JP2017040174A - Egr control system for internal combustion engine, internal combustion engine and egr control method for internal combustion engine - Google Patents

Abstract

An EGR system for an internal combustion engine that controls the opening degree of an EGR valve based on the in-cylinder oxygen concentration accurately calculates an intake air flow used for calculating an in-cylinder oxygen concentration calculation value, thereby improving the accuracy of EGR control. An internal combustion engine EGR control system, an internal combustion engine, and an internal combustion engine EGR control method that can be improved are provided. A correction term F1 by an engine coolant temperature Tclnt with a coolant correction coefficient C obtained in advance through experiments or tests in consideration of the influence of the engine coolant temperature on the in-cylinder intake flow rate Mcyl per cycle. Further, in order to correct the influence of the back pressure, correction is performed with the correction term F2 based on the exhaust pressure Pexm obtained from the result of the experiment or test or from the result of the cycle simulation. [Selection] Figure 3

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 lowered, 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 this connection, the 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 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 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. 4 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 that the opening degree of the EGR valve 16 is controlled based on the in-cylinder oxygen concentration so that the NOx concentration 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. ) Fifth control based on the difference (error) ΔD (= Dt−Dc) between the target oxygen concentration value Dt in the cylinder and the calculated oxygen concentration value Dc in the cylinder based on the input 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 unit 45 (C = Ca + Cb).

  More specifically, based on detection values from the intake system sensor group Sg1 such as the intake air flow rate sensor 21, the intake pressure sensor 22, the intake air temperature sensor 23, and the exhaust system sensor group Sg2 such as the exhaust lambda sensor 24, the first The controller 41X calculates the NOx concentration calculation value Nc. 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 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 considers the smoke limit for this target value Nt1. When the second NOx target value Nt2 is calculated and 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 target value Nt3 (= Nt2 × Ncf = Nt2 × Nd / 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 this EGR control system 40X for an internal combustion engine according to the prior art, in-cylinder oxygen concentration calculation value Dc calculated by the first control unit 41X is used to calculate the correction control amount Cb of the opening degree of the EGR valve 16 in the fifth control unit 45. However, when calculating the in-cylinder oxygen concentration calculation value Dc, the in-cylinder intake flow rate calculation unit 41Xa as shown in FIG. 5 uses the intake pressure Pinm, which is the detected value of the intake pressure sensor 22, and the intake air temperature sensor. An intake air flow rate (mass flow rate) Mcyl flowing into the cylinder 11c per combustion cycle (intake process → compression process → combustion process → exhaust process) is calculated using an intake air temperature Tinm that is a detected value of 23. .

In the prior art, the following equation (1) is used to calculate the intake flow rate Mcyl per cycle.

Here, Mcyl is the intake flow rate per combustion cycle (unit: g / cyl), Pinm is the intake pressure (unit: kPa), Vcyl is the cylinder volume per cycle (unit: m ³ ), and R is the gas constant (unit: J). / G · K), Tinm is the intake air temperature (unit: K), ηcyl is the volumetric efficiency, Tinmr is the reference value (unit: K) of the intake air temperature that is preset for the engine speed Ne and the fuel injection amount q. ), Α is an intake air temperature correction multiplier calculated by experiment.

  In this connection, in the calculation of the intake air amount, in addition to the correction by the cooling water temperature using the ratio of the cooling water temperature at the time of control and the cooling water temperature in the reference operation state, and the cooling water temperature correction multiplier. Furthermore, the air flow rate for calculating the intake air amount by correcting the volume efficiency variation by correcting the exhaust pressure using the ratio of the intake pressure to the exhaust pressure (intake to exhaust pressure) and the pressure correction multiplier. Sensor calibration devices and intake air amount calculation methods have been proposed (see, for example, Patent Documents 2 and 3).

  However, in the calculation of the intake air flow rate (intake air amount) in these prior arts, the intake pressure and the intake air temperature are used and the influence of the engine coolant temperature and the exhaust pressure is taken into consideration. The correction is based on the ratio between the temperature and the reference cooling water temperature and the ratio between the intake pressure and the exhaust pressure, and there is still room for improvement in order to increase the accuracy of the correction.

JP 2012-237290 A JP 2013-19399 A JP 2013-19400 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 based on the oxygen concentration in the cylinder. An EGR system for an internal combustion engine that controls the opening of a valve, and an EGR control system for an internal combustion engine that can improve the accuracy of EGR control by accurately calculating the intake flow rate used to calculate a calculated value of in-cylinder oxygen concentration, An object of the present invention is to provide an EGR control method for an internal combustion engine.

