JP2007009708A - Deterioration diagnostic device for linear air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent as much as possible a lowering in emission in diagnosing, and rapidly detect deterioration with high accuracy. <P>SOLUTION: Impulse disturbances LR, RL are output to a feedback control system a predetermined number of times. After outputting the disturbances LR, RL, a differential value D<SB>O2</SB>with the output PF of a linear air-fuel ratio sensor SW4 differentiated is output. The dead time L of the linear air-fuel ratio sensor and a time constant τ are calculated as determining parameter on the basis of the differential value D<SB>O2</SB>. It is determined whether or not the output PF of the linear air-fuel ratio sensor SW4 is converged, and generation of disturbances are reset when calculated dead time L is finished. Also, after resetting disturbances LR, RL, next disturbances RL, LR are generated when determining the convergence of the output PF of the linear air-fuel ratio sensor SW4. <P>COPYRIGHT: (C)2007,JPO&INPIT

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.

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

  In order to solve the above-described problems, the present invention 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. A disturbance generating means for outputting an impulse-like disturbance to the feedback control system a predetermined number of times, a differentiating means for outputting a differential value of the output of the linear air-fuel ratio sensor after the disturbance is output by the disturbance generating means, and a differential value output by the differentiating means Determination parameter calculation means for calculating the dead time and the time constant of the linear air-fuel ratio sensor as deterioration determination determination parameters, and a convergence determination means for determining whether or not the output of the linear air-fuel ratio sensor has converged. And the disturbance generating means resets the generation of the disturbance when the dead time calculation is completed, and after the disturbance is reset. A deterioration diagnosis device for the linear air-fuel ratio sensor, wherein the convergence determination unit and generates the next disturbance when determining the convergence of the output of the linear air-fuel ratio sensor. In this aspect, in diagnosing the deterioration of the linear air-fuel ratio sensor, the disturbance time is calculated after generating the disturbance, and the disturbance is reset after the calculation of the dead time. Since it is possible to execute the deterioration diagnosis while maintaining the fuel ratio, it is possible to suppress a reduction in emissions as much as possible. In addition, 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. 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 embodiment, counting is started when a disturbance is generated by the disturbance generating means, and a mask period corresponding to the sum of the dead time and the time constant of the feedback control system is counted as a period for restricting the disturbance reset of the disturbance generating means. A mask period counting means for maintaining the output of the disturbance while the mask period is counted, and the disturbance generating means outputs the disturbance. In the meantime, the dead time and the time constant are calculated based on the fact that the differential value output from the differentiating means exceeds a predetermined threshold value. In this aspect, while the mask period is counted by the mask period counting means, the disturbance generating means continues to output the disturbance, so that the convergence determining means is restricted from determining convergence until the mask period elapses. Become. Then, while the disturbance continues to be output during this mask period, the differentiating means outputs the differential value from the output of the linear air-fuel ratio sensor, and the determination parameter calculation means based on the output differential value causes the dead time and time constant. Therefore, the determination parameter calculation means always calculates the dead time while the mask period is counted, and executes the convergence determination only after the delay time of the feedback control system itself has elapsed. . This makes it possible to prevent erroneous determination due to involuntary disturbance. This mask period is for canceling the dead time and time constant of the feedback control system itself of the linear air-fuel ratio sensor. Usually, it takes time until oxygen in the exhaust gas comes into contact with the linear air-fuel ratio sensor. Therefore, the linear air-fuel ratio sensor itself has a dead time or a primary delay as a hardware restriction with respect to the actual air-fuel ratio. It will be. If the disturbance is stopped only with the differential value calculated without taking such dead time and first order lag into consideration, a misjudgment will occur, so the minimum dead time and first order lag will be reduced in hardware. While it is considered to occur, it is counted as a mask period, and until this mask period elapses, the determination parameter calculation means keeps calculating dead time and time constant so as to improve the accuracy of deterioration determination. .

