JP2017166356A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine control device capable of reducing the increase of a NOx concentration in the exhaust gas of an internal combustion engine due to the fact that an equivalence ratio is locally high in a combustion zone in a combustion chamber.SOLUTION: An actual combustion temperature is specified from the measured value of a NOx concentration on the basis of a correspondence between a NOx concentration measured in advance in an exhaust gas and a burning temperature. On the basis of a 2-area model, in which a combustion chamber inside (cylinder) is divided into a combustion area and a non-combustion area, an equivalence ratio in a combustion area capable of achieving that real combustion temperature is estimated. The valve closing timing of an intake valve is controlled so that the equivalence ratio estimated may approach a target equivalence ratio.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a control device for an internal combustion engine. More specifically, the present invention relates to a control device for an internal combustion engine that includes at least a phase variable mechanism of an intake valve.

  In this technical field, an exhaust gas recirculation device (hereinafter referred to as an “EGR device”) for the purpose of reducing nitrogen oxides (hereinafter sometimes referred to as “NOx”) discharged from an internal combustion engine into the atmosphere. Internal combustion engines are known that may be referred to. The EGR device can reduce the amount of NOx generated in the internal combustion engine by recirculating part of the exhaust gas to the intake system of the internal combustion engine to lower the combustion temperature of the air-fuel mixture in the combustion chamber.

  However, depending on the operating condition of the internal combustion engine, for example, the amount of exhaust gas recirculated by the EGR device (hereinafter sometimes referred to as “EGR amount”) becomes insufficient, and a sufficient NOx reduction effect is obtained. May not be possible. Therefore, in this technical field, a so-called “valve overlap” period is extended in an internal combustion engine provided with a phase variable mechanism of an intake valve and an exhaust valve (hereinafter sometimes referred to as “VVT mechanism”). A technique has been proposed in which internal EGR is executed to compensate for an insufficient EGR amount due to external EGR by an EGR device (see, for example, Patent Document 1).

JP 2008-150957 A

Masahiro Ishida, Noboru Matsumura, Hironobu Ueki, Masanori Yamaguchi, Takamine Tsuji, “Diesel Combustion Analysis by Two-Region Model (1st Report, Comparison of Model Analysis and Experiment), Japan Mechanics Journal (B), Japan Japan Society of Mechanical Engineers, May 25, 1994, Vol. 60, No. 573, p.

  As described above, in this technical field, a technique for achieving a sufficient NOx reduction effect by compensating for the shortage of the NOx reduction effect caused by the shortage of the EGR amount by the EGR device by the increase of the EGR amount by the VVT mechanism. It has been known. However, the increase in the NOx concentration in the exhaust gas of the internal combustion engine can be caused not only by a shortage of the EGR amount but also by a high (local) equivalence ratio in the combustion region in the combustion chamber. As is well known to those skilled in the art, the “equivalent ratio” is the ratio of the stoichiometric air-fuel ratio to the air-fuel ratio of the air-fuel mixture, and is the reciprocal of the excess air ratio.

  For example, as shown in the graph of FIG. 1, as the equivalence ratio (Φ) in the combustion region in the combustion chamber becomes larger than a predetermined range (shaded portion) including the target value (target equivalence ratio), The NOx concentration increases. On the other hand, as the equivalence ratio (Φ) in the combustion region in the combustion chamber becomes smaller than the predetermined range, noise worsens or unburned hydrocarbon (THC) in the exhaust increases due to misfire.

  In the control device for an internal combustion engine according to the above-described prior art, it is possible to suppress an increase in the NOx concentration due to a shortage of the EGR amount, but an increase in the NOx concentration due to a high equivalence ratio in the combustion region. It cannot be suppressed. That is, when the NOx concentration in the exhaust gas of the internal combustion engine is increased due to the high equivalence ratio in the combustion region, even if the EGR amount is increased, the equivalence ratio in the combustion region cannot be lowered. , NOx concentration cannot be lowered.

  Further, a high (local) equivalence ratio in the combustion region in the combustion chamber means that the fuel is excessively supplied to the region. Therefore, as shown in the graph of FIG. 2, as the equivalence ratio (Φ) in the combustion region in the combustion chamber becomes larger than a predetermined range (shaded portion) including the target value (target equivalence ratio), the internal combustion engine The fuel consumption rate increases (fuel consumption deteriorates). Such a state is undesirable from the viewpoint of resource saving and environmental protection. On the other hand, as the equivalence ratio (Φ) in the combustion region in the combustion chamber becomes smaller than the predetermined range, noise worsens or unburned hydrocarbon (THC) in the exhaust increases due to misfire.

