JP2006077659A - Irregularity diagnosing device for exhaust gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately determine regularity/irregularity of an exhaust gas sensor (catalyst downstream gas sensor) installed downstream of a catalyst for exhaust gas purification without deteriorating exhaust emission in a device performing irregularity diagnosis of a catalyst downstream side sensor. <P>SOLUTION: Air fuel ratio is temporally controlled to rich after recovery from fuel cut to promote reaction of occluded lean composition (occluded oxygen) of the catalyst and rich composition of exhaust gas and reduce lean composition occlusion quantity of the catalyst and a condition of the catalyst is quickly recovered to a near stoichiometric condition for reducing emission of lean composition such as NOx after recovery from fuel cut (after fuel injection restart). Response time between a predetermined voltage (in a embodiment 0.3 V → 0.5 V) of the catalyst downstream sensor from lean to rich is measured by using air fuel ratio rich control temporally executed after recovery from fuel cut and irregularity diagnosis of the catalyst downstream sensor based on the response time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an abnormality diagnosis device for an exhaust gas sensor that performs an abnormality diagnosis of an exhaust gas sensor installed on the downstream side of a catalyst for purifying exhaust gas.

In recent automobiles, for example, Patent Document 1 (Japanese Patent Laid-Open No. 4-16757), Patent Document 2 (Japanese Patent Laid-Open No. 8-177575), Patent Document 3 (Japanese Patent No. 3227912) and the like are used for exhaust gas purification. In addition to installing a catalyst in the exhaust pipe, an exhaust gas sensor such as an oxygen sensor and an air-fuel ratio sensor is installed upstream of the catalyst, and an exhaust gas sensor upstream of the catalyst (hereinafter referred to as “catalyst upstream side”). By controlling the air-fuel ratio (fuel injection amount) so that the air-fuel ratio of the exhaust gas detected by the “sensor” falls within the range of the purification window of the catalyst, the exhaust gas purification rate is increased. However, when the catalyst deteriorates, the exhaust gas purification rate decreases. Therefore, an exhaust gas sensor (hereinafter referred to as “catalyst downstream sensor”) is installed on the downstream side of the catalyst. There are some which judge the deterioration of the catalyst by monitoring the fuel ratio.
JP-A-4-16757 JP-A-8-177575 Japanese Patent No. 3227912

  In this system, if the downstream sensor of the catalyst deteriorates, the detection responsiveness is delayed. Therefore, there is a possibility that the catalyst that should originally be determined to be deteriorated is erroneously determined as not deteriorated. In order to avoid this erroneous determination, it is necessary to detect an abnormality in the catalyst downstream sensor early.

  Patent Documents 1 to 3 describe a technique for diagnosing abnormality by measuring the responsiveness of the upstream sensor of the catalyst by using the rich / lean switching of the air-fuel ratio by fuel cut during engine operation. This abnormality diagnosis technique for the catalyst upstream sensor cannot be applied to the abnormality diagnosis for the catalyst downstream sensor as it is. This is because, unlike the catalyst upstream sensor, the catalyst downstream sensor is affected by the state of the catalyst.

  In other words, the air-fuel ratio of the exhaust gas that passes through the catalyst changes considerably under the influence of the oxygen storage amount (lean component storage amount) of the catalyst, so the catalyst when the air-fuel ratio rich / lean on the upstream side of the catalyst is switched. The downstream air-fuel ratio behavior varies considerably depending on the oxygen storage amount of the catalyst. For this reason, even when the rich / lean switching of the air / fuel ratio on the upstream side of the catalyst does not appear as much as the output change of the downstream sensor of the catalyst, whether the response of the downstream sensor of the catalyst has deteriorated, Whether the air-fuel ratio is gradually changing cannot be distinguished, and there is a possibility that the normality / abnormality of the downstream sensor of the catalyst is erroneously determined.

  As a countermeasure, it is conceivable that the air-fuel ratio on the upstream side of the catalyst is greatly changed so that the change in the air-fuel ratio on the downstream side of the catalyst appears greatly during normal travel so as to diagnose the abnormality of the sensor on the downstream side of the catalyst. However, if the air-fuel ratio on the upstream side of the catalyst is greatly changed, the air-fuel ratio on the upstream side of the catalyst is changed beyond the purification capacity of the catalyst, and a problem that exhaust emission deteriorates occurs.

