JP2006090223A - Exhaust gas reflux diagnostic device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the diagnosis whether an exhaust gas reflux device normally works without the operation to deteriarate combustion for a diagnosis during the engine operation in a direct injection internal combustion engine. <P>SOLUTION: An actual ignition delay period is detected based on a valve opening period of a fuel injection nozzle and a fuel pressure, and this is compared with a standard ignition delay period when an exhaust gas reflux amount is normally controlled. When the actual ignition delay period changes beyond a predetermined allowable range for the standard ignition delay period, the exhaust gas reflux device is diagnosed to be abnormal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine, and more particularly to a device for diagnosing the failure.

  Exhaust gas recirculation (EGR) is effective as a technique for suppressing the generation of NOx during combustion of an internal combustion engine. On the other hand, exhaust gas recirculation directly affects flammability. Therefore, when the exhaust gas recirculation device or its control system fails, not only exhaust emission but also various performances such as noise, vibration, and torque are affected. Therefore, it is necessary to accurately diagnose whether or not the exhaust gas recirculation device operates normally and appropriate exhaust gas recirculation is performed.

As such a failure diagnosis apparatus for an EGR system, a device as disclosed in Patent Document 1 or Patent Document 2 is known. The technique disclosed in Patent Document 1 mainly diagnoses a mechanical failure of the EGR valve by forcibly opening and closing the EGR valve at the time of diagnosis and monitoring the change in the actual EGR amount. The technique disclosed in Patent Document 2 performs knock control by operating the ignition timing during diagnosis, and diagnoses whether or not a target exhaust gas recirculation amount is obtained from the ignition timing and the occurrence of knocking. It is a thing.
JP-A-8-31467 Japanese Patent Laid-Open No. 7-139437

  These conventional techniques have a problem that the output torque of the internal combustion engine fluctuates or combustion noise increases with the diagnosis of EGR. That is, in Patent Document 1, if the EGR valve normally opens and closes at the time of diagnosis, the exhaust gas recirculation amount and the combustion state fluctuate accordingly. In Cited Document 2, the exhaust gas recirculation amount varies with the operation of the ignition timing. Nevertheless, there is a risk that the combustion will deteriorate directly.

  In the present invention, on the premise of a direct injection internal combustion engine equipped with an exhaust gas recirculation device, a means for detecting the valve opening timing of the fuel injection nozzle and a means for detecting the combustion pressure are provided, from the valve opening timing and the combustion pressure. Means for calculating an actual ignition delay period and means for determining an abnormality of the exhaust gas return device based on a comparison between a reference ignition delay period determined according to the engine operating state and the actual ignition delay period are provided.

  The abnormality determination means diagnoses that the exhaust gas recirculation device is abnormal when the actual ignition delay period changes beyond a predetermined allowable fluctuation range with respect to the reference ignition delay period.

  According to the present invention, since it is possible to detect that the exhaust gas recirculation amount fluctuates abnormally from the relationship between the valve opening timing of the fuel injection nozzle and the fluctuation of the combustion pressure, an operation that causes deterioration in combustion is performed for diagnosis. This is unnecessary, and it is possible to accurately diagnose whether or not the exhaust gas recirculation device is operating normally during operation of the internal combustion engine.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a spark ignition type direct injection internal combustion engine to which the present invention is applicable. In the figure, 1 is an internal combustion engine body, 2 is an intake passage, and 3 is an exhaust passage. An air cleaner 4, an air flow meter 5, a compressor 6 c of an exhaust turbocharger 6, an intercooler 7, and a throttle valve 8 are interposed in the intake passage 2 from the upstream side. A turbine 6t of an exhaust turbocharger 6 and a catalytic converter 9 are interposed in the exhaust passage 3 from the upstream side.

  A portion of the exhaust passage 3 upstream of the turbine 6t and an intake collector portion 10 downstream of the throttle valve 8 of the intake passage 2 are connected by an EGR passage 11, and an exhaust gas recirculation amount (or EGR rate) is in the middle thereof. An EGR control valve 12 for controlling the operation is interposed.

  The opening degree of the EGR control valve 12, that is, the exhaust gas recirculation amount is controlled based on a control signal from the control unit 13. The control unit 13 is configured as a microcomputer including a CPU and its peripheral devices, and controls the fuel injection timing, the fuel injection amount, the ignition timing, and the opening degree of the EGR control valve 12 according to the engine operating state. In this case, the operating state includes a rotational speed signal from a crank angle sensor 14 provided in the engine body 1 and an intake air amount signal output from the air flow meter 5 as a load representative signal. The control unit 13 also controls the opening degree of the throttle valve 8 as necessary when exhaust gas recirculation is performed. In this case, an electronically controlled throttle valve device is applied as the throttle valve 8.

