JP2009293433A - Degradation diagnostic device and degradation diagnostic method for air-fuel ratio detecting means - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a degradation diagnosis of an air-fuel ratio sensor without an erroneous diagnosis even when an operating state changes. <P>SOLUTION: This degradation diagnostic device comprises: an air-fuel ratio detecting means 12; an air-fuel ratio feedback control means 14; a target air-fuel ratio setting means 14 periodically and repeatedly changing an air-fuel ratio in a rich direction and a lean direction; an identification means 14 performing sequential identification operation of response characteristic models of the air-fuel ratio detecting means 12; an operating state determining means 14 determining whether the operating state in sequential identification operation is a steady state or a nonsteady state; and a degradation determining means 14 determining the degradation of the air-fuel ratio detecting means 12 based on the response characteristics. The identification means 14 performs first sequential identification operation for inputting an estimated air-fuel ratio computed based on the fuel injection quantity, to the model, and second sequential identification operation for inputting a target air-fuel ratio to the model. The degradation determining means 14 determines degradation based on the result of the first sequential identification operation in the case of the steady state and based on the result of the second sequential identification operation in the case of the nonsteady state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a deterioration diagnosis of a sensor that detects an exhaust air-fuel ratio of an internal combustion engine.

  In order to reduce exhaust emission of an internal combustion engine, a control for determining a fuel injection amount in accordance with an air-fuel ratio of exhaust gas is known.

As a method of diagnosing deterioration of a sensor (air-fuel ratio sensor) for detecting the air-fuel ratio of exhaust gas, Patent Document 1 discloses an air-fuel ratio when the air-fuel ratio is forcibly changed by periodically increasing or decreasing the fuel injection amount. A method of detecting deterioration based on the locus length or area of the sensor output is disclosed.
JP 2005-30358 A

  However, in the method disclosed in Patent Document 1, the deterioration diagnosis can be performed accurately if the operating state does not change during the diagnosis, but if the operating state gradually changes during the diagnosis, the diagnosis is performed. In addition to the change in the air-fuel ratio, since the fuel injection amount correction for correcting the characteristic deviation of the fuel injection valve or the like is performed, it becomes difficult to control to the desired air-fuel ratio, and there is a risk of misdiagnosis. . That is, there is a problem that deterioration diagnosis can be performed only in a steady operation state.

  Therefore, an object of the present invention is to prevent misdiagnosis when the engine operating state changes without reducing the frequency of deterioration diagnosis.

  The deterioration diagnosis apparatus for air-fuel ratio detection means of the present invention includes an air-fuel ratio detection means for detecting the air-fuel ratio of exhaust gas from an internal combustion engine, and the fuel injection amount based on the detection value of the air-fuel ratio detection means, thereby changing the air-fuel ratio. The feedback control means for performing feedback control, the target air-fuel ratio setting means for periodically changing the air-fuel ratio in the rich direction and the lean direction for deterioration diagnosis, and the response characteristic model of the air-fuel ratio detection means for the change of the air-fuel ratio are sequentially An identification unit for performing identification calculation, an operation state determination unit for determining whether the operation state is a steady state during sequential identification calculation or an unsteady state in which the operation state is changed, and an air-fuel ratio detection unit based on response characteristics Deterioration determining means for determining deterioration of the fuel, and the identifying means inputs the estimated air-fuel ratio calculated based on the fuel injection amount during feedback control to the model The first sequential identification calculation and the second sequential identification calculation that inputs the target air-fuel ratio set by the target air-fuel ratio setting means to the model. Based on the result of the sequential identification calculation, the deterioration determination is performed based on the result of the second sequential identification calculation in the non-steady state.

  According to the present invention, when the operating state changes during the deterioration diagnosis, the deterioration determination is performed based on the result of the second sequential identification calculation using the target air-fuel ratio as an input. It is possible to prevent a decrease in the frequency of deterioration diagnosis while preventing erroneous diagnosis.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of an internal combustion engine system to which the present embodiment is applied. 1 is an engine, 2 is an intake passage, 3 is an exhaust passage, 4 is an intake valve, 5 is an exhaust valve, 12 is an air-fuel ratio sensor as air-fuel ratio detection means, 14 is feedback control means, target air-fuel ratio setting means, identification means A control unit serving as an operating state determination unit and a deterioration determination unit. A cylinder 6 is provided in the engine body 1, and a piston 10 is slidably disposed in the cylinder 6. Further, a spark plug 11 is provided on the ceiling surface of the cylinder 6 for spark ignition of the air-fuel mixture in the cylinder 6.

