JP2009144574A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device capable of preventing the trouble caused in next engine starting time when an alcoholic concentration correction learning value is not converged before stopping of an internal combustion engine in a flexible fuel vehicle. <P>SOLUTION: The air-fuel ratio control device for the internal combustion engine is provided with an air-fuel ratio sensor 23 arranged in an upstream exhaust passage of a three-way catalyst 20, and executes feedback control for correcting a fuel supply amount based on an output value of the air-fuel ratio sensor, and alcohol concentration correction learning control for learning the alcohol concentration correction leaning value. Convergence of the alcohol concentration correction learning value is determined based on at least one predetermined convergence determination condition, and an initial value of the alcohol concentration correction learning value in engine starting time is set to be an alcohol concentration correction learning value converged destination estimated value calculated by the feedback correction value and the alcohol concentration correction learning value in last stop time of the internal combustion engine when the engine is stopped before the alcohol concentration correction learning value is converged. <P>COPYRIGHT: (C)2009,JPO&INPIT

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

  By the way, in the flexible fuel vehicle, it is conceivable to perform alcohol concentration correction learning control for calculating an alcohol concentration correction learning value for adjusting the fuel supply amount in accordance with the alcohol concentration in the fuel.

  However, if the operation of the internal combustion engine is stopped before the alcohol concentration learning control is completed, that is, before the alcohol concentration correction learning value converges, the alcohol concentration correction learning value that has not converged at the time of the previous operation stop at the next engine start. Since the fuel supply amount is corrected by using the engine, problems such as a start failure in which the engine caused by fuel shortage does not start and stops, or knocking caused by excessive fuel may occur. That is, if the alcohol concentration correction learning value is corrected using a value that has not converged, the amount of fuel supplied may be too much or too little than the amount to be supplied.

  Accordingly, the present invention provides an air-fuel ratio control device for an internal combustion engine that prevents a malfunction that occurs at the next engine start when the alcohol concentration correction learning value does not converge by the time the internal combustion engine is stopped in a flexible fuel vehicle. Objective.

  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 And an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas, and a feedback correction value so that an output value of the air-fuel ratio sensor becomes a value corresponding to the target air-fuel ratio. Feedback means for correcting the fuel supply amount based on the above, and alcohol concentration correction learning means for learning the alcohol concentration correction learning value calculated based on the feedback correction value and correcting the fuel supply amount based thereon In the air-fuel ratio control apparatus for an internal combustion engine, the at least one convergence that the alcohol concentration correction learning value has converged is determined. Convergence determining means for determining based on a constant condition, and an alcohol concentration correction learning value convergence destination estimated value that is a value estimated that the alcohol concentration correction learning value converges based on the feedback correction value and the alcohol concentration correction learning value And an initial value of the alcohol concentration correction learning value at the start of the internal combustion engine at this time, when it is determined that the alcohol concentration correction learning value has not converged at the previous stop of the internal combustion engine, An air-fuel ratio control apparatus for an internal combustion engine is provided that uses the alcohol concentration correction learning value convergence destination estimated value obtained when the internal combustion engine was stopped last time.

  According to the present invention, in the flexible fuel vehicle, when the alcohol concentration correction learned value does not converge until the internal combustion engine is stopped, the alcohol concentration correction learned value converges that is considered to be closer to the true value than the learned value. By using the pre-estimated value as the alcohol concentration correction learning value at the next engine start, there is an effect of preventing the occurrence of problems at the start.

  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. The fuel containing alcohol is stored in the fuel tank 24, and is supplied to the fuel injection valve 11 by an electronically controlled fuel pump 25 having a variable discharge amount through a fuel supply pipe and injected. In the present embodiment, the three-way catalyst 20 is used as the exhaust purification catalyst. However, other types of catalysts such as a NOx storage reduction catalyst, a lean NOx catalyst, a DPNR, etc. may be used as long as they have oxygen storage capability. It may be used. Further, instead of the air-fuel ratio sensor 23, an oxygen sensor that generates an output voltage that varies greatly depending on whether the air-fuel ratio of the exhaust gas is richer or leaner than the stoichiometric air-fuel ratio may be used.

