JP2005054770A - Error detection device for air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect error without deteriorating emission and drivability when an error of an air-fuel ratio sensor is detected by increasing and decreasing fuel injection quantity by open loop control. <P>SOLUTION: The device is provided with a fuel injection quantity increase and decrease means periodically increasing and decreasing fuel injection quantity by open loop control with setting base fuel injection quantity TAU as a reference, an air-fuel ratio sensor 35 detecting air-fuel ratio, a difference acquisition means calculating difference ΔA/F between a target A/F output 60 and normalized A/F output 55 of output of the air-fuel ratio sensor 35 fluctuating according to increase and decrease of fuel injection quantity by the fuel injection quantity increase and decrease means, a base fuel injection control means controlling base fuel injection quantity TAU based on the difference ΔA/F, an error detection means detecting an error of the air-fuel ratio sensor based on output of the air-fuel ratio sensor 35. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an abnormality detection apparatus for an air-fuel ratio sensor, and is particularly suitable for application to an abnormality detection apparatus for an oxygen sensor that measures the oxygen concentration of exhaust gas from an internal combustion engine or the like.

  Conventionally, in order to reduce the emission in the exhaust gas of an internal combustion engine, the empty of the fuel mixture supplied to the internal combustion engine based on the output signal of an A / F sensor (oxygen sensor) attached to the exhaust system of the internal combustion engine The fuel ratio (A / F) is controlled.

  As a method for determining such an abnormality of the A / F sensor, the A / F is forcibly vibrated lean / rich by open loop control, and the abnormality of the A / F sensor is detected from the responsiveness of the sensor output at that time. The method is known.

Japanese Patent No. 2837690 JP-A-6-34597 JP-A-8-100635 Japanese Examined Patent Publication No. 7-42884

  When forcibly oscillating the A / F lean / rich by open loop control, a certain amount of fuel injection is increased or decreased with respect to the base fuel injection amount at which the A / F becomes stoichiometric. According to this method, since the fuel injection amount is not corrected according to the output of the A / F sensor unlike feedback control, the responsiveness of the A / F sensor can be directly detected. When an error is included in the fuel injection amount, it is not possible to perform control to correct the error and return the base fuel injection amount to a value corresponding to stoichiometry.

  The base fuel injection amount is determined according to the intake air amount. However, when the detected value of the intake air amount includes an error, there arises a problem that the base fuel injection amount varies according to the error. An error may also be included in the fuel injection amount by the fuel injection valve. Therefore, in the case of open loop control, it is difficult to set the base fuel injection amount to an accurate value corresponding to stoichiometry. If the fuel injection amount is increased or decreased with respect to the base fuel injection amount in a state where the base fuel injection amount deviates from the injection amount corresponding to the stoichiometry, the A / F is controlled to be excessively rich or lean. It will be done. This causes a problem that emissions and drivability deteriorate.

  Before the abnormality detection of the A / F sensor is performed by the open loop control, the air-fuel ratio is controlled by the feedback control. Therefore, the open loop control is performed based on the learning value of the deviation between the target A / F and the actual output in the feedback control. A method of setting the base fuel injection amount in is also conceivable. However, since the learning value itself in the feedback control also includes an error, it is difficult to accurately set the base fuel injection amount in the open loop control to a value corresponding to the stoichiometry based on the learning value.

  The present invention has been made to solve the above-described problems. When detecting an abnormality in the air-fuel ratio sensor by increasing or decreasing the fuel injection amount by open loop control, the emission and drivability are deteriorated. The purpose is to detect abnormalities.

  In order to achieve the above object, the first invention provides a fuel injection amount increasing / decreasing means for periodically increasing / decreasing the fuel injection amount based on the base fuel injection amount by open loop control, an air / fuel ratio sensor for detecting an air / fuel ratio, Deviation obtaining means for obtaining a deviation between the center value of the output of the air-fuel ratio sensor and the target value which fluctuates according to increase / decrease of the fuel injection amount by the fuel injection amount increase / decrease means, and based on the deviation, the base fuel injection amount A base injection amount control means for controlling the abnormality, and an abnormality detection means for detecting an abnormality of the air-fuel ratio sensor based on the output of the air-fuel ratio sensor.

  According to a second aspect, in the first aspect, the base injection amount control means performs control so that the deviation approaches zero.

  According to a third invention, in the first or second invention, the deviation acquisition means includes means for calculating a smoothed output of the output of the air-fuel ratio sensor, and the deviation is calculated using the smoothed output as the center value. It is characterized by seeking.

