JP4561498B2 - 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, a linear air-fuel ratio sensor is provided on the upstream side of the three-way catalyst, and an oxygen concentration sensor is provided on the downstream side. The upstream linear air-fuel ratio sensor outputs a detection value corresponding to the actual air-fuel ratio to the feedback control system, while the downstream oxygen concentration sensor maintains the target air-fuel ratio of the feedback control system at a predetermined air-fuel ratio. The detected value of the oxygen concentration is output to the sub-control element. 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 to increase the output fluctuation of the linear air-fuel ratio sensor. The response deterioration of the linear air-fuel ratio sensor is enlarged and detected based on the fact that the greater the degree of sensor deterioration, the longer the response cycle.
Japanese Patent No. 3377336

  By the way, there are two modes of response deterioration of the linear air-fuel ratio sensor: double-side deterioration and single-side deterioration. Both-side deterioration refers to response deterioration in which the responsiveness of sensor output changes to both rich and lean changes deteriorates. One-side deterioration refers to an air-fuel ratio from the lean side to the rich side, or from the rich side to the lean side. Is a response deterioration in which the responsiveness of the sensor output change is deteriorated with respect to only one of them.

  In both-side deterioration, the response of the output change of the linear air-fuel ratio sensor is deteriorated to both the lean side and the rich side. Therefore, although the response of the entire feedback is delayed, the average air-fuel ratio does not deviate from the target air-fuel ratio. On the other hand, when feedback control is performed on the air-fuel ratio based on the output of the linear air-fuel ratio sensor that has deteriorated on one side, the average air-fuel ratio deviates from the original target air-fuel ratio (center air-fuel ratio). There is a problem.

  In this regard, in the apparatus disclosed in Patent Document 1, since the output fluctuation of the linear air-fuel ratio sensor is enlarged, it is easy to determine the deterioration of the linear air-fuel ratio sensor for both-side deterioration. However, it has not been possible to determine whether or not the linear air-fuel ratio sensor has deteriorated on one side simply by increasing the output fluctuation. For this reason, if the feedback control of the air-fuel ratio is continued based on the deterioration diagnosis of Patent Document 1, the problem that the average air-fuel ratio deviates from the target air-fuel ratio cannot be avoided.

  The present invention has been made in view of the above problems, can prevent emission reduction at the time of diagnosis as much as possible, reliably detect one-side deterioration of the linear air-fuel ratio sensor, and shift the center air-fuel ratio. It is an object of the present invention to provide a deterioration diagnosis device for a linear air-fuel ratio sensor capable of correcting the above.

In order to solve the above problems, the present invention is disposed upstream of a feedback control system that performs air-fuel ratio feedback control based on the oxygen concentration in the exhaust gas of the engine and a catalyst that purifies the exhaust gas, A linear air-fuel ratio sensor that outputs a value proportional to the oxygen concentration in the exhaust gas purified by the catalyst and an oxygen concentration in the exhaust gas that is disposed downstream of the catalyst and purified by the catalyst An oxygen concentration sensor to output, a disturbance generating means for alternately outputting impulse-like disturbance to the lean side and rich side to the feedback control system when a predetermined diagnosis condition is satisfied, and a linear after the disturbance output by the disturbance generating means Differentiating means for outputting the differential value of the output of the air-fuel ratio sensor, and the dead time and time constant of the linear air-fuel ratio sensor based on the differential value output by the differentiating means Judgment parameter calculation means for calculating at least one of them as a determination parameter for independent deterioration determination on the lean side and rich side, and a determination parameter calculated from the disturbance on the lean side and the disturbance on the rich side at the time of deterioration diagnosis The difference from the determination parameter is calculated, and the deviation of the air-fuel ratio from the target air-fuel ratio by feedback control based on the output of the linear air-fuel ratio sensor is corrected based on the calculated difference and the detected value from the oxygen concentration sensor. Thus, the deterioration diagnosis apparatus for a linear air-fuel ratio sensor is provided with a center deviation correction means for correcting a reference input of the feedback control system . 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, It is possible to detect deterioration of the linear air-fuel ratio sensor by detecting at least one of the dead time and the time constant from the differential value of the output of the linear air-fuel ratio sensor. In addition, the difference between the determination parameter calculated from the disturbance on the lean side and the determination parameter calculated from the disturbance on the rich side at the time of deterioration diagnosis is calculated, and based on the calculated difference and the detected value from the oxygen concentration sensor The control for correcting the reference input of the feedback control system is executed so as to correct the deviation of the air-fuel ratio from the target air-fuel ratio by the feedback control based on the output of the linear air-fuel ratio sensor . Even when diagnosing a linear air-fuel ratio sensor whose response deterioration to disturbance has been diagnosed, the reference input of the feedback control system is being used during diagnosis due to the adoption of a configuration that adds disturbance to the rich side and lean side. There is no risk of shifting to the rich side or lean side. 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 has a correction element for correcting a reference input, and the center deviation correction means adjusts a correction amount by the correction element to correct a deviation of the reference input. In this aspect, the reference input of the forward element of the feedback control system can be adjusted to absorb the deviation from the target air-fuel ratio due to the deterioration of the linear air-fuel ratio sensor.

