition determination position F reaches the premixed combustion temperature (for example, 900 K) when the pilot injection is executed (the temperature law condition is satisfied). In addition, if the spray of the pilot injection fuel has reached the ignition determination position F and the equivalence ratio at the ignition determination position F is an equivalence ratio that can be ignited (the spray law condition is satisfied). At least in this ignition determination position F, the pilot injected fuel is ignited. On the other hand, even if the spray of the pilot injected fuel has not reached the ignition determination position F, or even if the pilot injected fuel has reached the ignition determination position F, the equivalence ratio at the ignition determination position F can be ignited, etc. If the quantity ratio is not reached or the temperature at the ignition determination position F has not reached the premixed combustion temperature, the pilot injected fuel will not be ignited at this ignition determination position F.

  In this manner, whether or not the pilot injection fuel is ignited can be determined based on the state of the spray of the pilot injection fuel at the ignition determination position F and the temperature at the ignition determination position F. In the present embodiment, an ignition index value is defined as a value correlated with the temperature of the ignition determination position F, and whether or not the pilot injection fuel is ignited at the ignition determination position F based on the ignition index value and the reference injection control amount. Determine whether. When the pilot injection fuel does not ignite, the reference injection control amount of the pilot injection fuel is corrected so that the pilot injection fuel ignites at the ignition determination position F.

  The outline of this pilot injection control will be described below.

  In this pilot injection control, (a) the distance between the virtual extension line L1 of the center line of the nozzle hole of the injector 23 and the exhaust valve 17 is the shortest (the distance t1 in FIG. 4). The ignition index value Ib correlated with the temperature of the ignition determination position F on the extension line L1, the exhaust gas state quantity in the previous cycle of the engine 1, the current intake gas state quantity introduced into the cylinder, the exhaust valve 17 and the operation calculated from the specifications of the injection hole of the injector 23, (b) the reference injection pressure of the pilot injection that is prescribed in advance according to the operating state (engine operating state) of the engine 1, and the reference injection An operation of acquiring at least one reference injection control amount corresponding to the current operating state of the engine 1 among the reference injection control amount of the amount and the reference injection timing, and (c) an ignition index value Ib and the current On the basis of the reference injection control amount acquired according to the operating state of the engine 1, it is determined whether or not the fuel injected by the pilot injection is ignited at the ignition determination position F when the pilot injection is executed. Operation, (d) An operation for calculating a correction amount of the injection control amount of the pilot injection for causing the fuel spray of the pilot injection to reach the ignition determination position F when it is determined that the fuel injected by the pilot injection does not ignite (E) The operation of correcting the pilot injection reference injection control amount with the correction amount and executing the pilot injection with the corrected injection control amount is sequentially performed. Details of the operations (a) to (e) will be described later.

  These operations are executed by the ECU 100. For this reason, in the ECU 100, the functional part that executes the operation (a) is configured as an ignition index value calculation unit in the present invention. Further, in the ECU 100, a functional part that executes the operation (b) is configured as a reference injection control amount acquisition unit referred to in the present invention. Further, in the ECU 100, a functional part that executes the operation (c) is configured as an ignition determination unit in the present invention. Further, in the ECU 100, a functional part that executes the operation (d) is configured as a correction amount calculation unit in the present invention. Further, in the ECU 100, a functional part that executes the operation (e) is configured as a pilot injection command unit in the present invention.

  These ignition index value calculation unit, reference injection control amount acquisition unit, ignition determination unit, correction amount calculation unit, and pilot injection command unit constitute a control device according to the present invention.

  Hereinafter, a specific procedure of the pilot injection control will be described with reference to the flowchart of FIG. This flowchart shows after every start of the engine 1 every time the crankshaft rotates by a predetermined angle (more specifically, every time before pilot injection is started in any cylinder; for example, the piston 13 is compressed Every time when the predetermined crank angle position is reached before reaching the dead point: Since the engine according to the present embodiment has four cylinders, the ECU 100 is repeatedly executed at every 180 ° CA). Hereinafter, a cylinder in which the pilot injection control amount is defined in the pilot injection control (a cylinder that has reached the timing before the pilot injection is started) is referred to as a control target cylinder.

