JP2019203445A - Smoke estimation device of internal combustion engine - Google Patents

Abstract

To estimate a smoke concentration and a smoke quantity in an exhaust gas of an internal combustion engine at higher accuracy.SOLUTION: A smoke estimation device of an internal combustion engine estimates a smoke concentration or a smoke quantity in an exhaust gas discharged from a combustion chamber of the internal combustion engine 1 in which fuel is directly injected into the combustion chamber 15. The smoke estimation device estimates a value of a parameter which changes according to a total surface area of fuel droplets injected into the combustion chamber, and calculates the smoke concentration or the smoke quantity on the basis of the estimated value of the parameter while taking into consideration that the smoke concentration or the smoke quantity in the exhaust gas discharged from the combustion chamber becomes low or small as the total surface area of the fuel droplets becomes large.SELECTED DRAWING: Figure 4

Description

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

  Conventionally, for a compression ignition type internal combustion engine, the amount of smoke generated in the combustion chamber is estimated, and the injection parameter from the fuel injection valve is set so that the estimated amount of smoke generated is equal to or less than a predetermined allowable upper limit value. Control is proposed (for example, patent document 1). In the device described in Patent Document 1, the amount of fuel whose equivalence ratio is locally 1 or more, the volume of a region including fuel spray at a predetermined time after fuel injection, the fuel injection period from the fuel injection valve, The smoke generation amount is estimated based on the above.

  In addition, the amount of smoke generated depends on, for example, the shape of the nozzle hole of the fuel injection valve, the travel distance of the spray tip from the fuel injection start timing to the fuel ignition timing, the equivalence ratio of the air-fuel mixture at the fuel ignition timing (For example, Patent Documents 2 and 3).

JP 2014-015895 A JP 2017-129046 A JP 2017-048708 A

  By the way, in the conventional smoke amount estimation method, the amount of smoke in the exhaust gas discharged from the combustion chamber is estimated by macroscopically capturing the fuel spray from the fuel injection valve. For example, in the apparatus described in Patent Document 1, a fuel spray from the fuel injection valve is macroscopically distinguished from a spray having an equivalence ratio of 1 or more and a spray having a ratio of less than 1, among which the equivalence ratio is 1 The smoke amount is estimated based on the amount of fuel contained in the spray as described above.

  However, the smoke amount estimation method that captures the fuel spray from the fuel injector only in a macro manner cannot always estimate the smoke amount in the exhaust gas with high accuracy. Therefore, in order to estimate the smoke amount with higher accuracy, it is necessary to estimate the fuel spray from the fuel injection valve even on a microscopic level.

  The present invention has been made in view of the above problems, and its object is to estimate the smoke concentration in the exhaust gas of the internal combustion engine by estimating the fuel spray from the fuel injection valve microscopically. The purpose is to estimate the smoke amount with higher accuracy.

  The present invention has been made to solve the above problems, and the gist thereof is as follows.

  (1) A smoke estimation device for an internal combustion engine for estimating a smoke concentration or a smoke amount in exhaust gas discharged from a combustion chamber of an internal combustion engine in which fuel is directly injected into the combustion chamber, the fuel being injected into the combustion chamber In the exhaust gas discharged from the combustion chamber, the larger the total surface area of the fuel droplets, the larger the total surface area of the fuel droplets. A smoke estimation device for an internal combustion engine that calculates the smoke concentration or the smoke amount on the assumption that the smoke concentration or the smoke amount becomes small.

  (2) Estimating the temperature in the combustion chamber when the air-fuel mixture burns in the combustion chamber, and based on the estimated temperature in the combustion chamber, the higher the temperature in the combustion chamber, the higher the temperature in the exhaust gas discharged from the combustion chamber. The smoke estimation device for an internal combustion engine according to (1), wherein the smoke concentration or the smoke amount is calculated assuming that the smoke concentration or the smoke amount is small.

  According to the present invention, the smoke concentration or the smoke amount in the exhaust gas of the internal combustion engine can be estimated with higher accuracy.

