JP2004124864A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct the deviation of the output characteristic of an air-fuel ratio sensor on the upstream side of a catalyst. <P>SOLUTION: The catalyst 13 is interposed in an exhaust passage 12 of an engine, and a first air-fuel ratio sensor (A/F sensor) 15 is provided on the upstream side of the catalyst, and a second air-fuel ratio sensor (O<SB>2</SB>sensor) 16 is provided on the downstream side of the catalyst. Before the catalyst 13 becomes active, independently of a target air-fuel ratio, a real air-fuel ratio is controlled to a theoretical air-fuel ratio, and a first correction rate for correcting the air-fuel ratio detected by the A/F sensor 15 on the basis of an output of the O<SB>2</SB>sensor 16 as a reference is computed. After the catalyst 13 becomes active, when the air-fuel ratio detected by the A/F sensor 15 coincides with the theoretical air-fuel ratio and an output of the O<SB>2</SB>sensor is rich or lean, a second correction rate for correcting the air-fuel ratio detected by the A/F sensor 15 on the basis of an output of the O<SB>2</SB>sensor as a reference is computed. When the catalyst is active, the air-fuel ratio detected by the a/F sensor 15 is corrected by the first correction rate and the second correction rate. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly, to a technique for correcting an air-fuel ratio detected by an air-fuel ratio sensor.
[0002]
[Prior art]
If the amount of oxygen stored in an exhaust purification catalyst (hereinafter, referred to as a catalyst) such as a three-way catalyst disposed in an exhaust passage of an internal combustion engine is too large, the reduction processing performance for NOx in exhaust gas is reduced, and the amount of accumulated oxygen is reduced. Is too small, the oxidizing performance for HC and CO in the exhaust gas is reduced. For this reason, there is a technique in which the oxygen storage amount of the catalyst is estimated based on the output of the air-fuel ratio sensor provided on the upstream side of the catalyst, and the air-fuel ratio is controlled so that the oxygen storage amount becomes the target oxygen storage amount. .
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-314342
[Problems to be solved by the invention]
However, in the case where the air-fuel ratio control is performed as described above, if the output characteristics of the air-fuel ratio sensor deviate due to variations in parts or deterioration over time, the estimation error of the oxygen storage amount of the catalyst increases. Therefore, the exhaust gas purification performance may not be maintained.
[0005]
The present invention has been made in order to solve such a problem, and it is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can correct a deviation in output characteristics of an air-fuel ratio sensor and can accurately detect an air-fuel ratio. Aim.
[0006]
[Means for Solving the Problems]
Therefore, the air-fuel ratio control device for the internal combustion engine according to the present invention corrects the detected air-fuel ratio of the first air-fuel ratio sensor upstream of the catalyst based on the output of the second air-fuel ratio sensor downstream of the catalyst before the activation of the catalyst. And calculating a second correction amount for correcting the air-fuel ratio detected by the first air-fuel ratio sensor with reference to the second air-fuel ratio sensor after the activation of the catalyst. Is activated, the air-fuel ratio detected by the first air-fuel ratio sensor is corrected based on the first correction amount and the second correction amount.
[0007]
In this manner, before the catalyst is activated, the first correction amount for correcting mainly the individual variation of the first air-fuel ratio sensor and the deviation of the output characteristics due to the deterioration with time is calculated, and the first air-fuel ratio sensor is used to calculate the first air-fuel ratio. The detected air-fuel ratio of the fuel ratio sensor can be corrected at an early stage, and after the catalyst is activated, a second correction amount for correcting a deviation of the output characteristic based mainly on the temperature characteristic of the first air-fuel ratio sensor is calculated, and the second correction amount is calculated. The detected air-fuel ratio of the first air-fuel ratio sensor can be accurately corrected by the first correction amount and the second correction amount.
[0008]
Thereby, the accuracy of the air-fuel ratio control based on the air-fuel ratio detected by the first air-fuel ratio sensor can be improved before and after the activation of the catalyst.
Further, the invention according to claim 2 is characterized in that the first correction amount calculating means performs the actual air-fuel ratio regardless of the target air-fuel ratio during the execution of the air-fuel ratio control based on the air-fuel ratio detected by the first air-fuel ratio sensor. Is controlled to be the stoichiometric air-fuel ratio to calculate the first correction amount.
