JP2009150264A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

An air-fuel ratio control apparatus for reducing an excess or deficiency of a fuel supply amount during alcohol concentration correction learning control in a flexible fuel vehicle is provided.
An air-fuel ratio sensor and an oxygen sensor arranged in an upstream exhaust passage and a downstream exhaust passage of a three-way catalyst are provided, and a fuel supply amount is corrected based on an output value of the air-fuel ratio sensor. Calculated based on feedback control, sub-feedback control for correcting the fuel supply amount based on the output value of the oxygen sensor, alcohol concentration correction learning control for learning the alcohol concentration correction learning value, and correction values in the sub-feedback control Execute sub-feedback learning control to learn the learning value, perform sub-feedback control to enrich the exhaust air-fuel ratio during learning when the alcohol concentration correction learning value increases, and exhaust when during learning when the alcohol concentration correction learning value decreases Sub-feedback control is performed to make the air-fuel ratio lean.
[Selection] Figure 1

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine.

  In addition to gasoline, there is an automobile called a so-called flexible fuel vehicle (FFV) that can run with a mixed fuel of various compositions of alcohol and gasoline. Since alcohol has a C (carbon) atom content different from that of normal gasoline, when supplying a mixed fuel of alcohol and gasoline to an internal combustion engine used in a flexible fuel vehicle, the fuel is supplied according to the alcohol concentration in the fuel. The amount needs to be adjusted.

  By the way, components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) are contained in the exhaust gas discharged from the internal combustion engine main body, and these components have been conventionally purified. Three-way catalyst is used. The three-way catalyst has a high purification capacity when the exhaust gas air-fuel ratio (hereinafter referred to as “exhaust air-fuel ratio”) is substantially the stoichiometric air-fuel ratio. In this case, it is necessary to control the amount of fuel supplied to the combustion chamber so that the exhaust air-fuel ratio becomes substantially the stoichiometric air-fuel ratio.

  Therefore, in the flexible fuel vehicle, an air-fuel ratio sensor capable of detecting the exhaust air-fuel ratio is provided in the upstream exhaust passage of the three-way catalyst so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio determined according to the alcohol concentration in the fuel. In addition, an air-fuel ratio control apparatus that performs feedback control for adjusting the amount of fuel supplied to the combustion chamber is known (see Patent Document 1).

JP 2004-308540 A

  However, the air-fuel ratio sensor may not be able to accurately detect the actual exhaust air-fuel ratio due to deterioration of the air-fuel ratio sensor due to the heat of the exhaust gas, especially due to a large change in the alcohol concentration in the fuel due to refueling or the like. . In such a case, the control accuracy of the exhaust air-fuel ratio by the above-described feedback control (hereinafter referred to as “main feedback control”) is lowered.

  Therefore, an air-fuel ratio sensor capable of detecting the exhaust air-fuel ratio is provided in the downstream exhaust passage of the three-way catalyst, and the output value of the upstream air-fuel ratio sensor is based on the output of the downstream air-fuel ratio sensor so that the actual exhaust air-fuel ratio is The exhaust air / fuel ratio control accuracy is improved by performing feedback control (hereinafter referred to as “sub-feedback control”) that corrects the output value of the upstream air / fuel ratio sensor (resulting in fuel supply amount) so that It can be improved.

  In such a configuration in which the air-fuel ratio sensor is disposed in the upstream and downstream exhaust passages of the three-way catalyst, there is a steady deviation between the output value of the upstream air-fuel ratio sensor and the actual exhaust air-fuel ratio. The corresponding learning value is calculated based on the correction amount in the sub feedback control, and the learning control for correcting the output value of the upstream air-fuel ratio sensor based on the calculated learning value (hereinafter referred to as “sub feedback learning control”). ).

  Further, the flexible fuel vehicle performs alcohol concentration correction learning control for calculating an alcohol concentration correction learning value for adjusting the fuel supply amount according to the alcohol concentration in the fuel, based on the feedback correction value by the main feedback control. It is possible.

  However, as described above, when the alcohol concentration changes greatly due to refueling or the like, the fuel supply is continued until the exhaust air-fuel ratio becomes a correction value and a learning value so that the stoichiometric air-fuel ratio according to the alcohol concentration in the fuel is set. An excess or deficiency of the amount may occur, which may cause deterioration of exhaust emission or drivability due to occurrence of knocking.

  Further, when the alcohol concentration changes greatly due to refueling or the like, the alcohol concentration correction learning control and the sub feedback control and the sub feedback learning control are simultaneously performed. However, it is dispersed into a learning value by alcohol concentration correction learning control, a correction value by sub feedback control, and a learning value by sub feedback learning control. Then, the accuracy of learning by alcohol concentration correction learning control deteriorates, and an excess or deficiency of the fuel supply amount occurs, which may cause deterioration of exhaust emission or drivability due to occurrence of knocking.

  Accordingly, the present invention provides an air-fuel ratio control apparatus for an internal combustion engine that can reduce an excess or deficiency of the fuel supply amount during alcohol concentration correction learning control in a flexible fuel vehicle, thereby preventing deterioration of exhaust emission and drivability. The purpose is to provide.

  In order to solve the above-described problem, according to the invention described in claim 1, an air-fuel ratio control apparatus for an internal combustion engine which can use alcohol and gasoline as fuels individually or in combination, and in an engine exhaust passage An upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor, which are respectively disposed in an upstream exhaust passage and a downstream exhaust passage of an exhaust purification catalyst provided in the exhaust gas and detect an air-fuel ratio of exhaust gas, and the upstream air-fuel ratio sensor Main feedback control means for correcting the fuel supply amount based on the feedback correction value so that the output value becomes a value corresponding to the target air-fuel ratio, the exhaust air-fuel ratio based on the output value of the upstream air-fuel ratio sensor, and the actual exhaust gas A sub-feedback that corrects the fuel supply amount so that the exhaust air-fuel ratio becomes the target air-fuel ratio based on the output value of the downstream air-fuel ratio sensor to compensate for the deviation from the air-fuel ratio. A control means, an alcohol concentration correction learning control means for learning an alcohol concentration correction learning value calculated based on the feedback correction value, and correcting the fuel supply amount based on the learned learning value, and a correction value in the sub feedback control means. In the air-fuel ratio control apparatus for an internal combustion engine, which includes a sub-feedback learning control unit that learns a learning value calculated based on the learning value and corrects the fuel supply amount based on the learning value, learning that the alcohol concentration correction learning value increases When the correction value in the sub-feedback control means is corrected so that the exhaust air-fuel ratio becomes richer than the target air-fuel ratio, and when learning to reduce the alcohol concentration correction learning value, The sub feedback so that the exhaust air / fuel ratio is leaner than the target air / fuel ratio. Air-fuel ratio control apparatus for correcting the correction value in control means.

  That is, according to the first aspect of the present invention, the excess or deficiency of the fuel supply amount that occurs in the process of learning by the alcohol concentration correction learning control is determined from the increase or decrease of the alcohol concentration correction learning value, and the fuel supply amount is adjusted accordingly. Therefore, the correction value in the sub feedback control is corrected to increase or decrease. Thereby, it becomes possible to prevent deterioration of exhaust emission and drivability.

