JP6032215B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to an improvement in cooperative control between EGR rate control and supercharging pressure control.

  Conventionally, an engine (for example, a diesel engine) equipped with an exhaust gas recirculation device and a variable displacement supercharger is known. The exhaust gas recirculation device controls the EGR rate of the intake system by adjusting the opening of the EGR valve. The variable capacity supercharger controls the supercharging pressure of the intake system by adjusting the opening of the nozzle vane.

  Patent Literature 1 and Patent Literature 2 disclose cooperative control between EGR rate control and supercharging pressure control. Specifically, the target EGR rate and the target supercharging pressure are determined according to the engine operating state. Then, the opening degree of the EGR valve is adjusted based on the amount of deviation between the actual EGR rate and the target EGR rate. Further, the nozzle vane opening degree is adjusted based on the amount of deviation between the actual supercharging pressure and the target supercharging pressure. By performing such EGR rate control and supercharging pressure control, it is possible to suppress the NOx emission amount and the HC emission amount in the exhaust gas within the limits of regulation.

JP 2013-151864 A JP 2012-82720 A

  However, in the conventional cooperative control of the EGR rate control and the supercharging pressure control, it is possible to shorten the time required to keep the NOx emission amount and the HC emission amount in the exhaust gas within the regulation range. Almost no consideration was given. Then, simply adjusting the opening degree of the EGR valve from the deviation amount between the actual EGR rate and the target EGR rate, and adjusting the nozzle vane opening degree from the deviation amount between the actual boost pressure and the target boost pressure, There is a limit to shortening the time required to keep the NOx emission amount and the HC emission amount within the limits of regulation. In particular, in the conventional cooperative control, it is difficult to shorten the time required to keep the NOx emission amount and the HC emission amount within the regulation range during the transient operation of the engine.

  The present invention has been made in view of the above points, and an object of the present invention is to reduce the time required to keep the NOx emission amount and the HC emission amount within the limits of regulation. It is to provide an engine control device.

-Solution principle of the invention-
The solution principle of the present invention taken in order to achieve the above-mentioned object is that the target EGR rate and the target supercharging pressure that minimize the time required to keep the NOx emission amount and the HC emission amount within the regulation range are respectively set. In other words, the EGR valve and the nozzle vane are controlled based on the obtained target EGR rate and the target supercharging pressure.

-Solution-
Specifically, the present invention is premised on a control device for an internal combustion engine that controls an EGR rate by an EGR valve and controls a supercharging pressure of intake air by a supercharger having a variable displacement mechanism. A target EGR rate control region calculating unit that calculates a target EGR rate control region in which the oxygen concentration in the cylinder is equal to or lower than the required oxygen concentration, and the gas amount in the cylinder is greater than or equal to the required gas amount. A target boost pressure control region calculation unit that calculates a target boost pressure control region, and an exhaust formation control region calculation unit that calculates an exhaust formation control region that satisfies both the target EGR rate control region and the target boost pressure control region And, based on the transient response of the EGR valve and the transient response of the variable displacement mechanism, the EGR rate and the boost pressure that can be reached in the shortest time among the EGR rate and the boost pressure in the exhaust establishment control region. Each is provided with a target value calculation unit that calculates the target EGR rate and the target boost pressure.

  By this specific matter, by making the oxygen concentration in the cylinder below the required oxygen concentration, it becomes possible to keep the NOx emission amount in the exhaust within the regulation range, and the gas amount in the cylinder more than the required gas amount By doing so, it becomes possible to suppress the HC emission amount in the exhaust gas within the range of regulation and to obtain the target EGR rate and the target supercharging pressure at which both of these can be achieved in the shortest time. . In particular, during the transient operation of the internal combustion engine, it is possible to shorten the time required to keep the NOx emission amount and the HC emission amount within the limits of regulation.

  In the present invention, it is possible to shorten the time required to keep the NOx emission amount and the HC emission amount within the regulation range, and it is possible to achieve early optimization of exhaust emission.

It is a figure which shows schematic structure 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 which shows an example of an EGR rate control area map. It is a figure which shows an example of a supercharging pressure control area | region map. It is a flowchart figure which shows the procedure of the cooperative control of EGR rate control and supercharging pressure control. FIG. 7A is a diagram for explaining operating points on the EGR rate control region map, and FIG. 7B is a diagram showing an operation amount map converted from the EGR rate control region map. FIG. 8A is a diagram for explaining operating points on the supercharging pressure control region map, and FIGS. 8B and 8C are operation amount maps converted from the supercharging pressure control region map. FIG. It is a figure which shows an example of an exhaust_gas | exhaustion establishment control area | region map. It is a figure showing the transient response of a supercharging pressure. It is a figure showing the transient response of an EGR rate. It is a figure which shows an example of the exhaust formation control area | region map for demonstrating the operation | movement which makes turbo total efficiency maximum efficiency.

  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 is configured as a diesel engine system having a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7 and the like as main parts.

