JP2017040173A - Egr control system for internal combustion engine, internal combustion engine and egr control method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR control system for an internal combustion engine, the internal combustion engine and an EGR control method for the same which can curb a variation in a control amount of an opening of an EGR valve and generation of EGR hunching while efficiently carrying out an operation for control regardless of whether an operation state of an engine is a normal state or a transition state.SOLUTION: When correcting an inner cylinder oxygen concentration target value Dt using a NOx correction coefficient NCf which is obtained by calculating: a NOx concentration calculation value Nc using detection values of an intake air flow rate sensor 21 and an exhaust random sensor 24; and a NOx correction coefficient NCf which is a ratio of a NOx concentration detection value Nd, a detection value of a NOx concentration sensor 20, to the NOx concentration calculation value Nc, an EGR control system calculates the NOx correction coefficient through moving average processing and changes at least either a length of a sampling period or a sampling interval for the moving average processing in accordance with an operation state of the internal combustion engine 10.SELECTED DRAWING: Figure 2

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 40 as shown in FIG. 2 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. ) 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 is based on detection values from the intake system sensor group Sg1 such as the intake flow rate sensor 21, the intake pressure sensor 22, and the intake temperature sensor 23 and the exhaust system sensor group Sg2 such as the exhaust lambda sensor 24. The unit 41 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, the NOx correction unit 46 inputs not only the NOx concentration sensor 20 but also the first control unit 41 to calculate the NOx correction coefficient NCf when the operating state of the internal combustion engine is a steady state. Detection values of various sensors such as an intake flow rate sensor (MAF sensor) 21, an intake pressure sensor 22, an intake air temperature sensor 23, and an exhaust lambda sensor 24 are used.

  In calculating the NOx correction coefficient NCf, the NOx correction coefficient NCf is calculated for each preset time (sample time), and the target value of the in-cylinder oxygen concentration is calculated using the calculated NOx correction coefficient NCf. Dt is calculated, and the control amount C of the opening degree of the EGR valve 16 is calculated.

  However, the NOx concentration detection value Nd includes a delay element, and there is a problem that a true NOx correction coefficient NCf cannot be obtained by comparison with the NOx concentration calculation value (model value) Nc at the same time. That is, the true NOx correction coefficient NCf cannot be obtained in real time.

  As a result, the NOx target value itself vibrates due to the movement of the EGR valve 16, and the fluctuation of the control amount of the opening degree of the EGR valve becomes large. Depending on the operating state of the internal combustion engine, the EGR hunting (opening of the EGR valve 16) There is a problem that a phenomenon in which the vibration continues following the target opening where the degree vibrates occurs. In particular, when the resolution during control of the EGR valve 16 is rough, there is a high possibility that this EGR hunting will occur.

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. The internal combustion engine EGR system controls the opening of the EGR valve based on the detected value of the engine and the in-cylinder oxygen concentration, and the in-cylinder oxygen is calculated using the calculated NOx correction coefficient when the engine is in a steady state. When correcting the concentration target value, it is possible to suppress the fluctuation of the control amount of the opening degree of the EGR valve while efficiently performing the calculation for the control, and to suppress the occurrence of EGR hunting. To provide an EGR system, an internal combustion engine, and an EGR 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 of the EGR valve based on an internal oxygen concentration target value, an intake flow sensor is provided in the intake passage, an exhaust lambda sensor and a NOx concentration sensor are provided in the exhaust passage, and A control device that controls the EGR system calculates a NOx concentration calculated value using the detected value of the intake flow sensor and the detected value of the exhaust lambda sensor, and detects the NOx concentration detected value that is the detected value of the NOx concentration sensor and the NOx. When calculating a NOx correction coefficient that is a ratio of the concentration calculation values and correcting the in-cylinder oxygen concentration target value using the NOx correction coefficient The NOx correction coefficient is calculated by moving average processing, and at least one of the length of a sampling period and the sampling interval for moving average processing of the NOx correction coefficient is changed according to the operating state of the internal combustion engine. Is done.

