JP5603825B2 - Air-fuel ratio sensor diagnostic device - Google Patents

Description

  The present invention relates to an air-fuel ratio sensor diagnostic apparatus, and more particularly to an air-fuel ratio sensor diagnostic apparatus capable of diagnosing an offset failure of an air-fuel ratio sensor of an internal combustion engine.

  Conventionally, in order to reduce air pollution caused by harmful gas discharged from a vehicle, various technological developments for suppressing harmful substances discharged from the vehicle have been promoted.

  As one of the developed technologies, for example, an on-board fault diagnosis device (OBD) is cited. The OBD detects or supervises an abnormality (for example, a sudden failure) of a device for which the vehicle itself takes measures against exhaust gas, so that an alarm is displayed or displayed to the driver by a warning light or the like when the abnormality occurs. Is a failure diagnosis device capable of storing and holding the data in a storage device. As a result, the driver can quickly and properly recognize the abnormality or failure of the device that takes measures against exhaust gas, and can perform maintenance of the vehicle, and can reduce harmful gas discharged from the vehicle.

  In particular, in the automobile industry in the United States, 1994-type vehicles have been required to detect a decrease in the catalyst purification rate, engine misfire, anomaly of oxygen sensor deterioration fuel evaporative emission control system for these OBDs, and these When an abnormality is detected by the OBD, a warning light on the instrument panel is lit to warn the driver, and the failure information is stored and can be read by a standardized scanning tool. (OBDII regulations). Under such restrictions, it is detected whether the air-fuel ratio sensor (LAF sensor) used in the internal combustion engine is abnormal or other equipment is abnormal, and for example, the air-fuel ratio sensor is 1.5 times the exhaust regulation value. In the event of a malfunction exceeding the limit, it is necessary to promptly warn the driver of the abnormality and encourage maintenance and repair of the vehicle.

  On the other hand, in the Japanese automobile industry, in recent years, vehicle exhaust gas measurement methods and standards for in-vehicle failure diagnosis devices have been revised. For example, since 2008, new vehicles with a total vehicle weight of 3.5 tons or less using gasoline or LPG as fuel. As a result, efforts to control harmful substances emitted from vehicles have become active, such as requiring the installation of advanced in-vehicle failure diagnosis devices. Development has become an essential issue.

  By the way, a control device for an internal combustion engine of a feedback system that controls the fuel injection amount based on information on exhaust gas components in the internal combustion engine as means for suppressing harmful gases in the exhaust gas of the vehicle and improving fuel consumption and drivability. It has been put into practical use.

  In Patent Document 1, an oxygen accumulation amount in the catalyst is calculated based on an output signal of an air-fuel ratio sensor arranged before the catalyst and an air flow rate, and the oxygen accumulation amount and an output signal of an oxygen sensor arranged after the catalyst are disclosed. The internal air-fuel ratio is controlled by calculating the center air-fuel ratio in the catalyst based on the above and correcting the target air-fuel ratio (air-fuel ratio feedback control) to control the fuel injection amount with higher accuracy. An apparatus is disclosed.

Japanese Patent No. 4338663

  By the way, in the control device, when an abnormality occurs in an exhaust gas component or a control system due to failure or deterioration of a sensor used in an internal combustion engine, for example, an air-fuel ratio sensor, the fuel injection amount is appropriately controlled. There is a problem that can not be.

  Here, examples of the failure mode of the air-fuel ratio sensor include response deterioration, stack (fixed), and offset failure. The offset means that the air-fuel ratio detected by the air-fuel ratio sensor deviates in an increasing direction or a decreasing direction with respect to the actual air-fuel ratio, and if the deviation amount becomes excessive, it is diagnosed that the air-fuel ratio sensor has an offset failure. Is done.

  Among the failure modes, particularly in the case of an offset failure of the air-fuel ratio sensor, it is conceivable to control (absorb) the offset deviation of the air-fuel ratio using a post-catalyst oxygen sensor. FIG. 8 shows an offset deviation control method based on an oxygen sensor. Here, the horizontal axis represents the actual air-fuel ratio, and the vertical axis represents the air-fuel ratio (RABF) detected by the air-fuel ratio sensor.

  As shown in the figure, for example, when the actual air-fuel ratio is 14.7, an offset deviation occurs upward or downward with respect to the air-fuel ratio sensor having the normal characteristic (solid line) L, and the characteristics of the air-fuel ratio sensor When the characteristics (broken lines) L1 and L2 are reached, the operating point moves to points a1 and a2 (in the directions of arrows A1 and A2), respectively. Then, since the detection value of the air-fuel ratio sensor deviates from 14.7, if it is instructed to control the actual air-fuel ratio at 14.7, the operating point is b1 by the air-fuel ratio sensor control. , B2 (arrow B1, B2 direction). However, the actual air-fuel ratios at this time are values at the points c1 and c2, respectively, and the air-fuel ratios at the points c1 and c2 become the output signal of the oxygen sensor. In the case of rich and offset offset downward, the oxygen sensor will indicate lean. Therefore, the target air-fuel ratio is corrected using the output signal of the oxygen sensor after the catalyst, that is, the operating point of points b1 and b2 is moved to point o (in the directions of arrows C1 and C2), so that the air-fuel ratio becomes 14 The offset deviation of the air-fuel ratio sensor is controlled (absorbed) so that.

