JP6551017B2 - EGR control system for internal combustion engine, internal combustion engine, and EGR control method for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, and an EGR control system for an internal combustion engine that controls the opening degree of the EGR valve based on the in-cylinder oxygen concentration, an internal combustion engine, And an EGR control method for an internal combustion engine.

  In general, an internal combustion engine such as a diesel engine mounted on a vehicle is provided with an EGR system in order to control the concentration of NOx (nitrogen oxide) contained in exhaust gas to a certain concentration or less. As shown in FIG. 1, the EGR system includes an EGR passage 14 that connects the exhaust passage 13 and the intake passage 12 of the internal combustion engine 10, an EGR cooler 15 that is provided in the EGR passage 14, an EGR valve 16, and the like. System 1. With this EGR system 1, a part of the exhaust gas G (EGR gas) Ge passing through the exhaust passage 13 is recirculated to the intake passage 12 via the EGR passage 14 and supplied into the cylinder 11 c together with the fresh air A. Thus, the combustion temperature in the cylinder 11c is reduced, and the concentration of NOx contained in the exhaust gas G is controlled. In general, it is known that the concentration of NOx contained in the exhaust gas G decreases as the combustion temperature in the cylinder 11c decreases.

  In addition, related to this, feedforward control is performed so that the flow rate of low pressure EGR becomes constant regardless of the load of the internal combustion engine, and the flow rate of high pressure EGR is set to its target so that the oxygen concentration in the exhaust becomes constant. An exhaust gas recirculation control device for an internal combustion engine that performs feedback control to a value has been proposed (see, for example, Patent Document 1).

  On the other hand, the inventors use the EGR control system 40X as shown in FIG. 5 to set the actual exhaust gas G to the first NOx target value Nt1 calculated based on the engine operating state such as the engine speed and the fuel injection amount. It has been considered to control the opening degree of the EGR valve 16 on the basis of the in-cylinder oxygen concentration so that the NOx concentration becomes.

  That is, the control amount C of the target opening degree that controls the opening degree of the EGR valve 16 is the basic control amount (pre-control amount) calculated by the feedforward control of the fourth control unit 44 based on the in-cylinder oxygen concentration target value Dt. ) Ca is calculated based on a difference (error) ΔD (= Dt−Dc) between the cylinder oxygen concentration target value Dt and the calculated value Dc of the cylinder oxygen concentration calculated based on inputs from various sensors. The valve control amount C is calculated by adding the correction control amount Cb calculated by the feedback control (PID control) of the control unit 45 (C = Ca + Cb).

  More specifically, the first control unit 41 calculates the NOx concentration based on the detection values from the sensor group Sg1, such as the intake air flow sensor 21, the intake pressure sensor 22, the intake temperature sensor 23, and the exhaust lambda sensor 24. Nc is calculated. At the same time, based on the idea that the calculated value for control is corrected using the value for correcting the calculated value based on the NOx concentration calculated value Nc based on the detected NOx concentration value Nd, the NOx concentration sensor 46X uses the NOx concentration sensor. The NOx concentration detection value Nd, which is 20 detection values, is input, and the NOx correction coefficient (correction ratio) Ncf = Nd / Nc is calculated from the NOx concentration detection value Nd and the NOx concentration calculation value Nc.

  On the other hand, the first NOx target value Nt1 is calculated by referring to the map data based on the engine speed and the fuel injection amount, and the second control unit 42 sets the smoke limit for the first NOx target value Nt1. The second NOx target value Nt2 is calculated in consideration, and further, when the operating state of the internal combustion engine is in the steady state, the third NOx target value Nt3 (= Nt2 × Ncf = Nt2 × Nd /) is calculated by multiplying the NOx correction coefficient Ncf. Nc) is calculated. When the operating state of the internal combustion engine is in a transient state, the third NOx target value Nt3 is calculated with the correction ratio set to 1 without performing correction using the NOx correction coefficient NCf (Nt3 = Nt2 × 1 = Nt2).

  With respect to the third NOx target value Nt3, the third control unit 43 calculates the in-cylinder oxygen concentration target value Dt, and the fourth control unit 44 calculates the basic control amount (target value of feedforward control (pre-control)). Pre-control amount) Ca is calculated. At the same time, the fifth control unit 45 inputs the in-cylinder oxygen concentration target value Dt and the in-cylinder oxygen concentration calculated value Dc calculated by the first control unit 41 to obtain a target value for feedback control (PID control). A certain correction control amount Cb is calculated. The adder 47 adds the basic control amount Ca and the correction control amount Cb to calculate the valve control amount C. With this valve control amount C, the opening degree of the EGR valve 16 is adjusted and controlled.

