JP5565096B2 - Output characteristic measuring method and output characteristic measuring apparatus for air-fuel ratio detecting means - Google Patents

Description

  The present invention relates to a method and apparatus for measuring the output characteristics of air-fuel ratio detection means for detecting the mixing ratio of air and fuel supplied to a combustion chamber of an engine.

  In an engine for an automobile or the like, in order to reduce fuel consumption and reduce the amount of harmful substances contained in exhaust gas, the mixing ratio (air-fuel ratio) of air and fuel supplied to the combustion chamber of the engine is reduced. It is controlled so as to be within a theoretical air fuel ratio or an appropriate range in the vicinity thereof. Specifically, the air-fuel ratio is based on the output value of the air-fuel ratio sensor provided in the exhaust passage. When the residual oxygen concentration in the exhaust gas is high (lean), the fuel injection amount is increased and the residual oxygen concentration is low. When (rich), the fuel injection amount is reduced and feedback control is performed to the theoretical air-fuel ratio or an appropriate range in the vicinity thereof.

  However, in the case of a multi-cylinder engine, since the air-fuel ratio sensor is installed in an exhaust collecting portion where the exhaust passages of a plurality of cylinders merge, even if the output value of the air-fuel ratio sensor is within the appropriate range, Some cylinders may have an air-fuel ratio abnormality. In recent years, it has been required to be able to determine an air-fuel ratio abnormality even in such a case.

  Patent Document 1 discloses a technique for making it possible to determine an air-fuel ratio abnormality even when an air-fuel ratio abnormality has occurred in only a specific part of the cylinders.

  Specifically, in the technique of Patent Document 1, when determining the air-fuel ratio abnormality, the absolute value of the change rate of the output value of the air-fuel ratio sensor is integrated for a predetermined time, and this integrated value is used for the determination. More specifically, when no air-fuel ratio abnormality has occurred in any of the cylinders, the output value of the air-fuel ratio sensor does not fluctuate greatly, so the integrated value is relatively small. When an air-fuel ratio abnormality occurs, the change in the output of the air-fuel ratio sensor increases when exhausting from this cylinder (abnormal cylinder), and the integrated value increases. Therefore, whether or not an air-fuel ratio abnormality has occurred in any of the cylinders can be determined based on whether or not the integrated value is greater than or equal to a predetermined value.

  Further, in order to detect an air-fuel ratio abnormality for a specific part of cylinders by the method as described above, it is necessary that the air-fuel ratio sensor can accurately detect the air-fuel ratio. There are variations in output characteristics due to degradation of the manufacturing process and manufacturing variations. Therefore, it is necessary to measure the output characteristics of the air-fuel ratio sensor in advance and correct the output value of the sensor according to the measurement result, and then determine whether there is an abnormality in the air-fuel ratio for a specific part of the cylinders. .

  The output characteristics of the air-fuel ratio sensor are measured by measuring changes in sensor output when the air-fuel ratio of all cylinders is intentionally changed to rich or lean, specifically, the amount of change in the output value, responsiveness, etc. Is done. In Patent Document 2, as an output characteristic of the air-fuel ratio sensor, a dead time when the air-fuel ratio is intentionally changed (a time until the sensor output starts changing after the air-fuel ratio is changed) is measured. Technology is disclosed.

JP 2008-121533 A JP 2006-9624 A

  By the way, the feedback control of the air-fuel ratio based on the output value of the air-fuel ratio sensor is performed uniformly for all the cylinders. Therefore, the air-fuel ratio sensor only needs to be able to respond to uniform air-fuel ratio changes for all the cylinders. This air-fuel ratio change occurs in a relatively long cycle, and the output change of the air-fuel ratio sensor at this time shows a relatively low-frequency waveform.

  FIG. 16 shows a specific example of measured values of output characteristics of the air-fuel ratio sensor with respect to low frequency (1 Hz) input. In FIG. 16, the horizontal axis indicates the time required for the output value of the sensor to reach 63% of the input value after the input of a predetermined value signal to the air-fuel ratio sensor (hereinafter referred to as “time constant”). The vertical axis represents the ratio (Y / X) of the output value Y to the input value X when a 1 Hz on / off signal is input to the air-fuel ratio sensor. Looking at the measured values in FIG. 16, it is easy to obtain an output value that is relatively close to the input value regardless of the time constant of the air-fuel ratio sensor, that is, the response performance of the sensor, for a low-frequency input. I understand.

  However, when an air-fuel ratio abnormality has occurred for a specific part of the cylinders, the residual oxygen concentration in the exhaust gas in the exhaust gas collection portion changes greatly each time exhaust from the abnormal cylinder is performed, This large concentration change occurs in a very short cycle. Therefore, if the output of the air-fuel ratio sensor can follow this concentration change, the output change shows a high-frequency waveform. For example, in a four-cylinder engine, when the rotational speed is 3000 rpm, if an air-fuel ratio abnormality has occurred in any one of the cylinders, the output change of the air-fuel ratio sensor shows a waveform of 25 Hz.

  FIG. 17 shows a specific example of measured values of the output characteristics of the air-fuel ratio sensor with respect to high frequency (25 Hz) input. In FIG. 17, the horizontal axis indicates the time constant of the air-fuel ratio sensor similar to that in FIG. 16, and the vertical axis indicates the ratio of the output value Y to the input value X when a 25 Hz on / off signal is input to the air-fuel ratio sensor. (Y / X) is shown. Referring to the measured values in FIG. 17, the output value is higher than the input value for a high-frequency input even when the time constant of the air-fuel ratio sensor is relatively small, that is, when the response performance of the sensor is relatively high. It can be seen that the output value becomes much lower as the time constant of the sensor increases.

  That is, as a result of measuring the output characteristics by the conventional method, even if the sensor has been confirmed to have sufficient response performance to perform the feedback control of the air-fuel ratio, the output of the sensor has a high frequency as described above. May not be able to follow changes in input. In this case, even when a high-frequency input change occurs due to an air-fuel ratio abnormality in a specific part of the cylinder, the output change of the sensor shows a waveform similar to that in the normal state. The occurrence of an air-fuel ratio abnormality cannot be accurately detected.

Therefore, the present invention enables an air-fuel ratio to be accurately determined when an air-fuel ratio abnormality has occurred only in a specific part of the cylinders, and to accurately perform air-fuel ratio feedback control. It is an object of the present invention to provide an output characteristic measuring method and an output characteristic measuring apparatus for a detecting means.

  In order to solve the above problems, the output characteristic measuring method and output characteristic measuring apparatus of the air-fuel ratio detecting means according to the present invention are configured as follows.