  According to a second aspect of the present invention, in the first aspect of the present invention, the degree of richness is changed according to the amount of increase in the alcohol concentration correction learned value, and the amount of decrease in the alcohol concentration correction learned value is reduced. An air-fuel ratio control apparatus for an internal combustion engine that changes the degree of lean accordingly is provided. That is, according to the second aspect of the present invention, by increasing or decreasing the correction value in the sub-feedback control according to the increase or decrease of the alcohol concentration correction learning value, it is possible to increase or decrease the fuel supply amount according to the excess or shortage of the supplied fuel. It becomes possible.

  According to a third aspect of the present invention, there is provided an air-fuel ratio control apparatus for an internal combustion engine capable of using alcohol and gasoline as fuels alone or in combination, the exhaust gas provided in the engine exhaust passage. An upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor, which are respectively disposed in the upstream exhaust passage and the downstream exhaust passage of the purification catalyst and detect the air-fuel ratio of the exhaust gas, and the output value of the upstream air-fuel ratio sensor are the target air The main feedback control means for correcting the fuel supply amount based on the feedback correction value so as to be a value corresponding to the fuel ratio, and the difference between the exhaust air / fuel ratio based on the output value of the upstream air / fuel ratio sensor and the actual exhaust air / fuel ratio Sub-feedback control means for correcting the fuel supply amount so that the exhaust air-fuel ratio becomes the target air-fuel ratio based on the output value of the downstream air-fuel ratio sensor to compensate for An alcohol concentration correction learning control unit that learns an alcohol concentration correction learning value calculated based on a feedback correction value and corrects the fuel supply amount based on the learned learning value, and a correction value calculated based on the correction value in the sub-feedback control unit In an air-fuel ratio control apparatus for an internal combustion engine comprising a sub-feedback learning control means for learning a learning value and correcting the fuel supply amount based on the learning value, when the alcohol concentration correction learning value is learned, An air-fuel ratio control apparatus for an internal combustion engine that limits correction in the feedback control means is provided.

  That is, in the invention according to claim 3, in the process of learning by alcohol concentration correction learning control, by restricting correction in the sub-feedback control means, the deterioration of learning accuracy by alcohol concentration correction learning control is prevented, As a result, the excess or deficiency of the fuel supply amount can be reduced, and the deterioration of exhaust emission and drivability can be prevented.

  According to the invention described in each claim, in the flexible fuel vehicle, it becomes possible to reduce the excess and deficiency of the fuel supply amount during the alcohol concentration correction learning control, thereby preventing the exhaust emission and the drivability from deteriorating. There is a common effect.

  Hereinafter, an air-fuel ratio control apparatus for an internal combustion engine according to the present invention, which can use alcohol and gasoline as fuels individually or in combination, will be described with reference to the drawings. FIG. 1 is an overall view of an internal combustion engine on which a control device of the present invention is mounted. The embodiment shown in FIG. 1 shows the case where the air-fuel ratio control apparatus of the present invention is used in an in-cylinder direct injection type spark ignition internal combustion engine, but other spark ignition type internal combustion engines and compression self-ignition internal combustion engines are shown. It can also be used for institutions.

  Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a piston that reciprocates in the cylinder block 2, 4 is a cylinder head fixed on the cylinder block 2, and 5 is a piston 3 and a cylinder head 4. A combustion chamber formed therebetween, 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, and 9 is an exhaust port. As shown in FIG. 1, a spark plug 10 is arranged at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is arranged around the inner wall surface of the cylinder head 4. A cavity 12 extending from the lower side of the fuel injection valve 11 to the lower side of the spark plug 10 is formed on the top surface of the piston 3.

  The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 is connected to an air cleaner (not shown) via an intake pipe 15. An air flow meter 16 is disposed in the intake pipe 15 and a throttle valve 18 driven by a step motor 17 is disposed. On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust manifold 19, and this exhaust manifold 19 is connected to a catalytic converter 21 containing a three-way catalyst 20. The outlet of the catalytic converter 21 is connected to the exhaust pipe 22. An air-fuel ratio sensor 23 is disposed in the exhaust manifold 19, that is, the exhaust passage upstream of the exhaust purification catalyst 20, and an oxygen sensor 24 is disposed in the exhaust pipe 22, that is, the exhaust passage downstream of the three-way catalyst 20. The The fuel containing alcohol is stored in the fuel tank 25, and is supplied to the fuel injection valve 11 by the electronically controlled fuel pump 26 with variable discharge amount through the fuel supply pipe and injected. In the present embodiment, the three-way catalyst 20 is used as the exhaust purification catalyst, but other types of catalysts such as a NOx storage reduction catalyst, a lean NOx catalyst, DPNR, etc. may be used as long as they have an oxygen storage capacity. Also good.

  The electronic control unit 31 comprises a digital computer, and is connected to each other via a bidirectional bus 32, a RAM (Random Access Memory) 33, a ROM (Read Only Memory) 34, a CPU (Microprocessor) 35, a backup RAM 36, an input. A port 37 and an output port 38 are provided. The backup RAM 36 is always connected to a power source, and the stored contents can be saved even when the vehicle ignition switch is turned off. Therefore, it is used to store learning values and the like which will be described later.

  The air flow meter 16 generates an output voltage proportional to the intake air flow rate, and the output voltage is input to the input port 37 via the corresponding AD converter 39. As shown in FIG. 2, the air-fuel ratio sensor 23 generates an output voltage substantially proportional to the air-fuel ratio of the exhaust gas based on the oxygen concentration in the exhaust gas passing through the exhaust manifold 19. On the other hand, as shown in FIG. 3, the oxygen sensor 24, based on the oxygen concentration in the exhaust gas passing through the exhaust pipe 22, that is, the exhaust gas after passing through the three-way catalyst 20, An output voltage that varies greatly depending on whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio AFT is generated. These output voltages are input to the input port 37 via the corresponding AD converter 39.

  A load sensor 42 that generates an output voltage proportional to the amount of depression of the accelerator pedal 41 is connected to the accelerator pedal 41, and the output voltage of the load sensor 42 is input to the input port 37 via the corresponding AD converter 39. The For example, the crank angle sensor 43 generates an output pulse every time the crankshaft rotates 30 degrees, and the output pulse is input to the input port 37. The CPU 35 calculates the engine speed Ne from the output pulse of the crank angle sensor 43. On the other hand, the output port 38 is connected to the spark plug 10, the fuel injection valve 11, and the step motor 17 via a corresponding drive circuit 39.

  The above-described three-way catalyst 20 has an oxygen storage capacity, so that when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 20 is lean, the three-way catalyst 20 stores oxygen in the exhaust gas and also the three-way catalyst 20. When the air-fuel ratio of the exhaust gas flowing into the exhaust gas is rich, the stored oxygen is released to oxidize and purify HC and CO contained in the exhaust gas.

  In order to effectively utilize the oxygen storage capacity of such a three-way catalyst 20, the three-way catalyst can be purified so that the exhaust gas can be purified even if the air-fuel ratio of the exhaust gas subsequently becomes rich or lean. It is necessary to maintain the amount of oxygen stored in the catalyst 20 at a predetermined amount (for example, half of the maximum oxygen storage amount). If the oxygen storage amount of the three-way catalyst 20 is maintained at the predetermined amount, the three-way catalyst 20 can always exhibit a certain degree of oxygen storage and oxygen release action, and as a result, the three-way catalyst. 20 makes it possible to always oxidize and reduce the components in the exhaust gas. For this reason, in this embodiment, in order to maintain the exhaust purification performance of the three-way catalyst 20, air-fuel ratio control is performed so as to keep the oxygen storage amount of the three-way catalyst constant.