  The intake passage 2 opens into the cylinder 6, and this opening is opened and closed by the intake valve 4. Similarly, the exhaust passage 3 opens into the cylinder 6, and this opening is opened and closed by the exhaust valve 5.

  In the intake passage 2, an air flow meter 9 that measures the intake air amount, a throttle valve 8 that adjusts the amount of air flowing into the cylinder 6, and a fuel that injects fuel into the intake passage 4 in order from the upstream side of the intake flow. An injection valve 7 is provided.

  An exhaust gas purification catalyst 13 for purifying exhaust gas is interposed in the exhaust passage 3, and an air-fuel ratio sensor 12 is provided upstream of the exhaust gas purification catalyst 13. As the exhaust purification catalyst 13, a three-way catalyst, an occlusion reduction type NOx catalyst, or the like can be used.

  The air-fuel ratio sensor 12 is a sensor that detects the oxygen concentration in the exhaust gas, and outputs a sensor voltage to the control unit 14. The control unit 14 calculates the air / fuel ratio based on this sensor voltage. The air-fuel ratio sensor 12 includes a heater for heating the sensor element, and suppresses deterioration of exhaust performance by activating the sensor at an early stage even during cold start.

  The control unit 14 controls the opening degree of the throttle valve 8 based on the detected values of the air flow meter 9, the air-fuel ratio sensor 12, the engine speed sensor 15, the accelerator opening degree sensor 16, the vehicle speed sensor 17, and other sensors (not shown). Fuel injection amount control, ignition timing control, fuel cut control during deceleration, idle stop control, air-fuel ratio feedback control, and the like are performed.

  The air-fuel ratio feedback control is a control for increasing or decreasing the fuel injection amount based on the detection value of the air-fuel ratio sensor 12 in order to maintain the exhaust air-fuel ratio in a stoichiometric state. The control unit 14 sets the fuel injection amount so that the air-fuel ratio becomes stoichiometric based on the detection value of the air flow meter 9, etc., but actually injects due to, for example, manufacturing errors or aging deterioration of the fuel injection valve 7 There may be a difference between the fuel amount and the fuel injection amount set by the control unit 14. Therefore, the actual air-fuel ratio of the exhaust gas is detected, and this is fed back to the fuel injection amount control to keep the air-fuel ratio of the exhaust gas stoichiometrically.

  By the way, the air-fuel ratio sensor 12 deteriorates its responsiveness to increase / decrease in the fuel injection amount due to aging degradation or the like. FIG. 2 is a diagram showing changes in the detected values of the normal air-fuel ratio sensor 12 and the deteriorated air-fuel ratio sensor 12 and the fuel correction coefficient when the air-fuel ratio is periodically changed. Here, the fuel correction coefficient is a coefficient for correcting the basic fuel injection amount calculated based on the target air-fuel ratio based on the detection value of the air-fuel ratio sensor 12. The rectangular wave in the figure indicates the target air-fuel ratio, and the curve indicates the case where the solid line is normal and the broken line is degraded.

  When the target air-fuel ratio swings to the rich side or lean side, the detection value of the air-fuel ratio sensor 12 also swings to the rich side or lean side. The fuel correction coefficient also changes according to the change in the detection value of the air-fuel ratio sensor 12. At this time, if the air-fuel ratio sensor 12 is normal, there is almost no delay time from when the target air-fuel ratio is switched until the detected value starts changing to the rich or lean method. However, if the target air-fuel ratio has deteriorated, this delay time becomes long, and if the target air-fuel ratio is changed repeatedly, it will not be possible to follow this change. As for the fuel correction coefficient, since the basic fuel injection amount changes when the target air-fuel ratio changes, the delay time does not increase due to the deterioration of the air-fuel ratio sensor 12. However, since the detected value is greatly deviated from the target air-fuel ratio, the fuel correction coefficient becomes a value that is largely corrected as compared with the normal case.

  Thus, when the air-fuel ratio sensor 12 deteriorates, it becomes difficult to perform accurate air-fuel ratio feedback control, and as a result, exhaust performance deteriorates.

  Therefore, the deterioration diagnosis of the air-fuel ratio sensor 12 is performed by executing the control described below.

  FIG. 3 is a flowchart showing the control logic for the deterioration diagnosis of the air-fuel ratio sensor 12.