  In a preferred aspect, the feedback control system includes gain switching means for reducing the gain of the sub-control element when the diagnosis condition is satisfied and returning the gain of the sub-control element to a normal value after the predetermined condition is satisfied after the diagnosis is completed. ing. In this aspect, since the control for reducing the gain of the sub-control element is executed at the time of the deterioration diagnosis, the feedback to the reference input when the disturbance is generated becomes gradual, and the divergence by the sub-control element can be prevented. In addition, it is possible to maintain the stability of the feedback control system as compared to the method of changing the control operation for the feedback control system.

  In a preferred embodiment, the transfer function of the sub control element is set so that the control operation of the sub control element is at least a PI operation during normal operation and the control operation of the sub control element is only the I operation during deterioration diagnosis. Transfer function setting means is provided. In this mode, during normal operation, the sub footback control system performs PI control or PID control, and during deterioration diagnosis, feedback control is performed only by the I operation, so the sub correction amount by the P term increases rapidly. Can be suppressed, and the output can be prevented from diverging.

  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. For this reason, 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 center deviation correction unit corrects the deviation of the reference input with respect to the target air-fuel ratio. It becomes possible to maintain the air-fuel ratio and prevent the emission from decreasing.

  As described above, according to the present invention, even when the linear air-fuel ratio sensor in which the response deterioration with respect to the lean side or rich side disturbance is advanced is diagnosed by the center deviation correction means at the time of deterioration diagnosis, This eliminates the possibility that the reference input of the feedback control system will shift to the rich side or lean side, so that it is possible to prevent emissions from being reduced as much as possible during diagnosis and to reliably detect deterioration on one side of the linear air-fuel ratio sensor. In addition, there is a remarkable effect that the deviation of the center air-fuel ratio can be corrected.

  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 outputs a signal that is approximately proportional to the oxygen concentration from the burned gas. The oxygen concentration sensor SW5 is configured so that the output voltage changes suddenly at an oxygen concentration corresponding to the stoichiometric air-fuel ratio, and by detecting whether the oxygen concentration is higher or lower than the stoichiometric air-fuel ratio on and off, the air-fuel ratio is detected. 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 this embodiment, the target air-fuel ratio of the engine 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 based on the operation signal AS corrected to 112.

  The “reference input IP” output from the reference input element 111 is an input signal directly applied to the closed loop as a reference for operating the feedback control system 110.

  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 a 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 includes a transfer function setting unit 117 capable of individually setting the transfer functions G _P (S) and G _S (S) of the control elements 114 and 115, and deterioration described later. At the time of diagnosis, a gain switching means 118 capable of changing the gains K _PP and K _SP of the control elements 114 and 115 and a center deviation correction means 119 for correcting a deviation of the target air-fuel ratio in the diagnosis process are functionally configured. (See FIG. 2).

