JP4604882B2 - 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 particularly, to a linear air-fuel ratio sensor that is provided in an engine exhaust system and that detects 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, air-fuel ratio feedback control is executed by PID operation during normal operation, and linear operation is performed by prohibiting D operation of the feedback control system and switching to PI operation during diagnosis. The output fluctuation of the air-fuel ratio sensor is expanded, and the response deterioration 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. However, at the time of diagnosis, the D operation is exclusively prohibited and the PI operation is performed. Since the switching is merely performed, changes in the transient characteristics (dead time and first-order lag) of the linear air-fuel ratio sensor cannot be detected. Therefore, although the deterioration of the linear air-fuel ratio sensor itself can be detected, the deterioration mode cannot be analyzed in detail.

  The present invention has been made in view of the above problems, and an object thereof is to provide a degradation diagnosis apparatus for a linear air-fuel ratio sensor that can analyze the degradation mode in detail.

In order to solve the above problems, the present invention provides a feedback control system that controls a target air-fuel ratio of an engine, a linear air-fuel ratio sensor that is provided in the feedback control system and outputs a value proportional to the oxygen concentration in exhaust gas, A main control element that is provided in the feedback control system and that outputs an output of the linear air-fuel ratio sensor and outputs an operation amount based on a difference between the output and a target value, and a predetermined diagnosis condition is established Sometimes a disturbance generating means for outputting an impulse-like disturbance to the feedback control system, a differentiating means for outputting a differential value of the output of the linear air-fuel ratio sensor after the disturbance is output by the disturbance generating means, and a differential value output by the differentiating means. Determination parameter that calculates at least one of the dead time and time constant of the linear air-fuel ratio sensor as a determination parameter for deterioration determination based on Calculating means, and gain switching means for reducing the gain of the main control element when the diagnostic condition is satisfied, the gain switching means after the diagnosis is completed, based on detection of the target air-fuel ratio and the linear air-fuel ratio sensor. the difference between the fuel ratio is all SANYO returned to normal value the gain when it becomes less than the predetermined value, the disturbance generating means with those to reset the generation of disturbance after completing the operation of the dead time An apparatus for diagnosing deterioration of a linear air-fuel ratio, characterized in that the next-time disturbance is generated when the convergence determination means determines the convergence of the output of the linear air-fuel ratio sensor after the disturbance is reset . In this aspect, when a predetermined diagnostic condition is satisfied, the disturbance generating means outputs an impulse-like disturbance to the feedback control system, so that the actual air-fuel ratio corresponding to the disturbance is output from the linear air-fuel ratio sensor, At least one of a dead time or a time constant is detected from the differential value of the output of the linear air-fuel ratio sensor, and a deterioration diagnosis is executed by detecting a change in a transient characteristic (dead time or time constant) of the linear air-fuel ratio sensor. It becomes possible. For this reason, it becomes possible to analyze not only the degradation of the linear air-fuel ratio sensor itself but also the degradation mode in detail. Moreover, since the control for reducing the gain of the main control element of the feedback control system is executed at the time of deterioration diagnosis, it is possible to prevent the feedback control system from diverging even though a disturbance is output. It becomes possible to maintain the stability of. Also, instead of returning the gain immediately after the diagnosis is completed, the gain is returned when the difference between the target air-fuel ratio and the actual air-fuel ratio based on the detection of the linear air-fuel ratio sensor is less than a predetermined value. It becomes possible to prevent the occurrence of divergence due to a large feedback correction later, and to suppress a reduction in emission due to control disturbance. In the present invention, the target air-fuel ratio of the engine is set to the theoretical air-fuel ratio (λ = 1) in principle. Furthermore, the “disturbance” generated by the disturbance generating means refers to an external action that temporarily disturbs the state of the feedback control system of the air-fuel ratio. As a specific example, the fuel injection amount is intentionally set to the rich side or By changing to the lean side, it is added to the feedback control system of the air-fuel ratio.

