JP2010106734A - Egr control method for internal combustion engine, and internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR control method for an internal combustion engine accurately determining whether or not an appropriate EGR control is performed to prevent EGR gas from being excessive to prevent misfire, and supplying a proper amount of EGR gas to secure an appropriate EGR ratio, in an internal combustion engine provided with an EGR system, and to provide an internal combustion engine. <P>SOLUTION: In an EGR control method for an internal combustion engine, a cylinder pressure progress calculation data Pcc(i) as time-series data of cylinder pressure in a preset period is calculated by using, as input, a cylinder pressure combustion model using an EGR ratio estimation value ηec or an EGR ratio target value ηet calculated from detection values of an EGR gas flow rate sensor 33 and an intake air amount sensor 14, and a deviation amount ΔPc between the cylinder pressure progress calculation data Pcc(i) and a cylinder pressure progress detection data Pcm(i) in a period detected by a cylinder pressure sensor 16 is acquired. When the deviation amount ΔPc becomes a preset threshold value ΔPc1 or more, it is determined that an EGR ratio satisfying the EGR ratio target value ηet is not achieved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an EGR control method for an internal combustion engine and an internal combustion engine. More specifically, in EGR control for an internal combustion engine, whether or not there is a difference between an EGR rate and an EGR rate target value in EGR control actually performed is accurately determined. When it is determined that the difference is greater than the preset threshold value, the EGR rate in the actual EGR control is required for the engine operating state by adjusting the EGR rate target value. The present invention relates to an EGR control method for an internal combustion engine and an internal combustion engine that can be adjusted to be adapted to the above.

  In an internal combustion engine such as a gasoline engine or a diesel engine, in order to reduce the amount of NOx (nitrogen oxide) generated, EGR (exhaust gas recirculation: exhaust gas) lowers the combustion temperature in the cylinder by returning a part of the exhaust gas to the intake side. EGR device for performing recirculation). In this EGR, in order to obtain a sufficient effect, it is necessary to appropriately control the EGR rate which is the ratio [G / (A + G)] of the EGR gas G to the fresh air A and the EGR gas G entering the cylinder. In the prior art, an actual EGR rate is estimated by using an intake air amount sensor such as an EGR gas flow rate sensor provided in the EGR passage or a MAF sensor provided in the intake passage, and the EGR passage is set so as to coincide with the EGR rate target value. The EGR valve and EGR cooler are controlled.

  However, since the EGR passage is connected to the exhaust passage and is easily affected by exhaust pulsation, a backflow that flows from the intake side to the exhaust side is generated in the EGR passage, resulting in a large measurement error of the EGR gas flow sensor. There is. In addition, the EGR gas flow rate sensor may cause an error in the measurement value due to condensation of water vapor present in the exhaust gas. If an error occurs in the measured value of the EGR gas flow sensor, even if the engine control unit (ECU) determines that the EGR rate target value is satisfied, EGR is not actually performed at an appropriate EGR rate. . If the actual EGR rate is lower than the EGR rate target value, the in-cylinder (in-cylinder) combustion temperature increases and the amount of NOx emissions increases. Conversely, if the actual EGR rate is higher than the EGR rate target value, oxygen is insufficient. Misfire will occur.

  In this connection, an intake pressure sensor for detecting intake pressure is provided downstream of the throttle valve in the intake passage, and at least the throttle valve opening, the EGR valve opening, and the engine are controlled by an engine control unit (ECU). The intake pressure when the EGR device operates normally is estimated based on the rotational speed of the EGR device, and the EGR device malfunctions when the deviation between the detected actual intake pressure and the estimated intake pressure exceeds a predetermined value An abnormality detection device for an exhaust gas recirculation device that is determined to be is proposed (for example, see Patent Document 1).