  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. The output voltage is input to the input port 37 via the corresponding AD converter 39. Further, the output signal of the open / close sensor 28 is 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, the step motor 17 and the fuel pump 25 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 air-fuel ratio sensor 23 disposed in the upstream exhaust passage from the three-way catalyst 20 supplies the exhaust air-fuel ratio (the exhaust passage upstream of the three-way catalyst 20, the combustion chamber 5 and the intake passage). The ratio of air to fuel) is detected, and feedback control is performed on 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. 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, 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 voltage at the stoichiometric 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 voltage corresponding to the stoichiometric air-fuel ratio after the change in alcohol concentration remains V0, and the tendency of the substantially proportional output voltage shifts as shown by the broken line with the same tendency. Therefore, as shown in FIG. 3, 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. 3, 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 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. 4 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 from the map shown in FIG. 3 based on the alcohol concentration correction learned value FALC read at step 102.

  Next, at step 105, the in-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 feedback control operation described later. Based on the above equation (1), the target fuel supply amount Qft (n) is calculated, 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, feedback control will be described. In the present embodiment, as feedback control, a 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 calculation. 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. 5 is a flowchart of the 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 an execution condition for feedback control is satisfied. The case where the execution condition of the 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 starting is not performed). In addition, the fuel cut control for stopping the fuel injection from the fuel injection valve during the engine operation is not being performed. If it is determined in step 111 that the feedback control execution condition is satisfied, the process proceeds to step 112. On the other hand, if it is determined in step 111 that the feedback control execution condition is not satisfied, the routine is terminated and the 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, the alcohol concentration correction learned value FALC and the AFT obtained from FIG. 3 are read as described above. Next, at step 114, based on the output value VAF (n) detected at step 112 and the AFT read at step 113, the map shown in FIG. 2 is used to calculate the actual air-fuel ratio 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 115, 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 116, 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.

  Next, alcohol concentration correction learning control will be described with reference to FIGS. First, the solid line shown in FIG. 6A indicates the feedback correction value FAF by 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 annealing value FAFSM is shown.

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 (4). 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 (4)

The above formula (4) and the following formula (5) similar to the above formula (1) represent the same formula for calculating the fuel injection amount Qft, and the first term and the second term correspond to the respective formulas. ing.
Qft = Mc / AFT + DQf (5)

Therefore, the relationship between the feedback correction value FAF and the fuel correction amount DQf is expressed by the following equation (6) from the second terms of the above equations (4) and (5). Hereinafter, an embodiment according to the present invention will be described using a feedback correction value FAF.
FAF = DQf / Qb (6)

  The solid line shown in FIG. 6B indicates the alcohol concentration correction learned value FALC, and the broken line indicates the alcohol concentration correction learned value convergence that is an estimated value that the alcohol concentration correction learned value FALC will eventually converge. The pre-estimated value FALTEST is shown.

  As shown in FIGS. 6 (A) and 6 (B), the alcohol concentration correction learning control is executed at regular intervals, and the feedback correction value FAF is set by 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.

  FIGS. 8 and 9 are flowcharts showing the alcohol concentration correction learning control operation for calculating the alcohol concentration correction learning value FALC, determining whether or not it has converged, and setting the alcohol concentration correction learning value convergence flag. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31.

  Referring to FIG. 8, first, in step 121, the feedback correction value FAF is read. Next, in step 122, the FAF read in step 121 is subjected to an annealing process to calculate a feedback correction annealing value FAFSM. Next, at step 123, the time counter CNT is incremented. Next, in step 124, it is determined whether or not the time counter CNT incremented in step 123 is greater than or equal to 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 125 to perform the alcohol concentration correction learning control. On the other hand, if the time counter CNT is smaller than the alcohol concentration correction learning control execution time CNTsadg in step 124, the routine is terminated without performing alcohol concentration correction learning control and alcohol concentration correction learning value convergence determination.