  According to a fourth invention, in the first or second invention, the deviation acquisition means includes means for calculating an average value of a rich peak value and a lean peak value of the air-fuel ratio sensor, and the average value The deviation is obtained by using as a center value.

  According to a fifth invention, in any one of the first to fourth inventions, the target value is an output of the air-fuel ratio sensor corresponding to a theoretical air-fuel ratio.

  In a sixth aspect based on any one of the first to fifth aspects, the deviation acquisition means obtains a center value of the output of the air-fuel ratio sensor using an output of a predetermined ratio of the output of the air-fuel ratio sensor. It is characterized by that.

  According to the first invention, the base fuel injection amount can be corrected based on the deviation between the output of the air-fuel ratio sensor and the target value when the fuel injection amount is periodically increased or decreased. It is possible to suppress excessive fluctuation to the lean side or the rich side, and it is possible to improve emission and drivability.

  According to the second aspect of the invention, control is performed such that the center value of the output of the air-fuel ratio sensor approaches the target value by performing control so that the deviation approaches 0.

  According to the third aspect, by calculating the smoothed output of the air-fuel ratio sensor, it is possible to obtain the center value of the output of the air-fuel ratio sensor that varies according to the increase or decrease of the fuel injection amount.

  According to the fourth aspect of the invention, by calculating the average value of the rich-side peak value and the lean-side peak value of the air-fuel ratio sensor, the center value of the output of the air-fuel ratio sensor that fluctuates according to the increase or decrease of the fuel injection amount Can be obtained.

  According to the fifth aspect, the base fuel injection amount can be controlled to a value corresponding to the theoretical air-fuel ratio by setting the target value to a value corresponding to the theoretical air-fuel ratio.

  According to the sixth aspect of the invention, since the center value of the output of the air-fuel ratio sensor is obtained using the output at a predetermined ratio of the output of the air-fuel ratio sensor, the fluctuation of the center value caused by the fluctuation of the output of the air-fuel ratio sensor is reduced. Can be minimized. Therefore, the center value of the output of the air-fuel ratio sensor can be converged in a short time, and the deviation between the center value and the target value can be obtained stably.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining an air-fuel ratio sensor abnormality detection device and its peripheral structure according to each embodiment of the present invention. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. The intake passage 12 includes an air filter 16 at an upstream end. The air filter 16 is assembled with an intake air temperature sensor 18 for detecting the intake air temperature THA (that is, the outside air temperature).

  An air flow meter 20 is disposed downstream of the air filter 16. The air flow meter 20 is a sensor that detects an air inflow amount Ga flowing through the intake passage 12. A throttle valve 22 is provided downstream of the air flow meter 20. A throttle sensor 24 that detects the throttle opening degree TA and an idle switch 26 that is turned on when the throttle valve 22 is fully closed are disposed in the vicinity of the throttle valve 22.

  A surge tank 28 is provided downstream of the throttle valve 22. Further, a fuel injection valve 30 for injecting fuel into the intake port of the internal combustion engine 10 is disposed further downstream of the surge tank 28.

In the exhaust passage 14, an upstream catalyst (start catalyst) 32 and a downstream catalyst (NO _X storage catalyst or three-way catalyst) 34 are arranged in series. An air-fuel ratio sensor (A / F sensor) 35 is disposed upstream of the upstream catalyst 32 in the exhaust passage 14. The air-fuel ratio sensor 35 is a sensor that detects the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 35 detects the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine 10 based on the oxygen concentration in the exhaust gas flowing into the upstream catalyst 32. It is to detect. An O 2 sensor 38 is disposed between the upstream catalyst 32 and the downstream catalyst 34 in the exhaust passage 14.

  As shown in FIG. 1, the abnormality detection device of the present embodiment includes an ECU (Electronic Control Unit) 40. In addition to the various sensors and the fuel injection valve 30 described above, a vehicle speed sensor 44 that detects the vehicle speed SPD and the like are connected to the ECU 40.

  The abnormality detection device of the present embodiment performs control (air-fuel ratio active control) for periodically increasing / decreasing the fuel injection amount injected from the fuel injection valve 30 based on the base injection amount by open loop control. A sensor abnormality is detected from the response of the fuel ratio sensor 35. By increasing or decreasing the fuel injection amount by open loop control, the responsiveness of the air-fuel ratio sensor 35 can be directly detected, and abnormality detection can be accurately performed.