  In a preferred embodiment, the control element of the feedback control system is provided with a necessary convergence period counting means for counting a minimum necessary convergence period necessary for convergence of disturbance, at the latest after resetting the disturbance by the disturbance generating means, and the convergence determination means includes: The convergence determination is performed after the elapse of the necessary convergence period. In this aspect, while the necessary convergence period is counted by the necessary convergence period counting unit, the convergence determination unit is restricted from determining convergence until the necessary convergence period elapses. For this reason, the disturbance generating means is prohibited from outputting the next disturbance until the necessary convergence period elapses after outputting one disturbance. This necessary convergence period is a minimum time required for the feedback control system of the linear air-fuel ratio sensor itself to converge the output to the target air-fuel ratio when a disturbance occurs. If the next disturbance is output without passing through the necessary convergence period, an erroneous determination will occur if another disturbance occurs during the convergence process and the output converges. Until the required convergence period elapses, even if the output has converged, after the convergence judgment is prohibited and the output is reliably converged, the next disturbance is generated to improve the accuracy of the degradation judgment. ing. The count start timing of the necessary convergence period is preferably when the disturbance is reset by the disturbance generating means. However, if the disturbance output period is sufficiently shorter than the convergence period, even when the disturbance output is started. Good.

  In a preferred embodiment, an intake air amount detecting means for detecting an intake air amount of the engine is provided, and the convergence determining means is configured to detect the intake air when the intake air amount exceeds the predetermined threshold value and changes to the decrease side. The convergence condition is stricter than when the amount is less than or equal to the threshold value. In this aspect, the determination criterion of the time constant accompanying the change in the intake air amount is corrected to improve the accuracy of the deterioration determination. In other words, when the intake air amount changes in the decreasing direction, the time constant also changes greatly.Therefore, even a linear air-fuel ratio sensor that has not progressed, the reaction is relatively slow, and an erroneous deterioration determination is made. Will come. Therefore, when the intake air amount changes by a predetermined amount to the decreasing side, the convergence condition is made strict, and the criterion for determining the time constant accompanying the change in the intake air amount is corrected.

  In a preferred embodiment, intake air amount detection means for detecting the intake air amount of the engine is provided, and the convergence determination means makes the convergence condition stricter as the intake air amount is smaller.

  In a preferred embodiment, the intake air amount detecting means for detecting the intake air amount of the engine, and the control element of the feedback control system counts the minimum necessary convergence period necessary for the convergence of the disturbance after the disturbance is reset by the disturbance generating means at the latest. Necessary convergence period counting means for performing convergence determination after the necessary convergence period has elapsed, and the necessary convergence time counting means is configured such that the amount of intake air has a predetermined threshold value. If the intake air amount is changed to the decreasing side, the necessary convergence period is set longer than in the case where the intake air amount is equal to or less than the threshold value.

  In a preferred embodiment, the intake air amount detecting means for detecting the intake air amount of the engine, and the control element of the feedback control system counts the minimum necessary convergence period necessary for the convergence of the disturbance after the disturbance is reset by the disturbance generating means at the latest. Necessary convergence period counting means for performing the convergence determination after the necessary convergence period elapses, and the necessary convergence time counting means is configured such that the smaller the intake air amount is, the more necessary convergence period is. Is set longer.

  As described above, according to the present invention, in diagnosing the deterioration of the linear air-fuel ratio sensor, it is possible to output a disturbance only for a minimum necessary period according to the deterioration state of the linear air-fuel ratio sensor. Deterioration diagnosis can be executed while the target air-fuel ratio of the feedback control system is maintained, so that it is possible to prevent as much as possible the emission reduction during diagnosis, and high-accuracy deterioration detection can be performed quickly. There is a remarkable effect that it can be executed.

  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. 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.

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

First, referring to FIG. 4 and FIG. 6, when the deterioration diagnosis program is executed, the CPU 101 waits for the diagnosis condition to be satisfied (step S1). Here, diagnostic conditions are
(1) The change amount of the engine rotation speed Ne detected by the rotation angle sensor SW1 is equal to or less than a predetermined change amount,
(2) The change amount of the throttle opening TVO detected by the throttle sensor SW3 is not more than a predetermined change amount, and (3) The change amount of the charging efficiency CE calculated by CE = Qa / Ne is not more than the predetermined change amount. It means that it is a so-called steady operation that satisfies all of the conditions.

  If the diagnostic conditions are not 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 is compared with the threshold value ThC as shown in FIG. 6 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 starting the diagnosis after the timer time reaches zero, the disturbances LR and RL occurrence times N _LR and N _RL are compared (step S6). If N _RL > N _LR is satisfied, the disturbance LR Is output to the feedback control system 110 (step S7), and if not established, the disturbance RL is output to the feedback control system 110 (step S8). 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 a disturbance LR (or RL), CPU 101 calculates the differential value D _O2 of the output PF of the linear air-fuel ratio sensor SW4 (step S9). Thereby, it becomes possible to grasp how the output PF of the linear air-fuel ratio sensor SW4 changes due to the disturbance LR (or RL). As described above, the CPU 101 of the present embodiment functionally configures a differentiating unit that outputs a differential value D _O2 obtained by differentiating the output PF of the linear air-fuel ratio sensor SW4 after the disturbance output by the disturbance generating unit 116.

