JP2008014234A - Abnormality diagnosing device for exhaust sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase opportunities in which abnormality diagnosis can be executed without dropping reliability of diagnosis results and quickly detect abnormality when abnormality occurs on an oxygen sensor. <P>SOLUTION: In an abnormality diagnosing device for an air fuel ratio sensor 14 forcibly changing air fuel ratio under a condition that measurement value of intake air quantity is predetermined criterion or higher and judging existence of abnormality of the air fuel ratio sensor 14 based on output state of detection signal after that, abnormality diagnosis of the air fuel ratio sensor 14 is performed with executing intake air quantity increase process forcibly increasing intake air quantity to reference quantity or more by increasing speed change ratio of a continuously variable transmission 1 connecting an engine 4 and a vehicle drive system and raising engine speed even if intake air quantity is less than the reference quantity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an abnormality diagnosis device for an exhaust sensor that is provided in an exhaust passage of an internal combustion engine and outputs a detection signal corresponding to the oxygen concentration of exhaust gas.

  As is well known, in a vehicle engine, air-fuel ratio feedback control is performed to correct the fuel injection amount based on a signal corresponding to the oxygen concentration of exhaust gas output from an exhaust sensor in order to maintain the air-fuel ratio appropriately. ing. In this exhaust sensor, characteristics such as output characteristics and responsiveness may change due to deterioration or disconnection due to exhaust heat, and the oxygen concentration detection accuracy may decrease. If air-fuel ratio feedback control is performed in such a state, control of the air-fuel ratio in accordance with the engine operating state is not performed properly, and there is a concern that the engine output will decrease or the exhaust properties will deteriorate. In view of this, conventionally, for example, as disclosed in Patent Document 1, abnormality diagnosis for detecting an abnormality of such an exhaust sensor is appropriately performed.

  This exhaust sensor abnormality diagnosis is based on the principle that the inversion cycle of the rich signal and the lean signal from the sensor during air-fuel ratio feedback control becomes longer when the electromotive force changes or the response decreases due to deterioration of the exhaust sensor. It is the one that paid attention. That is, when the actual inversion period between the rich signal and the lean signal from the exhaust sensor is longer than a predetermined determination value, it is determined that the exhaust sensor has deteriorated. Incidentally, this judgment value is calculated based on the intake air amount, and the inversion period of the output of the exhaust sensor becomes longer as the intake air amount becomes smaller. Therefore, this judgment value is set so as to increase accordingly. Yes. In addition, when the amount of intake air is extremely small, the response of the exhaust sensor naturally becomes sluggish due to a decrease in the exhaust flow velocity and a decrease in the amount of oxygen contained in the exhaust, and a diagnosis is made that it is erroneously abnormal even if the exhaust sensor is normal. Therefore, the execution of the abnormality diagnosis is suspended until the intake air amount is increased to an amount necessary for the diagnosis, and the abnormality diagnosis is not performed.

  Further, as seen in Patent Document 2, the air-fuel ratio of the air-fuel mixture is forcibly reversed based on a detection signal of an exhaust sensor provided on the downstream side of the catalyst device that purifies the exhaust, and the downstream side of the catalyst device. There is known an abnormality diagnosis method for diagnosing the abnormality based on an output mode of an exhaust sensor provided in the engine. In this method, when the air-fuel ratio of the exhaust gas is lean, oxygen in the exhaust gas is occluded.When the air-fuel ratio of the exhaust gas is rich, the oxygen storage function of the catalyst that releases the occluded oxygen into the exhaust gas is achieved. An abnormality diagnosis is performed based on the result. That is, when the exhaust sensor detects that the exhaust air-fuel ratio is lean, the fuel injection amount is gradually increased and corrected. In this case, the air-fuel ratio of the exhaust on the upstream side of the catalyst becomes rich. On the other hand, the air-fuel ratio of the exhaust gas on the downstream side of the catalyst becomes lean while the oxygen stored in the catalyst is released, and becomes rich after all the stored oxygen is released. On the other hand, when the exhaust sensor detects that the exhaust air-fuel ratio is rich, the fuel injection amount is gradually decreased and corrected. In this case, the air-fuel ratio of the exhaust on the upstream side of the catalyst becomes lean. On the other hand, the air-fuel ratio of exhaust on the downstream side of the catalyst becomes rich while the catalyst is storing oxygen in the exhaust, and the stored oxygen exceeds the limit oxygen storage amount of the catalyst and stores the oxygen. It becomes lean when it becomes impossible.

In this way, there is a time delay between the change of the air-fuel ratio of the exhaust upstream of the catalyst due to the oxygen storage action and the change of the air-fuel ratio of the exhaust downstream of the catalyst. Based on the above, the amount of oxygen occluded or released by the catalyst can be estimated. Further, the limit oxygen storage amount of the catalyst does not increase even if it decreases due to deterioration with time or the like. Therefore, when the estimated oxygen amount is larger than the initial limit oxygen storage amount of the catalyst, it can be diagnosed that the exhaust sensor is abnormal. However, since the estimated value of the amount of oxygen occluded (released) by the catalyst is calculated based on the activated state of the catalyst, for example, when the catalyst temperature is low and the catalyst is not activated, this oxygen The amount cannot be calculated accurately. In this case, even if the response of the exhaust sensor is delayed due to its deterioration, the exhaust gas whose oxygen concentration is richer or leaner than assumed on the downstream side of the catalyst flows, so that the output is the same as that of a normal exhaust sensor. May change without delay. That is, there is a possibility that an exhaust sensor in which an abnormality has occurred is misdiagnosed as normal. For this reason, when the catalyst temperature is low in this way, the execution of the abnormality diagnosis is suspended.
JP 2005-207249 A JP 2004-19542 A

  As described above, in the operation region where the intake air amount is small or the catalyst temperature is low, it is certainly avoided that the exhaust sensor is erroneously determined to be abnormal or normal by suspending execution of the exhaust sensor abnormality diagnosis. I can. However, if the intake air amount is low or the catalyst temperature is low, for example, when the vehicle must travel at a low speed due to traffic jams or the like, the exhaust sensor abnormality diagnosis is not performed for a long period of time. Therefore, even when there is an abnormality in the exhaust sensor, the detection is delayed, and the fuel injection amount is corrected based on the detection signal of the exhaust sensor in which this abnormality has occurred, resulting in deterioration of the engine combustion state and exhaust properties. There is a risk of inviting. Further, if the amount of intake air is small, the temperature rise due to the oxidation reaction in the catalyst is suppressed and the temperature of the catalyst is lowered, so that the same problem occurs.

  The present invention has been made in view of such a problem, and the object of the present invention is to increase the chances that an abnormality diagnosis can be performed without lowering the reliability of the diagnosis result, and an abnormality occurs in the exhaust sensor. An object of the present invention is to provide an abnormality diagnosis device for an exhaust sensor that can quickly detect this when it is.

  In order to solve the above-mentioned problem, the invention according to claim 1 is an abnormality of an exhaust sensor that is provided in an exhaust passage of a vehicle on which an engine is mounted and outputs a detection signal corresponding to the oxygen concentration of exhaust gas in the exhaust passage. The air-fuel ratio is forcibly changed on condition that the measured value of the intake air amount is equal to or greater than a predetermined determination value, and the exhaust gas is detected based on the output mode of the detection signal thereafter. In the exhaust gas sensor abnormality diagnosis device that determines whether there is an abnormality in the sensor, when the measured value of the intake air amount is less than the determination value, the gear ratio of the transmission that connects the engine and the vehicle drive system is increased. The gist is that the abnormality diagnosis is performed by executing an intake air amount increasing process for forcibly increasing the intake air amount to the determination value or more by increasing the engine rotation speed.

  According to this configuration, since the amount of oxygen that can be reacted by the exhaust sensor increases as the intake air amount increases, it is possible to increase the chances of performing abnormality diagnosis without reducing the reliability of the diagnosis result. When an abnormality has occurred in the sensor, this can be quickly detected.

  In order to solve the above-mentioned problem, the invention according to claim 2 is provided downstream of the catalyst device disposed in the exhaust passage of the vehicle on which the engine is mounted, and corresponds to the oxygen concentration of the exhaust in the exhaust passage. An abnormality diagnosis device for diagnosing an abnormality of the exhaust sensor that outputs the detected signal, wherein the air-fuel ratio is determined based on the detection signal on condition that the measured value of the catalyst temperature of the catalyst device is equal to or greater than a predetermined determination value In an exhaust sensor abnormality diagnosis device that forcibly changes and determines whether there is an abnormality in the exhaust sensor based on an output mode of the detection signal thereafter, when the measured value of the catalyst temperature is less than the determination value The intake air amount is increased by forcibly increasing the catalyst temperature to the determination value or higher by increasing the engine speed by increasing the transmission ratio of the transmission connecting the engine and the vehicle drive system. Suck Run the air amount increase processing and gist to carry out the abnormality diagnosis.

  According to the same configuration, the catalyst is activated by increasing the catalyst temperature as the exhaust gas flow rate increases, so that the possibility of performing abnormality diagnosis can be increased without lowering the reliability of the diagnosis result, When an abnormality occurs in the exhaust sensor, this can be quickly detected. Furthermore, since this is activated by the temperature rise of the catalyst, the exhaust sensor abnormality diagnosis can be executed while suppressing the deterioration of the exhaust properties caused by forcibly changing the air-fuel ratio.