  In the air-fuel ratio active control by the open loop control, the fuel injection amount is periodically increased or decreased by increasing or decreasing the predetermined injection amount ΔTau with respect to the base fuel injection amount TAU. The base fuel injection amount TAU is a fuel injection amount corresponding to the stoichiometric (= 14.6) air-fuel ratio, and is a value obtained based on the intake air amount Ga. ΔTau is a value obtained by multiplying the base fuel injection amount by a predetermined ratio. Accordingly, the base fuel injection amount TAU is different under different conditions of the intake air amount Ga, and the value of ΔTau is also different depending on the base fuel injection amount TAU.

  FIG. 2 shows the vehicle speed, the output of the A / F sensor 35 (A / F output 50), and the deviation between the A / F output 50 and the target A / F output 60 when air-fuel ratio active control is performed by open loop control. It is a timing chart which shows the fluctuation of (ΔA / F). In the example of FIG. 2, the air-fuel ratio active control is performed when the vehicle speed is 60 (km / h), 80 (km / h), and 100 (km / h). That is, in FIG. 2, air-fuel ratio active control is performed in a section from time t1 to time t2, a section from time t3 to time t4, and a section after time t5. Therefore, in these sections, the A / F output 50 varies between rich and lean as the fuel injection amount increases and decreases. In the apparatus of the present embodiment, the response of the air-fuel ratio sensor 35 is determined based on the locus length of the output obtained from the A / F output 50 or the area surrounded by the A / F output 50 and the target A / F output 60. Evaluation is performed and abnormality detection of the air-fuel ratio sensor 35 is performed. Here, the target A / F output 60 is an output of the A / F sensor 50 when an amount of fuel corresponding to the stoichiometry is injected from the fuel injection valve 30. The ECU 40 stores a value of the target A / F output 60 corresponding to the fuel injection amount in the fuel injection valve 30 in advance.

  As shown in FIG. 2, when the A / F is forcibly vibrated by open loop control, the center value of the A / F output 50 may deviate from the target A / F output 60. In the example of FIG. 2, the center value of the A / F output 50 is shifted to the lean side with respect to the target A / F output 60 when the vehicle speed is 60 (km / h) and 80 (km / h). When the vehicle speed is 100 (km / h), the center value of the A / F output 50 is shifted to the rich side with respect to the target A / F output 60. Thus, if the center value of the A / F output 50 deviates from the target A / F output, the emission and drivability may deteriorate.

  Therefore, in the apparatus of the present embodiment, the A / F output 50 that varies periodically is subjected to an annealing process to obtain the center value of the A / F output 50 (annealing A / F output 55). The fuel injection amount is feedback controlled so that the / F output 55 matches the target A / F60 output.

The A / F output 50 is detected from the air-fuel ratio sensor 35 at every predetermined timing. Then, using the A / F output 50 detected at each predetermined timing, a smoothed A / F output 55 is calculated from the following equation (1).
a _{n + 1} = a _n + (b _{n + 1} −a _n ) / K (1)

In the equation (1), b _{n + 1} is the A / F output 50 detected at the (n + 1) th time after starting the air-fuel ratio active control. A _{n + 1} is the annealed A / F output 55 calculated using b _{n + 1} . As shown in the equation (1), the annealing A / F output 55 (a _{n + 1} ) is calculated from the A / F output 50 (b _{n + 1} ) and the previously calculated annealing A / F output 55 (a _n ). Calculated. The A / F output 55 is detected, for example, every sampling period, and the arithmetic A / F output 55 is calculated by performing the calculation of the equation (1) for each sampling period. Since the smoothed A / F output 55 calculated from the equation (1) is not easily affected by the noise of the A / F output 50, the center value of the A / F output 50 that vibrates lean / rich is accurately calculated. be able to.

  After calculating the annealing A / F output 55, the deviation (stoichiometric deviation amount ΔA / F) between the annealing A / F output 55 and the target A / F output 60 is calculated. Then, the base fuel injection amount TAU is corrected according to ΔA / F by feedback control. Then, the fuel amount ΔTau is increased or decreased with respect to the corrected base fuel injection amount TAU.

  FIG. 3 is a timing chart showing respective outputs when the air-fuel ratio active control is performed while correcting the base fuel injection amount TAU by the method described above. Here, the base fuel injection amount TAU is feedback-controlled so that ΔA / F becomes zero. As a result, the A / F output 50 that has been shifted to the rich side or the lean side in FIG. 2 becomes an output centered on the target A / F output 60.