  First, in step ST1, the exhaust gas temperature Tei-1 in the previous cycle of the control target cylinder and the gas amount Gi-1 in the previous cycle of the control target cylinder are acquired.

  The exhaust gas temperature Tei-1 in the previous cycle is obtained based on an output signal from the exhaust temperature sensor 45a. That is, the exhaust gas temperature in the exhaust stroke of the previous cycle of the cylinder to be controlled is obtained based on the output signal from the exhaust temperature sensor 45a, etc., and stored in the RAM. In step ST1, this value is read as the exhaust gas temperature Tei-1 in the previous cycle.

  The gas amount Gi-1 in the previous cycle is the mass of the intake air introduced into the control target cylinder in the previous cycle of the control target cylinder, and is based on output signals from the air flow meter 43 and the intake air temperature sensor 49. Desired. That is, the intake air amount (intake air calculated based on the output signal from the air flow meter 43) during a predetermined period in the previous cycle (for example, during the period from when the intake valve 16 of the cylinder to be controlled is opened to when it is closed). The gas amount Gi-1 in the previous cycle is obtained from a predetermined arithmetic expression or map using the intake air temperature (the intake air temperature detected by the output signal from the intake air temperature sensor 49) as a parameter. Stored in the RAM. In step ST1, this value is read as the gas amount Gi-1 in the previous cycle. The larger the intake air amount and the lower the intake air temperature, the larger the gas amount Gi-1 is calculated. In addition, the EGR gas amount (EGR gas amount for achieving the EGR rate read from the EGR map) is added to the gas amount obtained based on the output signals from the air flow meter 43 and the intake air temperature sensor 49, and the previous time. The gas amount Gi-1 in the cycle may be calculated.

  In step ST2, the gas temperature (current gas temperature) Tii, the gas amount (current gas amount) Gi, and the gas composition (current gas composition) Ci in the cylinder in the current engine operating state are calculated.

  The current gas temperature Tii is calculated as a value corresponding to the compressed state of the gas accompanying the reciprocating movement of the piston 13. In other words, the intake gas sucked into the cylinder to be controlled in the intake stroke of the current cycle (the intake gas whose intake temperature is detected by the output signal from the intake temperature sensor 49) is the value after the intake valve 16 is closed. When the piston 13 is compressed by the upward movement of the piston 13 in the compression stroke, the intake gas depends on the piston position geometrically determined when the acquisition timing of the gas temperature Tii (crank angle position for acquiring the gas temperature Tii) is reached. Therefore, the gas temperature Tii at this timing can be calculated. In step ST2, this gas temperature Tii is acquired.

  The current gas amount Gi is the current intake air mass introduced into the cylinder to be controlled, and is obtained based on output signals from the air flow meter 43 and the intake air temperature sensor 49. For example, the intake air amount (the intake air amount calculated based on the output signal from the air flow meter 43) during a predetermined period of the current cycle (for example, during the period from when the intake valve 16 of the cylinder to be controlled is opened to when it is closed) ) And a predetermined arithmetic expression or map using the intake air temperature (the intake air temperature detected by the output signal from the intake air temperature sensor 49) as a parameter, the current gas amount Gi is obtained. The larger the intake air amount and the lower the intake air temperature, the larger the present gas amount Gi is calculated. Further, the current gas amount Gi is calculated by adding the EGR gas amount (EGR gas amount for achieving the EGR rate read from the EGR map) to the gas amount obtained based on the output signal from the air flow meter 43. You may make it do.

  The current gas composition Ci is the current oxygen concentration in the gas introduced into the cylinder to be controlled, and is obtained from the EGR rate, the air-fuel ratio (A / F), and the like. The EGR rate is read from the EGR map as described above. The air-fuel ratio is detected by an output signal from the air-fuel ratio sensor 4B. The current gas composition Ci is obtained from a predetermined arithmetic expression or map using the EGR rate and the air-fuel ratio (A / F) as parameters. The current gas composition Ci (oxygen concentration in the gas) is calculated as a higher value as the EGR rate is lower and as the air-fuel ratio (A / F) is larger.