  In a preferred aspect, the feedback control system is disposed on the downstream side of the catalyst that purifies the exhaust gas of the engine, and outputs an oxygen concentration sensor in the exhaust gas purified by the catalyst as a detection value; A detection value from the oxygen concentration sensor is input, and a sub-control element that corrects a target value based on a sub-correction amount based on the detection value is provided, and the gain switching means is configured to control the sub-control when the diagnosis condition is satisfied. The gain of the element is reduced. In this aspect, not only the feedback by the linear air-fuel ratio sensor but also the oxygen concentration sensor functions as a control element, and the reference input is corrected. In this aspect, since the gain of the transfer function of the sub-control element is also controlled by the gain switching means at the time of deterioration diagnosis, it is possible to prevent the feedback control system from diverging even though a disturbance is output. And the stability of the feedback control system can be maintained.

  In a preferred aspect, the disturbance generating means resets the generation of the disturbance when the dead time calculation is completed, and the convergence determining means determines the convergence of the output of the linear air-fuel ratio sensor after the reset of the disturbance. The next disturbance is generated. 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. Therefore, the diagnosis time can be shortened as much as possible, and an accurate deterioration diagnosis based on the dead time can be executed. Further, even when the disturbance output time is variable, the gain switching means reduces the gain of the open loop transfer function. And it is possible to prevent a reduction in emissions.

  As described above, according to the present invention, disturbance can be output in an impulse form, and the dead time and time constant of the linear air-fuel ratio sensor can be used as determination parameters to analyze the deterioration mode in detail. In spite of using such a disturbance, there is a remarkable effect that the divergence of the feedback control system can be prevented as much as possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail 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 rotation angle sensor SW1 that detects an engine rotation speed Ne of the crankshaft.

  In the cylinder head of the engine 10, 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 port are provided in these ports 15 and 16, respectively. Each valve 18 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. 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 purified 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, and a three-way catalyst 32 that is disposed downstream of the exhaust manifold 31 and purifies the burned gas discharged into the exhaust manifold 31. It has been. The exhaust system 30 is provided with a linear air-fuel ratio sensor SW4 disposed upstream of the three-way catalyst 32 and an oxygen concentration sensor SW5 disposed downstream. The linear air-fuel ratio sensor SW4 is for outputting a signal that is approximately proportional to the oxygen concentration from the burned gas. The oxygen concentration sensor SW5 is configured such that the output voltage changes abruptly at an oxygen concentration corresponding to the stoichiometric air-fuel ratio. The feedback control is executed. The linear air-fuel ratio sensor SW4 calculates an output corresponding to the actual air-fuel ratio of feedback control, whereas the oxygen concentration sensor SW5 calculates a detection value corresponding to the oxygen concentration of the burned gas after purification. Is. In the present embodiment, the target air-fuel ratio of the engine 10 is set to the theoretical air-fuel ratio (λ = 1) in principle.

  Each of the sensors SW1 to SW5 and the fuel injection valve 27 described above are connected to the control unit 100 to constitute an air-fuel ratio feedback control system.

  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 and is configured to output the corresponding signals Ne, Qa, TVO, PF, and SF to the CPU 101, respectively.

  The CPU 101 processes the signals Ne, Qa, TVO, PF, SF output from the sensors SW1 to SW5 based on the program stored in the auxiliary storage device 102, and controls the fuel injection valve 27 to set the air-fuel ratio. It is configured to perform feedback control.

  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, SF output from the sensors SW1 to SW5 and calculated values based on the signals Ne, Qa, TVO, PF, SF. 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 includes a reference input element 111 having a target air-fuel ratio (λ = 1) as a target value DV, a BIAS correction element 112 for correcting the reference input IP output from the reference input element 111, and a BIAS correction element. And a main control element 114 that determines an operation amount OV to the engine 10 (more specifically, the fuel injection valve 27) based on the operation signal AS corrected to 112.

  The BIAS correction element 112 corrects the reference input IP output from the reference input element 111, and the initial value is set to be zero.