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

  The supply pump 21 increases the pressure of the fuel pumped from the fuel tank and then supplies the fuel to the common rail 22 via the engine fuel passage 24. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) high pressure fuel at a predetermined pressure, and distributes the accumulated fuel to the injectors 23, 23,. The injector 23 is a piezo injector provided with a piezoelectric element (piezo element) inside, and the amount of fuel injected into the combustion chamber 3 can be adjusted by controlling the valve opening period.

  The intake system 6 includes an intake manifold 61 connected to an intake port 15 a formed in the cylinder head 15 (see FIG. 2), and an intake pipe 62 is connected to the intake manifold 61. The intake system 6 is provided with an air cleaner 63, an air flow meter 43, and an intake throttle valve (diesel throttle) 64 in 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. In addition, an exhaust purification unit 73 is disposed in the exhaust system 7. The exhaust purification unit 73 is provided with an NSR (NOx Storage Reduction) catalyst 74 and a DPF (Diesel Particle Filter) 75 as NOx storage reduction catalysts.

  As shown in FIG. 2, the cylinder block 11 is formed with a cylinder bore 12 for each cylinder (four cylinders), and a piston 13 is accommodated in each cylinder bore 12 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 portion of the cylinder block 11, the inner wall surface of the cylinder bore 12, and the top surface 13 a of the piston 13. A cavity (concave portion) 13 b is formed in a substantially central portion of the top surface 13 a of the piston 13, and this cavity 13 b also constitutes a part of the combustion chamber 3.

  As the shape of the cavity 13b, the concave dimension is small in the central portion (on the cylinder center line P), and the concave dimension is increased toward the outer peripheral side.

  The piston 13 is connected to a crankshaft that is an engine output shaft by a connecting rod 18. Further, a glow plug 19 is disposed toward the combustion chamber 3.

  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 supercharger (turbocharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor wheel 53 that are connected via a turbine shaft 51. The turbocharger 5 in the present embodiment is a variable nozzle turbocharger, and a variable nozzle vane mechanism (variable capacity mechanism) 54 is provided on the turbine wheel 52 side. The variable nozzle vane mechanism 54 includes a plurality of nozzle vanes 54a, 54a,... That change the flow area of the exhaust gas flow path of the turbine housing, and an actuator (not shown) that changes the opening of the nozzle vane 54a. Yes. Then, by changing the opening degree of the nozzle vane 54a by this actuator, the flow passage area (throat area) between the nozzle vanes 54a and 54a adjacent to each other is changed. By changing the throat area, the flow rate of the exhaust gas introduced toward the turbine wheel 52 is adjusted, and the rotational speed of the turbine wheel 52 and the compressor wheel 53 is adjusted, whereby the supercharging pressure can be adjusted. It has become. In addition, since the mechanism which changes the opening degree of this nozzle vane 54a is well-known, description here is abbreviate | omitted.

  The intake pipe 62 is provided with an intercooler 65 for cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5.

  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 a combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it to the combustion chamber 3, thereby reducing the amount of NOx generated. In addition, the EGR passage 8 is opened and closed steplessly by electronic control, and the exhaust gas passing through the EGR passage 8 (recirculating) is cooled by an EGR valve 81 that can freely adjust the exhaust flow rate flowing through the passage. An EGR cooler 82 is provided. The EGR passage 8, the EGR valve 81, the EGR cooler 82, and the like constitute an EGR device (exhaust gas recirculation device).

-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. The intake pressure sensor 48, the intake air temperature sensor 49, the in-cylinder pressure sensor 4A, the outside air temperature sensor 4B, the outside air pressure sensor 4C, and the like are connected.

  On the other hand, to the output circuit of the ECU 100, the supply pump 21, the injector 23, the variable nozzle vane mechanism 54, the intake throttle valve 64, the EGR valve 81, and the like are connected.

  Then, the ECU 100 executes various controls of the engine 1 based on outputs from the various sensors described above, calculated values obtained by arithmetic expressions using the output values, or various maps stored in the ROM. .

  For example, the ECU 100 executes pilot injection and main injection as fuel injection control of the injector 23. Since the function of these injections is well known, description here is omitted.

  Further, the ECU 100 executes the opening degree control of the nozzle vane 54 a provided in the variable nozzle vane mechanism 54 and the opening degree control of the EGR valve 81. These controls are performed by the following cooperative control.

-Cooperative control of EGR rate control and supercharging pressure control-
Next, cooperative control between EGR rate control and supercharging pressure control, which is a feature of the present embodiment, will be described.

  First, the outline of this cooperative control will be described.

  As described above, the EGR rate control is performed by adjusting the opening degree of the EGR valve 81 and controlling the exhaust gas recirculation amount toward the intake manifold 61 (controlling the EGR rate), whereby the combustion temperature in the combustion chamber 3 is controlled. This is a control for reducing the NOx generation amount.