  In step ST3, the specifications of the exhaust valve 17 are acquired. Specifically, the outer diameter D (see FIG. 4) of the umbrella portion of the exhaust valve 17, the heat capacity C of the exhaust valve 17, and the sandwich angle Dd between the intake and exhaust valves 16 and 17 are acquired. These specifications are fixed values and are stored in the ROM. In step ST3, these values are read out.

  In step ST4, the specifications of the injection hole of the injector 23 are acquired. Specifically, the cone angle Ic between the nozzle holes and the protruding dimension Id from the lower surface of the cylinder head 15 to the nozzle hole position (both see FIG. 4) are acquired. These specifications are also fixed values and are stored in the ROM. In step ST4, these values are read out.

  In step ST5, an ignition index value Ib is calculated. The ignition index value Ib is defined as a value correlated with the temperature at the ignition determination position F in FIG. 4 as described above.

  Specifically, the ignition index value Ib is determined by the exhaust gas temperature Tei-1 in the previous cycle of the control target cylinder, the gas amount Gi-1 in the previous cycle of the control target cylinder, the current gas temperature Tii, the current gas amount Gi, the current gas. Parameters are the composition Ci, the outer diameter D of the umbrella portion of the exhaust valve 17, the heat capacity C of the exhaust valve 17, the sandwich angle Dd between the intake and exhaust valves 16, 17, the cone angle Ic between the nozzle holes, and the protrusion dimension Id. It is calculated | required by the arithmetic formula prescribed | regulated previously or a map. The higher the exhaust gas temperature Tei-1 in the previous cycle of the control target cylinder, the higher the gas amount Gi-1 in the previous cycle of the control target cylinder, the higher the current gas temperature Tii, and the higher the current gas amount Gi. The ignition index value Ib is calculated as a larger value as the oxygen concentration of the current gas composition Ci is higher. The cone angle Ic between the nozzle holes becomes larger as the outer diameter D of the umbrella portion of the exhaust valve 17 is larger, the heat capacity C of the exhaust valve 17 is larger, and the sandwiching angle Dd between the intake and exhaust valves 16 and 17 is smaller. The ignition index value Ib is calculated as a larger value as the protrusion dimension Id is smaller as it is larger. That is, the ignition index value Ib is calculated as a larger value as the temperature or the structure of the ignition determination position F tends to increase. In other words, as the ignition index value Ib is obtained as a larger value, the pilot injected fuel is more likely to be ignited at the ignition determination position F.

  The operation of this step ST5 is the operation by the “ignition index value calculation unit” in the present invention, and the distance between the virtual extension line of the center line of the injection hole of the fuel injection valve and the exhaust valve is the shortest. The ignition index value that correlates with the temperature at the ignition judgment position on the virtual extension line is calculated based on the exhaust gas state quantity in the previous cycle of the internal combustion engine, the current intake gas state quantity introduced into the cylinder, and the exhaust valve specifications. , And the operation calculated from the specifications of the nozzle hole ”.

  In step ST6, a reference injection control amount (reference injection control amount of pilot injection) assigned to the operation grid point corresponding to the current engine speed and engine load (stored in the ROM) is acquired. Specifically, the reference injection pressure, the reference injection amount, and the reference injection timing assigned to the operation grid point are acquired.

  The operation of this step ST6 is the operation by the “reference injection control amount acquisition unit” according to the present invention, and the pilot injection reference injection pressure, the reference injection amount, and the reference injection that are defined in advance according to the engine operating state. This corresponds to an operation of acquiring at least one reference injection control amount corresponding to the current engine operating state among the reference injection control amounts at the time.

  In step ST7, it is determined whether or not the pilot injected fuel is ignited at the ignition determination position F. Specifically, as this determination method, an ignition determination value (a value that defines the ease of ignition) using a predetermined arithmetic expression or map that uses the ignition index value Ib and the reference injection control amount as parameters. And whether or not the ignition determination value exceeds a predetermined threshold A is determined.

