JP4678336B2 - Diagnostic apparatus and diagnostic method for air-fuel ratio sensor - Google Patents

Description

  The present invention relates to a technique for diagnosing abnormality / failure of an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine.

In the field of internal combustion engines for vehicles, an air-fuel ratio sensor is provided in an exhaust system, and the air-fuel ratio of the internal combustion engine is set to a target air-fuel ratio by, for example, changing the fuel injection amount based on the sensor output corresponding to the actual air-fuel ratio of the exhaust. In general, so-called air-fuel ratio feedback control, in which closed loop control is performed to a fuel ratio, for example, a theoretical air-fuel ratio, is performed. Such a sensor is obligated to diagnose abnormality / failure. For example, Patent Document 1 describes a diagnostic technique for a wide-range air-fuel ratio sensor. Briefly, after the engine is activated from the start of the engine, feedforward control toward a predetermined air-fuel ratio different from the stoichiometric air-fuel ratio (stoichiometric) is performed, and the sensor output corresponds to the stoichiometry during this feedforward control. If it is, it is determined that the sensor has an intermediate potential failure (abnormality). Further, when the sensor output corresponds to the stoichiometry during the fuel cut, it is determined that the sensor has an intermediate potential failure.
JP 2001-241346 A

  In the case of performing feedforward control toward a predetermined air-fuel ratio deviating from the stoichiometric air-fuel ratio in order to diagnose a sensor abnormality / failure as in the above-mentioned Patent Document 1, a decrease in engine operability during the diagnosis is performed. There is a concern that exhaust emissions will decline. Further, in Patent Document 1 described above, no consideration is given to sensor abnormalities / failures other than intermediate potential failures in which the sensor output is fixed in a voltage range other than that corresponding to stoichiometry. Furthermore, since the area where feedforward control is performed, that is, the area where sensor diagnosis is performed is limited to idle operation, for example, even if a sensor abnormality or failure occurs while the vehicle is running, the diagnosis is continued until the operation shifts to idle operation. Since it is not performed, there is a problem that the abnormality / failure cannot be detected.

  By the way, factors that cause poor control due to poor air-fuel ratio feedback control include the effects of evaporated fuel purged to the intake system by the evaporated fuel processing device, as well as failure of the fuel injection valve, air flow meter, and the like. . That is, due to the influence of the evaporated fuel purged to the intake system by the evaporated fuel processing device, for example, the switching cycle between rich and lean becomes longer, and the actual air-fuel ratio does not follow the target air-fuel ratio well. In order to return to a state where feedback control is normally performed from such feedback control failure caused by purge or the like, for example, at the time of control failure, the air-fuel ratio correction coefficient is initialized and clamped to “1” for a predetermined period. Thus, it is conceivable that the air-fuel ratio feedback control is temporarily interrupted and the fuel injection amount is controlled in an open loop.

  The present invention has been made paying attention to the fact that the feedback control is determined to be defective even when the air-fuel ratio sensor is abnormal or failed as described above, and the feedback control is interrupted.

The present invention relates to diagnosis of an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, and performs air-fuel ratio feedback control toward a target air-fuel ratio based on the sensor output of the air-fuel ratio sensor corresponding to the actual air-fuel ratio of exhaust gas. During the air-fuel ratio feedback control, a feedback control failure is detected in which the actual air-fuel ratio does not follow the target air-fuel ratio. When the control failure is determined, the air-fuel ratio feedback control is interrupted for a predetermined period. Then, after the air-fuel ratio feedback control is interrupted for the predetermined period, the air-fuel ratio feedback control is resumed, the control failure is determined, and the fluctuation range of the sensor output during the interruption of the air-fuel ratio feedback control is a predetermined reference. The number of interruptions of the air-fuel ratio feedback control due to repeated determination of the control failure without exceeding the fluctuation range is a predetermined reference number. Beyond determines that the air-fuel ratio sensor is abnormal, it is characterized in that.