First, the output characteristic measuring method of the air-fuel ratio detecting means according to the invention described in claim 1 of the present application is:
A method for measuring output characteristics of air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture in a combustion chamber of the engine based on an oxygen concentration in exhaust gas of a multi-cylinder engine,
A specific cylinder air-fuel ratio changing step of changing the air-fuel ratio for a specific cylinder of the engine under a predetermined condition;
A first output characteristic measuring step of measuring a high frequency output characteristic of the air-fuel ratio detecting means when the air-fuel ratio of the specific one cylinder is changed in the specific cylinder air-fuel ratio changing step;
Based on the high-frequency output characteristic measured in the first output characteristic measurement step, the first required for correcting the output value of the air-fuel ratio detecting means for detecting the air-fuel ratio difference between the cylinders of the engine. A first correction value calculating step for calculating a correction value;
A first output value correction step of correcting the output value of the air-fuel ratio detection means based on the first correction value calculated in the first correction value calculation step;
A first determination step of determining whether there is an abnormality in the air-fuel ratio difference between the cylinders based on the corrected output value obtained by the correction in the first output value correction step;
An all-cylinder air-fuel ratio changing step for uniformly changing the air-fuel ratio for all cylinders of the engine under predetermined conditions;
A second output characteristic measuring step of measuring a low frequency output characteristic of the air-fuel ratio detecting means when the air-fuel ratio of all cylinders is uniformly changed in the all-cylinder air-fuel ratio changing step;
Based on the low frequency output characteristic measured in the second output characteristic measurement step, the second required for correcting the output value of the air / fuel ratio detection means for feedback control of the air / fuel ratio for all cylinders of the engine. A second correction value calculating step for calculating the correction value of
A second output value correction step of correcting the output value of the air-fuel ratio detection means based on the second correction value calculated in the second correction value calculation step;
An air-fuel ratio control step of feedback-controlling the air-fuel ratio for all the cylinders of the engine based on the corrected output value obtained by the correction in the second output value correction step .

Furthermore, the invention of claim 2 is the invention of claim 1 ,
The first determination step is characterized by determining the presence or absence of abnormality based on a comparison between a determination parameter calculated based on the corrected output value and a predetermined threshold value.

Furthermore, the invention according to claim 3 is the invention according to claim 1 or 2 ,
In the first correction value calculation step, the median value of the values relating to the high-frequency output characteristics of the plurality of air-fuel ratio detection means at the time of shipment measured by the same method as in the first output characteristic measurement step; The first correction value is calculated based on a difference from the value related to the high-frequency output characteristic measured in the output characteristic measurement step.

The invention according to claim 4 is the invention according to claim 2 or claim 3 , wherein
Based on the high-frequency output characteristic measured in the first output characteristic measurement step, the air-fuel ratio detection means exhibits a response higher than a predetermined value that can be used to determine whether there is an abnormality in the air-fuel ratio difference between the cylinders. have a second determination step of determining whether the whether one,
The first determination step is executed when it is determined in the second determination step that the air-fuel ratio detection means has a response higher than a predetermined value .

Furthermore, the invention according to claim 5 is the invention according to any one of claims 1 to 4 ,
Based on the low-frequency output characteristics measured in the previous SL second output characteristic measuring step, a third determination step of determining whether or not normally capable of executing the feedback control using the air-fuel ratio detecting means It is characterized by having.

The invention according to claim 6 is the invention according to any one of claims 1 to 5 ,
In the first output characteristic measuring step, the maximum value of the change amount of the output value of the air-fuel ratio detecting means accompanying the change of the air-fuel ratio of the specific cylinder in the specific cylinder air-fuel ratio changing step, or the change amount It is characterized by measuring at least one of the time required for the to reach a predetermined amount.

Further, the invention according to claim 7 is the invention according to any one of claims 1 to 6 ,
The specific cylinder air-fuel ratio changing step is performed a plurality of times while varying the amount of change in the air-fuel ratio for the specific cylinder.
In the first output characteristic measuring step, a measured value showing higher responsiveness among a plurality of measured values obtained corresponding to the plurality of specific cylinder air-fuel ratio changing steps is employed.

The invention according to claim 8 is the invention according to any one of claims 1 to 7 ,
The first output characteristic measurement step is performed while switching the specific one cylinder that is the target of the specific cylinder air-fuel ratio changing step.

The invention according to claim 9 is the invention according to any one of claims 1 to 8 ,
When the air-fuel ratio is changed for the specific cylinder in the specific cylinder air-fuel ratio changing step, the air-fuel ratio is changed for the remaining cylinders so as to cancel out the air-fuel ratio change.

An output characteristic measuring device for an air-fuel ratio detecting means according to the invention of claim 10 comprises:
An apparatus for measuring output characteristics of air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture in a combustion chamber of the engine based on an oxygen concentration in exhaust gas of a multi-cylinder engine,
Air-fuel ratio adjusting means for adjusting the air-fuel ratio;
The high-frequency output characteristics of the air-fuel ratio detection means when the air-fuel ratio is changed by the air-fuel ratio adjustment means for a specific cylinder of the engine under a predetermined condition, and the cylinders of the engine under a predetermined condition Output characteristic measuring means for measuring the low frequency output characteristics of the air-fuel ratio detecting means when the air-fuel ratio is uniformly changed by the air-fuel ratio adjusting means;
Based on the high-frequency output characteristic measured by the output characteristic measuring means, a first correction value necessary for correcting the output value of the air-fuel ratio detecting means performed for detecting the air-fuel ratio difference between the cylinders of the engine is obtained. The second required for correction of the output value of the air-fuel ratio detecting means performed for feedback control of the air-fuel ratio for all the cylinders of the engine based on the low frequency output characteristics calculated and measured by the output characteristic measuring means Correction value calculating means for calculating the correction value of
Output value correction means for correcting the output value of the air-fuel ratio detection means based on the first correction value or the second correction value calculated by the correction value calculation means;
An air-fuel ratio abnormality determining means for determining presence / absence of abnormality in the air-fuel ratio difference between the cylinders based on a corrected output value obtained by correction based on the first correction value by the output value correcting means;
Feedback control means for feedback-controlling the air-fuel ratio for all cylinders of the engine based on the corrected output value obtained by the correction based on the second correction value by the output value correcting means .

First, according to the first aspect of the present invention, the air-fuel ratio is intentionally changed for only one specific cylinder in the specific cylinder air-fuel ratio changing step. Since the output characteristic (high frequency output characteristic) of the fuel ratio detecting means is measured, whether or not the air fuel ratio detecting means can follow the high frequency input change by this measurement, that is, the air fuel ratio detecting means is high frequency. It can be determined whether or not the output change can be indicated. Therefore, if the air-fuel ratio detection means that has been confirmed to show a high-frequency output change by this measurement, the first value necessary for correction is calculated based on the high-frequency output characteristics measured as described above. The output value of the air-fuel ratio detecting means is corrected based on the first correction value, so that the presence or absence of abnormality in the air-fuel ratio difference between the cylinders can be accurately determined based on the value obtained by the correction. can do. Further, since the output characteristic (low frequency output characteristic) of the air / fuel ratio detecting means when the air / fuel ratio is uniformly changed for all cylinders, that is, when a low frequency input change is given, the high frequency output characteristic and Can confirm different output characteristics. A second correction value is calculated based on the low-frequency output characteristics, and the output value of the air-fuel ratio detection unit is corrected based on the second correction value, so that the correction output value obtained by this correction is used. Thus, the air-fuel ratio feedback control can be performed with high accuracy.

Furthermore, according to the second aspect of the present invention, it is possible to accurately determine whether there is an abnormality in the air-fuel ratio difference between the cylinders based on a comparison between the determination parameter and a predetermined threshold value .

According to the third aspect of the present invention , the first correction value is a center of a value related to the high-frequency output characteristics measured as described above and the high-frequency output characteristics of a plurality of air-fuel ratio detection means at the time of shipment. because it is calculated based on the difference between the value, by using the first correction value, it is possible to correct the output value of the air-fuel ratio detecting means so as to cancel the variation of the high-frequency output characteristics.