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

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

Referring to FIG. 7, between the input x (t) and the output y (t) of the linear air-fuel ratio sensor SW4,
y (t) = x (t−L) (L ≧ 0) (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. 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. 4, 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 S10), and if it is established, calculates a dead time L of the linear air-fuel ratio sensor SW4 (step S11) and resets the disturbance caused by the disturbance generating means 116 (step S12).

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, 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 S14), and the time constant τ of the linear air-fuel ratio sensor SW4 is calculated from the differential peak value D _O2PK (step S15).

When the calculation of the time constant τ is completed, the CPU 101 determines whether the disturbance generated by the disturbance generating means 116 is to reduce or increase the fuel (step S16). In the case of an increase, the determination parameters (calculated time delay L, time constant τ) are stored in the main storage device 103 as _LR (steps S17 and S18), and the number of occurrences N _LR stored in the main storage device 103 is stored. , N _RL is incremented (steps S19 and S20).

Thereafter, for each disturbance LR, RL, it is determined whether or not the required number of times N _END has been completed (steps S21 and S22), 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. 8 is a flowchart showing details of the deterioration determination process.

Referring to FIG. 8, here, in order to determine the deterioration, the sum of the dead time L and the time constant τ is defined as the transition time T, and when the processing up to step S22 is completed, the CPU 101 detects the disturbance on the rich side. average transient time T _LR of the disturbance RL of LR and the lean side, T _RL to be respectively calculated (step S211). Next, the difference between the absolute values of both average transient times T _LR and T _RL is calculated, and it is determined whether or not the value exceeds a predetermined threshold value ThB (step S212). When the difference between the absolute values is large in each of the average transient times T _LR and T _RL , the air-fuel ratio control by the main control element 114 shifts to the rich side or the lean side. The difference between the absolute values of the average transition times T _LR and T _RL is calculated.

If both the average transient time T _LR, when the difference between the absolute value of T _RL is less than or equal to the threshold ThB, or turn, the sum of the absolute values of both average transient time T _LR, T _RL exceeds the threshold value ThA It is determined whether or not (step S213). If the sum of the absolute values of both average transient time T _LR, T _RL is large, sometimes running sub feedback control by the oxygen concentration sensor SW5, the feedback control becomes excessive correction, control becomes slow It is easy to diverge.

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

On the other hand, if the difference between the absolute values of the average transient times T _LR and T _RL exceeds the threshold value ThB in step S212, the rich average transient time T _LR is compared with the rich threshold value ThR. Then, it is determined whether or not 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 S11 in FIG. 4 and step S15 in FIG. 5 to functionally configure the determination parameter calculation unit.

  FIG. 9 is a graph showing the relationship between the time constant τ and the intake air amount Qa.

  Referring to FIG. 9, generally, as a characteristic of the linear air-fuel ratio sensor SW4, the time constant τ becomes longer as the intake air amount Qa detected by the airflow sensor SW2 increases. For example, a certain intake air amount When the intake air amount Qa is decreased by ΔQa in the decreasing direction from Qa1, the time constant τ is also decreased by Δτ. For this reason, when the threshold values ThC and dThC are always set to constant values for determining the convergence of the feedback control, even if the linear air-fuel ratio sensor SW4 is deteriorated, the intake air amount Qa is reduced. As a result, the time constant τ may be shortened, and normality may be determined. In view of this, the present embodiment is configured such that the threshold values ThC and dThC are changed according to the variation of the intake air amount Qa.

  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 subroutine, first, an intake air amount Qa and a change amount ΔQa of the intake air amount Qa to the decreasing side are calculated (step S201), and the calculated change amount ΔQa and a predetermined threshold are calculated. The value V _Qa is compared (step S202). When the change amount ΔQa exceeds the threshold value V _Qa , the convergence determination threshold values ThC and dThC are set to small values so that the convergence determination becomes strict (step S203). If the value is less than or equal to the value V _Qa , the convergence determination threshold values ThC and dThC are set to large values (step S204).

