JP2006125304A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid emission deterioration caused by evaporation purging as much as possible and to simply perform relatively exact purge learning. <P>SOLUTION: A basic fuel injection quantity after correction is obtained from relation that, on the assumption that an cylinder intake air volume is constant, a product of a command fuel injection quantity and a detected air-fuel ratio becomes equal to a product of a target air-fuel ratio and a target basic fuel injection quantity for bringing an actual air-fuel ratio of an engine to the target air-fuel ratio. A correction coefficient KF for the basic fuel injection quantity is calculated from a ratio of the basic fuel injection quantity after correction and a basic fuel injection quantity before correction to correct the basic fuel injection quantity. A filter time-constant of low pass filtering for calculation of a KF value at the time of purge is set smaller than that at the time of non-purge. In the purge, in addition to a KF value using a filter of a small time-constant provided for actual air-fuel ratio control, a KF value at the time of non-purge using a filter of a large time-constant is also calculated and purge learning is conducted with use of the KF value at the time of non-purge. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio of the internal combustion engine based on an output of an air-fuel ratio sensor disposed in an exhaust passage of the internal combustion engine. (In the following description, “internal combustion engine” may be simply referred to as “engine”, or “air-fuel ratio control device for internal combustion engine” may be simply referred to as “air-fuel ratio control device”.)

As an air-fuel ratio control device of this kind that has been widely known in the past, an upstream air-fuel ratio sensor disposed in the exhaust passage upstream of the catalyst device, and a downstream side disposed in the exhaust passage downstream of the catalyst device There are some which feedback control the air-fuel ratio based on the output value of the air-fuel ratio sensor. Specific examples of the conventional air-fuel ratio control device adopting such a configuration include those described in the following patent documents.
JP 2003-336535 A

  The air-fuel ratio control apparatus described in Patent Document 1 includes an upstream feedback (main feedback) loop based on the output of the upstream air-fuel ratio sensor and a downstream feedback (sub-feedback) loop based on the output of the downstream air-fuel ratio sensor. Have. In the air-fuel ratio control apparatus, feedback control of the air-fuel ratio is performed as follows.

  First, in-cylinder intake air that is drawn into the combustion chamber of the engine in the current combustion cycle based on the engine operating speed, the accelerator opening, the intake air flow rate detected by an air flow meter disposed in the intake passage, etc. A quantity is calculated. Next, based on the in-cylinder intake air amount and the target air-fuel ratio, the basic fuel injection amount before being corrected by the feedback control is acquired. Subsequently, the basic fuel injection amount is corrected based on the upstream feedback correction value based on the output of the upstream air-fuel ratio sensor and the downstream feedback correction value based on the output of the downstream air-fuel ratio sensor. A fuel injection amount is calculated. Then, by instructing the fuel injection device to inject the fuel of the command fuel injection amount, the fuel is injected in the intake passage or the combustion chamber.

  Here, proportional / integral control (PI control) or proportional / integral / differential control (PID control) is usually used for the above-described upstream side and downstream side feedback. This is because the integral term (I term) in the PI control and PID control has an effect of compensating a so-called steady-state deviation in the feedback control and converging the actual air-fuel ratio to the target air-fuel ratio.

  By the way, in the above-described conventional air-fuel ratio control device, due to the measurement error of the air flow meter due to dirt on the air flow meter or adhesion of foreign matter, the calculated value of the in-cylinder intake air amount is between the actual in-cylinder intake air amount. An error sometimes occurred. Further, since the basic fuel injection amount is calculated using the calculated value of the in-cylinder intake air amount including this error, an error may occur in the calculation of the basic fuel injection amount. In addition, an error may occur between the command fuel injection amount and the actual fuel injection amount due to mechanical factors around the fuel injection device (variation in fuel injection performance of the fuel injection device, clogging of the fuel injection device, etc.). was there. (The above-mentioned error in calculating the basic fuel injection amount due to the error in calculating the in-cylinder intake air amount and the error in the fuel injection amount due to mechanical factors around the fuel injection device are also referred to as “the mixture supply”. Collectively referred to as “mechanical error of the system”.)

  In this regard, according to the upstream feedback or the downstream feedback including the above-described integral term, although the mechanical error of the above-described mixture supply system can be compensated by the steady deviation compensation action of the integral term, There is room for improvement in compensation when the mechanical error changes suddenly (for example, immediately after foreign matter adhering to the air flow meter or clogging of the fuel injection device). That is, in order to obtain an appropriate feedback correction value to compensate for the sudden change in the mechanical error of the above-described mixture supply system, the calculation of the integral term performed by integrating the history history, etc. It took appropriate steps and time. For this reason, in the above-mentioned integral term, quick compensation for a sudden change in the mechanical error of the air-fuel mixture supply system is not achieved, and there is a concern that temporary emission deterioration may occur.

  In general, in an internal combustion engine, liquid fuel is evaporated in a fuel tank to generate fuel gas, and therefore an evaporated fuel processing mechanism is provided to prevent the fuel gas from being released into the atmosphere. ing. This evaporative fuel processing mechanism stores a canister configured to occlude fuel gas generated in a fuel tank while the engine is stopped, and to desorb the occluded fuel gas during operation of the engine and release it to the intake passage. I have. Even during engine operation, the liquid fuel circulating in the fuel circulation path between the fuel injector (injector) and the fuel tank is heated by heat transfer from the combustion chamber in the vicinity of the injector. When the liquid fuel thus returned returns to the fuel tank, the fuel that has reached a high temperature evaporates in the fuel tank to generate fuel gas. Therefore, in addition to the above-mentioned canister, the evaporative fuel processing mechanism is configured so that the fuel gas in the fuel tank generated due to fuel heating in the vicinity of the injector during engine operation is directly discharged to the intake passage. It is normal.

  Here, the above-described empty fuel gas is released by the desorbed fuel gas (canister purge gas) introduced from the canister into the intake passage or the evaporated fuel gas (tank vapor) introduced directly from the fuel tank into the intake passage without being occluded by the canister. The fuel-fuel ratio feedback control system may be subject to a large disturbance (hereinafter, the canister purge gas and the tank vapor are collectively referred to as “evaporated fuel gas.” In addition, the introduction of the canister purge gas into the intake passage and the tank) (The vapor introduction is generally referred to as “evaporation purge” or simply “purge”.) Even in the case of such an evaporative purge, there has been a concern that rapid compensation is not achieved with the integral term of the feedback control described above, and that temporary emission deterioration occurs.

  Therefore, when the evaporative purge is performed, the amount of fuel corresponding to the air-fuel ratio rich shift by the evaporative purge (hereinafter referred to as “excess fuel amount”) is relatively accurately obtained and subtracted from the basic fuel injection amount, so that the It is necessary to avoid sudden changes in the fuel ratio as much as possible. That is, it is necessary to acquire a purge learning value corresponding to this surplus fuel amount (hereinafter referred to as “purge learning”). Some conventional air-fuel ratio control devices perform this purge learning. However, even in such conventional air-fuel ratio control devices, in order to perform this purge learning relatively accurately, ordinary air-fuel ratio control is performed. It is necessary to provide a separate control system for purge learning control different from the above, and there is a problem that the air-fuel ratio control system becomes complicated.

  The present invention has been made in order to solve the above-described problems of the conventional air-fuel ratio control device, and its purpose is to easily and quickly compensate for the mechanical error of the air-fuel mixture supply system while evaporating the purge. This makes it possible to quickly compensate for fluctuations in the air-fuel ratio at the same time, and to easily perform purge learning with relatively high accuracy, thereby suppressing the deterioration of emissions caused by evaporation purge as much as possible and performing suitable air-fuel ratio control. An object of the present invention is to provide an air-fuel ratio control apparatus for an internal combustion engine that can be maintained.

  In order to achieve such an object, the present invention is configured such that a combustion chamber, an intake passage and an exhaust passage connected to the combustion chamber, and a fuel gas based on fuel evaporated in a fuel tank can be introduced into the intake passage. A fuel gas introduction path, a fuel injection device for injecting liquid fuel transported from the fuel tank in the intake passage or the combustion chamber by receiving an instruction to inject fuel of a command fuel injection amount, and the exhaust passage An air-fuel ratio control device applied to an internal combustion engine that includes a catalyst device disposed in the engine and an upstream air-fuel ratio sensor disposed in the exhaust passage upstream of the catalyst device has the following configuration. It is characterized by that.

  First, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention uses the estimated value of the current fuel injection amount corresponding to the target air-fuel ratio based on at least the operating speed of the internal combustion engine and the air flow rate in the intake passage as a basic fuel. A basic fuel injection amount acquisition unit that acquires the injection amount; and an arithmetic processing unit that includes a filter, based on the target air-fuel ratio, the detection signal of the upstream air-fuel ratio sensor, and the past commanded fuel injection amount A basic fuel injection amount correction value acquisition unit that acquires a calculation result corresponding to a basic fuel injection amount correction value for correcting the basic fuel injection amount by performing arithmetic processing in the arithmetic processing unit; and at least the calculation result (and Preferably, the fuel gas is introduced into the intake passage through the fuel gas introduction passage, and a command fuel injection amount calculation unit that calculates the current fuel injection amount based on the basic fuel injection amount). A purge learning unit that acquires a purge learning value that is an air-fuel ratio learning value based on the concentration of the fuel gas based on the calculation result in the basic fuel injection amount correction value acquisition unit when the fuel gas is introduced. .

  The basic fuel injection amount correction value acquisition unit includes a first filter used when the purge learning unit acquires the purge learning value, and the command fuel injection amount calculation unit when the fuel gas is introduced. And a second filter used when acquiring the calculation result provided to the first filter, wherein the first filter and the second filter are configured so that parameters relating to the response of the filter are different. (Here, the value acquired by the basic fuel injection amount correction value acquisition unit is not simply referred to as “basic fuel injection amount correction value”, but “calculation result corresponding to the basic fuel injection amount correction value”) The reason is that the value acquired based on the first filter may not be used for correcting the basic fuel injection amount but may be used only for purge learning. ).

  In other words, the basic fuel injection amount correction value acquisition unit includes, as the filter of the arithmetic processing unit, a first filter and a second filter having different parameters related to filter responsiveness, and the fuel gas introduction Sometimes, using the first filter, the basic fuel injection amount correction value (corresponding to the calculation result) provided to the purge learning unit is obtained and the command fuel is used using the second filter. The basic fuel injection amount correction value (calculation result corresponding to) provided to the injection amount calculation unit is acquired.

  According to the air-fuel ratio control apparatus of the present invention having such a configuration, first, the basic fuel injection amount is acquired based on at least the operating speed of the internal combustion engine and the air flow rate in the intake passage. Next, the fuel injection amount actually injected by the fuel injection device based on the acquired basic fuel injection amount is set so that the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber becomes the target air-fuel ratio. Based on the target air-fuel ratio, the detection signal of the upstream air-fuel ratio sensor, and the command fuel injection amount in the past so that the required fuel injection amount (hereinafter simply referred to as “necessary fuel injection amount”) is obtained. By performing arithmetic processing in the arithmetic processing unit, acquisition of a calculation result (acquisition of a basic fuel injection amount correction value) corresponding to the basic fuel injection amount correction value for correcting the basic fuel injection amount is performed. More specifically, for example, it is performed as follows.

  In general, the product of the fuel injection amount and the air-fuel ratio corresponds to the in-cylinder intake air amount. Under the assumption that the in-cylinder intake air amount sucked into the combustion chamber is constant, the fuel injection amount and the air-fuel ratio. The product of and becomes constant. Further, the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is reflected in the detected air-fuel ratio of the upstream air-fuel ratio sensor. Therefore, on the assumption that the product of the fuel injection amount and the air-fuel ratio is constant, the product of the detected air-fuel ratio and the command fuel injection amount at the time of fuel injection corresponding to the detected air-fuel ratio is the target air-fuel ratio. And a fuel injection amount (hereinafter simply referred to as “target fuel injection command value”) that should be instructed to the current fuel injection device in order to actually inject the required fuel injection amount. To establish. And based on such a relationship, based on the target air-fuel ratio, the detection signal of the upstream-side air-fuel ratio sensor and the past command fuel injection amount, a predetermined calculation process is performed, and by using this calculation result, A basic fuel injection amount correction value as a correction value for the basic fuel injection amount can be calculated. For example, if the product of the detected air-fuel ratio and the command fuel injection amount at the time of fuel injection corresponding to the detected air-fuel ratio is divided by the product of the target air-fuel ratio and the basic fuel injection amount, the target fuel injection command value A correction coefficient as a basic fuel injection amount correction value (a calculation result corresponding to) is obtained by a simple calculation.

  Then, based on the calculation result thus obtained, a corrected basic fuel injection amount as a value corresponding to the target fuel injection command value is obtained, and based on the obtained corrected basic fuel injection amount. The current command fuel injection amount is calculated, and a fuel injection instruction based on the calculated current command fuel injection amount is given to the fuel injection device.

  Thus, according to the above configuration, the target fuel injection command value for performing the fuel injection of the required fuel injection amount is the past command fuel injection amount and the fuel injection time corresponding to the past command fuel injection amount at the time of fuel injection. It is directly calculated by simple calculation using the air-fuel ratio detected by the upstream air-fuel ratio sensor (corresponding to the actual air-fuel ratio) and the target air-fuel ratio, and the mechanical error of the air-fuel mixture system (independent of air-fuel ratio feedback) ) Directly compensated.

  In addition, the purge learning unit is configured to perform the basic fuel injection amount correction value acquisition unit when the fuel gas (purge gas) is introduced into the intake passage via the fuel gas introduction path (when purging). Based on the calculation result, a purge learning value that is an air-fuel ratio learning value based on a fuel concentration in the purge gas (hereinafter abbreviated as a purge gas concentration) is acquired.

  That is, for example, if the operating speed of the internal combustion engine and the air flow rate in the intake passage are the same at the time of purging and at the time of non-purging (when the fuel gas is not introduced), the basic fuel injection amount is acquired. The basic fuel injection amount (before correction) acquired by the control unit and the mechanical error of the air-fuel mixture intake system are the same when purging and when not purging. Therefore, the calculation result acquired based on the air-fuel ratio output of the upstream air-fuel ratio sensor at the time of purging is an appropriate value that should be used for correcting the basic fuel injection amount to compensate for the rich air-fuel ratio fluctuation due to evaporation purge. Can be a good value.

  Therefore, for example, by sequentially learning (storing) the calculation result acquired at the time of purging as a purge learning value, a purge learning value that can be utilized for maintaining appropriate air-fuel ratio control at the time of evaporation purge is obtained. It is easily acquired. For example, at the time of the next purge, by performing the basic fuel injection amount correction using the purge learning value from the purge start time, it is possible to suppress the deterioration of the emission due to the air-fuel ratio fluctuation immediately after the purge starts as much as possible.

  Thus, according to the above-described configuration, the purge learning is performed by the calculation result of the calculation processing unit (originally “basic fuel injection amount correction value”) for acquiring the basic fuel injection amount correction value in the basic fuel injection amount correction value acquisition unit. By pursuing a value referred to as “purge”, purge learning can be easily performed without providing a special purge learning unit.

  Here, the feature of the configuration of the present invention is that, in particular, the basic fuel injection amount correction value acquisition unit uses the first filter used when the purge learning unit acquires the purge learning value, A second filter used when acquiring the calculation result provided to the command fuel injection amount calculation unit when the fuel gas is introduced, and the first filter and the second filter are filters The parameters relating to the responsiveness (hereinafter simply referred to as “responsiveness parameters”) are different.

