JP5195483B2 - Exhaust sensor diagnostic device - Google Patents

Description

  The present invention relates to an exhaust sensor diagnostic device disposed on the downstream side of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine.

  Conventionally, in order to grasp the purification state of exhaust components by the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine, an oxygen sensor as an exhaust sensor is provided on the downstream side of the catalyst in addition to the catalyst upstream exhaust sensor. Then, air-fuel ratio feedback control is executed in which the air-fuel ratio of the exhaust gas after passing through the catalyst is detected and a correction value is calculated for the air-fuel ratio correction value by the air-fuel ratio feedback control based on the catalyst upstream exhaust sensor.

  The oxygen sensor downstream of the catalyst is provided downstream of the catalyst having an oxygen storage function of storing oxygen in the exhaust when the air-fuel ratio of the exhaust passing therethrough is lean and releasing the stored oxygen when the air-fuel ratio is rich. Therefore, the oxygen storage amount of the catalyst can be estimated by monitoring the change in the air-fuel ratio on the downstream side of the catalyst after changing the air-fuel ratio on the upstream side of the catalyst.

  By the way, in the feedback control described above, the control is performed based on the output of the downstream oxygen sensor. Therefore, if an abnormality occurs in the oxygen sensor, a normal correction value cannot be calculated, and exhaust gas is sufficiently purified. There is a risk of being lost. Thus, an apparatus for diagnosing the presence or absence of abnormality of the downstream oxygen sensor has been proposed (see Patent Document 1).

  This is because the air-fuel ratio on the downstream side of the catalyst is suppressed in order to suppress the deterioration of the emission by shortening the time until the abnormality of the oxygen sensor is determined in the abnormality diagnosis of the oxygen sensor provided on the downstream side of the catalyst. The air-fuel ratio upstream of the catalyst is forcibly changed, and the estimated oxygen storage amount of the catalyst is calculated based on the air-fuel ratio downstream of the catalyst that changes at that time. Based on the comparison with the set value at the time), the presence or absence of abnormality of the oxygen sensor that detects the air-fuel ratio on the downstream side of the catalyst is diagnosed.

JP 2006-9700 A

  However, in the above conventional example, the air-fuel ratio on the upstream side of the catalyst is forcibly changed, and the estimated oxygen storage amount of the catalyst is calculated based on the air-fuel ratio on the downstream side of the catalyst that changes at that time. If the determination value is exceeded, it is determined that the oxygen sensor as an exhaust sensor is abnormal. Therefore, even if the response of the exhaust sensor is delayed, the catalyst is deteriorated and the estimated oxygen storage amount is reduced. There was a bug that could not be done.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust sensor diagnostic apparatus suitable for suppressing the influence of the oxygen storage amount of the upstream catalyst.

The present invention provides a catalyst activity rate estimation calculating means for detecting or calculating an activity rate of an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine until the catalyst is activated every time when the internal combustion engine is cold start , The air-fuel ratio active control means for forcibly changing the upstream air-fuel ratio of the catalyst between the rich side and the lean side after the cold start of the internal combustion engine, and the catalyst activity rate detected or calculated by the catalyst activity rate estimation calculating means , Abnormality determination in which an abnormality of the exhaust sensor is determined based on an output signal of the exhaust sensor obtained by operating the air-fuel ratio active means in an inactive state that is lower than a preset value after the cold start of the internal combustion engine e Bei means, wherein the abnormality determination means changes the speed from the rich side of the output signal of exhaust gas sensor to the lean side, the change rate from the lean side to the rich side, the rich-side shift amount, Lee It was to determine the abnormality of the exhaust gas sensor based on one or two or more parameters of the side shift.

Therefore, in the present invention, the air-fuel ratio active means is operated in the inactive state after the cold start of the internal combustion engine in which the catalyst activity rate detected or calculated by the catalyst activity rate estimation calculating means is lower than a preset value. Therefore, the exhaust sensor abnormality is judged based on the output signal of the obtained exhaust sensor, so that the response of the downstream exhaust sensor, dead time, Output shift diagnosis is possible. Further, it is possible to diagnose whether there is an abnormality in the downstream exhaust sensor without being affected by the degree of deterioration of the upstream catalyst.
In addition, since the diagnosis of the downstream exhaust sensor can be executed every time the cold engine is started, the frequency of diagnosis execution in the market can be sufficiently secured, and high-frequency diagnosis can be expected.
Further, since it is not affected by the oxygen storage function of the upstream catalyst, the amplitude / cycle of the air-fuel ratio A / F that is actively changed can be narrowed, so that the influence on the exhaust performance deterioration and the drivability deterioration can be reduced .
In addition, the abnormality determination means includes one or more of a change speed of the exhaust sensor output signal from the rich side to the lean side, a change speed from the lean side to the rich side, a rich side shift amount, and a lean side shift amount. Since the abnormality of the exhaust sensor is determined based on the parameter, the responsiveness of the downstream exhaust sensor can be accurately diagnosed.