  Further, by using the output signal of such an oxygen sensor, the target air-fuel ratio can be corrected in accordance with the state of the catalyst. In the case of a normal three-way catalyst, it is desirable to control the air-fuel ratio to 14.7 of the stoichiometric air-fuel ratio. However, the air-fuel ratio is not necessarily set depending on the operating region of the internal combustion engine, the deterioration state of the catalyst, the active state of the catalyst, etc. Control to 14.7 is not always good. Therefore, the oxygen accumulation amount in the catalyst is calculated within the control of the oxygen sensor, and the air-fuel ratio (center air-fuel ratio in the catalyst) with the highest exhaust gas purification rate is calculated from the calculated oxygen accumulation amount according to the condition of the catalyst. Thus, by correcting the target air-fuel ratio, air-fuel ratio feedback control corresponding to the operating region of the internal combustion engine or the like can be realized.

  However, the air-fuel ratio sensor is installed immediately after exhausting the internal combustion engine, is exposed to a high temperature and high pressure atmosphere, and is greatly affected by vibration, bad fuel, etc., and therefore deteriorates compared to other sensors. It tends to be easy. For example, in the case of a multi-cylinder engine, since the air-fuel ratio sensor is required to be controlled very accurately because it is affected by other combustion cycles, the detection accuracy of the air-fuel ratio sensor is extremely lowered due to some reasons as described above. Then, for example, the offset deviation of the air-fuel ratio sensor as shown in FIG. 8 cannot be controlled (absorbed), and the internal combustion engine may not be operated efficiently. Therefore, in order to efficiently operate the internal combustion engine and reliably suppress harmful gases emitted from the automobile, the air-fuel ratio sensor in the internal combustion engine can be detected quickly and accurately, and the sensor can be replaced appropriately. When it is necessary to take a corrective action, it is desired to develop a failure diagnosis apparatus that allows a driver to quickly recognize information on an abnormality such as a failure or deterioration.

  For example, in the failure mode, as an example of a response deterioration detection method, there is a method of measuring the number of rich and lean inversions calculated by air-fuel ratio feedback control within a predetermined time, and the rich and lean inversion within the predetermined time. When the number of times is extremely small, it is possible to warn the driver by determining that the air-fuel ratio sensor has failed.

  Further, as an example of a method for detecting the stack of the air-fuel ratio sensor, there is a method for detecting the relationship between the output signal of the air-fuel ratio sensor before the catalyst and the output signal of the oxygen sensor after the catalyst. If the state in which the signal indicates richness and the output signal of the oxygen sensor indicates leanness frequently occurs, it is possible to warn the driver by determining that the air-fuel ratio sensor has failed.

  On the other hand, in the offset failure of the air-fuel ratio sensor, if the offset deviation is relatively small, the offset deviation can be controlled (absorbed) to some extent using the output signal of the oxygen sensor, but if the deviation becomes large (offset) Failure), the offset deviation cannot be controlled (absorbed), and since the offset failure cannot be detected properly in the prior art, the driver cannot be warned of the offset failure of the air-fuel ratio sensor. is the current situation.

  The present invention has been made in view of the above problems, and an object of the present invention is to diagnose an offset failure of an air-fuel ratio sensor based on a central air-fuel ratio in a catalyst and a target air-fuel ratio correction amount. An object of the present invention is to provide a diagnostic device for a pre-catalyst air-fuel ratio sensor.

  In order to solve the above-described problems, an air-fuel ratio sensor diagnostic apparatus according to the present invention includes a catalyst disposed in an exhaust passage, an air-fuel ratio sensor that detects an air-fuel ratio upstream of the catalyst, and a downstream of the catalyst. A diagnostic device for an air-fuel ratio sensor of an internal combustion engine having an oxygen sensor for detecting an oxygen concentration in the exhaust gas on the side and an air flow rate detecting means for detecting an inflow air flow rate, wherein the diagnostic device comprises the air-fuel ratio Further, the failure of the air-fuel ratio sensor is diagnosed based on at least one of the central air-fuel ratio in the catalyst and the target air-fuel ratio correction amount calculated based on the air flow rate and the oxygen concentration.