  The present invention has been made in consideration of such circumstances, and therefore the object of the present invention is to detect abnormalities in the exhaust gas sensor that can accurately determine normality / abnormality of the downstream sensor of the catalyst without deteriorating exhaust emission. It is to provide a diagnostic device.

  In order to achieve the above object, the invention according to claim 1 is characterized in that the response from the lean to rich of the downstream sensor of the catalyst when the air-fuel ratio rich control is executed in the lean state of the catalyst (response time, sensor The slope of the output change or the like) is measured by the responsiveness measuring means, and the abnormality diagnosis of the downstream sensor of the catalyst is performed by the abnormality diagnosing means based on this responsiveness measurement value. That is, if the catalyst is in a lean state, it can be estimated that the air-fuel ratio on the downstream side of the catalyst is also in a lean state. Therefore, when air-fuel ratio rich control is executed in this state, the downstream side of the catalyst By measuring the responsiveness of the sensor from lean to rich, it is possible to accurately measure the responsiveness from lean to rich of the downstream sensor of the catalyst in a state where the catalyst is almost constant. Based on this, it is possible to accurately determine whether the catalyst downstream sensor is normal or abnormal. Moreover, since the state of the catalyst before the responsiveness measurement is in a lean state, even if the air-fuel ratio on the upstream side of the catalyst is greatly changed to the rich side so that the air-fuel ratio on the downstream side of the catalyst is surely changed to the rich side. The rich component of the exhaust gas can be purified by the catalyst, and the exhaust emission does not deteriorate.

  In this case, as described in claim 2, when the fuel cut or the air-fuel ratio lean control continues for a predetermined period or longer, it is determined that the catalyst is in the lean state, and the air-fuel ratio rich control is executed. An abnormality diagnosis of the downstream sensor of the catalyst may be executed by measuring the response of the sensor from lean to rich. In this way, while the engine is running, abnormality diagnosis of the catalyst downstream side sensor can be performed using fuel cut or air-fuel ratio lean control, and the oxygen storage amount of the catalyst increased by fuel cut or air-fuel ratio lean control ( The lean component storage amount) can be reduced by the air-fuel ratio rich control, and the NOx emission amount can be reduced.

  Further, as described in claim 3, when it is estimated that the lean component storage amount of the catalyst is saturated, the air-fuel ratio rich control is executed to measure the response from lean to rich of the downstream sensor of the catalyst. Thus, it is preferable to perform abnormality diagnosis of the catalyst downstream side sensor. In this way, when the abnormality of the downstream sensor of the catalyst is diagnosed, the response of the downstream sensor of the catalyst downstream from lean to rich can be measured with the catalyst always in a certain lean state. It is possible to measure, and the abnormality diagnosis accuracy of the catalyst downstream sensor can be improved.

  Further, as described in claim 4, it is preferable to set the rich degree by the air-fuel ratio rich control so that the state of the catalyst changes to the rich side. As a result, the air-fuel ratio on the downstream side of the catalyst can be reliably changed from lean to rich, and the responsiveness measurement accuracy can be improved.

  In addition, if the exhaust gas flow rate is small, the catalyst state may not change to the rich side even if the air-fuel ratio on the upstream side of the catalyst is changed from lean to rich. There is a possibility that it cannot be accurately discriminated whether it is deteriorating or whether the air-fuel ratio on the downstream side of the catalyst is gradually changing.

  As a countermeasure against this, it is preferable to prohibit the measurement of the responsiveness of the catalyst downstream sensor when the exhaust gas flow rate is equal to or less than a predetermined amount. In this way, it is possible to prevent erroneous determination of normality / abnormality of the catalyst downstream side sensor when the exhaust gas flow rate is small.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment embodying the best mode for carrying out the invention will be described with reference to the drawings.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. On the downstream side of the air flow meter 14, a throttle valve 16 whose opening is adjusted by a motor 15 such as a DC motor, and a throttle opening sensor 17 for detecting the throttle opening are provided.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. The surge tank 18 is provided with an intake manifold 20 for introducing air into each cylinder of the engine 11, and a fuel injection valve 21 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 20 of each cylinder. Yes. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of each ignition plug 22.