  In this exhaust gas recirculation device abnormality detection device, when calculating an estimated value of the intake pressure when the EGR device operates normally from the throttle opening, the EGR valve opening, and the engine rotation speed, it is read from a predetermined control map. Therefore, it is necessary to prepare this control map. This control map is set from measurement by a bench test or the like, and is stored in advance in a ROM of an engine control unit (ECU).

  This control map is a combination of three parameters: throttle opening, EGR valve opening, and engine speed under conditions where the EGR device operates normally in the bench test of the actual machine and the EGR execution conditions are satisfied. While changing variously, the intake pressure is measured and set for each combination. Since the intake pressure changes when the specifications of the internal combustion engine and the surrounding environment (atmospheric temperature, atmospheric pressure) are different, it is necessary to measure sequentially according to each condition, which takes much time. Therefore, there is a problem that a bench test for a long time is required.

  Furthermore, in an internal combustion engine equipped with an exhaust turbocharger, the fuel injection amount also affects the intake pressure. Therefore, it is necessary to estimate the intake pressure taking into account the fuel injection amount, and more control maps are required. Become. In addition, when a system such as a multistage supercharging system or a variable valve timing system is adopted, parameters that affect the intake pressure further increase. Therefore, it is necessary to set a control map that takes these parameters into account, and EGR control It is difficult to preset a control map that can ensure sufficient accuracy.

The abnormality detection device for the exhaust gas recirculation device only detects whether or not the EGR device is abnormal from the difference between the calculated value of the intake pressure and the detection value. It does not touch the continuation of the subsequent EGR control.
JP 2002-227727 A

  The present invention has been made in view of the above situation, and an object of the present invention is to accurately determine whether or not appropriate EGR control is being performed in an internal combustion engine equipped with an EGR system. EGR control of an internal combustion engine that can prevent misfire by preventing an excess of gas and can obtain a good NOx reduction effect by supplying an appropriate amount of EGR gas and ensuring an appropriate EGR rate It is to provide a method and an internal combustion engine.

  An EGR control method for an internal combustion engine for achieving the above object is an EGR rate estimated value calculated from an EGR rate target value or a detection value of an EGR gas flow rate sensor and an intake air amount sensor in an internal combustion engine equipped with an EGR system. Is used to calculate in-cylinder pressure progress calculation data, which is time-series data of in-cylinder pressure within a preset period, and the in-cylinder pressure progress calculation data and the in-cylinder pressure sensor The amount of deviation from the in-cylinder pressure progress detection data within the period detected by the above is obtained, and when the amount of deviation exceeds a preset threshold value, an EGR rate that satisfies the EGR rate target value can be achieved. It is a method characterized in that it is determined that it is not.

  According to this method, since the deviation amount between the in-cylinder pressure progress calculation data and the in-cylinder pressure progress detection data in the time-series data of the in-cylinder pressure within a preset period is used as a determination criterion, the actual EGR can be accurately performed. The difference between the rate and the EGR rate target value can be obtained, and it can be determined whether or not the EGR control is performed with an appropriate EGR rate with high accuracy. In particular, in an internal combustion engine that operates with a premixed compression ignition combustion system that is realized with a large amount of EGR and early injection, the ignition timing is greatly affected by the EGR rate, and therefore it is required to control the EGR rate more appropriately. So it is more effective.

  In the EGR control method for an internal combustion engine, the in-cylinder pressure progress calculation data includes the EGR rate target value or the EGR rate estimation value, a fuel injection timing control amount, a fuel injection amount control amount, and a fuel injection pressure control. The in-cylinder combustion model is calculated based on the measured value, the measured value of the intake pressure, the measured value of the intake air temperature, the measured value of the engine speed, or the control value.