1 is a system configuration diagram of a schematic configuration of a vehicle internal combustion engine and its peripheral devices including an exhaust sensor diagnostic device according to an embodiment of the present invention. FIG. 6 is an exhaust sensor diagnosis flowchart that is also executed at the time of cold start. The time chart which shows each change of the catalyst activity rate based on execution of a diagnostic flowchart, a target air fuel ratio, the output signal of a downstream exhaust sensor, etc. The exhaust sensor diagnosis flowchart in the exhaust sensor diagnosis apparatus showing the first example of the second embodiment of the present invention. The time chart which shows each change, such as a catalyst activity rate based on execution of the diagnostic flowchart in 1st Example, a target air fuel ratio, and an output signal of a downstream exhaust sensor. The exhaust sensor diagnosis flowchart in the exhaust sensor diagnosis apparatus showing a second example of the second embodiment of the present invention. The time chart which shows each change of the catalyst activity rate based on execution of the diagnostic flowchart in 2nd Example, a target air fuel ratio, the output signal of a downstream exhaust sensor, etc. FIG. The characteristic view which shows the sensor correction characteristic of 2nd Example of 2nd Embodiment of this invention. The time chart which shows each change of the catalyst activity rate based on execution of the diagnostic flowchart in the diagnostic apparatus of the exhaust sensor which shows 3rd Example of 2nd Embodiment of this invention, a target air fuel ratio, the output signal of a downstream exhaust sensor, etc. FIG. The characteristic view which shows the active control characteristic of the air fuel ratio of 3rd Example of 2nd Embodiment of this invention.

  Hereinafter, an exhaust sensor diagnosis apparatus according to the present invention will be described based on each embodiment.

(First embodiment)
FIG. 1 is a system configuration diagram of a schematic configuration of an internal combustion engine for a vehicle and its peripheral devices showing a first embodiment of an exhaust sensor diagnostic apparatus to which the present invention is applied.

  In FIG. 1, an intake air adjusted by opening control of a throttle valve 4 is introduced into an intake passage 2 of the internal combustion engine 1 through an air cleaner 3, and injected from an injector 5 provided downstream of the throttle valve 4. The mixed fuel is mixed and introduced into a combustion chamber (not shown) and burned in the combustion chamber. The amount of intake air (intake air amount) is detected by the air flow meter 6.

  In addition, an exhaust gas purification catalyst 8 for purifying components in the exhaust gas is provided in the exhaust passage 7 through which exhaust gas generated by combustion in the combustion chamber is sent. The catalyst 8 is a three-way catalyst that purifies the exhaust gas by oxidizing HC and CO in the exhaust gas and reducing NOx in the exhaust gas in a state where combustion near the stoichiometric air-fuel ratio is performed. The catalyst 8 stores oxygen in the exhaust when the air-fuel ratio of the exhaust passing therethrough is leaner than the stoichiometric air-fuel ratio, and releases the stored oxygen when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. Equipped with oxygen storage function. The catalyst 8 efficiently purifies all the main harmful components (HC, CO, NOx) in the exhaust gas by an oxidation-reduction reaction only in a narrow range where the air-fuel ratio of the air-fuel mixture to be burned is close to the theoretical air-fuel ratio. In order to detect this purification state, an air-fuel ratio sensor as an upstream exhaust sensor 9 is provided upstream of the catalyst 8, and an oxygen sensor as a downstream exhaust sensor 10 is provided downstream of the catalyst. Hereinafter, these sensors are referred to as “upstream exhaust sensor” and “downstream exhaust sensor”. Reference numeral 11 denotes a downstream catalyst having an HC trap function.

  The upstream exhaust sensor 9 composed of the air-fuel ratio sensor is a well-known limiting current oxygen sensor, and according to the oxygen concentration in the exhaust gas by providing a ceramic layer called a diffusion-controlling layer in the detection part of the concentration cell oxygen sensor. This is a sensor that can obtain an output current. That is, when the air-fuel ratio closely related to the oxygen concentration in the exhaust gas is the stoichiometric air-fuel ratio, the output current becomes “0”, and the output current increases in the negative direction as the air-fuel ratio becomes rich. As the air-fuel ratio becomes leaner, the output current increases in the positive direction. Therefore, based on the output of the upstream exhaust sensor 9, the lean degree or rich degree of the air-fuel ratio on the upstream side of the catalyst 8 can be detected.

  The downstream exhaust sensor 10 composed of the oxygen sensor is a well-known concentration cell type oxygen sensor, and its output characteristic is that an output of about 1 V is obtained when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and the air-fuel ratio is When the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, an output of about 0 V is obtained, and the output voltage changes greatly in the vicinity of the stoichiometric air-fuel ratio. Therefore, based on the output of the downstream exhaust sensor 10, it can be detected whether the air-fuel ratio on the downstream side of the catalyst 8 is lean or rich.