An output PF corresponding to the actual air-fuel ratio detected by the linear air-fuel ratio sensor SW4 is input between the BIAS correction element 112 and the main control element 114, and the main control element 114 receives the reference input. A predetermined transfer function including a gain K _PP is received by receiving an operation signal AS obtained by subtracting the correction amount SS of the BIAS correction element 112 from the reference input IP of the element 111 and further subtracting the output PF of the linear air-fuel ratio sensor SW4.
G _P (S) = K _PP {1+ (1 / T _I ) + T _D } (1)
However, the operation amount OV is output based on K _PP : proportional gain, T _I : integration time, and T _D : differentiation time. As is apparent from the equation (1), in the present embodiment, the main control element 114 is set to the transfer function G _P (S) of the PID operation. Although simplified in FIG. 3, based on the operation amount OV output from the main control element 114, the fuel injection valve 27 of the engine 10 injects fuel at a predetermined timing and injection amount, and the air-fuel mixture is the engine 10. Burned in. When the burned gas is discharged from the engine 10 to the exhaust system 30, the linear air-fuel ratio sensor SW4 detects the oxygen concentration of the burned gas on the upstream side of the three-way catalyst 32 and corresponds to the actual air-fuel ratio. The oxygen concentration sensor SW5 detects the oxygen concentration of the exhaust gas purified on the downstream side of the three-way catalyst 32 and outputs the detection value SF.

Next, a sub control element 115 is connected between the reference input element 111 and the BIAS correction element 112. The sub-control element 115 receives the detection value SF from the oxygen concentration sensor SW5, the predetermined transfer function including a gain K _SP
G _S (S) = K _SP {1+ (1 / T _I ) + T _D } (2)
However, the sub correction amount SbS is output based on K _SP : proportional gain, T _I : integration time, and T _D : differentiation time. Therefore, the operation signal AS from which the sub correction amount SbS has been subtracted is input to the main control element 114. As apparent from the equation (2), in the present embodiment, the sub control element 115 is set to the transfer function G _S (S) of the PID operation.

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 when a deterioration diagnosis of the linear air-fuel ratio sensor SW4 described below is performed 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 to the rich side or the lean side by giving an impulse-like disturbance to the fuel injection amount. In the following description, the disturbance when changing the air-fuel ratio to the rich side is expressed as LR, and the disturbance when changing the air-fuel ratio to the lean side is expressed as RL. The number of occurrences N _LR and N _RL of the disturbances LR and RL output from the disturbance generation means 116 is stored in the main storage device 103, respectively. Then, the same number of disturbances LR and RL are alternately output for the number of output times N _END set in advance in the deterioration diagnosis program. As a result, the air-fuel ratio intentionally changed by the diagnosis is neutralized, and the air-fuel ratio controlled by the main control element 114 is prevented from being disturbed more than necessary, thereby preventing the emission from being lowered.

Further, the feedback control system 110 according to the present embodiment is functionally configured with gain switching means 118 capable of changing the gains K _PP and K _SP of the control elements 114 and 115 at the time of deterioration diagnosis described later. .

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

First, referring to FIG. 4 and FIG. 6, when the deterioration diagnosis program is executed, the CPU 101 waits for the diagnosis condition to be satisfied (step S1). Here, diagnostic conditions are
(1) The change amount of the engine rotation speed Ne detected by the rotation angle sensor SW1 is equal to or less than 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 diagnostic conditions are not satisfied, such as during acceleration, the system waits until the diagnostic conditions are satisfied. If the diagnostic conditions are satisfied, the gain switching means 118 has the gains K _PP , K of both control elements 114, 115. _SP is changed small (step S2).

  By this control, the response of the main control element 114 to the main feedback amount of the linear air-fuel ratio sensor SW4 becomes gentle, and the sub control element 115 allows the sub-correction to be relatively small even when disturbances LR and RL are output at the time of diagnosis. The amount SbS is output.

  Next, the process proceeds to a convergence determination threshold value setting subroutine, and convergence determination threshold values ThC and dThC are set (step S3).