  Therefore, in the present embodiment, the exhaust air / fuel ratio (the upstream side air-fuel ratio sensor) 23 disposed in the upstream exhaust passage from the three-way catalyst 20 causes the exhaust air / fuel ratio (the exhaust passage upstream of the three-way catalyst 20, the combustion chamber 5). And the ratio of the air and fuel supplied to the intake passage) and the feedback control of the fuel supply amount from the fuel injection valve 11 so that the output value of the air-fuel ratio sensor 23 becomes a value corresponding to the stoichiometric air-fuel ratio. (Main feedback control) is performed. As a result, the exhaust air-fuel ratio is maintained in the vicinity of the stoichiometric air-fuel ratio, and as a result, the oxygen storage amount of the three-way catalyst is maintained constant, thereby improving exhaust emission.

Hereinafter, the main feedback control will be specifically described. First, in the present embodiment, a fuel amount (hereinafter referred to as “target fuel supply amount”) Qft (n) to be supplied from the fuel injection valve 11 to each cylinder is calculated by the following equation (1).
Qft (n) = Mc (n) / AFT + DQf (n-1) (1)

  Here, in the above formula (1), n is a value indicating the number of calculations in the ECU 31, and for example, Qft (n) represents the target fuel supply amount calculated by the nth calculation. Mc (n) indicates the amount of air expected to be sucked into the cylinder of each cylinder before the intake valve 6 is closed (hereinafter referred to as “in-cylinder intake air amount”). In order to calculate the in-cylinder intake air amount Mc (n), for example, the engine speed Ne and the flow rate of air passing through the intake pipe 15 (hereinafter referred to as “intake pipe passing air flow rate”) mt are used as arguments. A map or calculation formula is obtained in advance experimentally or by calculation, and this map or calculation formula is stored in the ROM 34. The in-cylinder intake air amount Mc (n) is calculated based on the engine speed Ne and the intake pipe passage air flow rate mt detected during engine operation by the above map or calculation formula.

  AFT indicates a target value of the exhaust air-fuel ratio, and in this embodiment, it is a stoichiometric air-fuel ratio that changes according to the alcohol concentration in the fuel. The output value at the theoretical air-fuel ratio shows a constant value V0 regardless of the alcohol concentration (see FIG. 2). That is, for example, when the theoretical air-fuel ratio at a certain alcohol concentration is AFT, it is assumed that the alcohol concentration is changed by refueling or the like and the theoretical air-fuel ratio becomes AFT ′. Even in this case, the output value corresponding to the stoichiometric air-fuel ratio after the change in alcohol concentration remains V0, and the tendency of the substantially proportional output value shifts as shown by the broken line with the same tendency. Therefore, as shown in FIG. 4, by using the alcohol concentration correction learned value FALC, the stoichiometric air-fuel ratio AFT corresponding to the alcohol concentration in the fuel can be obtained from the map or calculation formula of the learning value FALC and the theoretical air-fuel ratio AFT.

  The alcohol concentration correction learning value FALC is a learning value for correcting the basic fuel injection amount Qb according to the alcohol concentration in the fuel, and will be described in detail later. Referring to FIG. 4, for example, when E0 (the alcohol concentration in the fuel is 0%), the alcohol concentration correction learning value FALC is 1.0, and the theoretical air-fuel ratio is 14.7. In the case of E85 (85% ethanol mixed fuel), the alcohol concentration correction learned value FALC is 1.4, and the theoretical air-fuel ratio is 10.0.

  DQf represents a fuel correction amount calculated for main feedback control described later. The fuel injection valve 11 injects an amount of fuel corresponding to the target fuel supply amount calculated by the above equation (1).

  In the above description, the in-cylinder intake air amount Mc (n) is calculated based on a map or the like using the engine speed Ne and the intake pipe passage air flow rate mt as arguments. You may obtain | require by other methods, such as a calculation formula based on an opening degree, atmospheric pressure, etc.

  FIG. 5 is a flowchart of the target fuel supply amount calculation control operation for calculating the target fuel supply amount Qft (n) from the fuel injection valve 11. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31.

  First, at step 101, the engine speed Ne and the intake pipe passage air flow rate mt are detected by the crank angle sensor 43 and the air flow meter 16. Next, at step 102, an alcohol concentration correction learning value FALC, which will be described later, is read from the backup RAM 36. Next, in step 103, the in-cylinder intake air amount Mc (n) at the time of the n-th calculation is calculated by a map or a calculation formula based on the engine speed Ne detected in step 101 and the intake pipe passage air flow rate mt. Is done. Next, at step 104, the stoichiometric air-fuel ratio AFT corresponding to the alcohol concentration in the fuel is calculated by the map shown in FIG. 4 based on the alcohol concentration correction learning value FALC read at step 102.

  Next, at step 105, the cylinder intake air amount Mc (n) calculated at step 103 and the fuel correction amount DQf (n-1) at the time of the (n-1) th calculation calculated in the main feedback control operation described later. Based on the above, the target fuel supply amount Qft (n) is calculated by the above equation (1), and the routine is terminated. The fuel injection valve 11 injects an amount of fuel corresponding to the target fuel supply amount Qft (n) calculated in this way.

Next, main feedback control will be described. In the present embodiment, as the main feedback control, the fuel deviation amount ΔQf between the actual fuel supply amount calculated based on the output of the air-fuel ratio sensor 23 and the target fuel supply amount Qft described above is calculated for each number of calculations. The fuel correction amount DQf is calculated so that the fuel deviation amount ΔQf becomes zero. Specifically, the fuel correction amount DQf is calculated by the following equation (2). In the following formula (2), DQf (n−1) is the fuel correction amount in the (n−1) th calculation, that is, the previous calculation, Kmp indicates a proportional gain, and Kmi indicates an integral gain. These proportional gain Kmp and integral gain Kmi may be predetermined constant values or values that change in accordance with the engine operating state.

  FIG. 6 is a flowchart of the main feedback control operation for calculating the fuel correction amount DQf. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31.

  First, in step 111, it is determined whether or not an execution condition for main feedback control is satisfied. The case where the execution condition of the main feedback control is satisfied is, for example, that the internal combustion engine is not cold started (that is, the engine cooling water temperature is equal to or higher than a certain temperature and the fuel increase at the start is not performed, etc.) And the fuel cut control for stopping the fuel injection from the fuel injection valve during engine operation. If it is determined in step 111 that the main feedback control execution condition is satisfied, the process proceeds to step 112. On the other hand, when it is determined in step 111 that the execution condition for the main feedback control is not satisfied, the routine is terminated and the main feedback control is not executed.

  In step 112, the output value VAF (n) of the air-fuel ratio sensor 23 at the time of the nth calculation is detected. Next, at step 113, a sub-feedback correction value efsfb (n) and a sub-feedback learning value efsfbg, which are output correction values of the air-fuel ratio sensor 23 calculated by sub-feedback control and sub-feedback learning control described later, are detected at step 112. By adding to the output value VAF (n), the output value of the air-fuel ratio sensor 23 is corrected, and the corrected output value VAF ′ (n) at the time of the n-th calculation is calculated (VAF ′ (n) = VAF (n) + efsfb (n) + efsfbg (n)).

