JP4548249B2 - 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, 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 output fluctuation of the linear air-fuel ratio sensor is enlarged, and the response deterioration of the linear air-fuel ratio sensor is enlarged and detected based on the fact that the response cycle becomes longer as the degree of sensor deterioration is larger.
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 unavoidable.

  In particular, in Patent Document 1, one-side deterioration occurs (response deterioration in which the responsiveness of sensor output change deteriorates only for one of the air-fuel ratio when the air-fuel ratio changes from the lean side to the rich side or from the rich side to the lean side). If this is the case, there is a risk that the average air-fuel ratio deviates from the target air-fuel ratio.

  The present invention has been made in view of the above-described problem, and even when the linear air-fuel ratio sensor is deteriorated on one side, it is possible to prevent the emission reduction at the time of diagnosis as much as possible, and has high accuracy. It is an object of the present invention to provide a deterioration diagnosis device for a linear air-fuel ratio sensor capable of executing deterioration detection.

In order to solve the above-described problems, the present invention provides a deterioration diagnosis apparatus for a linear air-fuel ratio sensor that is provided in a feedback control system that controls a target air-fuel ratio of an engine and outputs a value proportional to the oxygen concentration in exhaust gas. By setting the air-fuel ratio alternately between the rich side and the lean side, a disturbance generating means for outputting an impulse-like disturbance to the feedback control system a predetermined number of times and a target time integral value of the disturbance output by the disturbance generating means are set. Target value setting means, 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, and a dead time and time constant of the linear air-fuel ratio sensor based on the differential value output by the differentiating means Determination parameter calculation means for calculating each of the rich side and the lean side as at least one of the deterioration determination parameters, and at least the differential value Comprising a disturbance resetting means for resetting the disturbance after exceeding a predetermined threshold value, the actual value calculating means for calculating actual time integral value of the actual output disturbance after resetting the disturbance, the disturbance reset means, The target value setting means for resetting the disturbance after the differential value exceeds a predetermined threshold value and the actual time integrated value of the disturbance currently output is equal to or greater than the target time integrated value of the disturbance; , compared the second and subsequent disturbance, a deterioration diagnosis device for the linear air-fuel ratio sensor, wherein the Ru der used to set the target time integral value to offset actual time integral value of the previous disturbance. In this aspect, since the deterioration diagnosis is executed by alternately changing the disturbance from the target air-fuel ratio to the rich side and the lean side, the disturbance on the rich side and the disturbance on the lean side are neutralized to each other, and the target air-fuel ratio is It becomes difficult for the deviation to occur. In addition, it is possible to calculate the determination parameter for each of the rich side and the lean side, and it is possible to execute a more detailed deterioration diagnosis. Further, when outputting the second and subsequent disturbances, the target time integrated value of the next disturbance is set so as to cancel the actual time integrated value of the previous disturbance, and the differential value has a predetermined threshold value. The disturbance is reset after the actual time integral value of the disturbance that exceeds the current value exceeds the target time integral value of the disturbance, so the disturbance is neutralized on the rich side and the lean side even in total, and the target It is possible to prevent adverse effects on the air-fuel ratio as much as possible. Further, since disturbance continues to be output until the calculated differential value exceeds a predetermined threshold value, the dead time can be reliably calculated even if a small target time integral value is set. 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. Further, the “time integral value” may be a value obtained by calculating the disturbance amplitude (range of change of the air-fuel ratio) and the output time area, and is a value obtained by calculating the amplitude, the air amount, and the volume of the output time. Also good. The “target time integral value” refers to the time integral value of the disturbance to be output by the disturbance generating means, and the “actual time integral value” refers to the time integral value of the disturbance actually output by the disturbance generating means.