When the convergence determination threshold values ThC and dThC are set, the convergence determination is performed based on the convergence determination threshold values ThC and dThC (step S4). In this convergence determination, the fluctuation range OP of the output PF of the linear air-fuel ratio sensor SW4 is compared with the threshold value ThC as shown in FIG. 6 in a state where the disturbances LR and RL by the disturbance generating means 116 are reset. At the same time, the fluctuation range dOP of the differential value D _O2 and the threshold value dThC are compared, and it is determined that the air-fuel ratio has converged when the fluctuation ranges OP and dOP are both less than the corresponding threshold values ThC and dThC. By executing step S4, the CPU 101 functionally constitutes a convergence determination unit.

If it is determined that the air-fuel ratio has converged, the CPU 101 starts a timer (step S5), and waits for the timer time to become zero due to the countdown of the timer (step S6). Then, after the timer reaches 0, the number of occurrences N _LR and N _{RL of the} disturbances LR and _RL are compared after the diagnosis is started (step S7). If N _RL > N _LR is satisfied, the disturbance LR Is output to the feedback control system 110 (step S8), and if not established, the disturbance RL is output to the feedback control system 110 (step S9). As a result, for example, as shown in FIG. 6, the disturbance LR is first output, which changes the output of the linear air-fuel ratio sensor SW4.

When the disturbance generating means 116 outputs the disturbance LR (or RL), the CPU 101 calculates the differential value D _O2 of the input output PF of the linear air-fuel ratio sensor SW4 (step S10). Thereby, it becomes possible to grasp how the output PF of 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 PF of the linear air-fuel ratio sensor SW4 after the disturbance output by the disturbance generating unit 116.

  Here, the detected value of the linear air-fuel ratio sensor SW4 usually has a predetermined dead time L and a time constant τ.

  FIG. 7 is a graph showing the step response characteristics of the linear air-fuel ratio sensor SW4.

Referring to FIG. 7, between the input x (t) and the output y (t) of the linear air-fuel ratio sensor SW4,
y (t) = x (t−L) (L ≧ 0) (3)
The linear air-fuel ratio sensor SW4 serving as a dead time element follows a transfer function of the following equation.

G (s) = Y (s) / X (s) = e ^−Ls (4)
However, Y (s): Complex function of output, X (s): Complex function of input Therefore, the step response h (t) of the linear air-fuel ratio sensor SW4 as a dead time element is expressed by the following equation by inverse Laplace transform. As shown in FIG.

h (t) = u (t−L) (5)
Where u (t): unit step function (1 (t ≧ 0) and 0 (t <0))
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, as shown in FIG. 4, the CPU 101 compares the calculated differential value ± D _O2 with a predetermined threshold value ± ThD, and + D _O2 > + ThD or -D _O2 <-ThD. Is established (step S11), and if established, the dead time L of the linear air-fuel ratio sensor SW4 is calculated (step S12), and the disturbance caused by the disturbance generating means 116 is reset (step S14).

Next, the time constant τ is the transfer function of the first-order lag element
G (s) = Y (s) / X (s) = K / (1-τ) (6)
Is a constant.

Step response h (t) obtained by inverse Laplace transform from this equation (6)
h (t) = K (1−e ^{−t / M} ) (7)
However, from K and M: constants,
h (t) | _{τ = M} = 0.632K (8)
Therefore, if the characteristic of the dead time L is added to this, the time constant τ and the step response h (t) of the linear air-fuel ratio sensor SW4 have the relationship shown in FIG.

  As is apparent from FIG. 7, the larger the time constant τ, the slower the rise of the step response waveform and the longer it takes to reach the final value. The time constant τ becomes longer as the deterioration of the linear air-fuel ratio sensor SW4 progresses.

Referring to FIG. 5, in this embodiment, in order to incorporate the time constant τ as an element of deterioration diagnosis, the differential peak value of the output of the linear air-fuel ratio sensor SW4 (the peak value of the differential value ± D _O2 output by the CPU 101). ) D _O2PK is calculated (step S15), and the time constant τ of the linear air-fuel ratio sensor SW4 is calculated from the differential peak value D _O2PK (step S16).

