JP2017020437A - Egr control system of internal combustion engine, internal combustion engine, and egr control method of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR control system of an internal combustion engine, the internal combustion engine, and an EGR control method of the internal combustion engine capable of improving, in particular, control accuracy in NOx control by using not NOx concentration but NOx mass in calculation of a target value of a cylinder oxygen concentration, and easily implementing NOx processing in an exhaust emission control processing unit, in the EGR system of the internal combustion engine controlling an opening of an EGR valve on the basis of the cylinder oxygen concentration of the internal combustion engine, in the internal combustion including the EGR system having an EGR valve in an EGR passage.SOLUTION: A control device 30 for controlling an EGR system 1 is constituted to control an opening of an EGR valve 16 on the basis of a cylinder oxygen concentration target value Dt corresponding to a NOx mass target value Nt3g as a target value in controlling a NOx amount discharged into an exhaust gas G.SELECTED DRAWING: Figure 2

Description

  The present invention is an internal combustion engine equipped with an EGR system having an EGR valve in an EGR passage, and the EGR control of the internal combustion engine controls the opening degree of the EGR valve based on the in-cylinder oxygen concentration of the internal combustion engine. The present invention relates to a system, an internal combustion engine, and an EGR control method for the 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 nitrogen oxides 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 lowered, and the concentration of nitrogen oxide contained in the exhaust gas G is controlled. In general, it is known that the concentration of nitrogen oxides contained in the exhaust gas G decreases as the combustion temperature in the cylinder 11c decreases.

  In this connection, feed-forward control is performed so that the flow rate of the low pressure EGR is constant regardless of the load of the internal combustion engine, and the flow rate of the high pressure EGR is set to the target value so that the oxygen concentration in the exhaust gas is constant. An exhaust gas recirculation control device for an internal combustion engine that performs feedback control 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. 3 to calculate the first NOx concentration target value (basic NOx concentration target value) Nt1 calculated based on the engine operating state such as the engine speed and the fuel injection amount. In addition, it has been considered to control the opening degree of the EGR valve 16 based on the in-cylinder oxygen concentration so that the actual NOx concentration in the exhaust gas G becomes equal.

  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 feedback control (PID control) of the control unit 45 (C = Ca + Cb).

  More specifically, the first control unit 41X calculates the NOx concentration based on the detected values from the intake system sensor group Sg1 such as the intake flow rate sensor 21, the intake pressure sensor 22, the intake air temperature sensor 23, and the exhaust lambda sensor 24. A value 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 46 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 concentration 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 performs smoke on the first NOx concentration target value Nt1. The second NOx concentration target value Nt2 is calculated in consideration of the limit. Further, when the operating state of the internal combustion engine is in a steady state, the NOx correction coefficient NCf is multiplied to obtain a third NOx concentration target value Nt3 (= Nt2 × NCf = Nt2 × Nd / Nc) (NOx concentration target value) is calculated. In addition, when the operating state of the internal combustion engine is in a transient state, the third NOx concentration target value Nt3 is calculated with the correction ratio being 1 without performing correction using the NOx correction coefficient NCf (Nt3 = Nt2 × 1 = Nt2).

  With respect to the third NOx concentration target value Nt3, the third control unit 43 calculates the in-cylinder oxygen concentration target value Dt, and the fourth control unit 44 calculates a basic control amount that is a target value for 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 41X to obtain the 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 this EGR control, correction for the second NOx concentration target value Nt2 by the NOx correction coefficient NCf is performed only when the operating state of the internal combustion engine is in a steady state. That is, when the operating state of the internal combustion engine is in a steady state, the third NOx concentration target value Nt3 is calculated by performing correction using the NOx correction coefficient NCf (Nt3 = Nt2 × NCf). When the operating state of the internal combustion engine is in a transient state, the NOx correction coefficient NCf is not corrected, and the NOx correction coefficient NCf is set to 1 to calculate the third NOx concentration target value Nt3 (Nt3 = Nt2 × 1 = Nt2).