  In a preferred aspect, the determination parameter calculation means calculates a dead time as a determination parameter, and the target value setting means is a minimum necessary for deterioration diagnosis of the linear air-fuel ratio sensor when the first disturbance occurs. The target time integration value is set, and the disturbance reset means resets the generation of the disturbance at the end of the calculation of the dead time after the first generation of the disturbance. In this mode, since the time integral value of the initial disturbance is set to a value that is necessary and sufficient for the deterioration diagnosis of the linear air-fuel ratio sensor, the output disturbance is set as small as possible to prevent adverse effects on the target air-fuel ratio. It becomes possible to do. In addition, with regard to this initial disturbance, the dead time is calculated after the initial disturbance is generated, and the disturbance is reset after the dead time calculation is completed. Even when diagnosing an advanced linear air-fuel ratio sensor, it is possible to reliably detect dead time and the like. In this embodiment, the “necessary minimum” means a disturbance area that a normal linear air-fuel ratio sensor will output.

  As described above, according to the present invention, the disturbance is neutralized on both the rich side and the lean side, and the adverse effect on the target air-fuel ratio can be prevented as much as possible. As a result, the linear air-fuel ratio sensor Even when one-side deterioration has occurred, it is possible to prevent the emission reduction at the time of diagnosis as much as possible, and there is a remarkable effect that it is possible to perform highly accurate deterioration detection.

  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 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, 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. Three-way catalyst 32 of the present embodiment, the oxygen storage function with the addition of CeO ₂ as an oxygen storage material in the oxidation catalyst: those having a (OSC Oxygen Storage Component). 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 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 to the engine 10 (more specifically, the fuel injection valve 27) based on the operation signal AS corrected to 112.

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. subtracting the correction amount SS of BIAS correction element 112 from a reference input IP elements 111, further receives the operation signal AS obtained by subtracting the output PF of the linear air-fuel ratio sensor SW4, predetermined transfer comprising a gain K _P function G _P (S ), The operation amount OV is output.

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 is configured to receive the detection value SF from the oxygen concentration sensor SW5 and output the sub correction amount SbS based on a predetermined transfer function G _S (S) including the gain K _S. . Therefore, the operation signal AS from which the sub correction amount SbS has been subtracted is input to the main control element 114.

Further, the feedback control system 110 according to the present embodiment is functionally configured with disturbance generating means 116 that alternately generates disturbances LR and RL. 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.

Next disturbance LR this disturbance generating means 116 is generated, in order to set the target time integration value I _T of RL, the feedback control system 110, target value setting means 119 is provided. A target time integration value I _T refers to the time the disturbance generating means 116 to be output integration value I. In this embodiment, the time integration value I, refers to a disturbance LR, amplitude ± H _dis (air-fuel ratio of the change width) Output time of RL [t _a, t _b] value of the area obtained by integrating at (oxygen moles) . In the present embodiment, the initial value of the target time integration value I _T by the target value setting means 119 is set to the minimum value for the deterioration diagnosis of the linear air-fuel ratio sensor SW4. As described later, actually output disturbance LR, the time integral value I of RL that actual time integral value I _R.

  4 to 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. 4, when the deterioration diagnosis program is executed, 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 met, such as during acceleration, the system waits until the diagnostic conditions are met.If the diagnostic conditions are met, the process proceeds to the convergence determination threshold setting subroutine to determine the convergence threshold. Values ThC and dThC are set (step S2).

When the convergence determination threshold values ThC and dThC are set, the convergence determination is executed based on the convergence determination threshold values ThC and dThC (step S3). In this convergence determination, the fluctuation range OP of the output PF of the linear air-fuel ratio sensor SW4 and the threshold value ThC are compared as shown in FIG. 7 in a state where the disturbances RL and LR 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 S3, 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 S4), and waits for the timer time to become zero due to the countdown of the timer (step S5). Then, after the timer time reaches 0, the CPU 101 first determines whether or not the current disturbances LR and RL are output for the first time after the diagnosis execution condition is satisfied (step S6). If the first time in this determination, the target value setting means 119 sets initial disturbance LR, the RL at minimum target time integration value I _T (step S7), and if the second or subsequent, last record The time integration value I _R is set to the current target time integration value I _T (step S8). For example, when steady running at 60 km / h, the amplitude ratio of the disturbance LR is set to 6%, and the intake air amount Qa is substantially constant at a certain value, the target time integrated value I _T of the first disturbance LR is , Approximately +27 (oxygen mole).