  According to the present invention, a simple control process using a process of temporarily interrupting the air-fuel ratio feedback control so as to return to a state in which feedback control is normally performed from a feedback control failure caused by purging or the like, The air-fuel ratio sensor can be diagnosed, and the calculation load and stored control processing can be reduced. In addition, it is not necessary to perform a special operation only for the diagnosis of the sensor, and if the air-fuel ratio feedback control is being performed, this feedback control failure determination is performed, so that the air-fuel ratio sensor is substantially diagnosed. Therefore, there are many opportunities for diagnosis, and it is possible to detect abnormalities and failures of the sensor at an early stage.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the system configuration of an internal combustion engine to which an air-fuel ratio sensor diagnostic apparatus according to an embodiment of the present invention is applied. In the combustion chamber 21 of the internal combustion engine 20, a spark plug 9 is disposed substantially at the upper center, and an intake passage 23 is connected via an intake valve 22 and an exhaust passage 25 is connected via an exhaust valve 24. ing. In the intake passage 23, in order from the upstream side, an air cleaner 26, an air flow meter 3 for measuring the intake flow rate, an electronically controlled throttle valve 27 for opening and closing the intake passage 23, and a throttle opening sensor 4 for detecting the throttle opening, A fuel injection valve 5 for injecting fuel into the intake port 23A of the intake passage 23 is provided. The present invention can be applied not only to such a port injection type internal combustion engine but also to a direct injection type internal combustion engine that directly injects fuel from a fuel injection valve into a combustion chamber.

A front catalyst 13 is disposed in the exhaust passage 25 at an upstream position near the combustion chamber 21 and at a relatively high exhaust temperature, or at an upstream position in the vicinity thereof, and further downstream than the front catalyst 13. Thus, the rear catalyst 14 is disposed at a position under the floor of the vehicle having a relatively low exhaust temperature. That is, in order to purify the exhaust gas with high efficiency including when the cold machine is started, the catalyst system is configured such that the catalyst is arranged in series at a plurality of locations having different ambient temperatures in the exhaust passage 25. The front catalyst 13 preferably has a three-way catalyst capable of reducing NO _x , HC and CO to almost 0 (zero) in the vicinity of the stoichiometric air-fuel ratio, and temporary HC discharged before the three-way catalyst is activated. The rear catalyst 14 is, for example, the above-described HC adsorption catalyst. However, not limited thereto, the above-mentioned three-way catalyst, other HC adsorption catalyst, to trap NO _X in an oxygen excess region, such as during the lean operation, releases NO _X during stoichiometric or rich operation, reducing to NO _X Other catalysts such as a trap catalyst may be used alone or in combination.

Further, the air-fuel ratio sensor 11 is provided in the exhaust passage 25 on the upstream side of the front catalyst 13. In this embodiment, the sensor 11 is a wide-range air-fuel ratio sensor that outputs a sensor output (voltage) corresponding to the actual air-fuel ratio of exhaust gas and can widely detect the actual air-fuel ratio of exhaust gas. However, the present invention can be applied to a device using a simple oxygen sensor (O ₂ sensor). The engine speed (engine speed) is calculated based on detection signals from, for example, a position (POS) sensor 7 that detects the rotational angle position of the crankshaft and a phase (PHASE) sensor 8 that detects the phase of the camshaft. . Further, a knock sensor 6 that detects the occurrence of knocking (knock) and a water temperature sensor 10 that detects the engine water temperature as the engine temperature are attached to the cylinder block of the internal combustion engine 20.

  As is well known, the canister 30 as a fuel evaporation processing device is filled with an adsorbent such as activated carbon, temporarily adsorbs the evaporated fuel in the fuel tank 31, and purges ( The desorbed gas containing the evaporated fuel is supplied to the intake passage 23 downstream of the throttle through the purge passage 32. A purge control valve 33 that controls the purge flow rate is provided in the purge passage 32.