  In the NOx control based on the EGR control described above, parameters related to NOx corresponding to the in-cylinder oxygen concentration target value Dt are the NOx concentration (first NOx concentration target value Nt1, second NOx concentration target value Nt2, third NOx concentration target value Nt3). It is said.

  Similar to this control, in general, in NOx control, control is based on the concentration of NOx contained in the exhaust gas. However, what should be considered as NOx actually discharged into the outside air is the NOx control. The NOx mass, which is the amount of NOx emitted rather than the concentration, is considered. The NOx mass is obtained by multiplying the NOx concentration by the exhaust gas flow rate, and the exhaust gas flow rate is related to the intake air amount and the fuel amount. In other words, this intake amount (mass) corresponds to the amount of supercharging by a turbocharger such as a turbocharger provided in the intake passage, and is related to atmospheric pressure, atmospheric temperature, supercharging pressure, supercharging temperature, etc. To do.

  For this reason, for example, when the engine is in a transient state and the supercharging amount is increased but the NOx concentration is controlled to be constant, the NOx mass resulting from the multiplication of the NOx concentration and the exhaust gas flow rate is supercharged. In contrast, when the control is performed at a constant NOx concentration, the NOx mass decreases with a decrease in the supercharging amount even though the supercharging amount decreases. It will be.

  And when controlling the EGR valve at the time of increase / decrease of the supercharging amount according to the target value of NOx concentration, when the supercharging amount increases, the NOx mass discharged increases and the supercharging amount decreases. In some cases, the amount of NOx discharged becomes small. Therefore, when the NOx concentration is targeted, it is not always possible to grasp whether the NOx mass discharged from the internal combustion engine can be efficiently reduced when considered as a whole. There is a problem that is difficult.

  Further, when the EGR control is performed with the NOx concentration when the exhaust gas flow rate is changing in the transient state of the internal combustion engine, the NOx mass discharged to the exhaust passage changes according to the change in the exhaust gas flow rate, and the exhaust gas purification processing device There is a problem that the influence on the control of the supply amount of the reducing agent is large. In particular, in urban driving of trucks and buses, since the transient state increases in the operating state of the internal combustion engine, this problem is important in terms of improving NOx purification.

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. In the EGR system for an internal combustion engine that controls the opening degree of the EGR valve based on the above, it is possible to improve the control accuracy of the NOx control, particularly using the NOx mass instead of the NOx concentration for calculating the target value of the in-cylinder oxygen concentration. Another object of the present invention is to provide an EGR control system for an internal combustion engine, an internal combustion engine, and an EGR control method for an internal combustion engine that can facilitate NOx treatment in an exhaust gas purification processing apparatus.

  An EGR control system for an internal combustion engine of the present invention for achieving the above object is an internal combustion engine including an EGR system configured to have an EGR valve in an EGR passage, and is based on an in-cylinder oxygen concentration target value. In the EGR control system for an internal combustion engine that controls the opening degree of the EGR valve, the control device that controls the EGR system corresponds to a NOx mass target value that is a target value for controlling the amount of NOx discharged into the exhaust gas. The opening degree of the EGR valve is controlled based on the in-cylinder oxygen concentration target value.

  In other words, in the present invention, the parameter relating to NOx for calculating the target value of the in-cylinder oxygen concentration for calculating the control amount of the opening degree of the EGR valve (control amount of NOx control) is not the NOx concentration of the prior art. , NOx mass. The NOx mass is obtained by multiplying the NOx concentration by the exhaust gas flow rate (mass) or the like, and this exhaust gas flow rate varies greatly when the operating state of the internal combustion engine is in a transient state. In addition, the supercharging pressure changes due to variations in the turbocharger products and changes over time.

  Therefore, since the EGR control is made to follow the NOx concentration target value in the prior art, there is a problem that the NOx mass increases or decreases even in the transient state even if the NOx concentration is constant. Since the EGR control is made to follow the NOx mass target value instead of the NOx concentration target value, even if the operating state of the internal combustion engine is in a transitional state and the exhaust gas flow rate fluctuates, increase / decrease in the NOx mass can be avoided.

