JP4618134B2 - Degradation diagnosis device for linear air-fuel ratio sensor - Google Patents

Description

  The present invention relates to a deterioration diagnosis apparatus for a linear air-fuel ratio sensor, and more specifically, a linear air-fuel ratio sensor that is provided in an engine exhaust system and that diagnoses deterioration of a linear air-fuel ratio sensor that outputs a value proportional to the oxygen concentration in exhaust gas. The present invention relates to a deterioration diagnosis device for a fuel ratio sensor.

Conventionally, as this type of linear air-fuel ratio sensor deterioration diagnosis device, for example, there is a technique disclosed in Patent Document 1. In the technique disclosed in Patent Document 1, during normal operation, air-fuel ratio feedback control is executed by PID operation, and during diagnosis, D operation of the feedback control system is prohibited and switched to PI operation. The fluctuation in the output of the linear air-fuel ratio sensor is expanded, and the response delay of the linear air-fuel ratio sensor is expanded and detected based on the fact that the response cycle becomes longer as the degree of sensor deterioration increases.
Japanese Patent No. 3377336

  In the device disclosed in Patent Document 1, since the output fluctuation of the linear air-fuel ratio sensor is enlarged, the deterioration determination of the linear air-fuel ratio sensor becomes easy, but the D operation is prohibited and switched to the PI operation at the time of diagnosis. As a result, the followability with respect to the target air-fuel ratio is reduced, and as a result, there is a problem that emission reduction at the time of diagnosis is inevitable.

  The present invention has been made in view of the above problems, and is capable of preventing as much as possible a decrease in emission during diagnosis and diagnosing deterioration of a linear air-fuel ratio sensor capable of quickly executing highly accurate deterioration detection. An object is to provide an apparatus.

In order to solve the above-described problems, the present invention is provided in a feedback control system that executes feedback control of an air-fuel ratio based on an oxygen concentration in an exhaust gas of an engine, and in the feedback control system. A linear air-fuel ratio sensor that outputs a value proportional to the oxygen concentration, a disturbance generating means that outputs an impulse-like disturbance to the feedback control system when a predetermined diagnostic condition is satisfied, and the linear after the disturbance is output by the disturbance generating means Determination parameter calculating means for calculating the dead time and time constant of the linear air-fuel ratio sensor based on the output of the air-fuel ratio sensor as determination parameters, and determining deterioration of the linear air-fuel ratio sensor based on the calculated determination parameter A determination means, wherein the determination parameter calculation means starts from a point in time when the dead time calculation is completed. Wherein the decision parameter calculating means is configured to start the measurement of the constant computation period time set in advance starting from the time of completion of the operation of the dead time, it calculates the time constant in the time constant operation period Is a deterioration diagnosis device for a linear air-fuel ratio sensor. In this aspect, since the dead time and the time constant are used as the determination parameters, it is possible to accurately execute the deterioration diagnosis with the air-fuel ratio sensor as “dead time + first-order lag element”. In addition, the measurement of the preset time constant calculation period starts from the time when the dead time calculation is completed, and the time constant is calculated within this time constant calculation period. It is possible to calculate a constant and prevent erroneous determination due to involuntary disturbance. Normally, the linear air-fuel ratio sensor is a process transfer function G (s) of “dead time + first-order lag element”.

(However, L is dead time, τ is time constant, K is gain)
Therefore, the time constant of the linear air-fuel ratio sensor can be predicted by calculating the dead time. Therefore, by setting the time constant calculation period and calculating the time constant within this time constant calculation period, it is possible to obtain an accurate time constant in the minimum necessary time. In addition, the most important “dead time” in control theory is used as a determination parameter, and this is used to determine the deterioration of the linear air-fuel ratio sensor. Therefore, there is only a negative air-fuel ratio, such as reducing the feedback gain. Detection of sensor deterioration can be accelerated as much as possible, and deterioration of exhaust performance can be prevented in advance. In the present invention, the “disturbance” generated by the disturbance generating means refers to an external action that transiently disturbs the state of the feedback control system of the air-fuel ratio. As a specific example, the fuel injection amount is intentionally rich. It is added to the feedback control system of the air-fuel ratio by changing to the lean side or the lean side.

  In a preferred aspect, the determination parameter calculation means calculates a dead time based on a time from the start of disturbance output by the disturbance generation means until a differential value obtained by differentiating the output of the linear air-fuel ratio sensor reaches a predetermined threshold value. In addition to calculation, the time constant is calculated based on the peak of the differential value during the time constant calculation period. In this aspect, since the dead time and the time constant are calculated based on the differential values of the output of the linear air-fuel ratio sensor, it is possible to achieve a more accurate deterioration diagnosis.