  Next, the alcohol concentration correction learning control performed in steps 125 and 126 will be described. In step 125, 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 126. In step 126, the feedback correction smoothed value FAFSM is reset to zero, and the process proceeds to step 127. Next, at step 127, the alcohol concentration correction learning count Ng is incremented.

  Next, after the alcohol concentration correction learning count Ng is incremented in step 127 of FIG. 8, the process proceeds to step 131 of FIG. Next, Step 131 to Step 133 are processes for obtaining the alcohol concentration correction learning value convergence destination estimated value FALTEST shown by a broken line in FIG.

  First, in step 131, the initial value FALCINT of the alcohol concentration correction learned value FALC at the time of starting the engine (that is, the alcohol concentration correction learned value FALC at the time of the previous engine stop) is subtracted from the alcohol concentration correction learned value FALC. The change amount ΔFALC of the current alcohol concentration correction learning value FALC from is calculated.

  Next, in step 132, a value obtained by adding the change amount ΔFALC of the alcohol concentration correction learning value FALC to the feedback correction value FAF, that is, the feedback correction value and the alcohol concentration correction learning number when it is assumed that the alcohol concentration correction learning control is not performed. From the map or calculation formula using Ng as an argument, the change amount ΔFALCEST of the alcohol concentration correction learning value convergence destination estimated value FALTEST from the initial value FALCINT of the alcohol concentration correction learning value FALC is obtained. This map or calculation formula is obtained experimentally or by calculation in advance and stored in the ROM 34.

  FIG. 11 shows an example of the above map for obtaining the change amount ΔFALEST. The horizontal axis is the alcohol concentration correction learning frequency Ng, and the vertical axis is the change amount ΔFALEST of the alcohol concentration correction learned value convergence destination estimated value FALTEST. The tendency according to the value of FAF + ΔFACL is shown. The larger the value of FAF + ΔFACL and the greater the number Ng of alcohol concentration correction learning, the greater the change amount ΔFALEST.

  Next, the process proceeds to step 133, and the alcohol concentration correction learning value convergence destination change value ΔFALCEST obtained in step 132 is added to the initial value FALCINT of the alcohol concentration correction learning value FALC to add the alcohol concentration correction learning value convergence destination. Estimated value FALTEST is calculated, and the process proceeds to step 134.

  In step 134, it is determined whether the alcohol concentration correction learning number Ng is equal to or greater than the alcohol concentration correction learning value convergence determination number Ngsfbg. That is, when the alcohol concentration correction learning number Ng is equal to or greater than a predetermined alcohol concentration correction learning value convergence determination number Ngsfbg, it is determined that the alcohol concentration correction learning value FALC has converged.

  Therefore, as shown in FIG. 6C, when the alcohol concentration correction learning number Ng is equal to or larger than the alcohol concentration correction learned value convergence determination number Ngsfbg, the routine proceeds to step 135 and the alcohol concentration correction learned value convergence flag SF is set. 1 is set, then the routine proceeds to step 137 where the time counter CNT is reset to zero and the routine is terminated. On the other hand, if the alcohol concentration correction learning number Ng is smaller than the alcohol concentration correction learned value convergence determination number Ngsfbg in step 134, the process proceeds to step 136, where the alcohol concentration correction learning value convergence flag SF is set to 0, and then Proceeding to step 137, the time counter CNT is reset to zero and the routine is terminated. The value of the alcohol concentration correction learned value convergence flag SF is stored in the backup RAM 36.

  The alcohol concentration correction learning value convergence determination number Ngsfbg is determined by, for example, stopping the internal combustion engine immediately after executing the alcohol concentration correction learning control for the number of times, and setting the alcohol concentration correction learning value FALC at the previous engine stop time at the next engine start. Even if the fuel injection amount is corrected by using this, the alcohol concentration correction learning frequency Ng that does not cause a problem at the start of the engine is determined in advance by experiments or the like.

