JP2017172541A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate an NOx discharge amount.SOLUTION: A control device 200 of an internal combustion engine 100 comprises: an NOx discharge amount calculation part for calculating an NOx discharge amount on the basis of the highest in-cylinder temperature when an equivalent ratio in a combustion region in a cylinder 10 is set as a prescribed equivalent ratio; a reference-figure indicated average effective pressure calculation part for calculating reference-figure indicated average effective pressure on the basis of an engine operation state; and a figure-indicated average effective pressure calculation part for calculating figure-indicated effective pressure on the basis of in-cylinder pressure. The NOx discharge amount calculation part calculates the highest in-cylinder temperature with the prescribed equivalent ratio as a reference equivalent ratio, reduces the NOx discharge amount which is calculated on the basis of the highest in-cylinder temperature as the figure-indicated average effective pressure becomes higher than the reference-figure indicated average effective pressure, or calculates the highest in-cylinder temperature with the prescribed equivalent ratio as an equivalent ratio which is smaller than the reference equivalent ratio as the figure-indicated average effective pressure becomes higher than the reference-figure indicated average effective pressure, and calculates the NOx discharge amount on the basis of the highest in-cylinder temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine.

  In Patent Document 1, as a conventional control device for an internal combustion engine, the maximum in-cylinder temperature in a cylinder is calculated on the assumption that the equivalence ratio φ in the combustion region in the cylinder is uniform at an arbitrary equivalence ratio, and the maximum An apparatus that estimates the amount of NOx in exhaust discharged from the cylinder based on the in-cylinder temperature (hereinafter referred to as “NOx emission amount”) is disclosed.

JP 2012-021432 A

  The above-described conventional control device for an internal combustion engine is based on the assumption that diffusion combustion is performed in the cylinder, and assuming that the equivalent ratio φ in the combustion region in the cylinder is 1, the maximum in-cylinder temperature in the cylinder. Was calculated. However, when the premixed gas is subjected to compression auto-ignition combustion in the cylinder, the equivalence ratio in the combustion region in the cylinder is smaller than 1, and the equivalence ratio in the combustion region in the cylinder changes greatly according to the engine operating state. To do. Therefore, in the above-described conventional control device for an internal combustion engine, there is a possibility that the estimation accuracy of the NOx emission amount when the premixed gas is subjected to compression self-ignition combustion in the cylinder is deteriorated.

  The present invention has been made paying attention to such problems, and it is an object of the present invention to make it possible to accurately estimate the NOx emission amount even when the premixed gas is subjected to compression self-ignition combustion in a cylinder. And

  In order to solve the above-described problems, according to an aspect of the present invention, an engine body and a cylinder pressure detection sensor for detecting the cylinder pressure of a cylinder of the engine body are provided, and the premixed gas is detected in the cylinder. When the internal combustion engine control device for controlling the internal combustion engine capable of performing compression auto-ignition combustion of the cylinder has the equivalent ratio in the combustion region in the cylinder as a predetermined equivalent ratio, the highest cylinder in one cycle in the cylinder Based on the internal temperature, the NOx emission amount calculation unit for calculating the NOx emission amount discharged from the cylinder, and based on the engine operating state, the equivalence ratio in the combustion region in the cylinder is set to a predetermined reference equivalence ratio. A reference indicated mean effective pressure calculating unit that calculates a reference indicated mean effective pressure, and an indicated mean effective pressure calculating unit that calculates the indicated mean effective pressure based on the in-cylinder pressure. The NOx concentration calculating unit calculates the maximum in-cylinder temperature using the predetermined equivalent ratio as the reference equivalent ratio, and the indicated average effective pressure is the reference indicated average effective pressure based on the NOx emission amount calculated based on the maximum in-cylinder temperature. The maximum in-cylinder temperature is calculated as an equivalent ratio smaller than the reference equivalent ratio as the indicated equivalent effective ratio becomes higher than the reference indicated average effective pressure. Based on the above, the NOx emission amount is calculated.

  According to this aspect of the present invention, the NOx emission amount can be accurately estimated even when the premixed gas is subjected to compression self-ignition combustion in the cylinder.

FIG. 1 is a schematic configuration diagram of an internal combustion engine and an electronic control unit that controls the internal combustion engine according to the first embodiment of the present invention. FIG. 2 is a diagram showing an operating region of the internal combustion engine according to the first embodiment of the present invention. FIG. 3 is a flowchart illustrating the NOx emission amount estimation control according to the first embodiment of the present invention. FIG. 4 is a table for calculating the NOx emission amount based on the maximum in-cylinder temperature. FIG. 5 is a table for calculating the NOx correction amount based on the difference value obtained by subtracting the reference indicated average effective pressure from the actual indicated effective average pressure. FIG. 6 is a flowchart illustrating NOx emission amount estimation control according to the second embodiment of the present invention. FIG. 7 is a map for calculating the actual equivalence ratio in the combustion region in the cylinder based on the actual illustrated effective average pressure and the reference illustrated average effective pressure. FIG. 8 is a table for calculating the NOx correction amount based on the actual equivalent ratio. FIG. 9 is a flowchart illustrating NOx emission amount estimation control according to the third embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to similar components.