  The ignition determination value is obtained by quantifying the ease of ignition of pilot injected fuel according to the ignition index value Ib and the reference injection control amount. The higher the ignition index value Ib, the higher the ignition determination value is calculated. As the reference injection control amount, the higher the reference injection pressure, the greater the reference injection amount, and the more advanced the reference injection timing, the easier the pilot injection fuel spray reaches the ignition determination position F. Since the equivalence ratio at the ignition judgment position F tends to be an equivalence ratio that can be ignited, the ignition judgment value is calculated as a high value.

  In other words, the threshold A is equal to the ratio of the equivalence ratio at the ignition determination position F when the temperature at the ignition determination position F has reached the premixed combustion temperature and the spray of the pilot injected fuel has reached the ignition determination position F. Is preliminarily defined as a value corresponding to the ignition determination value calculated when the equivalence ratio is ignitable. In other words, when the ignition determination value exceeds the threshold value A, the pilot injection fuel is ignited (ignited at the ignition determination position F), and the ignition determination value is equal to or less than the threshold value A. In this case, the pilot injection fuel does not ignite (does not ignite at the ignition determination position F), and is defined in advance based on experiments or simulations. As described above, the ignition determination position F is the highest temperature position in the cylinder. Therefore, if ignition is not performed at the ignition determination position F, the pilot injection fuel does not ignite throughout the cylinder (misfire). Will be).

  The operation of this step ST7 is the “operation by the ignition determination unit” in the present invention, and the pilot injection was executed based on the ignition index value and the reference injection control amount acquired according to the current engine operating state. Corresponds to the operation of determining whether or not the fuel injected by the pilot injection is ignited at the ignition determination position.

  If it is determined in step ST7 that the pilot injected fuel is not ignited (NO determination), the process proceeds to step ST8, and at least one of the pilot injection injection control amounts (pilot injection pressure, pilot injection amount, and pilot injection timing). 2) is calculated. That is, among the correction amount for the reference injection pressure (pilot injection pressure correction amount), the correction amount for the reference injection amount (pilot injection amount correction amount), and the correction amount for the reference injection timing (pilot injection timing correction amount) Calculate at least one. That is, as a cause that the pilot injected fuel does not ignite, even if the spray of the pilot injected fuel does not reach the ignition determination position F or the spray of the pilot injected fuel reaches the ignition determination position F, Since it is assumed that the equivalence ratio is not an ignitable equivalence ratio, the spray of the pilot injected fuel reaches the ignition judgment position F, and the equivalence ratio at the ignition judgment position F can be ignited. A correction amount of the injection control amount of the pilot injection is calculated so as to obtain a uniform ratio.

  Here, a case where one of the pilot injection pressure, the pilot injection amount, and the pilot injection timing is corrected will be described as an example.

  The correction amount is calculated by a predetermined arithmetic expression using the ignition index value Ib and the threshold A as variables. Alternatively, a map for obtaining the correction amount using a deviation (ΔA (= threshold A−ignition determination value)) between the threshold A and the ignition determination value as a parameter is created by experiment or the like and stored in the ROM of the ECU 100, and this map The correction amount may be obtained by referring to FIG.

  FIG. 6 is a diagram showing an example of a pilot injection pressure correction amount map used when correcting only the pilot injection pressure. The pilot injection pressure correction amount map is such that the pilot injection pressure correction amount is obtained as a larger value as the deviation ΔA (a value obtained by subtracting the ignition determination value from the threshold A) is larger. That is, as the deviation ΔA is larger, the pilot injection pressure is set higher to increase the penetration force of the pilot injected fuel, thereby increasing the spray arrival distance (the pilot injection fuel spray reaches the ignition determination position F and is ignited). The equivalence ratio at the determination position F is an equivalence ratio that can be ignited).

  FIG. 7 is a diagram showing an example of a pilot injection amount correction amount map used when correcting only the pilot injection amount. In the pilot injection amount correction amount map, the pilot injection amount correction amount is obtained as a larger value as the deviation ΔA is larger. In other words, the larger the deviation ΔA, the larger the pilot injection amount, thereby increasing the penetration force of the pilot injected fuel, thereby increasing the spray reach distance (the spray of the pilot injected fuel reaches the ignition determination position F and is ignited). The equivalence ratio at the determination position F is an equivalence ratio that can be ignited).