  As described above, the supercharging pressure control is introduced toward the turbine wheel 52 by adjusting the opening of the nozzle vane 54a and changing the flow passage area (throat area) between the adjacent nozzle vanes 54a, 54a. The exhaust gas flow rate is adjusted to adjust the rotational speed of the turbine wheel 52 and the compressor wheel 53, thereby adjusting the supercharging pressure. By adjusting the supercharging pressure, the amount of gas introduced into the cylinder can be adjusted. Thereby, it is possible to reduce the discharge amount of HC generated due to the shortage of the gas amount.

In the present embodiment, the following calculation processes are sequentially performed as cooperative control between the EGR rate control and the supercharging pressure control.
(1) Processing for calculating a target EGR rate control region in which the oxygen concentration in the cylinder is equal to or lower than the required oxygen concentration (processing for calculating the target EGR rate control region by the target EGR rate control region calculation unit).
(2) Processing for calculating a target boost pressure control region in which the gas amount in the cylinder is equal to or greater than the required gas amount (required cylinder gas amount) (calculation of the target boost pressure control region by the target boost pressure control region calculation unit) processing).
(3) Processing for calculating an exhaust establishment control region that satisfies both the target EGR rate control region and the target boost pressure control region (exhaust formation control region calculation processing by the exhaust formation control region calculation unit).
(4) Based on the transient response of the EGR valve 81 and the transient response of the variable nozzle vane mechanism 54, the EGR rate and excess pressure that can be reached in the shortest time out of the EGR rate and the supercharging pressure in the exhaust formation control region Processing for calculating the supply pressure as the target EGR rate and the target supercharging pressure, respectively (processing for calculating the target EGR rate and the target supercharging pressure by the target value calculation unit).

  In the calculation process (1), it corresponds to the current operation grid point in the EGR rate control region map defined for each operation grid point of the engine 1 (operation grid point determined by the engine speed and engine load). An EGR rate control region map is extracted, and a “target EGR rate control region” is obtained from this EGR rate control region map. These EGR rate control area maps are stored in the ROM. FIG. 4 shows an EGR rate control region map at a certain operation grid point. In this EGR rate control region map, the horizontal axis is the EGR rate, and the vertical axis is the oxygen excess rate. Further, the hatched area in the EGR rate control area map is a “target EGR rate control area” in which the oxygen concentration in the cylinder is equal to or lower than the required oxygen concentration. Here, the required oxygen concentration is the highest oxygen concentration in the oxygen concentration range in which the NOx emission amount in the exhaust gas can be suppressed within the regulation range. In other words, as long as the operation is performed in the target EGR rate control region indicated by the hatched lines, the oxygen concentration in the cylinder is equal to or less than the required oxygen concentration, and the NOx emission amount in the exhaust can be suppressed within the regulation range. Become.

  In the calculation process (2), a supercharging pressure control region map corresponding to the current operating lattice point is extracted from the supercharging pressure control region map defined for each operating lattice point of the engine 1, and this supercharging pressure is extracted. A “target boost pressure control region” is obtained from the control region map. These supercharging pressure control area maps are stored in the ROM. FIG. 5 shows a supercharging pressure control region map at a certain operation grid point. In this supercharging pressure control region map, the horizontal axis represents the gas temperature (intake air temperature) in the intake manifold 61, and the vertical axis represents the supercharging pressure. In addition, the hatched region in the supercharging pressure control region map is a “target supercharging pressure control region” in which the gas amount in the cylinder is equal to or greater than the required in-cylinder gas amount. Here, the required in-cylinder gas amount is the in-cylinder gas amount that is the lowest in the range of the in-cylinder gas amount in which the HC emission amount in the exhaust gas can be suppressed within the regulation range. In other words, as long as the engine is operated in the target supercharging pressure control region with the hatched lines, the amount of gas in the cylinder will be equal to or greater than the required in-cylinder gas amount, and the HC emission amount in the exhaust will be kept within the regulation range. Is possible.

  In the calculation process (3), based on the EGR rate control region map and the supercharging pressure control region map for the same grid point, the NOx emission amount in the exhaust gas can be suppressed within a regulation range, and A control region (exhaust establishment control region) in which the amount of HC emission in the exhaust can be suppressed within the regulation range is obtained. Specifically, an “exhaust establishment control region” is obtained by superimposing maps created by converting the maps (operation amount maps described later). At this time, since the coordinates of the EGR rate control area map and the supercharging pressure control area map are different, an operation amount map creation process for matching these coordinates is also performed (details will be described later).

  In the calculation process (4), an EGR that can minimize the time required to achieve an operation state in which both the NOx emission amount and the HC emission amount can be suppressed within the regulation range with respect to the current operation state. Calculate the rate and supercharging pressure. These are set as the target EGR rate and the target boost pressure. At this time, the transient response of the EGR rate determined in accordance with the amount of change in the EGR rate (the response of the EGR valve 81), and the transient response of the boost pressure determined in accordance with the amount of change in the boost pressure. The shortest time is calculated in consideration of (responsiveness of the variable nozzle vane mechanism 54), and based on this, the target EGR rate and the target supercharging pressure are determined.