  On the other hand, the exhaust pipe 23 (exhaust passage) of the engine 11 is provided with a catalyst 24 such as a three-way catalyst for purifying CO, HC, NOx, etc. in the exhaust gas. An exhaust gas sensor (hereinafter referred to as “catalyst upstream sensor”) 25 such as an air-fuel ratio sensor or oxygen sensor for detecting the air-fuel ratio or rich / lean is provided, and the exhaust gas rich / lean is detected downstream of the catalyst 24. An oxygen sensor (hereinafter referred to as “catalyst downstream sensor”) 26 is provided.

  A cooling water temperature sensor 27 that detects the cooling water temperature and a crank angle sensor 28 that outputs a pulse signal each time the crankshaft of the engine 11 rotates a predetermined crank angle are attached to the cylinder block of the engine 11. Based on the output signal of the crank angle sensor 28, the crank angle and the engine speed are detected.

  Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 29. The ECU 29 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium) to thereby determine the fuel injection amount of the fuel injection valve 21 according to the engine operating state. The ignition timing of the spark plug 22 is controlled.

  At that time, the ECU 29 executes an air-fuel ratio feedback control program (not shown) to control the air-fuel ratio (fuel injection amount) so that the detected air-fuel ratio of the catalyst upstream sensor 25 matches the target air-fuel ratio. Control is performed so that the air-fuel ratio on the upstream side of 24 falls within the purification window (near the stoichiometric) of the catalyst 24. At this time, the output of the catalyst downstream side sensor 26 is used to correct the target air-fuel ratio on the upstream side of the catalyst 24 or used for diagnosis of deterioration of the catalyst 24.

  Further, the ECU 29 executes a catalyst downstream side sensor abnormality diagnosis routine of FIG. 2 to be described later, thereby performing abnormality diagnosis of the catalyst downstream side sensor 26 using the fuel cut as follows. When a fuel cut is performed during engine operation, a large amount of oxygen (lean component) flows into the catalyst 24, so the oxygen storage amount (lean component storage amount) of the catalyst 24 increases and the state of the catalyst 24 becomes lean. It becomes the state of. For this reason, after returning from the fuel cut (after resuming fuel injection), the lean component of the exhaust gas cannot be sufficiently purified in the catalyst 24, and the amount of discharge of the lean component such as NOx tends to increase. Therefore, in this embodiment, in order to reduce the discharge amount of lean components such as NOx after returning from fuel cut (after resuming fuel injection), as shown in FIG. 3, after returning from fuel cut (after resuming fuel injection). The air-fuel ratio is temporarily controlled to be rich, and the reaction between the lean component of the catalyst 24 and the rich component of the exhaust gas is promoted to reduce the lean component storage amount of the catalyst 24, thereby promptly changing the state of the catalyst 24. It tries to recover near the stoiki.

  The abnormality diagnosis of the catalyst downstream side sensor 26 of the present embodiment uses the air-fuel ratio rich control that is temporarily executed after the fuel cut is restored (after the fuel injection is resumed), and the catalyst downstream side sensor 26 leans to rich. A response time between predetermined voltages (for example, 0.3 V → 0.5 V) is measured, and abnormality diagnosis of the catalyst downstream side sensor 26 is performed based on the response time.

  The processing contents of the catalyst downstream side sensor abnormality diagnosis routine of FIG. 2 for executing abnormality diagnosis of the catalyst downstream side sensor 26 of this embodiment will be described below. This routine is executed at a predetermined cycle (for example, a cycle of 5 ms) during engine operation, and serves as responsiveness measurement means and abnormality diagnosis means in the claims.

  When this routine is started, first, at step 101, it is determined whether or not the exhaust gas flow rate is greater than or equal to a predetermined amount based on whether or not the intake air amount is greater than or equal to a predetermined amount. If it is determined that the amount is less than the predetermined amount (the exhaust gas flow rate is less than the predetermined amount), this routine is terminated without executing the subsequent processing. If the exhaust gas flow rate is small, the state of the catalyst 24 does not change to the rich side even if the air-fuel ratio rich control is performed, so whether the response of the catalyst downstream sensor 26 is deteriorated or the downstream of the catalyst 24 is empty. This is because it cannot be accurately distinguished whether the fuel ratio is gradually changing.