  The downstream exhaust sensor 10 is provided on the downstream side of the catalyst 8 in order to monitor the state of the exhaust gas purification action of the catalyst 8. When the output of the upstream exhaust sensor 9 indicates rich, the downstream exhaust sensor 10 When the output is lean, it is possible to grasp that oxygen is released from the catalyst 8 and the oxidation action in the catalyst 8 is promoted. Further, when the output of the upstream exhaust sensor 9 indicates lean and the output of the downstream exhaust sensor 10 is rich, oxygen is occluded in the catalyst 8 and the reduction action in the catalyst 8 is promoted. I can grasp that.

  The catalyst 8 efficiently purifies all the main harmful components (HC, CO, NOx) in the exhaust gas by an oxidation-reduction reaction only in a narrow range where the air-fuel ratio of the air-fuel mixture to be burned is close to the theoretical air-fuel ratio. In order for such a catalyst 8 to function effectively, strict air-fuel ratio control is required in which the air-fuel ratio of the air-fuel mixture is adjusted to the center of a narrow range near the theoretical air-fuel ratio.

  Such control of the air-fuel ratio is performed by the engine control device 12. The engine control device 12 includes the air flow meter 6, the upstream exhaust sensor 9, the downstream exhaust sensor 10, an accelerator sensor (not shown) that detects the amount of depression of the accelerator pedal, or a rotation speed sensor (not shown) that detects the engine speed. Detection signals of various sensors are input. The throttle valve 4 and the injector 5 are driven and controlled in accordance with the operating conditions of the internal combustion engine 1 and the vehicle ascertained from the detection signals of these sensors, thereby controlling the air-fuel ratio as described above. The outline of the air-fuel ratio control by the engine control device 12 is as follows.

  First, the engine control device 12 obtains a required amount of intake air amount that is grasped according to the amount of depression of the accelerator pedal and the detection result of the engine speed, and the throttle valve 4 of the throttle valve 4 is obtained so as to obtain the intake air amount accordingly. Adjust the opening. On the other hand, an amount of fuel sufficient to obtain the theoretical air-fuel ratio is obtained from the actually measured value of the intake air amount detected by the air flow meter 6, thereby adjusting the fuel injection amount from the injector 5. Thereby, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber can be brought close to the stoichiometric air-fuel ratio to some extent.

  In addition, the engine control device 12 grasps the measured value of the air-fuel ratio upstream of the catalyst 8 based on the detection result of the upstream exhaust sensor 9 upstream of the catalyst 8, and the measured value and the target air-fuel ratio, that is, the theoretical value. The fuel injection amount of the injector 5 is feedback-corrected based on the air-fuel ratio feedback correction amount calculated based on the degree of deviation from the air-fuel ratio. This air-fuel ratio feedback control ensures the required accuracy of air-fuel ratio control.

  Further, the engine control device 12 estimates the oxygen storage state or oxygen release state of the catalyst 8 from the detection result of the downstream exhaust sensor 10 on the downstream side of the catalyst 8, and based on this estimation, the engine control device 12 corresponds to the air-fuel ratio feedback correction amount. Make corrections. In this correction process, the sub feedback correction amount calculated based on the output of the downstream exhaust sensor 10 is corrected to increase or decrease, and the air / fuel ratio feedback correction amount is corrected by the sub feedback correction amount.

  Specifically, while the output of the downstream exhaust sensor 10 is rich, the air-fuel ratio upstream of the catalyst 8 changes leaner by a certain amount, that is, the air-fuel ratio upstream of the catalyst 8 gradually increases. The sub feedback correction amount is increased to the minus side by a certain amount so as to approach the lean side. On the other hand, while the output of the downstream exhaust sensor 10 indicates lean, the air-fuel ratio on the upstream side of the catalyst 8 changes toward the rich by a certain amount, that is, the air-fuel ratio on the upstream side of the catalyst 8 gradually increases toward the rich side. As approaching, the sub feedback correction amount is increased by a certain amount to the plus side. By such sub-feedback control, the purification action of the catalyst 8 is effectively utilized.

  If an abnormality occurs in the downstream exhaust sensor 10 on the downstream side of the catalyst 8, the output signal does not reflect the actual air-fuel ratio of the exhaust, and the sub feedback control cannot be performed accurately. Furthermore, the correction of the air-fuel ratio feedback correction amount by the sub feedback correction amount may also have an adverse effect.

  Therefore, in this embodiment, the presence or absence of abnormality of the downstream exhaust sensor 10 is diagnosed through active control of the air-fuel ratio during the period until the catalyst 8 is activated every time the engine 1 is cold-started. In this active control, the target air-fuel ratio is reversed between rich (for example, target air-fuel ratio = 14.1) and lean (for example, target air-fuel ratio = 15.1).