When the calculation of the time constant τ is finished, the CPU 101 determines whether the disturbance generated by the disturbance generating means 116 is to reduce or increase the fuel (step S17). In the case of increase, the determination parameters (calculated time delay L, time constant τ) are stored in the main storage device 103 as _LR (steps S18 and S19), and the occurrence number N _LR stored in the main storage device 103 is stored. , N _RL is incremented (steps S20 and S21).

Thereafter, for each disturbance LR, RL, it is determined whether or not the required number of times N _END has been completed (steps S22 and S23), and any of the number of occurrences N _LR and N _RL is less than the required number of times N _END. Return to step S1 and repeat the process.

On the other hand, in steps S22 and S23, when any occurrence number N _LR , N _RL has reached the required number N _END , the value obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio is less than the predetermined threshold value ThAF. That is, it waits for the control to sufficiently converge (step S24). When the output has converged, the gains K _PP and K _SP of each control element 115 are returned to the original values (step S25). As a result, it is possible to suppress the output from diverging and return to normal feedback control without causing a reduction in emission from the diagnosis state. Thereafter, the control shifts to a deterioration determination process.

  As described above, in the present embodiment, the CPU 101 executes step S12 in FIG. 4 and step S16 in FIG.

  FIG. 8 is a flowchart showing details of the deterioration determination process.

Referring to FIG. 8, here, in order to determine the deterioration, the sum of the dead time L and the time constant τ is defined as the transition time T, and when the processing up to step S25 is completed, the CPU 101 Average transient times T _LR and T _RL related to the LR and the lean side disturbance RL are calculated (step S211). Next, the absolute value of the difference between the two 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 absolute value of the difference is large in each of the average transient times T _LR and T _RL , the air-fuel ratio control by the main control element 114 shifts to the rich side or the lean side. The absolute value of the difference between the two average transient times T _LR and T _RL is calculated.

If the absolute value of the difference between the two average transient times T _LR and T _RL is less than or equal to the threshold value ThB, then whether or not the sum of the two average transient times T _LR and T _RL exceeds the threshold value ThA is determined. Determination is made (step S213). If the sum of both average transient times T _LR and T _RL is large, the sub-feedback control may be executed by the oxygen concentration sensor SW5, the feedback control becomes overcorrected, and the control becomes slow and diverges. This is because it becomes easier.

If the sum of both average transient times T _LR and T _RL is less than or equal to the threshold ThA, it is determined that the transient time is normal (step S214). On the other hand, if the sum of the average transient times T _LR and T _RL exceeds the threshold value ThA, it is determined that the degradation 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 absolute value of the difference between the two average transient times T _LR and T _RL exceeds the threshold ThB in step S212, the rich average transient time T _LR is compared with the rich threshold ThR. Then, it is determined whether or not the transient side deterioration has occurred on the rich side (step S216). If the threshold value ThR is exceeded, it is determined that the rich side transient time T _LR deterioration has occurred (step S216). Step S217). On the other hand, if the average transient time T _LR is equal to or less than the threshold value ThR, the lean-side average transient time T _RL and the lean-side threshold value ThL are further compared, and whether transient time degradation has occurred on the lean side. It is determined whether or not (step S218). When the lean-side average transient time T _RL exceeds the threshold value ThL, it is determined that the lean-side transient time T _{RL has} deteriorated (step S219), and when it is within the threshold value ThL. A 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. Based on these determinations, in the present embodiment, as shown in Table 1, it is possible to analyze what kind of emission reduction is caused by the deterioration of the linear air-fuel ratio sensor SW4.

  FIG. 9 is a flowchart showing an example of the convergence determination threshold value setting subroutine (step S3) in FIG.