(First embodiment)
FIG. 1 is a schematic configuration diagram of an internal combustion engine 100 and an electronic control unit 200 that controls the internal combustion engine 100 according to a first embodiment of the present invention.

  The internal combustion engine 100 includes an engine body 1 having a plurality of cylinders 10, a fuel supply device 2, an intake device 3, an exhaust device 4, an intake valve device 5, and an exhaust valve device 6.

  The internal combustion engine according to the present embodiment includes premixed compression self-ignition combustion in which premixed gas (homogeneous premixed gas or stratified premixed gas) is compressed and ignited in each cylinder 10, and compressed air is fueled in each cylinder 10. The engine body 1 can be operated by selectively performing diffusion combustion in which the fuel is burned while being mixed with air. Hereinafter, details of each component of the internal combustion engine will be described.

  The engine body 1 burns fuel in each cylinder 10 to generate power for driving a vehicle, for example. The engine body 1 is provided with a pair of intake valves 50 and a pair of exhaust valves 60 for each cylinder. The engine body 1 is provided with one in-cylinder pressure sensor 210 for detecting the in-cylinder pressure of each cylinder 10 for each cylinder.

  The fuel supply device 2 includes an electronically controlled fuel injection valve 20, a delivery pipe 21, a supply pump 22, and a fuel tank 23.

  One fuel injection valve 20 is provided in each cylinder 10 so as to face the combustion chamber of each cylinder 10. The valve opening time (injection amount) and valve opening timing (injection timing) of the fuel injection valve 20 are changed by a control signal from the electronic control unit 200, and when the fuel injection valve 20 is opened, the fuel injection valve 20 changes to the cylinder 10. The fuel is directly injected into the inside.

  The delivery pipe 21 is connected to the fuel tank 23 via a pressure feed pipe 24. A supply pump 22 for pressurizing the fuel stored in the fuel tank 23 and supplying it to the delivery pipe 21 is provided in the middle of the pressure feeding pipe 24. The delivery pipe 21 temporarily stores the high-pressure fuel pumped from the supply pump 22. When the fuel injection valve 20 is opened, the high-pressure fuel stored in the delivery pipe 21 is directly injected into the cylinder from the fuel injection valve 20. The delivery pipe 21 is provided with a fuel pressure sensor 211 for detecting the fuel pressure in the delivery pipe 21, that is, the pressure (injection pressure) of the fuel injected from the fuel injection valve 20 into the cylinder.

  The supply pump 22 is configured to be able to change the discharge amount, and the discharge amount of the supply pump 22 is changed by a control signal from the electronic control unit 200. By controlling the discharge amount of the supply pump 22, the fuel pressure in the delivery pipe 21, that is, the injection pressure of the fuel injection valve 20 is controlled.

  The intake device 3 is a device for guiding intake air into each cylinder 10 and changes the state of intake air (intake pressure, intake air temperature, EGR (Exhaust Gas Recirculation) gas amount) taken into each cylinder 10. It is configured to be able to. The intake device 3 includes an intake passage 30, an intake manifold 31, and an EGR passage 32.

  One end of the intake passage 30 is connected to the air cleaner 34, and the other end is connected to the intake collector 31 a of the intake manifold 31. In the intake passage 30, an air flow meter 212, a compressor 71 of the exhaust turbocharger 7, an intercooler 35, and a throttle valve 36 are provided in order from the upstream.

  The air flow meter 212 detects the flow rate of air that flows in the intake passage 30 and is finally sucked into each cylinder 10 (hereinafter referred to as “in-cylinder intake air amount”).

  The compressor 71 includes a compressor housing 71a and a compressor wheel 71b disposed in the compressor housing 71a. The compressor wheel 71b is rotationally driven by the turbine wheel 72b of the exhaust turbocharger 7 mounted on the same axis, and compresses and discharges the intake air flowing into the compressor housing 71a. The turbine 72 of the exhaust turbocharger 7 is provided with a variable nozzle 72c for controlling the rotational speed of the turbine wheel 72b. By controlling the rotational speed of the turbine wheel 72b by the variable nozzle 72c, the compressor housing 71a. The pressure (supercharging pressure) of the intake air discharged from the inside is controlled.

  The intercooler 35 is a heat exchanger for cooling the intake air that has been compressed by the compressor 71 to a high temperature, for example, with traveling wind, cooling water, or the like.

  The throttle valve 36 adjusts the amount of intake air introduced into the intake manifold 31 by changing the cross-sectional area of the intake passage 30. The throttle valve 36 is driven to open and close by a throttle actuator 36a, and its opening (throttle opening) is detected by a throttle sensor 213.

  The intake manifold 31 is connected to the engine body 1, and distributes the intake air flowing in from the intake passage 30 to each cylinder 10 evenly through the intake port formed in the engine body 1. The intake collector 31a of the intake manifold 31 includes an intake pressure sensor 214 for detecting the pressure (intake pressure) of intake air sucked into each cylinder 10, and the temperature of intake air (intake air temperature) sucked into each cylinder 10. ) Is provided.

  The EGR passage 32 communicates the exhaust manifold 41 and the intake collector 31a of the intake manifold 31, and is a passage for returning a part of the exhaust discharged from each cylinder 10 to the intake collector 31a by a pressure difference. Hereinafter, the exhaust gas flowing into the EGR passage 32 is referred to as “EGR gas”. By recirculating the EGR gas to the intake collector 31a and thus to each cylinder 10, the combustion temperature can be reduced and the emission of nitrogen oxides (NOx) can be suppressed. The EGR passage 32 is provided with an EGR cooler 37 and an EGR valve 38 in order from the upstream.