  Next, another embodiment of the alcohol concentration correction learning control will be described with reference to FIG. 7A and 7B are the same as FIGS. 6A and 6B described above, respectively. In the embodiment shown in FIG. 6, the convergence of the alcohol concentration correction learning value FALC is determined using the alcohol concentration correction learning number Ng. In this embodiment, the alcohol concentration correction learning value convergence destination estimated value FALCEST is used to determine the alcohol concentration correction learning value FALC. The convergence of the density correction learning value FALC is determined.

  Steps 121 to 127 shown in FIG. 8 are the same in this embodiment, and steps 131 to 137 shown in FIG. 9 in the first embodiment are also changed from step 141 shown in FIG. It is substantially the same as step 147. However, only step 144 corresponding to step 134 in FIG. 9 is different.

  Therefore, only the difference will be described. In the first embodiment, the convergence of the alcohol concentration correction learning value FALC is determined using the alcohol concentration correction learning frequency Ng. In this embodiment, the alcohol concentration correction learning value convergence destination estimated value FALCEST is used as the alcohol concentration. It is determined whether or not the corrected learning value FALC has converged.

  Therefore, in step 144, as shown in FIG. 7C, an absolute value of a value obtained by subtracting the alcohol concentration correction learning value FALC from the alcohol concentration correction learning value convergence destination estimated value FALTEST is obtained, and the value is determined in advance. It is determined whether or not the alcohol concentration correction learning value convergence determination value TFC is smaller. That is, if the absolute value is smaller than the alcohol concentration correction learning value convergence determination value TFC, it is determined that the alcohol concentration correction learning value FALC has substantially converged, and the process proceeds to step 145. Next, as shown in FIG. 7D, in step 145, 1 is set to the alcohol concentration correction learned value convergence flag SF, and then the routine proceeds to step 147 where the time counter CNT is reset to zero and the routine is terminated. .

  On the other hand, if the absolute value is greater than or equal to the alcohol concentration correction learning value convergence determination value TFC, it is determined that the alcohol concentration correction learning value FALC has not yet converged, and the process proceeds to step 146. In step 146, 0 is set to the alcohol concentration correction learned value convergence flag SF, and then the routine proceeds to step 178, where the time counter CNT is reset to zero and the routine is ended. The value of the alcohol concentration correction learned value convergence flag SF is stored in the backup RAM 36.

  The alcohol concentration correction learning value convergence determination value TFC is obtained by, for example, executing alcohol concentration correction learning control, and the absolute value of a value obtained by subtracting the alcohol concentration correction learning value FALC from the alcohol concentration correction learning value convergence destination estimated value FALTEST is the alcohol concentration Even if the internal combustion engine is stopped immediately after it becomes smaller than the corrected learning value convergence determination value TFC and the fuel injection amount is corrected using the alcohol concentration correction learning value FALC at the time of the previous engine stop at the next engine start, A value that does not cause a problem at the time of start-up is determined in advance by experiments or the like.

  As described above, the convergence of the alcohol concentration correction learned value FALC is determined, but if the alcohol concentration correction learned value FALC has not converged when the engine is stopped, the fuel injection amount is corrected using the value at the next engine start. As a result, problems such as starting failure occur. Therefore, in this case, a malfunction such as a starting failure is prevented by performing an alcohol concentration correction learning value initial setting operation described below.

  FIG. 12 is a flowchart of an alcohol concentration correction learning value initial setting operation for setting an initial value to the alcohol concentration correction learning value FALC when the engine is started. This operation is performed by the ECU 31 as a routine that is executed only once when the engine is started.

  First, in step 151, the alcohol concentration correction learned value convergence flag SF is read from the backup RAM 36. Next, in step 152, it is determined whether or not the alcohol concentration correction learned value convergence flag SF read in step 151 is 1. If it is determined that the alcohol concentration correction learned value convergence flag SF is 1, the process proceeds to step 153.