  That is, for example, when the internal combustion engine is in a transient operation state, the gas flow state inside the internal combustion engine greatly fluctuates, so the basic fuel injection amount acquired by the basic fuel injection amount acquisition unit or the actual exhaust gas The air-fuel ratio can also fluctuate drastically at high frequencies exceeding a predetermined frequency. In such a case, the assumption that the product of the fuel injection amount and the air-fuel ratio is constant is lost, or the calculation result corresponding to the basic fuel injection amount correction value vibrates at a high frequency exceeding the predetermined frequency. Or the like, the basic fuel injection amount correction value may not be an appropriate value. Therefore, when the calculation result is obtained, an appropriate correction value of the basic fuel injection amount can be easily calculated by performing a filter process (preferably a low-pass filter process) that cuts a high frequency exceeding the predetermined frequency. And can be calculated with higher accuracy. From this point of view, the responsiveness parameter is in a direction that suppresses responsiveness (low-pass) within a range that does not impair the quickness of basic fuel injection amount correction when compared with the integral term in a general air-fuel ratio feedback control system. In the case of a filter, the value is preferably large.

  On the other hand, when the calculation result is acquired as described above, an evaporative purge in which the evaporative gas is introduced into the intake passage may be performed. This evaporative purge is a large disturbance in the air-fuel ratio control system, and thus temporarily There is a possibility that the emission will deteriorate. Therefore, in order to quickly compensate for this large disturbance and suppress the emission deterioration as much as possible, the responsiveness parameter should have a value that increases the responsiveness (in the case of a low-pass filter, the time constant is small). Is preferred.

  However, when performing purge learning, accurate learning cannot be performed if the calculation result in the basic fuel injection amount correction value acquisition unit that is the basis of purge learning vibrates at a high frequency. Therefore, at the time of purge learning, it is preferable that the responsiveness parameter is a value that suppresses responsiveness (in the case of a low-pass filter, the time constant is large).

  From the above, during purging, it was obtained based on the calculation result based on the output of the second filter having the response parameter in the direction of increasing the response (in the case of a low-pass filter, the time constant is small). The first responsiveness parameter having the responsiveness parameter (in the case of a low-pass filter having a large time constant) in a direction of suppressing responsiveness while compensating for air-fuel ratio fluctuation due to evaporation purge as quickly as possible by the basic fuel injection amount correction value. With the purge learning value based on the output of the filter, purge learning can be performed with high accuracy.

  More preferably, the basic fuel injection amount correction at the time of purging is performed as follows. That is, during a predetermined time immediately after the start of purging, the basic fuel injection amount correction value is acquired based on the purge learning value (basic fuel injection amount correction value at the past purge). Then, since the surplus fuel amount can be subtracted in advance from the basic fuel injection amount calculation value before correction by the basic fuel injection amount acquisition unit from the beginning of the current purge, sudden change of the actual air-fuel ratio due to evaporation purge is possible. It can be avoided as much as possible. After the predetermined time has elapsed, the basic fuel injection amount correction value is acquired based on the calculation result by the calculation processing unit such as the second filter based on the air-fuel ratio output of the upstream air-fuel ratio sensor at the present time.

  Here, it is preferable that the first filter is configured to be used also when the calculation result supplied to the command fuel injection amount calculation unit is acquired at the time of non-purge. That is, according to such a configuration, the output of the first filter is used regardless of whether it is purged or not. The calculation result of the basic fuel injection amount correction value acquisition unit based on the output of the first filter is used to acquire a basic fuel injection amount correction value when not purged, and is used for purge learning when purging. On the other hand, the calculation result of the basic fuel injection amount correction value acquisition unit based on the output of the second filter is used to acquire the basic fuel injection amount correction value during purge, but the basic fuel injection amount correction during non-purge. It is not used to get the value. As a result, both a purge time and a non-purge time can be obtained without providing a new means for obtaining a basic fuel injection amount correction value for performing stable and accurate basic fuel injection amount correction at the time of non-purge. Both maintenance of appropriate air-fuel ratio control and simple and accurate purge learning can be achieved.

  Second, the air-fuel ratio control apparatus of the present invention includes an upstream feedback correction value calculation unit that calculates an upstream feedback correction value that is an air-fuel ratio feedback correction value based on a detection signal of the upstream air-fuel ratio sensor, The command fuel injection amount calculation unit is preferably configured to correct the basic fuel injection amount corrected by the basic fuel injection amount correction unit with the upstream feedback correction value. According to this configuration, the basic fuel injection amount correction unit performs quick correction of the basic fuel injection amount, and compensation for air-fuel ratio fluctuation in the transient operation state is performed by upstream feedback control.

  Further, the upstream feedback correction value calculation unit calculates a feedback correction value by performing various arithmetic processes based on the output value of the upstream air-fuel ratio sensor. The predetermined upstream target value may be considered. That is, the upstream feedback correction value calculation unit (1) is a value obtained by subjecting a value resulting from a difference between the output value of the upstream air-fuel ratio sensor and a predetermined upstream target value to a predetermined high-pass filter processing, or (2 ) An upstream feedback correction value is calculated based on a value obtained by subjecting the output value of the upstream air-fuel ratio sensor to a predetermined high-pass filter process. In the case of (1), the predetermined upstream target value is preferably a value corresponding to the target air-fuel ratio. In addition, specific examples of the “value resulting from the difference between the output value of the upstream air-fuel ratio sensor and the predetermined upstream target value” include, for example, the difference between the sensor output value and the target value, the sensor output The actual cylinder that is the difference between the detected air-fuel ratio corresponding to the value (actual air-fuel ratio) and the target air-fuel ratio corresponding to the target value, and the cylinder intake air amount divided by the detected air-fuel ratio corresponding to the output value of the sensor The difference between the in-cylinder fuel supply amount and the in-cylinder intake air amount by the target in-cylinder fuel supply amount that is a value obtained by dividing the in-cylinder intake air amount by the target air-fuel ratio corresponding to the target value, and the like are mentioned. .

  Third, the air-fuel ratio control apparatus of the present invention is directed to an internal combustion engine that also includes a downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the catalyst device, A downstream feedback correction value calculation unit that calculates a downstream feedback correction value that is an air-fuel ratio feedback correction value based on a detection signal of the downstream air-fuel ratio sensor, and the command fuel injection amount calculation unit includes the basic fuel injection amount correction This is particularly suitable when the basic fuel injection amount corrected by the unit is corrected with the downstream feedback correction value.

  In such a configuration, the feedback correction value by the downstream feedback correction value calculation unit is detected by the downstream air-fuel ratio sensor in which the air-fuel ratio fluctuation is absorbed by the exhaust gas purification action of the catalyst and the detection of the air-fuel ratio fluctuation is delayed. This is based on the signal, and reflects the air-fuel ratio fluctuation with a relatively low amplitude at a low frequency equal to or lower than a predetermined frequency that can appear as a fluctuation in the air-fuel ratio downstream of the catalyst device. On the other hand, the correction of the basic fuel injection amount is quickly performed based on the detection signal of the upstream air-fuel ratio sensor without the detection delay due to the exhaust gas purification action of the catalyst described above, and is not affected by the downstream feedback correction value. Done. Thus, according to the above configuration, the basic fuel injection amount is quickly corrected while performing stable air-fuel ratio feedback control by the downstream feedback control.

  In particular, (A) the upstream feedback correction value calculation unit calculates a feedback correction value for the fuel injection amount based on a filter output signal obtained by high-pass filtering the filter input signal based on the detection signal of the upstream air-fuel ratio sensor. (B) In addition to the case of (A) described above, the downstream feedback correction value calculator further applies a low-pass filter input signal based on the detection signal of the downstream air-fuel ratio sensor. The configuration of the present invention works particularly well when the feedback correction value for the fuel injection amount is calculated based on the filtered filter output signal.

  That is, in the case of the above-described (A), in the upstream feedback control, the air-fuel ratio feedback control for the transient air-fuel ratio fluctuation is performed according to the high-pass filter output signal based on the detection signal of the upstream air-fuel ratio sensor. Further, in the case of (B) described above, in the downstream feedback control, the air-fuel ratio feedback control for the steady air-fuel ratio fluctuation is performed according to the low-pass filter output signal based on the detection signal of the downstream air-fuel ratio sensor. In the cases (A) and (B), between the upstream side feedback control and the downstream side feedback control, as described above, the former is compensation for transient high-frequency air-fuel ratio fluctuations, and the latter is steady. Thus, a role sharing such as compensation for low-frequency air-fuel ratio fluctuations occurs. In particular, in the case of (B), the high-pass filter processing is performed on the upstream air-fuel ratio sensor detection signal used for the upstream feedback control, and the low-pass filter processing is performed on the downstream air-fuel ratio sensor detection signal used for the downstream feedback control. Therefore, the upstream side feedback control and the downstream side feedback control operate in different frequency bands in the air-fuel ratio fluctuation. Therefore, even when the output value of the upstream air-fuel ratio sensor and the output value of the downstream air-fuel ratio sensor indicate the air-fuel ratio shifted in the opposite directions with respect to the target air-fuel ratio, upstream feedback control and It is prevented as much as possible that the downstream feedback control interferes with each other and the control is hunted. In addition, as described above, high-pass filter processing is performed in the upstream feedback control, so that substantially no integration processing can be performed. In downstream feedback control, detection of air-fuel ratio fluctuations is delayed by the exhaust gas purification action of the catalyst. Therefore, by performing the above-described basic fuel injection amount correction independently of each of these feedback controls, the mechanical error of the air-fuel mixture supply system can be easily and quickly performed together with stable air-fuel ratio feedback control to the target air-fuel ratio. In addition to being compensated, rapid compensation is made for large air-fuel ratio fluctuations due to evaporation purge.

  The downstream feedback correction value calculation unit is configured to calculate a feedback correction value based on a value resulting from a difference between the output value of the downstream air-fuel ratio sensor and a predetermined downstream target value. It is preferable. The predetermined downstream target value is preferably a value corresponding to the target air-fuel ratio. Here, for a specific example of “a value resulting from the difference between the output value of the downstream air-fuel ratio sensor and the predetermined downstream target value”, the “upstream air-fuel ratio sensor This is the same as a specific example of “a value resulting from a difference between an output value and a predetermined upstream target value”.

  In the basic fuel injection amount correction unit in the air-fuel ratio control apparatus of the present invention, the “past” command fuel injection amount is used for the basic fuel injection amount correction. Preferably, it is as follows.

  That is, as a preferred aspect of the present invention, from the fuel injection instruction to the fuel injection device until the air-fuel ratio of the exhaust due to the combustion of the fuel injected based on the injection instruction appears as the output value of the upstream air-fuel ratio sensor. A delay time acquisition unit for acquiring the delay time of the first time. The “past” command fuel injection amount is a command fuel injection amount related to an injection instruction at a time point before the delay time.

  In general, the fuel injection instruction is executed during the intake stroke or at a time before the intake stroke, and the injected fuel is ignited in the combustion chamber at a time near the compression top dead center that comes after that. Burn with. The exhaust gas generated by this combustion is discharged from the combustion chamber to the exhaust passage via the exhaust valve, and then moves in the exhaust passage to reach the detection portion of the upstream air-fuel ratio sensor. Further, it takes a predetermined time from when the exhaust gas reaches the detection unit of the upstream air-fuel ratio sensor until the air-fuel ratio (change) of the exhaust gas appears as an output value (change) of the sensor.

  From the above, there is a delay related to the combustion stroke between the time when the fuel injection command is issued and the time when the air-fuel ratio of the exhaust gas based on the combustion of the fuel injected according to the fuel injection command appears as the output value of the upstream air-fuel ratio sensor. (Delay delay), Delay related to movement of exhaust gas in exhaust passage (Transport delay), and Delay related to response of upstream air-fuel ratio sensor (Response delay) are required. In other words, the output value of the upstream air-fuel ratio sensor (currently) is a value representing the air-fuel ratio of the exhaust gas generated based on the fuel injection instruction executed before the delay time described above.

  However, the time for the above-described stroke delay and transport delay includes, for example, injection timing, ignition timing, specifications such as the size and number of cylinders of the internal combustion engine, engine rotation speed, in-cylinder intake air amount, cross-sectional area of the exhaust passage, etc. Can be easily obtained based on the above. In addition, the response time can be obtained in advance through experiments or the like in advance as response characteristics of the upstream air-fuel ratio sensor. Therefore, the delay time due to the process delay, transport delay, and response delay can be accurately acquired by the delay time acquisition unit.

  Therefore, when calculating the correction value for the basic fuel injection amount, (at the same time, use the current value as the output value of the upstream side air-fuel ratio sensor) at least the injection at the time point before the delay time as the command fuel injection amount If the value related to the instruction is used, the fuel injection instruction time point related to the generation of the exhaust gas of the air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor (at the present time) and the correction value of the basic fuel injection amount The time point of the fuel injection instruction corresponding to the commanded fuel injection amount used for the calculation of the value may coincide or be very close. Therefore, the correction value can be calculated with higher accuracy as a value for obtaining the target fuel injection command value.

  In this case, it is preferable that the delay time acquisition unit is configured to change the delay time according to an operating state of the internal combustion engine. As described above, the time related to the stroke delay and the transport delay varies depending on the operating state of the engine, such as the engine speed and the in-cylinder intake air amount. Therefore, according to the said structure, the said delay time can be acquired correctly irrespective of the driving | running state of an internal combustion engine.

  As described above, according to the present invention, even when a large disturbance to the air-fuel ratio control due to the evaporation purge occurs, the basic fuel injection amount correction with high responsiveness based on the output of the upstream air-fuel ratio sensor performs the purge operation. This makes it possible to perform purge learning with relatively high accuracy while promptly compensating for fluctuations in the air / fuel ratio of the engine, and thereby maintaining the preferred air / fuel ratio control by minimizing the emission deterioration caused by evaporation purge as much as possible. Is possible.

  Hereinafter, an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention (which may be simply abbreviated as “air-fuel ratio control apparatus” in the following description) that is considered best at the time of filing of the present application will be described with reference to the drawings. I will explain.

(Outline of Internal Combustion Engine of Embodiment)
FIG. 1 shows a schematic configuration of a system in which the air-fuel ratio control apparatus according to the present embodiment is applied to a spark ignition type multi-cylinder (four-cylinder) internal combustion engine 10. The internal combustion engine 10 includes a cylinder block unit 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head unit 30 fixed on the cylinder block unit 20, and a gasoline mixture in the cylinder block unit 20. And an exhaust system 50 for releasing exhaust gas from the cylinder block 20 to the outside.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 via the connecting rod 23, whereby the crankshaft 24 rotates. The heads of the cylinder 21 and the piston 22 form a combustion chamber 25 together with the cylinder head portion 30.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake camshaft that drives the intake valve 32, and continuously changes the phase angle of the intake camshaft. The variable intake timing device 33, the actuator 33 a of the variable intake timing device 33, the exhaust port 34 communicating with the combustion chamber 25, the exhaust valve 35 that opens and closes the exhaust port 34, the exhaust camshaft 36 that drives the exhaust valve 35, and the spark plug 37 An igniter 38 including an ignition coil that generates a high voltage to be applied to the spark plug 37, and an injector (fuel injection device) 39 that injects fuel into the intake port 31.

  The intake system 40 is provided in an intake pipe 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and the intake pipe 41. Throttle valve 43 for varying the opening cross-sectional area of the intake passage, throttle valve actuator 43a comprising a DC motor constituting throttle valve driving means, swirl control valve (hereinafter referred to as "SCV") 44, and DC motor. SCV actuator 44a, fuel tank 45 for storing liquid fuel, canister 46 capable of storing a predetermined amount of fuel gas, vapor collection tube 47 for introducing fuel gas evaporated in fuel tank 45 to canister 46, canister 46 The purge flow path 4 for introducing the fuel gas desorbed from the intake pipe 41 , And a purge control valve 49 interposed in the purge flow path 48. Here, the intake port 31 and the intake pipe 41 constitute an intake passage.