  In a preferred aspect, the determination parameter calculation means has time constant calculation period adjustment means for adjusting the time constant calculation period. In this aspect, the time constant can be appropriately calculated by appropriately adjusting the time constant calculation period according to various conditions at the time of diagnosis (for example, the operation time and the behavior of the output of the linear air-fuel ratio sensor).

  In a preferred aspect, there is provided operating state detecting means for detecting the operating state of the engine, and the time constant calculating period adjusting means adjusts the time constant calculating period according to the operating state detected by the operating state detecting means. It is. In this aspect, it is possible to suitably calculate the time constant regardless of the operating state.

  In a preferred aspect, the disturbance generating means outputs a rich disturbance for increasing the fuel injection amount to a rich side and a lean disturbance for decreasing the lean side for a plurality of times within a preset diagnosis period, and The determination unit averages the determination parameter for the lean side disturbance and the determination parameter for the rich side disturbance accumulated by the determination parameter calculation unit within the diagnosis period, and compares the average with a reference value to thereby determine the linear air-fuel ratio sensor. Is to determine the deterioration. In this aspect, since the disturbance is output a plurality of times, the determination parameter is calculated, and the deterioration of the linear air-fuel ratio sensor is determined based on the average value thereof, it is possible to realize a more accurate deterioration determination. Further, since the diagnosis period is set and the disturbance is output within the diagnosis period, the disturbance is output more than necessary, and the exhaust performance is not deteriorated. In addition, by setting the diagnosis period, consistency with other diagnosis controls can be easily achieved, and the degree of design freedom can be increased.

  In a preferred embodiment, the determination parameter calculation means cancels the calculation of the determination parameter related to the disturbance when the dead time cannot be calculated within the dead time calculation period counted from the start of output of the disturbance. The determination means outputs a deterioration determination when the determination parameter calculated within the diagnosis period is less than a preset minimum number of outputs. In this aspect, the dead time calculation period is counted from the start of the output of the disturbance, and if the dead time cannot be calculated within the dead time calculation period, the calculation of the determination parameter related to the disturbance is canceled. When the dead time cannot be calculated due to noise or the like, the data can be eliminated and a highly accurate determination parameter can be obtained. On the other hand, when the determination parameter calculated within the diagnosis period is less than the preset minimum number of outputs, a deterioration determination is output, so that it is poor with respect to the linear air-fuel ratio sensor that may be slightly deteriorated. By performing the determination, the fail-safe function can be enhanced. Normally, when the linear air-fuel ratio sensor is normal, the calculation of the required number of outputs is executed during the diagnosis period, but as the deterioration of the linear air-fuel ratio sensor progresses, feedback tends to diverge. The dead time is not detected, and the cumulative number of determination parameters decreases. In such a case, from the viewpoint of suppressing the deterioration of the exhaust performance, a safer determination diagnosis is performed by making a deterioration determination.

  In a preferred aspect, the disturbance generating means resets the generation of the disturbance when the dead time calculation is completed. In this aspect, it is possible to output a disturbance only for a necessary minimum period according to the deterioration state of the linear air-fuel ratio sensor. For this reason, the diagnosis period can be shortened as much as possible, and an accurate deterioration diagnosis based on the dead time can be executed.

  As described above, in the present invention, since the deterioration diagnosis of the linear air-fuel ratio sensor is executed as “dead time + first-order lag element”, it is not necessary to change the target air-fuel ratio. There is a remarkable effect that diagnosis can be performed.

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

  FIG. 1 is a system diagram of an engine 10 according to an embodiment of the present invention.

  Referring to FIG. 1, an engine 10 according to the degradation determination device 1 of the present embodiment is provided with a plurality of cylinders 11, and pistons 12 connected to a crankshaft (not shown) are provided in each cylinder 11. Is inserted, and the combustion chamber 14 is formed above it. The engine 10 is provided with a crank angle sensor SW1 that detects an engine rotational speed Ne of the crankshaft.

  In the cylinder head, an intake port 15 and an exhaust port 16 that open toward the combustion chamber 14 are formed for each cylinder 11, and an intake valve 17 and an exhaust valve 18 are provided in these ports 15 and 16. Each is equipped.

  The intake port 15 is provided with an intake system 20, and the exhaust port 16 is provided with an exhaust system 30.

  The intake system 20 includes an air cleaner 21 for purifying intake air at the upstream end. An element 22 is built in the air cleaner 21. A throttle body 23 is provided on the downstream side of the air cleaner 21. The throttle body 23 is provided with a throttle valve 24 that adjusts the intake air amount Qa flowing through the intake system 20. In the present embodiment, the throttle valve 24 is electronically controlled, and the valve opening amount is controlled by the actuator 124.