  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 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 transfer function setting means 117 transfers the transfer function G _S (S ) Is changed to the I operation (step S2).

  By this control, the sub control element 115 outputs a relatively small sub correction amount SbS even when the disturbances LR and RL are output at the time of diagnosis.

  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 a differential value D _O2 of the 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 detection 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, the CPU 101 compares the calculated differential value ± D _O2 with a predetermined threshold value ± ThD, as shown in FIG. 6, 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. As the deterioration of the linear air-fuel ratio sensor SW4 progresses, the time constant τ becomes longer.

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 is calculated from the differential peak value D _O2PK (step S16).

When the calculation of the time constant τ is completed, the CPU 101 determines whether the disturbance generated by the disturbance generation 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 and 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. First, it is determined whether or not the first time of the RL deterioration detection that is executed at the even number is executed (step S24), and if it is not executed, the process returns to step S1 and is executed. In such a case, center misalignment correction processing (steps S25 and S26) is executed. In this center deviation correction process, the sum of the dead time L and the time constant τ is defined as the transient time T, and the difference between the absolute values of the average transient times T _LR and T _RL related to the rich disturbance LR and the lean disturbance RL. | T _diff | is calculated (step S25). Next, the correction amount SS of the BIAS correction element 112 is adjusted according to the calculated difference | T _diff |. As described above, the initial value of the correction amount SS is 0. However, when it is determined that the reference input is shifted to the rich side as a result of the determination in step S25, the correction amount SS is adjusted to the lean side and is set to the lean side. If it is determined that there is a shift, the adjustment is made to the rich side. Thereby, even when the linear air-fuel ratio sensor SW4 is deteriorated with the dead time L and the time constant τ being different from the rich disturbance LR and the lean disturbance RL, the target air-fuel ratio is reduced. The reference input IP is configured not to deviate excessively. Then, it returns to step S1 and repeats a 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 S27). If the output has converged, the transfer function G _S (S) of the sub-control element 115 is returned to the PID operation of equation (2) (step S28). Thereby, it is possible to return to the normal feedback control without causing the output to diverge and without reducing the emission from the diagnosis state. Thereafter, the control shifts to a deterioration determination process.

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

Referring to FIG. 8, in this flow, the CPU 101 calculates average transient times T _LR and T _RL related to the rich disturbance LR and the lean disturbance RL (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. As described above, in the present embodiment, the CPU 101 executes step S12 in FIG. 4 and step S16 in FIG.

  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, the three-way catalyst 32 that purifies the exhaust gas of the engine 10 is controlled, and the feedback control system 110 that executes feedback control is disposed upstream of the three-way catalyst 32. A linear air-fuel ratio sensor SW4 that outputs a value proportional to the oxygen concentration in the exhaust gas purified by the three-way catalyst 32 as an output PF, and an impulse disturbance LR in the feedback control system 110 when a predetermined diagnostic condition is satisfied. The disturbance generating means 116 for alternately outputting RL to the lean side and the rich side, and the differentiating means for outputting the differential value D _O2 of the output PF of the linear air-fuel ratio sensor SW4 after the disturbance LR and RL are output by the disturbance generating means 116 and CPU101 of, drink linear sensor SW4 based on the differential value D _O2 which CPU101 is output as a differentiator CPU 101 as a determination parameter calculation means for calculating at least one of time L and time constant τ as a determination parameter for independent deterioration determination on the lean side and the rich side, and is calculated from disturbance RL on the lean side during deterioration diagnosis The difference | D _diff | between the determined determination parameter (for example, the absolute value of the transient time _TLR ) and the determination parameter calculated from the rich disturbance LR is calculated, and the reference input for the target air-fuel ratio is calculated based on the calculated difference Center deviation correction means 119 for correcting IP deviation is provided. For this reason, in the present embodiment, when a predetermined diagnosis condition is satisfied, the disturbance generating means 116 outputs impulse-like disturbances LR and RL to the feedback control system 110, so that the actual air-fuel ratio that has received the disturbances LR and RL. output PF corresponding the linear air-fuel ratio results input from the sensor SW4 to the main control element 114, detects at least one of the dead time L or time constant τ from the differential value D _O2 of the output PF of the linear air-fuel ratio sensor SW4 to It becomes possible to execute the deterioration diagnosis of the linear air-fuel ratio sensor SW4. Moreover, the determination parameter computed from disturbances RL lean side during degradation diagnosis (for example, the absolute value of the transition time T _LR) and decision parameters calculated from disturbances LR richer (e.g., the absolute value of the transition time T _RL) The difference | D _diff | is calculated, and control for correcting the deviation of the reference input IP with respect to the target air-fuel ratio is executed based on the calculated difference | D _diff |. Even when diagnosing the linear air-fuel ratio sensor SW4 whose response deterioration with respect to RL has progressed, a feedback control system is used during diagnosis due to the adoption of the disturbance LR and RL on the rich side and lean side. There is no possibility that the 110 reference input IP shifts to the rich side or the lean side.

