JP2012087754A - Failure detection device of egr system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect failure using an easy method, concerning an EGR system that distributes and introduces an EGR gas to a port of each cylinder.SOLUTION: A difference relative to a reference value K of an imbalance determination value L calculated when an EGR valve is opened is calculated with reference to the imbalance determination value L calculated when the EGR valve is closed. It is then determined as failure of the EGR system that the difference exceeds a predetermined threshold β. The imbalance determination value is a parameter expressing the magnitude of variation of the air-fuel ratio between the cylinders, and is calculated using a sensor signal related to an in-cylinder state of each cylinder, such as a signal of an in-cylinder pressure sensor.

Description

  The present invention relates to a failure detection apparatus for an EGR system that distributes and introduces EGR gas to each cylinder port through an EGR passage opened and closed by an EGR valve.

  There are two types of EGR systems that recirculate EGR gas, which is part of exhaust gas, and a type that introduces EGR gas into a surge tank and a type that introduces EGR gas into the intake port of each cylinder. From the viewpoint of controlling the EGR rate in the cylinder by the EGR valve and the maximum introduction amount of EGR gas, the latter intake port introduction type EGR system is desirable.

  However, an intake port introduction type EGR system tends to cause a difference between cylinders in the amount of EGR gas that can be introduced. Further, since the EGR gas is burnt gas, the EGR port may be blocked by the deposit. In that case, EGR gas hardly enters the cylinders closed by the deposit, and the EGR gas is largely distributed to other cylinders. Due to these factors, in the EGR system of the intake port introduction type, there is a possibility that a difference between cylinders may occur in the intake air amount of each cylinder.

  The difference between the cylinders in the intake air amount is not preferable because it causes a variation in the air-fuel ratio between the cylinders and reduces the emission performance of the internal combustion engine. For this reason, in the EGR system with the intake port introduction type, it is possible to detect the distribution variation of the EGR gas, which is the cause of the difference in the intake air amount between cylinders, as a failure of the system so that necessary measures such as maintenance can be performed immediately. It is requested to be.

  As a conventional method for detecting the distribution variation of EGR gas, a method disclosed in Japanese Patent Application Laid-Open No. 2009-108713 is known. According to the method disclosed in this publication, the difference in the injection amount between the cylinders is made zero by the injection pressure sensor built in the direct injection injector. Then, EGR gas is introduced in this state, and at that time, the EGR gas distribution variation is detected from the difference between the illustrated torques calculated from the in-cylinder pressure.

JP 2009-108713 A

  However, even when EGR gas is not introduced, there is a slight difference between the cylinders in the intake air amount of each cylinder. In particular, when the internal combustion engine is operated in a low rotation and low load range, the difference in the intake air amount between the cylinders is significant. The distribution variation of EGR gas detected by the method disclosed in the above publication includes the influence of the difference in intake air amount between cylinders when the EGR valve is closed, that is, the intake air amount due to causes other than the distribution variation of EGR gas. The effect of the difference between cylinders is also included. For this reason, the method disclosed in the above publication cannot always accurately detect a failure of the EGR system.

  The present invention has been made in view of the above-described problems, and relates to an EGR system that distributes and introduces EGR gas for each port of each cylinder, and an object thereof is to enable accurate detection of the failure. .

  In order to achieve the above object, a first invention is a failure detection apparatus for an EGR system that distributes and introduces EGR gas to each cylinder port through an EGR passage opened and closed by an EGR valve. An imbalance determination value calculating means for calculating an imbalance determination value which is a parameter indicating the magnitude of variation in the air-fuel ratio between cylinders using a sensor signal related to the in-cylinder state; and when the EGR valve is closed The failure of the EGR system is calculated by calculating the difference between the imbalance determination value calculated in the above and the imbalance determination value calculated when the EGR valve is opened and the difference exceeds a predetermined threshold value. Failure determination means for determining.

  According to a second aspect of the present invention, in the first aspect, the failure determination unit is configured on the condition that an imbalance determination value calculated when the EGR valve is closed is not more than a predetermined allowable limit value. It is characterized by executing failure determination of the EGR system.

  According to the first invention, since the failure of the EGR system is determined by the difference between the imbalance determination values when the EGR valve is closed and when the EGR valve is open, the intake air amount due to causes other than the distribution variation of the EGR gas It is possible to accurately detect a failure of the EGR system by eliminating the influence of the difference between the cylinders on the determination result.

  According to the second invention, in the situation where the difference between the cylinders of the intake air amount due to causes other than the distribution variation of the EGR gas exceeds the allowable limit, erroneous detection of the failure is prevented by refraining from determining the failure of the EGR system. Can do.