  The EGR cooler 37 is a heat exchanger for cooling the EGR gas with, for example, traveling wind or cooling water.

  The EGR valve 38 is an electromagnetic valve whose opening degree can be adjusted continuously or stepwise, and the opening degree is controlled by the electronic control unit 200. By controlling the opening degree of the EGR valve 38, the flow rate of the EGR gas to be recirculated to the intake collector 31a is adjusted.

  The exhaust device 4 is a device for discharging exhaust gas from the inside of each cylinder 10 and includes an exhaust manifold 41 and an exhaust passage 42.

  The exhaust manifold 41 is connected to the engine body 1 and collectively introduces exhaust discharged from each cylinder 10 into the exhaust passage 42.

  The exhaust passage 42 is provided with a turbine 72 of the exhaust turbocharger 7 and an exhaust aftertreatment device 43 in order from the upstream.

  The turbine 72 includes a turbine housing 72a and a turbine wheel 72b disposed in the turbine housing 72a. The turbine wheel 72b is rotationally driven by the energy of the exhaust gas flowing into the turbine housing 72a, and drives the compressor wheel 71b mounted coaxially.

  The variable nozzle 72c described above is provided outside the turbine wheel 72b. The variable nozzle 72 c functions as a throttle valve, and the nozzle opening (valve opening) of the variable nozzle 72 c is controlled by the electronic control unit 200. By changing the nozzle opening degree of the variable nozzle 72c, the flow rate of the exhaust for driving the turbine wheel 72b can be changed in the turbine housing 72a. That is, by changing the nozzle opening degree of the variable nozzle 72c, the supercharging pressure can be changed by changing the rotational speed of the turbine wheel 72b. Specifically, when the nozzle opening of the variable nozzle 72c is reduced (the variable nozzle 72c is throttled), the exhaust flow rate increases, the rotational speed of the turbine wheel 72b increases, and the supercharging pressure increases.

  The exhaust aftertreatment device 43 is a device for purifying exhaust gas and discharging it to the outside air, and includes various exhaust purification catalysts for purifying harmful substances, filters for collecting harmful substances, and the like.

  The intake valve operating device 5 is a device for opening and closing the intake valve 50 of each cylinder 10 and is provided in the engine body 1. The intake valve operating device 5 according to the present embodiment is configured such that the intake valve 50 of each cylinder 10 can be opened during the intake stroke. In this embodiment, an electromagnetic actuator controlled by the electronic control unit 200 is adopted as such an intake valve operating device 5, and the intake valve 50 of each cylinder 10 is driven to open and close by the electromagnetic actuator, thereby opening and closing the intake valve 50. The timing and lift amount are controlled to an arbitrary timing and lift amount.

  The exhaust valve device 6 is a device for opening and closing the exhaust valve 60 of each cylinder 10 and is provided in the engine body 1. The exhaust valve operating device 6 according to the present embodiment is configured so that the exhaust valve 60 of each cylinder 10 can be opened during the exhaust stroke, and can also be opened during the intake stroke as necessary. In this embodiment, an electromagnetic actuator controlled by the electronic control unit 200 is adopted as such an exhaust valve operating device 6, and the exhaust valve 60 of each cylinder 10 is driven to open and close by the electromagnetic actuator, thereby opening and closing the exhaust valve 60. The timing and lift amount are controlled to an arbitrary timing and lift amount.

  The intake valve device 5 and the exhaust valve device 6 are not limited to electromagnetic actuators. For example, the intake valve 50 and the exhaust valve 60 can be opened and closed and the lift amount can be changed by changing the cam profile by hydraulic pressure or the like. A valve device can also be employed.

  The electronic control unit 200 is composed of a digital computer and is connected to each other by a bi-directional bus 201. A ROM (read only memory) 202, a RAM (random access memory) 203, a CPU (microprocessor) 204, an input port 205, and an output port 206.

  Output signals from the above-described fuel pressure sensor 211, air flow meter 212, throttle sensor 213, intake pressure sensor 214, intake air temperature sensor 215, and the like are input to the input port 205 via the corresponding AD converters 207. The output voltage of the load sensor 217 that generates an output voltage proportional to the amount of depression of the accelerator pedal 221 (hereinafter referred to as “accelerator depression amount”) is input to the input port 205 via the corresponding AD converter 207. Is done. Further, an output signal of a crank angle sensor 218 that generates an output pulse every time the crankshaft of the engine body 1 rotates, for example, 15 ° is input to the input port 205 as a signal for calculating the engine rotation speed. As described above, output signals of various sensors necessary for controlling the internal combustion engine 100 are input to the input port 205.

  The output port 206 is connected to each electromagnetic actuator of the intake valve operating device 5, each electromagnetic actuator of the exhaust valve operating device 6, the fuel injection valve 20, the supply pump 22, the throttle actuator 36 a, and the EGR valve 38 via the corresponding drive circuit 208. And the variable nozzle 72c and the like.