FIG. 1 is a schematic configuration diagram of an internal combustion engine. FIG. 2 is a schematic cross-sectional view of the engine body of the internal combustion engine. FIG. 3 is a flowchart showing a control routine for target setting control for setting the target value of the injection parameter. FIG. 4 is a diagram showing the relationship between various parameters and smoke density. FIG. 5 is a view similar to FIG. 4 showing the relationship between m _O2 / Qm × Ismd and the smoke concentration. FIG. 6 is a diagram showing the relationship between the measured value and the estimated value of the smoke concentration.

  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>
≪Description of the internal combustion engine as a whole≫
First, the configuration of the internal combustion engine 1 in which the smoke estimation device according to the present embodiment is used will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram of an internal combustion engine 1. FIG. 2 is a schematic cross-sectional view of the engine body 10 of the internal combustion engine 1. The internal combustion engine of this embodiment is a compression self-ignition internal combustion engine in which light oil is used as fuel.

  As shown in FIGS. 1 and 2, the internal combustion engine 1 includes an engine body 10, a fuel supply device 30, an intake system 40, an exhaust system 50, an EGR mechanism 60, and a control device 70.

  The engine body 10 includes a cylinder block 12 in which a plurality of cylinders 11 are formed, and a cylinder head 13. A piston 14 that reciprocates in each cylinder 11 is disposed in each cylinder 11. A combustion chamber 15 in which the air-fuel mixture burns is formed in the cylinder 11 between the piston 14 and the cylinder head 13. A cavity 16 formed in a concave shape is formed on the top surface of the piston 14.

  As shown in FIG. 2, the cylinder head 13 is formed with an intake port 17 and an exhaust port 18. The intake port 17 and the exhaust port 18 communicate with the combustion chamber 15 of each cylinder 11. An intake valve 21 is disposed between the combustion chamber 15 and the intake port 17, and the intake valve 21 opens and closes the intake port 17. Similarly, an exhaust valve 22 is disposed between the combustion chamber 15 and the exhaust port 18, and the exhaust valve 22 opens and closes the exhaust port 18.

  As shown in FIG. 1, the fuel supply device 30 includes a fuel injection valve 31, a common rail 32, a fuel supply pipe 33, a fuel pump 34, and a fuel tank 35. The fuel injection valve 31 is disposed in the cylinder head 13 so as to inject fuel directly into the combustion chamber 15 of each cylinder 11. In particular, in the present embodiment, each fuel injection valve 31 is disposed at the center of the upper wall surface of each combustion chamber 15, and fuel is directed from the fuel injection valve 31 toward the peripheral portion in the cavity 16 formed in the piston 14. It is comprised so that F may be injected (FIG. 2).

  The fuel injection valve 31 is connected to a fuel tank 35 via a common rail 32 and a fuel supply pipe 33. A fuel pump 34 that pumps the fuel in the fuel tank 35 is disposed in the fuel supply pipe 33. The fuel pumped by the fuel pump 34 is supplied to the common rail 32 via the fuel supply pipe 33 and is directly injected into the combustion chamber 15 from the fuel injection valve 31 as the fuel injection valve 31 is opened. . In the present embodiment, the fuel pressure (injection pressure) when the fuel is injected from the fuel injection valve 31 into the combustion chamber 15 is adjusted by the fuel pump 34.

  The intake system 40 includes an intake manifold 41, an intake pipe 43, an air cleaner 44, a compressor 5a of an exhaust turbocharger 5, an intercooler 45, and a throttle valve 46. The intake port 17 of each cylinder 11 communicates with an intake manifold 41, and the intake manifold 41 communicates with an air cleaner 44 via an intake pipe 43. The intake pipe 43 is provided with a compressor 5a of an exhaust turbocharger 5 that compresses and discharges intake air flowing through the intake pipe 43, and an intercooler 45 that cools the air compressed by the compressor 5a. The intercooler 45 is disposed on the downstream side of the compressor 5a in the flow direction of the intake air. The throttle valve 46 is disposed in the intake pipe 43 between the intercooler 45 and the intake manifold 41. The throttle valve 46 is rotated by a throttle valve drive actuator 47, whereby the opening area of the intake passage can be changed. The intake port 17, the intake manifold 41, and the intake pipe 43 form an intake passage that supplies intake gas to the combustion chamber 15.