The invention according to claim 3 is the exhaust sensor abnormality diagnosis device according to claim 1 or 2, wherein the transmission is a continuously variable transmission.
According to this configuration, since the change in the engine speed is suppressed by gradually changing the gear ratio, the influence on drivability can be suppressed.

  In order to solve the above problems, the invention according to claim 4 is an abnormality of an exhaust sensor that is provided in an exhaust passage of a vehicle on which an engine is mounted and outputs a detection signal corresponding to the oxygen concentration of exhaust gas in the exhaust passage. The air-fuel ratio is forcibly changed on condition that the measured value of the intake air amount is equal to or greater than a predetermined determination value, and the exhaust gas is detected based on the output mode of the detection signal thereafter. In the exhaust sensor abnormality diagnosis device for determining whether there is an abnormality in the sensor, when the measured value of the intake air amount is less than the determination value, the throttle valve opening is forcibly increased to determine the intake air amount. The gist of the invention is to perform the abnormality diagnosis by executing an intake air amount increasing process for forcibly increasing the ignition timing to a value and changing the ignition timing to the retard side.

  According to this configuration, since the amount of oxygen that can be reacted by the exhaust sensor increases as the intake air amount increases, it is possible to increase the chances of performing abnormality diagnosis without reducing the reliability of the diagnosis result. When an abnormality has occurred in the sensor, this can be quickly detected. Furthermore, by executing the control to change the ignition timing to the retard side along with the forced increase control of the throttle valve opening, the throttle valve opening is changed and the intake air amount is increased. An increase in engine output can be suppressed, and a deterioration in drivability can be suppressed as much as possible.

  In order to solve the above-mentioned problem, the invention according to claim 5 is provided downstream of the catalyst device disposed in the exhaust passage of the vehicle on which the engine is mounted, and corresponds to the oxygen concentration of the exhaust in the exhaust passage. An abnormality diagnosis device for diagnosing an abnormality of the exhaust sensor that outputs the detected signal, wherein the air-fuel ratio is determined based on the detection signal on condition that the measured value of the catalyst temperature of the catalyst device is equal to or greater than a predetermined determination value In an exhaust sensor abnormality diagnosis device that forcibly changes and determines whether there is an abnormality in the exhaust sensor based on an output mode of the detection signal thereafter, when the measured value of the catalyst temperature is less than the determination value And an intake air amount increasing process for forcibly increasing the catalyst temperature to the determination value or more by forcibly increasing the opening of the throttle valve and changing the ignition timing to the retard side. And gist to carry out normal diagnostic.

  According to the same configuration, the catalyst is activated by increasing the catalyst temperature as the exhaust gas flow rate increases, so that the possibility of performing abnormality diagnosis can be increased without lowering the reliability of the diagnosis result, When an abnormality occurs in the exhaust sensor, this can be quickly detected. Furthermore, since this is activated by the temperature rise of the catalyst, the exhaust sensor abnormality diagnosis can be executed while suppressing the deterioration of the exhaust properties caused by forcibly changing the air-fuel ratio. In addition, the throttle valve opening was changed to increase the intake air amount by executing the control to change the ignition timing to the retard side together with the forced increase control of the throttle valve opening. The increase in engine output due to the engine can be suppressed, and the deterioration of drivability can be suppressed as much as possible.

  The invention according to claim 6 is the exhaust lower limit diagnosis apparatus according to any one of claims 1 to 5, wherein the measured value is set to a value lower than the determination value. If it is lower than that, the execution of the intake air amount increasing process is suspended.

  If the intake air volume increase process is performed while the measured value of the intake air volume or catalyst temperature is significantly below the respective judgment value at which abnormality diagnosis can be performed, the intake air quantity or catalyst temperature will exceed the respective judgment value. The time required to become longer. For this reason, the engine rotational speed and the like are in a state of increasing over a long period of time, and there is a concern about deterioration of the driver viridy due to this. In this regard, according to the above configuration, if the measured value of the intake air amount or the catalyst temperature is significantly below the respective determination values that can be subjected to the abnormality diagnosis, the execution of the intake air amount increasing process is suspended and the same process is performed. Is not executed, it is possible to suppress the deterioration of the driver viridy as described above.

  According to a seventh aspect of the present invention, in the exhaust gas sensor abnormality diagnosis device according to the sixth aspect, the intake air amount increasing process is executed when a state in which the measured value is equal to or greater than the execution lower limit value does not continue for a predetermined period. The gist of this is to withhold.

  If the intake air volume increase process is executed unconditionally when the measured value of the intake air volume or the catalyst temperature is equal to or greater than the above-described lower limit of execution, the measured value of the intake air volume or the catalyst temperature will be When the value fluctuates in the vicinity of the value, the intake air amount increasing process is intermittently executed, and the engine operating state is deteriorated. In this regard, according to the above configuration, when the measured value of the intake air amount or the temperature of the catalyst is equal to or higher than the execution lower limit value does not continue for a predetermined period, that is, when the engine operating state of the engine is not stable. Since the execution of the air amount increase process is suspended and the process is not executed, it is possible to suppress instability of the engine operation state due to the intermittent execution of the intake air amount increase process.

  According to an eighth aspect of the present invention, in the exhaust sensor abnormality diagnosis device according to any one of the first to seventh aspects, the measured value is the determination value when a predetermined period elapses after the intake air amount increasing process is started. If not, the gist is to stop the intake air amount increasing process.

  In this configuration, if the intake air amount or the catalyst temperature is not equal to or higher than the respective determination values at the time when a predetermined period has elapsed after the intake air amount increase processing is started, this control is stopped. Therefore, it is possible to suppress the deterioration of the driver viridy caused by increasing the intake air amount over a long period for abnormality diagnosis.

  According to a ninth aspect of the present invention, in the exhaust gas sensor abnormality diagnosis device according to any one of the first to eighth aspects, the state in which the measured value is equal to or greater than the determination value is continuously maintained for a predetermined period. The gist of the present invention is to forcibly change the air-fuel ratio on the condition that this is done, and to determine whether or not the exhaust sensor is abnormal based on the subsequent output mode of the detection signal.

  As described above, the control for forcibly changing the air-fuel ratio may cause deterioration of exhaust properties depending on the execution mode. In this regard, in the above configuration, only when the measured value of the intake air amount and the catalyst temperature is continuously maintained in a state where the measured value is equal to or higher than the respective determination values, that is, when there is a high possibility that the abnormality diagnosis can be completed, Since the control for forcibly changing the air-fuel ratio is executed, it is possible to suppress this control from being executed unnecessarily and to suppress the deterioration of the exhaust properties accompanying the execution of the control.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a schematic configuration of an engine mounted on an automobile and its control device. An abnormality diagnosis of the air-fuel ratio sensor according to the present embodiment is executed by this engine control device.

  As shown in FIG. 1, a continuously variable transmission 1 for transmitting the rotational torque of the output shaft to a vehicle drive system is drivably connected to a crankshaft that is an output shaft of the engine 4. Further, in the engine 4, the amount of air (intake air amount Q) taken into a combustion chamber (not shown) is adjusted through opening control of the throttle valve 3 provided in the intake passage 2, and the intake air and the fuel injection valve are adjusted. The fuel / air mixture injected through the fuel 5 burns in the combustion chamber. Exhaust gas after combustion is sent to the exhaust passage 6, and harmful components are purified by a catalyst device (hereinafter referred to as the three-way catalyst 7) provided with the three-way catalyst provided in the passage 6. More specifically, the three-way catalyst 7 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 three-way catalyst 7 stores oxygen in the exhaust when the air-fuel ratio of the exhaust gas passing through it is leaner than the stoichiometric air-fuel ratio, and stores the stored oxygen when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. It has an oxygen storage function to release.

  The engine 4 is provided with an electronic control unit 8 that executes various controls in accordance with the driving conditions of the vehicle. The electronic control device 8 receives detection signals from various sensors shown below in its input circuit.

  For example, an accelerator position sensor 10 for detecting the operation amount (accelerator operation amount) is provided in the vicinity of the accelerator pedal 9 that is depressed by the driver. The intake passage 2 is provided with a throttle position sensor 11 for detecting the opening of the throttle valve 3 (throttle opening), and the amount of air taken into the combustion chamber through the intake passage 2 (intake air amount Q). Is provided. The engine 4 is provided with a crank position sensor 13 for outputting a signal corresponding to the rotational phase and rotational speed of the crankshaft.

  In the exhaust passage 6, an air-fuel ratio sensor 14 is provided on the upstream side of the three-way catalyst 7, and an oxygen sensor 15 is provided on the downstream side of the three-way catalyst 7. The air-fuel ratio sensor 14 is a known limit current type oxygen sensor. This limiting current type oxygen sensor is a sensor that provides an output current according to the oxygen concentration in the exhaust gas by providing a ceramic layer called a diffusion rate limiting layer in the detection part of the concentration cell type oxygen sensor, and the air-fuel ratio of the air-fuel mixture When is the stoichiometric air-fuel ratio, its output current is “0”. Further, the output current decreases as the air-fuel ratio of the air-fuel mixture becomes rich, and the output current increases as the air-fuel ratio of the air-fuel mixture becomes leaner. Accordingly, based on the output of the air-fuel ratio sensor 14, the lean degree or rich degree of the air-fuel ratio of the air-fuel mixture flowing into the three-way catalyst 7 can be detected.