  Therefore, according to this configuration, the NOx parameter corresponding to the target value of the in-cylinder oxygen concentration for calculating the control amount of the opening degree of the EGR valve, that is, the control amount of NOx control, Since the NOx mass is used, the exhausted NOx mass can be grasped especially when the operating state of the internal combustion engine is in a transient state, and the exhausted NOx mass can be grasped more accurately and the cylinder can be grasped more accurately. Thus, it is possible to efficiently take measures against the NOx emission amount flowing out from the exhaust passage, and to easily reduce the total amount of NOx mass to be discharged.

  Further, regarding the NOx emission amount discharged from the cylinder into the exhaust passage, by changing from the concentration base to the mass base, consideration is given to fluctuations in the exhaust gas flow rate in calculation of the reducing agent supply amount in the exhaust gas processing, and the exhaust gas flow rate. Therefore, these calculations are simplified, and control for exhaust gas purification is facilitated.

  In the EGR control system of the internal combustion engine, the control device refers to the map data in which the NOx mass target value is set in advance when the operating state of the internal combustion engine is in a transient state. The in-cylinder oxygen concentration target value corresponding to the NOx mass target value is calculated, and the opening degree of the EGR valve is controlled based on the in-cylinder oxygen concentration target value. According to this configuration, the NOx treatment in the exhaust gas can be stably performed.

  Also, in the EGR control system for an internal combustion engine, a NOx concentration detection device is provided in an exhaust passage, and the control device calculates a NOx mass calculation value from a detection value of a sensor related to intake air, and the NOx concentration detection After calculating the actual NOx mass value via the mass converter from the actual NOx concentration value detected by the apparatus, a NOx correction coefficient is calculated from the NOx mass calculated value and the actual NOx mass actual value, and further engine operation is performed. A basic NOx mass target value is calculated based on the state, and the NOx mass target value is calculated from the basic NOx mass target value and the NOx correction coefficient.

  According to this configuration, since the NOx correction coefficient used for correcting the basic NOx mass target value is calculated after being converted to NOx mass instead of NOx concentration, the influence of the supercharging amount and the intake air corresponding to the supercharging amount Since the NOx correction coefficient can be calculated with the influence of atmospheric pressure, atmospheric temperature, etc. affecting the amount, the basic NOx mass target value can be corrected more accurately.

  Alternatively, in the above EGR control system for an internal combustion engine, a NOx concentration detection device is provided in an exhaust passage, and the control device calculates a NOx concentration calculation value from a detection value of a sensor related to intake air, and the NOx concentration detection After detecting the measured NOx concentration value, which is the detection value of the device, a NOx correction coefficient is calculated from the calculated NOx concentration value and the measured NOx concentration value, and further, a basic NOx mass target value is calculated based on the engine operating state The NOx mass target value is calculated from the basic NOx mass target value and the NOx correction coefficient.

  According to this configuration, the difference between the calculated NOx concentration value calculated from the actual measured value obtained from the sensor and the actual measured NOx concentration value detected from the NOx concentration sensor can be reflected in the NOx mass target value. The control accuracy according to the value can be further improved, and in particular, the control accuracy of the NOx control can be improved when the operating state of the internal combustion engine is in a transient state.

  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.

  An EGR control method for an internal combustion engine according to the present invention for achieving the above object is an internal combustion engine having an EGR system having an EGR valve in an EGR passage, and is based on a target value of oxygen concentration in a cylinder. Then, in the EGR control method for an internal combustion engine for controlling the opening degree of the EGR valve, based on the in-cylinder oxygen concentration target value corresponding to the NOx mass target value, which is a target value for controlling the amount of NOx discharged into the exhaust gas. Then, the opening degree of the EGR valve is controlled.