  On the other hand, if it is determined in step 101 that the intake air amount is greater than or equal to a predetermined amount (exhaust gas flow rate is greater than or equal to a predetermined amount), the process proceeds to step 102 and the air-fuel ratio after returning from fuel cut (after restarting fuel injection) It is determined whether or not the lean component storage amount (oxygen storage amount) of the catalyst 24 has been sufficiently reduced depending on whether or not the rich control has been performed for a predetermined time or more. If “No” is determined, the subsequent processing is performed. This routine is terminated without executing it.

  Thereafter, the air-fuel ratio rich control after returning from the fuel cut (after resuming fuel injection) is performed for a predetermined time or more, and it is possible to estimate that the lean component storage amount (oxygen storage amount) of the catalyst 24 has been sufficiently reduced. In step 103, the output voltage of the catalyst downstream sensor 26 is compared with a lean threshold voltage, for example, 0.15V. If the output voltage of the catalyst downstream sensor 26 is less than 0.15V, the fuel It is determined that the output voltage of the catalyst downstream side sensor 26 has sufficiently changed to the lean side due to the cut, the process proceeds to step 104, the diagnosis precondition flag FX is set to “1”, and this routine is ended. If the output voltage of the catalyst downstream sensor 26 is not sufficiently changed to the lean side due to the fuel cut, the response time of the catalyst downstream sensor 26 cannot be accurately measured, so the diagnosis precondition flag FX is “0”. The response time measurement / abnormality diagnosis of the catalyst downstream side sensor 26 is prohibited.

  On the other hand, if it is determined in step 103 that the output voltage of the catalyst downstream side sensor 26 is 0.15 V or more, the process proceeds to step 105, in which it is determined whether or not the diagnosis precondition flag FX is set to “1”. If “No” is determined, it is determined that the diagnosis precondition is not satisfied, and this routine is terminated without executing the subsequent processing.

  On the other hand, if it is determined in step 105 that the diagnosis precondition flag FX is set to “1”, it is determined that the diagnosis precondition is satisfied, and the subsequent steps 106 to 108 are performed. Thus, the response time until the output voltage of the catalyst downstream side sensor 26 reaches a predetermined voltage on the rich side (for example, 0.5 V) from a predetermined voltage on the lean side (for example, 0.3 V) is counted by the time counter TC. That is, when the output voltage of the catalyst downstream sensor 26 becomes equal to or higher than a predetermined voltage (eg, 0.3 V) on the lean side, the time counter TC starts counting up, and the output voltage of the catalyst downstream sensor 26 is on the rich side. When a predetermined voltage (for example, 0.5 V) is reached, the count-up operation of the time counter TC is terminated, and the process proceeds to step 109 where the response time TC of the catalyst downstream sensor 26 measured by the time counter TC is used as a determination value. If the response time TC is equal to or greater than the determination value, the process proceeds to step 110 where the catalyst downstream sensor 26 determines that the abnormality (responsiveness deterioration), and in the next step 111, the abnormality information is stored in the backup RAM or the like of the ECU 29. The information is stored in a rewritable nonvolatile memory and a warning is displayed to inform the driver. On the other hand, if the response time TC is less than the determination value, the process proceeds to step 112 where it is determined that the catalyst downstream sensor 26 is normal. Thereafter, the process proceeds to step 113, the time counter TC and the diagnostic precondition flag FX are reset, and this routine is terminated.

  According to the present embodiment described above, the air-fuel ratio rich control that is temporarily executed to reduce NOx after returning from the fuel cut (after restarting the fuel injection) is used to make the richness of the catalyst downstream side sensor 26 from lean to rich. Since the response time between predetermined voltages (for example, 0.3 V → 0.5 V) is measured, the response time from the lean of the catalyst downstream sensor 26 to the rich in the state of the catalyst 24 is almost constant. Measurement can be performed with high accuracy, and normality / abnormality of the catalyst downstream sensor 26 can be determined with high accuracy based on the response time. In addition, since the state of the catalyst 24 before the response time measurement is lean, the air-fuel ratio on the upstream side of the catalyst 24 is greatly increased on the rich side so that the air-fuel ratio on the downstream side of the catalyst 24 is surely changed to the rich side. Even if it is changed, the rich component of the exhaust gas can be purified by the catalyst 24, and the exhaust emission does not deteriorate.