  An intake manifold 25 is provided on the downstream side of the throttle body 23, and a branch intake passage 26 provided at the downstream end of the intake manifold 25 is connected to the intake port 15 of the corresponding cylinder 11. In the illustrated example, a fuel injection valve 27 is provided in the branch intake passage 26. In the intake system 20, an air flow sensor SW <b> 2 is disposed between the air cleaner 21 and the throttle body 23. The air flow sensor SW2 outputs the intake air amount Qa of the intake air filtered by the element 22. Further, the throttle body 23 is provided with a throttle sensor SW3 for detecting the throttle opening TVO of the throttle valve 24.

  The exhaust system 30 includes an exhaust manifold 31 connected to the exhaust port 16, a three-way catalyst 32 disposed on the downstream side of the exhaust manifold 31 to purify the burned gas discharged into the exhaust manifold 31, A linear air-fuel ratio sensor SW4 disposed on the upstream side of the three-way catalyst 32 is provided. The linear air-fuel ratio sensor SW4 is for executing feedback control of the air-fuel ratio A / F by outputting a signal substantially proportional to the oxygen concentration from the burned gas. In this embodiment, the target air-fuel ratio A / F of the engine is set to the theoretical air-fuel ratio (λ = 1) in principle.

  Further, in the present embodiment, an accelerator opening sensor SW5 for detecting an accelerator depression amount (not shown) is provided.

  The sensors SW1 to SW5 and the fuel injection valve 27 described above are connected to the control unit 100 to constitute a feedback control system for the air-fuel ratio A / F.

  FIG. 2 is a control circuit block diagram of the degradation determination apparatus 1 according to the present embodiment, and FIG. 3 is a block diagram of the degradation determination apparatus 1 realized by the control circuit of FIG.

  First, referring to FIG. 2, the control unit 100 includes a CPU 101, an auxiliary storage device 102 embodied by ROM, and a main storage device 103 embodied by RAM. Each of the sensors SW1 to SW5 described above is connected to the CPU 101 as an input element, and is configured to output corresponding signals Ne, Qa, TVO, PF, and AOF to the CPU 101, respectively.

  The CPU 101 processes the signals Ne, Qa, TVO, PF, and AOF output from the sensors SW1 to SW5 based on a program stored in the auxiliary storage device 102, and the fuel injection valve 27 connected as an output element. And the actuator 124 is controlled to feedback control the air-fuel ratio A / F.

  The auxiliary storage device 102 stores a deterioration diagnosis program to be described later in detail.

  In the process of executing the program stored in the auxiliary storage device 102, the main storage device 103 receives signals Ne, Qa, TVO, PF, AOF output from the sensors SW1 to SW5 and calculated values based on the signals. It is configured to memorize.

  Referring to FIG. 3, control unit 100 constitutes feedback control system 110 shown in FIG. The feedback control system 110 outputs a correction signal SS to the reference input element 111 having the target air-fuel ratio A / F (λ = 1) as the target value DV and the reference input IP output from the reference input element 111 for correction. A correction element 112 to be applied and a feedback element 114 for determining the operation amount OV based on the operation signal AS corrected by the correction element 112 are included.

  The output (actual air-fuel ratio) PF of the linear air-fuel ratio sensor SW4 is input between the correction element 112 and the feedback element 114, and the feedback element 114 is input from the reference input IP of the reference input element 111. In response to the operation signal AS obtained by subtracting the correction signal SS of the correction element 112 and further subtracting the output (actual air-fuel ratio) PF, the manipulated variable OV is output based on a predetermined transfer function G (S) including the feedback gain K. It is configured as follows.

Next, in the feedback control system 110 according to the present embodiment, the disturbance generating means 116 that generates the disturbances LR and RL alternately is functionally configured. This disturbance generating means 116 operates at the time of deterioration diagnosis of the linear air-fuel ratio sensor SW4 described below by executing a program stored in the auxiliary storage device 102. The disturbance generating means 116 is configured to transiently change the air-fuel ratio A / F to the rich side or the lean side by giving impulse-like disturbances LR and RL to the fuel injection amount. In the following description, the disturbance when the air-fuel ratio A / F is changed to the rich side is expressed as LR, and the disturbance when the air-fuel ratio A / F is changed to the lean side is expressed as RL. The output times N _LR and N _RL of the disturbances LR and RL output by the disturbance generating means 116 are stored in the main storage device 103, respectively. These output times N _LR and N _RL are set in advance in advance in the deterioration diagnosis program so as to be executed by an equal number of required times N _end . As a result, the air-fuel ratio A / F intentionally changed by the diagnosis is neutralized, and the air-fuel ratio A / F controlled by the feedback element 114 is not disturbed more than necessary, thereby preventing a reduction in emission. I am doing so.