  According to this configuration, by controlling the fluctuation range of the NOx correction coefficient, when the engine operating state is in a steady state and the calculated NOx correction coefficient is used to correct the in-cylinder oxygen concentration target value, the control is performed. Therefore, the variation in the control amount of the opening degree of the EGR valve can be suppressed, and the occurrence of EGR hunting can be suppressed.

  In the EGR control system for an internal combustion engine, the control device for controlling the EGR system may change at least one of the length of the sampling period and the sampling interval according to a combination of the engine speed and the load. Further, the control device for controlling the EGR system performs control to shorten the length of the sampling period or the sampling interval as the engine speed of the internal combustion engine increases, and as the load on the internal combustion engine increases, When configured to employ either one or both of the length of the sampling period and the control for shortening the sampling interval, the moving average processing of the NOx correction coefficient is performed according to the difference in the engine operating state in the steady state. It is possible to change the control amount of the opening degree of the EGR valve. To be able to obtain, it is possible to suppress the occurrence of EGR hunting. That is, as the engine speed of the internal combustion engine is larger and the load of the internal combustion engine is larger, the dead time is generally reduced due to an increase in the gas amount, so that the sampling period can be shortened. It is possible to grasp the difference in the operating state of the engine in a steady state and reflect it in the control.

  An internal combustion engine equipped with the above-described 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 target oxygen concentration value in the cylinder, the detected value of the intake flow sensor provided in the intake passage and the exhaust passage are controlled by the EGR system. A NOx concentration calculation value is calculated using a detection value of the provided exhaust lambda sensor, and NOx which is a ratio of the NOx concentration detection value which is a detection value of the NOx concentration sensor provided in the exhaust passage and the NOx concentration calculation value. When calculating the correction coefficient and correcting the in-cylinder oxygen concentration target value using the NOx correction coefficient, the NOx correction coefficient is calculated by a moving average process, and the A method of and changes in accordance with at least one of the length and the sampling interval of the sampling period for moving average processing Ox correction coefficient on the operating state of the internal combustion engine.

  In the EGR control method for an internal combustion engine, at least one of the length of the sampling period and the sampling interval is changed according to a combination of the engine speed and the load. Further, whether the length of the sampling period or the sampling interval is shortened as the engine speed of the internal combustion engine is increased, or whether the length of the sampling period or the sampling interval is shortened as the load of the internal combustion engine is increased. Either one or both are adopted.

  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 internal combustion engine EGR control system, internal combustion engine, and internal combustion engine EGR control method of the present invention, the engine operating state is in a steady state, and the calculated oxygen concentration target value is obtained using the calculated NOx correction coefficient. When the correction is performed, the fluctuation of the control amount of the opening degree of the EGR valve can be suppressed while efficiently performing the calculation for control, and the occurrence of EGR hunting can be suppressed.

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.

