JP4365830B2 - Air-fuel ratio sensor diagnostic device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio sensor diagnostic apparatus for an internal combustion engine, and more particularly to an air-fuel ratio sensor diagnostic apparatus for an internal combustion engine that diagnoses whether or not an air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine has deteriorated.

  In order to purify unburned hydrocarbons HC, carbon monoxide CO, and nitrogen oxides NOx, which are harmful components in exhaust gas discharged from an internal combustion engine, a three-way catalyst has conventionally been installed in the middle of the exhaust passage. ing. The three-way catalyst purifies harmful components most efficiently when the inflowing exhaust gas is in the vicinity of the stoichiometric air-fuel ratio.

  For this reason, an air-fuel ratio sensor for detecting the air-fuel ratio (oxygen concentration) in the exhaust gas is arranged in front of the three-way catalyst, and the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is controlled using the output of the air-fuel ratio sensor. Has been.

  Therefore, when the air-fuel ratio sensor is deteriorated or damaged due to some reason, the control accuracy of the air-fuel ratio is deteriorated, and the purification efficiency of the catalyst is lowered. For this reason, methods and devices for detecting changes in the characteristics of the air-fuel ratio sensor have been proposed.

  As an example of the technology for detecting the characteristic change of the air-fuel ratio sensor, the state of detection value change of the wide-area air-fuel ratio sensor at the time of target air-fuel ratio switching is detected, and the response deterioration of the wide-area air-fuel ratio sensor is detected from this detection result (For example, patent document 1), there exist what detects a gain characteristic and a response characteristic from the frequency response characteristic of the detection value of an air fuel ratio sensor, and detects a gain degradation and a response degradation (for example, patent document 2).

JP-A-10-169493 JP 2005-194891 A

  However, the wide-band air-fuel ratio sensor deterioration pattern includes not only response deterioration with a delayed response time but also gain deterioration in which the response itself increases or decreases. Therefore, the diagnosis method that detects only response deterioration detects gain deterioration. Cannot be performed, and there is a problem in diagnostic accuracy.

In the case where the gain characteristic and response characteristic are detected from the frequency response characteristic of the detection value of the air-fuel ratio sensor, and gain deterioration and response deterioration are detected, the air-fuel ratio must be forcibly oscillated to detect the response characteristic. In the meantime, influences such as deterioration of operability or exhaust deterioration may occur.

  The present invention has been made in view of the problem to be solved, and the object of the present invention is to detect the gain deterioration and the response deterioration of the air-fuel ratio sensor without deteriorating exhaust and operability. An object of the present invention is to provide an air-fuel ratio sensor diagnostic apparatus and diagnostic method for an internal combustion engine.

  In order to achieve the above object, an air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention is an air-fuel ratio sensor diagnostic apparatus for determining deterioration of a linear air-fuel ratio sensor provided in an exhaust passage of an internal combustion engine. Response time detecting means for detecting a response time that is a required time from when the fuel ratio is changed until the detected value of the linear air-fuel ratio sensor reaches a predetermined value, and based on the response time detected by the response time detecting means Deterioration index calculating means for calculating a deterioration index of the linear air-fuel ratio sensor, and deterioration determining means for determining deterioration of the linear air-fuel ratio sensor based on the deterioration index calculated by the deterioration index calculating means, Response time detection means, first response time detection means for detecting a first response time until the detection value of the linear air-fuel ratio sensor reaches a predetermined first predetermined value; Second response time detecting means for detecting a second response time until the detected value of the linear air-fuel ratio sensor reaches a second predetermined value greater than the first predetermined value, and the deterioration index calculating means includes at least First deterioration index calculating means for calculating a first deterioration index based on the first response time; and second deterioration index calculating means for calculating a second deterioration index based on at least the second response time; The deterioration determining means determines the deterioration of the linear air-fuel ratio sensor based on the first deterioration index and the second deterioration index.

  The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention is preferably configured such that a target air-fuel ratio change amount that is an absolute value of a difference between the target air-fuel ratio immediately before the change and the target air-fuel ratio immediately after the change is a predetermined value or more, The target air-fuel ratio immediately after the change is held until the second response time is detected by the second response time detection means.

  In the air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention, preferably, the first deterioration index calculating means and the second deterioration index calculating means are the difference, sum, product of the first response time and the second response time. The first deterioration index and the second deterioration index are calculated based on at least one of the quotients or the value of either the first response time or the second response time.

  In the air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention, it is preferable that the first deterioration index calculating means detects a response deterioration index for detecting an abnormality in the response time of the linear air-fuel ratio sensor based on the first response time. The second deterioration index calculating means calculates a gain deterioration index for detecting an abnormality in sensitivity to the air-fuel ratio of the linear air-fuel ratio sensor based on the first response time and the second response time.

In the air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention, preferably, the first deterioration index calculating means uses a value obtained by dividing the first response time by a predetermined value, or a first response time as a response deterioration index. The second deterioration index calculating means uses a value obtained by dividing the second response time by the first response time as a gain deterioration index.

  In the air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention, preferably, the target air-fuel ratio is changed after the change of the target air-fuel ratio until the first response time or the second response time is detected. In this case, the detection of the first response time and the second response time is stopped.

  The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention is preferably an intake air flow rate of the internal combustion engine detected by the air flow rate detection means for detecting the intake air flow rate of the internal combustion engine and the internal combustion engine detected by the rotation speed detection means. It has an operation state detection means for detecting a change in the engine speed, and the absolute value of the intake air amount change detected by the motion state detection means during the response time detection is a predetermined value or more, or an absolute value of the speed change If becomes equal to or greater than a predetermined value, detection of the first response time and the second response time is stopped.