  The control unit (engine control module) 1 is a known digital computer system including a CPU, a ROM, a RAM, and an input / output interface, and has a function of storing and executing various control processes. Various signals such as a starter signal and an ignition signal are input to the control unit 1 and various actuators based on the detection signals input from the various sensors 3, 4, 6-8, and 10-11. A control signal is output to the class and its operation is controlled. For example, the basic injection pulse width Tp is calculated based on detection signals from the air flow meter 3, the water temperature sensor 10, etc., and the air-fuel ratio closed-loop control is performed based on the sensor output of the air-fuel ratio sensor 11. That is, the basic injection pulse width Tp is mainly obtained from the intake air amount and the engine speed, and the air-fuel ratio feedback correction coefficient is obtained by pseudo PI control based on the sensor output of the air-fuel ratio sensor 11 corresponding to the actual air-fuel ratio of the exhaust gas. α is sequentially calculated, and the basic injection pulse width Tp is multiplied by the correction coefficient α to determine the final injection pulse width Ti, that is, the fuel injection amount. By this air-fuel ratio feedback control, the actual air-fuel ratio fluctuates so as to periodically swing around the target air-fuel ratio. Further, by performing duty control of ON / OFF of the purge control valve 33, the purge ON / OFF is switched and the purge flow rate is controlled.

  FIGS. 2 and 3 are flowcharts showing the flow of control processing executed repeatedly by the control unit 1 for each storage and extremely short period (for example, 10 ms or a predetermined crank angle). In step S11 of FIG. 2, the initialization request flag FLG of the air-fuel ratio correction coefficient α set by the routine of FIG. 3 is read. Referring to FIG. 3, in step S <b> 30, it is determined whether a condition for performing the air-fuel ratio feedback (F / B) control is satisfied. For example, air-fuel ratio feedback control is performed except at start-up, low water temperature, high water temperature, high load, deceleration, and immediately after a shift from N to D. If it is not in the operating range in which air-fuel ratio feedback control is performed, this routine is terminated.

  In step S31, based on the sensor output of the air-fuel ratio sensor 11, a state where the actual air-fuel ratio rAFS does not follow the target air-fuel ratio tAFS well during the air-fuel ratio feedback control, that is, an initialization request for the air-fuel ratio correction coefficient α is made. It is determined whether or not there is a certain state. For example, when the deviation of the actual air-fuel ratio rAFS with respect to the target air-fuel ratio tAFS exceeds a predetermined value exceeds the predetermined period, and as a result, the air-fuel ratio correction coefficient α sticks to the minimum or maximum limit, It is determined that there is a feedback control failure, and the processes of steps S32 to S34 are executed. In step S32, the initialization request flag FLG is set to “1”. In step S33, the air-fuel ratio feedback control is interrupted. Specifically, the air-fuel ratio correction coefficient α is forcibly initialized and clamped to “1 (100%)”, and the fuel injection amount is opened with another correction coefficient according to a parameter such as cooling water temperature. Loop control. In step S34, purging by the canister 30 is prohibited. Specifically, the purge control valve 33 is closed to prohibit the supply of gas containing evaporated fuel to the intake system.

  In step S35, it is determined whether a predetermined period ΔD1 (for example, about 4 to 6 seconds) has elapsed since the interruption of the feedback control in step S33 using an appropriate counter, timer, or the like. If the predetermined period ΔD1 has elapsed, the process proceeds to step S36, the flag FLG is set to 0 (zero), and the air-fuel ratio feedback control is resumed in step S37. That is, the air-fuel ratio correction coefficient α is calculated based on the sensor output, and the fuel injection amount is increased or decreased by the air-fuel ratio correction coefficient α.

  Referring to FIG. 2 again, in step S12, it is determined whether the flag FLG has been switched from 0 to 1. For example, the FLG value at the previous calculation is stored, and if the FLG value at the previous calculation is “0” and the current FLG value is “1”, it is determined that the FLG has been switched from 0 to 1. To do.

  When FLG is changed from 0 to 1, the value of the counter CLPCNT indicating the frequency and number of interruptions is incremented by 1, that is, CLPCNT is incremented by 1 (step S13), and the air-fuel ratio sensor 11 corresponding to the actual air-fuel ratio is updated. The sensor output maximum value AFSMAX and minimum value AFSMAX are initialized to “0” (step S14).

  In step S15, it is determined whether or not the value of the flag FLG is "1". If it is not 1, this routine is terminated. If it is 1, the process proceeds to step S16 and subsequent steps. In steps S16 and S17, if the actual air-fuel ratio (sensor output) rAFS exceeds the maximum value AFSMAX, the maximum value AFSMAX is updated to the current actual air-fuel ratio rAFS. In steps S18 and S19, if the actual air-fuel ratio rAFS is lower than the minimum value AFSMIN, the minimum value AFSMIN is updated to the current actual air-fuel ratio rAFS.