  The canister 46 is a well-known charcoal canister, and is provided in a casing in which a tank port 46a connected to the vapor collection pipe 47, a purge port 46b connected to the purge flow path 48, and an atmospheric port 46c are formed. The adsorbent 46d for adsorbing the fuel gas is housed. The atmospheric port 46c allows external air to flow through the canister so that when the purge control valve 49 is opened, a negative pressure generated in the intake pipe 41 causes a gas flow toward the intake pipe 41 in the purge flow path 48. 46 is an air communication hole for introduction into 46.

  The canister 46 has a direct gas flow path from the tank port 46a to the purge port 46b. When the purge control valve 49 is opened during the operation of the internal combustion engine 10 due to this gas flow path, the tank vapor generated in the fuel tank 45 flows into the canister 46 from the tank port 46a. It can be discharged from the purge port 46b as it is without being adsorbed by the adsorbent 46d later.

  Further, in this apparatus, both canister purge and tank vapor introduction are performed without any particular distinction. That is, the canister purge gas flowing from the atmospheric port 46c through the adsorbent 46d to the purge flow path 48 from the purge port 46b to the purge flow path 48 by the purge execution in this apparatus, the tank port 46a from the fuel tank 45, and the tank port 46a and the purge port 46b described above. The vapor gas mixed with the tank vapor flowing to the purge flow path 48 via the direct gas flow path between the two is sucked into the intake pipe 41 through the purge control valve 49.

  The purge control valve 49 is configured by a well-known VSV (vacuum switching valve) (in the following description of the present embodiment, the purge control valve 49 is abbreviated as “VSV 49”). The VSV 49 uses a so-called “normally closed type” on-off valve configured to open the flow path when energized and close the flow path when not energized.

  The exhaust system 50 includes an exhaust manifold 51 that communicates with the exhaust port 34, and an exhaust pipe (exhaust pipe) that is connected to the exhaust manifold 51 (actually, a collection portion of the exhaust manifolds 51 that communicate with each exhaust port 34). ) 52, an upstream side catalytic device 53 (also referred to as an upstream side catalytic converter or a start catalytic converter) disposed (intervened) in the exhaust pipe 52, hereinafter referred to as “first catalyst 53”). And a downstream side catalyst device 54 disposed (interposed) in the exhaust pipe 52 downstream of the first catalyst 53 (which is also referred to as an under-floor catalytic converter because it is disposed below the vehicle floor, (Hereinafter referred to as “second catalyst 54”). The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.

  On the other hand, the internal combustion engine 10 includes an air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a water temperature sensor 65, an exhaust passage upstream of the first catalyst 53 (in this example, each of the exhaust manifolds 51). An air-fuel ratio sensor 66 (hereinafter referred to as “upstream air-fuel ratio sensor 66”) disposed in a collecting portion), an exhaust passage downstream of the first catalyst 53 and upstream of the second catalyst 54. An air-fuel ratio sensor 67 (hereinafter referred to as a “downstream air-fuel ratio sensor 67”), an accelerator opening sensor 68, and a fuel that is a temperature sensor for detecting the fuel temperature in the fuel tank 45. A temperature sensor 69 is provided.

  The air flow meter 61 is configured by a known hot-wire air flow meter, and outputs a voltage Vg corresponding to the mass flow rate per unit time of the intake air flowing through the intake pipe 41. The relationship between the output Vg of the air flow meter 61 and the measured intake air amount (flow rate) Ga is as shown in FIG. The throttle position sensor 62 detects the opening of the throttle valve 43 and outputs a signal representing the throttle valve opening TA. The cam position sensor 63 generates a signal (G2 signal) having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). The crank position sensor 64 has a narrow pulse every time the crankshaft 24 rotates 10 ° and outputs a signal having a wide pulse every time the crankshaft 24 rotates 360 °. This signal represents the engine speed NE. The water temperature sensor 65 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  The upstream air-fuel ratio sensor 66 is a limiting current type oxygen concentration sensor, and outputs a current corresponding to the air-fuel ratio A / F as shown in FIG. 3, and an output value Vabyfs which is a voltage corresponding to this current. In particular, when the air-fuel ratio is the stoichiometric air-fuel ratio, the output value Vabyfs becomes the upstream target value Vstoich. As is apparent from FIG. 3, the upstream air-fuel ratio sensor 66 can accurately detect the air-fuel ratio A / F over a wide range.

  The downstream air-fuel ratio sensor 67 is an electromotive force type (concentration cell type) oxygen concentration sensor, and outputs an output value Voxs that is a voltage that suddenly changes in the vicinity of the theoretical air-fuel ratio, as shown in FIG. ing. More specifically, the downstream air-fuel ratio sensor 67 is approximately 0.1 (V) when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and is approximately 0.1 when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. When 9 (V) and the air-fuel ratio is the stoichiometric air-fuel ratio, a voltage of 0.5 (V) is output. The accelerator opening sensor 68 detects an operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal indicating the operation amount Accp of the accelerator pedal 81.

  The electric control device 70 includes a CPU 71 connected to each other by a bus, a routine (program) executed by the CPU 71, a table (look-up table, map), a ROM 72 in which parameters and the like are stored in advance, and the CPU 71 temporarily stores data as necessary. A microcomputer that includes a RAM 73 for storing data, a backup RAM 74 for storing data while the power is turned on, and holding the stored data while the power is shut off, an interface 75 including an AD converter, and the like. is there. The interface 75 is connected to the sensors 61 to 69, supplies signals from the sensors 61 to 69 to the CPU 71, and in response to instructions from the CPU 71, the actuator 33a, the igniter 38, the injector 39, and the throttle valve of the variable intake timing device 33. Drive signals are sent to the actuator 43a, the SCV actuator 44a, and the VSV 49.

<Evaporation purge control>
Since the VSV 49 is a so-called “normally closed type” on-off valve as described above, the fuel gas generated in the fuel tank 45 due to heating by sunlight or the like while the engine is stopped is the fuel tank 45, the vapor collection pipe 47. , The canister 46 and the closed space formed by the upstream side (canister 46 side) in the purge gas flow from the VSV 49 of the purge flow path 48 are filled. The fuel gas filled in the closed space is occluded in the canister 46 by being adsorbed by the adsorbent 46d.

  After that, all the conditions for performing the evaporative purge, such as (a) after warming up the engine, (b) during air-fuel ratio feedback, (c) accelerator ON, etc. Is established), the VSV 49 is opened. As is well known, when the VSV 49 is opened, the negative pressure generated in the intake pipe 41 causes the gas flow from the atmospheric port 46c of the canister 46 to the intake pipe 41 through the adsorbent 46d and the purge port 46b. When this gas flow passes through the adsorbent 46d, the fuel gas adsorbed by the adsorbent 46d is desorbed from the adsorbent 46d and purged into the intake pipe 41 as an evaporation gas. Here, as is well known, the purge rate (= vapor gas flow rate / (vapor gas flow rate + air flow meter detected air flow rate): unit is wt%) can be controlled by duty-controlling the VSV 49. The purge rate (target purge rate) that is normally applied during steady operation can be appropriately selected according to the operating state (for example, 10% during idling).

(Outline of air-fuel ratio control)
Next, an outline of the air-fuel ratio control of the engine performed by the air-fuel ratio control apparatus configured as described above will be described.

  As is well known, the first catalyst 53 (the same applies to the second catalyst 54) is configured by arranging a so-called three-way catalyst in a metal casing, and the gas flowing into the first catalyst 53. When the air-fuel ratio is substantially the stoichiometric air-fuel ratio, the three-way catalyst oxidizes HC and CO and reduces NOx, thereby purifying these harmful components with high efficiency. The three-way catalyst provided in the first catalyst 53 has a function of storing / releasing oxygen (oxygen storage function, oxygen storage / release function), and the oxygen storage / release function allows the air-fuel ratio to be the stoichiometric air-fuel ratio. HC, CO, and NOx can be purified even if they deviate to a certain extent. That is, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber (hereinafter sometimes referred to as “engine air-fuel ratio”) is lean and the gas flowing into the first catalyst 53 has a large amount of NOx. When included, the three-way catalyst provided in the first catalyst 53 takes oxygen molecules from NOx, occludes the oxygen molecules and reduces the NOx, thereby purifying NOx. Further, when the air-fuel ratio of the engine becomes rich and the gas flowing into the first catalyst 53 contains a large amount of HC and CO, the three-way catalyst releases the stored oxygen molecules and gives them to the HC and CO. This oxidizes HC and CO, thereby purifying HC and CO.

  Therefore, in order to efficiently purify a large amount of HC and CO into which the first catalyst 53 continuously flows, the three-way catalyst provided in the first catalyst 53 must store a large amount of oxygen. On the contrary, in order to efficiently purify a large amount of NOx that continuously flows in, the three-way catalyst must be in a state where it can sufficiently store oxygen. From the above, the purification capacity of the first catalyst 53 depends on the maximum oxygen amount (maximum oxygen storage amount) that the three-way catalyst can store.

  On the other hand, the three-way catalyst provided in the first catalyst 53 is deteriorated by poisoning due to lead or sulfur contained in the fuel, or heat applied to the catalyst, and accordingly, the maximum oxygen storage amount gradually decreases. As a result, the range of the catalyst window is narrowed. Even when the maximum oxygen storage amount is reduced and the catalyst window is narrowed, the air-fuel ratio of the gas discharged from the first catalyst 53 (accordingly, to suppress the emission emission amount continuously) The average air-fuel ratio of the gas flowing into the first catalyst 53 needs to be controlled with high precision so as to be very close to the stoichiometric air-fuel ratio.

  In view of this, the air-fuel ratio control apparatus of the present embodiment has an upstream feedback (hereinafter referred to as main feedback) using the output value of the upstream air-fuel ratio sensor 66 and a downstream feedback using the output value of the downstream air-fuel ratio sensor 67. Two air-fuel ratio feedback controls (hereinafter referred to as sub-feedback) are performed. In addition, fluctuations in the mechanical error of the air-fuel mixture supply system, which are difficult to compensate quickly and sufficiently by these feedback controls alone, and sudden fluctuations in the air-fuel ratio due to evaporation purge are subject to correction in each feedback control. This is compensated by correcting the basic fuel injection amount.

  More specifically, this air-fuel ratio control device (hereinafter also referred to as “the present device”) is shown in functional block diagrams of FIGS. 5 and 7 as shown in FIGS. 5 and 7. Each of the functional blocks A29 is configured. Hereinafter, each functional block will be described with reference to the drawings.

<Calculation of basic fuel injection amount>
First, the in-cylinder intake air amount calculation unit A1 stores the intake air flow rate Ga measured by the air flow meter 61, the engine rotational speed NE obtained based on the output of the crank position sensor 64, and the table stored in the ROM 72. Based on MapMc, in-cylinder intake air amount Mc (k), which is the current intake air amount of the cylinder that reaches the intake stroke, is obtained. Here, the subscript (k) indicates a value for the current intake stroke (hereinafter, the same applies to other physical quantities). The in-cylinder intake air amount Mc is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.

  The upstream target air-fuel ratio setting unit A2 is based on the engine rotational speed NE that is the operating state of the internal combustion engine 10, the throttle valve opening degree TA, and the like, and the upstream target air-fuel ratio abyfr (k ). The upstream target air-fuel ratio abyfr (k) is set to the stoichiometric air-fuel ratio except for special cases after the warm-up of the internal combustion engine 10, for example. Further, the upstream target air-fuel ratio abyfr is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.

  The pre-correction basic fuel injection amount calculation unit A3 uses the in-cylinder intake air amount Mc (k) obtained by the in-cylinder intake air amount calculation unit A1 as the upstream target air-fuel ratio set by the upstream target air-fuel ratio setting unit A2. By dividing by the abyfr (k), the target in-cylinder fuel supply amount Fcr (k) for the current intake stroke to make the engine air-fuel ratio the upstream target air-fuel ratio abyfr (k) (that is, the current correction) Obtain the previous basic fuel injection amount Fbaseb (k)). The target in-cylinder fuel supply amount Fcr and the pre-correction basic fuel injection amount Fbaseb are stored in the RAM 73 while corresponding to the intake stroke of each cylinder. The basic fuel injection amount calculation unit A3 before correction corresponds to the basic fuel injection amount acquisition unit.

  The correction coefficient setting unit A29 outputs the output KF1 from the first basic fuel injection amount correction coefficient acquisition unit A17, the output KF2 from the second basic fuel injection amount correction coefficient acquisition unit A27, and the correction coefficient according to the engine operating state. The basic fuel injection amount correction coefficient KF is set based on the outputs KFm and KFmp from the learning unit A28, and is output to the corrected basic fuel injection amount calculation unit A4. Details of the first basic fuel injection amount correction coefficient acquisition unit A17, the second basic fuel injection amount correction coefficient acquisition unit A27, the correction coefficient learning unit A28, and the correction coefficient setting unit A29 will be described later.

  The corrected basic fuel injection amount calculation unit A4 adds the basic fuel injection set by the correction coefficient setting unit A29 to the current uncorrected basic fuel injection amount Fbaseb (k) obtained by the uncorrected basic fuel injection amount calculation unit A3. By multiplying the amount correction coefficient KF, the corrected basic fuel injection amount Fbase is obtained.

  As described above, the present apparatus includes the cylinder intake air amount calculation unit A1, the upstream target air-fuel ratio setting unit A2, the uncorrected basic fuel injection amount calculation unit A3, the corrected basic fuel injection amount calculation unit A4, and the first basic fuel. The corrected basic fuel injection amount Fbase is obtained using the injection amount correction coefficient acquisition unit A17, the second basic fuel injection amount correction coefficient acquisition unit A27, the correction coefficient learning unit A28, and the correction coefficient setting unit A29. This corrected basic fuel injection amount Fbase is compensated for the air-fuel ratio fluctuation due to the mixture supply system mechanical error and evaporation purge obtained in the previous intake stroke, as will be described in detail later. In order to actually inject the fuel of the required fuel injection amount for making the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber coincide with the current upstream target air-fuel ratio abyfr (k), The target fuel injection command value (before the main and sub feedback) is the fuel injection amount command value to be instructed.

<Calculation of command fuel injection amount>
The command fuel injection amount calculation unit A5 adds a main feedback correction amount DFi_main and a sub feedback correction amount DFi_sub, which will be described later, to the corrected basic fuel injection amount Fbase (k), based on the following equation (1). The command fuel injection amount Fi (k) is obtained. The command fuel injection amount Fi (k) is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.
Fi (k) = Fbase (k) + DFi_main + DFi_sub (1)

  In this way, this apparatus is obtained by correcting the corrected basic fuel injection amount Fbase (k) based on the main feedback correction amount DFi_main and the sub feedback correction amount DFi_sub by the command fuel injection amount calculation unit A5. An instruction to inject fuel at the commanded fuel injection amount Fi (k) is given to the injector 39 for the cylinder that reaches the current intake stroke.

<Sub feedback control>
First, the downstream target value setting unit A6, like the upstream target air-fuel ratio setting unit A2, is based on the engine speed NE, which is the operating state of the internal combustion engine 10, the throttle valve opening TA, and the like. A downstream target value (predetermined downstream target value) Voxs_ref corresponding to the air-fuel ratio is determined. The downstream target value Voxs_ref is set to 0.5 (V), which is a value corresponding to the stoichiometric air-fuel ratio except for special cases, after the warm-up of the internal combustion engine 10, for example (see FIG. 4). reference.). In this example, the downstream target value Voxs_ref is set so that the downstream target air-fuel ratio corresponding to the downstream target value Voxs_ref always matches the upstream target air-fuel ratio abyfr (k).