  The oxygen sensor 15 is a well-known concentration cell type oxygen sensor. As for the output characteristics of the concentration cell type oxygen sensor, an output of about 1 V is obtained when the oxygen concentration is richer than the stoichiometric air-fuel ratio, and an output of about 0 V is obtained when the oxygen concentration is leaner than the stoichiometric air-fuel ratio. Further, the output voltage changes greatly in the vicinity of the theoretical air-fuel ratio. Therefore, it is possible to detect whether the air-fuel ratio on the downstream side of the three-way catalyst 7 is lean or rich based on the output of the oxygen sensor 15.

  By the way, the purification efficiency by the three-way catalyst 7 is strongly influenced by the air-fuel ratio of the air-fuel mixture, and the air-fuel ratio of the air-fuel mixture is set in the range near the stoichiometric air-fuel ratio in order to simultaneously purify the HC, CO, and Nox. There is a need. Therefore, in order to make this three-way catalyst 7 function effectively, air-fuel ratio control is performed in which the air-fuel ratio of the air-fuel mixture is adjusted to the center of the above range.

  The electronic control unit 8 controls the air-fuel ratio by drivingly controlling the throttle valve 3 and the fuel injection valve 5 in accordance with the operating conditions of the engine 4 and the vehicle that are grasped based on the detection signals from these sensors. (Air-fuel ratio feedback control) is performed. The outline of the air-fuel ratio control by the electronic control device 8 is as follows.

  First, the electronic control unit 8 obtains a required amount of intake air amount that is grasped according to the accelerator operation amount of the accelerator pedal 9 and the detection result of the engine speed, and the throttle valve so that the intake air amount corresponding to the required amount can be obtained. Adjust the opening of 3. On the other hand, a fuel amount sufficient to obtain the theoretical air-fuel ratio is obtained from the actual measured value of the intake air amount Q detected by the air flow meter 12, and the fuel injection amount of the fuel injection valve 5 is adjusted accordingly. Thereby, the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber can be brought close to the stoichiometric air-fuel ratio to some extent. However, since there are individual differences in the detection characteristics of the air flow meter 12 and the injection characteristics of the fuel injection valve 5, it is difficult to properly execute the required highly accurate air-fuel ratio control.

  Therefore, the electronic control unit 8 grasps the actual measurement value of the air-fuel ratio upstream of the three-way catalyst 7 based on the detection result of the air-fuel ratio sensor 14, and the difference between the actual measurement value and the target air-fuel ratio, that is, the theoretical air-fuel ratio. Based on the air-fuel ratio feedback correction amount calculated based on the degree, the fuel injection amount through the fuel injection valve 5 is feedback corrected. This air-fuel ratio feedback control ensures the required accuracy of air-fuel ratio control.

  Further, the electronic control unit 8 estimates the oxygen storage state or oxygen release state of the three-way catalyst 7 from the detection result of the oxygen sensor 15, and corrects the air-fuel ratio feedback correction amount based on this estimation. In this correction process, the sub-feedback correction amount calculated based on the output of the oxygen sensor 15 is increased or decreased, and the air-fuel ratio feedback correction amount is corrected by the sub-feedback correction amount. Specifically, while the output of the oxygen sensor 15 is rich, the sub-feedback correction amount is increased by a certain amount to the minus side so that the air-fuel ratio of the air-fuel mixture changes toward a lean amount by a certain amount. . On the other hand, while the output of the oxygen sensor 15 indicates lean, the air-fuel ratio upstream of the three-way catalyst 7 changes toward the rich by a certain amount, that is, the air-fuel ratio upstream of the three-way catalyst 7 gradually increases. The sub feedback correction amount is increased to the plus side by a certain amount so as to approach the rich side. By such sub-feedback control, the purification action of the three-way catalyst 7 is effectively utilized.

  Here, if an abnormality occurs in the exhaust sensor, that is, the air-fuel ratio sensor 14 in this embodiment, the output signal does not reflect the actual air-fuel ratio of the exhaust gas, and it is difficult to accurately execute the air-fuel ratio feedback control. It becomes. Therefore, in the present embodiment, the abnormality diagnosis process shown below is executed in order to diagnose the abnormality of the air-fuel ratio sensor 14. That is, when this abnormality diagnosis is executed, the target air-fuel ratio becomes rich (for example, target air-fuel ratio = 14.1) and lean (by changing the fuel injection amount each time the output of the oxygen sensor 15 is reversed. For example, the control (hereinafter referred to as “active control”) that reverses the target air-fuel ratio = 15.1) is executed. When this active control is executed, fuel corresponding to the target air-fuel ratio is injected through the fuel injection valve 5, so that the air-fuel ratio of the exhaust gas also changes between lean and rich. Therefore, the output of the air-fuel ratio sensor 14 also shifts between an output value corresponding to the case where the air-fuel ratio is rich and an output value corresponding to the case where the air-fuel ratio is lean. The abnormality diagnosis can be executed on the basis of the amplitude monitoring. That is, if the air-fuel ratio sensor 14 has an abnormality such as deterioration due to exhaust heat, for example, and the output value or the response is reduced, the amplitude of the output value is smaller than the assumed amplitude. Based on this, it can be diagnosed that the air-fuel ratio sensor 14 is abnormal. When the abnormality of the air-fuel ratio sensor 14 is diagnosed in this manner, the influence of the air-fuel ratio control on the engine state can be suppressed as much as possible by executing a predetermined fail-safe process.

  By the way, in order to execute this active control and abnormality diagnosis, the engine state is a predetermined condition, specifically, the measured value of the intake air amount (intake air amount Q) detected by the air flow meter 12 is a predetermined reference amount. It is necessary to be larger than Qa. If the abnormality diagnosis is performed in a state where this condition is not satisfied, the amount of oxygen contained in the exhaust gas is reduced because the amount of intake air is small, and the amount of change in the output of the air-fuel ratio sensor 14 is also reduced accordingly. Even if the fuel ratio sensor 14 is normal, there is a risk that it is erroneously diagnosed as being abnormal. In view of this, the condition that the intake air amount Q is higher than the predetermined reference amount Qa is used as an execution condition of the active control and abnormality diagnosis.

  However, when the abnormality diagnosis execution conditions are set in this way, the air-fuel ratio is extended over a long period of time when the operating region in which the intake air amount is limited to a small amount, for example, a situation where the vehicle has to travel at a low speed due to traffic jams or the like continues. The abnormality diagnosis of the sensor 14 is not performed. Therefore, even if an abnormality occurs in the air-fuel ratio sensor 14, the feedback correction of the fuel injection amount is performed based on the output signal of the air-fuel ratio sensor 14, and there is a possibility that the engine output is reduced and the exhaust property is deteriorated. . Therefore, in this embodiment, control is performed so that the diagnosis can be executed through a temporary change of the engine state even when the intake air amount is less than a value at which the abnormality diagnosis can be executed. It has been broken. Specifically, even when the value of the intake air amount Q is lower than the reference amount Qa described above, the gear ratio of the continuously variable transmission 1 that connects the engine 4 and the vehicle drive system is gradually increased. By executing the process for forcibly increasing the intake air amount to the reference amount Qa or more by increasing the engine speed (hereinafter referred to as “intake air amount increasing process”), the condition for executing the abnormality diagnosis is satisfied. I am doing so.

  Hereinafter, a series of processing procedures related to abnormality diagnosis including the intake air amount increase processing will be described with reference to FIGS. FIG. 2 is a flowchart showing a procedure of abnormality diagnosis processing for diagnosing the presence / absence of abnormality of the air-fuel ratio sensor 14. FIG. 3 is a flowchart showing a sequence of processing related to the execution of active control performed together with the abnormality diagnosis processing, and FIG. 4 shows a sequence of processing related to the execution of the intake air amount increase processing. It is a flowchart to show.

  The abnormality diagnosis process is started when the ignition switch is turned on, and is repeatedly executed at predetermined time intervals by the time interruption process. As shown in FIG. 2, in the abnormality diagnosis process, it is first determined whether or not the value of the active control execution flag AF is “1” (step S10). The active control execution flag AF is a flag indicating whether or not active control is being executed, and is set to “1” or “0” in the process shown in FIG. If the determination result in step S10 is negative, that is, if active control is not being executed, the process is temporarily terminated without executing abnormality diagnosis.

  On the other hand, if the determination result of step S10 is affirmative, the process proceeds to step S20 to determine whether air-fuel ratio feedback control is being executed. If the determination result of step S20 is negative, the air-fuel ratio feedback control is not executed and it cannot be determined whether the air-fuel ratio sensor 14 is abnormal. Therefore, the process ends without performing abnormality diagnosis.

  On the other hand, if the determination result in step S20 is affirmative, after waiting for a predetermined time from the start of the abnormality diagnosis process (step S30), whether or not the active control execution flag AF is “1” in step S40. Is determined. This is because the active control may be stopped due to a change in the engine operating state even during the execution of the active control, as will be described later, and the value of the active control execution flag AF is “1” after a predetermined time has elapsed. If not maintained, the execution of the abnormality diagnosis is stopped.