  As can be understood from the above description, according to the present invention, for example, when the internal combustion engine performs air-fuel ratio feedback control by the output signals of the air-fuel ratio sensor before the catalyst and the oxygen sensor after the catalyst, the air-fuel ratio sensor and the oxygen sensor From the relationship between the center air-fuel ratio in the catalyst calculated based on the output signal and the inflow air flow rate and the target air-fuel ratio correction amount, or from the center air-fuel ratio, the air-fuel ratio sensor offset failure including the deterioration state of the air-fuel ratio sensor is detected. It can be diagnosed accurately.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a basic configuration diagram of an entire internal combustion engine to which a control device including an air-fuel ratio sensor diagnostic device according to the present invention is applied. The block diagram which showed the control apparatus shown in FIG. The figure which showed the diagnostic parameter | index of the offset failure of the air fuel ratio sensor shown in FIG. The block diagram explaining the diagnostic apparatus of the air fuel ratio sensor shown in FIG. The flowchart of the diagnosis of the air fuel ratio sensor of the diagnostic apparatus of the air fuel ratio sensor shown in FIG. FIG. 3 is a flowchart of diagnosis area determination by the diagnosis area determination means shown in FIG. 2. FIG. 7 is an example of a flowchart of diagnosis area determination by the diagnosis area determination means shown in FIG. The figure explaining the offset shift of an air fuel ratio sensor.

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

  FIG. 1 shows a basic configuration of an entire internal combustion engine including a control device to which a diagnostic apparatus for an air-fuel ratio sensor according to the present invention is applied. In the illustrated embodiment, the case where the internal combustion engine has a single cylinder will be described. However, the present embodiment can be applied to a multi-cylinder internal combustion engine.

  An internal combustion engine 100 shown in FIG. 1 includes a cylinder 102 in which a combustion chamber 101 is formed, and an intake passage 103 and an exhaust passage 104 connected to the cylinder 102. Further, an ignition device 105 and a plate (or ring gear) 106 are further attached to the cylinder 102 of the internal combustion engine 100, and the rotational speed of the plate 106 is detected by the rotational speed detection means 118. .

  A fuel injection device 107 is attached to the intake passage 103. The flow rate of the air flowing from the air cleaner 108 is adjusted by the throttle valve 109, and then the predetermined angle from the fuel injection device 107 in the intake passage 103. The fuel is mixed with the fuel injected at, and supplied to the combustion chamber 101 of the cylinder 102. Here, air flow rate detection means 110 is provided in the intake passage 103 so that the flow rate of air after the flow rate is adjusted by the throttle valve 109 is detected.

  A three-way catalyst 111 is attached to the exhaust passage 104, and the exhaust gas after the fuel is burned in the combustion chamber 101 is purified by the three-way catalyst 111 and discharged to the outside. Here, an air-fuel ratio sensor 112 is attached upstream of the three-way catalyst 111 in the exhaust passage 104, and an oxygen sensor 113 is attached downstream of the three-way catalyst 111. The oxygen concentration after the three-way catalyst 111 is detected.

  The fuel injection device 107 is connected to the fuel tank 116 via a fuel pipe 115 provided with a pressure regulator 114, and the fuel F inside the fuel tank 116 is sucked and pressurized by the fuel pump 117. The fuel F is introduced into the fuel inlet of the fuel injection device 107 through the fuel pipe 115, and the excess fuel F is returned to the fuel tank 116.

  The control device 200 takes in the output signal QAR of the air flow rate detection means 110 and the rotational speed Ne of the plate 106 detected by the rotational speed detection means 118, calculates the fuel injection amount Ti, and calculates the injection amount of the fuel injection device 107. To control. At that time, the control device 200 further takes in the output signal RABF of the air-fuel ratio sensor 112 disposed in the exhaust passage 104 and corrects the fuel injection amount Ti so that the air-fuel ratio of the internal combustion engine 100 becomes the stoichiometric air-fuel ratio. Perform air-fuel ratio feedback control. In the illustrated control device 200, the output signal VO2R of the oxygen sensor 113 disposed in the exhaust passage 104 can also be taken in, and further advanced air-fuel ratio feedback control can be performed. The control device 200 also transmits control signals to the ignition device 105, the throttle valve 109, and the fuel pump 117, and controls the ignition timing of the ignition device 105, the opening degree of the throttle valve 109, and the like, for example. Efficient operation is being performed.

  Next, FIG. 2 shows an internal configuration of the control device 200 shown in FIG.

  First, the control device 200 includes an air-fuel ratio feedback control device that uses the output signal of the air-fuel ratio sensor 112 and a diagnostic device 250 that diagnoses the air-fuel ratio sensor 112.

  The air-fuel ratio feedback control device is executed mainly by the oxygen concentration control means 210, the target air-fuel ratio calculation means 220, the air-fuel ratio sensor control means 230, and the fuel injection control means 240. Usually, in the exhaust purification system using the three-way catalyst 111, the air-fuel ratio before the catalyst is set to the target air-fuel ratio (for example, the theoretical air-fuel ratio) by PI control or the like using the signal of the air-fuel ratio sensor 112 arranged before the catalyst. It is controlled to become. At that time, by applying the oxygen concentration control means 210 as shown in the figure, the target air-fuel ratio can be corrected by using the signal of the oxygen sensor 113 disposed after the catalyst, and the correction is performed by the air-fuel ratio sensor 112. While controlling (absorbing) the signal shift, the target air-fuel ratio can be matched with the air-fuel ratio required by the catalyst (in-catalyst center air-fuel ratio). As a result, more accurate air-fuel ratio feedback control can be realized, and the fuel injection amount of the fuel injected into the combustion chamber can be precisely controlled.