Furthermore, according to the fourth aspect of the present invention, the air-fuel ratio detection means can be used to determine whether there is an abnormality in the air-fuel ratio difference between the cylinders based on the high-frequency output characteristics measured as described above. Therefore, it is possible to accurately determine whether there is an abnormality in the air-fuel ratio difference between the cylinders by using an air-fuel ratio detecting unit having sufficient response performance.

Further, according to the fifth aspect of the present invention , based on the low frequency output characteristics measured as described above, whether or not the air / fuel ratio feedback control can be normally executed using the air / fuel ratio detecting means. Can be accurately determined.

According to the sixth aspect of the present invention, the maximum value of the change amount of the output value of the air-fuel ratio detection means accompanying the change of the air-fuel ratio for a specific cylinder as described above, or the change amount Since at least one of the time required until the value reaches the predetermined amount is measured as the high frequency output characteristic, the invention according to any one of claims 1 to 5 can be effectively realized.

According to the seventh aspect of the present invention, the specific cylinder air-fuel ratio changing step is performed a plurality of times while varying the amount of change in the air-fuel ratio, and a plurality of measured values for the high-frequency output characteristics obtained thereby are obtained. Among these, since the measured value showing higher responsiveness is adopted as the value of the high frequency output characteristic, the measurement of the high frequency output characteristic can be performed more appropriately.

According to the eighth aspect of the present invention, since the high frequency output characteristic is measured while the specific cylinder that is the target of the specific cylinder air-fuel ratio changing process is switched, the air-fuel ratio of any one of the cylinders is measured. When an abnormality occurs, in the specific cylinder air-fuel ratio changing step, it can be avoided that the air-fuel ratio change is executed only for the abnormal cylinder, and the air-fuel ratio change is executed reliably for a normal cylinder. Properties can be measured appropriately.

Furthermore, according to the ninth aspect of the invention, when the air-fuel ratio is changed for one specific cylinder in the specific cylinder air-fuel ratio changing step, the air-fuel ratio is set for the remaining cylinders so as to cancel the air-fuel ratio change. Therefore, even if the specific cylinder air-fuel ratio changing step is executed, it is possible to avoid the entire air-fuel ratio control from being biased to the lean side or the rich side, and the influence on the exhaust gas can be reduced.

According to the tenth aspect of the present invention, when the air-fuel ratio is intentionally changed only for a specific cylinder, that is, when a high-frequency input change is given, the output characteristics (high-frequency) of the air-fuel ratio detection means Output characteristic), the measurement can determine whether or not the air-fuel ratio detection means can follow a high-frequency input change, that is, the air-fuel ratio detection means can show a high-frequency output change. It can be determined whether or not there is. Therefore, if the air-fuel ratio detection means that has been confirmed to show a high-frequency output change by this measurement, the first value necessary for correction is calculated based on the high-frequency output characteristics measured as described above. The output value of the air-fuel ratio detecting means is corrected based on the first correction value, so that the presence or absence of abnormality in the air-fuel ratio difference between the cylinders can be accurately determined based on the value obtained by the correction. can do. Further, since the output characteristic (low frequency output characteristic) of the air / fuel ratio detecting means when the air / fuel ratio is uniformly changed for all cylinders, that is, when a low frequency input change is given, the high frequency output characteristic and Can confirm different output characteristics. A second correction value is calculated based on the low-frequency output characteristics, and the output value of the air-fuel ratio detection unit is corrected based on the second correction value, so that the correction output value obtained by this correction is used. Thus, the air-fuel ratio feedback control can be performed with high accuracy.

It is a schematic block diagram of the control system of a vehicle engine. It is a figure which shows the exhaust passage of an engine. It is a figure which shows the relationship between an air fuel ratio and the purification rate of a three way catalyst. It is a flowchart which shows the main routine regarding air fuel ratio control. It is a flowchart which shows the subroutine of measurement control of a low frequency output characteristic. It is a figure which shows the specific example of control which increases / decreases a fuel injection quantity intentionally in measurement control of a low frequency output characteristic. It is a figure which shows the specific example of a low frequency output characteristic. It is a flowchart which shows the flow of each process regarding the feedback control of an air fuel ratio. It is the figure which compared the time at the time of normal with respect to transition of the output value of an air fuel ratio sensor, and the time of the air fuel ratio abnormality about a specific part cylinder. It is a flowchart which shows the routine performed before the determination of the air fuel ratio abnormality about a specific one part cylinder. It is a flowchart which shows the subroutine of the measurement control of a high frequency output characteristic. It is a figure which shows the specific example of the control which increases / decreases a fuel injection quantity intentionally in measurement control of a high frequency output characteristic. It is a figure which shows the specific example of a high frequency output characteristic. It is a flowchart which shows the flow of each process for correct | amending the output value of an air fuel ratio sensor before the determination of the air fuel ratio abnormality about a specific cylinder. It is a flowchart which shows the flow of each process of determination control of the air fuel ratio abnormality about a specific one part cylinder. It is a figure which shows the specific example of the measured value of the output characteristic of the air fuel ratio sensor with respect to a low frequency (1 Hz) input. It is a figure which shows the specific example of the measured value of the output characteristic of the air fuel ratio sensor with respect to the input of a high frequency (25Hz).

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration diagram of a control system for a vehicle engine according to the present embodiment.

  The engine 1 is an in-line four-cylinder spark ignition direct injection gasoline engine, and various operations of the engine 1 are controlled by a PCM 21 including a CPU, a ROM, a RAM, an I / O interface circuit, and the like. In FIG. 1, only one of the four cylinders is shown, and the remaining three cylinders are not shown.

  The engine 1 includes a cylinder block 3 and a cylinder head 5 fixed to the upper portion of the cylinder block 3. The cylinder block 3 has a cylinder 13 for each cylinder. In each cylinder 13, a reciprocable piston 7 is fitted, and above the piston 7, a top surface of the piston 7, an inner wall surface of the cylinder 13, and a pent roof type bottom surface of the cylinder head 5. A combustion chamber 11 surrounded by is formed. The piston 7 is connected to a crankshaft (not shown) disposed in a crankcase below the piston 7 via a connecting rod 17.

  The cylinder block 3 is provided with an engine water temperature sensor 23 for detecting the temperature of cooling water flowing in a water jacket (not shown) and an engine oil temperature sensor 33 for detecting the temperature of the engine oil. .

  On the other hand, the cylinder head 5 is provided with a spark plug 9 for each cylinder 13. Each spark plug 9 is disposed so that its tip electrode faces the inside of the combustion chamber 11, and is connected to an ignition circuit 19 provided at the upper part of the cylinder head 5, for example.

  The ignition circuit 19 is configured to flow an ignition discharge current based on a control signal transmitted from the PCM 21 to cause the spark plug 9 to perform an ignition discharge. The ignition circuit 19 includes a capacitor 19a that is charged by ignition discharge of the spark plug 9, and an ion current detection circuit 19b that detects the current that flows when the charge of the capacitor 19a is discharged as an ion current. The detection signal of the ion current detected by the current detection circuit 19b is output to the PCM 21.