  In step S101, it is determined whether a diagnosis permission condition is satisfied. For example, it is determined that the diagnosis permission condition is satisfied when the following conditions i) to iii) are satisfied. i) It is determined whether or not a predetermined time has elapsed since the engine was started. This is to prevent misdiagnosis due to the influence of fuel increase at start-up and wall flow. ii) It is determined whether the air-fuel ratio sensor 12 is activated. This is to prevent erroneous diagnosis due to the diagnosis being performed while the air-fuel ratio sensor 12 is inactive. This determination is made based on the cooling water temperature. iii) It is determined whether the exhaust purification catalyst 13 is activated. In general, when the exhaust purification catalyst 13 is in an inactive state, control is performed such as maintaining the air-fuel ratio leaner than the stoichiometric system in order to reduce the HC emission amount or to activate it early. This is because the exhaust performance may be deteriorated if it is periodically changed. This determination can be made based on the coolant temperature or the output of the air-fuel ratio sensor 12.

  If the diagnosis permission condition is satisfied, the process proceeds to step S102. If the diagnosis permission condition is not satisfied, the process is terminated.

  In step S102, a target air-fuel ratio for diagnosis is set. That is, as shown in FIG. 2, the target air-fuel ratio is set such that the change in the rich direction and the change in the lean direction repeat periodically.

  In steps S103 and S104, the output characteristics of the air-fuel ratio sensor 12 are identified. Here, it is assumed that sequential identification calculation is performed by a Kalman filter in which an input value is an estimated air-fuel ratio and an output value is an actual air-fuel ratio based on a detection value of the air-fuel ratio sensor 12.

  In step S103, a calculation (first sequential identification calculation: hereinafter referred to as sequential identification calculation (a)) is performed using the estimated air-fuel ratio calculated from the fuel injection command value and the detected value of the air flow meter 9 as an input value. On the other hand, in step S104, a calculation using the target air-fuel ratio as an input value (second sequential identification calculation: sequential identification calculation (b)) is performed. Note that either of the calculations in steps S103 and S104 may be performed first, or both may be performed in parallel.

  In step S105, it is determined whether or not the operating state being diagnosed is a steady state. For example, the intake air amount before 300 ms is compared with the current intake air amount, and if the difference between the two is smaller than a preset threshold A, it is determined that the steady state is established, and if it is greater, it is determined that the unsteady state is established. . In the case of the steady state, the steady state flag is set in step S106 and the process proceeds to step S107. In the case of the non-steady state, the process is ended as it is.

  In step S107, whether or not the diagnosis end condition is satisfied is determined based on, for example, whether or not a predetermined period of time has elapsed since the start of diagnosis. The predetermined period is set to a time sufficient for performing the identification calculation.

  In step S108, it is determined whether or not the steady state determination flag is set (whether or not the steady state determination flag = 1). If it is set, the process proceeds to step S109. If it is not set, the process proceeds to step S110.

  In step S109, the result of the sequential identification calculation (a) is selected as a diagnostic parameter, and in step S110, the sequential identification calculation (b) is selected in the same manner.

  That is, if the operating state does not change during the diagnosis, the diagnosis is performed using the calculation result using the estimated air-fuel ratio based on the actual intake air amount detected by the air flow meter 9 as an input value, and the operating state changes during the diagnosis. In this case, an identification calculation result using the target air-fuel ratio as an input value is used.

  When the operating state changes, the fuel injection amount correction is applied in addition to the change in the fuel injection amount in accordance with the air-fuel ratio change for diagnosis. In such a case, the input value and output value (empty value) in the identification calculation are applied. Since the correlation with the output of the fuel ratio sensor 12 is deviated, the identification calculation is not performed correctly. As a result, even if the air-fuel ratio sensor 12 is normal, there is a possibility that it may be erroneously diagnosed that the air-fuel ratio sensor 12 has deteriorated. It is not possible.

  Therefore, as in the above control, an identification calculation using the target air-fuel ratio as an input value is also performed, and when the operating state changes, a diagnosis is performed using this calculation result. Thereby, the fall of the diagnosis frequency can be avoided.

  In step S111, deterioration determination is performed based on the diagnostic parameter selected in step S109 or step S110. Specifically, it is determined whether or not the gain at a specific frequency has decreased using the gain-frequency characteristics obtained as a result of the sequential identification calculation.

  FIG. 4 is a diagram illustrating an example of a Bode diagram obtained as a result of the sequential identification calculation. A solid line A indicates characteristics when the air-fuel ratio sensor 12 prepared in advance through experiments or the like is normal, and B, C and D indicate sequential identification calculation results. At a specific frequency (3 Hz in FIG. 4), it is determined whether it overlaps with a normal case like D, or is larger than a normal case, or smaller like B or C.