  More specifically, the oxygen concentration control means 210 sets the target air-fuel ratio correction amount TABFRO2 based on the output signal QAR of the air flow rate detection means 110, the output signal RABF of the air-fuel ratio sensor 112, and the output signal VO2R of the oxygen sensor 113. Calculate. Next, the target air-fuel ratio calculating means 220 calculates the target air-fuel ratio based on the calculation result. The air-fuel ratio sensor control means 230 calculates an air-fuel ratio sensor control amount based on the target air-fuel ratio and the output signal RABF of the air-fuel ratio sensor 112 so that the air-fuel ratio before the catalyst becomes the target air-fuel ratio, The calculation result is transmitted to the fuel injection control means 240. The fuel injection control means 240 is based on the calculation result transmitted from the air-fuel ratio sensor control means 230 and the output signal QAR of the air flow rate detection means 110 in order to control the fuel injection amount of the fuel injected into the combustion chamber. The fuel injection amount is calculated, and the control signal is transmitted to the fuel injection device 107.

  Next, the internal configuration of the oxygen concentration control means 210 will be described in more detail. The oxygen concentration control unit 210 includes an oxygen accumulation amount calculation unit 201 in the catalyst, a proportional correction value calculation unit 202, an integral correction value calculation unit 203, a central air-fuel ratio calculation unit 204 in the catalyst, and a target air-fuel ratio. The correction amount calculation means 205 is generally configured.

  In the oxygen accumulation amount calculation means 201, the air-fuel ratio RABF detected by the air-fuel ratio sensor 112, the intake air flow rate QAR detected by the air flow rate detection means 110, and the central air-fuel ratio calculation means 204 are calculated at least once before. The amount of oxygen accumulated in the catalyst is calculated from the obtained central air-fuel ratio. Next, in the proportional correction value calculating means 202, the integral correction value calculating means 203, and the central air-fuel ratio calculating means 204, the oxygen accumulation amount calculated by the oxygen accumulation amount calculating means 201 and the oxygen concentration VO2R detected by the oxygen sensor 113 are displayed. From these, the proportional correction value PB, the integral correction value IB, and the central air-fuel ratio CNTABF are calculated. Then, the target air-fuel ratio correction amount calculation means 205 calculates the target air-fuel ratio correction amount TABFRO2 based on these calculation results. As described above, the central air-fuel ratio CNTABF calculated by the central air-fuel ratio calculating unit 204 is also used for calculating the oxygen accumulation amount in the oxygen accumulation amount calculating unit 201.

  Next, the offset failure diagnosis of the air-fuel ratio sensor 112 executed in the control device 200 using the calculation result calculated in the air-fuel ratio feedback control device will be described. The offset failure diagnosis is mainly executed by the air-fuel ratio sensor diagnosis device 250. Here, the offset failure of the air-fuel ratio sensor 112 is an excessive state of the offset deviation. As described above, the oxygen concentration control unit 210 has a function of controlling (absorbing) the offset deviation of the air-fuel ratio sensor 112. Therefore, it is possible to diagnose the offset failure of the air-fuel ratio sensor 112 by monitoring the parameter calculated in the oxygen concentration control means 210. More specifically, the air-fuel ratio sensor diagnosis device 250 diagnoses an offset failure of the air-fuel ratio sensor 112 based on the target air-fuel ratio correction amount TABFRO2 and the central air-fuel ratio CNTABF calculated in the oxygen concentration control means 210.

  That is, the air / fuel ratio sensor diagnosis apparatus 250 includes an upper limit determination value calculation unit 251, a lower limit determination value calculation unit 252, a first failure diagnosis unit 253, a second failure diagnosis unit 254, and a diagnosis region determination unit 255. The upper limit determination value calculation means 251 and the lower limit determination value calculation means 252 are for determining the target air-fuel ratio correction amount TABFRO2 from the center air-fuel ratio CNTABF calculated by the center air-fuel ratio calculation means 204, respectively. An upper limit judgment value and a lower limit judgment value are calculated. Next, the first failure diagnosis means 253 compares the target air-fuel ratio correction amount TABFRO2 calculated by the target air-fuel ratio correction amount calculation means 205 with the upper limit determination value and the lower limit determination value. For example, the target air-fuel ratio correction amount TABFRO2 is the upper limit. If the determination value is greater than or equal to or the target air-fuel ratio correction amount TABFRO2 is less than or equal to the lower limit determination value, it is diagnosed that the air-fuel ratio sensor has an offset failure. This failure diagnosis is executed when the diagnosis region is determined by the diagnosis region determination means 255 and the execution of the failure diagnosis is permitted. Further, the second failure diagnosis means 254 executes an offset failure diagnosis of the air-fuel ratio sensor from the center air-fuel ratio CNTABF calculated by the center air-fuel ratio calculation means 204. For example, a failure diagnosis of the air-fuel ratio sensor is performed by comparing the central air-fuel ratio CNTABF with a predetermined value. In the second failure diagnosis unit 254, the diagnosis region is determined by the diagnosis region determination unit 255, and the failure diagnosis of the air-fuel ratio sensor is executed when the execution of the failure diagnosis is permitted.