  Referring to FIG. 9, in this example, a map 220 for obtaining threshold values ThC and dThC from intake air amount Qa is stored in main storage device 103 in advance, and the intake air amount detected from air flow sensor SW2 is stored. The threshold values ThC and dThC are indexed from Qa (step S305), and the convergence determination threshold values ThC and dThC are set (step S306). In this embodiment, as the intake air amount Qa decreases, the convergence determination threshold values ThC and dThC can be set smaller to make the convergence determination stricter. As described above, in the embodiment of FIG. 9, the air flow sensor SW2 for detecting the intake air amount Qa of the engine 10 is provided, and the convergence determination means functionally configured by the CPU 101 makes the convergence condition stricter as the intake air amount Qa is smaller. Is. As a result, the determination criterion for the time constant τ associated with the change in the intake air amount Qa can be corrected, and erroneous determination can be avoided.

As described above, in the present embodiment, when a predetermined diagnosis condition is satisfied, the disturbance generating means 116 outputs the impulse-like disturbances LR and RL to the feedback control system 110, thereby receiving the disturbances LR and RL. the results output PF corresponding to the actual air-fuel ratio is input from the linear sensor SW4 to the main control element 114, at least one of the linear air-fuel ratio dead time from the differential value D _O2 of the output PF of the sensor SW4 L or the time constant τ , And a deterioration diagnosis can be executed by detecting a change in the transient characteristics (dead time L and time constant τ) of the linear air-fuel ratio sensor SW4. For this reason, it becomes possible to analyze not only the degradation of the linear air-fuel ratio sensor SW4 but also the degradation mode in detail. Moreover, since control is performed to reduce the gains K _PP and K _SP of the open loop transfer functions G _P (S) and G _S (S) of the feedback control system 110 during the deterioration diagnosis, disturbances LR and RL are output. Nevertheless, the divergence of the feedback control system 110 can be prevented, and the stability of the feedback control system 110 can be maintained.

Further, in the present embodiment, the feedback control system 110 is arranged downstream of the catalyst 32 that purifies the exhaust gas of the engine 10, and outputs the oxygen concentration in the exhaust gas purified by the catalyst as the detection value SF. The gain switching means includes an oxygen concentration sensor SW5 and a sub-control element 115 that receives the detection value SF from the oxygen concentration sensor SW5 and adds a sub-correction amount based on the detection value SF to a reference input IP. The gain of the sub control element 115 is reduced when the diagnostic condition is satisfied. For this reason, in this embodiment, not only the feedback by the linear air-fuel ratio sensor SW4 but also the oxygen concentration sensor SW5 functions as a control element to correct the reference input IP. In this aspect, since the gain K _SP of the transfer function of the sub control element 115 is also controlled by the gain switching means 118 at the time of deterioration diagnosis, the feedback control is performed even though the disturbances LR and RL are output. Divergence of the system 110 can be prevented, and the stability of the feedback control system 110 can be maintained.

Further, in the present embodiment, the gain switching means 118 controls each control element 114 when the difference between the target air-fuel ratio and the actual air-fuel ratio based on the detection of the linear air-fuel ratio sensor SW4 satisfies a predetermined condition after completion of the diagnosis. The gains K _PP and K _SP of 115 are returned to normal values. For this reason, in this embodiment, it is possible to prevent divergence from occurring due to a large feedback correction after the gains K _PP and K _SP of the control elements 114 and 115 are changed, and to suppress a reduction in emission due to control disturbance. It becomes possible.

In the present embodiment, the disturbance generating means 116 resets the generation of the disturbances LR and RL when the calculation of the dead time L is completed, and the CPU 101 performs the linear air-fuel ratio sensor after the disturbances LR and RL are reset. When the convergence of the output PF of SW4 is determined, next disturbances LR and RL are generated. For this reason, in the present embodiment, it is possible to output the disturbances LR and RL for a necessary minimum period according to the deterioration state of the linear air-fuel ratio sensor SW4. Therefore, the diagnosis time can be shortened as much as possible, and an accurate deterioration diagnosis based on the dead time L can be executed. Even when the output times of the disturbances LR and RL are variable lengths as described above, the gain switching means 118 allows the gains K _PP and K of the open loop transfer functions G _P (s) and G _S (s). _{Since SP} is reduced, it becomes possible to prevent divergence of control in accordance with the output modes of the disturbances LR and RL, and to prevent a reduction in emissions.