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 pressure sensor and an intake temperature sensor are provided in an intake passage, an exhaust pressure sensor is provided in an exhaust passage, and engine cooling water is used. An engine coolant temperature sensor is provided in each flow path, and the control device for controlling the EGR system uses the detected value of the intake pressure sensor to calculate the intake flow rate used when calculating the target oxygen concentration in the cylinder. An intake pressure is Pinm, an intake air temperature detected by the intake air temperature sensor is Tinm (K), a gas constant is R, a cycle time is Assuming that the cylinder internal volume is Vcyl, the volumetric efficiency is ηcyl, the reference value of the intake air temperature preset with respect to the engine speed Ne and the fuel injection amount q is Tinmr (K), and the intake air temperature correction multiplier is α, the following ( For the intake flow rate Mcyl per cycle of the mass flow rate calculated by the equation (1),

排気圧力をＰｅｘｍとして、下記（３）式によって算出される排気圧力補正量Ｆ２とを乗じて、

補正後のサイクル当たり吸気流量Ｍｃｙｌｃを算出するように構成される。 The engine cooling water temperature is Tclnt (K), the engine cooling water temperature reference value set in advance for the engine speed Ne and the fuel injection amount q is Tclntr (K), and C is the cooling water correction coefficient. 2) a water temperature correction amount F1 calculated by the equation;

Taking the exhaust pressure as Pexm and multiplying by the exhaust pressure correction amount F2 calculated by the following equation (3),

An intake air flow rate Mcylc per cycle after correction is calculated.

  That is, the influence of the engine coolant temperature is taken into consideration with respect to the in-cylinder intake flow rate Mcyl per cycle, which is set by taking into consideration the influence of the intake pressure and the intake air temperature, and is calculated by the above equation (1). The correction term by the engine cooling water temperature Tclnt in the above equation (2) with the cooling water correction coefficient C obtained in advance through experiments or tests is used for the influence of the cooling water temperature Tclnt deviating from the cooling water temperature Tclntr in the reference operation state (engine (Cooling water temperature correction term) In order to correct by F1, and further to correct the influence of the back pressure, a correction term by the exhaust pressure Pexm of equation (3) obtained from the result of experiment or test or from the result of cycle simulation ( The exhaust pressure correction term is corrected by F2.

  That is, the correction by the water temperature correction amount F1 can correct the sensitivity to the volume efficiency due to the variation of the cooling loss, and the exhaust pressure correction amount F2 can correct the sensitivity to the volume efficiency due to the variation of the back pressure.

  The equation (3) is expressed in the form of a function. Specifically, the equation (3) is calculated with reference to map data of the value of F2 with Pinm as the vertical axis and Pexm as the horizontal axis. For example, in the map data as shown in FIG. 6, the standard volume efficiency value a referred to by the respective reference values of the intake pressure Pinm and the exhaust pressure Pexh, and the current intake pressure Pinm and the exhaust pressure Pexh are referred to. The ratio of the standard volumetric efficiency value b is the exhaust pressure correction amount (correction coefficient) F2.

  Further, considering the case of calculating the mass flow rate equation of the compressive fluid at the intake and exhaust ports, it is considered that the pressure ratio at each port affects the volume efficiency. That is, for example, when the exhaust pressure Pexm is high, the exhaust port pressure ratio becomes high, resulting in insufficient exhaust. Since this leads to an increase in cylinder gas pressure during the subsequent intake stroke, it is considered that the intake port pressure ratio is increased, resulting in a decrease in volumetric efficiency.

  More simply, in the calculation of the in-cylinder intake flow rate Mcyl in the internal combustion engine of the vehicle, in addition to the intake air temperature Tinm and the intake air pressure Pinm, the exhaust pressure Texm and the engine coolant temperature Tclnt are used as correction parameters. Make more accurate correction than the prior art. As the exhaust pressure Pexm, the exhaust port pressure or the outlet pressure of the EGR cooler can be used.

  According to this configuration, the intake air flow used for calculating the calculated oxygen concentration in the cylinder can be accurately calculated using the highly accurate in-cylinder intake flow calculated in consideration of the effects of the engine coolant temperature and the exhaust pressure. Since it can be calculated, the control amount of the opening degree of the EGR valve can be calculated with high accuracy, and as a result, the opening degree of the EGR valve can be controlled with high accuracy.

In the above EGR control system for an internal combustion engine, when the compression ratio is ε and the specific heat ratio is κ as the cylinder volume Vcyl per cycle, the intake pressure Pinm and the exhaust pressure Pexm are used to The cylinder internal volume V′cyl calculated by the formula (1) is used.