  The present invention has been made to solve the above problems. That is, the present invention provides a control device for an internal combustion engine that can reduce an increase in the concentration of NOx in the exhaust gas of the internal combustion engine due to the locally high equivalence ratio in the combustion region in the combustion chamber. One purpose.

  As a result of diligent research to solve the above-mentioned problems, the present inventor has determined the actual combustion temperature from the measured value of the NOx concentration based on the correspondence relationship between the NOx concentration in the exhaust gas and the combustion temperature, and the combustion chamber (in-cylinder) Based on a two-region model that divides the combustion region into an unburned region, the equivalence ratio in the combustion region that can achieve the actual combustion temperature is estimated, and the intake air is taken so that the estimated equivalence ratio approaches the target equivalence ratio. It has been found that the above object can be achieved by controlling the valve closing timing.

  In view of the above, the control device for an internal combustion engine according to the present invention (hereinafter sometimes referred to as “the present invention device”) has a concentration of nitrogen oxides contained in the exhaust gas discharged from the combustion chamber. A NOx sensor for detecting a certain NOx concentration, an in-cylinder pressure sensor for detecting an in-cylinder pressure that is a pressure in the combustion chamber, a fuel supply mechanism that controls a fuel supply amount that is an amount of combustion supplied to the combustion chamber, and at least an intake air The present invention is applied to an internal combustion engine that includes a variable valve phase mechanism that controls valve closing timing.

The internal combustion engine further includes an intake pressure sensor that detects or predicts intake pressure, and an intake air temperature sensor that detects or predicts intake air temperature.
The control device includes combustion temperature specifying means, combustion temperature estimating means, and equivalence ratio estimating means.

  The combustion temperature specifying means is based on the correspondence relationship between the NOx concentration stored in advance in the data storage means and the combustion temperature in the combustion chamber, and the NOx concentration detected by the NOx sensor is used to burn the fuel into the combustion chamber. An actual combustion temperature that is a combustion temperature in a combustion region that is a flame region that is generated is specified.

  The combustion temperature estimation means is configured to determine the in-cylinder pressure, the fuel supply amount, the intake pressure, and the intake temperature based on a two-region model that divides the combustion chamber into the combustion region and an unburned region that is the other region. Therefore, the estimated combustion temperature, which is the combustion temperature in the combustion region, is estimated in association with the equivalence ratio in the combustion region.

  The equivalence ratio estimation means is configured to estimate an estimated equivalence ratio, which is an equivalence ratio in the combustion region where the estimated combustion temperature coincides with the actual combustion temperature, based on the two-region model.

  In addition, the control device uses the valve phase variable mechanism when the estimated equivalent ratio is larger than the equivalent ratio tolerance that is a predetermined threshold with respect to the target equivalent ratio that is the target value of the equivalent ratio at that time. The closing timing of the intake valve is retarded. On the other hand, the control device is configured to advance the closing timing of the intake valve using the valve phase variable mechanism when the estimated equivalent ratio is smaller than the equivalent ratio tolerance with respect to the target equivalent ratio. Has been.

  As described above, the present invention device specifies the actual combustion temperature from the measured value of the NOx concentration based on the correspondence relationship between the NOx concentration in the exhaust gas and the combustion temperature. Furthermore, the device according to the present invention estimates the equivalence ratio in the combustion region where the actual combustion temperature can be achieved, based on a two-region model that divides the combustion chamber (cylinder) into a combustion region and an unburned region. In addition, the device of the present invention controls the closing timing of the intake valve so that the estimated equivalence ratio approaches the target equivalence ratio. Thereby, the increase in the NOx concentration in the exhaust gas of the internal combustion engine caused by the locally high equivalence ratio in the combustion region in the combustion chamber can be reduced.

  Other objects, other features and attendant advantages of the present invention will be readily understood from the description of the embodiments of the present invention described with reference to the following drawings.

It is a typical graph which shows the relationship between the equivalent ratio ((PHI)) in the combustion area | region in a combustion chamber, and the density | concentration of the nitrogen oxide (NOx) contained in exhaust_gas | exhaustion. It is a typical graph which shows the relationship between the equivalence ratio ((PHI)) in the combustion area | region in a combustion chamber, and the illustration fuel consumption rate (ISFC). It is a typical graph showing the correspondence of the combustion temperature in a combustion chamber, and the NOx density | concentration in exhaust_gas | exhaustion. It is a conceptual diagram of a 2 area | region model. It is a typical graph showing the change with respect to crank angle (ATDC) of the in-cylinder average temperature (Tc), the temperature (Tb) of a combustion area | region, and the temperature (Tu) of an unburned area | region. It is a flowchart showing the equivalence ratio control routine performed in the control apparatus for an internal combustion engine according to the present invention. It is a typical graph showing the log | history of the "combustion temperature (Tb) in a combustion area | region" calculated based on a 2 area | region model.