  As described above, according to the present embodiment, the disturbances LR and RL are output in an impulse form, and the dead time L and the time constant τ of the linear air-fuel ratio sensor SW4 are used as determination parameters to analyze the deterioration mode in detail. In addition, the divergence of the feedback control system 110 can be prevented as much as possible despite the use of such disturbances LR and RL.

  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, in actualizing the deterioration diagnosis, instead of the transition time T in the flowchart shown in FIG. 8, the process may be executed for each selected determination parameter (for each dead time L, for each time constant τ). 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 flowchart of the deterioration diagnosis program in this embodiment. It is a flowchart of the deterioration diagnosis program in this embodiment. 6 is a timing chart of signals obtained by executing the flowcharts of FIGS. 4 and 5. FIG. It is a graph which shows the step response characteristic of a linear air fuel ratio sensor. It is a flowchart which shows the detail of a deterioration determination process. 6 is a flowchart showing another example of a convergence determination threshold value setting subroutine in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Degradation determination apparatus 10 Engine 32 Three-way catalyst 100 Control unit 101 CPU (An example of a differentiation means and a determination parameter calculation means)
102 Auxiliary storage device 103 Main storage device 110 Feedback control system 111 Reference input element 112 BIAS correction element 114 Main control element 115 Sub control element 116 Disturbance generating means 118 Gain switching means D _O2 differential value DV Target value G _P , G _S transfer function IP reference input K _PP , K _SP gain L Dead time LR, RL Disturbance Ne Engine rotation speed PF Output of linear air-fuel ratio sensor corresponding to actual air-fuel ratio Qa Intake air amount SbS Sub correction amount SF Detection value SW1 Rotation angle sensor SW2 Air flow Sensor SW3 Throttle sensor SW4 Linear air-fuel ratio sensor SW5 Oxygen concentration sensor T Transient time _TRL , _TLR Average transient time τ Time constant

Claims (2)

A feedback control system for controlling the target air-fuel ratio of the engine;
A linear air-fuel ratio sensor that is provided in the feedback control system and outputs a value proportional to the oxygen concentration in the exhaust gas;
A main control element that is provided in the feedback control system and receives an output of the linear air-fuel ratio sensor and outputs an operation amount based on a difference between the output and a target value;
Disturbance generating means for outputting an impulse-like disturbance to the feedback control system when a predetermined diagnosis condition is satisfied;
Differential means for outputting a differential value of the output of the linear air-fuel ratio sensor after disturbance output by the disturbance generating means;
Determination parameter calculation means for calculating at least one of the dead time and the time constant of the linear air-fuel ratio sensor as a determination parameter for deterioration determination based on the differential value output by the differentiation means;
Gain switching means for reducing the gain of the main control element when the diagnostic condition is satisfied,
The gain switching unit state, and it is not returning the gain when the difference between the Jitsusora ratio based on the detection of the target air-fuel ratio and the linear air-fuel ratio sensor after the diagnosis end is less than the predetermined value to the normal value,
The disturbance generating means resets the generation of the disturbance when the dead time calculation is completed, and when the convergence determination means determines the convergence of the output of the linear air-fuel ratio sensor after the reset of the disturbance, the next disturbance deterioration diagnosis system for a linear air-fuel ratio sensor, characterized in that to generate. The deterioration diagnosis device for a linear air-fuel ratio sensor according to claim 1,
The feedback control system is disposed on the downstream side of the catalyst that purifies the exhaust gas of the engine, and outputs an oxygen concentration sensor in the exhaust gas purified by the catalyst as a detection value;
A detection value from the oxygen concentration sensor is input, and a sub-control element that corrects a target value based on a sub-correction amount based on the detection value, and
The linear air-fuel ratio sensor deterioration diagnosis apparatus according to claim 1, wherein the gain switching means reduces the gain of the sub control element when the diagnosis condition is satisfied.

Images