  FIG. 2 is a diagnostic flowchart for diagnosing the presence or absence of abnormality of the downstream exhaust sensor 10 and is executed at predetermined intervals by the engine control device in the inactive state of the catalyst 8 after the engine 1 is cold-started. Hereinafter, a procedure for diagnosing whether or not the downstream exhaust sensor 10 is abnormal will be described with reference to a diagnostic flowchart shown in FIG.

  When the engine 1 is started, first, in step S1, the temperature of the catalyst 8 is estimated and calculated. The temperature of the catalyst 8 varies depending on the catalyst temperature at the time of the previous engine stop, the engine stop time, the operation state after the engine start, and the like. Combustion obtained by multiplying the catalyst temperature at the previous engine stop stored in the ECM, the time from the previous engine stop to the engine start, the intake air amount introduced into the combustion chamber and the ignition timing reflecting the combustion temperature The catalyst temperature is estimated and calculated based on the amount of heat input to the catalyst 8 obtained by integrating the amount of heat generated in the chamber over time. Further, the accuracy of estimation can be improved by correcting the combustion temperature in accordance with the air-fuel ratio. A temperature sensor may be provided in the vicinity of the catalyst 8 or in the vicinity thereof to detect the catalyst temperature.

  In step S2, it is determined whether or not the catalyst temperature has reached the activation temperature (activation point). If the catalyst temperature exceeds the activation temperature and is activated, execution of the current diagnosis flowchart is stopped. The In this determination, when the catalyst temperature is lower than the activation temperature and is not completely activated, the process proceeds to step S3 in order to execute the current diagnosis flowchart.

  In step S3, active control of the air-fuel ratio that reverses the target air-fuel ratio between rich and lean is started. In the active control of the air-fuel ratio, the target air-fuel ratio is reversed between rich (for example, target air-fuel ratio = 14.1) and lean (for example, target air-fuel ratio = 15.1). In the active control of the air-fuel ratio, the actual value measured by the upstream exhaust sensor 9 is grasped for the air-fuel ratio upstream of the catalyst 8, and the air-fuel ratio feedback correction calculated based on the degree of deviation between the actual measured value and the target air-fuel ratio. This is executed by feedback correcting the fuel injection amount of the injector 5 based on the amount. It should be noted that a fuel amount sufficient to obtain a target air-fuel ratio that is reversed between rich and lean is obtained with respect to the actually measured value of the intake air amount detected by the air flow meter 6, and thereby the fuel injection amount from the injector 5. The air-fuel ratio active control of the open control may be used in which the air-fuel ratio is adjusted to be close to the theoretical air-fuel ratio to some extent.

  The target air-fuel ratio is larger than “14.1” on the rich side, for example, “14.2 to 14.5”, and smaller than “15.1” on the lean side. It is good also as 15.0-14.6 ". This is because the catalyst 8 has not yet been activated, so when the air-fuel ratio of the exhaust passing through is leaner than the stoichiometric air-fuel ratio, oxygen in the exhaust gas is occluded, and when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. This is because the so-called oxygen storage function for releasing the stored oxygen is not sufficiently exhibited, and the output of the downstream exhaust sensor 10 can react faithfully to the air-fuel ratio that changes actively. Further, for the same reason, the cycle of changing the air-fuel ratio to be actively changed to rich, lean, rich, etc. can be narrowed.

  In step S4, based on the output signal of the downstream exhaust sensor 10, the rich → lean reverse speed maximum value (here, the maximum value of the output signal decrease speed), the lean → rich reverse speed minimum value (here) In this case, the maximum value of the increase rate of the output signal is calculated), the response dead time, the rich shift amount, and the lean shift amount are calculated. By the way, since the upstream catalyst 8 has not yet been activated, when the air-fuel ratio of the exhaust passing through is leaner than the stoichiometric air-fuel ratio, oxygen in the exhaust gas is occluded, and the air-fuel ratio is richer than the stoichiometric air-fuel ratio. Sometimes the so-called oxygen storage function of releasing the stored oxygen is not sufficiently exhibited. Therefore, the downstream exhaust sensor 10 does not receive the influence of the oxygen storage function of the upstream catalyst 8 and responds to the air-fuel ratio active control, and outputs its output signal closer to “1 V” on the air-fuel ratio rich side. On the lean side of the air-fuel ratio, the output signal is changed between “0V” and output signal.

  When the downstream exhaust sensor 10 is normal, an “1V” output signal (rich shift amount) is obtained on the air-fuel ratio rich side, and an “0V” output signal (lean shift amount) is obtained on the air-fuel ratio lean side. The maximum value of the rich → lean reversal speed and the minimum value of the lean → rich reversal speed are obtained as specified numerical values.