  The electronic control unit 200 controls the internal combustion engine 100 by outputting a control signal for controlling each control component from the output port 206 based on the output signals of various sensors input to the input port 205. Hereinafter, control of the internal combustion engine 100 performed by the electronic control unit 200 will be described.

  The electronic control unit 200 switches the operation mode of the engine body 1 to either the premixed compression auto-ignition combustion mode or the diffusion combustion mode based on the engine operation state (engine rotation speed and engine load).

  Specifically, as shown in FIG. 2, the electronic control unit 200 switches the operation mode to the premixed compression auto-ignition combustion mode if the engine operation state is within the first operation region on the low rotation and low load side. The electronic control unit 200 switches the operation mode to the diffusion combustion mode if the engine operation state is within the second operation region on the high rotation high load side. The electronic control unit 200 performs combustion control according to each operation mode.

  When the operation mode is the premixed compression auto-ignition combustion mode, the electronic control unit 200 basically has a premixed gas (homogeneous mixed gas) having an air-fuel ratio (for example, about 30 to 40) leaner than the stoichiometric air-fuel ratio in the cylinder 10. (Or, a stratified mixture) is formed, and the premixture is compressed and self-ignited and combusted to operate the engine body 1.

  In addition, when the operation mode is the diffusion combustion mode, the electronic control unit 200 injects fuel into the compressed air that has become high temperature and high pressure in the cylinder 10 and performs diffusion combustion in which the fuel is burned while being mixed with air. The main body 1 is operated.

  By the way, if the NOx amount (NOx emission amount) in the exhaust discharged from each cylinder 10 can be accurately estimated, for example, a NOx storage reduction catalyst or a NOx selective reduction catalyst is used as the exhaust purification catalyst without using the NOx sensor. The amount of reducing agent necessary for reducing NOx can be accurately added to each catalyst based on the estimated NOx emission amount. Therefore, the NOx amount discharged to the outside air can be controlled to be equal to or less than a desired discharge amount while suppressing an increase in cost, so that deterioration of exhaust emission can be suppressed.

  The NOx emission amount discharged from each cylinder 10 has a correlation with the maximum in-cylinder temperature (combustion gas temperature) in one cycle of each cylinder 10 and is lower when the maximum in-cylinder temperature is higher. Less.

  Therefore, conventionally, the maximum in-cylinder temperature in one cycle of the cylinder 10 is calculated, and the NOx emission amount discharged from the cylinder 10 is estimated based on the maximum in-cylinder temperature. In this case, it is necessary to calculate the maximum in-cylinder temperature in one cycle in the cylinder 10, and a method for calculating the maximum in-cylinder temperature when diffusion combustion is performed in the cylinder 10 is known. Specifically, there are two regions in the cylinder 10, that is, a region where combustion is performed (hereinafter referred to as “combustion region”) and a region where combustion is not performed (hereinafter referred to as “unburned region”). There are known methods for calculating the maximum in-cylinder temperature in the cylinder 10 on the assumption that the equivalence ratio (local equivalence ratio) φ in the combustion region is uniform at an arbitrary equivalence ratio.

  Here, if diffusion combustion is performed in the cylinder 10, the equivalent ratio φ in the combustion region can be assumed to be approximately 1, although it is sparse when considering the entire cylinder 10. Therefore, the maximum in-cylinder temperature in the cylinder 10 can be accurately calculated by a known method.

  However, when premixed compression self-ignition combustion is performed in the cylinder 10, the fuel diffused in the cylinder 10 causes self-ignition at multiple points at the same time, so the equivalence ratio in the combustion region in the cylinder 10 is 1. Smaller than. Further, the equivalence ratio in the combustion region in the cylinder 10 also changes greatly according to the engine operating state. Therefore, the known method cannot accurately calculate the maximum in-cylinder temperature in the cylinder 10, and as a result, the estimation accuracy of the NOx emission amount deteriorates. Specifically, when premixed compression auto-ignition combustion is performed in the cylinder 10, the equivalent ratio in the combustion region in the cylinder 10 is less than 1 and the combustion is diluted, so that diffusion combustion is performed The combustion temperature of the combustion gas is lower than that. Therefore, the maximum in-cylinder temperature calculated by a known method tends to be higher than the actual maximum in-cylinder temperature, and as a result, the estimated NOx emission amount tends to be larger than the actual NOx emission amount.

  Thus, when the estimated value of the NOx emission amount becomes larger than the actual NOx emission amount, for example, a NOx storage reduction catalyst or a NOx selective reduction catalyst is used as the exhaust purification catalyst, and the reducing agent is based on the estimated NOx emission amount. When the amount of addition is controlled, the amount of addition of the reducing agent becomes excessive. As a result, exhaust emission is deteriorated because excess reducing agent is discharged to the outside air.

  Here, as the equivalence ratio φ in the combustion region in the cylinder 10 decreases, the combustion temperature of the combustion gas decreases and the specific heat ratio κ in the combustion region increases, so the engine thermal efficiency increases. When the premixed compression auto-ignition combustion is performed in the cylinder 10, the equivalence ratio φ in the combustion region is smaller than 1 as described above, so that the engine thermal efficiency is increased as compared with the case where the diffusion combustion is performed.