  Next, at step 153, the alcohol concentration correction learning value FALC at the previous engine stop is set in the alcohol concentration correction learning value FALC, and the routine is ended. That is, since the alcohol concentration correction learning value convergence flag SF is 1, the alcohol concentration correction learning value FALC has converged by the time of the previous engine stop. Therefore, if the alcohol concentration correction learning value FALC is used when starting the engine, problems such as starting failure do not occur.

  On the other hand, if it is determined in step 152 that the alcohol concentration correction learned value convergence flag SF is not 1, the process proceeds to step 154. In step 154, the alcohol concentration correction learned value convergence destination estimated value FALCEST at the previous engine stop is set in the alcohol concentration correction learned value FALC, and the routine ends. That is, since the alcohol concentration correction learned value convergence flag SF is not 1, the alcohol concentration correction learned value FALC has not converged until the previous engine stop. Therefore, if the alcohol concentration correction learned value FALC is used as it is at the time of engine start, problems such as start failure occur.

  On the other hand, the alcohol concentration correction learning value convergence destination estimated value FALTEST is an estimated value that the alcohol concentration correction learning value FALC converges, but is considered to be closer to a true value than the alcohol concentration correction learning value FALC before convergence. It is done. Therefore, if the alcohol concentration correction learned value FALC has not converged before the previous engine stop, the alcohol concentration correction learned value convergence destination estimated value FALTEST is used as the alcohol concentration correction learned value FALC at the time of starting.

  Next, another embodiment of the alcohol concentration correction learning value initial setting operation will be described with reference to the flowchart shown in FIG. The flowchart shown in FIG. 13 is almost the same as the flowchart of the alcohol concentration correction learned value initial setting operation shown in FIG. 12, but it is determined in step 162 that the alcohol concentration correction learned value convergence flag SF is not 1, and the process proceeds to step 164. Only the processing after progress is different. In step 164, the alcohol concentration correction learning value FALC is set to a value obtained by multiplying the alcohol concentration correction learning value convergence destination estimated value FALTEST at the previous engine stop by the correction coefficient α (α ≧ 1).

  That is, since the alcohol concentration correction learning value FALC has not converged when the engine is stopped, the alcohol concentration correction learning value convergence destination estimated value FALCEST, which is considered to be closer to the true value, is used. If insufficient, problems such as start-up failure will occur. Accordingly, in order to more reliably prevent the occurrence of a starting failure or the like, correction is performed so that more fuel is injected. The correction coefficient α may be a predetermined constant, or may be a value that changes based on other values such as an alcohol concentration correction learning value convergence destination estimated value FALTEST.

  By the way, the alcohol concentration correction learning value FALC can be used for correction of the fuel injection amount at the start, correction of the ignition timing, correction of the fuel injection amount at the cold time, and the like. Among them, the correction of the fuel injection amount at the start and the correction of the ignition timing using the alcohol concentration correction learning value FALC will be described below.

  First, a method of correcting the fuel injection amount at the time of starting the engine using the alcohol concentration correction learned value FALC set by the above-described alcohol concentration correction learning value initial setting operation will be described. Immediately after starting the engine until the crankshaft starts rotating and exceeds a certain number of rotations, misfire is particularly likely to occur. This number of rotations can be determined as the number of rotations Ne1 in advance through experiments or the like. Since the in-cylinder intake air amount Mc cannot be detected until the rotational speed Ne1 is reached, the control at the time of engine start will be described using not the basic fuel injection amount Qb but the fuel injection time TAU for each engine cycle.