  When the downstream exhaust sensor 10 has a failure such as deterioration, the output signal (rich shift amount) is lowered from “1 V” on the air-fuel ratio rich side, and the output signal (lean shift amount) on the air-fuel ratio lean side. ) Is increased from “0 V”, and the maximum value of the rich → lean reversal speed and the minimum value of the lean → rich reversal speed are also decreased from the specified values.

  In step S5, whether the rich-to-lean reversal speed maximum value calculated in step S4, the lean-to-rich reversal speed minimum value exceeds a preset reversal speed criterion (criteria), and the rich shift amount, lean It is determined whether or not the shift amount exceeds a preset shift amount criterion (criteria). If both the reverse speed criterion and the shift amount criterion are exceeded, the process proceeds to step S6, where it is determined that the downstream exhaust sensor 10 is normal. Further, in the above determination, if any one of them does not exceed, it proceeds to step S7 and determines that the downstream exhaust sensor 10 is abnormal.

  FIG. 3 is a time chart showing changes in the catalyst activation rate, the target air-fuel ratio, and the output signal of the downstream exhaust sensor 10 when the diagnosis flowchart is executed.

  That is, when the engine 1 is started at time t0, the exhaust gas combusted in the combustion chamber is sent to the catalyst 8 through the exhaust passage, and the catalyst 8 starts to rise in temperature due to the combustion gas (see A in the figure). . At the same time, step S1 is executed, and the catalyst activation state (catalyst activation rate / temperature) is calculated. Then, when the accumulated heat amount from the start of the engine 1 reaches a certain value, the target in step S3 at any time t1 during the catalyst inactivation until it is determined in step S2 that the catalyst 8 has been activated. The active control of the air-fuel ratio that reverses the air-fuel ratio between rich and lean is started.

  When active control of the air-fuel ratio is started, the target air-fuel ratio is reversed between rich (for example, target air-fuel ratio = 14.1) and lean (for example, target air-fuel ratio = 15.1), and upstream of the catalyst 8 The air fuel ratio of the injector 5 is ascertained by the upstream exhaust sensor 9, and the fuel injection amount of the injector 5 is fed back based on the air / fuel ratio feedback correction amount calculated based on the degree of deviation between the actual air fuel ratio and the target air / fuel ratio. It is executed by correcting (see B in the figure). This active control of the air-fuel ratio only provides a target air-fuel ratio that is reversed between rich and lean with respect to the actual measured value of the intake air amount detected by the air flow meter 6, as indicated by C in the figure. This may be an open control in which the amount of fuel is calculated and the amount of fuel injected from the injector 5 is adjusted thereby to bring the fuel air amount closer to the theoretical air-fuel ratio.

  At this time, since the upstream catalyst 8 has not yet been activated, oxygen in the exhaust gas is occluded when the air-fuel ratio of the exhaust passing through is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio is less than the stoichiometric air-fuel ratio. When rich, the stored oxygen is released and the so-called oxygen storage function is not fully exhibited. Therefore, the downstream exhaust sensor 10 does not receive the influence of the oxygen storage function of the upstream catalyst 8 and responds to the air-fuel ratio active control, and outputs its output signal closer to “1 V” on the air-fuel ratio rich side. On the lean side of the air-fuel ratio, the output signal is changed between “0V” and output (see D in the figure). In D in the figure, a solid line indicates an output change when the downstream exhaust sensor 10 is normal, and a broken line indicates an output change when the downstream exhaust sensor 10 has a failure such as deterioration.

  By executing step S4, based on the output signal of the downstream exhaust sensor 10 of D in the figure, the rich → lean reversal speed maximum value (the upper characteristic of E in the figure), lean → rich reversal speed minimum A value (lower characteristic E in the figure), rich shift amount (F characteristic in the figure), and lean shift amount (F characteristic in the figure) are calculated.

  When the downstream exhaust sensor 10 is normal, as shown by the solid line D in the figure, the output signal (rich shift amount) is raised to near “1V” on the air-fuel ratio rich side, and the output signal on the air-fuel ratio lean side. The (lean shift amount) is reduced to near “0V”, and the maximum value of the rich → lean reversal speed and the minimum value of the lean → rich reversal speed are also specified values. Therefore, the maximum value of the rich → lean reversal speed is changed as shown by the characteristic of the upper solid line E in the figure, and the minimum value of the lean → rich inversion speed is the lower solid line E in the figure. As shown in the characteristics. Further, the rich shift amount is changed as indicated by a solid line characteristic F in the figure, and the lean shift amount is changed as indicated by a solid line characteristic G in the figure.

  However, when the downstream exhaust sensor 10 has a failure such as deterioration, the output signal (rich shift amount) is lowered from “1V” on the rich side of the air-fuel ratio, as shown by the broken line D in FIG. On the lean side, the output signal (lean shift amount) will rise from "0V", and the rich → lean reverse speed maximum value and lean → rich reverse speed minimum value will also decrease from the specified value. It becomes. Therefore, the maximum value of the rich → lean reversal speed is changed as shown by the characteristic of the broken line on the upper side of E in the figure, and the minimum value of the lean → rich reversal speed is represented by the broken line on the lower side of E in the figure. As shown in the characteristics. Further, the rich shift amount is changed as indicated by a broken line characteristic F in the drawing, and the lean shift amount is changed as indicated by a broken line characteristic G in the drawing.