Next, the absolute values | H _dis | and the output times [t _a , t _b ] of the disturbances LR and RL are determined based on the set target time integration value I _T (step S9). In general the absolute value of the amplitude | H _dis | greater the while easily response deterioration even linear sensor SW4 advanced, the absolute value of the amplitude | H _dis | if is extremely small, the same target time integration value I _T even, since the linear sensor SW4 is unresponsive, in the present embodiment, in consideration of such characteristics, the absolute value of the amplitude | H _dis | set, then the output time [t _a , T _b ].

Next, referring to FIG. 5, after the absolute value of amplitude | H _dis | and the output time [t _a , t _b ] are determined, the number of occurrences N _LR and RL of disturbances LR and _RL are compared ( step S10), and when the N _RL> N _LR is satisfied, with the disturbance LR is outputted to the feedback control system 110 based on the set target time integration value I _T (step S11), and if not satisfied The disturbance RL is output to the feedback control system 110 based on the set target time integration value I _T (step S12). 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.

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 S13). 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. 8 is a graph showing the step response characteristics of the linear air-fuel ratio sensor SW4.

Referring to FIG. 8, there is a gap between input x (t) and output y (t) of linear air-fuel ratio sensor SW4.
y (t) = x (t−L) (L ≧ 0) (1)
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 (2)
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. This is determined as shown in FIG.

h (t) = u (t−L) (3)
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. To perform such control, CPU 101, as shown in FIG. 5, compare the calculated and differentiated value ± D _O2 and predetermined reset threshold _{± ThD, + D O2> +} ThD or -D _O2 <- The system waits for the establishment of ThD (step S14), and if it is established, the dead time L of the linear air-fuel ratio sensor SW4 is calculated (step S15).

Next, in the present embodiment, the current actual time integrated value I _R is calculated based on the current amplitude ± H _dis and the output time [t _a , t _b ] (step S16). Next, the actual time integrated value I _R is compared with the target time integrated value I _{T of the} disturbances LR and RL (step S17), and the actual time integrated value I _R becomes the target time integrated value I _T (that is, the previous actual value). The disturbances LR and RL are continuously output until the time integral value I _R ) or more is reached. Then, in step S17, the disturbance is reset only when the actual time integrated value I _R becomes equal to or greater than the target time integrated value I _T (step S18), and the process proceeds to the next step. Note that although the first time, since the last actual time integral value I _R is set to the minimum value required for diagnosis of the linear air-fuel ratio sensor SW4, the disturbance generator 116, the first disturbance LR, after RL generation, waste The generation of the disturbances LR and RL is reset when the calculation of the time L ends. Thus, in the present embodiment, the CPU 101 functionally configures the actual value calculation means.

As described above, in the determination of step S6 in FIG. 4, the second or subsequent disturbance LR, when outputting RL in step S8, the previous actual time integral value I _R is the current target time integration value I _T In this embodiment, when the CPU 101 outputs the second and subsequent disturbances, the target time for offsetting the actual time integrated value of the previous disturbance is executed by executing steps S6 to S17. a target value setting means 119 in the integrated value I _T to set the next disturbance, disturbance LR currently being output disturbance after actual time integral value I _R and RL becomes equal to or greater than the target time integral value I _T of the disturbance And a disturbance reset means for resetting the function. For example, as a result of setting the target time integration value I _T initial disturbance LR 27, alternately disturbance LR ten times, and outputs the RL, and it executed the deterioration diagnosis of the linear air-fuel ratio sensor SW4 degraded to the rich side When the first and second actual time integrated values I _R are +72 and −72, the results shown in Table 1 are obtained by executing steps S6 to S17.

As described above, in this embodiment, a substantial amount of disturbance LR, even when the output RL, lean side and the rich side and in actual time integral value I _R is canceled to prevent the center deviation of the air-fuel ratio It becomes possible.

