JP5111534B2 - EGR control device for internal combustion engine - Google Patents

Description

  The present invention relates to an EGR control device that controls an EGR flow rate to reduce NOx and the like contained in exhaust gas of an internal combustion engine.

  Diesel engines and lean burn engines are considered promising for improving the fuel efficiency of internal combustion engines. However, diesel engines and lean burn engines tend to contain a lot of NOx in the exhaust gas. In order to reduce NOx contained in the exhaust gas, it is effective to lower the combustion temperature, and exhaust gas recirculation (EGR) control for performing combustion control by returning a part of the exhaust gas to the intake side has been conventionally performed. ing.

  In gasoline engines, the introduction of EGR has been put to practical use in which knocking is suppressed and exhaust temperature is lowered to improve fuel efficiency.

  In a supercharged engine, if the pressure of the intake pipe increases in the supercharging region, the required EGR amount may not be obtained. Therefore, in recent years, practical application of a low pressure EGR system capable of increasing the EGR amount by introducing EGR upstream of the supercharger (compressor) has been studied.

  Patent Document 1 discloses an apparatus that estimates an EGR amount by an intake air amount sensor and a pressure sensor provided in an intake pipe and controls an EGR valve.

  Japanese Patent Application Laid-Open No. H10-228561 discloses an apparatus that estimates an EGR amount based on a detection signal from an intake air amount sensor and an oxygen concentration sensor provided in an intake pipe and controls an EGR valve.

JP-A-5-231244 JP 2009-74459 A

  Generally, an EGR valve for controlling the EGR amount causes a response delay from when a control signal is input until the actual EGR valve opening reaches a target value. For this reason, it is desirable to control the EGR valve by quickly estimating the EGR amount during transient operation such as acceleration / deceleration.

  In Patent Document 1, a pressure sensor provided in the intake pipe is used for estimating the EGR amount. However, since the intake pipe pressure rises after EGR gas is filled in the intake pipe downstream of the throttle valve, the EGR amount is estimated. A response delay corresponding to the capacity of the intake pipe is generated. As a result, an error occurs in the estimated value of the EGR amount during transient operation such as acceleration / deceleration.

  In Patent Document 2, an oxygen concentration sensor is used for estimating the EGR amount. However, the oxygen concentration sensor has a large response delay and causes a response delay in estimating the EGR amount. As a result, an error occurs in the estimated value of the EGR amount during transient operation such as acceleration / deceleration.

  For this reason, the above-described prior art has a problem that the EGR amount cannot be controlled to a target value suitable for exhaust gas reduction during transient operation, and a large amount of NOx and PM are exhausted.

  Further, in the method of estimating the EGR amount using the pressure sensor disclosed in Patent Document 1, it is difficult to accurately estimate the EGR amount because the intake pipe pressure varies even if the EGR amount is the same due to variations in valve timing. Met.

  Further, in the method of estimating the EGR amount by the oxygen concentration sensor provided in the intake pipe of Patent Document 2 above, the detection accuracy of the oxygen concentration sensor is generally high under the condition that the oxygen concentration of the intake pipe is higher than that of the exhaust pipe and the oxygen concentration is generally high. Therefore, the estimation accuracy of the EGR amount decreases.

  For this reason, in the above-described prior art, there is a case where an estimation error of the EGR amount occurs even during steady operation, and the amount of NOx and PM emissions increases.

  The EGR control device of the present invention is mainly applied to an internal combustion engine having a low-pressure EGR passage that introduces EGR gas upstream of a compressor, and estimates the EGR amount with high response and high accuracy to reduce NOx and PM emissions. The purpose is to do.