  The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention preferably calculates a deviation between a detected value of the linear air-fuel ratio sensor and the target air-fuel ratio, and determines whether the deviation is within a predetermined range. The air-fuel ratio sensor diagnosis is started by changing the target air-fuel ratio only when the deviation determination means determines that the deviation is within the predetermined range.

  In the air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention, preferably, the linear air-fuel ratio sensor is provided upstream of a three-way catalyst, an oxygen sensor is provided downstream of the three-way catalyst, and the linear air-fuel ratio sensor The catalyst deterioration determination means for detecting deterioration of the three-way catalyst based on the detection value of the catalyst and the detection value of the oxygen sensor, and the calculation result of the catalyst deterioration index calculation means is corrected based on the calculation result of the deterioration index calculation means And a catalyst deterioration determination correcting means.

  The air-fuel ratio sensor diagnosis apparatus according to the present invention preferably corrects the result of the three-way catalyst diagnosis based on at least one of the gain deterioration index and the response deterioration index.

  The air-fuel ratio sensor diagnosis apparatus for an internal combustion engine according to the present invention preferably prohibits the diagnosis of the three-way catalyst when the deterioration determination means determines that the linear air-fuel ratio sensor has deteriorated.

  In order to achieve the above object, an air-fuel ratio sensor diagnostic method for an internal combustion engine according to the present invention is an air-fuel ratio sensor diagnostic method for determining deterioration of a linear air-fuel ratio sensor provided in an exhaust passage, wherein A first response time until the detection value of the fuel ratio sensor reaches a predetermined first predetermined value, and a first response time until the detection value of the linear air-fuel ratio sensor reaches a second predetermined value greater than the first predetermined value. 2 response times are detected, a first deterioration index is calculated based on at least the first response time, a second deterioration index is calculated based on at least the second response time, and the first deterioration index and the second deterioration time are calculated. Degradation of the linear air-fuel ratio sensor is determined based on a degradation index.

  According to the air-fuel ratio sensor diagnostic apparatus for an internal combustion engine of the present invention, the response time of the linear air-fuel ratio sensor when the target air-fuel ratio changes stepwise is measured at two or more points, and a plurality of degradations are performed based on the response time. By calculating the index, it is possible to improve the diagnostic accuracy and performance of the linear air-fuel ratio sensor, and to specify the deterioration factor (gain deterioration, response deterioration).

  Embodiments of an air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows the overall configuration of a direct injection internal combustion engine (engine) to which an air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to the present invention is applied.

  The engine 107 defines a plurality of combustion chambers 107c by cylinder blocks 107b and pistons 107a.

  The intake air introduced into the combustion chamber 107c of the engine 107 is taken in from the inlet portion 102a of the air cleaner 102, passes through an air flow meter (air flow sensor) 103, which is one of the operating state measuring means of the internal combustion engine, and the intake air flow is reduced. The collector 106 is entered through the throttle body 105 in which the electric throttle valve 105a to be controlled is accommodated. The electric throttle valve 105a is driven by the electric motor 124 and the opening degree is set.

  The airflow sensor 103 outputs a signal representing the intake air flow rate to the control unit 115 which is an internal combustion engine control device. The throttle body 105 is provided with a throttle sensor 104 that detects the opening degree of the electric throttle valve 105a as one of the operating state measuring means of the internal combustion engine. The throttle sensor 104 outputs a signal indicating the opening degree of the electric throttle valve 105a to the control unit 115.

  The air sucked into the collector 106 is distributed and supplied to each combustion chamber 107c by the intake pipe 101 connected to the cylinder block 107b.

  Fuel such as gasoline is primarily pressurized from the fuel tank 108 by the fuel pump 109, regulated to a constant pressure by the fuel pressure regulator 110, and secondarily pressurized to a high pressure by the high-pressure fuel pump 111 and pumped to the common rail 126. Is done. The high pressure fuel is directly injected into the combustion chamber 107c by an injector 112 provided for each combustion chamber 107c.

  A fuel pressure sensor 121 that detects the pressure of the high-pressure fuel is attached to the common rail 126. The fuel pressure sensor 121 outputs a signal representing the pressure of the high pressure fuel to the control unit 115.

  A spark plug 114 is attached to the cylinder block 107b for each combustion chamber 107c. The fuel injected into the combustion chamber 107 c is ignited by the spark plug 114 by the ignition signal that has been increased in voltage by the ignition coil 113.

  A cam angle sensor 116 is attached to the camshaft 100 of the exhaust valve 107d. The cam angle sensor 116 outputs a signal for detecting the phase of the camshaft 100 to the control unit 115. Here, the cam angle sensor 116 may be attached to the camshaft 122 on the intake valve 107e side. A crank angle sensor 117 is provided on the crankshaft 107f in order to detect the rotation and phase of the crankshaft 107f of the engine 107. The crank angle sensor 117 outputs a signal representing the rotation and phase of the crankshaft 107 f to the control unit 115.

  A three-way catalyst 120 is provided in the exhaust pipe 119. A linear air-fuel ratio sensor 118 is provided on the upstream side of the three-way catalyst 120. The linear air-fuel ratio sensor 118 quantitatively detects oxygen in the exhaust gas and outputs a detection signal to the control unit 115. An oxygen sensor 125 that detects the presence or absence of oxygen in the exhaust gas is attached to the downstream side of the three-way catalyst 120. The oxygen sensor 125 outputs a signal indicating the presence or absence of oxygen in the exhaust gas to the control unit 115.