  In relation to the present invention, the control unit 13 calculates the actual ignition delay period from the means for detecting the valve opening timing of the fuel injection nozzle 16, the means for detecting the combustion pressure, and the valve opening start timing and the combustion pressure. And a function as means for determining an abnormality of the exhaust gas recirculation system based on a comparison between an actual ignition delay period and a reference ignition delay period (described later).

  Regarding the valve opening timing of the fuel injection nozzle 16, the timing at which the nozzle needle valve lifts is directly detected by a pressure sensor or the like, or a fuel injection signal calculated for fuel injection control (hereinafter referred to as "indicated fuel injection amount"). Can be used instead of detection of the actual valve opening timing. In this embodiment, a knock sensor 17 is provided to detect the combustion pressure. As the knock sensor 17, a spark ignition type internal combustion engine that is provided for ignition timing control can be used as it is.

  In FIG. 1, 18 is a water temperature sensor for detecting engine cooling water temperature, 19 is an intake air temperature sensor for detecting intake air temperature, and 20 is an atmospheric pressure sensor for detecting atmospheric pressure. It corresponds to a water temperature detecting means, an intake air temperature detecting means, and an atmospheric pressure detecting means. The significance of these will be described in the following sections related to control operations.

  FIG. 2 is a flowchart showing a main routine for EGR diagnosis executed by the controller 13. This routine is repeatedly executed at regular intervals together with other subroutines described later. The contents will be described below in order. In the following figures and description, the numbers indicated with the symbol S represent processing step numbers.

  In FIG. 2, it is first determined in S1 whether or not the current operating state of the internal combustion engine is a diagnosable condition. Details of the diagnosis permission condition will be described later. When it is a diagnosis permission condition, the process proceeds to a diagnosis process of S2 or less, and when it is not a diagnosis permission condition, the process of S2 or less is bypassed and the current routine is terminated.

  In S2, a reference ignition delay period DTb is calculated. The reference ignition delay period DTb is an ignition delay period when the EGR device operates normally and the EGR rate is controlled to the target value, and has a value corresponding to the operating state (rotation speed and fuel injection amount) in advance. It is obtained by searching for what has been experimentally obtained and mapped on the storage device of the controller 13 so as to be obtained. Details of the reference ignition delay period DTb will be described later.

  In S3, an actual ignition delay period DTa is obtained. The actual ignition delay period DTa is the time until the combustion pressure is detected by the knock sensor 17 on the basis of the valve opening start timing of the fuel injection nozzle 16 as described above. Details regarding the calculation of the actual ignition delay period DTa will be described later.

  In S4, for abnormality determination, a threshold value DTt is calculated which gives an allowable fluctuation range of the actual ignition delay period DTa in both positive and negative directions with the reference ignition delay period DTb as the center. Details thereof will be described later.

  In S5, the difference ΔDT is calculated by comparing the reference ignition delay period DTb with the actual ignition delay period DTa. ΔDT increases as the flow rate of the recirculated exhaust gas in the EGR control valve 12 and the EGR passage 11 deviates from the target value due to adhesion or failure of deposits included in the exhaust gas.

  In S6, it is determined whether or not the difference ΔDT in the ignition delay period has exceeded the abnormality determination threshold value DTt. If ΔDT exceeds the threshold value DTt in either the positive or negative direction, it is determined that the EGR device is abnormal, and if it does not exceed, the EGR device is determined to be normal (S7).

  FIG. 3 shows the relationship between the EGR rate and the ignition delay period, which are the criteria for the determination. As shown in the figure, as the EGR rate increases, the oxygen concentration in the air sucked by the engine decreases, so the ignition delay period becomes longer, and as the EGR rate decreases, the oxygen concentration in the intake air increases. The delay period is shortened. Therefore, it is possible to determine abnormality of the EGR device by setting a predetermined allowable fluctuation range based on the threshold for the ignition delay period.

  FIG. 4 shows details of S1 (diagnosis permission condition determination processing) in the flowchart of FIG. In S1 of FIG. 4, the engine coolant temperature is read. In S2, it is determined whether or not the water temperature has exceeded a specified value. If it exceeds, the process proceeds to S3, and if the water temperature is lower than the specified value, S3 or less. Bypassing and disallowing diagnosis (S10). The reason why the diagnosis is not performed when the cooling water temperature is below a predetermined value in this manner is that the compression temperature is low and the ignition delay period is not likely to be stably reproduced until the warm-up is completed. The accuracy of the diagnosis can be improved by avoiding the diagnosis under such conditions.