The output deviation amount calculation unit A7 is based on the following equation (2), at the current time set by the downstream target value setting unit A6 (specifically, the current injection instruction start time of Fi (k)). The output deviation amount DVoxs is obtained by subtracting the current output value Voxs of the downstream air-fuel ratio sensor 67 from the downstream target value Voxs_ref.
DVoxs = Voxs_ref−Voxs (2)

The low-pass filter A8 is a first-order filter as shown in the following formula (3) in which the characteristic is expressed using the Laplace operator s. In the following formula (3), τ1 is a time constant. The low-pass filter A8 substantially prohibits the passage of high-frequency components having a frequency (1 / τ1) or higher. The low-pass filter A8 receives the value of the output deviation amount DVoxs obtained by the output deviation amount calculation unit A7, and is a value after low-pass filtering the value of the output deviation amount DVoxs according to the following equation (3). Output the output deviation DVoxs_low after passing a certain low-pass filter.
1 / (1 + τ1 ・ s) (3)

The PID controller A9 performs the proportional / integral / differential processing (PID processing) on the output deviation amount DVoxs_low after passing through the low-pass filter, which is the output value of the low-pass filter A8, so that the sub feedback correction amount DFi_sub is calculated based on the following equation (4). Ask.
DFi_sub = Kp · DVoxs_low + Ki · SDVoxs_low + Kd · DDVoxs_low (4)

  In the equation (4), Kp is a preset proportional gain (proportional constant), Ki is a preset integral gain (integral constant), and Kd is a preset differential gain (differential constant). SDVoxs_low is a time integral value of the output deviation amount DVoxs_low after passing through the low-pass filter, and DDVoxs_low is a time differential value of the output deviation amount DVoxs_low after passing through the low-pass filter.

  In this way, this apparatus is based on the output deviation amount DVoxs (actually, the output deviation amount DVoxs_low after passing through the low-pass filter) that is the deviation between the downstream target value Voxs_ref and the output value Voxs of the downstream air-fuel ratio sensor 67. Sub-feedback correction amount DFi_sub is obtained, and after correction by main feedback control described later (by the main feedback correction amount DFi_main) by adding the sub-feedback correction amount DFi_sub to the corrected basic fuel injection amount Fbase (k) The corrected basic fuel injection amount Fbase (k) is corrected independently of the correction of the basic fuel injection amount Fbase (k).

  For example, if the average air-fuel ratio of the engine is lean and the output value Voxs of the downstream air-fuel ratio sensor 67 indicates a value corresponding to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, the output deviation amount calculation unit A7 Since the output deviation amount DVoxs obtained by the above equation becomes a positive value (see FIG. 4), the sub feedback correction amount DFi_sub obtained by the PID controller A9 becomes a positive value. Thereby, the command fuel injection amount Fi (k) obtained by the command fuel injection amount calculation unit A5 is controlled to be larger than the corrected basic fuel injection amount Fbase (k), and the engine air-fuel ratio becomes rich. Is done.

  On the contrary, when the average air-fuel ratio of the engine is rich, the output value Voxs of the downstream air-fuel ratio sensor 67 indicates a value corresponding to the air-fuel ratio that is richer than the theoretical air-fuel ratio. Since the output deviation amount DVoxs obtained by A7 becomes a negative value, the sub feedback correction amount DFi_sub obtained by the PID controller A9 becomes a negative value. Accordingly, the command fuel injection amount Fi (k) obtained by the command fuel injection amount calculation unit A5 is controlled to be smaller than the corrected basic fuel injection amount Fbase (k), and the air-fuel ratio of the engine becomes lean. Is done.

  Further, since the PID controller A9 includes the integral term Ki · SDVoxs_low, it is guaranteed that the output deviation amount DVoxs becomes zero in a steady state. In other words, the steady deviation between the downstream target value Voxs_ref and the output value Voxs of the downstream air-fuel ratio sensor 67 becomes zero. In the steady state, since the output deviation amount DVoxs becomes zero, the proportional terms Kp / DVoxs_low and the differential terms Kd / DDVoxs_low both become zero, so the sub feedback correction amount DFi_sub is equal to the value of the integral term Ki / SDVoxs_low. . This value is a value based on a time integral value of the deviation between the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxs_ref.

  By executing such integration processing in the PID controller A9, the above-mentioned mechanical error of the air-fuel mixture supply system and air-fuel ratio fluctuation due to evaporation purge can be compensated for, and the air-fuel ratio downstream of the first catalyst 53 in the steady state ( Therefore, the engine air-fuel ratio can converge to the downstream target air-fuel ratio (that is, the stoichiometric air-fuel ratio) corresponding to the downstream target value Voxs_ref. As described above, the downstream target value setting unit A6, the output deviation amount calculation unit A7, the low pass filter A8, and the PID controller A9 correspond to the downstream feedback correction value calculation unit.

<Main feedback control>
As described above, the first catalyst 53 has an oxygen storage function. Therefore, a relatively high frequency component (for example, the frequency (1 / τ1) or more) and a relatively low frequency (for example, the above-mentioned frequency (1 / τ1) or more) in the fluctuation of the air-fuel ratio of the exhaust gas upstream of the first catalyst 53 The low-frequency component having a frequency (1 / τ1) or less and a relatively small amplitude (amount of deviation from the theoretical air-fuel ratio) is completely absorbed by the oxygen storage function of the first catalyst 53, whereby the first catalyst It does not appear as fluctuations in the air-fuel ratio of the exhaust gas downstream of 53. Therefore, for example, when the internal combustion engine 10 is in a transient operation state and the air-fuel ratio of the exhaust gas greatly fluctuates at a high frequency equal to or higher than the frequency (1 / τ1), the fluctuation of the air-fuel ratio is detected by the downstream air-fuel ratio sensor. Since the output value Voxs of 67 does not appear, air-fuel ratio control (ie, compensation for sudden change of the air-fuel ratio in a transient operation state) for air-fuel ratio fluctuations of the same frequency (1 / τ1) or more can be executed by sub-feedback control. Can not. Therefore, in order to reliably compensate for a sudden change in the air-fuel ratio in the transient operation state, it is necessary to perform main feedback control that is air-fuel ratio control based on the output value Vabyfs of the upstream air-fuel ratio sensor 66.

  On the other hand, a low frequency component having a relatively low frequency (for example, equal to or less than the frequency (1 / τ1)) in the fluctuation of the air-fuel ratio of the exhaust gas upstream of the first catalyst 53 is a first catalyst. The oxygen storage function of 53 does not completely absorb, and appears as a change in the air-fuel ratio of the exhaust gas downstream of the first catalyst 53 with a slight delay. As a result, there is a case where the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the output value Voxs of the downstream air-fuel ratio sensor 67 become values indicating the air-fuel ratio shifted in the opposite directions with respect to the theoretical air-fuel ratio. . Therefore, in this case, if the engine air-fuel ratio control based on the main feedback control (main feedback correction amount DFi_main described later) and the sub-feedback control (accordingly, the sub-feedback correction amount DFi_sub) are performed simultaneously. Since the two air-fuel ratio controls interfere with each other, good engine air-fuel ratio control cannot be performed.

  From the above, a predetermined frequency (in this example, a frequency component that can appear as a fluctuation in the air-fuel ratio downstream of the first catalyst 53 among the frequency components in the fluctuation in the output value Vabyfs of the upstream air-fuel ratio sensor 66 (in this example). If the output value Vabyfs of the upstream air-fuel ratio sensor 66 after cutting the low frequency component below the frequency (1 / τ1)) is used for the main feedback control, the air-fuel ratio control interference of the engine occurs. Can be avoided, and compensation for sudden changes in the air-fuel ratio in the transient operation state can be reliably performed.

  Therefore, as shown in FIG. 5 described above, the present apparatus is configured to include the functional blocks A10 to A16. Hereinafter, each functional block will be described with reference to FIG.

<< Calculation of main feedback correction amount >>
First, the table conversion unit A10 defines the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the relationship between the upstream air-fuel ratio sensor output value Vabyfs and the air-fuel ratio A / F shown in FIG. Based on the above, the current detected air-fuel ratio abyfs (k) at the present time detected by the upstream air-fuel ratio sensor 66 (specifically, the current Fi (k) injection instruction start time) is obtained.

  The in-cylinder intake air amount delay unit A11 is determined for each intake stroke by the in-cylinder intake air amount calculation unit A1, and among the in-cylinder intake air amount Mc stored in the RAM 73, N cylinder strokes (N intake strokes) ) The in-cylinder intake air amount Mc of the cylinder that has reached the intake stroke before is read from the RAM 73, and this is set as the in-cylinder intake air amount Mc (k−N).

  The in-cylinder fuel supply amount calculation unit A12 obtains the in-cylinder intake air amount Mc (k−N) N strokes before the current stroke obtained by the in-cylinder intake air amount delay unit A11 by the table conversion unit A10. By dividing by the detected air-fuel ratio abyfs (k), the actual in-cylinder fuel supply amount Fc (k−N) N strokes before the present time is obtained. Here, the value N differs depending on the displacement of the internal combustion engine 10, the distance from the combustion chamber 25 to the upstream air-fuel ratio sensor 66, and the like.

  Thus, in order to obtain the actual in-cylinder fuel supply amount Fc (k−N) before the N stroke from the current time, the in-cylinder intake air amount Mc (k−N) before the N stroke from the current time is determined as the current The reason for dividing by the detected air-fuel ratio abyfs (k) is that a time L1 corresponding to the N stroke is required until the air-fuel mixture fueled in the combustion chamber 25 reaches the upstream air-fuel ratio sensor 66. It is.

  The target in-cylinder fuel supply amount delay unit A13 is the target in-cylinder fuel supply amount Fcr obtained for each intake stroke by the pre-correction basic fuel injection amount calculation unit A3 and stored in the RAM 73. The in-cylinder fuel supply amount Fcr is read from the RAM 73 and set as the target in-cylinder fuel supply amount Fcr (k−N).

The in-cylinder fuel supply amount deviation calculation unit A14 calculates the target in-cylinder fuel supply amount Fcr (k−N) N strokes before the current time set by the target in-cylinder fuel supply amount delay unit A13 based on the following equation (5). ) To obtain the in-cylinder fuel supply amount deviation DFc by subtracting the actual in-cylinder fuel supply amount Fc (k−N) N strokes before the present time obtained by the in-cylinder fuel supply amount calculation unit A12. This in-cylinder fuel supply amount deviation DFc is an amount representing the excess or deficiency of the fuel supplied into the cylinder at the time point before N strokes, and is the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the upstream target value ( When the upstream target air-fuel ratio abyfr is the stoichiometric air-fuel ratio, the value is based on a deviation from Vstoich) shown in FIG.
DFc = Fcr (k−N) −Fc (k−N) (5)

The high-pass filter A15 is a first-order filter as shown in the following formula (6) in which the characteristics are expressed using the Laplace operator s. In the following equation (6), τ1 is the same time constant as the time constant τ1 of the low-pass filter A8. The high-pass filter A15 substantially prohibits the passage of a low-frequency component having a frequency (1 / τ1) or less.
1-1 / (1 + τ1 · s) (6)

  The high-pass filter A15 inputs the value of the in-cylinder fuel supply amount deviation DFc obtained by the in-cylinder fuel supply amount deviation calculation unit A14, and the value of the in-cylinder fuel supply amount deviation DFc according to the equation (6). After passing the high-pass filter, the in-cylinder fuel supply amount deviation DFchi after passing the high-pass filter is output. Accordingly, the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter is a value after high-pass filtering is performed on a value based on the deviation between the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the upstream target value.

The PI controller A16 performs proportional / integral processing (PI processing) on the in-cylinder fuel supply amount deviation DFchi that has passed through the highpass filter, which is an output value of the highpass filter A15, so that the fuel before N strokes is calculated based on the following equation (7). The main feedback correction amount DFi_main for compensating for the excess or deficiency of the supply amount (excess or deficiency of only the high frequency component at or above the frequency (1 / τ1)) is obtained.
DFi_main = (Gphi / DFchi + Gihi / SDFchi) / KFB (7)

  In the equation (7), Gphi is a preset proportional gain (proportional constant), and Gihi is a preset integral gain (integral constant). SDFchi is a time integral value of the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter. The coefficient KFB is preferably variable depending on the engine rotational speed NE, the in-cylinder intake air amount Mc, and the like, but is set to “1” in this example. The main feedback correction amount DFi_main is used when the command fuel injection amount Fi (k) is obtained by the command fuel injection amount calculation unit A5 as described above.

  In this way, the present apparatus connects the main feedback control circuit and the sub feedback control circuit in parallel to the internal combustion engine 10. Then, this apparatus passes the high-pass filter, which is a value after high-pass filter processing of a value based on the deviation between the upstream target value corresponding to the upstream target air-fuel ratio abyfr and the output value Vabyfs of the upstream air-fuel ratio sensor 66. Based on the in-cylinder fuel supply amount deviation DFchi, a main feedback correction amount DFi_main is obtained, and by adding the main feedback correction amount DFi_main to the post-correction basic fuel injection amount Fbase, the above-described sub feedback control (sub feedback correction amount The corrected basic fuel injection amount Fbase is corrected independently of the correction of the corrected basic fuel injection amount Fbase (by DFi_sub).

  For example, when the air-fuel ratio of the engine suddenly changes and becomes lean, the current detected air-fuel ratio abyfs (k) obtained by the table conversion unit A10 is N strokes before the current time set by the upstream target air-fuel ratio setting unit A2. Is obtained as a leaner value (a larger value) than the upstream target air-fuel ratio abyfr (k−N). Therefore, the actual in-cylinder fuel supply amount Fc (k−N) obtained by the in-cylinder fuel supply amount calculation unit A12 is the target in-cylinder fuel supply amount Fcr ( k−N), and the in-cylinder fuel supply amount deviation DFc is obtained as a large positive value. Further, since the signal indicating the in-cylinder fuel supply amount deviation DFc has a high frequency component equal to or higher than the frequency (1 / τ1) due to a sudden change in the air-fuel ratio of the engine, it passes through the high-pass filter after passing through the high-pass filter A15. The rear cylinder fuel supply amount deviation DFchi is also a large positive value. Therefore, the main feedback correction amount DFi_main is a large positive value. Thus, the command fuel injection amount Fi (k) obtained by the command fuel injection amount calculation unit A5 is controlled to be larger than the corrected basic fuel injection amount Fbase and the engine air-fuel ratio becomes rich. .

  On the other hand, when the air-fuel ratio of the engine suddenly changes and becomes rich, the detected air-fuel ratio abyfs (k) this time is richer (smaller than the upstream target air-fuel ratio abyfr (k−N) N strokes before the current time. Value). Therefore, the actual in-cylinder fuel supply amount Fc (k−N) is larger than the target in-cylinder fuel supply amount Fcr (k−N), and the in-cylinder fuel supply amount deviation DFc is obtained as a negative value. Further, since the signal indicating the in-cylinder fuel supply amount deviation DFc due to a sudden change in the air-fuel ratio of the engine has a high frequency component equal to or higher than the frequency (1 / τ1), the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter. Is also a negative value. Therefore, the main feedback correction amount DFi_main is a negative value. As a result, the command fuel injection amount Fi (k) is controlled to be smaller than the corrected basic fuel injection amount Fbase so that the air-fuel ratio of the engine becomes lean. The table conversion unit A10, the cylinder intake air amount delay unit A11, the cylinder fuel supply amount calculation unit A12, the target cylinder fuel supply amount delay unit A13, the cylinder fuel supply amount deviation calculation unit A14, the high pass filter A15, and The PI controller A16 corresponds to an upstream feedback correction value calculation unit.

  In this manner, the substantial air-fuel ratio control with respect to the air-fuel ratio fluctuation below the frequency (1 / τ 1) that can appear as the air-fuel ratio fluctuation downstream of the first catalyst 53 can be reliably performed by the sub-feedback control. At the same time, since the low frequency component equal to or lower than the same frequency (1 / τ1) cannot pass through the high pass filter A15 and is not input to the PI controller A16, it is possible to avoid the above-described interference in the air / fuel ratio control of the engine. Further, since the high frequency component equal to or higher than the frequency (1 / τ1) in the variation of the air-fuel ratio of the engine (and hence the variation of the output value Vabyfs of the upstream air-fuel ratio sensor 66) passes through the high-pass filter A15, Compensation for a sudden change in the air-fuel ratio can be performed quickly and reliably by the main feedback control.