  In step S20, it is determined whether the fluctuation range (AFSMAX-AFSMIN) of the actual air-fuel ratio exceeds a predetermined reference fluctuation range ΔAFS0 set and stored in advance. If the fluctuation range (AFSMAX-AFSMIN) of the actual air-fuel ratio exceeds the reference fluctuation range ΔAFS0, the process proceeds to step S21, and the interruption count value CLPCNT is initialized to zero.

  In step S22, it is determined whether or not the number of interruptions CLPCNT is equal to or greater than a predetermined reference number NGCNT set and stored in advance. If CLPCNT is greater than or equal to NGCNT, the processing of step S23 and step S24 is executed. In step S23, it is determined that the air-fuel ratio sensor 11 is abnormal or out of order. In response to this determination, the driver is notified of the abnormality / failure of the sensor by a warning lamp or a warning sound, and control processing such as cancellation of air-fuel ratio feedback control is performed.

  In step S24, the maximum value AFSMAX and the minimum value AFSMIN of the actual air-fuel ratio at the time when this abnormality is determined are stored as DAFSX and DAFSN, respectively. Using these DAFSX and DAFSN, for example, if DAFSX and DAFSN are both small values close to 0 (V), the sensor is disconnected, and if it is close to 5 (V), it is short-circuited. Abnormal aspects can be identified.

  Such operational effects of the present embodiment will be described with reference to the time chart of FIG. At time T1, if the air-fuel ratio sensor 11 fails due to some trouble and the sensor output (voltage) is fixed at 0 V, for example, the sensor output (actual air-fuel ratio) rAFS follows the target air-fuel ratio tAFS well. The value of the air-fuel ratio correction coefficient α sticks to the limit value, and at time T2 after the lapse of the predetermined time ΔD2, it is determined that the feedback control is defective. As described above, the initialization request flag FLG is set to “1”. Is set. As a result, the feedback correction coefficient α is clamped (initialized) to “1”, the fuel injection amount is open-loop controlled with another correction coefficient according to parameters such as cooling water temperature, and purging by the canister 30 is prohibited. Is done. In addition, the sensor output (voltage value) is monitored from time T2 when it is determined that the feedback control is defective, and the minimum value AFSMIN and the maximum value AFSMAX are sequentially updated.

  When the predetermined period ΔD1 has elapsed since the interruption of the feedback control, the flag FLG is reset to “0” at time T3, and the above-described air-fuel ratio feedback control is resumed. Then, the fluctuation range of the actual air-fuel ratio, which is a deviation between the minimum value AFSMIN and the maximum value AFSMAX, does not exceed a predetermined reference fluctuation range, and the interruption of the feedback control is performed for a predetermined abnormality reference number NGCNT (in this example, “ 3)), the air-fuel ratio sensor 11 is determined to be abnormal / failure at time T4.

  If the air-fuel ratio sensor 11 is not abnormal or malfunctioning and the feedback control is in a control failure due to the influence of the purge flow rate, the feedback control is interrupted for a predetermined period ΔD1 to obtain a large amount of feedback control. In this case, the air-fuel ratio feedback control is normalized. In addition, when the initialization request FLG is clamped to “1” due to abnormality or failure of other parts such as the fuel injection valve and the spark plug, the fluctuation range of the sensor output far exceeds the reference fluctuation range ΔAFS0. Therefore, it is not determined that the air-fuel ratio sensor 11 is abnormal.

  According to the present embodiment as described above, a control process is used in which air-fuel ratio feedback control is temporarily interrupted so as to return to a state in which feedback control is normally performed from a feedback control failure caused by purging or the like. Then, the air-fuel ratio sensor 11 is obtained by a simple control process using the number of interruptions CLPCNT in a state where the frequency of interruption, more specifically, the fluctuation range of the sensor output (actual air-fuel ratio) does not exceed the reference fluctuation width ΔAFS0. Thus, it is possible to reduce the calculation load and the stored control processing. Further, if the air-fuel ratio feedback control is being performed, a feedback control failure determination is made, so that the air-fuel ratio sensor 11 is substantially diagnosed, and there are many opportunities for diagnosis, and sensor abnormalities / failures are detected. It can be detected at an early stage, and there is no need to perform a special operation only for sensor diagnosis. In addition, the minimum value AFSMIN and the maximum value AFSMAX when the sensor is diagnosed as having an abnormality / failure are stored, and the abnormal state of the air-fuel ratio sensor 11 can be easily identified using these values.