[0009]
In this way, even before the catalyst is activated, even if the target air-fuel ratio in the air-fuel ratio control is set to a value other than the stoichiometric air-fuel ratio, the actual air-fuel ratio is controlled to the stoichiometric air-fuel ratio, and the stoichiometric air-fuel ratio is adjusted. The first correction amount for correcting the deviation of the output characteristic of the first air-fuel ratio sensor can be calculated based on the output (detected air-fuel ratio) of the second air-fuel ratio sensor that can be detected well and stably. Thus, first, the detected air-fuel ratio of the first air-fuel ratio sensor can be corrected early by the first correction amount.
[0010]
According to the third aspect of the present invention, when the detected air-fuel ratio of the first air-fuel ratio sensor is a stoichiometric air-fuel ratio and the output of the second air-fuel ratio sensor is rich or lean, The correction amount is calculated.
With this configuration, after the catalyst is activated, the second correction amount is calculated only when it can be determined that the output characteristic of the first air-fuel ratio sensor has a deviation, so that the calculation load can be minimized. .
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a system configuration diagram of an engine according to an embodiment of the present invention. In FIG. 1, an air flow meter 3 for detecting an intake air flow rate Qa is provided in an intake passage 2 of an engine 1, and the intake air amount Qa is controlled by a throttle valve 4.
[0012]
The fuel injection valve 6 provided in the intake manifold 5 is driven to open by an injection signal from a control unit (C / U) 20 containing a microcomputer, and injects and supplies fuel.
An ignition plug 8 for performing spark ignition is provided in a combustion chamber 7 of the engine 1 and ignites an air-fuel mixture sucked through an intake valve 9 by spark ignition. The combustion exhaust gas is exhausted to an exhaust passage 12 via an exhaust valve 10 and an exhaust manifold 11, passes through a three-way catalyst 13, and a muffler 14, and is then released into the atmosphere.
[0013]
The three-way catalyst 13 has an oxygen storage capacity, adsorbs oxygen when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and desorbs oxygen when the exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio. It oxidizes CO and HC in the exhaust gas and reduces NOx to convert it to other harmless components (H ₂ O, CO ₂ , N ₂ ).
On the upstream side of the three-way catalyst 13, a so-called wide-range oxygen concentration sensor (hereinafter referred to as A / F sensor) 15 whose output changes linearly with respect to the air-fuel ratio is provided. A stoichiometric oxygen concentration sensor (hereinafter, referred to as an O ₂ sensor) 16 whose output value changes abruptly near the stoichiometric air-fuel ratio is provided downstream of 13.
[0014]
The control unit 20, the other of the air flow meter 3, A / F sensor 15 and _{O 2} sensor 16, the rotational speed sensor (crank angle sensor) 17 for detecting an engine rotational speed Ne, detects the engine coolant temperature Tw temperature Detection signals from various sensors such as a sensor 18 and a temperature sensor 19 for detecting the temperature of the three-way catalyst 13 are input.
[0015]
When the three-way catalyst 13 is in an inactive state, the control unit 20 sets a predetermined target air-fuel ratio TGLMD to promote activation of the three-way catalyst 13 and the like, and detects the air-fuel ratio detected by the A / F sensor 15. Is feedback-controlled (hereinafter referred to as air-fuel ratio feedback control before catalyst activation) so that the air-fuel ratio becomes the target air-fuel ratio TGLMD, and a first correction amount COLDHOS for correcting the air-fuel ratio detected by the A / F sensor 15. Is calculated (see FIGS. 2 and 3).
[0016]
On the other hand, when the three-way catalyst 13 is in an active state, the target oxygen storage amount is set, and the air-fuel ratio is feedback-controlled so that the oxygen storage amount becomes the target oxygen storage amount (hereinafter, based on the oxygen storage amount). The air-fuel ratio feedback control is performed), and a second correction amount HOTi for correcting the air-fuel ratio detected by the A / F sensor 15 is calculated (see FIGS. 5 and 6).
[0017]
FIG. 2 is a flowchart showing the air-fuel ratio feedback control before the activation of the catalyst. In FIG. 2, in step 1 (referred to as S1 in the figure, the same applies hereinafter), detection signals of the various sensors are read.