  Further, two intake ports 15 and two exhaust ports 25 communicating with the combustion chamber 11 are formed in the cylinder head 5 for each combustion chamber 11. An intake valve 35 is provided at the port opening of the intake port 15, and an exhaust valve 45 is provided at the port opening of the exhaust port 25. The intake valve 35 and the exhaust valve 45 are electromagnetic VVT (electromagnetic variable). The valve timing mechanism) 35a, 45a can be opened and closed independently at a predetermined timing. In addition, the intake valve 35 and the exhaust valve 45 can change the opening / closing operation timing to the advance side and the retard side by the electromagnetic VVTs 35 a and 45 a, thereby changing the overlap period and remaining in the combustion chamber 11. It is possible to change the amount of burnt gas.

  Furthermore, an intake passage 55 is provided in each cylinder so as to communicate with the intake port 15, and an exhaust passage 65 is provided so as to communicate with the exhaust port 25. The intake passage 55 and the exhaust passage 65 are connected to each other via an EGR passage 85. An electric EGR valve 51 provided in the EGR passage 85 and having an adjustable opening degree allows one of exhaust gases in the exhaust passage 65 to be connected. The part is returned to the intake passage 55.

  In addition, in the intake passage 55, the air cleaner 75, the intake air temperature sensor 43, the air flow sensor 29 for detecting the intake flow rate, the throttle valve 41 for restricting the intake passage 55, and the strength of the intake air flow in the combustion chamber 11 are sequentially provided from the upstream side. A TSCV (tumble swirl control valve) 31 to be adjusted and an injector (fuel injection valve) 39 for direct injection of gasoline for directly injecting and supplying supplied gasoline into the combustion chamber 11 are provided.

  On the other hand, as shown in FIG. 2, exhaust passages 65 (65a to 65d) extending from the four cylinders # 1 to # 4, respectively, are provided so as to be gathered by an exhaust gathering portion (egg manifold gathering portion) 95. An exhaust collecting passage 66 is formed from the collecting portion 95 toward the downstream side.

  The exhaust collecting passage 66 has an air-fuel ratio sensor 47 for detecting the air-fuel ratio of the air-fuel mixture in the combustion chamber 11 based on the oxygen concentration in the exhaust gas of the engine 1, and a catalytic converter 49 for purifying the exhaust gas. Is arranged. As the air-fuel ratio sensor 47, for example, a linear oxygen sensor that continuously detects the oxygen concentration is used. Further, the air-fuel ratio sensor 47 is disposed upstream of the catalytic converter 49 in the exhaust collecting passage 66. On the other hand, as the catalytic converter 49, for example, a three-way catalyst capable of simultaneously purifying three components of HC, CO, and NOx can be used.

  Returning to FIG. 1, in addition to the engine water temperature sensor 23, the airflow sensor 29, and the air-fuel ratio sensor 47 described above, the PCM 21 detects a throttle opening sensor 53 that detects the throttle opening, and an engine rotation that detects the engine speed. The number sensors 57 are electrically connected, and output signals of these sensors are inputted. The PCM 21 is electrically connected to various devices related to the operation of the engine 11, and transmits various control operations of the engine 1 to the various devices by transmitting control signals based on signals received from various sensors. Is configured to control.

  The PCM 21 includes an output characteristic measuring unit 21a that measures a later-described high-frequency output characteristic or low-frequency output characteristic of the air-fuel ratio sensor 47, an output value correction unit 21b that corrects an output value of the air-fuel ratio sensor 47, and the output value correction. A correction value calculation unit 21c that calculates a value necessary for correction by the unit 21b, and an air-fuel ratio abnormality determination unit that determines the presence or absence of an air-fuel ratio abnormality (abnormality about an air-fuel ratio difference between cylinders) for a specific part of cylinders 21d, a condition determination unit 21e that determines whether or not a condition for executing the measurement by the output characteristic measurement unit 21a or the determination by the air-fuel ratio abnormality determination unit 21d is satisfied, and the air-fuel ratio feedback based on the output of the air-fuel ratio sensor 47 And a feedback control unit 21f for controlling.

[Air-fuel ratio feedback control]
FIG. 3 shows the relationship between the air-fuel ratio and the exhaust purification rate by the catalytic converter 49. As shown in FIG. 3, when the air-fuel ratio is the stoichiometric air-fuel ratio (λ = 1) or an appropriate range in the vicinity thereof (the hatched portion in FIG. 3), all of HC, CO, and NOx show a high purification rate. When the air-fuel ratio is richer than the appropriate range, HC and CO are easily discharged without being purified, and when the air-fuel ratio is leaner than the appropriate range, the amount of NOx discharged increases. The appropriate range refers to, for example, a range from about 0.25 rich air-fuel ratio to about 0.25 lean air-fuel ratio with respect to the stoichiometric air-fuel ratio.

  Therefore, in order to suppress the discharge amount of harmful substances such as HC, CO, NOx, the feedback control unit 21f performs feedback control based on the output of the air-fuel ratio sensor 47 so that the air-fuel ratio falls within the appropriate range.

  As shown in the flowchart of FIG. 4, the air-fuel ratio feedback control (step SA3) is performed by measuring the low-frequency output characteristic of the air-fuel ratio sensor 47 (step SA1), the output characteristic measured at step SA1, and the PCM 21. This is performed after the output correction value CV1 is calculated (step SA2) based on the first reference characteristic stored in advance. The “low frequency output characteristics” as used in this specification means that the frequency is lower than that when the air-fuel ratio is intentionally changed for all cylinders, that is, when the air-fuel ratio is changed for a specific cylinder. It is assumed that the output characteristic of the air-fuel ratio sensor 47 is given.

  With reference to the flowchart shown in FIG. 5, a subroutine for measuring the low frequency output characteristic (step SA1 in FIG. 4) will be described.

  First, in step SB1, the engine speed Ne1 detected by the engine speed sensor 57, the throttle opening Th1 detected by the throttle opening sensor 53, the intake air flow rate A1 detected by the airflow sensor 29, and the engine water temperature The engine water temperature Tw1 detected by the sensor 23 is read by the condition determination unit 21e, and the process proceeds to Step SB2.

  In step SB2, the condition determination unit 21e determines whether or not an execution condition for output characteristic measurement of the air-fuel ratio sensor 47 is satisfied based on the information read in step SB1. Specifically, it is determined whether or not the operation state has a relatively small influence on the running performance even if the air-fuel ratio is changed to rich or lean. More specifically, for example, the engine water temperature Tw1 is warmed up. It is determined whether or not the temperature is equal to or higher than a predetermined temperature indicating completion, and / or whether or not the fluctuation amount of the engine speed Ne1, the intake charging efficiency and / or the throttle opening degree Th1 is sufficiently small and stable. .

  If it is determined in step SB2 that the output characteristic measurement execution condition is not satisfied, the process returns to step SB1, and if it is determined that the output characteristic measurement execution condition is satisfied, the process proceeds to step SB3.

  In step SB3, the output characteristic measuring unit 21a controls the air-fuel ratio to be uniformly changed for all the cylinders, thereby intentionally generating a relatively low-frequency air-fuel ratio change.

  Specifically, for example, the injector 39 of each cylinder is controlled so that the fuel injection amount is uniformly increased or decreased for all cylinders. More specifically, for example, as shown in FIG. 6, the increase in the fuel injection amount continued during the fuel injection process for four consecutive cylinders and the fuel injection process for four consecutive cylinders are continued. The reduction of the fuel injection amount is repeated alternately. In FIG. 6, reference numeral # 1 denotes a fuel injection process for the first cylinder, reference numeral # 2 denotes a fuel injection process for the second cylinder, reference numeral # 3 denotes a fuel injection process for the third cylinder, and reference numeral # 4 denotes a first fuel injection process. Each of the four cylinder fuel injection steps is shown.