  The exhaust system 50 includes an exhaust manifold 51, an exhaust pipe 52, a turbine 5 b of the exhaust turbocharger 5, and an exhaust aftertreatment device 53. The exhaust port 18 of each cylinder 11 communicates with an exhaust manifold 51, and the exhaust manifold 51 communicates with an exhaust pipe 52. The exhaust pipe 52 is provided with a turbine 5 b of the exhaust turbocharger 5. The turbine 5b is driven to rotate by the energy of the exhaust gas. The compressor 5a of the exhaust turbocharger 5 and the turbine 5b are connected by a rotating shaft. When the turbine 5b is driven to rotate, the compressor 5a rotates with this, and the intake air is compressed. The exhaust pipe 52 is provided with an exhaust aftertreatment device 53 on the downstream side in the exhaust flow direction of the turbine 5b. The exhaust aftertreatment device 53 is a device for purifying exhaust gas and discharging it into the outside air, and includes various exhaust purification catalysts for purifying harmful substances, filters for collecting harmful substances, and the like. The exhaust port 18, the exhaust manifold 51, and the exhaust pipe 52 form an exhaust passage for exhausting exhaust gas from the combustion chamber 15.

  The EGR mechanism 60 includes an EGR pipe 61, an EGR control valve 62, and an EGR cooler 63. The EGR pipe 61 is connected to the exhaust manifold 51 and the intake manifold 41 so as to communicate with each other. The EGR pipe 61 is provided with an EGR cooler 63 that cools the EGR gas flowing in the EGR pipe 61. In addition, the EGR pipe 61 is provided with an EGR control valve 62 that can change the opening area of the EGR passage formed by the EGR pipe 61. By controlling the opening degree of the EGR control valve 62, the flow rate of EGR gas recirculated from the exhaust manifold 51 to the intake manifold 41 is adjusted.

  The control device 70 includes an electronic control unit (ECU) 71 and various sensors. The ECU 71 is composed of a digital computer, and is connected to each other via a bidirectional bus 72, a RAM (random access memory) 73, a ROM (read only memory) 74, a CPU (microprocessor) 75, an input port 76, and An output port 77 is provided.

  The common rail 32 is provided with a fuel pressure sensor 82 for detecting the pressure of fuel in the common rail 32, that is, the pressure of fuel injected from the fuel injection valve 31 into the combustion chamber 15 (injection pressure). The intake pipe 43 is provided with an air flow meter 84 for detecting the flow rate of the air flowing through the intake pipe 43 on the upstream side of the compressor 5a of the exhaust turbocharger 5 in the intake flow direction. The throttle valve 46 is provided with a throttle opening sensor 85 for detecting the opening (throttle opening). The outputs of the fuel pressure sensor 82, the air flow meter 84, and the throttle opening degree sensor 85 are input to the input port 76 via the corresponding AD converter 78.

  A load sensor 89 that generates an output voltage proportional to the amount of depression of the accelerator pedal 88 is connected to the accelerator pedal 88, and the output voltage of the load sensor 89 is input to the input port 76 via the corresponding AD converter 78. The Therefore, in this embodiment, the depression amount of the accelerator pedal 88 is used as the engine load. The crank angle sensor 90 generates an output pulse every time the crankshaft of the engine body 10 rotates, for example, 10 degrees, and this output pulse is input to the input port 76. The CPU 75 calculates the engine speed from the output pulse of the crank angle sensor 90.

  On the other hand, the output port 77 of the ECU 71 is connected to each actuator that controls the operation of the internal combustion engine 1 via a corresponding drive circuit 79. In the example shown in FIGS. 1 and 2, the output port 77 is connected to the fuel injection valve 31, the fuel pump 34, the throttle valve drive actuator 47, and the EGR control valve 62. The ECU 71 outputs a control signal for controlling these actuators from the output port 77 to control the operation of the internal combustion engine 1.

≪Fuel injection control≫
Next, fuel injection control from the fuel injection valve 31 will be described with reference to FIG. In the internal combustion engine 1 configured as described above, the value of the injection parameter is basically set based on the value of a parameter representing the engine operating state (hereinafter also referred to as “operation parameter”). As an operation parameter, engine load, engine speed, etc. are mentioned, for example. On the other hand, as injection parameters, for example, fuel injection amount (injection amount in each fuel injection when performing multiple fuel injections), fuel injection timing (injection of each fuel injection when performing multiple fuel injections) Timing), number of fuel injections, fuel injection pressure, and the like.