<< First Embodiment >>
Hereinafter, a control device for an internal combustion engine according to a first embodiment of the present invention (hereinafter may be referred to as a “first device”) will be described with reference to the drawings.

<Constitution>
As described above, the internal combustion engine to which the first device is applied includes the NOx sensor that detects the NOx concentration that is the concentration of nitrogen oxide contained in the exhaust discharged from the combustion chamber, and the cylinder that is the pressure in the combustion chamber. An in-cylinder pressure sensor that detects an internal pressure, a fuel supply mechanism that controls a fuel supply amount that is the amount of combustion supplied into the combustion chamber, and a valve phase variable mechanism that controls at least the closing timing of the intake valve. The configurations of the NOx sensor, the in-cylinder pressure sensor, the fuel supply mechanism, and the valve phase variable mechanism are well known to those skilled in the art, and thus description thereof is omitted here.

  In addition to the above, the internal combustion engine to which the first device is applied further includes an intake pressure sensor that detects or predicts the intake pressure, and an intake air temperature sensor that detects or predicts the intake air temperature. The intake pressure sensor may be a pressure sensor that directly detects the pressure (intake pressure) of the intake air that is drawn into the combustion chamber via the intake port, or is based on other state quantities related to the intake pressure, etc. It may be a detecting means for predicting the intake pressure. The intake air temperature sensor may be a temperature sensor that directly detects the temperature of intake air (intake air temperature) taken into the combustion chamber through the intake port, or based on other state quantities related to the intake air temperature, etc. It may be a detecting means for predicting the intake air temperature.

  The first device is an electronic control unit (ECU) including a microcomputer as a main part, and transmits instruction signals to input ports and various actuators for receiving detection signals from various detection means. Output port. In this specification, the microcomputer includes a CPU, a data storage device such as a ROM and a RAM, and the CPU receives various detection signals and executes various arithmetic processes based on instructions (programs) stored in the ROM. Various functions are realized by transmitting various instruction signals. As a function realized in this way, the first device includes combustion temperature specifying means, combustion temperature estimating means, and equivalence ratio estimating means.

  The combustion temperature specifying means is based on the correspondence between the NOx concentration stored in advance in the data storage means (for example, ROM) and the combustion temperature in the combustion chamber, and from the NOx concentration detected by the NOx sensor, The actual combustion temperature, which is the combustion temperature in the combustion region that is the flame region, is determined. The “correspondence relationship between the NOx concentration and the combustion temperature in the combustion chamber” can be obtained, for example, by the following method.

  First, an actual machine or an experimental model is operated at various combustion temperatures, and the NOx concentration in the exhaust gas detected at that time is recorded. As an example of the correspondence relationship between the combustion temperature and the NOx concentration thus obtained, for example, a graph shown in FIG. 3 can be cited. As shown in FIG. 3, the higher the combustion temperature, the higher the NOx concentration in the exhaust gas. The correspondence relationship between the combustion temperature and the NOx concentration thus obtained is stored in a data storage device included in the first device, for example, as a data table (map) or a function (for example, an approximate function).

  The combustion temperature estimation means is configured to calculate combustion in the combustion region from the in-cylinder pressure, the fuel supply amount, the intake pressure, and the intake temperature based on a two-region model that divides the combustion chamber into a combustion region and an unburned region that is the other region The estimated combustion temperature, which is the temperature, is estimated in association with the equivalence ratio in the combustion region. The estimation of the estimated combustion temperature based on the two-region model and the two-region model will be described in detail later.

  The equivalence ratio estimation means is configured to estimate an estimated equivalence ratio that is an equivalence ratio in a combustion region where the estimated combustion temperature coincides with the actual combustion temperature, based on the two-region model. Specifically, an estimated combustion temperature that matches the actual combustion temperature specified by the combustion temperature specifying means is identified from the estimated combustion temperatures estimated in association with the equivalence ratio by the combustion temperature estimating means, and is specified. The equivalent ratio associated with the estimated combustion temperature is specified as the estimated equivalent ratio. The estimation of the estimated equivalent ratio based on the two-region model will also be described in detail later.

  In addition, when the estimated equivalent ratio is larger than the equivalent ratio tolerance that is a predetermined threshold with respect to the target equivalent ratio that is the target value of the equivalent ratio at that time, the first device uses the valve phase variable mechanism to The valve closing timing is configured to be retarded. On the other hand, the control device is configured to advance the closing timing of the intake valve using the valve phase variable mechanism when the estimated equivalent ratio is smaller than the equivalent ratio tolerance with respect to the target equivalent ratio. Has been.