As described above, in the form shown in FIG. 10, the airflow sensor SW2 is provided as the intake air amount detection means for detecting the intake air amount Qa of the engine, and the convergence determination means functionally configured by the CPU 101 has the intake air amount Qa of In the case where the amount of intake air Qa changes to the decrease side beyond a predetermined threshold value V _Qa , the convergence condition is made stricter than when the intake air amount Qa is equal to or less than the threshold value V _Qa . For this reason, in the embodiment shown in FIG. 10, the criterion for determining the time constant τ accompanying the change in the intake air amount Qa is corrected to improve the accuracy of the degradation determination. That is, when the intake air amount Qa changes in the decreasing direction, the time constant τ also changes greatly along with this, so even the linear air-fuel ratio sensor SW4 that has not progressed is relatively slow in reaction and deteriorated. An erroneous decision will be made. Therefore, when the intake air amount Qa changes by a predetermined amount to the decrease side, the convergence condition is made strict and the criterion for determining the time constant τ accompanying the change in the intake air amount Qa is corrected.

  FIG. 11 is a flowchart showing another example of the convergence determination threshold value setting subroutine (step S2) in FIG.

  Referring to FIG. 11, in this example, a map 220 for obtaining threshold values ThC and dThC from intake air amount Qa is stored in main memory 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. 11, 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. Also in the embodiment of FIG. 11, the determination criterion of the time constant τ associated with the change in the intake air amount Qa can be corrected, so that erroneous determination can be avoided.

  As described above, in this embodiment, in diagnosing the deterioration of the linear air-fuel ratio sensor SW4 that feeds back the control amount corresponding to the actual air-fuel ratio, after generating the disturbances LR and RL, the dead time L is calculated and the dead time is calculated. Since the disturbances LR and RL are reset after the calculation of the time L, the deterioration diagnosis can be executed while the target air-fuel ratio of the feedback control system 110 is maintained. It is possible to suppress the emission reduction as much as possible. In addition, it is possible to output the disturbances LR and RL for a minimum necessary 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.

  Therefore, according to the present embodiment, in diagnosing the deterioration of the linear air-fuel ratio sensor SW4 that feeds back the control amount corresponding to the actual air-fuel ratio, the disturbance is applied for a minimum period according to the deterioration state of the linear air-fuel ratio sensor SW4. It is possible to output LR and RL, and it is possible to execute a deterioration diagnosis while maintaining the target air-fuel ratio of the feedback control system 110, so that the emission reduction at the time of diagnosis can be reduced as much as possible. Therefore, it is possible to prevent the occurrence of the deterioration, and it is possible to quickly 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.

  FIG. 12 is a flowchart according to another embodiment of the present invention, and FIG. 13 is a timing chart obtained by executing the flowchart of FIG.

  With reference to FIGS. 12 and 13, in the embodiment shown in FIG. 12, a map 240 for determining the mask period Tmk based on the engine speed Ne and the load LD is stored in the main storage device 103 in advance. Then, between step S5 and step S6, step S30 for indexing the map 240 and step S31 for starting the timer for the indexed mask period Tmk are added, and between step S11 and step S12, Step S32 for determining the passage of the indexed mask period Tmk and step S33 for discarding the detection value of the convergence determination and returning to step S10 when the mask period Tmk has not elapsed are added. This is different from the flowcharts of FIGS.

This mask period Tmk is set to a length corresponding to the transition time T (sum of the dead time L and the time constant τ) of the normal linear air-fuel ratio sensor SW4. This mask period Tmk is for canceling the dead time and time constant of the feedback control system 110 itself of the linear air-fuel ratio sensor SW4. Usually, since it takes time until oxygen in the exhaust gas comes into contact with the linear air-fuel ratio sensor SW4, the linear air-fuel ratio sensor SW4 itself has a dead time and a first-order lag as hardware constraints with respect to the actual air-fuel ratio. Will be. If the disturbances LR and RL are stopped only by the differential value _D02 calculated without considering such dead time L and first-order lag, an erroneous determination occurs. While the dead time and the first-order delay are considered to occur, the mask period Tmk is counted, and until the mask period Tmk elapses, the CPU 101 as the determination parameter calculation means continues to calculate the dead time L and the time constant τ. Thus, the accuracy of the deterioration determination is increased.