  On the other hand, if the determination result in step S40 is affirmative, the process proceeds to step S50, the amplitude of the output value of the air-fuel ratio sensor 14 is calculated, and it is determined whether or not this value is greater than a predetermined threshold value. Executed. The principle of enabling abnormality diagnosis by such a method will be described with reference to FIG. FIG. 5 is a time chart showing changes in the output value of the air-fuel ratio sensor 14 and the fuel injection amount when active control is executed. As shown in FIG. 5, when active control is executed, the fuel injection valve The fuel injection amount through 5 is periodically increased or decreased. When the fuel injection amount decreases, the oxygen concentration in the exhaust passage 6 increases and the output from the air-fuel ratio sensor 14 increases. On the other hand, when the fuel injection amount increases, the oxygen concentration in the exhaust passage 6 decreases and the air-fuel ratio The output from the sensor 14 decreases. If the air-fuel ratio sensor 14 is normal at this time, its output value changes with a large amplitude L1 as shown by the solid line in FIG. 5, but if the air-fuel ratio sensor 14 is deteriorated, the output value of the air-fuel ratio sensor 14 Changes with an amplitude L2 that is relatively smaller than the amplitude L1, as indicated by a broken line. Therefore, if the air-fuel ratio sensor 14 is deteriorated, the amplitude L2 indicated by the difference between the maximum value and the minimum value of the output from the sensor is smaller than the amplitude L1 when normal, so the threshold value is larger than the amplitude L2. By setting a value that is large and smaller than the amplitude L1, it is possible to appropriately diagnose whether the air-fuel ratio sensor 14 is abnormal. In order to perform a more accurate abnormality diagnosis, an average value for a predetermined period is calculated for the amplitude of the output value in the air-fuel ratio sensor 14, and an abnormality is determined based on a comparison result between the calculated average value and the threshold value. It is desirable to diagnose the presence or absence.

  If the amplitude of the output value is smaller than the predetermined threshold value, the process proceeds to step S60 in FIG. 2 to diagnose that the air-fuel ratio sensor 14 is abnormal and the abnormality flag is set to “1”. When this abnormality diagnosis is performed, the process proceeds to step S70, the active control execution flag AF and the later-described increase control execution flag BF are set to “0”, and the abnormality diagnosis process is ended. Incidentally, when the abnormality diagnosis process of the air-fuel ratio sensor 14 is completed in this way, the abnormality diagnosis is not performed until the engine 4 is stopped and restarted.

  Next, the flow of processing related to active control will be described. Similarly, this active control is repeatedly executed at predetermined time intervals by a time interruption process. As shown in FIG. 3, first, in step S100, it is determined whether or not the active control execution flag AF is “1”. If this determination result is negative, that is, if active control is not being executed, the routine proceeds to step S110, where it is determined whether or not the intake air amount Q detected by the air flow meter 12 is greater than or equal to a predetermined reference amount Qa. . If the determination result of step S110 is negative, the process proceeds to step S121, and the value of the active area counter A1c is set to “0”. The active area counter A1c is a parameter indicating a period during which the engine operating state is maintained in a state where active control can be performed. Here, since the active control is no longer executable, the value of the active area counter A1c is initialized and the process is terminated.

  On the other hand, if the determination result of step S110 is affirmative, the process proceeds to step S120, and the value of the active area counter A1c is incremented. Next, the process proceeds to step S130, where it is determined whether or not the value of the active area counter A1c is equal to or greater than the reference counter value A1. This determination is executed in order to determine whether or not the engine operation state is maintained in a state where active control can be executed for a predetermined period. If the determination result is affirmative, an active control execution flag is set. AF is set to “1” (step S140), and the process ends. On the other hand, if the determination result of step S130 is negative, the process ends without executing the process of step S140.

  On the other hand, when the determination result of the previous step S100 is affirmative, the above-described active control is executed (step S200). In other words, when the exhaust air-fuel ratio detected by the oxygen sensor 15 is lean, the target air-fuel ratio is set to a rich value, and when the exhaust air-fuel ratio is rich, the target air-fuel ratio is set to a lean value. The With such control, the output value of the air-fuel ratio sensor 14 repeats increasing and decreasing.

  Next, the routine proceeds to step S210, where it is determined whether or not the intake air amount Q detected by the air flow meter 12 is smaller than the reference amount Qa. When the determination result is affirmative, the process proceeds to step S220, and the active control stop counter A2c is incremented. Then, it is determined whether or not the value of the active control stop counter A2c is greater than or equal to the reference counter value A2 (step S230). If the determination result is affirmative, the value of the active control execution flag AF is set to “0” (step S230). Step S240). In the processes of Steps S210 to S240, even when active control is being executed, the intake air amount may decrease due to a change in the engine operation state, and the conditions for the abnormality diagnosis may not be satisfied. Is executed to stop active control. When the value of the active control execution flag AF is set to “0” through this process, the determination in step S40 of the above-described abnormality diagnosis process is negative, and the abnormality diagnosis is stopped.

On the other hand, if the determination result of step S210 is negative, “0” is set to the value of the active control stop counter A2c, and the process ends (step S211).
Next, the flow of processing related to the intake air amount increase processing will be described with reference to the flowchart of FIG. Similarly, the intake air amount increasing process is repeatedly executed at predetermined time intervals by the time interruption process. As shown in FIG. 4, first, in step S300, it is determined whether or not an increase control execution flag BF for determining whether or not an intake air amount increasing process is being executed is “1”. When this determination result is negative, that is, when the intake air amount increase processing is not executed, the process proceeds to step S310, and whether or not the intake air amount Q detected by the air flow meter 12 is equal to or greater than a predetermined reference amount Qb. Determined. The reference amount Qb is a value lower than the reference amount Qa, and corresponds to the execution lower limit value of the intake air amount increasing process. Incidentally, the value of the reference amount Qb is set to a value that allows the intake air amount to be larger than the reference amount Qa without executing the intake air amount increasing process over a long period of time. If the determination result of step S310 is negative, the process proceeds to step S321, and the value of the increase area counter B1c is set to “0”. The increase area counter B1c is a parameter indicating a period during which the engine operating state is maintained in a state where increase control can be executed, that is, a state in which the intake air amount Q is maintained at or above the reference amount Qb. Here, since the intake air amount increase process is no longer executable, the value of the increase area counter B1c is initialized to “0” and the process ends.

  On the other hand, if the determination result of step S310 is affirmative, the process proceeds to step S320, and the value of the increase area counter B1c is incremented. Next, the process proceeds to step S330, where it is determined whether or not the value of the increase area counter B1c is equal to or greater than the reference counter value B1. This determination is executed in order to determine whether or not the engine operation state is maintained in a state where the intake air amount increase processing can be executed for a predetermined period. If the determination result is affirmative, increase control is performed. The execution flag BF is set to “1” (step S340), and the process ends. On the other hand, if the determination result of step S330 is negative, the process ends without executing the process of step S340.

  If the determination result of the previous step S300 is affirmative, the intake air amount increasing process described above is executed (step S400). That is, the engine speed is increased by gradually increasing the gear ratio of the continuously variable transmission 1 that connects the engine 4 and the vehicle drive system. Next, the process proceeds to step S410, and the value of the increase control counter B2c is incremented. The increase control counter B2c is a value indicating the execution period of the intake air amount increasing process. Next, it is determined whether or not the value of the increase control counter B2c is equal to or greater than a predetermined reference counter value B2, that is, whether or not the intake air amount increasing process is continued for a predetermined period (step S420). In this case, it is further determined whether or not the intake air amount Q detected by the air flow meter 12 is smaller than the reference amount Qa (step S430). If the determination result of step S430 is affirmative, the value of the increase control execution flag BF is set to “0”. Although the intake air amount increasing process is executed through the processes in steps S410 to S440, the intake air amount is a reference value necessary for executing the abnormality diagnosis of the air-fuel ratio sensor 14 within a predetermined period. When the reference amount Qa is not reached, the intake air amount increasing process is stopped. As a result, it is possible to suppress the deterioration of the driver viridy due to the increase in the intake air amount over a long period of time.

  Next, the operation obtained by the processing described above will be described with reference to FIGS. 6 to 8 are timing charts respectively showing one aspect of changes in the engine operating state during a series of processing for abnormality diagnosis.

  For example, FIG. 6 shows a case where the intake air amount increases due to the execution of the intake air amount increase process and abnormality diagnosis of the air-fuel ratio sensor 14 is executed. As shown in FIG. 6, since the intake air amount Q detected by the air flow meter 12 reaches the reference amount Qb at time t1, the value of the increase region flag is set to “1”, and at the same time, the increase region counter B1c Starts incrementing. Thereafter, when the intake air amount Q is maintained larger than the reference amount Qb and the value of the increase region counter B1c increases, the value of the increase region counter B1c reaches the reference counter value B1 and increases at the time t2. The value of the control execution flag BF is set to “1”. When the value of the increase control execution flag BF is set to “1”, the intake air amount increasing process is executed, the engine speed is increased, and the intake air amount Q is increased. When the intake air amount Q reaches the reference amount Qa at time t3, the value of the active region flag is set to “1”, and the increment of the active region counter A1c is started at the same time. Thereafter, when the intake air amount Q is maintained larger than the reference amount Qa and the value of the active region counter A1c increases, the value of the active region counter A1c reaches the reference counter value A1 at time t4 and the active control execution flag The AF value is set to “1”. As a result, active control is executed, and the fuel injection amount through the fuel injection valve 5 is forcibly increased or decreased. Then, abnormality diagnosis of the air-fuel ratio sensor 14 is executed on condition that the value of the active control execution flag AF is maintained at “1”. When the abnormality diagnosis is completed, the values of the increase control execution flag BF and the active control execution flag AF are set to “0” at time t5, and these processes are completed. By performing the intake air amount increase processing in this way, the intake air amount increases and the amount of oxygen that can be reacted by the air-fuel ratio sensor 14 increases. Therefore, an opportunity for performing abnormality diagnosis without reducing the reliability of the diagnosis result Therefore, when an abnormality occurs in the air-fuel ratio sensor 14, this can be detected promptly.