<Overview of basic fuel injection correction factor KF>
As described above, the integration process is executed in the PID controller A9, so that the above-described mechanical error of the air-fuel mixture supply system and the air-fuel ratio fluctuation due to the evaporation purge can be compensated for in the sub-feedback control. However, since the change in the air-fuel ratio of the engine is slightly delayed due to the effect of the oxygen storage function of the first catalyst 53 described above, it appears as a change in the air-fuel ratio of the exhaust gas downstream of the first catalyst 53. There is a problem that the sudden increase in the mechanical error of the air-fuel mixture supply system or the air-fuel ratio fluctuation due to the evaporation purge cannot be compensated immediately, and as a result, the emission emission amount temporarily increases.

  Therefore, it is necessary to be able to immediately compensate for the mechanical error of the air-fuel mixture supply system and the air-fuel ratio fluctuation caused by the evaporation purge even in the main feedback control without the influence of the delay due to the oxygen storage function. However, since the high pass filter process is a process having a function equivalent to the differential process (D process), in the main feedback control in which the value after passing through the high pass filter A15 is the input value of the PI controller A16, The integration process cannot be executed. Therefore, in the main feedback control, the mechanical error of the air-fuel mixture supply system and the air-fuel ratio fluctuation due to evaporation purge cannot be compensated.

  From the above, it is necessary to immediately compensate for the mechanical error of the air-fuel mixture supply system and the air-fuel ratio fluctuation due to evaporation purge without using the integration process by the main feedback control and the sub feedback control. For this purpose, the corrected basic fuel injection amount Fbase, which is a value other than the main feedback correction amount DFi_main and the sub feedback correction amount DFi_sub among the values for determining the command fuel injection amount Fi, is supplied to the combustion chamber. In order to set the actual air-fuel ratio of the engine to the target air-fuel ratio abyfr (that is, in order to make the actually injected fuel become the required fuel injection amount), the target to be instructed to be injected to the injector 39 of the cylinder that reaches the intake stroke The fuel injection command value (hereinafter referred to as “target basic fuel injection amount Fbaset”) needs to be corrected so as to match (approach).

  For this purpose, as can be understood from FIG. 5, a certain correction coefficient (basic fuel injection amount) is added to the current pre-correction basic fuel injection amount Fbaseb (k) which is the output value from the pre-correction basic fuel injection amount calculation unit A3. By multiplying by the correction coefficient (KF), it is necessary to make the basic fuel injection amount (after correction) subject to main feedback and sub-feedback as close as possible to (approach) the target basic fuel injection amount Fbaset It is. Hereinafter, a method for setting the basic fuel injection amount correction coefficient KF will be described.

In general, under the assumption that the in-cylinder intake air amount sucked into the combustion chamber is constant, the fuel injection amount and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber (and hence the air-fuel ratio of the exhaust gas) The product is constant. Therefore, under such an assumption, in general, the product of the command fuel injection amount Fi and the air-fuel ratio abyfs detected by the upstream air-fuel ratio sensor 66 is the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber. A relationship is established that is equal to the product of the target basic fuel injection amount Fbaset required for setting the target air-fuel ratio abyfr (k) and the target air-fuel ratio abyfr (k). Therefore, the target basic fuel injection amount Fbaset can be generally expressed according to the following equation (8).
Fbaset = (abyfs / abyfr (k)) ・ Fi (8)

Here, as described above, the value obtained by multiplying the basic fuel injection amount Fbaseb (k) before correction by the basic fuel injection amount correction coefficient KF is equal to the target basic fuel injection amount Fbaset obtained according to the equation (8). Since the correction coefficient KF is set as described above, the correction coefficient KF can be set according to the following equation (9).
KF = Fbaset / Fbaseb (k) (9)

  By the way, from the fuel injection instruction until the air-fuel ratio of the exhaust gas based on the combustion of the fuel injected by the injection instruction appears as the output value Vabyfs of the upstream air-fuel ratio sensor 66, the above-described process delay, transport delay, And a delay time L2 expressed as a sum of response delays. In other words, the air-fuel ratio abyfs detected by the upstream air-fuel ratio sensor 66 is a value representing the air-fuel ratio of the exhaust gas generated based on the fuel injection instruction executed before the delay time L2.

  Accordingly, when the target basic fuel injection amount Fbaset is calculated according to the above equation (8), the current detected air-fuel ratio abyfs (k) is used as the detected air-fuel ratio abyfs, while the command fuel injection amount Fi More specifically, the command fuel injection amount related to the fuel injection instruction executed before the M stroke (M intake strokes) corresponding to the delay time L2 from the current Fi (k) injection instruction start time). It is preferable that the command fuel injection amount Fi (k−M) before the M stroke is used from a certain present time.

  Then, the above-described stroke delay and the time related to the transport delay become shorter as the engine speed NE increases, and the time related to the transport delay tends to become shorter as the in-cylinder intake air amount Mc increases. is there. Accordingly, the delay time L2 (and therefore the value M) is, for example, the engine rotational speed NE, the in-cylinder intake air amount Mc (k), and the engine rotational speed NE and in-cylinder intake air shown in the graph of FIG. It can be obtained based on a table MapMc that defines the relationship between the quantity Mc and the number of strokes M.

  Further, when the engine is in a transient operation state, the detected air-fuel ratio abyfs, the command fuel injection amount Fi, and the pre-correction basic fuel injection amount Fbaseb can vary greatly at a high frequency equal to or higher than a predetermined frequency. In such a case, there is a possibility that the relationship shown in the equation (8) and the equation (9) cannot be maintained. Therefore, in order to perform stable air-fuel ratio control while eliminating the influence of such high frequency fluctuations, low-pass filter processing (or so-called annealing processing equivalent to low-pass filter processing) is performed when obtaining the basic fuel injection amount correction coefficient KF. Is preferably used.

<< Calculation of first basic fuel injection correction factor KF1 >>
From the above, the first basic fuel injection amount correction coefficient acquisition unit A17 includes the functional blocks (arithmetic processing units) A17a to A17d as shown in FIG. Has been. That is, the first basic fuel injection amount correction coefficient acquisition unit A17 includes a command fuel injection amount delay unit A17a for acquiring a command fuel injection amount Fi (k−M) before the M stroke corresponding to the delay time L2, This detected air-fuel ratio abyfs (k), which is a signal obtained by converting the output value of the upstream air-fuel ratio sensor 66 into an air-fuel ratio by the table conversion unit A10, and the current intake air that is an output signal from the upstream target air-fuel ratio setting unit A2 A target basic fuel injection amount calculation unit A17b that receives the upstream target air-fuel ratio abyfr (k) of the stroke and an output signal from the command fuel injection amount delay unit A17a, and a target basic fuel injection amount calculation unit A17b Basic fuel injection correction using the current target basic fuel injection amount Fbaset as an output signal and the current pre-correction basic fuel injection amount Fbaseb (k) as an output signal from the pre-correction basic fuel injection amount calculation unit A3 as inputs. Coefficient calculator A 17c, and a low-pass filter A17d that receives the output signal from the basic fuel injection amount correction coefficient calculation unit A17c and outputs the first basic fuel injection amount correction coefficient KF1.

The low-pass filter A17d is a first-order filter as shown in the following formula (10) that expresses the characteristics using the Laplace operator s. In the following equation (10), τ2 is a time constant (a parameter relating to the response of the filter). The low-pass filter A17d substantially prohibits the passage of high frequency components having a frequency (1 / τ2) or higher.
1 / (1 + τ2 ・ s) (10)

  The command fuel injection amount delay unit A17a is based on the above-described value M based on the above-described table MapMc stored in the ROM 72, the current engine speed NE, and the current in-cylinder intake air amount Mc (k). Ask for. Then, the command fuel injection amount delay unit A17a is determined for each intake stroke by the command fuel injection amount calculation unit A5, and among the command fuel injection amounts Fi stored in the RAM 73, M strokes (M intake strokes) from the present time. The previous value is read from the RAM 73 and set as the command fuel injection amount Fi (k−M).

The target basic fuel injection amount calculation unit A17b is obtained by dividing the value of the detected air-fuel ratio abyfs (k) by the current target air-fuel ratio abyfr (k) according to the following equation (11) corresponding to the above (8). The target basic fuel injection amount Fbaset is obtained by multiplying the value by the value of the command fuel injection amount Fi (k−M).
Fbaset = (abyfs (k) / abyfr (k)) ・ Fi (k−M) (11)

The basic fuel injection amount correction coefficient calculation unit A17c calculates the target basic fuel injection amount Fbaset obtained by the target basic fuel injection amount calculation unit A17b according to the following equation (12) corresponding to (9) above before the basic fuel injection amount before correction. By dividing by Fbaseb (k), the basic fuel injection amount correction coefficient KF0 before the low-pass filter processing is obtained.
KF0 = Fbaset / Fbaseb (k) (12)

  The low-pass filter A17d receives the value of the basic fuel injection amount correction coefficient KF0 before the low-pass filter processing obtained by the basic fuel injection amount correction coefficient calculation unit A17c as an input, and uses the value of the KF0 as a low-pass filter according to the equation (10). A basic fuel injection amount correction coefficient KF1, which is a value after processing, is output.

<< Calculation of second basic fuel injection correction factor KF2 >>
Further, the second basic fuel injection amount correction coefficient acquisition unit A27 has the same configuration as the first basic fuel injection amount correction coefficient acquisition unit A17, and is a functional block diagram shown in FIG. 7B. As shown, each command block includes a command fuel injection amount delay unit A27a, a target basic fuel injection amount calculation unit A27b, a basic fuel injection amount correction coefficient acquisition unit A27c, and a low-pass filter A27d. Has been.

  The low-pass filter A27d in the second basic fuel injection amount correction coefficient acquisition unit A27 receives the output signal from the basic fuel injection amount correction coefficient acquisition unit A27c and outputs a second basic fuel injection amount correction coefficient KF2. Here, the low-pass filter A27d substantially prohibits the passage of high-frequency components having a frequency (1 / τ3) or higher, like the low-pass filter A17d, and its time constant τ3 is the first basic fuel. It is set smaller than the time constant τ2 of the low-pass filter A17d in the injection amount correction coefficient acquisition unit A17.

<< Setting of basic fuel injection amount correction coefficient KF by correction coefficient setting section >>
When not purged, the first basic fuel injection amount correction coefficient KF1 obtained by the first basic fuel injection amount correction coefficient acquisition unit A17 is set as the basic fuel injection amount correction coefficient KF by the correction coefficient setting unit A29. As a result, it is output to the corrected basic fuel injection amount calculation unit A4 and used for obtaining the corrected basic fuel injection amount Fbase for obtaining the current command fuel injection amount Fi (k). On the other hand, the second basic fuel injection amount correction coefficient KF2 obtained by the second basic fuel injection amount correction coefficient acquisition unit A27 is the corrected basic fuel injection for obtaining the current command fuel injection amount Fi (k). It is not used for obtaining the quantity Fbase.

  On the other hand, at the time of purging, the second basic fuel injection amount correction coefficient KF2 obtained by the second basic fuel injection amount correction coefficient acquisition unit A27 is set as the basic fuel injection amount correction coefficient KF by the correction coefficient setting unit A29. Is output to the corrected basic fuel injection amount calculation unit A4 and is used for obtaining the corrected basic fuel injection amount Fbase for obtaining the current command fuel injection amount Fi (k). On the other hand, the first basic fuel injection amount correction coefficient KF1 obtained by the first basic fuel injection amount correction coefficient acquisition unit A17 is the basic fuel injection amount correction for obtaining the current command fuel injection amount Fi (k). Although not used as the coefficient KF, the correction coefficient learning unit A28 uses it for purge learning to suppress as much as possible the rapid fluctuation of the actual air-fuel ratio immediately after the start of purge.

  That is, as described above, the basic fuel injection amount correction by the basic fuel injection amount correction coefficient KF is performed based on the output of the upstream air-fuel ratio sensor 66 in order to quickly compensate for a mechanical error of the air-fuel mixture supply system. However, on the other hand, since there is a demand for realizing stable basic fuel injection amount correction by suppressing vibration with a large correction amount as much as possible, low pass filter processing is performed when acquiring the basic fuel injection amount correction coefficient KF. Done.

  For this reason, during normal steady operation (non-purge), the first basic fuel injection amount obtained by the first basic fuel injection amount correction coefficient acquisition unit A17 provided with the low-pass filter A17d having a relatively large time constant τ2. By setting the correction coefficient KF1 as the basic fuel injection amount correction coefficient KF in the correction coefficient setting unit A29, appropriate air-fuel ratio control by stable basic fuel injection amount correction can be maintained. As described above, the time constant τ2 of the low-pass filter A17d used at the time of non-purge is as much as possible within a range that does not hinder the quickness when compared with the responsiveness of the air-fuel ratio compensation by the main and sub-feedback (integral term). Larger is preferable.

  On the other hand, the evaporation purge corresponds to a sudden and large disturbance to the air-fuel ratio control system. Therefore, in order to quickly compensate for the fluctuation of the air-fuel ratio due to the evaporation purge by the basic fuel injection amount correction, the actual air-fuel ratio fluctuation (upstream air-fuel ratio) of the low-pass filter processing performed when acquiring the basic fuel injection amount correction coefficient KF is performed. It is necessary to improve the response to the detected air-fuel ratio of the fuel ratio sensor 66). Therefore, at the time of purging, the second basic fuel injection amount correction coefficient KF2 obtained by the second basic fuel injection amount correction coefficient acquisition unit A27 provided with the low-pass filter A27d having a time constant τ3 smaller than the time constant τ2 is the correction coefficient. By setting the basic fuel injection amount correction coefficient KF in the setting unit A29, the air-fuel ratio fluctuation due to the evaporation purge can be quickly compensated.

  Even when the air-fuel ratio is quickly compensated by the output value KF2 of the second basic fuel injection amount correction coefficient acquisition unit A27 provided with the low-pass filter A27d having a small time constant τ3 as described above at the time of purging, immediately after the purge is started. In this case, there is a concern that the emission temporarily deteriorates until the air-fuel ratio is effectively compensated by the second basic fuel injection amount correction coefficient KF2.

  Therefore, before the elapse of a predetermined time from the start of the purge, the correction coefficient setting unit A29 is based on the purge basic fuel injection amount correction coefficient learning value (hereinafter referred to as “purge learning value”) KFmp learned in the previous purge. A fuel injection amount correction coefficient KF is calculated, and after the predetermined time has elapsed, a basic fuel injection amount correction coefficient KF is calculated based on the second basic fuel injection amount correction coefficient KF2 to perform basic fuel injection amount correction. Hereinafter, acquisition of the purge learning value KFmp (purging learning) will be described.

<< Purge learning control >>
When the intake air flow rate Ga and the engine speed NE are the same (and therefore the in-cylinder intake air amount Mc (k) is the same) in the purge and non-purge periods, it is acquired by the pre-correction basic fuel injection amount calculation unit A3. The basic fuel injection amount Fbaseb (k) before correction and the mechanical error of the air-fuel mixture intake system are the same when purging and when not purging. Nevertheless, at the start of the first purge, the amount of fuel introduced into the combustion chamber 25 increases (becomes rich) by an amount corresponding to the amount of fuel in the purge gas than when not purged. Immediately after the air-fuel mixture shifted to the rich side at the start of the purge is burned in the combustion chamber 25, the air-fuel ratio output of the upstream air-fuel ratio sensor 66 is shifted to the rich side. The target basic fuel injection amount Fbaset calculated based on the air-fuel ratio output of the upstream side air-fuel ratio sensor 66 shifted to the rich side is obtained from the (normal) target basic fuel injection amount Fbaset calculated at the time of non-purge by evaporation purge. The surplus fuel amount, which is the fuel amount for the air-fuel ratio rich shift, is a compensated (subtracted) value. That is, in the same in-cylinder intake air amount Mc (k), the difference in the target basic fuel injection amount Fbaset between the non-purge time and the purge time excludes the influence of the mechanical error of the air-fuel mixture intake system. This corresponds to the pure surplus fuel amount.