  Since each calculation process in such cooperative control is performed, the “control device for an internal combustion engine” according to the present invention is configured by the ECU 100. As an input signal to the control device, a signal from each sensor such as a signal from the crank position sensor 40 and a signal from the intake pressure sensor 48 can be cited. The control device determines a target EGR rate and a target supercharging pressure based on these signals, outputs a control signal for achieving the target EGR rate to the EGR valve 81, and achieves the target supercharging pressure. A control signal for this is output to the variable nozzle vane mechanism 54.

  Hereinafter, the cooperative control procedure will be described with reference to the flowchart of FIG. 6 and the maps and graphs of FIGS.

  In this cooperative control, first, in step ST1, the current oxygen concentration in the cylinder is calculated. At this time, the oxygen concentration is calculated from the current EGR rate set by the opening degree of the EGR valve 81 (target EGR rate set at the present time) and the current oxygen excess rate. The oxygen excess rate is calculated based on the engine speed (calculated based on the output signal from the crank position sensor 40), the fuel injection amount (obtained from the injection amount command value to the injector 23), the supercharging pressure (intake It is calculated using parameters such as the intake air temperature (detected by the air flow meter 43), the intake air temperature (detected by the intake air temperature sensor 49), the intake air temperature (detected by the air flow meter 43).

  In step ST2, the oxygen concentration deviation is calculated by fitting the current oxygen concentration calculated in step ST1 to the EGR rate control region map corresponding to the current operation grid point. That is, the deviation between the required oxygen concentration, which is the upper limit value of the oxygen concentration allowed in the EGR rate control region map, and the current oxygen concentration is obtained. If the current oxygen concentration is lower than the required oxygen concentration and is within the target EGR rate control region (the target EGR rate control region obtained by the target EGR rate control region calculation unit), the deviation is allowed to decrease the EGR rate. The maximum value of the range. That is, even if the EGR rate is reduced by this deviation, the NOx emission amount can be suppressed within the regulation range. On the other hand, when the current oxygen concentration is higher than the required oxygen concentration and deviates from the target EGR rate control region, the deviation is the amount of increase in the EGR rate required to keep the NOx emission amount within the regulation range. It becomes.

  Point I in FIG. 7A shows an example of the current operating point (control point) on the EGR rate control region map in this case. In FIG. 7A, the current operating point is in the shaded area, that is, in the target EGR rate control area. In this case, since the oxygen concentration in the cylinder is equal to or lower than the required oxygen concentration, the NOx emission amount in the exhaust gas can be suppressed within the regulation range. Further, since this operating point has a deviation from the required oxygen concentration, even if the oxygen concentration is increased by an amount corresponding to this deviation (even if the EGR rate is reduced, the oxygen excess rate is reduced). Even if it is raised), it is possible to keep the NOx emission amount in the exhaust gas within the regulation range. That is, there is a margin for the adjustment range of the EGR rate.

  Next, in step ST3, the current gas amount in the cylinder is calculated. At this time, the gas amount is calculated based on the supercharging pressure, the intake air amount, the intake air temperature, and the like.

  In step ST4, the gas amount deviation is calculated by fitting the current in-cylinder gas amount calculated in step ST3 to the supercharging pressure control region map corresponding to the current operation grid point. That is, the deviation between the required in-cylinder gas amount that is the lower limit value of the gas amount required in the supercharging pressure control region map and the current in-cylinder gas amount is obtained. If the current in-cylinder gas amount is higher than the required in-cylinder gas amount and is within the target boost pressure control region (the target boost pressure control region calculated by the target boost pressure control region calculation unit), the deviation Is the maximum value within the allowable range of decrease in supercharging pressure. That is, even if the supercharging pressure is reduced by this deviation, the HC emission amount can be kept within the regulation range. On the other hand, when the current in-cylinder gas amount is lower than the required in-cylinder gas amount and deviates from the target boost pressure control region, the deviation is necessary to keep the HC emission amount within the regulation range. Increases the boost pressure.

  A point I ′ in FIG. 8A shows an example of the current operating point (control point) on the supercharging pressure control region map in this case. FIG. 8A shows a region where the current operating point is out of the shaded region, that is, a region out of the target boost pressure control region. In this case, since the amount of gas in the cylinder is less than the required amount of in-cylinder gas, the amount of HC emission in the exhaust cannot be suppressed within the regulation range. Also, since this operating point has a deviation from the required in-cylinder gas amount, if the in-cylinder gas amount is not increased by an amount corresponding to this deviation (if the boost pressure is not increased, or If the intake air temperature does not decrease), the HC emission amount in the exhaust cannot be kept within the regulation range.

  Next, in step ST5, an exhaust establishment control region in which the NOx emission amount can be suppressed within the restriction range and the HC emission amount can be suppressed within the restriction range is calculated (by the exhaust formation control region calculation unit). (Exhaust establishment control region calculation process). Specifically, an exhaust establishment control region map is created based on the EGR rate control region map and the boost pressure control region map.

  In creating this exhaust establishment control region map, first, an operation amount map corresponding to each of the EGR rate control region map and the supercharging pressure control region map is created. Hereinafter, creation of these operation amount maps will be described.