  This in-cylinder combustion model is also called a spray combustion prediction model in a diesel engine. The in-cylinder combustion model is input with engine speed, EGR rate, fuel injection timing, fuel injection amount, fuel injection pressure, intake pressure, and intake air temperature as inputs. It predicts the state, exhaust emission, engine torque, etc., and divides the spray generated by fuel injection into several regions and calculates the fuel evaporation, combustion, etc. in each region. It can be simulated (simulated) in a short time. By using this in-cylinder combustion model, it is not necessary to create a control map for each change in the surrounding environment (atmospheric pressure, atmospheric temperature, etc.) and different engine shapes.

  In the above EGR control method for an internal combustion engine, an ignition timing calculation value is calculated from the in-cylinder pressure progress calculation data, and an ignition timing detection value obtained from the in-cylinder pressure progress detection data or an ignition timing detected from an ignition sensor When the ignition timing calculated value is earlier than the ignition timing detected value compared with the detected value, the EGR rate target value is corrected to be decreased, and the ignition timing calculated value is later than the ignition timing detected value Corrects the EGR rate target value to increase.

  In this determination and correction, when the calculated ignition timing is earlier than the detected ignition timing value, the actual EGR rate is larger than the EGR rate target value, and EGR gas is excessively flowing into the cylinder, which may cause misfire. Therefore, the EGR rate target value is decreased and the actual EGR rate is lowered. In addition, when the calculated ignition timing is later than the detected ignition timing value, the actual EGR rate is smaller than the target EGR rate, and an appropriate EGR rate cannot be secured, leading to an increase in NOx emissions. Rate target value increases. As a result, the actual EGR rate is set to the required EGR rate.

  Further, an internal combustion engine for achieving the above object is an internal combustion engine provided with an EGR system and an EGR control means, wherein the EGR control means is configured to implement the EGR control method for the internal combustion engine. According to this configuration, since the deviation amount between the in-cylinder pressure progress calculation data and the in-cylinder pressure progress detection data in the time-series data of the in-cylinder pressure within a preset period is used as the determination criterion, the actual EGR is accurately obtained. The difference between the rate and the EGR rate target value can be obtained, and it can be determined whether or not the EGR control is performed more accurately at an appropriate EGR rate. Further, even when the actual EGR rate and the EGR rate target value are different, the EGR control can be performed so that the actual EGR rate becomes the required EGR rate.

  According to the EGR control method and the internal combustion engine of the internal combustion engine according to the present invention, the deviation amount between the in-cylinder pressure progress calculation data and the in-cylinder pressure progress detection data in the time-series data of the in-cylinder pressure within a preset period. Therefore, the deviation between the actual EGR rate and the target value of the EGR rate can be obtained with high accuracy, and it can be accurately determined whether the EGR control is being performed with the appropriate EGR rate. .

  Hereinafter, an engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an engine (internal combustion engine) 1 according to an embodiment of the present invention.

  The engine 1 is provided with an intake passage 2 and an exhaust passage 3, and a fuel injection mechanism 4 of the engine 1 is provided with a fuel injection nozzle 5 and a common rail 6, and performs fuel injection in the cylinder 7. Yes. Further, a turbocharger 8 is provided, the turbine 9 thereof is disposed in the exhaust passage 3, and the compressor 10 driven by the turbine 9 is disposed in the intake passage 2.

  Further, the exhaust throttle valve 11 is disposed in the exhaust passage 3, and the intake throttle valve 12 is disposed in the intake passage 2. An exhaust gas processing device 13 is disposed in the exhaust passage 3 on the downstream side of the turbine 9, and an intake air amount sensor (air cleaner) 14 is disposed in the intake passage 2 on the upstream side of the compressor 10. The EGR system 31 includes an EGR passage 32, an EGR valve 33, and an EGR cooler 34 that connect the exhaust passage 3 and the intake passage 2. In order to control the engine 1, a control device 15 called an ECU (engine control unit) is provided, and an in-cylinder pressure sensor 16 is further provided. At least one in-cylinder pressure sensor 16 is mounted on a cylinder (for example, four cylinders) of the engine 1. The intake manifold 1 a is provided with an intake pressure sensor 17 and an intake temperature sensor 18.