  Further, FIG. 7 shows a case where the intake air amount has not reached the reference amount Qa that allows the abnormality diagnosis of the air-fuel ratio sensor 14 even though the intake air amount increase processing is executed. As shown in FIG. 7, when the value of the increase control execution flag BF is set to “1” at time t2, the increment of the increase control counter B2c is started. When the increase control counter B2c reaches the reference counter value B2 at time t6, since the intake air amount Q has not reached the reference amount Qa, the value of the increase control execution flag BF is set to “0”. The intake air amount increasing process is stopped. Therefore, in this case, abnormality diagnosis of the air-fuel ratio sensor 14 is not executed. Thereby, it becomes possible to suppress the deterioration of the driver viridy due to the increase in the intake air amount over a long period of time.

  Further, FIG. 8 shows the case where the active control is executed by the intake air amount increasing process, and the case where the intake air amount is reduced due to the change of the engine operating state during the execution of the active control is shown. As shown in FIG. 8, the engine operating state in the period from time t1 to time t4 changes in the same manner as in the case shown in FIG. 6, but at time t7 after the active control is executed. At the time, the value of the intake air amount Q is lower than the reference amount Qa. Thus, when the intake air amount Q decreases during the execution of the active control, the increment of the active control stop counter A2c is started. Then, when the value of the active control stop counter A2c reaches the reference counter value A2 at time t8, the value of the active control execution flag AF is set to “0”, and the execution of the active control is stopped. In this case, the process ends without executing the abnormality diagnosis by the process of step S40 shown in FIG.

As described above, according to the abnormality diagnosis apparatus for an air-fuel ratio sensor according to the present embodiment, the following effects can be obtained.
(1) Even when the intake air amount Q is less than the reference amount Qa, the speed of the continuously variable transmission 1 connecting the engine 4 and the vehicle drive system is increased to increase the engine speed. An abnormality diagnosis is performed by executing an intake air amount increasing process for forcibly increasing the intake air amount Q to a reference amount Qa or more. As the amount of intake air increases in this way, the amount of oxygen that can be reacted by the air-fuel ratio sensor 14 increases, so that the possibility of performing abnormality diagnosis can be increased without degrading the reliability of the diagnosis result. If an abnormality has occurred in the sensor 14, this can be quickly detected.

  (2) Since the continuously variable transmission 1 is used as a transmission for increasing the gear ratio, a drastic change in the engine speed is suppressed by gradually changing the gear ratio, thereby suppressing the influence on drivability. can do.

  (3) When the intake air amount Q is lower than the reference amount Qb set to a value lower than the reference amount Qa, the execution of the intake air amount increasing process is suspended. By suspending the execution in this way, if the intake air amount Q is greatly below the reference amount Qa that can be diagnosed, the execution of the intake air amount increasing process is suspended and the process is not performed. . Therefore, it is possible to suppress the deterioration of drivability due to the engine speed increasing for a long time.

  (4) When the intake air amount Q is equal to or greater than the reference amount Qb does not continue for a predetermined period, the execution of the intake air amount increase process is suspended. Therefore, when the engine operating state of the engine is not stable, the execution of the intake air amount increasing process is suspended, and the engine operating state is not improved due to the intermittent execution of the intake air amount increasing process. Stabilization can be suppressed.

  (5) If the intake air amount Q is not equal to or greater than the reference amount Qa at the time when a predetermined period has elapsed after the intake air amount increase processing is started, the intake air amount increase processing is stopped. Therefore, it is possible to suppress the deterioration of the driver viridy caused by increasing the intake air amount over a long period for abnormality diagnosis.

  (6) The air-fuel ratio is forcibly changed on condition that the state where the intake air amount Q is equal to or greater than the reference amount Qa is maintained for a predetermined period, and the abnormality of the air-fuel ratio sensor 14 is based on the output mode of the subsequent detection signal. It was decided to determine the presence or absence. Therefore, the air-fuel ratio is forcibly changed only when the state where the intake air amount Q is equal to or greater than the reference amount Qa is maintained for a predetermined period, that is, when there is a high possibility that the abnormality diagnosis can be completed. Since the control is executed, it is possible to suppress this control from being executed unnecessarily and to suppress the deterioration of the exhaust properties accompanying the execution of the control.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, abnormality diagnosis of the exhaust sensor, that is, the oxygen sensor 15 provided on the downstream side of the three-way catalyst 7 in the present embodiment is executed. When diagnosing the abnormality of the oxygen sensor 15 (see FIG. 1), the catalyst temperature T of the three-way catalyst 7 is monitored instead of the intake air amount Q, and whether or not the diagnosis can be executed is determined based on the result. ing.

  Further, in order to determine whether or not the oxygen sensor 15 is abnormal, the output value of the oxygen sensor 15 is reversed between the lean signal and the rich signal at the theoretical air-fuel ratio, and the oxygen storage action of the three-way catalyst 7 An abnormality diagnosis is performed based on the above. That is, when the active control is executed as described above, the air-fuel ratio of the air-fuel mixture is forcibly changed based on the air-fuel ratio downstream of the three-way catalyst 7, and the change in the air-fuel ratio downstream of the three-way catalyst 7 thereafter. Based on this, it is possible to grasp the state in which all the oxygen stored in the three-way catalyst 7 has been released and the state in which the oxygen storage amount of the three-way catalyst 7 has reached the limit amount. Then, if the amount of oxygen flowing into the three-way catalyst 7 is integrated during a period when the air-fuel ratio of the air-fuel mixture is lean and the air-fuel ratio downstream of the three-way catalyst 7 is rich, the oxygen storage of the three-way catalyst 7 is performed. The quantity CIN can be estimated. On the other hand, if the oxygen shortage amount of the exhaust gas flowing into the three-way catalyst 7 during the period in which the air-fuel ratio of the air-fuel mixture is rich and the air-fuel ratio downstream of the three-way catalyst 7 is lean is integrated. The oxygen release amount COUT can be estimated. Since the oxygen released from the three-way catalyst 7 is oxygen originally stored in the three-way catalyst 7, the oxygen release amount COUT is substantially the same value as the oxygen storage amount CIN. Is a value indicating the oxygen storage amount.

  Here, if an abnormality occurs in the oxygen sensor 15 and only a lean signal or a rich signal is output, the output inversion timing of the oxygen sensor 15 is delayed or not inverted during the active control. Therefore, the estimated oxygen storage amount such as the oxygen storage amount CIN and the oxygen release amount COUT is calculated as a larger value than when the oxygen sensor 15 is normal. Therefore, when an excessively large oxygen storage amount CIN or oxygen release amount COUT is calculated, it can be diagnosed that an abnormality has occurred in the oxygen sensor 15.

  Hereinafter, the contents of the abnormality diagnosis according to the present embodiment will be described with reference to FIGS. FIG. 9 is a flowchart showing a procedure of abnormality diagnosis processing for diagnosing the presence or absence of abnormality of the oxygen sensor 15. FIG. 10 is a flowchart showing a sequence of processes related to the execution of the active control executed together with the abnormality diagnosis process, and FIG. 11 shows a sequence of processes related to the execution of the intake air amount increase process. It is a flowchart.

  As shown in FIG. 9, if the determination result of step S40 shown in FIG. 2 is affirmative, it is determined whether the output value of the oxygen sensor 15 is inverted between the lean signal and the rich signal (step S500). If the output of the oxygen sensor 15 is reversed, it can be determined that the oxygen sensor 15 is functioning normally, so that it is determined that the oxygen sensor 15 is normal and the process is terminated. To do. When it is determined that the oxygen sensor 15 is normal, the abnormality diagnosis is not performed until the engine 4 is stopped and restarted.

  On the other hand, when it is determined that the output value of the oxygen sensor 15 is not inverted, the process proceeds to step S510, where it is determined whether the output value of the oxygen sensor 15 is rich, and the determination result of this step S510 is affirmative, That is, when the rich determination is made, the routine proceeds to step 520, where it is further determined whether or not the output value of the air-fuel ratio sensor 14 is lean.

  When it is determined that the output value of the oxygen sensor 15 is rich and the output value of the air-fuel ratio sensor 14 is not lean, oxygen storage in the three-way catalyst 7 by active control has not yet been performed. In step S523, the oxygen storage amount CIN is reset to an initial value, that is, “0”, and the process is temporarily terminated.

  On the other hand, when it is determined that the output value of the oxygen sensor 15 is rich and the output value of the air-fuel ratio sensor 14 is lean, it is determined that oxygen storage in the three-way catalyst 7 by active control is being performed. Is done. Therefore, the oxygen storage amount CIN is integrated based on the following equation (1) (step S521).