  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. Are provided in the exhaust passage 13, and an NOx concentration sensor 20 for detecting the NOx concentration in the exhaust gas, which constitutes the exhaust system sensor group Sg2, and an exhaust lambda sensor (exhaust air excess) for detecting the excess air ratio of the exhaust gas. Rate sensor) 24 is provided. 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. This control device 30 is based on the 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 for each preset control time. The detection values of the sensors 21 to 24 are 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 in-cylinder oxygen concentration target value Dt and the calculated value Dc of the in-cylinder oxygen concentration based on inputs from various sensors. 5 The valve control amount C is calculated by adding the correction control amount Cb calculated by feedback control (PID control) of the controller 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 detects values from the intake system sensor group Sg1 such as the intake flow rate sensor 21, the intake pressure sensor 22, and the intake air temperature sensor 23 and the exhaust system sensor group Sg2 such as the exhaust lambda sensor 24. Based on this, the NOx concentration calculation 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, 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 referring to the map data based on the engine speed and the load (or fuel injection amount), and the first NOx target value Nt1 is input. In the second control unit 42, when the occurrence of smoke at the first NOx target value Nt1 is predicted from a preset calculation formula, map data, or the like, the NOx concentration is set so that smoke does not occur. The second NOx target value Nt2 is assumed. 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 third NOx target value Nt3 (= Nt2 × NCf = Nt2 × Nd / Nc) is calculated by multiplying by the NOx correction coefficient NCf. 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 calculates an in-cylinder oxygen concentration target value Dt for 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 amount, its oxygen concentration, and the internal EGR From the in-cylinder oxygen concentration target value Dt that is the target value of the in-cylinder oxygen concentration, the external EGR is determined based on the determination of the exhaust gas amount and oxygen concentration of the gas and the exhaust gas amount and oxygen concentration of the external EGR gas. The EGR gas amount Ge 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 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, the control device 30 that controls the EGR system 1 uses the detected value of the intake flow sensor 21 that is the intake system sensor group Sg1 and the detected value of the exhaust lambda sensor 24 of the exhaust system sensor group Sg2. A NOx concentration calculation value Nc is calculated, and a NOx correction coefficient NCf that is a ratio of the NOx concentration detection value Nd that is a detection value of the NOx concentration sensor 20 that is the exhaust system sensor group Sg2 and the NOx concentration calculation value Nc is calculated. When correcting the in-cylinder oxygen concentration target value Dt using the NOx correction coefficient NCf, the NOx correction coefficient NCf is calculated by the moving average process, and the length of the sampling period for performing the moving average process on the NOx correction coefficient NCf And at least one of the sampling intervals is changed in accordance with the operating state of the engine 10.

  Accordingly, by suppressing the fluctuation range of the NOx correction coefficient NCf, the control is performed when the in-cylinder oxygen concentration target value Dt is corrected using the calculated NOx correction coefficient NCf when the operating state of the engine 10 is in a steady state. Therefore, the fluctuation of the control amount C of the opening degree of the EGR valve 16 can be suppressed, and the occurrence of EGR hunting can be suppressed.

  Whether the engine operating state is a steady state or a transient state is determined or calculated in advance by, for example, a rate of change in the degree of opening of an accelerator pedal (not shown) provided in a driver's seat of a vehicle equipped with the engine 10. A transitional state when the threshold value exceeds a predetermined threshold value, or a transitional state when the rate of change of the fuel injection amount into the cylinder 11c of the engine 10 exceeds a preset or calculated threshold value. Can be judged.

  At least one of the length of the sampling period and the sampling interval is changed according to the combination of the engine speed of the engine 10 and the load. In addition, the control of reducing the length of the sampling period or the length of the sampling interval as the engine speed of the engine 10 is increased, and the length of the sampling period or the length of the sampling interval is shortened as the load on the engine 10 is increased. Either one or both of the controls to be adopted are adopted.

  Thereby, since the moving average process of the NOx correction coefficient NCf according to the difference in the operating state of the engine 10 in the steady state can be performed, the fluctuation of the control amount C of the opening degree of the EGR valve 16 can be suppressed, Generation of EGR hunting can be suppressed. That is, as the engine speed of the internal combustion engine is larger and the load of the internal combustion engine is larger, the dead time is generally reduced due to an increase in the gas amount, so that the sampling period can be shortened. It is possible to grasp the difference in the operating state of the engine in a steady state and reflect it in the control.

  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. This EGR control method for an internal combustion engine is an engine (internal combustion engine) 10 having an EGR system 1 constituted by having an EGR valve 16 in an EGR passage 14, and in-cylinder oxygen corresponding to the NOx concentration target value Nt1 of EGR. This is an EGR control method for an internal combustion engine that controls the opening degree of the EGR valve 16 based on the concentration target value Dt. In this method, the detected value of the intake flow rate sensor 21 provided in the intake passage 12 is controlled by the EGR system 1. NOx concentration calculated value Nc is calculated using the detected value of exhaust lambda sensor 24 provided in exhaust passage 13 and NOx concentration detected value Nd and NOx which are detected values of NOx concentration sensor 20 provided in exhaust passage 13 When calculating the NOx correction coefficient NCf, which is the ratio of the concentration calculation value Nc, and correcting the in-cylinder oxygen concentration target value Dt using this NOx correction coefficient NCf It calculates the NOx correction factor NCf by moving average process is a method for changing at least one of the length and the sampling interval of the sampling period for moving average processing of the NOx correction factor NCf in accordance with the operating condition of the engine 10.