  Next, an EGR control method for an internal combustion engine according to the present invention will be described. This EGR control method uses an engine 1 equipped with an EGR system 31 in a cylinder that receives an EGR rate estimated value ηec calculated from the detected value Vem of the EGR gas flow sensor 35 and the detected value Vam of the intake air amount sensor 14 as inputs. Using the combustion model, in-cylinder pressure progress calculation data Pcc (i) that is time-series data of the in-cylinder pressure within a preset period with respect to the crank angle is calculated. Here, i is a positive number, and i = 1, 2, 3,. . . . . I. Since the calculation is performed when the EGR rate estimated value ηec is equal to the EGR rate target value ηet, the EGR rate target value ηet may be input instead of the EGR rate estimated value ηec.

  Deviation ΔPc (= Σ | Pcc (i) between the in-cylinder pressure progress calculation data Pcc (i) and the in-cylinder pressure progress detection data Pcm (i) within the period Rac detected by the in-cylinder pressure sensor 18 -Pcm (i) |) is obtained, and it is determined that the EGR rate ηe satisfying the EGR rate target value ηet is not achieved when the deviation amount ΔPc is equal to or larger than a preset threshold value ΔPc1. Here, the integrated value of the absolute value of the difference between the two is adopted, but the present invention is not limited to this, and any amount that can appropriately express the deviation may be used. For example, the square of the difference (deviation) between the two is averaged. A standard deviation σ or the like obtained by taking the square root of the average value may be used.

  This EGR control method is determined according to a control flow for determination as shown in FIG. 2, for example. The control flow of FIG. 2 is called and executed in parallel with the EGR control from the advanced control flow as the engine starts. When the control flow in FIG. 2 starts, the engine operating state is read in step S11.

  As the data indicating the engine operation state read in step S11, the engine speed, the load, and the like are mainly used, and the amount necessary for the engine operation such as the engine coolant temperature is also read. Further, the control amount of each control device, such as the control amount Ftt of the fuel injection timing of the fuel injection device 4 and the like, the control amount Fvt of the fuel injection amount, the control amount Fpt of the fuel injection pressure, etc. is calculated, and as the EGR control amount, An EGR rate target value ηet is calculated. Further, an estimated EGR rate ηec is calculated from the detected value Vem from the EGR gas flow sensor 35 and the detected value Vam from the intake air amount sensor 14.

  In the next step S12, it is determined whether or not the EGR rate estimated value ηec is equal to the EGR rate target value ηet. Actually, in this determination, it is not a coincidence in a strict sense, but it is determined whether or not the EGR rate estimated value ηec is within an allowable range of control of the EGR rate target value ηet. That is, it is determined whether the EGR rate estimated value ηec is substantially equal to the EGR rate target value ηet. Thereby, it is determined whether or not the EGR rate estimated value ηec has finished following the EGR rate target value ηet. If they are not equal and have not been followed (NO), step S11 is repeated, and the process waits until the EGR rate estimated value ηec becomes the EGR rate target value ηet.

  If it is determined in step S12 that the EGR rate estimated value ηec is equal to the EGR rate target value ηet (YES), step S13 and step S14 are performed in parallel. In step S13, in-cylinder pressure progress detection data Pcm (i) by the in-cylinder pressure sensor 18 is calculated. On the other hand, in step S14, in-cylinder pressure progress calculation data Pcc (i) is calculated from the in-cylinder combustion model. An example of the in-cylinder pressure progress detection data Pcm (i) and the in-cylinder pressure progress calculation data Pcc (i) is shown in FIG.

  In this in-cylinder combustion model, the in-cylinder pressure progress calculation data Pcc (i) is converted into the EGR rate target value ηet, the fuel injection timing control amount Ftt, the fuel injection amount control amount Fvt, the fuel injection pressure control amount Fpt, the intake air Calculation is made based on the pressure measurement value Pim, the intake air temperature measurement value Tim, the engine rotation speed measurement value Nem, or the control value Nec. Note that these base values are calculated by the control device 15.