In step 2, the execution permission condition of the air-fuel ratio feedback control before the catalyst is activated is determined. Specifically, the execution permission condition is such that the A / F sensor 15 is in an active state, the three-way catalyst 13 is in an inactive state, and the like. Note that whether the A / F sensor 15 is in the active state is determined, for example, by the elapsed time after starting, and whether the three-way catalyst 13 is in the inactive state is detected by the temperature sensor 19. The determination is made based on the catalyst temperature.
[0018]
In step 3, the target air-fuel ratio TGLMD is set. In the present embodiment, the target air-fuel ratio TGLMD is first set to a value leaner than the stoichiometric air-fuel ratio (λ = 1) in order to promote activation of the three-way catalyst 13, and the like. At the same time, the stoichiometric air-fuel ratio gradually approaches (see FIG. 4).
In step 4, the theoretical value is calculated as follows from the intake air flow rate Qa detected based on the signal from the air flow meter 3 and the engine rotational speed Ne detected based on the signal from the rotation sensor 17. The basic fuel injection amount Tp corresponding to the air-fuel ratio is calculated.
[0019]
Tp = K · Qa / Ne (K is a constant)
In step 5, the final fuel injection amount Ti is calculated by the following equation.
Ti = Tp × TGLMD × α (α is an air-fuel ratio feedback correction coefficient)
Then, the control unit 20 outputs an injection pulse signal corresponding to the calculated fuel injection amount Ti to the fuel injection valve 6 at a predetermined timing synchronized with the engine rotation, and executes the fuel injection.
[0020]
FIG. 3 is a flowchart for calculating a first correction amount COLDHOS for correcting the detected air-fuel ratio of the A / F sensor 15.
In this flow, the O ₂ sensor 16 provided on the downstream side of the three-way catalyst 13 is less affected by heat and the like than the A / F sensor 15 provided on the upstream side, and the stoichiometric air-fuel ratio can be accurately and accurately determined. because it can stably detected, the actual air-fuel ratio regardless of the target air-fuel ratio TGLMD is changed to the stoichiometric air-fuel ratio, the a / F sensor 15 output of the O ₂ sensor 16 at this time (the detected air-fuel ratio) as a reference The first correction amount COLDHOS for correcting the detected air-fuel ratio is calculated.
[0021]
In FIG. 3, in step 11, it is determined whether or not a permission condition for calculating the first correction amount COLDHOS is satisfied. Specifically, the possible A / F sensor 15 and the O ₂ sensor 16 is active, the air-fuel ratio feedback control of the front catalyst activity is being executed or the like, and permit conditions.
In step 12, an air-fuel ratio downstream of the three-way catalyst 13 (catalyst downstream air-fuel ratio) FLTO2AFL is detected. Specifically, by referring to the table set in advance with a interpolation calculation, it converts the output voltage FLTO2 of the O ₂ sensor 16 in the air-fuel ratio (for A / F value conversion).
[0022]
In step 13, a deviation between the catalyst downstream air-fuel ratio FLTO2AFL and the stoichiometric air-fuel ratio (hereinafter referred to as a first deviation) FLTO2EER (= FLTO2AFL-1) is calculated.
In step 14, the shift correction amount SFTHOS of the A / F sensor 15 is calculated by proportional integral control based on the second deviation FLTO2ERR. Specifically, based on the proportional (P component) gain AFSHSPG and the integration (I component) gain AFSHSIG, the shift correction amount SFTHOS is calculated as in the following equation.
[0023]
SFTHOS = AFSHSG × FLTO2ERR + Σ (AFSHSIG × FLTO2ERR)
Here, the proportional gain AFSHSPG and integral gain AFSHSIG is based on output voltage FLTO2 of the _{O 2} sensor 16 is set by referring to a table set in advance with a interpolation calculation.
[0024]
In step 15, a deviation DLTTG (= TGLMD-1) between the target air-fuel ratio TGLMD and the stoichiometric air-fuel ratio (λ = 1) is calculated.
In step 16, a first correction amount COLDHOS (= SFTHOS-DLTTG) for correcting the detected air-fuel ratio of the A / F sensor 15 is calculated by subtracting the second deviation DLTTG from the shift correction amount SFTHOS.