  In the EGR control, as shown in FIG. 5, in the NOx correction unit 46X, when the operating state of the internal combustion engine is in the steady state, not only the NOx concentration sensor 20 but also the NOx concentration correction factor NCf is calculated. Detection values of various sensors such as an intake air flow rate sensor (MAF sensor) 21, an intake pressure sensor 22, an intake air temperature sensor 23, and an exhaust lambda sensor 24 that are input to the first control unit 41 are used.

  However, the intake air flow rate sensor 21 and the exhaust lambda sensor 24 have a range in which the measurement accuracy can be maintained and a range in which the measurement accuracy cannot be maintained depending on the characteristics and individual differences of the sensors, and the measurement accuracy deteriorates in a specific engine operating state. There is. For example, in the intake air flow sensor 21, the measurement accuracy is degraded when the intake air flow rate is equal to or less than a predetermined amount and the detected value is equal to or less than a specific value. Further, when the air-fuel ratio of the exhaust gas is on the lean side and the detected value is a specific value or more, the exhaust lambda sensor 24 is deteriorated in measurement accuracy or dull in sensitivity. Therefore, if the NOx correction coefficient NCf is calculated using the detected value in this specific engine operating state, the calculation accuracy of the NOx correction coefficient NCf is deteriorated, or conversely, the sensitivity becomes dull.

  Accordingly, when the control amount C of the opening degree of the EGR valve 16 is calculated in a state where the calculation accuracy of the NOx correction coefficient NCf is deteriorated and varies, the target opening degree of the EGR valve 16 based on the calculated control amount C varies. Therefore, the control accuracy of the opening degree of the EGR valve 16 is deteriorated. In addition, when the sensor sensitivity falls in a region, a sticking state occurs in which the target value of the opening degree of the EGR valve 16 does not change. Therefore, in a specific engine operating state, due to the measurement accuracy of the sensor, the calculation accuracy of the target value Dt of the in-cylinder oxygen concentration deteriorates, the accuracy of control of the opening degree of the EGR valve 16 deteriorates, and the exhaust gas The NOx concentration will deteriorate.

JP 2012-237290 A

  The present invention has been made in view of the above, and an object of the present invention is an internal combustion engine including an EGR system configured to have an EGR valve in an EGR passage, and a NOx concentration detection device provided in the exhaust passage. TECHNICAL FIELD The present invention relates to an EGR system for an internal combustion engine that controls the opening degree of an EGR valve based on the detected value of the engine and the in-cylinder oxygen concentration, and in particular, the detected value of the intake air flow rate, the detected value of the exhaust lambda, The deterioration of the control accuracy of the opening degree of the EGR valve can be suppressed by avoiding a decrease in the calculation accuracy of the NOx correction coefficient that is calculated based on the detected value and used for correcting the in-cylinder oxygen concentration. An EGR control system for an internal combustion engine, an internal combustion engine, and an EGR control method for the internal combustion engine are provided.

  In order to achieve the above object, an EGR control system for an internal combustion engine according to the present invention is an internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, and is a cylinder corresponding to an EGR NOx concentration target value. In an EGR control system for an internal combustion engine that controls the opening degree of the EGR valve based on an internal oxygen concentration target value, an intake air flow rate detection device is provided in the intake passage, and an exhaust lambda detection device and a NOx concentration detection device are provided in the exhaust passage. And the control device for controlling the EGR system uses a NOx correction coefficient that is a ratio of the detected value of the NOx concentration detecting device and the calculated value of the NOx concentration when the operating state of the internal combustion engine is in a steady state. When correcting the in-cylinder oxygen concentration target value, the operating state of the internal combustion engine or the detected value of the When a combination of detection values of the air lambda detection device is included in a preset detection value use range, the detection value of the intake air flow rate detection device, the detection value of the exhaust lambda detection device, and the NOx concentration detection device The detected value is used to calculate the NOx correction coefficient. When the detected value is out of the range of use, the NOx correction coefficient is set to 1.0, and the calculated NOx correction coefficient is used. Then, the opening degree of the EGR valve is controlled by correcting the in-cylinder oxygen concentration target value.

  This detection value use range (NOx correction coefficient adaptation range) is set in advance depending on the detection value reliability range of the intake air flow rate detection device (intake air flow rate sensor) and exhaust lambda detection device (exhaust lambda sensor). Since various factors affect the measurement accuracy of the detected value, the EGR valve is controlled based on the NOx correction coefficient calculated by using the detected value of the intake air flow rate and the detected value of the exhaust lambda in an experiment or the like. A range in which no inconvenience occurs when the opening degree is controlled is set as a detection value use range.