  In S3, the intake air temperature is read. In S4, it is determined whether or not the intake air temperature is within a specified range. If the intake air temperature is within the specified range, the process proceeds to S5. The reason why the diagnosis is not performed when the intake air temperature is outside the specified range is that the compression temperature changes due to the intake air temperature and the ignition delay period is affected. The accuracy of the diagnosis can be improved by avoiding the diagnosis in the above.

  In S5, the engine speed is read, and in S6, the time change rate of the speed is calculated. Next, in S7, it is determined whether or not the time change rate of the engine speed is within a specified range. If it is within the specified range, the process proceeds to S8, and if it is out of the specified range, the diagnosis is not permitted. In this way, it is determined whether or not the engine is in a steady state at the rotational speed, and diagnosis is permitted only in the steady state, thereby improving the accuracy of diagnosis.

  In S8, a time change rate of the commanded fuel injection amount is calculated. In S9, it is determined whether or not the time change rate of the commanded fuel injection amount is within a specified range. If so, diagnosis is not permitted (S10). In this way, it is determined whether the engine is in a steady state at the load, and diagnosis is allowed only when the load fluctuation is small, thereby improving the accuracy of diagnosis.

  FIG. 5 shows the details of the process of S2 (reference ignition delay period DTb calculation) in the flowchart of FIG. In FIG. 5, the current engine speed is read in S1, and the commanded fuel injection amount is read in S2. The command fuel injection amount is a fuel injection amount command value calculated in the control unit 13 as described above.

  In S3, the reference ignition delay period DTb corresponding to the read rotation speed and the commanded fuel injection amount is read out from a map (see FIG. 6) that has been experimentally formed in advance so as to give the aforementioned reference ignition delay period.

  The engine coolant temperature is read from the water temperature sensor 18 in S4, the atmospheric pressure is read from the atmospheric pressure sensor 20 in S5, and the intake air temperature is read from the intake air temperature sensor 19 in S6.

  In S7, the ignition delay period calculated in S3 is corrected with the coolant temperature. This is performed by multiplying the ignition delay period correction coefficient with respect to the cooling water temperature as shown in FIG. The ignition delay period correction coefficient for the cooling water temperature is corrected so that the ignition delay period becomes shorter as the cooling water temperature becomes higher, and the reference ignition delay period is corrected in a decreasing direction as the cooling water temperature increases. ing.

  In S8, the ignition delay period calculated in S7 is corrected with atmospheric pressure. This is performed by multiplying the ignition delay period correction coefficient for atmospheric pressure as shown in FIG. The ignition delay correction coefficient for the atmospheric pressure corresponds to the fact that the ignition delay period becomes longer as the atmospheric pressure decreases and the oxygen density decreases, and the reference ignition delay period is corrected to increase as the atmospheric pressure decreases. Like to do.

  In S9, the ignition delay period calculated in S8 is corrected with the intake air temperature. This is performed by multiplying the ignition delay period correction coefficient with respect to the intake air temperature as shown in FIG. The ignition delay period correction coefficient with respect to the intake air temperature is corrected so that the reference ignition delay period is corrected in an increasing direction as the intake air temperature decreases, corresponding to the fact that the ignition delay period becomes longer as the intake air temperature decreases. I have to.

  FIG. 10 shows details of the process of S3 (actual ignition delay period DTa calculation) in the flowchart of FIG. In FIG. 10, S1 determines the start of the fuel injection valve opening (nozzle needle valve rise), and shifts to the process of S2 or less at the valve opening start time, and performs the following process at the valve opening start time. This is a condition determination for detouring and terminating the current routine.

  In S2, a timer for measuring the ignition delay period is started. In S3, it is determined whether or not the knock sensor 17 has detected combustion vibration. When the combustion vibration is detected, a determination is made in S4, and if not detected, the condition is returned to immediately after S2.

  In S4, it is determined that combustion has started, and the timer count is stopped. The reading value of the timer at this time is defined as an actual ignition delay period DTa.

  FIG. 11 is an explanatory diagram of the actual ignition delay period, and FIG. 12 is a schematic diagram of the knock sensor output waveform. The knock sensor detection waveform is shaped into a rectangular wave through a filter and amplification processing.

  FIG. 13 shows details of the process of S4 (threshold DTt calculation process) in the flowchart of FIG. The calculation procedure of the threshold value DTt is the same as the calculation of the reference ignition delay period DTb in S2 of FIG. Here, the threshold value DTt can be changed according to the engine speed and the commanded fuel injection amount (engine load). This is because, for example, the NOx emission sharing rate when the vehicle equipped with the internal combustion engine according to the present embodiment travels in a predetermined mode depends on the engine speed and the commanded fuel injection amount. In the region where the influence on the emission is large, the threshold DTt is reduced to narrow the allowable fluctuation range of the ignition delay period. On the other hand, in the region where the influence on the NOx emission due to the change in the EGR rate is small, the threshold DTt is increased. This is to widen the allowable fluctuation range.