  Further, in the above-described EGR control method for an internal combustion engine, when the operating state of the internal combustion engine is in a transient state, the NOx mass target value is referred to, for example, by referring to map data set in advance. A cylinder oxygen concentration target value corresponding to the NOx mass target value is calculated, and the opening degree of the EGR valve is controlled based on the cylinder oxygen concentration target value.

  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, an internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, the cylinder of the internal combustion engine In an EGR system for an internal combustion engine that controls the opening degree of an EGR valve based on the internal oxygen concentration, the NOx concentration, not the NOx concentration, is used for calculating the target value of the in-cylinder oxygen concentration. It is possible to improve the control accuracy of the NOx control in the transient state, and to facilitate the NOx processing in the exhaust gas purification processing device.

It is a figure which shows typically the structure of the EGR system in the internal combustion engine of embodiment which concerns on this 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 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 has the same effects as the EGR control system 40 of the internal combustion engine described later. The effect of this can be achieved.

  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 engine 10 is mixed and compressed with fuel injected from a fuel injection device (not shown), and the fuel burns 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).

  Further, in the intake passage 12, an intake flow sensor (MAF sensor) 21 that detects the intake flow rate, an intake pressure sensor 22 that detects the intake pressure, and an intake temperature sensor 23 that detects the intake temperature, which constitute the intake system sensor group Sg1. The exhaust passage 13 is provided with a NOx concentration sensor 20 that detects the NOx concentration in the exhaust gas and an exhaust lambda sensor 24 that detects the excess air ratio of the exhaust gas, which constitute the exhaust system sensor group Sg2. . The signals of these sensors 20 to 24 are transmitted to the control device 30 to be described later every preset control time.

  Moreover, the control apparatus 30 for the EGR control system 40 which controls the EGR system 1 of the internal combustion engine of this invention is provided. The control device 30 sets the sensors 20 to 24 for each preset control time based on signals transmitted from the sensors 21 to 23 of the intake system sensor group Sg1 and the sensors 20 and 24 of the exhaust system sensor group Sg2. The detection value is calculated and necessary detection value data is stored. The control device 30 is normally incorporated in an engine control unit (ECU) that controls the overall operation state 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 cylinder oxygen concentration target value Dt and the cylinder oxygen concentration calculated value Dc calculated based on the input from various sensors. The valve control amount C is calculated by adding the correction control amount Cb calculated by feedback control (PID control) of the control unit 45 (C = Ca + Cb).

  In the present invention, the control device 30 that controls the EGR system 1 is set to the in-cylinder oxygen concentration target value Dt corresponding to the NOx mass target value Nt3g that is a target value for controlling the amount of NOx discharged into the exhaust gas G. Based on this, the opening degree of the EGR valve 16 is controlled.

  That is, the parameter relating to NOx for calculating the in-cylinder oxygen concentration target value Dt for calculating the control amount of the opening degree of the EGR valve 16 (control amount of NOx control) C is not the NOx concentration of the prior art but the NOx. Mass. This NOx mass is obtained by multiplying the NOx concentration by the exhaust gas flow rate (mass) or the like, but this exhaust gas flow rate varies greatly when the engine operating state is in a transient state. In addition, the supercharging pressure changes due to variations in the turbocharger products and changes over time.

  Therefore, in the prior art, the EGR control is made to follow the NOx concentration target value Nt3. In particular, in the transient state, there is a problem that the NOx mass increases or decreases even if the NOx concentration is constant. Then, by causing EGR control to follow the NOx mass target value Nt3g instead of the NOx concentration target value Nt3, increase / decrease in NOx mass can be avoided even when the engine operating state is in a transient state and the exhaust gas flow rate varies. .

  In addition, when the engine operating state is in a transient state, the control device 30 refers to the map data in which the NOx mass target value Nt3g is set in advance, and the cylinder corresponding to the referenced NOx mass target value Nt3g. When the internal oxygen concentration target value Dt is calculated and the opening degree of the EGR valve 16 is controlled based on the in-cylinder oxygen concentration target value Dt, the NOx in the exhaust gas G can be obtained even if the engine operation state is a transient state. Processing can be performed stably.