  In this way, by performing the air-fuel ratio active control while correcting the base fuel injection amount TAU, the center value of the A / F output 50 forcibly oscillated rich / lean is obtained as shown in FIG. 60 can be substantially matched. As a result, the air-fuel ratio can be prevented from fluctuating excessively or leanly, and deterioration of emission and drivability can be suppressed.

  In the example of FIG. 3, the stoichiometric deviation amount ΔA / F is calculated based on the smoothed A / F output 55, but the average value of the peak value on the rich side and the peak value on the lean side of the A / F output 50 is obtained. The deviation between the average value and the target A / F 60 may be the stoichiometric deviation amount ΔA / F.

  Next, based on the flowchart of FIG.4 and FIG.5, the procedure of the process in the abnormality detection apparatus concerning this embodiment is demonstrated. FIG. 4 shows a process for correcting the base fuel injection amount TAU. FIG. 5 shows a process for determining an abnormality of the air-fuel ratio sensor 35.

  First, a process of correcting the base fuel injection amount TAU will be described based on the flowchart of FIG. First, in step S1, it is determined whether or not an active control condition is satisfied. Here, the case where the active control condition is satisfied is the case where the load condition is small such as during constant speed operation, the case where the air-fuel ratio sensor 35 has reached the active state, or the case where the water temperature has reached an appropriate temperature. When the catalyst temperature has reached an appropriate temperature, etc. If the active control condition is satisfied, the process proceeds to step S2. If the active control condition is not satisfied, the process waits in step S1.

In step S2, a base fuel injection amount TAU is calculated. The base fuel injection amount TAU is a function of the intake air amount Ga. Here, the base fuel injection amount TAU is calculated from the current intake air amount Ga and the theoretical air-fuel ratio. In the next step S3, the base fuel injection amount TAU is multiplied by a correction coefficient α to calculate a correction value TAU _{correction value} for the base fuel injection amount TAU. As will be described later, the correction coefficient α is a function of the stoichiometric deviation amount ΔA / F, and the initial value of α is set to 1, for example.

In the next step S4, an active injection amount TAU _A is calculated. Here, the active injection amount TAU _A is calculated by adding or subtracting the fuel injection amount ΔTau at a constant ratio (= s) of the TAU _{correction value} to the TAU _{correction value} . That is, TAU _A = TAU _{correction value} ± s × TAU _{correction value} is calculated to calculate rich side and lean side TAU _A , respectively.

In the next step S5, air-fuel ratio active control with the active injection amount TAU _A is performed, and the fuel injection amount is increased or decreased at a predetermined cycle. In the next step S6, the A / F output 50 obtained from the air-fuel ratio sensor 35 at this time is detected.

  In the next step S7, the trajectory length of the A / F output 50 detected in step S6 is obtained. In the next step S8, the A / F output 50 is subjected to an annealing process to obtain an annealing A / F output 55. In the next step S9, the difference between the smoothed A / F output 55 and the target A / F output 60 is taken to calculate the stoichiometric deviation amount ΔA / F.

  In the next step S10, it is determined whether or not the stoichiometric deviation amount ΔA / F is equal to or smaller than a predetermined threshold value TH. That is, here, it is determined whether or not ΔA / F ≦ TH. When ΔA / F ≦ TH, since the stoichiometric deviation amount ΔA / F is within the allowable range, it is not necessary to correct the base fuel injection amount TAU. Accordingly, in this case, the process proceeds to step S11, and the value of the correction coefficient α is initialized (α = 1).

On the other hand, if ΔA / F> TH in step S10, the stoichiometric deviation amount ΔA / F exceeds the allowable range, so the base fuel injection amount TAU needs to be corrected. In this case, the process proceeds to step S12 and a correction coefficient α corresponding to the stoichiometric deviation amount ΔA / F is obtained. At this time, the correction coefficient α is obtained from a map that defines the relationship between ΔA / F and the correction coefficient α. Alternatively, the correction coefficient α may be calculated by multiplying ΔA / F by a predetermined gain G. After step S12, the process returns to step S3, and the processes after step S3 are performed again. At this time, in step S3, since the value of the correction coefficient α is set to a value corresponding to the stoichiometric deviation amount ΔA / F, the base fuel injection amount TAU is corrected in accordance with the stoichiometric deviation amount ΔA / F. A value TAU _{correction value} can be obtained. In step S4, an active injection amount TAU _A is calculated based on the correction value TAU _{correction value} . In step S5, air-fuel ratio active control is performed using the active injection amount TAU _A.