  Moreover, since the NOx emission sharing ratio varies depending on the engine model and the vehicle type, it is preferable that the setting of the threshold value DTt can be changed. FIG. 14 shows an example of setting the EGR variation limit. Note that the threshold value DTt is previously determined by experiment and mapped.

  Although the said embodiment showed the example of application of this invention to a spark ignition internal combustion engine, it is not restricted to this, This invention is applicable also to a compression ignition engine.

1 is a schematic configuration diagram showing an example of an internal combustion engine to which the present invention is applicable. The 1st flowchart which shows the control routine of embodiment of this invention. The characteristic line figure which shows the determination area of the relationship between an ignition delay period and an EGR rate, and an ignition delay period. The 2nd flowchart which shows the control routine of embodiment of this invention. The 3rd flowchart which shows the control routine of embodiment of this invention. Explanatory drawing of the map which gives a reference | standard ignition delay period from an engine speed and fuel injection quantity. Explanatory drawing of the map which gives the correction coefficient of the reference | standard ignition delay period by engine cooling water temperature. Explanatory drawing of the map which gives the correction coefficient of the reference | standard ignition delay period by atmospheric pressure. Explanatory drawing of the map which gives the correction coefficient of the reference | standard ignition delay period by intake air temperature. The 4th flowchart which shows the control routine of embodiment of this invention. The timing diagram showing the detection method of the ignition delay period. The timing diagram showing the waveform shaping state of a knock sensor signal. The 5th flowchart which shows the control routine of embodiment of this invention. Explanatory drawing of the map which gives the variation limit of an EGR rate from an engine speed and fuel injection amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine main body 2 Intake passage 3 Exhaust passage 5 Air flow meter (intake air amount detection means)
11 EGR passage 12 EGR control valve 13 Control unit 14 Crank angle sensor (rotation speed detecting means)
16 Fuel injection nozzle 17 Knock sensor (combustion pressure detection means)
18 Water temperature sensor (cooling water temperature detection means)
19 Intake air temperature sensor (intake air temperature detection means)
20 Atmospheric pressure sensor (Atmospheric pressure detection means)

Claims (7)

In a direct injection internal combustion engine equipped with an exhaust gas recirculation device,
Means for detecting the opening timing of the fuel injection nozzle;
Means for detecting the combustion pressure;
Means for calculating an actual ignition delay period from the valve opening timing and the combustion pressure;
Based on a comparison between the reference ignition delay period determined according to the engine operating state and the actual ignition delay period, exhaust is performed when the actual ignition delay period changes beyond a predetermined allowable fluctuation range with respect to the reference ignition delay period. Means for determining that the reflux device is abnormal;
An exhaust gas recirculation diagnosis apparatus for an internal combustion engine, comprising:   The abnormality determination means includes means for detecting an engine speed and a fuel injection amount, and is configured to set the reference ignition delay period based on the engine speed and the fuel injection amount. The exhaust gas recirculation diagnosis device for an internal combustion engine according to claim.   2. The exhaust gas recirculation diagnosis for an internal combustion engine according to claim 1, wherein the abnormality determination means includes means for detecting a coolant temperature of the internal combustion engine, and corrects the reference ignition delay period in a decreasing direction as the engine coolant temperature increases. apparatus.   The exhaust gas recirculation diagnosis apparatus for an internal combustion engine according to claim 1, wherein the abnormality determination means includes means for detecting atmospheric pressure, and corrects the reference ignition delay period in a decreasing direction as the atmospheric pressure decreases.   2. The exhaust gas recirculation diagnosis apparatus for an internal combustion engine according to claim 1, wherein the abnormality determination means includes means for detecting an intake air temperature of the internal combustion engine, and corrects the ignition delay period in a decreasing direction as the intake air temperature decreases.   The exhaust gas recirculation diagnosis apparatus for an internal combustion engine according to claim 1, wherein the combustion pressure detection means is a knock sensor. The abnormality determining means includes
Means for detecting the cooling water temperature, intake air temperature, rotation speed, fuel injection amount of the internal combustion engine,
The cooling water temperature is within a predetermined allowable cooling water temperature range;
And the intake air temperature is within a predetermined allowable intake air temperature range,
And the rate of time change of the rotational speed is within a predetermined allowable range,
And the time change rate of the fuel injection amount is within a predetermined allowable range,
The exhaust gas recirculation diagnosis apparatus for an internal combustion engine according to claim 1, wherein diagnosis of the exhaust gas recirculation apparatus is executed on the condition of

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