Current oxygen storage amount CIN = previous oxygen storage amount CIN
+ 0.23 × ΔA / F × fuel injection amount F (1)
Here, “current oxygen storage amount CIN” is the latest oxygen storage amount CIN calculated in the current execution cycle, and “previous oxygen storage amount CIN” is the past oxygen storage amount calculated in the previous execution cycle. The quantity CIN. “0.23” is the ratio of oxygen in the air, and “ΔA / F” is a value obtained by subtracting the theoretical air-fuel ratio from the air-fuel ratio detected by the air-fuel ratio sensor 14. The “fuel injection amount F” is a value set in fuel injection control that is executed separately from the present process, and is the amount of fuel supplied to the engine 4 when the present process is executed. In the above equation (1), the value obtained by “ΔA / F × fuel injection amount F” is a value corresponding to the amount of unburned air that has flowed into the three-way catalyst 7 during the execution period of this process. A value obtained by multiplying “0.23” corresponds to the unburned oxygen amount. Since this unburned oxygen is stored in the three-way catalyst 7, according to the above formula (1), an integrated value of the amount of oxygen stored in the three-way catalyst 7 during the execution period of this process is obtained. The accumulation of the oxygen storage amount CIN is continued until a negative determination is made in step S522, which will be described later, and then an affirmative determination is made in step S500 or an affirmative determination is made in step S522.

  When the oxygen storage amount CIN in this process is thus calculated, it is next determined whether or not the oxygen storage amount CIN exceeds the rich abnormality determination value α (step S522). The rich abnormality determination value α is a value for determining that an abnormality has occurred in the oxygen sensor 15 and that the output value indicates only rich, and is set based on the following equation (2). Is done.

Current rich abnormality determination value α = previous rich abnormality determination value α +
{(Previous accumulated oxygen storage amount CINF−Previous rich abnormality determination value α) / n} (2)
Here, the “current rich abnormality determination value α” is a determination value in the present process that is repeatedly executed this time. In addition, the “previous rich abnormality determination value α” is an abnormality diagnosis process performed at a past execution time different from the execution time of the main process repeatedly executed this time, that is, when an abnormality diagnosis execution condition has been satisfied before. This is the determination value used in the previous abnormality diagnosis process performed in (1). In addition, the “previous accumulated oxygen storage amount CINF” is accumulated in the above-described abnormality diagnosis process performed in the past execution timing, that is, in the previous abnormality diagnosis process performed when the abnormality diagnosis execution condition was satisfied before. In other words, it is the final oxygen storage amount CIN at the end of the previous abnormality diagnosis process. Accordingly, in the above equation (2), the value obtained by “(previous accumulated oxygen storage amount CINF−previous rich abnormality determination value α)” is an estimate calculated when the previous abnormality diagnosis process is executed. It shows the degree of deviation between the oxygen storage amount and the judgment value at that time. Then, the degree of divergence is added to the “previous rich abnormality determination value α”, and the rich abnormality determination value α in the present processing that is repeatedly executed this time is set. Note that “n” is a constant for determining how much the degree of deviation is reflected in the previous rich abnormality determination value α. In this embodiment, “n = 32”. The value can be changed as appropriate.

  If it is determined in step S522 that the oxygen storage amount CIN is equal to or less than the rich abnormality determination value α, the abnormality determination is suspended and the present process is temporarily terminated. On the other hand, when it is determined in step S522 that the oxygen storage amount CIN exceeds the rich abnormality determination value α, the oxygen storage amount CIN is calculated as an excessively large value. It is determined that That is, the output value sticks to the rich side, and it is determined that there is an abnormality that it cannot be detected that the exhaust air / fuel ratio is lean, and the abnormality flag is set to “1” (step S60). ). When such a determination is made, the active control execution flag AF and the increase control execution flag BF are set to “0” (step S70), and this process is terminated. Incidentally, when the abnormality diagnosis process of the oxygen sensor 15 is completed in this way, the abnormality diagnosis is not performed until the engine 4 is stopped and restarted.

Further, when a negative determination is made in the previous step S510, the following processing is performed.
It is determined whether or not the output value of the oxygen sensor 15 is rich, and when the rich determination is not made, that is, when the output value of the oxygen sensor 15 is lean, whether or not the output value of the air-fuel ratio sensor 14 is rich. A determination is made (step S530).

  When it is determined that the output value of the oxygen sensor 15 is lean and the output of the air-fuel ratio sensor 14 is not rich, it is determined that oxygen release from the three-way catalyst 7 by active control has not yet been performed. Then, the oxygen release amount COUT is reset to the initial value, that is, “0” (step S533), and this process is temporarily ended.

  On the other hand, when it is determined that the output value of the oxygen sensor 15 is lean and the output value of the air-fuel ratio sensor 14 is rich, it is determined that oxygen is being released from the three-way catalyst 7 by active control. Is done. Therefore, the oxygen release amount COUT is integrated based on the following equation (3) (step S531).

Current oxygen release amount COUT = previous oxygen release amount COUT
+ 0.23 × ΔA / F × fuel injection amount F (3)
Here, “current oxygen release amount COUT” is the latest oxygen release amount COUT calculated in the current execution cycle, and “previous oxygen release amount COUT” is the past oxygen release calculated in the previous execution cycle. The quantity COUT. “0.23” is the ratio of oxygen in the air, and “ΔA / F” is a value obtained by subtracting the theoretical air-fuel ratio from the air-fuel ratio detected by the air-fuel ratio sensor 14. The “fuel injection amount F” is a value set in fuel injection control that is executed separately from the present process, and is the amount of fuel supplied to the engine 4 when the present process is executed. In the above equation (3), the value obtained by “ΔA / F × fuel injection amount F” is necessary to burn the unburned fuel that has flowed into the three-way catalyst 7 during the execution period of this process. This is a value corresponding to a large amount of air, and corresponds to an air shortage amount of exhaust. Therefore, a value obtained by multiplying this by “0.23” corresponds to the oxygen deficiency. Since this deficient oxygen is released from the three-way catalyst 7, according to the above equation (3), an integrated value of the amount of oxygen released from the three-way catalyst 7 during the execution period of this process is obtained. The integration of the oxygen release amount COUT is continued until a negative determination is made in step S532, which will be described later, and then an affirmative determination is made in step S500 or an affirmative determination is made in step S532.

  When the oxygen release amount COUT in the current process is thus calculated, it is next determined whether or not the oxygen release amount COUT exceeds the lean abnormality determination value β (step S532). This lean abnormality determination value β is a value for determining that an abnormality has occurred in the oxygen sensor 15 and that its output value indicates only lean, and is set based on the following equation (4): Is done.

The current lean abnormality determination value β = the previous lean abnormality determination value β +
{(Previous accumulated oxygen release amount COUTF−Previous lean abnormality determination value β) / n} (4)
Here, the “current lean abnormality determination value β” is a determination value in this process that is repeatedly executed this time. In addition, the “previous lean abnormality determination value β” is an abnormality diagnosis process performed at a past execution time that is different from the execution time of this process that is repeatedly executed this time, that is, when an abnormality diagnosis execution condition has been satisfied before. This is the determination value used in the previous abnormality diagnosis process performed in (1). In addition, the “previous accumulated oxygen release amount COUTF” is accumulated in the above-described abnormality diagnosis process performed in the past execution timing, that is, in the previous abnormality diagnosis process performed when the abnormality diagnosis execution condition was satisfied before. In other words, the final oxygen release amount COUT is the value of the final oxygen release amount COUT at the end of the previous abnormality diagnosis process. Accordingly, in the above equation (4), the value obtained by “(previous accumulated oxygen release amount COUTF−previous lean abnormality determination value β)” is the estimated oxygen release amount (estimated when the previous diagnosis process is executed). This shows the degree of deviation between the oxygen storage amount) and the judgment value at that time. Then, the degree of divergence is added to the “previous lean abnormality determination value β”, and the lean abnormality determination value β in the present processing that is repeatedly executed this time is set. Note that “n” is a constant for determining the degree to which the degree of deviation is reflected in the previous lean abnormality determination value β. In this embodiment, “n = 32”. The value can be changed as appropriate.

  When it is determined that the oxygen release amount COUT is equal to or less than the lean abnormality determination value β, the abnormality determination is suspended and this process is temporarily terminated. On the other hand, when it is determined that the oxygen release amount COUT exceeds the lean abnormality determination value β, it is determined that the oxygen sensor 15 is lean abnormal because the oxygen release amount COUT is calculated as an excessively large value. Is done. That is, it is determined that there is an abnormality that the output value is stuck to the lean side and it cannot be detected that the exhaust air-fuel ratio is rich, and the value of the abnormality flag is set to "1" (step) S60). When such a determination is made, the values of the active control execution flag AF and the increase control execution flag BF are set to “0” (step S70), and this process is terminated. In this case, as in the case described above, the abnormality diagnosis is not performed until the engine 4 is stopped and restarted.

  As described above, in the present embodiment, in order to determine whether the oxygen storage amount CIN and the oxygen release amount COUT of the three-way catalyst 7 are excessively large values, those values are used as rich abnormality determination value α and lean abnormality. Compared with the determination value β, the presence or absence of abnormality of the oxygen sensor 15 is diagnosed based on the comparison result.