As a result, in this embodiment, as shown in FIG. 13, the counting is started when the disturbances LR and RL are generated by the disturbance generating means 116, and the dead time L and the mask period corresponding to the time constant of the feedback control system 110 are included. The mask period counting means for counting Tmk is functionally configured, and the disturbance generating means 116 maintains the outputs of the disturbances LR and RL while the mask period Tmk is counted. For this reason, in this embodiment, the convergence determination is restricted until the mask period Tmk elapses. While the disturbances LR and RL continue to be output during the mask period Tmk, the differential value D _O2 is output from the output of the linear air-fuel ratio sensor SW4, and the dead time L is determined based on the output differential value D _O2. Since the calculation is performed, the dead time L is always calculated while the mask period Tmk is counted, and the convergence determination is executed only after the delay time T of the feedback control system 110 itself has elapsed. This makes it possible to prevent erroneous determination due to involuntary disturbance.

  FIG. 14 is a flowchart showing a more specific aspect of the present invention, and FIG. 15 is a timing chart obtained by executing the flowchart of FIG.

  Referring to FIGS. 14 and 15, in the embodiment shown in each figure, step S40 for setting the required convergence time TC is provided after step S12, and the previous disturbance LR, between step S5 and step S6, is provided. It is determined that the necessary convergence time TC elapses after RL, and if it has not elapsed, the process returns to step S4 to insert step S41 so as to reset the timer, as shown in FIGS. This is different from the embodiment.

  The necessary convergence period TC is a minimum time required for the feedback control system 110 itself to converge the output to the target air-fuel ratio when disturbances LR and RL occur. When the next disturbance LR, RL is output without passing through the necessary convergence period TC, an erroneous determination is made when the output converges due to another disturbance LR, RL occurring during the convergence process. Therefore, until the required convergence period TC elapses, even if the output has converged, after the convergence determination is prohibited and the output is reliably converged, the next disturbances LR and RL are generated. Thus, the accuracy of the deterioration determination is increased.

  As a result, in the embodiment of FIG. 14, the convergence determination is restricted until the required convergence period TC elapses. Therefore, the disturbance generation unit 116 outputs one disturbance LR (or RL), Until the necessary convergence period TC elapses, the output of the next disturbance RL (or LR) is prohibited. Thereby, it is possible to prevent erroneous convergence determination due to involuntary disturbance and to accurately calculate the delay time T in the next disturbance RL (or LR).

  The count start timing of the necessary convergence period TC may be counted at the latest after the disturbances LR and RL are reset by the disturbance generation unit 116, and preferably when the disturbances LR and RL are reset by the disturbance generation unit 116. Good. Since the output periods of the disturbances LR and RL vary depending on the deterioration state of the linear air-fuel ratio sensor SW4, the required convergence period TC can be easily controlled if the count start timing is set when the disturbances LR and RL are reset. However, when the output periods of the disturbances LR and RL are sufficiently shorter than the convergence period, the disturbances LR and RL may be set at the start of output. Conversely, a variable that matches the feedback performance of the feedback control system 110 may be set in the necessary convergence period TC. As described above, in the present embodiment, the CPU 101 functionally configures the necessary convergence period counting unit that counts the necessary convergence period TC to be counted after the disturbance LR and RL are reset by the disturbance generation unit 116 at the latest.

  Furthermore, when the present embodiment is embodied, if the intake air amount Qa exceeds the predetermined threshold and changes to the decrease side, the necessary convergence is required as compared with the case where the intake air amount Qa is equal to or less than the threshold. The period TC may be set longer.

  Alternatively, the required convergence period TC may be set longer as the intake air amount Qa is smaller.

  Further, the mask period shown in FIGS. 12 and 13 and the necessary convergence period shown in FIGS. 14 and 15 can be realized in the same flow.