  In a diesel engine, this in-cylinder combustion model is also called a spray combustion prediction model, and the engine speed Ne, EGR rate ηe, fuel injection timing Ft, fuel injection amount Fv, fuel injection pressure Fp, intake air pressure Pi, intake air temperature Ti Is used to predict the in-cylinder combustion state, exhaust emission, engine torque, etc., and divide the spray generated by fuel injection into several regions and calculate the fuel evaporation, combustion, etc. in each region Thus, spray combustion in the cylinder can be simulated (simulated) in a short time. By using this in-cylinder combustion model, it is not necessary to create a control map for each change in the surrounding environment (atmospheric pressure, atmospheric temperature, etc.) and different engine shapes.

  After the calculation in step S13 and step S14, the process goes to step S15, and the deviation amount ΔPc between them is calculated as ΔPc = Σ | Pcc (i) −Pcm (i) |. This Σ is integrated with i = 1 to I. In the next step S16, the deviation amount ΔPc is compared with the threshold value ΔPc1. In this comparison, when the deviation amount ΔPc is equal to or smaller than the threshold value ΔPc1 (YES), the EGR rate estimated value ηec is close to the actual EGR rate ηe, and the process returns. If the deviation amount ΔPc is larger than the threshold value ΔPc1 in the comparison in step S16 (NO), it is determined that the EGR rate estimated value ηec is far from the actual EGR rate ηe, and the process goes to step S17.

  In step S17, an ignition timing calculation value Tfc is calculated from the in-cylinder pressure progress calculation data Pcc (i), and an ignition timing detection value Tfm is calculated from the in-cylinder pressure progress detection data Pcm (i). If an ignition sensor is provided, the ignition timing detected from this ignition sensor is set as an ignition timing detection value Tfm. This ignition timing can be easily calculated and detected because the in-cylinder pressure changes rapidly.

  In the next step S18, the ignition timing calculated value Tfc and the ignition timing detected value Tfm are compared, and if the ignition timing calculated value Tfc is earlier than the ignition timing detected value Tfm, an EGR rate target value that is a target control amount of the EGR rate. ηet is adjusted to decrease, and when the ignition timing calculated value Tfc is later than the ignition timing detection value Tfm, the EGR rate target value ηet is adjusted to increase. After making this adjustment, return. FIG. 4 shows the case where the ignition timing calculated value Tfc is earlier than the ignition timing detected value Tfm, and FIG. 5 shows the case where the ignition timing calculated value Tfc is later than the ignition timing detected value Tfm.

  In the determination and adjustment in step S18, when the ignition timing calculated value Tfc is earlier than the ignition timing detection value Tfm, the actual EGR rate is large, and the EGR gas flows excessively into the cylinder, which may cause misfire. The EGR rate target value ηet, which is the target control amount of the EGR rate, is decreased to lower the actual EGR rate. In addition, when the calculated ignition timing Tfc is slower than the detected ignition timing Tfm, the actual EGR rate is small and an appropriate EGR rate cannot be secured, leading to an increase in NOx emissions. Correct to increase.

  The control flow of FIG. 2 returns and returns to the advanced control flow, and is then repeatedly called and executed in parallel with the EGR control from the advanced control flow. The control flow of FIG. finish. When the EGR control is not executed, the control flow of FIG. 2 cannot be used, so that the control flow of FIG. 2 is not called, and the execution of the control flow of FIG. 2 is interrupted.

  According to the above-described EGR control method and internal combustion engine (engine) of the internal combustion engine, the deviation between the in-cylinder pressure progress calculation data and the in-cylinder pressure progress detection data, which is time-series data of the in-cylinder pressure within a preset period. Since the quantity is used as a determination criterion, the deviation between the actual EGR rate and the target value of the EGR rate can be obtained with high accuracy, so that whether or not the EGR control is actually performed at an appropriate EGR rate is determined. It can be determined with high accuracy.