[0025]
In step 17, the detected air-fuel ratio of the A / F sensor 15 is corrected by the first correction amount COLHOS.
Then, in step 18, the processing of steps 2 to 17 is repeated until the end condition of the calculation of the first correction amount COLHOS is satisfied. Incidentally, the termination condition, the O ₂ within a predetermined range output voltage comprises a stoichiometric air-fuel ratio equivalent value of the sensor 16 (e.g., 600～650MV) it is and the condition is that continues for a predetermined time. If the end condition is satisfied, the process proceeds to step 19, where the first correction amount COLDHOS at that time is stored in the memory.
[0026]
Due to the second deviation DLTTG, air-fuel ratio control based on the air-fuel ratio detected by the A / F sensor 15 controls the catalyst upstream-side air-fuel ratio to the stoichiometric air-fuel ratio regardless of the target air-fuel ratio TGLMD. when the detected air-fuel ratio of the O ₂ sensor 16 is not the stoichiometric air-fuel ratio in this state, the shift because it can determine the deviation in the output characteristic of the a / F sensor 15 has occurred, so as to correct the deviation The correction amount SFTHOS is calculated.
[0027]
Therefore, the actual air-fuel ratio is controlled to the stoichiometric air-fuel ratio irrespective of the target air-fuel ratio TGLMD in the air-fuel ratio control by repeating the processing of steps 2 to 17 until the end condition is satisfied, and the stoichiometric air-fuel ratio is increased. This makes it possible to correct the detected air-fuel ratio of the a / F sensor 15 the output of the O ₂ sensor 16 which can detect accurately and stably as a reference. As a result, it is possible to accurately correct the deviation of the output characteristics due to individual variation of the A / F sensor 15 or deterioration with time.
[0028]
On the other hand, when the condition for permitting the calculation of the first correction amount COLDHOS is not satisfied (step 11) and when the catalyst activation time elapses before the end condition of the calculation of the first correction amount COLDHOS is satisfied (step 20), Then, the control is ended by setting the first correction amount COLHOS to 0 (step 21). FIG. 4 is a timing chart for calculating the correction amount COLDHOS described above.
[0029]
FIG. 5 is a flowchart showing the air-fuel ratio feedback control (OSC control) based on the oxygen storage amount of the three-way catalyst 13.
In FIG. 5, in step 31, the detection signals of the various sensors are read.
In step 32, a condition for permitting the execution of the air-fuel ratio feedback control based on the oxygen storage amount is determined. Specifically, the execution permission condition is that the A / F sensor 15 or the like has no failure, that the three-way catalyst 13 is in an active state, and the like.
[0030]
In step 33, the first correction amount COLDHOS (see FIG. 3) and a second correction amount HOTi (see FIG. 6) described later are added to the air-fuel ratio detected by the A / F sensor 15, and the actual air upstream of the catalyst is added. The fuel ratio λr is detected.
In step 34, the oxygen storage amount Os of the three-way catalyst 13 is calculated by the following equation.
[0031]
Os = (λr-1) × Qa × os + Os0
Here, Qa: intake air amount, os: oxygen adsorption / desorption speed (os = oss> 0 when λr> 1, os = ops <0 when λr <1), Os0: last calculated value step of oxygen storage amount At 35, a deviation ΔOs (= Os−OSC) between the calculated oxygen storage amount Os and the target oxygen storage amount OSC is calculated. The target oxygen storage amount OSC is usually set as 50% of the maximum oxygen storage amount, but may be set according to the operating state.
[0032]
In step 36, a target air-fuel ratio λt on the upstream side of the catalyst is calculated by a predetermined process (for example, proportional integral derivative control) based on the deviation ΔOs.
Here, when the calculated value Os of the oxygen storage amount of the three-way catalyst 13 is larger than the target oxygen storage amount OSC (ΔOs <0), the target air-fuel ratio λt becomes rich, and the calculated value Os becomes smaller than the target oxygen storage amount OSC. When smaller (ΔOs> 0), the target air-fuel ratio λt is lean.
[0033]
In step 37, a fuel injection amount Ti (Tp × λt) is calculated by multiplying the basic air-fuel ratio Tp (= K × Qa / Ne) corresponding to the stoichiometric air-fuel ratio by the target air-fuel ratio λt. Then, the control unit 20 outputs an injection pulse signal corresponding to the calculated fuel injection amount Ti to the fuel injection valve 6 at a predetermined timing synchronized with the engine rotation, and executes the fuel injection.