  This detection value use range may be set, for example, for the operating state of the internal combustion engine that can be expressed by a combination of the engine speed and the load (or fuel injection amount). Also, the detection value of the intake air flow rate and the detection of the exhaust lambda A combination of values, in other words, a combination of a measurement error range of the detected value of the intake air flow rate and a measurement error range of the detection value of the exhaust lambda may be set. When setting the measurement error, a tolerance range such as a calibration curve of each sensor can be used.

  Then, within this detected value use range, a NOx correction coefficient is calculated using these detected values, and a control amount of the opening degree of the EGR valve is calculated based on the calculated NOx correction coefficient. The opening degree of the EGR valve is changed by the calculated control amount to control the opening degree of the EGR valve to the target opening degree. On the other hand, when it is out of the detection value use range, the NOx correction coefficient is calculated as 1.0 without using the NOx correction coefficient calculated using these detection values.

  Therefore, according to this configuration, the NOx correction coefficient calculated using these detected values is used only when the engine is in an operating state in which the measurement accuracy of the intake air flow rate detection device and the exhaust lambda detection device is maintained. Deterioration of the calculation accuracy of the correction coefficient can be suppressed, and deterioration of the calculation accuracy of the control amount of the opening degree of the EGR valve can be suppressed.

  In the EGR control system for an internal combustion engine, the control device may be configured such that the operation state of the internal combustion engine or a combination of a detection value of the intake air flow rate detection device and a detection value of the exhaust lambda detection device is the detection value. The calculated value of the NOx concentration in the exhaust gas calculated using the detection value of the intake air flow rate detection device and the detection value of the exhaust lambda detection device even when included in the value use range, It is configured to determine whether or not the detected value of the NOx concentration detecting device is within a preset allowable range, and when the detected value is not within the allowable range, the NOx correction coefficient is set to 1.0. Ru.

  This is when the operating state of the internal combustion engine or a combination of the detected value of the intake air flow rate and the detected value of the exhaust lambda is included in the detected value usage range and the measurement accuracy of the intake air flow rate and the exhaust lambda is maintained. However, the calculated value of the NOx concentration contained in the exhaust gas calculated using the detected value of the intake air flow rate and the detected value of the exhaust lambda is a measurement error based on the individual difference of the NOx concentration detecting device (NOx concentration sensor). Calculated as 1.0 without using the calculated NOx correction coefficient when outside the allowable range, and using the calculated NOx correction coefficient when it falls within the preset allowable range from the range. The opening degree of the EGR valve is controlled using the NOx correction coefficient.

  That is, the detected value of NOx concentration and the calculated value of NOx concentration are compared to determine whether the measurement accuracy is low based on the detected value of the intake air flow rate and the detected value of the exhaust lambda. In this case, the NOx correction coefficient calculated using the detected value of the intake air flow rate and the detected value of the exhaust lambda is not used, and deterioration of the accuracy of calculating the NOx correction coefficient is prevented.

  This avoids the occurrence of EGR hunting, which is a phenomenon in which the opening of the EGR valve vibrates in the vicinity of the target opening due to variations in the calculated value of the NOx concentration, and opens the EGR valve in a region where the sensor sensitivity is low. Prevent sticking of the upper limit of the degree.

  An internal combustion engine equipped with the EGR control system for an internal combustion engine can achieve the same effects as the EGR control system for the internal combustion engine.

Further, an EGR control method for an internal combustion engine of the present invention for achieving the above object is an internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, and corresponds to an NOx concentration target value of EGR. In the EGR control method for an internal combustion engine that controls the opening degree of the EGR valve based on the in-cylinder oxygen concentration target value, when the operating state of the internal combustion engine is in a steady state, the detected value of the NOx concentration detection device When the in-cylinder oxygen concentration target value is corrected using a NOx correction coefficient that is a ratio of calculated values of NOx concentration, the operation state of the internal combustion engine or the detection of the intake air flow rate detection device provided in the intake passage and a value, when a combination of detected values of the provided in the exhaust passage exhaust lambda detection device is included in the preset detection values used within the range, the detected value of the intake air flow rate detection device The NOx correction coefficient is calculated using the detection value of the exhaust lambda detection device and the detection value of the NOx concentration detection device, and the NOx correction coefficient is set to 1.0 when it is out of the detection value use range. The method is characterized in that the calculated in-cylinder oxygen concentration target value is corrected using the calculated NOx correction coefficient, and the opening degree of the EGR valve is controlled.