Note In Table 1, when the absolute value of the second actual time integral value I _R is larger than the absolute value of the target time integration value I _T is so that the difference remains, a third and subsequent disturbances In the output of, such a difference does not occur by executing the flowcharts shown in FIGS. Therefore, in the present embodiment, the oxygen storage function (OSC) of the three-way catalyst 32 is obtained by appropriately setting the initial target time integration value _IT in an experiment or the like, thereby calculating the difference when the one-side deterioration occurs. This makes it possible to make the value sufficiently small to be absorbed. In other words, even when setting the target time integral value I _T initial sufficiently large value, the second and subsequent disturbance LR, the output of the RL, so disturbance LR, RL are canceled, the deviations of the target air-fuel ratio Not only can this be prevented, it is also possible to prevent emissions from being reduced as much as possible.

Next, the time constant τ is the transfer function of the first-order lag element
G (s) = Y (s) / X (s) = K / (1-τ) (4)
Is a constant.

Step response h (t) obtained by inverse Laplace transform from this equation (4)
h (t) = K (1−e ^{−t / M} ) (5)
However, from K and M: constants,
h (t) | _{τ = M} = 0.632K (6)
Therefore, when 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 clear from FIG. 8, 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.

Therefore, in the present embodiment, as shown in FIG. 6, 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 (differential value ± D _O2 peak value output by the CPU 101). calculates the D _O2PK (step S20), so that calculates the constant τ when the linear sensor SW4 from the differential peak value D _O2PK (step S21).

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 S22). for increasing the LR, respectively decision parameter (computed dead time L, the time constant tau) and stored into the main storage device 103 (step S23, S24), number of times of occurrence are stored in the main storage device 103 N _LR , N _RL is incremented (steps S25 and S26).

Thereafter, for each disturbance LR, RL, it is determined whether or not the required number of times N _END has been completed (steps S27 and S28), and any of the number of occurrences N _LR and N _RL is less than the required number of times N _END. In step S1, the process is repeated, and when both occurrences 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, 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 S22 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). When 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 S15 in FIG. 5 and step S21 in FIG. 6 to functionally configure the determination parameter calculation unit.

  FIG. 10 is a flowchart showing an example of the convergence determination threshold value setting subroutine (step S2) in FIG.

  Referring to FIG. 10, in this example, 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 S205), and the convergence determination threshold values ThC and dThC are set (step S206). 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. 10, the air flow sensor SW2 for detecting the intake air amount Qa of the engine 10 is provided, and the convergence determining means functionally configured by the CPU 101 makes the convergence condition stricter as the intake air amount Qa is smaller. As a result of correcting the determination criterion of the time constant τ accompanying the change in the intake air amount Qa, it is possible to avoid erroneous determination.

As described above, in the present embodiment, the disturbance LR and RL are alternately changed from the target air-fuel ratio to the rich side and the lean side, and the deterioration diagnosis is executed. Therefore, the rich side disturbances LR and RL and the lean side The disturbances LR and RL are neutralized with each other, and deviation from the target air-fuel ratio is less likely to occur. Further, the determination parameter (dead time L, time constant τ, or transient time T) can be calculated for each of the rich side and the lean side, and finer deterioration diagnosis can be executed. Further, the second or subsequent disturbance LR, when outputting the RL, previous disturbance LR, with the following disturbance LR, the target time integral value I _T and RL is set so as to cancel the time-integrated value of RL, the beyond differential value ± D _O2 is the predetermined threshold value ± ThD, and disturbance LR which currently being output, actual time integral value I _R and RL becomes to the disturbance LR, or target time integral value I _T of RL After that, the disturbances LR and RL are reset. Therefore, as shown in Table 1, the disturbances LR and RL are neutralized on the rich side and the lean side as much as possible to prevent the adverse effect on the target air-fuel ratio as much as possible. It becomes possible. Also, the computed differential value ± D _O2 until exceeds a predetermined threshold value ± ThD, disturbance LR, since RL is continuously output, setting a small target time integration value I _T, reliably dead time L can be calculated.