[0034]
FIG. 6 is a flowchart for calculating the second correction amount HOTi for correcting the detected air-fuel ratio of the A / F sensor 15.
This flow is determined if the output characteristic of the A / F sensor 15 is deviated if the O ₂ sensor 16 detects rich or lean while the A / F sensor 15 detects the stoichiometric air-fuel ratio. because it can, and calculates the second correction amount HOTi for correcting the detected air-fuel ratio of the a / F sensor 15 based on the output of the O ₂ sensor 16 at this time in each operating region.
[0035]
In FIG. 6, in step 41, the engine operation area determined based on the detection signals from the various sensors is read.
In step 42, it is determined whether the conditions for calculating the second correction amount HOTi are satisfied. Specifically, the calculation conditions include that the three-way catalyst 13 is in an active state, that the air-fuel ratio feedback control based on the oxygen storage amount is being performed, and the like. If this calculation condition is satisfied, the process proceeds to step 43.
[0036]
In step 43, it is determined whether the air-fuel ratio detected by the A / F sensor 15 is a stoichiometric air-fuel ratio. When the air-fuel ratio detected by the A / F sensor 15 is the stoichiometric air-fuel ratio, the process proceeds to step 44.
In step 44 and 45, a state in which the O ₂ sensor 16 has detected the rich or lean is determined whether or not the predetermined time or longer. For example determines, when the output voltage FLTO2 of the _{O 2} sensor 16 is the stoichiometric air-fuel ratio when the 600～650MV, whether the output voltage FLTO2 of the _{O 2} sensor is less than 600 mV, or by greater than 650 mV. If the O ₂ sensor 16 has detected the rich or lean, the routine proceeds to step 46.
[0037]
In step 46, on the basis of the _{O 2} sensor output voltage FLO, sets the correction amount HOTHOSnew with reference to the table set in advance.
When A / F sensor 15 has detected the stoichiometric air-fuel ratio (i.e., when the catalyst upstream-side air-fuel ratio is controlled to the stoichiometric air-fuel ratio) in, O ₂ sensor 16 continues the rich or lean for a predetermined time or more When the detection is made, the actual air-fuel ratio is rich or lean because the output characteristic of the A / F sensor 15 is shifted, and as a result, the oxygen storage amount of the three-way catalyst 13 is reduced. It is considered that the minimum amount or the maximum amount has been reached.
[0038]
When the O ₂ sensor 16 detects rich, the A / F sensor 15 detects leaner than the actual air-fuel ratio, and when the O ₂ sensor 16 detects lean, the A / F sensor 15 detects It can be estimated that the detection is richer than the actual air-fuel ratio.
Therefore, when the O ₂ sensor 16 detects richness, a correction amount is set such that the air-fuel ratio detected by the A / F sensor 15 decreases as the richness increases, and when the O ₂ sensor 16 detects leanness, If a correction amount is set such that the air-fuel ratio detected by the A / F sensor 15 increases as the leaner, the deviation of the output characteristics of the A / F sensor 15 can be corrected.
[0039]
The table used in this step 46, which has been preset in view of the above, by referring to the table based on the output voltage FLO2 of the O ₂ sensor, the output characteristic of the A / F sensor 15 An appropriate correction amount according to the deviation can be set.
In step 47, it is determined whether or not the previous value HOTild1 of the second correction amount in the current operation region (hereinafter referred to as operation region 1) is stored. If the previous value HOTild1 of the second correction amount is stored, the process proceeds to step S48. On the other hand, if the previous value HOTild1 of the second correction amount is not stored, the process proceeds to step 52, and the correction amount HOTHOSnew set in step 46 (this time) is used for correcting the air-fuel ratio detected by the A / F sensor 15. The correction amount is HOTi.
[0040]
In step 48, the previous value HOTild1 of the second correction amount in the current operation region is read.
In step 49, the change rate HOTRATIO of the second correction amount in the current operation region is calculated by the following equation.