  In the EGR control method for an internal combustion engine described above, the operating state of the internal combustion engine or a combination of a detection value of the intake air flow rate detection device and a detection value of the exhaust lambda detection device is within the detection value use range. Even if it is included, the calculated value of the NOx concentration in the exhaust gas calculated using the detected value of the intake air flow rate detecting device and the detected value of the exhaust lambda detecting device is the NOx concentration detecting device. It is determined whether the detected value is within a preset allowable range. If the detected value is not within the allowable range, the NOx correction coefficient is set to 1.0.

  According to these methods, the same operational effects as those of the EGR control system for the internal combustion engine can be obtained.

  According to the EGR control system for an internal combustion engine, the internal combustion engine, and the EGR control method for an internal combustion engine of the present invention, the intake air is only in the engine operating state in which the measurement accuracy of the intake air flow rate detection device and the exhaust lambda detection device is maintained. Since the NOx correction coefficient calculated using the detected value of the flow rate and the detected value of the exhaust lambda is used, it is possible to avoid a decrease in the calculation accuracy of the NOx correction coefficient used for correcting the in-cylinder oxygen concentration, The deterioration of the control accuracy of the opening degree of the EGR valve can be suppressed.

FIG. 1 is a view schematically showing a configuration of an EGR system in an internal combustion engine of an embodiment according to the present invention. It is a figure which shows typically the structure of the EGR control system of the internal combustion engine of embodiment which concerns on this invention. It is a figure which shows the control flow of the EGR control method of the internal combustion engine of embodiment which concerns on this invention. It is a figure which shows an example of the detection value use range with respect to the combination of the detection value of suction air flow rate detection, and the detection value of exhaust lambda. It is a figure which shows typically the structure of the EGR control system of the internal combustion engine in a prior art.

  Hereinafter, an EGR control system for an internal combustion engine, an internal combustion engine, and an EGR control method for an internal combustion engine according to embodiments of the present invention will be described with reference to the drawings. The internal combustion engine of the embodiment according to the present invention is configured to include the EGR control system 40 of the internal combustion engine of the embodiment according to the present invention, and is similar to the operation and effect exhibited by the EGR control system 40 of the internal combustion engine described later. The effects and effects of

  As shown in FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 10 according to an embodiment of the present invention includes an EGR system 1, and includes an engine body 11, an intake passage 12, an exhaust passage 13, and an EGR passage 14. ing. The EGR passage 14 is provided by connecting the exhaust passage 13 and the intake passage 12, and is provided with an EGR cooler 15 and an EGR valve 16 that use engine cooling water as a cooling medium in order from the upstream side.

  Then, fresh air A introduced from the atmosphere is sent to the combustion chamber in the cylinder (cylinder) 11c together with the EGR gas Ge flowing into the intake manifold 11a from the EGR passage 14 as necessary. The fuel is mixed and compressed with the fuel injected from a fuel injection device (not shown), and the fuel is burned to generate power in the engine 10. Then, the exhaust gas G generated by combustion in the engine 10 flows out from the exhaust manifold 11b to the exhaust passage 13, but part of it flows as EGR gas Ge into the EGR passage 14, and the remaining exhaust gas Ga (= G-Ge). ) Is purified by an exhaust purification device (not shown) and then released to the atmosphere via a muffler (not shown).

  The intake passage 12 includes an intake air flow sensor (MAF sensor: intake air flow detection device) 21 that detects an intake air flow rate, an intake pressure sensor 22 that detects intake pressure, and an intake temperature sensor 23 that detects intake temperature. The exhaust passage 13 is provided with a NOx concentration sensor (NOx concentration detection device) 20 for detecting the NOx concentration in the exhaust gas, and an exhaust lambda sensor (exhaust air excess rate sensor: exhaust gas) for detecting the excess air ratio of the exhaust gas. A lambda detector 24) is provided. These sensors 21 to 24 form a sensor group Sg1, and signals from these sensors 20 to 24 are transmitted to a control device 30 described later at preset control times.

  A control device 30 for an EGR control system 40 for controlling the EGR system 1 of the internal combustion engine of the present invention is also provided. The control device 30 calculates the detection values of the sensors 20 to 24 for each preset control time based on the signals transmitted from the NOx concentration sensor 20 and the sensors 21 to 24 of the sensor group Sg1, and is necessary. Detected detection value data (usually the latest detection value data) is stored. The control device 30 is generally incorporated in an engine control unit (ECU) that controls the overall operating condition of the engine 10, but may be provided independently.