  With this configuration, the influence of the exhaust pressure Pexm can be further taken in, and the intake flow rate used for calculating the cylinder oxygen concentration calculation value can be calculated with higher accuracy.

  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, the control device that controls the EGR system calculates the in-cylinder oxygen concentration target value. In calculating the intake flow rate to be used, the intake pressure, which is the detection value of the intake pressure sensor, is Pinm, the intake temperature, which is the detection value of the intake temperature sensor, is Tinm (K), the gas constant is R, the cylinder volume per cycle is Vcyl, Volumetric efficiency ηcyl, reference value of intake air temperature preset for engine speed Ne and fuel injection amount q, Tinmr (K), intake air temperature correction As the number alpha, with respect to the following (1) intake per cycle mass flow calculated by the flow rate mcyl,

排気圧力をＰｅｘｍとして、下記（３）式によって算出される排気圧力補正量Ｆ２とを乗じて、

補正後のサイクル当たり吸気流量Ｍｃｙｌｃを算出することを特徴とする方法である。 The engine cooling water temperature is Tclnt (K), the engine cooling water temperature reference value set in advance for the engine speed Ne and the fuel injection amount q is Tclntr (K), and C is the cooling water correction coefficient. 2) a water temperature correction amount F1 calculated by the equation;

Taking the exhaust pressure as Pexm and multiplying by the exhaust pressure correction amount F2 calculated by the following equation (3),

In this method, the corrected intake air flow rate Mcylc per cycle is calculated.

Further, in the above EGR control method for an internal combustion engine, when the compression ratio is ε and the specific heat ratio is κ, the intake pressure Pinm and the exhaust pressure Pexm are used as follows. Use the cylinder's net volume V′cyl per cycle calculated by the equation (4).

  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, a highly accurate in-cylinder intake flow rate calculated in consideration of the effects of engine coolant temperature and exhaust pressure is obtained. Therefore, the intake flow rate used for calculating the calculated value of the oxygen concentration in the cylinder can be calculated with high accuracy, so that the control amount of the opening degree of the EGR valve can be calculated with high accuracy. The degree can be controlled with high accuracy.

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 the input-output relationship of the one part cylinder intake air flow rate calculation part of the 1st control part of FIG. It is a figure which shows typically the structure of the EGR control system of the internal combustion engine of a prior art. FIG. 5 is a diagram illustrating an input / output relationship of a part of the cylinder intake air flow rate calculation unit of the first control unit of FIG. 4. It is a figure which shows typically the example of the relationship between the exhaust pressure correction amount with respect to intake pressure and exhaust pressure.

  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 air 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 that detects the intake air temperature, which constitute the intake system sensor group Sg1. 23, and the exhaust passage 13 is provided with a NOx concentration sensor 20 for detecting the NOx concentration in the exhaust gas and an exhaust lambda sensor 24 for detecting the excess air ratio of the exhaust gas. The signals of these sensors 20 to 24 are transmitted to the control device 30 to be described later every preset control time. In FIG. 1, the intake pressure sensor 22 and the intake temperature sensor 23 are disposed in the intake passage 12, but may be disposed in the intake manifold 11a.

  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 calculates the detection values of the sensors 20 to 24 for each preset control time based on the signals transmitted from the sensors 20 to 24, and stores necessary detection value data. To do. 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.

  Further, an exhaust pressure sensor (exhaust pressure detection device) 25 is provided in the exhaust passage 13 of the engine 10, and an engine coolant temperature sensor (engine coolant temperature) is provided in the flow path 17 for the engine coolant W that cools the engine 10. Detection device) 26 is provided. Similarly to the sensors 20 to 24, the signals of these sensors 25 and 26 are transmitted to the control device 30 every preset control time, and the control device 30 is based on the signals transmitted from the sensors 25 and 26. Thus, the detection values of the sensors 25 and 26 are calculated, and necessary detection value data (usually, the latest detection value data) is stored.

  The exhaust pressure sensor 25 may be provided not in the exhaust passage 13 but in the exhaust port or the EGR passage 14 on the outlet side of the EGR cooler 15. In this case, since the EGR gas Ge is easier to detect by the exhaust pressure sensor 25 than the exhaust gas G, the detection accuracy of the exhaust pressure sensor 25 can be improved.

  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 calculates the detection values of the sensors 20 to 24 for each preset control time based on the signals transmitted from the sensors 20 to 24, and stores necessary detection value data. To do. 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).