HOTRATIO = (HOTHOSnew + HOTild1) / HOTild1
In step 50, it is determined whether or not the operation region has changed (whether or not the operation region has changed from the operation region 1 to the operation region 2). If the operating region has changed, the process proceeds to step 50, and if the operating region has not changed, the process proceeds to step 53, where the correction amount HOTHOSnew set in step 46 (this time) is the last correction amount of the second correction amount in the same operating region. The value HOTild1 is added to obtain a second correction amount HOTi.
[0041]
In step 51, the second correction amount HOTi when the operation region changes is calculated as follows.
HOTi = HOTRATIO × HOTild2
Here, HOTRATIO is the correction amount change rate calculated in step 49 in the operating region 1 before the change, and HOTild2 is the previous value of the second correction amount in the operating region 2 after the change.
[0042]
If the operating range changes, the exhaust gas temperature also changes, so that the output (detected air-fuel ratio) of the A / F sensor 15 may change depending on the temperature characteristics. In this case, _{O 2} output voltage FLO2 the sensor 16 is also made to vary, the correction amount HOTHOSnew, which are set on the basis of the output voltage FLO2 of the _{O 2} sensor 16 in the operation region before the change, it Even if the second correction amount HOTi is calculated using this, the correction amount will not be an appropriate correction amount in the changed operation region.
[0043]
Accordingly, the second correction amount HOTi is stored for each operation region, and the second correction amount is changed in the changed operation region 2 in the same tendency as the operation region 1 before the change. The second correction amount HOTi is calculated by multiplying the previous value HOTild2 of the second correction amount in the operation region 2 by the correction amount change rate HOTRATIO.
[0044]
As a result, even when the operating region changes during the calculation of the second correction amount HOTi, the appropriate second correction amount HOTi corresponding to the changed operating region 2 can be calculated. Then, after the second correction amount HOTi is calculated in any of steps 51 to 53, the process proceeds to step 54, where the detected air-fuel ratio of the A / F sensor 15 is calculated by using the first correction amount COLDHOS (see FIG. 3) and the aforementioned The correction is performed by the second correction amount HOTi according to the following equation, and the process proceeds to step 55.
[0045]
The catalyst upstream-side air-fuel ratio = the air-fuel ratio detected by the A / F sensor 15 + the first correction amount COLDHOS + the second correction amount HOTi.
In step 55, the second correction amount HOTi is stored and updated for each operation region. By calculating the flow of such second correction amount HOTi is repeated, ultimately, results in the calculation of the second correction amount HOTi in step 44 until the O ₂ sensor 16 detects the stoichiometric air-fuel ratio is repeated, The second correction amount HOTOi at this time is stored for each operation region.
[0046]
The second correction amount HOTi is calculated after correcting the air-fuel ratio detected by the A / F sensor 15 with the first correction amount COLDHOS (see step 54), and is mainly based on the temperature characteristic. The deviation of the output characteristics of the F sensor 15 will be corrected.
As described above, according to the present embodiment, the first correction for correcting the air-fuel ratio detected by the A / F sensor 15 (for correcting the deviation of the output characteristics) when the three-way catalyst 13 is in the inactive state. In addition to calculating the amount COLDHOS and calculating the second correction amount HOTi for correcting the detected air-fuel ratio of the A / F sensor 15 even after the activation of the three-way catalyst 13, the output characteristic of the A / F sensor 15 The displacement can be corrected with high accuracy. In particular, since the second correction amount HOTi is calculated for each operation region, it is possible to correct a shift in the output characteristic of the A / F sensor 15 due to a change in the exhaust gas temperature (a shift due to the temperature characteristic).
[0047]
Thus, in the air-fuel ratio feedback control based on the oxygen storage amount, the oxygen storage amount of the three-way catalyst 13 can be accurately estimated, and the exhaust gas purification performance can be maintained high.
Incidentally, those in the present embodiment, the downstream side of the three-way catalyst 13 is provided with the stoichiometric type oxygen concentration sensor output value is suddenly changed at the stoichiometric air-fuel ratio near (O ₂ sensor), limited to this Instead, similarly to the upstream side, a so-called wide-range oxygen concentration sensor (A / F sensor) whose output changes linearly with respect to the air-fuel ratio may be provided.