In the present embodiment, the target value setting means 119, first disturbance LR, at the time of RL occurs, is for setting the minimum target time integration value I _T required deterioration diagnosis of the linear air-fuel ratio sensor SW4 The disturbance reset means resets the generation of the disturbances LR and RL at the end of the calculation of the dead time L after the first generation of the disturbances LR and RL. Therefore, in this embodiment, the first disturbance LR, since the target time integral value I _T and RL is set to the desired value sufficient degradation diagnosis of the linear air-fuel ratio sensor SW4, disturbance LR output, Kakyu the RL Therefore, it is possible to prevent the adverse effect on the target air-fuel ratio. Further, regarding the first disturbances LR and RL, after the first disturbances LR and RL are generated, the dead time L is calculated, and after the calculation of the dead time L, the disturbances LR and RL are reset. Therefore, even when diagnosing the linear air-fuel ratio sensor SW4 whose deterioration has been advanced with the smallest possible disturbances LR and RL, the dead time L and the like can be reliably detected.

  As described above, according to the present embodiment, the disturbances LR and RL are neutralized on the rich side and the lean side even in total, and the adverse effect on the target air-fuel ratio can be prevented as much as possible. Even when the sensor SW4 is deteriorated on one side, it is possible to prevent the emission reduction at the time of diagnosis as much as possible, and it is possible to perform highly accurate deterioration detection. .

  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 time integration value, disturbance LR, amplitude ± H _dis and the intake air amount Qa and the output time of RL [t _a, t _b] may be a value determined volume of. Further, the initial amplitude ± H _dis may be set to a small value according to the response characteristic of the linear air-fuel ratio sensor SW4, and the amplitude ± H _dis may be gradually increased.

  Further, when the deterioration diagnosis is realized, the flowchart shown in FIG. 9 may be executed for each dead time L and each time constant τ to determine each deterioration state.

  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. 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. 4 to 6. 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. It is a flowchart which shows an example of the 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, a determination parameter setting means, a disturbance reset means, a performance value calculation means)
110 Feedback control system 116 Disturbance generating means 119 Target value setting means D _O2 differential value D _O2PK differential peak value I Time integrated value I _R Actual time integrated value I _T Target time integrated value L Dead time LR, RL Disturbance PF Corresponding output SF of linear air-fuel ratio sensor Detection value SW4 Linear air-fuel ratio sensor SW5 Oxygen concentration sensor T _LR , T _RL Average transient time TVO Throttle opening τ Time constant

Claims (2)

A linear air-fuel ratio sensor deterioration diagnosis device that is provided in a feedback control system that controls a target air-fuel ratio of an engine and outputs a value proportional to an oxygen concentration in exhaust gas,
Disturbance generating means for outputting impulse-like disturbance to the feedback control system a predetermined number of times by alternately changing the air-fuel ratio between the rich side and the lean side;
Target value setting means for setting a target time integral value of the disturbance output by the disturbance generating means;
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 each of the rich side and the lean side as 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 differentiating means as a determination parameter for deterioration determination;
Disturbance resetting means for resetting disturbance after at least the differential value exceeds a predetermined threshold;
With actual value calculation means for calculating the actual time integral value of the disturbance actually output after the reset of the disturbance,
The disturbance reset means resets the disturbance after the differential value exceeds a predetermined threshold value and the actual time integrated value of the disturbance currently output becomes equal to or greater than the target time integrated value of the disturbance. ,
The target value setting means, to the second and subsequent disturbances, previous linear air-fuel ratio deterioration diagnosis device of the sensor, wherein the Ru der used to set the target time integral value to offset actual time integral value of the disturbance . The deterioration diagnosis device for a linear air-fuel ratio sensor according to claim 1,
The determination parameter calculation means calculates at least a dead time as a determination parameter,
The target value setting means sets a minimum target time integral value necessary for the deterioration diagnosis of the linear air-fuel ratio sensor when the first disturbance occurs.
The degradation resetting apparatus for a linear air-fuel ratio sensor, wherein the disturbance reset means resets the generation of disturbance at the end of calculation of dead time after the first generation of disturbance.

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