  As described above, the “target equivalent ratio” reduces the increase in NOx concentration in exhaust gas, the increase in fuel consumption of the internal combustion engine, the deterioration of noise, and the increase in unburned hydrocarbon (THC) in exhaust due to misfire. This is the target value of the equivalence ratio determined to be. For example, the target equivalent ratio can be obtained from the target air-fuel ratio (A / F) in the internal combustion engine at that time.

  The above "equivalent ratio tolerance" is acceptable from the viewpoint of reducing the increase in NOx concentration in the exhaust, increase in the fuel consumption rate of the internal combustion engine, worsening noise, and increase in unburned hydrocarbon (THC) in the exhaust due to misfire. This is the magnitude (absolute value) of the difference between the possible target equivalent ratio and the estimated equivalent ratio. The specific magnitude of such equivalence ratio tolerance is, for example, NOx concentration in exhaust gas, fuel consumption rate, noise, occurrence of misfire, and THC concentration in exhaust gas when operating an internal combustion engine at various equivalence ratios. Can be determined by an experiment or the like for obtaining a difference between the target equivalent ratio and the estimated equivalent ratio when each is within the allowable range.

  Therefore, when the estimated equivalent ratio is larger than the equivalent ratio tolerance relative to the target equivalent ratio (that is, when the estimated equivalent ratio is excessive), the increase in the NOx concentration in the exhaust gas and / or the fuel consumption rate of the internal combustion engine May increase. However, in this case, the first device retards the closing timing of the intake valve using the valve phase variable mechanism. As a result, the amount of air sucked into the combustion chamber increases, so that the equivalence ratio in the combustion region decreases and approaches the target equivalence ratio.

  On the other hand, when the estimated equivalent ratio is smaller than the equivalent ratio tolerance with respect to the target equivalent ratio (that is, when the estimated equivalent ratio is too small), the unburned hydrocarbon (THC) in the exhaust due to the deterioration of noise and misfiring. May increase. However, in this case, the first device uses the valve phase variable mechanism to advance the closing timing of the intake valve. As a result, the amount of air sucked into the combustion chamber is reduced, so that the equivalence ratio in the combustion region increases and approaches the target equivalence ratio. The range of change when the intake valve closing timing is retarded and / or advanced may be a predetermined constant value, or the magnitude of the difference between the target equivalent ratio and the estimated equivalent ratio. The value may vary depending on

  As described above, the first device identifies the actual combustion temperature from the measured value of the NOx concentration based on the correspondence relationship between the NOx concentration in the exhaust gas and the combustion temperature, and sets the combustion chamber to the combustion region and the unburned region. Based on the divided two-region model, the equivalence ratio in the combustion region where the actual combustion temperature can be achieved is estimated, and the valve closing timing of the intake valve is controlled so that the estimated equivalence ratio approaches the target equivalence ratio. Thereby, the increase in the NOx concentration and / or the fuel consumption rate in the exhaust gas of the internal combustion engine due to the locally high equivalence ratio in the combustion region in the combustion chamber can be reduced.

(Estimation principle of estimated combustion temperature and estimated equivalence ratio based on two-region model)
Here, the estimation principle of the estimated combustion temperature and the estimated equivalent ratio based on the above-described two-region model will be described in detail. For example, as shown in FIG. 4, the “two-region model” divides the combustion chamber into a combustion region that is a flame region generated in the combustion chamber by combustion of fuel and an unburned region that is a region other than the combustion region, This is a model for calculating the temperature history and the like. In FIG. 4, one combustion region and one unburned region are depicted as if they exist in the combustion chamber. However, in reality, one combustion region and one unburned region are not necessarily generated one by one. That is, the two-region model shown in FIG. 4 is a conceptual model that is simplified for easy understanding.

  As described in Non-Patent Document 1, the average temperature (Tc) in the cylinder is based on the gas equation of state, the cylinder pressure (P), the combustion chamber volume (V), and the gas existing in the cylinder. It represents with the following formula | equation (1) using gross mass (Gc). R is a gas constant.

  In the above equation, the total mass (Gc) of the gas present in the cylinder is the mass of the air (Ga) filled in the combustion chamber, the mass of the residual gas (Gr), and the mass of fuel supplied to the combustion chamber (Gi). ) And is expressed by the following equation (2).