  First, an operation amount map for obtaining an EGR rate adjustment range is created based on the EGR rate control region map and the current operating point. FIG. 7B shows this manipulated variable map. This operation amount map is converted from the EGR rate control region map shown in FIG. In this manipulated variable map, the horizontal axis is the amount of change in EGR rate (ΔEGR rate), the vertical axis is the amount of change in supercharging pressure (Δsupercharging pressure), and the current operating point I is plotted on the horizontal axis (ΔEGR rate). It is located on the (axis). That is, the manipulated variable map is obtained by converting the horizontal axis into the ΔEGR rate and the vertical axis into the Δ supercharging pressure from the EGR rate control region map in FIG. In this map conversion, there is a correlation between the supercharging pressure and the oxygen excess rate, so the vertical axis conversion between these maps is possible. That is, as the supercharging pressure increases, the oxygen excess rate also increases. From this relationship, the vertical axis can be converted between these maps. In the operation amount map shown in FIG. 7B, it is possible to keep the NOx emission amount in the exhaust gas within the regulation range even if the ΔEGR rate and the Δ supercharging pressure are changed in the hatched region. It has become.

  Further, an operation amount map for obtaining an adjustment range of the supercharging pressure is created based on the supercharging pressure control region map and the current operating point. Specifically, after the boost pressure control region map shown in FIG. 8A is converted into a primary operation amount map shown in FIG. 8B, a secondary operation amount shown in FIG. Convert to a map. In the primary manipulated variable map, the horizontal axis is the amount of change in intake air temperature (ΔTb), the vertical axis is the amount of change in supercharging pressure (Δsupercharging pressure), and the current operating point I ′ is plotted on the horizontal axis (ΔTb). It is located on the (axis). That is, the primary manipulated variable map is obtained by converting the horizontal axis into ΔTb and the vertical axis into Δ supercharging pressure from the supercharging pressure control region map in FIG. In the secondary manipulated variable map, the horizontal axis is the amount of change in EGR rate (ΔEGR rate), the vertical axis is the amount of change in supercharging pressure (Δsupercharging pressure), and the current operating point I ′ is It is located on the axis (ΔEGR rate axis). The secondary operation amount map is obtained by converting the horizontal axis into the ΔEGR rate from the primary operation amount map. In converting from the primary operation amount map to the secondary operation amount map, there is a correlation between the EGR rate and the intake air temperature, so that the horizontal axis can be converted between these maps. In other words, since the intake air temperature increases as the EGR rate increases, the horizontal axis between these maps can be converted from this relationship. In the secondary operation amount map shown in FIG. 8C, the HC emission amount in the exhaust cannot be suppressed within the regulation range unless the supercharging pressure is increased.

  In this way, after creating the operation amount map (FIG. 7B) based on the EGR rate control region map and the secondary operation amount map based on the supercharging pressure control region map (FIG. 8C), exhaust gas is created. The establishment control area is calculated. Specifically, the exhaust establishment control region map is created by superimposing the operation amount maps. FIG. 9 shows this exhaust establishment control region map.

  In this exhaust formation control region map, the hatched region in the operation amount map (FIG. 7B) based on the EGR rate control region map (NOx in exhaust even if the EGR rate and supercharging pressure are changed). The region in which the discharge amount can be suppressed within the regulation range) and the hatched region (EGR rate and supercharging pressure) in the secondary operation amount map (FIG. 8C) based on the supercharging pressure control region map The region where the HC emission amount in the exhaust gas can be kept within the regulation range even when the exhaust gas is changed (the hatched region in FIG. 9) is the exhaust gas establishment control region. In other words, this exhaust establishment control region is a region in which the NOx emission amount can be suppressed within the regulation range, and the HC emission amount can be suppressed within the regulation range. When the current operating point is out of the exhaust establishment control region (upper side in the exhaust establishment control region map), the NOx emission amount is suppressed within the regulation range due to the high oxygen concentration. It is in a state where it is not possible. On the other hand, if the current operating point is below the exhaust establishment control region (lower side in the exhaust establishment control region map), the HC emission amount is within the regulation range due to the small amount of gas. It will be in the state which cannot be suppressed.

  Next, the process proceeds to step ST6, in which it is determined whether or not the current operating point is within the exhaust establishment control region (the hatched region) on the exhaust establishment control region map. That is, at the current operating point, it is determined whether the NOx emission amount can be suppressed within the regulation range and the HC emission amount can be suppressed within the regulation range.

  When the current operating point is not within the exhaust gas control range, that is, when at least one of the NOx emission amount and the HC emission amount is not within the regulation range and NO is determined in step ST6 Then, the process proceeds to step ST7. In step ST7, a transient response Kp of the supercharging pressure (responsiveness of the variable nozzle vane mechanism 54) and a transient response Ke of the EGR rate (responsiveness of the EGR valve 81) are read. Specifically, the transient response Kp of the supercharging pressure changes in accordance with the amount of change in supercharging pressure (Δsupercharging pressure). Further, the transient responsiveness Ke of the EGR rate changes according to the amount of change in the EGR rate (ΔEGR rate). In the ROM, the transient response Kp of the boost pressure corresponding to the Δ boost pressure and the transient response Ke of the EGR rate corresponding to the ΔEGR rate are stored in advance corresponding to each operation grid point of the engine 1. Has been.