The first configuration of the present invention for solving the above problem is to detect an EGR passage communicating the exhaust pipe and the intake pipe, an EGR valve attached to the EGR passage, and an intake air amount flowing into the intake pipe Applied to an internal combustion engine equipped with an air amount detecting means,
A flow rate adjusting valve or a throttle portion provided in the intake pipe downstream of the junction portion of the intake pipe and the EGR passage, a pressure at an upstream position and a pressure at a downstream position of the flow rate adjusting valve or the throttle portion, or an upstream position and a downstream position A pressure detecting means for detecting a pressure difference between the pressure adjusting means, a means for detecting an intake air temperature in the intake pipe, a means for calculating an opening area of the flow regulating valve or the throttle, and an upstream position of the flow regulating valve or the throttle. A gas flow rate calculating means for calculating a flow rate of the mixed gas passing through the flow rate adjusting valve or the throttle portion from the pressure difference between the pressure and the downstream position, the opening area, and the intake air temperature; the flow rate of the mixed gas and the intake air And means for controlling the opening degree of the EGR valve in accordance with the flow rate of the EGR gas calculated by the difference in amount.

  In the second configuration of the present invention, the gas flow rate calculation means calibrates the flow rate calculation value of the mixed gas from the intake air amount detection value by the air amount detection means when the EGR valve is closed. I made it.

  According to a third configuration of the present invention, the gas flow rate calculation means is based on a detected value of the intake air amount by the air amount detection means when the EGR valve is closed and at a low load including idling or during deceleration. The flow rate calculation value of the mixed gas was calibrated.

  According to the configuration of the first EGR control device of the present invention, the EGR amount can be estimated with high response from the pressure difference between the upstream position and the downstream position of the flow rate adjusting valve or the throttle portion, and acceleration / deceleration, etc. Since the EGR amount can be controlled to an optimum amount for exhaust gas reduction even during transient operation, the NOx and PM emissions can be reduced.

  According to the configuration of the second EGR control device of the present invention, the EGR amount can be estimated with high accuracy by calibrating the calculated value of the mixed gas amount by the intake air amount detecting means, and the EGR amount is always optimal for exhaust gas reduction. Since it can be controlled to an appropriate amount, NOx and PM emissions can be reduced.

  According to the configuration of the third EGR control device of the present invention, when the calibration is performed with the EGR valve closed or the EGR valve closed forcibly, the calibration is performed at low load or deceleration. Thus, an error in estimating the EGR amount due to leakage of the EGR valve can be reduced. Further, it is possible to prevent an increase in the discharge amount of NOx and the like due to forcibly closing the EGR valve.

  According to the EGR control device of the present invention, the EGR amount can be estimated with high response and high accuracy, and can be controlled to the optimum EGR amount for exhaust gas reduction at all times, so that NOx, PM during transient operation or steady operation Can be reduced.

The structural example when the EGR control apparatus of this invention is applied to an engine. The hardware block diagram of the EGR control apparatus of this invention. The flowchart of the EGR control apparatus of this invention. The figure which shows the correction | amendment characteristic of the EGR control apparatus of this invention. The flowchart of the calibration part of the EGR control apparatus of this invention.

  Examples of the present invention will be described below.

  An embodiment in which the EGR control device of the present invention is applied to a diesel engine will be described. Here, the EGR control device of the present invention is not limited to a diesel engine, but can also be applied to a gasoline engine that controls the EGR flow rate.

  Intake air of a diesel engine (hereinafter referred to as engine 1) shown in FIG. 1 is taken in from an air cleaner 3 provided in an intake pipe 2 and is supercharged by a compressor 4 </ b> A of a turbocharger 4. Here, the intake air amount is measured by the intake air amount sensor 15. The supercharged air is cooled by the intercooler 5 and sucked into the combustion chamber 9 through the intake manifold 8. The intake air amount is controlled by the supercharging efficiency of the turbocharger 4 (variable capacity) and the throttle valve 6. The throttle valve 6 is provided with a motor (not shown) for driving the throttle valve and an opening sensor 19 for detecting the throttle opening.

  A fuel injection valve 10 for injecting fuel into the combustion chamber 8 is attached to the engine 1.