  More specifically, the first control unit 41 calculates the NOx concentration based on the detection values from the intake system sensor group Sg1 such as the intake flow rate sensor 21, the intake pressure sensor 22, the intake air temperature sensor 23, the exhaust lambda sensor 24, and the like. A value Nc and a cylinder oxygen concentration calculation value Dc are calculated.

  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 in consideration of the exhaust gas amount and oxygen concentration of the internal EGR gas, without calculating only the intake air amount and oxygen concentration, and the exhaust gas amount and oxygen concentration of the external EGR gas. It is preferable.

  Then, the NOx amount generated in the cylinder and the NOx concentration of the exhaust gas exhausted from the cylinder are calculated from the calculated oxygen concentration value Dc in the cylinder and the estimated value of the combustion temperature, and set as the NOx concentration calculated value Nc. Further, the intake gas flow rate (mass) is calculated from the detected value of the intake system sensor group Sg1 related to intake air, and the NOx concentration calculated value Nc is multiplied by the exhaust gas flow rate obtained by adding the intake gas flow rate and the fuel injection amount to NOx. The calculated mass value Ncg is calculated.

  At the same time, based on the idea that the calculated value for control is corrected using the correction value calculated based on the detected value detected by the NOx concentration sensor 20, the NOx concentration that is the detected value of the NOx concentration sensor 20 is used. A NOx mass calculation value Ndg is calculated from the actual measurement value Nd via the mass converter 48, and the NOx correction unit 46 calculates the NOx correction coefficient NCfg from the NOx mass calculation value Ncg and the NOx mass calculation value Ndg.

  On the other hand, the second control unit 42 calculates the first NOx mass target value (basic NOx mass target value) Nt1g by referring to the map data based on the engine speed and the fuel injection amount, and this first NOx mass target. In the second control unit 42 to which the value Nt1g is input, a detection value of the exhaust lambda sensor 24 is input, and smoke is generated at the first NOx mass target value Nt1g. In the case where it is predicted from the above, the NOx concentration at which smoke does not occur is set as the second NOx mass target value Nt2g. A so-called smoke limit is performed. If there is no possibility of smoke, the first NOx mass target value Nt1g is used as it is as the second NOx mass target value Nt2g. Thereby, the second NOx mass target value Nt2g is calculated.

  Furthermore, when the operating state of the internal combustion engine is in a steady state, the NOx correction coefficient NCfg is multiplied to calculate a third NOx mass target value Nt3g (= Nt2g × NCfg = Nt2g × Ndg / Ncg). On the other hand, in the transient state, the third NOx mass target value Nt3g is calculated with the correction ratio set to 1 without performing the correction using the NOx correction coefficient NCfg (Nt3g = Nt2g × 1 = Nt2g). That is, the NOx mass target value Nt3g is calculated from the basic NOx mass target value Nt1g and the NOx correction coefficient NCfg.

  According to this configuration, the NOx correction coefficient NCfg used for correcting the second NOx mass target value Nt2g is calculated after being converted to NOx mass instead of the NOx concentration, which corresponds to the influence of the supercharging amount and the supercharging amount. Since the NOx correction coefficient NCfg can be calculated with the influence of atmospheric pressure, atmospheric temperature, etc. affecting the intake air amount to be corrected, the second NOx mass target value Nt2g can be corrected more accurately.

  Further, the second control unit 42 calculates the NOx concentration calculation value Nc and detects the NOx concentration actual measurement value Nd, which is the detection value of the NOx concentration sensor 20, similarly to the prior art shown in FIG. The NOx correction coefficient NCf = Nd / Nc is calculated from the calculated concentration value Nc and the measured NOx concentration value Nd, and the NOx mass target value Nt3g is calculated from the NOx correction coefficient NCf and the first NOx mass target value Nt1g. May be. In this case, the NOx correction coefficient NCf is calculated not on the basis of the NOx mass but on the basis of the NOx concentration. Strictly speaking, the NOx mass target value Nt3g is calculated by multiplying the second NOx mass target value Nt2g by the NOx correction coefficient NCf.