  The control unit 115 is of an electronic control type by a microcomputer, and performs fuel pressure control, air-fuel ratio control, ignition control, and deterioration diagnosis of the linear air-fuel ratio sensor 118.

  Here, the cylinder injection type internal combustion engine has been described. However, the present invention is not limited to this, and the present invention can also be applied to a port injection internal combustion engine in which an injector 112 is attached to an intake port (see FIG. 2).

  Embodiment 1 of an air-fuel ratio control apparatus and an air-fuel ratio sensor diagnostic apparatus according to the present invention will be described with reference to FIG.

  The air-fuel ratio control device includes air-fuel ratio control means 206 and target air-fuel ratio setting means 207 that sets the target air-fuel ratio. The air-fuel ratio control unit 206 calculates the fuel injection amount based on the detected value of oxygen in the exhaust gas detected by the linear air-fuel ratio sensor 118 and the output of the target air-fuel ratio setting unit 207, and outputs a fuel injection command to the injector 112. To do.

  The air-fuel ratio sensor diagnostic apparatus includes response time detection means 208, deterioration index calculation means 211, and deterioration determination means 214.

  The response time detection means 208 is a required time from when the target air-fuel ratio set by the target air-fuel ratio setting means 207 is changed until the detection value of the linear air-fuel ratio sensor 118 reaches a predetermined value (target air-fuel ratio). Measure a certain response time. The deterioration index calculation unit 211 calculates a deterioration index based on the response time measured by the response time detection unit 208. The deterioration determining unit 214 determines whether the linear air-fuel ratio sensor 118 has deteriorated based on the deterioration index calculated by the deterioration index calculating unit 211.

  The feature of the first embodiment is that the response time measurement means 208 includes a first response time detection means 209 and a second response time detection means 210, and the first response time varies depending on the first condition depending on different conditions from one response waveform of the linear air-fuel ratio sensor 118. Response time T1 and second response time T2 are detected, and deterioration index calculating means 211 first deterioration index calculating means 212 for individually calculating the deterioration index based on each of first response time T1 and second response time T2. And the second deterioration index calculating means 213.

  The deterioration index calculating means 211 is linearly empty from two deterioration indexes, ie, a first deterioration index I1 calculated by the first deterioration index calculating means 212 and a second deterioration index I2 calculated by the second deterioration index calculating means 213. The presence / absence of deterioration of the fuel ratio sensor 118 is determined.

  That is, in the present embodiment, a plurality of response times are detected from one response waveform of the linear air-fuel ratio sensor 118, and a different deterioration index is calculated according to each of the response times. Thereby, it is possible to distinguish and detect a plurality of deterioration states (response deterioration, gain deterioration) that may occur in the linear air-fuel ratio sensor 118.

  FIG. 3 shows a processing flow of air-fuel ratio sensor diagnosis by the air-fuel ratio sensor diagnostic apparatus according to the first embodiment.

  After starting the air-fuel ratio sensor diagnosis, first, the target air-fuel ratio is changed (step S301), and the values of the first response time T1 and the second response time T2 are cleared (step S302).

  Thereafter, the actual air-fuel ratio is detected from the detection value of the linear air-fuel ratio sensor 118, and time measurement (response time detection) from the target air-fuel ratio change time is performed (step S303). Then, it is monitored whether the air-fuel ratio sensor diagnosis interruption condition is satisfied (step S304). Examples of conditions for interrupting the air-fuel ratio sensor diagnosis include a subsequent change in the target air-fuel ratio and a fuel cut.

  When the air-fuel ratio sensor diagnosis interruption condition is satisfied, the air-fuel ratio sensor diagnosis process is immediately terminated to prevent erroneous diagnosis.

  If the interruption condition is not satisfied, it is determined whether or not the actual air-fuel ratio detected by the linear air-fuel ratio sensor 118 is equal to or more than the first predetermined value G1 and T1 = 0 (step S305). If the actual air-fuel ratio is greater than or equal to the first predetermined value G1 and T1 = 0, the first response time detection means 209 detects the first response time T1 from the time measurement value at that time (step S307). Then, the first deterioration index calculating means 212 calculates the first deterioration index I1 based on the first response time T1 (step S309). If the actual air-fuel ratio is greater than or equal to the first predetermined value G1 and the condition of T1 = 0 is not satisfied, the process returns to step S303.

  If the interruption condition is not satisfied, it is determined whether the actual air-fuel ratio detected by the linear air-fuel ratio sensor 118 is equal to or greater than the second predetermined value G2 and T2 = 0 (step S306). . If the actual air-fuel ratio is equal to or greater than the second predetermined value G2 and T2 = 0, the second response time detection means 210 detects the second response time T2 from the time measurement value at that time (step S308). Then, the second deterioration index calculating means 213 calculates the second deterioration index I2 based on the first response time T1 and the second response time T2 (step S309). If the actual air-fuel ratio is equal to or greater than the second predetermined value G2 and the condition of T1 = 0 is not satisfied, the process returns to step S303.

  What is important here is that the first predetermined value G1 and the second predetermined value G2 are different values and have a relationship of G1 <G2. For example, the first predetermined value G1 is a point (change amount × 0.1) that provides a 10% response to a value immediately before the change of the target air-fuel ratio and a target air-fuel ratio change amount that is the value immediately after the change. The predetermined value G2 is a point (change amount × 0.64) that gives a 64% response to the value immediately before the change of the target air-fuel ratio and the target air-fuel ratio change amount that is the value immediately after the change.