  Next, processing for determining an abnormality of the air-fuel ratio sensor 35 will be described based on the flowchart of FIG. First, in step S21, it is determined whether a diagnosis determination condition is satisfied. Here, for example, it is determined whether or not the fuel injection amount has been increased or decreased a predetermined number of times. When the fuel injection amount is increased or decreased a predetermined number of times or more, the trajectory length of the A / F output 50 necessary for performing the abnormality determination is calculated, so it is determined that the diagnosis determination condition is satisfied. The process proceeds to step S22. On the other hand, when the increase / decrease in the fuel injection amount has not reached the predetermined number of times, the locus length of the A / F output 50 has not reached the value for performing the abnormality determination, so it is determined that the diagnosis determination condition is not satisfied, and the process Is terminated (RETURN).

  In step S22, the trajectory length of the A / F sensor output 50 calculated by the process of step S7 in FIG. 4 is integrated, and it is determined whether or not the integrated value is equal to or less than a predetermined specified value. If the integrated value of the trajectory length is equal to or smaller than the predetermined specified value in step S22, the A / F sensor output 50 has decreased, so the process proceeds to step S23, and abnormality determination of the air-fuel ratio sensor 35 is performed. On the other hand, if the integrated value of the trajectory length is larger than the predetermined specified value in step S22, a normal A / F sensor output 50 is obtained, so that the process proceeds to step S24 and it is determined that the air-fuel ratio sensor 35 is normal. To do.

According to the processing of FIG. 4, the stoichiometric deviation amount ΔA / F is calculated from the deviation between the smoothed A / F output 55 and the target A / F output 60, and the stoichiometric deviation amount ΔA / F is fed back to obtain the base fuel injection amount. Since the TAU correction value TAU _{correction value} is calculated, the base fuel injection amount TAU can be corrected to an amount corresponding to the theoretical air-fuel ratio. By optimizing the base fuel injection amount TAU, it is possible to suppress the air-fuel ratio from fluctuating excessively to the lean side or the rich side in the air-fuel ratio active control, and the emission and drivability deteriorate. Can be prevented.

  In the process of FIG. 5, the abnormality determination of the air-fuel ratio sensor 35 is performed based on the locus length of the A / F sensor output 50. However, the area surrounded by the A / F output 50 and the target A / F output 60 is determined. Abnormality determination may be performed based on this.

  As described above, according to the first embodiment, when air-fuel ratio active control is performed by open loop control to detect abnormality of the air-fuel ratio sensor 35, the center value of the A / F output 50 is equal to the target A / F 60. Control can be performed so as to match. Therefore, it is possible to prevent the air-fuel ratio from fluctuating excessively toward the lean side or the rich side, and it is possible to suppress the deterioration of emission and drivability.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described. In the second embodiment, when the abnormality of the air-fuel ratio sensor 35 is detected by the method of the first embodiment, the center value of the A / F output 50 is made to coincide with the target A / F 60 in a shorter time and with higher accuracy. is there.

  As described in the first embodiment, the annealing A / F output 55 is calculated from the equation (1). At this time, since the A / F output 50 periodically changes to rich / lean, if the smoothing coefficient K in the equation (1) is small, the annealing A / F output 55 also changes to rich / lean. May end up. In this case, since the deviation (stoichiometric deviation amount ΔA / F) between the annealing A / F output 55 and the target A / F 60 varies, the feedback amount to the base fuel injection amount TAU varies. In such a case, in order to improve the controllability of the feedback amount to the base fuel injection amount TAU, it is desirable to increase the smoothing coefficient K in the equation (1) as much as possible.

  However, if the annealing coefficient K is increased too much, the time until the annealing A / F output 55 converges and reaches a constant value becomes longer, and the annealing A / F with respect to the center value of the A / F output 50 is increased. The output 55 is delayed. In this case, since the time until the A / F output 55 coincides with the center value of the A / F output 50 is relatively long, the base fuel injection amount TAU is controlled to set the center value of the A / F output 50. There may be a case where a certain time is required until the target A / F 60 is matched.

  For this reason, in the second embodiment, the A / F output 50 is reduced to obtain the reduced A / F output 52 in order to suppress the influence on the control due to the fluctuation of the annealing A / F output 55. . Then, an annealing process is performed on the reduced A / F output 52.