  The maximum value of the rich-> lean reversal speed, the minimum value of the lean-> rich reversal speed, the rich shift amount, and the lean shift amount are set in advance in step S5 as a preset reversal speed reference (the upper and lower one-dot chain lines of E in FIG. ), When compared with a preset shift amount reference (the alternate long and short dash lines in the figure), if both the reverse speed reference and the shift amount reference are exceeded, the downstream exhaust sensor 10 If it is determined to be normal and neither of them has exceeded, it can be determined that the downstream exhaust sensor 10 is abnormal.

  As described above, in the present embodiment, the active control of the air-fuel ratio is performed in the catalyst inactive state at each cold start, and the downstream exhaust sensor 10 fails based on the output change of the downstream exhaust sensor 10 of the catalyst 8. Therefore, the responsiveness, dead time, and output shift of the downstream exhaust sensor 10 can be accurately diagnosed without being affected by the oxygen storage function of the upstream catalyst 8. Further, it is possible to diagnose whether there is an abnormality in the downstream exhaust sensor 10 without being affected by the degree of deterioration of the upstream catalyst 8. Moreover, since the diagnosis of the downstream exhaust sensor 10 can be executed every time the cooler is started, the diagnosis execution frequency in the market can be sufficiently secured, and high-frequency diagnosis can be expected. Furthermore, since it is not affected by the oxygen storage function of the upstream catalyst 8, the amplitude / cycle of the air-fuel ratio A / F that is actively changed can be narrowed, so that the influence on the exhaust performance deterioration and the operability deterioration can be reduced.

  In the present embodiment, the following effects can be achieved.

  (A) The catalyst activity rate estimation calculation means (step S1) for detecting or calculating the activity rate of the exhaust purification catalyst 8 disposed in the exhaust passage 7 of the internal combustion engine 1 and the upstream air-fuel ratio of the catalyst 8 are rich. In an inactive state where the air-fuel ratio active control means (step S3) forcibly changing between the lean side and the lean side, and the catalyst activity rate detected or calculated by the catalyst activity rate estimation calculating means is lower than a preset value, And an abnormality determining unit (step S4 to step S5) for operating the air-fuel ratio active unit and determining an abnormality of the exhaust sensor 10 based on an output signal of the exhaust sensor 10 obtained.

  That is, based on the output signal of the exhaust sensor 10 obtained by operating the air-fuel ratio active means in the inactive state where the catalyst activity rate detected or calculated by the catalyst activity rate estimation calculating means is lower than a preset value. Since the abnormality of the exhaust sensor 10 is determined, the responsiveness / dead time / output shift of the downstream exhaust sensor 10 can be accurately diagnosed without being affected by the oxygen storage function of the upstream catalyst 8. Further, it is possible to diagnose whether there is an abnormality in the downstream exhaust sensor 10 without being affected by the degree of deterioration of the upstream catalyst 8. Moreover, since the diagnosis of the downstream exhaust sensor 10 can be executed every time the cooler is started, the diagnosis execution frequency in the market can be sufficiently secured, and high-frequency diagnosis can be expected. Furthermore, since it is not affected by the oxygen storage function of the upstream catalyst 8, the amplitude / cycle of the air-fuel ratio A / F that is actively changed can be narrowed, so that the influence on the exhaust performance deterioration and the operability deterioration can be reduced.

  (A) The abnormality determination means (step S4 to step S5) is a change speed of the output signal of the exhaust sensor 10 from the rich side to the lean side, a change speed from the lean side to the rich side, a rich side shift amount, and a lean side shift. Since abnormality of the exhaust sensor 10 is determined based on one or more parameters of the quantity, the responsiveness of the downstream exhaust sensor 10 can be accurately diagnosed.

(Second Embodiment)
FIGS. 4 to 10 show a second embodiment of an exhaust sensor diagnostic apparatus to which the present invention is applied, FIGS. 4 and 5 show an exhaust sensor diagnostic apparatus of the first embodiment, and FIGS. 6 to 8 show a second embodiment. FIGS. 9 to 10 show an exhaust sensor diagnostic apparatus according to the third embodiment. In the present embodiment, a configuration considering the progress of activation of the catalyst 8 is added to the first embodiment. The same devices as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.

  As the activation of the catalyst 8 arranged in the exhaust passage 7 progresses, the oxygen in the exhaust is occluded when the air-fuel ratio of the exhaust passing therethrough is leaner than the stoichiometric air-fuel ratio. When it is richer than the air-fuel ratio, a so-called oxygen storage function for releasing the stored oxygen is activated and enhanced. For this reason, the output signal of the downstream exhaust sensor 10 when the active control of the air-fuel ratio is performed is attenuated as the activation of the catalyst 8 progresses.