  The relationship between the operation parameter and the injection parameter is experimentally obtained in advance and is stored in the ROM 74 of the ECU 71 as a map or a calculation formula. Basically, the relationship between the operation parameter and the injection parameter is such that the output of the internal combustion engine 1 becomes an appropriate value corresponding to the engine load in each engine operation state, while the fuel consumption of the internal combustion engine 1 and the exhaust emission from the internal combustion engine 1. Is set to be good. During operation of the internal combustion engine, values of various operation parameters of the internal combustion engine 1 are detected, and each target of the injection parameter is determined based on the relationship obtained in advance based on the detected value of the operation parameter. A value is calculated. Then, the fuel injection valve 31 and the fuel pump 34 are controlled so that the actual injection parameter value becomes the target value.

  By the way, in the compression ignition type internal combustion engine, when the combustion state of the air-fuel mixture in the combustion chamber 15 deteriorates, exhaust gas containing smoke is discharged from the combustion chamber 15. The relationship between the operation parameter and the injection parameter described above is that the smoke concentration in the exhaust gas discharged from the combustion chamber 15 (hereinafter also referred to as “smoke concentration”) appropriately maintains the output and fuel consumption of the internal combustion engine 1. However, it is set to be as small as possible.

  However, for example, when the operating parameters used for calculating the target value of the injection parameter are only the engine load and the engine speed, for example, the smoke concentration of the exhaust gas is not necessarily kept small in all engine operating states. It is difficult to do. On the other hand, when the operation parameter used to calculate the target value of the injection parameter includes many various parameters other than the engine load and the engine speed, the optimum injection parameter is determined for each operation state determined by these operation parameters. Enormous man-hours are required for setting.

  Therefore, in the present embodiment, the number of operation parameters used for calculating the target value of the injection parameter is relatively reduced to reduce the adaptation man-hour. In addition, in the present embodiment, the smoke concentration of the exhaust gas is estimated during operation of the internal combustion engine, and when the estimated smoke concentration is larger than a preset smoke upper limit concentration, it is set based on the operation parameter. The injection parameter value is corrected so that the smoke density becomes small.

  FIG. 3 is a flowchart showing a control routine for target setting control for setting the target value of the injection parameter. The illustrated control routine is performed by interruption at regular time intervals.

  As shown in FIG. 3, first, in step S11, values of various parameters are detected or calculated. As this parameter, in addition to the operation parameter used for calculating the target value of the injection parameter, the value of the operation parameter used for calculating the estimated value of the smoke emission concentration is detected or calculated.

  Specifically, for example, the engine load is detected by the load sensor 89, the engine rotation speed is calculated based on the output of the crank angle sensor 90, and the fuel injection pressure is detected based on the output of the fuel pressure sensor 82. The In addition, the mass of oxygen supplied into the combustion chamber 15 is calculated based on the intake air amount calculated based on the output of the air flow meter 84 and the opening degree of the EGR control valve 62. Specifically, as the amount of intake air calculated by the air flow meter 84 increases, the mass of oxygen supplied into the combustion chamber 15 increases, and as the opening degree of the EGR control valve 62 increases, it is supplied into the combustion chamber 15. The mass of oxygen is calculated on the assumption that the mass of oxygen decreases.

  Next, in step S12, the target value of the injection parameter is calculated based on the value of the operation parameter detected or calculated in step S11. In the present embodiment, target values such as the fuel injection amount, the fuel injection timing, the fuel injection pressure, and the number of fuel injections are calculated based on the engine load and the engine speed. Specifically, for example, the fuel injection amount is set such that the total fuel injection amount in one cycle increases as the engine load increases. Further, the fuel injection timing is set so that, for example, the injection timing of each fuel injection is advanced as the engine speed increases. For example, the fuel injection pressure is set so as to increase as the engine load increases so that appropriate injection can be maintained even when the in-cylinder pressure increases.