  However, the increase and / or decrease in the fuel injection amount in step SB3 may be continued during the fuel injection process for five or more consecutive cylinders. Further, it is not always necessary to change the air-fuel ratio by increasing or decreasing the fuel injection amount. For example, it is conceivable to change the air-fuel ratio by increasing or decreasing the intake air amount.

  In the next step SB4, measurement of the low frequency output characteristic is executed by the output characteristic measuring unit 21a, and the process proceeds to step SB5.

  Specifically, in step SB4, the output change of the air-fuel ratio sensor 47 in a state where the air-fuel ratio is uniformly changed for all the cylinders in the process of step SB3 is monitored, and the low-frequency output characteristics of the sensor 47 are measured. . More specifically, for example, as shown in FIG. 7, a dead time t1 of output change of the sensor 47 that occurs when the air-fuel ratio is changed to the lean side, and a sensor that occurs when the air-fuel ratio is changed to the rich side At least the dead time t2 of the output change of 47, the output change rate α of the sensor 47 when the air-fuel ratio is changed to the lean side, and the output change rate β of the sensor 47 when the air-fuel ratio is changed to the rich side Either one is measured as a low frequency output characteristic. In the present specification, “dead time” refers to the time required for the output value of the sensor 47 to change after the air-fuel ratio is changed by the output characteristic measurement unit 21a, and “output change rate” It is assumed that the change amount of the output value per unit time when the output value of the sensor 47 starts to change as the air-fuel ratio is changed by the output characteristic measuring unit 21a.

  Finally, in step SB5, it is determined whether or not the measurement of the low frequency output characteristic in step SB4 has been executed a predetermined number of times. If it is determined in step SB5 that the measurement of the low frequency output characteristic has not been performed a predetermined number of times, the process returns to step SB1, and if it is determined that the measurement has been performed a predetermined number of times, the routine of FIG. 5 (step SA1 in FIG. 4) is performed. Step) ends.

  Next, calculation of the output correction value CV1 (step SA2 in FIG. 4) will be described.

  The output correction value CV1 is a value necessary for correcting the output value OV1 of the air-fuel ratio sensor 47 performed in the air-fuel ratio feedback control. More specifically, the output correction value CV1 is multiplied by the output value OV1 of the sensor 47 in the correction. It is a coefficient.

  As described above, the output correction value CV1 is calculated based on the low-frequency output characteristic measured in step SA1 in FIG. 4 (specifically, step SB4 in FIG. 5) and the first reference characteristic. The Here, the first reference characteristic is set to the median value of the low-frequency output characteristics of the plurality of air-fuel ratio sensors 47 having variations due to individual differences (deterioration and manufacturing variations). Specifically, a plurality of new air-fuel ratio sensors 47 are used as samples, and low frequency output characteristics (for example, dead time or / and output change rate) are measured for each sample as in step SA1 in FIG. The median of the measured values is set as the first reference characteristic (for example, the reference dead time or the reference output change rate).

  The output correction value CV1 is based on the map stored in advance in the PCM 21. The low frequency output characteristic measured in step SA1 in FIG. 4 (specifically, step SB4 in FIG. 5) is greater than the first reference characteristic. Is smaller than the first reference characteristic so that the output value OV1 of the sensor 47 is increased (specifically, a value greater than 1). The value is calculated to be a value that decreases OV1 (specifically, a value less than 1).

  A subroutine for air-fuel ratio feedback control (step SA3 in FIG. 4) will be described with reference to the flowchart shown in FIG.

  First, in step SC1, the low frequency output characteristic of the sensor 47 measured in step SA1 in FIG. 4 is read by the feedback control unit 21f, and the output correction value CV1 calculated in step SA2 in FIG. 4 is output as the output value correction unit 21b. The process proceeds to step SC2.

  In step SC2, the feedback control unit 21f determines whether or not the low frequency output characteristic read in step SC1 is a value that can appropriately execute the feedback control of the air-fuel ratio. Specifically, for example, whether or not a dead time as a specific value of the low frequency output characteristic is equal to or less than a predetermined value stored in the PCM 21 in advance, and / or an output change rate as a specific value of the low frequency output characteristic Is greater than or equal to a predetermined value stored in the PCM 21 in advance.

  If it is determined in step SC2 that the feedback control cannot be properly executed, the routine of FIG. 8 ends. If it is determined that the feedback control can be properly executed, the process proceeds to step SC3.

  In step SC3, the feedback controller 21f reads the output value OV1 of the air-fuel ratio sensor 47, and the process proceeds to step SC4.

  In step SC4, the output value OV1 read in step SC3 is corrected according to the low frequency output characteristic of the sensor 47 by the output value correction unit 21b. Specifically, the output value OV1 is corrected by multiplying the output value OV1 read in step SC3 by the output correction value CV1 read in step SC1.

  In the next step SC5, the feedback control unit 21f calculates the increase / decrease amount of the fuel injection amount based on the difference between the output value OV2 corrected in step SC4 and the feedback control target value TG. In step SC5, the increase / decrease amount of the fuel injection amount is calculated so as to increase as the deviation amount between the output value OV2 and the target value TG increases.

  In the following step SC6, the fuel injection amount is increased or decreased by the amount calculated in step SC5 by the feedback control unit 21f, whereby the air-fuel ratio is controlled to approach the target value TG, and the routine of FIG. finish.

  By performing such feedback control, as long as the control state is normal, the air-fuel ratio is maintained in the appropriate range, thereby reliably suppressing HC, CO, and NOx emissions.

  However, if the fuel supply pump, the air-fuel ratio sensor 47, or the injector 39 fails, the air-fuel ratio control cannot be performed normally.

  When this air-fuel ratio abnormality occurs in all cylinders, the oxygen concentration in the exhaust collecting portion 95 is always higher or lower than the normal value, so that the air-fuel ratio abnormality is easily made based on the output value of the air-fuel ratio sensor 47. Can be detected.

  On the other hand, when the air-fuel ratio abnormality occurs only in a specific part of the cylinders, the oxygen concentration in the exhaust collecting portion 95 becomes higher or lower than the normal value only when the exhaust gas from the abnormal cylinders passes. The concentration changes with a very short period. For this reason, the output of the air-fuel ratio sensor 47 may not be able to follow this change in oxygen concentration, and an air-fuel ratio abnormality for a specific part of the cylinders cannot always be detected with high accuracy. Therefore, in the present embodiment, the presence or absence of an air-fuel ratio abnormality for a specific part of the cylinders is determined by the procedure described later. This will be described in more detail below.

[Determination of air-fuel ratio abnormality for a specific cylinder]
As shown by the solid line in FIG. 9, when the air-fuel ratio is normal, that is, when no air-fuel ratio abnormality has occurred in any of the cylinders, the air-fuel ratio difference hardly occurs between the cylinders. The vicinity of the value TG changes with a relatively small amplitude. On the other hand, as shown by the broken line in FIG. 9, when an air-fuel ratio abnormality occurs between one specific cylinder and the remaining cylinder due to an air-fuel ratio abnormality occurring in one specific cylinder, Since the air-fuel ratio significantly increases or decreases every time the exhaust gas is exhausted, the output value of the air-fuel ratio sensor 47 changes with a large amplitude and shows a relatively high-frequency waveform.