  Therefore, based on the premise that the pre-correction basic fuel injection amount Fbaseb (k) is the same for the same in-cylinder intake air amount Mc (k) and the above equation (9), the first basic fuel injection at the non-purging time The deviation between the amount correction coefficient KF1nonpurge and the first basic fuel injection amount correction coefficient KF1purge at the time of purge is a value reflecting the above-described surplus fuel amount. That is, the first basic fuel injection amount correction coefficient KF1purge at the time of purging is caused by the evaporative purge in addition to the first basic fuel injection amount correction coefficient KF1nonpurge at the time of non-purge that compensates for the mechanical error of the air-fuel mixture intake system described above. This value compensates for air-fuel ratio fluctuations. Therefore, the first basic fuel injection amount correction coefficient KF1purge at the time of the previous purge for the same in-cylinder intake air amount Mc (k) is learned and stored in the RAM 73 as the purge learning value KFmp, and based on this, the basic fuel is determined. By calculating the injection amount correction coefficient KF and correcting the basic fuel injection amount, at the time of the second and subsequent purges with the same in-cylinder intake air amount Mc (k), the air-fuel ratio fluctuations due to the purge immediately after the purge is started Will be compensated to some extent.

  Here, the learning of the purge learning value KFmp described above is performed by the correction coefficient learning unit A28, the first basic fuel injection amount correction coefficient acquisition unit provided with the low-pass filter A17d having a large time constant τ2 after the elapse of time t0 from the purge start time. When the output value from A17 (first basic fuel injection amount correction coefficient KF1) is sufficiently stable, the output value of the first basic fuel injection amount correction coefficient KF1 is stored in the RAM 73 as a learning value. As a result, accurate purge learning is performed.

  FIG. 8 shows an outline of the purge learning at the time of the first purge as described above and the second air-fuel ratio control (in the same classification of the in-cylinder intake air amount Mc (k)) using the purge learning value by this purge learning. I will explain it.

First, at the time of the first purge, as shown in FIG. 8A, the air-fuel ratio fluctuations to the rich side due to the evaporative purge from the initial purge start time (t _PGR = 0) (exactly after a predetermined transport delay time elapses). Appears in the upstream air-fuel ratio sensor 66, the output value KF1 of the first basic fuel injection amount correction coefficient acquisition unit A17 and the output value KF2 of the second basic fuel injection amount correction coefficient acquisition unit A27 vary.

  In this case, since the output value KF2 of the second basic fuel injection amount correction coefficient acquisition unit A27 is based on the output of the low-pass filter A27d having a small time constant τ3, it has high responsiveness to air-fuel ratio fluctuations due to evaporation purge. Follow. Therefore, the basic fuel injection amount correction coefficient KF is calculated by the correction coefficient setting unit A29 based on the output value KF2 of the second basic fuel injection amount correction coefficient acquisition unit A27. As a result, the rapid air-fuel ratio fluctuation due to the initial (before purge learning) evaporation purge is compensated with high responsiveness.

On the other hand, the output value KF1 of the first basic fuel injection amount correction coefficient acquisition unit A17 is based on the output of the low-pass filter A17d having a large time constant τ2, and therefore gradually changes to a constant value KFmp while fluctuating at a low frequency. Shows a behavior that converges. Therefore, after the purge time has elapsed by the predetermined time t0 (t _PGR = t0), the output value of KF1 is acquired as the purge learning value KFmp. That is, as apparent from FIG. 8A, when the purge time has elapsed for a predetermined time t0 (t _PGR = t0), the value of KF2 fluctuates at a high frequency, whereas the value of KF1 fluctuates. Therefore, purge learning can be performed with high accuracy by sequentially learning KF1 to KFmp from the time point t _PGR = t0.

  After the purge learning is performed as described above, the basic fuel injection amount correction at the time of purging is performed based on the learning value KFmp. Therefore, as shown in FIG. 8B, the air-fuel ratio fluctuation during the purge after purge learning (especially immediately after the start of the purge) is suppressed more than during the first purge (see FIG. 8A).

  When the purge time reaches t0 during the second purge shown in FIG. 8B, KFmp is sequentially learned as in FIG. 8A. In the third and subsequent purges (in the same classification of the in-cylinder intake air amount Mc (k)), the same processing as in the second purge described above is performed.

In this sequential learning (update of stored value) of KFmp, the updated value KFmp to be newly stored this time is obtained by the following equation (13) based on the previous value of KFmp ′ and the current value of KF1.
KFmp = KFmp ′ − (KFmp′−KF1) × β (13)

<< Storage processing of basic fuel injection amount correction coefficient >>
In “when the output value Vabyfs of the upstream air-fuel ratio sensor 66 does not become a normal value” such as during the warm-up operation of the internal combustion engine, the detected air-fuel ratio abyfs does not become a value that accurately represents the air-fuel ratio of the exhaust gas. In such a case, the value of the basic fuel injection amount correction coefficient KF calculated according to the equation (11) (and the equation (12)) using the value of the detected air-fuel ratio abyfs is also the basic fuel injection amount before correction. It is not a value for accurately correcting Fbaseb (k) so that it becomes the target basic fuel injection amount Fbaset. Therefore, in such a case, the basic fuel injection amount correction coefficient KF calculated according to the above equations (11) and (12) should not be used for correcting the pre-correction basic fuel injection amount Fbaseb (k).

  Therefore, this apparatus is not purged and only when “the output value Vabyfs of the upstream air-fuel ratio sensor 66 becomes a normal value (specifically, when a main feedback condition described later is satisfied)”. The basic fuel injection amount Fbaseb (k) before correction is corrected using the basic fuel injection amount correction coefficient KF calculated according to the above equation (11) and the above equation (12), and the calculated first The value of the basic fuel injection amount correction coefficient KF1 is sequentially stored and updated in the backup RAM 74 as the basic fuel injection amount correction coefficient storage value KFm by the correction coefficient learning unit A28.

  Here, when the intake air flow rate Ga increases (and hence the in-cylinder intake air amount Mc also increases), the mechanical error of the air-fuel mixture supply system, such as a Ga measurement error by the air flow meter 61, naturally increases. There is a tendency to increase according to Mc (thus, the value of the basic fuel injection amount correction coefficient KF increases according to the in-cylinder intake air amount Mc). Therefore, as shown in FIG. 9, the present apparatus divides the possible range of the cylinder intake air amount Mc into a plurality of (in this example, four) classifications. Then, every time the new first basic fuel injection amount correction coefficient KF1 is calculated, the present apparatus selects the class to which the current in-cylinder intake air amount Mc (k) belongs and corresponds to the selected class. The basic fuel injection amount correction coefficient memory value KFm (j) (j: 1, 2, 3, 4) is updated and stored based on the calculated first basic fuel injection amount correction coefficient KF1. To go.

Regarding this sequential update of KFm, the update value KFm to be newly stored this time is obtained by the following equation (14) based on the previous KFm ′ value and the current KF1 value.
KFm = KFm ′ − (KFm′−KF1) × α (14)

  On the other hand, in the case where “the output value Vabyfs of the upstream side air-fuel ratio sensor 66 does not become a normal value (specifically, when a main feedback condition described later is not satisfied)” The classification to which the amount Mc (k) belongs is selected, and the classification selected from the basic fuel injection amount correction coefficient stored values KFm (j) (j: 1, 2, 3, 4) stored in the backup RAM 74 The basic fuel injection amount correction coefficient stored value KFm is used in place of the basic fuel injection amount correction coefficient KF calculated according to the equations (11) and (12). The fuel injection amount Fbaseb (k) is corrected. As a result, even when “the output value Vabyfs of the upstream air-fuel ratio sensor 66 does not become a normal value”, the basic fuel injection amount Fbaseb (k) before correction is made to coincide with the target basic fuel injection amount Fbaset with a certain degree of accuracy. As a result, the mechanical error of the mixture supply system is compensated to some extent.

  However, when the evaporation purge is being performed, the value of the basic fuel injection amount correction coefficient KF in a state where disturbance to the air-fuel ratio control system due to the evaporation purge has entered is “the output value Vabyfs of the upstream air-fuel ratio sensor 66 is a normal value. It should not be learned as a correction value for “if not”. Therefore, when the evaporative purge is being performed, the basic fuel injection amount correction coefficient stored value KFm is not updated.

  As described above, the first basic fuel injection amount correction coefficient acquisition unit A17 and the second basic fuel injection amount correction coefficient acquisition unit A27 have reached the fuel injection time point (more specifically, the time point when the injection instruction is started). Each time, KF1 and KF2 are acquired using the functional blocks A17a to A17d and A27a to A27d. Further, the correction coefficient learning unit A28 learns the basic fuel injection amount correction coefficient during purge and non-purge. Further, the correction coefficient setting unit A29 calculates a basic fuel injection amount correction coefficient KF based on KF1, KF2, KFm, and KFmp according to the operating state of the engine. Then, the present apparatus corrects the next uncorrected basic fuel injection amount Fbaseb by multiplying the next uncorrected basic fuel injection amount Fbaseb by the basic fuel injection amount correction coefficient KF set this time in this way ( That is, the next corrected basic fuel injection amount Fbase is determined). Therefore, the corrected basic fuel injection amount Fbase for the next time matches (approaches) the fuel injection amount to be instructed for injection in order to set the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to the target air-fuel ratio abyfr. As a result, while the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled toward the target air-fuel ratio abyfr, the mechanical error of the air-fuel mixture supply system and the air-fuel ratio fluctuation due to evaporation purge are quickly compensated. Go.

  Thus, according to the above-described configuration, the second basic fuel obtained by the second basic fuel injection amount correction coefficient acquisition unit A27 provided with the low-pass filter A27d having a small time constant τ3 is used for the actual air-fuel ratio compensation at the time of purging. Since the injection amount correction coefficient KF2 is used, fluctuations in the air-fuel ratio due to evaporation purge can be quickly compensated. On the other hand, purge learning at the time of purging is performed using the first basic fuel injection amount correction coefficient KF1 obtained by the first basic fuel injection amount correction coefficient acquisition unit A17 provided with the low-pass filter A17d having a large time constant τ2. As a result, purge learning with high accuracy can be performed. That is, according to the above configuration, the purge learning can be performed with high accuracy while compensating for the air-fuel ratio fluctuation due to the evaporation purge as quickly as possible.

  Further, according to the above configuration, the first basic fuel injection amount correction obtained by the first basic fuel injection amount correction coefficient acquisition unit A17 includes the actual air-fuel ratio compensation during non-purge and the purge learning during purge. Since the process is performed using the coefficient KF1, the quickest possible compensation of the air-fuel ratio fluctuation due to the above-described evaporation purge and accurate purge learning can be achieved with a simple control system configuration.

As described above, the first basic fuel injection amount correction coefficient acquisition unit A17 and the second basic fuel injection amount correction coefficient acquisition unit A27 correspond to the basic fuel injection amount correction value acquisition unit, and the first basic fuel injection amount correction coefficient acquisition unit A17. The low-pass filter A17d corresponds to the first filter, and the low-pass filter A27d of the second basic fuel injection amount correction coefficient acquisition unit A27 corresponds to the second filter. The correction coefficient learning unit A28 corresponds to the purge learning unit.
The above is the outline of the air-fuel ratio feedback control of the engine by this apparatus.

(Actual operation)
Next, actual operation of the air-fuel ratio control apparatus will be described.

<Air-fuel ratio feedback control>
The CPU 71 performs a routine for calculating the fuel injection amount Fi shown in the flowchart of FIG. 10 and instructing the fuel injection. The crank angle of each cylinder is a predetermined crank angle before each intake top dead center (for example, BTDC 90 ° CA). Each time it becomes, it is executed repeatedly. Therefore, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts processing of the “Fi calculation / injection” routine 1000.

  First, in step 1005, based on the intake air flow rate Ga measured by the air flow meter 61, the engine rotational speed NE, and the above-described table MapMc, a cylinder that reaches the current intake stroke (hereinafter referred to as “fuel injection cylinder”). In this case, the in-cylinder intake air amount Mc (k) taken in this time is estimated and determined.

  Next, the CPU 71 proceeds to step 1010, in which the value obtained by dividing the estimated in-cylinder intake air amount Mc (k) by the current target air-fuel ratio abyfr (k) is the current pre-correction basic fuel injection amount Fbaseb ( Determine as k). Thereafter, the CPU 71 proceeds to step 1015 to store the basic fuel injection amount correction coefficient storage value KFm (j) (j: 1, 2, 2) stored in the backup RAM 74 in the pre-correction basic fuel injection amount Fbaseb (k). 3), a value corresponding to the value of in-cylinder intake air amount Mc (k) determined in the previous step 1005 is read out and determined as the value of “KFm” in this flow.

  Subsequently, the CPU 71 proceeds to step 1020 to determine whether or not the main feedback condition is satisfied. Here, the main feedback condition is, for example, that the coolant temperature THW of the engine is equal to or higher than the first predetermined temperature and the upstream air-fuel ratio sensor 66 is normal (including that the engine is in an active state). This is established when the intake air amount (load) per rotation is a predetermined value or less. That is, the fact that the main feedback condition is satisfied corresponds to the above-described “when the output value Vabyfs of the upstream air-fuel ratio sensor 66 becomes a normal value”.

  When the main feedback condition is not satisfied (step 1020 = “No”), the CPU 71 proceeds to step 1025, sets the determined KFm value as the basic fuel injection amount correction coefficient KF, and then proceeds to step 1030. A value obtained by multiplying the basic fuel injection amount Fbaseb (k) before correction by the basic fuel injection amount correction coefficient KF set in step 1025 is set as the corrected basic fuel injection amount Fbase. Next, the CPU 71 proceeds to step 1035 to obtain the corrected basic fuel injection amount Fbase obtained as described above according to the equation (1) by a routine described later (at the time of the previous fuel injection). The value obtained by adding the latest main feedback correction amount DFi_main and the latest sub feedback correction amount DFi_sub obtained in the routine described later (at the time of the previous fuel injection) to the current command fuel injection amount Fi (k) Asking. Then, the CPU 71 proceeds to step 1040 to instruct fuel injection of the command fuel injection amount Fi (k). Specifically, when the fuel injection start time calculated separately by a routine (not shown) arrives, the CPU 71 instructs to open the injector 39 of the fuel injection cylinder for a time corresponding to the commanded fuel injection amount Fi (k). Is performed on the injector 39 to inject fuel. Then, the CPU 71 proceeds to step 1095 to end the present routine tentatively.

  When the main feedback condition is satisfied (step 1020 = “Yes”), the CPU 71 proceeds to step 1045 to determine whether the purge condition is satisfied.

  If the purge condition is not satisfied (step 1045 = “No”), since the purge is not currently being performed, the CPU 71 proceeds to step 1050 and is obtained by a routine described later (at the time of the previous fuel injection). A value obtained by multiplying the latest first basic fuel injection amount correction coefficient KF1 by the value of the determined KFm is set as the basic fuel injection amount correction coefficient KF. Thereafter, steps 1030, 1035, 1040, and 1095 are sequentially executed in the same manner as described above to perform normal (non-purge) basic fuel injection amount correction.

  If the purge condition is satisfied (step 1045 = “Yes”), since the purge is currently being performed, the CPU 71 proceeds to step 1060 to determine whether or not the purge learning value KFmp has not been calculated.