1 is a configuration diagram showing a system configuration of an internal combustion engine to which an embodiment of the present invention is applied. The flowchart which shows the flow of the diagnostic process of an air fuel ratio sensor. 6 is a flowchart showing a flow of initialization request flag setting processing and feedback control interruption processing. The time chart which shows the flow of control at the time of abnormality of an air fuel ratio sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Control part 11 ... Air-fuel ratio sensor 13 ... Front catalyst 14 ... Rear catalyst 20 ... Internal combustion engine 25 ... Exhaust passage (exhaust system)
30 ... Canister (evaporative fuel treatment device)
33 ... Purge control valve

Claims (5)

An air-fuel ratio sensor provided in the exhaust system of the internal combustion engine, and a control unit that performs air-fuel ratio feedback control toward the target air-fuel ratio based on the sensor output of the air-fuel ratio sensor according to the actual air-fuel ratio of the exhaust In the diagnostic apparatus for an air-fuel ratio sensor,
The control unit
During the air-fuel ratio feedback control, determine a feedback control failure that the actual air-fuel ratio does not follow the target air-fuel ratio,
When the control failure is determined, the air-fuel ratio feedback control is interrupted for a predetermined period,
After interruption of the air-fuel ratio feedback control for the predetermined period, the air-fuel ratio feedback control is restarted, and the control failure is determined,
The fluctuation range of the sensor output during the interruption of the air-fuel ratio feedback control does not exceed the predetermined reference fluctuation width, and the number of interruptions of the air-fuel ratio feedback control due to repeated determination of the control failure exceeds the predetermined reference number And determining that the air-fuel ratio sensor is abnormal.
A diagnostic apparatus for an air-fuel ratio sensor. Diagnosis device for an air-fuel ratio sensor according to claim 1, wherein the air-fuel ratio sensor is Ru der those widely detectable wide-area the actual air-fuel ratio. The control unit calculates the fluctuation range based on a deviation between the maximum value and the minimum value of the sensor output, and determines the maximum value and the minimum value when it is determined that the air-fuel ratio sensor is abnormal. Remember,
Diagnosis device for an air-fuel ratio sensor according to claim 1 or 2, characterized in that it is identifiable aspects of abnormality of the air-fuel ratio sensor on the basis of the maximum value and the minimum value that this stored. An evaporative fuel processing device that temporarily adsorbs evaporative fuel generated in the fuel system, purges the fuel and supplies it to the intake system, and a purge control valve that controls the purge flow rate;
The air-fuel ratio according to any one of claims 1 to 3, wherein when the control unit determines that the feedback control is poor, the air-fuel ratio feedback control is interrupted for a predetermined period and the purge is prohibited. Sensor diagnostic device. In the diagnostic method of the air-fuel ratio sensor provided in the exhaust system of the internal combustion engine,
Based on the sensor output of the air-fuel ratio sensor corresponding to the actual air-fuel ratio of the exhaust, air-fuel ratio feedback control toward the target air-fuel ratio is performed,
During this air-fuel ratio feedback control, a feedback control failure that the actual air-fuel ratio does not follow the target air-fuel ratio is determined,
When the control failure is determined, the air-fuel ratio feedback control is interrupted for a predetermined period,
After interruption of the air-fuel ratio feedback control for the predetermined period, the air-fuel ratio feedback control is restarted and the control failure is determined,
The fluctuation range of the sensor output during the interruption of the air-fuel ratio feedback control does not exceed the predetermined reference fluctuation width, and the number of interruptions of the air-fuel ratio feedback control due to repeated determination of the control failure exceeds the predetermined reference number And determining that the air-fuel ratio sensor is abnormal.
A diagnostic method for an air-fuel ratio sensor.

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