  In this embodiment, the feedback control system 110 has a BIAS correction element 112 for correcting the reference input IP, and the center deviation correction means 119 adjusts the correction amount by the BIAS correction element 112 to adjust the reference input IP. This is to correct the deviation. For this reason, in this embodiment, it is possible to adjust the reference input IP of the reference input element 111 of the feedback control system 110 to absorb the deviation from the target air-fuel ratio due to the deterioration of the linear air-fuel ratio sensor SW4.

  In the present embodiment, the feedback control system 110 is arranged downstream of the three-way catalyst 32, and outputs an oxygen concentration in the exhaust gas purified by the three-way catalyst 32 as a detection value SF. Then, the output PF of the linear air-fuel ratio sensor SW4 is input, the main control element 114 that outputs the operation amount OV based on the output PF and the reference input IP, and the detection value SF from the oxygen concentration sensor SW5 are input. And a sub control element 115 that adds a sub correction amount SbS based on the detection value SF to the reference input IP. For this reason, in this embodiment, not only the feedback by the linear air-fuel ratio sensor SW4 but also the oxygen concentration sensor functions as a control element, and the reference input IP is corrected. Also in this aspect, the center deviation correction unit 119 performs the correction of the reference input IP with respect to the target air-fuel ratio, so that it is possible to realize the correction in consideration of the sub-control elements.

  In particular, in this embodiment, during normal operation, the control operation of the sub control element 115 is at least a PI operation, and at the time of deterioration diagnosis, the control operation of the sub control element 115 is only the I operation. A transfer function setting means 117 for setting a transfer function is provided. Therefore, in the present embodiment, the sub footback control system performs PI control or PID control during normal operation and feedback control is performed only by the I operation during degradation diagnosis. Therefore, the sub correction amount SbS by the P term is used. It is possible to suppress a sudden increase in the output and to prevent the output from diverging.

  In this 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 converges the output PF after the disturbances LR and RL are reset. Is determined, the next disturbance LR, RL is 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. For this reason, 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, the deviation of the reference input IP with respect to the target air-fuel ratio is corrected by the center deviation correction unit 119. Corresponding to the output mode, it becomes possible to maintain the target air-fuel ratio and prevent the emission from being lowered.

  As described above, according to the present embodiment, when the linear air-fuel ratio sensor SW4 in which the response deterioration with respect to the disturbance LR or RL on the lean side or the rich side has progressed is diagnosed by the center deviation correction means during the deterioration diagnosis. Even in such a case, since there is no possibility that the reference input IP of the feedback control system 110 shifts to the rich side or the lean side during diagnosis, it is possible to prevent the emission reduction at the time of diagnosis as much as possible, and the linear air-fuel ratio sensor SW4. As a result, it is possible to reliably detect the one-side deterioration of the gas and to correct the deviation of the central air-fuel ratio (original target air-fuel ratio).