  The failure diagnosis results of the first failure diagnosis means 253 and the second failure diagnosis means 254 are stored in a storage device such as a RAM or ROM shown in FIG. 1, for example, and a standardized scan tool is connected to the vehicle. Therefore, it can be read by the scan tool. Further, the first failure diagnosis means 253 and the second failure diagnosis means 254 are connected to, for example, a warning light on an instrument panel, and make the driver recognize the failure diagnosis result by turning on the warning light or the like. it can.

  Next, FIG. 3 explains the diagnostic index of the offset failure of the air-fuel ratio sensor shown in FIG.

  First, the calculation inside the oxygen concentration control means 210 will be specifically described. The oxygen accumulation amount calculation means 201 uses the air-fuel ratio RABF, the air flow rate QAR, and the central air-fuel ratio CNTABF, and is based on the following equation (1). Then, the oxygen accumulation amount OSEST in the three-way catalyst is calculated.

ここで、「ｏｌｄ」とは、ループ演算における前回時の演算結果を意味するものである。

Here, “old” means the previous calculation result in the loop calculation.

  The proportional correction value calculation means 202, the integral correction value calculation means 203, and the central air-fuel ratio calculation means 204 are respectively the oxygen accumulation amount OSEST calculated by the oxygen accumulation amount calculation means 201 and the oxygen concentration detected by the oxygen sensor 113. Map 1, map 2, and map 3 based on VO2R are prepared in advance. Therefore, in the proportional correction value calculation means 202, the integral correction value calculation means 203, and the central air-fuel ratio calculation means 204, the proportional correction values are obtained from the oxygen accumulation amount OSEST, the oxygen concentration VO2R, and their maps 1, 2, and 3, respectively. PB, integral correction value IB, and center air-fuel ratio CNTABF can be calculated. Then, the target air-fuel ratio correction amount calculating means 205 calculates the target air-fuel ratio correction amount TABFRO2 by adding the proportional correction value PB, the integral correction value IB, and the central air-fuel ratio CNTABF.

  By the way, as the occurrence state of the offset failure of the air-fuel ratio sensor 112, there are rapid deterioration and deterioration with time.

  When the air-fuel ratio sensor 112 is rapidly deteriorated in the occurrence of the offset failure, the output signal VO2R of the oxygen sensor 113 is likely to be influenced via the three-way catalyst 111. Accordingly, when the proportional correction value PB and the integral correction value IB change relatively large, the target air-fuel ratio correction amount TABFRO2 that is the output value of the oxygen concentration control means 210 changes relatively large. Based on the calculation result, the target air-fuel ratio calculated by the target air-fuel ratio calculating means 220 is corrected, and the air-fuel ratio sensor control means 230 controls the output signal RABF of the air-fuel ratio sensor to be the actual air-fuel ratio. Will be. Thus, in the case of sudden offset deterioration, the offset failure of the output signal RABF of the air-fuel ratio sensor 112 is mainly reflected in the target air-fuel ratio correction amount TABFRO2. Therefore, the offset failure diagnosis of the air-fuel ratio sensor 112 can be performed by monitoring the target air-fuel ratio correction amount TABFRO2 as a diagnostic index.

  On the other hand, when the air-fuel ratio sensor 112 is deteriorated with time, the influence is less likely to be exerted on the output signal VO2R of the oxygen sensor as compared with the case of rapid deterioration. Therefore, the target air-fuel ratio correction amount TABFRO2 does not change so much and the output signal RABF of the air-fuel ratio sensor 112 is not controlled to the actual air-fuel ratio in the air-fuel ratio sensor control means 230. That is, in this control apparatus, the control operation of RABF-CNTABF_old = 0 in the oxygen accumulation amount calculation unit 201 becomes dominant. As described above, in the case of offset deterioration with time, the influence is relatively large on the central air-fuel ratio CNTABF calculated by the central air-fuel ratio calculating means 204. Therefore, the offset failure diagnosis of the air-fuel ratio sensor 112 can be performed by monitoring the central air-fuel ratio CNTABF as a diagnostic index.

  Thus, by using the target air-fuel ratio correction amount TABFRO2 and the center air-fuel ratio CNTABF as diagnostic indicators, it is possible to diagnose an offset failure of the air-fuel ratio sensor 112 regardless of the deterioration state of the air-fuel ratio sensor 112, and The deterioration state of the air-fuel ratio sensor 112 can be accurately diagnosed by detecting which of the air-fuel ratio correction amount TABFRO2 and the central air-fuel ratio CNTABF is detected.