  As shown in FIG. 10, when the determination result in step S100 shown in FIG. 3 is affirmative, the process proceeds to step S111 and the catalyst temperature T detected by the temperature sensor 16 indicated by the broken line in FIG. Is determined to be equal to or higher than the reference temperature Ta. If the determination result in step S111 is affirmative, that is, if the three-way catalyst 7 is sufficiently activated, the process proceeds to step S120, and if the determination result is negative, the process proceeds to step S121.

  If the three-way catalyst 7 is not sufficiently heated, the oxygen storage function in the exhaust gas by the three-way catalyst 7 is not accurately performed, so the oxygen sensor 15 accurately calculates the oxygen storage amount CIN and the oxygen release amount COUT. I can't. Therefore, when it is determined that the activation of the three-way catalyst 7 is not sufficient, the execution of the active control and the abnormality diagnosis of the oxygen sensor 15 is suspended.

  Similarly, whether or not the catalyst temperature T is lower than the reference temperature Ta is determined after the execution of the active control in step S200 (step S211). When this determination result is affirmative, that is, when the three-way catalyst 7 changes to an inactive state during execution of active control, the value of the active control stop counter A2c is incremented to stop execution of active control and abnormality diagnosis ( Step S220).

  Further, as shown in FIG. 11, the catalyst temperature T is also used for the determination for determining whether or not the intake air amount increasing process is executed. That is, if the determination result of step S300 is negative, it is determined whether the catalyst temperature T is equal to or higher than the reference temperature Tb (step S311). If the determination result is affirmative, the value of the increase area counter B1c is incremented to execute the intake air amount increase process (step S320). If the determination result in step S420 is affirmative, it is determined whether or not the catalyst temperature T is lower than the reference temperature Ta (step S431). If the determination result is affirmative, that is, if the catalyst temperature T does not reach the reference temperature Ta even though the intake air amount increase processing is executed, the increase control execution flag BF is set to stop the intake air amount increase control. Is set to “0” (step S440).

  Next, the operation obtained by the processing described above will be described with reference to FIGS. 12 to 14 are timing charts respectively showing one mode of changes in the engine operating state during a series of processing for abnormality diagnosis.

  For example, FIG. 12 shows a case where the catalyst temperature T rises due to the execution of the intake air amount increasing process and abnormality diagnosis of the oxygen sensor 15 is executed. As shown in FIG. 12, since the catalyst temperature T detected by the temperature sensor 16 at the time t1 has reached the reference temperature Tb, the value of the increase region flag is set to “1”, and the increase region counter B1c Increment is started. Thereafter, when the catalyst temperature T is maintained higher than the reference temperature Tb and the value of the increase region counter B1c increases, the value of the increase region counter B1c reaches the reference counter value B1 at time t2 and increases. The value of the control execution flag BF is set to “1”. When the value of the increase control execution flag BF is set to “1”, the intake air amount increasing process is executed, the engine speed is increased, and the catalyst temperature T is increased. When the catalyst temperature T reaches the reference temperature Ta at time t3, the value of the active region flag is set to “1”, and the increment of the active region counter A1c is started at the same time. After that, when the catalyst temperature T remains higher than the reference temperature Ta and the value of the active area counter A1c increases, the value of the active area counter A1c reaches the reference counter value A1 at time t4 and the active control execution flag AF Is set to “1”. As a result, active control is executed, and the fuel injection amount through the fuel injection valve 5 is forcibly increased or decreased. Then, abnormality diagnosis of the oxygen sensor 15 is executed on condition that the value of the active control execution flag AF is maintained at “1”. When the abnormality diagnosis is completed, the values of the increase control execution flag BF and the active control execution flag AF are set to “0” at time t5, and these processes are completed. By performing the intake air amount increase processing in this way, the catalyst temperature rises and the amount of oxygen that can be reacted by the oxygen sensor 15 increases. Therefore, the chances of performing abnormality diagnosis are increased without reducing the reliability of the diagnosis result. Thus, when an abnormality occurs in the oxygen sensor 15, this can be detected promptly.

  FIG. 13 shows a case where the catalyst temperature T has not reached the reference temperature Ta at which the abnormality diagnosis of the oxygen sensor 15 can be performed despite the intake air amount increasing process being executed. As shown in FIG. 13, when the value of the increase control execution flag BF is set to “1” at time t2, the increment of the increase control counter B2c is started. When the increase control counter B2c reaches the reference counter value B2 at time t6, since the catalyst temperature T has not reached the reference temperature Ta, the value of the increase control execution flag BF is set to “0” and suction is performed. The air volume increasing process is stopped. Therefore, in this case, the abnormality diagnosis of the oxygen sensor 15 is not executed. Thereby, it becomes possible to suppress the deterioration of the driver viridy due to the increase in the intake air amount over a long period of time.

  Further, FIG. 14 shows the case where the active control is executed by the intake air amount increasing process, but the catalyst temperature is lowered due to the change of the engine operating state during the execution of the active control. As shown in FIG. 14, the engine operating state in the period from time t1 to time t4 changes in the same manner as in the case shown in FIG. 6, but at time t7 after the active control is executed. At the time, the value of the catalyst temperature T is lower than the reference temperature Ta. Thus, when the catalyst temperature T decreases during the execution of the active control, the increment of the active control stop counter A2c is started. Then, when the value of the active control stop counter A2c reaches the reference counter value A2 at time t8, the value of the active control execution flag AF is set to “0”, and the execution of the active control is stopped. In this case, when the execution of the active control is stopped, the process ends without executing the abnormality diagnosis by the process of step S40 shown in FIG.

As described above, according to the abnormality diagnosis apparatus for an air-fuel ratio sensor according to the present embodiment, the following effects can be obtained.
(7) Even when the catalyst temperature T is lower than the reference temperature Ta, the gear ratio of the continuously variable transmission 1 that connects the engine 4 and the vehicle drive system is gradually increased to increase the engine speed. Accordingly, the abnormality diagnosis is performed by executing the intake air amount increasing process for forcibly increasing the catalyst temperature to the reference temperature Ta or higher. Since the three-way catalyst 7 is activated as the catalyst temperature rises as the exhaust flow rate increases in this way, it is possible to increase the chances of performing an abnormality diagnosis without reducing the reliability of the diagnosis result. When an abnormality occurs in the oxygen sensor 15, this can be detected promptly.

  (8) When the catalyst temperature T is lower than the reference temperature Tb set to a value lower than the reference temperature Ta, the execution of the intake air amount increasing process is suspended. By suspending the execution in this way, if the catalyst temperature is significantly below the reference temperature Ta at which abnormality diagnosis can be performed, the intake air amount increasing process is suspended and the process is not performed. Therefore, it is possible to suppress the deterioration of drivability due to the engine speed increasing for a long time.

  (9) Since this is activated by the temperature rise of the three-way catalyst 7, the abnormality diagnosis of the oxygen sensor 15 can be executed while suppressing the deterioration of the exhaust properties caused by forcibly changing the air-fuel ratio. it can.

  (10) When the state where the catalyst temperature T is equal to or higher than the reference temperature Tb does not continue for a predetermined period, the execution of the intake air amount increasing process is suspended. Therefore, when the state where the catalyst temperature T is equal to or higher than the reference temperature Tb does not continue for a predetermined period, that is, when the engine operating state is not stable, the intake air amount increase process is suspended and the process is not performed. Instability of the engine operating state due to intermittent execution of the intake air amount increasing process can be suppressed.

  (11) If the catalyst temperature T is not equal to or higher than the reference temperature Ta at the time when a predetermined period has elapsed after the intake air amount increase process is started, the intake air amount increase process is stopped. Therefore, it is possible to suppress the deterioration of the driver viridy caused by increasing the intake air amount over a long period for abnormality diagnosis.

  (12) The air-fuel ratio is forcibly changed on condition that the state where the catalyst temperature T is equal to or higher than the reference temperature Ta is continuously maintained for a predetermined period, and the oxygen sensor 15 The presence or absence of abnormality was determined. Therefore, the control for forcibly changing the air-fuel ratio is executed only when the catalyst temperature T is continuously maintained in a state where the temperature is equal to or higher than the reference temperature Ta, that is, when there is a high possibility that the abnormality diagnosis can be completed. Therefore, it is possible to suppress this control from being performed unnecessarily, and to suppress deterioration in exhaust properties associated with the execution of the control.

The embodiment described above can be implemented with appropriate modifications as follows.
In the first embodiment, the amplitude of the output value of the air-fuel ratio sensor 14 is used to diagnose the presence or absence of abnormality of the air-fuel ratio sensor 14, but the average value of the amplitudes of the output values during a predetermined period is used as this amplitude. A configuration for performing the same diagnosis may be employed. By performing the abnormality diagnosis using the average value in this way, it is possible to realize a more stable abnormality diagnosis in which the influence of disturbances such as so-called noise is reduced.

In the second embodiment, the determination value α and the determination value β are updated based on the oxygen storage amount, but fixed values may be used for the determination values α and β.
In the first and second embodiments, if each sensor is abnormal, the presence or absence of abnormality of the sensor is diagnosed based on the fact that the cycle of inversion of the output value of the sensor becomes longer. A configuration may be adopted.