  Next, the control map M1 (see FIG. 5) stored in the auxiliary storage device 102 will be described.

FIG. 4 is a graph showing the relationship between the intake air amount Qa created based on experimental values and the time constant calculation period _Tdam .

  As will be described in detail later, the deterioration diagnosis program stored in the auxiliary storage device 102 calculates the dead time L and the time constant τ based on the output (actual air-fuel ratio) PF of the linear air-fuel ratio sensor SW4. When calculating the time constant τ, the time required for the calculation depends on the intake air amount of the engine 10. Therefore, in the present embodiment, a control map M1 based on the graph as shown in FIG. 4 is created, and a necessary and sufficient period is provided based on the control map M1, and the time constant τ is calculated.

  5 and 6 are flowcharts of the deterioration diagnosis program in the present embodiment. FIG. 7 is a timing chart of signals obtained by executing the flowcharts of FIGS.

First, referring to FIG. 5 and FIG. 7, when the deterioration diagnosis program is executed, the CPU 101 waits for the diagnosis condition to be satisfied (step S20). Here, diagnostic conditions are
(1) The change amount of the engine rotation speed Ne detected by the crank angle sensor SW1 is a predetermined change amount,
(2) The change amount of the throttle opening TVO detected by the throttle sensor SW3 is not more than a predetermined change amount, and (3) The change amount of the charging efficiency CE calculated by CE = Qa / Ne is not more than the predetermined change amount. It means that it is a so-called steady operation that satisfies all of the conditions.

If the diagnosis condition is not satisfied, such as during acceleration, the process waits until the diagnosis condition is satisfied. If the diagnosis condition is satisfied, the diagnosis period _Tdia is set (step S21), and the diagnosis period T has elapsed. If so, the process proceeds to the deterioration diagnosis determination process shown in FIG. 9 (step S22). Since the diagnosis processing of the engine 10 requires processing not only the linear air-fuel ratio sensor SW4 but also several items in a short time, a diagnosis period T _dia is provided, and when this diagnosis period T _dia has elapsed, By forcibly ending the diagnosis process based on the outputs of the disturbances LR and RL, an accurate deterioration diagnosis is achieved in a necessary and sufficient time.

The measurement of the diagnosis period T _dia is started, and before the diagnosis period T _dia expires, the disturbances LR and RL output times N _LR and N _RL after the start of the measurement of the diagnosis period T _dia are compared (step S23). When N _RL > N _LR is satisfied, the disturbance LR is output to the feedback control system 110 (step S24), and when not satisfied, the disturbance RL is output to the feedback control system 110 (step S25). . As a result, for example, as shown in FIG. 7, a disturbance LR is first output, which changes the output of the linear air-fuel ratio sensor SW4.

Next, in this embodiment, when the disturbance generating means 116 outputs the disturbance LR (or RL), the measurement of the dead time calculation period _Tded is started (step S26). The dead time L is a fundamental control parameter, and increasing its accuracy has extremely important significance in terms of control theory. For this reason, when the dead time L cannot be calculated within a predetermined time due to the influence of involuntary disturbance, the calculation accuracy of the dead time L is increased as a data detection failure. . On the other hand, when the delay of the dead time L exceeds a predetermined amount due to the deterioration of the linear air-fuel ratio sensor SW4, it is possible to respond passively by reducing the feedback gain K, but it is no longer appropriate. Feedback control cannot be performed. Therefore, in the present embodiment, when the above-described data detection failures occur frequently, deterioration determination is made as described later.

When the measurement of the dead time calculation period _{Tded in} step S26 starts, the CPU 101 of the control unit 100 calculates the input differential value D _O2 of the actual air-fuel ratio PF (step S27). As a result, it is possible to grasp how the actual air-fuel ratio PF output from the linear air-fuel ratio sensor SW4 changes due to the disturbance LR (or RL). As described above, the CPU 101 of the present embodiment functionally configures a differentiating unit that outputs a differential value D _O2 obtained by differentiating the output (actual air-fuel ratio) PF of the linear air-fuel ratio sensor SW4 after the disturbance output by the disturbance generating unit 116. Yes.