  Here, the control amount C of the target opening that controls the opening of the EGR valve 16 is a basic control amount (pre-control) calculated by feedforward control of the fourth control unit 44 based on the in-cylinder oxygen concentration target value Dt. The amount (Ca) is calculated based on the difference (error) ΔD (= Dt−Dc) between the in-cylinder oxygen concentration target value Dt and the calculated value Dc of the in-cylinder oxygen concentration based on inputs from various sensors. The valve control amount C is calculated by adding the correction control amount Cb calculated by the feedback control (PID control) of the control unit 45 (C = Ca + Cb).

  That is, in the engine 10 including the EGR system 1 configured to include the EGR valve 16 in the EGR passage 14, the EGR valve 16 is based on the in-cylinder oxygen concentration target value Dt corresponding to the NOx concentration target value Nt1 of EGR. It is the EGR control system 40 of the internal combustion engine which controls the opening degree.

  More specifically, the first control unit 41 calculates the NOx concentration calculated value based on the detected values from the sensor group Sg1 such as the intake air flow rate sensor 21, the intake pressure sensor 22, the intake air temperature sensor 23, the exhaust lambda sensor 24, and the like. Calculate Nc.

  It is preferable to consider the internal EGR gas when calculating the cylinder oxygen concentration calculation value Dc. That is, since the NOx amount generated in the cylinder is related to the in-cylinder oxygen concentration calculation value Dc with respect to the total exhaust gas amount in the cylinder, the in-cylinder oxygen concentration calculation value Dc with respect to the total exhaust gas amount in the cylinder is The in-cylinder oxygen concentration calculation value Dc is calculated by taking into account the exhaust gas amount and the oxygen concentration of the internal EGR gas, without calculating only the intake air amount and the oxygen concentration, the exhaust gas amount of the external EGR gas and the inside of the oxygen concentration. It is preferable to calculate.

  Then, the NOx amount generated in the cylinder and the NOx concentration of the exhaust gas exhausted from the cylinder are calculated from the in-cylinder oxygen concentration calculated value Dc and the like, and set as the NOx concentration calculated value Nc.

  At the same time, the NOx concentration detection value Nd detected by the NOx concentration sensor 20 is used as a basis to correct the calculated value for control using the value for correcting the calculated value by the NOx concentration calculated value Nc. The correction unit 46 receives the NOx concentration detection value Nd, which is the detection value of the NOx concentration sensor 20, and calculates a NOx correction coefficient (correction ratio) Ncf = Nd / Nc from the NOx concentration detection value Nd and the NOx concentration calculation value Nc. calculate.

  On the other hand, the second control unit 42 calculates the first NOx target value Nt1 by inputting the detection value of the exhaust lambda sensor 24 and referring to the map data based on the engine speed and the fuel injection amount. In the second control unit 42 to which the first NOx target value Nt1 is input, the detection value of the exhaust lambda sensor 24 is input, and smoke is generated at the first NOx target value Nt1. When predicted from map data or the like, the NOx concentration at which smoke does not occur is taken as the second NOx target value Nt2. So-called smoke limit is performed. If there is no possibility that smoke will occur, the first NOx target value Nt1 is set as the second NOx target value Nt2 as it is. Thereby, the second NOx target value Nt2 is calculated.

  Further, when the operating state of the internal combustion engine is in a steady state, the NOx correction coefficient Ncf is multiplied to calculate a third NOx target value Nt3 (= Nt2 × Ncf = Nt2 × Nd / Nc). On the other hand, when it is in the transient state, the third NOx target value Nt3 is calculated with the correction ratio being 1 (Nt3 = Nt2 × 1 = Nt2), without performing the correction using the NOx correction coefficient NCf.

  Then, the third control unit 43 inputs the detection values of the intake pressure sensor 22 and the intake temperature sensor 23, and calculates the in-cylinder oxygen concentration target value Dt with respect to the third NOx target value Nt3. The fourth control unit 44 calculates a basic control amount (pre-control amount) Ca that is a target value for feedforward control (pre-control) with respect to the calculated in-cylinder oxygen concentration target value Dt. In calculating the basic control amount Ca, it is preferable to consider the internal EGR gas.

  In the fourth control unit 44, the front-rear pressure of the EGR valve 16 detected by a differential pressure sensor (not shown) provided before and after the EGR valve 16, the temperature sensor provided in the EGR passage 14 downstream of the EGR valve 16 ( It is preferable to obtain a more accurate relationship between the flow rate of the EGR gas Ge and the opening degree of the EGR valve 16 using the temperature of the EGR gas Ge detected in (not shown).