  Next, at step 114, as described above, the alcohol concentration correction learning value FALC and the AFT obtained from FIG. 4 are read. Next, at step 115, based on the corrected output value VAF ′ (n) calculated at step 113 and the AFT read at step 114, using the map shown in FIG. AFR (n) is calculated. The actual air-fuel ratio AFR (n) calculated in this way is a value that substantially matches the actual air-fuel ratio of the exhaust gas flowing into the three-way catalyst 20 at the time of the n-th calculation.

Next, at step 116, the fuel deviation amount ΔQf between the fuel supply amount calculated based on the output of the air-fuel ratio sensor 23 and the target fuel supply amount Qft is calculated by the following equation (3). In the following formula (3), values in the nth calculation are used for the cylinder intake air amount Mc and the target fuel supply amount Qft, but values before the nth calculation are used. May be used.
ΔQf (n) = Mc (n) / AFR (n) −Qft (n) (3)

  In step 117, the fuel correction amount DQf (n) at the time of the nth calculation is calculated by the above equation (2), and the routine is ended. The calculated fuel correction amount DQf (n) is used in step 105 of the operation shown in FIG.

  By the way, the output of the air-fuel ratio sensor 23 may be shifted due to the deterioration of the air-fuel ratio sensor 23 due to the heat of the exhaust gas. In such a case, the air-fuel ratio sensor 23 that originally generates an output value as shown by a solid line in FIG. 2 generates an output value as shown by a broken line in FIG. 2, for example. When a deviation occurs in the output value of the air-fuel ratio sensor 23 as described above, the air-fuel ratio sensor 23 generates an output value that is generated when, for example, the exhaust air-fuel ratio is the stoichiometric air-fuel ratio, rather than the stoichiometric air-fuel ratio. It is generated when it is lean. Therefore, in this embodiment, the sub-feedback control using the oxygen sensor (downstream air-fuel ratio sensor) 24 compensates for the deviation generated in the output value of the air-fuel ratio sensor 23, and the output value of the air-fuel ratio sensor 23 becomes the actual value. A value corresponding to the exhaust air-fuel ratio is set.

  That is, as shown in FIG. 3, the oxygen sensor 24 can detect whether the exhaust air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio, and whether it is richer than the stoichiometric air-fuel ratio or lean. There is almost no deviation in the determination of whether there is any. Therefore, when the actual exhaust air-fuel ratio is lean, the output value of the oxygen sensor 24 is low, and when the actual exhaust air-fuel ratio is rich, the output value of the oxygen sensor 24 is high. It has become. Therefore, when the actual exhaust air-fuel ratio is substantially the stoichiometric air-fuel ratio, that is, when the up-and-down is repeated near the stoichiometric air-fuel ratio, the output value of the oxygen sensor 24 repeatedly reverses between a high value and a low value. . Therefore, in the present embodiment, the output value of the air-fuel ratio sensor 23 is corrected so that the inversion between the high value and the low value of the oxygen sensor 24 is repeated.

  FIG. 7 is a time chart of the actual exhaust air-fuel ratio, the output value of the oxygen sensor, the sub feedback correction value efsfb, and the sub feedback learning value efsfbg. In the time chart of FIG. 7, although the actual exhaust air-fuel ratio is controlled so as to become the stoichiometric air-fuel ratio, a deviation occurs in the air-fuel ratio sensor 23 and the actual exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. In this case, the deviation occurring in the air-fuel ratio sensor 23 is compensated.

  In the example shown in FIG. 7, at the time t0, the actual exhaust air-fuel ratio is not the stoichiometric air-fuel ratio, but is leaner than the stoichiometric air-fuel ratio. This is because when the air-fuel ratio sensor 23 is deviated and the actual exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio sensor 23 outputs an output value corresponding to the stoichiometric air-fuel ratio. This is because it is output. At this time, the output value of the oxygen sensor 24 is a low value.

  As described above, the sub feedback correction value efsfb is added to the output value VAF (n) in order to calculate the corrected output value VAF ′ (n) in step 113 of FIG. Accordingly, when the sub-feedback correction value efsfb is a positive value, the output value VO of the air-fuel ratio sensor 23 is corrected to the lean side, and when it is a negative value, the output of the air-fuel ratio sensor 23 is corrected. The value VO is corrected to the rich side. As the absolute value of the sub-feedback correction value efsfb increases, the output value VO of the air-fuel ratio sensor 23 is corrected larger.

  If the output value of the oxygen sensor 24 is low even though the output value of the air-fuel ratio sensor 23 is substantially the stoichiometric air-fuel ratio, it means that the output value of the air-fuel ratio sensor 23 is shifted to the rich side. means. Therefore, in the present embodiment, when the output value of the oxygen sensor 24 is a low value, the value of the sub-feedback correction value efsfb is increased as shown in FIG. It is supposed to be corrected to the lean side. On the other hand, when the output value of the oxygen sensor 24 is high even though the output value of the air-fuel ratio sensor 23 is substantially the stoichiometric air-fuel ratio, the value of the sub feedback correction value efsfb is decreased to The output value of the fuel ratio sensor 23 is corrected to the rich side.

Specifically, the value of the sub feedback correction value efsfb is calculated by the following equation (4). In the following equation (4), Ksp represents a proportional gain, and Ksi represents an integral gain. ΔVO (n) represents an output deviation between the target output value (in this embodiment, a value corresponding to the theoretical air-fuel ratio) and the output value of the oxygen sensor 24 at the n-th calculation.

  In the example shown in FIG. 7, as the value of the sub feedback correction value efsfb increases, the deviation generated in the output value of the air-fuel ratio sensor 23 is corrected, and the actual exhaust air-fuel ratio gradually approaches the stoichiometric air-fuel ratio. Go.

  Thus, the output value of the air-fuel ratio sensor 23 is appropriately corrected by the sub feedback control. However, for example, when the internal combustion engine is stopped, the sub feedback control is interrupted, and as a result, the value of the sub feedback correction value efsfb becomes zero. Reset. Thereafter, when the internal combustion engine is started again, the sub feedback control is resumed. However, the sub feedback correction value efsfb stored in the normal RAM 33 is reset to zero. It takes time to correct the output value to an appropriate value again.

  Therefore, in the present embodiment, the sub-feedback learning value efsfbg corresponding to the steady deviation occurring between the output value of the air-fuel ratio sensor 23 and the value corresponding to the actual exhaust air-fuel ratio is used as the sub-feedback correction value efsfb. 6 and the output value VAF of the air-fuel ratio sensor 23 is corrected based on the calculated sub-feedback learning value efsfbg as shown in step 113 of FIG. Is called “sub-feedback learning control”). Since the sub-feedback learning value efsfbg calculated in this way is stored in the backup RAM 36, it is not deleted even after the internal combustion engine is stopped. Therefore, if the sub-feedback learning value efsfbg is used, the output value of the air-fuel ratio sensor 23 can be corrected again to an appropriate value relatively early.

  Specifically, if the sub-feedback correction value efsfb is a positive value when the predetermined time ΔT has elapsed from the previous learning time (that is, the sub-feedback learning value efsfbg calculation time), the sub-feedback learning value efsfbg is At the same time, when the sub feedback correction value efsfb is a negative value, the sub feedback learning value efsfbg is decreased. Further, the amount of increase or decrease of the sub feedback learning value efsfbg is set to increase as the absolute value of the sub feedback correction value efsfb increases.