[0048]
Further, a configuration may be adopted in which only the second correction amount HOTi is calculated without calculating the first correction amount COLHOS. In this case, the second correction amount HOTi makes it possible to correct individual variations of the A / F sensor 15, deterioration over time, and deviation of output characteristics based on temperature characteristics.
Further, technical ideas other than the claims that can be grasped from the embodiment will be described below together with their effects.
(A) In the air-fuel ratio control device for an internal combustion engine according to claim 1 or 2, the first correction amount calculating means includes: a deviation between a detected air-fuel ratio of the second air-fuel ratio sensor and a stoichiometric air-fuel ratio; The first correction amount is calculated based on a deviation between a target air-fuel ratio and a stoichiometric air-fuel ratio.
[0049]
With this configuration, even when the target air-fuel ratio in the air-fuel ratio control is set to a value other than the stoichiometric air-fuel ratio, the actual air-fuel ratio is controlled to the stoichiometric air-fuel ratio, and the influence of heat or the like is small. Correcting the deviation of the output characteristic of the first air-fuel ratio sensor based on the output (detected air-fuel ratio) of the second air-fuel ratio sensor capable of accurately and stably detecting the fuel ratio (for correcting the detected air-fuel ratio) 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the second correction amount calculating means calculates the second correction amount for each operating region of the engine. And storing it.
[0050]
According to this configuration, the second correction amount corresponding to the exhaust gas temperature that changes according to the operation range can be read to correct the air-fuel ratio detected by the first air-fuel ratio sensor. The deviation of the output characteristics can be corrected accurately and easily.
(C) In the air-fuel ratio control apparatus for an internal combustion engine according to claim 1, the first correction amount calculation means and the second correction amount calculation means make the output of the second air-fuel ratio sensor a stoichiometric air-fuel ratio equivalent value. Up to this point, the first correction amount or the second correction amount is changed.
[0051]
With this configuration, the correction of the air-fuel ratio detected by the first air-fuel ratio sensor is gradually performed, so that accurate correction based on the stoichiometric air-fuel ratio can be performed while preventing overcorrection.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an engine according to an embodiment of the present invention.
FIG. 2 is a flowchart showing air-fuel ratio control before catalyst activation.
FIG. 3 is a flowchart showing calculation of a first correction amount COLDHOS of a detected air-fuel ratio.
FIG. 4 is a timing chart showing calculation of a first correction amount COLDHOS of a detected air-fuel ratio.
FIG. 5 is a flowchart showing air-fuel ratio control based on the oxygen storage amount.
FIG. 6 is a flowchart showing calculation of a second correction amount HOTi of the detected air-fuel ratio.
[Explanation of symbols]
1 ... engine, 3 ... air flow meter, 6 ... fuel injection valve, 12 ... exhaust passage, 13 ... three-way catalyst, 15 ... A / F sensor, 16 ... _{O 2} sensor, 20 ... control unit

Claims (3)

An air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio upstream of a catalyst interposed in an exhaust passage of the engine,
A first air-fuel ratio sensor provided upstream of the catalyst and detecting an air-fuel ratio upstream of the catalyst;
A second air-fuel ratio sensor provided downstream of the catalyst and detecting an air-fuel ratio downstream of the catalyst;
A first correction amount calculating unit configured to calculate a first correction amount for correcting an air-fuel ratio detected by the first air-fuel ratio sensor based on an output of the second air-fuel ratio sensor before the catalyst activation;
Second correction amount calculating means for calculating a second correction amount for correcting the detected air-fuel ratio of the first air-fuel ratio sensor based on the output of the second air-fuel ratio sensor after the catalyst activation;
Correction means for correcting the detected air-fuel ratio of the first air-fuel ratio sensor based on the first correction amount and the second correction amount when the catalyst is activated;
An air-fuel ratio control device for an internal combustion engine, comprising: The first correction amount calculating means controls the actual air-fuel ratio to be the stoichiometric air-fuel ratio regardless of the target air-fuel ratio during the execution of the air-fuel ratio control based on the air-fuel ratio detected by the first air-fuel ratio sensor. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the first correction amount is calculated by the first correction amount. The second correction amount calculation means calculates the second correction amount when the detected air-fuel ratio of the first air-fuel ratio sensor is a stoichiometric air-fuel ratio and the output of the second air-fuel ratio sensor is rich or lean. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio is calculated.

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