1 is a schematic diagram showing a configuration of an internal combustion engine system according to an embodiment of the present invention. It is a flowchart which shows the routine for the failure detection of the EGR system performed by ECU in embodiment of this invention. It is a flowchart which shows the routine for calculation of the A / F imbalance judgment value performed by ECU in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing the configuration of the internal combustion engine system of the present embodiment. The internal combustion engine system of the present embodiment includes an internal combustion engine 2, an EGR system 10 that introduces EGR gas into the internal combustion engine 2, and an ECU 20 that comprehensively controls the operation of the internal combustion engine system. The internal combustion engine 2 of the present embodiment is a spark ignition type 4-cycle reciprocating engine. Further, the multi-cylinder internal combustion engine having a plurality of cylinders 4 is provided with an in-cylinder pressure sensor 22 attached to each cylinder 4. The EGR system 10 includes an EGR passage 12 that branches from the exhaust passage 6 of the internal combustion engine 2, an EGR valve 14 that is disposed in the EGR passage 12, and a plurality of EGR passages 16 in which the EGR passage 12 is branched for each cylinder. Yes. The EGR passage 16 is connected to the intake port 8 of each cylinder.

  In the internal combustion engine system of the present embodiment, the ECU 20 functions as a failure detection device that detects a failure of the EGR system 10. Here, the failure of the EGR system 10 means that the amount of EGR gas introduced from each EGR passage 16 to the intake port 8 of each cylinder has an unacceptable variation among the cylinders. When the ECU 20 functions as a failure detection device that detects such a failure, the ECU 20 executes a routine shown in the flowchart of FIG.

  According to the routine shown in FIG. 2, it is first determined whether or not the EGR valve 14 is closed (step S2). If the EGR valve 14 is open, the process proceeds to No route, and this routine ends. However, this routine is repeatedly executed during operation of the internal combustion engine 2. If the EGR valve 14 is closed at the determination timing of step S2, the process proceeds to Yes route and the process of step S4 is performed.

  In step S4, the reference value K for the A / F imbalance determination value is calculated. The A / F imbalance determination value is a parameter indicating the degree of variation in the air-fuel ratio between cylinders, and a sensor value indicating the in-cylinder state of each cylinder can be used for the calculation. Sensor values that can be used to calculate the imbalance determination value include the output value of the in-cylinder pressure sensor and the output value of the air-fuel ratio sensor. Moreover, the calculation method of the imbalance determination value using a certain sensor value is not one but various calculation methods are proposed. In the present invention, there is no limitation on the sensor value to be used and the method for calculating the imbalance determination value using the sensor value. The calculation method of the A / F imbalance determination value described below is an example of a calculation method that can be used in the present invention.

  In the present embodiment, the ECU 20 calculates the A / F imbalance determination value according to the routine shown in the flowchart of FIG. According to the routine shown in FIG. 3, the ignition timing unified control is first executed (step S102). In the unified ignition timing control, the ignition timing control for each cylinder is stopped, and the ignition timing of each cylinder is made the same. For example, the ignition timing of the cylinder in which the air-fuel ratio is relatively lean among the cylinders is selected as the reference ignition timing, and the ignition timings of the other cylinders are adjusted to the reference ignition timing.

  In the next step S104, the signal of the in-cylinder pressure sensor 22 of each cylinder is AD-converted in synchronization with the crank angle, and the combustion ratio MFB is calculated using the sensor signal. In the next step S106, the maximum rate of change CS when the combustion rate MFB changes according to the crank angle is determined based on the data indicating the relationship between the combustion rate MFB and the crank angle in each cylinder obtained in step S104. Calculated every time. In step S108, the maximum rate of change CS of each cylinder calculated in step S106 is compared, and the cylinder having the largest deviation of the maximum rate of change CS generated with respect to other cylinders is specified among all the cylinders.

  Finally, in step S110, the cylinder specified in step S108 is an abnormal cylinder and the other cylinders are normal cylinders, and the ratio between the maximum change rate CS of the abnormal cylinder and the average value of the maximum change rate CS of the normal cylinder is calculated. Is done. This ratio is adopted as the A / F imbalance determination value.

  Returning to the routine shown in FIG. 2 again, the explanation about the failure detection of the EGR system 10 will be continued. In step S4, in the state where the EGR valve 14 is closed, the A / F imbalance determination value is calculated according to the calculation procedure described above. The A / F imbalance determination value is adopted as the reference value K and held in the memory of the ECU 20. In addition, there is no limitation in the operating conditions at the time of performing the process of step S4. For example, it may be a low rotation and low load range where the difference in the intake air amount between the cylinders becomes significant.