  Therefore, for example, it is conceivable to determine whether or not there is an abnormality in the air-fuel ratio for a specific part of the cylinders based on whether or not the amplitude of the output value of the air-fuel ratio sensor 47 is a predetermined value or more. However, since the response of the air-fuel ratio sensor 47 has individual differences due to deterioration and manufacturing variations, even the sensor 47 that can be used for the air-fuel ratio feedback control described above has a specific part as described above. In some cases, it may not be possible to follow a high-frequency air-fuel ratio change caused by an air-fuel ratio abnormality of the cylinder. Therefore, when determining the presence or absence of an air-fuel ratio abnormality for a specific part of the cylinders based on the output value of the sensor 47, it is necessary to determine in advance whether or not the sensor 47 can cope with such a determination.

  Therefore, the routine shown in the flowchart of FIG. 10 is executed before the air-fuel ratio abnormality determination for the specific cylinder.

  In the routine of FIG. 10, first, the high-frequency output characteristic of the air-fuel ratio sensor 47 is measured (step SD1), then the output characteristic measured in step SD1 and the second reference characteristic stored in advance in the PCM 21 The output correction value CV3 is calculated based on (step SD2). Finally, the output value OV3 of the air-fuel ratio sensor 47 is corrected using the output correction value CV3 calculated in step SD2 (step SD3). The term “high frequency output characteristics” as used in this specification refers to the input of a high frequency compared to when the air-fuel ratio is intentionally changed for a specific cylinder, that is, when the air-fuel ratio is uniformly changed for all cylinders. This means the output characteristic of the air-fuel ratio sensor 47 when.

  With reference to the flowchart shown in FIG. 11, a subroutine for measuring the high-frequency output characteristics (step SD1 in FIG. 10) will be described.

  First, in step SE1, the engine speed Ne1 detected by the engine speed sensor 57, the throttle opening Th1 detected by the throttle opening sensor 53, the intake air flow rate A1 detected by the airflow sensor 29, and the engine water temperature. The engine coolant temperature Tw1 detected by the sensor 23 is read by the condition determination unit 21e, and the process proceeds to step SE2.

  In step SE2, the condition determination unit 21e determines whether or not an execution condition for the output characteristic measurement of the air-fuel ratio sensor 47 is satisfied based on the information read in step SE1. Specifically, it is determined whether or not the operating state has a relatively small influence on the running performance even if the air-fuel ratio is changed to rich or lean for a specific cylinder. More specifically, for example, the engine Whether or not the water temperature Tw1 is equal to or higher than a predetermined temperature indicating completion of warm-up, and / or whether or not the fluctuation amount of the engine speed Ne1, the intake charging efficiency and / or the throttle opening degree Th1 is sufficiently small and stable. Is determined.

  If it is determined in step SE2 that the output characteristic measurement execution condition is not satisfied, the process returns to step SE1, and if it is determined that the output characteristic measurement execution condition is satisfied, the process proceeds to step SE3.

  In step SE3, the output characteristic measuring unit 21a controls the air-fuel ratio to change with respect to a specific cylinder, thereby intentionally generating a relatively high-frequency air-fuel ratio change.

  Specifically, for example, the injector 39 of the specific cylinder is controlled so that the fuel injection amount increases or decreases for the specific cylinder. More specifically, for example, as shown in FIG. 12A, the fuel injection amount is increased only for the first cylinder # 1, or as shown in FIG. 12B, fuel injection is performed only for the first cylinder # 1. The amount is reduced. In FIG. 12, reference numeral # 1 denotes a fuel injection process for the first cylinder, reference numeral # 2 denotes a fuel injection process for the second cylinder, reference numeral # 3 denotes a fuel injection process for the third cylinder, and reference numeral # 4 denotes a first fuel injection process. Each of the four cylinder fuel injection steps is shown.

  However, the cylinder in which the fuel injection amount is increased or decreased is not limited to the first cylinder # 1, but the fuel injection amount for any one of the second cylinder # 2, the third cylinder # 3, or the fourth cylinder # 4. Needless to say, it may be increased or decreased. Further, it is not always necessary to change the air-fuel ratio by increasing or decreasing the fuel injection amount. For example, it is conceivable to change the air-fuel ratio by increasing or decreasing the intake air amount.

  Further, in this embodiment, the air-fuel ratio is changed only for the same cylinder in step SE3. However, the cylinder in which the air-fuel ratio is changed in step SE3 may be switched as appropriate. The cylinder to be changed may be switched between the first to fourth cylinders # 1, # 2, # 3, and # 4 in a predetermined order or randomly. The cylinder switching may be performed every time or may be performed every predetermined number of times. As described above, by appropriately switching the cylinders to be subjected to step SE3, even when an air-fuel ratio abnormality occurs in any one of the cylinders, a high-frequency air-fuel ratio change can be generated using the remaining cylinders. Therefore, the measurement of the high-frequency output characteristic (step SE4) described later can be appropriately executed.

  The process of step SE3 is performed a plurality of times while varying the amount of change in the air-fuel ratio for a specific cylinder, specifically, the amount of increase / decrease in the fuel injection amount. More specifically, for example, the fuel injection amount is controlled to increase by a predetermined amount in the first step of step SE3, and the fuel injection amount is controlled to decrease by the same amount in the second step of step SE3. Is done.

  In the step SE3, it is preferable that the air-fuel ratio is changed for the remaining cylinders so as to cancel the air-fuel ratio change for the specific cylinder. In this case, specifically, when the air-fuel ratio is changed to the rich side for a specific cylinder, the air-fuel ratio is changed to the lean side for the remaining three cylinders, and the air-fuel ratio is changed to the lean side for the specific cylinder. When changed, the air-fuel ratio of the remaining three cylinders is changed to the rich side. At this time, it is preferable that the air-fuel ratio change amount for the remaining three cylinders is evenly distributed so as to be smaller than the air-fuel ratio change amount for one specific cylinder. Thereby, even if the process of step SE3 is executed, it is possible to avoid that the entire air-fuel ratio control is biased to the lean side or the rich side, and the influence on the exhaust gas can be reduced.

  In the next step SE4, the output characteristic measuring unit 21a measures the high frequency output characteristic, and the process proceeds to step SE5.

  Specifically, in step SE4, the output change of the air-fuel ratio sensor 47 in a state where the air-fuel ratio is changed for a specific cylinder in the process of step SE3 is monitored, and the high-frequency output characteristic of the sensor 47 is measured. More specifically, for example, when the air-fuel ratio is changed to the lean side for a specific cylinder in step SE3, as shown in FIG. 13, the peak value OVp on the lean side of the output value of the air-fuel ratio sensor 47 is Measured as high frequency output characteristics.

  If the air-fuel ratio is changed to the rich side for a specific cylinder in step SE3, the peak value on the rich side of the output value of the air-fuel ratio sensor 47 may be measured as the high-frequency output characteristics. In addition to the peak value of the output value of the sensor 47, various values can be used as the high frequency output characteristics. For example, as shown in FIG. 13, the air-fuel ratio for a specific cylinder is changed. The time t2 required to reach the peak value from time t2, or the time t4 obtained by subtracting the dead time t3 from the time t2 may be used as the high frequency output characteristics. Furthermore, a plurality of types of values may be measured as the high frequency output characteristics.