  Further, at least one of the length of the sampling period and the sampling interval is changed according to the combination of the engine speed and the load. Further, either or both of the length of the sampling period or the sampling interval is shortened as the engine speed of the engine 10 is increased, or the length of the sampling period or the sampling interval is shortened as the load of the engine 10 is increased. Is adopted.

  According to the internal combustion engine EGR control system 40, the engine (internal combustion engine) 10, and the internal combustion engine EGR control method configured as described above, the operating state of the engine 10 is in a steady state by suppressing the fluctuation range of the NOx correction coefficient. When the calculated in-cylinder oxygen concentration target value Dt is corrected using the calculated NOx correction coefficient NCf, the fluctuation of the control amount C of the opening degree of the EGR valve 16 is suppressed while performing the calculation for efficient control. And the occurrence of EGR hunting 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 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 Sg2 Exhaust system sensor group

Claims (7)

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 flow sensor is provided in the intake passage, an exhaust lambda sensor and a NOx concentration sensor are provided in the exhaust passage,
A control device for controlling the EGR system,
A NOx concentration calculation value is calculated using the detection value of the intake flow sensor and the detection value of the exhaust lambda sensor, and NOx correction that is the ratio of the NOx concentration detection value that is the detection value of the NOx concentration sensor and the NOx concentration calculation value When calculating a coefficient and correcting the in-cylinder oxygen concentration target value using the NOx correction coefficient,
While calculating the NOx correction coefficient by a moving average process,
An EGR control system for an internal combustion engine configured to change at least one of a length of a sampling period and a sampling interval for performing a moving average process on the NOx correction coefficient in accordance with an operating state of the internal combustion engine. A control device for controlling the EGR system,
The EGR control system for an internal combustion engine according to claim 1, wherein at least one of the length of the sampling period and the sampling interval is changed according to a combination of an engine speed and a load. A control device for controlling the EGR system,
Control for shortening the length of the sampling period or the sampling interval as the engine speed of the internal combustion engine increases;
3. The EGR control system for an internal combustion engine according to claim 1, wherein either or both of the control for shortening the length of the sampling period or the sampling interval as the load on the internal combustion engine increases is adopted. .   An internal combustion engine equipped with the EGR control system for an internal combustion engine according to any one of claims 1 to 3. 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,
In the control of the EGR system,
The NOx concentration calculated value is calculated using the detected value of the intake flow rate sensor provided in the intake passage and the detected value of the exhaust lambda sensor provided in the exhaust passage, and is the detected value of the NOx concentration sensor provided in the exhaust passage. When calculating a NOx correction coefficient that is a ratio of the detected NOx concentration value and the calculated NOx concentration value and correcting the in-cylinder oxygen concentration target value using the NOx correction coefficient,
While calculating the NOx correction coefficient by a moving average process,
An EGR control method for an internal combustion engine, wherein at least one of a length of a sampling period and a sampling interval for performing a moving average process on the NOx correction coefficient is changed according to an operating state of the internal combustion engine.   6. The EGR control method for an internal combustion engine according to claim 5, wherein at least one of the length of the sampling period and the sampling interval is changed according to a combination of an engine speed and a load. The longer the engine speed of the internal combustion engine, the shorter the sampling period or the sampling interval,
7. The EGR control method for an internal combustion engine according to claim 5, wherein either or both of the length of the sampling period and the sampling interval are shortened as the load on the internal combustion engine is increased.

Images