  In addition, in this embodiment, while the engine is running, abnormality diagnosis of the catalyst downstream side sensor 26 can be performed by using the fuel cut, and the oxygen storage amount (lean component storage amount) of the catalyst 24 increased by the fuel cut is emptied. It can be reduced by the fuel ratio rich control, and the NOx emission amount can be reduced.

  Furthermore, in this embodiment, only when the output voltage of the catalyst downstream sensor 26 has sufficiently changed to the lean side (for example, less than 0.15 V) due to the fuel cut (in other words, the lean component occlusion amount of the catalyst 24 due to the fuel cut). Since the response time of the catalyst downstream sensor 26 is measured only when it is estimated that the catalyst has become saturated), the response time of the catalyst downstream sensor 26 is accurately measured with the catalyst 24 always in a certain lean state. can do.

  In this embodiment, the response time until the output voltage of the catalyst downstream sensor 26 reaches the rich predetermined voltage (for example, 0.5 V) from the lean predetermined voltage (for example, 0.3 V) is measured. Therefore, the response time of the catalyst downstream sensor 26 until the state of the catalyst 24 changes to the rich side by the air-fuel ratio rich control can be measured, and the accuracy of the response time can be further improved.

  Further, considering that the exhaust gas flow rate is small, the state of the catalyst 24 may not change to the rich side even if the air-fuel ratio rich control is performed after the fuel cut is restored (after the fuel injection is resumed). In the embodiment, since the measurement of the response time is prohibited when the exhaust gas flow rate (intake air amount) is less than or equal to the predetermined amount, the normality / abnormality of the catalyst downstream sensor 26 is erroneously detected when the exhaust gas flow rate is small. Judgment can be prevented in advance.

  In this embodiment, the response time is measured as information indicating the response of the catalyst downstream sensor 26. However, the inclination of the output change of the catalyst downstream sensor 26 is measured, or the output change for a predetermined time is measured. The amount may be measured.

  In the present embodiment, the response time measurement / abnormality diagnosis of the catalyst downstream side sensor 26 is executed by using the fuel cut. However, when the air-fuel ratio lean control continues for a predetermined period or longer, the state of the catalyst 24 It may be determined that is in a lean state, air-fuel ratio rich control is executed, and response time measurement / abnormality diagnosis of the catalyst downstream side sensor 26 may be executed.

It is a schematic block diagram of the whole engine control system in one Example of this invention. It is a flowchart which shows the flow of a process of a catalyst downstream sensor abnormality diagnosis routine. It is a time chart for demonstrating the abnormality diagnosis method of the catalyst downstream sensor of an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe, 24 ... Catalyst, 25 ... Catalyst upstream sensor, 26 ... Catalyst downstream Sensor, 29 ... ECU (abnormality diagnosis means, response measurement means)

Claims (5)

In the exhaust gas sensor installed on the downstream side of the exhaust gas purification catalyst (hereinafter referred to as “catalyst downstream sensor”),
Responsiveness measuring means for measuring the response from lean to rich of the catalyst downstream side sensor when air-fuel ratio rich control is executed in a lean state of the catalyst;
An abnormality diagnosis device for an exhaust gas sensor, comprising: abnormality diagnosis means for performing abnormality diagnosis of the catalyst downstream side sensor based on a response from lean to rich of the catalyst downstream side sensor.   When the fuel cut or air-fuel ratio lean control continues for a predetermined period or longer, the responsiveness measuring means determines that the state of the catalyst is a lean state and executes the air-fuel ratio rich control, and the downstream side of the catalyst The abnormality diagnosis device for an exhaust gas sensor according to claim 1, wherein the response of the sensor from lean to rich is measured.   The responsiveness measuring means executes the air-fuel ratio rich control when it is estimated that the lean component storage amount of the catalyst is saturated, and determines the responsiveness of the catalyst downstream side sensor from lean to rich. The abnormality diagnosis device for an exhaust gas sensor according to claim 1, wherein the abnormality diagnosis device measures the abnormality.   The exhaust gas sensor abnormality according to any one of claims 1 to 3, wherein the responsiveness measuring means sets the rich degree by the air-fuel ratio rich control so that the state of the catalyst changes to the rich side. Diagnostic device.   The abnormality of the exhaust gas sensor according to any one of claims 1 to 4, wherein the responsiveness measuring means includes means for prohibiting the responsiveness measurement when an exhaust gas flow rate is a predetermined amount or less. Diagnostic device.

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