  Note that the first deterioration index I1 may also be calculated based on the first response time T1 and the second response time T2 using an arithmetic expression different from the arithmetic expression of the second deterioration index I2.

  Then, the deterioration determination unit 214 determines the deterioration of the linear air-fuel ratio sensor 118 by distinguishing between response deterioration and gain deterioration based on the first deterioration index I1 and the second deterioration index I2.

  FIG. 4 is an example of a time chart when the flowchart shown in FIG. 3 is executed. A change amount R1 is given so as to change the target air-fuel ratio stepwise, and a first response time T1 when a detection value of the linear air-fuel ratio sensor 118 (hereinafter referred to as an actual air-fuel ratio) becomes a first predetermined value G1, and an actual sky The second response time T2 when the fuel ratio reaches the predetermined value T2 is detected, and based on these, the first deterioration index I1 and the second deterioration index I2 are calculated.

  The change of the target air-fuel ratio by the change amount R1 is held until the first response time T1 and the second response time T2 are detected. In the present embodiment, the target air-fuel ratio change amount R1 is set to +1.4. However, the change amount R1 may use a value other than this, and the sign may be negative.

  Further, the response time may be obtained by integrating the sampling period after the change of the target air-fuel ratio, and the value may be detected after the first response time T1 and the second response time T2 are fixed as shown in the figure. You may detect in real time (dotted line in a figure). Further, the first deterioration index I1 and the second deterioration index I2 may be calculated at any timing after the detection of the first response time T1 and the second response time T2.

  5 and 6 show response waveforms of the output signal (actual air-fuel ratio) of the linear air-fuel ratio sensor 118 after the target air-fuel ratio is changed.

  The response waveform of the linear air-fuel ratio sensor 118 varies depending on the type of deterioration of the linear air-fuel ratio sensor 118. 5 shows a waveform when the linear air-fuel ratio sensor 118 is normal (solid line) and a waveform when the gain is deteriorated (broken line). FIG. 6 shows a waveform when the linear air-fuel ratio sensor 118 is normal (solid line) and response deterioration. A time waveform (broken line) is shown.

  As for gain degradation, as shown in FIG. 5, the response waveform is different between normal and gain degradation in the region of the first predetermined value G1 or more, but in the region of the first predetermined value G1 or less, the response waveform is different. The waveforms are almost the same at all times and when the gain is degraded. That is, the first response time T1n at the normal time and the first response time T1g at the time of gain deterioration are substantially the same, but the second response time T2n at the normal time and the first response time T1n at the time of gain deterioration are the same. The second response time T2g is greatly different.

  Regarding the response deterioration, as shown in FIG. 6, the response waveforms do not coincide between the normal state and the response deterioration over the entire area. That is, the first response time T1n at the normal time and the first response time T1r at the time of response deterioration, the second response time T2n at the normal time, and the second response time T2g at the time of response deterioration are different.

As described above, the first response time T1 when the actual air-fuel ratio becomes the first predetermined value G1 has sensitivity to the response deterioration, and the second response time when the actual air-fuel ratio becomes the second predetermined value G2. T2 means that both deterioration of response and gain are sensitive.
The present inventors have confirmed through experiments that the linear air-fuel ratio sensor has the above-described relationship between the deterioration and the response waveform.

  FIG. 7 shows an example of a method for determining the deterioration of the linear air-fuel ratio sensor 118 using the deterioration indexes (first deterioration index I1, second deterioration index I2). In this embodiment, as the deterioration progresses, the deterioration index increases. Therefore, it is determined that the deterioration index is greater than or equal to a predetermined threshold, and if it is less than that, it is determined normal.

  Since the first response time T1 and the second response time T2 are sensitive to deterioration, respectively, as shown in FIG. 8, the first response time T1 itself is used as the first deterioration index I1 and the second response time. T2 itself may be used as the second deterioration index I2. In addition, the first deterioration index I1 and the second deterioration index I2 may be calculated values obtained by performing four arithmetic operations using the first response time T1 and the second response time T2. For example, the second deterioration index I2 may be a calculated value of any of I2 = T2−T1, I2 = T1 + T2, I2 = T1 × T2, and I2 = T2 ÷ T1.

  The first deterioration index I1 can be used as a response deterioration index Ir for detecting response deterioration in which the response time of the linear air-fuel ratio sensor 118 is delayed. The response deterioration index Ir may be a response time T1 or a value (T1 / T0) obtained by dividing the first response time T1 by a predetermined value (reference value) T0. As the predetermined value T0, a value obtained by measuring in advance the response time T1 when the linear air-fuel ratio sensor 118 is normal is used. The predetermined value T0 may be calculated by calculation based on the intake air amount or the injected fuel amount.

  The second deterioration index I2 can be used as a gain deterioration index Ig for detecting gain deterioration that decreases the sensitivity of the linear air-fuel ratio sensor 118. As the gain deterioration index Ig, a value (T2 / T1) obtained by dividing the second response time T2 by the first response time T1 was used.

As described with reference to FIGS. 4 to 6, the second response time T2 is sensitive to response deterioration and gain deterioration. On the other hand, the first response time T1 is sensitive only to response deterioration and is almost constant in gain deterioration. Furthermore, since the second response time T2 and the first response time T1 have a positive correlation that the second response time T2 increases as the response time T1 increases in response deterioration, (T2 / T1) More sensitive to gain degradation than degradation. Therefore, (T2 / T1) use have Rukoto preferably as gain deterioration index Ig.