  A high-pressure EGR passage 25 for introducing EGR gas from the exhaust pipe 11 to the collecting portion of the intake manifold 8 is provided, and an EGR valve 26 and an EGR cooler 27 are attached to the high-pressure EGR passage 25.

  A catalyst 28 and a DPF 29 are provided in the exhaust pipe 11 downstream of the turbine 4B. A low pressure EGR passage 13 is provided for taking EGR gas from the exhaust pipe 12 downstream of the DPF 29 and introducing EGR gas upstream of the compressor 4 </ b> A of the intake pipe 2. The low pressure EGR passage 13 is provided with an EGR valve 14 and an EGR cooler 17.

  In the EGR control device of the present invention, the pressure of the intake passage upstream of the throttle valve 6 (intake throttle portion) and the intake air downstream of the throttle valve 6 are estimated in order to detect the flow rate of the mixed gas of intake air and EGR gas and estimate the EGR flow rate. A pressure sensor 20 capable of detecting the pressure difference between the passages is provided. 21 and 22 are pressure introduction parts. Here, the pressure sensor 20 of the present embodiment is configured to detect not only the differential pressure upstream and downstream of the throttle valve, but also the absolute pressure of the intake passage upstream of the throttle valve. The sensor for detecting the absolute pressure may be provided separately from the pressure sensor 20 (differential pressure sensor). In addition, a pressure sensor that detects the absolute pressure of the intake passage upstream of the throttle valve 6 and the absolute pressure of the downstream intake passage may be provided to calculate the differential pressure upstream and downstream of the throttle valve.

  An intake air temperature sensor 18 is provided downstream of the intercooler 5.

  The engine control device 30 includes the function of the EGR control device, takes in signals from each sensor, calculates a control amount, and outputs a control signal to each actuator.

  The configuration of the engine control device 30 is shown in FIG. A crank angle sensor (not shown) for detecting the crank angle position and rotation speed of the engine, an intake air amount sensor 15, an intake air temperature sensor 18, a throttle sensor 19, a pressure sensor 20, and other signals are transmitted via an input circuit 31. It is captured by the computer 32. The microcomputer 32 includes a CPU 33, a ROM (read memory) 34, and a RAM (write memory) 35.

  The microcomputer 32 calculates the fuel injection amount (injection valve pulse width), the throttle valve opening (target value), the EGR valve opening (target value), etc., and outputs the fuel injection valve 10 and the throttle valve via the output circuit 36. 6, output to each actuator such as the EGR valve 14 and the EGR valve 26.

  A method for estimating the EGR flow rate in the EGR control device (engine control device) of the present invention will be described with reference to the flowchart of FIG.

  The following calculation for estimating the EGR flow rate is performed every predetermined cycle, for example, every 10 msec cycle.

  In step 100, it is determined whether or not the condition for introducing EGR gas from the low pressure EGR passage is satisfied. In general, EGR gas is introduced from the low-pressure EGR passage when the pressure of the intake manifold 8 increases due to supercharging by the compressor 4A and the differential pressure with respect to the exhaust pipe decreases and the required EGR flow rate cannot be obtained.

  If the conditions for introducing the EGR gas are satisfied, parameters required for estimating the EGR flow rate in step 110 and step 120: intake air amount Qa, intake air temperature Tt, throttle valve opening α, and pressure upstream and downstream of the throttle valve The difference ΔP and the absolute pressure Pt upstream of the throttle valve are taken in from the signals of the sensors.

  Next, at step 130, a target EGR rate Rt suitable for exhaust gas reduction is read. The target EGR rate is stored in advance in a memory (ROM 34) and is generally set as a map for the load and the rotational speed.

  Next, at step 140, the target EGR flow rate Qet is calculated from the intake air amount Qa and the target EGR rate Rt by the following equation.