  In step S6, it is determined whether the reference value K of the A / F imbalance determination value calculated in step S4 is less than a predetermined threshold value α. The A / F imbalance determination value is a parameter indicating that the greater the value, the greater the variation in the air-fuel ratio between the cylinders. The threshold value α is a value corresponding to the limit of a range in which the variation in the air-fuel ratio between the cylinders is allowable, that is, an allowable limit value. Therefore, when the reference value K is equal to or greater than the threshold value α, it is determined that the variation in the air-fuel ratio among the cylinders is abnormal, and the A / F imbalance abnormality flag is turned ON (step S8). In response to the A / F imbalance abnormality flag being turned ON, a warning lamp (MIL) is turned on to notify the driver of the occurrence of abnormality (step S18).

  As described above, when the air-fuel ratio varies between the cylinders in a state where the EGR valve 14 is closed, the process for notifying that is preferentially executed, and failure detection of the EGR system 10 is performed. The processing for is interrupted there. This is because the difference between the cylinders of the intake air amount due to causes other than the dispersion of EGR gas distribution is large, which may cause noise and affect the failure determination of the EGR system. According to this routine, in the situation where the reference value K is greater than or equal to the threshold value α, the failure determination of the EGR system 10 is countered, thereby preventing erroneous detection of failure.

  On the other hand, when the reference value K is less than the threshold value α, the process for detecting the failure of the EGR system 10 is continued. First, in step S10, the EGR valve 14 is opened and EGR gas is introduced into each cylinder. Then, after the introduction state of EGR gas to each cylinder becomes steady, the A / F imbalance determination value is calculated according to the above-described calculation procedure (step S12). In addition, it is preferable that the driving | running conditions at the time of performing the process of step S12 are the same conditions as the driving | running conditions at the time of performing the process of step S4, or a close condition.

  In the next step S14, a difference between the A / F imbalance determination value L calculated in step S12 and the reference value K is calculated, and it is determined whether the difference exceeds a predetermined threshold value β. The difference between the A / F imbalance determination value L and the reference value K when the EGR valve 14 is opened indicates the magnitude of the difference between the cylinders in the intake air amount due to EGR gas distribution variation. Therefore, the greater this difference, the higher the probability that a failure has occurred in the EGR system 10. According to this routine, if the difference between the A / F imbalance determination value L and the reference value K is equal to or less than the threshold value β, it is determined that the EGR system 10 is normal.

  According to this routine, when the difference between the A / F imbalance determination value L and the reference value K exceeds the threshold value β, it is determined that a failure has occurred in the EGR system 10. In this case, the EGR system abnormality flag is turned on (step S16), and when the EGR system abnormality flag is turned on, a warning lamp (MIL) is turned on to notify the driver of the occurrence of the abnormality. (Step S18).

  According to the failure detection of the EGR system 10 by the above-described method, the failure of the EGR system 10 due to the difference in the A / F imbalance determination value when the EGR valve 14 is closed and when the EGR valve 14 is opened. Therefore, it is possible to accurately detect the failure of the EGR system 10 by eliminating the influence of the difference between the intake air amounts due to causes other than the dispersion of the EGR gas on the determination result.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the present invention is applied to the EGR system of a spark ignition engine, but the present invention is also applicable to an EGR system of a diesel engine. In that case, instead of the above-described method for calculating the imbalance determination value, a method for calculating the imbalance determination value suitable for the diesel engine may be employed.

2 Internal combustion engine 4 Cylinder 6 Exhaust passage 8 Intake port 10 EGR system 12 EGR passage 14 EGR valve 16 EGR passage 20 ECU
22 In-cylinder pressure sensor

Claims (2)

A failure detection device for an EGR system that distributes and introduces EGR gas to each cylinder port through an EGR passage opened and closed by an EGR valve,
An imbalance determination value calculating means for calculating an imbalance determination value, which is a parameter indicating the magnitude of variation in the air-fuel ratio between cylinders, using a sensor signal related to the in-cylinder state of each cylinder;
The difference between the imbalance determination value calculated when the EGR valve is closed and the imbalance determination value calculated when the EGR valve is opened is calculated, and the difference exceeds a predetermined threshold value. Failure determination means for determining that the EGR system has exceeded the failure,
A failure detection apparatus for an EGR system, comprising:   The failure determination means performs the failure determination of the EGR system on the condition that an imbalance determination value calculated when the EGR valve is closed is less than a predetermined allowable limit value. The failure detection apparatus for an EGR system according to claim 1.

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