  The mass (Gb) of the gas existing in the combustion region is obtained as the sum of the mass (Gf) of the fuel existing in the combustion region and the mass (Gab) of air existing in the combustion region. The mass (Gf) of the fuel existing in the combustion region is calculated from the heat receiving rate derived based on the change in the in-cylinder pressure (P) or the like. The mass (Gab) of air existing in the combustion region is calculated from the mass (Gf) and the theoretical air amount (Lth) of fuel existing in the combustion region based on the equivalence ratio (Φ) in the combustion region. Therefore, the mass (Gb) of the gas existing in the combustion region is expressed by the following formula (3).

  Since the unburned region is a region other than the combustion region in the combustion chamber, the mass (Gu) of the gas existing in the unburned region is expressed by the following equation (4).

  Incidentally, as described above, the average temperature (Tc) in the cylinder can be calculated by the equation (1). However, as shown in the graph of FIG. 5, the temperature (Tb) in the combustion region and the temperature (Tu) in the unburned region show different changes, and the average temperature (Tc) in the cylinder is an average value of these. . Further, it is the maximum value (Tmax) of the combustion temperature (Tb) in the combustion region that affects the NOx concentration in the exhaust gas.

The temperature (Tu) in the unburned region is expressed by the following equation (5) based on the adiabatic isentropic change. In the following equation, P ₀ and T ₀ are the in-cylinder pressure and in-cylinder average temperature before the fuel is ignited, and k is the specific heat ratio.

  On the other hand, the temperature (Tb) of the combustion region is expressed by the following equation (6) based on the sum of the internal energy of the gas existing in the combustion chamber (cylinder). In other words, the combustion temperature estimating means can estimate the temperature (Tb) (estimated combustion temperature) of the combustion region at that time point by the equation (6). In the following formula, Cvc, Cvu, and Cvb are constant volume specific heats of gases existing in the entire cylinder (average), unburned region, and burning region, respectively.

  Furthermore, the volume (Vb) of the gas existing in the combustion region is expressed by the following equation (7) based on the gas equation of state. Rb is a gas constant in the combustion region.

  As described above, according to the two-region model, it is possible to calculate the history of “the combustion temperature (Tb) in the combustion region” that affects the NOx concentration in the exhaust gas.

  By the way, as is apparent from the equation (3), the mass (Gb) of the gas existing in the combustion region changes according to the equivalent ratio (Φ) in the combustion region. As a result, as is clear from the equation (6), the temperature (Tb) of the combustion region also changes according to the equivalence ratio (Φ) in the combustion region.

  Therefore, the equivalence ratio estimating means specifies the equivalent ratio (Φ) that gives the estimated combustion temperature (Tmax) that matches the actual combustion temperature (Tmax (M)) specified by the combustion temperature specifying means as described above. The equivalence ratio (Φb) (estimated equivalence ratio) of the combustion region at that time can be estimated. Then, as described above, the first device controls the closing timing of the intake valve so that the estimated equivalent ratio (Φb) thus estimated approaches the target equivalent ratio (Φtgt). Thereby, the increase in the NOx concentration and / or the fuel consumption rate in the exhaust gas of the internal combustion engine due to the locally high equivalence ratio in the combustion region in the combustion chamber can be reduced.

<Operation>
The specific operation of the first device based on the configuration and principle described above will be described in detail below with reference to the flowchart of FIG. First, in step S110, the CPU included in the ECU constituting the first device determines whether or not the internal combustion engine to be applied is in a steady state. The “steady state” here means a state where the operating state of the internal combustion engine is not in a transitional state, such as a state after the internal combustion engine is warmed up and in an idle operation.

  If it is determined in step S110 that the internal combustion engine is not in a steady state (S110: No), for example, detection of state quantities such as NOx concentration in the exhaust, in-cylinder pressure, intake pressure and intake air temperature, and a two-region model are used. It is difficult to accurately estimate various state quantities based thereon. Therefore, the CPU ends the routine once.

  On the other hand, when it is determined in step S110 that the internal combustion engine is in a steady state (S110: Yes), the CPU proceeds to the next step S120, and the concentration of nitrogen oxides contained in the exhaust discharged from the combustion chamber. The actual measured value (NOx (M)) of the NOx concentration is acquired from the NOx sensor. Then, the CPU proceeds to the next step S130 to determine whether or not the acquired NOx (M) deviates from the NOx concentration target value (NOxtgt). Note that the “NOx concentration target value (NOxtgt)” here does not necessarily indicate a specific value, but is acceptable from the viewpoint of, for example, the maintenance (deterioration prevention) of exhaust-related members of the internal combustion engine and environmental protection. It may be a range. In this case, in step S130, the CPU determines whether or not the acquired NOx (M) deviates from the allowable range.