  Note that the response deterioration index Ir can be obtained by, for example, addition, subtraction, and multiplication of the first response time T1 and the predetermined value T0, and the gain deterioration index Ig is also the same as the first response time T1 and the second response time. It can also be obtained by addition, subtraction, and multiplication of time T2. Moreover, it is also possible to combine a plurality of these.

  An example of the deterioration determination of the linear air-fuel ratio sensor 118 performed by the deterioration determination unit 214 using the deterioration index (response deterioration index Ir, gain deterioration index Ig) obtained in this way will be described with reference to FIGS. To do.

  FIG. 9 shows response deterioration determination based on the response deterioration index Ir. In this embodiment, the response deterioration index Ir increases as the response deterioration progresses. If the response deterioration index Ir exceeds a predetermined threshold value, it is determined as deterioration, and if it is lower than that, it is determined as normal.

  FIG. 10 shows gain deterioration determination based on the gain deterioration index Ig. The gain degradation index Ig increases as the gain decreases. For this reason, assuming gain deterioration that increases the gain, an upper limit and a lower limit are set for a predetermined threshold value. If the gain deterioration index exceeds the upper limit and lower limit, it is determined to be deteriorated, and it is determined to be normal when it is between the upper limit and the lower limit. To do.

  As described above, the gain deterioration and the response deterioration of the linear air-fuel ratio sensor 118 can be specified and detected without deteriorating the exhaust and the drivability.

  Next, a second embodiment of the air-fuel ratio control device and the air-fuel ratio sensor diagnostic device according to the present invention will be described with reference to FIG. 11, parts corresponding to those in FIG. 2 are denoted by the same reference numerals as those in FIG.

In Embodiment 2, to that of the first embodiment, has a new, and deviation determining means 1313, was added to the operating condition detecting means 1314 configured. By adding these means, the detection accuracy of the response times T1 and T2 is improved, and the linear air-fuel ratio sensor 118 can be diagnosed more precisely.

  As a function of the added means, the deviation determination means 1313 calculates a deviation between the actual air-fuel ratio and the target air-fuel ratio, and determines whether the deviation is within a predetermined deviation convergence determination range. The deviation determination result by the deviation determination means 1313 is input to the target air-fuel ratio setting means 207, and the change of the target air-fuel ratio for air-fuel ratio sensor diagnosis is permitted only when the air-fuel ratio deviation is within a predetermined deviation convergence determination range. If this is not the case, in order to prevent erroneous diagnosis, change of the target air-fuel ratio for air-fuel ratio sensor diagnosis is prohibited so that air-fuel ratio sensor diagnosis is not performed.

  The operating state detection means 1314 detects fluctuations in the intake air flow rate and the engine speed from the outputs of the air flow meter 103 and the crank angle sensor 117. Information relating to the operating state of the engine 107 detected by the operating state detecting means 1314 (information relating to fluctuations in air flow rate and engine speed) is input to the response time detecting means 208. The response time detection means 208 is used to prevent a misdiagnosis when the absolute value of the fluctuation of the intake air flow rate is at least one of a predetermined value or the absolute value of the fluctuation of the engine speed is at least one of a predetermined value. Detection is prohibited (stopped) so that air-fuel ratio sensor diagnosis is not performed.

  The deterioration index calculating unit 211 includes a response deterioration index calculating unit 1315 instead of the first deterioration index calculating unit 212, and a gain deterioration index calculating unit 1316 instead of the second deterioration index calculating unit 213.

  The response deterioration index calculating means 1315 calculates the response deterioration index Ir based on the first response time T1 detected by the first response time detecting means 209.

  The gain deterioration index calculating means 1316 calculates the gain deterioration index Ig based on the first response time T1 detected by the first response time detecting means 209 and the second response time T2 detected by the second response time detecting means 210. To do.

  FIG. 12 shows a processing flow of air-fuel ratio sensor diagnosis by the air-fuel ratio sensor diagnostic apparatus according to the second embodiment.

  After starting the air-fuel ratio sensor diagnosis, first, the actual air-fuel ratio is detected from the output signal of the linear air-fuel ratio sensor 118 (step S1401). Then, the deviation determination means 1313 determines whether or not the deviation between the actual air-fuel ratio and the target air-fuel ratio is within a predetermined deviation convergence determination range. Here, the deviation convergence determination range is ± 0.001 with respect to the target air-fuel ratio. This range may be a value of 0.001 or more, and may be a value of 0.001 or less. Alternatively, it may be determined based on the detection accuracy required for the intake air flow rate, the first response time T1, and the second response time T2.

  If the deviation between the actual air-fuel ratio and the target air-fuel ratio is outside the predetermined deviation convergence determination range, the process returns to step S1401.

  If the deviation between the actual air-fuel ratio and the target air-fuel ratio is within a predetermined deviation convergence determination range, the target air-fuel ratio is changed (step S1403), and the values of the first response time T1 and the second response time T2 are cleared (step S1403). S1404).

  Next, the actual air-fuel ratio, response time, intake air flow rate, and engine speed are detected (step S1405). Thereafter, it is monitored whether the air-fuel ratio sensor diagnosis interruption condition is satisfied (step S1406).