  When this NOx correction coefficient NCf is used, the difference between the NOx concentration calculation value Nc calculated from the actual measurement value obtained from the sensor and the NOx concentration actual measurement value Nd detected from the NOx concentration sensor 20 is defined as the third NOx mass target value Nt3g. Since this can be reflected, the control accuracy based on the in-cylinder oxygen concentration target value Dt can be further improved, and in particular, the control accuracy of NOx control can be improved when the engine operating state is in a transient state.

  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 for the third NOx mass target value Nt3g. 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, and the exhaust gas amount and oxygen concentration in the internal EGR gas And the oxygen concentration target value Dto of the external EGR is calculated from the in-cylinder oxygen concentration target value Dt, which is the target value of the oxygen concentration in the cylinder, using the determination of the exhaust gas amount and the oxygen concentration of the external EGR gas. Then, the EGR gas amount Ge in the external EGR is calculated, and the opening degree of the EGR valve 16 that can supply the EGR gas amount Ge is defined as a pre-control amount Ca.

  In parallel with this, the fifth controller 45 calculates the in-cylinder oxygen concentration target value Dt calculated for the third NOx mass target value Nt3g by the third controller 43 and the cylinder calculated by the first controller 41. The internal 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.

  For further understanding, the EGR control system 40 according to the embodiment of the present invention shown in FIG. 2 has three differences compared to the prior art EGR control system 40X shown in FIG.

  The first point is that the first NOx concentration target value (basic NOx concentration target value) Nt1 calculated based on the engine operating state such as the engine speed and the fuel injection amount is changed to the first NOx mass target value (basic NOx mass target value) Nt1g. Is to convert to

  The second point is that the first control unit 41 is provided with a mass conversion function (d / g in FIG. 2) from NOx concentration to NOx mass, and this mass conversion function converts the NOx concentration calculated value Nc into the NOx mass calculated value. It is to convert to Ncg.

  The third point is that a mass converter 48 for converting the NOx concentration to the NOx mass is provided, and the NOx mass actual measurement value from the NOx concentration actual measurement value Nd, which is a detected value of the NOx concentration sensor 20, via the mass converter 48. After calculating Ndg, the NOx correction coefficient NCfg is calculated from the calculated NOx mass value Ncg and the measured NOx mass value Ndg.

  As described above, the EGR control system 40 for an internal combustion engine according to the embodiment of the present invention is the engine 10 provided with the EGR system 1 configured by including the EGR valve 16 in the EGR passage 14, and the in-cylinder oxygen concentration target value. In the EGR control system 40 of the internal combustion engine that controls the opening degree of the EGR valve 16 based on Dt, the control device 30 that controls the EGR system 1 uses the target value for controlling the amount of NOx discharged into the exhaust gas G. The opening degree of the EGR valve 16 is controlled based on the in-cylinder oxygen concentration target value Dt corresponding to a certain NOx mass target value Ntg3.

  In addition, when the engine operating state is in a transient state, the control device 30 refers to the map data in which the NOx mass target value Nt3g is set in advance, and the cylinder corresponding to the referenced NOx mass target value Nt3g. An internal oxygen concentration target value Dt is calculated, and the opening degree of the EGR valve 16 is controlled based on the in-cylinder oxygen concentration target value Dt.

  Further, the NOx concentration sensor 20 is provided in the exhaust passage 13, and the control device 30 calculates the NOx mass calculation value Ncg from the detection value of the sensor related to intake air, and measures the NOx concentration that is the detection value of the NOx concentration sensor 20. After calculating the NOx mass actual measurement value Ndg from the value Nd via the mass converter 48, the NOx correction coefficient NCfg (= Ndg / Ncg) is calculated from the NOx mass calculated value Ncg and the NOx mass actual measurement value Ndg. The basic NOx mass target value Nt1g is calculated based on the operating state, and the NOx mass target value Nt3g is calculated from the basic NOx mass target value Nt1g and the NOx correction coefficient NCfg.