  When the purge learning value KFmp has not been calculated (step 1060 = “Yes”), the CPU 71 proceeds to step 1065, and the latest second basic fuel obtained in a routine described later (at the time of the previous fuel injection). A value obtained by multiplying the injection amount correction coefficient KF2 by the value of the determined KFm is set as the basic fuel injection amount correction coefficient KF. Thereafter, steps 1030, 1035, 1040, and 1095 are sequentially executed in the same manner as described above to perform basic fuel injection amount correction at the time of purge before purge learning. That is, when purge learning is not performed, such as at the time of the first purge, purge learning is performed using the stable output value KF1 of the first basic fuel injection amount correction coefficient acquisition unit A17 with suppressed responsiveness as described above. While performing (a specific flow will be described later), the actual air-fuel ratio compensation for the purge is performed using the output value KF2 of the second basic fuel injection amount correction coefficient acquisition unit A27 with improved responsiveness immediately after the start of the purge. Done quickly.

  On the other hand, when the purge learning value KFmp has been calculated (step 1060 = “No”), the CPU 71 proceeds to step 1070 and the latest second obtained in the routine described later (at the time of the previous fuel injection). A value obtained by multiplying the basic fuel injection amount correction coefficient KF2 by the value of the determined KFm and the purge learning value KFmp is set as the basic fuel injection amount correction coefficient KF. Thereafter, steps 1030, 1035, 1040, and 1095 are sequentially executed in the same manner as described above to perform basic fuel injection amount correction at the time of purge after purge learning. This makes it possible to maintain good air-fuel ratio control in which emission deterioration is suppressed as much as possible by using the purge learning value KFmp even immediately after the start of purge.

  As described above, the basic fuel injection amount Fbaseb (k) before correction is corrected by the appropriate value of the basic fuel injection amount correction coefficient KF according to the operation state such as the presence or absence of purge or the presence or absence of purge learning. The fuel injection instruction of the command fuel injection amount Fi (k) after the base fuel injection amount Fbaseb (k) before correction (that is, the base fuel injection amount Fbase after correction) is subjected to the main feedback correction and the sub feedback correction is the fuel. The fuel is injected into the injection cylinder.

<Calculation of main feedback correction amount>
Next, the operation when calculating the main feedback correction amount DFi_main in the main feedback control will be described. The CPU 71 executes the “main feedback correction amount DFi_main calculation” routine 1100 shown in the flowchart of FIG. 11 for the fuel injection cylinder. Each time the injection start time (injection instruction start time) arrives, it is repeatedly executed. Accordingly, when the fuel injection start timing has arrived for the fuel injection cylinder, the CPU 71 starts the processing of the routine 1100. First, in step 1105, it is determined whether or not the main feedback condition is satisfied. This main feedback condition is the same as the main feedback condition in the previous step 1005.

  Now, assuming that the main feedback condition is satisfied, the CPU 71 makes a “Yes” determination at step 1105 to proceed to step 1110, and the upstream air-fuel ratio sensor at the present time (ie, the injection instruction start time). The current detected air-fuel ratio abyfs (k) is obtained by converting the output value Vabyfs of 66 based on the table shown in FIG.

  Next, the CPU 71 proceeds to step 1115 to obtain the in-cylinder intake air amount Mc (k−N), which is the intake air amount of the cylinder that has reached the intake stroke before N strokes (N intake strokes) from the present time. By dividing by the detected air-fuel ratio abyfs (k), the actual in-cylinder fuel supply amount Fc (k−N) N strokes before the present time is obtained.

  Next, the CPU 71 proceeds to step 1120 and divides the in-cylinder intake air amount Mc (k−N) N strokes before the current time by the target air-fuel ratio abyfr (k−N) N strokes before the current time, thereby starting from the current time. The target in-cylinder fuel supply amount Fcr (k−N) before N strokes is obtained.

  Then, the CPU 71 proceeds to step 1125, and in-cylinder fuel supply is performed by subtracting the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N) according to the equation (5). Set as quantity deviation DFc. That is, the in-cylinder fuel supply amount deviation DFc is an amount representing the excess or deficiency of the fuel supplied into the cylinder at the time point before N strokes. Next, the CPU 71 proceeds to step 1130, where the in-cylinder fuel supply amount deviation DFc is high-pass filtered by the high-pass filter A15 to obtain the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter.

  Next, the CPU 71 proceeds to step 1135 to obtain the main feedback correction amount DFi_main according to the equation shown in step 1135 based on the equation (7), and then in step 1140, the in-cylinder fuel supply amount after passing through the high-pass filter at that time After adding the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter obtained in step 1130 to the integral value SDFchi of the deviation DFchi to obtain a new integrated value SDFchi of in-cylinder fuel supply amount deviation after passing through the high-pass filter, Proceeding to step 1195, the present routine is temporarily terminated.

  As described above, the main feedback correction amount DFi_main is obtained, and this main feedback correction amount DFi_main is reflected in the command fuel injection amount Fi (k) in step 1035 of FIG. Air-fuel ratio control is executed.

  On the other hand, if the main feedback condition is not satisfied at the time of determination in step 1105, the CPU 71 determines “No” in step 1105 and proceeds to step 1145 to set the value of the main feedback correction amount DFi_main to “0”. Thereafter, the routine proceeds to step 1195 to end the present routine tentatively. As described above, when the main feedback condition is not satisfied, the main feedback correction amount DFi_main is set to “0” and the correction of the air-fuel ratio of the engine based on the main feedback control is not performed.

<Calculation of sub feedback correction amount>
Next, the operation when calculating the sub-feedback correction amount DFi_sub in the sub-feedback control will be described. The CPU 71 executes the “sub-feedback correction amount DFi_sub calculation” routine 1200 shown in the flowchart of FIG. Each time the injection start time (injection instruction start time) arrives, it is repeatedly executed. Therefore, when the fuel injection start timing comes for the fuel injection cylinder, the CPU 71 starts the processing of the routine 1200, and first, at step 1205, it is determined whether or not the sub feedback control condition is satisfied. The sub feedback control condition is satisfied, for example, when the engine coolant temperature THW is equal to or higher than a second predetermined temperature higher than the first predetermined temperature in addition to the main feedback condition in step 1015 (and step 1105) described above. .

  Now, assuming that the sub-feedback control condition is satisfied, the CPU 71 determines “Yes” in step 1205 and proceeds to step 1210. From the downstream target value Voxs_ref according to the above equation (2), the CPU 71 proceeds to step 1210. The output deviation amount DVoxs is obtained by subtracting the output value Voxs of the downstream air-fuel ratio sensor 67.

Next, the CPU 71 proceeds to step 1215 to low-pass filter the output deviation amount DVoxs with the low-pass filter A8 to obtain an output deviation amount DVoxs_low after passing through the low-pass filter. In the following step 1220, the following equation (13) is obtained. Based on this, a differential value DDVoxs_low of the output deviation amount DVoxs_low after passing through the low-pass filter is obtained.
DDVoxs_low = (DVoxs_low−DVoxs_low1) / Δt (13)

  In the above equation (13), DVoxs_low1 is the previous value of the output deviation amount DVoxs_low after passing through the low-pass filter set (updated) in step 1235 described later at the time of the previous execution of this routine. Δt is the time from the time when this routine was executed last time to the time when it was executed this time.

  Next, the CPU 71 proceeds to step 1225, obtains the sub feedback correction amount DFi_sub according to the equation (4), and then proceeds to step 1230, where the integrated value SDVoxs_low of the output deviation amount after passing through the low-pass filter at that time is changed to step 1215. Is added to the output deviation amount DVoxs_low after passing through the low-pass filter to obtain a new integrated value SDVoxs_low of the output deviation amount after passing through the low-pass filter, and in step 1235, the output after passing through the low-pass filter is obtained in step 1215. After setting the deviation amount DVoxs_low as the previous value DVoxs_low1 of the output deviation amount DVoxs_low after passing through the low-pass filter, the routine proceeds to step 1295 and this routine is once ended.

  Thus, the sub-feedback correction amount DFi_sub is obtained, and this sub-feedback correction amount DFi_sub is reflected in the command fuel injection amount Fi (k) in step 1035 of FIG. Air-fuel ratio control is executed.

  On the other hand, if the sub feedback control condition is not satisfied at the time of the determination in step 1205, the CPU 71 determines “No” in step 1205 and proceeds to step 1240 to set the value of the sub feedback correction amount DFi_sub to “0”. Then, the process proceeds to step 1295 to end the present routine tentatively. Thus, when the sub-feedback control condition is not satisfied, the sub-feedback correction amount DFi_sub is set to “0”, and the correction of the air-fuel ratio of the engine based on the sub-feedback control is not performed.

<Calculation of first basic fuel injection amount correction coefficient KF1 and storage of KFm and KFmp>
Next, the operation for calculating the first basic fuel injection amount correction coefficient KF1 will be described. The CPU 71 executes the "calculation of the first basic fuel injection amount correction coefficient KF1" routine 1300 shown in the flowchart of FIG. Each time the fuel injection start timing (injection instruction start time) arrives for the cylinder, it is repeatedly executed. Accordingly, when the fuel injection start timing comes for the fuel injection cylinder, the CPU 71 starts the processing of the routine 1300. First, in step 1305, the CPU 71 determines whether or not the main feedback condition is satisfied. If the determination is “No”, the CPU 71 immediately proceeds to step 1395 to end the present routine tentatively. In this case, the calculation of the first basic fuel injection amount correction coefficient KF1 and the storage process of the value of the correction coefficient KF1 in the backup RAM 74 are not executed. This main feedback condition is the same as the main feedback condition in the previous step 1005 (and the sub feedback condition in step 1105).

  Now, assuming that the main feedback condition is satisfied, the CPU 71 determines “Yes” in step 1305 and proceeds to step 1310 to determine the current engine speed NE and the previous step of FIG. A value M is obtained based on the current in-cylinder intake air amount Mc (k) obtained at 1005 and the table MapMc shown in FIG. 6, and the command fuel injection amount Fi (k−M before M strokes from the present time). ) And the current detected air-fuel ratio abyfs (k) obtained in step 1110 of FIG. 11 and the target air-fuel ratio abyfr (k) used in step 1010 of FIG. ) And the equation (11), the target basic fuel injection amount Fbaset is obtained, and in the following step 1315, the target basic fuel injection amount Fbaset and the current step 1010 shown in FIG. Before correction And the fuel injection amount Fbaseb (k), the (12) based on the equation, obtaining a low-pass filter process before the base fuel injection quantity correction coefficient KF0.

  Next, the CPU 71 proceeds to step 1320, and obtains a first basic fuel injection amount correction coefficient KF1 by low-pass filtering KF0 with the low-pass filter A17d based on the time constant τ2.

  Subsequently, the CPU 71 proceeds to step 1325 to determine whether or not the purge condition described above is satisfied.

  If the purge condition is not satisfied (step 1325 = “No”), since the purge is not currently being performed, the CPU 71 proceeds to step 1330 and, like step 1050 in FIG. 10, the predetermined time from the end of the previous purge. It is determined whether t2 has elapsed (that is, not immediately after the end of purging).

  If it is not immediately after the end of purging (step 1330 = “Yes”), the CPU 71 proceeds to step 1335 and according to the value of the cylinder intake air amount Mc (k) determined in step 1005 of FIG. Based on the calculated value of the first basic fuel injection amount correction coefficient KF1, the value of the selected basic fuel injection amount correction coefficient stored value KFm (j) (j: 1 to 4) is calculated using the above equation (14). After updating and storing it in the corresponding memory of the backup RAM 74, the routine proceeds to step 1395 and this routine is once terminated. As a result, when the main feedback condition is satisfied, every time the fuel injection start timing arrives for the fuel injection cylinder, the calculation of the first basic fuel injection amount correction coefficient KF1 and the value of KFm by the value of the correction coefficient KF1 Update / storage processing to the backup RAM 74 is executed. The first basic fuel injection amount correction coefficient KF1 is used in step 1055 of the routine shown in FIG. 10 executed for the next fuel injection cylinder, so that the next pre-correction basic fuel injection amount Fbaseb is calculated this time. The correction is made according to the basic fuel injection amount correction coefficient KF.

  On the other hand, if the purge is immediately after completion (step 1330 = “No”), in FIG. 10 described above, the basic fuel injection amount correction coefficient KF is compulsory as in step 1050 = “No” → step 1020 → step 1025. Therefore, the update / store processing of KFm in the backup RAM 74 according to the value of the first basic fuel injection amount correction coefficient KF1 is not executed.

If the purge condition is satisfied (step 1325 = “Yes”), since the purge is currently being performed, the CPU 71 proceeds to step 1340 to check whether a predetermined time t0 has elapsed from the start of the purge (this purge time t _PGR is t0). Is reached). Until the current purge time t _PGR reaches t0, step 1340 is “No” determination, so the CPU 71 proceeds to step 1395 to end the present routine once (the purge learning in step 1345 is not performed). On the other hand, when the current purge time t _PGR has reached t0 (step 1340 = “Yes”), the CPU 71 proceeds to step 1345 to determine the purge learning value KFmp as the first basic fuel injection amount correction coefficient KF1. Is updated sequentially using the above equation (13) and stored in the corresponding memory of the RAM 73, and then the routine proceeds to step 1395 to end the present routine tentatively.

<Calculation of the second basic fuel injection correction factor KF2>
Next, the operation for calculating the second basic fuel injection amount correction coefficient KF2 will be described. The CPU 71 executes the "calculation of the second basic fuel injection amount correction coefficient KF2" routine 1400 shown in the flowchart of FIG. Each time the fuel injection start timing (injection instruction start time) arrives for the cylinder, it is repeatedly executed. Accordingly, when the fuel injection start time comes for the fuel injection cylinder, the CPU 71 starts the processing of the routine 1400. First, in step 1405, the CPU 71 determines whether or not the main feedback condition is satisfied. If the determination is “No”, the CPU 71 immediately proceeds to step 1495 to end the present routine tentatively. In this case, the calculation process of the second basic fuel injection amount correction coefficient KF2 is not executed. The main feedback condition in step 1405 is the same as step 1305 in FIG.

  Now, assuming that the main feedback condition is satisfied, the CPU 71 determines “Yes” in step 1405 and proceeds to step 1410. Thereafter, the same steps as steps 1310 to 1320 in FIG. 1410 to 1420 are executed. That is, in step 1410, based on the current engine speed NE, the current in-cylinder intake air amount Mc (k) obtained in step 1005 of FIG. 10, and the table MapMc shown in FIG. Then, the value M is obtained, the command fuel injection amount Fi (k−M) before the M stroke is obtained from the present time, and the present detected air-fuel ratio abyfs (k) obtained in step 1110 of FIG. ) And the current target air-fuel ratio abyfr (k) used in step 1010 of FIG. 10 and the above equation (11), the target basic fuel injection amount Fbaset is obtained. Based on the target basic fuel injection amount Fbaset, the current pre-correction basic fuel injection amount Fbaseb (k) obtained in step 1010 of FIG. A fuel injection amount correction coefficient KF0 is obtained.

  Next, the CPU 71 proceeds to step 1420 to obtain a second basic fuel injection amount correction coefficient KF2 by low-pass filtering KF0 with the low-pass filter A27d based on the time constant τ3, and once ends this routine.

  As described above, according to the embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, the command fuel injection amount Fi is assumed under the assumption that the cylinder intake air amount sucked into the combustion chamber is constant. (Actually, Fi (k−M)) and the air-fuel ratio abyfs (k) detected by the upstream air-fuel ratio sensor 66 are the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber. The target basic fuel injection amount Fbaset (= (abyfs (k) / abyfr (k)) from the relationship that it is equal to the product of the target basic fuel injection amount Fbaset required for (k) and the target air-fuel ratio abyfr (k) ) · Fi (k−M)), and the basic fuel injection amount correction coefficient KF (= Fbaset / Fbaseb () by dividing the target basic fuel injection amount Fbaset by the base fuel injection amount Fbaseb (k) before correction. k)) is obtained (actually, as described above, the low-pass filter processing is also executed).