  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, the embodiment shown in FIGS. 10 and 11 can be adopted.

  10 and 11 are flowcharts of a deterioration diagnosis program according to another embodiment of the present invention.

In the embodiment shown in each figure, instead of changing the setting of the transfer function in step S2 in FIG. 4, the gain K _SP in the equation (2) is set small (step S102), and step S28 in FIG. The point which performs the process which returns the gain _KSP to a normal value (step S128) differs from embodiment of FIG. 4 and FIG.

In this manner, the embodiment shown in FIGS. 10 and 11, to reduce the gain K _SP of the sub-control element 115 upon establishment of the diagnostic condition, usually the gain K _SP of the sub-control element 115 after a predetermined condition is satisfied after the diagnosis end Gain switching means 118 for returning the value is provided. For this reason, in the present embodiment, since the control for reducing the gain of the sub control element 115 is executed at the time of deterioration diagnosis, feedback to the reference input IP when the disturbances LR and RL are generated becomes gentle, and the sub control is performed. The divergence due to the element 115 can be prevented, and the stability of the feedback control system 110 can be maintained as compared with the method of changing the control operation for the feedback control system 110.

  Further, in embodying the present invention, the flowcharts of FIGS. 4 and 5 and the flowcharts of FIGS. 10 and 11 may be combined to change the transfer function and reduce the gain.

  In addition, when actualizing the deterioration diagnosis and center deviation correction, instead of the transition time T in the flowchart shown in FIG. 5 or the flowchart shown in FIG. 8, every determination parameter (for each dead time L, time constant) is selected. The process may be executed every τ).

  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. It is a flowchart of the deterioration diagnosis program in another embodiment of the present invention. It is a flowchart of the deterioration diagnosis program in another embodiment of the present invention.

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 generation means 117 Transfer function setting means 118 Gain switching means 119 Center deviation correction 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 SS correction amount 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 (5)

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 arranged upstream of the catalyst for purifying the exhaust gas and outputting a value proportional to the oxygen concentration in the exhaust gas purified by the catalyst;
An oxygen concentration sensor disposed downstream of the catalyst and outputting the detected oxygen concentration in the exhaust gas purified by the catalyst;
Disturbance generating means for alternately outputting an impulse-like disturbance to the lean side and the rich side to the feedback control system when a predetermined diagnosis condition is established;
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 based on the differential value output by the differentiation means as a determination parameter for independent deterioration determination on the lean side and the rich side;
The difference between the determination parameter calculated from the disturbance on the lean side and the determination parameter calculated from the disturbance on the rich side during the deterioration diagnosis is calculated, and based on the calculated difference and the detection value from the oxygen concentration sensor, And a center deviation correction means for correcting a reference input of the feedback control system so as to correct a deviation of the air-fuel ratio from the target air-fuel ratio by feedback control based on the output of the linear air-fuel ratio sensor. Air-fuel ratio sensor deterioration diagnosis device. The deterioration diagnosis device for a linear air-fuel ratio sensor according to claim 1,
The feedback control system has a correction element for correcting a reference input, and the center deviation correction means corrects a deviation of the reference input by adjusting a correction amount by the correction element. Degradation diagnosis device for a fuel ratio sensor. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to claim 1 or 2,
The feedback control system has gain switching means for reducing the gain of the sub-control element when the diagnosis condition is satisfied and returning the gain of the sub-control element to a normal value after the predetermined condition is satisfied after completion of the diagnosis. A characteristic deterioration diagnosis device for a linear air-fuel ratio sensor. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to any one of claims 1 to 3 ,
Transfer function setting means for setting the transfer function of the sub control element so that the control operation of the sub control element is at least a PI operation during normal operation and the control operation of the sub control element is only an I operation during deterioration diagnosis deterioration diagnosis system for a linear air-fuel ratio sensor, characterized in that are provided. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to any one of claims 1 to 4 ,
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.

Images