  If it is determined in step S130 that NOx (M) does not deviate from NOxtgt (S130: No), the concentration of nitrogen oxides contained in the exhaust gas is within the allowable range, so no special measures are required. is there. Therefore, the CPU ends the routine once. On the other hand, if it is determined in step S130 that NOx (M) has deviated from NOxtgt (S130: Yes), the CPU proceeds to the next step S140, where the NOx concentration and combustion stored in advance in the data storage means are burned. Based on the correspondence relationship with the combustion temperature in the room, the actual combustion temperature, which is the combustion temperature in the combustion region, is specified from the NOx concentration detected by the NOx sensor. Specifically, the CPU specifies the actual combustion temperature (Tmax (M)) corresponding to NOx (M) with reference to the data table (map) representing the correspondence relationship stored in the ROM.

  Next, the CPU estimates the estimated combustion temperature (Tmax) and the equivalent ratio (Φ) based on the above-described two-region model, and the estimated combustion temperature (Tmax) that matches the actual combustion temperature (Tmax (M)). ) Is estimated as the estimated equivalent ratio (Φb). Specifically, the CPU calculates the history of the combustion temperature (Tb) for various equivalent ratios (Φ), and calculates the maximum value as the estimated combustion temperature (Tmax) corresponding to each equivalent ratio (Φ). To do. Then, an estimated combustion temperature (Tmax) that matches the actual combustion temperature (Tmax (M)) is specified from these estimated combustion temperatures (Tmax), and the corresponding equivalent ratio (Φ) is set as the estimated equivalent ratio (Φb). presume.

  In this example, the CPU gradually reduces the value of the equivalence ratio (Φ) from the value predicted to give the highest estimated combustion temperature (Tmax), while estimating the equivalent ratio (Φ). A combustion temperature (Tmax) is calculated. Then, the value of the equivalent ratio (Φ) when the estimated combustion temperature (Tmax) first becomes equal to or lower than the actual combustion temperature (Tmax (M)) is estimated as the value of the estimated equivalent ratio (Φb).

  Specifically, the CPU proceeds to the next step S150, and sets the preset initial value (Φini) of the equivalence ratio as the equivalence ratio Φ in the combustion region. In this example, “1” is adopted as the initial value (Φini) of the equivalence ratio. When the equivalence ratio is 1, the air-fuel ratio in the combustion region matches the stoichiometric air-fuel ratio, so that the highest estimated combustion temperature (Tmax) is obtained.

  Next, the CPU proceeds to step S160, and calculates a history of “combustion temperature (Tb) in the combustion region” that affects the NOx concentration in the exhaust based on the above-described two-region model. An example of the history of the combustion temperature (Tb) calculated in this way is shown in the graph of FIG. The curve shown in the graph represents a change (history) with respect to the crank angle (ATDC) of the temperature (Tb) of the combustion region, and the maximum value is calculated as the estimated combustion temperature (Tmax). In the graph of FIG. 7, the history of the combustion temperature (Tb) calculated for the first time with the initial value Φini (= 1) as the equivalent ratio Φ in the combustion region appears as the curve on the highest temperature side. Thus, the estimated combustion temperature Tmax estimated for the first time is displayed as “Tmax (1)”. Since Tmax (1) deviates significantly (highly) from the actual combustion temperature (Tmax (M)) indicated by the one-dot chain line, the equivalent ratio (Φb) in the combustion region is equal to the equivalent ratio Φ (= 1). Is expected to be very different (much lower than 1).

Next, the CPU proceeds to step S170 to determine whether or not the estimated combustion temperature (Tmax) calculated as described above is equal to or lower than the actual combustion temperature (Tmax (M)). When it is determined in step S170 that the estimated combustion temperature (Tmax) is not equal to or lower than the actual combustion temperature (Tmax (M)) (S170: No), the CPU proceeds to the next step S180, and the value of the equivalence ratio (Φ) Is reduced by a predetermined reduction width (ΔΦ ₁ ). Then, the CPU repeats the processes in steps S160 and S170 described above.

  The history of the combustion temperature (Tb) calculated at the second and third times in step S160 repeatedly executed as described above, and the estimated combustion temperatures (Tmax (2) and Tmax (3) calculated as the maximum values of these histories. )) Is also shown in the graph of FIG. As shown in FIG. 7, the estimated combustion temperature (Tmax (2) and Tmax (3)) is also lowered with a decrease in the equivalence ratio (Φ).

  Eventually, when the estimated combustion temperature (Tmax) becomes equal to or lower than the actual combustion temperature (Tmax (M)), the CPU makes a “Yes” determination at step S170 to proceed to the next step S190, where the equivalent ratio (Φ) at that time point is reached. Is estimated as the estimated equivalent ratio (Φb).