  Examples of the interruption conditions in the present embodiment include a change in the target air-fuel ratio, fuel cut, fluctuations in the intake air flow rate greater than or equal to a predetermined value | Q |, and fluctuations in engine speed greater than or equal to a predetermined value | N |. In the present embodiment, Q is 100 [g / min], and N is 500 [rpm]. For these Q and N, values greater than this may be used, and values less than this may be used. Alternatively, it may be determined based on the detection accuracy required for the intake air flow rate, the first response time T1, and the second response time T2.

  When the air-fuel ratio sensor diagnosis interruption condition is satisfied, the air-fuel ratio sensor diagnosis process is immediately terminated to prevent erroneous diagnosis.

  If the interruption condition is not satisfied, it is determined whether or not the actual air-fuel ratio detected by the linear air-fuel ratio sensor 118 is not less than the first predetermined value G1 and T1 = 0 (step S1407). If the actual air-fuel ratio is equal to or greater than the first predetermined value G1 and T1 = 0, the first response time detection means 209 detects the first response time T1 from the time measurement value at that time (step S1409). Then, the response deterioration index calculating means 1315 calculates the response deterioration index Ir based on the first response time T1 (step S1411). If the actual air-fuel ratio is greater than or equal to the first predetermined value G1 and the condition of T1 = 0 is not satisfied, the process returns to step S1405.

  If the interruption condition is not satisfied, it is determined whether or not the actual air-fuel ratio detected by the linear air-fuel ratio sensor 118 is equal to or greater than the second predetermined value G2 and T2 = 0 (step S1408). . If the actual air-fuel ratio is equal to or greater than the second predetermined value G2 and T2 = 0, the second response time detection means 210 detects the second response time T2 from the time measurement value at that time (step S1410). Then, the gain deterioration index calculating means 1316 calculates the gain deterioration index Ig based on the first response time T1 and the second response time T2 (step S1412). If the actual air-fuel ratio is greater than or equal to the second predetermined value G2 and the condition of T1 = 0 is not satisfied, the process returns to step S1405.

  Then, the deterioration determining means 214 determines the deterioration of the linear air-fuel ratio sensor 118 by distinguishing between the response deterioration and the gain deterioration based on the response deterioration index Ir and the gain deterioration index Ig.

FIG. 13 is an example of a time chart when the flowchart shown in FIG. 12 is executed.
After the deviation between the actual air-fuel ratio and the target air-fuel ratio enters the deviation convergence determination range, the target air-fuel ratio is changed stepwise. Thereafter, a first response time T1 when the actual air-fuel ratio becomes the first predetermined value G1 and a second response time T2 when the actual air-fuel ratio becomes the second predetermined value G2 are detected, respectively, and based on these, a response deterioration index Ir and gain deterioration index Ig are calculated.

  FIG. 14 is another example of a time chart when the flowchart shown in FIG. 12 is executed. As shown in FIG. 13, as in the time chart, the target air-fuel ratio is changed stepwise after the deviation between the actual air-fuel ratio and the target air-fuel ratio enters the deviation convergence determination range. Thereafter, during detection of the first response time T1 when the actual air-fuel ratio becomes the first predetermined value G1, or during detection of the second response time T2 when the actual air-fuel ratio becomes the second predetermined value G2, for example, suction When the fluctuation of the air flow rate exceeds the fluctuation allowable threshold, the detection of the first response time T1 and the second response time T2 is stopped.

  Here, in this embodiment, the fluctuation of the intake air flow rate is calculated based on the intake air flow rate when the target air-fuel ratio is switched. For the fluctuation of the intake air flow rate, an integrated value or an average value of the air flow rate during response time measurement may be used. Further, based on these, correction values of the first response time T1 and the second response time T2 may be calculated and corrected.

  As described above, it is possible to identify and detect the gain deterioration and the response deterioration of the linear air-fuel ratio sensor 118 without exacerbating the possibility of erroneous diagnosis without deteriorating exhaust gas and operability.

  Next, Embodiment 3 of the air-fuel ratio control device and the air-fuel ratio sensor diagnostic device according to the present invention will be described with reference to FIG. In FIG. 15 as well, portions corresponding to those in FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and description thereof is omitted.

  In this embodiment, a catalyst deterioration determination unit 1713 and a catalyst deterioration determination correction unit 1714 are added.

  By adding these means, when the linear air-fuel ratio sensor 118 has deteriorated such that the catalyst diagnosis is an erroneous diagnosis, the catalyst diagnosis can be performed without making an erroneous diagnosis. Further, both catalyst diagnosis and linear air-fuel ratio sensor diagnosis can be performed using the same actual air-fuel ratio response.

  As a function of the added means, the catalyst deterioration determination means 1713 calculates the deterioration determination index of the three-way catalyst 120 from the detection value of the linear air-fuel ratio sensor 118 and the detection value of the oxygen sensor 125, and determines the deterioration of the three-way catalyst 120. Diagnose.

  When the deterioration determination unit 214 determines that the linear air-fuel ratio sensor 118 is deteriorated, the diagnosis of the three-way catalyst 120 by the catalyst deterioration determination unit 1713 is prohibited.

  The catalyst deterioration determination correction unit 1714 corrects the determination result of the catalyst deterioration determination unit 1713 based on the calculation result of the deterioration index calculation unit 211.

  FIG. 16 shows a processing flow of air-fuel ratio sensor diagnosis by the air-fuel ratio sensor diagnostic apparatus according to the third embodiment.

  After starting the air-fuel ratio sensor diagnosis, first, the actual air-fuel ratio is detected from the output signal of the linear air-fuel ratio sensor 118 (step S1801).