  Therefore, based on the engine thermal efficiency when diffusion combustion is performed, that is, the engine thermal efficiency when the equivalence ratio φ in the combustion region in the cylinder 10 is assumed to be 1, the premixed compression auto-ignition combustion is higher than the reference engine thermal efficiency. It can be determined how much the equivalent ratio φ in the combustion region in the cylinder 10 is smaller than 1 by determining how much the actual engine thermal efficiency when performing the above. That is, by determining how much the actual engine thermal efficiency is higher than the reference engine thermal efficiency, an actual equivalent ratio (hereinafter referred to as “actual equivalent ratio”) φr in the combustion region in the cylinder 10 can be estimated, and It can be determined how much the combustion temperature of the combustion gas is lowered and, as a result, how much the NOx emission amount is reduced.

  Therefore, if it is determined how much the actual engine thermal efficiency is higher than the standard engine thermal efficiency, the NOx emission amount calculated by the known method described above can be corrected based on the determination result, and the actual The NOx emission amount can be calculated with high accuracy.

  Therefore, in the present embodiment, the known average method described above is calculated by calculating the indicated mean effective pressure, which is one of the indexes representing the engine thermal efficiency, based on the in-cylinder pressure, and comparing it with the reference average effective pressure as a reference. The NOx emission amount calculated in step 1 was corrected based on the comparison result. Hereinafter, the NOx emission amount estimation control according to this embodiment will be described.

  FIG. 3 is a flowchart illustrating the NOx emission amount estimation control according to the present embodiment. The electronic control unit 200 repeatedly executes this routine at a predetermined calculation cycle.

  In step S1, the electronic control unit 200 reads the engine rotational speed calculated based on the output signal of the crank angle sensor 218 and the engine load detected by the load sensor 217, and detects the engine operating state.

  In step S2, the electronic control unit 200 refers to the IMEP calculation map stored in advance in the ROM 202, and calculates the reference indicated mean effective pressure IMEPt based on the engine operating state. The IMEP calculation map indicates that the indicated mean effective pressure that should be generated in the cylinder 10 (that is, the reference indicated mean effective pressure IMEPt) when the equivalent ratio φ in the combustion region in the cylinder 10 is a predetermined reference equivalent ratio φt. Is obtained by an experiment or the like in advance for each engine operating state and is mapped. In the present embodiment, the reference equivalent ratio φt is 1.

  In step S <b> 3, the electronic control unit 200 determines the actual indicated average effective pressure (hereinafter referred to as “actually indicated effective average pressure”) of the cylinder 10 in which combustion has been performed based on the in-cylinder pressure P detected by the in-cylinder pressure sensor. ) Calculate IMEPg.

Specifically, first, the electronic control unit 200 calculates the illustrated work IWc during the compression stroke from the following equation (1) based on the change in the in-cylinder pressure P during the compression stroke (finger pressure), and the expansion stroke. Based on the change in the in-cylinder pressure P, the illustrated work IWe during the expansion stroke is calculated from the following equation (2). P _θi is the in-cylinder pressure at the crank angle θi, and P _{θi + 1} is the in-cylinder pressure at the crank angle θi + 1. V _θi is the in-cylinder volume at the crank angle θi, and V _{θi + 1} is the in-cylinder volume at the crank angle θi + 1.

Next, the electronic control unit 200 calculates the actual illustrated effective average pressure IMEPg from the following equation (3) based on the illustrated work IWc during the compression stroke, the illustrated work IWe during the expansion stroke, and the in-cylinder volume V.

  In step S4 to step S9, the electronic control unit 200 calculates the maximum in-cylinder temperature by the known method described above. Hereinafter, specific processing contents of each step will be described.

In step S4, the electronic control unit 200 refers to a map or the like stored in advance in the ROM, and the in-cylinder intake air amount detected by the air flow meter 212 and the EGR rate set in advance according to the engine operating state. Based on the above, the in-cylinder gas amount Gc and the in-cylinder oxygen concentration O ₂ in are calculated.

In step S5, the electronic control unit 200 performs the following on the basis of the in-cylinder pressure P _θ and the in-cylinder volume V _θ at any crank angle θ during the intake stroke, the in-cylinder gas amount Gc, and the gas constant R The in-cylinder average temperature Tc is calculated from the gas state equation (4).

  In step S6, the electronic control unit 200 calculates a gas amount in the combustion region (hereinafter referred to as “combustion gas amount (burned gas amount)”) Gb. Specifically, the electronic control unit 200 first calculates the heat generation rate (dQ / dθ) for each crank angle θ from the following equation (5) based on the first law of thermodynamics, and calculates this heat generation rate. The heat generation amount Q is calculated by integrating as in the following equation (6). In Equation (5), κ is a specific heat ratio.

Next, the electronic control unit 200 calculates the combustion gas amount Gb from the following equation (7) based on the calculated heat generation amount Q. Here, the heat generation amount Q is generated by the combustion of fuel in the cylinder 10. The unit calorific value Hu when the unit amount of fuel burns is a physical property value of the fuel and is a known value. Therefore, the fuel amount in the cylinder 10 can be calculated by dividing the heat generation amount Q by the unit heat generation amount Hu. Therefore, the combustion gas amount Gb can be calculated by the following equation (7). In the equation (7), 21 is the oxygen concentration in the air. AFR is a stoichiometric air-fuel ratio corresponding to the fuel used. Thus, in this embodiment, since AFR is the stoichiometric air-fuel ratio, the combustion gas amount Gb calculated by the equation (7) is the combustion when the equivalent ratio φ in the combustion region in the cylinder 10 is assumed to be 1. Gas amount.