It should be noted that the above-described reduction width (ΔΦ ₁ ) can be a predetermined fixed value. In this case, the greater the decrease width (ΔΦ ₁ ), the greater the decrease width of the estimated combustion temperature (Tmax). Therefore, the number of executions of step S160 that is repeatedly executed until the estimated combustion temperature (Tmax) becomes equal to or lower than the actual combustion temperature (Tmax (M)) is reduced, and the calculation load on the CPU can be reduced. However, there is a possibility that the difference between the estimated combustion temperature (Tmax) and the actual combustion temperature (Tmax (M)) when the estimated combustion temperature (Tmax) first becomes equal to or lower than the actual combustion temperature (Tmax (M)) is increased. Will increase. As a result, the possibility that the estimation accuracy of the estimated equivalent ratio (Φb) is lowered increases. Conversely, the smaller the reduction width (ΔΦ ₁ ), the higher the calculation load of the CPU, but the estimation accuracy of the estimated equivalent ratio (Φb) increases.

Therefore, the specific size of the reduction width (ΔΦ ₁ ) can be determined as appropriate according to the calculation capability of the CPU and the estimated accuracy of the estimated equivalent ratio (Φb). Alternatively, the magnitude of the decrease width (ΔΦ ₁ ) may be determined according to the magnitude of the difference between the estimated combustion temperature (Tmax) and the actual combustion temperature (Tmax (M)). According to this, it is possible to increase the estimation accuracy of the estimated equivalent ratio (Φb) while reducing an increase in the calculation load of the CPU.

Next, the CPU proceeds to step S200 to determine whether or not the estimated equivalent ratio (Φb) estimated as described above is within an allowable range. Specifically, the CPU determines an equivalence ratio tolerance (ΔΦ ₂ ) in which the degree of deviation of the estimated equivalent ratio (Φb) from the target equivalent ratio (Φtgt) that is the target value of the equivalent ratio at that time is a predetermined threshold value. It is determined whether it is above. In other words, the CPU determines that the estimated equivalent ratio (Φb) is greater than the target equivalent ratio (Φtgt) minus the equivalent ratio tolerance (ΔΦ ₂ ), and the target equivalent ratio (Φtgt) is equivalent to the equivalent ratio tolerance (ΔΦ). ₂ ) It is determined whether or not it is within a range (within an allowable range) smaller than the value added.

  When it is determined in step S200 that the estimated equivalent ratio (Φb) deviates from the allowable range (S200: No), the CPU proceeds to the next step S210, where the estimated equivalent ratio (Φb) is the target equivalent ratio ( It is determined whether it is larger than (Φtgt).

When it is determined in step S210 that the estimated equivalent ratio (Φb) is larger than the target equivalent ratio (Φtgt) (S210: Yes), the target equivalent ratio (Φtgt) that is the target value of the equivalent ratio at that time is determined. The estimated equivalent ratio (Φb) is greater than an equivalent ratio tolerance (ΔΦ ₂ ) that is a predetermined threshold. That is, due to the high (rich) equivalence ratio (Φ) in the combustion region, the NOx concentration (NOx (M)) in the exhaust gas of the internal combustion engine increases and / or the fuel consumption deteriorates. There is a high probability that

  Accordingly, the CPU proceeds to the next step S220, and retards the valve closing timing (IVC) of the intake valve using the valve phase variable mechanism. As a result, the amount of air taken into the combustion chamber can be increased, and the equivalent ratio (Φ) in the combustion region can be reduced to approach the target equivalent ratio (Φtgt). As a result, it is possible to reduce the increase in NOx concentration (NOx (M)) in the exhaust gas of the internal combustion engine and the deterioration of fuel consumption.

On the other hand, when it is determined in step S210 that the estimated equivalent ratio (Φb) is not larger (smaller) than the target equivalent ratio (Φtgt) (S210: No), the target equivalent ratio that is the target value of the equivalent ratio at that time The estimated equivalent ratio (Φb) is smaller than the equivalent ratio tolerance (ΔΦ ₂ ), which is a predetermined threshold, with respect to (Φtgt). That is, due to the low (local) equivalence ratio (Φ) in the combustion region, noise deterioration and / or an increase in unburned hydrocarbons (THC) in the exhaust due to misfiring occurs. There is a high probability of being.