Next, in step S13, the smoke upper limit concentration m _s lim is calculated based on the value of the operation parameter detected or calculated in step S11. In the present embodiment, the smoke upper limit concentration m _s lim is calculated based on the engine load and the engine speed. The relationship between the engine load and the engine speed and the smoke upper limit concentration m _s lim differs depending on the type of the internal combustion engine 1. For example, the smoke upper limit concentration m _s lim is set smaller as the engine speed decreases. This is because when the engine rotational speed is low, the flow rate of the exhaust gas is slowed down, and fine particles are likely to adhere to the exhaust pipe 52 and the turbine 5b of the exhaust turbocharger 5.

Next, in step S14, an estimated value m _{s of} smoke concentration is calculated based on the value of the operating parameter detected or calculated in step S11. A specific estimation method will be described later.

Next, in step S15, it is determined whether or not the smoke concentration estimated value m _s calculated in step S14 is larger than the smoke upper limit concentration m _s lim calculated in step S13. When it is determined that the smoke density estimated value m _s is equal to or less than the smoke upper limit density m _s lim, the control routine is terminated. Therefore, fuel injection from the fuel injection valve 31 is performed based on the target value of the injection parameter calculated in step S12.

On the other hand, when it is determined in step S15 that the smoke density estimated value m _s is larger than the smoke upper limit density m _s lim, the process proceeds to step S16. In step S16, the target value of the injection parameter calculated in step S12 is corrected so that the amount of smoke discharged is reduced. Specifically, for example, the injection pressure of the fuel injected from the fuel injection valve 31 is increased, or the number of fuel injections is increased so that after injection is added after the main injection.

≪Smoke concentration estimation≫
Next, the smoke concentration estimation method in step S14 of FIG. 3 will be described. In the present embodiment, the smoke concentration is estimated in the ECU 71. Therefore, the ECU 71 functions as a smoke estimation device that estimates the smoke concentration discharged from the combustion chamber 15.

In the present embodiment, the smoke concentration estimated value m _s is calculated by the following equation (1).
In the above formula (1), m _O2 represents the mass (g) of oxygen supplied to the combustion chamber 15, and Qm represents fuel injection in the main injection from the fuel injection valve 31 into the combustion chamber 15 in each cycle. It represents the quantity (mm ³ ). Further, A _s1 and A _s2 are positive constants and are identified based on the measurement result of the actual machine. The main injection means fuel injection with the largest amount of fuel when fuel injection is performed in a plurality of times, and is fuel injection that contributes to the output of the internal combustion engine 1. The main injection is basically performed near the compression top dead center.

In addition, Ismd in the formula (1) is a coefficient proportional to the total surface area of all droplets of fuel injected from the fuel injection valve 31 into the combustion chamber 15 (hereinafter referred to as “droplet surface area coefficient”). Is calculated by the following equation (2).
In Formula (2), SMD represents the average particle diameter (mm) of all droplets of fuel injected from the fuel injection valve 31 into the combustion chamber 15, and in this embodiment, SMD is the Sauter average particle diameter. Represents. Referring to Equation (2), Ismd can be said to be a coefficient proportional to a value obtained by multiplying the surface area of each droplet by the number of droplets.

The average particle diameter SMD of the fuel droplets used in the formula (2) is calculated by the following formula (3).
SMD = 72.36 × Pcr ^-0.38 × do (3)
Pcr in the formula (3) represents an injection pressure when fuel is injected from the fuel injection valve 31 into the combustion chamber 15. Further, do in the expression (3) represents the diameter of the injection hole of the fuel injection valve 31. The nozzle hole diameter is determined by the structure of the fuel injection valve 31 and does not change during operation of the internal combustion engine 1. Therefore, the nozzle hole diameter do can be considered as a constant determined for each type of the fuel injection valve 31.

  During the operation of the internal combustion engine 1, the smoke concentration is estimated as follows using these equations (1) to (3). First, the fuel pressure detected by the fuel pressure sensor 82 is substituted into the above equation (3), whereby the average particle diameter SMD of the fuel droplets is calculated. Thereafter, the droplet surface area coefficient Ismd is calculated by substituting the average particle size SMD calculated in this way into the above equation (2).

On the other hand, as described above, the mass m _{O2 of} oxygen supplied into the combustion chamber 15 is calculated based on the intake air amount calculated based on the output of the air flow meter 84 and the opening degree of the EGR control valve 62. (Step S11 in FIG. 3). In addition, the fuel injection amount (target value) Qm of the main injection from the fuel injection valve 31 is acquired from the target value (step S12 in FIG. 3) of the fuel injection amount calculated as described above. Then, in addition to the mass m _{O2 of} oxygen and the fuel injection amount Qm of the main injection, the droplet surface area coefficient Ismd calculated using the equation (2) is substituted into the equation (1) to estimate the smoke concentration. The value m _s is calculated.