  FIG. 4 specifically illustrates the air-fuel ratio sensor diagnostic apparatus 250 shown in FIG.

  As described above, since the influence of the output signal VO2R of the oxygen sensor 113 is likely to appear depending on the deterioration state of the air-fuel ratio sensor 112, such as rapid deterioration or deterioration with time, the air-fuel ratio sensor diagnosis apparatus 250 may be less likely to appear. , The offset failure of the air-fuel ratio sensor 112 is diagnosed using the target air-fuel ratio correction amount TABFRO2 and the central air-fuel ratio CNTABF as diagnostic indicators.

  First, the first failure diagnosis means 253 for diagnosing an offset failure particularly when the air-fuel ratio sensor 112 is rapidly deteriorated will be described.

  First, based on the central air-fuel ratio CNTABF, the first failure diagnosis means 253 calculates an upper limit determination value and a lower limit calculation value that are used as determination indexes. Specifically, the weighted average value for the center air-fuel ratio CNTABF or the learning value for each operation region is converted by the center air-fuel ratio conversion means 256, and the upper limit determination value calculation means 251 adds a predetermined value α to the conversion result. The upper limit judgment value is calculated. Further, the lower limit determination value calculation means 252 calculates a lower limit determination value by subtracting the predetermined value β from the weighted average value for the central air-fuel ratio or the learning value for each operation region. The predetermined value α and the predetermined value β can be the same value. Further, the predetermined value α and the predetermined value β can be calculated from the table 1 and the table 2 based on the weighted average value for the center air-fuel ratio converted by the center air-fuel ratio conversion means 256 or the learning value for each operation region.

  In the first failure diagnosis means 253, when the target air-fuel ratio correction amount TABFRO2 is larger than the upper limit determination value, or when the target air-fuel ratio correction amount TABFRO2 is smaller than the lower limit determination value, an offset failure of the air-fuel ratio sensor 112 occurs. Diagnose it. Thus, by calculating the upper limit determination value and the lower limit determination value from the weighted average value or learning value for the center air-fuel ratio CNTABF, the target air-fuel ratio correction amount TABFRO2 is an excessive value with respect to the center air-fuel ratio CNTABF. The state can be determined as an offset failure. This failure diagnosis is executed when the diagnosis area determination means 255 permits the execution of the failure diagnosis.

  Next, the second failure diagnosing means 254 for diagnosing an offset failure particularly when the air-fuel ratio sensor 112 is deteriorated with time will be described.

  The second failure diagnosis means 254 diagnoses that the air-fuel ratio sensor 112 is an offset failure when the center air-fuel ratio CNTABF is larger than the constant γ or when the center air-fuel ratio CNTABF is smaller than the constant ζ. Here, since the central air-fuel ratio CNTABF in the catalyst is unlikely to deviate significantly from the theoretical air-fuel ratio of 14.7, it is preferable to set the constant γ and the constant ζ to be close to 14.7. . The failure diagnosis is executed when the diagnosis of the failure diagnosis is permitted by the diagnosis area determination unit 255, as in the first failure diagnosis unit 253.

  The air-fuel ratio sensor failure diagnosis method by the air-fuel ratio sensor diagnosis apparatus of the above embodiment will be described below. FIG. 5 shows a flowchart of the air-fuel ratio sensor failure diagnosis of the air-fuel ratio sensor diagnostic device 250.

  First, in step 501, the air-fuel ratio RABF before the catalyst is measured by the air-fuel ratio sensor 112. In step 502, the oxygen concentration VO2R after the catalyst is measured by the oxygen sensor 113. In step 503, the intake air flowing into the internal combustion engine is measured. Measure the flow rate QAR. In step 504, the oxygen accumulation amount OSEST in the catalyst is calculated from the air-fuel ratio RABF, the air flow rate QAR, and the central air-fuel ratio CANTABF. In step 505, the proportional correction value PB is calculated from the oxygen accumulation amount OSEST and the oxygen concentration VO2R based on the map 1, and in step 506, the integral correction is performed based on the map 2 from the oxygen accumulation amount OSEST and the oxygen concentration VO2R. The value IB is calculated, and in step 507, the central air-fuel ratio CNTABF in the catalyst is calculated based on the map 3 from the oxygen accumulation amount OSEST and the oxygen concentration VO2R. In step 508, the proportional correction value PB, the integral correction value IB, and the central air-fuel ratio CNTABF are added to calculate the target air-fuel ratio correction amount TABFRO2. In step 509, the previous values of the integral correction value IB, the central air-fuel ratio CNTABF, and the oxygen accumulation amount OSEST are set as the integral correction value IB_old, the central air-fuel ratio CNTABF_old, and the oxygen accumulation amount OSEST_old, respectively. Note that the integral correction value IB_old, the central air-fuel ratio CNTABF_old, and the oxygen accumulation amount OSEST_old are used in the calculations in step 504 and step 506.