  Next, it is determined whether or not a catalyst diagnosis permission condition is satisfied (step S1802). The catalyst diagnosis permission condition includes that the actual air-fuel ratio is within a predetermined deviation convergence determination range. If the catalyst diagnosis permission condition is satisfied, the target air-fuel ratio is changed (step S1803).

  Thereafter, the actual air-fuel ratio and response time are detected (step S1804), and the linear air-fuel ratio sensor 118 is diagnosed (step S1805). Then, a catalyst diagnosis correction value is calculated based on the diagnosis result (step S1806).

Further, after the target air-fuel ratio is changed, the actual air-fuel ratio and the output of the oxygen sensor 125 are detected (step S1807), and a catalyst deterioration determination index is calculated based on that (step S1808).
Further, the catalyst deterioration determination index is corrected based on the calculated catalyst deterioration determination correction value (step S1809).

  FIG. 17 is an example of a time chart when the flowchart shown in FIG. 16 is executed. After the deviation between the actual air-fuel ratio and the target air-fuel ratio enters the deviation convergence determination range, the target air-fuel ratio is changed stepwise. Thereafter, a catalyst deterioration determination index is calculated from the difference between the actual air-fuel ratio and the response time of the oxygen sensor output with respect to the step change of the target air-fuel ratio. The gain deterioration index Ig of the linear air-fuel ratio sensor 118 is calculated using the first response time T1 and the second response time T2 of the actual air-fuel ratio during that time, and the catalyst deterioration determination correction value C is calculated based on the gain deterioration index Ig. Calculate.

  When the catalyst deterioration determination index C is calculated, the catalyst deterioration determination index is corrected based on the catalyst deterioration determination correction value C. The catalyst deterioration determination correction value C may be calculated based on the response deterioration index Ir, or may be calculated using two of the gain deterioration index Ig and the response deterioration index Ir.

  FIG. 18 shows the relationship between the gain deterioration index Ig and the catalyst deterioration determination correction value C. In the present embodiment, the gain decreases as the gain deterioration index Ig increases. When the gain is small, the true value of the actual air-fuel ratio is larger than the actual air-fuel ratio, so that the catalyst deterioration determination index C is calculated to be small. Therefore, the catalyst deterioration determination correction value C increases with the gain deterioration index Ig. Become bigger.

  FIG. 19 shows the relationship between the response deterioration index Ir and the catalyst deterioration determination correction value C. In the present embodiment, as the response deterioration index Ir increases, the response delay increases, and the difference in response time between the outputs of the linear air-fuel ratio sensor 118 and the oxygen sensor 125 at the time of catalyst diagnosis is reduced. Is computed smaller. Therefore, the catalyst deterioration determination correction value C increases as the response deterioration index Ir increases.

1 is an overall configuration diagram showing an overall configuration of a direct injection internal combustion engine to which an air-fuel ratio sensor diagnostic device according to the present invention is applied. 1 is a block diagram showing Embodiment 1 of an air-fuel ratio control device and an air-fuel ratio sensor diagnostic device according to the present invention. 5 is a flowchart showing a processing flow of air-fuel ratio sensor diagnosis by the air-fuel ratio sensor diagnostic apparatus according to the first embodiment. The time chart at the time of implementing the flowchart shown in FIG. The graph which shows an example of the response waveform at the time of gain degradation of a linear air fuel ratio sensor. The graph which shows an example of the response waveform at the time of the response deterioration of a linear air fuel ratio sensor. The graph which shows the relationship between degradation of a linear air fuel ratio sensor, and a degradation parameter | index. The graph which shows an example of the computing equation of a 1st degradation parameter | index and a 2nd degradation parameter | index. The graph which shows an example of the relationship between response delay time and a response degradation parameter | index. The graph which shows an example of the relationship between gain degradation and a gain degradation parameter | index. The block diagram which shows Embodiment 2 of the air fuel ratio control apparatus and the air fuel ratio sensor diagnostic apparatus by this invention. 9 is a flowchart showing a processing flow of air-fuel ratio sensor diagnosis by an air-fuel ratio sensor diagnostic apparatus according to Embodiment 2. The time chart at the time of implementing the flowchart shown in FIG. The time chart at the time of implementing the flowchart shown in FIG. FIG. 5 is a block diagram showing Embodiment 3 of an air-fuel ratio control device and an air-fuel ratio sensor diagnostic device according to the present invention. 9 is a flowchart showing a processing flow of air-fuel ratio sensor diagnosis by an air-fuel ratio sensor diagnostic apparatus according to Embodiment 3. The time chart at the time of implementing the flowchart shown in FIG. The graph which shows the relationship between a gain degradation parameter | index and a catalyst degradation determination correction value. The graph which shows the relationship between a response deterioration parameter | index and a catalyst deterioration determination correction value.