  Therefore, the CPU proceeds to the next step S230, and advances the valve closing timing (IVC) of the intake valve using the valve phase variable mechanism. As a result, the amount of air sucked into the combustion chamber can be reduced, and the equivalent ratio (Φ) in the combustion region can be increased to approach the target equivalent ratio (Φtgt). As a result, it is possible to reduce an increase in unburned hydrocarbons (THC) in the exhaust gas due to noise deterioration and misfire.

  By the way, when it is determined in step S200 that the estimated equivalent ratio (Φb) does not deviate from the allowable range (is within the allowable range) (S200: Yes), the NOx concentration in the exhaust gas is actually measured in step S130 described above. The reason that the value (NOx (M)) deviates from the target value (NOxtgt) of the NOx concentration is considered to be caused by causes other than the equivalent ratio (Φ) in the combustion region. As such a cause, an excess or deficiency of the EGR amount as described at the beginning is assumed.

  Therefore, if it is determined in step S200 that the estimated equivalent ratio (Φb) does not deviate from the allowable range (is within the allowable range) (S200: Yes), the CPU proceeds to the next step S310, and the exhaust is being performed. It is determined whether the actual measured value of NOx concentration (NOx (M)) is larger than the target value of NOx concentration (NOxtgt).

  If it is determined in step S310 that it is greater than NOx (M) NOxtgt (S310: Yes), there is a high probability that the combustion temperature has risen due to an insufficient EGR amount. Therefore, the CPU accounts for the ratio (EGR rate) of the exhaust gas recirculated to the intake system of the internal combustion engine by the EGR device (hereinafter sometimes referred to as “EGR gas”) in the intake air sucked into the combustion chamber. Is raised. Specifically, as described above, the valve overlap period is extended to increase the EGR amount by internal EGR, or in an internal combustion engine equipped with an EGR device, the EGR valve opening is increased to increase the EGR amount by external EGR. Or increase it. As a result, the combustion temperature can be lowered by increasing (up) the EGR rate, and the NOx concentration in the exhaust gas can be lowered.

  On the other hand, if it is determined in step S310 that it is not larger (smaller) than NOx (M) NOxtgt (S310: No), generation of soot (PM) due to oxygen deficiency due to excessive EGR amount, etc. There is a high probability that this problem has occurred. Therefore, the CPU decreases (downs) the EGR rate. Specifically, the EGR amount due to internal EGR is reduced by shortening the valve overlap period, or in an internal combustion engine equipped with an EGR device, the EGR valve opening is decreased to reduce the EGR amount due to external EGR. . As a result, it is possible to reduce problems such as generation of soot (PM) due to oxygen shortage due to a decrease (down) in the EGR rate.

  As mentioned above, for the purpose of explaining the present invention, the embodiment having a specific configuration has been described with reference to the accompanying drawings sometimes, but the scope of the present invention is limited to the embodiment exemplified above. Needless to say, modifications should be made as appropriate within the scope of the matters described in the claims and the specification.

Claims (1)

NOx sensor for detecting NOx concentration which is concentration of nitrogen oxide contained in exhaust gas discharged from combustion chamber, in-cylinder pressure sensor for detecting in-cylinder pressure which is pressure in combustion chamber, and combustion supplied into combustion chamber A control device for an internal combustion engine, comprising: a fuel supply mechanism that controls a fuel supply amount that is an amount of
The internal combustion engine
An intake pressure sensor for detecting or predicting the intake pressure;
An intake air temperature sensor for detecting or predicting the intake air temperature;
Further comprising
The controller is
Combustion that is a flame region generated in the combustion chamber by combustion of the fuel from the NOx concentration detected by the NOx sensor based on the correspondence relationship between the NOx concentration stored in advance in the data storage means and the combustion temperature in the combustion chamber A combustion temperature specifying means for specifying an actual combustion temperature that is a combustion temperature in the region;
Based on a two-region model that divides the combustion chamber into the combustion region and an unburned region that is the other region, from the in-cylinder pressure, the fuel supply amount, the intake pressure, and the intake air temperature, Combustion temperature estimation means for estimating an estimated combustion temperature that is a combustion temperature in association with an equivalent ratio in the combustion region;
An equivalent ratio estimation means for estimating an estimated equivalent ratio that is an equivalent ratio in the combustion region where the estimated combustion temperature matches the actual combustion temperature based on the two-region model;
With
When the estimated equivalent ratio is larger than the equivalent ratio tolerance, which is a predetermined threshold, with respect to the target equivalent ratio that is the target value of the equivalent ratio at that time, the valve timing variable mechanism is used to set the closing timing of the intake valve. When the estimated equivalent ratio is smaller than the equivalent ratio tolerance with respect to the target equivalent ratio, the valve timing variable mechanism is used to advance the closing timing of the intake valve.
Control device for internal combustion engine.

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