Here, the linear air-fuel ratio sensor SW4 is “dead time + first-order lag element”. Therefore, in this embodiment, the system waits for the dead time L to elapse, detects the end of the dead time L, and resets the disturbances LR and RL. In order to execute such control, the CPU 101 waits for the calculated differential value D _O2 to exceed a predetermined threshold value + ThD, −ThD as shown in FIG. 7 (step S28). Here, if the differential value D _O2 calculated in step S27 is equal to or less than the threshold values + ThD and −ThD, in this embodiment, it is first determined whether or not it is within the dead time calculation period T _ded ( Step S29) If it is within the dead time calculation period T _ded , the process returns to step S27 to repeat the process, and if the dead time calculation period T _ded has elapsed, the disturbances LR and RL are reset (step S30). ) And return to step S22. For this reason, in this embodiment, when the dead time L is not calculated within the predetermined dead time calculation period T _ded , it is canceled as the detection by the disturbance LR (or RL) is impossible. become. This eliminates the defect detection data of the dead time L due to disturbance or the like to improve the accuracy of the deterioration diagnosis, and when such defect detection data frequently occurs before the end of the diagnosis period _Tdia , the deterioration diagnosis Can be defeated.

On the other hand, if it is determined in step S28 that the calculated differential value D _O2 exceeds the threshold values + ThD and -ThD, the dead time L of the linear air-fuel ratio sensor SW4 is calculated (step S31), and the disturbance generating means is calculated. The disturbances LR and RL due to 116 are reset (step S32). In this way, by resetting the disturbances LR and RL when the calculation of the dead time L is completed, the disturbances LR and RL are not output more than necessary, and the deterioration diagnosis can be performed while maintaining the target air-fuel ratio. It becomes possible.

Next, in the present embodiment, the measurement of the time constant calculation period _Tdam is started when the disturbances LR and RL are reset (step S33). This time constant calculation period T _dam is also set to execute the deterioration diagnosis in a necessary and sufficient time. As described above, since the linear air-fuel ratio sensor SW4 can be handled as “dead time + first-order lag element”, the time constant τ of the linear air-fuel ratio sensor SW4 is predicted by calculating the dead time L. It becomes possible to do. Accordingly, the time constant calculation period T _dam is set in step S33, and the time constant τ is calculated within the time constant calculation period T _dam , thereby _{obtaining the} accurate time constant τ in the minimum necessary time. It is.

Next, the time constant calculation period T _dam will be described.

  FIG. 8 is a graph showing the relationship between the intake air amount and the differential value, where (A) shows a low load operation and (B) shows a high load operation.

Referring to FIGS. 8A and 8B, when the operating state of the engine 10 is low load operation, since the intake air amount Qa of the engine 10 is small, the exhaust flow rate is slow and the delay of the dead time L becomes large. The output (actual air-fuel ratio) PF of the linear air-fuel ratio sensor SW4 exhibits a gradual change characteristic. On the other hand, during high load operation, the intake air amount Qa is large, so the exhaust flow rate is fast, the delay of the dead time L is small, and the output (actual air / fuel ratio) PF of the linear air / fuel ratio sensor SW4 also changes sharply. Show properties. Therefore, as described with reference to FIG. 4, a control map M1 is determined so that the time constant calculation period T _dam varies according to the intake air amount Qa (or engine load) by experiments or the like. By determining the time constant calculation period T _dam based on this, it becomes possible to execute a very suitable deterioration diagnosis process.

Returning to FIG. 5, the time constant computation period T _dam is set, the peak value D _O2PK of the computed differential value D _O2 is calculated in step S27 (step S34). In this embodiment, after this calculation, it is determined whether or not the time constant calculation period T _dam has passed (step S35), and the peak value D _O2PK is calculated in this time constant calculation period T _dam . Repeated. As a result, the peak value D _O2PK of the differential value D _O2 , that is, the time constant τ can be calculated within a necessary and sufficient time in an appropriate time constant calculation period T _dam set based on the control map M1. .

Beyond a constant operation period T _dam time constant τ is calculated when the calculated peak value D _O2PK (step S36). As described above, since the linear air-fuel ratio sensor SW4 can be handled as “dead time + first-order lag element”, the peak value D _O2PK of the differential value D _O2 within the time constant calculation period T _dam is calculated. Thus, the time constant τ can be obtained.

Referring to FIG. 6, when the calculation of time constant τ is completed, CPU 101 determines whether the disturbance generated by disturbance generating means 116 is to reduce or increase the fuel (step S37). The deterioration detection values (calculated time delay L, time constant τ) are stored in the main storage device 103 as RL when the disturbance is in the decreasing direction and LR when the increase is in the increasing direction (steps S38 and S39), respectively. The output times N _LR and N _RL stored in the device 103 are incremented (steps S40 and S41).