The reduced A / F output 52 is calculated from the following equation.
Reduction A / F output = target A / F + (A / F output−target A / F) / S
In the above equation, the coefficient S indicates a reduction ratio when the A / F output 50 is reduced. Here, since the reduced A / F output 52 is preferably about 1/3 to 1/5 of the A / F output 50, the value of the coefficient S is set to about 3-5.

  When the reduced A / F output 52 is larger than 1/3 of the A / F output, the effect of reducing the A / F output 50 is reduced. On the other hand, if the reduced A / F output 52 is smaller than 1/5 of the A / F output, the smoothed A / F output 55 obtained from the reduced A / F output 52 is also reduced, so that the stoichiometric deviation amount ΔA / F is reduced. It may become smaller and controllability may be reduced. Accordingly, the reduced A / F output 52 is preferably about 1/3 to 1/5 of the A / F output 50.

  FIG. 6 is a timing chart showing the A / F output 50, the reduced A / F output 52, the annealing A / F output 55, and the target A / F 60.

  In FIG. 6, after the A / F output 50 is reduced to obtain a reduced A / F output 52, the annealing process described in the first embodiment is performed on the reduced A / F output 52. / F output 55 is obtained. Thereby, the fluctuation | variation of the annealing A / F output 55 resulting from the fluctuation | variation of the A / F output 50 can be suppressed to the minimum.

  As a result, it is possible to suppress variation in the deviation (stoichiometric deviation amount ΔA / F) between the annealing A / F output 55 and the target A / F 60, and the same as in the first embodiment based on the annealing A / F output 55. It is possible to improve the controllability of the feedback amount to the base fuel injection amount TAU.

  Further, since the value of the smoothing coefficient K can be set to a smaller value, the time until the smoothed A / F output 55 converges to a constant value can be shortened. In addition, the time delay of the A / F output 55 can be minimized. Therefore, according to the method of the second embodiment, the controllability of the base fuel injection amount TAU can be improved with the smoothing coefficient K being reduced. As a result, the base fuel injection amount TAU can reach the target A / F 60 in a short time.

  FIG. 7 is a timing chart showing respective outputs when the air-fuel ratio active control is performed while correcting the base fuel injection amount TAU by the method of the second embodiment. In the timing chart of FIG. 7, the A / F output (A / F output 50, smoothed A / F output 55, reduced A / F output 52, target A / F 60), F / B correction coefficient α, fuel injection amount, The air-fuel ratio learning value is shown. The F / B correction coefficient α in FIG. 7 is a coefficient corresponding to the correction coefficient α described in FIG. 4 and is a function of the stoichiometric deviation amount ΔA / F.

  In the example of the timing chart of FIG. 7, the value of the smoothing coefficient K is set to a smaller value, and K = 32. In order to confirm the controllability of the base fuel injection amount TAU when the smoothing coefficient K is reduced, the air-fuel ratio learning value is intentionally changed at time t11 and time t12. That is, the air-fuel ratio learning value is changed to the lean side by 0.05 (5%) at time 11 and the air-fuel ratio learning value is changed to the rich side by 0.05 (5%) at time t12. Yes. Thus, immediately after the air-fuel ratio learning value is changed to the lean side at time t11, the base fuel injection amount TAU changes to the lean side, and immediately after the air-fuel ratio learning value is changed to the rich side at time t12, The fuel injection amount TAU fluctuates to the rich side.

  As shown in FIG. 7, when the base fuel injection amount TAU changes to the lean side at time t11, the A / F output 50 and the reduced A / F output 52 change to the lean side and are calculated from the reduced A / F output 52. The annealing A / F output 55 also changes to the lean side.

  When the annealing A / F output 55 fluctuates to the lean side, the deviation ΔA / F between the annealing A / F output 55 and the target A / F output 60 increases, and the value of ΔA / F is increased as shown in FIG. Accordingly, the value of the correction coefficient α is set to a value larger than 1. Accordingly, by multiplying the correction coefficient α by the base fuel injection amount TAU, the base fuel injection amount TAU is corrected to the stoichiometric side based on the correction coefficient α.

  Similarly, when the base fuel injection amount TAU changes to the rich side at time t12, the A / F output 50 and the reduced A / F output 52 change to the rich side, and the annealing A calculated from the reduced A / F output 52 is calculated. / F output 55 fluctuates to the rich side.