  In the diagnosis apparatus of the first example of the present embodiment shown in FIGS. 4 and 5, the oxygen storage function is activated and enhanced as the activation of the catalyst 8 progresses, and the output signal of the downstream exhaust sensor 10 is attenuated. In consideration of this, the criterion as the criterion is made variable. Other configurations are the same as those in the first embodiment.

  That is, the closer the catalyst 8 is to the active state, the lower the diagnostic parameters of the downstream exhaust sensor 10 (the rich → lean reverse speed maximum value, the lean → rich reverse speed minimum value, the rich shift amount, and the lean shift amount). Therefore, since it is easy to determine that it is abnormal, in step S10, the criterion (determination criterion) is made variable so as to decrease according to the catalyst activity rate.

  Specifically, with respect to the maximum value of the rich-to-lean reversal speed in FIG. 5E, the reversal speed reference H1 is set when the catalyst active state is low, and the reversal speed reference is set as the catalyst active state increases. When the catalytic activity state finally becomes high, it is changed to the reverse speed reference H2. Similarly, with respect to the minimum value of the lean-to-rich inversion speed, the inversion speed reference L1 is set when the catalyst activation state is low, and the inversion speed reference is increased as the catalyst activation state increases, and finally the catalyst When the active state becomes high, it is changed to the reversal speed reference L2.

  Also, the rich shift amount and the lean shift amount in FIGS. 5 (F) and 5 (G) are also set to the shift amount standards LH1 and LN1 when the catalyst active state is low, and the shift amount reference as the catalyst active state increases. Is lowered and raised, and when the catalyst active state eventually becomes higher, the shift amount is changed to the reference values LH2 and LN2.

  By varying the criteria described above, it is possible to accurately determine the abnormality of the downstream exhaust sensor 10 without being affected by the attenuation of the output signal of the downstream exhaust sensor 10 due to the progress of catalyst activation.

  In the diagnostic apparatus of the second example of the present embodiment shown in FIGS. 6 to 8, the oxygen storage function is activated and enhanced as the activation of the catalyst 8 progresses, and the output signal of the downstream exhaust sensor 10 is attenuated. In consideration of this, the output signal of the downstream exhaust sensor 10 is amplified and corrected in accordance with the activity rate of the catalyst 8. Other configurations are the same as those in the first embodiment.

  That is, the closer the catalyst 8 is to the active state, the lower the diagnostic parameters of the downstream exhaust sensor 10 (the rich → lean reverse speed maximum value, the lean → rich reverse speed minimum value, the rich shift amount, and the lean shift amount). Therefore, in step S11, the output signal of the downstream exhaust sensor 10 is amplified and corrected according to the catalyst activation rate so that an output equivalent to that when the catalyst is inactive can be obtained. To do.

  Specifically, as shown in FIG. 8, as the activity rate of the catalyst 8 is increased, the correction rate to be added to the output signal of the downstream exhaust sensor 10 is gradually increased from 1 time, and the obtained corrected value is obtained. As shown in FIG. 7E, the output signal of the downstream exhaust sensor 10 is set to be equivalent to that when the catalyst is inactive.

  As a result, the reverse speed reference for the maximum value of the rich → lean reverse speed to be compared, the reverse speed reference for the minimum value of the lean → rich reverse speed, and the shift quantity standard for the rich shift amount / lean shift amount in step S5 A standard at the time of inactivity, for example, a standard equivalent to the comparative standard in the first embodiment can be used.

  By correcting the output signal of the downstream exhaust sensor 10 as described above, the abnormality determination of the downstream exhaust sensor 10 can be performed accurately without being affected by the attenuation of the output signal of the downstream exhaust sensor 10 due to the progress of catalyst activation.

  In the diagnostic apparatus of the third example of the present embodiment shown in FIGS. 9 and 10, the oxygen storage function is activated and enhanced as the activation of the catalyst 8 progresses, and the output signal of the downstream exhaust sensor 10 is attenuated. In consideration of this, the input amplitude of the active control of the air-fuel ratio is amplified and corrected in accordance with the activity rate of the catalyst 8. Other configurations are the same as those in the first embodiment.

  That is, the closer the catalyst 8 is to the active state, the lower the diagnostic parameters of the downstream exhaust sensor 10 (the rich → lean reverse speed maximum value, the lean → rich reverse speed minimum value, the rich shift amount, and the lean shift amount). Therefore, in step S11, the input amplitude of the air-fuel ratio active control is amplified and corrected according to the catalyst activation rate, so that an output equivalent to that when the catalyst is inactive can be obtained. To.