  It should be noted that an allowable range may be provided for the amount of gain decrease, and the amount of decrease from the normal gain may be within a predetermined range as a normal region.

  If it is almost overlapped with the normal case or larger than the normal case, the process proceeds to step S112, where it is determined to be normal, and if it is smaller, the process proceeds to step S113, where it is determined to be deteriorated.

  As described above, in the present embodiment, the following effects can be obtained.

  (1) An air-fuel ratio sensor 12 that detects the air-fuel ratio of the exhaust gas from the engine 1, feedback control means that performs feedback control of the air-fuel ratio by changing the fuel injection amount based on the detected value of the air-fuel ratio sensor 12, and deterioration diagnosis Target air-fuel ratio setting means for periodically changing the air-fuel ratio in a rich direction and a lean direction, identification means for sequentially identifying and calculating the response characteristic model of the air-fuel ratio sensor 12 with respect to changes in the air-fuel ratio, and operating during the sequential identification calculation A control unit 14 as an operation state determination unit that determines whether the state is a steady state in which the state does not change or an unsteady state in which the operation state changes, and a deterioration determination unit that determines deterioration of the air-fuel ratio sensor 12 based on response characteristics. The first air-fuel ratio calculated based on the fuel injection amount during feedback control is input to the model. The next identification calculation and the second sequential identification calculation that inputs the target air-fuel ratio set by the target air-fuel ratio setting means to the model are performed. Based on the result of the first sequential identification calculation in a steady state In the case of the unsteady state, the deterioration determination is performed based on the result of the second sequential identification calculation. Therefore, the deterioration diagnosis of the air-fuel ratio sensor 12 can be performed without making a false diagnosis even in the unsteady state. It becomes. Thereby, the fall of the frequency of deterioration diagnosis can be prevented.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

It is a block diagram of the system to which this embodiment is applied. It is a figure which shows the change of the air fuel ratio sensor detected value with respect to the change of an air fuel ratio, and a fuel correction coefficient. It is a flowchart which shows the control logic of a deterioration diagnosis. It is a Bode diagram obtained as a result of sequential identification calculation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 3 Exhaust passage 4 Intake valve 5 Exhaust valve 6 Cylinder 7 Fuel injection valve 8 Throttle valve 9 Air flow meter 10 Piston 11 Spark plug 12 Air-fuel ratio sensor 13 Exhaust purification catalyst 14 Control unit 15 Engine speed sensor 16 Accelerator opening Degree sensor 17 Vehicle speed sensor

Claims (3)

Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas of the internal combustion engine;
Feedback control means for performing feedback control of the air-fuel ratio by changing the fuel injection amount based on the detection value of the air-fuel ratio detection means;
Target air-fuel ratio setting means for periodically and repeatedly changing the air-fuel ratio in the rich direction and the lean direction for deterioration diagnosis;
An identification unit for sequentially identifying and calculating a response characteristic model of the air-fuel ratio detection unit with respect to a change in the air-fuel ratio;
An operation state determination means for determining whether the operation state is a steady state that does not change during the sequential identification calculation or whether the operation state is an unsteady state;
Deterioration determining means for determining deterioration of the air-fuel ratio detecting means based on the response characteristics;
With
The identification means inputs a first sequential identification calculation that inputs an estimated air-fuel ratio calculated based on the fuel injection amount during the feedback control to the model, and a target air-fuel ratio set by the target air-fuel ratio setting means And a second sequential identification operation
The deterioration determination means performs deterioration determination based on the result of the first sequential identification calculation when in a steady state, and based on the result of the second sequential identification calculation when in a non-steady state. A deterioration diagnosis apparatus for air-fuel ratio detection means.   The deterioration determining means determines that the deterioration is caused when a difference in a specific frequency between the gain of the identified response characteristic model and the gain of the response characteristic in a normal case is larger than a predetermined threshold. The deterioration diagnosis apparatus for air-fuel ratio detection means according to claim 1. The target air-fuel ratio is periodically and repeatedly changed in the rich direction and the lean direction,
A first sequential identification operation for inputting an estimated air-fuel ratio calculated based on a fuel injection amount during feedback control accompanying a periodic change of the target air-fuel ratio to the model, and a second sequential input for inputting the target air-fuel ratio to the model The sequential identification calculation of
It was determined whether the operation state was a steady state that did not change during the sequential identification calculation or whether the operation state was an unsteady state,
The deterioration determination is performed based on the result of the first sequential identification calculation when in a steady state, and based on the result of the second sequential identification calculation when in a non-steady state. A deterioration diagnosis method for air-fuel ratio detection means.

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