  In step 510, the weighted average value of the center air-fuel ratio CNTABF or the learning value CNTABFLT for each operation region is converted. In step 511, an upper limit determination value is calculated based on Table 1 from the CNTABFLT, and in step 512, a lower limit determination value is calculated based on Table 2 from CNTABFLT. In step 513, a diagnosis area is determined, and it is determined whether or not execution of failure diagnosis is permitted. If the execution of failure diagnosis is permitted in step 513, the process proceeds to step 514 and step 515, and if not permitted, failure diagnosis is not executed. In step 514, it is determined whether the target air-fuel ratio correction amount TABFRO2 is larger than the upper limit determination value or smaller than the lower limit determination value, and the target air-fuel ratio correction amount TABFRO2 is larger than the upper limit determination value or lower limit determination value. If it is smaller, the process proceeds to step 516, and it is determined that an offset failure has occurred. In step 515, it is determined whether or not the center air-fuel ratio CNTABF is larger than the constant γ or smaller than the constant ζ. If the center air-fuel ratio CNTABF is larger than the constant γ or smaller than the constant ζ. In step 516, it is determined that an offset failure has occurred. If it is determined in step 514 that the target air-fuel ratio correction amount TABFRO2 is not less than the lower limit determination value and not more than the upper limit determination value, and the center air-fuel ratio CNTABF is not less than a constant ζ and not more than a constant γ, the process proceeds to step 517. It is determined that there is no offset failure. Note that the diagnostic region determination in step 513 can be performed prior to step 510. Further, after it is determined in step 514 that the target air-fuel ratio correction amount TABFRO2 is not less than the lower limit determination value and not more than the upper limit determination value, the determination in step 515 is performed, and in step 515, the center air-fuel ratio CNTABF is more than a constant ζ and a constant γ It can also be determined that there is no offset failure when it is determined that:

  If it is determined in step 516 that an offset failure has occurred, for example, a warning lamp on the instrument panel is turned on to allow the driver to recognize the determination result.

  Next, the diagnosis area determination (in the diagnosis area determination means 255) in step 513 will be described. FIG. 6 shows a flowchart of diagnosis area determination by the diagnosis area determination means 255, and FIG. 7 shows an example thereof.

  As shown in FIG. 6, in step 601, various conditions of the diagnosis area are determined. Specifically, the rotational speed of the internal combustion engine is within a predetermined range, the load of the internal combustion engine is within a predetermined range, the water temperature is a predetermined value or more, the vehicle speed is within a predetermined range, or the intake air temperature is Whether it is within the predetermined range, the atmospheric pressure is below the predetermined value, the battery voltage is within the predetermined range, the fuel is not being cut (non-fuel cut state), the air-fuel ratio control feedback is being performed, or other than the air-fuel ratio sensor is used Each of the sensors (for example, an air flow rate detection means and an oxygen sensor) is determined whether or not it has failed. If all of these conditions are satisfied, the process proceeds to step 602, where it is determined that it is within the diagnosis area, and execution of failure diagnosis is permitted. If any one of the above conditions is not satisfied, the process proceeds to step 603, where it is determined that the condition is out of the diagnosis area and execution of the failure diagnosis is not permitted.

  FIG. 7 shows an example of a flowchart of the diagnosis area determination. Step 601 shown in FIG. 6 is sequentially executed from step 701 to step 710. That is, in step 701, it is determined whether the rotational speed of the internal combustion engine is within a predetermined range. In step 702, it is determined whether the load of the internal combustion engine is within a predetermined range. In step 703, it is determined whether the water temperature is equal to or higher than a predetermined value. In step 704, it is determined whether the vehicle speed is within a predetermined range. In step 705, it is determined whether the intake air temperature is within a predetermined range. In step 706, it is determined whether the atmospheric pressure is a predetermined value or less. In step 707, it is determined whether the battery voltage is within a predetermined range. In step 708, it is determined whether a fuel cut is in progress. In step 709, it is determined whether air-fuel ratio control feedback is being performed. In step 710, it is determined whether there is a failure in a sensor other than the air-fuel ratio sensor. If all of the conditions in steps 701 to 710 are satisfied, it is determined in step 711 that the region is within the diagnosis area. If any one of the conditions in steps 701 to 710 is not satisfied, it is determined in step 712 that the region is outside the diagnosis region.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. . Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  This is a diagnostic device for diagnosing an offset failure of an air-fuel ratio sensor in front of a catalyst attached to an internal combustion engine, and is an essential technique for strengthening vehicle self-diagnosis regulations.