In particular, in the present embodiment, the sub feedback correction value efsfb and the sub feedback learning value efsfbg when the predetermined time ΔT has elapsed from the previous learning time are updated by the following equations (5) and (6), respectively. In the following formulas (5) and (6), α is an annealing rate (0 <α ≦ 1) indicating the uptake ratio. Therefore, in the example shown in FIG. 6, since the sub feedback correction value efsfb is a positive value at time t1, the sub feedback correction value efsfb is decreased and the sub feedback learning value according to the following equations (5) and (6). efsfbg increases. Similarly, since the sub feedback correction value efsfb is a positive value at time t2, the sub feedback correction value efsfb is decreased and the sub feedback learning value efsfbg is increased by the following equations (5) and (6).
efsfb = efsfb−efsfb · α (5)
efsfbg = efsfbg + efsfb · α (6)

  The sub-feedback learning value efsfbg calculated in this way is added to the output value VAF (n) in order to calculate the corrected output value VAF ′ (n) in step 113 of FIG. 6 as described above. The sub-feedback learning value efsfbg is stored in the backup RAM 36 and is not deleted even after the internal combustion engine is stopped. Therefore, even when the sub feedback correction value efsfb is reset to zero when the operation is restarted after the internal combustion engine is stopped, the output value of the air-fuel ratio sensor 23 is quickly and appropriately set using the sub feedback learning value efsfbg. Can be corrected to a value.

  In the above example, the amount of increase or decrease of the sub feedback learning value efsfbg increases as the absolute value of the sub feedback correction value efsfb increases, but it does not change according to the sub feedback correction value efsfb. It may be a certain amount. In this case, for example, the sub feedback correction value efsfb is incorporated into the sub feedback learning value efsfbg only when the absolute value of the sub feedback correction value efsfb is greater than or equal to a predetermined value.

  FIG. 8 is a flowchart showing operations of sub feedback control for calculating the sub feedback correction value efsfb and sub feedback learning control for calculating the sub feedback learning value efsfbg. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31.

  First, in step 121, it is determined whether or not a sub feedback control execution condition is satisfied. When the sub feedback control execution condition is satisfied, for example, as in the case of the main feedback control execution condition, the internal combustion engine is not cold started, and the fuel injection from the fuel injection valve is performed during engine operation. For example, the fuel cut control is not being performed. If it is determined in step 121 that the sub feedback control execution condition is satisfied, the routine proceeds to step 122, where the sub feedback control is executed. On the other hand, if it is determined in step 121 that the sub feedback control execution condition is not satisfied, the routine is terminated, and the sub feedback control and the sub feedback learning control are not executed.

In step 122, the output value VO (n) of the oxygen sensor 24 at the time of the nth calculation is detected. Next, at step 123, an output deviation ΔVO (n) between the target output value VOT and the output value VO (n) of the oxygen sensor 24 detected at step 122 is calculated (ΔVO (n) = VOT−VO (n )). In step 124, the value of the proportional term Msp (n) at the time of the nth calculation is calculated by the following equation (7).
Msp (n) = Ksp · ΔVO (n) (7)

Next, at step 125, the value of the integral term Msi (n) at the time of the n-th calculation is calculated by the following equation (8), and the routine proceeds to step 126. In step 126, based on the value of the proportional term Msp (n) calculated in step 145 and the value of the integral term Mip (n) calculated in step 125, the output correction amount efsfb (n) is calculated by the following equation (9). Is calculated.
Msi (n) = Msi (n−1) + Ksi · VO (n) (8)
efsfb (n) = Msp (n) + Msi (n) (9)

  Next, at step 127, it is determined whether or not the execution condition of the sub feedback learning control is satisfied. When the execution condition of the sub feedback learning control is satisfied, for example, when a predetermined time or more has passed since the fuel cut control was canceled, the sub feedback control is performed a predetermined number of times from the previous execution of the sub feedback learning control. If it is, it will be raised. If it is determined in step 127 that the execution condition of the sub feedback learning control is satisfied, the process proceeds to step 128, and the sub feedback learning control is executed by the above formulas (5) and (6). Conversely, if it is determined that the execution condition for the sub feedback learning control is not satisfied, the routine is terminated and the sub feedback learning control is not executed.

  In addition, although the case where PI control was performed as sub feedback control was shown in the said embodiment, other controls, such as PID control, may be performed.

  Next, alcohol concentration correction learning control will be described with reference to FIGS. 9 (A) to 9 (C). First, the solid line shown in FIG. 9A indicates the feedback correction value FAF by the main feedback control, and the broken line performs an annealing process (smoothing process) using a low-pass filter or the like on the feedback correction value FAF, for example. The feedback correction annealed value FAFSM is shown. The solid line shown in FIG. 9B indicates the alcohol concentration correction learning value FALC.

Here, the feedback correction value FAF is a coefficient for feedback correction of the basic fuel injection amount Qb when calculating the fuel injection amount Qft calculated based on the following equation (10). FALC is an alcohol concentration correction learning value, which is a learning value for correcting the basic fuel injection amount Qb in accordance with the alcohol concentration in the fuel. The alcohol concentration correction learning value FALC is stored in the backup RAM 36.
Qft = Qb · (1 + FALC) + Qb · FAF (10)

The above expression (10) and the following expression (11) similar to the above expression (1) represent the same expression for calculating the fuel injection amount Qft, and the first and second terms correspond to the respective expressions. ing.
Qft = Mc / AFT + DQf (11)

Accordingly, the relationship between the feedback correction value FAF and the fuel correction amount DQf is expressed as in Expression (12) from the second term of Expression (10) and Expression (11). Hereinafter, an embodiment according to the present invention will be described using a feedback correction value FAF.
FAF = DQf / Qb (12)

  As shown in FIGS. 9A and 9B, the alcohol concentration correction learning control is executed at regular intervals, and the feedback correction value FAF is set to the feedback correction smoothed value FAFSM at the time of execution. At the same time, the alcohol concentration correction learning value FALC is increased, and the feedback correction smoothed value FAFSM is reset to zero.

  By repeating the alcohol concentration correction learning control, the alcohol concentration correction learning value FALC gradually approaches a correction value suitable for the alcohol concentration in the fuel so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. However, if the change in the alcohol concentration in the fuel is very large due to refueling, etc., excess or deficiency will occur in the fuel supply amount until it converges to the optimal correction value and learning value according to the alcohol concentration. As described above, there is a problem that exhaust emission deteriorates and drivability deteriorates. Therefore, in the present invention, in addition to the correction of the fuel supply amount by the normal main feedback control, the sub-feedback correction value efsfb is corrected in accordance with the change in the alcohol concentration as will be described below. The above problem is solved by reducing the excess and deficiency.

  This will be described using, for example, a case where the alcohol concentration in the fuel is increased by refueling or the like. The fact that the alcohol concentration has increased means that the exhaust air-fuel ratio does not become the stoichiometric air-fuel ratio unless more fuel is supplied than at present. Therefore, it is necessary to increase the sub feedback correction value efsfb. As a method of increasing the sub feedback correction value efsfb, first, a method of changing the target voltage will be described.

  Here, FIGS. 10A to 10C show the relationship between time and the output value VO of the oxygen sensor 24. FIG. 10A shows the output value VO of the oxygen sensor 24 by conventional sub-feedback control. The output value at the rich air-fuel ratio (for example, 0.8 V) and the output value at the lean air-fuel ratio (for example, for example) The output value Vm (for example, 0.5 V) (see FIG. 3) at a theoretical air-fuel ratio substantially in the middle of 0.2 V) is set as the target output value VOT.