In step S7, the electronic control unit 200 calculates the gas temperature in the unburned region (hereinafter referred to as “unburned gas temperature”) Tu. Specifically, the electronic control unit 200 calculates the unburned gas temperature Tu from the following equation (8) on the assumption that the inside of the cylinder 10 is adiabatically changed (isentropic change). Note that P _θivc in Expression (8) is the in-cylinder pressure at the intake valve closing timing θivc, and the in-cylinder pressure detected by the in-cylinder pressure sensor at the intake valve closing timing θivc can be used. T _θivc is the in-cylinder temperature at the intake valve closing timing θivc, and is based on the in-cylinder pressure P _θivc , the in-cylinder volume V _{θivc at the} intake valve closing timing θivc, the in-cylinder gas amount Gc, and the gas constant R. And what was computed by the state equation of gas can be used.

In step S8, the electronic control unit 200 calculates a gas temperature (hereinafter referred to as “combustion gas temperature”) Tb in the combustion region. Specifically, the electronic control unit 200 assumes that the sum of the internal energy of the unburned region and the combustion region is equal to the sum of the internal energy of the entire cylinder obtained based on the in-cylinder average temperature Tc. The combustion gas temperature Tb is calculated from the equation (9).

  In step S9, the electronic control unit 200 sets the maximum value of the combustion gas temperature Tb in one cycle as the maximum in-cylinder temperature Tbmax.

  In step S10, the electronic control unit 200 refers to the table shown in FIG. 4 stored in advance in the ROM 202, and calculates the NOx emission amount based on the maximum in-cylinder temperature Tbmax.

  In step S11 to step S12, the electronic control unit 200 performs correction to reduce the NOx emission amount calculated in step S10 as the actual illustrated effective average pressure IMEPg becomes higher than the reference illustrated average effective pressure IMEPt. Hereinafter, specific processing contents of each step will be described.

  In step S11, the electronic control unit 200 refers to the table of FIG. 5 stored in advance in the ROM 202, and based on the difference value X obtained by subtracting the reference indicated average effective pressure IMEPt from the actual indicated effective average pressure IMEPg, the NOx correction amount. Is calculated. As shown in FIG. 5, the NOx correction amount increases as the difference value X increases. This is because, as the actual indicated effective average pressure IMEPg is higher than the reference indicated average effective pressure IMEPt, the actual equivalent ratio (hereinafter referred to as “actual equivalent ratio”) φr in the combustion region in the cylinder 10 is greater than the reference equivalent ratio φt. This is because it can be determined that the amount of NOx emission has decreased, and the NOx emission amount can also be determined to decrease according to the amount of decrease in the equivalence ratio φ.

  In step S12, the electronic control unit 200 corrects the NOx emission amount calculated in step S10 based on the NOx correction amount. Specifically, the electronic control unit 200 performs correction by subtracting the NOx correction amount from the NOx emission amount calculated in step S10, and calculates the final NOx emission amount.

  According to the present embodiment described above, the engine body 1 and the in-cylinder pressure sensor 210 for detecting the in-cylinder pressure of the cylinder 10 of the engine body 1 are provided. During one cycle in the cylinder 10 when the electronic control unit 200 (control device) for controlling the internal combustion engine 100 capable of ignition combustion sets the equivalent ratio in the combustion region in the cylinder 10 to a predetermined equivalent ratio. Based on the maximum in-cylinder temperature in the engine, the NOx emission amount calculation unit for calculating the NOx emission amount discharged from the cylinder 10 and the equivalence ratio in the combustion region in the cylinder 10 are determined in advance based on the engine operating state. A reference indicated mean effective pressure calculating unit for calculating a reference indicated mean effective pressure IMEPt with a reference equivalent ratio, and an indicated mean for calculating an actual indicated mean effective pressure IMEPg based on the in-cylinder pressure. Comprising a effective pressure calculation unit, a. The NOx emission amount calculation unit calculates the maximum in-cylinder temperature using the predetermined equivalent ratio as a reference equivalent ratio, and the actual illustrated average effective pressure IMEPg indicates the NOx emission amount calculated based on the maximum in-cylinder temperature. The higher the average effective pressure IMEPt, the lower the pressure.

  The actual equivalent ratio φr in the combustion region in the cylinder 10 becomes smaller than the reference equivalent ratio φt as the actual indicated average effective pressure IMEPg becomes higher than the reference indicated average effective pressure IMEPt. Therefore, the actual maximum in-cylinder temperature is also higher than the maximum in-cylinder temperature when the equivalent ratio in the combustion region in the cylinder 10 is set as the reference equivalent ratio as the actual indicated average effective pressure IMEPg is higher than the reference indicated average effective pressure IMEPt. Also lower. Therefore, as shown in this embodiment, the actual indicated average effective pressure IMEPg is the reference indicated average, which is the NOx emission amount calculated based on the maximum in-cylinder temperature when the equivalent ratio in the combustion region in the cylinder 10 is set as the reference equivalent ratio. By reducing the higher the effective pressure IMEPt, the NOx emission amount corresponding to the actual equivalent ratio φr can be calculated. Therefore, according to the present embodiment, even when the premixed gas is subjected to compression self-ignition combustion in the cylinder 10, the NOx emission amount can be accurately estimated.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. This embodiment is different from the first embodiment in the method of calculating the NOx correction amount. Hereinafter, this difference will be mainly described.