Qet = Qa × (Rt / 1−Rt) (Formula 1)
Here, the intake air amount is adjusted to an amount suitable for exhaust gas reduction by controlling the turbocharger (supercharging efficiency) and the throttle valve.

Next, at step 150, the estimated value Qg of the mixed gas amount (total intake gas amount) of the intake air and the EGR gas is determined from the pressure difference ΔP upstream and downstream of the throttle valve, the absolute pressure Pt upstream of the throttle valve, the intake air temperature Tt, and The throttle valve opening area (throttle opening area) A ₂ is calculated by the following equation.

Here, the opening area A ₂ of the throttle valve is calculated from the detected value of the throttle opening by the throttle valve opening sensor.

  Here, in order to ensure the estimation accuracy of the total intake gas amount based on the pressure difference ΔP, the throttle valve opening is controlled so that ΔP becomes a predetermined value or more.

  At this time, if ΔP is large, the pump loss increases. Therefore, when the total intake gas amount fluctuates, the throttle valve opening is adjusted to control ΔP to a necessary minimum value. Specifically, when the total intake gas amount is small, the throttle valve opening is reduced to ensure the pressure difference necessary for gas amount detection. When the total intake gas amount is large, the pump is caused by pressure loss of the throttle valve. Increase the throttle valve opening so that the loss does not increase.

  Moreover, since ΔP varies due to the influence of intake pulsation, it is desirable to reduce the variation by performing filter processing or the like on the pressure sensor signal.

  Next, at step 160, the estimated value Qe of the current EGR flow rate is calculated by the difference (Qg−Qa) between the total intake gas amount estimated value Qg and the intake air amount Qa.

  Here, the intake air amount Qa may be corrected in consideration of transport delay from the intake air amount sensor position of the intake pipe to the throttle valve.

  Thus, the estimated value of the EGR flow rate calculated from the pressure difference between the upstream and downstream of the throttle valve is not affected by the transportation delay due to the intake pipe capacity from the throttle valve to the combustion chamber, and the absolute pressure of the conventional intake manifold is Compared to the method of detecting and estimating the EGR flow rate, the response delay in estimating the EGR flow rate can be reduced.

  Further, in the conventional method of estimating the EGR flow rate from the signal of the oxygen concentration sensor provided in the intake pipe, a large response delay of about 200 to 300 ms occurs, whereas in the EGR flow rate estimation method of the present invention, the estimation of the EGR flow rate is performed. Response delay can be reduced to about several tens of ms.

  Next, the deviation between Qe and the target EGR flow rate Qet is calculated, and the EGR valve opening is feedback-controlled so that Qe matches Qet.

  In step 170, the feedback correction amount CEGR of the EGR valve opening (opening area) is calculated by the following equation.

_{CEGR n = CEGR n-1 +} DEGR ... ( Equation 3)
DEGR: Correction amount update value per calculation cycle CEGR _n : Current correction amount calculation value CEGR _n-1 : Previous correction amount calculation value DEGR is stored in advance in a memory as a correction characteristic (table) for the deviation Qe-Qet shown in FIG. Then, the correction amount for the deviation Qe-Qet is read from the table and is set as DEGR.

  Next, at step 180, the target EGR valve opening is calculated by the following equation or the like, and a control signal is output to the EGR valve.

Target EGR valve opening (opening area) AEGR = AEGRBS × (1 + CEGR) (Formula 4)
AEGRBS: Opening area basic value AEGRBS (opening area basic value) is stored in advance in a memory as a map for load, rotation, and the like.

  Here, in order to improve the estimation accuracy of the EGR flow rate, the calculated value of the total intake gas amount Q in step 150 may be calibrated in advance by the following procedure.

  In step 200 of FIG. 5, it is determined whether the calibration condition is satisfied. Calibration conditions include idling, steady operation, and deceleration. When the EGR valve is closed, the total intake gas amount Qg coincides with the intake air amount Qa. Therefore, calibration is performed when the EGR valve is closed. Here, if there is leakage of the EGR valve, an error occurs at the time of calibration. Therefore, it is preferable to calibrate at a low load or a low speed when the exhaust pressure is relatively small.