≪Action ・ Effect≫
According to the present embodiment, the smoke concentration can be estimated with high accuracy by estimating the smoke concentration as described above. Hereinafter, the reason will be described with reference to FIG.

FIG. 4 is a diagram showing the relationship between various parameters and smoke density. In particular, FIG. 4 shows the relationship when the engine speed is 1250 rpm and the fuel injection amount of the main injection in one cycle is 30 mm ³ . FIG. 4 shows the relationship at different injection pressures. For example, the rhombus indicates the case where the injection pressure is 140 MPa, and the white triangle indicates the case where the injection pressure is 90 MPa.

FIG. 4A shows the relationship between the smoke concentration and the value m _O2 / Qm obtained by dividing the mass of oxygen by the fuel injection amount of the main injection. As can be seen from FIG. 4 (A), even if m _O2 / Qm is the same, if the injection pressure is different, the smoke density varies greatly. In particular, the tendency is remarkable in the region where m _O2 / Qm is small, that is, the region where the mass of oxygen is small and the fuel injection amount of the main injection is large. Therefore, it can be seen that if the smoke concentration is estimated based on m _O2 / Qm, a large error may occur in the estimated value.

FIG. 4B shows the relationship between the smoke concentration and the value m _O2 / Qm × Pcr obtained by dividing the mass of oxygen by the fuel injection amount of the main injection and multiplying by the injection pressure. As can be seen from FIG. 4 (B), the though variation is smaller than in the case of m _O2 / Qm shown in FIG. 4 (A), even m _O2 / Qm × Pcr is the same the injection pressure differs Some variation occurs in the smoke concentration. In particular, this tendency is remarkable in the region where m _O2 / Qm × Pcr is small. Therefore, it can be seen that even if the smoke concentration is estimated based on m _O2 / Qm × Pcr, a relatively large error can occur in the estimated value.

FIG. 4C shows the relationship between the smoke concentration and the value m _O2 / Qm × Ismd obtained by dividing the mass of oxygen by the fuel injection amount of the main injection and multiplying by Ismd. As can be seen from FIG. 4 (C), when m _O2 / Qm × Ismd is the same, the variation in the smoke concentration is small even if the injection pressure has a different value. Therefore, it can be seen that if the smoke concentration is estimated based on m _O2 / Qm × Ismd, an error occurring in the estimated value can be reduced.

Here, Ismd is a coefficient proportional to the total surface area of all droplets of fuel injected from the fuel injection valve 31 into the combustion chamber 15. As can be seen from FIG. 4C, the smoke concentration decreases as Ismd increases, that is, as the total surface area of all droplets of fuel increases. In the present embodiment, the constants A _s1 and A _s2 in Equation (1) are appropriately set according to this tendency, so that the smoke density can be estimated with high accuracy.

≪Modification≫
Note that the above embodiment is premised on an internal combustion engine in which an air-fuel mixture burns mainly by diffusion combustion. However, even in an internal combustion engine in which the air-fuel mixture burns by premixed combustion, the smoke concentration can be estimated by the method described above. However, when the air-fuel mixture burns by premixed combustion, the ignition delay time from when the fuel is injected from the fuel injection valve until the air-fuel mixture self-ignites is relatively long, and the ignition delay time affects the smoke concentration.

In particular, if the ignition delay time is long, the fuel and air in the air-fuel mixture are likely to be mixed, and as a result, smoke is less likely to occur. Therefore, in the internal combustion engine in which the air-fuel mixture burns by premixed combustion, the smoke concentration m _s is calculated by the following equation (4).
In the above equation (4), td is the ignition delay period (s), and the fuel injection timing, the temperature and pressure in the combustion chamber 15 when the intake valve 21 is closed, using the Livengood-Wu integral equation, etc. Calculated based on

  In the above embodiment, the smoke concentration is calculated, but instead, the amount of smoke in the exhaust gas discharged from the combustion chamber 15 may be calculated. The smoke amount can be calculated by multiplying the exhaust gas flow rate by the concentration of the exhaust gas.