  The transient response can be replaced with the time required to achieve the required amount of change (the amount of change in supercharging pressure, the amount of change in EGR rate). FIG. 10 is a graph showing the relationship between the Δ supercharging pressure and the required time corresponding to the Δ supercharging pressure (transient response of the supercharging pressure). FIG. 11 is a graph showing the relationship between the ΔEGR rate and the required time (transient responsiveness of the EGR rate) according to the ΔEGR rate. These pieces of information are stored in the ROM corresponding to each operation grid point of the engine 1.

  In this way, after reading the transient response Kp of the supercharging pressure and the transient response Ke of the EGR rate, the process proceeds to step ST8, and the shortest time (the shortest arrival time) for shifting the operating point into the exhaust gas establishment control region. ) Is calculated.

  This shortest arrival time is calculated as follows. Here, as shown in FIGS. 7 to 9, the case where the current operating point is in the target EGR rate control region and is out of the target boost pressure control region will be described as an example. That is, the case where there is an operating point below the exhaust establishment control region in the exhaust establishment control region map of FIG. 9 will be described as an example.

  First, in order to shift the operating point into the exhaust establishment control region, a point on the lowermost line L1 of the exhaust establishment control region in the exhaust establishment control region map (on the straight line L1 indicated by the broken line in FIG. 9). It is necessary to shift the operating point to Now, let this straight line L1 be the following formula (1).

Δsupercharging pressure = a × ΔEGR rate + b (1)
Here, a and b are constants.

  Next, the time required to shift the supercharging pressure to the state closest to the current operating point in the exhaust gas establishment control region (a point on the straight line L1) is t1, and the EGR rate is Let t2 be the time required to shift to the state closest to the operating point (point on the straight line L1). In this case, the total time required to shift the operating point into the exhaust gas establishment control region is given by the following equation (2).

t = t1 + t2 (2)
Here, since the current operating point is within the target EGR rate control region and is out of the target boost pressure control region, the value that can be taken as the Δ boost pressure is a “positive” value (the boost pressure). Is the value on the side that raises. That is, “Δsupercharging pressure> 0”. Further, the ΔEGR rate can take any value of “positive” and “negative” (value on the side of increasing the EGR rate and value on the side of lowering). That is, “ΔEGR rate> 0” or “ΔEGR rate <0”.

  Hereinafter, the time t is calculated separately for each case.

(When Δsupercharging pressure> 0, ΔEGR rate> 0)
In this case, the time t is given by the following equation (3).

t = f (Δsupercharging pressure) + h (ΔEGR rate) (3)
Here, f is a function for obtaining the time t1 according to the transient response Kp of the supercharging pressure when Δsupercharging pressure> 0 (see FIG. 10). Actually, the Δ supercharging pressure is higher than the broken line in FIG. Further, h is a function for obtaining the time t2 according to the transient response Ke of the EGR rate when ΔEGR rate> 0 (see FIG. 11). In practice, the ΔEGR rate is higher than the broken line in FIG. 11 and is a positive value.

  Substituting equation (1) into equation (3) yields equation (4).

t = f (a × ΔEGR rate + b) + h (ΔEGR rate)
= M (ΔEGR rate) (4)
That is, the time t is a value obtained from a function (function m) having only the ΔEGR rate as a variable.

  For this reason, the minimum value of the time t can be calculated from the equation (4). Hereinafter, the minimum value of the time t is “ta”.

(ΔSupercharging pressure> 0, ΔEGR rate <0)
In this case, the time t is given by the following equation (5).

t = f (Δsupercharging pressure) + k (ΔEGR rate) (5)
Here, k is a function for obtaining the time t2 according to the transient response Ke of the EGR rate when ΔEGR rate <0 (see FIG. 11). In practice, the ΔEGR rate is higher than the broken line in FIG. 11 and is a negative value.

  Substituting equation (1) into equation (5) yields equation (6).

t = f (a × ΔEGR rate + b) + k (ΔEGR rate)
= N (ΔEGR rate) (6)
That is, also in this case, the time t is a value obtained from a function (function n) having only the ΔEGR rate as a variable.

  For this reason, the minimum value of time t can be calculated from this equation (6). Hereinafter, the minimum value of the time t is assumed to be “tb”.

  Then, the shorter one of the obtained minimum values “ta” and “tb” of the time t is calculated as the shortest arrival time “tmin”.

  Thereby, the shortest arrival time tmin for shifting the operating point into the exhaust gas establishment control region is calculated.