  Then, the next pre-correction basic fuel injection amount Fbaseb is corrected by multiplying the basic fuel injection amount Fbaseb before correction by this basic fuel injection amount correction coefficient KF (that is, the next basic fuel injection amount Fbase after correction). Will be determined). Therefore, the corrected basic fuel injection amount Fbase for the next time matches (approaches) the fuel injection amount to be instructed for injection in order to set the actual air-fuel ratio of the air-fuel mixture supplied to the combustion chamber to the target air-fuel ratio abyfr. As a result, the mechanical error of the air-fuel mixture supply system is quickly compensated while the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is controlled toward the target air-fuel ratio abyfr.

  Furthermore, according to the embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, the basic fuel injection amount correction is performed by the second basic fuel injection amount correction coefficient acquisition unit A27 having a low-pass filter with a small time constant τ3 at the time of purging. As a result, air-fuel ratio fluctuations due to evaporation purge can be compensated as quickly as possible. Further, when the non-purge is performed, the basic fuel injection amount correction is performed by the first basic fuel injection amount correction coefficient acquisition unit A17 provided with a low-pass filter having a large time constant τ2, thereby stably compensating for the mechanical error of the air-fuel mixture intake system. Is done. Further, at the time of purging, relatively accurate purge learning can be performed by performing purge learning based on the calculation result in the first basic fuel injection amount correction coefficient acquisition unit A17. Accordingly, it is possible to perform purge learning with relatively high accuracy while maintaining appropriate air-fuel ratio control and suppressing emission deterioration as much as possible regardless of purge or non-purge.

(Suggestion of modification)
Note that, as described above, the embodiment is merely an example of the embodiment of the present invention considered to be the best at the time of filing of the present application, and the present invention is not limited to the above-described embodiment. Of course, various modifications can be made without departing from the essential part of the present invention.

  For example, the embodiment has both the main feedback and the sub feedback in addition to the basic fuel injection amount correction. However, even if one or both of the main feedback and the sub feedback are absent, It does not diminish any action or effect.

  Further, the “fuel injection amount” in the embodiment is not a concept limited to the literally “fuel amount”. For example, it is a concept that includes an amount related to the drive time of an injector (fuel injection device), that is, a fuel injection time and a duty ratio of a drive pulse, and further includes a coefficient for obtaining a fuel amount, a fuel injection time, and a duty ratio. Of course.

  Further, in the embodiment, as shown in FIG. 7, the low-pass is calculated from the detected air-fuel ratio abyfs (k), the command fuel injection amount Fi (k−M), and the basic fuel injection amount Fbaseb (k) before correction. The basic fuel injection amount correction coefficient KF0 (= (abyfs (k) · Fi (k−M)) / (abyfr (k) · Fbaseb (k))) before filtering is obtained, and the basic fuel injection amount before low-pass filtering is calculated. The first and second basic fuel injection amount correction coefficients KF1 and KF2 are obtained by low-pass filtering the correction coefficient KF0 with a low-pass filter. Instead, the detected air-fuel ratio abyfs (k), command fuel The injection amount Fi (k−M) and the pre-correction basic fuel injection amount Fbaseb (k) are respectively subjected to low-pass filter processing, and then the first and second basic fuel injection amounts are used using the values after the low-pass filter processing. Correction coefficients KF1 and KF2 may be obtained.

  Further, instead of the low-pass filter and the high-pass filter in the embodiment, it is also possible to use a so-called band-pass filter that cuts frequencies other than those within a predetermined range. Furthermore, as is well known, the “filter” is a so-called soft filter, and is naturally a concept including an annealing process and the like. In this annealing process, the parameter corresponds to an annealing coefficient.

  Further, in the above embodiment, the value M (value corresponding to the delay time) for the command fuel injection amount Fi (k−M) M strokes before the current stroke used when obtaining the basic fuel injection amount correction coefficient KF. Is obtained based on the engine speed NE, the in-cylinder intake air amount Mc (k), and the table MapMc shown in FIG. 6, but the value M may be set to a predetermined constant value.

  In the embodiment, as shown in FIG. 7, the current detected air-fuel ratio abyfs (k), the commanded fuel injection amount Fi (k−M) before the M stroke from the current time, and the current target air-fuel ratio abyfr (k ) And the current basic fuel injection amount Fbaseb (k) before correction, the basic fuel injection amount correction coefficient KF is obtained. The current detected air-fuel ratio abyfs (k), the command fuel injection before M strokes from the present time The basic fuel injection amount based on the amount Fi (k−M), the target air-fuel ratio abyfr (k−M) before the M stroke from the current time, and the uncorrected basic fuel injection amount Fbaseb (k−M) before the M stroke from the current time You may comprise so that the correction coefficient KF may be calculated | required.

  In each of the above embodiments, in the main feedback control, the actual in-cylinder fuel supply amount Fc (k−N) N strokes before the current time from the target in-cylinder fuel supply amount Fcr (k−N) N times before the current time. The main feedback correction amount DFi_main is obtained based on the in-cylinder fuel supply amount deviation DFc, which is a value obtained by subtracting N), but N strokes from the current detected air-fuel ratio abyfs (k) by the upstream air-fuel ratio sensor 66 are The main feedback correction amount DFi_main may be obtained based on a value obtained by subtracting the previous target air-fuel ratio abyfr (k−N).

  In the above embodiment, the time constant τ3 of the low-pass filter A27d used for correcting the basic fuel injection amount at the time of purging was a constant value, but changed according to the evaporation purge state such as the purge rate, purge time, purge gas concentration, etc. You may make it do. In this case, for example, a step of acquiring the time constant τ 3 according to the evaporation purge state may be added immediately before step 1320 in the flowchart of FIG.

  In the embodiment, both canister purge and tank vapor introduction are performed without any particular distinction. However, as described above, as described above, the “evaporation purge” is a “canister purge” for releasing (purging) the fuel gas stored in the canister 46 from the canister 46 (the adsorbent 46d) to the intake pipe 41 while the engine is stopped. In addition, “tank vapor introduction” for releasing (purging) the tank vapor from the fuel tank 45 by introducing the tank vapor filled in the fuel tank 45 into the intake pipe 41 can be performed.

  Further, the evaporative purge mainly for the canister purge needs to be performed promptly after the engine operation is started when the above purge condition is satisfied. On the other hand, the fuel temperature is not so high until some time elapses after the engine operation is started. Since it has not risen, the amount of tank vapor generated is relatively small. Therefore, the evaporation purge is performed immediately when the purge condition is satisfied until the integrated value of the purge time from the start of engine operation (hereinafter referred to as “purge integrated time”) reaches a predetermined value, and reaches the predetermined time. After the purge condition is satisfied, it is preferably performed when the fuel temperature sensor 69 detects that the fuel in the fuel tank 45 has reached a predetermined temperature or higher.

  Specifically, for example, the evaporative purge gas is mainly the canister purge gas until the purge integrated time reaches a predetermined value, and this canister purge gas concentration decreases with the purge integrated time. The degree of disturbance also decreases with the purge integration time. Therefore, the time constant τ3 is decreased with the purge integration time. The time constant τ3 can be decreased according to the purge integration time by decrementing a predetermined value from the initial value, acquiring a value based on a predetermined function or map, or the like. After the purge integration time reaches a predetermined value, it is highly possible that the fuel gas stored in the canister 46 is almost released, while the fuel temperature rises and a large amount of tank vapor is generated. Is likely to have occurred. Therefore, after the purge integrated time reaches the predetermined value, the purge gas concentration is estimated according to the detected fuel temperature of the fuel temperature sensor 69 installed in the fuel tank 45, and a predetermined time constant corresponding to the estimated purge gas concentration. A time constant τ3 is obtained based on the map. Here, the above-described function and time constant map can be obtained in advance by a predetermined experiment and stored in the ROM 72 or the backup RAM 74.

  As a result, more appropriate basic fuel injection amount correction at the time of purge corresponding to the evaporation purge state that can vary depending on the operating state is performed, so that the deterioration of emissions due to air-fuel ratio fluctuation at the time of purge is more effective. Can be suppressed.

  Further, in the above-described embodiment, the first low-pass filter A17d (first filter with reduced responsiveness) having a large time constant used for actual air-fuel ratio control during non-purge and purge learning during purge is provided. 1 Basic fuel injection amount correction coefficient acquisition unit A17 and a low-pass filter A27d (second filter having higher response than the first filter) having a small time constant used for actual air-fuel ratio control during purging Although the second basic fuel injection amount correction coefficient acquisition unit A27 is provided separately, only the low-pass filter may be switched by combining both.

  Further, the first basic fuel injection amount correction coefficient acquisition unit A17 can change the filter time constant when acquiring the basic fuel injection amount correction coefficient storage value KFm during non-purge and when acquiring the purge learning value KFmp. It may be configured. Alternatively, a third basic fuel injection amount correction coefficient acquisition unit including a third filter used only for purge learning may be provided separately from the actual air-fuel ratio control during non-purge.

1 is a schematic view of an internal combustion engine to which an air-fuel ratio control apparatus according to an embodiment of the present invention is applied. It is the graph which showed the relationship between the output voltage of an air flow meter, and the measured intake air flow rate. 6 is a graph showing the relationship between the output voltage of the upstream air-fuel ratio sensor and the air-fuel ratio. It is the graph which showed the relationship between the output voltage of a downstream air fuel ratio sensor, and an air fuel ratio. It is a functional block diagram of the air fuel ratio control device concerning a 1st embodiment. It is the graph which showed the table which prescribes | regulates the relationship between an engine speed, the cylinder intake air amount, and the stroke number corresponded to delay time. It is a functional block diagram of a basic fuel injection amount correction coefficient setting unit. It is a time chart for demonstrating the outline of the air fuel ratio control at the time of purge. It is the figure which showed a mode that the calculated basic fuel injection amount correction coefficient was classify | categorized according to the cylinder intake air amount, and was memorize | stored in backup RAM. It is the flowchart which showed the routine for calculating command fuel injection quantity and performing injection instruction | indication. 5 is a flowchart showing a routine for calculating a main feedback correction amount. It is the flowchart which showed the routine for calculating the sub feedback correction amount. It is the flowchart which showed the routine for performing calculation and learning of the 1st basic fuel injection quantity correction coefficient. It is the flowchart which showed the routine for calculating the 2nd basic fuel injection quantity correction coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 39 ... Injector, 45 ... Fuel tank, 46 ... Canister, 47 ... Vapor collection pipe, 48 ... Purge flow path, 49 ... Purge control valve (VSV), 51 ... Exhaust manifold, 53 ... 1st catalyst, 66 ... Upstream air-fuel ratio sensor, 67 ... Downstream air-fuel ratio sensor, 70 ... Electric control device, 71 ... CPU, 74 ... Backup RAM, A3 ... Basic fuel injection amount calculation unit before correction, A4 ... After-correction basic fuel injection amount calculation unit, A5 ... command fuel injection amount calculation unit, A17 ... first basic fuel injection amount correction coefficient acquisition unit, A17d ... low pass filter, A27 ... first basic fuel injection amount correction coefficient acquisition unit, A27d ... Low-pass filter, A28 ... Correction coefficient learning unit, A29 ... Correction coefficient setting unit

Claims (4)

A combustion chamber, an intake passage and an exhaust passage connected to the combustion chamber, a fuel gas introduction passage configured to be able to introduce fuel gas based on fuel evaporated in the fuel tank into the intake passage, and a command fuel injection amount A fuel injection device that injects the liquid fuel transported from the fuel tank in the intake passage or the combustion chamber by receiving the fuel injection instruction, a catalyst device disposed in the exhaust passage, and a catalyst thereof In an air-fuel ratio control device for an internal combustion engine, which is applied to an internal combustion engine comprising an upstream air-fuel ratio sensor disposed in the exhaust passage upstream of the device,
A basic fuel injection amount acquisition unit that acquires an estimated value of the current fuel injection amount corresponding to a target air-fuel ratio as a basic fuel injection amount based on at least the operating speed of the internal combustion engine and the air flow rate in the intake passage;
An arithmetic processing unit including a filter, wherein the arithmetic processing unit performs arithmetic processing based on the target air-fuel ratio, the detection signal of the upstream air-fuel ratio sensor, and the past commanded fuel injection amount, whereby the basic fuel injection A basic fuel injection amount correction value acquisition unit for acquiring a calculation result corresponding to a basic fuel injection amount correction value for correcting the amount;
An upstream feedback correction value calculation unit that calculates an upstream feedback correction value that is an air-fuel ratio feedback correction value based on a detection signal of the upstream air-fuel ratio sensor;
A command fuel injection amount calculation unit that calculates the current command fuel injection amount based on the calculation result and the upstream feedback correction value;
When the fuel gas is introduced into the intake passage through the fuel gas introduction passage, an empty space based on the concentration of the fuel gas is obtained based on the calculation result in the basic fuel injection amount correction value acquisition unit. A purge learning unit for acquiring a purge learning value that is a fuel ratio learning value;
With
The basic fuel injection amount correction value acquisition unit supplies the first filter used when the purge learning unit acquires the purge learning value and the command fuel injection amount calculation unit when the fuel gas is introduced. An internal combustion engine configured to have different parameters relating to the responsiveness of the filter, the second filter used when acquiring the operation result to be obtained Air-fuel ratio control device. A combustion chamber, an intake passage and an exhaust passage connected to the combustion chamber, a fuel gas introduction passage configured to be able to introduce fuel gas based on fuel evaporated in the fuel tank into the intake passage, and a command fuel injection amount A fuel injection device that injects the liquid fuel transported from the fuel tank in the intake passage or the combustion chamber by receiving the fuel injection instruction, a catalyst device disposed in the exhaust passage, and a catalyst thereof In an air-fuel ratio control device for an internal combustion engine, which is applied to an internal combustion engine comprising an upstream air-fuel ratio sensor disposed in the exhaust passage upstream of the device,
A basic fuel injection amount acquisition unit that acquires an estimated value of the current fuel injection amount corresponding to a target air-fuel ratio as a basic fuel injection amount based on at least the operating speed of the internal combustion engine and the air flow rate in the intake passage;
An arithmetic processing unit including a filter, wherein the arithmetic processing unit performs arithmetic processing based on the target air-fuel ratio, the detection signal of the upstream air-fuel ratio sensor, and the past commanded fuel injection amount, whereby the basic fuel injection A basic fuel injection amount correction value acquisition unit for acquiring a calculation result corresponding to a basic fuel injection amount correction value for correcting the amount;
A command fuel injection amount calculation unit that calculates the current command fuel injection amount based on at least the calculation result;
When the fuel gas is introduced into the intake passage through the fuel gas introduction passage, an empty space based on the concentration of the fuel gas is obtained based on the calculation result in the basic fuel injection amount correction value acquisition unit. A purge learning unit for acquiring a purge learning value that is a fuel ratio learning value;
With
The basic fuel injection amount correction value acquisition unit supplies the first filter used when the purge learning unit acquires the purge learning value and the command fuel injection amount calculation unit when the fuel gas is introduced. An internal combustion engine configured to have different parameters relating to the responsiveness of the filter, the second filter used when acquiring the operation result to be obtained Air-fuel ratio control device. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2,
The internal combustion engine includes a downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the catalyst device,
A downstream feedback correction value calculation unit that calculates a downstream feedback correction value that is an air-fuel ratio feedback correction value based on a detection signal of the downstream air-fuel ratio sensor;
The command fuel injection amount calculation unit is an air-fuel ratio control apparatus for an internal combustion engine configured to calculate the current command fuel injection amount based on the downstream feedback correction value. An air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3,
The first filter is configured to be used also when acquiring the calculation result provided to the command fuel injection amount calculation unit when the fuel gas is not introduced and the fuel gas is not introduced. An air-fuel ratio control apparatus for an internal combustion engine.

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