  When the annealing A / F output 55 fluctuates to the rich side, the deviation ΔA / F between the annealing A / F output 55 and the target A / F output 60 increases, and the value of ΔA / F is increased as shown in FIG. Accordingly, the value of the correction coefficient α is set to a value smaller than 1. Accordingly, by multiplying the correction coefficient α by the base fuel injection amount TAU, the base fuel injection amount TAU is corrected to the stoichiometric side based on the correction coefficient α.

  As shown in FIG. 7, even when the smoothing coefficient K is reduced, the A / F output 50 varies from two to three cycles from time t11 and time t12 when the air-fuel ratio learning value is changed by 5%. After elapses, the base fuel injection amount TAU converges to stoichiometry. Therefore, according to the method of the second embodiment, the base fuel injection amount TAU can be converged to a desired value in a short time by obtaining the smoothed A / F output 55 from the reduced A / F output 52. is there.

  Next, processing for correcting the base fuel injection amount TAU in Embodiment 2 will be described based on the flowchart of FIG. First, in step S21, it is determined whether or not an active control condition is satisfied. Here, the case where the active control condition is satisfied is the case where the load condition is small such as during constant speed operation, the case where the air-fuel ratio sensor 35 has reached the active state, or the case where the water temperature has reached an appropriate temperature. When the catalyst temperature has reached an appropriate temperature, etc. If the active control condition is satisfied, the process proceeds to step S22. If the active control condition is not satisfied, the process waits in step S21.

In step S22, a base fuel injection amount TAU is calculated. The base fuel injection amount TAU is a function of the intake air amount Ga. Here, the base fuel injection amount TAU is calculated from the current intake air amount Ga and the theoretical air-fuel ratio. In the next step S23, the base fuel injection amount TAU is multiplied by a correction coefficient α to calculate a correction value TAU _{correction value} for the base fuel injection amount TAU. As will be described later, the correction coefficient α is a function of the stoichiometric deviation amount ΔA / F, and the initial value of α is set to 1, for example.

In the next step S24, an active injection amount TAU _A is calculated. Here, the active injection amount TAU _A is calculated by adding or subtracting the fuel injection amount ΔTau at a constant ratio (= s) of the TAU _{correction value} to the TAU _{correction value} . That is, TAU _A = TAU _{correction value} ± s × TAU _{correction value} is calculated to calculate rich side and lean side TAU _A , respectively.

In the next step S25, air-fuel ratio active control is performed with the active injection amount TAU _A , and the fuel injection amount is increased or decreased in a predetermined cycle. In the next step S26, the A / F output 50 obtained from the air-fuel ratio sensor 35 at this time is detected. In the next step S27, the locus length of the A / F output 50 detected in step S26 is obtained.

  In the next step S28, a reduced A / F output 52 is calculated from the A / F output 50 detected in step S26. In the next step S29, the reduced A / F output 52 calculated in step S28 is subjected to an annealing process to obtain an annealing A / F output 55. In the next step S30, the difference between the smoothed A / F output 55 and the target A / F output 60 is taken to calculate the stoichiometric deviation amount ΔA / F.

  In the next step S31, it is determined whether or not the stoichiometric deviation amount ΔA / F is equal to or smaller than a predetermined threshold value TH. That is, here, it is determined whether or not ΔA / F ≦ TH. When ΔA / F ≦ TH, since the stoichiometric deviation amount ΔA / F is within the allowable range, it is not necessary to correct the base fuel injection amount TAU. Accordingly, in this case, the process proceeds to step S32, and the value of the correction coefficient α is initialized (α = 1).

  On the other hand, if ΔA / F> TH in step S31, the stoichiometric deviation amount ΔA / F exceeds the allowable range, so the base fuel injection amount TAU needs to be corrected. In this case, the process proceeds to step S33, and a correction coefficient α corresponding to the stoichiometric deviation amount ΔA / F is obtained. At this time, the correction coefficient α is obtained from a map that defines the relationship between ΔA / F and the correction coefficient α. Alternatively, the correction coefficient α may be calculated by multiplying ΔA / F by a predetermined gain G. After step S33, the process returns to step S23, and the processes after step S23 are performed again. At this time, since the value of the correction coefficient α is set to a value corresponding to the stoichiometric deviation amount ΔA / F in step S23, the base fuel injection amount TAU can be corrected according to the stoichiometric deviation amount ΔA / F. It becomes.

  After the process of FIG. 8 is completed, the process of determining an abnormality of the air-fuel ratio sensor 35 is performed based on the flowchart of FIG.