  Specifically, as shown in FIG. 10, as the activation rate of the catalyst 8 is increased, the correction rate to be added to the input amplitude of the active control of the air-fuel ratio is gradually increased from 1 to obtain the corrected post-correction The output amplitude of the active control of the air-fuel ratio is changed as shown in FIG. 9 (B or C), and as shown in FIG. 9 (D), the output signal of the downstream exhaust sensor 10 is obtained when the catalyst is inactive. Make equivalent output.

  As a result, the reverse speed reference for the maximum value of the rich → lean reverse speed to be compared, the reverse speed reference for the minimum value of the lean → rich reverse speed, and the shift quantity standard for the rich shift amount / lean shift amount in step S5 A standard at the time of inactivity, for example, a standard equivalent to the comparative standard in the first embodiment can be used.

  By correcting the input signal of the air-fuel ratio active control as described above, the abnormality determination of the downstream exhaust sensor 10 can be performed accurately without being affected by the attenuation of the output signal of the downstream exhaust sensor 10 due to the progress of catalyst activation.

  In the present embodiment, in addition to the effects (a) and (b) in the first embodiment, the following effects can be achieved.

  (C) In the first embodiment, the abnormality determination means (step S4-step S10-step S5) outputs the output of the exhaust sensor 10 in accordance with the increase in the catalyst activity rate from the catalyst activity rate estimation calculation means (step S1). Since the abnormality criterion for the signal is lowered, a diagnosis in consideration of the catalyst activity rate can be performed, and the diagnosis accuracy can be improved. In addition, since the amplitude of the air-fuel ratio that is actively controlled between the rich side and the lean side can be narrower than when the catalyst is active, the impact on the exhaust performance degradation can be reduced, and the diagnosis time can also be shortened. Can do.

  (D) In the second embodiment, the abnormality determination means (step S11-step S4-step S5) outputs the exhaust sensor 10 in accordance with the increase in the catalyst activity rate from the catalyst activity rate estimation calculation means (step S1). Since the signal is increased and corrected, a diagnosis in consideration of the catalyst activity rate can be performed, and the diagnosis accuracy can be improved. In addition, since the amplitude of the air-fuel ratio that is actively controlled between the rich side and the lean side can be narrower than when the catalyst is active, the impact on the exhaust performance degradation can be reduced, and the diagnosis time can also be shortened. Can do.

  (E) In the third embodiment, the abnormality determination means (step S11-step S4-step S5) is an air-fuel ratio active control means according to the increase in the catalyst activity rate from the catalyst activity rate estimation calculation means (step S1). Since the air-fuel ratio amplitude is increased, the diagnosis considering the catalyst activity rate can be performed, and the diagnosis accuracy can be improved. In addition, since the amplitude of the air-fuel ratio that is actively controlled between the rich side and the lean side can be narrower than when the catalyst is active, the impact on the exhaust performance degradation can be reduced, and the diagnosis time can also be shortened. Can do.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine, engine 2 Intake passage 3 Air cleaner 4 Throttle valve 5 Injector 6 Air flow meter 7 Exhaust passage 8 Catalyst 9 Upstream sensor 10 Downstream sensor 12 Engine control device

Claims (4)

An exhaust sensor diagnostic device for detecting a downstream air-fuel ratio of an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine,
Catalyst activity rate estimation calculating means for detecting or calculating the activity rate of the catalyst until the catalyst is activated each time the internal combustion engine is cold-started ;
An air-fuel ratio active control means for forcibly changing the upstream air-fuel ratio of the catalyst between the rich side and the lean side after the cold start of the internal combustion engine ;
The inactive state in which the catalyst activity rate detected or calculated by the catalyst activity rate estimation calculation means is lower than a preset value after the cold engine start of the internal combustion engine is obtained by operating the air-fuel ratio active means. Bei example and abnormality determination means for determining an abnormality of the exhaust gas sensor based on the output signal of the exhaust sensor to be, a,
The abnormality determination means includes one or more parameters of a change speed of the exhaust sensor output signal from the rich side to the lean side, a change speed from the lean side to the rich side, a rich side shift amount, and a lean side shift amount. An exhaust sensor diagnosis device, wherein an abnormality of the exhaust sensor is determined based on the above . 2. The exhaust sensor diagnosis according to claim 1, wherein the abnormality determination unit lowers an abnormality determination criterion for an output signal of the exhaust sensor in accordance with an increase in the catalyst activity rate from the catalyst activity rate estimation calculation unit. apparatus. 3. The exhaust sensor according to claim 1, wherein the abnormality determination unit corrects an increase in the output signal of the exhaust sensor in accordance with an increase in the catalyst activity rate from the catalyst activity rate estimation calculation unit. Diagnostic device. The said abnormality determination means increases the air-fuel ratio amplitude by the air-fuel ratio active control means in accordance with the increase in the catalyst activity rate from the catalyst activity rate estimation calculation means. Exhaust sensor diagnostic device.

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