  In step SE4, a measurement value is obtained corresponding to each of the processes in step SE3 that is performed a plurality of times, and the measurement value indicating the highest responsiveness among the plurality of measurement values (for example, the highest peak value OVp). Or the shortest time t2, t4) is adopted as the high-frequency output characteristic.

  Finally, in step SE5, it is determined whether or not the measurement of the high frequency output characteristic in step SE4 has been executed a predetermined number of times. As described above, when the cylinder to be subjected to step SE3 is appropriately switched between the four cylinders, it is preferable that the determination threshold value in step SE5 is set to a multiple of four (the number of cylinders).

  If it is determined in step SE5 that the measurement of the high frequency output characteristic has not been performed a predetermined number of times, the process returns to step SE1, and if it is determined that the measurement has been performed a predetermined number of times, the routine of FIG. 11 (step SD1 in FIG. 10). ) Ends.

  Next, calculation of the output correction value CV3 (step SD2 in FIG. 10) will be described.

  The output correction value CV3 is a value necessary for the correction of the output value OV1 of the air-fuel ratio sensor 47 performed in step SD3 of FIG. 10, and more specifically, is multiplied by the output value OV1 of the sensor 47 at the time of the correction. It is a coefficient.

  Further, as described above, the output correction value CV3 is calculated based on the high frequency output characteristic measured in step SD1 in FIG. 10 (specifically, step SE4 in FIG. 11) and the second reference characteristic. . Here, the second reference characteristic is set to the median value of the high-frequency output characteristics of the plurality of air-fuel ratio sensors 47 having variations due to individual differences (deterioration and manufacturing variations). Specifically, a plurality of new air-fuel ratio sensors 47 are used as samples, and high frequency output characteristics (for example, the peak value VOp) are measured for each sample as in step SD1 in FIG. The value is set as a second reference characteristic (for example, a reference peak value).

  The output correction value CV3 is based on the map stored in advance in the PCM 21. The high frequency output characteristic measured in step SD1 in FIG. 10 (specifically, step SE4 in FIG. 11) is higher than the second reference characteristic. When the high frequency output characteristic is larger than the second reference characteristic, the output value of the sensor 47 is increased so that the output value OV1 of the sensor 47 is increased (specifically, a value larger than 1). It is calculated to be a value that decreases OV1 (specifically, a value less than 1).

  Next, the subroutine of step SD3 in FIG. 10 will be described with reference to the flowchart shown in FIG.

  First, in step SF1, the engine speed Ne2 detected by the engine speed sensor 57, the throttle opening Th2 detected by the throttle opening sensor 53, the intake air flow rate A2 detected by the airflow sensor 29, and the engine water temperature The engine water temperature Tw2 detected by the sensor 23, the output correction value CV3 calculated in step SD2 in FIG. 10, and the high-frequency output characteristic of the air-fuel ratio sensor 47 measured in step SD1 in FIG. 10 (step SE4 in FIG. 11). Are read by the condition determination unit 21e, and the process proceeds to Step SF2.

  In step SF2, the condition determination unit 21e determines whether or not the execution condition for determining the air-fuel ratio abnormality for the specific cylinder is satisfied based on the information read in step SF1. Specifically, it is determined whether or not the high-frequency output characteristic of the sensor 47 is a value that exhibits a response that is high enough to be used for determining the air-fuel ratio abnormality of a specific cylinder. More specifically, for example, whether or not the peak value OVp measured in step SE4 in FIG. 11 is greater than or equal to a predetermined value, and / or the times t2 and t4 measured in step SE4 are predetermined values. It is determined whether or not: In addition to this, whether or not the engine speed Ne2 is equal to or higher than a predetermined speed, and whether or not the fluctuation amount of the engine speed Ne2, the intake charging efficiency and / or the throttle opening degree Th2 is sufficiently small and stable. Is determined.

  If it is determined in step SF2 that the condition for determining the air-fuel ratio abnormality of the specific cylinder is not satisfied, the process returns to step SF1, and it is determined that the condition for determining the air-fuel ratio abnormality of the specific cylinder is satisfied. If YES, the process proceeds to step SF3.

  In step SF3, the correction value calculation unit 21c reads the engine speed Ne1 read in the measurement of the high-frequency output characteristic (step SE1 in FIG. 11), the engine speed Ne2 read in step SF1, and the same in step SF1. The determination correction value CV4 is calculated based on the output correction value CV3 read in. This correction value CV4 for determination is a value obtained by correcting the output correction value CV3 corresponding to the change in the engine speed from the time of measuring the high-frequency output characteristic to the time of correcting the output value OV3 of the sensor 47. Specifically, the determination correction value CV4 is calculated so as to be smaller than the output correction value CV1 when the engine speed decreases, that is, when the engine speed Ne2 is smaller than the engine speed Ne1. Is calculated, that is, when the engine speed Ne2 is larger than the engine speed Ne1, the output correction value CV1 is calculated to be larger.

  In the next step SF4, the output value OV3 of the air-fuel ratio sensor 47 is read by the output value correction unit 21b. In the subsequent step SF5, the output value OV3 read in step SF4 and the determination value calculated in step SF3 are used. Based on the correction value CV4, the determination output value OV4 is calculated. Specifically, the determination output value OV4 is calculated by multiplying the output value OV3 by the determination correction value CV4.

  Finally, in step SF6, determination of the air-fuel ratio abnormality for a specific part of the cylinders is executed based on the determination output value OV4 calculated in step SF5, and the routine of FIG. 14 ends.

  With reference to the flowchart shown in FIG. 15, a subroutine for determining an air-fuel ratio abnormality (step SF6 in FIG. 14) for a specific part of the cylinders will be described.

  First, in step SG1, the excess air ratio λ (determination output value OV4 / theoretical air-fuel ratio) is calculated based on the determination output value OV4 calculated in step SF5 of FIG. 14, and the process proceeds to step SG2.

  In step SG2, the excess air ratio λ calculated in the immediately preceding step SG1 is set to λ (i), and the excess air ratio λ calculated in step SG1 immediately before the immediately preceding step SG1 is set to λ (i−1). The difference value λd {= λ (i−1) −λ (i)} of the excess air ratio λ is calculated, and the process proceeds to step SG3.

  In step SG3, an integrated value λs of the absolute value | λd | of the difference value λd is calculated, and the process proceeds to step SG4. Specifically, when the integrated value λs calculated in the previous step SG3 is λs (i−1), the current integrated value λs is immediately before the previous integrated value λs (i−1). It is obtained by adding the absolute value | λd | of the difference value λd calculated in step SG2.

  In step SG4, it is determined whether or not a predetermined time has elapsed since the start of the routine of FIG. 15, that is, whether or not the integration process in steps SG1 to SG3 has been executed for a predetermined time.

  If it is determined in step SG4 that the predetermined time has not elapsed, the process returns to step SG1 to continue the integration process. If it is determined that the predetermined time has elapsed, the process proceeds to step SG5.

  In step SG5, it is determined whether or not the integrated value λs calculated in step SG3 is larger than a predetermined threshold value.

  If it is determined in step SG5 that the integrated value λs is equal to or less than the predetermined threshold value, the air-fuel ratio difference between the cylinders is normal, that is, the air-fuel ratio abnormality has not occurred for some specific cylinders. Determination is made (step SG8).