  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, in the first control unit 41, the NOx concentration is based on the detection values from the intake system sensor group Sg1 such as the intake air flow rate sensor 21, the intake pressure sensor 22, the intake air temperature sensor 23, and the exhaust lambda sensor 24. A calculated value Nc is 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 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, based on the idea that the calculated value for control is corrected using the calculated value based on the calculated NOx concentration value Nc based on the detected NOx concentration value Nd detected by the NOx concentration sensor 20, the NOx correction is performed. The NOx concentration detection value Nd, which is a detection value of the NOx concentration sensor 20, is input to the unit 46, and a NOx correction coefficient (correction ratio) Ncf = Nd / Nc is calculated from the NOx concentration detection value Nd and the NOx concentration calculation value Nc. To do.

  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 set as the second NOx target value Nt2. A 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, in the 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).

  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.

  In parallel with this, the fifth controller 45 calculates the in-cylinder oxygen concentration target value Dt calculated for the third NOx target value Nt3 by the third controller 43 and the in-cylinder calculated by the first controller 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, when the control device 30 that controls the EGR system 1 calculates the intake flow rate used when calculating the in-cylinder oxygen concentration target value Dt, the intake pressure Pinm, which is a detected value of the intake pressure sensor 22, The intake air temperature Tinm (K), which is a detected value of the intake air temperature sensor 23, the gas constant R, the cylinder volume per cycle Vcyl, the volume efficiency ηcyl, the engine speed Ne, and the fuel injection amount q are set in advance. , The intake air flow rate Mcyl per cycle of the mass flow rate is calculated by the following equation (1) using the reference value Tinmr (K) and the intake air temperature correction multiplier α.

更に、吸気圧力Ｐｉｎｍと排気圧力Ｐｅｘｍを用いて、下記（３）式によって排気圧力補正量Ｆ２を算出する。

Further, the engine coolant temperature reference value Tclntr (K) and the coolant correction coefficient C, which are preset for the engine coolant temperature Tclnt (K), the engine speed Ne, and the fuel injection amount q, are used as follows. The water temperature correction amount F1 is calculated by the equation (2).

Further, the exhaust pressure correction amount F2 is calculated by the following equation (3) using the intake pressure Pinm and the exhaust pressure Pexm.

  The corrected intake air flow rate Mcylc per cycle is calculated by multiplying the intake air flow rate Mcyl per cycle by both the water temperature correction amount F1 and the exhaust pressure correction amount F2.

  That is, the influence of the engine coolant temperature is considered with respect to the in-cylinder intake flow rate Mcyl per cycle, which is set by taking into consideration the effects of the intake pressure Pinm and the intake temperature Tinm, and calculated by the above-described equation (1). Then, the correction term by the engine coolant temperature Tclnt of the above equation (2) with the coolant correction coefficient C obtained in advance through experiments or tests is used for the influence of the coolant temperature Tclnt that deviates from the coolant temperature Tclntr in the reference operation state. (Engine coolant temperature correction term) Correct with F1. Further, in order to correct the influence of the back pressure, correction is made with a correction term (exhaust pressure correction term) F2 by the exhaust pressure Pexm of the equation (3) obtained from the result of the experiment or test or from the result of the cycle simulation.

  That is, the correction by the water temperature correction amount F1 can correct the sensitivity to the volume efficiency due to the variation of the cooling loss, and the exhaust pressure correction amount F2 can correct the sensitivity to the volume efficiency due to the variation of the back pressure.

  The expression (3) is expressed in the form of a function. Specifically, for example, as illustrated in FIG. 6, the intake pressure Pinm is on the vertical axis and the exhaust pressure Pexm is on the horizontal axis. The exhaust pressure correction amount F2 is calculated with reference to preset map data or the like. More specifically, in this map data, the standard volume efficiency value a referred to by the respective reference values of the intake pressure Pinm and the exhaust pressure Pexh, and the standard referred to by the current intake pressure Pinm and the exhaust pressure Pexh. The ratio of the volumetric efficiency value b is the exhaust pressure correction amount (correction coefficient) F2.

  Further, considering the case of calculating the mass flow rate equation of the compressive fluid at the intake and exhaust ports, it is considered that the pressure ratio at each port affects the volume efficiency. That is, for example, when the exhaust pressure Pexm is high, the exhaust port pressure ratio becomes high, resulting in insufficient exhaust. Since this leads to an increase in cylinder gas pressure during the subsequent intake stroke, it is considered that the intake port pressure ratio is increased, resulting in a decrease in volumetric efficiency.

  Then, an in-cylinder intake flow rate Mcyl per cycle is calculated.

Further, the cylinder internal volume per cycle calculated by the following equation (4) using the compression ratio ε, the specific heat ratio κ, the intake pressure Pinm, and the exhaust pressure Pexm as the cylinder internal volume Vcyl used in the above calculation. Use of the volume V′cyl is more preferable because the influence of the exhaust pressure Pexm can be taken in and the intake flow rate used for calculating the cylinder oxygen concentration calculation value Dc can be calculated with higher accuracy.