The fuel injection time TAU from when the crankshaft starts to rotate until it reaches the rotational speed Ne1 is expressed by the following equation (7). Here, TAUSTB is the starting basic fuel injection time, and is calculated by, for example, a map or a calculation formula obtained in advance by experiment or calculation from the water temperature and the rotational speed as arguments. KALCST is a starting injection time correction coefficient (KALCST ≧ 1), and is calculated based on the map shown in FIG. 14 using the alcohol concentration correction learning value FALC. The map shown in FIG. 14 is obtained in advance by experiment or calculation formula, and this map or calculation formula is stored in the ROM 34. According to the equation (7) and the map of FIG. 14, the larger the alcohol concentration correction learned value FALC is, the longer the fuel injection time TAU is corrected, that is, the fuel injection amount is increased.
TAU = TAUSTB / KALCST (7)

  FIG. 15 is a flowchart of the fuel injection time setting operation for setting the fuel injection time TAU. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31 after the alcohol concentration correction learning value initial setting operation is executed at the time of engine start.

  First, at step 171, the engine speed Ne is read. Next, at step 172, it is judged if the engine speed Ne read at step 171 is smaller than a predetermined speed Ne1 set in advance. If the engine speed Ne is smaller than the predetermined engine speed Ne1, it is determined that the engine is starting, and the routine proceeds to step 173. In step 173, a starting injection time correction coefficient KALCST is calculated based on the map of FIG. Next, at step 174, the fuel injection time TAU is set based on equation (7), and the routine ends. On the other hand, if the engine speed Ne is greater than or equal to the predetermined speed Ne1 in step 172, the process proceeds to step 175. In step 175, the fuel injection amount Qft is calculated based on the equation (4), and then the process proceeds to step 176. In step 176, based on the fuel injection amount Qft calculated in step 175, a fuel injection time TAU in which the amount can be injected is calculated, and the routine ends.

Next, a method of correcting the ignition timing using the alcohol concentration correction learning value FALC set by the above-described alcohol concentration correction learning value initial setting operation will be described. The ignition timing SA is calculated by the following equation (8). Here, SABSE represents the basic ignition timing and is obtained from, for example, a map of the engine speed Ne and the engine load KL, and this map is stored in the ROM 34. SAALC (SAALC ≧ 0) indicates an ignition timing correction value based on the alcohol concentration, and is obtained from the map shown in FIG. The map shown in FIG. 16 is obtained in advance by experiments or the like and stored in the ROM 34. According to this map, the ignition timing is corrected so as to advance as the alcohol concentration increases. That is, the alcohol fuel has a high octane number, and a larger torque can be obtained by advancing the ignition timing.
SA = SABSE + SAALC (8)

  Next, another embodiment for correcting the ignition timing will be described with reference to FIG. FIG. 17 is a flowchart of an ignition timing correction operation for correcting the ignition timing. This operation is performed as a routine executed by interruption every predetermined time predetermined by the ECU 31.

  First, at step 181, the alcohol concentration correction learned value convergence flag SF is read from the backup RAM 36. Next, in step 182, it is determined whether or not the alcohol concentration correction learned value convergence flag SF read in step 181 is zero. If it is determined that the alcohol concentration correction learned value convergence flag SF is not 0, the process proceeds to step 183. When the alcohol concentration correction learning value convergence flag SF is not 0, it is 1, and the alcohol concentration correction learning value FALC has converged at the previous engine stop. Therefore, in step 183, the ignition timing is not corrected according to the present embodiment, the basic ignition timing SABSE is set as the ignition timing SA, and the routine is terminated.

  On the other hand, if it is determined in step 182 that the alcohol concentration correction learned value convergence flag SF is 0, the process proceeds to step 184. In step 184, the engine speed Ne is read. Next, at step 185, it is determined whether or not the engine speed Ne read at step 184 is smaller than a predetermined speed Ne2. Here, the rotation speed Ne2 is between the rotation speed range in the first half of the engine start that is likely to cause a start failure immediately after the engine start and the rotation speed range in the second half of the engine start that is likely to cause knocking. Desired. If it is determined that the engine speed Ne is smaller than the predetermined speed Ne2, the process proceeds to step 186.