  That is, the in-cylinder oxygen concentration target value Dt with respect to the total exhaust gas amount in the cylinder related to the NOx amount generated in the cylinder, the exhaust gas amount and oxygen concentration in the cylinder, the air flow rate and oxygen concentration, and the internal EGR gas The external EGR gas amount is determined from the in-cylinder oxygen concentration target value Dt, which is the target value of the in-cylinder oxygen concentration, using the fact that the exhaust gas amount and oxygen concentration and the exhaust gas amount and oxygen concentration of the external EGR gas are determined. Ge is calculated, and the opening degree of the EGR valve 16 that can supply this EGR gas amount Ge is defined as a pre-control amount Ca.

  At the same time, the in-cylinder oxygen concentration target value Dt calculated by the fifth control unit 45 for the third NOx target value Nt3 by the third control unit 43 and the cylinder interior calculated by the first control unit 41 An oxygen concentration calculation value Dc is input to calculate a correction control amount Cb that is a target value for feedback control (PID control). Then, the adding unit 47 adds the basic control amount Ca and the correction control amount Cb to calculate the valve control amount C. The valve opening amount of the EGR valve 16 is adjusted and controlled by the valve control amount C.

  In the present invention, the control device 30 that controls the EGR system 1 is the NOx correction unit 46, and the detected value Nd of the NOx concentration sensor 20 and the calculated value Nc of the NOx concentration Nc when the engine operating state is a steady state. When correcting the in-cylinder oxygen concentration target value Dt using the NOx correction coefficient Ncf (= Nd / Nc) which is the ratio of the engine operation state, the detection value use range in which the engine operating state is preset (NOx correction coefficient adaptation range) 4, or as illustrated in FIG. 4, the combination of the detected value m of the intake air flow rate sensor 21 and the detected value λ of the exhaust lambda sensor 24 is a preset detected value use range (NOx correction). When it is included in the coefficient adaptation range AR (m ≧ m1 and λ ≦ λ1), the detected value of the intake air flow rate sensor 21, the detected value of the exhaust lambda sensor 24, and the NOx concentration sensor The NOx correction coefficient Ncf is calculated using 20 detected values Nd, and when it is outside the detected value use range AR, the NOx correction coefficient Ncf is calculated to be 1.0, and this calculated NOx correction coefficient Ncf. Is used to correct the in-cylinder oxygen concentration target value Dt to control the opening degree of the EGR valve 16.

  In addition, the control device 30 is in the engine operating state or when the combination of the detection value m of the intake air flow rate sensor 21 and the detection value λ of the exhaust lambda sensor 24 is included in a preset detection value use range AR. Even if the detected value m of the exhaust air flow sensor 21 and the detected value λ of the exhaust lambda sensor 24 are used to calculate the NOx concentration calculated value Nc in the exhaust gas in advance in the detected value Nd of the NOx concentration sensor 20. It is determined whether it is within the set allowable range MR, and when it is not within the allowable range MR, the NOx correction coefficient Ncf is set to 1.0 for calculation.

  That is, by comparing the detected value Nd of the NOx concentration with the calculated value Nc of the NOx concentration, it is determined whether or not the measurement accuracy of the detected value m of the intake air flow rate and the detected value λ of the exhaust lambda is low. The NOx correction coefficient Ncf is set to 1.0 without using the NOx correction coefficient Ncf calculated using the detected value m of the intake air flow and the detected value λ of the exhaust lambda. The deterioration of the calculation accuracy of the coefficient Ncf is prevented.

  Next, an EGR control method for an internal combustion engine according to the present invention using the EGR control system 40 for the internal combustion engine will be described with reference to the control flow of FIG. The control flow of FIG. 3 is a control flow that is called from the advanced control flow at every control time when the engine 10 is in an operating state, and returns to the advanced control flow after execution. As long as it is in the state, it is shown as a control flow called repeatedly. In the middle of the control based on the control flow of FIG. 3, when the internal combustion engine stops operating, an interruption occurs, and the return is made to return to the advanced control flow, and is terminated when the advanced control flow ends. Do.

  When the control flow of FIG. 3 is started, in step S11, the intake air flow rate sensor 21, the exhaust lambda sensor 24 and the NOx concentration sensor 20 detect the intake air flow rate m, the exhaust lambda λ and the NOx concentration Nd. After this detection, the process proceeds to step S12.