  As described above, here, the case where the current operating point is in the target EGR rate control region and out of the target boost pressure control region has been described as an example. That is, the case where there is an operating point below the exhaust establishment control region in the exhaust establishment control region map of FIG. 9 has been described as an example. If the current operating point is within the target boost pressure control region and is out of the target EGR rate control region (the operating point is above the exhaust establishment control region in the exhaust establishment control region map of FIG. 9). In some cases, in order to shift the operating point into the exhaust establishment control region, a point on the uppermost line L2 of the exhaust establishment control region in the exhaust establishment control region map of FIG. 9 (shown by a solid line in FIG. 9). The above calculation is performed so as to shift to a point on the straight line L2. In this case, the value that can be taken by the Δ supercharging pressure can be either “positive” or “negative” (the value on the side that increases the supercharging pressure and the value that decreases the value). That is, “Δsupercharging pressure> 0” or “supercharging pressure <0”. Further, a value that can be taken by the ΔEGR rate is a “positive” value (a value on the side that increases the EGR rate). That is, “ΔEGR rate> 0”. For this reason, the minimum value of the time t is determined for each of the cases “Δ supercharging pressure> 0, ΔEGR rate> 0” and “Δsupercharging pressure <0, ΔEGR rate> 0”. The arrival time tmin is calculated.

  Further, if the current operating point is out of the target EGR rate control region and out of the target supercharging pressure control region (this is the operating point indicated by point II in the exhaust establishment control region map of FIG. 9). In order to shift the operating point into the exhaust establishment control region, the intersection of the lowermost line L1 and the uppermost line L2 in the exhaust establishment control region in the exhaust establishment control region map of FIG. The above-described calculation is performed so as to shift to. Further, in this case, a value that can be taken by the Δ supercharging pressure is a “positive” value (a value on the side that increases the supercharging pressure). That is, “Δsupercharging pressure> 0”. Further, a value that can be taken by the ΔEGR rate is a “positive” value (a value on the side that increases the EGR rate). That is, “ΔEGR rate> 0”. For this reason, the shortest arrival time tmin in the case “Δ supercharging pressure> 0, ΔEGR rate> 0” is calculated.

  After calculating the shortest arrival time tmin as described above, the process proceeds to step ST9, where the ΔEGR rate which is a control amount required to shift the operating point to the exhaust gas establishment control region (point on the straight line L1) and Calculate the Δ supercharging pressure.

  The ΔEGR rate is calculated by substituting the shortest arrival time tmin into t in Equation (4). Further, when calculating the Δ supercharging pressure, it is obtained by substituting the obtained ΔEGR rate into the equation (1). The ΔEGR rate and Δsupercharging pressure obtained here correspond to X (control amount of EGR rate) and Y (control amount of supercharging pressure) in FIG.

  In step ST10, a value obtained by adding the ΔEGR rate obtained as described above to the current EGR rate is calculated as the target EGR rate (calculation of the target EGR rate by the target value calculation unit). When the ΔEGR rate is a “positive” value, a value obtained by adding this ΔEGR rate to the current EGR rate is the target EGR rate. When the ΔEGR rate is a “negative” value, a value obtained by subtracting the ΔEGR rate from the current EGR rate is the target EGR rate.

  Similarly, a value obtained by adding the Δ supercharging pressure obtained as described above to the current supercharging pressure is calculated as a target supercharging pressure (the target supercharging pressure by the target value calculating unit). Calculation). When the Δ supercharging pressure is a “positive” value, a value obtained by adding this Δsupercharging pressure to the current supercharging pressure becomes the target supercharging pressure. Further, when the Δ supercharging pressure is a “negative” value, a value obtained by subtracting this Δ supercharging pressure from the current supercharging pressure becomes the target supercharging pressure.

  In step ST11, the opening degree control of the EGR valve 81 is executed so that the EGR rate becomes the calculated target EGR rate. Further, the opening degree control of the nozzle vane 54a is executed so that the supercharging pressure becomes the calculated target supercharging pressure.

  As the opening control of the EGR valve 81 for achieving the target EGR rate, feedback control is performed to calculate the actual EGR rate and bring the actual EGR rate closer to the target EGR rate. In calculating the actual EGR rate, for example, the opening degree of the EGR valve 81 detected by an EGR valve opening degree sensor (not shown), the intake air temperature detected by the intake air temperature sensor 49, and the intake air pressure detected by the intake pressure sensor 48 are used. Using pressure or the like as a parameter, it is obtained from a predetermined arithmetic expression or map stored in advance in the ROM. Further, as the opening degree control of the nozzle vane 54a for achieving the target boost pressure, feedback control is performed to calculate the actual boost pressure and bring the actual boost pressure closer to the target boost pressure. The actual boost pressure is obtained from the intake pressure detected by the intake pressure sensor 48, for example.

  By performing the opening degree control of the EGR valve 81 and the opening degree control of the nozzle vane 54a, the NOx emission amount can be suppressed within the regulation range in the shortest time and the HC emission amount can be regulated. Can be kept within the range.