Explanation of symbols

101 Intake pipe 102 Air cleaner 103 Air flow meter 104 Throttle sensor 105 Throttle body 106 Collector 107 In-cylinder injection internal combustion engine 109 Fuel pump 111 High-pressure fuel pump 112 Injector 113 Ignition coil 114 Spark plug 115 Control unit 116 Cam angle sensor 117 Crank angle sensor 118 Air-fuel ratio sensor 125 Oxygen sensor 126 Common rail 206 Air-fuel ratio control means 207 Target air-fuel ratio setting means 208 Response time detection means 209 First response time detection means 210 Second response time detection means 211 Degradation index calculation means 212 First deterioration index calculation means 213 Second deterioration index calculating means 214 Degradation determining means 1313 Deviation determining means 1314 Operating state detecting means 1315 Response deterioration index calculating means 1316 Gain deterioration index calculating means 17 13 Catalyst degradation determination means 1714 Catalyst degradation determination correction means

Claims (12)

An air-fuel ratio sensor diagnostic apparatus for an internal combustion engine that determines deterioration of a linear air-fuel ratio sensor provided in an exhaust passage, from when a target air-fuel ratio is changed until a detection value of the linear air-fuel ratio sensor reaches a predetermined value Response time detecting means for detecting a response time that is a required time; deterioration index calculating means for calculating a deterioration index of the linear air-fuel ratio sensor based on the response time detected by the response time detecting means; and the deterioration index calculating Deterioration determining means for determining deterioration of the linear air-fuel ratio sensor based on a deterioration index calculated by the means,
The response time detection means includes first response time detection means for detecting a first response time until a detection value of the linear air-fuel ratio sensor reaches a predetermined first predetermined value, and detection of the linear air-fuel ratio sensor. Second response time detecting means for detecting a second response time until a value reaches a second predetermined value greater than the first predetermined value;
The deterioration index calculating means calculates a first deterioration index calculating means for calculating a first deterioration index based on at least the first response time, and a second deterioration calculating a second deterioration index based on at least the second response time. An index calculation means,
The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine, wherein the deterioration determination means determines deterioration of the linear air-fuel ratio sensor based on the first deterioration index and the second deterioration index.   The target air-fuel ratio change amount, which is the absolute value of the difference between the target air-fuel ratio immediately before the change and the target air-fuel ratio immediately after the change, is set to a predetermined value or more, and the target air-fuel ratio immediately after the change is determined by the second response time detection means. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to claim 1, wherein the second response time is maintained until it is detected.   The first deterioration index calculating means and the second deterioration index calculating means are at least one of a difference, a sum, a product, and a quotient of the first response time and the second response time, or the first response time and the first response time. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to claim 1 or 2, wherein the first deterioration index and the second deterioration index are calculated based on one of two response times.   The first deterioration index calculating means calculates a response deterioration index for detecting an abnormality in the response time of the linear air-fuel ratio sensor based on the first response time, and the second deterioration index calculating means is the first response time. 3. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to claim 1, wherein a gain deterioration index calculation for detecting an abnormality in sensitivity to the air-fuel ratio of the linear air-fuel ratio sensor is performed based on the second response time. The first deterioration index calculating means uses a value obtained by dividing the first response time by a predetermined value or a first response time as a response deterioration index, and the second deterioration index calculating means uses the second response time as the first response time. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to claim 1 or 2, wherein a value obtained by dividing by time is used as a gain deterioration index.   If the target air-fuel ratio is changed before the first response time or the second response time is detected after the change of the target air-fuel ratio, the detection of the first response time and the second response time is performed. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein   An operating state detecting means for detecting an intake air flow rate of the internal combustion engine detected by an air flow rate detecting means for detecting an intake air flow rate of the internal combustion engine and a change in the rotational speed of the internal combustion engine detected by the rotational speed detecting means; If the absolute value of the intake air amount change detected by the motion state detecting means is greater than or equal to a predetermined value or the absolute value of the rotation speed change is greater than or equal to a predetermined value during response time detection, the first response time and the first 7. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to claim 1, wherein the detection of two response times is stopped.   Deviation determination means for calculating a deviation between the detected value of the linear air-fuel ratio sensor and the target air-fuel ratio and determining whether the deviation is within a predetermined range, and the deviation within the predetermined range by the deviation determination means. The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to any one of claims 1 to 7, wherein the air-fuel ratio sensor diagnosis is started by changing the target air-fuel ratio only when it is determined that there is. The linear air-fuel ratio sensor is provided on the upstream side of the three-way catalyst, and an oxygen sensor is provided downstream of the three-way catalyst. The three-way catalyst is based on the detection value of the linear air-fuel ratio sensor and the detection value of the oxygen sensor. Catalyst deterioration determination means for detecting catalyst deterioration;
Catalyst deterioration determination correction means for correcting the calculation result of the catalyst deterioration index calculation means based on the calculation result of the deterioration index calculation means;
The air-fuel ratio sensor diagnostic apparatus for an internal combustion engine according to any one of claims 1 to 8, characterized by comprising:   The air-fuel ratio sensor diagnosis apparatus for an internal combustion engine according to claim 9, wherein the result of the three-way catalyst diagnosis is corrected based on at least one of the gain deterioration index and the response deterioration index.   The air-fuel ratio of an internal combustion engine according to claim 9 or 10, wherein when the deterioration determination means determines that the linear air-fuel ratio sensor is deteriorated, diagnosis of the three-way catalyst is prohibited. Sensor diagnostic device. An air-fuel ratio sensor diagnostic method for an internal combustion engine for performing deterioration determination of a linear air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine,
A first response time until the detection value of the linear air-fuel ratio sensor reaches a predetermined first predetermined value, and a detection value of the linear air-fuel ratio sensor reaches a second predetermined value that is greater than the first predetermined value. Second response time is detected, a first deterioration index is calculated based on at least the first response time, a second deterioration index is calculated based on at least the second response time, and the first deterioration index and An air-fuel ratio sensor diagnostic method for an internal combustion engine, wherein deterioration of the linear air-fuel ratio sensor is determined based on the second deterioration index.

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