  In the above embodiment, the droplet surface coefficient Ismd is used to estimate the smoke concentration. However, other parameters may be used as long as the parameter values change according to the total surface area of the fuel droplets injected into the combustion chamber 15. Specifically, for example, a parameter indicating the average particle diameter of fuel droplets such as Sauter average particle diameter can be used instead of Ismd.

<Second embodiment>
Next, with reference to FIG.5 and FIG.6, the control apparatus which concerns on 2nd embodiment is demonstrated. The configuration and control of the control device according to the second embodiment are basically the same as the configuration and control of the control device according to the first embodiment. Below, it demonstrates focusing on a different part from the control apparatus which concerns on 1st embodiment.

Incidentally, FIG. 4C shows the relationship between m _O2 / Qm × Ismd and the smoke concentration when the engine speed is 1250 rpm and the fuel injection amount of the main injection in one cycle is 30 mm ³ . However, as the engine speed and engine load change, the relationship between m _O2 / Qm × Ismd and the smoke concentration also changes.

FIG. 5 is a view similar to FIG. 4 showing the relationship between m _O2 / Qm × Ismd and the smoke concentration. When the engine speed is 1250 rpm and the injection amount of the main injection in one cycle is 30 mm ³ , m _O2 / Qm × Ismd and the smoke concentration have an average relationship as shown by a broken line in FIG. However, when the engine load increases and the injection amount of the main injection reaches 60 mm ³ , m _O2 / Qm × Ismd and the smoke concentration have the relationship shown by the solid line in FIG.

As can be seen from FIG. 5, when the engine operating state changes, the relationship between m _O2 / Qm × Ismd and the smoke concentration also changes accordingly. Therefore, in order to accurately estimate the smoke concentration, the relationship between m _O2 / Qm × Ismd and the smoke concentration is adapted for each engine operating state of the internal combustion engine 1, that is, for each engine speed and each engine load. Need to ask. However, in order to obtain the relationship between m _O2 / Qm × Ismd and the smoke concentration for each engine operating state by changing the engine operating state in this way, a huge amount of man-hours is required.

By the way, according to the research of the inventors of the present application, the main factor that changes the relationship between m _O2 / Qm × Ismd and the smoke concentration depending on the engine load and the engine speed is smoke reoxidation. all right. That is, part of the smoke once generated in the combustion chamber 15 is oxidized and purified again in the combustion chamber 15, and the amount of smoke reoxidized at this time depends on the engine load, engine speed, and the like. It changes according to the engine operating state. However, m _O2 / Qm × influence of reoxidation of the smoke not taken into account in Ismd, thus m _O2 / Qm × Ismd from only able to accurately estimate the smoke density when changing the engine operating condition There wasn't.

Therefore, in the present embodiment, the smoke concentration is calculated in consideration of the effect of reoxidation in which part of the smoke once generated in the combustion chamber 15 is oxidized again in the combustion chamber 15. Specifically, in the present embodiment, the smoke concentration estimated value m _s ^′ is calculated by the following equation (5).
In the above equation (5), m _s is an estimated value of smoke concentration calculated by the above equation (1) (referred to as “basic estimated value” in the present embodiment).

Further, f _Tcyl in the above formula (5) is a first reoxidation term calculated by the following formula (6), and f _Ne in the above formula (5) is calculated by the following formula (7). Second reoxidation term.
In the above equation (6), Tcyl represents the maximum temperature (in-cylinder maximum temperature) in the combustion chamber 15 that accompanies combustion of the air-fuel mixture in the combustion chamber 15. The in-cylinder maximum temperature Tcyl is calculated based on, for example, the engine load and the engine speed, using a map having these parameters as arguments. Moreover, AT1 and AT2 in the formula (6) are positive constants, and are identified based on the measurement result of the actual machine. In the equation (6), if the parameter represents the temperature in the combustion chamber 15 that has increased with the combustion of the air-fuel mixture, such as the average value of the temperature in the combustion chamber 15 after the air-fuel mixture combustion, Other parameters may be used instead of the temperature Tcyl.