  Alternatively, the NOx concentration sensor 20 is provided in the exhaust passage 13, and the control device 30 calculates the NOx concentration calculation value Nc from the detection value of the sensor related to intake air, and the NOx concentration actual measurement that is the detection value of the NOx concentration sensor 20. After detecting the value Nd, the NOx correction coefficient NCf (= Nd / Nc) is calculated from the calculated NOx concentration value Nc and the measured NOx concentration value Nd, and further the basic NOx mass target value Nt1g is calculated based on the engine operating state. The NOx mass target value Nt3g is calculated from the basic NOx mass target value Nt1g and the NOx correction coefficient NCf.

  Next, an EGR control method for the internal combustion engine in the EGR control system 40 for the internal combustion engine will be described. This method is an internal combustion engine that controls an opening degree of an EGR valve 16 based on an in-cylinder oxygen concentration target value Dt in an engine 10 having an EGR system 1 configured by including an EGR valve 16 in an EGR passage 14. In this method, the EGR valve 16 is based on the in-cylinder oxygen concentration target value Dt corresponding to the NOx mass target value Nt3g, which is a target value for controlling the amount of NOx discharged into the exhaust gas G. The opening degree is controlled.

  In addition, when the engine operating state is in a transient state, the target oxygen concentration target value in the cylinder corresponding to the referred NOx mass target value Nt3g is obtained by referring to the preset map data for the NOx mass target value Nt3g. Dt is calculated, and the opening degree of the EGR valve 16 is controlled based on the in-cylinder oxygen concentration target value Dt.

  According to the EGR control system 40 for the internal combustion engine, the engine (internal combustion engine) 10 and the EGR control method for the internal combustion engine configured as described above, the engine provided with the EGR system 1 having the EGR valve 16 in the EGR passage 14. 10, in the EGR system of the internal combustion engine that controls the opening degree of the EGR valve 16 based on the in-cylinder oxygen concentration Dt of the engine 10, the NOx mass is calculated instead of the NOx concentration in calculating the target value Dt of the in-cylinder oxygen concentration. In particular, it is possible to improve the control accuracy of the NOx control particularly when the engine operating state is a transient state, and to facilitate the NOx processing in the exhaust gas purification processing apparatus.

  That is, in the present invention, the NOx concentration parameter for calculating the target value Dt of the in-cylinder oxygen concentration for calculating the control amount of the opening degree of the EGR valve 16 (the control amount of NOx control) is used as the NOx concentration of the prior art. Instead, the mass is NOx.

  Therefore, in the prior art, the EGR control is made to follow the NOx concentration target value Nt3. In particular, in the transient state, there is a problem that the NOx mass increases or decreases even if the NOx concentration is constant. Since the EGR control is made to follow the NOx mass target value Nt3g instead of the NOx concentration target value Nt3, even if the engine operating state is in a transitional state and the exhaust gas flow rate fluctuates, increase / decrease in the NOx mass can be avoided.

  Therefore, the NOx parameter corresponding to the target value Dt of the in-cylinder oxygen concentration for calculating the control amount of the opening degree of the EGR valve 16, that is, the control amount of NOx control, is not the NOx concentration of the prior art, but the NOx mass. Therefore, in particular, when the engine operating state is in a transient state, the NOx mass discharged can be grasped, and the NOx mass discharged as a whole can be grasped more accurately, and the cylinder 11c to the exhaust passage 14 can be grasped. It is possible to efficiently take measures against the outflowing NOx emission amount, and it is easy to reduce the total amount of exhausted NOx mass.

  Further, regarding the NOx emission amount discharged from the cylinder 11c into the exhaust passage 14, the concentration base is changed to the mass base, so that the exhaust gas flow rate can be considered in the exhaust gas processing by considering the supply amount of the reducing agent and the like. Since there is no need to consider the correction of the gas flow rate, these calculations are simplified and control for exhaust gas purification is facilitated.