  In particular, in an internal combustion engine that operates with a premixed compression ignition combustion system that is realized with a large amount of EGR and early injection, the ignition timing is greatly affected by the EGR rate, and therefore it is required to control the EGR rate more appropriately. So it is more effective.

  Further, according to the EGR control method and the internal combustion engine of the internal combustion engine, the calculation data Pcc (i) and the detection data Pcm (i) of the in-cylinder pressure are used as the determination criteria, so that the devices 33 and 34 of the EGR system 31 are used. , 35, even if there is an abnormality, the calculated ignition timing Tfc obtained from the in-cylinder pressure progress calculation data Pcc (i) and the detection data Pcm (i) is compared with the detection value Tfm to obtain an appropriate EGR rate. Therefore, the EGR valve 34 and the like can be controlled so that proper in-cylinder combustion can be obtained. Thereby, even when the EGR devices 33, 34, and 35 are abnormal, it is possible to obtain misfire prevention and NOx reduction effects.

  Furthermore, in the EGR control method for an internal combustion engine and the internal combustion engine, the value calculated by the in-cylinder combustion model that takes into account the effects of differences in the engine system and the surrounding environment may be used as a criterion. There is no need to have map data for control with a large number of data including.

It is a figure which shows the structure of the engine of embodiment of this invention. It is a figure which shows an example of the control flow of the EGR control method of the internal combustion engine in embodiment of this invention. It is a figure which shows an example of the relationship between cylinder pressure progress calculation data and cylinder pressure progress detection data. It is a figure which shows an example of the relationship between main cylinder pressure progress calculation data and cylinder pressure progress detection data in case ignition timing calculation value is earlier than ignition timing detection value. It is a figure which shows an example of the relationship between main cylinder pressure progress calculation data and cylinder pressure progress detection data in case ignition timing calculation value is later than ignition timing detection value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 14 Intake air amount sensor 16 In-cylinder pressure sensor 17 Intake pressure sensor 18 Intake temperature sensor 35 EGR gas flow sensor

Claims (4)

  In an internal combustion engine equipped with an EGR system, a period set in advance using an in-cylinder combustion model that receives an EGR rate target value or an EGR rate estimated value calculated from an EGR gas flow rate sensor and a detected value of an intake air amount sensor. In-cylinder pressure progress calculation data that is time-series data of the in-cylinder pressure is calculated, and between the in-cylinder pressure progress calculation data and the in-cylinder pressure progress detection data within the period detected by the in-cylinder pressure sensor. And determining that an EGR rate that satisfies the EGR rate target value is not achieved when the deviation amount is equal to or greater than a preset threshold value. .   The in-cylinder pressure progress calculation data includes the EGR rate target value or the EGR rate estimation value, the control amount of the fuel injection timing, the control amount of the fuel injection amount, the control amount of the fuel injection pressure, the measured value of the intake pressure, the intake air temperature The EGR control method for an internal combustion engine according to claim 1, wherein the EGR control method is calculated by the in-cylinder combustion model based on the measured value.   The ignition timing calculation value is calculated from the in-cylinder pressure progress calculation data, and compared with the ignition timing detection value obtained from the in-cylinder pressure progress detection data or the ignition timing detection value detected from the ignition sensor, and the ignition timing calculation When the value is earlier than the ignition timing detection value, the EGR rate target value is corrected to decrease, and when the ignition timing calculated value is later than the ignition timing detection value, the EGR rate target value is increased. The EGR control method for an internal combustion engine according to claim 1, wherein the EGR control method corrects to:   An internal combustion engine comprising an EGR system and an EGR control means, wherein the EGR control means implements the EGR control method for an internal combustion engine according to any one of claims 1, 2, and 3.

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