  In contrast, in FIG. 10B, the target output value VOT is set to a value higher than the theoretical air-fuel ratio output value VM (for example, 0.7 V), that is, on the rich side. Since the output tendency with the passage of time of the output value VO of the oxygen sensor 24 illustrated by the solid line does not change, the average value of the sub feedback correction value efsfb in a certain time increases, and as a result, the fuel supply amount increases. That is, by setting the target output value VOT to a value higher than the theoretical air-fuel ratio output value VM, as described in step 123 of FIG. 8 described above, the lean air-fuel ratio is less than the negative output deviation ΔVO at the time of rich air-fuel ratio. The positive output deviation ΔVO at the time increases, and on average, the positive output deviation ΔVO becomes a positive output deviation ΔVO, and the fuel supply amount can be increased.

  The above has been described for the case where the alcohol concentration is increased. Naturally, when the alcohol concentration is decreased, the target output value VOT of the oxygen sensor 24 is set to a value lower than the theoretical air-fuel ratio output value VM. The fuel supply amount can be reduced.

  FIGS. 11 and 12 are flowcharts showing an alcohol concentration correction learning control operation for obtaining an alcohol concentration correction learning value and changing the target output value of the oxygen sensor 24 in accordance with a change in the alcohol concentration correction learning value. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31.

  Referring to FIG. 11, first, at step 131, the feedback correction value FAF is read. Next, in step 132, the FAF read in step 131 is subjected to a smoothing process to calculate a feedback correction smoothed value FAFSM. Next, at step 133, the time counter CNT is incremented. Next, at step 134, it is determined whether or not the time counter CNT incremented at step 133 is equal to or greater than the alcohol concentration correction learning control execution interval CNTsadg. Here, if the time counter CNT is equal to or longer than the alcohol concentration correction learning control execution time CNTsadg, the routine proceeds to step 135 to perform the alcohol concentration correction learning control. On the other hand, in step 134, when the time counter CNT is smaller than the alcohol concentration correction learning control execution time CNTsadg, the routine is terminated without changing the alcohol concentration correction learning control and the target output value.

  Next, in step 135, the previous alcohol concentration correction learning value FALC is set to the previous alcohol concentration correction learning value FALCp in order to obtain the difference between the previous value of the alcohol concentration correction learning value FALC to be described later and the current learning value. Proceed to 136.

  Next, the alcohol concentration correction learning control performed in steps 136 and 137 will be described. In step 136, the alcohol concentration correction learned value FALC is calculated by adding the feedback correction smoothed value FAFSM to the previous value. At the same time, the feedback correction value FAF is calculated by subtracting the feedback correction smoothed value FAFSM that is added to the alcohol concentration correction learning value FALC from the previous value. Thereafter, the process proceeds to step 137. In step 137, the feedback correction smoothed value FAFSM is reset to zero, and the process proceeds to step 138.

  Next, in step 138, the previous alcohol concentration correction learning value FALCp set in step 135 is subtracted from the learned alcohol concentration correction learning value FALC obtained in step 136 to calculate an alcohol concentration correction learning value deviation ΔFALC, and then Proceed to step 141.

  Next, at step 141 in FIG. 12, the target output change amount VOC is calculated from the absolute value of the alcohol concentration correction learning value deviation ΔFALC calculated at step 138. For this purpose, a relationship between the absolute value of the alcohol concentration correction learning value deviation ΔFALC and the target output change amount VOC is obtained in advance by a map or a calculation formula experimentally or by calculation, and this map or calculation formula is stored in the ROM 34.

  FIG. 13 shows an example of this map. According to this, when the absolute value of the alcohol concentration correction learned value deviation ΔFALC is smaller than the predetermined value FALCdsh, that is, when the change amount of the alcohol concentration correction learned value FALC is small, the target output change amount VOC is zero. . That is, when the change amount of the alcohol concentration correction learned value FALC is small, it is considered that problems such as deterioration of exhaust emission and deterioration of drivability are unlikely to occur, so that the normal output value of the oxygen sensor 24 is not changed. Sub feedback control is performed.

  On the other hand, when the absolute value of the alcohol concentration correction learning value deviation ΔFALC is larger than a predetermined value FALCdsh, that is, when the change amount of the alcohol concentration correction learning value FALC is large, the target output change amount VOC is the alcohol concentration correction learning value. The deviation ΔFALC increases according to the absolute value. That is, when the change amount of the alcohol concentration correction learning value deviation ΔFALC is large, problems such as deterioration of exhaust emission and deterioration of drivability are likely to occur during the correction or learning process. Change the fuel supply amount.

  In step 141, the target output change amount VOC is set, and then the process proceeds to step 142. Next, at step 142, it is determined whether or not the alcohol concentration correction learned value deviation ΔFALC is 0 or more. When the alcohol concentration correction learning value deviation ΔFALC is 0 or more, the routine proceeds to step 143. Here, when the alcohol concentration correction learning value deviation ΔFALC is 0 or more, alcohol concentration correction learning is performed in the direction in which the alcohol concentration increases, that is, the alcohol concentration in the fuel has increased due to fueling or the like. Means. Therefore, this is the same as the example described above with reference to FIG. 10B, and it is necessary to change the target output value VOT to a value higher than the theoretical air-fuel ratio output value VM. Accordingly, in step 143, the target output change amount VOC calculated in step 141 is added to the target output value VOT, and then the routine proceeds to step 145, where the time counter CNT is reset to zero and the routine is terminated.

  On the other hand, if the alcohol concentration correction learned value deviation ΔFALC is less than 0 in step 142, the process proceeds to step 144. Here, when the alcohol concentration correction learning value deviation ΔFALC is less than 0, the alcohol concentration correction learning is performed in the direction in which the alcohol concentration decreases, that is, the alcohol concentration in the fuel has decreased due to fueling or the like. Means. Therefore, contrary to the example described with reference to FIG. 10B, it is necessary to change the target output value VOT to a value lower than the theoretical air-fuel ratio output value VM. Accordingly, at step 144, the target output change value VOC calculated at step 141 is subtracted from the target output value VOT, and then the routine proceeds to step 145 where the time counter CNT is reset to zero and the routine is terminated.

  The first embodiment described above uses a method of correcting the sub-feedback correction value efsfb by changing the target output value VOT as a method of correcting the sub-feedback correction value efsfb according to a change in alcohol concentration. . Next, as a second embodiment, a method for changing the proportional gain Ksp used in the above equations (4) and (7) relating to the calculation of the sub feedback correction value efsfb will be described.

  FIG. 10C shows a change in the output value VO of the oxygen sensor 24 by changing the proportional gain Ksp when the alcohol concentration in the fuel is increased by refueling or the like, as in FIG. 10B. Yes.

  Specifically, in FIG. 10C, the proportional gain Ksp is different depending on whether the output value VO of the oxygen sensor 24 is on the rich side or on the lean side of the theoretical air-fuel ratio output value VM. It is set. That is, when the output value VO of the oxygen sensor 24 is richer than the theoretical air-fuel ratio output value VM, the proportional gain is the rich-time proportional gain Kspr, and the output value VO of the oxygen sensor 24 is greater than the theoretical air-fuel ratio output value VM. If the proportional gain in the case of being on the lean side is the lean time proportional gain Kspl, in FIG. 10C, the lean time proportional gain Kspl is set larger than the rich time proportional gain Kspr.