  In step S12, it is determined whether or not the combination of the intake air flow rate m and the exhaust lambda λ detected in step S11 is included in the detection value use range AR. When it is not included in the detected value use range AR (NO), it is determined that the calculation accuracy of the NOx correction coefficient NCf is not maintained, and the process proceeds to step S16 to set the NOx correction coefficient NCf to 1.0. , And proceeds to step S17.

  If the detected value usage range AR is included in step S12 (YES), the measurement accuracy of the intake air flow rate sensor 21 and the exhaust lambda sensor 24 is maintained, and the calculation accuracy of the NOx correction coefficient NCf is maintained. It is determined that the region is in the area to be processed, and the process proceeds to step S13.

  In step S13, the calculated value Nc of the concentration of NOx contained in the exhaust gas Ga is calculated based on the detected value (intake air flow) m of the intake air flow sensor 21 and the detected value (exhaust lambda) λ of the exhaust lambda sensor 24. While the calculated value Nc of NOx concentration is based on the error range of the calibration curve including individual differences of the detected value (NOx concentration detected value) Nd of the NOx concentration sensor 20 detected in step S11, the allowable range MR is Set or calculate. After setting or calculating the allowable range MR, the process proceeds to step S14.

  In step S14, it is determined whether or not the calculated value Nc of the NOx concentration is included in the allowable range MR. In step S14, when it is not included in the allowable range MR (NO), it is determined that the calculation accuracy of the NOx correction coefficient NCf is not in the range to be maintained, and the process proceeds to step S16. .0 and proceed to step S17.

  On the other hand, if the calculated value Nc of the NOx concentration is included in the allowable range MR (YES), the NOx correction coefficient NCf is calculated using the intake air flow rate m and the exhaust lambda λ in step S15, and the process proceeds to step S17. move on.

  In step S17, the cylinder oxygen concentration target value Dt is corrected using the NOx correction coefficient NCf, the control amount C of the opening degree of the EGR valve 16 is calculated based on the cylinder oxygen concentration target value Dt, and the return The opening degree of the EGR valve 16 is controlled by the returned upper control flow.

By the above control, the EGR control method for the internal combustion engine according to the embodiment of the present invention can be carried out. This EGR control method for the internal combustion engine includes the EGR system 1 configured by including the EGR valve 16 in the EGR passage 14. The internal combustion engine 10 is an EGR control method for an internal combustion engine that controls the opening degree of the EGR valve 16 based on the in-cylinder oxygen concentration target value Dt corresponding to the NOx concentration target value Nt1 of EGR. In the steady state, when the in-cylinder oxygen concentration target value Dt is corrected using the NOx correction coefficient Ncf, which is the ratio of the detected value Nd of the NOx concentration sensor 20 and the calculated value Nc of NOx concentration, the engine operating state , or a combination of the detection value λ of the exhaust lambda sensor 24 provided with the detection value m of the intake air flow sensor 21 provided in the intake passage 12 to the exhaust passage 13, When the detected value usage range AR is within the range, the detected value m of the intake air flow rate sensor 21, the detected value λ of the exhaust lambda sensor 24, and the detected value Nd of the NOx concentration sensor 20 are used. When Ncf is calculated and is outside the detection value usage range AR, the NOx correction coefficient Ncf is set to 1.0, and the calculated in-cylinder oxygen concentration target value Dt is corrected using the calculated NOx correction coefficient Ncf. Thus, the opening degree of the EGR valve 16 is controlled.

Furthermore, even when the engine operating state or the combination of the detection value m of the intake air flow sensor 21 and the detection value λ of the exhaust lambda sensor 24 is included in the detection value use range AR, the intake air flow rate The calculated value Nc of the NOx concentration in the exhaust gas calculated using the detection value m of the sensor 21 and the detection value λ of the exhaust lambda sensor 24 is a preset allowable range MR in the detection value Nd of the NOx concentration sensor 20. If it is not within the allowable range MR, the NOx correction coefficient Ncf is calculated to be 1.0.

  According to the EGR control system 40 of the internal combustion engine, the engine (internal combustion engine) 10, and the EGR control method of the internal combustion engine configured as described above, the engine operating state in which the measurement accuracy of the intake air flow rate sensor 21 and the exhaust lambda sensor 24 is maintained. Since the NOx correction coefficient NCf calculated using the detected value m of the intake air flow rate sensor 21 and the detected value λ of the exhaust lambda sensor 24 is used only when A decrease in the calculation accuracy of the correction coefficient Ncf can be avoided, and a deterioration in the control accuracy of the opening degree of the EGR valve 16 can be suppressed.