  FIG. 8 is a diagram showing an example of a pilot injection timing correction amount map used when correcting only the pilot injection timing. In this pilot injection timing correction amount map, the correction amount is obtained as a value that increases the amount of shift of the pilot injection timing to the advance side as the deviation ΔA increases. That is, with respect to the pilot injection executed before the piston 13 reaches compression top dead center, the pilot injection is performed in a situation where the in-cylinder pressure is low by setting the pilot injection timing to the advance side as the deviation ΔA is larger. Thus, the spray reach distance is lengthened (the spray of the fuel injected by the pilot injection reaches the ignition determination position F, and the equivalence ratio at the ignition determination position F becomes an equivalence ratio that can be ignited).

  Further, when correcting a plurality of injection control amounts among the pilot injection pressure, pilot injection amount and pilot injection timing, the relationship between the correction amount of the plurality of injection control amounts and the spray reach distance is verified by experiments, etc. A correction amount map is created based on the verification result, and each injection control amount is corrected according to the correction amount map.

  The operation of step ST8 is the operation by the correction amount calculation unit referred to in the present invention, and when the ignition determination unit determines that the fuel injected by the pilot injection does not ignite, the pilot is placed at the ignition determination position. This corresponds to “operation for calculating the correction amount of the injection control amount of the pilot injection for reaching the fuel spray of the injection”.

  In step ST9, the final injection control amount of pilot injection is determined. That is, when the pilot injection pressure correction amount is calculated in step ST8, this pilot injection pressure correction amount is added to the reference injection pressure, and this is determined as the final pilot injection pressure. If the pilot injection amount correction amount is calculated in step ST8, the pilot injection amount correction amount is added to the reference injection amount, and this is determined as the final pilot injection amount. If the pilot injection timing correction amount is calculated in step ST8, the pilot injection timing correction amount is added to the reference injection timing (corrected to the advance side), and this is determined as the final pilot injection timing. To do. After determining the final injection control amount of pilot injection in this way, the process proceeds to step ST10.

  In step ST10, it is determined whether or not the pilot injection execution timing has come (the crank angle position has reached the pilot crank execution crank angle position). For example, when the pilot injection timing correction amount is calculated in step ST8, it is determined whether or not the pilot injection timing corrected by this pilot injection timing correction amount (the final pilot injection timing determined in step ST9) has been reached. judge. When the pilot injection timing is not corrected, it is determined whether or not the reference injection timing assigned to the current engine speed and engine load (operation grid point) has been reached.

  If the pilot injection execution timing has not yet been reached, a NO determination is made in step ST10 to wait until this execution timing is reached.

  When the pilot injection execution timing is reached and YES is determined in step ST10, the process proceeds to step ST11, and pilot injection is executed.

  That is, when the pilot injection pressure correction amount is calculated in step ST8, the pilot injection is executed with the final pilot injection pressure corrected with the pilot injection pressure correction amount. Specifically, the target rail pressure is changed, and the supply pump 21 is controlled accordingly.

  When the pilot injection amount correction amount is calculated in step ST8, pilot injection is executed with the final pilot injection amount corrected with this pilot injection amount correction amount. Specifically, the valve opening period of the injector 23 is controlled so as to obtain the final pilot injection amount according to the rail pressure.

  The operation of this step ST11 is the “operation by the pilot injection command unit, which is an operation for correcting the reference injection control amount of the pilot injection with the correction amount and executing the pilot injection with the corrected injection control amount” in the present invention. It corresponds to.

  The above operation is repeated every time the crankshaft rotates by a predetermined angle (every time before pilot injection is started in any cylinder).

  Since such pilot injection control is performed, the control device for the internal combustion engine according to the present invention is configured by the ECU 100 (more specifically, by each functional portion in the ECU 100 described above). This control device receives each signal from the crank position sensor 40, rail pressure sensor 41, air flow meter 43, exhaust temperature sensor 45a, accelerator opening sensor 47, intake air temperature sensor 49, etc. as an input signal. Yes. In addition, this control device is configured to output a pilot injection command signal as an output signal to each injector 23.