  On the other hand, if it is determined in step SG5 that the integrated value λs is greater than the predetermined threshold value, an abnormality has occurred with respect to the air-fuel ratio difference between the cylinders, that is, an air-fuel ratio abnormality has occurred for a specific part of the cylinders. It is determined that the alarm is being performed (step SG6), and an alarm is activated (step SG7). The operation of the alarm in step SG7 is performed, for example, by blinking the warning lamp 59 or the like, thereby notifying the occupant that an air-fuel ratio abnormality has occurred in a specific part of the cylinders.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

  1: Engine, 11: Combustion chamber, 21: PCM, 21a: Output characteristic measurement unit, 21b: Output value correction unit, 21c: Correction value calculation unit, 21d: Air-fuel ratio abnormality determination unit, 21e: Condition determination unit, 21f: Feedback control unit, 39: injector (air-fuel ratio adjusting means), 47: air-fuel ratio sensor, 49: catalytic converter, 59: warning lamp, 65: exhaust passage, 66: exhaust collecting passage, 95: exhaust collecting portion.

Claims (10)

A method for measuring output characteristics of air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture in a combustion chamber of the engine based on an oxygen concentration in exhaust gas of a multi-cylinder engine,
A specific cylinder air-fuel ratio changing step of changing the air-fuel ratio for a specific cylinder of the engine under a predetermined condition;
A first output characteristic measuring step of measuring a high frequency output characteristic of the air-fuel ratio detecting means when the air-fuel ratio of the specific one cylinder is changed in the specific cylinder air-fuel ratio changing step;
Based on the high-frequency output characteristic measured in the first output characteristic measurement step, the first required for correcting the output value of the air-fuel ratio detecting means for detecting the air-fuel ratio difference between the cylinders of the engine. A first correction value calculating step for calculating a correction value;
A first output value correction step of correcting the output value of the air-fuel ratio detection means based on the first correction value calculated in the first correction value calculation step;
A first determination step of determining whether there is an abnormality in the air-fuel ratio difference between the cylinders based on the corrected output value obtained by the correction in the first output value correction step;
An all-cylinder air-fuel ratio changing step for uniformly changing the air-fuel ratio for all cylinders of the engine under predetermined conditions;
A second output characteristic measuring step of measuring a low frequency output characteristic of the air-fuel ratio detecting means when the air-fuel ratio of all cylinders is uniformly changed in the all-cylinder air-fuel ratio changing step;
Based on the low frequency output characteristic measured in the second output characteristic measurement step, the second required for correcting the output value of the air / fuel ratio detection means for feedback control of the air / fuel ratio for all cylinders of the engine. A second correction value calculating step for calculating the correction value of
A second output value correction step of correcting the output value of the air-fuel ratio detection means based on the second correction value calculated in the second correction value calculation step;
An air-fuel ratio control step of feedback-controlling the air-fuel ratio for all cylinders of the engine based on the corrected output value obtained by the correction in the second output value correction step . Output characteristic measurement method. 2. The air-fuel ratio according to claim 1, wherein the first determination step determines whether there is an abnormality based on a comparison between a determination parameter calculated based on the corrected output value and a predetermined threshold value. Method for measuring output characteristics of detection means.   In the first correction value calculation step, the median value of the values relating to the high-frequency output characteristics of the plurality of air-fuel ratio detection means at the time of shipment measured by the same method as in the first output characteristic measurement step; 3. The output of the air-fuel ratio detection means according to claim 1, wherein the first correction value is calculated based on a difference from a value related to the high-frequency output characteristic measured in the output characteristic measurement step. Characteristic measurement method. Based on the high-frequency output characteristic measured in the first output characteristic measurement step, the air-fuel ratio detection means exhibits a response higher than a predetermined value that can be used to determine whether there is an abnormality in the air-fuel ratio difference between the cylinders. Having a second determination step of determining whether or not
3. The method according to claim 2, wherein the first determination step is executed when it is determined in the second determination step that the air-fuel ratio detection means has a response higher than a predetermined value. 4. The method for measuring output characteristics of the air-fuel ratio detecting means according to 3. Based on the low-frequency output characteristics measured in the previous SL second output characteristic measuring step, a third determination step of determining whether or not normally capable of executing the feedback control using the air-fuel ratio detecting means 5. The method for measuring output characteristics of an air-fuel ratio detecting means according to claim 1, further comprising:   In the first output characteristic measuring step, the maximum value of the change amount of the output value of the air-fuel ratio detecting means accompanying the change of the air-fuel ratio of the specific cylinder in the specific cylinder air-fuel ratio changing step, or the change amount 6. The method for measuring output characteristics of air-fuel ratio detecting means according to any one of claims 1 to 5, wherein at least one of the time required for the air to reach a predetermined amount is measured. The specific cylinder air-fuel ratio changing step is performed a plurality of times while varying the amount of change in the air-fuel ratio for the specific cylinder.
The measurement value showing higher responsiveness among a plurality of measurement values obtained corresponding to the plurality of specific cylinder air-fuel ratio changing steps is employed in the first output characteristic measurement step. The method for measuring output characteristics of the air-fuel ratio detecting means according to any one of claims 1 to 6.   8. The first output characteristic measurement step is executed while switching the specific one cylinder to be subjected to the specific cylinder air-fuel ratio changing step. 8. A method for measuring output characteristics of the air-fuel ratio detecting means.   The air-fuel ratio is changed for the remaining cylinders so as to cancel out the change in the air-fuel ratio when the air-fuel ratio is changed for the specific cylinder in the specific cylinder air-fuel ratio changing step. 9. The method for measuring output characteristics of air-fuel ratio detection means according to any one of items 8 to 9. An apparatus for measuring output characteristics of air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture in a combustion chamber of the engine based on an oxygen concentration in exhaust gas of a multi-cylinder engine,
Air-fuel ratio adjusting means for adjusting the air-fuel ratio;
The high-frequency output characteristics of the air-fuel ratio detection means when the air-fuel ratio is changed by the air-fuel ratio adjustment means for a specific cylinder of the engine under a predetermined condition, and the cylinders of the engine under a predetermined condition Output characteristic measuring means for measuring the low frequency output characteristics of the air-fuel ratio detecting means when the air-fuel ratio is uniformly changed by the air-fuel ratio adjusting means;
Based on the high-frequency output characteristic measured by the output characteristic measuring means, a first correction value necessary for correcting the output value of the air-fuel ratio detecting means performed for detecting the air-fuel ratio difference between the cylinders of the engine is obtained. The second required for correction of the output value of the air-fuel ratio detecting means performed for feedback control of the air-fuel ratio for all the cylinders of the engine based on the low frequency output characteristics calculated and measured by the output characteristic measuring means Correction value calculating means for calculating the correction value of
Output value correction means for correcting the output value of the air-fuel ratio detection means based on the first correction value or the second correction value calculated by the correction value calculation means;
An air-fuel ratio abnormality determining means for determining presence / absence of abnormality in the air-fuel ratio difference between the cylinders based on a corrected output value obtained by correction based on the first correction value by the output value correcting means;
Feedback control means for feedback-controlling the air-fuel ratio for all cylinders of the engine based on the corrected output value obtained by the correction based on the second correction value by the output value correcting means. An output characteristic measuring device for the fuel ratio detecting means.

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