  When the output value VO of the oxygen sensor 24 is rich and lean, the target output value VOT, that is, the output deviation ΔVO from the theoretical air-fuel ratio output value VM is substantially equal. As a result, the lean value with a large proportional gain is richer. The sub feedback correction value efsfb becomes larger than the time. Therefore, the fuel supply amount can be finally increased.

  In the above, the case where the alcohol concentration is increased has been described. Naturally, when the alcohol concentration is decreased, the fuel supply amount is reduced by reversing the magnitude relationship between the rich time proportional gain Kspr and the lean time proportional gain Kspl. Can be reduced.

  FIG. 14 is a flowchart showing the operations of the sub feedback control and the sub feedback learning control according to the present embodiment similar to the flowchart shown in FIG. 8 for switching the proportional gain Ksp according to the exhaust air / fuel ratio. 8 is different from the flowchart shown in FIG. 8 in that steps 154 to 156 are added after step 153 corresponding to step 123 in FIG.

  Only the points different from the flowchart shown in FIG. 8 will be described. After calculating the output deviation ΔVO (n) of the oxygen sensor 24 in step 153, the process proceeds to step 154. In step 154, it is determined whether or not ΔVO (n) is 0 or more, that is, whether or not the exhaust air-fuel ratio is lean. If it is determined in step 154 that ΔVO (n) is equal to or greater than 0, that is, the exhaust air-fuel ratio is lean, the process proceeds to step 155, the lean proportional gain Kspl is set to the proportional gain Ksp, and the process proceeds to step 157. move on. On the other hand, if it is determined in step 154 that ΔVO (n) is less than 0, that is, the exhaust air-fuel ratio is rich, the process proceeds to step 156, where the rich time proportional gain Kspr is set to the proportional gain Ksp. Proceed to The processing after step 157 is the same as the processing after step 124 in FIG.

  FIG. 15 is a flowchart showing the latter half of the alcohol concentration correction learning control operation for determining the lean-time proportional gain Kspl and the rich-time proportional gain Kspr that are set to the proportional gain Ksp in step 155 or 156 shown in FIG. . The first half of the alcohol concentration correction learning control operation is the same as in FIG.

  Therefore, after calculating the alcohol concentration correction learned value deviation ΔFALC in step 138 of FIG. 11, the process then proceeds to step 171 of FIG. In step 171, a gain correction coefficient GK is calculated from the absolute value of the alcohol concentration correction learning value deviation ΔFALC calculated in step 138. For this purpose, a relationship between the absolute value of the alcohol concentration correction learned value deviation ΔFALC and the gain correction coefficient GK is obtained in advance by a map or a calculation formula experimentally or by calculation, and this map or calculation formula is stored in the ROM 34.

  FIG. 16 shows an example of this map. According to this, when the absolute value of the alcohol concentration correction learning value deviation ΔFALC is smaller than the predetermined value FALCdsh, that is, when the change amount of the alcohol concentration correction learning value FALC is small, the gain correction coefficient GK is 1.0. is there. That is, when the change amount of the alcohol concentration correction learned value FALC is small, it is considered that problems such as exhaust emission deterioration and drivability deterioration are unlikely to occur. Therefore, normal sub-feedback control is performed without changing the proportional gain Ksp. Done.

  On the other hand, when the absolute value of the alcohol concentration correction learning value deviation ΔFALC is larger than a predetermined value FALCdsh, that is, when the change amount of the alcohol concentration correction learning value FALC is large, the gain correction coefficient GK is the alcohol concentration correction learning value deviation. It decreases according to the absolute value of ΔFALC. That is, when the change amount of the alcohol concentration correction learning value deviation ΔFALC is large, problems such as deterioration of exhaust emission and deterioration of drivability are likely to occur in the correction or learning process, and therefore the proportional gain Ksp is 1.0. Multiply the following gain correction coefficient GK to adjust the fuel supply amount.

  In step 171, after setting the gain correction coefficient GK, the process proceeds to step 172. Next, at step 172, it is determined whether or not the alcohol concentration correction learned value deviation ΔFALC is 0 or more. If the alcohol concentration correction learned value deviation ΔFALC is 0 or more, the process proceeds to step 173. Here, when the alcohol concentration correction learning value deviation ΔFALC is 0 or more, alcohol concentration correction learning is performed in the direction in which the alcohol concentration increases, that is, the alcohol concentration in the fuel has increased due to fueling or the like. Means. Therefore, this is the same case as the example described with reference to FIG. 10C, and it is necessary to set the lean proportional gain Kspl larger than the rich proportional gain Kspr. Accordingly, in step 173, the rich proportional gain Kspr is set to a value obtained by multiplying the normal proportional gain Ksp by the gain correction coefficient GK, the normal proportional gain is set to the lean proportional gain Kspl, and then the process proceeds to step 175. The time counter CNT is reset to zero to end the routine.

  On the other hand, if the alcohol concentration correction learned value deviation ΔFALC is less than 0 in step 172, the process proceeds to step 174. Here, when the alcohol concentration correction learning value deviation ΔFALC is less than 0, the alcohol concentration correction learning is performed in the direction in which the alcohol concentration decreases, that is, the alcohol concentration in the fuel has decreased due to fueling or the like. Means. Therefore, contrary to the example described with reference to FIG. 10C, it is necessary to set the rich time proportional gain Kspr larger than the lean time proportional gain Kspl. Accordingly, in step 174, the normal proportional gain Ksp is set as the rich time proportional gain Kspr, and the value obtained by multiplying the normal proportional gain by the gain correction coefficient GK is set as the lean time proportional gain Kspl. The time counter CNT is reset to zero to end the routine.

  By the way, when the alcohol concentration greatly changes due to refueling or the like, the sub-feedback control and the sub-feedback learning control are performed simultaneously with the alcohol concentration correction learning control. That is, the alcohol concentration deviation to be learned and corrected by the alcohol concentration correction learning control is dispersed in the alcohol concentration correction learning value FALC, the sub feedback correction value efsfb, and the sub feedback learning value efsfbg, and the alcohol concentration correction learning is performed. It causes the problem of deterioration of learning accuracy by control.

  Therefore, in the present invention, when the change in the alcohol concentration is large, the alcohol concentration correction learning control can be performed more accurately by limiting the correction and learning by the sub feedback control and the sub feedback learning control.

  FIG. 17 is a flowchart showing operations of sub-feedback control and sub-feedback learning control according to this embodiment similar to the flowchart shown in FIG. 8 for limiting correction and learning of the sub-feedback correction value efsfb and the sub-feedback learning value efsfbg. It is. 8 differs from the flowchart shown in FIG. 8 only in the processing in step 186 corresponding to step 126 in FIG.

  Specifically, when calculating the sub feedback correction value efsfb in step 186, the whole is multiplied by the sub feedback correction value correction coefficient COF (0 ≦ COF ≦ 1). As a result, correction by sub-feedback control can be limited, and at the same time, learning by sub-feedback learning control calculated in step 189 is also limited.

  FIG. 18 is a flowchart showing the latter half of the alcohol concentration correction learning control operation for determining the sub feedback correction value correction coefficient COF used in step 186 shown in FIG. The first half of the alcohol concentration correction learning control operation is the same as in FIG.

  Therefore, after calculating the alcohol concentration correction learned value deviation ΔFALC in step 138 of FIG. 11, the process then proceeds to step 191 of FIG. In step 191, the sub feedback correction value correction coefficient COF is calculated from the absolute value of the alcohol concentration correction learning value deviation ΔFALC calculated in step 138. For this purpose, a relationship between the absolute value of the alcohol concentration correction learning value deviation ΔFALC and the sub feedback correction value correction coefficient COF is obtained in advance by a map or a calculation formula or by calculation, and this map or calculation formula is stored in the ROM 34. .