In the formula (7), Ne represents the engine speed (rpm). The engine speed Ne is calculated based on the output of the crank angle sensor 90. In addition, A _ne1 and A _ne2 in equation (7) are positive constants, and are identified based on the measurement results of the actual machine.

The first reoxidation term f _Tcyl and the second reoxidation term f _Ne represented by the above formulas (6) and (7) express smoke reoxidation. That is, as the in-cylinder maximum temperature Tcyl increases, the smoke generated in the combustion chamber 15 is more easily reoxidized in the combustion chamber 15. The value of the first reoxidation term f _Tcyl represented by the equation (6) increases as the in-cylinder maximum temperature Tcyl increases, and thus the estimated smoke concentration value m _s ^′ calculated by the equation (5) decreases. Therefore, the first reoxidation term f _Tcyl expresses that the smoke is more easily reoxidized as the in-cylinder maximum temperature Tcyl is higher, and the smoke concentration in the exhaust gas discharged from the combustion chamber 15 is reduced. I can say that.

Further, the higher the engine speed, the shorter the time required for smoke reoxidation in the combustion chamber 15, and the smoke generated in the combustion chamber 15 is less likely to be reoxidized in the combustion chamber 15. The value of the second reoxidation term f _Ne expressed by the equation (7) increases as the engine speed increases, and thus the smoke concentration estimated value m _s ^′ calculated by the equation (5) increases. Therefore, it can be said that the second reoxidation term f _Ne expresses that the smoke is less likely to be reoxidized as the engine rotational speed Ne increases, and that the smoke concentration in the exhaust gas discharged from the combustion chamber 15 increases. .

  FIG. 6 is a diagram showing the relationship between the measured value and the estimated value of the smoke concentration. In particular, FIG. 6 shows the relationship when the engine speed and the engine load (fuel injection amount) are set to a plurality of different values. FIG. 6A shows a case where the smoke concentration is estimated based on the equation (1) without changing the constant according to the engine speed and the engine load. On the other hand, FIG. 6B shows a case where the smoke concentration is estimated based on the equation (5).

As shown in FIG. 6A, when the smoke concentration is estimated based on the equation (1), the estimated value of the smoke concentration and the actual measurement value are relatively close in some operating states ( For example, when the engine rotational speed is 1250 rpm and the fuel injection amount is 30 mm ³ ). However, in many operating states, the estimated value of smoke concentration and the actually measured value are very different.

  On the other hand, as shown in FIG. 6B, when the smoke concentration is estimated based on the equation (5), the estimated value and the measured value of the smoke concentration are relatively close in most operating states. Take. Therefore, by estimating the smoke concentration based on the equation (5), the smoke concentration can be accurately estimated regardless of the engine operating state.

In particular, in the present embodiment, since it is not necessary to obtain the relationship between m _O2 / Qm × Ismd and the smoke concentration for each engine operating state, the number of man-hours for adaptation can be reduced. That is, in the present embodiment, it is possible to accurately estimate the smoke concentration while reducing the adaptation man-hours.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 10 Engine main body 15 Combustion chamber 30 Fuel supply apparatus 31 Fuel injection valve 34 Fuel pump 70 Control apparatus 71 Electronic control unit (ECU)
82 Fuel pressure sensor 84 Air flow meter 89 Load sensor 90 Crank angle sensor

Claims (2)

A smoke estimation device for an internal combustion engine for estimating a smoke concentration or a smoke amount in exhaust gas discharged from a combustion chamber of an internal combustion engine in which fuel is directly injected into the combustion chamber,
A value of a parameter that changes in accordance with the total surface area of the fuel droplets injected into the combustion chamber is estimated. Based on the estimated value of the parameter, the larger the total surface area of the fuel droplets, the greater the distance from the combustion chamber. A smoke estimation device for an internal combustion engine, which calculates a smoke concentration or a smoke amount on the assumption that a smoke concentration or a smoke amount in exhaust gas discharged becomes small. Estimate the temperature in the combustion chamber when the air-fuel mixture burns in the combustion chamber,
The smoke concentration or the smoke amount is calculated on the basis of the estimated temperature in the combustion chamber, assuming that the smoke concentration or the smoke amount in the exhaust gas discharged from the combustion chamber decreases as the temperature in the combustion chamber increases. Item 2. The smoke estimation device for an internal combustion engine according to Item 1.