  As described above, according to the second embodiment, after the A / F output 50 is reduced to obtain the reduced A / F output 52, the smoothing process is performed on the reduced A / F output 52. Therefore, the fluctuation of the annealing A / F output 55 can be suppressed. Therefore, it is possible to suppress the fluctuation of the deviation (stoichiometric deviation amount ΔA / F) between the annealing A / F output 55 and the target A / F 60 and to improve the controllability of the feedback amount to the base fuel injection amount TAU. It becomes.

  Further, since the value of the smoothing coefficient K can be set to a smaller value, the time until the smoothed A / F output 55 converges to a constant value can be shortened. In addition, the time delay of the A / F output 55 can be minimized. Therefore, the controllability of the base fuel injection amount TAU can be improved with the smoothing coefficient K being reduced, and the base fuel injection amount TAU can reach the target A / F 60 in a short time.

  In the second embodiment, the smoothing deviation amount ΔA / F is calculated by obtaining the smoothed A / F output 55 from the reduced A / F output 52. However, as described in the first embodiment, the reduced A / F output is calculated. An average value of the peak value on the rich side and the peak value on the lean side of the output 52 may be obtained, and the deviation between the average value and the target A / F 60 may be used as the stoichiometric deviation amount ΔA / F.

  Further, after the smoothed A / F output 55 is obtained directly from the A / F output 50 by the method of the first embodiment, the smoothed A / F output 55 may be reduced. Even with this method, fluctuations in the reduced smoothed A / F output can be minimized, and the controllability of the base fuel injection amount TAU can be improved.

It is a schematic diagram for demonstrating the abnormality detection apparatus of the air fuel ratio sensor concerning each embodiment of this invention, and its periphery structure. It is a timing chart which shows each output at the time of performing air-fuel ratio active control by open loop control. 6 is a timing chart showing outputs when air-fuel ratio active control is performed while correcting a base fuel injection amount. 5 is a flowchart showing a process of correcting a base fuel injection amount TAU in the abnormality detection apparatus according to the first embodiment of the present invention. 4 is a flowchart showing a process for determining an abnormality of an air-fuel ratio sensor in the abnormality detection device according to the first exemplary embodiment of the present invention. In Embodiment 2 of this invention, it is a timing chart which shows A / F output, annealing A / F output, reduction | restoration A / F output, and target A / F. 7 is a timing chart showing outputs when air-fuel ratio active control is performed while correcting a base fuel injection amount TAU in Embodiment 2 of the present invention. 7 is a flowchart illustrating a process of correcting a base fuel injection amount TAU in the abnormality detection device according to the second exemplary embodiment of the present invention.

Explanation of symbols

30 Fuel Injection Valve 35 A / F Sensor 40 ECU

Claims (6)

Fuel injection amount increasing / decreasing means for periodically increasing / decreasing the fuel injection amount based on the base fuel injection amount by open loop control;
An air-fuel ratio sensor for detecting the air-fuel ratio;
Deviation acquisition means for obtaining a deviation between the center value of the output of the air-fuel ratio sensor and the target value, which fluctuates according to increase / decrease of the fuel injection amount by the fuel injection amount increase / decrease means,
Base injection amount control means for controlling the base fuel injection amount based on the deviation;
An abnormality detecting means for detecting an abnormality of the air-fuel ratio sensor based on the output of the air-fuel ratio sensor;
An abnormality detection device for an air-fuel ratio sensor comprising:   The abnormality detection device for an air-fuel ratio sensor according to claim 1, wherein the base injection amount control means controls the deviation to approach zero.   The air-fuel ratio according to claim 1 or 2, wherein the deviation acquisition means includes means for calculating a smoothed output of the output of the air-fuel ratio sensor, and the deviation is obtained with the smoothed output as the center value. Sensor abnormality detection device.   The deviation acquisition means includes means for calculating an average value of a peak value on a rich side and a peak value on a lean side of the air-fuel ratio sensor, and the deviation is obtained using the average value as the central value. Item 3. An air-fuel ratio sensor abnormality detection device according to Item 1 or 2.   The abnormality detection apparatus for an air-fuel ratio sensor according to any one of claims 1 to 4, wherein the target value is an output of the air-fuel ratio sensor corresponding to a theoretical air-fuel ratio.   The air-fuel ratio according to any one of claims 1 to 5, wherein the deviation acquisition means obtains a center value of the output of the air-fuel ratio sensor using an output of a predetermined ratio of the output of the air-fuel ratio sensor. Sensor abnormality detection device.

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