  In the first embodiment described above, the NOx correction amount is calculated directly from the actual indicated effective average pressure IMEPg and the reference indicated average effective pressure IMEPt. However, in the present embodiment, the NOx correction amount is indirectly calculated therefrom. To do. Specifically, in the present embodiment, the actual equivalent ratio φr in the combustion region in the cylinder 10 is first calculated based on the actual illustrated effective average pressure IMEPg and the reference illustrated average effective pressure IMEPt. Then, the NOx correction amount is calculated based on the actual equivalent ratio φ.

  By calculating the actual equivalent ratio φr in this way, for example, if the target equivalent ratio in the combustion region in the cylinder 10 corresponding to the engine operating state can be calculated with reference to a map or the like, the actual equivalent ratio φr can be calculated. For example, the fuel injection pressure or the like can be feedback controlled so as to achieve the target equivalent ratio. As a result, when the actual equivalent ratio φr deviates from the target equivalent ratio, the actual equivalent ratio φr can be quickly controlled to the target equivalent ratio. Hereinafter, the NOx emission amount estimation control according to this embodiment will be described.

  FIG. 6 is a flowchart illustrating the NOx emission amount estimation control according to this embodiment. The electronic control unit 200 repeatedly executes this routine at a predetermined calculation cycle.

  Since the processing contents from step S1 to step S10 and step S12 are the same as those in the first embodiment described above, description thereof is omitted here.

  In step S21, the electronic control unit 200 refers to the map of FIG. 7 which is created in advance by experiments or the like and stored in the ROM 202, and based on the actual illustrated effective average pressure IMEPg and the reference illustrated average effective pressure IMEPt, The actual equivalence ratio φr in the combustion region in the cylinder 10 is calculated.

  As shown in the map of FIG. 7, when the actual indicated effective average pressure IMEPg and the reference indicated average effective pressure IMEPt coincide, that is, the difference obtained by subtracting the reference indicated average effective pressure IMEPt from the actual indicated effective average pressure IMEPg. When the value X is zero, the actual equivalent ratio φr becomes the reference equivalent ratio φt (= 1). As the actual illustrated effective average pressure IMEPg becomes higher than the reference illustrated average effective pressure IMEPt, that is, as the difference value X increases, the actual equivalent ratio φr becomes smaller than the reference equivalent ratio φt.

  In step S22, the NOx correction amount is calculated based on the actual equivalent ratio φr with reference to the table of FIG. As shown in FIG. 8, the NOx correction amount increases as the actual equivalent ratio φr decreases.

  As described above, also in the present embodiment, the correction for reducing the NOx emission amount calculated in step S10 is performed as the actual illustrated effective average pressure IMEPg becomes larger than the reference illustrated average effective pressure IMEPt. Therefore, also in this embodiment, the same effect as the first embodiment can be obtained.

  Further, according to this embodiment, when the actual equivalent ratio φr deviates from the target equivalent ratio, the actual equivalent ratio φr can be quickly controlled to the target equivalent ratio. Therefore, the engine body is operated while the actual equivalent ratio φr deviates from the target equivalent ratio, and deterioration of fuel consumption and exhaust emission can be suppressed.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the present embodiment, the maximum in-cylinder temperature in one cycle in the cylinder is calculated when the equivalent ratio in the combustion region in the cylinder 10 is the actual equivalent ratio φr, and the NOx emission amount is calculated based on the maximum in-cylinder temperature. Is different from the first embodiment in that it is directly estimated with high accuracy. Hereinafter, this difference will be mainly described.

  FIG. 9 is a flowchart illustrating the NOx emission amount estimation control according to this embodiment. The electronic control unit 200 repeatedly executes this routine at a predetermined calculation cycle.

  Since the processing contents from step S1 to step S5 and from step S7 to step S10 are the same as those in the first embodiment, description thereof is omitted here.

  In step S31, the electronic control unit 200 refers to the map of FIG. 7 described above, and based on the actual illustrated effective average pressure IMEPg and the standard illustrated average effective pressure IMEPt, the actual equivalent ratio in the combustion region in the cylinder 10 is determined. φr is calculated. As described above, the actual equivalent ratio φr becomes smaller than the reference equivalent ratio φt (= 1) as the actual indicated effective average pressure IMEPg is higher than the reference indicated average effective pressure IMEPt.

In step S32, the electronic control unit 200 calculates the heat generation amount Q from the above-described equations (5) and (6). In the present embodiment, the electronic control unit 200 calculates the combustion gas amount Gb from the following equation (7 ′) based on the calculated heat generation amount Q.

  As shown in Expression (7 '), in this embodiment, the theoretical air-fuel ratio AFR corresponding to the fuel used is divided by the actual equivalent ratio φr calculated in step S31 to obtain the actual air-fuel ratio. Thereby, the combustion gas amount Gb calculated by the equation (7 ′) is the combustion gas amount when the equivalent ratio φ in the combustion region in the cylinder 10 is set to the actual equivalent ratio φr.