  FIG. 19 shows an example of this map. According to this, when the absolute value of the alcohol concentration correction learned value deviation ΔFALC is smaller than a predetermined value FALCdsh, that is, when the change amount of the alcohol concentration correction learned value FALC is small, the sub feedback correction value correction coefficient COF is 1. .0. That is, when the change amount of the alcohol concentration correction learning value FALC is small, it is considered that the influence of the alcohol concentration correction learning control by the sub feedback control and the sub feedback learning control on the learning accuracy is small. Normal sub-feedback control and sub-feedback learning control are performed without limiting correction and learning by control.

  On the other hand, when the absolute value of the alcohol concentration correction learned value deviation ΔFALC is larger than a predetermined value FALCdsh, that is, when the change amount of the alcohol concentration correction learned value FALC is large, the sub feedback correction value correction coefficient COF is the alcohol concentration correction. It decreases according to the absolute value of the learning value deviation ΔFALC. That is, when the amount of change in the alcohol concentration correction learning value deviation ΔFALC is large, it is considered that the influence on the learning accuracy of the alcohol concentration correction learning control by the sub feedback control and the sub feedback learning control is large, so the sub feedback correction value efsfb The sub feedback correction value correction coefficient COF of 1.0 or less is multiplied to limit correction and learning by the sub feedback control and the sub feedback learning control.

  In step 191, after calculating the sub feedback correction value correction coefficient COF, the process proceeds to step 192, where the time counter CNT is reset to zero and the routine is terminated.

  The correction and the learning limitation by the sub-feedback control and the sub-feedback learning control according to the change in the alcohol concentration in this embodiment are the adjustment of the fuel supply amount by the change of the target output value VOT in the first embodiment described above and You may implement together with adjustment of the fuel supply amount by the change of the proportional gain Ksp in 2nd embodiment.

It is a figure of the whole internal combustion engine in which the air fuel ratio control device of the present invention is used. It is the figure which showed the relationship between an exhaust air fuel ratio and the output value of an air fuel ratio sensor. It is the figure which showed the relationship between an exhaust air fuel ratio and the output voltage of an oxygen sensor. It is the figure which showed the relationship between alcohol concentration correction | amendment learning value and a theoretical air fuel ratio. It is a flowchart which shows target fuel supply amount calculation control operation. It is a flowchart which shows main feedback control operation. It is a time chart of an exhaust air fuel ratio, an output value of an oxygen sensor, a sub feedback correction value, and a sub feedback learning value. It is a flowchart which shows a sub feedback control operation and a sub feedback learning control operation. It is a time chart of alcohol concentration correction | amendment learning control operation. It is the figure which showed the relationship between time and the output voltage of an oxygen sensor. It is a part of flowchart of alcohol concentration correction | amendment learning control operation. 12 is a part of a flowchart of an alcohol concentration correction learning control operation continued from FIG. 11. It is the figure which showed the relationship between alcohol concentration correction | amendment learning value deviation and target output change amount. It is a flowchart which shows another embodiment of sub feedback control operation and sub feedback learning control operation. FIG. 12 is a part of another embodiment of a flowchart of an alcohol concentration correction learning control operation continued from FIG. 11. It is the figure which showed the relationship between alcohol concentration correction | amendment learning value deviation and the gain correction coefficient GK. It is a flowchart which shows another embodiment of sub feedback control operation and sub feedback learning control operation. FIG. 12 is a part of still another embodiment of a flowchart of an alcohol concentration correction learning control operation continued from FIG. 11. It is the figure which showed the relationship between alcohol concentration correction | amendment learning value deviation and the sub feedback correction value correction coefficient COF.

Explanation of symbols

1 Engine Body 3 Piston 5 Combustion Chamber 6 Intake Valve 8 Exhaust Valve 10 Spark Plug 11 Fuel Injection Valve 31 ECU
23 Air-fuel ratio sensor 24 Oxygen sensor 42 Load sensor 43 Crank angle sensor

Claims (3)

  An air-fuel ratio control apparatus for an internal combustion engine that can use alcohol and gasoline alone or in combination as fuel, and in an upstream exhaust passage and a downstream exhaust passage of an exhaust purification catalyst provided in an engine exhaust passage The upstream side air-fuel ratio sensor and the downstream side air-fuel ratio sensor that are respectively disposed and detect the air-fuel ratio of the exhaust gas, and the feedback correction value so that the output value of the upstream side air-fuel ratio sensor becomes a value corresponding to the target air-fuel ratio. Main feedback control means for correcting the fuel supply amount based on the output value of the downstream air-fuel ratio sensor to compensate for the deviation between the exhaust air-fuel ratio based on the output value of the upstream air-fuel ratio sensor and the actual exhaust air-fuel ratio Sub-feedback control means for correcting the fuel supply amount so that the exhaust air-fuel ratio becomes the target air-fuel ratio, and calculated based on the feedback correction value. Learning the alcohol concentration correction learning value and correcting the fuel supply amount based on the learned learning value, and learning the learning value calculated based on the correction value in the sub-feedback control unit In an air-fuel ratio control apparatus for an internal combustion engine comprising sub-feedback learning control means for correcting the fuel supply amount, when the learning is performed to increase the alcohol concentration correction learning value, the exhaust air-fuel ratio is the target air-fuel ratio. When the correction value in the sub-feedback control means is corrected so as to be richer than the fuel ratio and learning is performed to decrease the alcohol concentration correction learning value, the exhaust air / fuel ratio becomes leaner than the target air / fuel ratio. An air-fuel ratio control device for an internal combustion engine that corrects the correction value in the sub-feedback control means .   The amount of increase in the correction value in the sub-feedback control means is changed according to the amount of increase in the alcohol concentration correction learning value, and the amount of decrease in the correction value in the sub-feedback control means according to the amount of decrease in the alcohol concentration correction learning value The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio is changed.   An air-fuel ratio control apparatus for an internal combustion engine that can use alcohol and gasoline alone or in combination as fuel, and in an upstream exhaust passage and a downstream exhaust passage of an exhaust purification catalyst provided in an engine exhaust passage The upstream side air-fuel ratio sensor and the downstream side air-fuel ratio sensor that are respectively disposed and detect the air-fuel ratio of the exhaust gas, and the feedback correction value so that the output value of the upstream side air-fuel ratio sensor becomes a value corresponding to the target air-fuel ratio. Main feedback control means for correcting the fuel supply amount based on the output value of the downstream air-fuel ratio sensor to compensate for the deviation between the exhaust air-fuel ratio based on the output value of the upstream air-fuel ratio sensor and the actual exhaust air-fuel ratio Sub-feedback control means for correcting the fuel supply amount so that the exhaust air-fuel ratio becomes the target air-fuel ratio, and calculated based on the feedback correction value. Learning the alcohol concentration correction learning value and correcting the fuel supply amount based on the learned learning value, and learning the learning value calculated based on the correction value in the sub-feedback control unit In the air-fuel ratio control apparatus for an internal combustion engine comprising the sub-feedback learning control means for correcting the fuel supply amount, when the alcohol concentration correction learning value is learned, the correction in the sub-feedback control means is limited. An air-fuel ratio control apparatus for an internal combustion engine.

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