DESCRIPTION OF SYMBOLS 100 ... Internal combustion engine, 101 ... Combustion chamber, 102 ... Cylinder, 103 ... Intake passage, 104 ... Exhaust passage, 105 ... Ignition device, 106 ... Plate or ring gear, 107 ... Fuel injection device, 108 ... Air cleaner, 109 ... Throttle valve DESCRIPTION OF SYMBOLS 110 ... Air flow detection means 111 ... Three-way catalyst, 112 ... Air-fuel ratio sensor, 113 ... Oxygen sensor, 114 ... Pressure regulator, 115 ... Fuel pipe, 116 ... Fuel tank, 117 ... Fuel pump, 118 ... Detection of rotation speed Means 200, control unit 201, oxygen accumulation amount calculating means 202, proportional correction value calculating means 203, integral correction value calculating means 204, central air-fuel ratio calculating means 205 205 target air-fuel ratio correction amount calculating means , 210 ... oxygen concentration control means, 220 ... target air-fuel ratio calculation means, 230 ... air-fuel ratio sensor control means, 240 ... Fuel injection control means, 250 ... Air-fuel ratio sensor diagnostic device, 251 ... Upper limit determination value calculation means, 252 ... Lower limit determination value calculation means, 253 ... First failure diagnosis means, 254 ... Second failure diagnosis means, 255 ... Diagnosis region Determining means, 256 ... central air-fuel ratio converting means

Claims (11)

A catalyst disposed in the exhaust passage, an air-fuel ratio sensor that detects an air-fuel ratio upstream of the catalyst, an oxygen sensor that detects an oxygen concentration in exhaust gas downstream of the catalyst, and an inflow air flow rate An air-fuel ratio sensor diagnostic apparatus for an internal combustion engine having an air flow rate detection means,
The diagnostic device includes a central air-fuel ratio and a target air-fuel ratio correction amount in the catalyst that are calculated based on the air-fuel ratio, the air flow rate, and the oxygen concentration, and the target air-fuel ratio that is calculated based on the central air-fuel ratio. A diagnostic apparatus for an air-fuel ratio sensor, comprising: a first failure diagnostic means for diagnosing a malfunction of the air-fuel ratio sensor based on an upper limit judgment value and a lower limit judgment value relating to a fuel ratio correction amount . The upper limit determination value is calculated by adding a first predetermined value to a weighted average value for the central air-fuel ratio or a learning value for each operation region,
2. The air-fuel ratio according to claim 1 , wherein the lower limit determination value is calculated by subtracting a second predetermined value from the weighted average value with respect to the central air-fuel ratio or the learning value for each operation region. Sensor diagnostic device. 3. The air-fuel ratio sensor according to claim 2 , wherein the first predetermined value is calculated from a first table based on the weighted average value for the central air-fuel ratio or the learning value for each operation region. Diagnostic device. 3. The air-fuel ratio sensor according to claim 2 , wherein the second predetermined value is calculated from a second table based on the weighted average value for the central air-fuel ratio or the learning value for each operation region. Diagnostic device. The first failure diagnosis means diagnoses a failure of the air-fuel ratio sensor when the target air-fuel ratio correction amount is larger than the upper limit determination value or when the target air-fuel ratio correction amount is smaller than the lower limit determination value. The air-fuel ratio sensor diagnostic apparatus according to any one of claims 1 to 4 , wherein: The air-fuel ratio sensor diagnosis according to any one of claims 1 to 5 , wherein the diagnosis device further comprises second failure diagnosis means for diagnosing a failure of the air-fuel ratio sensor based on the central air-fuel ratio. apparatus. The second failure diagnosis means diagnoses a failure of the air-fuel ratio sensor when the center air-fuel ratio is larger than a third predetermined value or when the center air-fuel ratio is smaller than a fourth predetermined value. The diagnostic apparatus for an air-fuel ratio sensor according to claim 6 . 8. The air-fuel ratio sensor diagnostic apparatus according to claim 7 , wherein at least one of the third predetermined value and the fourth predetermined value is calculated based on a theoretical air-fuel ratio. The air-fuel ratio sensor according to any one of claims 1 to 8 , wherein the diagnosis device further includes a diagnosis region determination unit that determines a diagnosis region in order to permit execution of the diagnosis of the air-fuel ratio sensor. Diagnostic device. The diagnostic region determination means is configured such that the rotational speed of the internal combustion engine is within a predetermined range, the load is within a predetermined range, the water temperature is within a predetermined range, the vehicle speed is within a predetermined range, the inflow air temperature of the internal combustion engine is within a predetermined range, and the atmospheric pressure is When the internal-combustion engine is in a non-fuel cut state, during the air-fuel ratio feedback control, or when a sensor used other than the air-fuel ratio sensor has not failed, the failure diagnosis of the air-fuel ratio sensor is executed. The air-fuel ratio sensor diagnostic apparatus according to claim 9 , wherein the air-fuel ratio sensor is permitted. The central air-fuel ratio is calculated based on the oxygen accumulation amount in the catalyst and the oxygen concentration calculated based on the central air-fuel ratio, the air-fuel ratio, and the air flow rate,
The target air-fuel ratio correction amount is diagnostic apparatus of the air-fuel ratio sensor according to claim 1, wherein 10 to be calculated based on at least the center air-fuel ratio.

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