  Further, in realizing the deterioration diagnosis, the flowchart shown in FIG. 8 may be executed for each dead time L and for 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. 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. It is a graph which shows the relationship between a time constant and the amount of intake air. It is a flowchart which shows an example of the convergence determination threshold value setting subroutine in FIG. 6 is a flowchart showing another example of a convergence determination threshold value setting subroutine in FIG. 6 is a flowchart according to another embodiment of the present invention. It is a timing chart obtained by performing the flowchart of FIG. It is a flowchart which shows the more specific aspect of this invention. It is a timing chart obtained by performing the flowchart of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Degradation determination apparatus 10 Engine 20 Intake system 27 Fuel injection valve 30 Exhaust system 32 Three-way catalyst 100 Control unit 101 CPU (differentiation means, determination parameter calculation means, convergence determination means, mask period count means, example of necessary convergence period count means )
102 Auxiliary storage device 103 Main storage device 110 Feedback control system 116 Disturbance generating means 220 Map 240 Map D _O2 differential value D _O2PK differential peak value DV Target value IP Reference input L _Dead time Ne Engine speed N _END output frequency N _LR , N _RL occurrence frequency OV Manipulation amount PF Output of linear air-fuel ratio sensor corresponding to actual air-fuel ratio Qa Intake air amount LR, RL Disturbance SW1 Rotation angle sensor SW2 Air flow sensor (an example of intake air amount detection means)
SW3 Throttle sensor SW4 Linear air-fuel ratio sensor SW5 Oxygen concentration sensor T Transient time TC Necessary convergence period ThA, ThB, ThC, dThC, + ThD, -ThD, ThL, ThR Threshold value Tmk Mask period T _RL , T _LR Average transient time TVO Throttle opening V _Qa differential value Δ Air-fuel ratio change amount ΔQa Intake air change amount τ Time constant

Claims (7)

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 an impulse-like disturbance a predetermined number of times to the feedback control system;
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 the dead time and time constant of the linear air-fuel ratio sensor as the determination parameters for deterioration determination based on the differential value output by the differentiation means;
Convergence determining means for determining whether or not the output of the linear air-fuel ratio sensor has converged,
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 A deterioration diagnosis apparatus for a linear air-fuel ratio sensor, characterized in that The deterioration diagnosis device for a linear air-fuel ratio sensor according to claim 1,
A mask period count that starts counting when a disturbance is generated by the disturbance generating means and counts a mask period corresponding to the sum of the dead time and the time constant of the feedback control system as a period for restricting the disturbance reset of the disturbance generating means Providing means,
The disturbance generating means maintains the output of the disturbance while the mask period is counted,
The determination parameter calculating means calculates a dead time and a time constant based on the fact that the differential value output by the differentiating means exceeds a predetermined threshold while the disturbance generating means outputs the disturbance. A deterioration diagnosis apparatus 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,
The control element of the feedback control system is provided with a necessary convergence period counting means for counting the minimum necessary convergence period necessary for the convergence of the disturbance, at the latest after resetting the disturbance by the disturbance generating means,
The linear air-fuel ratio sensor deterioration diagnosis apparatus according to claim 1, wherein the convergence determination means executes a convergence determination after elapse of the necessary convergence period. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to any one of claims 1 to 3,
Intake air amount detection means for detecting the intake air amount of the engine is provided,
The convergence determination means makes the convergence condition stricter when the intake air amount exceeds the predetermined threshold and changes to the decrease side compared to when the intake air amount is equal to or less than the threshold. A deterioration diagnosis apparatus 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,
Intake air amount detection means for detecting the intake air amount of the engine is provided,
The degradation determination device for a linear air-fuel ratio sensor, wherein the convergence determination means makes the convergence condition stricter as the amount of intake air is smaller. The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to claim 1 or 2,
Intake air amount detection means for detecting the intake air amount of the engine;
A control element of the feedback control system is provided with a necessary convergence period counting means for counting a minimum necessary convergence period necessary for convergence of disturbance, at the latest after resetting the disturbance by the disturbance generating means,
The convergence determination means performs a convergence determination after the necessary convergence period has elapsed,
The necessary convergence time counting means sets the necessary convergence period longer when the intake air amount exceeds the predetermined threshold value and changes to the decrease side compared to when the intake air amount is equal to or less than the threshold value. A deterioration diagnosis apparatus for a linear air-fuel ratio sensor, characterized in that: The deterioration diagnosis apparatus for a linear air-fuel ratio sensor according to claim 1 or 2,
Intake air amount detection means for detecting the intake air amount of the engine;
A control element of the feedback control system is provided with a necessary convergence period counting means for counting a minimum necessary convergence period necessary for convergence of disturbance, at the latest after resetting the disturbance by the disturbance generating means,
The convergence determination means performs a convergence determination after the necessary convergence period has elapsed,
The degradation diagnosis apparatus for a linear air-fuel ratio sensor, wherein the necessary convergence time counting means sets a longer necessary convergence period as the amount of intake air is smaller.

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