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 flow sensor (MAF sensor)
22 Intake pressure sensor 23 Intake temperature sensor 24 Exhaust lambda sensor 30 Control device 40, 40X EGR control system 41, 41X of internal combustion engine First control unit 42 Second control unit 43 Third control unit 44 Fourth control unit 45 Fifth control Unit 46 NOx correction unit 47 Addition unit 48 Mass converter 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 Nt1 First NOx concentration target value (basic NOx concentration target value)
Nt2 Second NOx concentration target value Nt3 Third NOx concentration target value (NOx concentration target value)
Nt1g First NOx mass target value (basic NOx mass target value)
Nt2g Second NOx mass target value Nt3g Third NOx mass target value (NOx mass target value)
Nc NOx concentration calculation value Ncg NOx mass calculation value Nd NOx concentration detection value (NOx concentration actual measurement value)
Ndg NOx mass calculation value G, Ga exhaust gas Ge EGR gas NCf, NCfg NOx correction coefficient Sg1 Intake system sensor group

Claims (7)

An internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, wherein the opening degree of the EGR valve is controlled based on an in-cylinder oxygen concentration target value.
A control device for controlling the EGR system,
The opening degree of the EGR valve is controlled based on a cylinder oxygen concentration target value corresponding to a NOx mass target value, which is a target value for controlling the amount of NOx discharged into the exhaust gas. An EGR control system for an internal combustion engine. The control device is
When the operating state of the internal combustion engine is in a transient state, the in-cylinder oxygen concentration target corresponding to the referenced NOx mass target value is obtained by referring to map data in which the NOx mass target value is set in advance. The EGR control system for an internal combustion engine according to claim 1, wherein the EGR control system is configured to calculate a value and control an opening degree of the EGR valve based on the in-cylinder oxygen concentration target value. A NOx concentration detection device is provided in the exhaust passage,
The control device is
After calculating a NOx mass calculation value from a detection value of a sensor related to intake air, and calculating a NOx mass measurement value via a mass converter from a NOx concentration measurement value that is a detection value of the NOx concentration detection device, A NOx correction coefficient is calculated from the calculated NOx mass value and the actual measured NOx mass value,
Further, the basic NOx mass target value is calculated based on the engine operating state, and the NOx mass target value is calculated from the basic NOx mass target value and the NOx correction coefficient. An EGR control system for an internal combustion engine as described. A NOx concentration detection device is provided in the exhaust passage,
The control device is
After calculating a NOx concentration calculation value from a detection value of a sensor related to intake air and detecting a NOx concentration actual measurement value that is a detection value of the NOx concentration detection device, the NOx concentration calculation value and the NOx concentration actual measurement value are NOx correction coefficient is calculated from
Further, the basic NOx mass target value is calculated based on the engine operating state, and the NOx mass target value is calculated from the basic NOx mass target value and the NOx correction coefficient. An EGR control system for an internal combustion engine as described.   An internal combustion engine comprising the EGR control system for an internal combustion engine according to any one of claims 1 to 4. In an internal combustion engine having an EGR system configured to have an EGR valve in an EGR passage, the EGR control method for an internal combustion engine that controls the opening degree of the EGR valve based on a target value of oxygen concentration in a cylinder.
An opening of the EGR valve is controlled based on a cylinder oxygen concentration target value corresponding to a NOx mass target value, which is a target value for controlling the amount of NOx discharged into the exhaust gas. EGR control method.   When the operating state of the internal combustion engine is in a transient state, the in-cylinder oxygen concentration target corresponding to the referenced NOx mass target value is obtained by referring to map data in which the NOx mass target value is set in advance. 7. The EGR control method for an internal combustion engine according to claim 6, wherein a value is calculated and the opening degree of the EGR valve is controlled based on the in-cylinder oxygen concentration target value.

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