1 EGR system for internal combustion engine 10 Engine (internal combustion engine)
11 Engine body 11a Intake manifold 11b Exhaust manifold 11c Cylinder 12 Intake passage 13 Exhaust passage 14 EGR passage 15 EGR cooler 16 EGR valve 20 NOx concentration sensor (NOx concentration detection device)
21 Intake air flow rate sensor (MAF sensor: Intake air flow rate detection device)
22 Intake pressure sensor 23 Intake temperature sensor 24 Exhaust lambda sensor (exhaust excess rate sensor: exhaust lambda detection device)
30 control device 40, 40X EGR control system 41 for internal combustion engine first control unit 42 second control unit 43 third control unit 44 fourth control unit 45 fifth control unit 46, 46X NOx correction unit 47 addition unit A fresh air C EGR valve opening control amount Ca EGR valve opening basic control amount Cb EGR valve opening correction control amount Dt In-cylinder oxygen concentration target value Dc In-cylinder oxygen concentration calculation value G, Ga Exhaust gas Ge EGR gas NCf NOx correction coefficient Sg1 sensor group

Claims (5)

An internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, wherein the internal combustion engine controls the opening degree of the EGR valve based on an in-cylinder oxygen concentration target value corresponding to a NOx concentration target value of EGR. In the engine EGR control system,
An intake air flow rate detection device is provided in the intake passage, an exhaust lambda detection device and a NOx concentration detection device are provided in the exhaust passage,
A control device for controlling the EGR system,
When the operating state of the internal combustion engine is in a steady state, when correcting the in-cylinder oxygen concentration target value using a NOx correction coefficient that is a ratio of a detected value of the NOx concentration detecting device and a calculated value of the NOx concentration In addition,
When the combination of the operating state of the internal combustion engine or the detection value of the intake air flow rate detection device and the detection value of the exhaust lambda detection device is included in a preset detection value use range, the intake air flow rate The NOx correction coefficient is calculated using the detection value of the detection device, the detection value of the exhaust lambda detection device, and the detection value of the NOx concentration detection device, and the NOx correction coefficient is out of the detection value use range. Is calculated as 1.0,
An EGR control system of an internal combustion engine configured to control the opening degree of the EGR valve by correcting the in-cylinder oxygen concentration target value using the calculated NOx correction coefficient. The control device is
Even when the operating state of the internal combustion engine or the combination of the detected value of the intake air flow rate detection device and the detected value of the exhaust lambda detection device is included in the detected value use range,
The calculated value of NOx concentration in the exhaust gas calculated using the detected value of the intake air flow rate detection device and the detected value of the exhaust lambda detection device is a preset allowance in the detected value of the NOx concentration detection device The EGR control system for an internal combustion engine according to claim 1, wherein the NOx correction coefficient is set to 1.0 to determine whether or not it is within the range, and when it is not within the allowable range. .   An internal combustion engine comprising the EGR control system for an internal combustion engine according to claim 1 or 2. An internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage and controlling an opening degree of the EGR valve based on an in-cylinder oxygen concentration target value corresponding to an EGR NOx concentration target value In the EGR control method of the engine,
When the operation state of the internal combustion engine is in a steady state, when correcting the in-cylinder oxygen concentration target value using a NOx correction coefficient that is a ratio of the detected value of the NOx concentration detecting device and the calculated value of the NOx concentration. ,
The combination of the operating state of the internal combustion engine or the detection value of the intake air flow rate detection device provided in the intake passage and the detection value of the exhaust lambda detection device provided in the exhaust passage is within a preset detection value use range. When it is included, the NOx correction coefficient is calculated using the detected value of the intake air flow rate detecting device, the detected value of the exhaust lambda detecting device and the detected value of the NOx concentration detecting device, and the detected value is out of use range Is calculated by setting the NOx correction coefficient to 1.0,
An EGR control method for an internal combustion engine, comprising: correcting the in-cylinder oxygen concentration target value using the calculated NOx correction coefficient; and controlling an opening degree of the EGR valve. Even when the combination of the operating state of the internal combustion engine or the detection value of the intake air flow rate detection device and the detection value of the exhaust lambda detection device is included in the detection value use range,
The calculated value of the NOx concentration in the exhaust gas calculated using the detection value of the intake air flow rate detection device and the detection value of the exhaust lambda detection device is a preset tolerance in the detection value of the NOx concentration detection device. 5. The EGR control method for an internal combustion engine according to claim 4, wherein it is determined whether or not it is within the range, and when it is not within the allowable range, the NOx correction coefficient is calculated to be 1.0. .

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