  As described above, according to the EGR control system 40 of the internal combustion engine, the internal combustion engine, and the EGR control method of the internal combustion engine of the present invention, the accuracy calculated in consideration of the influence of the engine coolant temperature Tclnt and the influence of the exhaust pressure Pexm. Since the intake air flow rate used for calculating the in-cylinder oxygen concentration calculation value Dc can be accurately calculated using the high in-cylinder intake air flow rate Mcyl, the control amount C of the opening degree of the EGR valve 16 can be calculated with high accuracy. As a result, the opening degree of the EGR valve 16 can be controlled with high accuracy.

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 17 Engine cooling water passage 20 NOx concentration sensor (NOx concentration detection device)
21 Intake air flow rate sensor (MAF sensor: Intake flow rate detection device)
22 Intake pressure sensor 23 Intake temperature sensor 24 Exhaust lambda sensor (exhaust excess ratio sensor: exhaust lambda detection device)
30 control device 40 EGR control system 41 of internal combustion engine 1st control part 42 2nd control part 43 3rd control part 44 4th control part 45 5th control part 46 NOx correction | amendment part 47 addition part 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 calculated value G, Ga Exhaust gas Ge EGR gas NCf NOx correction coefficient Sg1 Intake system sensor group W Engine cooling water

Claims (5)

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 engine EGR control system,
An intake pressure sensor and an intake temperature sensor are provided in the intake passage, an exhaust pressure sensor is provided in the exhaust passage, and an engine coolant temperature sensor is provided in the engine coolant flow path.
When calculating the intake flow rate used when the control device for controlling the EGR system calculates the in-cylinder oxygen concentration target value,
The intake pressure, which is the detected value of the intake pressure sensor, is Pinm, the intake temperature, which is the detected value of the intake temperature sensor, is Tinm (K), the gas constant is R, the cylinder volume per cycle is Vcyl, the volume efficiency is ηcyl, The reference value of the intake air temperature set in advance for the engine speed Ne and the fuel injection amount q is Tinmr (K), the intake air temperature correction multiplier is α, and the mass flow rate calculated by the following equation (1) per cycle For the intake flow rate Mcyl

The engine cooling water temperature is Tclnt (K), the engine cooling water temperature reference value set in advance for the engine speed Ne and the fuel injection amount q is Tclntr (K), and C is the cooling water correction coefficient. 2) a water temperature correction amount F1 calculated by the equation;

Taking the exhaust pressure as Pexm and multiplying by the exhaust pressure correction amount F2 calculated by the following equation (3),

An EGR control system for an internal combustion engine configured to calculate an intake air flow rate Mcylc per cycle after correction. The controller calculates the following equation (4) using the intake pressure Pinm and the exhaust pressure Pexm when the compression ratio is ε and the specific heat ratio is κ as the cylinder volume per cycle Vcyl. Using the in-cylinder net volume V′cyl per cycle.

The EGR control system for an internal combustion engine according to claim 1 configured as described above.   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 calculating the intake flow rate used when the control device for controlling the EGR system calculates the in-cylinder oxygen concentration target value,
The intake pressure, which is the detection value of the intake pressure sensor, is Pinm, the intake temperature, which is the detection value of the intake temperature sensor, is Tinm (K), the gas constant is R, the cylinder volume per cycle is Vcyl, the volume efficiency is ηcyl, and the engine speed The intake air flow rate per cycle of the mass flow rate calculated by the following equation (1) where the reference value of the intake air temperature set in advance for the number Ne and the fuel injection amount q is Tinmr (K) and the intake air temperature correction multiplier is α. For Mcyl

The engine cooling water temperature is Tclnt (K), the engine cooling water temperature reference value set in advance for the engine speed Ne and the fuel injection amount q is Tclntr (K), and C is the cooling water correction coefficient. 2) a water temperature correction amount F1 calculated by the equation;

Taking the exhaust pressure as Pexm and multiplying by the exhaust pressure correction amount F2 calculated by the following equation (3),

An EGR control method for an internal combustion engine, wherein an intake air flow rate Mcylc per cycle after correction is calculated. The cylinder per cycle calculated by the following equation (4) using the intake pressure Pinm and the exhaust pressure Pexm when the compression ratio is ε and the specific heat ratio is κ as the cylinder internal volume Vcyl per cycle. Use the inner net volume V'cyl,

The EGR control method for an internal combustion engine according to claim 4.

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