Next, for each disturbance LR, RL, it is determined whether or not the required diagnosis number N _END has been completed (steps S42 and S43), and any of the output times N _LR and N _RL is less than the required diagnosis number N _END . In this case, the process returns to step S22 and the process is repeated. If both the output times N _LR and N _RL have been completed, the process proceeds to the deterioration determination process.

  FIG. 9 is a flowchart showing details of the deterioration determination process.

  Referring to FIG. 9, here, the sum of dead time L and time constant τ is defined as transient time T in order to determine deterioration. Needless to say, the transition time T may be only the dead time L or only the time constant τ.

When the processing up to step S43 is completed, the CPU 101 first determines whether or not the counted disturbance times _LR and _RL are equal to or greater than a predetermined minimum value N _min (step S209, _RL) . S210), when they are smaller than the minimum value N _min, immediately determines that the transient time lag (step S217, S219). Normally, when the linear air-fuel ratio sensor SW4 is normal, the required number of outputs N _LR and N _RL are calculated within the diagnosis period T _dia , whereas when the linear air-fuel ratio sensor SW4 deteriorates, Since the feedback is likely to diverge, the dead time L is not detected, and the cumulative number of determination parameters decreases. In such a case, from the viewpoint of suppressing a decrease in exhaust performance, by making a deterioration determination, a safer determination diagnosis (that is, a failure determination) for a linear air-fuel ratio sensor that may be slightly deteriorated. By doing this, the fail-safe function is enhanced. As a result, during the diagnosis period _Tdia , when the dead time L is not detected frequently due to the processing from step S25 to S29 in FIG. 5, the deterioration determination is made.

When the counted numbers N _LR and N _{RL of the} counted disturbances LR and RL are equal to or greater than a predetermined minimum value N _min , the CPU 101 determines the average transient time T _LR related to the rich disturbance LR and the lean disturbance RL, T _RL is calculated (step S211). Next, the difference between the absolute values of both average transient times T _LR and T _RL is calculated, and it is determined whether or not the value exceeds a predetermined threshold value ThB (step S212). When the difference between the absolute values is large in each of the average transient times T _LR and T _RL , the air-fuel ratio control by the feedback element 114 is shifted to the rich side or the lean side. In order to prevent such a shift, The difference between the absolute values of both average transient times T _LR and T _RL is calculated.

If both the average transient time T _LR, when the difference between the absolute value of T _RL is less than or equal to the threshold ThB, or turn, the sum of the absolute values of both average transient time T _LR, T _RL exceeds the threshold value ThA It is determined whether or not (step S213). This is because when the sum of the absolute values of both average transient times T _LR and T _RL is large, the feedback control is overcorrected, and the control becomes slow and tends to diverge.

If the sum of absolute values of both average transient times T _LR and T _RL is equal to or less than the threshold value ThA, it is determined that the transient time T is normal (step S214). On the other hand, when the sum of the absolute values of both average transient times T _LR and T _RL exceeds the threshold value ThA, it is determined that the deterioration of the linear air-fuel ratio sensor SW4 occurs on both the rich side and the lean side. (Step S215).

On the other hand, if the difference between the absolute values of the average transient times T _LR and T _RL exceeds the threshold value ThB in step S212, the rich average transient time T _LR is compared with the rich threshold value ThR. Then, it is determined whether or not there is a transient time delay on the rich side (step S216). If the threshold value ThR is exceeded, it is determined that a rich transient time delay has occurred (step S217). ). Further, if the average transit time T _LR is equal to or less than the threshold ThR is further comparison with the threshold value ThL average transit time of the lean side T _RL and lean, or the transient time delay in the lean side occurs It is determined whether or not (step S218). If the lean-side average transient time T _RL exceeds the threshold ThL, it is determined that a lean-side transient time delay has occurred (step S219), and if it is within the threshold ThL, normal Judgment is made. Depending on the settings of the threshold values ThB and ThA, step S218 may be omitted, and if NO is determined in step S216, the determination in step S219 may be performed as it is.

  Then, when any of steps S214, S215, S217, and S219 ends, the process ends.

As described above, in the present embodiment, the dead time L and the time constant τ are used as determination parameters, so that the deterioration diagnosis can be accurately executed with the air-fuel ratio sensor as “dead time + first-order lag element”. become. In addition, since the time constant τ is calculated within the preset time constant calculation period T _{dam from} the detection of the dead time L, the time constant τ is calculated in the minimum necessary time, and is involuntary. It is possible to prevent misjudgment due to disturbances LR and RL. Also, when setting the constant computing time T _dam, by calculating the time constant τ at the time constant calculation period within T _dam, it is possible to determine the constants τ exact time at minimum time. Further, since the most important “dead time L” in the control theory is used as a determination parameter, and the deterioration determination of the linear air-fuel ratio sensor SW4 is performed based on the determination parameter, a substantially passive countermeasure such as lowering the gain K is performed. However, the deterioration detection of the only linear air-fuel ratio sensor SW4 becomes as quick as possible, and it becomes possible to prevent the exhaust performance from deteriorating.