  Next, at step 186, a value obtained by adding the correction value β (β ≧ 0) to the basic ignition timing SABSE is set to the ignition timing SA, and the routine is ended. That is, here, since the engine speed Ne is smaller than the predetermined speed Ne2, the engine is in a state of being prone to start failure, so the correction value β is added to advance the ignition timing. By advancing the ignition timing, it is possible to obtain a larger torque than when ignition is performed at a normal ignition timing, and it is possible to avoid a starting failure.

  On the other hand, if it is determined in step 185 that the engine speed Ne is equal to or greater than the predetermined engine speed Ne2, the process proceeds to step 187. In this case, a starting failure immediately after starting the engine does not occur, so that the occurrence of knocking becomes a problem this time. Accordingly, in step 187, a value obtained by subtracting the correction value γ (γ ≧ 0) from the basic ignition timing SABSE is set, and the routine is terminated. That is, knocking is prevented by retarding the ignition timing.

  The correction value β and the correction value γ may be predetermined constants, or values that change based on other values such as the alcohol concentration correction learning value FALC.

  The correction methods for the fuel injection amount, the ignition timing, and the like have been described using some embodiments so far, but each method may be applied alone or in any combination.

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 voltage of an air fuel ratio 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 feedback control operation. It is a time chart of alcohol concentration correction | amendment learning control operation. It is a time chart of alcohol concentration correction learning control operation by another embodiment. It is a part of flowchart of alcohol concentration correction | amendment learning control operation. 9 is a part of a flowchart of an alcohol concentration correction learning control operation continued from FIG. 8. FIG. 9 is a part of another embodiment of a flowchart of an alcohol concentration correction learning control operation continued from FIG. 8. It is a figure which shows the relationship of the variation | change_quantity (DELTA) FALCEST and FAF + (DELTA) FACL of alcohol concentration correction | amendment learning frequency Ng, alcohol concentration correction | amendment learning value convergence destination estimated value FALTEST. It is a flowchart which shows alcohol concentration correction | amendment learning value initial setting operation. It is a flowchart which shows alcohol concentration correction | amendment learning value initial setting operation by another embodiment. It is the figure which showed the relationship between alcohol concentration correction | amendment learning value and the injection amount correction coefficient at the time of starting. It is a flowchart which shows fuel injection time setting operation at the time of starting. It is the figure which showed the relationship between an alcohol concentration correction | amendment learning value and an ignition timing correction value. It is a flowchart which shows ignition timing correction | amendment operation.

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 42 Load sensor 43 Crank angle sensor

Claims (1)

  An air-fuel ratio control apparatus for an internal combustion engine that can use alcohol and gasoline alone or in combination as fuel, and is disposed in an upstream exhaust passage of an exhaust purification catalyst provided in the engine exhaust passage. An air-fuel ratio sensor for detecting the air-fuel ratio, feedback means for correcting the fuel supply amount based on the feedback correction value so that the output value of the air-fuel ratio sensor becomes a value corresponding to the target air-fuel ratio, and the feedback correction value In the air-fuel ratio control apparatus for an internal combustion engine, the alcohol concentration correction learning value converges in an air-fuel ratio control apparatus for an internal combustion engine that includes an alcohol concentration correction learning value that is calculated based on the alcohol concentration correction learning value and that corrects the fuel supply amount based on the learned alcohol concentration correction learning value. Convergence determining means for determining based on at least one predetermined convergence determination condition, and the feed And a means for obtaining an alcohol concentration correction learning value convergence destination estimated value that is a value estimated to converge the alcohol concentration correction learning value based on the alcohol correction correction value and the alcohol concentration correction learning value. When it is determined that the alcohol concentration correction learned value has not converged when the engine is stopped, the initial value of the alcohol concentration correction learned value at the start of the internal combustion engine is set to the alcohol that was obtained at the previous stop of the internal combustion engine. An air-fuel ratio control apparatus for an internal combustion engine that uses a concentration correction learning value convergence destination estimated value.

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