  Therefore, in step S8, the combustion gas temperature Tb calculated by the above equation (9) using this combustion gas amount Gb is also the combustion when the equivalent ratio φ in the combustion region in the cylinder 10 is set to the actual equivalent ratio φr. It becomes gas temperature. Therefore, the maximum in-cylinder temperature Tbmax calculated in step S9 is also the maximum in-cylinder temperature when the equivalent ratio φ in the combustion region in the cylinder 10 is set to the actual equivalent ratio φr.

  Thus, in the present embodiment, the cylinder 10 is utilized by utilizing the fact that the actual equivalent ratio φr becomes smaller than the reference equivalent ratio φt (= 1) as the actual indicated effective average pressure IMEPg becomes higher than the reference indicated average effective pressure IMEPt. The maximum in-cylinder temperature is calculated as an equivalent ratio in the combustion region of which is smaller than the reference equivalent ratio φt as the indicated average effective pressure becomes higher than the reference indicated average effective pressure IMEPt. Therefore, in the present embodiment, even when premixed compression self-ignition combustion is performed, the maximum in-cylinder temperature Tbmax can be accurately estimated in accordance with the change in the equivalence ratio φ according to the engine operating state. Therefore, in step S10, the NOx emission amount can be directly and accurately calculated from the maximum in-cylinder temperature Tbmax calculated in step S9.

  According to the present embodiment described above, the engine main body and the in-cylinder pressure sensor for detecting the in-cylinder pressure of the cylinder 10 of the engine main body are provided, and the premixed gas is compressed and self-ignited and combusted in the cylinder 10. When the electronic control unit 200 (control device) for controlling the internal combustion engine capable of controlling the equivalent ratio in the combustion region in the cylinder 10 assumes a predetermined equivalent ratio, the highest in-cylinder in one cycle in the cylinder 10 A NOx emission amount calculation unit for calculating the NOx emission amount discharged from the cylinder 10 based on the temperature, an indicated average effective pressure calculation unit for calculating the actual indicated average effective pressure IMEPg based on the in-cylinder pressure, and an engine A reference indicated average effective pressure calculating unit that calculates a reference indicated average effective pressure IMEPt when the equivalent ratio in the combustion region in the cylinder 10 is set to a predetermined reference equivalent ratio based on the operating state; And the NOx concentration calculation unit calculates the maximum in-cylinder temperature as the predetermined equivalent ratio as an equivalent ratio that is smaller than the reference equivalent ratio as the actual indicated average effective pressure IMEPg is larger than the reference indicated average effective pressure IMEPt. The NOx emission amount is calculated based on the maximum in-cylinder temperature.

  Even if comprised in this way, the NOx discharge | emission amount according to real equivalent ratio (phi) r is computable like 1st Embodiment. Therefore, even when the premixed gas is subjected to compression self-ignition combustion in the cylinder 10, the NOx emission amount can be accurately estimated.

  Further, according to the present embodiment, the table for calculating the NOx correction amount as described above with reference to FIGS. 5 and 8 becomes unnecessary, and the NOx emission amount can be estimated directly and accurately from the calculated maximum in-cylinder temperature Tbmax. it can. Therefore, it is possible to reduce the man-hours required for creating the table.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  For example, the internal combustion engine 100 in each of the above-described embodiments is configured to perform premixed compression auto-ignition combustion in the first operation region and perform diffusion combustion in the second operation region to operate the engine body. It had been. However, in at least a part of the operation region, in the internal combustion engine configured to perform the operation of the engine body by performing the premixed compression auto-ignition combustion, the NOx emission amount estimation described in each of the above embodiments is performed. Control may be performed.

1 Engine Body 10 Cylinder 100 Internal Combustion Engine 200 Electronic Control Unit (Control Device)
210 In-cylinder pressure sensor

Claims (1)

The engine body,
An in-cylinder pressure sensor for detecting an in-cylinder pressure of a cylinder of the engine body;
With
A control device for an internal combustion engine for controlling an internal combustion engine capable of performing compression auto-ignition combustion of a premixed gas in the cylinder,
A NOx emission amount calculation unit that calculates the NOx emission amount discharged from the cylinder based on the maximum in-cylinder temperature in one cycle in the cylinder when the equivalent ratio in the combustion region in the cylinder is a predetermined equivalent ratio. When,
A reference indicated mean effective pressure calculating unit that calculates a reference indicated mean effective pressure when the equivalence ratio in the combustion region in the cylinder is set to a predetermined reference equivalent ratio based on the engine operating state;
Based on the in-cylinder pressure, an indicated mean effective pressure calculating unit that calculates an indicated mean effective pressure;
With
The NOx emission amount calculation unit
The maximum in-cylinder temperature is calculated using the predetermined equivalent ratio as the reference equivalent ratio, and the NOx emission amount calculated based on the maximum in-cylinder temperature is calculated from the reference indicated average effective pressure. The maximum equivalent in-cylinder temperature is calculated as an equivalent ratio that is smaller than the reference equivalent ratio as the indicated average effective pressure is higher than the reference indicated average effective pressure. Configured to calculate the NOx emission based on a maximum in-cylinder temperature;
Control device for internal combustion engine.

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