In the present embodiment, the dead time L is calculated based on the time from the start of output of the disturbances LR and RL until the differential value D _O2 obtained by differentiating the output of the linear air-fuel ratio sensor SW4 reaches a predetermined threshold value ± ThD. In addition to calculation, the time constant τ is calculated based on the peak of the differential value D _O2 during the time constant calculation period T _dam . For this reason, in the present embodiment, the dead time L and the time constant τ are calculated based on the differential value D _O2 of the output of the linear air-fuel ratio sensor SW4, respectively, so that a more accurate deterioration diagnosis can be achieved. .

In this embodiment, the control map M1 is provided to adjust the time constant calculation period _Tdam . For this reason, in the present embodiment, the time constant calculation period _Tdam is appropriately adjusted according to various conditions at the time of diagnosis (for example, the operation time and the behavior of the output of the linear air-fuel ratio sensor SW4), and the time constant τ is appropriately calculated. It becomes possible to do.

Further, in the present embodiment, the control unit 100 functionally configures an operation state detection unit that detects the operation state of the engine 10, and the operation state detected by the control unit 100 as the operation state detection unit is set. Accordingly, the time constant calculation period T _dam is adjusted. For this reason, in this embodiment, it becomes possible to calculate time constant (tau) suitably irrespective of a driving | running state.

Further, in the present embodiment, the rich side disturbances LR and RL that increase the fuel injection amount to the rich side and the lean side disturbances LR and RL that decrease the fuel injection amount within the preset diagnosis period _Tdia are alternately output the same. The determination parameter for the disturbance LR and RL on the lean side (transition time T) and the determination parameter for the disturbance LR and RL on the rich side, which are output multiple times, and integrated within the diagnosis period _Tdia The deterioration of the linear air-fuel ratio sensor SW4 is determined by comparing with ThA, ThB, ThR, and ThL. For this reason, in this embodiment, it becomes possible to implement a more accurate deterioration determination. In addition, since the diagnosis period T _dia is set and the disturbances LR and RL are output within the diagnosis period T _dia , the disturbances LR and RL are output more than necessary, and the exhaust performance is not deteriorated. In addition, by setting the diagnosis period _Tdia , consistency with other diagnosis controls can be easily achieved, and the degree of design freedom can be increased.

In the present embodiment, when the dead time L cannot be calculated within the dead time calculation period T _ded counted from the start of output of the disturbances LR and RL, the determination parameters related to the disturbances LR and RL are determined. The determination means outputs a deterioration determination when the determination parameter calculated within the diagnosis period _Tdia is less than the preset minimum output count _Nmin . Therefore, in this embodiment, the dead time calculation period T _ded is counted from the start of output of the disturbances LR and RL, and if the dead time L cannot be calculated within the dead time calculation period T _ded , Since the calculation of the determination parameters regarding the disturbances LR and RL is cancelled, it is possible to eliminate the data and obtain a highly accurate determination parameter when the dead time L cannot be calculated due to noise or the like. On the other hand, when the determination parameter calculated within the diagnosis period T _dia is less than the preset minimum output count N _min , the deterioration determination is output, so the linear air-fuel ratio sensor SW4 that may be slightly deteriorated is output. It is possible to enhance the fail-safe function by performing the defect determination for.

Further, in this embodiment, when calculating the time constant τ, the generation of the disturbances LR and RL is reset when the calculation of the dead time L is completed. Therefore, the minimum necessary according to the deterioration state of the linear air-fuel ratio sensor SW4. It is possible to output the disturbances LR and RL only during the period. For this reason, the diagnosis period _Tdia can be shortened as much as possible, and an accurate deterioration diagnosis based on the dead time L can be executed.

  As described above, in this embodiment, the deterioration diagnosis of the linear air-fuel ratio sensor SW4 can be executed as “dead time + first-order lag element”, so that it is not necessary to change the target air-fuel ratio, and the accuracy can be accurately determined with extremely high accuracy. It is possible to perform a remarkable deterioration diagnosis.

  The above-described embodiments are merely preferred specific examples of the present invention, and the present invention is not limited to the above-described embodiments. For example, as a method of obtaining the dead time L and the time constant τ, it is not always necessary to calculate the differential value, and a method of directly determining from the output value or output period of the linear air-fuel ratio sensor SW4 may be adopted. Good.

  It goes without saying that various modifications can be made within the scope of the claims of the present invention.