  On the other hand, if it is determined in step ST6 that the current operating point is within the exhaust establishment control region (the hatched region in FIG. 9) on the exhaust establishment control region map, This means that the NOx emission amount can be kept within the regulation range, and the HC emission amount can be kept within the regulation range. For example, as shown in FIG. 12, this is the case where the operating point I is in the exhaust establishment control region (shaded area) in the exhaust establishment control region map.

  In the present embodiment, cooperative control is performed so that the overall efficiency of the turbocharger 5 becomes the maximum efficiency in such a situation. That is, if YES is determined in step ST6, the process proceeds to step ST12, and the target turbo total efficiency in the current engine operation state (operation grid point) is read. This target turbo overall efficiency is stored in the ROM for each operating grid point.

  The turbo overall efficiency is represented by the product of turbine efficiency, compressor efficiency, and mechanical efficiency. Turbine efficiency is the turbine work divided by the amount of exhaust energy lost in the turbine. The compressor efficiency is the air compression work divided by the turbine work. The mechanical efficiency is the ratio of the remaining energy amount obtained by subtracting the loss caused by the frictional resistance of bearings and seals to the exhaust energy amount given to the turbine.

  Thereafter, the process proceeds to step ST13, and the shortest arrival time for shifting the operating point to the operating point at which the turbo overall efficiency becomes the maximum efficiency is calculated. The calculation of the shortest arrival time is performed in the same manner as the processing in step ST8.

  Thereafter, in the same manner as described above, the ΔEGR rate and Δsupercharging pressure calculation processing in step ST9, the target EGR rate and target supercharging pressure calculation processing in step ST10, and the opening degree of the EGR valve 81 in step ST11 Control and opening degree control of the nozzle vane 54a are performed. In the example shown in FIG. 12, the operating point at which the overall turbo efficiency is maximum is III in the figure, and the ΔEGR rate and Δsupercharging pressure calculation processing for achieving this operating point III is performed, An EGR rate and a target boost pressure are obtained.

  As described above, when the current operating point is within the exhaust gas control region on the exhaust gas control region map, the operating point at which the turbo overall efficiency becomes the maximum efficiency is set as the target EGR rate and the target boost pressure, respectively. Thus, the opening degree control of the EGR valve 81 and the opening degree control of the nozzle vane 54a are performed. For this reason, in the shortest time, the NOx emission amount can be kept within the regulation range, the HC emission amount can be kept within the regulation range, and the overall turbo efficiency can be maximized. .

  By repeating the above operation, it is possible to shorten the time required to keep the NOx emission amount and the HC emission amount within the limits of regulation. In particular, even during the transient operation of the engine 1, it is possible to shorten the time required to keep the NOx emission amount and the HC emission amount within the limits of regulation.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to the in-line four-cylinder diesel engine 1 mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited. Further, the present invention is not limited to diesel engines using light oil as fuel, but can also be applied to engines using gasoline or other fuels.

  In the above embodiment, the time required to shift the supercharging pressure to the state closest to the current operating point (the point on the straight line L1) in the exhaust establishment control region is t1, and the EGR rate is controlled by exhaust establishment control. The time required to move to the state closest to the current operating point in the region (the point on the straight line L1) is t2, and the sum (t1 + t2) of these is used to move the operating point into the exhaust gas control region. Was set as the total time required. The present invention is not limited to this, and considering that the adjustment operation of the EGR rate and the adjustment operation of the supercharging pressure are performed in parallel, the longer one of the time t1 and the time t2 is exhausted as the operating point. It is also possible to set as the total time required for shifting to the establishment control area.

  Moreover, although the said embodiment demonstrated the case where this invention was applied to the conventional vehicle (vehicle which mounted only the engine as a driving force source), with respect to a hybrid vehicle (vehicle which mounted the engine and the electric motor as a driving force source). However, the present invention is applicable.

  The present invention can be applied to a correction operation of the fuel injection amount and the intake air amount in a diesel engine mounted on an automobile.

1 engine (internal combustion engine)
5 Turbocharger (supercharger)
54 Variable nozzle vane mechanism (variable capacity mechanism)
81 EGR valve 100 ECU

Claims (1)

In a control device for an internal combustion engine that controls an EGR rate by an EGR valve and controls a supercharging pressure of intake air by a supercharger having a variable displacement mechanism,
A target EGR rate control region calculation unit for calculating a target EGR rate control region in which the oxygen concentration in the cylinder is equal to or lower than the required oxygen concentration;
A target boost pressure control region calculation unit for calculating a target boost pressure control region in which the gas amount in the cylinder is equal to or greater than the required gas amount;
An exhaust establishment control region calculating unit that calculates an exhaust establishment control region that satisfies both the target EGR rate control region and the target boost pressure control region;
Based on the transient responsiveness of the EGR valve and the transient responsiveness of the variable displacement mechanism, the EGR rate and the supercharging pressure that can be reached in the shortest time among the EGR rate and supercharging pressure in the exhaust gas control region are respectively set as targets. A control apparatus for an internal combustion engine, comprising: a target value calculation unit configured to calculate an EGR rate and a target boost pressure.

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