  If the calibration condition is satisfied, it is determined in step 210 whether the EGR valve is closed. Here, the EGR valve may be forcibly closed for a short time for calibration.

  Further, when the calibration is performed by forcibly closing the EGR valve, the calibration is performed at a low load with a low combustion temperature and at a deceleration to prevent an increase in the amount of NOx and the like emitted by closing the EGR valve.

  If the EGR valve is closed, in step 220, the intake air amount detection value Qa by the intake air amount sensor is read.

  From Equation 2, the following equation is obtained with the calibration coefficient of Qg as Kc.

  Since Qg = Qa when the EGR valve is closed, Kc can be calculated by the following equation by substituting into Equation 5.

  The calibration coefficient Kc calculated at this time is stored in the memory, and Kc is read when calculating the total intake gas amount Qg in step 150 in FIG.

  Here, the calibration coefficient Kc may be obtained under a plurality of operating conditions with different intake air amounts, and the calibration coefficient Kc may be stored in the memory for each operating condition.

  As a result, it is possible to reduce an estimation error of the total intake gas amount Qg due to a change in the throttle opening area (throttle sectional area) due to the contamination of the throttle valve, an error of the throttle opening sensor, an error of the pressure sensor or the intake temperature sensor, and the like. .

  Furthermore, according to the estimation method of the EGR flow rate, even if the intake air amount sensor has an error, the estimated value of Qg has an error of almost the same ratio as the intake air amount sensor by calibration. As described above, the EGR rate is not affected by the error of the intake air amount sensor, and there is an advantage that the control error of the EGR rate is hardly caused by the error of the intake air amount sensor.

  As a result, the control accuracy of the EGR rate can be improved, and the amount of engine NOx emissions can be reduced.

  In step 240, a calibration end flag is set after completion of calibration (after calculation of the calibration coefficient Kc).

  The present invention relates to internal combustion engine control, and is applicable not only to automobiles but also to marine engines, construction machine engines, and semi-fixed generator engines.

6 Throttle valve (throttle part)
9 Combustion chamber 13 Low pressure EGR passage 14 EGR valve 15 Intake air amount sensor 18 Intake air temperature sensor 20 Pressure sensor

Claims (3)

Applied to an internal combustion engine having an EGR passage communicating an exhaust pipe and an intake pipe, an EGR valve attached to the EGR passage, and an air amount detecting means for detecting an intake air amount flowing into the intake pipe;
A flow rate adjustment valve or throttle portion provided in the intake pipe downstream of the merge portion of the intake pipe and the EGR passage, a pressure at the upstream position and a pressure at the downstream position of the flow rate adjustment valve or the throttle portion, or an upstream position and a downstream position Pressure detecting means for detecting a pressure difference between positions, means for detecting an intake air temperature in the intake pipe, means for calculating an opening area of the flow rate adjusting valve or the throttle portion, upstream of the flow rate adjusting valve or the throttle portion A gas flow rate calculating means for calculating a flow rate of the mixed gas passing through the flow rate adjusting valve or the throttle part from the intake air temperature, a pressure difference between the position pressure and the downstream position, the opening area, and the flow rate of the mixed gas. An EGR control device comprising means for controlling the opening of the EGR valve in accordance with the flow rate of EGR gas calculated by the difference in the intake air amount.   The said gas flow rate calculation means calibrates the flow rate calculation value of the said mixed gas from the intake air amount detection value by the said air amount detection means when the said EGR valve is closed. EGR control device.   The gas flow rate calculation means calibrates the calculated flow rate value of the mixed gas from the detected value of the intake air amount by the air amount detection means at a low load including idling or when the vehicle is decelerated while the EGR valve is closed. The EGR control device according to claim 1, wherein:

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