1 is a system diagram of an engine according to an embodiment of the present invention. It is a control circuit block diagram of the degradation determination apparatus which concerns on this embodiment. It is a block diagram of the deterioration determination apparatus implement | achieved by the control circuit of FIG. It is a graph which shows the relationship between the amount of intake air created based on the experimental value, and a time constant calculation period. It is a flowchart of the deterioration diagnosis program in this embodiment. It is a flowchart of the deterioration diagnosis program in this embodiment. FIG. 7 is a timing chart of signals obtained by executing the flowcharts of FIGS. 5 and 6. FIG. It is a graph which shows the relationship between an intake air amount and a differential value, (A) shows the time of low load operation, (B) shows the time of high load operation. It is a flowchart which shows the detail of a deterioration determination process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Degradation determination apparatus 10 Engine 20 Intake system 27 Fuel injection valve 30 Exhaust system 32 Three-way catalyst 100 Control unit (an example of differentiation means, determination parameter calculation means, determination means, time constant calculation period adjustment means)
110 Feedback control system 116 Disturbance generating means M1 map D _O2 differential value D _O2PK differential peak value L dead time N _END diagnosis count N _LR , N _RL output count PF output (actual air-fuel ratio)
Qa Intake air amount LR, RL Disturbance SW1 Crank angle sensor SW2 Air flow sensor (an example of intake air amount detection means)
SW3 throttle sensor SW4 linear sensor SW5 accelerator opening sensor T transient time ThA, ThB, ThC, dThC, + ThD, -ThD, ThL, ThR threshold T _RL, T _LR average transient time T _dam time constant computation period TVO Throttle opening τ Time constant

Claims (7)

A feedback control system that performs feedback control of the air-fuel ratio based on the oxygen concentration in the exhaust gas of the engine;
A linear air-fuel ratio sensor provided in the feedback control system and outputting a value proportional to the oxygen concentration in the exhaust gas;
Disturbance generating means for outputting an impulse-like disturbance to the feedback control system when a predetermined diagnosis condition is satisfied;
Determination parameter calculation means for calculating a dead time and a time constant of the linear air-fuel ratio sensor as determination parameters based on the output of the linear air-fuel ratio sensor after the disturbance output by the disturbance generation means;
Determination means for determining deterioration of the linear air-fuel ratio sensor based on the calculated determination parameter;
The determination parameter calculation means starts measurement of a preset time constant calculation period starting from the time point when the dead time calculation is completed, and calculates the time constant within the time constant calculation time. A linear air-fuel ratio sensor deterioration diagnosis device. The deterioration diagnosis device for a linear air-fuel ratio sensor according to claim 1,
The determination parameter calculation means calculates a dead time based on the time from the start of disturbance output by the disturbance generation means until the differential value obtained by differentiating the output of the linear air-fuel ratio sensor reaches a predetermined threshold value. A deterioration diagnosis apparatus for a linear air-fuel ratio sensor, which calculates a time constant based on a peak of the differential value during the time constant calculation period. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to claim 1 or 2,
The deterioration diagnosis apparatus for a linear air-fuel ratio sensor, wherein the determination parameter calculation means includes time constant calculation period adjustment means for adjusting the time constant calculation period. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to claim 3,
An operating state detecting means for detecting the operating state of the engine is provided,
The linear air-fuel ratio sensor deterioration diagnosis device, wherein the time constant calculation period adjusting means adjusts the time constant calculation period according to the operating condition detected by the operating condition detecting means. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to any one of claims 1 to 4,
The disturbance generating means outputs a rich disturbance for increasing the fuel injection amount to the rich side and a lean disturbance for decreasing the lean side a plurality of times within a preset diagnosis period, and a plurality of times.
The determination unit averages the determination parameter for the lean side disturbance and the determination parameter for the rich side disturbance accumulated by the determination parameter calculation unit within the diagnosis period, and compares the average with a reference value, thereby calculating the linear air-fuel ratio. A deterioration diagnosis apparatus for a linear air-fuel ratio sensor, characterized by determining deterioration of the sensor. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to claim 5,
The determination parameter calculation means cancels the calculation of the determination parameter related to the disturbance when the calculation of the dead time within the dead time calculation period counted from the start of output of the disturbance is not possible,
The determination unit outputs a deterioration determination when a determination parameter calculated within the diagnosis period is less than a preset minimum output count. Deterioration diagnosis of a linear air-fuel ratio sensor, apparatus. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to any one of claims 1 to 6,
The deterioration diagnosis device for a linear air-fuel ratio sensor, wherein the disturbance generating means resets the generation of the disturbance when the calculation of the dead time is completed.

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