  -The transmission of the engine 4 does not have to be a continuously variable transmission. For example, an automatic transmission may be employed. In this case, as the intake air amount increasing process, control for lowering the gear position of the automatic transmission is performed.

  As the intake air amount increasing process, control for forcibly increasing the opening of the throttle valve 3 and changing the ignition timing to the retard side may be executed. Also in this case, the amount of oxygen that can be reacted by the air-fuel ratio sensor 14 increases as the intake air amount increases, and the catalyst temperature of the three-way catalyst 7 rises as the exhaust flow rate increases, and the catalyst 7 is activated. To do. For this reason, it is possible to increase the chances that the abnormality diagnosis can be performed without reducing the reliability of the diagnosis result, and it is possible to quickly detect an abnormality in the air-fuel ratio sensor 14 or the oxygen sensor 15. become able to. Further, by executing the control for forcibly increasing the opening degree of the throttle valve 3 and the control for changing the ignition timing to the retard side, the opening degree of the throttle valve 3 is changed to increase the intake air amount. Therefore, it is possible to suppress the increase in the engine output due to the occurrence of the failure and to suppress the deterioration of the drivability as much as possible.

  In the second embodiment, the configuration in which the temperature of the three-way catalyst 7 is detected by the temperature sensor 16 is shown, but instead, based on the intake air amount, the fuel injection amount, the period rotation speed, or a combination of these parameters. The catalyst temperature T may be estimated.

The values set as the rich and lean target air-fuel ratios during the active control are not limited to the values shown in the above embodiment, and other rich values and lean values can be set.
Instead of the process of waiting for a predetermined time during the abnormality diagnosis process of each sensor as in step S30 of FIG. 2, a process of waiting until the output value of the sensor is inverted a predetermined number of times may be executed. Further, in the case of a configuration in which the execution of the active control is not stopped in the middle of the execution, it is not necessary to provide such a waiting time.

  -Adopting a configuration in which active control and intake air amount increase processing are executed when the determination value is reached even if the intake air amount Q or the catalyst temperature T is not maintained for a predetermined period of time. Also good. Even if such a configuration is adopted, especially when the difference between the reference amount Qa and the reference amount Qb and the difference between the reference temperature Ta and the reference temperature Tb are small, the influence on drivability and exhaust properties is suppressed as much as possible. can do.

  A configuration may be adopted in which the intake air amount processing is continued until the intake air amount Q becomes equal to or higher than the reference amount Qa and until the catalyst temperature T becomes equal to or higher than the reference temperature Ta.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows schematic structure of the engine which becomes the application object mainly about 1st Embodiment which actualized the abnormality diagnosis apparatus of the air fuel ratio sensor concerning this invention. The flowchart which shows the specific process sequence concerning the abnormality diagnosis process which diagnoses the presence or absence of abnormality of an air fuel ratio sensor. The flowchart which shows the specific process sequence concerning execution of the active control performed with an abnormality diagnosis process. The flowchart which shows the specific process sequence concerning execution of an intake air amount increase process. The time chart which shows the aspect of the change of the output of an air fuel ratio sensor and fuel injection amount at the time of performing active control. The timing chart which shows the one aspect | mode of the change of the engine operating state in a series of processes concerning abnormality diagnosis. The timing chart which shows the one aspect | mode of the change of the engine operating state in a series of processes concerning abnormality diagnosis. The timing chart which shows the one aspect | mode of the change of the engine operating state in a series of processes concerning abnormality diagnosis. The flowchart which shows the specific process sequence concerning the abnormality diagnosis process which diagnoses the presence or absence of abnormality of the oxygen sensor in 2nd Embodiment. The flowchart which shows the specific process sequence concerning execution of the active control performed together with the abnormality diagnosis process in 2nd Embodiment. The flowchart which shows the specific process sequence concerning execution of the intake air amount increase process in 2nd Embodiment. The timing chart which shows the one aspect | mode of the change of the engine operating state in a series of processes concerning the abnormality diagnosis in 2nd Embodiment. The timing chart which shows the one aspect | mode of the change of the engine operating state in a series of processes concerning the abnormality diagnosis in 2nd Embodiment. The timing chart which shows the one aspect | mode of the change of the engine operating state in a series of processes concerning the abnormality diagnosis in 2nd Embodiment.

Explanation of symbols

  Q: intake air amount, T: catalyst temperature, 3 ... throttle valve, 6 ... exhaust passage, 7 ... three-way catalyst, 14 ... air-fuel ratio sensor, 15 ... oxygen sensor, 16 ... continuously variable transmission.

Claims (9)

An abnormality diagnosis device for diagnosing an abnormality of an exhaust sensor that is provided in an exhaust passage of a vehicle equipped with an engine and outputs a detection signal corresponding to the oxygen concentration of exhaust gas in the exhaust passage, wherein a measured value of an intake air amount is In the exhaust gas sensor abnormality diagnosis device that forcibly changes the air-fuel ratio on the condition that it is equal to or greater than a predetermined determination value, and determines whether there is an abnormality in the exhaust sensor based on the output mode of the detection signal thereafter,
When the measured value of the intake air amount is less than the determination value, the intake air amount is determined by increasing the gear ratio of a transmission connecting the engine and the vehicle drive system to increase the engine speed. An abnormality diagnosis apparatus for an exhaust sensor, wherein the abnormality diagnosis is performed by executing an intake air amount increase process for forcibly increasing the value to a value or more. An abnormality diagnosis device that diagnoses an abnormality of an exhaust sensor that is provided downstream of a catalyst device disposed in an exhaust passage of a vehicle on which an engine is mounted and outputs a detection signal corresponding to the oxygen concentration of exhaust gas in the exhaust passage. The air-fuel ratio is forcibly changed based on the detection signal on the condition that the measured value of the catalyst temperature of the catalyst device is equal to or greater than a predetermined determination value, and based on the output mode of the detection signal thereafter In the exhaust gas sensor abnormality diagnosis device for determining whether or not the exhaust sensor is abnormal,
When the measured value of the catalyst temperature is less than the determination value, the intake air amount is increased by increasing the gear ratio of the transmission connecting the engine and the vehicle drive system to increase the engine rotation speed. An exhaust sensor abnormality diagnosing device, wherein the abnormality diagnosis is performed by executing an intake air amount increasing process for forcibly increasing the catalyst temperature to the determination value or more. In the exhaust gas sensor abnormality diagnosis device according to claim 1 or 2,
The exhaust sensor abnormality diagnosis device, wherein the transmission is a continuously variable transmission. An abnormality diagnosis device for diagnosing an abnormality of an exhaust sensor that is provided in an exhaust passage of a vehicle equipped with an engine and outputs a detection signal corresponding to the oxygen concentration of exhaust gas in the exhaust passage, wherein a measured value of an intake air amount is In the exhaust gas sensor abnormality diagnosis device that forcibly changes the air-fuel ratio on the condition that it is equal to or greater than a predetermined determination value, and determines whether there is an abnormality in the exhaust sensor based on the output mode of the detection signal thereafter,
When the measured value of the intake air amount is less than the judgment value, the throttle valve opening is forcibly increased to forcibly increase the intake air amount to the judgment value or more and the ignition timing is retarded. An abnormality diagnosis device for an exhaust sensor, wherein the abnormality diagnosis is performed by executing an intake air amount increase process to be changed to An abnormality diagnosis device that diagnoses an abnormality of an exhaust sensor that is provided downstream of a catalyst device disposed in an exhaust passage of a vehicle on which an engine is mounted and outputs a detection signal corresponding to the oxygen concentration of exhaust gas in the exhaust passage. The air-fuel ratio is forcibly changed based on the detection signal on the condition that the measured value of the catalyst temperature of the catalyst device is equal to or greater than a predetermined determination value, and based on the output mode of the detection signal thereafter In the exhaust gas sensor abnormality diagnosis device for determining whether or not the exhaust sensor is abnormal,
When the measured value of the catalyst temperature is less than the determination value, the catalyst temperature is forcibly increased to the determination value or more by forcibly increasing the throttle valve opening and changing the ignition timing to the retard side. An exhaust sensor abnormality diagnosis device characterized in that the abnormality diagnosis is performed by executing a process for increasing the intake air amount that is increased as desired. In the exhaust gas sensor abnormality diagnosis device according to any one of claims 1 to 5,
The exhaust sensor abnormality diagnosis device, wherein execution of the intake air amount increase processing is suspended when the measured value is lower than an execution lower limit value set to a value lower than the determination value. In the exhaust gas sensor abnormality diagnosis device according to claim 6,
The exhaust sensor abnormality diagnosis device, wherein execution of the intake air amount increase processing is suspended when a state where the measured value is equal to or greater than the execution lower limit value is not continued for a predetermined period. In the exhaust gas sensor abnormality diagnosis device according to any one of claims 1 to 7,
The exhaust sensor abnormality diagnosis device, wherein the intake air amount increase process is stopped when the measured value is not greater than or equal to the determination value at the elapse of a predetermined period from the start of the intake air amount increase process. In the exhaust gas sensor abnormality diagnosis device according to any one of claims 1 to 8,
The air-fuel ratio is forcibly changed under the condition that the state where the measured value is equal to or higher than the determination value is continuously maintained for a predetermined period, and the abnormality of the exhaust sensor is detected based on the output mode of the detection signal thereafter. Exhaust sensor abnormality diagnosis device characterized by determining presence or absence.

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