  As described above, in the present embodiment, pilot injection is performed with an injection control amount that is corrected according to the presence or absence of ignition of pilot injected fuel (estimated presence or absence of ignition) at a specific position (ignition determination position F) in the cylinder. To do. That is, when the pilot injection fuel is not ignited at the ignition determination position F, the pilot injection fuel can be ignited at the ignition determination position F by correcting the reference injection control amount of the pilot injection. I try to make it. For this reason, it is possible to optimize the injection control amount of the pilot injection. As a result, misfire of the pilot injected fuel can be prevented. Further, the fuel injection rate can be improved without increasing the injection amount of the pilot injection fuel more than necessary.

Further, in the present embodiment, the injection control amount is corrected by feedforward control according to the estimation of the presence or absence of ignition of pilot injected fuel. For this reason, it is possible to prevent the misfire of pilot injected fuel and the amount of pilot injected fuel from becoming unnecessarily large. As a result, it is possible to prevent misfire and improve the fuel consumption rate even during a transient time when the operating state of the engine 1 fluctuates.
In the embodiment described above, the current gas temperature Tii, the current gas amount Gi, and the current gas composition Ci at the timing when the piston 13 reaches the predetermined crank angle position before reaching the compression top dead center are calculated, and these calculated values are used. Thus, the ignition index value Ib is calculated. The present invention is not limited to this, and estimates the gas temperature, gas amount, and gas composition at the reference injection timing (reference injection timing of pilot injection) assigned to the operation grid point corresponding to the current engine speed and engine load, respectively. The ignition index value Ib may be calculated using these estimated values.

  Moreover, the said embodiment demonstrated the case where this invention was applied to the in-line 4 cylinder diesel engine 1 mounted in the motor vehicle. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited.

  Moreover, although the said embodiment demonstrated the case where this invention was applied to the engine 1 of a conventional vehicle (vehicle which mounted only an engine as a driving force source), the vehicle which mounts an engine and an electric motor as a driving force source. The present invention can also be applied to the engine.

  The present invention is applicable to pilot injection control in a diesel engine mounted on an automobile.

1 engine (internal combustion engine)
3 Combustion chamber 15b Exhaust port 17 Exhaust valve 23 Injector (fuel injection valve)
100 ECU
F Ignition determination position Ib Ignition index value L1 Virtual extension line of nozzle hole center line

Claims (1)

The present invention is applied to a compression self-ignition internal combustion engine having a fuel injection valve that injects fuel into a cylinder and an exhaust valve that opens and closes an exhaust port that discharges exhaust gas generated in the cylinder. In the control device that executes pilot injection prior to main injection as fuel injection of
An ignition index value correlated with the temperature of the ignition determination position on the virtual extension line where the distance between the virtual extension line of the center line of the injection hole of the fuel injection valve and the exhaust valve is the shortest is an internal combustion engine. An exhaust gas state quantity in the previous cycle, a current intake gas state quantity introduced into the cylinder, specifications of the exhaust valve, and an ignition index value calculation unit that calculates from the specifications of the nozzle hole; ,
At least one reference injection corresponding to the current engine operating state among the reference injection pressure, the reference injection amount, and the reference injection control amount of the reference injection timing that is defined in advance according to the engine operating state A reference injection control amount acquisition unit for acquiring a control amount;
Whether the fuel injected in the pilot injection is ignited at the ignition determination position when the pilot injection is executed based on the ignition index value and the reference injection control amount acquired in accordance with the current engine operating state An ignition determination unit for determining whether or not,
When the ignition determination unit determines that the fuel injected by the pilot injection does not ignite, calculates a correction amount of the injection control amount of the pilot injection for causing the fuel injection of the pilot injection to reach the ignition determination position A correction amount calculation unit to perform,
A pilot injection command unit that corrects the reference injection control amount of the pilot injection with the correction amount, and executes the pilot injection with the corrected injection control amount;
A control device for an internal combustion engine, comprising:

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